Capacity Of Strip Footings Research Articles

Failure modes and bearing capacity of strip footings on soft ground reinforced by floating stone columns

This study evaluates the failure modes and the bearing capacity of soft ground reinforced by a group of floating stone columns. A finite difference method was adopted to analyze the performance of reinforced ground under strip footings subjected to a vertical load. The investigation was carried out by varying the aspect ratio of the reinforced zone, the area replacement ratio, and the surface surcharge. General shear failure of the reinforced ground was investigated numerically without the surcharge. The results show the existence of an effective length of the columns for the bearing capacity factors N c and N γ. When certain surcharge was applied, the failure mode of the reinforced ground changed from the general shear failure to the block failure. The aspect ratio of the reinforced zone and the area replacement ratio also contributed to this failure mode transition. A counterintuitive trend of the bearing capacity factor N q can be justified with a shift in the critical failure mode. An upper-bound limit method based on the general shear failure mode was presented, and the results agree well with those of the previous studies of reinforced ground. Equivalent properties based on the area-weighted average of the stone columns and clay parameters were used to convert the individual column model to an equivalent area model. The numerical model produced reasonable equivalent properties. Finally, a theoretical method based on the comparison of the analytical equations for different failure modes was developed for engineering design. Good agreement was found between the theoretical and numerical results for the critical failure mode and its corresponding bearing capacity factors.

Seismic bearing capacity of strip footings on fiber reinforced soils by the stress characteristics method

Seismic bearing capacity of strip footings on fiber reinforced soils by the stress characteristics method

Bearing capacity of strip footings on a stone masonry trench in clay

Bearing capacity of strip footings on a stone masonry trench in clay

Bearing Capacity of Strip Footings Resting on Granular Soil Overlying Soft Clay

In the present research, an analytical method is applied to determine the bearing capacity of strip footing on two layers of soil. Bearing capacity is calculated according to soil resistance beneath the foundation and a virtual retaining wall method. To determine the bearing capacity of the footing in the said method, the active and passive forces on the retaining wall are considered equal along the edges. The active and passive forces of each of the two soil layers are found, and the results are applied to calculate the footing bearing capacity. Among the many advantages of this method are the possibility to determine depth of the rupture surface beneath the footing, and the ability to study the effects of the soil’s second layer on the footing bearing capacity. This study also examines the effects of soil improvement beneath the footing, as well as the depth and width of the compacted area on bearing capacity. A thorough analysis is conducted on soil layer thickness, soil cohesion and friction angle, footing depth and width, the width of the compacted soil beneath the footing, and the depth of underground water. A MATLAB program was used for calculation and deduction. In order to study the effects of various parameters on two layers of soil, results were compared with the bearing capacity of the footing on one soil layer in various situations. The bearing capacity of the footing was then compared with previous experimental methods, and the results obtained were reliable.

The bearing capacity factor N γ of strip footings on c–ϕ–γ soil using the method of characteristics

BackgroundThe method of characteristics (also called as the slip-line method) is used to calculate the bearing capacity of strip footings on ponderable soil. The soil is assumed to be a rigid plastic that conforms to the Mohr–Coulomb criterion. The solution procedures proposed in this paper is implemented using a finite difference method and suitable for both smooth and rough footings. By accounting for the influence of the cohesion c, the friction angle ϕ and the unit weight γ of the soil in one failure mechanism, the solution can strictly satisfy the required boundary conditions.ResultsThe numerical solution of Nγ are consistent with published complete solutions based on cohesionless soil with no surcharge load. The relationship of Nγ between smooth and rough foundations is discussed which indicates that the value of Nγ for a smooth footing is only half or more of that for a rough footing. The influence of λ (λ = (q + ccot ϕ)/γB) on Nγ is studied. Finally, a curve-fitting formula that simultaneously considers both ϕ and λ is proposed and is used to produce a series of Nγ versus λ curves.ConclusionsThe surcharge ratio λ and roughness of the footing base both have significant impacts on Nγ. The formula for the bearing capacity on c–ϕ–γ soil can be still expressed by Terzaghi’s equation except that the bearing capacity factor Nγ depends on the surcharge ratio λ in addition to the friction angle ϕ. Comparisons with the exact solutions obtained from numerical results indicate that the proposed formula is able to provide an accurate approximation with an error of no more than ±2 %.

Behaviour of strip footing on oil-contaminated sand slope

This paper presents an experimental and theoretical programme aimed at promoting a greater understanding of the behaviour of strip footing on oil-contaminated sand slope. Contaminated sand layers were prepared by mixing sand with an oil content of 0–3% by weight of dried sand. A broad series of conditions, including uncontaminated cases, was tested by varying parameters such as the thickness of the contaminated sand layer, the type of oil contamination, the slope angle and the edge distance of the footing relative to the slope crest. A plane-strain elastoplastic theoretical model using finite-element analyses was additionally performed to supplement the results of the model tests. The results indicate that the ultimate bearing capacity of strip footings on the contaminated sloping ground can be drastically decreased with increasing the thickness of the contaminated sand layer and the slope angle. To design a footing on oil-contaminated sand slope, it would be necessary to reduce the value of the bearing capacity factor Nγaccording to the type and percentage of the contaminated oil. The investigation also provides knowledge to revise the foundation design of the existing structures subjected to contamination.

Seismic Bearing Capacity of Strip Footings on Pile-Stabilized Slopes

This paper develops an analytical method to calculate seismic bearing capacity of a strip footing, which is located on a slope reinforced with rows of pile. The resistance of passive pile is determined based on normal and shear stress of the soil around the pile, which is then compared to other analytical methods. This comparison indicates an acceptable agreement. The variants of the study include location of pile rows, location of footing with respect to the slope crest, foundation depth, and horizontal seismic coefficient. The footing seismic bearing capacity is calculated based on seismic slope stability with limit analysis method (yield acceleration coefficient of reinforced slope with pile row) as well as soil stability beneath the footing by means of virtual retaining wall method. The main objective is to determine and establish the relation between various parameters and seismic bearing capacities of the footing, and to find the best location of the pile row that gives the best improvement in the footing seismic bearing capacity. Results indicate that stabilizing the earth slope with rows of piles has a significant effect on the improvement of seismic bearing capacity of the footing. In addition, the results of the present method are compared with those, reported by others, to demonstrate a reasonable agreement.

Estimating Bearing Capacity of Strip Footings over Two-Layered Sandy Soils Using the Characteristic Lines Method

A study on the bearing capacity of strip footings over sandy-layered soils has been conducted using the stress characteristic lines method. Traditional bearing capacity theories for specifying the ultimate bearing capacity of shallow foundations are based on the idea that the bearing layer is homogenous and infinite. In practice, layered soils are mainly being used. The stress characteristic lines method is a powerful numerical tool that can solve stability problems in geotechnical engineering. In the present paper, an appropriate algorithm is derived for estimating the static bearing capacity of strip footing located on two-layered soils using the stress characteristic lines method. Numerical and experimental examples are presented, to validate the proposed algorithm. Graphs and equations illustrate the effective depth of strip footings located on two-layered soils. If the friction angles of the top and bottom layers are 30° and 35°, respectively, the depth effect of the top layer is estimated to be 0.76 of the foundation’s width.

Bearing capacity of strip footings by incorporating a non-associated flow rule in lower bound limit analysis

A plane strain lower bound limit analysis technique in combination with the finite elements and nonlinear programming has been used to investigate the effect of considering a non-associated flow rule on the bearing capacity of a rigid strip footing. The results are derived in terms of bearing capacity factors Nc, Nq, and Nγ on account of the components of soil cohesion (c), surcharge pressure (q), and unit weight (γ), respectively. The results clearly indicate the increase in the magnitude of bearing capacity factors with an increase in the magnitudes of dilative coefficient (η). It is expected that the charts provided in this note will be quite helpful for the practicing engineers.

Reliability-Based Analysis of Bearing Capacity of Strip Footings Considering Anisotropic Correlation of Spatially Varying Undrained Shear Strength

AbstractA reliability-based analysis of the bearing capacity of strip footings considering the spatial variability of undrained shear strength of clay was performed using the random FEM. The effect of anisotropic correlation of spatially varying undrained shear strength on the mean and standard deviation of bearing capacity was obtained using the random FEM. It was found that the anisotropic correlation of undrained shear strength significantly affects the bearing capacity. The mean bearing capacity was found to be minimal for a specific combination of horizontal and vertical scales of fluctuation. The coefficient of variation of the bearing capacity increased with increases in horizontal or vertical scales of fluctuation, or both. The factor of safety required to achieve a specified target failure probability for different scales of fluctuation and coefficients of variation of the undrained shear strength of clay is presented.

Bearing capacity of strip footings on unsaturated soils by the slip line theory

The bearing capacity of strip footings on unsaturated soils is studied using slip line theory. The suction profiles considered are non-uniform with depth and correspond to vertical flow of water by infiltration or evaporation. The slip line theory assumes a plastic equilibrium state of a Mohr–Coulomb soil in which suction influences are included using the effective stress concept. This paper shows the similar and independent effects of cohesion and the contribution of suction to the effective stress in the governing equations. It shows that the influence of a non-uniform suction profile on bearing capacity is significant, and the depth to the ground water table and the footing width have significant roles in how much suction influences the bearing capacity. By approximating the contribution of suction to the effective stress as a function that varies linearly with depth, the effect of suction on bearing capacity is represented in dimensionless form in separate charts for smooth and rough footings. Using the charts the bearing capacity can be determined for any combination of friction angle, footing width, surcharge, soil unit weight and linear profiles of cohesion and the contribution of suction to the effective stress. An example is given which highlights the significant influence suction can have. These charts also permit assessment of bearing capacity changes that may occur when changes to suction are expected, due to seasonal fluctuations of soil moisture, drought or flooding.

New and Simple Equations for Ultimate Bearing Capacity of Strip Footings on Two-Layered Clays: Numerical study

AbstractIn this paper, two very simple and accurate equations are introduced that enable geotechnical engineers to determine the undrained ultimate bearing capacity of shallow strip foundations resting on two-layered clays. Results of the analyses show that in the case of weak-over-strong clay, usually general shear failure occurs, and in the case of strong-over-weak clay, the soil will most likely experience punching failure with a large amount of plastic settlement before it reaches its ultimate bearing capacity. This study applied the finite-difference method using a computer program to evaluate the undrained bearing capacity for all cases analyzed. The Mohr-Coulomb failure criterion was used for modeling the plastic behavior of soil. Simple equations are presented for cases of both strong-over-weak clay and weak-over-strong clay representing the bearing capacity of shallow foundations resting on two-layered clays. Results of this study are verified by acceptable statistical methods, and advantages of ...

Bearing capacity of strip footing in reinforced granular bed over soft non-homogeneous ground stabilized with granular trench

This paper presents a method to estimate the bearing capacity of a strip footing embedded in a geosynthetic reinforced granular bed over soft non-homogeneous ground, i.e., increase of undrained shear strength with depth, stabilized with granular trench. Madhav and Vitkar’s solution for bearing capacity of granular trench-supported strip footing in soft ground together with Meyerhof’s punching failure mechanism for dense sand overlying soft clay, extended to include the effect of axial tension in the reinforcement, form the basis of the analysis. A parametric study is performed and charts are developed to quantify the contributions of various parameters on the degree of bearing capacity improvement. The results of the present study are compared with experimental results from literature.

Bearing capacity of strip footings on unsaturated soils by the slip line theory

The bearing capacity of strip footings on unsaturated soils is studied using slip line theory. The suction profiles considered are non-uniform with depth and correspond to vertical flow of water by infiltration or evaporation. The slip line theory assumes a plastic equilibrium state of a Mohr-Coulomb soil in which suction influences are included using the effective stress concept. This paper shows that the influence of a non-uniform suction profile on bearing capacity is significant. When the contribution of suction to the effective stress can be approximated as a function that varies linearly with depth, the effects of suction on bearing capacity can be represented in dimensionless form in separate charts for smooth and rough footings. Using the charts the bearing capacity can be determined for any combination of friction angle, footing width, surcharge, soil unit weight and linear profiles of cohesion and the contribution of suction to the effective stress.

Low-cost alternatives to estimate unsaturated soil shear strength parameters

The bearing capacity of strip footings on unsaturated soils is studied using slip line theory. The suction profiles considered are non-uniform with depth and correspond to vertical flow of water by infiltration or evaporation. The slip line theory assumes a plastic equilibrium state of a Mohr-Coulomb soil in which suction influences are included using the effective stress concept. This paper shows that the influence of a non-uniform suction profile on bearing capacity is significant. When the contribution of suction to the effective stress can be approximated as a function that varies linearly with depth, the effects of suction on bearing capacity can be represented in dimensionless form in separate charts for smooth and rough footings. Using the charts the bearing capacity can be determined for any combination of friction angle, footing width, surcharge, soil unit weight and linear profiles of cohesion and the contribution of suction to the effective stress.

Numerical Solution of Bearing Capacity of Strip Footing in Soft Rock

Numerical Solution of Bearing Capacity of Strip Footing in Soft Rock

Seismic bearing capacity of strip footings on rock masses using the Hoek–Brown failure criterion

In this paper, the bearing capacity of strip footings on rock masses has been studied in the seismic case. The stress characteristics or slip line method was used for analysis. The problem was analyzed in the plane strain condition using the Hoek–Brown failure criterion. First, the equilibrium equations along the stress characteristics were obtained and the rock failure criterion was applied. Then, the equations were solved using the finite difference method. A computer code has been provided for analysis. Given the footing and rock parameters, the code can calculate the stress characteristics network and obtain the stress distribution under the footing. The seismic effects have been applied as the horizontal and vertical pseudo-static coefficients. The results of this paper are very close to those of the other studies. The seismic bearing capacity of weightless rock masses can be obtained using the proposed equations and graphs without calculating the whole stress characteristics network.

Evaluation of Bearing Capacity of Strip Footing Using Random Layers Concept

Abstract The paper deals with evaluation of bearing capacity of strip foundation on random purely cohesive soil. The approach proposed combines random field theory in the form of random layers with classical limit analysis and Monte Carlo simulation. For given realization of random the bearing capacity of strip footing is evaluated by employing the kinematic approach of yield design theory. The results in the form of histograms for both bearing capacity of footing as well as optimal depth of failure mechanism are obtained for different thickness of random layers. For zero and infinite thickness of random layer the values of depth of failure mechanism as well as bearing capacity assessment are derived in a closed form. Finally based on a sequence of Monte Carlo simulations the bearing capacity of strip footing corresponding to a certain probability of failure is estimated. While the mean value of the foundation bearing capacity increases with the thickness of the random layers, the ultimate load corresponding to a certain probability of failure appears to be a decreasing function of random layers thickness.

Soluciones de forma cerrada para la capacidad de carga de zapatas en suelos anisotrópicos cohesivos

Simple closed-form solutions for the undrained bearing capacity of strip footings on anisotropic cohesive soils are derived employing kinematical approach of limit analysis. Both modified Hill-type and translational failure mechanisms, with variable wedge angles, are attempted and the best upper bound for each mechanism has been analytically determined leading to an analytical expression for the bearing capacity factor. The influence of degree of soil anisotropy on the corresponding value for the bearing capacity factor has also been evaluated. For a wide range of degree of anisotropy, the improvement in the predicted upper bound values does not warrant the use of the modified Hill-type mechanism. Instead, the conventional Hill-type failure mechanism, with a fixed wedge angle of p/4, provides a simple and concise analytical expression for the bearing capacity factor that is analytically equivalent to the conventional Prandtl - Reissner bearing capacity factor for the case of isotropic soil multiplied by the average of the sum of degree of anisotropy plus unity. Rev. ing. constr. [online]. 2015, vol.30, n.2, pp. 109-125. ISSN 0718-5073. http://dx.doi.org/10.4067/S0718-50732015000200003

Bearing capacity of strip footings on two-layered clay under combined loading

In this paper, a lower bound limit analysis in conjunction with finite elements and second-order cone programming (SOCP) is used to determine the bearing capacity of a rigid strip footing placed on two-layered clay subjected to inclined or eccentric loading. The footing is founded on the free surface of the soil mass with no surcharge applied. Two types of footing–soil interfaces are considered: (1) zero tensile capacity and (2) non-zero tensile capacity. The numerical results are presented in the form of failure envelopes in the loading plane, and the corresponding failure mechanisms are also presented. The size and shape of the failure envelopes are dependent on (1) the undrained shear strength ratio (cu1/cu2), where cu1 and cu2 are the undrained shear strength of the top and bottom clay, respectively, and (2) the normalized thickness D/B of the upper clay, where D is the thickness of the top clay layer and B is the width of the footing.