Showing papers on "Discontinuity (geotechnical engineering) published in 2006"
TL;DR: In this paper, the authors synthesize all the available data on failure processes in granular rock and provide a geological framework for the corresponding structures, which includes sharp discontinuities made up of two surfaces similar to elastic crack models, and tabular structures resulting from strain localization into narrow bands.
306 citations
TL;DR: In this paper, a 3D laser scanning profilometer system was used to measure the surface roughness of a single rock joint under both constant normal load (CNL) and constant normal stiffness (CNS) conditions and measured the surfaces of rock joints before and after shearing.
184 citations
TL;DR: A complicated structure is found, showing single and double reflections ranging in depth from 640 to 720 kilometers, that requires the existence of multiple phase transitions at the base of the transition zone, consistent with pyrolite mantle composition.
Abstract: The 660-kilometer discontinuity, which separates Earth's upper and lower mantle, has been detected routinely on a global scale in underside reflections of precursors to SS shear waves. Here, we report observations of this discontinuity in many different regions, using precursors to compressional PP waves. The apparent absence of such precursors in previous studies had posed major problems for models of mantle composition. We find a complicated structure, showing single and double reflections ranging in depth from 640 to 720 kilometers, that requires the existence of multiple phase transitions at the base of the transition zone. The results are consistent with a pyrolite mantle composition.
175 citations
TL;DR: In this article, the authors explored the nature of plane-strain hydraulic fracture growth in the presence of pre-existing fractures such as joints without or with secondary flaws, and derived the governing equations for quasi-static fluid-driven fracture growth.
Abstract: SUMMARY In this study, we explore the nature of plane-strain hydraulic fracture growth in the presence of pre-existing fractures such as joints without or with secondary flaws. The 2-D plane-strain fracture studied can be taken as a cross-section through the short dimensions of an elongated 3-D fracture or as an approximate representation of the leading edge of a 3-D fracture where the edge curvature is negligible. The fluid-driven fracture intersects a pre-existing fracture to which it is initially perpendicular and is assumed not to immediately cross, but is rather deflected into the pre-existing fracture. The intersection results in branching of the fracture and associated fluid flow into the pre-existing fracture. Further growth results in opening and frictional sliding along the pre-existing fracture. Fracture propagation in an impermeable homogeneous elastic medium and fluid invasion into a pre-existing fracture are both driven by an incompressible, Newtonian fluid injected at a constant rate. The frictional stress on the surfaces of pre-existing fractures is assumed to obey the Coulomb law. The governing equations for quasi-static fluid-driven fracture growth are given and a scaling is introduced to help identify important parameters. The displacement discontinuity method and the finite difference method are employed to deal with this coupling mechanism of rock fracture and fluid flow. In order to account for fluid lag, a method for separately tracking the crack tip and the fluid front is included in the numerical model. Numerical results are obtained for internal pressure, frictional contact stresses, opening and shear displacements, and fluid lag size, as well as for fracture re-initiation from secondary flaws. After fracture intersection, the hydraulic fracture growth mode changes from tensile to shearing. This contributes to increased injection pressure and to a reduction in fracture width. In the presence of pre-existing fractures, the fluid-driven cracks can be arrested or retarded in growth rate as a result of diversion of fluid flow into and frictional sliding along the pre-existing fractures. Frictional behaviour significantly affects the ability of the fluid to enter or penetrate the pre-existing fracture only for those situations where the fluid front is within a certain distance from the intersecting point. Importantly, fluid penetration requires higher injection pressure for frictionally weak pre-existing fractures. Fracture re-initiation from secondary flaws can reduce the injection pressure, but re-initiation is suppressed by large sliding on pre-existing fractures that are frictionally weak.
135 citations
TL;DR: In this paper, a P-wave whole mantle tomography revealed a low velocity region oceanward of the Northern Honshu slab of the Pacific plate at depths around the 410-km seismic discontinuity.
102 citations
TL;DR: In this article, the authors investigated the structure of upper mantle discontinuities in the central Pacific including the Hawaiian hot spot using a high-quality broadband seismic data set of precursors to the phase SS.
Abstract: [1] Using a high-quality broadband seismic data set of precursors to the phase SS, we investigate the structure of upper mantle discontinuities beneath the central Pacific including the Hawaiian hot spot. We image structure by stacking over 4000 records into geographic bins, retaining periods down to 5 s. We consider the effects of correcting for four separate tomographic models of mantle heterogeneity, excluding data at distances containing phases that potentially interfere with precursors. We find evidence for peak-to-peak topography of 15–20 km on the 670-km discontinuity and 7–28 km of topography on the 400-km discontinuity. Weak reflections are detected from discontinuities near 220- and 520-km depth. The average transition zone thickness beneath our region is approximately 242 ± 3 km, very similar to previous estimates of the global average. Lateral transition zone thinning and thickening weakly correlate with reduced and increased transition zone shear velocity, respectively, consistent with a thermal origin to topographical variations on the discontinuities within our study region. The transition zone beneath Hawaii and to the east of the Line Island Chain is thinned by up to 20 km in a province spanning nearly 1000 km, suggesting an excess mantle temperature of ∼200 K. In the oldest crustal regions of our study area (>100 Ma), the 400-km discontinuity is relatively shallow, and the transition zone is relatively thick (250–255 km); a possible explanation for this pattern includes small-scale convection in the upper mantle bringing colder material into the transition zone.
82 citations
TL;DR: In this article, a general technique to embed non-uniform displacement discontinuities into standard solid finite elements is presented, based on the decomposition of the kinematic fields into a component related to the deformation of the solid portion of the element and one related to rigid-body motion due to a displacement discontinuity.
69 citations
TL;DR: In this article, a numerical model based on progressive damage within an elastic interaction framework was proposed to simulate these observations, which revealed complex patterns in both space (fractal properties of damage structures as roughness and gouge), time (clustering, particular trends when the failure approaches) and energy domains (power-law distributions of energy release bursts).
Abstract: The deformation of rocks is associated with microcracks nucleation and propagation, i.e. damage. The accumulation of damage and its spatial localization lead to the creation of a macroscale discontinuity, a so-called “fault” in geological terms, and to the failure of the material, i.e., a dramatic decrease of the mechanical properties as strength and modulus. The damage process can be studied both statically by direct observation of thin sections and dynamically by recording acoustic waves emitted by crack propagation (acoustic emission). Here we first review such observations concerning geological objects over scales ranging from the laboratory sample scale (dm) to seismically active faults (km), including cliffs and rock masses (Dm, hm). These observations reveal complex patterns in both space (fractal properties of damage structures as roughness and gouge), time (clustering, particular trends when the failure approaches) and energy domains (power-law distributions of energy release bursts). We use a numerical model based on progressive damage within an elastic interaction framework which allows us to simulate these observations. This study shows that the failure in rocks can be the result of damage accumulation.
66 citations
TL;DR: In this article, a numerical model formulated within the framework of a nonsymmetric strong discontinuity approach for fracture simulations of plain concrete is presented, based on the fixed crack concept and makes use of the concept of the elements with embedded discontinuities.
64 citations
TL;DR: In this article, a series of laboratory tests were carried out to verify the theoretical solutions obtained by Cai and Zhao, including ultrasonic tests across an aluminium specimen (calibration tests), intact cement mortar specimens, single fracture specimens, and two-fracture specimens.
Abstract: Fractures and other non-welded discontinuities are important mechanical and hydraulic features of rock masses. Their effect on wave propagation can be modelled as a boundary condition by displacement discontinuity methods. For small-amplitude wave incidence, such as an ultrasonic waves, the magnitude of the stress wave is too small to mobilize non-linear fracture deformation, and so linear models are adopted in these studies to describe fracture deformational behaviour. J.G. Cai and J. Zhao (Int. J. Rock Min, Sci., 2000, 37(4), 661–682.) used the method of characteristics to examine P-wave attenuation across linear deformable fractures by considering interfracture wave reflections. In the present study, a series of laboratory tests were carried out to verify the theoretical solutions obtained by Cai and Zhao. These included ultrasonic tests across an aluminium specimen (calibration tests), intact cement mortar specimens, single-fracture specimens, and two-fracture specimens. During the tests, ultrasonic w...
62 citations
TL;DR: In this article, the use of higher order crack tip elements and a higher order displacement discontinuity method is investigated to investigate the effect of these elements on the accuracy of the results in some crack problems.
TL;DR: In this article, the authors highlight fault discontinuities for seismic data interpretation, and remove other discontinuity attributes for this purpose, such as diapirs, stratigraphic changes, and noise.
Abstract: Seismic-discontinuity attributes quantify the degree to which neighboring seismic traces vary from each other (Bahorich and Farmer, 1995). They detect abrupt lateral changes in seismic data character caused by faults, diapirs, stratigraphic changes, and noise. An important application is to highlight fault discontinuities for seismic data interpretation. For this purpose, other discontinuities are considered noise and should be removed (Ashbridge et al., 2000; Pedersen et al., 2002; AlBinHassan and Marfurt, 2003).
TL;DR: In this article, stacks of several seismic phases having different sensitivities to mantle transition zone structure are examined separately and jointly using a nonlinear inversion method, consistent but nonunique, seismological models emerge.
Abstract: We examine stacks of several seismic phases having different sensitivities to mantle transition zone structure. When analyzed separately, underside P and S reflections (PdP and SdS) are suggestive of very different structures despite similar raypaths and data coverage. By stacking the radial component of PdP rather than the vertical PdP, we show that this difference does not result from interference from other more steeply inclined phases such as PKP and Ppdpdiff. In general, stacks of P-to-S converted phases (Pds) appear to lack evidence of a 520-km discontinuity when examined without other phases. When these phases and stacked topside P reflections (Ppdp) are analyzed jointly using a nonlinear inversion method, consistent but nonunique, seismological models emerge. These models show that a discontinuity at ∼653 km depth has smaller contrasts in density and velocity than found in most previous studies. A sub-660 gradient can account for the majority of this difference. A 1.6 ± 0.5% P-velocity contrast and a 2.2 ± 0.3% density contrast at ∼518 km depth without a S-velocity contrast can explain the lack of a P520s, together with robust Pp520p and S520S phases. For models parameterized with a finite thickness for each discontinuity, the 410-km discontinuity is consistently ∼3 times thicker than the 660-km discontinuity.
TL;DR: In this article, a method of geometrical distribution of discontinuities in rock masses by image processing is presented and used to make networks of rock joints from the construction field.
TL;DR: In this paper, the authors examined the response of a fracture in porothermoelastic rock when subjected to stress, pore pressure, and temperature perturbations, and the contribution of each mechanism to the temporal variation of fracture opening was studied to elucidate its effect.
Abstract: Thermally induced volumetric changes in rock result in pore pressure variations, and lead to a coupling between the thermal and poromechanical processes. This paper examines the response of a fracture in porothermoelastic rock when subjected to stress, pore pressure, and temperature perturbations. The contribution of each mechanism to the temporal variation of fracture opening is studied to elucidate its effect. This is achieved by development and use of a transient displacement discontinuity (DD) boundary element method for porothermoelasticity. While the full range of the crack opening due to the applied loads is investigated with the porothermoelastic DD, the asymptotic crack opening is ascertained analytically. Good agreement is observed between the numerical and analytical calculations. The results of the study show that, as expected, an applied stress causes the fracture to open while a pore pressure loading reduces the fracture width (aperture). In contrast to the pore pressure effect, cooling of the crack surfaces increases the fracture aperture. It is found that the impact of cooling can be more significant when compared to that of hydraulic loading (i.e., an applied stress and pore pressure) and can cause significant permeability enhancement, particularly for injection/extraction operations that are carried out over a long period of time in geothermal reservoirs.
TL;DR: In this article, an extension of a boundary element method to fatigue growth analysis of mixed-mode cracked plane elastic bodies is presented, where the left or the right crack-tip element is placed locally at the corresponding left or right crack tip on top of nonsingular displacement discontinuity elements that cover the entire crack surface and the other boundaries.
TL;DR: In this paper, the Cauchy singular integral equation for the crack is derived by integral transform, and the allocation method is used to get the numerical solution, which indicates that the weak discontinuity is an important factor affecting the SIFs of the interfacial crack.
TL;DR: New scaling relations near the ferromagnetic-Griffiths transition are obtained, including the prediction of a discontinuity on the analogue of the critical isotherm, supporting its identification as a Griffiths ferromagnet.
Abstract: From a heuristic calculation of the leading order essential singularity in the distribution of Yang-Lee zeroes, we obtain new scaling relations near the ferromagnetic-Griffiths transition, including the prediction of a discontinuity on the analogue of the critical isotherm. We show that experimental data for the magnetization and heat capacity of La(0.7)Ca(0.3)MnO(3) are consistent with these predictions, thus supporting its identification as a Griffiths ferromagnet.
TL;DR: In this paper, the deformation changes within fractured rocks present a large frequency range and can be both static and dynamic, while dynamic changes are best represented by seismic waves produced by earthquake sources.
TL;DR: In this article, limit-equilibrium techniques, finite-difference (FLAC) and distinct-element (UDEC) codes were used to investigate the failure mechanism of the East Gate Landslide.
TL;DR: In this paper, a procedure for measuring the acoustic scattering matrix coefficients of a duct discontinuity for higher order acoustic duct mode propagation conditions is described and tested, which requires measurement of pressure waves per mode coming in and out of the discontinuity.
Abstract: A procedure for measuring the acoustic scattering matrix coefficients of a duct discontinuity for higher order acoustic duct mode propagation conditions is described and tested. The technique requires measurement of pressure waves per mode coming in and out of the discontinuity. Assuming N cut-on modes, the (2N)2 scattering matrix coefficients are determined after repeating the experiment for N linearly independent pressure distributions for at least two load configurations. Experiments were conducted for a straight duct and a reactive chamber. A good agreement was found between experiment and theory except near cut-off frequencies. The overdetermination method based on four loads was shown to improve the results. An analytical simulation of the experiment was developed to compute the influence on the [S] calculation of an error in temperature and total modal pressure assumed to be representative of a real measurement situation. This simulation with a discussion explains the discrepancies between experiment and theory. The test with the chamber shows that the load method fails as expected in determining the coefficients associated to the wave coming in the discontinuity from the open end side because of the property of the middle duct to filter modes making the results very sensitive to uncertainties.
TL;DR: In this paper, the authors constrain SH wave velocity structures near the 660-km discontinuity beneath South America and northeast Asia, using triplicated phases near the discontinuity recorded in the epicentral distance range of 10°-35° for three deep events.
Abstract: [1] We constrain SH wave velocity structures near the 660-km discontinuity beneath South America and northeast Asia, using triplicated phases near the discontinuity recorded in the epicentral distance range of 10°–35° for three deep events. We then explore mineralogical and compositional models appropriate for explaining the inferred seismic structures between the two regions. SH velocity structures near the 660-km discontinuity are found to be different in the two regions. Beneath South America, the velocity gradient above the 660-km discontinuity is larger than that of Preliminary Earth Reference Model (PREM), while the velocity jump across the discontinuity is the same as PREM. Beneath northeast Asia, the velocity gradient above the 660-km discontinuity is the same as that of PREM, while the velocity jump across the discontinuity is larger than PREM. Both regions are characterized by a large velocity gradient extending about 80 km deep below the 660-km discontinuity. The different velocity structures require different mineralogical models in the transition zone in the two regions. The larger velocity gradient above the 660-km discontinuity beneath South America requires existence of the ilmenite phase in the bottom of transition zone, while that beneath northeast Asia can be explained by the temperature and pressure dependence of elastic properties of the major mantle mineral assemblages. The observed large velocity gradients in the top of the lower mantle can be explained by gradual transformation of garnet to perovskite persisting to greater depths. The velocity jump across the 660-km discontinuity beneath South America, in the presence of the ilmenite phase in the bottom of the transition zone, requires a bulk composition of more garnet than the pyrolite model, while a larger velocity jump across the discontinuity beneath northeast Asia requires a larger fraction of garnet transforming to perovskite across the discontinuity than what is required for explaining PREM. These different mineralogical models can be caused by different mantle temperature or composition, especially the aluminum content in mantle composition. The presence of garnet 80 km below the 660-km discontinuity in the two regions may be explained by a uniform composition in the lower mantle with an aluminum content of 3.4%. The existence of ilmenite in the bottom of the transition zone beneath South America and the absence of ilmenite beneath northeast Asia can be explained by either a difference in mantle temperature of about 100°C (with that beneath South America being lower) between the two regions assuming a uniform mantle composition or, alternatively, a difference in aluminum content of about 1% (with that beneath South America being lower) between the two regions without invoking a temperature difference between the two regions. We also discuss conditions of mantle composition and temperature that double discontinuities may occur near the 660-km depth, as well as the depth separation and velocity jumps of the double discontinuities. For the inferred mantle temperature and composition beneath South America and northeast Asia, the maximum separation of the double discontinuities is 20 km and cannot be resolved by the SH wave data.
TL;DR: In this article, S to P waves converted at the mid-mantle discontinuity were observed on the stacked diagrams with a negative slowness relative to the P wave and a conversion depth ranging from ∼1080 km in the west to ∼930km in the east.
Abstract: [1] S to P conversions were employed to derive a coherent discontinuity structure beneath Indonesia. Analysis of data recorded by three regional arrays from nine deep earthquakes not only confirmed the results of previous studies on the existence of the mid-mantle discontinuity beneath the Java arc but also revealed its presence north to Kalimantan Island. S to P waves converted at the discontinuity were observed on the stacked diagrams with a negative slowness relative to the P wave and a conversion depth ranging from ∼1080 km in the west to ∼930 km in the east.
TL;DR: In this article, the authors present a numerical approach for modeling multiple crack fatigue growth in a plane elastic infinite plate, which involves a generation of Bueckner's principle, a displacement discontinuity method with crack-tip elements (a boundary element method) proposed recently by the author and an extension of Paris' law to a multiple crack problem under mixed-mode loading.
TL;DR: In this paper, the authors investigate the topography of the major upper mantle discontinuities by separating the effects of the topographical and volumetric velocity heterogeneity in P receiver functions from 55 seismograph stations.
TL;DR: A framework is proposed here that is based upon a meshed based partition of unity method, also known as the numerical manifold method, that divides the discontinuities posed by joints or faults into two groups.
TL;DR: In this paper, the authors used the boundary element method to compute complex stress intensity factors at bifurcated cracks by using the constant displacement discontinuity element presented by Crouch and Starfield.
TL;DR: In this paper, the direction of development of a thin fracture process zone at the tip of an interfacial crack in a piecewise homogeneous isotropic elastoplastic body is modeled by a straight line of tangential displacement discontinuity.
Abstract: The Wiener-Hopf method is used to study, under the conditions of plane strain, the direction of development of a thin fracture process zone at the tip of an interfacial crack in a piecewise homogeneous isotropic elastoplastic body. The zone is modeled by a straight line of tangential displacement discontinuity that emerges from the crack tip at an angle to the interface. The dependences of the zone length and the angle on the load and other parameters of the problem are investigated
TL;DR: In this article, a verification of fracture energy density is presented as a fundamental fracture threshold in hot-mix asphalt mixtures using the semicircular bending (SCB) test, which was enhanced by a digital image correlation system capable of providing a dense and accurate displacement-strain field of composite materials at the microstructural level.
Abstract: A verification of fracture energy density is presented as a fundamental fracture threshold in hot-mix asphalt. Fracture energy density was evaluated with the semicircular bending (SCB) test. Experimental analyses were enhanced by a digital image correlation system capable of providing a dense and accurate displacement-strain field of composite materials at the microstructural level and suitable for describing the cracking behavior of materials at crack initiation. The resulting fracture behavior in the SCB was predicted with a displacement discontinuity method to explicitly model the microstructure of asphalt mixtures and to predict their fracture energy density. The input parameters for the displacement discontinuity micromechanical model of the SCB were obtained from the Superpave® indirect tensile test. The predicted crack initiation and crack propagation patterns are consistent with observed cracking behavior. The results also imply that fracture in mixtures can be modeled effectively with a micromech...
TL;DR: In this article, the lower boundary of a subducting slab is detected by depth conversion analysis using a recent 3D tomographic velocity model using waveforms from 249 teleseismic events collected by Hi-net and Jarray short-period stations in NE Japan.