Application of extended distinct element method with lattice model to collapse analysis of RC bridges

This paper proposes a simple lattice model for collapse analysis of RC bridges subjected to earthquakes by using the extended distinct element method (EDEM). In the model, a concrete element consists of lumped masses connected to one another by springs, and a reinforcement bar is represented by a discrete model or an integrated model. The proposed lattice model is simple but its parameters are reasonably defined. It has fewer element nodes and connecting springs, which will be of benefit by shortening the CPU time. The processes to determine the initial stiffness of concrete and steel springs, the parameters of the constitutive model and the fracture criteria for springs are described. A re‐contact spring model is also proposed to simulate the re‐contact of the concrete after fracture of springs; and a general grid searching method is used to decrease the CPU time for judging re‐contact after fracture. The lattice model is assessed by numerical simulations and experiments. As an application, a damaged single‐column pier subjected to the Kobe Earthquake in 1995 is analysed by EDEM with the proposed model. The simulation results indicate that the proposed model predicts well qualitatively the collapse process of RC bridges. Copyright © 2003 John Wiley & Sons, Ltd.     

Evaluating foundation mass,damping and stiffness by the least‐squares method

This paper discusses how to use the three‐dimensional (3D) time‐domain finite‐element method incorporating the least‐squares method to calculate the equivalent foundation mass, damping and stiffness matrices. Numerical simulations indicate that the accuracy of these equivalent matrices is acceptable when the applied harmonic force of 1+sine is used. Moreover, the accuracy of the least‐squares method using the 1+sine force is not sensitive to the first time step for inclusion of data. Since the finite‐element method can model problems flexibly, the equivalent mass, damping and stiffness matrices of very complicated soil profiles and foundations can be established without difficulty using this least‐squares method. Copyright © 2003 John Wiley & Sons, Ltd.     

冻土路基表面的融化指数与冻结指数

在冻土层之上筑路，由于会改变地-气界面的热物理特性，进而影响冻土层的热力→动力稳定性，故而修筑一定高度的路基成为保护冻土层所采取的一种常规措施．在修筑路基之后，与路基边坡的朝向有关的热效应是冻土路基工程保护措施必须考虑的问题．在数理分析与数值模拟分析的基础上，给出了可根据气温的年最大和最小月平均值计算路基表面的融化指数与冻结指数以及有关热状况参数的方法，并以青藏铁路北麓河段2002年为例进行了计算分析．实例分析表明，即便是没有修筑道路，北麓河地区的冻土也已经处于临界状态；路基相对的两个坡面，由于朝向不同会造成温度分布的强非均匀性，其中南和偏南方向与北和偏北方向的路基坡面热状况差异最大，有必要对路基相对的两个坡面采用不同的防护措施，一方面改善就地取土修筑路基对其下伏冻土层的直接不良影响，同时也尽可能减小路基表面温度分布的非均匀性，以避免纵向裂缝的发生。     

地震荷载作用下温度和围压对冻土强度影响的试验研究

通过对重塑冻结兰州黄土的动三轴试验，较系统研究了地震荷载作用下冻土的动强度特性，并且定量研究了其在不同温度(-2℃、-5℃、-7℃)和围压(1MPa、3MPa、5MPa)条件下的变化规律．结果发现：冻结黄土的动抗剪强度随围压的增大、温度的降低、振次的减少而增大；动粘聚力Cd随振次的减小和温度的降低而增大；动内摩擦角吼随振次的增大和温度的降低而增大。     

基于GIS的土壤质量评价研究

介绍了基于GIS土壤质量等级评价的实现过程。探讨了土壤等级评价因子的选择和因子权重的确定方法。在分析了几种常用方法在土壤质量评价中的应用特点并指出几种方法的局限性之后，提出了顾及因子稳定性的多元线性回归分析法，并以南方某地为例进行了实例分析。     

地面沉陷对路基的破坏影响及其防治技术

根据地下资源开发地区岩层与地表移动机理，研究了地面沉陷时路基产生的破坏影响，分析、总结了路基沉陷特征，给出了确定路基和矿柱强度及稳定性的验算方法，以及路基出现坍塌或滑坡等灾害事故的评估方法，提出了地面沉陷区路基防治技术，并列举了治理路基沉陷的例子。     

黑土的水土流失及其保育治理

黑土因其肥沃而闻名，但其退化和水土流失问题往往易被忽略。虽然在人类影响下的现代环境过程开始较晚，但黑土区的环境已发生了较大的变化。对黑土水土流失的现状进行了评价，指出了黑土保育治理的必要性与紧迫性，提出了治理保育措施。     

滑带土粘土矿物定向性的x射线衍射及其对滑坡的作用

本文首先论述了粘土矿物颗粒定向排列测定的基本原理并提出粘土矿物定向性定量评价方法,然后根据实例—庙上北滑坡的滑带土粘土矿物的X射线衍射结果,进行定向性定量分析计算,得出滑带土粘土矿物颗粒的定向度为弱到中等定向,并以中等定向为主。因而在水的往返作用下,滑带土具一定的胀缩性及胀缩的不均匀性,再加上粘土矿物本身亦具有的胀缩性及胀缩的可逆性和循环性,故导致滑带土抗剪强度和结构强度不断降低,大大影响斜坡的稳定性。     

Deformation at Stromboli volcano (Italy) revealed by rock mechanics and structural geology

We approach the reconstruction of the recent structural evolution of Stromboli volcano (Italy) and the analysis of the interplay between tectonics, gravity and volcanic deformation. By tying together structural, lithostratigraphic and rock mechanics data, we establish that since 100 ka BP, the edifice has faulted and jointed mainly along NE-striking planes. Faults mostly dip to the NW with normal displacement. Taking also into account the presence of a NW-trending regional least principal stress and of tectonic earthquake hypocenters inside the cone, we suggest that this fracturing can be related to the transmission of tectonic forces from the basement to the cone. Dyking concentrated along a main NE-trending weakness zone (NEZ) across the volcano summit, resembling a volcanic rift, whose geometry is governed by the tectonic field. In the past 13 ka, Stromboli experienced a reorganisation of the strain field, which was linked with the development of four sector collapses affecting the NW flank, alternating with growth phases. The tectonic strain field interplayed with dyking and fracturing related to unbuttressing along the collapse shoulders. We propose that tectonics control the geometry of dykes inside the cone and that these, in turn, contribute to destabilise the cone flanks.     

新疆盐渍土分散性研究

通过研究分析盐渍土及改变盐渍含量对分散性试验的影响,认为土块试验、针孔试验对受高钠离子影响的盐渍土分散性评价是较为有效的方法。新疆土料石膏发育,环境水中Ca2+离子丰富,分散性评价最好在工程实际情况下进行。