平坦地基上山区高填方路堤变形及稳定性分析

山区地形地貌多变,地基条件复杂,高填方路堤的不均匀变形和失稳破坏时有发生.针对山区高路堤的基本特点,利用有限元法分析了平坦地基上高填方路堤的工程特性及不同填方高度、软弱地基厚度、填筑速率、压实度下山区高路堤的弹塑性固结问题,得出山区高路堤变形与破坏问题的规律.利用此规律可以较为全面地认识山区高路堤的变形与破坏形态,有效地指导实际施工.     

斜坡软弱地基路基稳定性及变形规律分析

根据斜坡软弱地基上路堤填筑的工程特点,结合工程实例进行定量计算,分析软土强度指标、软弱土层厚度、路堤高度和地层坡度等几何参数,对斜坡软弱地基稳定特性及路基变形规律的影响.指出抗剪强度指标ψ、C以及地层坡度对斜坡软弱地基路基影响明显,软弱土层厚度和路堤高度的影响随数值增大趋于收敛;工程中可将1:10软弱土层坡度作为路基支护加固的临界指标.     

群桩条件下刚性桩加固斜坡软弱地基路堤稳定性分析

针对刚性群桩加固斜坡软弱地基路堤的应用还不充分问题。通过有限元软件ABAQUS建立刚性群桩加固斜坡软弱地基路堤的三维数值分析模型,对比分析了刚性桩桩距、桩身弹性模量等设计参数对桩内力、变形的影响及其对路堤加固效果的影响。研究表明:经刚性群桩加固后,斜坡软弱地基的整体稳定性得到显著提高;与无桩加固相比,路堤最大沉降值减小约1.5～1.93倍,地基的侧向变形值减小约1.46～2倍;随着刚性桩弹性模量、嵌固深度增加,刚性桩的受力状态影响不大,刚性桩最大竖向应力和最大桩身土压力的变化幅度均小于10%;桩距对刚性桩的受力状态、水平位移影响较为显著;对比分析桩距和桩弹性模量对路堤沉降值的影响,研究发现桩距是影响路堤沉降的主要因素。因此综合考虑路堤稳定性、桩身受力以及工程的经济性,本工程刚性群桩桩距选择为2 m,弹性模量选择为10 GPa。     

下覆倾斜地层软土桩-网复合地基破坏机理试验

为研究嵌岩桩和摩擦桩同时存在下桩-网复合地基的破坏机理,以浙江沿海某高速铁路工段为背景,基于典型断面开展相似比尺为1∶100的土工离心机模型试验,分析下覆倾斜地层软土桩-网复合地基的变形特征及破坏模式.结果表明:路堤顶面的竖向、水平位移主要发生在施工阶段及工后静置阶段,且进入运营阶段后亦有明显发展,路堤顶面竖向沉降差随运营时间的推移逐渐增长;复合地基的沉降呈非对称分布,形成一个偏向下覆倾斜地层斜坡向下一侧的不对称沉降盆;在上部荷载作用下,复合地基的沉降主要由下卧层的压缩、桩体的向上向下刺入及桩体倾倒或横移3部分组成;桩顶水平位移沿下覆地层斜坡向下方向逐渐增大并伴随不同程度的淤泥质黏土绕流破坏,桩顶竖向位移呈现偏向下覆地层斜坡向下一侧的不对称“V”字型分布;嵌岩桩的潜在破坏模式为弯拉或弯剪破坏,斜坡桩的潜在破坏模式为弯剪或倾倒破坏,摩擦桩的潜在破坏模式为倾倒及横移破坏.通过试验可知,采用等长桩的桩网复合结构对下覆倾斜地层软土地基进行处理是不合理的,将威胁高铁的安全运营.此外,对此类既有铁路地基的维护及有效加固措施亟待进一步研究.     

山区水下填方路堤边坡的稳定性分析

山区水下填方路堤在修筑过程中,由于无法对水位以下的原状山体进行清表和修坡处理,填方路堤与原有山体之间会存在软弱层,导致出现边坡稳定性问题.以千黄高速浙江省大湾区路段工程为背景,采用有限元软件GeoStudio,对水下填方路堤进行数值模拟,分析路堤边坡稳定性受水下填方路堤与原状山体之间的软弱层及水位变化的影响.研究结果表明,软弱层的厚度、力学参数、相对位置和水位的变化对路堤边坡稳定性有一定影响,路堤边坡的稳定性随着软弱层厚度的增加而减小;随着软弱层位置的不断上移,路堤边坡的稳定性系数先是下降较快,随后变缓;当路堤内部存在软弱层时,渗流力对路堤边坡稳定性的影响较为明显.因此,存在软弱层时水位变化对路堤整体稳定性的影响与没有软弱层时有较大差异.     

山区贴坡路堤工作性状模型试验研究

随着我国西部大开发建设的深入和公路建设的发展,贴坡高填方路堤已经成为西部高等级公路常见的路基形式.结合山区高速公路建设的实践,采用大型室内模型试验,对贴坡路堤工作性状进行了研究,重点介绍了该模型的试验设计、测试和试验数据分析方法.主要对试验过程中路堤内部应力、坡面位移进行了观测和分析,得出了在顶部静载作用下路堤的工作性状,试验结果表明：斜坡地基上填方路堤在填筑过程中,路堤内部应力与填筑高度呈正比,同一路堤填筑面上其应力大小不等;在加载过程中,路堤内部应力随加载面距离的增大而减小,同一路堤填筑面上其应力大小也不等;最大沉降位移出现在加载面位置,在其他位置沉降值较小;最大水平位移出现在坡肩处或滑面与坡面的交线处,在其他位置较小.     

公路扩建刚性桩和竖向土工材料加固研究

为控制软土地基公路拓宽工程中新旧路堤的差异沉降,提出一种新的软土地基处理方式,即综合应用刚性桩和竖向土工材料进行公路拓宽地基处理。为把握路堤荷载作用下综合应用刚性桩和竖向土工材料加固直接拼接方式的拓宽路堤工作性状,应用FLAC3D建立三维分析模型。通过数值模拟计算,从加固前后路堤的沉降、地基侧向位移和稳定性等方面进行了分析研究。计算结果表明:刚性桩和竖向土工材料的综合应用能够有效控制地基土体侧向位移,从而能够减小新老路基的总体沉降和路堤顶面的差异沉降,加固效果明显。     

环向加筋碎石桩复合地基路堤稳定性分析

环向加筋碎石桩复合地基在加固软基工程中得到了广泛应用,在加固路基工程中,路堤边坡稳定性计算对工程设计具有重要意义。文中通过对采用环向加筋碎石桩加固路堤时边坡失稳破坏模式进行三维有限元分析,揭示了路堤失稳时环向加筋碎石桩的破坏模式和路堤失稳模式,研究了地基土强度对路堤边坡的安全系数的影响。在此基础之上,对比分析了采用瑞典条分法、毕肖普条分法和规范圆弧条分法计算环向加筋碎石桩复合地基路堤边坡稳定性的适用性。研究表明:文中建立的数值模型能够较好地反映环向加筋碎石桩复合地基路堤稳定性;路堤失稳时环向加筋约束碎石桩发生受弯破坏;由于没有考虑环向加筋碎石桩的约束作用,瑞典条分法、毕肖普条分法和规范圆弧条分法的计算结果均较为保守,但毕肖普法计算结果最为接近数值计算结果。     

地震荷载作用下桩承式加筋路堤动力响应分析

桩承式加筋路堤具有工期短,成本低以及沉降变形小等优点,在工程中得到了广泛应用.为了研究地震荷载作用下桩承式加筋路堤的动力特性,建立了桩承式加筋路堤的数值分析动力模型,分析了水平地震波El-Centro作用下桩承式加筋路堤的动力响应.同时,研究了路堤加速度、动剪应力和路堤动位移等动力特性,分析了CFG桩和土工格栅的内力峰值分布.最后,对土工格栅抗拉模量和桩间距进行了参数分析,研究了水平地震荷载作用下土工格栅抗拉模量和桩间距对桩承式加筋路堤动力响应特性的影响.数值分析结果表明:桩承式加筋路堤在右坡面接近坡脚处,剪切应变增量最大;增大格栅抗拉模量能增强桩承式加筋路堤的抗震性能,而且对增强竖向地震稳定性比水平向地震稳定性效果更明显.     

软土地基施工期稳定性分析评价方法的探讨

在软土地基上填筑路堤时,必须对其稳定性作出合理的评价。本文提出孔隙压力法、有效应力路径法、有效固结应力验算法、侧向位移法等四种施工期稳定性评价方法,以及实例综合分析评价,对于软基路堤施工程序的设计有着重要指导意义。     

基于有限元法的重力坝双斜面抗滑稳定分析

对坝基含双斜面软弱结构面的某重力坝工程挡水坝段,以非线性有限元法进行静力荷载作用下的深层抗滑稳定研究.计算结果表明,当坝基内含有双斜面软弱结构面时,在超载过程中,坝体沿该双斜结构面向下游滑动,其中坝踵附近的软弱结构面最危险,坝趾下游结构面次之,判定超载安全系数K=3.0～4.0.并通过刚体极限平衡法对有限元计算结果进行...     

Numerical analysis on seismic behavior of railway earth embankment: A case study

A numerical case study on the seismic behavior of embankment was carried out based on a prototype of earth embankment in Yun-Gui Railway(from Kunming City to Nanning City) in southwest of China. A full-scale model of earth embankment was established by means of numerical simulation with FLAC~(3D) code. The numerical results were verified by shaking table test. The seismic behaviors of earth embankment were studied, including the horizontal acceleration response, the vertical acceleration response, the dynamic displacement response, and the block state of earth embankment. Results show that the acceleration magnification near the embankment slope is larger than that in internal earth embankment body. With the increase of input peak acceleration, the horizontal acceleration magnification presents a decreasing trend. The horizontal acceleration response at the top of embankment is more sensitive to the intensity of ground motion than that at the bottom of embankment. The embankment presents an obvious nonlinear-plastic characteristic when the input horizontal peak acceleration is larger than 0.3 g. The maximum residual deformation occurs in the middle of embankment slope surface instead of at the top of embankment. The upper part of embankment experiences tension failure without shear failure, and area at the bottom of embankment around the symmetry-axis of embankment mainly presents shear failure under the earthquake loading. The tension failure and shear failure repeatedly occur along the slope surface of earth embankment.     

Stress and deformation due to embankment widening with different treatment techniques

A two-dimensional(2-D) finite element(FE) model was developed to analyze the deformation and stress of embankment on soft ground due to widening with different treatment techniques.It is found that the embankment widening induces transverse gradient change due to differential settlements and horizontal outward movements at the shoulder of the existing embankment.Embankment widening also increases the shear stress along the slope of the existing embankment,especially at the foot of slope.The failure potentia...     

黄土路基湿化特性的离心模型研究

本文根据黄土地基上的筑路特点,运用离心模型试验研究了黄土路基的特性,获得了在不同路基深度及不同路堤高度下黄土路基,因降雨等而引起的湿化沉降与水平变形分布及路堤破坏情况,并对其分布规律和破坏原因进行了分析,所得成果对黄土地区公路建设具有实际指导意义。     

某面板堆石坝应力及变形的有限元分析

基于邓肯-张E-B模型,建立了某面板堆石坝的有限元计算模型,获得了施工期、正常蓄水期和水位骤降期的坝体、面板应力及变形的分布和变化规律.结果表明:该混凝土面板堆石坝的坝体应力及变形性状正常,变形值在可接受范围内;坝体发生剪切破坏的可能性较小;趾板下覆的坝基较小范围内,存在应力集中和小主应力方向受拉的现象;库水位的大幅度变化对面板的挠度影响明显;坝基中断层只是对坝基的应力分布形态有影响,对坝体的应力变形影响微弱.     

A case study of seismic response of earth embankment foundation on liquefiable soils

A case study of seismic response of an earth embankment foundation on liquefiable soils in Kansai area, western Japan was presented. Based on a calibrated cyclic elasto-plastic constitutive model for liquefiable sand and Biot dynamic coupled theory, the seismic analysis was carried out by using a dynamic effective stress finite element method under plane strain condition. A recent design study was illustrated in detail for a river earth embankment subjected to seismic excitation on the saturated deposits with liquefiable sands. Simulated results of the embankment foundation during liquefaction were obtained for acceleration, displacement, and excess pore water pressures, which were considered to yield useful results for earthquake geotechnical design. The results show that the foundation soil reaches a fully liquefied state with high excess pore pressure ratios approaching to 1.0 due to the earthquake shaking. At the end of the earthquake, the extensive liquefaction causes about 1.0 m lateral spreading at the toe and 60 cm settlement at the crest of the earth embankment.     

挡土墙土压力非线性分布的计算方法研究

基于数学方法对斜单元体进行力和力矩的平衡分析,得到了墙背粗糙且填土坡面倾斜情况下的土压力解析解,并进一步分析了填土坡面倾角对土压力的影响。对比分析表明:经典朗肯土压力理论可看作是解析解在墙背光滑、填土坡面水平情况下的特例;在填土内摩擦角一定时,挡土墙墙后滑动楔体的极限破裂角随着填土坡面倾角或墙土之间摩擦角的增大而减小。基于解析解得到的土压力分布呈现明显的非线性特征,且在填土面水平情况下挡土墙墙脚处的土压力为0,这与实测数据取得了很好的一致。分析还表明,随着填土坡面倾角的增大,墙脚处的土压力不再接近0反而越来越大。文中的求解方法还可进一步拓展至探求填土为粘性土情况下挡土墙上土压力的解析解。     

Stress and deformation due to embankment widening with different treatment techniques

A two-dimensional (2-D) finite element (FE) model was developed to analyze the deformation and stress of embankment on soft ground due to widening with different treatment techniques. It is found that the embankment widening induces transverse gradient change due to differential settlements and horizontal outward movements at the shoulder of the existing embankment. Embankment widening also increases the shear stress along the slope of the existing embankment, especially at the foot of slope. The failure potential due to embankment widening may increase with the increase of widening width when the widening width is smaller than 8.5 m, but may decrease with the increase of widening width as the widening width is greater than 8.5 m. The effectiveness of four ground and embankment treatment techniques, including geosynthetic reinforcement, light-weight embankment, deep mixed columns, and separating wall were compared. The results indicate that these treatments reduce the differential settlements and improve the stability. The light-weight embankment has the most effectiveness among four treatments. By using the fly-ash backfill material in widening, the transverse gradient change decreases from 0.5%–1.3% to 0.26%–0.8% and the maximum horizontal displacement decreases from 2.76 cm to 1.44 cm.     

后张预应力混凝土摇摆墙非线性分析

为分析后张预应力摇摆墙通过摇摆界面处墙趾的张合行为降低结构损伤和震后残余变形的特性,须解决墙趾节点约束释放后的局部行为、沿墙通长布置的后张无黏结预应力应力变化与摇摆机制关系等关键问题.结合非线性宏单元的思路,用多个轴压弹簧模拟墙体与基础界面水平接缝开合行为及接缝区域力学特性,用共转桁架单元模拟预应力筋受力特征,提出了基...