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|The ISRM commission on testing methods has recently presented Suggested Methods for rock stress determination (Kim & Franklin, 1987). This proposes that even if the magnitude of in situ stress is not sufficient to cause significant ground problems, the optimum shape, orientation, and layout of underground structures can be significantly affected by it. In the design of underground excavations, the engineer often requires a knowledge of the average in situ stress tensor in the rock mass. However, attempts to measure a stress state applicable to design have proved frustrating, and a high degree of uncertainty is introduced by the variability in results. In the belief that deduced fluctuations are random in nature, many separate measurements are often made, so that a more reliable stress tensor average, and some indication of the associated variance (see Dyke et al., 1986) can be calculated. Unfortunately, this approach is limited by economic considerations and, as with any sampling procedure, it is imperative to understand the sources of measured variability, in order to design an optimum measurement programme. Cundall(1987) itemised the main causes of stress variability as a. Instrument and measurement errors, and b. Natural fluctuations of stress from point to point, induced by the action of a boundary stress on the internal rock structure. At least four categories exist: i. inhomogeneous rock, bedding, intrusions etc.; ii. differential contraction, creep, or changes in rock properties with time; iii. proximity to faults or discontinuities; iv. cycles of tectonic activity that cause movement on joints. The latter was successfully investigated using the distinct element programme UDEC. In this paper, the contribution of items (iii) and (iv) (i.e. the items related to discontinuities) to the total stress variability will be discussed, for the kind of rock mass shown in Figure 1. Although many authors have concluded that rock joints have an influence on the stress in their vicinity, a more analytical approach is required if the stress distribution associated with different jointed rock masses is to be (i) compared, and (ii) related to routinely measured joint parameters. If this can be achieved then, prior to any attempt to measure stress in a jointed rock mass, a consideration of joint geometry, joint deformability, and the geological kinematics of joints (e.g. the magnitude and direction of previous movements), can place valuable `common sense' constraints on the expected stress system for minimal extra cost.|
Additional chapters/articles from the SME-ICGCM book Rock Mechanics as a Guide for Efficient Utilization of Natural Resources
|Rock Mechanics And Ground Control For Underground Mining And||Underground Storage, With Emphasis On Storage In Excavated R||Rock Classification For Portal Design||Laboratory And Field Characterization Of Immediate Floor Str||Comparative Study Of Western US Longwall Panel Entry Systems||Supercomputer Assisted Three-Dimensional Finite Element Anal||DEPOWS - A Powered Support Selection Model||A Study Of Displacement Field Of Main Roof In Longwall Minin||Cavability Investigation Of A Stratabound Copper Deposit, To||Influence Of Discontinuity Orientations And Strength On Cava||Premining Stability Analysis Of A Shaft Pillar At The Homest||Identification Of Critical Slope Failure Surfaces With Criti||Improving Design Methodology For Innovative Rock Mechanics D||Stability Evaluation Of Alternative Designs Of Drift-And-Fil||In Situ Stress For Underground Excavation Design In A Natura||Application Of Physical And Mathematical Modelling In Underg||Complex Seismic Trace Attributes In Coal Exploration||Changes In Seismic Measurements With Blast Induced Fracturin||Changes In The Seismic Properties Of The Cover Produced By L||Crosshole Seismics: Applications In Mining||Geotechnical Mapping By Seismic Imaging In Underground Mines||Experimental Study Of Line Electrode Method To Detect Underg||Time-Dependent Behavior Of Rocks: Laboratory Tests On Hollow||Pillar Sizing||An Applications Approach To Barrier Pillar Design For Improv||Yield Pillar Application Under Strong Roof And Strong Floor||Methods To Determine Pillar Stress Distribution And Its Effe||Correlation Between Unconfined Compressive And Point Load St||Study Of Coal Fragmentation Under Conical Bit Indentation||Development of in-situ stress measurement technique using ul||Understanding the hydraulic pressure cell||Development of a mechanistic model for prediction of maximum||Subsidence prediction using a laminated linear model||Subsidence and environmental impacts in Japanese coal mining||Surface damage due to longwall mining - A case study||Pre-mining stresses at some hard rock mines in the Canadian||Estimation of in-situ material strength||The research on the mechanical properties of hard roof in un||Relationship between the clay fabric of roof shales and roof||Failure mechanisms in ultra-close seam mining||An analysis of roof-pillar-weak floor interaction in partial||Finite element analysis and comparison of shaly mine roof su||Stability analysis and characterization of ground subsidence||Subsidence monitoring at a shallow partial extraction room-a||Assessment of surface fracture depth and intensity due to su||Prediction of surface movement with emphasis on horizontal d||Numerical simulation of coal pillar loading with the aid of||Three-dimensional FEM analysis to sale field measurements fr||Front abutment effects on supplemental support in predriven||Direct determination of failure surfaces in earth slopes||Hydraulic stowing - A solution for subsidence due to undergr||Research on the rational structure of tensible rockbolt and||System behavior analysis of the ground movement around a lon||CISPM - A subsidence prediction model||Dynamic rock anchors||Ropes mine crown pillar rock mechanics||Deformation and failure-time prediction in rock mechanics||Influence of joints on the elastic response of a LFUFL stope||Support selection of mine roadways by means of a computer pr||Theoretical analysis of breaking strength of mine pillars an||A comparison between two- and three-dimensional numerical mo|