Rock Mass Characterization and Rock Property Variability Considerations for Tunnel and Cavern Design

Geotechnical design input parameters, such as in situ stress field, rock mass strength parameters and deformation modulus, are never known precisely. There are always uncertainties involved in these parameters, some are intrinsic and others are due to lack of knowledge or understanding of these parameters. To quantify the effects of these uncertainties on tunnel and cavern design, it is necessary to utilize probabilistic analysis methods. In the present study, a quantitative, probabilistic approach to use the Geological Strength Index (GSI) system for rock mass characterization is presented. It employs the block volume and a joint condition factor as quantitative characterization factors to determine the GSI values. The approach is built on the linkage between descriptive geological terms and measurable field parameters such as joint spacing and joint roughness, which are random variables. Using GSI values obtained from field mapping data, and in combination with the intact rock strength properties, the probability density distributions of rock mass strength parameters and elastic moduli of the jointed rock mass can be calculated using Monte Carlo method. Furthermore, probabilistic analysis of tunnel and cavern stability based on the variable input parameters is conducted employing the point estimate method. One example is given to illustrate how to consider the variability of in situ stress and the rock mass properties in tunnel and cavern design. The method presents an approach for systematic assessment of uncertainty in rock mass characterization in rock engineering, and it can assist us to better understand how uncertainty arises and how the rock support system design decision may be affected by it.

[1]  Nick Barton,et al.  Engineering classification of rock masses for the design of tunnel support , 1974 .

[2]  J. A. Hudson,et al.  Information, uncertainty and decision making in site investigation for rock engineering , 1997 .

[3]  O. Zienkiewicz,et al.  Rock mechanics in engineering practice , 1968 .

[4]  P. K. Kaiser,et al.  Consideration of uncertainty in modelling the behaviour of underground excavations , 2010 .

[5]  Evert Hoek,et al.  HOEK-BROWN FAILURE CRITERION - 2002 EDITION , 2002 .

[6]  P. K. Kaiser,et al.  Support of underground excavations in hard rock , 1995 .

[7]  P. Pells,et al.  Developments in the design of tunnels and caverns in the Triassic rocks of the Sydney region , 2002 .

[8]  M. Cai.  Practical Estimates of Tensile Strength and Hoek–Brown Strength Parameter mi of Brittle Rocks , 2010 .

[9]  Emilio Rosenblueth,et al.  Two-point estimates in probabilities , 1981 .

[10]  E. T. Brown,et al.  Underground excavations in rock , 1980 .

[11]  John A. Hudson,et al.  Discontinuity spacings in rock , 1976 .

[12]  Y. Tasaka,et al.  A JOINT AND ROCK FAILURE STRAIN-SOFTENING MODEL AND ITS APPLICATION TO THE EXCAVATION SIMULATION OF LARGE-SCALE UNDERGROUND CAVERNS , 2000 .

[13]  Peter K. Kaiser,et al.  Numerical simulation of cumulative damage and seismic energy release during brittle rock failure-Part I: Fundamentals , 1998 .

[14]  Evert Hoek,et al.  Big Tunnels in Bad Rock , 2001 .

[15]  Herbert H. Einstein,et al.  Characterizing rock joint geometry with joint system models , 1988 .

[16]  Sarah Lichtenstein,et al.  Empirical scaling of common verbal phrases associated with numerical probabilities , 1967 .

[17]  S. Priest,et al.  ESTIMATION OF DISCONTINUITY SPACING AND TRACE LENGTH USING SCANLINE SURVEYS , 1981 .

[18]  Diederichs,et al.  Underground Works In Hard Rock Tunnelling And Mining , 2000 .

[19]  Alfred J. Hendron,et al.  Rock Engineering for Underground Caverns , 1971 .

[20]  Bo-Hyun Kim,et al.  Estimation of Block Sizes for Rock Masses with Non-persistent Joints , 2007 .

[21]  E. T. Brown,et al.  Rock Mechanics: For Underground Mining , 1985 .

[22]  Chung-In Lee,et al.  Estimation of joint length distribution using window sampling , 2001 .

[23]  Peter K. Kaiser,et al.  Stress, instability and design of underground excavations , 2003 .

[24]  P. K. Kaiser,et al.  Estimation of rock mass deformation modulus and strength of jointed hard rock masses using the GSI system , 2004 .

[25]  P. K. Kaiser,et al.  Determination of residual strength parameters of jointed rock masses using the GSI system , 2007 .

[26]  Ming Cai,et al.  Visualization of rock mass classification systems , 2006 .

[27]  Z. Bieniawski.  Determining rock mass deformability: experience from case histories , 1978 .

[28]  Nick Barton,et al.  Estimation Of Support Requirements For Underground Excavations , 1975 .

[29]  Ming Cai,et al.  Comparative Study of Rock Support System Design Practice for Large-Scale Underground Excavations , 2000 .

[30]  E. Hoek,et al.  Empirical estimation of rock mass modulus , 2006 .

[31]  S. Sakurai,et al.  Direct Strain Evaluation Technique In Construction Of Underground Opening , 1981 .

[32]  Li-Yi Wei,et al.  Part I: fundamentals , 2007, SIGGRAPH Courses.

[33]  Ming Cai,et al.  Generalized crack initiation and crack damage stress thresholds of brittle rock masses near underground excavations , 2004 .

[34]  Arild Palmström,et al.  Use and misuse of rock mass classification systems with particular reference to the Q-system , 2006 .

[35]  Z. T. Bieniawski,et al.  Rock mechanics design in mining and tunneling , 1984 .

[36]  E. Hoek,et al.  Predicting tunnel squeezing problems in weak heterogeneous rock masses , 2000 .