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There are many field situations where at least a moderate increase in the bearing capacity in weak clays is desired. One of the solutions for such situations is stabilization by installing a granular pile or stone column using empirical designs. The plane strain version of a granular pile is a granular trench. In the present investigation a failure mechanism is postulated for the granular trench and analytical expressions are derived for the ultimate bearing capacity of footings on such stabilized soils. Bearing capacity factors are presented for various combinations of the parameters considered. From the present study it has been reaffirmed that a granular trench significantly reinforces weak clay deposits.

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SUMMARYA new method is proposed for the optimum design of nailed soil slopes. A rigorous method of stability analysis, namely the Janbu's method, is modified in the limit equilibrium formulation, considering the effect of reinforcement. Only the tensile resistance of the reinforcement is included and the effects of shear and bending neglected. The total reinforcement force required to raise the factor of safety to a desired value has been minimized with the inclinations of the reinforcement and the distribution of the reinforcement forces as decision variables. In order to illustrate the efficacy of the proposed method, the results are compared with the available solutions. The effect of the number and relative locations of the reinforcements on the amount of reinforcement required, is studied. The lengths of reinforcement required to raise the factor of safety to various desired values and the corresponding optimum designs are presented. The acceptability of the critical surface is verified, by ensuring that the shear and normal stresses are positive along the critical surface.

Soil-reinforcement pull-out tests are essential for evaluating the strength, integrity, and effectiveness of the soil-reinforcement system. In this paper, a new pull-out test model that calculates the soil-geosynthetic reinforcement interface shear stress for highly extensible geosynthetic reinforcement is proposed. Based on a new bilinear interface shear model, the geosynthetic pull-out test results are calculated with regard to the variation of the mobilised geosynthetic tension with distance, geosynthetic pre-yield and post-yield behaviour, and the effective and extended length of the geosynthetic reinforcement. The resulting nonlinear equation for the soil-geosynthetic interface shear stress pull-out mechanism is nondimensionalised, expressed in a finite difference form, and solved numerically using the Gauss-Siedel technique. A parametric study is carried out for a range of relative stiffness values and interface shear stresses. The normalised load-displacement relationship and the variation of the pull-out force and reinforcement displacements, with distance along the reinforcement, are presented. The values calculated using the proposed model are compared with experimental pull-out test results for a needle-punched, nonwoven geotextile, polyester fibres coated with polyethylene, and nylon reinforcements.

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