Bending the Foundation Beam on Elastic Base by Two Reaction Coefficient of Winkler’s Subgrade

A new method for analysis of counter beams is presented in the paper. The analysis has taken into account their stiffness EI, Winkler’s space with modulus of subgrade reaction k and equality deformities of the foundation beam with the ground. The solution is found by using the numerical analysis of the Winkler’s model, with variation of different moduli of the subgrade reaction k2 outside the force zone r, while under the force P exists the modulus of the subgrade reaction k, up to the definition of minimum bending moments. The exponential function k2(r), as the geometric position of the minimum moments is approximately assumed. From the potential energy conditions of the reciprocity of displacement and reaction, the width of the zone r and the modulus of the subgrade reaction k2 are explicitly determined, introducing in the calculation initial and calculation soil displacement wsi successively. At the end of the paper, it presented numerical example in which the influence of k and k2 values on bending moments of the counter beam is analyzed. The essential idea of this paper is to decrease the quantity of the reinforcement in the foundations, beams, i.e. to obtain a cost-efficient foundation construction.

THE AXISYMMETRIC MIXED BOUNDARY-VALUE PROBLEM OF THE VERTICAL VIBRATION OF A RIGID FOUNDATIONON SATURATED LAYERED SOIL SUBGRADE

Based on the theory of elastic wave propagation in saturated soil subgrade established by the author of this paper, the axisymmetric vertical vibration of a rigid circular foundation resting on partially saturated soil subgrade which is composed of a dry elastic layer and it saturated substratum is studied. The analysis relied on the use of integral transform techniques and a pair of dual integral equations governing the vertical vibration of the rigid foundation is listed under the consideration of mixed boundary-value condition. The results tire reduced to the case for saturated half-space. The set of dual integral equations are reduced to a Fredholm integral equation of the second kind and solved by numerical procedures, Numerical examples are given at the end of the paper and plots of the dynamic compliance coefficient C-b versus the dimensionless frequency a(0) are presented.

Study of the Bearing Capacity at the Variable Cross-Section of A Riser- Surface Casing Composite Pile

Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development.The offshore oil well structure includes a riser and a surface casing.The riser,surface casing and oil well cement can be considered special variable cross-section piles.Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production.In this paper,the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load.The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion,the influencing factors of the bearing capacity coefficient N_(c) are revealed,and the calculation method of N_(c) is proposed.By comparing the calculation results with the results of the centrifuge test,the accuracy and applicability of the calculation method are verified.The results show that the riser composite pile has a rigid core in the soil under the variable cross-section,which increases the bearing capacity at the variable cross-section.

Energy-based dynamic parameter identification for Pasternak foundation model

Parameter identification of Pasternak foundation models(PFM)is never satisfactory,which discourages the application and popularization of PFM.In the present study,an energy-based model to predict the dynamic foundation coefficients was proposed using the vibration kinetic energy and potential energy of a Pasternak foundation-rigid plate system.On the basis of the Pasternak foundation,the relationship among the natural frequency,dynamic foundation coefficients,rigid plate configuration,and vibrating soil equivalent mass per unit area was considered.To obtain the natural frequencies of the Pasternak foundation-rigid plate system,dynamic tests were performed.Using two or more dynamic test results of various rigid plates on a foundation,a set of equations of dynamic foundation coefficients was set up to directly identify the foundation coefficients and equivalent mass per unit area of vibrating soil.The feasibility of the proposed method was verified by comparing it with the outdoor and indoor test results and finite element analysis results.When the proposed method is used to obtain the dynamic parameters,PFM can be generalized and applied more widely in engineering practice.

An analytical p-y curve method based on compressive soil pressure model in sand soil

With the high-quality development of urban buildings,higher requirements are come up with for lateral bearing capacity of laterally loaded piles.Consequently,a more accurate analysis to predict the lateral response of the pile within an allowable displacement is an important issue.However,the current p-y curve methods cannot fully take into account the pile-soil interaction,which will lead to a large calculation difference.In this paper,a new analytical p-y curve is established and a finite difference method for determining the lateral response of pile is proposed,which can consider the separation effect of pile-soil interface and the coefficient of circumferential friction resistance.In particular,an analytical expression is developed to determine the compressive soil pressure by dividing the compressive soil pressure into two parts:initial compressive soil pressure and increment of compressive soil pressure.In addition,the relationship between compressive soil pressure and horizontal displacement of the pile is established based on the reasonable assumption.The correctness of the proposed method is verified through four examples.Based on the verified method,a parametric analysis is also conducted to investigate the influences of factors on lateral response of the pile,including internal friction angle,pile length and elastic modulus of pile.

基坑中软土的水平抗力系数几种确定方法探讨

该文围绕基坑中软土的的水平抗力系数的确定方法开展了探讨,分析了基坑规程中土的水平反力系数的比例系数m值的来源,分析了水平抗力系数确定的理论,罗列了现行规范中软土的水平抗力系数的经验值,最后通过案例分析,将3种土的水平抗力系数的计算方法(m值、k值和c值)的计算结果与实测进行了比较,发现按目前基坑规程公式计算的软土的水平反力系数的比例系数m值偏小的现象。

考虑桩土变形协调的复合地基设计方法

目前在复合地基的设计中,由于采用桩体压缩模量计算得到的复合压缩模量偏大,造成复合地基加固区沉降被低估;另外桩和桩间土承载力发挥系数取值主观性较强,导致复合地基承载力计算结果偏大。针对上述两个问题,从复合地基形成机理出发,指出桩及桩间土共同直接承担荷载时必须保证桩土变形协调。桩土变形协调的条件是:(1)桩刺入垫层的深度不能超过垫层厚度;(2)桩宜设置为摩擦桩。在此前提下,分别计算桩及桩间土的沉降,利用桩土变形协调方法得到了桩土应力比和承载力发挥系数理论值,进而得到加固区的沉降计算方法。工程算例证实,从保证复合地基有效设计和工程安全的角度出发,应该根据桩土变形协调来进行复合地基设计计算。

沉井在淤泥质软土地基下的应用研究

以青岛胶州海岸冲积平原软土地区某过河沉井工程为例,通过验算沉井在软土地基的下沉稳定系数,综合分析沉井突沉行为机理,提出了采用水泥土搅拌桩加固沉井刃脚处淤泥质土从而提高刃脚下土地基承载力的方法以减小沉井下沉稳定系数,避免沉井下沉时出现突沉行为,为该地区类似地质条件下的沉井结构设计应用研究提供借鉴。

考虑桩-土共同作用的减沉桩设计方法适用性分析

针对复杂地层中减沉桩基础适用性的问题,基于大量实际工程探讨场地地基与建筑类型、最大沉降控制标准与桩土刚度分布等因素对减沉桩基设计结果的影响,提出以节约用桩量为优化目标的减沉桩基础应用准则和设计方法,并通过工程案例验证了方法的合理性。结果表明:减沉桩基础对多种场地和建筑物类型具有较好的适应性,基础重要性等级、天然地基承载力和桩土刚度分布是决定其应用的关键因素;从节约用桩量和保证基础整体安全性出发,建议软土和硬土地区建筑物所在场地的天然地基承载力满足率不低于0.5和0.65;从保证筏板承载力贡献率考虑,Gibson地基和分层地基的无量纲影响系数建议不低于2.3和1.5;满足上述各项要求可作为判定减沉桩基础适用的基本前提。

坝坡基坑岩土非线性压力破坏下应力敏感性试验研究

以某地水库大坝基坑岩土为研究对象,进行坝坡基坑岩土非线性压力破坏下应力敏感性试验研究。基于岩土渗透率和渗透系数指标,利用非线性破坏规则分析坝坡基坑岩土的应力敏感性。结果表明:岩土非线性参数对坝坡基坑地基承载力影响较大,随着岩土曲率系数增大,承载力系数逐步降低,其中重度影响系数对岩土极限承载力的影响不敏感;渗透率与孔隙流体内压成正比,且围压较大时岩土渗透率受内压影响变化较小,应力不敏感,相反,围压较小时岩土应力敏感性较强;在围压不同阶段,渗透系数对含石率变化的敏感系数曲线,随着含石率的增加呈现先降低后上升再下降的总体态势,含石率为60%时,岩土渗透系数对含石率变化敏感性最高,应力敏感性最高。

基于离心机实验的海上风力机大直径单桩桩土作用研究

地基基础是海上风电结构所受载荷的最终承载者,针对中国沿海软弱超固结软土地基开展力学特性研究。通过离心模型试验方法对单桩基础形式的静力特性进行分析和对比。研究结果揭示通过离心模型试验模拟桩基础的有效性,该方法能准确捕捉现场地基的应力分布及桩与土体之间的相互作用特性。在软黏土环境中,针对不同直径的单桩进行的分析表明,其变形行为及桩土相互作用机制呈现出显著的差异性。规范中的p-y曲线不适用于中国近海土质,据试验结果提出地基无量纲水平抗力系数随埋深变化和与循环应力幅值相关的循环弱化因子计算模型。

软土地区高铁桥梁桩基比例系数合理取值研究

在高速铁路桥梁设计中,选取合理的桥梁桩基地基系数的比例系数m值是重要问题。本文依托天津滨海新区铁路项目,进行了单桩和群桩的水平静载试验,对不同水平荷载作用下单桩桩端和群桩承台的水平位移变化规律进行了分析。基于试验结果,对地基土水平抗力系数的比例系数m值进行了计算与拟合,给出了合理的软土地区m值的取值。结果表明:单桩与群桩m值-位移曲线较为接近,随着位移的增加,m值呈现指数型下降趋势。根据拟合结果,对单桩m值进行了推定,建议单桩m值取10MN/m^(4),群桩m值取2.6MN/m^(4)。与规范值相比,单桩m值更大,而群桩m值略小。

考虑地质影响的深基坑复合土钉墙最优支护参数选择技术

通过勘察一区域综合办公写字楼主楼获取土层详细指标,利用土钉抗力参数计算选取最佳土钉墙材料,并设计深基坑复合土钉墙支护方案与施工流程。将设计好的施工方案输入到FLAC3D软件中模拟深基坑支护结构,模拟不同地质影响下的侧压力系数。经试验验证:当土钉参数为5排、钢管嵌固深度参数为2 m时,支护结构可以最大程度降低深基坑的水平位移与沉降;在侧压力系数较大情况下,可以保持较低的竖直位移与深基坑坑底隆起值,具有较好的支护效果。

基于Spearman相关系数的接地电阻与土壤体积含水量相关性分析

【目的】防雷接地是防雷工程设计、施工和验收中的主要工作。通过了解土壤体积含水量对接地电阻的影响,能有效减少其对防雷接地设计的影响。【方法】对重庆市南川区金佛山国家综合气象观测专项试验外场2021年的接地电阻值和不同深度(地下0.1m、0.2 m、0.3 m、0.4 m、0.5 m、1.0 m)的土壤体积含水量数据进行特征分析,并对接地电阻、土壤体积含水量日均值进行正态性检验,利用Spearman相关系数进行相关性分析。【结果】深度为0.1~1.0 m时,接地电阻与不同深度的土壤体积含水量之间均呈现负相关关系,与深度为0.5 m的土壤体积含水量之间相关度最强,与接地极的埋深较为一致。【结论】对防雷接地设计有一定的参考价值。

塑性混凝土配合比设计及试验方法探讨

塑性混凝土已成功应用于三峡二期围堰防渗墙。结合工程实际探讨了塑性混凝土原材料的选择和配合比设计的基本方法 ,并总结了塑性混凝土的物理力学性能和参数试验方法。试验表明 ,优化配合比设计后的塑性混凝土能满足防渗墙良好的变形和防渗性能的工程设计要求。

影响强夯加固深度的因素分析

分析了众多影响加固深度的因素,并对已有加固深度计算公式进行了分类,指出只有三者的共同发展,才能逐步完善强夯的理论研究。

确定斜坡地基比例系数m值的模型试验研究

为研究斜坡坡度及水平荷载作用角度对斜坡地基比例系数m值的影响,设计并完成了一系列斜坡地基刚性桩水平承载室内模型试验,测得了不同斜坡坡度及水平荷载作用角度下地基比例系数m值.试验发现:斜坡地基比例系数m值随地面处桩身水平位移x、斜坡坡度α及水平荷载作用角度β增加呈非线性减小,当x>10mm时,m值几乎保持为一定值,并据此建立了斜坡地基比例系数m值与坡度α及荷载作用角度β之间的拟合关系式.理论与试验对比分析表明:根据考虑斜坡空间效应影响确定的斜坡地基比例系数m值,计算得到的桩身内力、位移与实测结果最接近,最大计算误差小于10%;斜坡桩基设计时,建议取地面处桩身水平位移x=10mm对应的m值.

球模型包裹法设计透水混凝土配合比

提出一种新的透水混凝土配合比设计方法,以球作为粗骨料颗粒的计算模型,测算单位体积粗骨料总表面积,再与裹浆厚度、水灰比和粗骨料堆积密度四个参数确定配合比。试验表明:在一定范围内,骨料粒径越大,水泥浆包裹越薄,透水混凝土的透水系数越大,强度越小,耐酸性能越差。通过材料的内部孔隙结构分析其性能变化规律,验证了该方法的合理性。

土壤结皮坡面流水动力学特征

为了深入探讨土壤结皮对侵蚀的影响机制以及两者之间的关系,以10°坡为例,在变流量(1.0,1.4,2.0,2.4和2.8 L/min)条件下进行室内冲刷试验,研究土壤结皮坡面径流水动力学特征(平均流速、平均径流深度、雷诺数、水流剪切力、水流功率、阻力系数)并分析坡面流水动力学参数与土壤侵蚀量的关系。结果表明,土壤结皮对坡面流水动力学参数影响显著。土壤结皮坡面雷诺数始终小于500,坡面流流态为层流;土壤结皮坡面具有较大坡面流流速,较小径流深度、水流剪切力和水流功率。结皮坡面的土壤侵蚀量明显低于无结皮坡面的土壤侵蚀量。土壤侵蚀量与坡面水动力学参数相关关系显著(相关系数R>0.90),土壤侵蚀量与雷诺数呈线性正相关,与水流剪切力、水流功率的对数呈线性正相关,与阻力系数呈线性负相关。因此,在本研究中,单纯从径流冲刷侵蚀的角度土壤结皮的存在有利于减小坡面土壤侵蚀量。由于降雨因素对土壤结皮的侵蚀效应影响较大,将雨滴打击与径流冲刷相结合才能更好地研究土壤结皮对侵蚀的影响机制。

用静力触探参数确定地基土水平地基抗力系数的比例系数m值——以天津地区为例

承受水平荷载作用的桩基,规范中常采用m法进行桩基水平承载力的计算,地基土水平地基抗力系数的比例系数m值在规范中根据地基土的状态、类别以表格给出。在地基勘察中,现在广泛采用静力触探试验,直接利用静力触探数据给出比例系数m值,将使桩基设计所用参数更加直接准确。本文利用天津地区地层大量静力触探资料与地基土状态数据,利用统计分析回归方法,总结出地基土的液性指数IL与静力触探参数锥尖阻力qc及摩阻比Rf间的关系式,针对天津的地层土体,给出利用静力触探资料查用m值的表格,为桩基的设计计算提供资料。