软弱地层深挖基坑中工程桩偏位分析

某软土地基上建造多栋毗邻的小高层住宅,在地下车库基坑的开挖过程中,软土流动推挤坑内桩基导致偏位。文章以上述工程为背景,借助三维有限差分程序FLAC3D,选取简化计算模型,对基坑开挖流动土体作用下工程桩的反应性状进行了模拟与分析,并与实测值进行了比较,最后讨论了影响桩基变形的相关因素,可为分析软土地区基坑开挖对坑内工程桩影响时提供一定的理论指导。     

深基坑桩锚支护体系主动区土压力试验研究

通过深大基坑桩锚支护体系主动区土压力现场试验,依据基坑工程时空效应理念,研究分析了在深大基坑开挖过程中桩锚支护体系的受力特性,得出了主动区土压力随开挖进程发展而变化的分布规律,对类似深大基坑支护体系设计时的土压力计算具有重要参考价值。     

振动沉管粒料桩在高路堤软基处理中的应用

通过四川成南高速公路NO .E4合同段振动沉管粒料桩、塑料排水板与砂粒垫层综合处治法在高填路堤软基处理的施工实践, 总结出在山岭重丘区高填路堤软基处理的施工工艺、质量控制, 桩身密实度检测, 垂直沉降与侧位移监控等一套系统方法, 通过现场实测数据与设计沉降数据对比, 得出高填路堤软基处理地段综合运用新技术、新工艺与新材料的成功经验, 具有一定的推广价值。     

Low-frequency sound wave parameter measurement in gravels

Experiments were performed to measure the various sound-wave propagation parameters of two kinds of gravel, a crushed limestone and a stream-formed “pea gravel”, at frequencies between 25 and 200 Hz. The apparatus was a very large standing-wave tube with an array of microphones along its entire length. Measurements were made with the tube in the vertical position, filled to various depths, with a pressure-doubling barrier at the bottom. Values were determined for wavelength and attenuation in the gravel and for input impedance at the boundary between gravel and air. The basic analysis method was to fit the parameters of a presumed Green’s function representing the standing wave in the tube to the measured sound pressure amplitudes measured by the microphones. This worked well for some frequencies and some depths of gravel. In other cases, various modifications of the method gave more consistent results. For crushed limestone, the estimates of phase velocity and attenuation increased monotonically with frequency, ranging between 150 and 250 m/s and 0.1 and 0.8 Np/m, respectively. For pea gravel, the estimates increased monotonically with frequency, with values between 160 and 205 m/s and 0.4 and 1.1 Np/m, respectively.     

Effect of aggregate stockpile configuration and layout on dust emissions in an open yard

Fugitive dust emissions from stockpiles in an open storage yard of industrial sites and the subsequent atmospheric dust dispersion have brought about many environmental and economic problems. From the operational point of view, stockpile configuration and the pile’s layout parameters have to be considered due to the area restriction in a given location when designing an open storage system for bulk material like coal or iron ore. This paper employs CFD (Computational Fluid Dynamics) approach to describe the flow over the oval pile with flat-topped geometry under different wind directions. The results are compared to EPA experimental value to validate the simulation. Different pile arrangement scenarios with a constant material volume and a fixed height are comprehensively investigated. Data obtained are then integrated to estimate dust emissions of stockpiles by using the EPA estimation mode. Results suggest that changing pile arrangement space as well as pile configuration can reduce dust emissions in the open storage yard. It is found that, for the range of wind conditions and pile layouts tested, the eroded dusts produced by the flat-topped oval stockpile is 13–60% lower than the values of conical piles. In a real yard where many piles are stocked with specific arrangement spaces, a shadow effect created by the upward piles makes the exposure of downwind piles less to the wind erosion. Results show that compact arrangement among the flat-topped piles along dominant wind direction has a good overall protecting effect from wind and favors to minimize the eroded dusts.     

过湿黄土砾石桩复合地基处理的试验研究

过湿黄土是指含水量较高的黄土。过湿黄土土体含水量高、饱和度大、压缩性高以及土体浸水后强度显著降低。其性质随土体含水量变化而变化,给工程建设带来一定影响。本文结合某高速公路过湿黄土地基砾石桩复合地基的工程实践以及原位测试,分析加固前后复合地基的强度和变形,研究过湿黄土的力学特性。并总结不同成桩工艺对过湿黄土复合地基的加固适用性以及地基处理要点。     

DEM investigation of strain behaviour and force chain evolution of gravel–sand mixtures subjected to cyclic loading

The strain characteristic and load transmission of mixed granular matter are different from those of homogeneous granular matter. Cyclic loading renders the mechanical behaviours of mixed granular matter more complex. To investigate the dynamic responses of gravel–sand mixtures, the discrete element method (DEM) was used to simulate the cyclic loading of gravel–sand mixtures with low fines contents. Macroscopically, the evolution of the axial strain and volumetric strain was investigated. Mesoscopically, the coordination number and contact force anisotropy were studied, and the evolution of strong and weak contacts was explored from two dimensions of loading time and local space. The simulation results show that increasing fines content can accelerate the development of the axial strain and volumetric strain but has little effect on the evolution of contact forces. Strong contacts tend to develop along the loading boundary, presenting the spatial difference. Weak contacts are firstly controlled by confining pressure and then controlled by axial stress, while strong contacts are mainly controlled by axial stress throughout the whole cyclic loading. Once compression failure occurs, the release of axial stress causes the reduction of strong contact proportion in all local regions. These findings are helpful to understand the dynamic responses of gravel–sand mixtures, especially in deformation behaviours and the Spatio-temporal evolution of contact forces.     

长条形基坑带顶部支撑排桩支护体系空间变形研究

提出了一种建立具有固定双面约束多点摩擦的多体系统动力学方程的方法. 用笛卡尔坐标阵 描述系统的位形,根据局部方法的递推关系建立系统的约束方程,应用第一类Lagrange方程 建立该系统的动力学方程,使得具有摩擦的约束面的法向力与Lagrange乘子一一对应,便于 摩擦力的分析与计算,并用矩阵形式给出了摩擦力的广义力的一般表达式. 应用增广法将微 分-代数方程组转化为常微分方程组,并用分块矩阵的形式给出,以便于方程的编程与计算. 给出了一种改进的试算法,可提高计算效率. 最后给出了一个算例,应用试算法和RK法对算 例进行了数值仿真.