Showing papers on "Discontinuity (geotechnical engineering) published in 2013"
TL;DR: In this article, a new P wave tomographic model of the mantle was constructed using more than 10 million travel times and the finite-frequency effect of seismic rays was taken into account by calculating banana-donut kernels at 2´Hz for all first arrival time data, and at 01´µHz for broadband differential travel time data based on this model, a systematic survey for subducted slab images was developed for the circum-Pacific.
Abstract: A new P wave tomographic model of the mantle was constructed using more than 10 million travel times The finite-frequency effect of seismic rays was taken into account by calculating banana-donut kernels at 2 Hz for all first arrival time data, and at 01 Hz for broadband differential travel time data Based on this model, a systematic survey for subducted slab images was developed for the circum-Pacific; including the Kurile, Honshu, Izu-Bonin, Mariana, Java, Tonga-Kermadec, southern and northern South America, and Central America, arcs This survey revealed a progressive lateral variation of the configuration of slabs along arc(s), which we interpret as an indication for successive stages of slab subduction through the Bullen's transition region with the 660 km discontinuity at the middle We identified the four distinct stages: I - slab stagnant above the 660 km discontinuity; II - slab penetrating the 660 km discontinuity; III - slab trapped in the uppermost lower mantle (at a depth of 660–1000 km); and IV - slab descending well into the deep lower mantle The majority of slab images are found to be either at Stage I or III, suggesting that Stages I and III are relatively stable or neutral and II and IV are relatively unstable or transient There is a remarkable distinction for the deepest hypocentral distribution between slabs at Stage I and slabs at Stages II or III
381 citations
17 Mar 2013
223 citations
TL;DR: In this article, the boundary between Earth's rigid lithosphere and ductile asthenosphere is marked by a seismic discontinuity, and it is shown that melts should pond at pressures that correspond to the lithosphere-asthenosphere boundary.
Abstract: The boundary between Earth’s rigid lithosphere and ductile asthenosphere is marked by a seismic discontinuity. Laboratory experiments on basaltic magmas show that melts should pond at pressures that correspond to the lithosphere–asthenosphere boundary. Thus, magma ponding could explain the observed seismic discontinuity.
136 citations
01 Jan 2013
TL;DR: In this paper, the authors developed a new analytical model, called OpenT, that solves the elasticity problem of a hydraulic fracture contact with a pre-existing discontinuity natural fracture (NF) and the condition for HF re-initiation at the NF.
Abstract: We develop a new analytical model, called OpenT, that solves the elasticity problem of a hydraulic fracture (HF) contact with a pre-existing discontinuity natural fracture (NF) and the condition for HF re-initiation at the NF. The model also accounts for fluid penetration into the permeable NFs. For any angle of fracture intersection, the elastic problem of a blunted dislocation discontinuity is solved for the opening and sliding generated at the discontinuity. The sites and orientations of a new tensile crack nucleation are determined based on a mixed stress- and energy-criterion. In the case of tilted fracture intersection, the finite offset of the new crack initiation point along the discontinuity is computed. We show that aside from known controlling parameters such stress contrast, cohesional and frictional properties of the NFs and angle of intersection, the fluid injection parameters such as the injection rate and the fluid viscosity are of first-order in the crossing behavior. The model is compared to three independent laboratory experiments, analytical criteria of Blanton, extended Renshaw−Pollard, as well as fully coupled numerical simulations. The relative computational efficiency of OpenT model (compared to the numerical models) makes the model attractive for implementation in modern engineering tools simulating hydraulic fracture propagation in naturally fractured environments.
119 citations
TL;DR: In this article, the role of phase transformations on radial and lateral velocity and density variations in the Earth's mantle is examined and specific attention is given to the chemical interaction among the multiple components in the entire system.
Abstract: The role of phase transformations on radial and lateral velocity and density variations in the Earth's mantle is examined. Pyrolite is taken as a reference chemical composition. Specific attention is given to the chemical interaction among the multiple components in the entire system. In particular, aluminum influences the width and depth of the 410 km discontinuity. The velocities and density at the 410 km discontinuity are rather insensitive to lateral variations of the temperature aside from the change in the depth of the discontinuity. Formation of CaSiO 3 perovskite may be an important contributor to the 520 km discontinuity. Aluminum also plays a major role in defining the character of the 660 km discontinuity. Slight variations in Al content or temperature from the reference model changes the magnitude of the 660 velocity increase by a factor of two. Ilmenite forming phase transitions will introduce lateral velocity variations resulting from lowered temperatures that can be mistaken as a slab sitting on the 660 km discontinuity. These many different implications result from considering the whole chemical system.
111 citations
TL;DR: This paper presents the development of the algorithms used in the software program PlaneDetect for the automated identification and mapping of planar discontinuities within a 3-dimensional surface model of a jointed rockmass.
106 citations
TL;DR: In this article, the authors review seismic observations of discontinuity properties, including their depth, topography, sharpness, and amplitude, and show that the magnitude of the velocity and density increases across the discontinuities are poorly constrained by many seismic observations; they are currently best resolved from measurements of the amplitudes of reflected phases.
Abstract: The upper mantle seismic discontinuities provide important constraints on models of mantle composition and dynamics. New observations of reflected and converted phases from the discontinuities have made possible more detailed measurements of discontinuity structure than are provided by traditional analyses of refracted waveforms. This paper reviews seismic observations of discontinuity properties, including their depth, topography, sharpness, and amplitude. Topography on the 410- and 660-km discontinuities is largely uncorrelated at global scales, and the 660 topography is significantly larger in peak-to-peak amplitude. The positions of subduction zones are correlated with depressions in the 660-km discontinuity, consistent with tomography results indicating the presence of large cold (fast) regions deep in the transition zone. A significant fraction of the velocity increases near 410 and 660 km occur over a depth interval less than 5 km; the 520-km reflector is more diffuse and appears to occur over a 10 to 50 km depth interval. The magnitude of the velocity and density increases across the discontinuities are poorly constrained by many seismic observations; they are currently best resolved from measurements of the amplitudes of reflected phases.
99 citations
TL;DR: In this article, a new automatic method for discontinuity traces mapping and sampling on a rock mass digital model is described, where traces are detected directly as surface breaklines, by means of maximum and minimum principal curvature values of the vertices that constitute the model surface.
91 citations
TL;DR: In this paper, the authors reported the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface prepared on (110)-oriented SrTiO 3, with a LaO3-layer thickness-dependent metal-insulator transition.
Abstract: The observation of a high-mobility two-dimensional electron gas between two insulating complex oxides, especially LaAlO3/SrTiO3, has enhanced the potential of oxides for electronics. The occurrence of this conductivity is believed to be driven by polarization discontinuity, leading to an electronic reconstruction. In this scenario, the crystal orientation has an important role and no conductivity would be expected, for example, for the interface between LaAlO3 and (110)-oriented SrTiO3, which should not have a polarization discontinuity. Here we report the observation of unexpected conductivity at the LaAlO3/SrTiO3 interface prepared on (110)-oriented SrTiO3, with a LaAlO3-layer thickness-dependent metal-insulator transition. Density functional theory calculation reveals that electronic reconstruction, and thus conductivity, is still possible at this (110) interface by considering the energetically favourable (110) interface structure, that is, buckled TiO2/LaO, in which the polarization discontinuity is still present. The conductivity was further found to be strongly anisotropic along the different crystallographic directions with potential for anisotropic superconductivity and magnetism, leading to possible new physics and applications.
89 citations
TL;DR: In this paper, the authors demonstrate the spatial and temporal relationships and compatibility between lateral midcrustal extrusive flow and wedge taper processes within an evolving orogen, and demonstrate the presence of a structural, metamorphic, and geochronologic discontinuity.
87 citations
TL;DR: In this article, a series of direct shear tests were performed using an advanced shear box that allows the injection of water into the discontinuity to assess the decrease in the mechanical properties of clay-infilled discontinuities due to water saturation.
TL;DR: In this article, the results of numerical simulation of the hydraulic fracturing process in an oil-well using the Distinct Element Method were described and the numerical simulation was performed in various in-situ stress conditions with the consideration of a transient flow algorithm for fluid flow.
TL;DR: In this article, a series of dynamic tests using a split Hopkinson rock bar was conducted on a simulated sand-filled fracture, and the experimental results showed that stress wave attenuation across the filled fracture is strongly affected by wave reflection and transmission at the fracture interfaces and the dynamic compaction of the filling sand.
17 May 2013
TL;DR: In this paper, the authors investigated the problem of a hydraulic fracture propagation through a weakly cohesive frictional discontinuity for different conditions of fracture toughness, in situ stresses, fracture intersection angle, injection parameters and permeability of the pre-existing fracture.
Abstract: We investigated the problem of a hydraulic fracture propagation through a weakly cohesive frictional discontinuity for different conditions of fracture toughness, in situ stresses, fracture intersection angle, injection parameters and permeability of the pre-existing fracture. The parametric sensitivity of the fracture interaction process, in terms of crossing versus arresting of the hydraulic fracture at the discontinuity, was performed using numerical simulations through an extensive parameter space representative of hydraulic fracturing field conditions. The effect of the pre-existing fracture permeability on the crossing behavior was analyzed using a simple analytical model. We showed that the injection rate and viscosity of fracturing fluid are the key parameters controlling the crossing/non-crossing interaction behavior, in addition to already known fracture interaction angle and in-situ stress parameters. We have also found that the pre-existing fracture hydraulic aperture, when as large as that of the hydraulic fracture aperture, has significant influence on the interaction and may more likely cause the hydraulic fracture to arrest.
TL;DR: In this paper, the influence of water on major phase transformations in the Earth's mantle with implications for seismic discontinuity structure and mantle dynamics is summarized. But, the results are based on quench multianvil and in situ X-ray diffraction studies.
Abstract: In this chapter we summarize recent results on the influence of water on major phase transformations in the Earth's mantle with implications for seismic discontinuity structure and mantle dynamics The experimental data are based on quench multianvil and in situ X-ray diffraction studies Differences in water solubility between olivine and wadsleyite, and between ringwoodite and Mg-perovskite + ferropericlase may displace the phase transition boundaries, which are responsible for the 410- and 660-km discontinuities, respectively The results show that water expands the stability field of wadsleyite to lower pressures, which is consistent with broadening of the 410-km discontinuity in some regions of the mantle A significant shift of the wadsleyite-ringwoodite phase transition to higher pressure caused by water may also be responsible for depth variations or absence of the 520-km discontinuity Study of the post-spinel transformation in hydrous pyrolite indicates that the phase boundary also shifts to higher pressures Displacement of this boundary with ∼2 wt% H 2 O corresponds to about 15 km at 1473 K Thus, presence of water could account for half of the observed 30-40 km depressions at the 660-km discontinuity in subduction zones at this temperature Study of the post-garnet transformation in anhydrous and hydrous MORB show that this phase boundary shifts to the lower pressures by ∼2 GPa with the addition of 2-5 wt% water This observation demonstrates that the density crossover between peridotite and basaltic components near 660 km might be absent under hydrous conditions, inhibiting the separation of these components at the 660-km discontinuity
TL;DR: In this paper, a random set distinct element method (RS-DEM) has been developed and applied in the stability analysis of a rock slope from China in order to evaluate the influence of the discontinuity of joints of rock material on the slope stability.
TL;DR: In this article, a three-dimensional numerical model used combines the finite element method and the poroelastic displacement discontinuity method to analyze the potential for formation failure resulting from pressurization of the hydraulic fracture.
TL;DR: In this paper, the authors further investigate the seismic response of a set of parallel rock fractures filled with viscoelastic materials, following the work by Zhu et al. They use split Hopkinson rock bar (SHRB) technique to simulate 1-D P-wave propagation across the sand-filled parallel fractures.
Abstract: The purpose of this study is to further investigate the seismic response of a set of parallel rock fractures filled with viscoelastic materials, following the work by Zhu et al. Dry quartz sands are used to represent the viscoelastic materials. The split Hopkinson rock bar (SHRB) technique is modified to simulate 1-D P-wave propagation across the sand-filled parallel fractures. At first, the displacement and stress discontinuity model (DSDM) describes the seismic response of a sand-filled single fracture. The modified recursive method (MRM) then predicts the seismic response of the sand-filled parallel fractures. The SHRB tests verify the theoretical predictions by DSDM for the sand-filled single fracture and by MRM for the sand-filled parallel fractures. The filling sands cause stress discontinuity across the fractures and promote displacement discontinuity. The wave transmission coefficient for the sand-filled parallel fractures depends on wave superposition between the fractures, which is similar to the effect of fracture spacing on the wave transmission coefficient for the non-filled parallel fractures.
TL;DR: In this paper, the extended finite element method (X-FEM) is used to simplify the meshing of complex 3D networks of discontinuities with junctions in order to solve matrix conditioning issues.
Abstract: The extended finite element method (X-FEM) has been developed to minimize requirements on the mesh in a problem with a displacement discontinuity. We present the development carried out to take advantage of the X-FEM approach in simplifying the meshing of complex 3D networks of discontinuities with junctions. Contact with large sliding along the branched discontinuities is discussed. Solutions are proposed and discussed to solve some matrix conditioning issues. Several examples are presented in this paper in order to prove the efficiency of the proposed approach.
TL;DR: In this article, the sensitivity of the precursors to intermittent seismic structure was addressed using an axisymmetric finite difference model of wave propagation in the mantle, and it was shown that the precurors are sensitive to structures ≥500 km in lateral extent and that the observations of this discontinuity are plausibly tied to lateral variations in basaltic composition of the upper mantle related to dynamics, such as plumes and subduction.
Abstract: [1] Intermittent seismic discontinuities near 250–300 km depth beneath South America and the Pacific basin are detected with high-resolution seismic array methods that use SS and PP precursors recorded at the High Lava Plains Seismic Experiment and the EarthScope Transportable Array. The transformation of coesite to stishovite in an eclogite-rich mantle composition produces a seismic discontinuity near 300 km depth; lateral changes in basalt fraction of the upper mantle will thus produce an intermittent seismic discontinuity. The sensitivity of the precursors to intermittent seismic structure is addressed using an axisymmetric finite difference model of wave propagation in the mantle. These numerical experiments find that the precursors are sensitive to structures ≥500 km in lateral extent and that the observations of this discontinuity are plausibly tied to lateral variations in basaltic composition of the upper mantle related to dynamics, such as plumes and subduction.
TL;DR: In this paper, the authors provide an overview of contrast of elastomechanical parameters across the Moho, basically contrasts in seismic wave velocities, density and yield strength.
TL;DR: In this article, the role of different tectonic features on the development of both local and large scale rock slope instabilities occurring in Turtle Mountain is investigated by combining remote methods with detailed field surveys.
TL;DR: In this paper, the authors estimate temperature anomalies and water content in the mantle transition zone from the depth of the "660-km discontinuity" and tomographically determined P-velocity anomalies.
Abstract: We estimate temperature anomalies and water content in the mantle transition zone from the depth of the "660-km discontinuity" and tomographically determined P-velocity anomalies. We assume a linear dependence of the discontinuity depths and P-velocity on temperature anomaly and water content. Beneath the Philippine Sea, where the Pacific plate is subducted, temperature anomalies are as low as -500K to -700 K within and near the stagnant Pacific slab and the water content is estimated to be in the range of 1-1.4 wt.%H 2 O. The west Philippine basin, away from the Pacific slab, does not have a significant temperature anomaly or water content. Beneath western Japan, where the Pacific slab is subducted, we obtain temperature anomalies up to -300 to -600 K and water content up to 1-1.5 wt.%H 2 O. Many problems remain to be solved for obtaining a definitive conclusion on the presence of water and quantitative estimates of temperature and water content. Estimates of the temperature anomaly and water content are highly sensitive to the input seismic parameters (the discontinuity depths and P-velocities) and the assumed dependence of the seismic parameters on temperature and water content determined from experimental studies. More accurate estimates of the seismic parameters and the experimental data measured under the pressure and temperature conditions of the mantle transition zone are necessary. Anelastic attenuation is probably enhanced by water, which might break down the linear dependence of the discontinuity depths and P-velocity on temperature anomaly and water content. A non-linear optimization approach using better seismic and experimental data may be required for obtaining more conclusive evidence for the presence of water.
TL;DR: Stress-hybrid quadrilateral finite element with embedded strong discontinuity for failure analysis of plane stress solids was used in this article, where the authors proposed a new finite element for plane stress analysis.
Abstract: Stress-hybrid quadrilateral finite element with embedded strong discontinuity for failure analysis of plane stress solids
TL;DR: In this article, a mesoscopic masonry model is presented in which joints are modelled by weak and strong discontinuities through the partition of unity property of finite element shape functions.
TL;DR: In this article, the deformation modulus of a rock mass is measured by in situ tests, such as plate bearing, flat jack, pressure chamber, borehole jacking and dilatometer tests.
Abstract: It is often difficult to directly obtain specific design parameters of interest. In these situations, estimation based on empirical correlations is an alternative. The deformation modulus of a rock mass, which is important to know for engineering projects, is measured by in situ tests, such as plate bearing, flat jack, pressure chamber, borehole jacking and dilatometer tests. Nevertheless, these in situ tests are expensive, time consuming and sometimes even impossible. Many attempts have been made to estimate the E modulus using easy-to-obtain parameters of a rock mass. This paper reviews previous studies and the equations that have been developed. In addition, this study presents a new relation developed using a database of 82 dilatometer test results gathered from two dam sites and a tunnel site. Statistical analyses were performed to correlate accessible rock parameters with measured E modulus values from in situ tests. Knowing that discontinuity characteristics and the strength of rock materials are t...
Book•
23 Dec 2013
TL;DR: Racial Blackness and the Discontinuity of Western Modernity as discussed by the authors is a re-examination of the relationship between the black experience and Western modernity written by Lindon Barrett, who was tragically murdered in 2008.
Abstract: Racial Blackness and the Discontinuity of Western Modernity (University of Illinois Press, 2014) is a brilliant and pathbreaking re-examination of the relationship between the black experience and Western modernity. Written by Lindon Barrett, who was tragically murdered in 2008, the conference aims to outline the making of this posthumously published volume, critically assess its contribution while locating it within the wider context of Barrett’s life and legacy. With the exception of the last year of his life, Lindon Barrett spent his entire academic career serving the University of California, Irvine campus. Recruited in 1990 as an Assistant Professor of English and Comparative Literature, Barrett rose to become a full professor and distinguished himself as a founding member of the Program in African American Studies, which he served as Director from 2004 to 2007. He joined the University of California, Riverside in 2007. Barrett also authored Blackness and Value: Seeing Double (Cambridge University Press, 1999) and numerous scholarly essays and book chapters, including in the flagship journal Callaloo, which he served as Associate Editor from 1997 to 2000.
TL;DR: In this article, the authors extend the cohesive surface model to include in-plane kinematic quantities, which can capture a variety of fracture phenomena, such as delamination buckling and splitting cracks, that are difficult, if not impossible, to describe within conventional cohesive surface models.
Abstract: In the cohesive surface model cohesive tractions are transmitted across a two-dimensional surface, which is embedded in a three-dimensional continuum. The relevant kinematic quantities are the local crack opening displacement and the crack sliding displacement, but there is no kinematic quantity that represents the stretching of the fracture plane. As a consequence, in-plane stresses are absent, and fracture phenomena as splitting cracks in concrete and masonry, or crazing in polymers, which are governed by stress triaxiality, cannot be represented properly. In this paper we extend the cohesive surface model to include in-plane kinematic quantities. Since the full strain tensor is now available, a three-dimensional stress state can be computed in a straightforward manner. The cohesive band model is regarded as a subgrid scale fracture model, which has a small, yet finite thickness at the subgrid scale, but can be considered as having a zero thickness in the discretisation method that is used at the macroscopic scale. The standard cohesive surface formulation is obtained when the cohesive band width goes to zero. In principle, any discretisation method that can capture a discontinuity can be used, but partition-of-unity based finite element methods and isogeometric finite element analysis seem to have an advantage since they can naturally incorporate the continuum mechanics. When using interface finite elements, traction oscillations that can occur prior to the opening of a cohesive crack, persist for the cohesive band model. Example calculations show that Poisson contraction influences the results, since there is a coupling between the crack opening and the in-plane normal strain in the cohesive band. This coupling holds promise for capturing a variety of fracture phenomena, such as delamination buckling and splitting cracks, that are difficult, if not impossible, to describe within a conventional cohesive surface model.
TL;DR: In this paper, the authors examined the mantle discontinuities in the United States and Gulf of Mexico using multiple ScS reverberations from earthquakes in Central and South America captured by 65 broadband and long-period seismometers.
Abstract: We examine mantle discontinuities beneath the United States and Gulf of Mexico using multiple ScS reverberations from earthquakes in Central and South America captured by 65 broadband and long-period seismometers across the United States. The depths of discontinuities and the impedance contrasts across them were estimated using a hierarchical waveform inversion and stacking method. The path-averaged depth of the 410-km discontinuity varies moderately across the study area and is particularly shallow (∼395 km) beneath the eastern United States. Topography on the 660-km discontinuity is more subdued and is close to the global mean depth. The 520-km discontinuity is seen consistently across the study area, though both the depth and the impedance contrast of the discontinuity vary significantly. Corridors in the eastern United States and Gulf of Mexico have extremely strong 520-km discontinuities relative to the corresponding 410-km and 660-km discontinuities. We attribute the shallow 410-km and strong 520-km discontinuities beneath the eastern United States and Gulf of Mexico to a locally water-rich transition zone.
TL;DR: In this paper, fatigue crack growth simulations of bi-material interfacial cracks have been performed using extended finite element method (XFEM) under thermo-elastic loading.
Abstract: In this paper, fatigue crack growth simulations of bi-material interfacial cracks have been performed using extended finite element method (XFEM) under thermo-elastic loading. The material discontinuity (interface) has been modelled by a signed distance function whereas a strong discontinuity (crack) has been modelled by two functions i.e. Heaviside and asymptotic crack tip enrichment functions. The values of stress intensity factors are extracted from the XFEM solution by domain based interaction integral approach. Standard Paris fatigue crack growth law is used for the life estimation of various model problems. The results obtained by XFEM for an interfacial edge and centre cracks are compared with those obtained by finite element method based on a remeshing approach.