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

Abstract

In the present study, the bearing capacity of rectangular footings resting on multilayer geosynthetic-reinforced granular fill overlying soft soil is investigated. Five different sizes of model footings are chosen in such a way that the aspect ratio of the footings is varied as 1.0 (square), 1.5 (rectangular), and 2.0 (rectangular). The effectiveness of multilayer reinforcement is assessed by comparing the bearing capacity improvement factor, settlement reduction factor, and load-spread angle. The variations of these factors with the aspect ratio of the footings are also studied. The optimum value of the thickness of granular fill over soft soil and sizes of the reinforcement as obtained for single-layer reinforcement placed at the granular fill-clay interface are selected for the entire test program. In some of the model tests, the reinforcement layers are instrumented with strain gauges to study the strain distribution along the reinforcement layers. The test results show that the improvement factor and settlement reduction increase with a decrease in the aspect ratio of the footing, and the increment is more for the multilayer-reinforced case (N > 1). However, the increment is more for the constant width case than with the constant length case of the footing. The load-spread angle increases with an increase of the L/B ratio of the rectangular footings, and the rate of increment decreases due to an increase in the number of reinforcement. An analytical solution is also proposed to estimate the ultimate bearing capacity of rectangular footings with various aspect ratios resting on the multilayer geosynthetic-reinforced granular fill of limited thickness underlain by soft soil. The predictions of the bearing capacity made by the developed model are found to be in good agreement with the experimental results.