Dynamic Characteristics of Granite Subjected to Intermediate Loading Rate

Summary A large diameter split Hopkinson pressure bar (SHPB) has been developed. This equipment is briefly described, together with a shaped striker that initiates a half-sine incident waveform to obtain the complete stress-strain relationship of the Bukit Timah granite at medium strain rate. Good constant strain rate was derived, and the dynamic complete stress-strain curves and energy absorption of the granite were measured at a strain rate between 20 and 60 per second. Repeated impact between 60–90% of the static strength of the granite was also conducted. Results from the tests show that the cumulative damage of the granite depends on the peak stress of the dynamic loads with a fixed duration. The dynamic fracture strength of the granite loaded at medium strain rate is directly proportional to the cube root of the strain rate. For the granite loaded at this strain rate, Youngs modulus is unchanged. Energy absorption of the samples loading to fragmentation determined its fragmented size distribution. At high strain rate, the rock possesses large energy absorption and the particle size of the fragments is much smaller.     

基于完全三叉树的快速推进法地震波走时计算

快速推进法(简称FMM)在地震波走时计算中有着精度高、效率高的特点,但窄带扩展每次都要寻找最小走时。当网格节点较多时,寻找最小走时非常耗时。在保证精度的前提下,为了提高计算效率,笔者对堆排序的排序方式做了改进,将完全三叉树排序方法引入到快速推进法地震波走时计算中。模型试算结果表明,基于完全三叉树快速推进法计算出的地震波走时与用完全二叉树方法的精度一致,且前者比后者效率提高约10%。     

Micromechanical Modelling of the Complete Stress–Strain Relationship for Crack Weakened Rock Subjected to Compressive Loading

Summary  A micromechanics-based model, able to quantify the effect of various parameters on the complete stress–strain relationship, is described. The closed-form explicit expression for the complete stress–strain relationship of a rock material containing an echelon cracks arrangement subjected to compressive loading is obtained. The complete stress–strain relationship including the stages of linear elasticity, non-linear hardening and strain softening is established. The results show that the complete stress–strain relationship and the strength of rock with echelon cracks depend on the crack interface friction coefficient, the sliding crack spacing, the perpendicular distance between the two adjacent rows, the fracture toughness of rock material and orientation of the cracks. The present model is used to evaluate the complete stress–strain relationship and strength for crack-weakened rock at the underground cavern complex of the Ertan Hydroelectric Project. The predicted strength is in agreement with that obtained by the Hoek–Brown criterion. The numerical results obtained with the complete stress–strain relationship seem to be in good agreement with the measured values. Author’s address: Xiao-Ping Zhou, School of Civil Engineering, Chongqing University, 443002 Chongqing, P.R. China     

Application of Importance Sampling Method in Sliding Failure Simulation of Caisson Breakwaters

It is assumed that the storm wave takes place once a year during the design period, and N histories of storm waves are generated on the basis of wave spectrum corresponding to the N-year design period. The responses of the breakwater to the N histories of storm waves in the N-year design period are calculated by mass-spring-dashpot mode and taken as a set of samples. The failure probability of caisson breakwaters during the design period of N years is obtained by the statistical analysis of many sets of samples. It is the key issue to improve the efficiency of the common Monte Carlo simulation method in the failure probability estimation of caisson breakwaters in the complete life cycle. In this paper, the kernel method of importance sampling, which can greatly increase the efficiency of failure probability calculation of caisson breakwaters, is proposed to estimate the failure probability of caisson breakwaters in the complete life cycle. The effectiveness of the kernel method is investigated by an example. It is indicated that the calculation efficiency of the kernel method is over 10 times the common Monte Carlo simulation method.     

脆性岩石全应力-应变过程渗流特性试验研究

为了探讨岩石在整个变形过程中渗透性变化特点,取三峡永久船闸高边坡花岗岩与山西万家寨水电站高边坡灰岩试样分别进行不同围压条件下全应力-应变过程渗流试验。试验结果表明：岩石在破坏前后不同变形阶段渗流特性具有明显不同;岩石变形过程渗透性与变形破坏形式密切相关。在试验基础上进一步探讨了岩石全应力-应变过程渗流特点之机理,为研究水电工程节理裂隙岩体应力场与渗流场耦合问题提供有价值的支持。     

煤岩两体模型变形破坏数值模拟

采用拉格朗日元法,在弹性岩石与弹性-应变软化煤体所构成的平面应变两体模型的上、下端面上不存在水平方向摩擦力条件下,模拟了模型的破坏过程、岩石高度对模型及煤体全程应力-应变曲线、煤体变形速率、煤体破坏模式及剪切应变增量分布的影响。结果表明,当模型的全程应力-应变曲线达到峰值时煤体内部的剪切带图案已经十分明显,在模型的应变硬化阶段,煤体中的应变局部化可视为模型失稳破坏的前兆,随岩石高度的增加,模型应力-应变曲线的软化段变得陡峭,这与单轴压缩条件下的解析解在定性上是一致的;煤体应力-应变曲线的软化段变得平缓,煤体消耗能量的能力增强;弹性阶段煤体的变形速率降低;煤体内部的剪切应变增量增加。煤体应力-应变曲线的软化段的斜率、弹性阶段煤体的变形速率、煤体内部的剪切应变增量及塑性耗散能都受岩石高度的影响,说明了岩石几何尺寸对煤体的影响(煤岩相互作用)是不容忽视的。     

Dynamics of unsaturated soils using various finite element formulations

Unsaturated soils are three‐phase porous media consisting of a solid skeleton, pore liquid, and pore gas. The coupled mathematical equations representing the dynamics of unsaturated soils can be derived based on the theory of mixtures. Solution of these fully coupled governing equations for unsaturated soils requires tremendous computational resources because three individual phases and interactions between them have to be taken into account. The fully coupled equations governing the dynamics of unsaturated soils are first presented and then two finite element formulations of the governing equations are presented and implemented within a finite element framework. The finite element implementation of all the terms in the governing equations results in the complete formulation and is solved for the first time in this paper. A computationally efficient reduced formulation is obtained by neglecting the relative accelerations and velocities of liquid and gas in the governing equations to investigate the effects of fluid flow in the overall behavior. These two formulations are used to simulate the behavior of an unsaturated silty soil embankment subjected to base shaking and compared with the results from another commonly used partially reduced formulation that neglects the relative accelerations, but takes into account the relative velocities. The stress–strain response of the solid skeleton is modeled as both elastic and elastoplastic in all three analyses. In the elastic analyses no permanent deformations are predicted and the displacements of the partially reduced formulation are in between those of the reduced and complete formulations. The frequency of vibration of the complete formulation in the elastic analysis is closer to the predominant frequency of the base motion and smaller than the frequencies of vibration of the other two analyses. Proper consideration of damping due to fluid flows in the complete formulation is the likely reason for this difference. Permanent deformations are predicted by all three formulations for the elastoplastic analyses. The complete formulation, however, predicts reductions in pore fluid pressures following strong shaking resulting in somewhat smaller displacements than the reduced formulation. The results from complete and reduced formulations are otherwise comparable for elastoplastic analyses. For the elastoplastic analysis, the partially reduced formulation leads to stiffer response than the other two formulations. The likely reason for this stiffer response in the elastoplastic analysis is the interpolation scheme (linear displacement and linear pore fluid pressures) used in the finite element implementation of the partially reduced formulation. Copyright © 2008 John Wiley & Sons, Ltd.     

2009年夏季西太平洋副热带高压北抬原因初探

利用数值模式再分析数据和常规观测资料,分析研究2009年6-8月西太平洋副热带高压(以下简称副高)连续5次北抬至偏北位置,且异常稳定维持,造成江淮流域干旱少雨(空梅)之缘由.通过合成、相关等分析方法探讨西风带、副热带、热带主要大气环流系统之间的相互影响和作用,并利用全型涡度方程探讨副高北抬和强度维持的主要机制.结果表明:(1)西风带波动的传播与副高变化关系密切,西太平洋副高的北抬过程起始于中段副高(140°～160°E)强度加强;(2)副高北抬之前孟加拉湾东部有明显的对流活动,对于副高的北抬和加强有一定的指示意义,而副高南侧的对流活动与副高北抬之间是一种伴随关系;(3)涡度场变化分析可知,副高北抬的关键因素是中高纬度槽脊变化引起的东亚沿海负涡度的增加.     

超细钻孔压浆桩施工技术的应用

介绍了在水上施工凉亭、曲桥等荷载较小建筑物基础时,采用了直径Ф219mm的超细钻孔压浆桩.阐述了用质量轻的SH30型工程钻机,只需搭设简易的水上平台,采用价格低廉的污水泵就能钻孔压浆桩的施工.     

完备剩余幂集格的经典同构对象

本文在格L是完备剩余格的条件下,引入关于L-集合套的张量积和蕴涵运算,证明了L-集合套关于这2种运算构成完备剩余格。本文还进一步证明该完备剩余格恰好与完备剩余幂集格是同构的,从而建立起完备剩余格环境下的L-集表现定理。