Earthquake retrofit of highway/railway embankments by sheet-pile walls

A series of highly instrumented dynamic centrifuge model tests were performed to investigate the potential of using sheet-pile walls for mitigating the adverse effects of foundation liquefaction on overlying highway embankments. The response of a prototype 4.5 m high cohesive highway embankment supported on a 6 m thick loose saturated sand layer was analyzed under dynamic base excitation conditions. In a series of four separate model tests, this embankment-foundation system was studied first without, and then with the following three different liquefaction countermeasure techniques, all involving sheet-piles: (a) sheet-pile extending to the foundation surface, (b) sheet-pile with toe area gravel surcharge berm, and (c) sheet-pile with toe area gravel surcharge berm extending into the foundation. Model response was monitored by numerous accelerometers, pore pressure transducers, and displacement gages. The underlying mechanism and effectiveness of each countermeasure is discussed based on the recorded dynamic response. All of the implemented countermeasures were found to significantly reduce embankment deformations. Particularly in the case of the sheet-pile with toe area gravel berm, cracking and lateral spreading of the embankment were practically eliminated. This revised version was published online in July 2006 with corrections to the Cover Date.     

预应力锚索桩板墙动态响应规律研究

随着公路交通流量增加及超载车辆增多,交通荷载对支挡结构的受力变形特性影响越来越大。通过FLAC3D软件建立预应力锚索桩板墙空间分析模型,并与现场动应变测试结果进行比较,探讨了交通荷载作用下挡墙的受力变形机制。结果表明：交通荷载在路基与挡墙中所反映的影响深度大致都为2 m左右,正常情况下（重型汽车满载、行驶在行车道上）作用在预应力锚索桩板墙上的动土压力大约为该处挡墙静止土压力的10 %。     

一种新型板桩码头结构的离心模拟

卸荷式地连墙板桩结构码头是国内自主创新的深水码头结构,为了深入认识这一板桩码头结构在设计荷载下的工作性状和土与结构共同作用机制,结合某一拟建码头泊位的卸荷式地连墙板桩码头结构设计方案验证需要,进行了3组大型土工离心模型试验研究。其中2组为重复性的模型试验,以验证设计方案的可行性;第3组则模拟了无卸荷平台结构的地连墙板桩码头结构设计方案,以比较有无卸荷平台的板桩码头来揭示全直桩卸荷平台结构的卸荷效果。并且介绍了码头结构离心模拟技术,包括模型设计、模型制作和模型测量及试验步骤等关键内容。     

钱塘江河口护塘丁坝的研究进展

从作为河道整治或护岸的辅助建筑物的丁坝的原型观测、模型试验到工程实践等多种手段对钱塘江强潮河口段各个历史阶段护塘丁坝的研究成果进行了回顾和总结。钱塘江护塘丁坝技术在抗击强涌潮的过程中被不断推进、发展和创新,为钱塘江海塘的防护发挥了至关重要的作用。     

Earth pressure on an unloading-type sheet-pile: High-pile beam-slab wharf structure

Abstract

This study analyzes a new wharf structure using a method to calculate earth pressure on a covered type sheet-pile wharf. The earth pressure on the riverside of the sheet pile and the landside of the concrete compresol pile is calculated using the earth pressure theories of Coulomb and Rankine. The earth pressure of the landside of the sheet pile and riverside of the concrete compresol pile is deduced by considering the soil arching and plate-unloading effects and a parallel walls theory. To analyze the distribution of earth pressure on the unloading sheet-pile, geotechnical-centrifuge model tests were conducted to validate the design structure of the newly reconstructed wharf structure. The test results show that the earth pressure on the riverside of the sheet pile is high at the end of the wall, decreases slightly, initially, with the increase in the depth, and then increases rapidly. However, the earth pressure on the landside of the sheet-pile initially increases to a maximum with depth and then decreases slowly with depth. With the increase in depth, the earth pressure on the riverside of the concrete compresol pile increases, while that on the landside of the concrete compresol pile first increases and then decreases.     

高速铁路小变形下陡坡地基路肩桩板墙力学响应

掌握高速铁路陡坡地基条件下路肩桩板墙力学特性是路堤侧向变形控制的关键。以贵广高速铁路某陡坡地基路肩桩板墙为试验工点,对墙背土压力、桩身内力与变形进行了900余天现场长期观测,讨论了墙后路堤分层填筑引起的墙土侧向变形形态差异及机械碾压残余应力对土压力分布的影响。结果表明：适应高速铁路小变形要求的强约束、深锚固路肩桩板墙能有效控制陡坡地基路堤侧向变形,桩体仅呈0.94‰的近似刚性转动,填筑完成后变形约占30%,且1.0～1.5 a趋于稳定;经碾压密实的墙后粗粒土填料,即使在小变形下依然能达到主动土压力状态;分层填筑引起墙后填土侧向变形呈现的“上小下大”分布形态与墙体位移相反,是墙背土压力呈现出中部大、两端小抛物线分布模式的重要因素;基于适筋梁受力状态及平截面假定,分别结合实测钢筋应力与混凝土应变换算得到的桩身弯矩具有良好的一致性,与极限地基反力法的理论计算吻合。     

基于贝叶斯方法的船坞双排钢板桩围堰整体稳定性可靠度分析

双排钢板桩围堰的整体稳定性具有较大的不确定性,同样安全系数情况下对应的失稳概率可能不同。为了更准确地分析双排钢板桩围堰的整体稳定性,降低稳定性分析中的不确定性,采用贝叶斯方法对船坞双排钢板桩围堰的整体稳定性进行可靠度分析。首先通过统计数据获取土体参数的先验分布,然后基于实测数据采用贝叶斯方法更新参数以得到后验分布,最后根据参数的后验分布采用一次二阶矩计算围堰结构的可靠度。贝叶斯方法从理论的角度解决了已有工程经验和实际案例数据两方面信息有效综合的问题,能在更接近实际情况的前提下进行可靠度分析。     

遮帘式板桩码头地基地震液化破坏机理

遮帘式板桩码头作为一种新型的板桩结构型式,其抗震性能研究是设计建造过程中的重要环节。在FEM-FDM水土耦合计算的平台上引入循环弹塑性本构模型,借助FORTRAN编程软件形成饱和砂土动力液化分析的数值方法,可有效模拟饱和砂土在地震动力作用下的非线性及大变形特性,同时也可模拟砂土液化流动对遮帘桩和前墙的动土压力。研究表明:地震作用下可液化土层超孔隙水压力比增长并发生较大的水平流动变形,对前墙的水平破坏大于竖向破坏;前墙剪力最大值位于海床与前墙交界处;遮帘桩剪力最大值位移与前墙底平行的位置;后拉杆拉力逐渐变大,前拉杆拉力逐渐变小。通过对板桩码头地震液化灾害的分析,可为抗震和抗液化设计提供参考依据。     

桩板墙土拱效应及土压力传递特性试验研究

为更深入地研究桩板墙背侧的土拱效应,分析其土压力荷载的作用规律及传递特性,进一步揭示桩板墙土拱效应与荷载分配之间的联系,采用现场大型试验及室内模型试验开展相关的监测研究工作。基于对土拱结构承载机制的认识,将作用于桩背侧与桩间挡板中部土压力的比值作为衡量土拱效应作用效果的直观标准。在某一自然边坡上,设计施工桩板墙堆载试验的模型槽,在挡土板与抗滑桩背侧分别安装土压力计,并开展持续21 d的现场试验监测。现场试验结果表明,随着时间的发展,该土压力的比值呈现先增加后趋于稳定的特点,时间效应相对较显著。还设计多工况室内模型推桩试验,为深入分析桩板墙背侧土拱效应与土压力传递特性之间的关系,试验重点对挡板刚度、桩间距、填料性质和挡板布置方式对桩板墙土拱效应的影响进行对比研究,并揭示被动状态下桩板墙背侧的土压力传递特性。     

船坞施工中钢板桩围护技术与监测

在坞口挖土过程中，因围堰位移较大，采取在开挖处进行回填土，并采用双排钢板桩作为临时支护，内设三道支撑分层、分段开挖，同时加强对围堰及坞口支护的监测，使得整个围堰安全地度过坞口施工期。