ABSTRACT: The progressive shear failure development and evolution in brittle to brittle-ductile rock masses behavior is characterized by non-linear, inhomogeneous stress and strain distributions through the media in which various fracture modes intervene in sequence during simple shear displacement. The progressive failure of zones under simple shear deformation is progressive in at least two ways and is influenced by the normal stress magnitude and dilatancy. The progressive failure extends to all scales and is responsible for a marked shear strength scale effect. This paper demonstrates how the rotational and non-coaxial strain characterizing zones submitted to simple shear deformation influence the sequential development and evolution of tension and shear fractures under mode I and n of fracture propagation and their subsequent behavior with shear displacement. The behavioral complexity of a such zone during progressive failure is rather difficult to model, because shear displacement measurements integrate all kinds of variables and phenomena into one single parameter. Stability of workings in rock masses may demonstrate problems if such modes of deformation and failure are induced in the rock media.
ABSTRACT: The objective of this U.S. Bureau of Mines investigation was to characterize the change in the overburden due to mining of a 270 m wide longwall panel. The overburden thickness ranged from 95 to 105 m. Five-anchor, multipoint borehole extensometers (MPBX) were installed in each of five coreholes to measure subsurface displacement. Survey data of an array coincident with the boreholes show that surface movement began when the longwall face was about 45 m in front of any point. Over 90% of the total subsidence was achieved when the face was one overburden thickness past a point. Overburden failure was detected by the MPBX units when a borehole was undermined. Overburden failure occurred first in the center of the panel and then migrated outward toward the panel margins. The overburden appeared to collapse vertically as a unit and was laterally restricted to the mined-out area of the panel.
ABSTRACT: A penstock rock slope was analyzed by two methods of stability analysis. They are a limiting equilibrium analysis initially developed by Goodman and Bray, and Discontinuous Deformation Analysis (DDA). Because the latter needs no assumption of a failure mode, and takes into account the deformability and real-time response of a slope, it proved to be more versatile and realistic.
ABSTRACT: A study was conducted using Dynamic Discontinuous Deformation Analysis to model the joint compliance of a model material developed for the Topapah Springs welded tuff located at Yucca Mountain, Nevada. The model used physical properties measured from laboratory tests, a typical or average aperture, and a simulated joint roughness. The degree of joint closure, or remaining aperture, could be controlled by applied stress level. Full closure of the joint was ultimately obtained in the model, and the results compared well with laboratory compliance tests.
ABSTRACT: Creep of the rocks surrounding a horizontal tunnel is considered. It is shown where the rock becomes dilatant, where compressible, if and where failure will occur and how much rock will be involved, where and when creep failure is to be expected, and how creep failure spreads into the mass of rock. The influence of an internal pressure on the above phenomena is also studied.
ABSTRACT: In recent years, internal state variable models have gained popularity for describing the behavior of rocksalt. Among the various advantages of such models, the possibility to distinguish between kinematic and isotropic hardening phenomena is of the outmost importance, as physical (microscopic) evidences clearly show that both aspects must be considered in properly formulated constitutive equations. However, if the mixed nature of hardening is fairly well established from the micromechanical point of view, it is usually not clear how one should proceed to separate the components of hardening from macroscopic test results. In this paper, the authors present a general approach aimed at obtaining experimentally these informations from laboratory tests on rocksalt samples. The proposed procedure is based on the use of triaxial compression tests. Using schematic and experimental results on rocksalt, it is shown how such tests can be used to isolated the kinematic and isotropic components. A previously developed model is used to illustrate the procedure.
ABSTRACT: Rock Mechanics techniques are becoming increasingly important in oil and gas reservoir exploration and development. The discrete fracture approach is one of the most promising of these, since it provides a more realistic geological description of in situ conditions. This paper provides an overview of recent developments in continuum and discontinuum rock mechanics approaches for oil and gas applications, and presents a number of brief case studies of applications of discrete fracture approaches.
Understanding and modeling seismic wave propagation from nuclear explosions require information on the behavior of rocks in the source region under appropriate loading conditions. Within the source region the rocks are loaded in uniaxial strain; during unloading damage occurs, permanently altering the rocks. Rock properties measured at the laboratory scale constrain the models. Static and dynamic elastic moduli and attenuation as a function of mean stress and strain amplitude are incorporated into forward models to determine particle velocity and displacements and time histories in the nearfield.
An underground nuclear explosion in granite was detonated near Semipalatinsk as part of a Joint Verification Experiment with the USSR. In order to model the range of possible responses and further our understanding of the relationship between static and dynamic moduli, a suite of experiments was performed on five granites representative of the source region.
Although the chaotic fabric of melange (from the French, mélange, or mixture) is characteristic of rocks formed within the accretion prisms of subduction zones, geologists disagree about the details of melange formation (Raymond and Terranova, 1984), as reflected in the many aliases of melange (e.g., chaotic formations, wildflysch, mega-breccia, argille scagliose and friction carpets). For engineering purposes, Medley (1994) considers melange to be a bimrock (block-in-matrix rock) which he defines as "a mixture of relatively large, competent blocks within a bonded matrix of finer and weaker texture", a definition that ignores rock genesis. Bimrocks similar to melange that are formed from cataclasis and fragmentation include breccias, coarse pyroclastics, lahars and tillites. Other bimrocks form from weathering (decomposed granite) or sedimentation (boulder conglomerates). Analagous soils, such as colluvium and till are termed bimsoils.
Melange bodies have been identified in the mountains of over 60 countries (Medley, 1994) and are exemplified by the Franciscan Assemblage (the Franciscan) a regional-scale jumble in northern California. Typically, the Franciscan contains chaotic zones of relatively strong blocks of greywacke sandstone, chert, basalts, limestone and exotic metamorphic rocks embedded within a matrix of pervasively sheared shale and argillite. The blocks range between sand particles and mountain masses, are irregularly shaped, and generally trend NNW-SSE (Figure 1). Shears are confined to the weak shale matrix, which flows around the closely jointed blocks. The sheared shale, and the sheared serpentinite bodies common in the Franciscan, are both responsible for the myriad earth-flow landslides of the Fransciscan. Also, encounters with unpredictably distributed blocks in melanges cause expensive surprises during earthwork excavations and foundation preparations.
ABSTRACT: Scaly clay is an argillaceous sediment, with a pervasive fabric of lenticular, highly polished, curved, slickensided surfaces and is commonly associated with mélange formations. In regions subject to tropical weathering regimes outcrops of this material erode rapidly giving rise to extensive badlands topography. Islands such as Barbados and Taiwan lose considerable areas of agricultural land to badlands generation each year and associated landslides disrupt settlements and communications.
A programme of laboratory studies has been completed to characterise the physical, mineralogical and mechanical properties of undisturbed samples of these materials. The samples, collected from different depths within weathering profiles, between ground surface and fresh materials with no sign of weathering at depth were each subject to similar experiments. These data illustrate important changes during weathering, including destruction of the original sedimentary structure, a large increase in pore volume and variations in strength.