The laboratory shear tests on Apache Leap tuff have been conducted to investigate the joint dilatant behavior and the influence of surface roughness, sample size, water and shear velocity on joint shear behavior, and to compare the fit between Coulomb's linear and Archard's non-linear model. Experimental results indicate that the dilation of rock joint is influenced by joint surface roughness and normal stress. Surface roughness also determines joint shear strength. Sample scale influences the following joint properties, e.g. peak shear strength, peak dilation angle, peak shear displacement and mode of shear failure. This effect depends on normal stress. The shear strength of rock joint also varies with the presence of water and shear velocity. Archard's power law generally gives a better fit on the experimental data than does Coulomb's linear law.

A comprehensive study is made of the response to horizontal base shaking of a uniform viscoelastic soil stratum retained by two vertical rigid walls. The system is assumed to experience a space-invariant horizontal motion along its base. Both harmonic and earth-quake ground motions are considered. The study is motivated by the need for a simple method of analysis and numerical data which may be used reliably and cost effectively in the design of such structures. A simple, approximate method of analysis is employed and its accuracy assessed by comparing its predictions with those obtained by a more nearly exact method. The study is presented in two parts. In the first part, the walls are assumed to be fixed at the base, whereas in second part, they are considered to be elastically constrained against rotation. The response quantities examined include the dynamic wall pressures and the associated forces and moments. Comprehensive numerical data are presented which elucidate the effects and relative importance of the numerous parameters involved. The results presented provide a convenient framework for the analysis of more complex soil-wall systems as well.

Two current challenges in seismic imaging are to obtain more detailed images of complex structures from reflection data and to constrain the regional structure of the Earth using wide-angle data. These are complex problems for which traditional methods fail because they are based on too many simplifying assumptions. I develop a unified approach which addresses these tasks by starting with a fundamental problem formulation, leading to a practical numerical solution which converges rapidly. It is based on pre-stack depth migration and cell-stripping tomography in heterogeneous media, which allow layer-stripping and retain all the information from the data, incorporates a depth focusing technique for improved image resolution and utilizes user-interaction and geologic input to guide and constrain the imaging process. I first describe a fast and accurate dynamic ray-tracing scheme in heterogeneous media which allows complex model definition and rapid two-point ray tracing. This ray tracing method is then used to compute Green functions in a layer-stripping pre-stack depth migration algorithm. The algorithm itself is based on a Kirchhoff integral in heterogeneous media using exact weighting factors and specialized to 2.5 D migration. I examine the migration results with a depth-focusing technique which analyzes common image panels for horizontal alignment, relating the degree of non alignment, or Migration Moveout (MMO) to corrections in the velocity model along the raypaths. Finally, I develop a cell-stripping tomography (CST) algorithm which distributes velocity residuals only to the relevant cells, allowing resolution of both horizontal and vertical discontinuities and providing starting models for migration. Although computer-intensive, this unified approach is successful both in synthetic tests and for obtaining local and regional images of the edge of the Santa Maria basin in central California. It is more faithful to the velocity and dip information contained in the data, allows more control over the imaging process and with available computing power promises to be routinely applicable.

In crosswell seismic experiments, seismic sources are fired in one well, and the wave-fields generated are measured in another well. The goal of the crosswell seismology is to find physical parameters, especially the velocities, of the rocks between the wells from these measurements. This amounts to the mathematical problem of solving a coefficient inverse problem of the multidimensional acoustic wave equation. We consider two inversion methods in this thesis: traveltime inversion via traveltime tomography and waveform inversion via differential semblance optimization. The main results are obtained for traveltime tomography and differential semblance optimization under the non-caustic assumption. The main result for traveltime tomography is that the objective function is smooth, and vanishing gradient implies a global minimizer if the data is noise free. The main result for DSO approach is that the objective function is smooth and a critical point is kinematically close to the true velocity model if the noise level is low enough, the source wavelet is oscillatory enough, and the DSO parameter is small enough. We also discuss to some extent the two methods in the presence of caustics.

Seismic techniques and tools have not routinely been transferred to ground-penetrating radar (GPR) studies due to computational, financial, and logistical limitations. A simple processing package was developed to aid in the processing of GPR data for those without access to commercial seismic processing packages. An idealized processing flow was derived and utilized to aid in the processing of GPR datasets. Several three-dimensional GPR datasets were collected, processed, and analyzed. Many limitations were overcome by utilizing a two-pass method of migration adopted from the seismic community. Multi-offset three-dimensional data were acquired to improve imaging by means of derivation of improved subsurface velocity information and increased signal to noise ratio. Many targets with varying shapes, orientations, and electromagnetic properties were buried and successfully imaged. Three-dimensional imaging was much improved and the resolving of features and objects buried in the subsurface became possible with modest computational capabilities.

A visco-elastic analytical model is presented for the simulation of large scale groundwater flow and land subsidence. Groundwater flow is simulated by a two-dimensional flow model. Land subsidence is modeled vertically by using the Taylor-Merchant one dimensional consolidation theory. In application, multiple aquifers are generalized by using a field approach based on a few 'bulk parameters', which allows the direct use of records obtainable in situ. / The visco-elastic model is applied to analyze and predict the land subsidence in Bangkok, Thailand. The results demonstrate that the visco-elastic model can yield a satisfactory prediction of consolidation that is better than that obtained with the classical Theis-Jacob approach. / Predictions of the piezometric head and subsidence for the 20 years from 1981-2000 were made based on the following three scenarios: (1) a constant withdrawal at 1980's rate, (2) a cessation of all pumping wells, and (3) simultaneous pumping and injection, with injection exceeding 1980's pumping rate by 50%.

The mechanical behavior of fractures in geological media is important to geotechnical and geoenvironmental engineering. Considerable investigations have been conducted on, firstly, the characterization of the fracture topography and secondly, on the assessment of the influence of fracture topography on the mechanical behavior, particularly the dilatancy of the discontinuity. The studies of the mechanical behavior of fracture surfaces have invariably been concerned with the examination of the mechanics of the contact surfaces, to the virtual exclusion of the progress of failure zones into regions adjacent to the contacting fracture surfaces. This thesis conducts a computational assessment of the role of geomaterial plasticity and surface topography on the behavior of a fracture. The computational modelling takes accounts of the irregularity of the joint surface, the frictional and elasticity characteristics of the contact zones, the elasto-plastic failure of the material and incompatible deformations that arise during shear of an irregular fracture surface. The computational shear responses are compared for the cases where a regular fracture surface exhibits identical shear behavior in the presence of geomaterial plasticity. For an irregular joint, it is observed that the shear behavior is relatively unaffected by material plasticity. Variation of dilatancy with shear cycles, however, can be directly attributed to the presence of material plasticity. Plastic energy dissipation is related to the normal restraints specified. Shear behavior of a specific joint appears to depend mainly on the interfacial behavior of the limited number of asperity contact during shear. The surface geometry of these asperities governs the dilatancy and their slopes control the peak shear resistance. The thesis also examines briefly the influence of initial separation of joints on the shear behavior.

Ground preparation design encompasses problems of ground characterization, equipment selection and performance. Ground characterization has in the past been the subject of empirical diggability classification schemes based on case studies. A new system is proposed for evaluating the ease of excavation of different ground conditions, is put forward. This has been applied successfully in different field studies. While such empirical schemes are useful to mining design, there still remains a basic lack of understanding of machine-ground interaction in the excavation process. This will be essential for long term machine and method advancement. / This thesis reviews the approach and methodology adopted for the development of predictive digging models in mining. Past theoretical attempts to model soil-rock cutting processes are critically evaluated and an analytical digging model applicable to fragmented rock is proposed. Physical modelling studies, concentrating on the interaction between machine and spoil characteristics, are reported. These considered in particular the digging profile propagated by cable shovel operation, the impact of geotechnical parameters on the profile, and the efficiency of digging in fragmented rock. These were undertaken in a controlled laboratory environment based upon an instrumented scale model and photographic studies. The salient parameters influencing the efficiency of the digging processes are identified and a bucket filling model for cable shovels is proposed.

There are a number of engineering situations where fluid-saturated geological media can be subjected to thermal effects. These include the disposal of heat-emitting nuclear fuel wastes in saturated geological formations, extraction of energy resources such as oil and natural gas by steam injection and the recovery of geothermal energy by ground source heat exchangers. The objective of this thesis is to study the coupled thermal-hydrological-mechanical (T-H-M) response of fractured geological media by the computational implementation of mathematical models. From the generalization of Biot's classical theory of consolidation of a saturated porous elastic medium to include thermal effects, we first derived the equations governing coupled T-H-M processes in saturated geological media. In order to obtain numerical solutions for the governing equations, the finite element method was used. A finite element computer code, FRACON (FRActured media CONsolidation), was developed in order to simulate plane strain and axisymmetric problems. Eight-noded isoparametric elements were developed to represent the intact regions of the geological medium, while special joint elements were developed to simulate discrete joints. The intact regions of the geological medium was assumed to exhibit linear elasticbehaviour. The joints between intact regions were modelled by constitutive relationships which reproduced both linear elastic and nonlinear elasto-plastic responses. The elasto-plastic stress-strain relationship of the joint, was formulated by appeal to classical theories of interface plasticity. The elasto-plastic model for joint behaviour thus formulated is capable of reproducing many of the fundamental features of mechanical behaviour associated with naturally occuring joints, such as dilation under shear and strain softening due to surface asperity degradation. Furthermore, the thesis presents a physically-based hydraulic model of the joint that permits the inclusion of the effec / The development of the FRACON code followed an extensive procedure of code verification via analytical solutions and intercode comparison. A unique set of benchmark problems was proposed in order to perform code verification for coupled T-H-M. / The FRACON code was used to interpret certain laboratory and field experiments, including the following: (1) coupled T-H-M laboratory experiment on a block of cementitious material; (2) lab experiments on joint shear behaviour under constant normal stress and constant normal stiffness conditions; (3) coupled shear-flow laboratory experiment on a joint; (4) Field experiments of fluid injection in a horizontal fracture in a granitic rock mass. / Lastly, the FRACON code was used to simulate the coupled T-H-M response of a rock mass to radiogenic heat from nuclear fuel wastes buried in the rock formation. The coupled H-M response of this rock mass to a future glaciation scenario was also simulated. It was shown that the mechanical/hydraulic regimes of the rock mass could be significantly changed by the above two factors. The importance of the consideration of T-H-M processes in the overall scheme of safety assessment of sites targeted for nuclear fuel waste repositories is supported by the findings of this thesis.

<p> Enhanced Geothermal Systems (EGS) have substantial potential as a domestic energy source and is well suited as an alternative to diversify the national energy portfolio due to its high levels of heat and recoverable energy. Hydraulic fracture stimulation of low permeability EGS reservoir rock is widely employed to develop this resource and is generally required to make unconventional resources an economically viable resource. Significant challenges for EGS technology include poor connectivity between injection and production wells during stimulation and difficulty predicting fracture growth (Tester, et al. 2006). This, coupled with notable advances in oil and gas recovery, has made hydraulic fracture mechanics the subject of considerable study. </p><p> Acoustic emissions, or microseisms, contribute greatly to these studies and have been employed on a wide range of topics in rock mechanic studies. At Colorado School of Mines, acoustic emission technology has been employed to monitor stimulation of cubic granite samples under heated and true triaxial stress environments to simulate deep reservoir conditions. Recorded AE activity was used to determine proper location of production well placement while additional analysis on the fracture process using characteristics such as wave amplitude and hit rates were used to identify stages of activity during fracture propagation. Study of the spatial and time dependence of the initiation and growth of rock fractures is critical to understanding the processes that govern fracture behavior and require details that are not accessible to alternative methods of analysis. Acoustic emissions can provide crucial information and represent an important part of rock mechanics studies.</p>