Comparative analysis on performance of vertical drain improved clay deposit under vacuum or surcharge loading

This paper presents two well-instrumented large-scale field tests of PVD-improved soft soil with vacuum and surcharge preloading, respectively. The two large-scale field tests were conducted adjacent to each other with the same preload. A comparative analysis was performed to investigate the performance of subsoil (i.e., the ground settlement, the layered settlement, the lateral displacement of subsoil and pore water pressure) under vacuum preloading and equivalent surcharge preloading. Some design methods were verified based on the field data. Cone Penetration Tests (CPT) and Vane Shear Tests (VST) were conducted to assess the improvement effects on subsoil after preloading. The results showed that as compared with surcharge preloading, vacuum preloading mitigated the differential settlement of the ground. The vacuum pressure transmitted into the soil with a minor loss through the PVD length. From a practical point of view, the improvement effects by vacuum preloading and surcharge preloading were similar in terms of influence depth and soil strength based on the in-situ tests.     

十圩港大桥反吊支架设计与施工

结合工程实例，对反吊支架体系的设计进行了介绍，从支架体系的安装、堆载预压、过程监控、支架体系的调整及拆除等环节阐述了支架体系的施工方法，并对其体系进行了验算，为类似桥梁提供了施工经验。     

压机组合框架结构的预紧参数优化

经典组合结构压机机架的预紧设计在以横梁为刚体的假设下,给出不开缝条件和预紧设计方法,与真实情况不符。在以横梁为弹性体的假设下,给出压机组合框架结构新的不开缝条件,并用温度场迭加法模拟因预紧产生的框架内力。文中采用约束变尺度法建立了确定预紧力和拉杆直径的优化计算模型,算例表明该方法可行。     

起始水力梯度对真空预压下砂井地基固结过程的影响

针对粘土中孔隙水渗流存在起始水力梯度的现象,将考虑起始水力梯度的非Darcy渗流方程引入传统的砂井固结理论对其进行修正,并给出了真空预压下砂井地基固结近似解。探讨起始水力梯度对真空预压下砂井地基固结过程的影响,包括渗流前锋面的运动规律、孔隙水压力的分布变化规律和平均固结度的变化规律。结果表明,由于存在起始水力梯度,会延缓真空压力的传播,进而影响孔隙水的渗流和整个土层的固结速度。起始水力梯度越大,滞后现象越明显。此外,起始水力梯度的存在将使平均孔隙水压力逐渐趋于某一稳定值,但无法达到真空压力,所以最终平均固结度将小于100%,且其值随起始水力梯度的增大而减小。     

真空预压软基处理法在深基坑支护工程中的应用

软弱地基上的深基坑开挖一直是基础工程的重难点,关系到边坡稳定、基坑支护成本、桩基的安全等问题。中山港口某项目,占地面积5.3万m2,基坑深约4 m,地处深厚淤泥之上,如何保证基坑开挖以及工程桩的安全成为重难点。经70余天的真空预压处理,场地沉降约1 m,基底上下5 m范围内的淤泥固结成了软塑状的淤泥质土,其承载力等力学性能得到很大提高,使基坑支护工程和土方开挖的难度大大降低。文章以该项目深基坑支护工程为背景,详细论述了真空预压软基处理方法的施工工艺、处理效果以及施工注意事项,其在深基坑支护工程中的成功运用可供类似工程参考。     

铝合金电阻点焊预压接触分析

为了探究铝合金电阻点焊的接触压力分布及初始导电区域,利用ABAQUS软件建立球面形电极条件下的预压接触二维轴对称有限元模型并对模型施加不同的电极压力.在可视化模块中得到了各个接触面上接触压力随载荷变化曲线、电极上的轴力分布云图及工件内的有效塑性应变云图.有限元分析结果表明,各接触面上的接触压力分布是不均匀的,电极-工件间的接触压力受电极球形端面轴向应力分布影响;工件间接触压力与材料所处状态有关;随着电极压力的增大,工件间接触半径呈线性增长.说明电阻点焊时可以通过选取不同截面的电极来改善接触压力的分布,进而改变初始导电区域的大小.     

气泡混合轻质土置换高速公路路堤工后沉降研究

以申嘉湖杭高速公路（练杭段）堆载预压处理段路基沉降速率较大断面采用气泡混合轻质土置换高速公路路堤为例,采用土体弹塑性本构模型及Sjerrum等时e—lgp曲线理论,对置换后地基土体的应力路径变化进行理论分析,地基土处于超固结状态;通过现场实测沉降资料,置换前处理段沉降观测点月沉降量在14mm～18mm,置换后沉降观测点月沉降量在2nm～4mm,沉降速率收敛较快,处理后效果明显,能够有效减少工后沉降。结果表明,采用气泡混合轻质土置换高速公路路堤不仅施工方便,质量容易控制,而且处理效果显著,是一种有效的减少软土地基工后沉降的控制方法。     

真空-堆载联合预压法在软土路基处理中的应用

以苏州市工业园区桑田岛河湖相软土地基为研究背景,介绍了真空-堆载联合预压法的加固机理和桑田岛软土地基的工程地质条件,经过现场踏勘和室内土工试验的分析拟采用真空-堆载联合预压法对该软土地基进行处理。通过对真空预压试验段的地表沉降、水平位移的监测分析,对路基加固效果进行了评价,认为本试验段采用真空-堆载联合预压法处理是成功的,有效的提高了软土地基的物理力学性质及承载能力,在类似工程中推广应用是可行的。     

Vacuum preloading combined electroosmotic strengthening of ultra-soft soil

To assess the effectiveness of vacuum preloading combined electroosmotic strengthening of ultra-soft soil and study the mechanism of the process, a comprehensive experimental investigation was performed. A laboratory test cell was designed and applied to evaluate the vacuum preloading combined electroosmosis. Several factors were taken into consideration, including the directions of the electroosmotic current and water induced by vacuum preloading and the replenishment of groundwater from the surrounding area. The results indicate that electroosmosis together with vacuum preloading improve the soil strength greatly, with an increase of approximately 60%, and reduce the water content of the soil on the basis of consolidation of vacuum preloading, howeve~ further settlement is not obvious with only 1.7 mm. The reinforcement effect of vacuum preloading combined electroosmosis is better than that of electroosmosis after vacuum preloading. Elemental analysis using X-ray fluorescence proves that the soil strengthening during electroosmotic period in this work is mainly caused by electroosmosis-induced electrochemical reactions, the concentrations of Al2O3 in the VPCEO region increase by 2.2%, 1.5%, and 0.9% at the anode, the midpoint between the electrodes, and the cathode, respectively.     

大面积堆载作用下地基变形影响分析

通过具体工程实例,对大面积堆载作用下软土地基变形进行了详细计算与分析,并与复合地基处理后的地基变形量进行了对比。分析认为大面积堆载对地基变形影响深度较大,超出了常规荷载作用下的影响深度;与复合地基相比,大面积堆载地基变形量要多出25倍左右;大面积堆载影响深度范围内,要考虑负摩阻力作用。