Fracture mechanics analysis of multiple cracks in anisotropic media     

Chia‐Huei Tu  C.‐S. Chen  T.‐T. Yu 《国际地质力学数值与分析法杂志》2011,35(11):1226-1242

This paper presents a single‐domain boundary element method (BEM) for linear elastic fracture mechanics analysis in the two‐dimensional anisotropic material. In this formulation, the displacement integral equation is collocated on the un‐cracked boundary only, and the traction integral equation is collocated on one side of the crack surface only. A special crack‐tip element was introduced to capture exactly the crack‐tip behavior. A computer program with the FORTRAN language has been developed to effectively calculate the stress intensity factors of an anisotropic material. This BEM program has been verified having a good accuracy with the previous researches. Furthermore, by analyzing the different anisotropic degree cracks in a finite plate, we found that the stress intensity factors of crack tips had apparent influence by the geometry forms of cracks and media with different anisotropic degrees. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Semi‐analytical solution to one‐dimensional consolidation for unsaturated soils with semi‐permeable drainage boundary under time‐dependent loading          下载免费PDF全文

L. Wang  D. A. Sun  A. F. Qin  Y. F. Xu 《国际地质力学数值与分析法杂志》2017,41(16):1636-1655

This paper presents semi‐analytical solutions to Fredlund and Hasan's one‐dimensional consolidation of unsaturated soils with semi‐permeable drainage boundary under time‐dependent loadings. Two variables are introduced to transform two coupled governing equations of pore‐water and pore‐air pressures into an equivalent set of partial differential equations, which are easily solved by the Laplace transform. The pore‐water pressure, pore‐air pressure and settlement are obtained in the Laplace domain. Crump's method is adopted to perform the inverse Laplace transform in order to obtain semi‐analytical solutions in time domain. It is shown that the present solutions are more general and have a good agreement with the existing solutions from literatures. Furthermore, the current solutions can also be degenerated into conventional solutions to one‐dimensional consolidation of unsaturated soils with homogeneous boundaries. Finally, several numerical examples are provided to illustrate consolidation behavior of unsaturated soils under four types of time‐dependent loadings, including instantaneous loading, ramp loading, exponential loading and sinusoidal loading. Parametric studies are illustrated by variations of pore‐air pressure, pore‐water pressure and settlement at different values of the ratio of air–water permeability coefficient, depth and loading parameters. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

Limitations of suction‐controlled triaxial tests in the characterization of unsaturated soils          下载免费PDF全文

X. Zhang 《国际地质力学数值与分析法杂志》2016,40(2):269-296

Behavior of unsaturated soils is influenced by many factors, and the influences of these factors are usually coupled together. Suction‐controlled triaxial (SCTX) tests are considered to allow researchers to investigate influences of individual variables on unsaturated soils under specified stress path with controls of stresses, pore water, and air pressures. In the past 50 years, SCTX testing method has been established as a standard approach to characterize constitutive behavior of unsaturated soils. Most important concepts for modern unsaturated soil mechanics were developed upon results from the SCTX tests. Among these, one of the most important contributions in the constitutive modeling of elasto‐plastic behavior for unsaturated soils is the Barcelona basic model (BBM) proposed by Alonso et al. in 1990. The BBM successfully explained many features of unsaturated soils and received extensive acceptance. However, the SCTX tests are designed based upon the divide‐and‐conquer approach in which an implicit assumption is used: soil behavior is stress‐path independent. However, it is well‐established that unsaturated soil behavior is elasto‐plastic and stress‐path dependent. It is found that the SCTX tests in fact cannot control the stress path of an unsaturated soil during loading. This incapability, in combination with complicated loading/collapse behavior of unsaturated soils, makes the SCTX tests for characterizing unsaturated soil questionable. This paper discusses the limitations of the SCTX tests in the characterization of unsaturated soils. A possible solution to the problem was proposed based on a newly developed modified state surface approach. The discussions are limited for isotropic conditions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

A note on the consolidation settlement of a rigid circular foundation on a poroelastic halfspace          下载免费PDF全文

Jueun Kim  A.P.S. Selvadurai 《国际地质力学数值与分析法杂志》2016,40(14):2003-2016

This paper uses Biot's poroelasticity approach to examine the consolidation behaviour of a rigid foundation with a frictionless base in contact with a poroelastic halfspace. The mathematical development of the mixed boundary value problem involves a set of dual integral equations in the Laplace transform domain which cannot be conveniently solved by employing conventional procedures. In this paper, a numerical solution is developed using a scheme where the contact normal stress is approximated by a discretized equivalent. The influence of limiting drainage boundary conditions at the entire surface of the halfspace on the degree of consolidation of the rigid circular foundation is investigated. The results obtained in this study are compared with the corresponding results given in the literature. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Stress‐dependent hardening and failure surfaces of dry sand     

W. Ehlers  O. Avci 《国际地质力学数值与分析法杂志》2013,37(8):787-809

During several triaxial compression experiments on plastic hardening, softening, and failure properties of dense sand specimens, it was found on various stress paths that the size of the failure surface was not constant. Instead, it changed depending on the current state of hydrostatic pressure. This finding is in contrast to the standard opinion consisting of the fact that the failure surface remains constant, once it has been reached during an experiment or in situ. In general, the behaviour of cohesionless granular‐material‐like sand is somehow characterised in between fluid and solid, where the solid behaviour results from the angle of internal friction and the confining pressure. Although the friction angle is an intrinsic material property, the confining pressure varies with the boundary conditions, thus defining different solid properties like plastic hardening, softening, and also failure. Based on our findings, it was the goal of the present contribution to introduce an improved setting for the plastic strain hardening and softening behaviour including the newly found yield properties at the limit state. For the identification of the material parameters, a complete triaxial experimental analysis of the tested sand is given. The overall elasto‐plasticity concept is validated by numerical computations of several laboratory foundation‐ and slope‐failure experiments. The performance of the proposed approach is compared with the standard concept of a constant failure surface, where the corresponding yield surfaces are understood as contours of equivalent plastic work or plastic strain. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

In situ stress field of eastern Australia     

R. R. Hillis  J. R. Enever  S. D. Reynolds 《Australian Journal of Earth Sciences》2013,60(5):813-825

New in situ data based on hydraulic fracturing and overcoring have been compiled for eastern Australia, increasing from 23 to 110 the number of in situ stress analyses available for the area between and including the Bowen and Sydney Basins. The Bowen Basin displays a consistent north‐northeast maximum horizontal stress (σ_H) orientation over some 500 km. Stress orientations in the Sydney Basin are more variable than in the Bowen Basin, with areas of the Sydney Basin exhibiting north‐northeast, northeast, east‐west and bimodal σ_H orientations. Most new data indicate that the overburden stress (σ_V) is the minimum principal stress in both the Bowen and Sydney Basins. The Sydney Basin is relatively seismically active, whereas the Bowen Basin is relatively aseismic. Despite the fact that in situ stress measurements sample the stress field at shallower depth than the seismogenic zone, there is a correlation between the stress measurements and seismicity in the two areas. Mohr‐Coulomb analysis of the propensity for failure in the Sydney Basin suggests 41% of the new in situ stress data are indicative of failure, as opposed to 13% in the Bowen Basin. The multiple pre‐existing structural grains in the Sydney Basin further emphasise the difference between propensity for failure in the two areas. Previous modelling of intraplate stresses due to plate boundary forces has been less successful at predicting stress orientations in eastern than in western and central Australia. Nonetheless, stress orientation in the Bowen Basin is consistent with that predicted by modelling of stresses due to plate boundary forces. Variable stress orientations in the Sydney Basin suggest that more local sources of stress, such as those associated with the continental margin and with local structure, significantly influence stress orientation. The effect of local sources of stress may be relatively pronounced because stresses due to plate boundary forces result in low horizontal stress anisotropy in the Sydney Basin.  相似文献   

The behavior of magneto-acoustic-gravity waves near the cusp resonance in a lossless,compressible, isothermal,stratified, electrically conducting and uniformly magnetized atmosphere. II: The valve effect     

Leon P. J. Kamp 《地球物理与天体物理流体动力学》2013,107(4):257-271

Abstract

In the present paper the behavior of (internal) magneto-acoustic-gravity waves near the cusp resonance in a lossless, compressible, isothermal, stratified, electrically conducting atmosphere that is permeated by a uniform, nearly horizontal magnetic field is re-addressed (Kamp, 1989). The previously analyzed linear conversion of long acoustic-gravity waves into short magneto-acoustic waves that carry off the energy from the resonance region along the magnetic field, is re-analyzed with boundary layer techniques that are based on the smallness of the vertical component of the magnetic field. More specifically the existence of the so-called valve effect for the generated magneto-acoustic mode near the critical level is explicitly demonstrated and shown to be governed by two rivalling effects.  相似文献   

A practical and efficient numerical scheme for the analysis of steady state unconfined seepage flows     

Mohammad Hossein Bazyar  Adel Graili 《国际地质力学数值与分析法杂志》2012,36(16):1793-1812

The scaled boundary finite‐element method (SBFEM), a novel semi‐analytical technique, is applied to the analysis of the confined and unconfined seepage flow. This method combines the advantages of the finite‐element method and the boundary element method. In this method, only the boundary of the domain is discretized; no fundamental solution is required, and singularity problems can be modeled rigorously. Anisotropic and nonhomogeneous materials satisfying similarity are modeled without additional efforts. In this paper, SBFE equations and solution procedures for the analysis of seepage flow are outlined. The accuracy of the proposed method in modeling singularity problems is demonstrated by analyzing seepage flow under a concrete dam with a cutoff at heel. As only the boundary is discretized, the variable mesh technique is advisable for modeling unconfined seepage analyses. The accuracy, effectiveness, and efficiency of the method are demonstrated by modeling several unconfined seepage flow problems. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Flat boundaries and their effect on sand testing     

G. Marketos  Malcolm D. Bolton 《国际地质力学数值与分析法杂志》2010,34(8):821-837

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Effect of atmospheric CO₂ and solar activity on wind regime and water column stability in the major global upwelling areas     

B. Patti  C. Guisande  I. Riveiro  P. Thejll  A. Cuttitta  A. Bonanno  G. Basilone  G. Buscaino  S. Mazzola 《Estuarine, Coastal and Shelf Science》2010

It is not clear whether global warming will favour or reduce global ocean phytoplankton productivity in coastal areas. Moreover, the relative contributions made by natural and/or anthropogenic factors to possible changes in phytoplankton productivity are not clear. As the relationship between primary production and alongshore wind forcing is well established for the Eastern Boundary Current (EBC) ecosystems, our aim is to determine whether the changes experienced over the last five decades (1958–2007) in atmospheric CO₂ and solar activity have been able to affect the wind regime and water column stability in the most biologically productive upwelling areas of California, Canary, Humboldt and Benguela. We approached the work by statistically studying the effect of solar activity and atmospheric CO₂ on surface alongshore wind stress and on water column stability. There was an increasing trend in wind stress and water column stability in all the upwelling areas over the period studied (with the single exception of stability in the California EBC system). The analysis of detrended series evidenced significant relationships between atmospheric CO₂ concentration and wind stress and water column stability in the coastal upwelling areas investigated. In addition, wind stress and stability data were found to be consistent, with negative linear relationships between wind stress and CO₂ in most of the sites in the Benguela, Canary and Humboldt regions associated, as expected, to positive relationships when water column stability is used as regressand. The results of the present study suggest that greenhouse gas forcing, independent of its well known general increasing trend, was able to decrease wind stress intensity and increase water column stability for the period 1958 to present in most of the sites of the four Eastern Boundary Ecosystems studied, with the one exception of the California region. Conversely, the impact of solar activity appeared to be quite low compared to the greenhouse gas forcing.  相似文献