Dynamic impedance of pile and caisson foundations

Abstract

The dynamic impedance of a pile or caisson foundation embedded in a homogeneous visco elastic half‐space was evaluated using the hybrid method. The soil‐foundation system is partitioned into a near‐field and a far‐field by choosing a cylindrical interface passing through the soil region very close to the foundation. The near‐field is modeled by the finite element method while the far‐field is characterized by a frequency‐dependent impedance matrix through the continuum approach. From the results presented, it is shown that the proposed method is very effective and can be widely used for parameter studies in engineering applications.     

Numerical Analysis of Laterally Loaded Long Piles in Cohesionless Soil

The capability of piles to withstand horizontal loads is a major design issue. The current research work aims to investigate numerically the responses of laterally loaded piles at working load employing the concept of a beam-on-Winkler-foundation model. The governing differential equation for a laterally loaded pile on elastic subgrade is derived. Based on Legendre-Galerkin method and Runge-Kutta formulas of order four and five, the flexural equation of long piles embedded in homogeneous sandy soils with modulus of subgrade reaction linearly variable with depth is solved for both free- and fixed-headed piles. Mathematica, as one of the world's leading computational software, was employed for the implementation of solutions. The proposed numerical techniques provide the responses for the entire pile length under the applied lateral load. The utilized numerical approaches are validated against experimental and analytical results of previously published works showing a more accurate estimation of the response of laterally loaded piles. Therefore, the proposed approaches can maintain both mathematical simplicity and comparable accuracy with the experimental results.     

Highlighting the base zone effect on the compression and recovery properties of the rugs with innovating Double-Base Persian rug

This paper investigates the compression and recovery properties of the rugs by highlighting the base zone effect. To fulfill this purpose, a new type of rug named Double-Base Persian Rug was prepared. In the new rug, the warping was done such that we have two sets of warp sheets (back base and front base warp yarns). So that, a gap between these two bases were created that could be filled with various types of fillers. A total of seven rug samples; a conventional Persian rug as the base of comparison and six new types of rug samples were produced. Then, the compression and recovery properties of the rug samples were investigated by static loading test. Generally, the results indicated that the rug base structure and the inherent characteristics of the materials used in the rug base as a filler positive affect the rug compression and recovery properties.     

PHC管桩工程特性分析

以PHC管桩加固某电厂古河道地基为依托,进行了PHC管桩受力特性研究。利用桩身预先埋设的光纤传感器,并借助静载荷试验、高应变和静力触探等现场测试手段,研究了PHC管桩在不同级别荷载作用下桩身沿深度的受力分布特征,发现PHC管桩侧摩阻力不仅与地基土层性质相关,而且其分布特征也与桩埋置深度有很大关系;桩体上段摩阻力较小,中间段发挥度最大,下段桩身轴力衰减较快;根据试验结果提出了PHC管桩单桩承载力修正公式,用该式求得PHC管桩单桩承载力与静载荷试验结果吻合,说明修正公式是合理的。     

岩溶地基中超长桩承载力数值计算方法

针对岩溶地区溶沟、溶洞发育等复杂地层,提出基于最小势能原理的超长桩穿越岩溶地层时的承载力计算方法。首先,构建适用于岩溶地层的桩侧摩阻力计算模型;其次,分别推导了非岩溶地层和岩溶地层中桩身的能量平衡方程,并由此得到桩身单元的位移、轴力计算式;再次,基于最小势能原理推导了桩身的势能增量计算式,并采用黄金分割搜索法作为计算程序的收敛算法。最后,以娄新资水大桥桩基工程为算例,采用文中方法对工程桩进行计算,计算结果表明超长桩穿越岩溶地层时的承载力计算方法合理可行。     

水平受荷桩非线性m法研究

大量试验表明,水平荷载作用的单桩的m值随桩身泥面位移增大逐渐减小,然而现有相关规范没有给出大位移情况下m值的取值范围和选取方法,这对于实际工程设计的参数选择造成了一定困难。在大量的桩基水平静载荷试验实测资料的基础上,采用数理统计的方法建立了不同土质条件下土体的m值与桩身泥面位移的相互关系式,可用来计算水平推力桩在大位移情况下的m值,算例表明该方法具有较可靠的精度和较强的实用性。     

时域垂直载重桩反应与土体模式应用

本文以不同土壤弹簧和依时性阻尼系数 ,配合波动方程有限差分解仿真基桩反应。由t-z和Q-z曲线方程式所推求的弹性土层弹簧系数和依据三维波传递动力阻抗函数所建立之转换阻尼 ,可仿真桩载重反应。基桩位移量和位移历史和土 -桩界面模式相关。本研究模式和其它学者建议模式之差异显现于单调载重的桩顶位移量和冲击载重作用后桩顶位移之衰减 ,调整转换阻尼参数和土壤弹簧系数值可减少分析差异。透过土层弹簧系数修正 ,该项分析模式可仿真桩设计位移曲线和现场桩载重试验数据。     

经编毛巾织物的计算机仿真

 本文介绍了经编毛巾织物的编织原理和设计方法,以毛圈建模数据分析和毛圈形态影响因素分析为基础重点提出了一种经编毛巾织物仿真的新方法——毛圈模型填充法。通过研究单个毛圈建模数据中各要素与组织结构、原料之间的关系,建立了理想状态下的基础毛圈模型,接着分析了影响毛圈实际形态的各因素之间的关系,并在此基础上研究了如何生成形态各异的仿真用毛圈模型以及毛圈模型数据库的建立方法,最后运用计算机技术实现了经编毛巾织物的仿真。     

小麦堆修正剑桥模型的参数研究

通过TSZ-6A应变控制式三轴仪对小麦堆(宁麦13号)进行三轴压缩试验,测定并计算出小麦堆修正剑桥模型的参数:临界状态应力比M、对数硬化模量λ、等向膨胀指数κ和弹性模量E。试验结果表明:小麦堆含水率为10.20%,12.46%,14.05%w.b.时,临界状态应力比M分别为0.924 9,1.013 1,0.978 5;对数硬化模量λ分别为0.067 7,0.061 3,0.073 3;等向膨胀指数κ分别为0.025 4,0.027 0,0.026 3。含水率对M、λ和κ无显著性影响,对试验数据进行分析,推导出弹性模量E与广义剪切力q和平均主应力p的关系式。     

散粮堆底部压力颗粒流数值模拟分析

在前期散粮堆底部压力现场试验研究的基础上,利用PFC3D软件建立了相应的颗粒流数值模型,对散粮堆底部压力进行数值模拟分析。根据数值模拟得到的数据,利用MATLAB绘制了散粮堆底部压力分布三维网格图,直观地反映散粮堆底部压力分布形态。数值模拟结果表明,散粮堆底部压力分布是非均匀的,与现行的粮食平房仓设计规范以及传统的连续介质力学理论有所不同。数值模拟结果与前期现场试验结果基本吻合,进一步证实了散粮堆底部压力非均匀分布的特性,加深了对散体力学特性的认识和理解。