Capacity Of Rectangular Footings Research Articles

Lower bound analysis of rectangular footings with interface adhesion factors on nonhomogeneous clays

Solutions based on lower bound limit analysis provide a safe estimate of stability, and thus they are valuable for design and analysis in practice. In this paper, new lower bound solutions of the undrained bearing capacity of rectangular footings are first presented with consideration of adhesion factors at soil–footing interfaces and linearly increasing strength with the depth of clays. The new solutions of the problem are numerically derived using three-dimensional lower bound finite element limit analysis with semidefinite programming. The new solutions are expressed in terms of dimensionless parameters, including footing aspect ratios, adhesion factors at soil–footing interfaces, and normalized strength gradient factors. A statistically algebraic equation of the undrained bearing capacity of rectangular footings is also proposed for the first time.

Scale effects on the ultimate bearing capacity of rectangular footings placed on slopes

Evaluating the bearing capacity of footing near slopes is typically performed under two-dimensional conditions. However, rectangular footings, particularly with footing aspect ratios approaching unity do not adhere to the assumption of plane-strain conditions. In this study, the scale effects of rectangular footings near slopes are investigated by using upper- and lower-bound finite element limit analysis. The results indicate that when the longitudinal directions of a footing and slope are parallel, ignoring scale effects may result in overly conservative design for bearing capacity. However, when the longitudinal directions of a footing and slope are orthogonal, rectangular footings may have more significant scale effects than square footings and it may not be conservative to simplify three-dimensional conditions to plane-strain solutions. In addition, footing shape has a significant influence on the observed failure mechanism, demonstrating a transition in failure mechanism with changing aspect ratio. Generally, the presence of a larger internal friction angle amplifies observed bearing capacity scale effects. However, contrasting behavior may occur when the longitudinal direction of footings is perpendicular to the longitudinal direction of slope face. Finally, bearing capacity scale effects become most significant when the footing is embedded with rough sidewalls near tall and steep slopes.

Effects of aspect ratio of footings on bearing capacity for geogrid-reinforced sand over soft soil

Model plate load tests of rigid rectangular footings of different aspect ratios resting on sand overlying soft soil with or without a layer of geogrid at the interface are presented. The width (B) and length (L) of the footings are chosen so that the L/B ratio (aspect ratio) is varied as 1.0, 1.5, and 2.0. The study aims to investigate the effects of the aspect ratio of the rectangular footings and the thickness of the sand layer on bearing capacity, settlement characteristics, load-spread angle, and sizes of geogrid layer (at optimum sand thickness). The strain distribution along the reinforcement is also studied. Based on the test results, an analytical method is proposed to calculate the load carrying capacity of rectangular footings resting on reinforced or unreinforced sand over soft soil. It is found that the optimum sand thickness to footing width ratio is not dependent on the aspect ratio of the rectangular footings. However, the optimum sizes of geogrid reinforcement increase with an increase in aspect ratio of the footings. Also, the load-spread angle increases with an increase in aspect ratio. It is also observed that the load-spread angle in the lengthways direction of a footing is smaller than that in the widthways direction, and it is more pronounced in the case of reinforced soil compared to unreinforced soil.

Bearing Capacity of Rectangular Footings on Multilayer Geosynthetic-Reinforced Granular Fill over Soft Soil

Bearing Capacity of Rectangular Footings on Multilayer Geosynthetic-Reinforced Granular Fill over Soft Soil

Bearing capacity of rectangular footings in uniform clay with deep embedment

This letter is concerned with the undrained bearing capacity of rectangular footings with various aspect ratios and embedment ratios in uniform clay. It covers thin plate foundations with low aspect ratios and high embedment depth with embedment ratio up to 150. The work is based on small strain finite element analysis (FEA). After verification of the FEA model against existing solutions of the bearing capacity factors of rectangular footings, a series of FEA results are obtained. Based on the FEA results, a simple formulation is proposed to calculate the bearing capacity factor for rectangle footing with different aspect ratio in any embedment depth, extending the existing solutions to cover a wider ranges of footing aspect ratios and embedment ratios.

Shape effects on the capacity of rectangular footings under general loading

Ultimate limit states under vertical (V), moment (M) and horizontal (H) loading of rectangular footings with varying breadth-to-length aspect ratios (B/L) are compared with predictions for plane-strain conditions. Footing/soil interfaces unable to sustain tension and with unlimited tensile resistance are considered. Finite element and analytical predictions are reported, and results are presented as failure envelopes in VH, VM and VMH load space. Vertical and moment capacity of rectangular footings, with either zero or unlimited tension interfaces, is shown to increase with reducing footing length, for foundations of a given bearing area. For footings unable to sustain tension, footing aspect ratio does not affect the shape of the failure envelope: therefore ultimate limit states of a footing of any aspect ratio can be derived from a unique envelope scaled by the appropriate ultimate limit loads defining its apex points. A closed-form expression is proposed to describe the shape of the normalised VMH envelope. The shape of failure envelopes for footings able to sustain tension is dependent on footing geometry.

Discussion: Bearing Capacity of Rectangular Footings on Geogrid-Reinforced Sand

Discussion: Bearing Capacity of Rectangular Footings on Geogrid-Reinforced Sand

Bearing capacity of rectangular footings on geogrid-reinforced sand

Bearing capacity of rectangular footings on geogrid-reinforced sand

Bearing Capacity of Rectangular Footings on Geogrid‐Reinforced Sand

A study was undertaken to investigate the bearing capacity of rectangular footings on geogrid‐reinforced sand by performing laboratory model tests as well as finite‐element analyses. The effects of the depth to the first layer of reinforcement, vertical spacing of reinforcement layers, number of reinforcement layers, and the size of reinforcement sheet on the bearing capacity were investigated. Both the experimental and analytical studies indicated that there was an optimum reinfprcement embedment depth at which the bearing capacity was the highest when single‐layer reinforcement was used. Also, there appeared to be an optimum reinforcement spacing for multi‐layer reinforced sand. The bearing capacity of reinforced sand was also found to increase with reinforcement layer number and reinforcement size when the reinforcement was placed within a certain effective zone. In addition, the analysis indicated that increasing reinforcement stiffness beyond a certain value would not bring about further increase in the bearing capacity.

Bearing capacity of rectangular footings on clays of strength increasing linearly with depth : Nakase, A Soils Found, V21, N4, Dec 1981, P101–108

Bearing capacity of rectangular footings on clays of strength increasing linearly with depth : Nakase, A Soils Found, V21, N4, Dec 1981, P101–108

Bearing Capacity of Rectangular Footings on Clays of Strength Increasing Linearly With Depth

A complete set of bearing capacity factors for rectangular footings on clays of undrained shear strength (angle of shear resistance = 0) increasing linearly with depth was compiled by combining the exact plasticity solution for continuous footings and the slip circle solution for rectangular footings. Effect of increasing strength with depth was expressed in term of the ratio kb/co, where k is the rate of increase in strength with depth, co is the strength at the clay surface and b is footing width. It is examined that the value of kb/co likely to be encountered in practice is within the range from 0.2 to 30. As compared with results of the present analysis, three other kinds of bearing capacity formulae proposed for the case of strength increasing with depth, were found to overestimate the bearing capacity. The maximum extent of overestimation expected in practical problem is almost 300%. A set of approximate expressions for bearing capacity factor was proposed for convenience of practical use, which is a function of the ratio kb/co and the footing shape b/l. The maximum extent of underestimation by these approximate expressions is 5%. (TRRL)