c92 Anexo v Informe Geotecnico

SIGA Minería & Geotecnia S.A.

Av. Diego de Almagro Nº 5210, Ñuñoa, Santiago de Chile • Fono: (56-02) 7990 900 • Fax: (56-02) 7990 901 • www.siga.cl

INFORME GEOTECNICO FINAL PROYECTO 06–1705–01

" PROGRAMA DE ENSAYOS DE CARACTERIZACION MECANICA DE ROCAS, PROYECTO TIGRESA ”

Preparado para:

COMPAÑIA MINERA CARMEN BAJO COPIAPO

Elaborado por: DIVISION LABORATORIO DE MECANICA DE ROCAS

SIGA MINERIA & GEOTECNIA S.A.

NOVIEMBRE – 2007


Programa de Ensayos de Caracterización Mecánica Informe Geotécnico Final, Proyecto 06–1705–01 de Rocas, Proyecto Tigresa, Cía. Minera Carmen Bajo, Copiapó Indice de Contenido

INDICE DE CONTENIDO Página 1. Introducción. 1. 2. Programa de Ensayos Geomecánicos. 1. 2.1 Identificación de Muestras 1. 2.2 Programa de Ensayos Realizados 1. 3. Metodología de Trabajo. 2. 4. Preparación de Muestras. 2. 5. Peso Unitario (Método Geométrico). 3. 6. Peso Unitario (Método de Inmersión). 4. 7. Porosidad Aparente. 4. 8. Compresión Uniaxial Simple. 5. 9. Módulos Elásticos Estáticos. 6. 10. Compresión Triaxial Simple. 7. 11. Tracción Indirecta. 8. 12. Módulos Elásticos Dinámicos. 9. 13. Angulo de Fricción Básico (Tilt Test). 10. 14. Presentación de Resultados. 11. 14.1 Peso Unitario. 11. 14.2 Porosidad – Absorción. 11. 14.3 Angulo de Fricción Básico. 12. 14.4 Compresión Uniaxial Simple. 12. 14.5 Módulos Elásticos Estáticos. 12. 14.6 Velocidad de Ondas P&S. 12. 14.7 Módulos Elásticos Dinámicos. 13. 14.8 Tracción Indirecta. 13. 14.9 Compresión Triaxial Simple. 13. Criterio de Falla Mohr–Columb: Roca Intacta 13. Criterio de Hoek&Brown: Roca Intacta 14. Criterio Generalizado de Hoek&Brown: Masa Rocosa 14. 15. Observaciones. 15. 16. Referencias & Bibliografía. 16. ANEXOS. Anexo Resultados: Diorita de Brea No Alterada Anexo Resultados: Diorita de Brea con Vetillas Anexo Resultados: Diorita de Brea Alterada Anexo Gráficos de Ensayos Triaxiales Anexo Bibliografía Anexo Fotografías


Programa de Ensayos de Caracterización Mecánica Informe Geotécnico Final, Proyecto 06–1705–01 de Rocas, Proyecto Tigresa, Cía. Minera Carmen Bajo, Copiapó Página 1.

1. INTRODUCCION. El presente documento corresponde al Informe Técnico de Resultados del Programa de Ensayos de Caracterización de Rocas del Proyecto Tigresa, realizado por la División Laboratorio de Mecánica de Rocas de SIGA Minería & Geotecnia S.A., para la Cía. Minera Carmen Bajo, según lo solicitado por el Sr. Ioan Filip.

2. PROGRAMA DE ENSAYOS GEOMECANICOS.

2.1 IDENTIFICACION DE MUESTRAS. Las muestras enviadas al Laboratorio de Mecánica de Rocas de SIGA consistieron de testigos de sondajes ± 41 mm. de diámetro, a partir de los cuales se obtuvieron las probetas para los ensayos. Estas muestras comprendieron los siguientes 3 grupos de roca: Diorita de Brea no Alterada (7 muestras) Diorita de Brea con Vetillas (5 muestras) Diorita de Brea Alterada (8 muestras)

2.2 PROGRAMA DE ENSAYOS REALIZADOS. El programa de ensayos geotécnicos comprendió la determinación de los siguientes parámetros: - Peso Unitario Seco - Porosidad Aparente - Absorción (peso-volumen) - Tracción Indirecta - Compresión Uniaxial Simple - Compresión Triaxial Simple (c, φ) - Módulos Elásticos Estáticos (E, ν) - Módulos Elásticos Dinámicos (Ed, νd) - Velocidades de Ondas P&S (Vp & Vs) - Angulo de Fricción Básico (φb)



3. METODOLOGIA DE TRABAJO. La metodología que utiliza SIGA en los ensayos de su Laboratorio de Mecánica de Rocas, se basa en normas y procedimientos propuestos por diversas instituciones especialistas en la materia, entre las cuales destacan, por ejemplo: ISRM : International Society for Rock Mechanics ASTM : American Society for Testing and Materials CANMET : Canada Centre for Mineral and Energy Technology USBM : United State of America Bureau of Mines

4. PREPARACION DE MUESTRAS. La preparación de las muestras se realizó según la norma establecida para cada ensayo en particular, destructivo, o no destructivo. En el caso de una probeta de roca intacta, con la forma de un cilindro recto perfecto, la preparación se basa en la norma ASTM D–4543. La preparación de probetas para el presente programa de ensayos, se realizó mediante las siguientes etapas secuenciales. - Dimensionamiento de cada testigo mediante 2 cortes diamantinos,

diametrales, a fin de obtener una probeta con una geometría cuya razón longitud a diámetro es igual, o muy cercana a 2.

- Rectificado de las 2 caras basales de las probetas, a fin de obtener

el paralelismo entre ellas y poder distribuir uniformemente la carga de compresión aplicada sobre ella.

- Verificación del paralelismo de las 2 caras basales de las probetas,

con una tolerancia máxima de 1 milésima de pulgada, la cual, si es excedida, las probetas vuelven a la etapa de rectificado.

En el caso del ensayo de tracción indirecta, las muestras consistieron de discos de roca de ± 41 mm. de diámetro con un espesor variable, y entre 10 y 11 mm.



5. PESO UNITARIO (Método Geométrico). Este método está basado en la norma ASTM D–2845, y en el método sugerido por la ISRM, Commission on Standardization of Laboratory and Field Tests, Committe on Laboratory Tests. Es aplicable a muestras de geometría muy regular, y cuyo volumen se puede determinar en base a sus dimensiones geométricas, las que en el caso de una probeta cilíndrica, corresponden a su diámetro, D, y a su altura, L, determinadas mediante mediciones micrométricas. Para efectos del cálculo de su volumen, este diámetro D corresponde al promedio aritmético de 3 mediciones del diámetro de la probeta, las que se realizan en la base, a media altura, y en su parte superior. De similar manera, la altura L corresponde al promedio aritmético de 2 mediciones de la altura de la probeta, las que se realizan en 2 líneas paralelas, y ubicadas en sentido opuesto, a unos 180º. El peso de la probeta se determina en una balanza de precisión (con una resolución de ± 0.01 g). La fórmula para el cálculo del peso unitario, o simplemente densidad aparente, corresponde a la siguiente:

γ = Pp / Vp en que: γ = Peso Unitario Pp = Peso total de la probeta Vp = Volumen total de la probeta Vp = 0.25 π D² L D = Diámetro promedio de la probeta L = Largo promedio de la probeta Según el Grado de Saturación (S) de la muestra se obtiene: - Peso Unitario Natural (con 0%<S<100%) - Peso Unitario Seco (con S=0%) - Peso Unitario Saturado (con S=100%)



6. PESO UNITARIO (Método de Inmersión). Este método está basado en la norma ASTM C–97, y en los métodos sugeridos por la ISRM y el CANMET. El método de inmersión (Buoyancy) se usa en muestras cuyo volumen no puede ser determinado en base a sus dimensiones geométricas. El peso unitario se determina mediante la siguiente expresión.

γ = ρw Pm / (Psat – Psus) en la cual: γ = Peso Unitario Pm = Peso total de la muestra Vm = Volumen total de la muestra = (Psat–Psus) Psat = Peso saturado (inmersión en agua destilada, 48 horas) Psus = Peso suspendido (en recipiente con agua destilada)

7. POROSIDAD APARENTE. Con los parámetros obtenidos en este método se puede determinar la porosidad de la muestra, la cual está dada por la siguiente expresión.

n = Vp / Vm × 100 en que: n = Porosidad Vp = Volumen de poros = (Psat–Psec) Vm = Volumen de la muestra = (Psat–Psus) Psec = Peso seco (en horno a 105 ºC por 24 horas) Psat = Peso saturado (inmersión en agua destilada, 48 horas) Psus = Peso suspendido (en recipiente con agua destilada) El grado de absorción se obtiene con las siguientes expresiones.

Ap = (Psat – Psec) / Psec × 100 Av = G Ap en las cuales: Ap = Grado de Absorción en peso (%) Av = Grado de Absorción en volumen (%) G = Peso específico del material



8. COMPRESION UNIAXIAL SIMPLE. Este ensayo permite evaluar la resistencia a la compresión uniaxial, o no confinada, a una probeta cilíndrica de roca según el procedimiento indicado en norma ASTM D–2938, y el procedimiento sugerido por la ISRM, Commission on Standardization of Laboratory and Field Tests, Committe on Laboratory Tests. Tal como se ha indicado, el proceso de preparación de probetas para este ensayo, se realiza de acuerdo al procedimiento establecido en la norma ASTM D–4543. La probeta debe tener una razón a largo a diámetro igual a 2, con sus caras basales paralelas entre sí, para permitir la distribución uniforme de la carga de compresión axial que es aplicada sobre la probeta. Básicamente, el procedimiento de este ensayo consiste en aplicar una carga de compresión axial, normal a las caras basales de la probeta, y según incrementos predeterminados de carga, hasta que se produce la ruptura de la probeta mediante un modo de falla característico. La fórmula de cálculo de la resistencia a la compresión uniaxial simple (C.U.S) se expresa de la siguiente manera.

σc = Q / A en que: σc = Esfuerzo de ruptura en compresión uniaxial Q = Carga máxima de compresión, o de ruptura A = Area en que se aplica la carga A = 0.25 π D² D = Diámetro de la probeta Además, se procedió a determinar la resistencia a la compresión de la roca intacta con el criterio de falla empírico de Hoek&Brown, en base a los datos obtenidos en los ensayos de compresión triaxial.



9. MODULOS ELASTICOS ESTATICOS. La obtención de los módulos elásticos estáticos se realiza de acuerdo al procedimiento indicado en la norma ASTM D–3148, utilizando para el registro de las deformaciones que experimentan las probetas al ser sometidas a una carga de compresión axial, el sistema sensor LVDT (Linear Variable Differential Transformers), o el sistema de estampillas elastométricas Strain Gage. Básicamente, el procedimiento de este ensayo consiste en aplicar una carga de compresión sobre una probeta, de acuerdo a incrementos de carga predeterminados, y registrar simultáneamente la carga aplicada, y la deformación axial y diametral que la probeta experimenta. Con los pares de valores así obtenidos, se confeccionan los gráficos de esfuerzo v/s deformación axial y deformación axial v/s deformación diametral, para analizar las curvas de comportamiento y determinar el valor numérico de las constantes elásticas del material involucrado: es decir, el Módulo de Young y la Razón de Poisson. Ambos valores se determinan aproximadamente al 50% de Q, en que Q corresponde a la resistencia a la compresión uniaxial, no confinada, de la probeta ensayada, o del material correspondiente. El Módulo de Young promedio corresponde a la pendiente de la curva esfuerzo axial v/s deformación axial, determinada en el tramo lineal de esta curva, empleando la técnica de mínimos cuadrados para obtener la recta de ajuste con los puntos del tramo indicado. A su vez, la Razón de Poisson corresponde a la pendiente de la curva deformación axial v/s deformación diametral, determinada también en el tramo de comportamiento lineal de la curva. De esta manera, el Módulo de Young y la Razón de Poisson quedan definidos numéricamente por las siguientes expresiones.

E = ∆σa / ∆εa ν = (∆σa /∆εa) / (∆σa /∆εd) σa = Esfuerzo de compresión axial εa,εd = Deformaciones axial y diametral



10. COMPRESION TRIAXIAL SIMPLE. Este ensayo se basa en el procedimiento de la Norma ASTM D-2664, y en el método sugerido por la ISRM, Commission on Standardization of Laboratory & Field Tests, Committe on Laboratory Tests. El ensayo está orientado a determinar la resistencia de una probeta cilíndrica de roca intacta en un estado de compresión triaxial. Tal como se ha indicado, el proceso de preparación de probetas para este ensayo, se realiza de acuerdo al procedimiento establecido en la norma ASTM D–4543. La probeta debe tener una razón Largo a Diámetro igual a 2, con sus caras basales paralelas entre sí, para permitir la distribución uniforme de la carga de compresión axial que se aplica sobre ella. Básicamente, el procedimiento de este ensayo consiste en aplicar una carga de compresión axial a una probeta que está sometida, en forma simultánea, a una presión de confinamiento lateral constante, hasta la ruptura de la probeta. La resistencia a la compresión triaxial se obtiene mediante la siguiente conocida relación de esfuerzos.

σtx = Q / A en la cual: σtx = Resistencia a la compresión triaxial Q = Carga de ruptura en compresión triaxial A = Area en que se aplica la carga axial D = Diámetro de la probeta Del análisis de los resultados obtenidos en una serie de ensayos, con diversas presiones de confinamiento, se determinan los 2 parámetros de resistencia de la roca intacta: cohesión y ángulo de fricción interna. Además, se procedió a determinar los parámetros del criterio de falla empírico de Hoek&Brown de la roca intacta, así como los parámetros resistentes para la masa rocosa de acuerdo a este criterio.



11. TRACCION INDIRECTA (Método Brasileño). Este ensayo está basado en el procedimiento indicado por CANMET, Pit Slope Manual, Supplement 3–1, Laboratory Classifications Tests, y en el método sugerido por la ISRM, Commission on Standardization of Laboratory and Field Tests, Committe on Laboratory Tests, así como en la norma ASTM D–3967 (Splitting Tensile Strength). Básicamente, el ensayo consiste en aplicar una carga de compresión lineal sobre una muestra de roca con la forma de disco, hasta que se produce la ruptura del disco en la forma de una fractura vertical. La ruptura del disco se produce al desarrollarse esfuerzos de tracción en dirección perpendicular a la dirección en que se aplica la carga de compresión lineal (eje vertical del disco). Este disco debe tener un diámetro (D) mayor o igual que 50 mm, y un espesor (T) entre 0.20–0.75 D, y la carga compresiva aplicada sobre el disco se distribuye linealmente en su eje longitudinal mediante dos placas metálicas, una en la parte superior y la otra en la inferior. De esta manera, la resistencia a la tracción indirecta se determina con la siguiente expresión.

σt = 2 P / π D T σt = 0.636 P / D T

en que: σt = Resistencia a la tracción indirecta P = Carga máxima de compresión, o de ruptura D = Diámetro del disco de roca T = Espesor del disco de roca (con T/D entre 0.20 y 0.75) El valor de resistencia a la tracción obtenido en este ensayo es mayor que el valor de la resistencia a la tracción directa obtenida mediante el ensayo de tracción uniaxial simple.



12. MODULOS ELASTICOS DINAMICOS. La determinación de los módulos elásticos dinámicos, ultrasónicos, se realiza mediante la norma ASTM D-2845, que es aplicable a probetas cilíndricas de rocas de características homogéneas e isótropas. Las velocidades de propagación de la Onda de Compresión, Vp, y de la Onda Corte, Vs, se obtienen mediante el método de generación de pulsos con ultrasonido. Las velocidades de onda se obtienen con las siguientes expresiones.

Vp = Lp / Tp Vs = Ls / Ts en las cuales: Vp = Velocidad de propagación de la onda P Vs = Velocidad de propagación de la onda S Lp = Distancia recorrida por la onda P Ls = Distancia recorrida por la onda S Tp = Tiempo efectivo de recorrido de la onda P Ts = Tiempo efectivo de recorrido de la onda S A su vez, los módulos elásticos dinámicos se determinan en base a la velocidad de propagación de dichas ondas, y la densidad del material a través del cual ellas se propagan. Los módulos elásticos dinámicos se obtienen mediante las siguientes expresiones de cálculo basadas en la teoría de elasticidad lineal.

Ed = ρ Vs² ( 3Vp² – 4 Vs²) / ( Vp² – Vs²) µd = ( Vp² – 2Vs²) / 2 (Vp² – Vs²)

Gd = ρ Vs² en las cuales: Ed = Módulo de elasticidad dinámico Gd = Módulo de corte dinámico µd = Razón de Poisson dinámica Vp = Velocidad de propagación de onda P Vs = Velocidad de propagación de onda S ρ = Densidad de la roca



13. ANGULO DE FRICCION BASICO (Tilt Test). Este ángulo se obtuvo con el método sugerido por B. Stimpson (ISRM Int. J. Rock Mech. Min. Sci. Vol 18, 1981). El procedimiento de ensayo (Tilt Test) utiliza un dispositivo mecánico simple denominado Mesa de Fricción, que consiste en una superficie plana (mesa) que puede inclinarse entre 0º y 90º sobre la horizontal, y un lector del ángulo de inclinación de la mesa en el ensayo. Este método requiere el montaje de 3 testigos cilíndricos en la mesa de fricción, de igual diámetro, con el siguiente esquema. Dos testigos ubicados en la parte inferior, e impedidos de deslizar, y el tercero ubicado sobre los anteriores, posibilitado de deslizar a lo largo del contacto con los testigos inferiores al inclinar la mesa, con lo cual el ángulo de fricción básico se determina con la siguiente expresión.

φb = arc–tan (1.155 tanα) en que: φb = Angulo de fricción básico α = Angulo de inclinación de la mesa (Tilt) El ángulo de inclinación es el que produce el deslizamiento del testigo superior sobre los inferiores (punto de ruptura del equilibrio límite), y el cálculo asume idéntico ángulo de fricción en sus contactos. Este ángulo de fricción básico se utiliza en la ecuación empírica para estimar la resistencia al corte máxima de una discontinuidad, según la siguiente relación general (N. Barton & V. Choubey, 1977).

σsm = σn tan(JRC log(JCS/σn) + φb) en la cual: σsm = Resistencia al corte máxima σn = Esfuerzo normal sobre el plano JRC = Coeficiente de rugosidad JCS = Resistencia de las paredes φb = Angulo de fricción básico



14. PRESENTACION DE RESULTADOS. Los resultados de este programa de ensayos se presentan tabulados y graficados adecuadamente, indicándose los parámetros geotécnicos de interés determinados con planilla de cálculo Excel.

14.1 PESO UNITARIO: El peso unitario se determinó con el método geométrico, en probetas con forma de un cilíndrico recto perfecto. Peso Unitario (Método Geométrico).

Tipo de Roca Identificado (Unidad Litológica)

P. Unitario MG (t/m³)

Desviación Estándar

D. de Brea no Alterada 2,90 0,01 D. de Brea con Vetillas 2,89 0,03 D. de Brea Alterada 2,90 0,05 P. Unitario MG = Peso Unitario con Método Geométrico (Caliper)

Adicionalmente, se determinó el peso unitario trozos de testigos con el método de inmersión.

Tipo de Roca Identificado (Unidad Litológica)

P. Unitario MI (t/m³)

Desviación Estándar

D. de Brea no Alterada 2,89 0,03 D. de Brea con Vetillas 2,89 0,05 D. de Brea Alterada 2,88 0,06 P. Unitario MI = Peso Unitario con Método de Inmersión (Buoyancy)

14.2 POROSIDAD – ABSORCION: Los valores obtenidos en estos ensayos son los siguientes.

Tipo de Roca (Unidad Litológica)

Porosidad (%)

Absorción en Peso (%)

Absorción en Volumen (%)

DB no Alterada 0,46 ± 0,15 0,16 ± 0,05 0,46 ± 0,15 DB con Vetillas 0,42 ± 0,19 0,15 ± 0,07 0,42 ± 0,19 DB Alterada 0,44 ± 0,15 0,15 ± 0,05 0,44 ± 0,15



14.3 ANGULO DE FRICCION BASICO: Los valores promedios obtenidos en este ensayo son los siguientes.

Tipo de Roca Identificado Ang. de Fricción Básico (º)

Desviación Estandar

D. de Brea no Alterada 32,5 1,1 D. de Brea con Vetillas 33,6 1,1 D. de Brea Alterada 34,3 1,3

14.4 COMPRESION UNIAXIAL SIMPLE: Los valores promedios obtenidos (con selección), son los siguientes.

Tipo de Roca Identificado CUS50 (MPa) Desv. Estandar D. de Brea no Alterada (2 datos) 215,5 10,1 D. de Brea con Vetillas (1 dato) 204,8 - D. de Brea Alterada (2 datos) 191,3 25,8

14.5 MODULOS ELASTICOS ESTATICOS: Los valores promedios obtenidos, son los siguientes.

Tipo de Roca Identificado M. de Young (GPa) R. de Poisson (–) D. de Brea no Alterada (3 datos) 53,78 ± 3,84 0,29 ± 0,02 D. de Brea con Vetillas (2 datos) 47,72 ± 35,47 0,26 ± 0,06 D. de Brea Alterada (3 datos) 46,92 ± 19,33 0,12 ± 0,01

14.6 VELOCIDAD DE ONDAS P&S: Los valores promedios obtenidos son los siguientes.

Tipo de Roca Vp (m/s) Vs (m/s) D. de Brea no Alterada 5316 ± 95 3114 ± 62 D. de Brea con Vetillas 5315 ± 361 3143 ± 259 D. de Brea Alterada 5512 ± 236 3234 ± 167



14.7 MODULOS ELASTICOS DINAMICOS: Los valores promedios obtenidos son los siguientes.

Tipo de Roca M. de Young (GPa)

M. de Rigidez (GPa)

R. de Poisson (–)

D. de Brea no Alterada 69,8 ± 2,3 28,2 ± 1,0 0,24 ± 0,01 D. de Brea con Vetillas 70,3 ± 10,3 28,7 ± 4,5 0,23 ± 0,02 D. de Brea Alterada 75,6 ± 8,4 30,6 ± 3,7 0,24 ± 0,01

14.8 TRACCION INDIRECTA: Los valores promedios obtenidos (sin selección), son los siguientes.

Tipo de Roca T. Indirecta (MPa) Desv. Estandar D. de Brea no Alterada 15,4 3,0 D. de Brea con Vetillas 17,5 2,1 D. de Brea Alterada 14,6 4,4

14.9 COMPRESION TRIAXIAL SIMPLE: Todos los valores obtenidos en el ensayo triaxial se procesaron con el software RockData para determinar los parámetros típicos de la roca intacta según los Criterios de Mohr–Coulomb y Hoek&Brown. Además, se determinaron los parámetros típicos para la masa rocosa en base al Criterio Generalizado de Hoek&Brown, adoptando valores estimados para las variables GSI y D. Criterio de Falla de Mohr–Coulomb: Roca Intacta. (Criterio de Mohr–Coulomb: σs = co+σn tanφ

Parámetros Resistentes (Criterio Mohr–Coulomb) Diorita de Brea

Cohesión, co (MPa) 23,56 Angulo de Fricción, φ (°) 48,51 Coefic. de Correlación 0.8445



Criterio de Falla de Hoek&Brown: Roca Intacta. (Criterio Original de Hoek&Brown: σ1 = σ3+σc√(mσ3/σc +s)

Parámetros Resistentes (Criterio Hoek&Brown) Diorita de Brea

Compresión Uniaxial Simple (MPa) 119,16 Resistencia a la Tracción (MPa) –6,79 Parámetro mi (con s=1) 17,50 Coeficiente de Correlación 0.80409

Criterio Generalizado de Hoek&Brown: Masa Rocosa. (Criterio de Hoek&Brown: σ1 = σ3+σc (mbσ3/σc+s)ª Para el criterio de falla generalizado de Hoek&Brown se determinaron con el software RocData los parámetros de la masa rocosa indicados en la siguiente tabla, y en las figuras anexas.

Parámetros Resistentes (Criterio de Hoek&Brown) Diorita de Brea

Resistencia a la Compresión (MPa) 20,385 Resistencia a la Tracción (MPa) –0,532 Parámetros mb / s / a 7,264 / 0,0357 /0,501 Módulo de Deformación, E (MPa) 8793,77 Parámetros de Clasificación GSI= 70 y D= 0

Para efectos de esta aplicación interactiva se adoptaron los siguientes valores de los parámetros de caracterización de la masa rocosa. Parámetro de Resistencia: Sigma-c. Este corresponde a la resistencia a la compresión de la roca intacta, y es determinada de los ensayos triaxiales por RocData. Parámetro Empírico: mi. Este corresponde al parámetro m para la roca intacta requerido para el criterio de Hoek&Brown (s=1 para la roca intacta), y es determinado con los datos de ensayos triaxiales por RocData. Parámetro Empírico: mb. Este corresponde al parámetro m para la masa rocosa, y que también es determinado por RocData.



Indice Geológico de Resistencia: GSI=70. Este valor debe ser estimado, y que en esta aplicación corresponde al valor medio asociado a una muestra de roca intacta, o a una masa de roca in situ masiva con muy pocas discontinuidades de superficies no rugosas, levemente meteorizadas y alteradas (ver Tablas para GSI en el Anexo Bibliografía). Un valor más representativo para el GSI puede ser definido por Cía. Minera Carmen Bajo. Factor de Perturbación: D=0. Este corresponde al grado de perturbación de la masa rocosa por los efectos de la tronadura, asociado a una reducción de los parámetros resistentes de la masa rocosa (perturbación geotécnica). El parámetro D=0 asume una excelente tronadura controlada con nula perturbación geotécnica, o daño, en la roca (ver en Anexo Bibliografía: Hoek&Brown Failure Criterion – 2002 Edition).

15. OBSERVACIONES. El desarrollo de este programa de ensayos se considera técnicamente satisfactorio, aunque no exento de la natural problemática asociada a las características físicas y estructurales en el comportamiento de los materiales rocosos. Es necesario indicar que SIGA ha procesado la información en forma estándar, según normas, sin efectuar un análisis exhaustivo de ella, ya que ello excedería el alcance de este servicio de laboratorio. Sin embargo, esta información es presentada en forma detallada, a fin de que Cía. Minera Carmen Bajo pueda analizarla con la metodología que estime conveniente.



16. REFERENCIAS & BIBLIOGRAFIA.

1. Rock Characterization, Testing and Monitoring. ISRM Suggested Methods, E.T. Brown, Editor, 1981

2. Pit Slope Manual, Chapter 3: Mechanical Properties. CANMET: Canada Centre for Mineral & Energy Technology

3. Annual Book of ASTM Standards, Vol 04.08, Soil and Rock. American Society for Testing and Materials, 1996

5. A Suggested Technique for Determining the Basic Friction Angle of Rock Surfaces Using Cores. Stimpson, B., ISRM Journal, Vol. 13, 1976

6. Strength of Jointed Rock Masses. Hoek, E., Rankine Lecture, Geotechnique 33

7. Strength of Rock and Rock Masses. Hoek, E., ISRM New Jornal, 2

8. The Hoek–Brown Failure Criterion – a 1998 Update. E. Hoek & E. T. Brown, 1988.

9. GSI: A Geological Friendly Tool for Rock Mass Strength Estimation. Paul Marinos and Evert Hoek

10. Hoek–Brown Failure Criterion – 2002 Edition. E. Hoek, C. Carranza-Torres & B. Corkum.

11. ROCKDATA: User`Guide Hoek, E. & Shah, S., U, of Toronto, 1991.

12. ROCKDATA: Version 4.0, User`Guide Rocscience Inc., 2007.

13. ROCLAB: User`Guide Rocscience Inc., 2004


Programa de Ensayos de Caracterización Mecánica Informe Geotécnico Final, Proyecto 06–1705–01 de Rocas, Proyecto Tigresa, Cía. Minera Carmen Bajo, Copiapó Anexo Resultados

ANEXO RESULTADOS

DIORITA DE BREA NO ALTERADA

PESO UNITARIO SECO POROSIDAD APARENTE

ABSORCION: PESO–VOLUMEN ANGULO DE FRICCION BASICO

COMPRESION UNIAXIAL SIMPLE MODULOS ELASTICOS ESTATICOS

VELOCIDAD DE ONDAS P&S MODULOS ELASTICOS DINAMICOS

TRACCION INDIRECTA COMPRESION TRIAXIAL SIMPLE



Unidad : Diorita de Brea No Alterada Ensayo : Peso Unitario (Método Geométrico–Caliper)

(Determinado en Probetas Cilíndricas)

Rotulación Probeta ML Diámetro

(mm.) Longitud

(mm.) Peso Seco

(g) P. Unitario MG

(t/m³) Tig 1 3,0 41,0 83,6 319,17 2,89 Tig 1 5,0 41,0 85,7 325,80 2,88 Tig 2 6,0 41,0 85,7 330,45 2,92 Tig 6 16,5 41,0 83,6 319,80 2,90 Tig 18 27,0 41,0 85,0 326,23 2,91 Tig 20 10,0 41,0 83,2 320,17 2,91 Tig 20 13,0 41,0 85,0 326,59 2,91

Unidad : Diorita de Brea No Alterada Ensayo : Porosidad Aparente (Método de Inmersión–Buoyancy)

(Determinada en Trozos de Testigos)

Rotulación Probeta ML P. Seco

(g) P. Satu.

(g) P. Susp.

(g) P. Unitario MI

(t/m³) Porosidad

(%) Tig 1 3,0 240,60 241,14 157,13 2,86 0,64 Tig 1 5,0 158,63 158,98 103,33 2,85 0,63 Tig 2 6,0 262,80 263,21 173,07 2,92 0,45 Tig 6 16,5 243,57 243,98 159,79 2,89 0,49 Tig 18 27,0 259,76 260,00 171,41 2,93 0,27 Tig 20 10,0 298,44 298,90 195,84 2,90 0,45 Tig 20 13,0 209,87 210,08 137,39 2,89 0,29



Unidad : Diorita de Brea No Alterada Ensayo : Absorción en Peso–Volumen (Método de Inmersión)



(g) P. Satu.

(g) P. Susp.

(g) Absorción en

Peso (%) Absorción en Volumen (%)

Tig 1 3,0 240,60 241,14 157,13 0,22 0,64 Tig 1 5,0 158,63 158,98 103,33 0,22 0,63 Tig 2 6,0 262,80 263,21 173,07 0,16 0,45 Tig 6 16,5 243,57 243,98 159,79 0,17 0,49 Tig 18 27,0 259,76 260,00 171,41 0,09 0,27 Tig 20 10,0 298,44 298,90 195,84 0,15 0,45 Tig 20 13,0 209,87 210,08 137,39 0,10 0,29

P. Sat.u. = Peso Saturado P. Susp. = Peso Suspendido Unidad : Diorita de Brea No Alterada Ensayo : Angulo de Fricción Básico (Tilt Test)

Rotulación Muestras

Experimento Nº

Inclinación Mesa de Fricción (º)

Ang. de Fricción Básico (º)

Tig 1 30 34 Tig 2 1 28 32 Tig 6 29 33 Tig 2 28 32 Tig 6 2 27 30

Tig 18 29 33 Tig 6 30 34

Tig 18 3 27 30 Tig 20 29 33 Tig 20 29 33 Tig 18 4 30 34 Tig 20 28 32 Tig 1 30 34

Tig 18 5 29 33 Tig 20 30 34



Unidad : Diorita de Brea No Alterada Ensayo : Compresión Uniaxial Simple (C.U.S.)

(Experimental y Corregida a φ= 50 mm)

Rotulación Muestra ML C.U.S.

(kg/cm²) C.U.S.(50 mm)


(MPa) Tipo de Falla Observada

Tig 18 27,0 2.201 2.123 208,4 Matriz Tig 20 10,0 2.351 2.268 222,6 Matriz Tig 20 13,0 876 846 83,0 Matriz-Estructura

Unidad : Diorita de Brea No Alterada Ensayo : Módulos Elásticos Estáticos (Young–Poisson)

Rotulación Muestra

ML C.U.S.(50 mm) (MPa)

Módulo de Young (GPa)

Razón de Poisson (–)

Tig 18 27,0 208,4 57,84 0,12 Tig 20 10,0 222,6 53,30 0,09 Tig 20 13,0 83,0 50,20 0,10

Unidad : Diorita de Brea No Alterada Ensayo : Módulos Elásticos Dinámicos (Young–Rigidez–Poisson)

Velocidad de Ondas P&S (Vp & Vs)

Rotulación Muestra ML

Velocidad de Onda P

(m/s)

Velocidad de Onda S

(m/s)

Módulo de Elasticidad

(GPa)

Módulo de Rigidez (GPa)

Razón de Poisson

(–) Tig 18 27,0 5.314 3.149 71,0 28,9 0,23 Tig 1 5,0 5.465 3.195 72,9 29,4 0,24 Tig 20 10,0 5.203 3.083 68,0 27,7 0,23 Tig 2 6,0 5.289 3.108 69,7 28,2 0,24 Tig 20 13,0 5.310 3.034 67,4 26,8 0,26



Unidad : Diorita de Brea No Alterada Ensayo : Tracción Indirecta (Método Brasileño)

(Tipo de Muestra: Discos de Roca)

Rotulación Muestra ML Diámetro

(mm) Espesor

(mm) Carga de

Ruptura (N) T. Indirecta

(kg/cm²) T. Indirecta

(MPa) Tig 1 5,0 41,0 10,3 11.351 174,4 17,1 Tig 6 16,5 41,0 10,0 9.605 152,0 14,9 Tig 18 27,0 41,0 10,0 6.985 110,5 10,8 Tig 20 10,0 41,0 10,0 12.225 193,4 19,0 Tig 20 13,0 41,0 10,7 10.478 154,9 15,2

Unidad : Diorita de Brea No Alterada Ensayo : Compresión Triaxial Simple (CTx)


(mm) Carga de

Ruptura (Kg)Sigma–1

(MPa) Sigma–3

(MPa) Tig 1 3,0 41,0 17.717 131,7 2,9 Tig 1 5,0 41,0 24.573 182,7 7,9 Tig 2 6,0 41,0 28.490 211,8 9,8 Tig 6 16,5 41,0 32.675 242,9 13,7

Sigma–1 = Esfuerzo Principal de Ruptura Sigma–3 = Presión de Confinamiento



ANEXO RESULTADOS

DIORITA DE BREA CON VETILLAS








Unidad : Diorita de Brea Con Vetillas Ensayo : Peso Unitario (Método Geométrico–Caliper)



(mm.) Longitud

(mm.) Peso Seco

(g) P. Unitario MG

(t/m³) Tig 3 18,0 41,0 84,8 325,41 2,91 Tig 9 9,0 41,0 84,8 317,75 2,84 Tig 6 16,0 41,0 84,9 323,83 2,89 Tig 6 11,0 41,0 83,2 319,31 2,91 Tig 18 13,0 41,0 85,9 330,84 2,92

Unidad : Diorita de Brea Con Vetillas Ensayo : Porosidad Aparente (Método de Inmersión–Buoyancy)



(g) P. Satu.

(g) P. Susp.

(g) P. Unitario MI

(t/m³) Porosidad

(%) Tig 3 18,0 293,89 294,47 191,40 2,85 0,56 Tig 9 9,0 256,80 257,12 167,17 2,85 0,36 Tig 6 11,0 244,94 245,37 160,63 2,89 0,51 Tig 6 16,0 245,00 245,10 160,13 2,88 0,12 Tig 18 13,0 171,99 172,32 114,34 2,97 0,57

P. Satu. = Peso Saturado P. Susp. = Peso Suspendido



Unidad : Diorita de Brea Con Vetillas Ensayo : Absorción en Peso–Volumen (Método de Inmersión)



(g) P. Satu.

(g) P. Susp.

(g) Absorción en


Tig 3 18,0 293,89 294,47 191,40 0,20 0,56 Tig 9 9,0 256,80 257,12 167,17 0,12 0,36 Tig 6 11,0 244,94 245,37 160,63 0,18 0,51 Tig 6 16,0 245,00 245,10 160,13 0,04 0,12 Tig 18 13,0 171,99 172,32 114,34 0,19 0,57

P. Satu. = Peso Saturado P. Susp. = Peso Suspendido Unidad : Diorita de Brea Con Vetillas Ensayo : Angulo de Fricción Básico (Tilt Test)

(Determinada en Testigos Cilíndricos con Método de Kenty)


Experimento Nº



Tig 3 31 35 Tig 9 1 28 32 Tig 6 30 34 Tig 9 29 33 Tig 6 2 30 34 Tig 6 31 35 Tig 6 28 32 Tig 6 3 30 34

Tig 18 31 35 Tig 3 30 34 Tig 6 4 31 35

Tig 18 30 34 Tig 9 31 35 Tig 6 5 29 33

Tig 18 30 34



Unidad : Diorita de Brea Con Vetillas Ensayo : Compresión Uniaxial Simple (C.U.S.)






Tig 6 11,0 2.162,6 2.086,7 204,8 Matriz Tig 18 13,0 660,2 637,0 62,5 Matriz-Estructura

Unidad : Diorita de Brea Con Vetillas Ensayo : Módulos Elásticos Estáticos (Young–Poisson)

Rotulación Muestra




Tig 6 11,0 204,8 72,80 0,15 Tig 18 13,0 62,5 22,64 0,07

Unidad : Diorita de Brea Con Vetillas Ensayo : Módulos Elásticos Dinámicos (Young–Rigidez–Poisson)



Velocidad de Onda P

(m/s)

Velocidad de Onda S

(m/s)


(GPa)


Razón de Poisson




Unidad : Diorita de Brea Con Vetillas Ensayo : Tracción Indirecta (Método Brasileño)



(mm.) Espesor (mm.)

Carga de Ruptura (N)

T. Indirecta (kg/cm²)

T. Indirecta (MPa)

Tig 3 18,0 41,0 10,4 13.971 212,6 20,9 Tig 9 9,0 41,0 10,8 12.225 179,1 17,6 Tig 6 11,0 41,0 10,0 11.351 179,6 17,6 Tig 6 16,0 41,0 10,9 11.351 164,8 16,2 Tig 18 13,0 41,0 10,7 10.478 154,9 15,2

Unidad : Diorita de Brea Con Vetillas Ensayo : Compresión Triaxial Simple (CTx)

Rotulación Muestra ML Carga de


(MPa) Sigma–3

(MPa) Tig 3 18,0 17.183 127,7 2,9 Tig 9 9,0 21.813 162,1 5,9 Tig 6 16,0 29.648 220,4 15,7




ANEXO RESULTADOS

DIORITA DE BREA ALTERADA








Unidad : Diorita de Brea Alterada Ensayo : Peso Unitario (Método Geométrico–Caliper)



(mm.) Longitud

(mm.) Peso Seco

(g) P. Unitario MG

(t/m³) Tig 1 6,0 41,0 85,3 328,66 2,92 Tig 4 10,6 41,0 85,3 325,44 2,89 Tig 3 13,0 41,0 84,5 322,07 2,89 Tig 3 14,5 41,0 84,5 320,31 2,87 Tig 7 37,0 41,0 85,9 342,42 3,02 Tig 7 41,0 41,0 87,4 330,06 2,86 Tig 19 13,0 41,0 87,4 333,31 2,89 Tig 19 18,0 41,0 85,3 324,98 2,89

Unidad : Diorita de Brea Alterada Ensayo : Porosidad Aparente (Método de Inmersión–Buoyancy)



(g) P. Satu.

(g) P. Susp.

(g) P. Unitario MI

(t/m³) Porosidad

(%) Tig 1 6,0 285,48 285,91 186,24 2,86 0,43 Tig 4 10,0 235,16 235,58 152,71 2,84 0,51 Tig 3 13,0 286,14 286,66 186,02 2,84 0,52 Tig 3 14,5 177,64 177,86 115,92 2,87 0,36 Tig 7 37,0 162,85 163,19 109,17 3,01 0,63 Tig 7 41,0 218,35 218,50 141,34 2,83 0,19 Tig 19 13,0 168,79 168,97 110,87 2,91 0,31 Tig 19 18,0 248,25 248,74 162,84 2,89 0,57

P. Satu. = Peso Saturado P. Susp. = Peso Suspendido



Unidad : Diorita de Brea Alterada Ensayo : Absorción en Peso–Volumen (Método de Inmersión)



(g) P. Satu.

(g) P. Susp.

(g) Absorción en


Tig 1 6,0 285,48 285,91 186,24 0,15 0,43 Tig 4 10,0 235,16 235,58 152,71 0,18 0,51 Tig 3 13,0 286,14 286,66 186,02 0,18 0,52 Tig 3 14,5 177,64 177,86 115,92 0,12 0,36 Tig 7 37,0 162,85 163,19 109,17 0,21 0,63 Tig 7 41,0 218,35 218,50 141,34 0,07 0,19 Tig 19 13,0 168,79 168,97 110,87 0,11 0,31 Tig 19 18,0 248,25 248,74 162,84 0,20 0,57

P. Satu. = Peso Saturado P. Susp. = Peso Suspendido Unidad : Diorita de Brea Alterada Ensayo : Angulo de Fricción Básico (Tilt Test)


Experimento Nº



Tig 1 30 34 Tig 4 1 32 36 Tig 3 31 35 Tig 4 29 33 Tig 3 2 30 34 Tig 7 31 35 Tig 1 31 35 Tig 7 3 29 33

Tig 19 30 34 Tig 3 33 37 Tig 7 4 31 35

Tig 19 32 36 Tig 1 30 34

Tig 19 5 29 33 Tig 4 30 34



Unidad : Diorita de Brea Alterada Ensayo : Compresión Uniaxial Simple (C.U.S.)






Tig 7 37,0 2.213 2.135 209,5 Matriz Tig 7 41,0 1.827 1.763 173,0 Matriz Tig 19 13,0 934 901 88,5 Matriz-Estructura

Unidad : Diorita de Brea Alterada Ensayo : Módulos Elásticos Estáticos (Young–Poisson)

Rotulación Muestra




Tig 7 37,0 209,5 67,51 0,15 Tig 7 41,0 173,0 29,17 0,07 Tig 19 13,0 88,5 44,08 0,19

Unidad : Diorita de Brea Alterada Ensayo : Módulos Elásticos Dinámicos (Young–Rigidez–Poisson)



Velocidad de Onda P

(m/s)

Velocidad de Onda S

(m/s)


(GPa)


Razón de Poisson




Unidad : Diorita de Brea Alterada Ensayo : Tracción Indirecta (Método Brasileño)



(mm) Espesor

(mm) Carga de

Ruptura (N) T. Indirecta

(kg/cm²) T. Indirecta

(MPa) Tig 3 14,5 41,0 10,8 11.351 166,3 16,3 Tig 7 37,0 41,0 10,1 13.971 218,9 21,5 Tig 7 41,0 41,0 10,0 6.985 110,5 10,8 Tig 19 13,0 41,0 10,2 7.859 121,9 12,0 Tig 19 18,0 41,0 10,0 7.859 124,3 12,2

Unidad : Diorita de Brea No Alterada Ensayo : Compresión Triaxial Simple (CTx)

Rotulación Muestra ML Carga de


(MPa) Sigma–3

(MPa) Tig 1 6,0 27.333 203,2 7,9 Tig 4 10,6 29.470 219,0 11,8 Tig 19 18,0 30.182 224,3 13,7 Tig 3 13,0 30.716 228,3 15,7 Tig 3 14,5 31.072 231,0 17,7



Programa de Ensayos de Caracterización Mecánica Informe Geotécnico Final, Proyecto 06–1705–01 de Rocas, Proyecto Tigresa, Cía. Minera Carmen Bajo, Copiapó Anexo Gráficos

ANEXO GRAFICOS

DIORITA DE BREA ENSAYOS DE COMPRESION TRIAXIAL SIMPLE



Gráfico de Resultados Diorita de Brea – Proyecto Tigresa

Ensayos de Compresión Triaxial Simple Criterio de Falla de Mohr – Coulomb

Relación Sigma–1 v/s Sigma–3 Círculos y Envolvente Lineal de Mohr (Datos Procesados con Software ROCDATA Version 4.0)

Sigma–1 = Esfuerzo Principal de Ruptura (Major principal stress) Sigma–3 = Presión de Confinamiento (Minor principal stress) Sigma–S = Esfuerzo de Corte (Shear stress) Sigma–N = Esfuerzo Normal (Normal stress) ––– = Valores Ajustados ––– = Datos de Ensayos Triaxiales




Ensayos de Compresión Triaxial Simple Criterio de Falla de Hoek & Brown

Relación Sigma–1 v/s Sigma–3 Relación Sigma–S v/s Sigma–N (Datos Procesados con Software ROCDATA Version 4.0)

Sigma–1 = Esfuerzo Principal de Ruptura (Major principal stress) Sigma–3 = Presión de Confinamiento (Minor principal stress) Sigma–S = Esfuerzo de Corte (Shear stress) Sigma–N = Esfuerzo Normal (Normal stress) ––– = Criterio de Hoek & Brown




Ensayos de Compresión Triaxial Simple Parámetros de Mohr Coulomb ajustados del Criterio de Falla de Hoek & Brown

Envolvente a Sigma–1 v/s Sigma–3 Envolvente a Sigma–S v/s Sigma–N (Datos Procesados con Software ROCDATA Version 4.0)

Sigma–1 = Esfuerzo Principal de Ruptura (Major principal stress) Sigma–3 = Presión de Confinamiento (Minor principal stress) Sigma–S = Esfuerzo de Corte (Shear stress) Sigma–N = Esfuerzo Normal (Normal stress) ––– = Criterio de Hoek & Brown ––– = Criterio de Mohr–Coulomb ajustado




Ensayos de Compresión Triaxial Simple Criterios de Falla de Hoek & Brown y de Mohr Coulomb

Envolvente a Sigma–1 v/s Sigma–3 Envolvente a Sigma–S v/s Sigma–N (Datos Procesados con Software ROCDATA Version 4.0)

Sigma–1 = Esfuerzo Principal de Ruptura (Major principal stress) Sigma–3 = Presión de Confinamiento (Minor principal stress) Sigma–S = Esfuerzo de Corte (Shear stress) Sigma–N = Esfuerzo Normal (Normal stress) ––– = Criterio de Hoek & Brown ––– = Criterio de Mohr–Coulomb


Programa de Ensayos de Caracterización Mecánica Informe Geotécnico Final, Proyecto 06–1705–01 de Rocas, Proyecto Tigresa, Cía. Minera Carmen Bajo, Copiapó Anexo Bibliografía

ANEXO BIBLIOGRAFIA

Hoek–Brown Failure Criterion–2002 Edition. Evert. Hoek, Carlos Carranza-Torres and Brent

Corkum, 2002

The Geological Strength Index: Applications and Limitations.

V. Marinos, P. Marinos and E. Hoek, 2005

HOEK-BROWN FAILURE CRITERION – 2002 EDITION Evert Hoek Consulting Engineer, Vancouver, Canada Carlos Carranza-Torres Itasca Consulting Group Inc., Minneapolis, USA Brent Corkum Rocscience Inc., Toronto, Canada ABSTRACT: The Hoek-Brown failure criterion for rock masses is widely accepted and has been applied in a large number of projects around the world. While, in general, it has been found to be satisfactory, there are some uncertainties and inaccuracies that have made the criterion inconvenient to apply and to incorporate into numerical models and limit equilibrium programs. In particular, the difficulty of finding an acceptable equivalent friction angle and cohesive strength for a given rock mass has been a problem since the publication of the criterion in 1980. This paper resolves all these issues and sets out a recommended sequence of calculations for applying the criterion. An associated Windows program called “RocLab” has been developed to provide a convenient means of solving and plotting the equations presented in this paper. 1. INTRODUCTION Hoek and Brown [1, 2] introduced their failure criterion in an attempt to provide input data for the analyses required for the design of underground excavations in hard rock. The criterion was derived from the results of research into the brittle failure of intact rock by Hoek [3] and on model studies of jointed rock mass behaviour by Brown [4]. The criterion started from the properties of intact rock and then introduced factors to reduce these properties on the basis of the characteristics of joints in a rock mass. The authors sought to link the empirical criterion to geological observations by means of one of the available rock mass classification schemes and, for this purpose, they chose the Rock Mass Rating proposed by Bieniawski [5]. Because of the lack of suitable alternatives, the criterion was soon adopted by the rock mechanics community and its use quickly spread beyond the original limits used in deriving the strength reduction relationships. Consequently, it became necessary to re-examine these relationships and to introduce new elements from time to time to account for the wide range of practical problems to which the criterion was being applied. Typical of these enhancements were the introduction of the idea of “undisturbed” and “disturbed” rock masses Hoek and Brown [6], and the introduction of a modified criterion to force the rock mass tensile

strength to zero for very poor quality rock masses (Hoek, Wood and Shah, [7]). One of the early difficulties arose because many geotechnical problems, particularly slope stability issues, are more conveniently dealt with in terms of shear and normal stresses rather than the principal stress relationships of the original Hoek-Brown riterion, defined by the equation: c

5.0'3'

3'1

++= sm

cici σ

σσσσ (1)

where '

1σ and '

3σ are the major and minor effective principal stresses at failure

ciσ is the uniaxial compressive strength of the intact rock material and

m and s are material constants, where s = 1 for intact rock.

An exact relationship between equation 1 and the normal and shear stresses at failure was derived by J. W. Bray (reported by Hoek [8]) and later by Ucar [9] and Londe1 [10]. Hoek [12] discussed the derivation of equivalent friction angles and cohesive strengths for various practical situations. These derivations were based 1 Londe’s equations were later found to contain errors although the concepts introduced by Londe were extremely important in the application of the Hoek-Brown criterion to tunnelling problems (Carranza-Torres and Fairhurst, [11])

upon tangents to the Mohr envelope derived by Bray. Hoek [13] suggested that the cohesive strength determined by fitting a tangent to the curvilinear Mohr envelope is an upper bound value and may give optimistic results in stability calculations. Consequently, an average value, determined by fitting a linear Mohr-Coulomb relationship by least squares methods, may be more appropriate. In this paper Hoek also introduced the concept of the Generalized Hoek-Brown criterion in which the shape of the principal stress plot or the Mohr envelope could be adjusted by means of a variable coefficient a in place of the square root term in equation 1.

−−

=D

GSIs39100exp (4)

( ) (5) 3/2015/

61

21 −− −+= eea GSI

D is a factor which depends upon the degree of disturbance to which the rock mass has been subjected by blast damage and stress relaxation. It varies from 0 for undisturbed in situ rock masses to 1 for very disturbed rock masses. Guidelines for the selection of D are discussed in a later section. The uniaxial compressive strength is obtained by setting in equation 2, giving: 0'

3 =σ

acic s.σσ = (6) Hoek and Brown [14] attempted to consolidate all

the previous enhancements into a comprehensive presentation of the failure criterion and they gave a number of worked examples to illustrate its practical application.

and, the tensile strength is:

b

cit m

sσσ −= (7)

Equation 7 is obtained by setting in

equation 2. This represents a condition of biaxial tension. Hoek [8] showed that, for brittle materials, the uniaxial tensile strength is equal to the biaxial tensile strength.

tσσσ == '3

'1In addition to the changes in the equations, it was

also recognised that the Rock Mass Rating of Bieniawski was no longer adequate as a vehicle for relating the failure criterion to geological observations in the field, particularly for very weak rock masses. This resulted in the introduction of the Geological Strength Index (GSI) by Hoek, Wood and Shah [7], Hoek [13] and Hoek, Kaiser and Bawden [15]. This index was subsequently extended for weak rock masses in a series of papers by Hoek, Marinos and Benissi [16], Hoek and Marinos [17, 18] and Marinos and Hoek [19].

Note that the “switch” at GSI = 25 for the coefficients s and a (Hoek and Brown, [14]) has been eliminated in equations 4 and 5 which give smooth continuous transitions for the entire range of GSI values. The numerical values of a and s, given by these equations, are very close to those given by the previous equations and it is not necessary for readers to revisit and make corrections to old calculations.

The Geological Strength Index will not be discussed in the following text, which will concentrate on the sequence of calculations now proposed for the application of the Generalized Hoek Brown criterion to jointed rock masses.

Normal and shear stresses are related to principal stresses by the equations published by Balmer [20].

1

122 ''

''''''1'

31

31313

+

−⋅

−−

+=

σσ

σσσσσσσ

dd

ddn (8) 2. GENERALIZED HOEK-BROWN CRITERION

This is expressed as

( )1''

''''

131

313 +

−=σσ

σσσστ

dd

dd (9) a

cibci sm

++=

σσσσσ

'3'

3'1 (2)

where ( ) 1'''

3311

−++=

acibb smamdd σσσσ (10) where mb is a reduced value of the material constant

mi and is given by

−−

=D

GSImm ib 1428100exp (3) 3. MODULUS OF DEFORMATION

The rock mass modulus of deformation is given by: s and a are constants for the rock mass given by the

following relationships: )40/)10((101002

1)( −⋅

−= GSIci

mDGPaE

σ (11a)

The equivalent plot, in terms of the major and minor principal stresses, is defined by: Equation 11a applies for ≤ciσ 100 MPa. For >ciσ

100 MPa, use equation 11b.

''

'

'

'''

31 sin1sin1

sin1cos2 σ

φφ

φφσ

−

++

−=

c (15) )40/)10((10

21)( −⋅

−= GSI

mDGPaE (11b)

Note that the original equation proposed by Hoek and Brown [14] has been modified, by the inclusion of the factor D, to allow for the effects of blast damage and stress relaxation. 4. MOHR-COULOMB CRITERION Since most geotechnical software is still written in terms of the Mohr-Coulomb failure criterion, it is necessary to determine equivalent angles of friction and cohesive strengths for each rock mass and stress range. This is done by fitting an average linear relationship to the curve generated by solving equation 2 for a range of minor principal stress values defined by '

3 max3σσσ <<t , as illustrated in

Figure 1. The fitting process involves balancing the areas above and below the Mohr-Coulomb plot. This results in the following equations for the angle of friction and cohesive strength : 'φ 'c

++++

+=

−

−−

1'

1'1'

)(6)2)(1(2

)(6sin

3

3

abb

abb

n

n

msamaa

msam

σ

σφ (12)

[ ]

( ) ( ))2)(1()(61)2)(1(

)()1()21(

1'

1'''

3

33

aamsamaa

msmasac

abb

abbci

n

nn

++++++

+−++=

−

−

σ

σσσ

(13)

Figure 1: Relationships between major and minor principal stresses for Hoek-Brown and equivalent Mohr-Coulomb criteria. 5. ROCK MASS STRENGTH The uniaxial compressive strength of the rock mass

cσ is given by equation 6. Failure initiates at the boundary of an excavation when cσ is exceeded by the stress induced on that boundary. The failure propagates from this initiation point into a biaxial stress field and it eventually stabilizes when the local strength, defined by equation 2, is higher than the induced stresses and . Most numerical models can follow this process of fracture propagation and this level of detailed analysis is very important when considering the stability of excavations in rock and when designing support systems.

'1σ

'3σ

where cin σσσ 'max33 =

Note that the value of '

max3σ , the upper limit of

confining stress over which the relationship between the Hoek-Brown and the Mohr-Coulomb criteria is considered, has to be determined for each individual case. Guidelines for selecting these values for slopes as well as shallow and deep tunnels are presented later. The Mohr-Coulomb shear strength τ , for a given normal stress σ , is found by substitution of these values of and 'c 'φ in to the equation:

'' tanφστ += c (14)

However, there are times when it is useful to consider the overall behaviour of a rock mass rather than the detailed failure propagation process described above. For example, when considering the strength of a pillar, it is useful to have an estimate of the overall strength of the pillar rather

than a detailed knowledge of the extent of fracture propagation in the pillar. This leads to the concept of a global “rock mass strength” and Hoek and Brown [14] proposed that this could be estimated from the Mohr-Coulomb relationship:

'

'''

sin1cos2

φφσ

−=

ccm

(16) with and determined for the stress range 'c 'φ

4/cit σσσ < '3< giving

( )

)2)(1(24))8(4( 1

'aa

smsmasm abbb

cicm +++−−+

⋅=−

σσ (17)

6. DETERMINATION OF σ′3MAX The issue of determining the appropriate value of

for use in equations 12 and 13 depends upon the specific application. Two cases will be investigated:

'max3σ

1. Tunnels − where the value of is that

which gives equivalent characteristic curves for the two failure criteria for deep tunnels or equivalent subsidence profiles for shallow tunnels.

'max3σ

2. Slopes – here the calculated factor of safety and the shape and location of the failure surface have to be equivalent.

For the case of deep tunnels, closed form solutions for both the Generalized Hoek-Brown and the Mohr-Coulomb criteria have been used to generate hundreds of solutions and to find the value of that gives equivalent characteristic curves.

'max3σ

For shallow tunnels, where the depth below surface is less than 3 tunnel diameters, comparative numerical studies of the extent of failure and the magnitude of surface subsidence gave an identical relationship to that obtained for deep tunnels, provided that caving to surface is avoided. The results of the studies for deep tunnels are plotted in Figure 2 and the fitted equation for both cases is:

94.0'

'

'max3 47.0

−

=

Hcm

cm γσ

σ

σ (18)

where is the rock mass strength, defined by equation 17,

'cmσ

γ is the unit weight of the rock mass

and H is the depth of the tunnel below surface. In cases where the horizontal stress is higher than the vertical stress, the horizontal stress value should be used in place of Hγ .

'

'3

σ

σ

Figure 2: Relationship for the calculation of σ′3max for equivalent Mohr-Coulomb and Hoek-Brown parameters for tunnels. Equation 18 applies to all underground excavations, which are surrounded by a zone of failure that does not extend to surface. For studies of problems such as block caving in mines it is recommended that no attempt should be made to relate the Hoek-Brown and Mohr-Coulomb parameters and that the determination of material properties and subsequent analysis should be based on only one of these criteria. Similar studies for slopes, using Bishop’s circular failure analysis for a wide range of slope geometries and rock mass properties, gave:

91.0'

max 72.0−

=

Hcm

cm γσ (19)

where H is the height of the slope. 7. ESTIMATION OF DISTURBANCE FACTOR D Experience in the design of slopes in very large open pit mines has shown that the Hoek-Brown criterion for undisturbed in situ rock masses (D = 0) results in rock mass properties that are too optimistic [21, 22]. The effects of heavy blast

damage as well as stress relief due to removal of the overburden result in disturbance of the rock mass. It is considered that the “disturbed” rock mass properties [6], D = 1 in equations 3 and 4, are more appropriate for these rock masses. Lorig and Varona [23] showed that factors such as the lateral confinement produced by different radii of curvature of slopes (in plan) as compared with their height also have an influence on the degree of disturbance. Sonmez and Ulusay [24] back-analysed five slope failures in open pit coal mines in Turkey and attempted to assign disturbance factors to each rock mass based upon their assessment of the rock mass properties predicted by the Hoek-Brown criterion. Unfortunately, one of the slope failures appears to be structurally controlled while another consists of a transported waste pile. The authors consider that the Hoek-Brown criterion is not applicable to these two cases. Cheng and Liu [25] report the results of very careful back analysis of deformation measurements, from extensometers placed before the commencement of excavation, in the Mingtan power cavern in Taiwan. It was found that a zone of blast damage extended for a distance of approximately 2 m around all large excavations. The back-calculated strength and deformation properties of the damaged rock mass give an equivalent disturbance factor D = 0.7. From these references it is clear that a large number of factors can influence the degree of disturbance in the rock mass surrounding an excavation and that it may never be possible to quantify these factors precisely. However, based on their experience and on an analysis of all the details contained in these papers, the authors have attempted to draw up a set of guidelines for estimating the factor D and these are summarised in Table 1. The influence of this disturbance factor can be large. This is illustrated by a typical example in which ciσ = 50 MPa, mi = 10 and GSI = 45. For an undisturbed in situ rock mass surrounding a tunnel at a depth of 100 m, with a disturbance factor D = 0, the equivalent friction angle is 47.16° while the cohesive strength is c 0.58 MPa. A rock mass with the same basic parameters but in highly disturbed slope of 100 m height, with a disturbance factor of D = 1, has an equivalent friction angle of

27.61° and a cohesive strength of 0.35 MPa.

='φ

='

='φ ='c

Note that these are guidelines only and the reader would be well advised to apply the values given with caution. However, they can be used to provide a realistic starting point for any design and, if the observed or measured performance of the excavation turns out to be better than predicted, the disturbance factors can be adjusted downwards. 8. CONCLUSION A number of uncertainties and practical problems in using the Hoek-Brown failure criterion have been addressed in this paper. Wherever possible, an attempt has been made to provide a rigorous and unambiguous method for calculating or estimating the input parameters required for the analysis. These methods have all been implemented in a Windows program called “RocLab” that can be downloaded (free) from www.rocscience.com. This program includes tables and charts for estimating the uniaxial compressive strength of the intact rock elements ( ciσ ), the material constant mi and the Geological Strength Index (GSI). 9. ACKNOWLEDGEMENTS The authors wish to acknowledge the contributions of Professor E.T. Brown in reviewing a draft of this paper and in participating in the development of the Hoek-Brown criterion for the past 25 years.

http://www.rocscience.com/

able 1: Guidelines for estimating disturbance factor D T Appearance of rock mass Description of rock mass Suggested

value of D

Excellent quality controlled blasting or excavation by Tunnel Boring Machine results in minimal disturbance to the confined rock mass surrounding a tunnel.

D = 0

Mechanical or hand excavation in poor quality rock masses (no blasting) results in minimal disturbance to he surrounding rock mass. t

Where squeezing problems result in significant floor heave, disturbance can be severe unless a temporary invert, as shown in the photograph, is placed.

D = 0

D = 0.5 No invert

Very poor quality blasting in a hard rock tunnel results in severe local damage, extending 2 or 3 m, in the surrounding rock mass.

D = 0.8

Small scale blasting in civil engineering slopes results in modest rock mass damage, particularly if controlled blasting is used as shown on the left hand side of the photograph. However, stress relief results in some disturbance.

D = 0.7 Good blasting

D = 1.0

Poor blasting

Very large open pit mine slopes suffer significant disturbance due to heavy production blasting and also due to stress relief from overburden removal. In some softer rocks excavation can be carried out by ripping and dozing and the degree of damage to the slopes is less.

D = 1.0

Production blasting

D = 0.7

Mechanical excavation

10. REFERENCES 1. Hoek, E. and Brown, E.T. 1980. Empirical strength

criterion for rock masses. J. Geotech. Engng Div., ASCE 106 (GT9), 1013-1035.

2. Hoek, E. and Brown, E.T. 1980. Underground Excavations in Rock, London, Instn Min. Metall.

3. Hoek, E. 1968. Brittle failure of rock. In Rock Mechanics in Engineering Practice . (eds K.G. Stagg and O.C. Zienkiewicz), 99-124. London: Wiley

4. Brown, E.T. 1970. Strength of models of rock with intermittent joints. J. Soil Mech. Foundn Div., ASCE 96, SM6, 1935-1949.

5. Bieniawski Z.T. 1976. Rock mass classification in rock engineering. In Exploration for Rock Engineering, Proc. of the Symp., (ed. Z.T. Bieniawski) 1, 97-106. Cape Town, Balkema.

6. Hoek, E. and Brown, E.T. 1988. The Hoek-Brown failure criterion - a 1988 update. Proc. 15th Canadian Rock Mech. Symp. (ed. J.C. Curran), 31-38. Toronto, Dept. Civil Engineering, University of Toronto.

7. Hoek, E., Wood D. and Shah S. 1992. A modified Hoek-Brown criterion for jointed rock masses. Proc. Rock Characterization, Symp. Int. Soc. Rock Mech.: Eurock ‘92, (ed. J.A. Hudson), 209-214. London, Brit. Geotech. Soc.

8. Hoek, E. 1983. Strength of jointed rock masses, 23rd. Rankine Lecture. Géotechnique 33 (3), 187-223.

9. Ucar, R. (1986) Determination of shear failure envelope in rock masses. J. Geotech. Engg. Div. ASCE. 112, (3), 303-315.

10. Londe, P. 1988. Discussion on the determination of the shear stress failure in rock masses. ASCE J Geotech Eng Div, 14, (3), 374-6.

11. Carranza-Torres, C., and Fairhurst, C. 1999. General formulation of the elasto-plastic response of openings in rock using the Hoek-Brown failure criterion. Int. J. Rock Mech. Min. Sci., 36 (6), 777-809.

12. Hoek, E. 1990. Estimating Mohr-Coulomb friction and cohesion values from the Hoek-Brown failure criterion. Intnl. J. Rock Mech. & Mining Sci. & Geomechanics Abstracts. 12 (3), 227-229.

13. Hoek, E. 1994. Strength of rock and rock masses, ISRM News Journal, 2 (2), 4-16.

14. Hoek, E. and Brown, E.T. 1997. Practical estimates of rock mass strength. Intnl. J. Rock Mech. & Mining Sci. & Geomechanics Abstracts. 34 (8), 1165-1186.

15. Hoek, E., Kaiser P.K. and Bawden W.F. 1995. Support of underground excavations in hard rock. Rotterdam, Balkema.

16. Hoek, E., Marinos, P. and Benissi, M. 1998. Applicability of the Geological Strength Index (GSI) classification for very weak and sheared rock masses. The case of the Athens Schist Formation. Bull. Engg. Geol. Env. 57(2), 151-160.

17. Marinos, P and Hoek, E. 2000. GSI – A geologically friendly tool for rock mass strength estimation. Proc. GeoEng2000 Conference, Melbourne.

18. Hoek, E. and Marinos, P. 2000. Predicting Tunnel Squeezing. Tunnels and Tunnelling International. Part 1 – November 2000, Part 2 – December, 2000

19. Marinos. P, and Hoek, E. 2001. – Estimating the geotechnical properties of heterogeneous rock masses such as flysch. Accepted for publication in the Bulletin of the International Association of Engineering Geologists

20. Balmer, G. 1952. A general analytical solution for Mohr's envelope. Am. Soc. Test. Mat. 52, 1260-1271.

21. Sjöberg, J., Sharp, J.C., and Malorey, D.J. 2001 Slope stability at Aznalcóllar. In Slope stability in surface mining. (eds. W.A. Hustrulid, M.J. McCarter and D.J.A. Van Zyl). Littleton: Society for Mining, Metallurgy and Exploration, Inc., 183-202.

22. Pierce, M., Brandshaug, T., and Ward, M. 2001 Slope stability assessment at the Main Cresson Mine. In Slope stability in surface mining. (eds. W.A. Hustrulid, M.J. McCarter and D.J.A. Van Zyl). Littleton: Society for Mining, Metallurgy and Exploration, Inc., 239-250.

23. Lorig, L., and Varona, P. 2001 Practical slope-stability analysis using finite-difference codes. In Slope stability in surface mining. (eds. W.A. Hustrulid, M.J. McCarter and D.J.A. Van Zyl). Littleton: Society for Mining, Metallurgy and Exploration, Inc., 115-124.

24. Sonmez, H., and Ulusay, R. 1999. Modifications to the geological strength index (GSI) and their applicability to the stability of slopes. Int. J. Rock Mech. Min. Sci., 36 (6), 743-760.

25. Cheng, Y., and Liu, S. 1990. Power caverns of the Mingtan Pumped Storage Project, Taiwan. In Comprehensive Rock Engineering. (ed. J.A. Hudson), Oxford: Pergamon, 5, 111-132.

COPYRIGHT NOTICE

The following document is subject to copyright agreements. The attached copy is provided for your personal use on the understanding that you will not distribute it and that you will not include it in other published documents.

Dr Evert Hoek Evert Hoek Consulting Engineer Inc. 3034 Edgemont Boulevard P.O. Box 75516 North Vancouver, B.C. Canada V7R 4X1 Email: [email protected]

mailto:[email protected]

V. Marinos

P. Marinos

E. Hoek

The geological strength index: applicationsand limitations

Received: 7 September 2004Accepted: 9 October 2004Published online: 2 February 2005� Springer-Verlag 2005

Abstract The geological strength in-dex (GSI) is a system of rock-masscharacterization that has beendeveloped in engineering rockmechanics to meet the need for reli-able input data, particularly thoserelated to rock-mass properties re-quired as inputs into numericalanalysis or closed form solutions fordesigning tunnels, slopes or founda-tions in rocks. The geological char-acter of rock material, together withthe visual assessment of the mass itforms, is used as a direct input to theselection of parameters relevant forthe prediction of rock-mass strengthand deformability. This approachenables a rock mass to be consideredas a mechanical continuum withoutlosing the influence geology has on itsmechanical properties. It also pro-vides a field method for characteriz-ing difficult-to-describe rock masses.After a decade of application of theGSI and its variations in quantitativecharacterization of rock mass, thispaper attempts to answer questionsthat have been raised by the usersabout the appropriate selection of theindex for a range of rock masses un-der various conditions. Recommen-dations on the use of GSI are givenand, in addition, cases where the GSIis not applicable are discussed. Moreparticularly, a discussion and sug-gestions are presented on issues suchas the size of the rock mass to beconsidered, its anisotropy, the influ-ence of great depth, the presence of

ground water, the aperture and theinfilling of discontinuities and theproperties of weathered rock massesand soft rocks.

Resume Le Geological Strength In-dex (GSI) est un systeme de classifi-cation des massifs rocheuxdeveloppe en mecanique des roches.Il permet d’obtenir les donnees rel-atives aux proprietes de massesrocheuses, donnees necessaires pourdes simulations numeriques ou per-mettant le dimensionnement d’ouv-rages:tunnels, pentes ou fondationsrocheuses. Les caracteristiquesgeologiques de la matrice rocheuseainsi que celles relatives a la struc-ture du massif correspondant sontdirectement utilisees pour obtenir lesparametres appropries relatifs a ladeformabilite et la resistance de lamasse rocheuse. Cette approchepermet de considerer une masserocheuse comme un milieu continu,le role des caracteristiques geologi-ques sur les proprietes mecaniquesn’etant pas oblitere. Elle apporteaussi une methode de terrain pourcaracteriser des masses rocheusesdifficiles a decrire. Apres une decen-nie d’application du GeologicalStrength Index et de ses variantespour caracteriser des masses roche-uses, cet article tente de repondreaux questions formulees par lesutilisateurs concernant le choix leplus approprie de cet index pour unelarge gamme de massifs rocheux.

Bull Eng Geol Environ (2005) 64: 55–65DOI 10.1007/s10064-004-0270-5 ORIGINAL PAPER

V. Marinos (&) Æ P. MarinosSchool of Civil Engineering,Geotechnical Department,National Technical University of Athens,9 Iroon Polytechniou str.,157 80 Athens, GreeceE-mail: [email protected]: [email protected]

E. HoekConsulting Engineer,Vancouver, CanadaE-mail: [email protected]

Introduction

Design in rock masses

A few decades ago, the tools for designing tunnelsstarted to change. Although still crude, numericalmethods were being developed that offered the promisefor much more detailed analysis of difficult undergroundexcavation problems which, in a number of cases, falloutside the ideal range of application of the tunnelreinforcement classifications such as the RMR systemintroduced by Bieniawski (1973) and the Q systempublished by Barton et al. (1974) both furthermore ex-panded in the following years. There is absolutely noproblem with the concept of these classifications andthere are hundreds of kilometres of tunnels that havebeen successfully constructed on the basis of theirapplication. However, this approach is ideally suited tosituations in which the rock mass behaviour is relativelysimple, for example for RMR values between about 30–70 and moderate stress levels. In other words, slidingand rotation of intact rock pieces essentially control thefailure process. These approaches are less reliable forsqueezing, swelling, clearly defined structural failures orspalling, slabbing and rock-bursting under very highstress conditions. More importantly, these classificationsystems are of little help in providing information for thedesign of sequentially installed temporary reinforcementand the support required to control progressive failure indifficult tunnelling conditions.

Numerical tools available today allow the tunneldesigner to analyse these progressive failure processesand the sequentially installed reinforcement and supportnecessary to maintain the stability of the advancingtunnel until the final reinforcing or supporting structurecan be installed. However, these numerical tools requirereliable input information on the strength and defor-mation characteristics of the rock mass surrounding thetunnel. As it is practically impossible to determine thisinformation by direct in situ testing (except for back-analysis of already constructed tunnels) there was a needfor some method for estimating the rock-mass propertiesfrom the intact rock properties and the characteristics of

the discontinuities in the rock mass. This resulted in thedevelopment of the rock-mass failure criterion by Hoekand Brown (1980).

The Geological Strength Index (GSI): developmenthistory

Hoek and Brown recognized that a rock-mass failurecriterion would have no practical value unless it could berelated to geological observations that could be madequickly and easily by an engineering geologist or geol-ogist in the field. They considered developing a newclassification system during the evolution of the criterionin the late 1970s but they soon gave up the idea andsettled for the already published RMR system. It wasappreciated that the RMR system (and the Q system)were developed for the estimation of undergroundexcavation and support, and that they included param-eters that are not required for the estimation of rock-mass properties. The groundwater and structuralorientation parameters in RMR and the groundwaterand stress parameters in Q are dealt with explicitly ineffective stress numerical analyses and the incorporationof these parameters into the rock-mass property estimateresults is inappropriate. Hence, it was recommendedthat only the first four parameters of the RMR system(intact rock strength, RQD rating, joint spacing andjoint conditions) should be used for the estimation ofrock-mass properties, if this system had to be used.

In the early days the use of the RMR classification(modified as described above) worked well because mostof the problems were in reasonable quality rock masses(30<RMR<70) under moderate stress conditions.However, it soon became obvious that the RMR systemwas difficult to apply to rock masses that are of verypoor quality. The relationship between RMR and theconstants m and s of the Hoek–Brown failure criterionbegins to break down for severely fractured and weakrock masses.

Both the RMR and the Q classifications include andare heavily dependent upon the RQD classificationintroduced by Deere (1964). Since RQD in most of the

Des recommandations quant al’usage du GSI sont donnees et, deplus, des cas ou le GSI n’est pasapplicable sont discutes. Plus par-ticulierement, des suggestions sontapportees sur des questions relativesa la taille de masse rocheuse a con-siderer, son anisotropie, l»influencedes grandes profondeurs, la presence

d’eau, l’ouverture et le remplissagedes discontinuites ainsi que les pro-prietes des masses rocheuses altereeset des roches tendres.

Keywords Geological StrengthIndex Æ Rock mass Æ Geologicalstructure Æ Mechanical properties ÆSelection of the GSI

Mots cles Geological StrengthIndex Æ Massif rocheux Æ Structuregeologique Æ Proprietes mecaniques ÆConditions d»utilisation du GSI

56

weak rock masses is essentially zero or meaningless, itbecame necessary to consider an alternative classifica-tion system. The required system would not includeRQD, would place greater emphasis on basic geologicalobservations of rock-mass characteristics, reflect thematerial, its structure and its geological history andwould be developed specifically for the estimation ofrock mass properties rather than for tunnel reinforce-ment and support. This new classification, now calledGSI, started life in Toronto with engineering geologyinput from David Wood (Hoek et al. 1992). The index

and its use for the Hoek and Brown failure criterion wasfurther developed by Hoek (1994), Hoek et al. (1995)and Hoek and Brown (1997) but it was still a hard rocksystem roughly equivalent to RMR. Since 1998, EvertHoek and Paul Marinos, dealing with incredibly difficultmaterials encountered in tunnelling in Greece, developedthe GSI system to the present form to include poorquality rock masses (Fig. 1) (Hoek et al. 1998; Marinosand Hoek 2000, 2001). They also extended its applica-tion for heterogeneous rock masses as shown in Fig. 2(Marinos and Hoek 2001).

Fig. 1 General chart for GSIestimates from the geologicalobservations

57

Functions of the Geological Strength Index

The heart of the GSI classification is a careful engi-neering geology description of the rock mass which isessentially qualitative, because it was felt that the num-bers associated with RMR and Q-systems were largelymeaningless for the weak and heterogeneous rock mas-ses. Note that the GSI system was never intended as areplacement for RMR or Q as it has no rock-massreinforcement or support design capability—its onlyfunction is the estimation of rock-mass properties.

This index is based upon an assessment of thelithology, structure and condition of discontinuity sur-

faces in the rock mass and it is estimated from visualexamination of the rock mass exposed in outcrops, insurface excavations such as road cuts and in tunnel facesand borehole cores. The GSI, by combining the twofundamental parameters of the geological process, theblockiness of the mass and the conditions of disconti-nuities, respects the main geological constraints thatgovern a formation and is thus a geologically soundindex that is simple to apply in the field.

Once a GSI ‘‘number’’ has been decided upon, thisnumber is entered into a set of empirically developedequations to estimate the rock-mass properties whichcan then be used as input into some form of numerical

Fig. 2 Geological strengthindex estimates for heteroge-neous rock masses such asFlysch

58

analysis or closed-form solution. The index is used inconjunction with appropriate values for the unconfinedcompressive strength of the intact rock rci and the pet-rographic constant mi, to calculate the mechanicalproperties of a rock mass, in particular the compressivestrength of the rock mass (rcm) and its deformationmodulus (E). Updated values of mi, can be found inMarinos and Hoek (2000) or in the RocLab program.Basic procedures are explained in Hoek and Brown(1997) but a more recent refinement of the empiricalequations and the relation between the Hoek–Brownand the Mohr–Coulomb criteria have been addressed byHoek et al. (2002) for appropriate ranges of stressencountered in tunnels and slopes. This paper and theassociated program RocLab can be downloaded fromhttp://www.rocscience.com.

Note that attempts to ‘‘quantify’’ the GSI classifica-tion to satisfy the perception that ‘‘engineers are happierwith numbers’’ (Cai et al. 2004; Sonmez and Ulusay1999) are interesting but have to be applied with caution.The quantification processes used are related to thefrequency and orientation of discontinuities and arelimited to rock masses in which these numbers can easilybe measured. The quantifications do not work well intectonically disturbed rock masses in which the struc-tural fabric has been destroyed. In such rock masses theauthors recommend the use of the original qualitativeapproach based on careful visual observations.

Suggestions for using GSI

After a decade of application of the GSI and its varia-tions for the characterization of the rock mass, this pa-per attempts to answer questions that have been raisedby users about the appropriate selection of the index forvarious rock masses under various conditions.

When not to use GSI

The GSI classification system is based upon theassumption that the rock mass contains a sufficientnumber of ‘‘randomly’’ oriented discontinuities suchthat it behaves as an isotropic mass. In other words, thebehaviour of the rock mass is independent of thedirection of the applied loads. Therefore, it is clear thatthe GSI system should not be applied to those rockmasses in which there is a clearly defined dominantstructural orientation. Undisturbed slate is an exampleof a rock mass in which the mechanical behaviour ishighly anisotropic and which should not be assigned aGSI value based upon the charts presented in Figs. 1, 2.However, the Hoek–Brown criterion and the GSI chartcan be applied with caution if the failure of such rockmasses is not controlled by their anisotropy (e.g. in the

case of a slope when the dominant structural disconti-nuity set dips into the slope and failure may occurthrough the rock mass). For rock masses with a struc-ture such as that shown in the sixth (last) row of the GSIchart (Fig. 1), anisotropy is not a major issue as thedifference in the strength of the rock and that of thediscontinuities within it is small.

It is also inappropriate to assign GSI values toexcavated faces in strong hard rock with a few discon-tinuities spaced at distances of similar magnitude to thedimensions of the tunnel or slope under consideration.In such cases the stability of the tunnel or slope will becontrolled by the three-dimensional geometry of theintersecting discontinuities and the free faces created bythe excavation. Obviously, the GSI classification doesnot apply to such cases.

Geological description in the GSI chart

In dealing with specific rock masses it is suggested thatthe selection of the appropriate case in the GSI chartshould not be limited to the visual similarity with thesketches of the structure of the rock mass as they appearin the charts. The associated descriptions must also beread carefully, so that the most suitable structure ischosen. The most appropriate case may well lie at someintermediate point between the limited number of sket-ches or descriptions included in the charts.

Projection of GSI values into the ground

Outcrops, excavated slopes tunnel faces and boreholecores are the most common sources of information forthe estimation of the GSI value of a rock mass. Howshould the numbers estimated from these sources beprojected or extrapolated into the rock mass behind aslope or ahead of a tunnel?

Outcrops are an extremely valuable source of data inthe initial stages of a project but they suffer from thedisadvantage that surface relaxation, weathering and/oralteration may have significantly influenced the appear-ance of the rock-mass components. This disadvantagecan be overcome (where permissible) by trial trenchesbut, unless these are machine excavated to considerabledepth, there is no guarantee that the effects of deepweathering will have been eliminated. Judgement istherefore required in order to allow for these weatheringand alteration effects in assessing the most probable GSIvalue at the depth of the proposed excavation.

Excavated slope and tunnel faces are probably themost reliable source of information for GSI estimatesprovided that these faces are reasonably close to and inthe same rock mass as the structure under investigation.In hard strong rock masses it is important that an

59

appropriate allowance be made for damage due tomechanical excavation or blasting. As the purpose ofestimating GSI is to assign properties to the undisturbedrock mass in which a tunnel or slope is to be excavated,failure to allow for the effects of blast damage whenassessing GSI will result in the assignment of values thatare too conservative. Therefore, if borehole data areabsent, it is important that the engineering geologist orgeologist attempts to ‘‘look behind’’ the surface damageand try to assign the GSI value on the basis of theinherent structures in the rock mass. This problem be-comes less significant in weak and tectonically disturbedrock masses as excavation is generally carried out by‘‘gentle’’ mechanical means and the amount of surfacedamage is negligible compared to that which alreadyexists in the rock mass.

Borehole cores are the best source of data at depth,but it has to be recognized that it is necessary toextrapolate the one-dimensional information providedby the core to the three-dimensional in situ rock mass.However, this is a problem common to all boreholeinvestigations, and most experienced engineering geolo-gists are comfortable with this extrapolation process.Multiple boreholes and inclined boreholes can be ofgreat help in the interpretation of rock-mass character-istics at depth.

For stability analysis of a slope, the evaluation isbased on the rock mass through which it is anticipatedthat a potential failure plane could pass. The estimationof GSI values in these cases requires considerable judg-ment, particularly when the failure plane can passthrough several zones of different quality. Mean valuesmay not be appropriate in this case.

For tunnels, the index should be assessed for thevolume of rock involved in carrying loads, e.g. for aboutone diameter around the tunnel in the case of tunnelbehaviour or more locally in the case of a structure suchas an elephant foot.

For particularly sensitive or critical structures, suchas underground powerhouse caverns, the informationobtained from the sources discussed above may not beconsidered adequate, particularly as the design advancesbeyond the preliminary stages. In these cases, the use ofsmall exploration tunnels can be considered and thismethod of data gathering will often be found to behighly cost effective.

Figure 3 provides a visual summary of some of theadjustments discussed in the previous paragraphs. Whendirect assessment of depth conditions is not available,upward adjustment of the GSI value to allow for theeffects of surface disturbance, weathering and alterationare indicated in the upper (white) part of the GSI chart.Obviously, the magnitude of the shift will vary from caseto case and will depend upon the judgement and expe-rience of the observer. In the lower (shaded) part of thechart, adjustments are not normally required as the rock

mass is already disintegrated or sheared and this damagepersists with depth.

Anisotropy

As discussed above, the Hoek–Brown criterion (andother similar criteria) requires that the rock mass behaveisotropically and that failure does not follow a prefer-ential direction imposed by the orientation of a specificdiscontinuity or a combination of two or three discon-tinuities. In these cases, the use of GSI is meaningless asthe failure is governed by the shear strength of thesediscontinuities and not of the rock mass. Cases, how-ever, where the criterion and the GSI chart can rea-sonably be used were discussed above.

However, in a numerical analysis involving a singlewell-defined discontinuity such as a shear zone or fault,it is sometimes appropriate to apply the Hoek–Browncriterion to the overall rock mass and to superimpose thediscontinuity as a significantly weaker element. In thiscase, the GSI value assigned to the rock mass shouldignore the single major discontinuity. The properties ofthis discontinuity may fit the lower portion of the GSIchart or they may require a different approach such aslaboratory shear testing of soft clay fillings.

Aperture of discontinuities

The strength and deformation characteristics of a rockmass are dependent upon the interlocking of the indi-vidual pieces of intact rock that make up the mass.Obviously, the aperture of the discontinuities that sep-arate these individual pieces has an important influenceupon the rock-mass properties.

There is no specific reference to the aperture of thediscontinuities in the GSI charts but a ‘‘disturbancefactor’’ D has been provided in the most recent versionof the Hoek–Brown failure criterion (Hoek et al. 2002).This factor ranges from D=0 for undisturbed rockmasses, such as those excavated by a tunnel boringmachine, to D=1 for extremely disturbed rock massessuch as open pit mine slopes that have been subjected tovery heavy production blasting. The factor allows forthe disruption of the interlocking of the individual rockpieces as a result of opening of the discontinuities.

The incorporation of the disturbance factor D intothe empirical equations used to estimate the rock-massstrength and deformation characteristics is based uponback-analysis of excavated tunnels and slopes. At thisstage (2004) there is relatively little experience in the useof this factor, and it may be necessary to adjust itsparticipation in the equations as more field evidenceis accumulated. However, the limited experience thatis available suggests that this factor does provide a

60

reasonable estimate of the influence of damage due tostress relaxation or blasting of excavated rock faces.

Note that this damage decreases with depth into therock mass and, in numerical modelling, it is generallyappropriate to simulate this decrease by dividing therock mass into a number of zones with decreasing valuesof D being applied to successive zones as the distancefrom the face increases. In one example, which involvedthe construction of a large underground powerhousecavern in interbedded sandstones and siltstones, it wasfound that the blast damaged zone was surrounding

each excavation perimeter to a depth of about 2 m(Cheng and Liu 1990). Carefully controlled blasting wasused in this cavern excavation and the limited extent ofthe blast damage can be considered typical of that forcivil engineering tunnels excavated by drill and blastmethods. On the other hand, in very large open pit mineslopes in which blasts can involve many tons of explo-sives, blast damage has been observed up to 100 m ormore behind the excavated slope face. Hoek and Karz-ulovic (2000) have given some guidance on the extent ofthis damage and its impact on rock mass properties.

Fig. 3 Suggested projection ofinformation from observationsin outcrops to depth. Whitearea: a shifting to the left or tothe left and upwards is recom-mended; the extent of the shiftshown in the chart is indicativeand should be based on geo-logical judgement. Shadowedarea: shifting is less or notapplicable as poor quality isretained in depth in brecciated,mylonitized or shear zones

61

Geological Strength Index at great depth

In hard rock, great depth (e.g. 1,000 m or more) therock-mass structure is so tight that the mass behaviourapproaches that of the intact rock. In this case, the GSIvalue approaches 100 and the application of the GSIsystem is no longer meaningful.

The failure process that controls the stability ofunderground excavations under these conditions isdominated by brittle fracture initiation and propagation,which leads to spalling, slabbing and, in extreme cases,rock-bursts. Considerable research effort has been de-voted to the study of these brittle fracture processes anda recent paper by Diederichs et al. (2004) provides auseful summary of this work. Cundall et al. (2003) haveintroduced a set of post-failure flow rules for numericalmodelling which cover the transition from tensile toshear fracture that occurs during the process of brittlefracture propagation around highly stressed excavationsin hard rock masses.

When tectonic disturbance is important and persistswith depth, these comments do not apply and theGSI charts may be applicable, but should be used withcaution.

Discontinuities with filling materials

The GSI charts can be used to estimate the character-istics of rock-masses with discontinuities with fillingmaterials using the descriptions in the columns of pooror very poor condition of discontinuities. If the fillingmaterial is systematic and thick (e.g. more than few cm)or shear zones are present with clayey material then theuse of the GSI chart for heterogeneous rock masses(Fig. 2) is recommended.

The influence of water

The shear strength of the rock mass is reduced by thepresence of water in the discontinuities or the fillingmaterials when these are prone to deterioration as aresult of changes in moisture content. This is particularlyvalid in the fair to very poor categories of discontinuitieswhere a shift to the right may be made for wet condi-tions (Fig. 4).

Water pressure is dealt with by effective stress anal-ysis in design and it is independent of the GSI charac-terization of the rock mass.

Weathered rock masses

The GSI values for weathered rock masses are shifted tothe right of those of the same rock masses when these areunweathered. If the weathering has penetrated into theintact rock pieces that make up the mass (e.g. in weath-

ered granites) then the constant mi and the unconfinedstrength of the rci of the Hoek and Brown criterion mustalso be reduced. If the weathering has penetrated therock to the extent that the discontinuities and the struc-ture have been lost, then the rock mass must be assessedas a soil and the GSI system no longer applies.

Heterogeneous and lithologically varied sedimentaryrock masses

The GSI has recently been extended to accommodatesome of the most variable of rock masses, includingextremely poor quality sheared rock masses of weakschistose materials (such as siltstones, clay shales orphyllites) sometime inter-bedded with strong rock (suchas sandstones, limestones or quartzites). A GSI chart forflysch has been published in Marinos and Hoek (2001)and is reproduced in Fig. 2. For lithologically varied buttectonically undisturbed rock masses, such as themolasses, a new GSI chart is (Hoek et al. 2005).

Rocks of low strength

When rocks such as marls, claystones, siltstones andweak sandstones are developed in stable conditions or apost tectonic environment, they present a simple struc-ture with few discontinuities. Even when bedding planesexist they do not always appear as clearly defined dis-continuity surfaces.

In such cases, the use of theGSI chart for the ‘‘blocky’’or ‘‘massive’’ rock masses (Fig. 1) is applicable. The dis-continuities, although they are limited in number, cannotbe better than fair (usually fair or poor) and hence theGSIvalues tend to be in the range of 40–60. In these cases, thelow strength of the rock mass results from low values ofthe intact strength rci and the constant mi.

When these rocks form continuous masses with nodiscontinuities, the rock mass can be treated as intactwith engineering parameters given directly by laboratorytesting. In such cases the GSI classification is notapplicable.

Precision of the GSI classification system

The ‘‘qualitative’’ GSI system works well for engineeringgeologists since it is consistent with their experience indescribing rocks and rock masses during logging andmapping. In some cases, engineers tend to be uncom-fortable with the system because it does not containparameters that can be measured in order to improve theprecision of the estimated GSI value.

The authors, two of whom graduated as engineers, donot share this concern as they feel that it is not mean-ingful to attempt to assign a precise number to the GSI

62

value for a typical rock mass. In all but the very simplestof cases, GSI is best described by assigning it a range ofvalues. For analytical purposes this range may be definedby a normal distribution with the mean and standarddeviation values assigned on the basis of common sense.

In the earlier period of the GSI application it wasproposed that correlation of ‘‘adjusted’’ RMR and Qvalues with GSI be used for providing the necessaryinput for the solution of the Hoek and Brown criterion.Although this procedure may work with the betterquality rock masses, it is meaningless in the range of

weak (e.g. GSI<35), very weak and heterogeneous rockmasses where these correlations are not recommended.

Estimation of intact strength rci and the constant mi

While this paper is concerned primarily with the GSIclassification, it would not be appropriate to leave therelated topic of the Hoek–Brown failure criterion with-out briefly mentioning the estimation of intact strengthrci and the constant mi.

Fig. 4 In fair to very poorcategories of discontinuities, ashift to the right is necessary forwet conditions as the surfaces ofthe discontinuities or the fillingmaterials are usually prone todeterioration as a result ofchange in the moisture content.The shift to the right is moresubstantial in the low qualityrange of rock mass (last linesand columns)

63

The influence of the intact rock strength rci is at leastas important as the value of GSI in the overall estimateof rock mass properties by means of the Hoek–Browncriterion. Ideally, rci should be determined by directlaboratory testing under carefully controlled conditions.However, in many cases, this is not possible because oftime or budget constraints, or because it is not possibleto recover samples for laboratory testing (particularly inthe case of weak, thinly schistose or tectonically dis-turbed rock masses where discontinuities are included inthe laboratory samples). Under such circumstances,estimates of the value of rci have to be made on thebasis of published information, simple index tests or bydescriptive grades such as those published by theInternational Society for Rock Mechanics (Brown1981).

Experience has shown that there is a tendency tounderestimate the value of the intact rock strength inmany cases. This is particularly so in weak and tecton-ically disturbed rock masses where the characteristics ofthe intact rock components tend to be masked by thesurrounding sheared or weathered material. Theseunderestimations can have serious implications forengineering design and care has to be taken to ensurethat realistic estimates of intact strength are made asearly as possible in the project. In tunnelling, such esti-mates can be refined on the basis of a detailed back-analysis of the tunnel deformation and, while this mayrequire considerable effort and even the involvement ofspecialists in numerical analysis, the attempt will gen-erally be repaid many times over in the cost savingsachieved by more realistic designs.

The value of the constant mi, as for the case of theintact strength rci, is best determined by direct labora-tory testing. However, when this is not possible, anestimate based upon published values (e.g. in the pro-gram RocLab) is generally acceptable as the overallinfluence of the value of mi on the rock-mass strength issignificantly less than that of either GSI or rci.

GSI and contract documents

One of the most important contractual problems in rockconstruction and particularly in tunnelling is the issue of‘‘changed ground conditions’’. There are invariablyarguments between the owner and the contractor on thenature of the ground specified in the contract and thatactually encountered during construction. In order toovercome this problem there has been a tendency tospecify the anticipated conditions in terms of the RMRor Q tunnelling classifications. More recently somecontracts have used the GSI classification for this pur-pose, and the authors are strongly opposed to this trend.As discussed earlier in this paper, RMR and Q weredeveloped for the purposes of estimating tunnel rein-

forcement or support whereas GSI was developed solelyfor the purpose of estimating rock-mass strength.Therefore, GSI is only one element in a tunnel designprocess and cannot be used, on its own, to specify tun-nelling conditions.

The use of any classification system to specify antic-ipated tunnelling conditions is always a problem as thesesystems are open to a variety of interpretations,depending upon the experience and level of conservatismof the observer. This can result in significant differencesin RMR or Q values for a particular rock mass and, ifthese differences fall on either side of a major ‘‘change’’point in excavation or support type, this can haveimportant financial consequences.

The geotechnical baseline report (Essex 1997)was introduced in an attempt to overcome some ofthese difficulties and has attracted an increasingamount of international attention in tunnelling1. Thisreport, produced by the Owner and included inthe contract documents, attempts to describe therock mass and the anticipated tunnelling conditionsas accurately as possible and to provide a rationalbasis for contractual discussions and payment. The au-thors of this paper recommend that this concept shouldbe used in place of the traditional tunnel classificationsfor the purpose of specifying anticipated tunnelconditions.

Conclusions

Rock-mass characterization has an important role in thefuture of engineering geology in extending its usefulness,not only to define a conceptual model of the site geol-ogy, but also for the quantification needed for analyses‘‘to ensure that the idealization (for modelling) does notmisinterpret actuality’’ (Knill 2003). If it is carried out inconjunction with numerical modelling, rock-mass char-acterization presents the prospect of a far better under-standing of the reasons for rock-mass behaviour(Chandler et al. 2004). The GSI has considerable po-tential for use in rock engineering because it permits themanifold aspects of rock to be quantified therebyenhancing geological logic and reducing engineeringuncertainty. Its use allows the influence of variables,which make up a rock mass, to be assessed and hence thebehaviour of rock masses to be explained more clearly.One of the advantages of the index is that the geologicalreasoning it embodies allows adjustments of its ratingsto cover a wide range of rock masses and conditionsbut it also allows us to understand the limits of itsapplication.

1A simple search for ‘‘geotechnical baseline report’’ on the Internetwill reveal the extent of this interest.

64

References

Barton NR, Lien R, Lunde J (1974) Engi-neering classification of rock masses forthe design of tunnel support. RockMech 6(4):189–239

Bieniawski ZT (1973) Engineering classifi-cation of jointed rock masses. Trans SAfr Inst Civ Eng 15:335–344

Brown ET (ed) (1981) Rock characteriza-tion, testing and monitoring—ISRMsuggested methods. Pergamon, Oxford,pp 171–183

Cai M, Kaiser PK, Uno H, Tasaka Y,Minami M (2004) Estimation of rockmass strength and deformation modu-lus of jointed hard rock masses usingthe GSI system. Int J Rock Mech MinSci 41(1):3–19

Chandler RJ, de Freitas MH, Marinos P(2004) Geotechnical characterization ofsoils and rocks: a geological perspective.Advances in geotechnical engineering:the Skempton conference, vol 1, Tho-mas Telford, London, pp 67–102

Cheng Y, Liu SC (1990) Power caverns ofthe Mingtan Pumped Storage Project,Taiwan. In: JA Hudson (ed) Compre-hensive Rock Engineering, vol 5, pp111–132

Cundall P, Carranza-Torres C, Hart R(2003) A new constitutive model basedon the Hoek–Brown criterion. In:Brummer et al. (eds) Proceedings of the3rd international symposium on FLACand FLAC3D numerical modelling inGeomechanics, Sudbury, October 21–24, pp 17–25

Deere DU (1964) Technical description ofrock cores for engineering purposes.Rock Mech Eng Geol 1(1):17–22

Diederichs MS, Kaiser PK, Eberhardt E(2004) Damage initiation and propaga-tion in hard rock during tunnelling andthe influence of near-face stress rota-tion. Int J Rock Mech Min Sci41(5):785–812

Essex RJ (1997) Geotechnical baseline re-ports for underground construction.American Society of Civil Engineers,Reston

Hoek E (1994) Strength of rock and rockmasses. News J ISRM 2(2):4–16

Hoek E, Brown ET (1980) Undergroundexcavations in rock. Institution ofMining and Metallurgy, London

Hoek E, Brown ET (1997) Practical esti-mates of rock mass strength. Int J RockMech Min Sci Geomech Abstr 34:1165–1186

Hoek E, Karzulovic A (2000) Rock massproperties for surface mines. In: Hu-stralid WA, McCarter MK, van ZylDJA (eds) Slope stability in surfacemining. Society for Mining, Metallur-gical and Exploration (SME), Littleton,pp 59–70

Hoek E, Wood D, Shah S (1992) A modi-fied Hoek–Brown criterion for jointedrock masses. In: Hudson JA (ed) Pro-ceedings of the rock mechanic sympo-sium. International Society of RockMechanics Eurock’’ 92, British Geo-technical Society, London, pp 209–214

Hoek E, Marinos P, Marinos V (2005)Characterization and engineering prop-erties of tectonically undisturbed butlithologically varied sedimentary rockmasses under publication. Int J RockMech Min Sci

Hoek E, Kaiser PK, Bawden WF (1995)Support of underground excavations inhard rock. AA Balkema, Rotterdam

Hoek E, Marinos P, Benissi M (1998)Applicability of the geological strengthindex (GSI) classification for weak andsheared rock masses—the case of theAthens schist formation. Bull Eng GeolEnv 57(2):151–160

Hoek E, Caranza-Torres CT, Corcum B(2002) Hoek–Brown failure criterion-2002 edition. In: Bawden HRW, CurranJ, Telsenicki M (eds) Proceedings of theNorth American Rock MechanicsSociety (NARMS-TAC 2002). MiningInnovation and Technology, Toronto,pp 267–273

Knill J (2003) Core values (1st Hans-Closslecture). Bull Eng Geol Env 62:1–34

Marinos P, Hoek E (2000) GSI: a geologi-cally friendly tool for rock massstrength estimation. In: Proceedings ofthe GeoEng2000 at the internationalconference on geotechnical and geolog-ical engineering, Melbourne, Technom-ic publishers, Lancaster, pp 1422–1446

Marinos P, Hoek E (2001) Estimating thegeotechnical properties of heteroge-neous rock masses such as flysch. BullEng Geol Env 60:82–92

Sonmez H, Ulusay R (1999) Modificationsto the geological strength index (GSI)and their applicability to the stability ofslopes. Int J Rock Mech Min Sci36:743–760

65


Programa de Ensayos de Caracterización Mecánica Informe Geotécnico Final, Proyecto 06–1705–01 de Rocas, Proyecto Tigresa, Cía. Minera Carmen Bajo, Copiapó Anexo Fotografías

ANEXO FOTOGRAFIAS DIORITA DE BREA

TRACCION INDIRECTA COMPRESION TRIAXIAL SIMPLE COMPRESION UNIAXIAL SIMPLE



ENSAYOS TRACCION INDIRECTA

DIORITA DE BREA: NO ALTERADA

Tig 3 ml 14,5

Tig 7 ml 41

Tig 19 ml 13

Tig 7 ml 37

Tig 19 ml 18



DIORITA DE BREA: CON VETILLAS

Tig 3 ml 18

Tig 6 ml 11

Tig 18 ml 13

Tig 9 ml 9

Tig 6 ml 16



DIORITA DE BREA: ALTERADA

Tig 20 ml 13

Tig 18 ml 27

Tig 6 ml 16,5

Tig 20 ml 10

Tig 1 ml 5



COMPRESION TRIAXIAL SIMPLE DIORITA DE BREA: NO ALTERADA

Tig 6 ml 16,5

Tig2 ml 6

Tig 1 ml 5

Tig 1 ml 3




Tig 3 ml 18

Tig 9 ml 9

Tig 6 ml 16

Tig 19 ml 18



DIORITA DE BREA. ALTERADA

Tig 3 ml 14,5

Tig 3 ml 13

Tig 4 ml 10,6

Tig 1 ml 6



COMPRESIÓN UNIAXIAL SIMPLE

DIORITA DE BREA: ALTERADA

Tig 7 ml 37

Tig 19 ml 13

Tig 7 ml 41



DIORITA DE BREA: NO ALTERADA

Tig 20 ml 10

Tig 20 ml 13

Tig 18 ml 27




Tig 6 ml 11

Tig 18 ml 13



MUESTRAS USADAS PARA DETERMINACION DE POROSIDAD

Documents

c92 Anexo v Informe Geotecnico