拉剪应力状态下岩体裂隙扩展的断裂力学机制及物理模型试验

开挖卸荷岩体裂隙面通常处于拉剪应力状态。在裂隙应力和变形状态分析的基础上,采用线弹性断裂力学理论和物理模型试验研究了拉剪应力状态下裂隙扩展的力学机制。岩体裂隙在拉剪应力状态下沿裂隙面间的滑动抗剪摩擦力消失,裂隙起裂沿Ⅰ型张拉裂隙断裂韧度KⅠ最小的方向起裂,并最终发展与卸荷拉应力方向垂直;拉剪应力状态下岩体的总位移方向平行于拉应力方向,通过合理的位移假设,基于能量及线弹性断裂力学理论,求解了拉剪应力状态下分支裂隙扩展过程中尖端的动态应力强度因子和扩展长度判据;通过拉剪应力状态下单裂隙扩展物理模型试验验证了理论推导的正确性。

水泥混凝土基面上沥青铺装剪应力分析与评价

考虑到直接计算最危险破裂面上剪应力的不便性,提出了用八面体剪应力代替最危险破裂面上剪应力,并用于分析与评价沥青铺装结构抗剪切能力的方法。结果表明:力学分析获取八面体剪应力的方法,配合无侧限抗压试验和贯入试验确定材料抗剪切参数的方法,可共同构成分析和评价沥青铺装抗剪切能力的有效方法体系。其八面体剪应力沿深度的分布曲线,可为沥青铺装设计和材料选择提供重要参考。

不同半刚性基层参数对沥青路面层间剪应力影响数值分析

为研究不同半刚性基层参数对沥青路面层间剪应力的影响,采用有限元数值分析方法建立了三维数值仿真模型,分析了路面纵向坡度、水平力系数、行车速度和外界温度对半刚性基层沥青路面工作性能的影响.结果表明:路面纵坡坡度变化对半刚性沥青面层基层顶部和底部剪应力影响小;水平力系数增加会增大基层顶部和面层底部纵向剪应力和竖向剪应力;行车速度增大会减小基层顶部和面层底部的纵向剪应力和横向剪应力以及面层底部竖向剪应力减小,但基层顶部竖向剪应力会增大;基层顶部纵向和横向剪应力会随温度升高呈先减小后增大变化规律,面层底部纵向和横向剪应力呈增大趋势,基层顶部竖向剪应力呈减小趋势.研究结果可为半刚性基层沥青路面结构设计提供理论依据.

考虑黏聚效应的黏土应力路径本构模型

为了合理描述平均主应力增大或减小时黏土的弹塑性变形,尤其对最小主应力小于零时加载路径下土的弹塑性变形问题,利用摩擦块模型揭示土的摩擦强度和黏聚强度机理,给出土的抗剪强度公式.结合土的黏聚强度特性,将子午面划分为φ硬化区和c硬化区.在φ硬化区,将超固结状态对塑性变形的影响考虑进应力路径本构模型中,从而得到塑性变形的计算方法;在c硬化区,利用双曲线关系来描述黏聚力与剪应变的关系,结合剪胀方程确定塑性体应变,建立考虑黏聚效应的黏土应力路径本构模型.该模型仅有6个材料参数,且各参数的物理意义明确.通过试验结果对模型的验证表明,建立的本构模型能合理描述复杂应力条件,尤其是拉伸荷载作用下土的应力应变关系.

岩石在不同围压条件下破坏过程的模拟研究

利用RFPA系统对不同围压条件下岩石的剪应力状态、最大主应力状态及宏观破坏模式进行模拟研究,为实际操作提供较精确的数据基础。

Particle breakage and the mobilized drained shear strengths of sand

This paper presents particle breakage and the mobilized drained shear strengths of sand with the purpose of clarifying the influence of particle breakage on the mobilized shear strengths of sand. Several drained triaxial tests were carried out on Silica sand No.5 under 3 MPa confining pressure to produce the pre-crushed sands in simulating the high- pressure shear process on soil to result in particle breakage, and then the pre-crushed sands were re- sheared in series of drained triaxial tests to investigate the mobilized strengths of the pre-crushed sands in detecting the influence of particle breakage. It was found that, by deteriorating strain-stress behavior, particle breakage resulted in change of stress-dilataney behavior in translation and rotation of the relation of the dilatancy factor and the effective principal stress ratio. For a given initial void ratio, particle breakage resulted in impairment of dilatancy behavior of soil to be more contractive in deterioration of the mobilized friction angle and the mobilized dilatancy angle and reduction of void ratio. However, particle breakage resulted in increase of the mobilized basic friction angle especially before failure. In addition, the influence of particle breakage on the mobilized strengths was revealed to be influenced by the shear stress-strain state.

Preliminary Study on Simulation of Global Seismic Activities with Global Strain Rate

The relationship between the strain rate field observed by GPS and global distribution of strong earthquakes is analyzed in this work. How do we recognize the characteristics of global seismic activities with space observation technology? A preliminary model of Cellular Automata that could simulate the global seismic activities both in time and space has been established based on the results of global strain rate field provided by the GSRM Program. The grid of the model is evenly divided,which is consistent with that of GSRM.The status of each cell is its strain state,and is adjusted according to the evolution rules.Maximum shear strain criterion is adopted in the evolution of the Cellular Automata. The threshold for cells in surface expansion is 80% of that for those in compression. The preliminary model could in general simulate the main characteristics of the distribution of the global seismic activities. It could exhibit in general the global distribution of weak and active tectonic activities. Although the preliminary Cellular Automata model needs to be improved in many aspects,the result suggests the possibility of modeling the general features of rather complicated global seismic activities based on the strain rates obtained by GPS and other observations.

细粒硫酸盐渍土抗剪强度特性试验研究

影响天然硫酸盐渍土强度的因素众多,规律难以探索。为确定含盐量对硫酸盐渍土抗剪强度的影响,通过直剪试验研究了不同含盐量的硫酸盐渍土抗剪强度特性。研究表明:在直剪应力状态下,剪应力-剪切位移关系曲线有应变硬化(加工硬化)和应变软化(加工软化)两种形态,取决于含盐量、含水量、法向应力等因素。抗剪强度包线近似为折线型,与传统结构性土体包线形态一致,表明了硫酸盐渍土在直剪应力状态下仍然属于结构性土体。易溶盐含量对抗剪强度影响较大,总的变化趋势是:随着含盐量的增加,相同法向应力作用下的硫酸盐渍土的抗剪强度有不同程度的先减小后增大再减小的特点。当含水量ω=21%时,粘聚力c随易溶盐含量的增大呈指数形式的增长,c∈[2.9kPa,10.4kPa];当ω=25%时,c∈[3.2kPa,12.4kPa];内摩擦角φ随易溶盐含量的增大变化范围较小,总体的变化趋势呈现出先减小后增加再减小的特点;当ω=21%时,φ∈[11.5°,13.4°];在ω=25%时,φ∈[10.6°,12.9°]。

钙质砂单调及循环单剪试验研究

为探究单剪应力路径下钙质砂的力学特性及颗粒破碎演化规律,对浸水后的钙质砂进行了一系列常应力、常体积单调及循环单剪试验.结果表明:钙质砂颗粒破碎程度随初始竖向应力、循环应力、循环应变及循环次数的增加而增加,但试验结束时钙质砂相对破碎指数与输入能量之间存在比较固定的关系;循环试验的相变应力比明显小于单调试验;常应力试验的累计体应变随循环次数的增加而增加且与累计剪应变间存在近似双曲线关系;颗粒形状对钙质砂颗粒的破碎模式有明显影响,对不规则颗粒形态的钙质砂而言,颗粒破碎也导致其变得更规则.