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桩承式路堤土拱效应发挥过程研究 总被引：4，自引：0，他引：4
通过三维模型试验对桩承式路堤中土拱效应发挥过程进行了研究,重点分析了不同桩顶盖板尺寸、不同加筋方式下应力折减系数与差异沉降之间的关系。结果表明,土拱效应随变形的增加而发挥;加筋材料的设置减小了差异沉降,削弱了填土中的土拱效应,荷载向桩顶的传递是土拱效应和拉膜效应共同作用的结果。采用有限元法对桩间距、填土高度等未能在模型试验中考虑的关键因素进行了参数敏感性分析,总结了土拱效应发挥过程的相关规律。根据有限元计算结果、试验数据和文献中收集到的实测资料,提出用土拱效应发挥系数和归一化位移来描述土拱效应的发挥过程,建议二者之间采用双曲线方程模拟,从而在设计中体现土拱效应随位移的发展,并满足路堤填土、加筋材料和地基之间的变形协调要求。 相似文献
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对于桩承式路堤作用效应的研究目前主要侧重于对静荷载作用下桩土应力比和土拱效应等,较少考虑动荷载的影响,而车辆运行产生的动应力会对路堤中的土拱产生一定的影响,进而影响桩承式路堤的整体性能。为了分析静、动荷载作用下桩承式加筋路堤的性能变化,采用可视化模型试验和颗粒流数值模拟相结合的方法,对桩承式路堤在静载和动载下的应力传递和变形性状进行研究,分析动载作用下填土高度、桩帽、桩距、加筋形式、荷载频率的影响。试验结果表明,在动载下无筋路堤的桩顶的应力减小,而桩间的应力和位移增大,并且变化的幅度均比加筋路堤大,加筋材料的设置有利于减小动载的影响效应,但不同加筋形式下桩承式路堤的工作性状有所不同,受动载影响程度的大小主要与土拱效应的强弱有关。设置双层加筋时,因加筋材料与周围砂土形成半刚性平台,土拱效应减弱,故受动载影响的程度最小,单层加筋时,格栅设于桩顶上方10 cm比格栅置于桩顶受动载影响的程度明显减小,颗粒流的模拟结果验证了以上结果,并且进一步得出随荷载频率的增加、填土高度与桩净距的减小,动载的影响效应增大的结论。 相似文献
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桩承式加筋路堤三维土拱效应试验研究 总被引：2，自引：0，他引：2
桩承式加筋路堤受力性状比较复杂,土拱效应对路堤的承载变形性状具有重要影响。通过三维土拱效应模型试验,研究桩-土相对位移、路堤高度、桩帽净间距和水平加筋体拉伸强度等因素对桩土应力比及路堤沉降的影响。结果表明：土拱效应发挥程度与桩-土相对位移密切相关,存在一个临界桩-土相对位移使得桩土应力比达到最大值,该临界桩-土相对位移约为6～8 mm。路堤高度与桩帽净间距之比越大,桩土应力比越大,路堤顶面差异沉降越小;桩帽宽度与桩帽净间距之比越大,桩土应力比越大,路堤顶面差异沉降越小。设置水平加筋体能有效提高桩土应力比并减小路堤顶面沉降;路堤越低,水平加筋体对桩土应力比的提高作用及对路面沉降的减小作用越明显;水平加筋体拉伸强度越高,这种作用越明显。桩承式加筋路堤三维土拱效应等沉面高度与桩帽净间距之比约为3.5。 相似文献
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软土地基上填筑高路堤常常面临地基承载力不足、沉降和不均匀沉降过大等问题。桩承式加筋路堤能够有效地解决这些难题。通过理论分析和有限元数值模拟,研究了路堤填土-加筋材料-桩体-桩间土之间的相互作用机理,讨论了路堤填土中的土拱效率、桩体效率、路堤底面差异沉降和筋材拉力的变化规律。研究结果表明,填土中的土拱效应和筋材张力膜效应能够有效地提高桩体效率,防止软土屈服;筋材内部拉力呈非线性分布,桩顶边缘处筋材拉力最大。 相似文献
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长短桩组合路堤桩三维复合拱土拱效应分析 总被引：1，自引：0，他引：1
基于等长桩路堤桩土拱效应的Hewlett分析方法,提出均布荷载作用下长短桩组合路堤桩的三维复合拱土拱效应分析方法。采用有限元法形象描绘土拱效应形成的应力集中形态随长桩与短桩的桩长比不同时的变化,基于此提出三维复合拱的基本理论框架。引入土拱效应系数来表征土拱的强度状态,建立桩帽顶部平面的应力平衡微分方程,结合边界条件及土拱效应系数之间的关系计算长桩和短桩的桩-土应力比;当加筋体存在时,分区域对加筋体进行变形假设,建立考虑加筋体拉力的桩帽顶部应力平衡微分方程。与离心模型试验和现场实测结果及有限元方法的模拟结果进行比较,验证了此方法的合理性,进一步开展参数分析对主要影响因素进行等级评价。分析表明,加筋体的存在明显增大桩-土应力比,尤其当桩帽覆盖率比较小时效果更为明显。 相似文献
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为了分析素混凝土桩复合地基支承路堤沉降变形特征和失稳破坏机制,建立了3组不同桩间距的素混凝土桩复合地基支承路堤离心试验模型及其数值模型。结果表明：在路堤填土自重、轨道和车辆荷载作用下,改变桩间距对素混凝土桩复合地基支承路堤沉降变形、桩体应变、加筋垫层和桩体破坏模式具有显著的影响;当桩间距不大于4倍桩径时,加筋垫层整体基本保持完好,路堤下素混凝土桩复合地基沉降能逐渐趋于稳定,而桩间距达到6倍桩径后,桩顶刺穿加筋垫层,加筋垫层对桩土变形协调和传递荷载作用失效,素混凝土桩复合地基支承路堤沉降持续增大;当桩间距达到4倍桩径时,素混凝土桩最大应变值发生随上部荷载的增大反而减小的突变现象,最靠近坡脚的素混凝土桩最先产生弯曲破坏而不是剪切破坏,当桩间距增大至6倍桩径时,桩体弯曲破坏逐渐往路堤中心方向发展。 相似文献
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桩承式路堤土拱效应有限元研究 总被引：4，自引：1，他引：3
路堤下设置的带承台桩,除了承担承台上方的填土重量外,通过土拱效应还承担桩间土上方的部分重量。将填土重量的大部分传递到地基深部,既增加了路基的稳定性,又减小了路基的沉降。上海国际赛车场建造在软土地基上,为了满足工程需要,除使用了EPS轻质填筑材料外,还在填筑高度较高的地段采用了桩承式路堤作为地基加固方式。为了深入研究土拱效应的工作机制,对上海国际赛车场路堤桩的承台与承台间土压力分布进行了原位测试,并结合实际工况进行有限元分析。结果表明：除了承台上方的土压力相对承台间土有应力集中现象外,承台边缘相对承台中部也有应力集中现象。对EPS的加入和桩体性质的各项参数对于土拱效应产生的影响进行了分析。 相似文献
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桩承加筋路堤中路堤与褥垫层共同作用理论分析 总被引：1，自引：0，他引：1
从桩承加筋路堤中加筋褥垫层与路堤填土共同作用的实际情况出发,利用弹性力学对路堤填土单元进行了力学平衡分析,同时考虑到加筋褥垫层的工作状态类似于连续梁板的特性,根据PCC桩承加筋路堤的设计参数及现场测试结果,将现浇混凝土薄壁管桩（PCC）桩承加筋路堤中的加筋褥垫层视为弹性薄板,再根据薄板小挠度理论,推导出了桩土差异沉降等计算公式。又根据填土与褥垫层变形协调、应力连续的条件,在忽略褥垫层材料本身压缩量的前提下将加筋褥垫层变形分析与填土变形分析相结合,提出了求解填土等沉面高度、桩土应力、桩土差异沉降的方法,最后通过与现场实测结果对比,验证了方法的正确性。 相似文献
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桩承式加筋路堤在高速公路软基处理中得到了广泛应用,但目前对其承载变形机制还缺乏深刻认识。结合南京长江第四大桥北接线段软基加固工程,基于数值方法对现浇X形桩桩承式加筋路堤中桩土沉降、桩土应力、桩身轴力及超静孔隙水压力的发展变化规律进行了分析。研究结果表明,受土拱效应影响,路堤填筑荷载主要由桩体承担,桩及桩间土土压力在路堤填筑过程中均逐渐增大,在软基固结过程中,桩顶土压力继续增大而桩间土土压力逐渐减小,最终趋于各自的稳定值;路堤填筑过程中桩身轴力增长较快,现浇X形桩桩身上部较大部分区段存在负摩阻力,桩身中性点位置经历了先逐渐上移、而后向下移动,最终趋于稳定的过程。 相似文献
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DEM analysis of “soil”-arching within geogrid-reinforced and unreinforced pile-supported embankments
Geogrid-reinforced and pile-supported (GRPS) embankments have been widely used in road engineering due to their economy and effectiveness. The soil arching effect is a key factor in the load transfer mechanism of GRPS technique. In this study, a series of numerical simulations are conducted with the particle flow code PFC2D to study the evolution of soil arching with increasing surcharge. First, an Improved Multi-layer Compaction Method (IMCM) is proposed and applied to establish the Discrete Element Method (DEM) models with more reasonable initial stress states. Validation is then conducted by comparing the DEM results with experimental data. Second, detailed macro-behaviour (e.g., efficacy) and micro-behaviour (e.g., contact forces and fabric anisotropy) analyses are performed. Finally, parametric study is performed to identify the effects of two key factors, i.e., the stiffness of subsoil and the grain composition of embankment fill. Simulation results indicate that the strong force network (SN) serves as a load-carrying force chain, which is the main component of soil arching; while the weak force network (WN) acts as a support system. When a pile-supported embankment is high enough, the soil arching will experience three stages as the surcharge increases. In the first stage, the soil arching develops and its effect is strengthened gradually. In the second stage, the soil arching is fully mobilized and experiences a “forming-failure-reforming” process as the surcharge increases. While in the third stage, the embankment is unable to form a new stable soil arching and the efficacy decreases gradually. However, for the GRPS embankment, due to the reinforcement of geogrid, the third stage will not occur throughout the entire surcharge range of interest in this study. On the basis of the macro- and micro-results, the conclusion can be drawn that the presence of geogrid does not alter the failure mode of soil arching under the surcharge, though it is able to evidently improve the efficacy of load transfer and enhance the stability of soil arching. 相似文献
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The numerical predictions obtained with the Melanie and MIT-E3 models are compared. Firstly, the performance of the constitutive models is checked against undrained triaxial tests. The models are then used to replicate the behaviour of an embankment built on soft clay. The numerical results are compared with the field data in terms of settlements, lateral displacements and excess pore pressures. Additionally, the numerical predictions are also analysed in terms of yield area, contours of vertical effective stresses, horizontal effective stresses and shear stresses and in terms of effective stress paths. 相似文献
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在对半挖半填路堤病害及成因分析的基础上,分析了加筋路堤格栅工作机制。通过现场试验,对采用格栅加筋法处理的路堤挖填交界区域进行了原位观测,观测了路堤填土完成时路面沉降、竖向土压力及格栅变形情况。通过建立有限元分析模型,对路堤填筑完成时格栅的拉力及位移进行了分析,并对不同路面荷载和格栅刚度条件下,格栅的拉力与位移进行了计算。结果表明：路堤挖填交界处铺设格栅后,路面局部差异沉降较小。填方区域格栅底部土压力与填土自重应力相当,格栅存在有效加筋长度,在挖填交界面附近产生较大变形和拉力。上层格栅比下层格栅沉降曲线平缓,下层格栅的拉力在交界区域会陡然增大。路面荷载对格栅拉力和位移有一定影响,随埋深增加影响减小,格栅的竖向位移随着荷载增大略有增大,格栅在挖填交界面附近拉力增大。随格栅刚度增大,其拉力也增大,而位移变化很小。 相似文献
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The behaviour of an embankment built on a Portuguese soft soil is analysed considering the material and geometric non-linearity associated with a coupled soil–water formulation. The numerical predictions are compared with the field data in terms of settlements, horizontal displacements and excess pore water pressures. The repercussions of including the large displacements formulation are also studied. It is found that the analysis considering large displacements results in a decrease in settlements and an increase in the rate of excess pore pressure dissipation, both of which are related to the reduction of the thickness of a deformable layer. 相似文献
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堤防的沉降和稳定问题是软土地基上新建堤防工程必须考虑的重要问题。结合南京市长江干堤提升工程小年圩新筑堤项目,开展了软土地基上新建堤防施工全过程的现场监测与分析,主要包括表层沉降、分层沉降、土体侧向位移、土压力、孔隙水压力以及地下水位等内容。基于Plaxis有限元数值软件,建立了软土地基上新建堤防施工填筑过程的数值模型,通过与现场监测结果的对比分析,验证了所建立的数值模型的准确性和可靠性;续而重点分析了填筑速率、填筑间歇时间等关键性施工控制指标对软基上堤防沉降的影响规律。研究结果表明,当单次填筑厚度小于1 m时,单次填筑厚度对整体沉降的影响较小,因此结合实际施工要求,建议单次填土厚度为0.5～1.0 m。相关研究成果可以为类似软基上新建堤防施工质量控制提供参考依据。 相似文献
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The mechanical behavior of natural clays is affected by their inherent anisotropy and metastable soil structure. A simple hierarchical model that considers initial anisotropy and destructuration was formulated within the framework of critical state soil mechanics. In the proposed model, stress sensitivity and a destructuration index were introduced to account for the degree of bonding and the rate of destructuration, respectively. An inclined yield surface was used to incorporate the effect of the initial anisotropy. The proposed model can be degenerated to the Modified Cam Clay model by setting the initial stress sensitivity equal to unity and using a horizontal yield surface. Reasonable agreement between the model simulations and the experimental results on a variety of stress paths demonstrated that the proposed model can capture well the deformation behavior of natural clay and reconstituted soil. The model was implemented into the finite element program for the numerical analysis of an embankment on soft clay improved with prefabricated vertical drains. The numerical predictions were compared with the field-measured data in terms of embankment settlement. Additionally, the numerical simulations were analyzed in terms of horizontal displacements, excess pore water pressure, mean effective stress and volumetric strain. All of the simulations and comparisons indicate the importance of considering the effects of plastic anisotropy, interparticle bonding and destructuration caused by loading beyond yield stress and field disturbance in analyzing the behavior of an embankment on natural soft clay. 相似文献
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Three-dimensional analysis of embankments on soft soils incorporating vertical drains by finite element method 总被引：4，自引：0，他引：4
Jos Leito Borges 《Computers and Geotechnics》2004,31(8):665-676
Three-dimensional behaviour of an embankment on soft soils incorporating vertical drains is analysed by a numerical model based on the finite element method. The model, which incorporates the Biot’s consolidation theory (coupled formulation of the flow and equilibrium equations) and constitutive relations simulated by the p–q–θ critical state model, is applied on both the embankment with vertical drains (three-dimensional analysis) and the same problem but without vertical drains (two-dimensional analysis). Special emphasis is given to the analysis, during and after the construction period, of the excess pore pressures, settlements, horizontal displacements and stress levels. 相似文献
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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。 相似文献
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为明确填方路堤荷载下强夯碎石墩的变形特征与其路堤稳定性的内在关联,针对“山地型”软土地区某高速铁路车站高填方路堤的失稳破坏现象,基于现场实测数据和三维数值分析模型,着重研究了不同位置强夯碎石墩墩体的鼓胀变形与侧向弯曲变形规律,并定义墩体鼓胀率和最大侧向弯曲值对其变形特征予以描述。研究结果表明:路堤荷载作用下不同位置的强夯碎石墩发生不同程度的鼓胀变形和侧向弯曲变形,其中鼓胀变形主要由上覆路堤荷载所产生的压缩鼓胀和路堤侧滑所产生的滑动剪切鼓胀所组成,且其最大鼓胀变形区域集中在距桩端1~2倍桩直径范围内;位于强夯碎石墩复合地基潜在滑裂面剪入口附近墩体的鼓胀率最大(0.75%),约为路堤中心处墩体鼓胀率的1.5倍,表明该处以滑动剪切鼓胀变形为主。沿路堤中心线向外不同位置的强夯碎石墩墩体的最大侧向弯曲变形的发展规律近似呈三段线模式,其中潜在滑裂面剪入口附近的17#墩体为其侧向弯曲变形开始陡增的拐点,表明17#与其附近墩体为控制路堤侧向变形与稳定的关键构件。路堤填筑过程中所出现数条裂缝的原因可能在于强夯碎石墩的剪切破坏而致使路堤出现整体滑移所引起的,建议在采用散体材料桩复合地基处治“山地型”软弱地基时,应配合其他加固措施以确保填方路堤的整体稳定性。 相似文献