基于颗粒介质的桩承式路堤土拱效应试验分析

土拱效应的形成和荷载传递机制是进行桩承式路堤中桩土相互作用分析的关键性技术问题。为了探究宏观土拱效应形态的演化过程,借助于传统的光弹试验技术,研制出一种直径为3 mm的聚碳酸酯颗粒,通过自制的加载装置和光测力学图像处理系统,实现了桩承式路堤内部应力分布的可视化,直接观测到模型内部力链网格的产生、分布及变化,求得不同高跨比下桩土应力比变化,并与数值模拟的对比分析。结果表明,随着高跨比的减小,土拱形状由三角形变为半圆形,桩土应力比逐渐减小,当填土高度与桩间距的比值 时,可以形成完整的土拱;当 时,土拱效应开始消失。     

加筋路堤临界高度上限分析

依据加筋理论,假定加筋路堤边坡的破裂面为对数螺旋面,运用极限分析的上限原理推导加筋路堤临界高度的上限解。在不计加筋力时,该解与无筋路堤的临界高度一致。结合算例,得出加筋能提高路堤临界高度的结论。     

土工格室加筋土垫层路堤临界高度研究

土工格室能有效减少软土地基上路堤的变形,并增强其稳定性,但对于土工格室加筋土垫层路堤的临界高度还少有研究。采用极限平衡分析方法,假定地基在路堤荷载作用下呈圆弧滑动破坏模式,将格室及其内的填土视为复合体,考虑格室复合体的应力扩散作用和侧向限制作用,提出了路堤临界高度的计算模型,并将该模型值与建立的有限差分模型结果进行对比,然后讨论了格室高度、应力扩散角及格室复合体与地基接触面摩擦系数对路堤临界高度的影响规律。结果表明,理论分析和数值计算结果吻合较好;加筋路堤的临界高度明显大于未加筋路堤的临界高度,并且增加此3种影响因素的取值均能提高路堤的临界高度;同时增强格室的侧向限制作用比提高格室高度和应力扩散角更有利于路堤的稳定。     

Shear strength studies on soil-quarry dust mixtures

Due to the high demand for rubble and aggregates for construction purposes, rubble quarries and aggregate crushers are very common. Out of the different quarry wastes, quarry dust is one, which is produced in abundance. About 20–25% of the total production in each crusher unit is left out as the waste material-quarry dust. Bulk utilization of this waste material is possible through geotechnical applications like embankments, back-fill material, sub-base material and the like. It becomes a useful additive to the natural soil to improve its strength characteristics. For the above applications one of the important engineering properties is the shear strength. The purpose of the present investigation is to understand the shear strength behavior of quarry dust and soil-quarry dust mixes.     

Bridge–embankment interaction under transverse ground excitation

Seismic performance and dynamic response of bridge–embankments during strong or moderate ground excitations are investigated through finite element (FE) modelling and detailed dynamic analysis. Previous research studies have established that bridge–embankments exhibit increasingly flexible performance under high‐shear deformation levels and that soil displacements at bridge abutment supports may be significant particularly in the transverse direction. The 2D equation of motion is solved for the embankment, in order to evaluate the dynamic characteristics and to describe explicitly the seismic performance and dynamic response under transverse excitations accounting for soil nonlinearities, soil–structure interaction and imposed boundary conditions (BCs). Using the proposed model, equivalent elastic analysis was performed so as to evaluate the dynamic response of approach embankments while accounting for soil–structure interaction. The analytical procedures were applied in the case of a well‐documented bridge with monolithic supports (Painter Street Overcrossing, PSO) which had been instrumented and embankment participation was identified from its response records after the 1971 San Fernando earthquake. The dynamic characteristics and dynamic response of the PSO embankments were evaluated for alternative BCs accounting for soil–structure interaction. Explicit expressions for the evaluation of the critical embankment length L_c are provided in order to quantify soil contribution to the overall bridge system under strong intensity ground excitations. The dynamic response of the entire bridge system (deck–abutments–embankments) was also evaluated through simplified models that considered soil–structure interaction. Results obtained from this analysis are correlated with those of detailed 3D FE models and field data with good agreement. Copyright © 2007 John Wiley & Sons, Ltd.     

Stability assessment of a circular earth dam

Stability of a circular earth dam is assessed for radial cracking potential and static slope stability using continuum mechanics‐based three‐dimensional numerical models. Comparisons of numerical model results for a circular water tank with vertical walls and different radii with their analytical counterparts are included to support the validity of the ideas and their implementation in the continuum mechanics‐based computer program used. Effects of sloping wall faces and Poisson's ratio on computed deformations and stresses are also included. The same numerical models are used to assess stability of a circular dam in terms of factor‐of‐safety and associated failure surface. Three‐dimensional slope stability analysis results are compared with continuum based two‐dimensional slope stability analysis results to assess the magnitude of 3D effects. Example problems are included to illustrate the use of ideas presented. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

Y型沉管灌注桩加筋路堤力学性状试验研究

结合申嘉湖杭（上海―嘉兴―湖州―杭州）高速公路嘉兴段Y型沉管灌注桩处理桥头软基实体工程,通过路堤填筑荷载下Y型沉管灌注桩加筋路堤路基表面及桩帽上下应力分布的现场试验研究,获得了路堤荷载下桩帽间土体表面应力、桩帽上应力及桩帽下土体表面应力的分布及变化规律,比较了距桩不同位置处桩帽间土体表面应力差别、桩帽上与桩帽下应力差别、桩帽下与桩帽间土体表面应力差别、桩帽上与桩顶上应力差别,分析了桩-土应力比及荷载分担比在路堤填筑荷载下变化趋势及规律。通过特殊加载时间段,分析了路堤填筑加载后应力及桩-土应力比调整规律。通过路堤进入预压期后的观测数据,分析了路堤进入预压期后桩-土应力比及荷载分担比变化规律。     

Field Placement and Evaluation of Stabilized Dredged Material (SDM) from the New York/New Jersey Harbor

Since the 1997 local ban on ocean dumping of dredged sediments, the States of New York and New Jersey have pursued a policy of environmentally sound solutions to the management of dredged material, including beneficial use of stabilized dredged material (SDM) in transportation applications. A pilot study was initiated in 1998 to evaluate the use of SDM in the construction of highway embankments. Utilizing 80,000 cubic yards of dredged material, two embankments were constructed from SDM on a commercial development area adjacent to the Harbor. Geotechnical properties and handling of SDM were evaluated both during and one year post ? construction. This article presents the evaluation of the embankments themselves, including constructability and performance. The results demonstrate that SDM satisfies most of the geotechnical criteria for fill construction, except those for durability, requiring proper coverage and protection similar to that provided for fills constructed on cohesive soils. This same characteristic precludes long term stockpiling of SDM prior to final placement, limiting applications to those that have schedules overlapping with dredging projects. Increased costs for the use of SDM can be as high as $8 per cubic yard over traditional fills; however, this cost may be recouped through management fees collected from dredging projects.     

Recent floods in Bangladesh: Possible causes and solutions

In recent years the frequency of abnormal floods in Bangladesh has increased substantially, causing serious damage to lives and property. The most crucial questions that need to be addressed are: what really causes the havoc-creating floods and is there any solution to the problem? The heavy monsoon downpour and synchronization of flood-peaks of the major rivers are generally considered to be the main causes of the floods. Some underlying factors also deserve serious consideration as possible contributors to the recent floods: change in the base level of the rivers due to local sea level rise and subsidence, inadequate sediment accumulation on flood plains, a possible increase in the watershed area due to seismic and neotectonic activities in the region, river bed aggradation due to siltation and damming of rivers, soil erosion due to unwise tilling practices, deforestation in the upstream region, and excessive development and population growth. Without regional cooperation among the co-riparian nations any major interbasin flood control activity is considered to be almost impossible. However, among other proposals in this paper, extensive annual dredging of the rivers, channels and creeks, and reoccupation of the abandoned channels in Bangladesh through re-excavations could still increase the water carrying capacity of the rivers. Land elevations could be increased if the dredged or excavated materials are dispersed on the flood plains, which would in turn reduce the severity of floods.     

桩承式路堤承载特性的颗粒流模拟

现有的土拱效应计算方法中,由于采用的计算模型不同,计算结果差异很大。文中克服传统连续介质力学模型的宏观连续性假设,采用二维颗粒流程序（PFC）建立基于模型试验的细观数值分析模型,对桩承式路堤中土体接触力、应力分布、主应力方向、竖向位移进行分析,并比较计算和实测结果,研究土拱效应的荷载传递机制。同时,对不同桩帽、桩间距、填土高度、颗粒大小、摩擦角的情况进行PFC方法的参数敏感性分析。研究结果表明,桩承式路堤桩顶处局部范围可按弹性核考虑;土拱的分布型式受桩帽型式、桩净距、格栅的影响;实际土拱作用的影响范围主要集中在路堤底面以上约1倍桩净距的区域;土拱内部的竖向应力和水平应力均随深度非线性改变,桩土应力比随着荷载水平、土体内摩擦角、颗粒大小的增大而增加。