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1.
Experimental results are presented in this paper to study the strain softening behaviour of a marine dredged sand under plane-strain conditions. K0 consolidated drained and undrained tests were conducted using a new plane-strain apparatus to characterize the strain softening behaviour of the sand under plane-strain conditions. For medium dense specimens, strain softening and shear bands were observed to occur under both drained and undrained conditions. For very loose specimens, no shear bands were observed and critical states were reached within the homogeneous deformation region in both drained and undrained tests. Strain softening was observed to occur at small strain for very loose specimens under undrained conditions. Two types of strain softening, the homogenous softening and banding softening, were identified and the conditions for strain softening were established. The results obtained from this study were compared with the studies by Han and Vardoulakis (Géotechnique 41(1):49–78, 1991), Finno et al. (J Geotech Eng ASCE 122(6):462–473, 1996, Géotechnique 47(1):149–165, 1997) and Mokni and Desrues (Mech Cohes-Frict Mat 4:419–441, 1998). 相似文献
2.
《Geomechanics and Geoengineering》2013,8(2):85-96
The results of an experimental study of the undrained behaviour of Changi sand under axisymmetric and plane-strain conditions are presented. K0 consolidated undrained plane-strain tests and K0 or isotropically consolidated triaxial tests on very loose and medium dense specimens were conducted. The undrained behaviour of sand at very loose and medium dense states under plane-strain conditions was characterised and compared with that under axisymmetric conditions. It was observed that the undrained behaviour of very loose and medium dense sand under plane strain is similar to that under axisymmetric conditions. However, because of the formation of shear bands in plane-strain tests, the post-peak behaviour of medium dense sand in plane strain is different from that in triaxial tests. It was also established that an instability line for plane-strain conditions can be defined in a way similar to that for axisymmetric conditions. Using the state parameter, a unified relationship between the normalised slope of instability line and the state parameters can be established for both axisymmetric and plane-strain conditions. Using this relationship, the instability conditions established under axisymmetric conditions can be used for plane-strain conditions. 相似文献
3.
The aim of the present paper is to numerically analyse the behaviour of frozen sand by using a viscoplastic constitutive model with strain softening. A constitutive model has been developed introducing the stress history tensor which is a functional of the stress history, with respect to a generalized time measure. It is shown that Adachi and Oka's model is applicable to the results of triaxial tests on a frozen Toyoura sand at different strain rates. First, the instability of the model is discussed within the framework of bifurcation theory. The model is then implemented into a FEM code to numerically simulate the behaviour under plane strain conditions. From the numerical results, it is revealed that the formation of shear bands is possible and the characteristics of strain localization, such as shear banding, depend on the strain rates. 相似文献
4.
This paper investigates the pull-out behaviour (particularly the bearing resistance) of a steel grid reinforcement embedded in silty sand using laboratory tests and numerical analyses. It is demonstrated that the various common analytical equations for calculating the bearing component of pull-out resistance give a wide range of calculated values, up to about 200% disparity. The disparity will increase further if the issue of whether to use the peak or critical state friction angle is brought in. Furthermore, these equations suggest that the bearing resistance factor, Nq, is only a function of soil friction angle which is not consistent with some design guidelines. In this investigation, a series of large scale laboratory pull-out tests under different test pressures were conducted. The test results unambiguously confirmed that the Nq factor is a function of test pressure. A modified equation for calculating Nq is also proposed. To have more in-depth understanding of the pull-out behaviour, the tests were modelled numerically. The input parameters for the numerical analysis were obtained from laboratory triaxial tests. The analysis results were compared with the experimental results. Good agreement between experimental and numerical results was achieved if the strain-softening behaviour from peak strength to critical state condition was captured by the soil model used. 相似文献
5.
Constant shear drained tests (CSD) are probably the most suitable to simulate the strength and deformation behaviour of soils
in slopes under water infiltration conditions or lateral stress relief. This is significant because soil behaviour following
a CSD stress path could differ from that of traditional compression triaxial tests. In this paper, CSD tests on sand following
an alternative procedure are presented and discussed. The modified CSD tests were conducted by increasing the pore water pressure
at a constant rate from one end of the specimen with water free to drain from the opposite end. Among the results from specimens
consolidated at variable initial void ratios and principal stress ratios it was revealed that specimens showed a tendency
to dilate even for loose sands; failure was reached at low axial strains; and a pre-failure type of instability could be identified.
The modified procedure has the potential to provide new insights into the failure mechanisms of slopes under a water infiltration
condition. 相似文献
6.
Wave velocity and stress/strain in rock brittle failure 总被引：1，自引：1，他引：0
This paper reports the relationship between wave velocity and stress/strain during rock brittle failure under compression. It is assumed that the rock is a strain-softening medium whose strength can be described by Weibull’s distribution. Based on renormalization group theory, it is found that the stress ratio λ c (the ratio of the stress at the critical point to the peak stress) depends mainly on the homogeneity index or shape parameter m in the Weibull’s distribution for the rock. Measured stress–strain curves and corresponding wave velocity–strain curves in four case studies suggest that the changes caused by internal cracking are correlated to variations of rock wave velocity, and the stress at the critical point on the stress–strain curve is considered to correspond to the rapid decreasing point on the wave velocity–strain curve. For uniaxial compression, the critical stress ratio λ c is derived to be about 75.4 %, which is very close to the measured value. 相似文献
7.
Poul V. Lade 《国际地质力学数值与分析法杂志》2006,30(4):307-333
Data from three‐dimensional experiments performed on sand in true triaxial equipment have been reviewed to sort out apparent disarray resulting from their interpretation. This has been done based on analyses made possible by recent developments and understanding of factors influencing sand behaviour: occurrence of shear banding, boundary conditions and/or specimen slenderness ratio, cross‐anisotropy, and stability of experimental technique. These factors are reviewed and test data from the literature are evaluated. Experimental data are divided into three groups in which: (a) homogeneous behaviour controls the sand strength; (b) shear banding affects the shape of the three‐dimensional failure surface in the midrange of values of b=(σ2?σ3)/(σ1?σ3), and (c) the data has been misinterpreted. Appropriate interpretation of three‐dimensional strength data for sand exhibiting isotropic, homogeneous behaviour is represented by a smoothly rounded triangular failure surface expressible in terms of the first and third stress invariants. Shear banding effects will cause the failure surface to be ‘indented’ in the midrange of b‐values in all sectors of the octahedral plane. Effects of cross‐anisotropy will result in lower strengths in sector III than in sector I of the octahedral plane, and the failure surface will appear as rotated around the stress origin in principal stress space. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
8.
9.
This paper presents the creep behaviour of intact and remoulded specimens of fibrous peat obtained from a field site near Anzac, Alberta, Canada. The creep behaviour was investigated by means of long-term drained and undrained triaxial tests. The development of volumetric, axial, and undrained axial strain and strain rate during drained and undrained creep tests under variable stress conditions is presented. The stress – strain – strain rate (p′–ε v–\(\dot{\varepsilon }_{\text{v}}\)) relationship is found to be unique for different stress and loading durations. The p′–ε v–\(\dot{\varepsilon }_{\text{v}}\) relationship is analysed and represented by creep isotaches. The applicability of different creep models developed for normally consolidated clay is discussed and applied to define the development of creep strain in fibrous peat under varying isotropic and deviator stresses. The secondary consolidation coefficient for evaluating the volumetric strain rate of peat is found to be applicable with some limits. The drained creep behaviour of remoulded peat specimens differs from the behaviour shown by Shelby tube specimens, whereas the undrained creep behaviour in remoulded and Shelby tube specimens is similar. 相似文献
10.
Since cross-anisotropic sand behaves differently when the loading direction or the stress state changes, the influences of the loading direction and the intermediate principal stress ratio (b = (σ 2 ? σ 3)/(σ 1 ? σ 3)) on the initiation of strain localization need study. According to the loading angle (angle between the major principal stress direction and the normal of bedding plane), a 3D non-coaxial non-associated elasto-plasticity hardening model was proposed by modifying Lode angle formulation of the Mohr–Coulomb yield function and the stress–dilatancy function. By using bifurcation analysis, the model was used to predict the initiation of strain localization under plane strain and true triaxial conditions. The predictions of the plane strain tests show that the major principal strain at the bifurcation points increases with the loading angle, while the stress ratio decreases with the loading angle. According to the loading angle and the intermediate principal stress ratio, the true triaxial tests were analyzed in three sectors. The stress–strain behavior and the volumetric strain in each sector can be well captured by the proposed model. Strain localization occurs in most b value conditions in all three sectors except for those which are close to triaxial compression condition (b = 0). The difference between the peak shear strength corresponding to the strain localization and the ultimate shear strength corresponding to plastic limit becomes obvious when the b value is near 0.4. The influence of bifurcation on the shear strength becomes weak when the loading direction changes from perpendicular to the bedding plane to parallel. The bifurcation analysis based on the proposed model gives out major principal strain and peak shear strength at the initiation of strain localization; the given results are consistent with experiments. 相似文献
11.
Ismail Benessalah Ahmed Arab Pascal Villard Khayra Merabet Rachid Bouferra 《Geotechnical and Geological Engineering》2016,34(6):1775-1790
During the last earthquake that occurred in Chlef (El Asnam 1980, Algeria), a significant decrease in the shear strength has caused major damages to several civil and hydraulic structures (earth dams, embankments, bridges, slopes and buildings), especially for the saturated sandy soil of the areas near Chlef valley. This paper presents a laboratory study of drained compression triaxial tests conducted on sandy soil reinforced with horizontal layers of geotextile, in order to study the influence of geotextile layer characteristics both on shear stress–strain and on volumetric change–strain. Tests were carried out on medium and dense sand. The experimental programme includes some drained compression tests performed on reinforced sand samples, for different values of the geotextile layers number (N g), of confining pressure (\( \sigma_{\text{c}}^{\prime } \)) and relative density (D r). The test results have shown that the contribution of the geotextile at low values of the axial strain (ε 1) is negligible, for higher values of (ε 1); geotextile induces a quasi-linear increase in the deviator stress (q) and leads to an increase in the volume contractiveness within the reinforced samples. A negligible influence of geotextile layers number (N g) on the stress–strain behaviour and the volumetric change has been shown, when normalized with N g. The results indicate that the contribution of geotextile to the stress–strain mobilization increases with increasing confining pressure, while its contribution to the volume contraction decreases with the increase in the confining pressure. 相似文献
12.
M. Soleiman Dehkordi K. Shahriar P. Moarefvand M. Gharouninik 《Arabian Journal of Geosciences》2013,6(4):1241-1248
Estimation of rock load is a very important issue because the selection of a support system is highly related to this parameter. Several methods are used to estimate this parameter such as experimental, empirical, and numerical methods. This study propose a new empirical method to estimate the rock load in squeezing ground condition using actual collapses data of Emamzade Hashem tunnel of Iran based on the ration of the post-failure residual strain energy to the pre-failure stored strain energy. Prediction of squeezing ground condition in this study is performed based on Jethwa, Singh, and Hoek criterions. Results show that some sections in shale and sandstone of the Shemshak formation are prone to squeezing. Finally, the relation between the rock load and the ratio of the post-failure residual strain energy to the pre-failure stored strain energy, Ψ, in squeezing ground condition is estimated. Based on the statistical analysis, the maximum correlation between both parameters is achieved when Alejano’s equations are used to estimate the drop modulus. As the rock mass behavior changes from elastic–plastic to elastic–brittle, the drop modulus changes from 0 to infinite. The reason is that by increasing the quality of rock mass and reducing the minimum principal stresses, the ratio of post-failure residual strain energy to pre-failure stored strain energy and rock load height (H p) reduce. So, regression analysis is used to investigate the relation between the rock load height and the ratio of post-failure residual strain energy to pre-failure stored strain energy, and finally, a formulation is presented to determine rock load height based on power function. 相似文献
13.
In this paper results of triaxial and true triaxial testing conducted on physical models of a rock mass are used to describe its post failure behaviour. The specimens comprised of three continuous joint sets and were prepared from blocks of sand lime model material. The testing was performed using a True Triaxial System (TTS) developed by the authors. The results show strain hardening, strain softening and plastic behaviour in the simulated rock mass specimens depending upon joint geometry and stress state. Expressions are suggested to estimate post peak modulus in triaxial and true triaxial stress conditions. Finally, a zonation table is proposed to assess the strain hardening, softening and plasticity behaviour of a rock mass material with the help of joint geometry and confining stress conditions at site. 相似文献
14.
Roof falls in coal mines may occur within a few months to a few years after excavation. In this paper, we proposed the use of relaxation tests as a substitute for time-dependent tests. The relation between creep behavior and relaxation behavior was numerically investigated and demonstrates that the material assigned with creep model can show relaxation behavior. Then the relaxation model was developed by modifying the Burgers creep model. Numerical simulation of a relaxation test on a simulated rock model in 3DEC yielded results that were similar to theoretical prediction. A relaxation test was performed on two groups of specimens under varying load conditions. Results from the laboratory tests validated the approach of using relaxation test to determine time-dependent properties. Finally, time-dependent properties were investigated by performing relaxation tests at different stages of a complete stress–strain curve. The relaxation test during strain-softening was unsuccessful; however, the relaxation behavior at residual stage in post-failure region was more significant than that in pre-failure region and the sudden drop in stress indicated there was strength deterioration due to the accumulation of viscous strain. 相似文献
15.
饱和粉砂不稳定性的试验研究 总被引：3，自引：0，他引：3
通过对净砂和级配良好粉砂(含10 %粉土)进行一系列三轴固结不排水试验（CU）,研究了粉土、孔隙比和围压对饱和粉砂不稳定性的影响。试验结果表明,净砂与粉砂在不排水剪切条件下均会出现应变软化现象（即不稳定性）。同一围压下脆性指数(IB)随孔隙比增加,但不稳定线的应力比随孔隙比增加而减小。引用等效粒间孔隙比(ege)后,净砂和粉砂在ege-ln p?平面上拥有基本相同的临界状态线。在临界状态理论及等效粒间孔隙比的基础上,提出在同一修正状态参数(?ge)下净砂和级配良好粉砂有相似的不稳定性。 相似文献
16.
The normal and shear strains obtained in torsion shear tests may be interpreted in two different ways to gain insight into (1) the type of plastic potential to be employed in hardening plasticity stress–strain models, and (2) the coincidence in physical space of the plastic strain increment direction with the stress direction during principal stress rotation. Thirty-four drained torsion shear tests were performed on hollow cylinder specimens of Santa Monica Beach sand deposited by dry pluviation. Twenty-six tests were performed on tall specimens with height of 40 cm, and eight tests were performed on short specimens with height of 25 cm to investigate the effect of the specimen height on the soil behavior in hollow cylinder specimens. Each test was conducted with the same, constant inside and outside confining pressure, σr, thus tying the value of b = (σ2–σ3)/(σ1– σ3) to the inclination, β, of the major principal stress. The directions of strain increment vectors at failure are compared with the directions corresponding to associated and non-associated flow. The relation between the directions of major principal strain increment and major principal stress during rotation of principal stress axes in physical space are investigated. 相似文献
17.
Rotational shear is the type of loading path where samples are subjected to cyclic rotation of principal stress directions while the magnitudes of principal stresses are maintained constant. This paper presents results from an experimental investigation on the drained deformation behaviour of saturated sand in rotational shear conducted in a hollow cylinder apparatus. Two types of granular materials, Leighton Buzzard sand and glass beads are tested. A range of influential factors are investigated including the material density, the deviatoric stress level, and the intermediate principal stress. It is observed that the volumetric strain during rotational shear is mainly contractive and most of strains are generated during the first 20 cycles. The mechanical behaviour of sand under rotational shear is generally non-coaxial, i.e., there is no coincidence between the principal axes of stress and incremental strain, and the variation of the non-coaxiality shows a periodic trend during the tests. The stress ratio has a significant effect on soil response in rotational shear. The larger the stress ratio, the more contractive behaviour and the lower degree of non-coaxiality are induced. The test also demonstrates that the effect of the intermediate principal stress, material density and particle shape on the results is pronounced. 相似文献
18.
Fatin N. Altuhafi Béatrice A. Baudet Peter Sammonds 《Quaternary Science Reviews》2009,28(7-8):693-707
Soft sediments can deform under both changes in stress and changes in strain rate, as well as during sustained loading (e.g. creep). In glacial conditions, soft subglacial sediments can contribute to glacier movements, and when the ice/sediment system is coupled, the rate-sensitivity of the sub-layer can affect the velocity of the glacier. These issues have been the object of studies by several geologists. In parallel, the effects of time and strain rate on the behaviour of soils have been studied for many years by geotechnical engineers, to estimate the long-term performance of ground structures. This paper applies the knowledge acquired in soil mechanics to a geological problem: results on two glacial sediments of different origins, obtained from advanced geotechnical laboratory tests, are presented and analysed in the light of recent advances in soil mechanics. Independently of time effects, the test data show that the pre-failure behaviour is not elastic but that the sediments develop plastic strains before reaching their peak strength, with the stiffness gradually degrading. Results from tests performed with variable strain rates suggest that the time-dependent (viscous) behaviour of the sediments may be governed by their mineralogy, in particular the presence of plastic fines. The viscous behaviour observed in the plastic tills seems to affect the pre-failure behaviour only, for example the yield surface, stiffness, strength, but the criteria of failure, e.g. critical or residual angle of failure are found to be constant and independent of strain rate. The test data also suggest that the viscous behaviour may be related to stress level, being more prevalent at low stresses. These results, obtained under laboratory-controlled conditions, over a large range of strains, pre- and post-peak strength, are a necessary step towards developing constitutive models for subglacial sediments rigorously. It is only after this has been achieved that such models should be implemented in finite element code to analyse ice/sediment systems, with the aim to understand glacier movements better. 相似文献
19.
The effect of drained pre-shearing on the undrained behaviour of loose sand with a small amount of fines 总被引：1，自引：1，他引：0
D. C. Bobei D. Wanatowski M. M. Rahman S. R. Lo C. T. Gnanendran 《Acta Geotechnica》2013,8(3):311-322
Stress history is recognised to play a major role in determining stress–strain behaviour of soil in undrained shearing. Most experimental studies on the effects of stress history on undrained behaviour are mainly limited to clean sand. In this paper, an experimental study carried out to investigate the effect of stress history on the undrained behaviour of loose sand with a small amount of fines is presented. Four series of triaxial compression tests, with different types of drained stress histories to near-failure prior to commencement of undrained shearing, were conducted. The experimental results indicate that drained pre-shearing to near-failure affects significantly the undrained behaviour of loose sand. In general, the drained pre-shearing improves the subsequent undrained behaviour of loose sand to the extent that liquefaction may not occur. It is shown that the effect of drained pre-shearing cannot be explained by the reduction in void ratio induced by drained pre-shearing. However, for specimens subjected to drained pre-shearing, $ p_{{{\text{d}}0}}^{\prime } $ / $ p_{{{\text{u}}0}}^{\prime } $ can be used as a parameter for analysing the effects of preloading history. It is also shown that for different preloading histories that brought the same change in void ratio or state parameter, drained pre-shearing to near-failure is the most effective, whereas pre-compression alone is the least effective in improving subsequent undrained behaviour of loose sand. 相似文献
20.
This paper presents an advanced constitutive model for unsaturated soils, using Bishop’s effective stress (σ′) and the effective degree of saturation (Se) as two fundamental constitutive variables in the proposed constitutive model. A sub-loading surface and a unified hardening parameter (H) are introduced into the σ′–Se modelling framework to interpret the effects of initial density on coupled hydro-mechanical behaviour of compacted soils. Compared with existing models in the literature, the main advantage of the proposed model that it is capable of modelling hydro-mechanical behaviour of unsaturated soils compacted to different initial densities, such as the dependence of loading–collapse volume on initial void ratio and density effect on the shearing-induced saturation change. The proposed model requires 13 material parameters, all of which can be calibrated through conventional laboratory tests. Numerical studies are conducted to assess the performance of the model for a hypothetical soil under two typical hydro-mechanical loading scenarios. The proposed advanced unsaturated soil model is then validated against a number of experimental results for both isotropic and triaxial conditions reported in the literature. 相似文献