Bearing capacity of rectangular footing on reinforced soil

In the present paper, a method of analysis for calculating the pressure intensity corresponding to a given settlement for a rectangular footing resting on reinforced soil foundation has been presented. The process has been simplified by presenting non-dimensional charts for the various terms used in the analysis, which can be directly used by practicing engineers. An empirical method has been suggested to find out the ultimate bearing capacity of footing on reinforced soil. The results have been validated with large-scale model tests also. The procedure has been made clear by giving an illustrative example. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analysis of square and rectangular footings subjected to eccentric-inclined load resting on reinforced sand

In the present paper, a method of analysis for calculating the pressure intensity corresponding to a given settlement for eccentrically and obliquely loaded square and rectangular footings resting on reinforced soil foundation has been presented. The process has been simplified by presenting non-dimensional charts for the various terms used in the analysis, which can be directly used by practicing engineers. An approximate method has been suggested to find out the ultimate bearing capacity of such footings on reinforced soil. The results have been validated with the model test results. The procedure has been made clear by giving an illustrative example.     

Pressure–settlement characteristics of rectangular footings on reinforced sand

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.     

Bearing capacity tests of strip footings on reinforced layered soil

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.     

Nonlinear elastic analysis of shallow footings subjected to eccentric inclined loads

In this study, the behaviour of shallow foundations subjected to eccentric inclined loads is presented using nonlinear elastic finite element analysis. The material non-linearity of the soil has been taken into consideration by employing the hyperbolic stress-strain model. The formulation of an isoparametric interface/joint element which is used between footing base and soil media has been presented. Tests have been conducted to determine the characteristics of soil-footing interface. Forty cases of strip footing resting on sand and subjected to eccentric-inclined load which were studied by Agrawal (1986) through model tests, have been analysed. The predicted pressure-settlement, pressure-horizontal displacement and pressure-tilt characteristics have been compared with experimental results of Agrawal (1986) and a reasonable agreement between the two has been observed.     

土工加筋抗冻胀工作机制的研究

在分凝势理论的基础上，建立了一套考虑温度、水分及冻土－未冻土－筋材体系应力变形诸因素耦合预测加筋土冻胀和筋材拉力的计算方法，并对一维冻结室内模拟试验进行了理论分析和数值计算。通过对加筋消减冻胀及其抗冻胀工作机制的分析，提出了加筋材料对土体施加的约束，不仅减小了土体的冻胀速率，而且还使冻胀位移向未冻土区发展，从而可有效地消减土体冻胀的结论。     

Stress distribution beneath rigid circular foundations on sands

The calculation of stresses induced inside the soil mass by the foundation loads forms an essential step in most of the geotechnical engineering problems dealing with the probable behaviour of foundations. The distribution of stresses on horizontal planes containing reinforcements at various depths is required in the analysis and design of reinforced soil foundations. An accurate evaluation of contact pressure distribution at the interface is a prerequisite for the computation of stresses inside the soil mass. Of the several approaches the elastic-plastic approach of computing the contact pressure distribution appears to be reasonable. Using this approach non-dimensional equations have been derived for calculating the contact pressure distribution beneath rigid circular foundations on sands. The contact pressure distribution so derived has been used for computing the stresses at various points using elastic theory. The results have been graphically presented and are compared with Boussinesq's distribution for uniform contact pressure.     

Nonlinear analysis of footings on granular bed–stone column improved soft soil

In this paper, a model for the analysis of footings having finite flexural rigidity resting on a granular bed on top of stone columns improved saturated soft (clayey) soil has been proposed. Soft soil has been modeled as a Kelvin–Voigt body to represent its time dependent behavior. Pasternak shear layer has been used to represent the granular layer and the stone columns have been idealized by means of nonlinear Winkler springs. Nonlinear behavior of granular fill, soft soil and stone columns has been invoked by means of hyperbolic constitutive relationships. Governing differential equations for the soil–foundation system have been obtained and finite difference method has been adopted for solving these, using the Gauss-elimination iterative scheme. Detailed parametric study for a combined footing has been carried out to study the influence of parameters, like magnitude of applied load, flexural rigidity of footing, diameter of stone column, spacing of stone column, ultimate bearing capacity of granular fill, poor foundation soil and stone column, relative stiffness of stone columns and degree of consolidation, on flexural response of the footing.     

Bearing capacity of square footings on reinforced layered soil

In the present study, an approximate method has been suggested to calculate the ultimate bearing capacity of a square footing resting on reinforced layered soil. The soil is reinforced with horizontal layers of reinforcement in the top layer of soil only. The pre requisite to the method is the ultimate bearing capacity of unreinforced layered soil, which can be determined from the methods already available in literature. The results have been validated with the model tests conducted on two layered soil compacted at different densities and the top layer reinforced with horizontal layers of geogrid reinforcement.     

Analysis and Design of Retaining Wall having Reinforced Cohesive Frictional Backfill

The case of a rigid wall with inclined back face retaining reinforced cohesive-frictional backfill subjected to uniformly distributed surcharge load has been analyzed using limit equilibrium approach. The analysis considers the stability of an element of the failure wedge, which is assumed to develop in the reinforced earth mass adjoining the back face of wall. The non-dimensional charts have been developed for computing the lateral earth pressure on wall and the height of its point of application above the base of wall. The theoretical findings have been verified by model tests on a rigid wall retaining a dry cohesive-frictional soil reinforced by geogrid strips. Experimental results are in good agreement with the theoretical predictions. A design example has been included to illustrate the design procedure.     

A homogenization method for estimating the bearing capacity of soils reinforced by columns

The ultimate bearing capacity problem of a strip foundation resting on a soil reinforced by a group of regularly spaced columns is investigated in the situation when both the native soil and reinforcing material are purely cohesive. Making use of the yield design homogenization approach, it is shown that such a problem may be dealt with as a plane strain yield design problem, provided that the reinforced soil macroscopic strength condition has been previously determined. Lower and upper bound estimates for such a macroscopic criterion are obtained, thus giving evidence of the reinforced soil strong anisotropy. Performing the upper bound kinematic approach on the homogenized bearing capacity problem, by using the classical Prandtl's failure mechanism, makes it then possible to derive analytical upper bound estimates for the reinforced foundation bearing capacity, as a function of the reinforced soil parameters (volume fraction and cohesion ratio), as well as of the relative extension of the reinforced area. It is shown in particular that such an estimate is closer to the exact value of the ultimate bearing capacity, than that derived from a direct analysis which implicitly assumes that the reinforced soil is an isotropic material. Copyright © 2005 John Wiley & Sons, Ltd.     

Soil–Structure Interaction of Damped Infinite Beams on Extensible Geosynthetic Reinforced Earth Beds Under Moving Loads

In the present paper, soil-structure interaction analysis of an infinite beam resting on extensible geosynthetic reinforced earth beds has been carried out for an applied load moving with constant velocity. The viscous damping of the soil-foundation system has been given due consideration in the analytical procedure. The infinite beam has been treated as resting on a granular fill layer overlying the naturally occurring weak soil layer. Geosynthetic layer has been provided in the granular fill layer and has been considered as extensible. This extensible nature has been incorporated with the help of no slip and the compatibility conditions at the interface between reinforcing layer and the neighboring soil. These conditions help in eliminating the two interfacial shear stress parameters and in considering the tensile modulus of geosynthetic layer in the analysis. The influence of various parameters, like magnitude and velocity of applied moving load, viscous damping, relative stiffness of granular fill and tensile modulus of geosynthetic layer, on the response of soil-foundation system has been studied. It has been observed that all these parameters affect the response significantly, however, the effect of velocity of moving load and viscous damping has been found to be more significant especially at higher velocities.     

柔性板桩板墙加固斜坡填方地基的土压力分配问题研究

通过对桩板墙挡土板的受力变形特征分析,指出桩间采用柔性挡土板时,作用于挡土板上的土压力相对较小。在对比分析拟化简仓法与卸荷拱法的基础上,针对当前挡土板土压力计算中存在的问题,对柔性板桩板墙加固斜坡填方地基展开试验研究,并重点研究桩前、桩后施工挡土板时墙后土压力的分布规律。通过对布置在挡土板上的位移计及预埋的土压力计进行监测,结果表明,挡土板布置在桩前时其挠曲变形及承受的土压力值较小,且桩间土拱效应更易得到发挥。挡土板上土压力自上而下多呈抛物线型分布,而作用于桩背侧的土压力分布相对复杂。通过对桩后布置挡土板的土压力分布规律进行为期21 d的监测,研究了土压力变化的时间效应。     

双参数黏弹性地基上连续配筋混凝土路面振动参数分析

以连续配筋混凝土路面（CRCP）近年来应用比较广泛的路面结构形式为研究对象,采用考虑地基压缩系数和水平剪切系数的双参数地基模型,建立了考虑地基土体滞回阻尼的黏弹性地基上CRCP的振动微分方程,运用三角级数和Fourier变换得到了简谐、矩形均布荷载作用下路面竖向位移的解答,并利用Fourier逆变换得到了数值结果,较为全面的分析了荷载速度、频率、路面配筋率、板厚以及地基参数对板的动力响应的影响。研究结果可为路面动力响应分析及连续配筋混凝土路面的质量评价提供参考。     

Interference effect of two closely-spaced shallow strip foundations on geogrid-reinforced sand

Summary Geotextiles and geogrids are now being used extensively in many civil engineering construction works. This study presents some laboratory model test results for the ultimate bearing capacity of an isolated, and two closely-spaced, strip foundations resting on unreinforced sand, and sand reinforced with layers of geogrid. Based on the model test results, the variation of the group efficiency with the centre-to-centre spacing of the foundation has been determined.     

预应力锚杆柔性支护喷射混凝土面层上的土压力

针对锚喷支护设计中面层土压力计算模式存在的问题,以预应力锚杆柔性支护技术为研究对象,假定锚杆间的土拱为二维平面拱,推导出了一种作用在喷射混凝土面层上的土压力计算方法,得到了面层土压力的分布曲线。分析土体黏聚力 、内摩擦角 、外摩擦角 和锚杆水平间距 对面层土压力的影响,并与简仓法计算结果进行了对比。结果表明, 越小,面层土压力越大,且简仓法计算值明显小于文中计算值; 对面层土压力最大值无影响;面层土压力最大值与 成正比; 对面层土压力也有明显影响,在实际工程设计中,不应忽略 对减小面层土压力的贡献。最后给出了计算面层上的土压力简化公式。     

Bearing Capacity of Eccentrically–Obliquely Loaded Footings Resting on Fiber-Reinforced Sand

This paper presents the method proposed to calculate the bearing capacity of a square footing under oblique and eccentric oblique loading condition (satisfying both shear failure and settlement criteria) resting on fiber reinforced sand layer underlain by sand with geosynthetic/fabric sheet at the interface. Large direct shear tests were carried out to investigate the shear strength parameters of sand and randomly distributed fiber reinforced sand (RDFS) and soil-plastic fabric sheet bond. The ultimate bearing capacity of RDFS was determined using direct shear results. Non-dimensional charts proposed by Kumar (Behaviour of eccentrically–obliquely loaded footing on reinforced earth slab. Ph.D. thesis, University of Roorkee, Roorkee, India, 2002) were used to consider the contribution of plastic fabric sheet in increasing the bearing capacity. Also, for calculating the settlement, horizontal deformation and tilt at a given pressure the regression analysis of plate load test data have been carried out. The predicted values of ultimate bearing capacity, settlement, horizontal deformation and tilt are compared with the experimental values which are in good agreement with each other. There appeared to be an increase in the residual shear strength and angle of internal friction of RDFS.     

黏弹性地基上路面板在多轮荷载作用下的响应分析

将内配纵向钢筋的路面视为置于黏弹性Winkler地基上的正交各向异性薄板,假设板在荷载运动方向上为无限长,车辆轮载被简化成包含自振频率的矩形均布移动荷载。应用三角级数及Fourier变换方法,得到了单轮荷载作用下路面竖向位移的表达式。在Fourier变换域内,利用叠加原理分别得到了前后双轮荷载和平行双轮荷载作用下路面竖向位移的解析解答。在此基础上,推导出连续配筋混凝土路面上受4轮车辆荷载作用时轮载附近位移的稳态响应表达式。利用数值积分方法对表达式进行Fourier逆变换,得到了数值结果,并全面地分析了多轮荷载作用时荷载间距、相位差、荷载速度、频率、地基阻尼以及配筋率对路面竖向位移响应的影响。     

The role of non-linear deformation analyses in the design of a reinforced soil berm at Red River U-frame lock No. 1

This paper describes a design application of non-linear deformation analysis to a complex soil–structure–foundation interaction problem through use of a finite element analysis. The problem consists of a proposed renovation to an existing soil-founded U-frame lock structure consisting of construction of a densely reinforced soil berm adjacent to an existing lock wall. Major questions facing the designer involve reduction of the earth pressure on the lock wall, layout of the reinforcing in the soil berm, and collateral effects of berm construction on the U-frame lock structure. A non-linear deformation analysis played a central role in addressing all of these questions. Berm construction and four operational load cases were used to understand the performance of the reinforced berm and to discern interactions among the lock, the backfill, the foundation strata of the U-frame lock, the reinforced berm, and the foundation strata of the reinforced berm. Insight gained from the soil–structure–foundation interaction analyses led to an alteration to the proposed reinforcement layout to enhance the performance of the reinforced soil berm.     

Equivalent Continuum Simulations of Geocell Reinforced Sand Beds Supporting Strip Footings

This paper presents an equivalent continuum method for simulating the behaviour of geocell reinforced sand foundation beds, using finite element technique. An equivalent composite model is used for numerically simulating the improvement in the strength and stiffness of sand confined with geocells. Shear strength of geocell encased sand is derived from the additional confining pressure due to geocell using hoop tension theory. The stiffness of geocell encased sand is represented by an empirical equation in terms of the stiffness of the unreinforced sand and the tensile modulus of the geocell material. Numerical simulations of strip footings resting on sand bed are carried out with and without geocell layer, varying parameters like, the dimensions of geocell layer, pocket size, depth of placement of geocell layer and the tensile modulus of the geocell material. The results of numerical analyses are validated with the corresponding experimental results. The comparison between the numerical results and the experimental results is found to be reasonably good. Some significant observations on the mechanism of geocell reinforcement have been presented in this paper.