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1.
The ultimate bearing capacity of strip footings resting on subsoil consisting of a strong sand layer (reinforced/unreinforced)
overlying a low bearing capacity sand deposit has been investigated. Three principal problems were analysed based on results
obtained from the model tests as follows: (1) the effect of stratified subsoil on the foundations bearing capacity; (2) the
effect of reinforcing the top layer with horizontal layers of geogrid reinforcement on the bearing capacity; (3) effect of
reinforcing stratified subsoil (reinforced and unreinforced) on the settlement of the foundation. It has been observed that
reinforcing the subsoil after replacing the top layer of soil with a well-graded soil is beneficial as the mobilization of
soil-reinforcement frictional resistance will increase. 相似文献
2.
加筋带布置对地基承载力的影响 总被引：2，自引：3，他引：2
现场原位载荷试验表明：素碎石薄垫层(Z/B=0.2)地基经土工带加筋后，能提高地基承载力。通过承载力比BCR分析加筋层数Ⅳ、加筋首层间距U、加筋带间距H、加筋线密度LDR对地基承载力的影响，并对极限稳定时筋带的设计拉力进行了讨论，提出用筋带的设计强度预估加筋地基极限承载力。 相似文献
3.
水平加筋是广泛应用的软土地基处理方法之一,而水平加筋地基极限承载力的确定是其地基处理设计的重要依据。因此,首先结合条形基础下水平加筋地基的工程特点,在探讨其承载机制和破坏特点的基础上,考虑破坏间断面上筋材与地基土体的变形协调,构建出反映加筋参数变化影响的可变破坏模式及机动允许速度场;然后,在此基础上,通过重点研究筋材的能量耗散分析方法,并引入上限极限分析理论,建立出条形基础下水平加筋地基极限承载力分析模型,再引入序列二次规划优化分析理论,建立出条形基础下水平加筋地基极限承载力确定方法,它能充分反映加筋设计参数对地基破坏模式及承载力的影响;最后,通过试验结果与该方法及现有同类分析模型结果的比较分析,表明了该模型与方法的合理性与可行性。 相似文献
4.
为探究土工格室加筋路堤在循环荷载及静载下的各种性能,利用美国GCTS公司的USTX-2000加载装置进行加载,通过改变加筋层数、格室高度,格室焊距对土工格室加筋路堤进行一系列模型试验。对各种工况下加筋路堤极限承载力、长期循环荷载及固定振次循环荷载后极限承载力的变化进行研究。试验表明,土工格室加筋能显著提高地基极限承载力并能显著减小坡顶和坡中临界破坏时的法向累积变形,在加筋间距一定的情况下,加筋层数增加和格室高度增大均可不同程度提高极限承载力并减小临界破坏时坡顶法向累积变形,格室焊距的减小也可在一定程度提高极限承载力,格室焊距对边坡法向变形影响不大;长期循环荷载下固定间距加筋层数对路堤竖向累积沉降量影响不大,而对边坡坡顶法向累积变形有一定影响,格室高度增大和格室焊距减小均可不同程度减小路堤竖向累积沉降量和坡面法向累积变形;越靠近加载点处,路堤土压力值受加筋影响越显著,加筋提高了土体刚度和密实度,使加筋路堤土压力值较无筋路堤明显增大;对于无筋路堤,改变动载幅值和振次均导致振后极限承载力有不同程度的降低,而对于加筋路堤,当动载幅值≥30 kPa或动载振次≥1 000时,振后极限承载力均有不同程度的提高。 相似文献
5.
基于传统的极限平衡条分法,利用临界滑动场法计算了条形基础的加筋地基极限承载力。假定土体处于极限平衡状态时,土体与筋材间存在均匀的摩擦力,通过建立土体条块极限平衡方程,推导了地基承载力的递推关系式。首先,设定计算土体范围,并划分条块和离散状态点;其次,根据递推公式计算各个状态点的参数,并搜索临界滑面;最后,根据搜索出的滑面计算地基承载力。通过实例比较进一步验证了计算结果的可靠性,并分析了首层筋带埋深、铺设层数和长度对地基承载力和滑面位置的影响。研究结果表明：地基承载力随着筋带埋深的增加先增大后减小;随着层数和长度的增加先逐渐增大,最后趋于稳定;滑面位置的变化规律主要是垂直影响深度和水平影响范围增大或减小。该方法原理简单、易于编程,为条形基础加筋地基承载力的计算提供了一种新思路,是临界滑动场法在地基承载力计算中的推广应用。 相似文献
6.
Experimental Study of Bearing Capacity of Granular Soils,Reinforced with Innovative Grid-Anchor System 总被引：1，自引：0，他引：1
Mansour Mosallanezhad Nader Hataf Arsalan Ghahramani 《Geotechnical and Geological Engineering》2008,26(3):299-312
The pull-out resistance of reinforcing elements is one of the most significant factors in increasing the bearing capacity
of geosynthetic reinforced soils. In this research a new reinforcing element that includes elements (anchors) attached to
ordinary geogrid for increasing the pull-out resistance of reinforcements is introduced. Reinforcement therefore consists
of geogrid and anchors with cubic elements that attached to the geogrid, named (by the authors) Grid-Anchor. A total of 45
load tests were performed to investigate the bearing capacity of square footing on sand reinforced with this system. The effect
of depth of the first reinforcement layer, the vertical spacing, the number and width of reinforcement layers, the distance
that anchors are effective, effect of relative density, low strain stiffness and stiffness after local shear were investigated.
Laboratory tests showed that when a single layer of reinforcement is used there is an optimum reinforcement embedment depth
for which the bearing capacity is the greatest. There also appeared to be an optimum vertical spacing of reinforcing layers
for multi-layer reinforced sand. The bearing capacity was also found to increase with increasing number of reinforcement layer,
if the reinforcement were placed within a range of effective depth. The effect of soil density also is investigated. Finally
the results were compared with the bearing capacity of footings on non-reinforced sand and sand reinforced with ordinary geogrid
and the advantages of the Grid-Anchor were highlighted. Test results indicated that the use of Grid-Anchor to reinforce the
sand increased the ultimate bearing capacity of shallow square footing by a factor of 3.0 and 1.8 times compared to that for
un-reinforced soil and soil reinforced with ordinary geogrid, respectively. 相似文献
7.
针对加筋挡墙顶部受条形基础载荷作用时的工作性能开展试验研究,分析条形基础距挡墙面板距离对基础极限承载力、加筋挡墙变形特点、筋材应变和破坏模式的影响。试验结果表明：基础极限承载力随基础偏移距离 增加呈现先增大后减小的趋势,且在 为 （ 为挡墙高度）时达到最大值;条形基础加载至破坏前一级载荷时,基础沉降与挡墙高度比值均小于2%,面板水平位移与挡墙高度比值均小于1%,且当 小于0.6时,面板顶部水平位移明显大于中底部;各层筋材中应变最大值随 增加而逐渐向远离面板方向发展,且筋材最大应变由最初出现在顶层而转向中间层;顶部受条形基础载荷作用下加筋挡墙破坏以3种模式为主,即顶层面板挤出的浅层破坏、破坏面沿基础边缘发展并向深部推进和加筋挡墙整体破坏。 相似文献
8.
S. Benmebarek S. Benmoussa L. Belounar N. Benmebarek 《Geotechnical and Geological Engineering》2012,30(4):907-923
Natural soils are often deposited in layers. The estimation of the bearing capacity of the soil, using conventional bearing capacity theory based on the properties of the top layer, introduces significant inaccuracies if the thickness of the top layer is comparable to the width of the rigid footing placed on the soil surface. Saturated normally consolidated and lightly overconsolidated clays indicate that under undrained condition the cohesion of soil mass increases almost linearly with depth. A few theoretical studies have been proposed in the literature to incorporate the variation of cohesion with depth in the computation of the ultimate bearing capacity of strip and circular footings. In this paper, after reviewing previous works, numerical computations using the FLAC code (Fast Lagrangian Analyses of Continua) are reported to evaluate the two layered clays effect on the bearing capacity beneath rigid strip footing subject to axial static load. The results of the bearing capacity relating to the relative thickness of the top layer, the strength ratio of the soil two-layered clays and the rates of the increase of soil cohesion with depth are presented in Tables and graphs. The obtained results are compared with previous published results available in the literature. 相似文献
9.
高压喷射注浆法可以在软弱下卧土层中直接形成加固桩体对软土地基进行加固。对这种加固方法形成的地基进行了一组模型试验,其中包含了天然地基和加固地基,加固地基中设置了一组3×3的加固桩体,通过对比研究了直接加固软弱下卧土层的地基处理方法对地基工作性状的影响。结果表明：直接加固软弱下卧土层的方法能很好地改善地基的沉降特性,提高地基的承载能力。加固桩体能有效地传递荷载,使加固区软弱土体的压缩量大大减小。随着荷载的增加,加固桩体顶端承担的荷载大体呈线性增加,桩顶轴力表现为角桩最大,边桩次之,中心桩最小。加固桩体上部受负摩阻力作用,下部受正摩阻力作用,桩身最大轴力位于距桩顶25 cm处。加固区的平均桩-土应力比随荷载的增加而减小。 相似文献
10.
加筋土桥台作为承载结构,其承载力及其影响因素备受关注。以美国鲍曼桥为工程原型,通过大比例缩尺模型的静载试验研究加筋土柔性桥台的承载性能。试验研究中,以有纺土工织物为筋材,共设置3组加筋土柔性桥台模型的载荷试验,主要考察桥梁基座的位置,即桥梁承载区外沿与面板的水平净距对桥台承载力的影响及其变化规律。试验结果表明,水平净距是影响加筋土桥台承载性能的重要因素,承载能力随水平净距的增大而增大,但增幅快速递减;桥台面层水平位移和顶部沉降均随水平净距的逐渐增大而减小,且减小趋势表现出收敛特征;随着水平净距增大,筋材应变极值减小,桥台整体稳定性增强,表现出良好的复合体特性。试验研究结果还表明,美国现行规范关于加筋土桥台承载力计算方法可能仅限于特定的填料和加筋布置方式,因此在工程实践中宜结合工程实际。 相似文献
11.
In this study, four groups of different types of bridge foundation model are tested to research the horizontal bearing behavior of caisson-pile composite foundation in lab based on the Qiongzhou Strait bridge project. The Q-s curve and horizontal ultimate bearing capacity of these four groups of foundations in sandy soil layer are obtained. Pile bending moment and shear force of pile shaft are analyzed in detail. At the same time, the load sharing ratio of caisson and piles is discussed. The results show that the horizontal ultimate bearing capacities of a single caisson foundation are increased by 1.2 times, 1.6 times and 2 times respectively with adding skirts, steel pipe pile, or steel pipe pile and the skirt. The maximum bending moment point is in the middle of the pile shaft, i.e. at about 0.5 m under the mud surface. The horizontal load is borne mainly by the upper caisson foundation and soil layers above the middle upper part of pile. The maximum shear force is found at the joint of pile top of steel pipe and caisson pile, where the reinforcement measures should be taken in practical engineering. The research achievements could provide a better reference for design or construction of caisson-pile composite foundation. 相似文献
12.
以琼州海峡跨海大桥工程为背景,通过4组不同型式深水桥梁基础模型试验,对新型带桩沉箱复合基础的水平向承载性能进行了初步研究。试验得到了4组模型在砂性土层中的Q-s曲线及水平向极限承载力,并对复合基础在各级水平荷载下的桩身弯矩和剪力进行了详细分析,同时对沉箱-桩荷载分担比展开了讨论。试验结果表明：当增加裙边、钢管桩、或同时增加钢管桩和裙边后能够使单体沉箱基础的水平向极限承载力分别提高1.2倍、1.6倍和2.0倍;桩身最大弯矩点均出现在桩身中部即泥面下约0.5 m处。水平荷载主要由上部沉箱基础及桩身中上部土体承担,钢管桩桩顶与沉箱连接部位出现最大剪力,在实际工程中应在此处采取加固措施。研究成果可为这一新型深水桥梁基础的推广应用提供诸多有益参考。 相似文献
13.
Arvind Kumar Baljit Singh Walia Swami Saran 《Geotechnical and Geological Engineering》2005,23(4):469-481
A method has been proposed to obtain the pressure–settlement characteristics of rectangular footings resting on reinforced sand based on constitutive laws of soils. The confining effect of the reinforcement provided in the soil at different layers has been incorporated in the analysis by considering the equivalent stresses generated due to friction at the soil– reinforcement interface. The prerequisite of the method is the value of ultimate bearing capacity, which can be obtained from the approaches already available in literature. The value of settlement may be read directly from pressure–settlement curves for the given pressure intensity. Therefore, the rectangular footing resting on reinforced sand can be proportioned satisfying shear failure and settlement criteria. 相似文献
14.
Bearing capacity of two close strip footings on soft clay reinforced with geotextile 总被引：1，自引：1，他引：0
For many years ago, the beneficial effects of using reinforcement to improve the property of soil have been demonstrated. Over the last three decades, the use of polymeric reinforcement such as geotextile has increased in geotechnical engineering. Among the possible applications, earth reinforcement techniques have become useful and economical techniques to solve many problems in geotechnical engineering practice, such as improve the bearing capacity and settlement characteristics of the footing. This research presents the effect of geotextile inclusion on the bearing capacity of two close strip footings located at the surface of soft clay. A broad series of finite element analysis were performed on two footings with width of 1 and 2 m using two-dimensional plane strain model using the computer code Plaxis (ver 8). Only one type of soft clay was used for the analysis, and the soil was represented by two yielding criteria including hardening soil model and Mohr–Coulomb model, while reinforcement was represented by elastic element, and at the interface between the reinforcements and soft clay, interface elements have been used. A wide range of boundary conditions, including unreinforced and reinforced cases, was analyzed by varying parameters such as number of geotextile layers, vertical spacing of layers, depth to topmost layer of geotextile, tensile stiffness of geotextile layers, and distance of between two footings. From numerical results, the bearing capacity ratio and the interference factor of the foundations have been estimated. On the basis of the analysis performed in this research, it can be concluded that there is a best distance between footings and optimum depth for topmost layer to achieve maximum bearing capacity for closely spaced strip footings. The bearing capacity was also found to increase with increasing number of reinforcement layers if the reinforcements were placed within a range of effective depths. In addition, the analysis indicated that increasing reinforcement stiffness beyond a threshold value does not result in a further increase in the bearing capacity. 相似文献
15.
分别针对纯砂地基、水平加筋地基和新型三维立体加筋(简称横-竖加筋)地基进行了多组模型试验。主要研究了单层横-竖加筋深度和横-竖加筋层数对地基的影响,并通过与水平加筋地基的比较,结合横-竖地基砂土滑移面的形状,初步分析了横-竖加筋地基的加固机制。试验结果表明,同等试验条件下,横-竖筋的加筋效果较水平筋的好,对于单层横-竖加筋地基,加筋效果随加筋深度的增加而减弱,加筋深度超过一定范围后,加筋对地基受力性能的改善不明显。对于多层横-竖加筋地基,随加筋层数的增加,承载力增加,沉降减小。 相似文献
16.
台阶式加筋土挡墙变形与力学特性尚待进一步深入研究。利用模型试验综合分析台阶宽度、上墙筋材长度和筋材层间距对两级台阶式加筋土挡墙性能的影响,试验结果表明:当台阶宽度由1.3H1(H1为下墙高度)减至0.4H1、筋材层间距减小或上墙筋材长度增加时,挡墙顶部沉降明显减少,且墙顶极限承载力显著增加;台阶式加筋土挡墙水平变形受台阶宽度和上墙筋材长度的影响显著,顶部加载时以上墙中部“鼓肚”和下墙沿墙高逐渐增大为主;增加台阶宽度使上墙底部垂直土压力增加,而下墙靠近墙面侧垂直土压力显著减小,增加上墙筋材长度和减少层间距使垂直土压力向远离墙面一侧发展;顶部加载时台阶式加筋土挡墙滑动面始于加载板后缘,绕过上墙墙底承台并贯通于下墙顶部土体,其破坏模式以上墙深层滑动破坏为主。 相似文献
17.
目前通过对软土地基预加固处理来提高桩基水平承载力已被工程界认可,但如何在工程前期设计过程中估算软土地基预处理后桩基水平承载力提高值仍是技术难点。基于此,参考Bowles[1]的地基土水平抗力计算式,同时考虑成层软土地基预排水固结处理影响,通过数学推导,推求出根据原状软土室内土工试验抗剪强度指标及预加固处理时间,估算软土地基预处理后桩基水平承载力提高值的实用计算方法。考虑桩侧土弹塑性屈服影响,推导出成层软土中水平受荷桩弹塑性解析解及塑性区深度的计算式,给出了桩顶水平位移、桩身最大弯矩的无量纲计算式及相关计算源代码。依托于浙江省某水闸桩基工程案例,根据提出的计算方法对桩基水平承载力、桩顶水平位移及桩身最大弯矩等性状进行预估计算,并与地基预处理前、后现场试桩检测值进行验证对比,认为桩基水平承载力、桩顶水平位移及桩身最大弯矩等预估计算成果与工程现场试桩的检测值较接近,对类似工程设计具有较好的参考价值。 相似文献
18.
By using the upper bound finite‐elements limit analysis, with an inclusion of single and two horizontal layers of reinforcements, the ultimate bearing capacity has been computed for a rigid strip footing placed over (i) fully granular, (ii) cohesive‐frictional, and (iii) fully cohesive soils. It is assumed that (i) the reinforcements are structurally strong so that no axial tension failure can occur, (ii) the reinforcement sheets have negligible resistance to bending, and (iii) the shear failure can take place between the reinforcement and soil mass. It is expected that the different approximations on which the analysis has been based would generally remain applicable for reinforcements in the form of geogrid sheets. A method has been proposed to incorporate the effect of the reinforcement in the analysis. The efficiency factors, ηc and ηγ, to be multiplied with Nc and Nγ , for finding the bearing capacity of reinforced foundations, have been established. The results have been obtained (i) for different values of ? in case of fully granular and cohesive‐frictional soils, and (ii) for different rates at which the cohesion increases with depth for a fully cohesive soil. The optimum positions of the reinforcements' layers have also been determined. The effect of the reinforcements' length on the results has also been analyzed. As compared to cohesive soils, the granular soils, especially with higher values of ?, cause a much greater increase in the bearing capacity. The results compare reasonably well with the available theoretical and experimental data from literature. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
19.
The paper pertains to the pseudo-static seismic stability analysis of reinforced soil structures. Using limit equilibrium
method and assuming the failure surface to be logarithmic spiral, analysis has been conducted to maintain internal stability
against both tensile and pullout failure of the reinforcements. The external stability of the reinforced earth wall is also
assessed in terms of its sliding, overturning, eccentricity and bearing modes of failure. The influence of the intensity of
the surcharge load placed on the backfill is also considered in the analysis. The obtained results are validated by comparing
the same with those reported in literature. Studies have also been made regarding the influence of backfill soil friction
angle, horizontal and vertical seismic accelerations, surcharge load, the tensile strength of reinforcement, pullout length
of the reinforcement and number of reinforcement layers on the seismic stability against various failure modes as mentioned
earlier. 相似文献
20.
为了对软弱淤泥土进行加固,使之满足工程建设所需的一定承载力,在试验基地采用固结-固化复合技术对淤泥进行加固研究。试验时,将一定厚度淤泥分为浅层固化加固层和深层固结加固层;浅层（≤1 m）淤泥采用固化技术进行加固,使之形成高强度硬壳层;对于深层（＞1 m）淤泥,采用真空预压技术进行加固,以提高深层淤泥的承载力并控制加固土体的后期沉降量。试验结果表明,当固化剂掺量为0.6%～5.0%时,浅层固化淤泥承载力特征值在109～330 kPa;固结-固化复合技术对土体加固效果突出,分层加固土体整体的承载力特征值在89～230 kPa;浅层淤泥经过固化处理后,土体强度较高,对地表荷载起到了明显的扩散作用,有效地减小了地表荷载在下卧层土体中产生的附加应力;多数试验单元浅层固化土的应力扩散角在19.474°～26.303°之间。 相似文献