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1.
《Geomechanics and Geoengineering》2013,8(2):151-162
In this paper, finite element analysis is used to predict the undrained bearing capacity of strip, square and circular footings resting on layered clays. The soil profile consists of two clay layers with different thicknesses and properties. The results are compared with previous solutions for strip footings on layered clays. The bearing-capacity behaviour is discussed and the bearing-capacity factors are given for various cases involving a range of layer thicknesses and properties of the two clay soil layers. 相似文献
2.
The paper presents a model for the analysis of granular foundation beds reinforced with several geosynthetic layers. Such
reinforced granular beds are often placed on soft soil strata for an efficient and economical transfer of superstructure load.
The granular bed is modeled by the Pasternak shear layer and the geosynthetic reinforcement layers by stretched rough elastic
membranes. The soft soil is represented by a series of nonlinear springs. The reinforcement has been considered to be extensible
and it is assumed that the deformation at the interface of the reinforcements and soil are same. The nonlinear behavior of
the granular bed and the soft soil is considered. Plane strain conditions are considered for the loading and reinforced foundation
soil system. An iterative finite difference scheme is applied for obtaining the solution and results are presented in nondimensional
form. The results from the proposed model are compared to the results obtained for multilayer inextensible geosynthetic reinforcement
system. Significant reduction in the settlement has been observed when the number of reinforcement layer is increased. In
case of inextensible reinforcements as the number of reinforcement layer is increased the settlement is decreased with a decreasing
rate, but in case of extensible reinforcement the reduction rate is almost constant. Nonlinear behavior of the soft soil decreases
as number of reinforcement layer is increased. The effect of the stiffness of the geosynthetic layer on the settlement response
becomes insignificant for multilayer reinforced system, but the mobilized tension in the reinforcement layers increases as
the stiffness of the geosynthetic layers increases. 相似文献
3.
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
4.
Experimental and analytical investigations on bearing capacity of strip footing in reinforced sand backfills and flexible retaining wall 总被引：2，自引：1，他引：1
This study focuses on the experimental and analytical investigations of small-scale physical model tests. For this purpose, a set of tests were conducted with and without reinforcement on the top of the backfill. The specimens were different in terms of parameters like the number of geotextile layers, the vertical distance between layers and the strip footing distance from the wall. Soil failure in the bearing capacity step and the backfill shear zones was analysed using particle image velocimetry methods. Bearing capacity of the strip footings was studied using analytical procedures. The results indicate that a reinforcing top zone of the flexible retaining structures may be more appropriate than unreinforced case. The ultimate bearing capacity and wall deflection can be significantly improved by increasing the number of reinforcement layers. When the three layers of reinforcement are used, there is an optimum vertical spacing of the layers at which the bearing capacity is the greatest (h/H?=?0.12, d/H?=?0.33 and u?=?B). The study shows that the analytical solution and the results from the experimental models are in good agreement. 相似文献
5.
The limit analysis method has been widely used in the stability analysis of geotechnical problems including the bearing capacity of foundations. Two main approaches have been followed in the limit analysis to improve the calculation of the bearing capacity of foundations. One approach is to combine limit analysis with the finite element method and linear/nonlinear programming. The other is to use a multi-rigid-block mechanism to obtain an upper-bound solution. In this paper, the multi-rigid-block upper-bound method with a modified failure mechanism from that of Florkiewicz [Florkiewicz A. Upper bound to bearing capacity of layered soils. Can Geotech J 1989;26(4):730–6.] was employed to calculate the bearing capacity of foundations. Attention was paid particularly to the bearing capacity of strip footings over a two-layered soil. In order to verify the effectiveness of the modified mechanism, comparisons were made with other well-known solutions. The results showed improvements over the best available multi-rigid-block upper-bound solutions given by Michalowski and Shi [Michalowski RL, Shi L. Bearing capacity of footings over two-layer foundation soils. J Geotech Eng ASCE 1995;121(5):421–8.], and fair consistence with the results from the finite element limit analysis in Shiau et al. [Shiau JS, Lyamin AV, Sloan SW. Bearing capacity of a sand layer on clay by finite element limit analysis. Can Geotech J 2003;40(5):900–15.]. 相似文献
6.
土工格栅加筋土地基平板载荷试验研究 总被引：2，自引：0，他引：2
在近年来的岩土工程实践中,土工合成材料加筋土技术得到越来越广泛的应用。采用平板载荷板试验方法,进行了多组加筋砂土地基模型试验,监测和分析了不同加筋材料（双向格栅与四向格栅）和加筋层数对土工格栅加筋土地基承载特性的影响。研究结果表明：土工格栅加筋土地基与无筋地基相比,承载性能得到改善,双层加筋明显优于单层加筋;土工格栅加筋限制了浅层地基的侧向变形,相同荷载下地基沉降减小,可恢复变形增大;模型试验中测得加筋材料应变和拉力很小,与土工格栅强度相比,拉伸模量对加筋土地基承载力的贡献更大。 相似文献
7.
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
8.
Razieh Moradi Aminaton Marto Ahmad Safuan A. Rashid Mohammad Moeen Moradi Abideen Adekunle Ganiyu Suksun Horpibulsuk 《Environmental Earth Sciences》2018,77(3):100
Granular column technique is a soil improvement method used to increase the bearing capacity of a soft soil area by replacing the soil with a group of granular column materials. The by-product utilisation is a worldwide interest for sustainable infrastructure development. Bottom ash, which is a combustion deposit derived from coal burning, is a potential by-product that could be used alternatively to sand or aggregate as a green granular column material. This research is to study the potential use of the bottom ash column-improved soft clay by conducting a series of small-scale physical modelling test. The bearing capacity behaviour and failure mode of soft clay improved with end-bearing group of bottom ash columns with and without geotextile encasement are investigated. The bearing capacity of soft clay is significantly enhanced by the inclusion of bottom ash columns; that is, 239% of bearing capacity improvement is observed with only 13% of improvement area. The bulging of the bottom ash column is transferred to buckling failure with higher bearing capacity when the bottom ash column is encased by geotextile. The outcome of this research leads to the usage of bottom ash by-product as a granular column material in sustainable soil improvement technique. 相似文献
9.
This paper presents results of meticulous laboratory testing and numerical simulations on the effect of reinforcement on the
low-strain stiffness and bearing capacity of shallow foundations on dry sand. The effect of the location and the number of
reinforcement layers is studied in the laboratory, whereas numerical simulations are used to study the reinforcement-foundation
interaction. Laboratory tests show an increase of 100, 200, and 275% not only in bearing capacity but also in low-strain stiffness
(linear load–displacement behaviour) of a square foundation when one, two, and three layers of reinforcement are used, respectively.
The specimen preparation technique is found to be crucial for the repeatability and reliability of the laboratory results
(less than 5% variability). Numerical simulations demonstrate that if reinforcements are placed up to a depth of one footing
width (B) below the foundation, better re-distribution of the load to deeper layers is achieved, thus reducing the stresses and strains
underneath the foundation. Numerical simulations and experimental results clearly identify a critical zone between 0.3 and
0.5B, where maximum benefits not only on the bearing capacity but also on the low-strain stiffness of the foundation are obtained.
Therefore, soil reinforcement can also be used to reduce low-strain vibrations of foundations. 相似文献
10.
土工织物加筋技术在工程中得到了广泛的应用,取得了良好的加固效果。但对于土工织物加筋机制尚缺乏明确和统一地认识,加筋理论研究落后于工程实践。为此,进行了坡顶加载条件下土工织物加固黏性土坡和素土边坡的离心模型试验,记录和再现了素土边坡和加筋土坡在坡顶加载条件下的变形破坏过程。主要基于变形分析探讨了黏性土坡在土工织物简单加固条件下的加固效果和加筋机制。结果表明,土工织物加筋可以有效地提高黏性土坡的极限承载力,加筋带的存在改变了土体的位移场,扩大了坡顶加载的影响区域,加筋后滑裂面明显后移。加筋带对土体的局部作用和作用范围,随着土体变形的增大而增大和扩展 相似文献
11.
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
12.
非均质地基承载力及破坏模式的FLAC数值分析 总被引：3，自引：0，他引：3
利用基于Lagrangian显式差分的FLAC算法，通过数值计算，对黏结力随深度线性增长的非均质地基上条形基础和圆形基础的极限承载力及地基破坏模式进行了对比计算与系统分析。研究表明：（1）随着地基黏结力沿深度非均匀变化系数的增大，地基的破坏范围逐渐集中在地基表层和基础两侧：（2）即使地基的非均质程度较小，当将非均质地基近似地按均质地基考虑时，由此所估算的承载力可能过于保守；（3）地基承载力系数随黏结力沿深度非均匀变化系数的增大而非线性地增大。与数值解相比，skempton与Peck等近似公式均可能高估了非均质地基承载力。 相似文献
13.
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
14.
复合加载情况下精确求解非均质地基上条形基础的极限承载力以及评价影响极限承载力的相关因素,具有很强的工程实用与理论参考价值。基于极限平衡原理,在Mohr-Coulomb破坏准则的基础上,将非均质地基上条形基础极限承载力问题等价为一个边界待定的泛函极值问题。利用变分原理得到与平衡方程相等价的积分约束条件以及相应的欧拉方程与横截条件。引入问题边界条件,利用VC++6.0编制了数值计算程序,求得了复合加载情况下非均质地基破坏时的滑裂面函数与破坏包络曲线。从理论上研究了土体内摩擦角、土体黏聚力、土层强度比与地下水位变化等因素对地基破坏包络曲线的影响。研究结果表明,其解答是地基极限承载力真实解的某一最小上限。 相似文献
15.
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
16.
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
17.
A. J. Choobbasti A. Zahmatkesh R. Noorzad 《Geotechnical and Geological Engineering》2011,29(5):675-684
Stone columns (or granular piles) are increasingly being used for ground improvement. This study investigates the qualitative
and quantitative improvement in soft clay by stone columns. Finite element analyses were carried out to evaluate the performance
of stone columns in soft clay. A drained analysis was carried out using Mohr–Coulomb’s criterion for soft clay, stones, and
sand. The interface elements were used at the interface between the stone column and soft clay. Analyses and calculations
were carried out to determine equivalent parameters of soil/columns system. The bearing capacity ratio (BCR) of the soil has
been estimated for homogeneous and heterogeneous soil. The results have shown that the values of BCR for homogeneous soil
are obviously higher than those for heterogeneous soil. 相似文献
18.
In most marine reclamation projects, sand fill is placed directly on soft marine seabed soils. The sand particles can easily penetrate into the soft marine soils, and the soft soil can also move into the pore spaces inside the sand at the initial contact interface between the sand and the soft marine soil. In this case, the permeability and the volume of the sand above the initial surface are reduced. To avoid this problem, a geotextile separator is often placed on the surface of the soft marine soils before placing the sand. In this study, a two-dimensional physical model is utilized to study the geotextile separator effects. The initial conditions of a clayey soil, sand fill, and surcharge loading were kept the same in the physical model test with the only difference being that a geotextile separator was either placed on the clay surface or omitted. The settlements of the initial interface were recorded and compared for the two cases without or with the geotextile separator. The particle size distribution of the soils taken across the interface zone for different time durations was then measured, analyzed, and compared. Based on an analysis of the results, the sand percolation depth was 40 mm and fine particle suffusion was apparent when the sand was placed directly on the marine slurry surface without a geotextile separator. However, when a geotextile separator was used sand percolation was avoided, and the fine particle suffusion was effectively diminished. A relative fine particle fraction is defined to illustrate the migration of fine particles from the clay to the sand soils. The fine particle percentages of the Hong Kong Marine Deposits–sand mixtures were calculated for the cases with and without a geotextile separator using an empirical formula and micromechanical modeling to obtain a better understanding of the effects of geotextile separators in practice.
相似文献19.
20.
Kousik Deb N. Sivakugan Sarvesh Chandra P. K. Basudhar 《Geotechnical and Geological Engineering》2007,25(6):639-646
In this paper, considering the plain strain conditions, a numerical study has been conducted to investigate the behavior of
multi layer geosynthetic-reinforced granular bed overlying a soft soil using the Fast Lagrangian Analysis of Continua (FLAC)
program. The granular fill, soft soil, and geosynthetic reinforcements are considered as linear elastic materials. The geosynthetic
reinforcements are modeled as cable elements fully bonded with the surrounding soil, thus neglecting any slip. The results
obtained from the present investigation showed very close agreement when compared with the results of finite element analysis
and lumped parameter modeling. The distribution of vertical, lateral and shear stresses in the soil are greatly affected as
the number of reinforcement layers is increased. If the tensile stiffness of geosynthetic layers increases and its value is
no more than 4,000–5,000 kN/m, the settlement of the reinforced foundation decreases significantly. The reduction in settlement
is insignificant when the tensile strength of the geosynthetics exceed the above value. 相似文献