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大面积堆填或开挖时深厚软土地层内部常产生较大滑移,这为该类地层中考虑桩土作用的抗滑桩分析带来较大困难。考虑深厚软土的滑移性状,针对既有悬臂桩法计算存在的问题进行修正,滑动面上部桩身受荷段的桩身荷载采用等腰三角形分布且极值点为极限侧土压力,设滑动面下部桩身锚固段上侧桩周软土为理想弹塑性以考虑软土大位移条件,下侧为弹性状态,并通过位移叠加原理对传统方法求解产生滑动面不连续的缺陷进行修正。通过现场桩侧堆载试验验证,修正悬臂桩法的弯矩和位移计算结果较好,桩顶位移误差小于3%,桩身最大弯矩误差小于10%。所提方法有助于深厚软土地层抗滑桩的设计和计算。 相似文献
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软土区桥头路堤填筑会给下卧软土层带来一定的位移场,导致典型的软土-桩基相互作用,会威胁到桥梁的建设与正常使用.研究开展了软土-桩基相互作用的1∶1原位试验,根据桩顶偏移、桩身拉压应变、桩身弯矩、桩侧土抗力和桩周孔隙水压力等监测数据,对路堤填筑引发的软土-桩基相互作用进行了深入分析.研究得出,在相同大小的堆载作用下,桩径... 相似文献
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建立了三维数值模型,进行堆载-弹塑性地基-桩基共同作用有限元数值分析。在地面超载条件下,对自由场土体的侧向位移模式进行了探讨,得出了土体侧向变形规律。在此基础上,对堆载作用下邻近桩基的力学性状进行了分析,包括不同堆载大小、不同堆载距离和不同桩间距等情况下桩基的侧向变形和弯矩的变化规律。分析结果表明：随着堆载的增加,桩基的变形和弯矩都有显著的增长,桩基逐渐弯曲。在同样条件下,增加桩的刚度,桩身弯矩迅速减小,桩身刚度很大时,会发生整体侧移。桩间距和堆载距离对桩身弯矩和变形有重要影响,随着桩间距和堆载距离的增大,桩身的变形和弯矩都将减小。 相似文献
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《岩土力学》2017,(5):1454-1462
波浪循环荷载通过堤身和砂质土置换层传递给软土地基,在软土地基中产生循环动应力,使软黏土发生不排水强度弱化现象,严重影响格型钢板桩防波堤承载性能。结合工程算例,基于动力有限元法建立考虑软土循环弱化效应的格型钢板桩防波堤三维弹塑性动力分析模型,对软土地基在循环荷载作用下最大孔压增长规律以及不排水强度弱化特性进行研究。建立格型钢板桩-软土地基系统动力稳定性分析方法,对格型钢板桩-软土地基系统的破坏模式、稳定性以及沉降变形特性进行分析。结果表明:最大孔隙水压力主要分布在格体周围软土层,主、副格仓底部及部分桩-土接触部位的不排水强度发生明显弱化。考虑软土地基循环弱化效应时,格型钢板桩-软土地基系统的稳定性安全系数显著降低。建议在实际工程中应考虑软土地基循环弱化效应对格型钢板桩防波堤稳定性的影响。 相似文献
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在大型圆形煤场中采用桩-网复合地基是火电厂地基方案设计的新思路,该方案不仅要考虑地基土层的强度满足上部荷载的要求,还需要考虑堆载区内土体的变形对环基的影响。通过对圆形煤场中桩-网复合地基原体试验研究,介绍了在大面积堆载下如何进行桩、土及垫层中应力与应变的测试,设计了2套堆载与测试方案,在试验1区铺设了2层土工格栅,而在试验2区未铺设土工格栅。根据在2个试验区所获得的测试成果,研究了大面积堆载对堆载区内外土体变形的影响深度与范围,对比分析了不同高程处垫层与土体的竖向及侧向应力随深度的变化规律,结合堆载区中桩与边桩的桩身轴力变化,计算出上部桩侧土体对桩所产生的负摩阻力,并依据承台顶面附近测得的垫层与土层的应力,计算出桩土分担荷载的比例,以及桩土应力比的大小与变化规律。在此基础上得到土工格栅对大面积堆载区内外土体应变与应力的影响程度,从而可以为大型圆形煤场桩-网复合地基方案的设计与施工提供客观的技术参数与建议。 相似文献
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采用三维有限元程序建立了一长为6 m、直径为0.8 m的加筋碎石桩复合地基流固耦合数值模型,分析了其在堆载和孔压消散过程中的荷载传递和变形特性。较传统碎石桩,加筋碎石桩复合地基桩土应力比显著增大,超孔压、沉降和桩身侧向变形显著减小,且随筋材刚度的增大,其性能进一步改善。加筋碎石桩复合地基在桩间土固结过程中产生明显的桩土差异沉降,形成土拱效应,使得堆载结束后桩土应力比变化很小。筋材长度对加筋碎石桩复合地基桩土应力比和沉降影响显著,应对其全长加筋才能保证桩体刚度和有效减少沉降。 相似文献
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基于一维和三维固结挤土桩沉降时效计算分析 总被引：1，自引：0，他引：1
饱和软黏土地基中的挤土桩,施工引起的桩侧土体超孔隙水压力消散和竖向荷载引起的桩底土体固结是导致其沉降的主要因素。基于三维固结理论,研究了桩侧地基土再固结沉降的变化规律,并从桩-土相互作用的原理出发,结合边界条件,推导出了在桩侧地基土再固结沉降的作用下挤土桩沉降的计算公式。运用太沙基一维固结理论并采用分层总和法计算竖向荷载作用下桩底土体的沉降。提出了饱和软土中挤土桩沉降时效的计算方法。并对工程实例进行了计算分析,其结果符合工程实际沉降规律。 相似文献
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This paper presents a numerical formulation of a three dimensional embedded beam element for the modeling of piles, which incorporates an explicit interaction surface between soil and pile. The formulation is herein implemented for lateral loading of piles but is able to represent soil–pile interaction phenomena in a general manner for different types of loading conditions or ground movements. The model assumes perfect adherence between beam and soil along the interaction surface. The paper presents a comparison of the results obtained by means of the present formulation and by means of a previously formulated embedded pile element without interaction surface, as well as reference semi‐analytical solutions and a fully 3D finite element (FE) model. It is seen that the proposed embedded element provides a better convergence behavior than a previously formulated embedded element and is able to reproduce key features of a full 3D FE model. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Three-dimensional (3D) numerical analyses have been carried out to study the behaviour of a single pile to adjacent tunnelling in the lateral direction of the pile. The numerical analyses have included comparisons between the current study, previous elastic solutions and advanced 3D elasto-plastic analyses. In the numerical analyses, the interaction between the tunnel, the pile and the soil next to the pile has been analysed. The study includes the axial force distributions on the pile, the relative shear displacement between the pile and the soil, the shear stresses at the soil next to the pile and the pile settlement. In particular, the shear stress transfer mechanism along the pile related to tunnel advancement has been analysed by using interface elements allowing soil slip. It has been found that existing solutions may not accurately estimate the pile behaviour since several key issues are not included. Due to changes in the relative shear displacement between the pile and the soil next to the pile with tunnel advancement, the shear stresses and axial force distributions along the pile change drastically. Downward shear stress develops at the upper part of the pile, while upward shear stress is mobilised at the lower part of the pile, resulting in a compressive force on the pile. A maximum compressive force of about 0.25–0.52Pa was developed on the pile, solely due to tunnelling, depending on the pile tip locations relative to the tunnel position, where Pa is the service pile loading prior to tunnelling. The majority of the axial force on the pile developed within ±2D in the transverse direction (behind and ahead of piles) relative to the pile position, where D is the tunnel diameter. In addition, mobilisation of shear strength at the pile–soil interface was found to be a key factor governing pile–soil–tunnelling interaction. The reduction of apparent allowable pile capacity due to tunnelling was dependent on the pile location relative to the tunnel position. Some insights into the pile behaviour in tunnelling obtained from the numerical analyses will be reported and discussed. 相似文献
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斜坡上的桩基础的承载性能是复杂多变的。对于四川西部山地地形较广泛,且地基覆盖层多为特有的碎石土地层来说,水平受荷桩的相关研究还较少。为了研究碎石土地基斜坡上单桩基础的水平承载特性及桩土间的相互作用,通过现场水平静载荷试验在坡度为0°、15°、30°、45°的条件下,探讨桩身变形、桩身弯矩、土压力的变化。运用FLAC3D有限元分析软件得出水平荷载作用下,碎石土斜坡不同坡度的桩基础与桩周土之间的应力云图、位移云图的变化特点。将数值模拟结果与现场试验结果进行了对比,提出了单桩水平临界荷载和极限荷载在不同坡度区间内取值时的折减系数,为实际工程提供一定的参考。 相似文献
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Y. K. CHOW 《国际地质力学数值与分析法杂志》1996,20(9):635-646
Piles used for the stabilization of slopes have to be adequately designed to resist the induced lateral loads due to the movement of the unstable slope. In this paper, a numerical method is presented for the analysis of this problem. In this approach, the piles are modelled using beam finite elements. The soil response at the individual piles is modelled using the modulus of subgrade reaction and pile–soil–pile interaction considered using the theory of elasticity. Two case histories, one for single pile and the other for pile group, are analysed which show that the numerical model can predict the general characteristics of the piles reasonably well. The study suggests that the design of the piles based on the computed response from single pile analysis, ignoring group effects, may be unduly conservative. 相似文献
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I-Hsuan Ho 《Geomechanics and Geoengineering》2017,12(4):234-249
This paper presents the analytical methods of slope-stabilising piles using the three-dimensional (3-D) finite element (FE) analysis with the strength reduction method (SRM). This 3-D FE model is employed to overcome the limitations observed in two-dimensional (2-D) FE analysis. The solutions obtained from 3-D FE analyses are verified to be less conservative in this paper. The 3-D analysis is considered to be of particular importance to pile-slope problems. The soil that flows between piles cannot be taken account properly in the 2-D FE analysis. The method adopted in this paper can avoid the assumption of soil movement and the pressure distribution along the piles subjected to soil movement. The numerical analysis employs the Mohr–Coulomb failure criterion with the strength reduction technique for soil and an elastic member for piles. The spacing effect of the pile is considered in the 3-D model, the S/D (S: centre to centre, D: diameter of pile) ratio, equal to 4.0, is found to be equivalent to the single pile stabilisation. The middle portion of the slope is identified as the optimal location to place the piles. The proper length of the pile, which can be used to stabilise the slope, is also examined using 3-D FE analyses. It is concluded that L/H greater or equal 0.70 is recommended (L: pile length, H: slope height). The numerical analyses are conducted based on a coupled analysis, which simultaneously considers both the slope stability and the pile response. The failure mechanisms of the pile-slope system subjected to the pile locations, pile head conditions and pile length are each discussed. The contact pressure, shear force and moment along the piles are presented to illustrate the pile stabilising mechanism herein. 相似文献
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W. D. Guo 《国际地质力学数值与分析法杂志》2014,38(18):1969-1989
Recent study indicates that the response of rigid passive piles is dominated by elastic pile–soil interaction and may be estimated using theory for lateral piles. The difference lies in that passive piles normally are associated with a large scatter of the ratio of maximum bending moment over maximum shear force and induce a limiting pressure that is ~1/3 that on laterally loaded piles. This disparity prompts this study. This paper proposes pressure‐based pile–soil models and develops their associated solutions to capture response of rigid piles subjected to soil movement. The impact of soil movement was encapsulated into a power‐law distributed loading over a sliding depth, and load transfer model was adopted to mimic the pile–soil interaction. The solutions are presented in explicit expressions and can be readily obtained. They are capable of capturing responses of model piles in a sliding soil owing to the impact of sliding depth and relative strength between sliding and stable layer on limiting force prior to ultimate state. In comparison with available solutions for ultimate state, this study reveals the 1/3 limiting pressure (of the active piles) on passive piles was induced by elastic interaction. The current models employing distributed pressure for moving soil are more pertinent to passive piles (rather than plastic soil flow). An example calculation against instrumented model piles is provided, which demonstrates the accuracy of the current solutions for design slope stabilising piles. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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A modulus‐multiplier approach, which applies a reduction factor to the modulus of single pile p–y curves to account for the group effect, is presented for analysing the response of each individual pile in a laterally loaded pile group with any geometric arrangement based on non‐linear pile–soil–pile interaction. The pile–soil–pile interaction is conducted using a 3D non‐linear finite element approach. The interaction effect between piles under various loading directions is investigated in this paper. Group effects can be neglected at a pile spacing of 9 times the pile diameter for piles along the direction of the lateral load and at a pile spacing of 6 times the pile diameter for piles normal to the direction of loading. The modulus multipliers for a pair of piles are developed as a function of pile spacing for departure angle of 0, 90, and 180sup>/sup> with respect to the loading direction. The procedure proposed for computing the response of any individual pile within a pile group is verified using two well‐documented full‐scale pile load tests. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献