Canadian hard rock mine extraction practices have commonly created shallow stopes, 12% of which have caved to surface, from instabilities originating from stope hangingwalls, crowns or footwalls. To date, however, mine operators have applied few of the available data gathering and design tools to strike a balance between maximum economic excavation dimension and stope viability. The preference has been to use personal mining experience. / Several common rock mass environments are surveyed as well as the various ways in which shallow stopes have failed. It has been found that these rock masses develop gravity-induced movement in the form of plug failures, ravelling of rock blocks, strata failures, chimneying disintegration, and rock mass block caving. / New failure-specific analytical equations are developed here for these common failure mechanisms. They address the mechanics of the failure process and incorporate the capability to arrive at the ultimate failure outline, for comparison to the location of the bedrock surface. / This research has shown that: plug failures occur along steep, uninterrupted discontinuities bounding large blocks. Plug failure potential reduces substantially with confining compressive stress, discontinuity inclination, the absence of low friction surfaces and shearing of intact rock interrupting the discontinuity. Ravelling requires little peripheral confining stress for stabilization and prevention of block falls or slides. However, inherent conditions such as shallow dipping or vertically dipping joints can cause block falls to develop to surface. Low confining stresses, resulting from multiple stope extraction in orthogonal horizontal directions, would offer conditions suitable for plug and ravelling failures. Strata failures are caused by excessive stope spans, but the limited loading received from above strata is such, that the failure cavity created is of limited vertical extent, some 25% of the stope width. Chimneying disintegration occurs in weak rock masses with low cohesion, over narrow openings that can be as deep as 275 m. The onset of chimneying disintegration can be created by compressive stresses, but develops as a result of mobilization of the rock mass by gravity in active shear. Block caving requires large spans to develop, and stabilizing could be overcome from arching stresses overcoming bulk arching strength. Controlling instability elements are tabulated for these failure mechanisms. A limit equilibrium correlation between span and cohesion for chimneying disintegration is presented, and the controlling limits between the occurrence of chimneying disintegration and block caving is discussed. Ravelling and chimneying disintegration are the most expected failure mechanisms for shallow stopes of hard rock mines. Although failure of the shallow stope may start around its periphery, stope failure to surface would likely occur in or close to the surface crown pillar. / Although the analytical equations developed require input of in situ stresses defined by numerical modelling in order to yield a precise answer, conventional numerical modelling or empirical methods are shown to be unable to predict stope failures as the analytical equations have. A step-by-step stability analysis procedure is presented, incorporating rockmass environment, expected failure mechanism(s), and applicable data gathering and anlytical methods. (Abstract shortened by UMI.)

Rockbursts may cause damages to underground openings and to equipment, and constitute a major hazard to the safety of mine workers. One method that can be used to evaluate if there is a rockburst potential is to compare the stiffness of the failed rock with that of the surrounding rock mass. This method has been applied successfully in the past to rockbursts involving fracturing of the rock mass. / This thesis deals with the development of a similar approach for rockbursts involving a violent slip along major geological discontinuities. To evaluate the post-peak shear stiffness of a discontinuity, a new non-linear constitutive model for rock joint was developed. This model is based on two exponential formulations expressing the two phenomena taking part in the shearing process: friction resistance along surfaces and shearing of asperities. Compared with test results, the model showed a correlation factor (R2) of 0.90. The model was then implemented in an existing boundary element code to evaluate the interaction between underground openings and nearby geological discontinuities. Verification of the implementation was done by reproducing direct shear tests on a discontinuity. Parametric analyses were performed on the new model that highlighted the most important parameters. Methods to obtain the different stiffnesses involved in the violent slip process were developed. Examples of applications were given to illustrate the proposed methods. / Finally, an alternative method to evaluate the fault-slip rockburst potential was developed. This new method relies on a linear analysis and the calculation of a new index called the Out-of-Balance Index or OBI. The OBI showed some agreement with the stiffness approach.

A nonlinear finite element model, called MINE-PAL, has been developed for elasto-plastic, large deformation analysis of underground and surface mining excavations. The model accounts for both material nonlinearity due to yielding and strain-hardening and strain-softening effects and geometric nonlinearity due to large deformations. The finite element equations are formulated using incremental plasticity theory with Total Lagrangian approach where the Kirchhoff stress tensor and Green strain increment tensor are used. The model is developed for use on microcomputer system and is designed to perform 2-D nonlinear analysis of mine excavations in multiple-material domain, thus predicting the distribution of elastic, strain-softening, strain-hardening and residual strength zones. The model accommodates any arbitrary stope geometry and it allows for a variety of mining-type loading conditions in situ stresses, gravity loading and boundary tractions. Special provision has been made to permit the simulation of backfill as in situ stress-free material. Stress-space strain-softening is invoked into model using the concept of damage parameter in the incremental stress-strain relation. / In addition to model verification and sensitivity analysis, two numerical modelling case studies have been undertaken. The first case study is of a narrow vein mine with backfill which is located in the province of Karnchanaburi, Thailand. The second case study is about a room-and-pillar design of a potash deposit in the province of Chaiyaphum, Thailand.

This thesis proposed a petrofabric classification of the rock mass domains and rock units encountered at the Birchtree Mine in the Thompson Nickel Belt (TNB), Manitoba. A program of field and laboratory studies has enabled the classification to be related to both geological and physical-mechanical properties. The classification has been aimed to advance TNB mining, mineral exploration and processing research. / The thesis also considers the genesis and nature of both inherent and mining-induced rock mass damage at the Birchtree mine. An inherent rock mass damage index, D$ sb{ rm I}$, has been derived, based upon the rock unit intact strength, together with the quantity and conditions of any meso- and macro-structure present. D$ sb{ rm I}$ was closely related to rock mass domains. The physical characteristics of rock mass damage in mine developments induced both through drill-and-blast and roadheader mining were also monitored at the Birchtree Mine. This permitted the formation of a mining-induced rock mass damage index, D$ sb{ rm M}$. This was based upon decrease in the intact strength, half cast/tool marks, normalized scaling time, drift condition rating, and orientation of local structure. The type and intensity of mining-induced damage was found to be clearly related to the nature of the rock mass units and domains, as evident in their inherent damage. / Two types of mining-induced damage mechanism were evident at Birchtree. Firstly, in the inherently weak rock mass ($ rm D sb{I}10$), such as the Metasedimentary Domain, the rock units are foliated with wider spaced joints. More energy is evidently required to fragment the rock mass through what was observed to be predominantly intact rock breakage controlled by foliation. These two damage mechanisms were also clearly evident from analysis of drift and fragmentation morphology survey data. The damage mechanism associated with both forms of mining appeared to be similar, although the intensity of machine-induced damage was significantly less. Rock mass damage related to ground stress redistribution was also observed. / This thesis was motivated by the need to understand, control and minimize mining-induced damage, particularly in serpentized ultramafic domains which will host most of the future TNB mining at depth. It thus concludes by reviewing a proposed strategy for rock mass damage sensing and control in underground development and stoping, based upon the experience at Birchtree.

A boundary element model was developed for stress/stability analysis of underground excavations in the vicinity of faults. The boundary element formulation adopts the Fictitious Stress Method for the simulation of excavation boundaries and the Displacement Discontinuity Method for the representation of faults. With the assumption that deformations and stress changes can generally be attributed to the presence of faults rather than to elastoplasticity of the rock mass, the numerical model employed a linear elastic constitutive relation for the rock, and nonlinear behaviour for the fault. This assumption is particularly justified in hard rock environment. Following a comprehensive review of constitutive models for rock joints, both deformation and peak strength models were incorporated for modelling the mechanical behaviour of the fault. Deformation or stiffness models include Goodman's constant stiffness model and Barton-Bandis' nonlinear model. The latter, considers the effect of a wide range of parameters such as coupling between shear and normal stresses and displacement, joint closure, joint separation, hardening followed by postpeak or residual behaviour. Peak strength models include Mohr-Coulomb and Barton-Bandis which employs a mobilized nonlinear shear strength envelope. An incremental, in situ stress relaxation algorithm is developed and implemented for the nonlinear analysis of the faults. / Model verification was done by a comparison of its predictions with previously published results found in the literature. The comparison showed excellent agreement. A model sensitivity analysis was then carried out to compare the response of different discontinuity models. A case study of an underground hard rock mine was conducted to examine the stability of a mining ore zone intersected by faults. / A user friendly graphical interface was developed to help generate the data and interpret the output results more efficiently.

This thesis investigates in detail the stress memory of hard rocks under uniaxial compressive conditions as a time-saving and inexpensive alternative to traditional in-situ stress measurement techniques. Extensive laboratory experiments are carried out to assess the influence of parameters such as transducer/amplifier frequency response, signal definition parameters, stress rate, strain rate, specimen size, stress level, delay time, temperature, water content, confining pressure, and directional loading on the Kaiser Effect of Stanstead granite and other rock types. Based on these findings and a new data processing techniques developed for estimating the previous stress level, a testing procedure is suggested and used to determine in-situ stresses from core samples with respect to their drilling orientations. In two case studies, the estimated stresses using the Kaiser Effect phenomenon are in good agreement with values obtained from conventional techniques while in the third study, no stress value was obtained due to the inability of the rock type to generate acoustic emissions. The results of this investigation show that the Kaiser Effect could become an economical method of stress measurement in hard and isotropic rock types.

Particle behaviour during the downwards, pneumatic injection of powder into an aqueous medium (water) has been investigated by means of a new method which involves direct measurement by making use of an Aqueous Particle Sensor (APS) unit. Through this method, phenomena and parameters related to injection processes, such as gas-particle jet penetration distance, jet diameter, jet cone angle, particle dispersion and distribution within the liquid have been investigated both qualitatively and quantitatively. Flow observations comprised part of the experimental program for the purpose of confirming the characteristics of the "gas-only" and "gas-powder" injection regimes reported by previous workers. / The effect of gas and powder flow rates (powder/gas loading ratio) in determining the injection regimes and particle behaviour within the liquid were the main parameters investigated. / It was demonstrated that the jetting regime can be easily achieved as a result of increased momentum transfer from the particles to the gas phase. However, this required a high loading of particles. Entrainment of gas with the injected particles took place not only during coupled flow (jetting) but also during decoupled (bubbling) flow, such that some gas was always entrained by the particles and penetrated the liquid as a gas-particle jet, leaving large gas bubbles at the lance tip. It was further demonstrated that the gas flow rate had a greater effect on particle suspension within the liquid than did the powder flow rate.

In this thesis the behavior of fully grouted, untensioned cable bolts and their application to the stabilization of underground openings are investigated. The study program undertaken involves field, laboratory and numerical studies which aim to improve understanding of the role of passive cable bolting in rock mass support. The higher residual load carrying capacity of the cable and the grout-aggregate mix is compared with that of the conventional grout (cement + water). / Based on the variational approach, an analytical model has been developed to calculate the distribution of shear bond stress along the embedded length of a cable bolt. A parametric study is then undertaken to illustrate the support behavior of cable bolts with different grout compositions. / A special finite element for the cable bolt was formulated and integrated into existing finite element code called MSAP2D, in order to allow the simulation of cable bolts in underground excavations. / A practical example is presented to demonstrate the effect of cable bolts on the stability of the opening. The simulation is carried out using the newly developed numerical model with cable bolt simulation capability.

The applications and limitations of pillars in underground mines is a subject that is of great importance to many mining companies, both new and old, but unfortunately has received little attention in the mining literature. Where underground pillars are used, the determination of suitable sizes present a problem about which little is known. An attempt has been made to gain an understanding of the factors involved in this problem by reviewing both theoretical and practical information on the subject. With this at hand, an attempt has been made to analyse pillar designs used in the Elliot Lake Uranium District, Ontario.

Mining has been termed the industry where in capital is depleted to reap profits. In this respect it differs from other basic industries such as farming, fishing or logging, which are also concerned with the initial exploitation of natural resources. In these industries, certain precautions and practices are adopted in due course to encourage and allow nature to rejuvenate and replenish the area. Thus it may be periodically reworked indefinitely, once the proper rotation schedule is established. In the mining industry, however, a company which owns a certain area can mine that area once only, and in order to find new ore, must mine to ever increasing depths.