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1.
Geomaterials such as soils and rocks can exhibit inherent anisotropy due to the preferred orientation of mineral grains and/or cracks. They can also be partially saturated with multiple types of fluids occupying the pore space. The anisotropic and unsaturated behaviors of geomaterials can be highly interdependent. Experimental studies have shown that the elastic parameters of rocks evolve with saturation. The effect of saturation has also been shown to differ between directions in transversely isotropic clay rock. This gives rise to saturation-dependent stiffness anisotropy. Similarly, permeability anisotropy can also be saturation-dependent. In this study, constitutive equations accommodating saturation-dependent stiffness and hydraulic anisotropy are presented. A linear function is used to describe the relationship between the elastic parameters and saturation, while the relative permeability–saturation relationship is characterized with a log-linear function. These equations are implemented into a hydromechanical framework to investigate the effects of saturation-dependent properties on the shrinkage behavior of clay rocks. Numerical simulations are presented to demonstrate the role of saturation-dependent stiffness and hydraulic anisotropy in shrinkage behavior. The results highlight that strain anisotropy and time evolution of pore pressures are substantially influenced by saturation-dependent stiffness and hydraulic anisotropy.
相似文献2.
SummaryThe Influence of Rock Anisotropy on Stress Measurements by Overcoring Techniques A medium is anisotropic if its properties vary with direction. This is the general characteristic of many rocks, for example, schists, slates, gneisses, phyllites and other metamorphic rocks. Bedded and regularly jointed rocks also display anisotropic behavior.This paper is concerned with the influence of rock anisotropy on in-situ stress measurements. It is limited, to stress measurements by overcoring techniques for which strains and displacements are recorded either on the walls of a pilot hole at the end of one or several boreholes or within instrumented solid or hollow inclusions perfectly bonded to the surface of the pilot hole. The rock is described as homogeneous, continuous, anisotropic and linearly elastic.The following questions are answered with special emphasis on rocks that can be classed as transversely isotropic or orthotropic: the number of independent measurements obtainable in a single borehole; the number of boreholes required to determine the in-situ stress field; the influence of rock anisotropy on these numbers; the influence of the anisotropy type and the error involved by neglecting rock anisotropy.With 5 Figures 相似文献
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为建立更为完善的岩石统计损伤本构模型,针对现有模型难以反映某些岩石在三轴试验条件下弹性模量随围压变化而改变的特性,从不同类型空隙对岩石变形性质的影响入手,深入分析了岩石弹性模量变化的机理,并在此基础上,依据弹性参数与岩石中未闭合裂隙数的关系建立了岩石弹性模量变化的分析方法。之后,引入统计损伤理论,考虑损伤阈值的影响和残余强度变形特征,建立了可模拟岩石变形全过程的统计损伤本构模型,并给出了基于三轴压缩试验曲线的模型参数确定方法。本文模型可反映岩石弹性模量随围压变化而改变的特性,且具备现有模型的优点,对岩石变形全过程模拟效果良好。最后,通过试验曲线与本文及同类模型理论曲线的对比分析,表明了本文模型的合理性与优越性。 相似文献
4.
The velocity of elastic waves has been measured along the principal fabric directions in 110 Alpine rocks, and these data are analyzed in conjunction with previously measured data on density, porosity, specific heat, and thermal diffusivity for the same rocks. Particular attention is given to the anisotropy in the thermal and elastic properties which are up to three times larger in the direction of lineation than in the direction perpendicular to the foliation. The correlations among the various scalar properties and the average thermal and elastic properties are in general weak and are overshadowed by variations due to mineralogy. However, relative thermal and elastic properties show a significant positive correlation, and for gneisses, schists, ultramafic rocks and carbonate rocks it is meaningful to predict thermal anisotropy on the basis of elastic anisotropy. 相似文献
5.
Planes of weakness like schistosity and foliation affect the strength and deformational behaviors of rocks. In this paper, an attempt has been made to study the elastic and strength behavior of slate rocks obtained from foundation of Sardasht dam site in Iran. Wet and dry specimens with different orientation of foliation were evaluated under uniaxial, triaxial, and Brazilian tests. According to the results obtained, slate mechanically pronounced U-shaped anisotropy in uniaxial and triaxial compression tests. In addition, the degree of anisotropy for the slates tested in current study was relatively high, showing the effect of foliation plane on strength and elastic parameters. It was concluded that stiffness of the samples decrease as the angle of anisotropy reaches 30–40°. This change was more pronounced for wet comparing to dry samples. However, the tensile strength obtained during Brazilian tests indicated that there is no apparent relationship between angle of anisotropy and tensile strength. However, increasing the water saturation decreased the tensile strength of the samples. The calculated elastic moduli referring to different anisotropy angles could be valuable for the design of various engineering structures in planar textured rock masses. 相似文献
6.
Clayey rocks are frequently chosen as a geological barrier material for underground repositories. The inherent anisotropic mechanical behavior and the evolution of mechanical behavior with water content are two crucial material properties for the safety analysis of these structures. The present paper focuses on numerical modeling of the inherent anisotropy and the effect of water content, as well as the interactions of these properties in partially saturated clayey rocks with preferably oriented bedding planes. A discrete thermodynamic approach is adopted for describing the inherent anisotropic mechanical behavior, and the anisotropy of the elastic parameters, plastic evolution and damage evolution are considered. Capillary pressure is introduced to describe the effect of the water content with the help of the effective stress concept, and a procedure for the identification of the model parameters is presented. Finally, the proposed model is applied to a study of triaxial compression tests of argillite with different orientations of the bedding planes and variable water content. In summary, the main features of the studied material are well reproduced by the model. 相似文献
7.
Many clay rocks have distinct bedding planes. Experimental studies have shown that their mechanical properties evolve with the degree of saturation (DOS), often with higher stiffness and strength after drying. For transversely isotropic rocks, the effects of saturation can differ between the bed-normal (BN) and bed-parallel (BP) directions, which gives rise to saturation-dependent stiffness and strength anisotropy. Accurate prediction of the mechanical behavior of clay rocks under partially saturated conditions requires numerical models that can capture the evolving elastic and plastic anisotropy with DOS. In this study, we present an anisotropy framework for coupled solid deformation-fluid flow in unsaturated elastoplastic media. We incorporate saturation-dependent strength anisotropy into an anisotropic modified Cam-Clay (MCC) model and consider the evolving anisotropy in both the elastic and plastic responses. The model was calibrated using experimental data from triaxial tests to demonstrate its capability in capturing strength anisotropy at various levels of saturation. Through numerical simulations, we demonstrate the role of evolving stiffness and strength anisotropy in the mechanical behavior of clay rocks. Plane strain simulations of triaxial compression tests were also conducted to demonstrate the impacts of material anisotropy and DOS on the mechanical and fluid flow responses. 相似文献
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榴辉岩的弹性波速评述 总被引：2，自引：0，他引：2
文中评述了榴辉岩的密度和高温高压下的纵波速度、速度各向异性、泊松比以及榴辉岩声软化现象的成因 ,着重介绍了榴辉岩的密度和波速对探讨岩石圈物质组成、莫霍界面性质、超高压岩石对实现壳幔物质交换的重要意义。榴辉岩的密度为 3 2～ 3 6 5g·cm-3 ,其中超高压榴辉岩具有更高的密度 (3 4～ 3 6 5g·cm-3 )。榴辉岩的纵波速度 (vp)在 1GPa时为 7 3～8 9km·s-1,其裂隙闭合压力可能高于 1GPa。榴辉岩的压力系数为 0 3～ 0 4km·s-1·GPa-1,温度系数为 - 3 4× 10 -4 km·s-1·℃ -1。它具有最弱的vP 各向异性 (<3% )。超高压榴辉岩的泊松比为 0 2 54～ 0 2 75。大别山榴辉岩的密度和波速研究表明 ,现今的大别山深部地壳可能依然存在榴辉岩 ,但数量应很少 ;大别山上地幔具有同超高压榴辉岩类似的弹性特征 ;拆沉作用是解释超高压榴辉岩折返机制的重要模式之一 ;榴辉岩的形成过程包含了壳幔物质循环作用 ,一部分榴辉岩已拆沉进入深部地幔 ,另一部分则快速折返至地壳内或通过其他构造作用进一步抬升、暴露地表。 相似文献
10.
Lower crustal and upper mantle rocks exposed at the earth's surface present direct possibility to measure their physical properties that must be, in other cases, interpreted using indirect methods. The results of these direct measurements can be then used for the corrections of models based on the indirect data. Elastic properties are among the most important parameters studied in geophysics and employed in many fields of earth sciences. In laboratory, dynamic elastic properties are commonly tested in three mutually perpendicular directions. The spatial distribution of P- and S-wave velocities are then computed using textural data, modal composition, density and elastic constants. During such computation, it is virtually impossible to involve all microfabric parameters like different types of microcracking, micropores, mineral alteration or quality of grain boundaries.
In this study, complete 3D ultrasonic transmission of spherical samples in 132 independent directions at several levels of confining pressure up to 400 MPa has been employed for study of selected mafic and ultrabasic rocks sampled in and nearby Balmuccia ultrabasic massif (Ivrea zone, Southern Alps, NW Italy). This method revealed large directional variance of maximum P-wave velocity and different symmetries (orthorhombic vs. transversal isotropic) of elastic waves 3D distribution that has not been recorded on these rocks before. Moreover, one dunite sample exhibits P-wave velocity approaching to that of olivine single crystal being interpreted as influence of CPO. 相似文献
11.
Determining elastic constants of transversely isotropic rocks using Brazilian test and iterative procedure 总被引：1，自引：0，他引：1
The elastic constants of rocks are the basic parameters for rock mechanics, and play a very important role in engineering design. There are many laboratory methods to determine the elastic constants of transversely isotropic rocks, and the Brazilian test is a popular method. This paper presented a method combination of the Brazilian test, back calculation, and iterative procedure to evaluate the five independent elastic constants of transversely isotropic rocks in laboratory. The strain data at the centre of discs were obtained using Brazilian test. The stresses at the centre of discs were computed using numerical programs. By using back calculation, the temporary elastic constants were computed after the stresses and stains were substituted into elastic mechanics equations. After iterative procedure, the convergent values of the elastic constants can be obtained. One numerical example and three experimental cases were proposed to show the applicability of this method. The convergent values of the five independent elastic constants can be obtained in no more than 10 iterative cycles. The results coming from numerical analysis method exhibited satisfactory outcome in accordance with those of generalized reduced gradient method. The merits of this method include convenient specimen preparation of the Brazilian test, simple iterative procedure, and readily available commercially numerical programs, so that this method can be easily popularized in research and engineering analysis. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
12.
An anisotropic geomechanical model for jointed rock mass is presented. Simultaneously with deriving the orthotropic anisotropy elastic parameters along the positive axis, the equivalent compliance matrix for the deflection axis orthotropic anisotropy was derived through a three-dimensional coordinate transformation. In addition, Singh’s analysis of the stress concentration effects of intermittent joints was adopted, based on two groups of intermittent joints and a set of cross-cutting joints in the jointed rock mass. The stress concentration effects caused by intermittent joints and the coupling effect of cross-cutting joints along the deflection-axis are also considered. The proposed anisotropic mechanics parameters method is applied to determine the deformation parameters of jointed granite at the Taishan Nuclear Power Station. Combined with the deterministic mechanical parameters of rock blocks and joints, the deformation parameters and their variability in jointed rock masses are estimated quantitatively. The computed results show that jointed granite at the Taishan Nuclear Power Station exhibits typical anisotropic mechanical characteristics; the elastic moduli in the two horizontal directions were similar, but the elastic modulus in the vertical direction was much greater. Jointed rock elastic moduli in the two horizontal and vertical directions were respectively about 24% and 37% of the core of rock, showing weakly orthotropic anisotropy; the ratio of elastic moduli in the vertical and horizontal directions was 1.53, clearly indicating the transversely isotropic rock mass mechanical characteristics. The method can be popularized to solve other rock mechanics problems in nuclear power engineering. 相似文献
13.
磁化率各向异性地学应用综述 总被引：10，自引：1，他引：9
本文综述了磁化率各向异性在地学中应用的现状、存在问题及发展趋势。重点介绍了磁化率各向异性在岩石变形分析中应用的最新研究成果、不足之处及改进方法,同时文章也介绍了磁化率各向异性在岩浆岩、沉积岩（物）及沉积环境方面的应用情况及最新进展 。 相似文献
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岩石的结构、构造往往具有不均一性，因而表现出物理力学性质的各向异性。超声波技术就是通过研究岩石的各向异性来了解岩石的构造变形特征和微观构造。本文论述了这一方法的基本原理，介绍了检测方法，探讨了如何应用此法来确定主应变轴的空间方位和划分不同构造变形期次、确定岩石中微孔隙的排列方位和矿物定向组构、恢复古构造应力汤、区分原生和次生各向异性等。 相似文献
16.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(2):133-139
Shear deformation in calcite-rich rocks can produce strong lattice preferred orientations (LPO), which result in a high anisotropy of bulk seismic properties because of the high elastic anisotropy of calcite (32% Vp anisotropy). Deformed rocks often show also strong shape preferred orientations (SPO). Theories for averaging the elastic properties have not yet satisfactorily predicted the contribution to the seismic anisotropy caused by the SPO alone.A calcite mylonite from Carrara (Italy) was investigated, which is characterised by a strong SPO and a weak LPO. It was composed of about 80% calcite, then white mica, quartz and hematite. Flattening of mica and of calcite grains defined the mylonitic foliation, and elongation of calcite grains defined the lineation. On average calcite grains have aspect ratios of about 2.5:1.6:1, and grain sizes of about 10 μm. At 400 MPa confining pressure, the measured Vp (km/s) parallel to the lineation (X direction) was highest (6.63), lower in the intermediate Y direction (6.47); the Vp normal to the foliation (Z direction) was lowest (6.30). This yielded a Vp anisotropy of 5%. The LPO, determined by automated electron backscatter diffraction (EBSD), was very weak (texture index 1.1), with intensities between 0.6 and 1.6 m.r.d. in the c-axis pole figure. Extrapolation of the texture index to an infinite number of orientation measurements indicated that the observed variations were mostly random noise in the orientation distributions and that the bulk rock texture was random. The Vp anisotropy of the Voigt, Reuss and Hill averages calculated from this calcite LPO is predicted to be close to zero. Adding 5% of muscovite with (001) perfectly aligned parallel to the foliation, we calculated a total anisotropy of 2.8%. The anisotropy calculated for the special directions X, Y and Z remained at 2.6% only.It was concluded that the measured seismic anisotropy cannot be explained by the LPO of calcite and by 5% of mica alone. It is also attributed to the strong SPO and to further grain boundary effects. 相似文献
17.
The finite element method has often been used to simulate excavation. When the soil is linearly elastic, the results of excavation should be independent of the number of stages in the excavation process, and lack of such independence indicates an incorrect procedure. The simple direct method described in this paper provides the required independence in the case of linearly elastic materials, and hence can be used for multi-stage excavation in non-linear problems without excessive errors. However methods whose errors increase with the number of stages of excavation are quite unsuitable for non-linear problems. Alternative methods of analysis, errors arising from the inability of the elements to model adequately the stress gradients near the toe of the excavation and excavation adjacent to a diaphragm wall are discussed. 相似文献
18.
通过模拟并分析各向异性页岩岩石物理模型,研究页岩中干酪根含量变化对页岩弹性各向异性的影响,其结果为应用AVO方法定量解释页岩储层厚度和干酪根含量提供依据。岩石物理模型预测了页岩速度和各向异性参数随干酪根含量的变化规律。应用传播矩阵方法计算薄层页岩的AVO响应,得到反射系数关于页岩层厚度、入射波频率、干酪根含量和入射角的函数。数值模拟结果表明:在干酪根含量不变且在同一入射角下的反射系数在频率域呈周期变化,该周期与薄层厚度成反比;对同一频率入射波和相同入射角,反射系数幅值随干酪根含量增加而变大。 相似文献
19.
Diansen Yang Serge Chanchole Pierre Valli Liufeng Chen 《Rock Mechanics and Rock Engineering》2013,46(2):247-257
Due to various factors, such as sedimentation, layered morphology of clay minerals, in situ stress, etc., argillite rocks often exhibit anisotropic behavior. In order to study the anisotropic properties of the Callovo-Oxfordian (COx) argillite of the Meuse–Haute-Marne site in France considered as a possible host rock for high-level radioactive nuclear waste repository, a series of tests including uniaxial compression and dehydration and hydration at different constant applied stress levels are carried out. In this study, a specific setup combining moisture and mechanical loading with optical observation is used and it allows to continuously capture surface images from which the full-field strains are determined by using Digital Image Correlation techniques. The results show evidence of the mechanical and hydric anisotropy of the material. The anisotropy parameters are identified, assuming the studied argillite as transversely isotropic. The shrinkage and swelling depend on the applied stress and the angle with respect to the vertical direction of the mechanical load and the stratification plane, and this dependence is quantified. The non-linearity and the hysteresis observed during dehydration and hydration cycles are discussed. 相似文献
20.
During the ascent, emplacement and post-emplacement deformation of igneous rocks, two or more phases of deformation that overprint
each other are often depicted. These overprints, when magnetic minerals are present, are recorded in magnetic fabric. In this
contribution, overprints are studied by means of numerical modeling, following several basic scenarios common to igneous rocks.
Biotite and amphibole that occur often together in igneous rocks are considered as carriers of the anisotropy of magnetic
susceptibility. Modeling shows that (1) a constrictional fabric with a low degree of anisotropy as commonly recorded in magmatic
rocks may result from a deformation overprint and not necessarily from an extensional/transtensional regime, and (2) that
the constrictional AMS fabrics originates from orthogonal superimposition of a deformation event on an AMS fabric inherited
from earlier magma emplacement history. Therefore, the interpretation of a constrictional fabric must be performed with caution.
Numerical modeling may provide a suitable help in strengthening the interpretation of real magnetic fabric data. 相似文献