含液各向异性多孔介质应变局部化分析

工程中的含液多孔介质如饱和或非饱和岩土材料往往具有各向异性特性。采用Rudnicki建立的针对岩土材料的各向异性本构模型,对轴对称压缩试验中的含液多孔介质骨架的各向异性力学行为进行了分析;基于不连续分叉理论,导出了静态非渗流条件下处于轴对称应力状态的含液多孔介质应变局部化发生的临界模量、剪切带方向以及不连续速度矢量的显式表达式,在此基础上计算并讨论了材料参数变化和孔隙液体存在对各向异性多孔介质应变局部化的影响。     

盐溶液饱和黏土的力学行为模拟

由于黏性土表面带有丰富的负电荷,孔隙水溶液化学状态的变化对黏性土的物理力学特性存在明显影响。随着化学-力学耦合的相关岩土工程问题日益突出,进行有效的化学-力学耦合行为的数值分析评价显得尤为重要。因此,建立一个简单有效的考虑化学-力学耦合的本构模型是非常关键的。基于传统的修正剑桥模型,提出了一个简单的化学-力学耦合模型。该模型采用渗透吸力π描述孔隙水的化学状态,建立了前期屈服应力,临界状态线斜率M和弹性刚度与渗透吸力π之间的关系式,从而实现了模型对盐溶液饱和黏性土的变形和强度特性的有效模拟。通过与试验数据的对比和分析,说明该模型能有效地模拟孔隙盐溶液饱和黏性土的等向压缩行为、 状态下压缩行为以及 状态下化学-力学循环加载行为。此外,通过对黏性土三轴压缩试验的模拟,说明该模型能反映黏性土三轴应力状态下的基本力学特征。     

Dielectric relaxation in oil-bearing clayey rocks

The dielectric properties of the bentonite–oil–salt solution mixtures with different water and oil saturation were experimentally studied in the frequency range of 10 kHz to 4 GHz at 25–60 °C. It has been established that besides the region of the Debye water relaxation, there are two more relaxation regions resulting from the interfacial interaction of the mixture components in this frequency range. To describe the dielectric permittivity and equivalent conductivity of the mixture, a spectroscopic model taking into account the multifrequency relaxation is proposed. The dependence of the model parameters on the water saturation and temperatures of the samples has been determined. The experimental data are compared with the modeling results, and the error of prediction for the dielectric permittivity and conductivity of mixture is estimated using the proposed model.     

非饱和土化学-塑性耦合本构行为的数值模拟

基于Hueckel提出的饱和黏土化学-塑性本构模型和Gallipoli提出的非饱和土弹塑性本构模型,提出了一个新的非饱和多孔介质的化学-塑性本构模型,并建立了该模型的隐式积分算法,算法中考虑了化学软化和非饱和吸力的影响。在已有的非饱和多孔介质有限元分析程序平台上进行了程序研发,对孔隙水中化学污染物浓度变化对非饱和土力学行为的影响进行数值模拟,使所研制的程序能够进行岩土工程问题的化学-力学耦合非线性分析。     

Modeling crack propagation path of anisotropic rocks using boundary element method

In a cracked material, the stress intensity factors (SIFs) at the crack tips, which govern the crack propagation and are associated with the strength of the material, are strongly affected by the crack inclination angle and the orientation with respect to the principal direction of anisotropy. In this paper, a formulation of the boundary element method (BEM), based on the relative displacements of the crack tip, is used to determine the mixed‐mode SIFs of isotropic and anisotropic rocks. Numerical examples of the application of the formulation for different crack inclination angles, crack lengths, and degree of material anisotropy are presented. Furthermore, the BEM formulation combined with the maximum circumferential stress criterion is adopted to predict the crack initiation angles and simulate the crack propagation paths. The propagation path in cracked straight through Brazilian disc specimen is numerically predicted and the results of numerical and experimental data compared with the actual laboratory observations. Good agreement is found between the two approaches. The proposed BEM formulation is therefore suitable to simulate the process of crack propagation. Copyright © 2008 John Wiley & Sons, Ltd.     

Modeling the 3D crack network and anisotropic permeability of saturated cracked soil

Cracks on a natural soil surface provide preferential pathways for water infiltration and contaminant solute transport. Before the mechanical property and permeability of cracked soil can be studied, a crack network model must first be established. Based on statistical analysis of crack geometry from field observations, a new method of representing a 3D crack network was developed. A horizontal plane of a crack network was derived using the Voronoi diagram. Each vertical crack was idealized as an inverted triangular prism. The 3D permeability tensor was determined by modeling the water flow through the crack network. A computer program was developed to generate a 3D crack network automatically and compute the permeability tensor of cracked soil at different depths. The model was verified by comparing the measured permeability and computed permeability of cracked soil. The results showed that the computed permeability was consistent with the measured permeability.     

盐溶液饱和黏土的等向压缩特性

利用不同浓度NaCl溶液饱和黏土,进行等向压缩试验并分析渗透吸力对等向压缩特性的影响规律。试验结果表明：渗透吸力对于黏土的等向压缩行为存在明显影响,主要体现在对初始弹性压缩线斜率、初始屈服应力的影响上。随着渗透吸力的增大,初始弹性压缩线斜率增大、初始屈服应力逐渐减小;而渗透吸力对弹塑段压缩线斜率和卸荷回弹线斜率影响不大。基于等向压缩试验结果,建立了盐溶液饱和黏土的本构模型,经过验证该模型能有效地模拟盐溶液饱和黏土的等向压缩特性。此外,该模型还可以模拟恒定等向压力下渗透吸力改变引起的试样变形。该等向压缩试验结果及所建立的模型为进一步分析及模拟化学-力学耦合行为提供了数据支持和理论基础。     

Extensional structures in anisotropic rocks

A distinct class of structures can form as a result of extension along a plane of anisotropy (foliation). The effect of the foliation is to decrease the ductility of the material in this orientation so that brittle fractures or shear-bands develop. Foliation boudinage is caused by brittle failure; extensional fractures cause symmetric boudinage, and shear fractures cause asymmetric boudinage.Extensional crenulation cleavage is defined by sets of small-scale ductile shear-bands along the limbs of very open microfolds in the foliation. The sense of movement on the shear-bands is such as to cause a component of extension along the older foliation. Conjugate cleavage sets indicate coaxial shortening normal to the foliation; the shortening axis bisects the obtuse angle between the sets. A single set indicates oblique or non-coaxial deformation.Extensional crenulation cleavage is microstructurally and genetically distinct from other types of cleavage. It does not occur as an axial plane structure in folds, and has no fixed relationship to the finite strain axes. It is common in mylonite zones, and may be favoured by crystal-plastic and cataclastic deformational mechanisms. These cause grain-size reduction, and hence softening, which favour the development of shear-bands.     

Modeling cohesive fracture propagation in partially saturated porous media with the assumed enhanced strain method

Acta Geotechnica - The assumed enhanced strain (AES) method is developed to simulate cohesive fracture propagation in the partially saturated porous media which includes the solid skeleton and the...     

Indirect tensile testing of anisotropic rocks

SummaryIndirect Tensile Testing of Anisotropic Rocks The tensile strength of rock materials is a parameter relevant to many rock mechanics applications. Rocks are often anisotropic in nature. Therefore, it is of interest to investigate suitable experimental methods for tensile testing to be used with these rocks. An attempt is made in this paper to see if the indirect methods adopted for testing isotropic rocks can be applied. Two rock types with transversely isotropic behavior are tested by loading discs and rings along their diameter. The finite element method is used in order to correlate the tensile stress, for which tensile failure is assumed to occur in each test, with the orientation of the axes of anisotropy. It is shown that the experimental results can be appropriately explained by this method and a parameter be defined which allows one to describe the law of variation of tensile strength with the anisotropy of deformability.

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ZusammenfassungIndirekte Zugfestigkeitsprüfung anisotroper Gesteine Die Zugfestigkeit eines Gesteins stellt bei felsmechanischen Betrachtungen einen wichtigen Parameter dar. Die bisherigen Wege, diesen Parameter zu erfassen, setzen ein isotropes, homogenes Medium voraus. Da der natürliche Fels stets anisotrop und inhomogen ist, prüfen die Autoren die Möglichkeit, indirekte Zugversuche, wie sie bisher angewandt wurden, auf anisotrope Medien zu übertragen.Die Autoren untersuchen das Verhalten von Granitgneis und Serpentinschiefer mit Transversal-Anisotropie. Die Untersuchung erfolgt im Druckversuch an Scheiben und Ringen längs des vertikalen Durchmessers, wie es für homogenes und isotropes Material im Sinne der klassischen Elastizitätstheorie üblich ist.Durch Anwendung der Finite-Element-Methode gelingt es, die Beziehungen zwischen Bruch-Zugspannung und Abweichung der Anisotropie-Achse zu ermitteln.Auf diesem Wege werden die experimentellen Ergebnisse erklärbar. Darüber hinaus ist es möglich, einen Parameter zu bestimmen, der es erlaubt, einen gesetzmäßigen Zusammenhang zwischen der Zugfestigkeit und dem Grad der Anisotropie des Gesteins zu ermitteln.

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RésuméEssais indirects de traction sur des roches anisotropes La connaissance de la contrainte de traction à la rupture est un paramètre important dans le domaine de la Mécanique des Roches. Etant donné que la plupart des roches sont anisotropes, il est intéressant de développer des essais capables de donner la contrainte de rupture à la traction de ces roches. Dans ce travail on a cherché à vérifier si les essais indirects de traction utilisés depuis longtemps pour des roches isotropes sont valables aussi pour des roches anisotropes. Dans ce but on a examiné le comportement de deux types de roche à isotropie transversale en exécutant des essais de compression le long d'un diamètre sur des disques et des anneaux. La méthode des éléments finis a été appliquée dans le but de disposer d'une corrélation entre la contrainte de traction pour laquelle la rupture a lieu, avec l'orientation de l'axe d'anisotropie. On a ainsi déduit que les résultats expérimentaux peuvent être interprétés par cette méthode et qu'il est possible aussi de définir un paramètre qui permet d'en tirer une loi de variation de la résistance à la traction en fonction de l'anisotropie de la déformabilité.

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With 16 Figures     

沉积岩的一种各向异性模型

给出了沉积岩的一种各向异性模型。用一个各向异性参数描述这类材料的固有各向异性，各向异性参数和单轴抗压强度是一个分布函数，其分布用一个微结构张量和加载方向表示。建立了一个描述各向异性沉积岩变形过程的全塑性模型。用该模型对这一些三轴试验进行了模拟，结果表明该模型能有效地描述沉积岩的固有各向异性。     

Residual-state creep behavior of typical clayey soils

There are few places in the world to monitor aseismic creep. One of them is the Ismetpasa segment of the North Anatolian Fault. The observations in the Ismetpasa showed that the creep rate progressively decreased along the 40 years before the 1999 Kocaeli-Golcuk (Mw = 7.6) earthquake and then started increasing. This phenomenon might be a systematic of the creeping segments. If it is the case, this behavior can be utilized for early warning before the expected major earthquake in the Marmara Sea. In this study, the creep rate of the segment has been studied by GPS and InSAR technologies. The results showed that the rate has decreased to 1.3 cm a year. This result might be an indication of stress starting increase. If the segment retains the decreasing trend and it is ceased by a major earthquake, it would be a proof of the relationship between the creep process and the earthquakes. Then, the creep process might be utilized for early warning.     

A cap model for partially saturated soils

The present paper deals with the extension of a cap model in order to describe the material behavior of partially saturated soils, in particular, of partially saturated sands and silts. The soil model is formulated in terms of two stress state variables, using net stress and matric suction and, alternatively, the average soil skeleton stress and suction, the latter playing the role of a stress‐like plastic internal variable. The yield surface, consisting of a shear failure surface and a hardening cap surface, the plastic potentials for the non‐associated flow rule and the hardening law for the cap are extended by taking into account the effects of matric suction on the material behavior. Furthermore, the third invariant of the deviatoric stress tensor is taken into account in the formulation of the yield surfaces. The developed model is validated by the numerical simulation of an extensive series of suction controlled tests for a silty sand, which were conducted at different constant values of suction. Although both versions of the soil model yield identical results for stress paths at constant values of matric suction, differences are encountered for stress paths involving wetting. Copyright © 2007 John Wiley & Sons, Ltd.     

On the constitutive modeling of partially saturated interfaces

Generalization of soil–structure interface models from dry/saturated states to consider partially saturated states is studied in this paper. For this purpose, basic constitutive equations of a conventional elasto-plastic interface model are firstly presented. Then, consideration is given to the effect of partial saturation on definition of effective stress, location of the critical state line as well as the impact of interface state on plastic hardening modulus and dilatancy. For each concern, proper independent approaches together with associated constitutive equations are discussed to be included in the basic model as complementary ingredients. Among many different possibilities to combine complementary constitutive equations for effective stress, relocation of the critical state line with degree of saturation, and impact of the interface state on plastic hardening modulus and dilatancy, six essential cases are selected. Evaluations show that all six cases can realistically consider the impact of partial degree of saturation on the peak and residual shear strengths as well as the volume change behavior of unsaturated interfaces.     

Stress induced time dependent behavior of clayey soils

It is shown that time compression curve obtained from one-dimensional consolidation curve in the laboratory may include six phases. These are initial compression, first primary compression, transition from first primary compression to second primary compression, second primary compression, and transition from second primary compression to creep and lastly creep. This paper attempts to identify the quantitative beginnings and characteristics of these phases. A mathematical characteristic of all the soils that follow primary consolidation as per Terzaghi’s one dimensional consolidation theory is derived. It is known as the constant of primary consolidation. It is used to study the beginning of secondary consolidation and its effects on primary consolidation. Another characteristic of soils for creep and total absence of primary compression is derived. Methods are suggested for the determination of coefficients of Primary and Secondary consolidations and the compression index.     

Poroelastic behaviour of saturated brittle rock with anisotropic damage

A new anisotropic poroelastic damage model is proposed for saturated brittle porous materials. The model is formulated in the framework of the continuum damage mechanics. A second‐rank symmetric tensor is used to characterize material damage due to oriented microcracks. The classic Biot poroelastic theory is then extended to include poroelastic damage coupling. Both the deterioration of elastic properties and poroelastic coefficients is taken into account. A suitable procedure for determination of model parameters from standard laboratory tests is presented. The validity of the model is tested through comparison between numerical predictions and experimental data in various loading conditions. The overall performance of the model is evaluated. The choice of relevant effective stress for the microcrack propagation criterion in saturated cohesive geomaterials is discussed. Copyright © 2000 John Wiley & Sons, Ltd.     

Compressional behavior of clayey sand and transition fines content

Clayey sand can be considered as a composite matrix of coarse and fine grains. The interaction between coarser and finer grain matrices affects the overall stress–strain behavior of these soils. Intergranular void ratio, e_s (which is the void ratio of the coarser grain matrix) can be utilized as an alternative parameter to express the compressive response of such soils. Oedometer tests conducted on reconstituted kaolinite–sand mixtures indicate that initial conditions, percentage of fines, and stress conditions influence the compression characteristics evidently. Tests showed that, up to a fraction of fines, which is named as transition fines content (FC_t), compression behavior of the mixtures is mainly controlled by the sand grains. When concentration of fines exceeds FC_t, kaolinite controls the compression. It was found that FC_t varies between 19% and 34% depending on the above mentioned factors. This range of fines content is also consistent with various values reported in literature regarding the strength alteration. Performed direct shear tests revealed that there is also a close relationship between transition fines content and shear strength, which is harmonic with the oedometer test results.     

循环荷载下饱和重塑黏质粉土的动力特性研究

选取宁波饱和重塑黏质粉土,开展了黏质粉土的动三轴试验,研究了围压、动应力、排水条件、温度及频率等因素对土动力特性的影响,提出了采用相对动应力来分析不同围压、不同动应力下土的累积塑性应变变化规律,并建立了孔压—累积塑性应变关系的经验公式,结果表明:累积塑性应变随着相对动应力的增大而增大;温度越高,累积塑性应变值越小,且相同温度增量（△T=15℃）条件下的累积塑性应变增量也随之减小;建立的孔压-累积塑性应变经验公式可用于长期振动荷载作用后黏质粉土的孔压计算。     

Alkali earth elements in Vendian-Cambrian clayey rocks, the East European Platform

Low Sr and Ca contents in fine-grained terrigenous rocks of the Vendian sedimentary cover in the East European Platform may be related to the following reasons: (1) the absence of authigenic carbonates in Vendian mudstones owing to desalination of epiplatformal sedimentary basins; (2) significant contribution of the chemically weathered rocks in the formation of the Vendian cover of the East European Platform.