砂岩岩石力学参数各向异性研究

对胜利油田不同深度的四口井的砂岩岩芯进行了三轴压缩试验和动态岩石力学参数试验。根据获得的垂直地层方向和平行地层方向的试验数据,计算了各岩石力学参数的各向异性系数。通过分析围压以及深度对各向异性系数的影响,给出了砂岩峰值强度各项异性系数、静泊松比各向异性系数、纵波波速各向异性系数、纵横波速比和动泊松比各向异性系数与深度的拟合公式。发现峰值强度、纵波波速和纵横波速比的各向异性系数都随着深度的增加而减小,而泊松比各向异性系数随着深度的增加而增大。动、静弹性模量各向异性系数与深度相关性都很差,动弹性模量各向异性较弱,静弹性模量相对较强。     

类岩石材料力学特性的试验及数值模拟研究

在进行多组不同配比类岩石材料单轴压缩试验和巴西试验的基础上,详细分析了石膏水泥比和石英砂含量对类岩石材料的单轴抗压强度、抗拉强度及弹性模量等力学参数的影响规律,力图找到适合模拟现场砂质泥岩的类岩石材料及配合比。利用颗粒流程序(PFC)模拟,进一步研究了高径比和围压对类岩石材料力学特性的影响。结果表明:随着石膏水泥比的增大,抗压强度和弹性模量均逐渐减小,而抗拉强度逐渐增大;随着石英粉含量的增大,抗压强度和弹性模量均先增大后减小,而抗拉强度则为先减小后增大。结合单轴压缩过程的声发射特征,揭示了裂纹扩展与声发射有密切的关系。PFC2D模拟获得的力学参数与室内试验相近,破裂模式也与实际情况相似。通过尺寸效应的研究可知试样的高径比在2.0~2.5较合理。随着围压的增大,试样的峰值强度、残余强度、峰值应变及弹性模量等力学参数均增大,且围压会改变试样的破裂模式。     

多组贯穿闭合裂隙岩体变形模型研究

根据等效岩体理论,并考虑闭合裂隙面摩擦效应,建立了含多组贯穿闭合裂隙岩体的数学模型,给出了岩体轴向应变、等效弹性模量与等效泊松比的表达式,系统地研究了岩块性质和裂隙参数对等效弹性模量与等效泊松比的影响。结果表明:岩块弹性模量对等效弹性模量与等效泊松比的影响随弹性模量增大而逐渐减弱,等效泊松比与岩块泊松比近似呈正比例关系;当裂隙角度小于50°时,裂隙几何参数对等效弹性模量影响较大,对等效泊松比影响较小,随着角度增大,影响逐渐减弱;岩体变形受裂隙组数影响较大,由于闭合裂隙面的摩擦效应及多组裂隙间的制约作用,含两组及三组裂隙时岩体变形较小,只含一组裂隙时岩体变形最大,无裂隙岩体变形几乎可以忽略。     

考虑初始缺陷与弹性模量的岩石变形破坏过程模拟方法

针对扰动作用下岩石存在初始缺陷的特点,通过探讨含初始缺陷岩石变形力学特征,根据含初始缺陷岩石弹性模量的变化情况,建立了初始损伤的确定方法。然后,引入几何损伤理论,通过分析三轴压缩条件下岩石损伤演化规律,建立了含初始缺陷岩石损伤模型,进而建立了考虑初始缺陷与弹性模量的岩石统计损伤本构模型,并给出了参数的确定方法。最后,通过砂岩三轴压缩试验资料分析得出:本文理论模型能够反映不同围压作用下含初始缺陷岩石的变形破坏全过程,与试验曲线较为接近;且常见损伤模型是本文理论模型的特例,表明本文模型和方法具有一定的合理性与可行性。     

加载速率影响的单裂隙类岩石试样能量演化规律

为了研究加载速率对单裂隙类岩石试样破坏过程中能量演化进程的影响规律,分析裂隙类岩石试样在不同加载速率下的能量响应特征,以预埋金属薄片方法制作的裂隙类岩石试件为研究对象,基于RMT-150B对单裂隙类岩石试样进行四级加载速率下的单轴压缩试验,获得四级加载速率下裂隙类岩石试样力学性能。试验结果表明:单裂隙类岩石试样峰值强度与加载速率呈正相关性,但增长速率随加载速率的增加而减小;当加载速度不断增大时,峰值处试样弹性应变能积聚能力增强,但是耗散应变能随加载速率的增大而逐渐减小;裂隙试样在峰值后会累积弹性应变能,但其积聚能力随加载速率的增大而有所削弱;裂隙试样耗散应变能转化速率在峰值前处于较低水平,在峰值后伴随宏观破裂面的贯通而骤增,表明单裂隙类岩石试样内部能量演化进程与其破坏规律之间具有内在联系。     

一种由圆柱体试件的侧向压缩力-位移关系同时测量材料弹性模量和泊松比的新方法

材料的弹性模量和泊松比是材料表征的重要力学参数,传统的压缩试验需要同时测量荷载、压缩和横向变形,才能实现对弹性模量和泊松比的同时测量。本文从Hertz接触理论出发,推导出弹性圆柱体在侧向压缩下的位移-力关系公式,在该关系式中位移与力的关系除与试件的几何尺寸相关外,还取决于材料的弹性模量和泊松比。因此,可以通过对侧向压缩试验测得的力-位移关系进行非线性拟合,得到材料的弹性模量和泊松比。本文通过对硅胶材料开展轴向与侧向压缩试验,对比两种试验测量得到的弹性模量和泊松比,结果较为一致,验证了本文提出方法的可行性。对于模量较小的软物质,因加载过程的荷载常常较小,系统测量的位移可代表试件的变形位移,故本文提出的新测量方法特别适合应用于该类型材料的相关性能测量。     

含不同倾角单裂隙类岩石单轴强度及蠕变速率的研究

为了研究裂隙类岩石材料在单轴压缩和蠕变条件下的力学性质及裂纹扩展规律,通过预埋铁片的方法制作出含不同倾角的单裂隙类岩石试件,建立贯通裂隙类岩石单轴压缩强度模型,分析破坏形式。研究表明,预制裂隙倾角对类岩石试件峰值强度的影响显著,裂纹倾角越小,单轴抗压强度越低,即倾角为0°时单轴抗压强度为6.98MPa,90°时为10.85MPa,呈单调递增的趋势。建立裂隙面模型,分析类岩石试件的破坏形式,大致为两类:一类是通过预制裂隙拉剪破坏;另一类是通过裂隙的拉伸破坏。蠕变速率随着裂隙倾角的增大先增大后减小,在90°时的蠕变速率最低,在30°时蠕变速率最高。     

骨细胞培养过程对羟基磷灰石力学性质影响的研究

采用数字图像相关方法研究骨细胞对人造羟基磷灰石力学性质的影响.采用了三种试样:羟基磷灰石试样、培养了骨细胞的羟基磷灰石试样、用戊二醛溶液浸泡的羟基磷灰石试样(与培养骨细胞同样环境但不培养骨细胞).研究得到了试样完整的应力-应变曲线;同时测出弹性模量和泊松比,还测量了压缩极限应力.实验结果表明试样的应力-应变曲线在断裂前呈良好的线性关系;戊二醛溶液不影响羟基磷灰石的弹性模量和泊松比,但会使压缩极限应力降低;骨细胞培养过程能使羟基磷灰石材料的弹性模量和强度增加(所培养的骨细胞约占表面积3.75%).对照显示,羟基磷灰石培养骨细胞后其弹性模量增加了15.2%,压缩极限应力增加了26.1%.     

单轴压缩下断续节理岩体动态损伤本构模型

断续节理将对工程岩体的强度及变形等力学特性产生显著影响,损伤力学中视节理为岩体的一种宏观损伤,因而采用损伤张量来刻画其对岩体的影响。目前学术界提出了用节理的几何、强度及变形等3类参数来描述节理的物理力学性质,而目前的岩体损伤张量计算方法都只涉及前2类参数,均没有涉及其变形参数即法向及切向刚度。为此,在前人研究的基础上,基于断裂及损伤理论提出了考虑节理法向及切向刚度的单轴压缩下单条断续节理引起的损伤张量计算公式,进而通过考虑节理间相互作用给出了单组单排或多排节理岩体损伤张量计算公式。其次,以岩石细观动态损伤模型为基础,结合宏细观损伤耦合观点提出了一个能够同时考虑节理几何、强度及变形参数的断续节理岩体动态损伤本构模型。最后,利用该模型讨论了节理参数及载荷应变率等对岩体动态力学特性的影响,认为节理长度减小及摩擦角增大将导致岩体动态峰值强度及弹性模量增大;岩体动态峰值强度及弹性模量则随着节理法向及切向刚度的增大分别减小或增大;而当节理法向及切向刚度按照同一比例增大时,岩体动态峰值强度及弹性模量则是增大的。岩体动态峰值强度与载荷应变率呈正相关。     

不同围压下含天然贯通节理岩石卸载破坏机理研究

二郎山特长高速公路隧道断裂带较多，受此影响，隧道开挖后岩爆灾害十分严重．从此隧道中取样制备成含天然贯通节理试件，进行常规单轴压缩室内试验，获取基本力学参数和破坏模式．本文以室内实验结果为依据，确定数值试验时所采用的岩石和节理的力学参数，利用RFPA软件开展数值试验，研究了不同围压同轴向荷载下卸掉围压诱发岩石失稳破坏机理．试验结果表明，五种不同围压(5、10、15、20、25 MPa)卸载后应力-应变曲线均呈“断崖式”跌落，试样均突然破坏，与现场岩爆情况吻合；受贯通节理影响，不同围压试样的具体破坏形态、声发射数量最大值出现时刻有所差异；在卸载阶段五种试样声发射累积数量都突然急剧增大．     

Mechanical behaviour of the upper layers of a sandy loam soil under shear loading

The mechanical behaviour of the upper layers of a sandy loam soil was studied under standard triaxial compression and direct shear box tests. Variations of soil material properties were investigated at four different initial dry bulk densities of 1410, 1520, 1610 and 1670 kg/m³. Soil deformation and volume change under the triaxial compression loading were also studied at these bulk densities. Results from the two tests showed increases in the soil mechanical properties with the initial dry bulk density. The internal friction angle values measured with the triaxial compression apparatus exceeded those measured with the direct shear box. In contrast, the soil cohesion values measured with the direct shear box exceeded those measured with the triaxial compression apparatus. Under the triaxial compression test, the loose soil samples underwent contraction and volume reduction, whereas the dense samples swelled and failure cracks appeared clearly at various planes. The soil contraction for the former case characterizes the occurrence of soil compaction, whereas the cracks propagation and volume increase in the latter case characterizes the breaking up and loosening of soil during tillage operations. For the loose and moderately compacted states, the engineering Poisson's ratio increased with the axial strain until loading was completed. It also increased at the compacted and very compacted states until reaching given loading stages, after which its value started to decrease. This shifting in the engineering Poisson's ratio during loading may provide another identification of the moment of soil failure occurrence, in addition to that of the maximum shear stress.     

319国道重庆段裸洞隧道灰岩力学特性试验研究

裸洞隧道在长期使用过程中,围岩遭受风化、地下水及区域地应力等不利因素的作用,导致岩体性质恶化,影响隧道的正常使用。在调研统计的基础上,选取319国道重庆至武隆段大溪河裸洞隧道为研究对象,对其表层及深层灰岩进行了室内单轴压缩、三轴压缩力学特性试验并对单轴压缩作用下的声发射特性进行了研究。结果表明:单轴压缩作用下两种岩样均出现脆性破坏特征,三轴压缩条件下,两种岩样呈压缩为主的延性扩容破坏,声发射可较好地表征岩石单轴压缩破坏过程;获得了两种岩样的基本力学参数,深层岩样强度为表层岩样强度的2.13倍,弹性模量、泊松比、内聚力、内摩擦角分别是表层岩样的1.04倍,0.63倍,1.45倍,1.37倍。研究结果可为该地区裸洞隧道的长期安全性与稳定性提供有益的理论支撑。     

裂隙岩体损伤局部化破坏分岔模型及其应用

采用概率统计方法分析节理裂隙岩体的几何特征，定义了反映裂隙岩体几何特征的组构张量．基于不可逆热力学理论，通过裂纹扩展的细观分析，得出了损伤的发展机理和演化方程，把损伤演化和裂隙的几何特征的变化联系起来，建立了弹塑性损伤本构关系．为分析含有节理裂隙岩体在发生局部化破坏时的特征，通过对发生局部化时的裂隙岩体的分析。构造了适用于节理裂隙岩体局部化分析的不连续分岔模型．利用非线性规划数值解法，可以得出局部化破坏的方向特征．在有限元方法中，根据该模型给出了节理裂隙岩体相关的算例，分析表明该模型用于分析裂隙岩体的局部化破坏是有效的．     

Stress singularities at crack corners

In this paper the stress and displacement fields near an embedded crack corner in a linear elastic medium are analytically computed. The conical-spherical coordinate system is introduced to solve this problem. It is observed that the strength of the stress singularity depends on the angle of the crack corner. The singularity becomes weaker, varying from r ^-1 to r ⁰, as the angle of the crack corner varies from 360° to 0°. Both symmetric and skew-symmetric loadings give the same variation of the behavior of the stress singularity. It is also found that the order of the singularity is independent of the Poisson's ratio, unlike the corner cracks at a free surface where Poisson's ratio affects the results.     

ANISOTROPIC EFFECTS OF QUASI-ISOTROPIC COMPOSITES (II)——APPLICATIONS AND MICRO-MECHANICAL ANALYSIS

Up to now, the analysis on anisotropic effects of quasi-isotropic composites to material structures has not been found in literatures. In the present paper the strength model for triaxial woven materials proposed in Part (I) ^[1] is applied to study the problems of an infinitely large plate of triaxial woven material containing either an elliptic hole or a crack. To the elliptic hole problem the remote critical loading as a function of the geometric parameters of woven materials is analysed, and to the crack problem, the cracking orientation is examined. Finally, the elasticity and strength models for a triaxial woven material proposed in Part(I) are verified in terms of micro-mechanical analysis.Project supported by the National Natural Science Foundation of China and the State Education Commission Foundation of China     

近场动力学研究进展与岩石破裂过程模拟

近场动力学（Peridynamics，PD）作为一种新兴的非局部性理论，在非连续处不需要任何处理，能够很好表述模型从连续到非连续的过程。首先，在PD基本理论简介的基础上，系统回顾了PD的国内外研究现状。其次，采用键型PD理论对非均匀性的圆孔岩板单轴拉伸破裂过程进行了二维数值模拟，采用态型PD理论对单轴、常规三轴以及真三轴等不同压缩条件下的岩石破裂过程进行了三维数值模拟，并以加拿大Mine-by隧洞为例对现场岩体破裂过程进行了模拟，结果表明PD在岩石破裂过程模拟上具有较强适用性。最后，指出当前PD在岩石破裂过程模拟中存在的主要问题和未来值得开展的若干研究课题。     

含微裂纹材料的损伤理论

本文从含微裂纹材料的变形能出发引出了裂纹的方位张量。在考虑裂纹受压闭合与滑动摩擦的基础上,给出了损伤张量、损伤应变及有效弹性常数。文中给出了损伤机构离散化的方法,并对方位密度给出了演化方程。最后给出一个单向拉压的应力应变关系例子,并揭示了裂纹扩展时的应力突跌现象。     

Experimental investigation on strength and failure behavior of pre-cracked marble under conventional triaxial compression

Fractures in natural rocks have an important effect on the strength and failure behavior of rock mass, which are often evaluated in rock engineering practice. The theoretical evaluation of mechanical behavior of fractured rock mass has no satisfactory answer due to the role of confining pressure and crack geometry. Therefore, in this paper, conventional triaxial compression experiments were carried out to study the strength and failure behavior of marble samples with two pre-existing closed cracks in non-overlapping geometry. Based on the experimental results of a number of triaxial compression tests, the effect of crack coalescence on the axial supporting capacity and deformation property were investigated with different confining pressures. The results show that intact samples and flawed samples (marble with pre-existing cracks) have different deformation properties after peak stress, which change from brittleness to plasticity and ductility with the increase of confining pressure. The peak strength and failure mode are found depending not only on the geometry of flaw, but also on the confining pressure. The strength of flawed samples shows distinct non-linear behavior, which is in a better agreement with non-linear Hoek–Brown criterion than linear Mohr–Coulomb criterion. For a kind of rock that has been evaluated as a Hoek–Brown material, a new evaluation criterion is put forward by adopting optimal approximation polynomial theory, which can be used to confirm more precisely the strength parameters (cohesion and internal friction angle) of flawed samples. For intact samples, the marble leads to typical shear failure mode with a single fracture surface under different confining pressures, while for flawed samples, under uniaxial compression and a lower confining pressure (σ₃ = 10 MPa), tests for coarse and medium marble (the coarse and medium refer to the grain size) exhibit three basic failure modes, i.e., tensile mode, shear mode, and mixed mode (tensile and shear). Shear mode is associated with lower strength behavior. However, under higher confining pressures (σ₃ = 30 MPa), for coarse marble, the axial supporting capacity is not related to the geometry of flaw. The friction among crystal grains determines the strength behavior of coarse marble. For medium marble, the failure mode and deformation behavior are dependent on the crack coalescence in the sample. The present research provides increased understanding of the fundamental nature of rock failure under conventional triaxial compression.     

MICROMECHANICS ANALYSIS FOR UNSATURATED GRANULAR SOILS

This paper aims at establishing an anisotropic stress expression for unsaturated pendular-state granular soils. Using the second-order fabric tensor, we formulate a micromechanics scheme of soils with statistically averaging method, and reveal that the macroscopic average stress of unsaturated granular soils in pendular-state is not isotropic. Not only is the stress from contact forces anisotropic due to the fabric, but also the capillary stress is directional dependent, which is different from the common point that the capillary stress is isotropic. The capillary stress of unsaturated pendular-state granular soils is determined by the orientation distribution of contact normals, so it is closely related to the initial and induced anisotropy of soils. Finally, DEM numerical simulations of triaxial compression tests of pendular-state soils at different degrees of saturation are used to verify the existence of above anisotropy of stresses.     

Strain strengthening effects in Witwatersrand quartzite

A series of uniaxial compression specimens were tested over a range of applied ram displacement rates of 8.9 × 10⁻⁴ to 8.9 mm/sec to elucidate the effects of loading rate on the uniaxial compressive fracture stress of Witwatersrand quartzite. It was demonstrated that even within standard loading rate ranges, considerable scatter in the fracture strength (under uniaxial compression) existed in this particular quartzite rock. Nevertheless, a definite trend of increasing fracture resistance with increasing monotonic loading rate was evident inasmuch that increasing the loading rate (strain rate) by four orders of magnitude increase the fracture strength by almost 2.8 times. Prior fatigue loading also produced a significant strain strengthening as the uniaxial compressive fracture stress tended to increase in a sigmoidal fashion with increasing number of fatigue cycles prior to testing. Indeed, the fracture strength of quartzite was almost doubled in value after 10⁻ cycles. Plane strain fracture toughness tests utilising three point bend specimens were conducted and an average of K_lc = 1.7 MPa√m was realized. In both the uniaxial compression tests and the fracture toughness tests, failure occurred by crack extension predominantly by a transgranular flat cleavage-like mode through pure quartzite (silica) regions. However, crack extension was also observed to occur in an intergranular “ductile-like” mode through areas associated with inclusions prevalent in the quartzite.