Limit analysis method for active earth pressure on laggings between stabilizing piles

Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground, laggings are usually installed to avoid collapse of soil between piles. Evaluating the earth pressure acting on laggings is of great importance in design process. Since laggings are usually less stiff than piles, the lateral pressure on lagging is much closer to active earth pressure. In order to estimate the lateral earth pressure on lagging more accurately, first, a model test of cantilever stabilizing pile and lagging systems was carried out. Then, basing the experimental results, a three-dimensional sliding wedge model was established. Last, the calculation process of the total active force on lagging is presented based on the kinematic approach of limit analysis. A comparison is made between the total active force on lagging calculated by the formula presented in this study and the force on a same-size rigid retaining wall obtained from Rankine's theory. It is found that the proposed method fits well with the experimental results. Parametric studies show that the total active force on lagging increases with the growth of the lagging height and the lagging clear span; while decreases as the soil internal friction angle and soil cohesion increase.     

A theoretical analysis of the bearing performance of vertically loaded large-diameter pipe pile groups

This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups. The interactions between group piles result in different bearing performance of both a single pile and pile groups. Considering the pile group effect and the skin friction from both outer and inner soils, an analytical solution is developed to calculate the settlement and axial force in large-diameter pipe pile groups. The analytical solution was verified by centrifuge and field testing results. An extensive parametric analysis was performed to study the bearing performance of the pipe pile groups. The results reveal that the axial forces in group piles are not the same. The larger the distance from central pile, the larger the axial force. The axial force in the central pile is the smallest, while that in corner piles is the largest. The axial force on the top of the corner piles decreases while that in the central pile increases with increasing of pile spacing and decreasing of pile length. The axial force in side piles varies little with the variations of pile spacing, pile length, and shear modulus of the soil and is approximately equal to the average load shared by one pile. For a pile group, the larger the pile length is, the larger the influence radius is. As a result, the pile group effect is more apparent for a larger pile length. The settlement of pile groups decreases with increasing of the pile number in the group and the shear modulus of the underlying soil.     

嘉兴市地下水资源开发区域规划

本文通过区域水文地质条件、地下水动态及环境地质问题的分析研究,针对当前嘉兴市地表水遭受污染,地下水严重超采,造成区域地下水位下降及地面沉降等环境地质问题,利用长期监测资料进行地下水开来资源评价,提出合理开发利用地下水资源的区域规划意见,为政府部门水资源综合规划、确定地下水开采量、实施地下水资源开发利用监督管理提供了科学依据。     

大直径深埋顶管施工对地表沉降的影响

顶管施工因非开挖或少开挖而在城市建设中应用广泛,但顶管施工引起的地表沉降不容忽视。依托佛山市某电力隧道顶管工程,通过现场实测、数值模拟及Peck经验公式的方法研究了顶管施工引起的地表沉降规律,探讨了管-土摩擦、注浆压力及支护压力对地表沉降的影响。结果表明：顶管施工引起的横向地表沉降在距轴线约4倍管径范围内变化较大,管-土摩擦的改变对横向地表距轴线约3倍管径范围内的地表沉降影响较大,对纵向地表距开挖面约1倍管径范围内的地表沉降影响较小;注浆压力的增大能够抑制地表沉降;支护压力的改变对横向地表距轴线约2倍管径范围内的地表沉降影响较大。研究结果可为控制顶管施工引起地表沉降措施的制定提供参考;同时,实测值、模拟值及Peck经验公式所得到的地表沉降变化趋势和大小相近,验证了数值模拟及Peck经验公式在实际工程中预测地表沉降的可行性。     

基于“三段法”的锚拉桩桩身内力计算方法与应用

针对抗滑桩常因地质条件、地形地貌等原因导致受荷段底面与嵌固段顶面不在同一水平面的情况,将此段划为次受荷段,并推导了次受荷段桩后设计荷载大小计算公式和荷载分布公式,以及在弹性地基梁和悬臂梁模型下的适用于悬臂桩和锚索桩内力与挠度计算通用公式。以巴东县焦家湾移民安置点库岸防护工程预应力锚索桩为例,研究次受荷段对抗滑桩内力和挠度影响。结果表明:忽略次受荷段后土压力作用的传统计算方法会使桩身弯矩计算结果偏小,导致桩身配筋量不足,存在设计安全隐患。再以锚索排数、位置为控制变量,研究其对预应力锚索桩内力和挠度的影响,提出预应力锚索可有效地降低抗滑桩工程造价;增加预应力锚索的排数有利于调节抗滑桩内力分布,设计时应优先考虑将锚索设置为多排锚索。      

Study on adverse effects of groundwater level rising induced by land creation engineering in hilly and gully area of the Loess Plateau

Land creation projects have been implemented in China to expand urban space in mountainous areas. In addition to the predictable settlement brought about by filling construction,varying degrees of land subsidence and engineering failures have a demonstrated relationship to groundwater level fluctuation induced by land creation engineering. In this work, we adopted a typical large-scale land creation project, Yan'an New City in Shaanxi province, West China, as our study area. Prior to conducting the main experiment,preliminary field investigation and groundwater level monitoring were conducted to determine the groundwater fluctuation trend induced by land creation engineering. Although a blind drainage system was implemented, the depth aspect of groundwater level changes after large-scale land creation still needed to be addressed. To study the degree of impact and the settlement mechanism induced by the rising groundwater level, we conducted a Water Immersion Test(WIT) in a typical land creation site for 107 days. The rising groundwater level was simulated by injecting water from the bottom of the filling foundation. During the WIT, the soil water content, surface subsidence, and internal settlement of soil at different depths were obtained. Surface subsidence development could be categorized into four stages during the water level increase. The second stage, which is defined as the point when the groundwater level rises to 10 m,marked the critical point in the process. Furthermore,it was ascertained that the local settlement in regions that were originally composed of steep slopes is larger than that in originally flat areas. In addition, ground cracks and sinkholes in the study area were inspected;and it was determined that they would become new channels that would accelerate water infiltration and exacerbate the settlement. Based on the results from our field investigation and testing, several suggestions are proposed for land creation projects to mitigate issues associated with construction-induced groundwater level rising.     

FEM for stability analysis against overturning of portal water injection sheet pile

Portal water injection sheet pile （PWISP）, as a retaining wall, appeared in seashore engineering in 2000. Although there have been many systematic methods addressing the issue, there are very few focusing on the new structure because of the difficulties in defining the earth pressure between the two piles. A new method is proposed in this paper to obtain the earth pressure between the PWISPs. Stability analysis against overturning follows as a consequence. Using Finite Element Analysis （FEA） software ANSYS, both the nonlinear characteristics of the soil and those of the contact elements are taken into account to obtain the earth pressure distribution on the contact surface. Based on the results of the FEA, Rankin＇s theory and the slip plane theory, the formula of the earth pressure on the inner surfaces between the piles is given. Assuming the PWISP as the analysis object and the earth pressure as an outside force acting upon it, the equation of stability against overturning of the PWISP is presented. Finally, some parameters are discussed about the stability of the PWISP against overturning, such as the embedded depth of the front pile, the distance between the two rows of piles, the internal friction angle and the cohesion of the earth. The results show that the increase of the cohesion and the internal friction angle will decrease the distance and the embedded depth, and therefore enhance the stability against overturning. Specifically, when the distance is 1/3-2/3 of the maximal excavation depth, the two rows of piles give the best performance in stability.     

地铁换乘站基坑变形流固耦合数值分析研究

地铁换乘站基坑在施工过程中要严格控制其变形及对周边环境产生的影响。尽管流固耦合与非流固耦合分析结果有一定差异,但现有地铁换乘站基坑开挖变形计算中较少考虑流固耦合作用。本文针对济南长途汽车站地铁换乘站进行基坑变形分析,建立了考虑流固耦合的三维有限元模型,根据模拟结果,确定出地连墙最大侧向位移及地面沉降最大值发生的位置,并对地铁换乘站基坑变形规律进行了总结和分析。本文研究成果可以为类似地下工程基坑分析计算和施工设计提供有益参考与借鉴。     

成层土中轴横受荷桩水平响应的非线性解

对于承受轴向荷载的水平受荷桩，以往研究大多基于线弹性或弹塑性水平荷载传递模型。为提升轴横受荷桩的计算设计水平，采用轴向荷载传递法计算桩身轴力，考虑桩身轴力引起的P-Δ效应，基于双曲线型水平荷载传递模型考虑桩-土体系变形的非线性特征，对成层土中轴横受荷桩的水平响应进行分析求解，得到了轴横荷载作用下桩身变形和内力的非线性有限差分解，并采用MATLAB语言编制了计算程序。使用模型试验算例与基于现场试验的有限元算例对非线性解的准确性进行对比验证，结果表明:计算结果与算例数据吻合良好，可靠性较高；采用不同荷载传递模型的计算结果在不同荷载水平下有所差异，在较大荷载水平下桩-土变形的非线性特点不容忽视。      

西安地铁隧道穿越饱和软黄土地段的地表沉降监测

以西安地铁一号线朝阳门站—康复路站区段饱和软黄土地铁隧道为研究对象,通过施工期现场地表沉降变形监测,分析了在饱和软黄土特殊地层条件下隧道浅埋暗挖法施工引起的该区段地表沉降变形规律以及地表沉降槽分布特征。结果表明:在饱和软黄土隧道开挖时,随着掌子面的推进,隧道顶地表沉降可分为沉降微小阶段、沉降显著发展阶段、沉降缓慢阶段和沉降稳定阶段;单线隧道开挖后的最大地表沉降量为18.89mm,双线隧道开挖后的最大地表沉降量为36.4mm;已开挖隧道对围岩土体的扰动作用使得后开挖隧道的地表沉降发展较大;双线隧道的地表沉降槽宽度接近单线隧道沉降槽宽度的2倍,因此可以将其近似为单线隧道地表沉降槽宽度与双线隧道轴线中点距离之和;单线隧道开挖后地表沉降槽宽度为8.4～9.3m,双线隧道开挖后地表沉降槽宽度为16.2～17.5m;隧道开挖施工的沉降槽宽度参数为0.435～0.467,单线隧道开挖后的地层损失率为0.765%～1.324%,双线隧道开挖后的地层损失率为1.231%～2.200%。     

层状地基中桩的轴向静载沉降特性

采用双折线荷载传递函数,根据桩在竖向静载下的荷载分布与传递规律,运用功的互等定律,导出了一组确定层状地基中桩的轴向荷载沉降曲线的解析简化递推算式,可根据桩侧介质的分布情况和桩的形状对桩进行沉降分析模拟,能较精确确定桩的轴向静载沉降曲线,同时推导了桩顶刚度系数的迭代公式,以此为基础可确定桩的承载力。结合运用实例进行了论证,说明了方法的有效性和正确性。     

局部桩筏基础的设计与施工

以加拿大多伦多市某工程为例,介绍了在复杂地质条件下采用局部桩筏基础(PPRF)的设计及施工问题;探讨了设计PPRF的决定性因素;在保持PPRF设计的完整性前提下,提出了单位沉降量的准则,并用于筏板和桩的设计;计算了PPRF的滑移及转动;最后,采用有效方法对该工程采用的局部桩筏基础进行了计算分析.结果表明,PPRF的设计主要取决于侧向土压力、分布不均的建筑荷载以及地基土的非均匀承载力,工程桩应主要布置在沉降较大的区域,即位于筏板基础承受高压力而土体承载力较低的西北部.探讨局部桩筏基础的设计与施工为该类型工程的基础设计提供了一个新的解决途径.     

新增大楼对地倾斜观测的影响

根据弹性力学的基本理论 ,建立了水平矩形薄板模型 ,推导了计算此类薄板影响地倾斜的基本公式。通过该模型的模拟计算 ,分别得出了由大楼质量造成的附加引力位对观测点水平摆的偏转角度和大楼负荷产生的地倾斜 ,并针对厦门地震台的实际情况 ,讨论了大楼对地倾斜观测的影响。     

考虑土-结构相互作用下基岩深度对核反应堆厂房基础地震响应的影响

地震会对核电站安全造成影响。随着核电站的数量越来越多,有必要关注在地震下核电站的安全。核反应堆厂房是核电站重要的组成部分,研究其地震响应对核电站有着重要意义。基于直接法,考虑了3种不同场地(中硬土、软岩、硬岩)在地震下的塑性变形和土的滞回阻尼,使用FLAC3D对土-核反应堆厂房模型系统进行了三维建模。为了捕捉上部结构与下部岩石/土壤之间的分离与滑动,在核反应堆厂房基础与岩石/土壤表面设置接触面单元。上层结构以集总质量模型模拟,同时考虑土-结构相互作用下基岩深度对核反应堆厂房基础地震响应的影响,最终得到核反应堆厂房结构杆件的加速度反应谱、剪力、基础的摇动和基础不均匀沉降以及侧向位移。结果表明：在中硬土场地中,位移、剪切力随基岩深度的增大而减小;在硬岩场地中,位移和剪切力响应的规律呈相反趋势;在软岩场地中,上部结构响应的规律较为复杂。对于基础摇动和基础不均匀沉降,在中硬土场地中,其呈现的规律随基岩深度增大而减小;在软岩和硬岩场地中,并无明显规律。基础不均匀沉降可直接反映结构的破坏情况。中硬土场地下基础不均匀沉降超过容许值,所以基础不均匀沉降对核反应堆厂房的影响不容忽视,这对核电站的安全设计...     

基岩面形状对土体变形破坏的影响实验研究

采用离心模型试验研究基岩面形状对重力式加筋挡土墙土体变形破坏的影响,基岩面形状设置为直线形和台阶形,直线情况下基岩与挡墙分别围成三角形和梯形,台阶则分为两级台阶和三级台阶,试验共进行4组。试验结果表明,水平位移和沉降变化剧烈的位置主要在土体顶部靠近挡墙的位置,近岩面处土体水平位移和沉降都比较小;在挡土墙底部基岩与挡墙之间应当有足够的水平距离才有利于土体的稳定;基岩与挡墙所围形状为三角形时对土体的变形和稳定最为不利,基岩与挡墙围成梯形或基岩为台阶形时对土体稳定比较有利。     

Application of high-density resistivity method in archaeological investigation of Sumicheng ancient city site

The authors employ the high-density resistivity method during an archaeological investigation of Sumicheng site,an ancient city of the Tang Dynasty,to find evidence of human activities and locate a favorable target for archaeological excavation in the southern part of the outer city.There are two obvious high-resistivity structures,the south wall of the inner city and an ancient building near the south gate along the outer city wall,of which the resistivities are indicative of rammed soil foundations.The south wall of the inner city is continuous but is cut off abruptly to the east,which we suggest it is due to either wall damage or destruction.The resistivity signature of the target area is verified by archaeological excavation,proving the feasibility and effectiveness of implementing the high-density resistivity method for archaeological exploration.     

山东大学齐鲁医院综合楼工程对济南泉水的影响分析

通过对山东大学齐鲁医院门诊保健综合楼工程建设对泉水是否影响的论证,认为场区内第四系碎屑岩孔隙裂隙水与奥陶系裂隙岩溶水为2个不同的含水系统。拟建工程在开挖深度内未揭穿第四系砾岩层,保留部分砾岩层作为基底持力层,并保持了下伏黏土的天然隔水性能,不会阻挡地下水径流补给通道,对泉水不会造成影响。     

Engineering geological investigations for the foundations of large structures-examples of a concrete dam and a long bridge in Portugal

The safety of large structures requires adequate foundations, which implies a good knowledge of the geological and geotechnical conditions of the respective ground. In general, that is only possible through engineering geological studies which include proper site investigation techniques, adapted to the nature of the ground (rock mass or soil) and to the associated engineering problems. The paper illustrates the studies carried out for the design of the foundations of Ribeiradio 76 m high concrete gravity dam in a difficult rock mass and of Vasco da Gama Bridge, 13 km long, crossing the Tagus River in Lisbon, Portugal, through piles 75 m deep.     

Settlement patterns of mountainous half-filled and half-cut widened subgrade with retaining wall

The settlement of widened highway subgrade in mountainous area is not only affected by the interaction between new and existing subgrade, but also seriously restricted by the external retaining wall. Based on the practical engineering of half-filled and half-cut widened mountainous highway subgrade with external balance weight retaining wall(BWRW), a sophisticated finite element numerical model is established. The evolution law of subgrade settlement is revealed during the whole process of new subgrade filling and BWRW inclination after construction. The settlement component of subgrade is clarified considering whether the existing pavement continues to be used. The results show that the additional settlement caused by the BWRW inclination after construction cannot be ignored in the widening and reconstruction of mountainous highway subgrade. In addition, pursuant to the comprehensive design of subgrade and pavement, the component of subgrade settlement should be determined according to whether the existing pavement continues to be used, while considering the influence of BWRW inclination after construction. When the existing pavement continues to be used, the settlement of the existing subgrade is caused by the new subgrade filling and the BWRW inclination after construction. On the contrary, the settlement is only caused by the BWRW inclination after construction.     

大同--运城高速公路某软基复合地基检测结果分析

以山西大运高速公路某段软基处理为例,从挤密碎石桩的加固机理和破坏方式入手,通过对软基复合地基的原位测试结果分析,得出碎石桩不但提高了地基的承载力,增加了桩间土的强度,减少了地基沉降,而且消除或减轻了地基的液化,使复合地基承载力达到了设计要求,特别是为以后在高速公路修筑中的软基处理提供了参考资料.