Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1979. / Bibliography: leaves 146-150. / by James Francis Scheimer. / Ph.D.

Thesis. 1975. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Vita. / Bibliography: leaves 158-162. / by David V. Fitterman. / Ph.D.

Sonic wave methods can be used to provide information on the engineering properties of rocks. The advantages of such techniques include minimal sample preparation, fast site preparation for field tests, reproducible and nondestructive tests, and capability for large scale testing. During this research an extensive review of the most widely accepted engineering rock classification systems was undertaken and their principles, advantages and disadvantages are presented in detail. The mathematical equations describing wave propagation through elastic and viscoelastic media are analyzed in order to determine the dynamic parameters most likely related to static properties. A detailed description of the instrumentation and experimental procedures used for sonic testing is presented. Based on the experimental data, a correlation between the most characteristic static and dynamic properties was established. These relationships can be used to modify existing engineering rock classification systems, by appropriately substituting static properties by the much easier to measure, in the field and in the laboratory, sonic wave parameters. Furthermore, a classification scheme was developed, incorporating information pertaining to the static modulus of elasticity and frequency of joints from sonic wave information. / Master of Science

Assessing long-term rock stability is an important aspect in the analysis of slopes, dam and bridge foundations, and other infrastructure. Rock behavior over tens to thousands of years must be anticipated when predicting the performance of, for example, an underground containment facility for nuclear waste. At such long time scales, the time dependence of rock failure, typically ignored in short time scale analyses, has a significant effect and must be included in the analysis. Since time-dependent rock behavior is thought to be caused by the subcritical growth of microcracks, a time-dependent analysis should incorporate a method of simulating subcritical crack growth. In this thesis, a rock bridge damage model was developed using the finite element program Abaqus to simulate subcritical crack growth for all three modes of crack tip displacement in three-dimensional rock masses. Since subcritical crack growth is not among the damage initiation and evolution criteria available in Abaqus, its effect was included in the model through the USDFLD user subroutine. Material properties for the damage model were obtained through laboratory fracture toughness testing of Escabrosa limestone from Kartchner Caverns. Tests included the grooved disk test for mode I, the punch-through shear with confining pressure test for mode II, and the circumferentially-notched cylindrical specimen test for mode III. The subcritical crack growth parameters n and A were calculated for all three modes using the constant stress-rate method. Fracture test results were compared with a previous study by Tae Young Ko at the University of Arizona, which tested Coconino sandstone and determined that the subcritical crack growth parameters were consistent among modes. This thesis expands upon Ko's work by adding the characterization of a second rock material in all three modes; results indicate that for Escabrosa limestone the subcritical crack growth parameters are not consistent among modes. Additionally, the Escabrosa limestone composing the caverns ranges from a more homogeneous, even-grained texture to a more heterogeneous texture consisting of coarse-grained veins and solution cavities set in a fine-grained matrix. To determine if the veined regions are more susceptible to fracturing and act as the nuclei of rock bridge failure, the fracture toughness tests were conducted separately for each texture. Results indicate that the more heterogeneous limestone has a higher fracture strength, fracture toughness, and subcritical crack growth index n than the more homogeneous limestone. This is in agreement with previous studies that determined that a more complex and heterogeneous microstructure produces a larger microcrack process zone and a more tortuous crack path, leading to higher fracture energies and larger values of n. Application of the rock bridge damage model to a simplified Kartchner cave room with a single roof block provided visualization of decreasing rock bridge size and produced time-to-failure estimates of 1,251 to 65,850 years. Multiple models were run to study the effect of (i) using material properties from each of the two textures identified in the Escabrosa limestone and (ii) varying the in-situ stress ratio, K. Both the value of K and the choice of Escabrosa texture had a large effect on the estimated time-to-failure, indicating that for future modeling of Kartchner accurate estimation of the in-situ stress ratio is as important as field identification of homogeneous vs. heterogeneous textures.

Pour étudier le comportement mécanique des massifs rocheux, en prenant en compte le réseau des discontinuités au sein de la roche intacte, cette recherche a pour objectif la représentation du massif par des modèles géométriques basés sur des relevés de terrain et l'analyse de ces modèles par l'utilisation d'outils informatiques adaptés pour les milieux granulaires. Le premier chapitre fait l'état de l'art des roches fracturées, des méthodes numériques de la mécanique des roches et des approches du calcul de structure d'un tunnel. Ces études conduisent à la proposition d'une méthodologie depuis les recherches in situ jusqu'à la modélisation et l'analyse mécanique, présentée dans le deuxième chapitre. Le massif rocheux est d'abord représenté géométriquement par la distribution de ses discontinuités, et l'utilisation du logiciel RESOBLOK basé sur la méthode du Réseau de Fractures Discrètes. Les modèles mécaniques de massifs rocheux sont ensuite présentés à partir des données sur les études de l'histoire du massif, et des mesures faites sur site et en laboratoire. Les modèles numériques en 3D sont analysés par l'utilisation du logiciel LMGC90 basé sur la méthode de la Dynamique des Contacts Non Réguliers. Les premières applications de la méthodologie sont exposées : la création d'une roche numérique pour simuler un essai de compression triaxiale, et la simulation d'une excavation multi phases d'un tunnel au rocher. La méthodologie proposée a été appliquée sur le marbre blanc de Saint Béat (Haute Garonne, France) et les résultats préliminaires sont donnés dans le chapitre trois. Les réponses mécaniques de la roche numérique sont analysées et son comportement est caractérisé. / Aimed at studying the mechanical behaviour of rock mass and considering the presence of the discontinuity network in the intact rock, this research concentrates on how the rock can be represented in suitable geometrical models, on the basis of site measurements, and then appropriately analysed using computer tools developed for the study of granular media. The first chapter deals with a bibliographical study on fractured rock and tunnel engineering. Different computational methods of rock mechanics are introduced. Simultaneously, three principal approaches for tunnel structural design are recalled. These studies lead to the proposition of a methodology from the in situ investigation to in-door modelling and mechanical analysis, presented in the second chapters. The rock mass is first geometrically represented through the distribution of discontinuities in the rock mass and the use of the RESOBLOK code based on the Discrete Fracture Network method. Mechanical models of rock mass are then presented from the data of historical studies on the rock mass and from laboratory and in situ measurements. The 3D computational models are analysed using the LMGC90 based on the Non Smooth Contact Dynamics method. The first two applications of the methodology are introduced: the generation of the numerical rock for the simulation of the triaxial compression test, and the simulation of multi-phase excavation of rock tunnel. The proposed methodology has been applied on the white marble of Saint Béat (Haute Garonne, France) and the initial results are given in the third chapter. The mechanical responses of the numerical rock mass are analysed and the bulk behaviour of the rock is evaluated.

This thesis investigates pressure stimulated voltages (PSVs) in manmade and geological materials using a field capable and commercially viable electric potential sensor (EPS) technology. Sensing technologies are of great importance for the structural health monitoring (SHM) of manmade and geological structures and are critical for improving the health and safety of humans and infrastructure. A wide variety of sensing technologies are needed to assess damage over structures. Work by others involves measuring pressure stimulated electrical emissions (PSEs) (i.e. the study of pressure stimulated voltage, electric field and current) that are related to acoustic emissions (AEs) in rock and cement mortar, and also mechanical properties. Although these studies yield promising results, the measurement tools (laboratory electrometers and electromagnetic emissions (EME) antennas) are not suitable for field use. This is predominantly because of the need of Faraday shielding to reduce noise, plus the impracticalities and high costs associated with using laboratory instruments for SHM. However, the EPS developed at the University of Sussex is capable of measuring PSVs in rocks and is field capable. In this thesis, PSVs in rocks and man-made materials were measured using two EPS variants. An existing capacitively coupled sensor was used to measure high frequency (25.5 mHz to 750 kHz) transient PSVs associated with cracking. In addition, a novel directly coupled smart EPS was developed for monitoring low frequency (DC to 250 Hz) PSVs associated with applied stress. A signal conditioning and data reduction procedure was developed for PSV emissions analogous to methods used for AE. A new robust method for measuring PSV was established in which cylindrical material specimens were instrumented with strain gauges, piezo transducers and EPSs to measure strain, AE and PSV respectively and a force transducer was used to measure the applied load. The results showed that PSVs were detected in a wide range of piezo and non-piezo rocks and for the first time in concrete, in the range of millivolts (0.32 mV – 1180 mV). Faraday shielding the experiments was not necessary as with other PSE monitoring technologies. For oven dried materials there was some degree of correlation between PSV high frequency transient signals and AE (i.e. cracking). Rocks had cross-correlation coefficients ranging from 0.13 to 0.86, and the cross-correlation coefficient for concrete (0.24) was lower than most rock lithologies. Environmental conditions and the stage of uniaxial deformation of materials influence PSV-AE cross-correlations. Water or saline saturation of materials generally reduced the PSV-AE cross correlation coefficients. During the cyclic loading of various rock lithology, a work hardening effect was observed in the PSV emissions analogous to the well-known Kaiser and Felicity effect of AE. A likely reason for the PSV-AE correlations is that PSVs are generated by the movement and separation of fresh charged fracture surfaces. EPS could be a cost effective and more advanced technology for detecting cracking in structures and in combination with piezo transducers, could be used to identify material deformation stages. There was a linear relationship between applied stress and DC/low frequency PSV in piezo rocks (r2 = 0.84) but not non-piezo rocks (r2 = 0.0063). The piezoelectric effect of quartz is the most likely generation mechanism behind the PSV-stress relationship. The novel, directly coupled, smart EPS is a successful design as it has the necessary high input impedance and low noise characteristics for measuring PSVs noninvasively at low frequencies. EPS could be the first non-invasive technology for in-situ stress measurement in quartz bearing rocks; current methods involve disturbing the rock mass and are expensive to implement. In conclusion, the results show that the EPS-PSV measurement technique is viable for the SHM of rocks and concrete. Although, factors such as material composition, environmental condition and type of material deformation influence PSV characteristics and would need to be accounted for in real world applications. Future directions for the research would involve the development of a “real time” PSV event detection system for long term monitoring of structures for SHM applications. Additionally, large scale testing of different material samples in different environmental conditions and the testing of larger structures using arrays of EPS would be necessary before commercialisation. Future commercialisation could result in a restively coupled broadband monolithic semiconductor EPS being developed for SHM to monitor PSVs associated with applied stress and cracking events simultaneously. This would produce a more cost effective and advanced tool than existing technologies, such as piezo transducers for monitoring AE and in-situ stress monitoring techniques.

Coupled Thermal-Hydrological-Mechanical-Chemical (THMC) processes that exist in the development of different geo-resources (e.g. deep geothermal and shale gas) affect the fracture response (i.e. aperture and permeability), which in turn influences the reservoir production. The main goal of this study was to experimentally evaluate the impact of THMC processes on the response of rock specimens relevant for deep geothermal and shale gas formations. The effects of THMC processes were investigated on: (i) success of the hydraulic fracturing/hydro-shearing mechanism during stimulation stage, and (ii) closure of the created network of fractures during production stage. The elastic, cyclic, creep, and failure characteristics of different intact reservoir rocks in both short- and long-term were investigated to evaluate their response in stimulation stage. In addition, a series of flow tests on fractured reservoir cores were conducted to evaluate how THMC processes affect fracture response subjected to different stress levels, temperatures, composition of injected fluid, and injection rate. Moreover, the sensitivity of ultrasonic signatures (i.e. velocity, amplitude, attenuation, and time-frequency content) to (i) microstructural changes in the intact rocks, and (ii) flow-induced alterations of aperture/permeability in the fractured rocks were investigated. Analysis of hydraulic data, chemical composition of the effluent, ultrasonic signatures, and X-Ray micro-CT and SEM images, provided invaluable information that facilitated interpretation of the effects of coupled THMC processes on fracture response.

published_or_final_version / Applied Geosciences / Master / Master of Science

A combined geological and rock mechanics approach to tunnel face behaviour prediction, based on improved understanding of brittle fracture processes during TBM excavation, was developed to complement empirical design and performance prediction for TBM tunnelling in hard rock geological conditions. A major challenge of this research was combining geological and engineering terminology, methods, and objectives to construct a unified Geomechanical Characterisation Scheme. The goal of this system is to describe the spalling sensitivity of hard, massive, highly stressed crystalline rock, often deformed by tectonic processes. Geological, lab strength testing and TBM machine data were used to quantify the impact of interrelated geological factors, such as mineralogy, grain size, fabric and the heterogeneity of all these factors at micro and macro scale, on spalling sensitivity and to combine these factors within a TBM advance framework. This was achieved by incorporating aspects of geology, tectonics, mineralogy, material strength theory, fracture process theory and induced stresses. Three main approaches were used to verify and calibrate the Geomechanical Characterisation Scheme: geological and TBM data collection from tunnels in massive, highly-stressed rock, interpretation of published mineral-specific investigations of rock yielding processes, and numerical modelling the rock yielding processes in simulated strength tests and the TBM cutting process. The TBM performance investigation was used to identify the mechanism behind the chipping processes and quantify adverse conditions for chipping, including tough rock conditions and stress induced face instability. The literature review was used to identify the critical geological parameters for rock yielding processes and obtain strength and stiffness values for mineral-specific constitutive models. A texture-generating algorithm was developed to create realistic rock analogues and to provide user control over geological characteristics such as mineralogy, grain size and fabric. This methodology was applied to investigate the TBM chipping process to calibrate the Geomechanical Characterisation Scheme. A Chipping Resistance Factor was developed to combine the quantified geological characteristic factors and laboratory strength values to predict conditions with high risk of poor chipping performance arising from tough rock. A Stress-Related Chip Potential Factor was developed to estimate conditions with high risk of advance rate reduction arising from stress-induced face instability. / Thesis (Ph.D, Geological Sciences & Geological Engineering) -- Queen's University, 2008-09-25 23:58:58.071

Spatial clustering of seismic events in mines has been widely reported in literature. Despite obvious visual correlations between spatial clusters of seismic events and geomechanical structures in mines (such as pillars, dykes and faults), very limited research has been undertaken to utilise this information to filter seismic data. A linkage between spatial seismic event clusters and discrete rockmass failure mechanisms is tenuous and not well established using current seismic analysis techniques. A seismic event clustering methodology is proposed. The first component of the methodology uses a complete-linkage (CLINK) clustering routine to identify relatively compact clusters of seismic events. The CLINK clusters are then subjected to a singlelink clustering process, which uses spatial location and seismic source parameters as similarity measures. The resultant