Some Studies on Prestressed Reinforced Granular Beds Overlying Weak Soil

This paper mainly investigates, from a series of laboratory scale bearing capacity tests carried out on a model square footing, the improvement in bearing capacity and reduction in settlement of a geonet reinforced granular bed (RGB) overlying weak soil due to prestressing the reinforcement. The parameters are the strength of the underlying weak soil, thickness of the granular bed, and magnitude and direction of prestressing force. The settlements at the interface are also measured. The addition of prestress to geonet reinforcement results in significant improvement in the load carrying capacity and settlement response of the prestressed geonet RGB. Improvement in bearing capacity is found to be more with biaxial prestressing than with uniaxial prestressing. Experimental results are also used to validate a proposed numerical model. The BCR (bearing capacity ratio) values predicted from this model are found to be in good agreement with the experimentally obtained BCR values. Finite element analyses are also carried out using the programme PLAXIS, to study the effect of prestressing the reinforcement. Results obtained from finite element analyses are also found to be in good agreement with the experimental results. 1. Introduction Soil reinforcing technique, using geosynthetics, has become a major ground improvement technique in geotechnical practice over the last three decades [1]. Its use is growing rapidly as worldwide development of infrastructure poses an increasing demand for land reclamation and utilization of soft foundation soils. Placing a granular bed over weak soil is the simplest technique of ground improvement that reduces settlements and increases bearing capacity of weak soil. The use of geosynthetic reinforced granular bed (RGB) over weak soil further reduces settlement and increases the bearing capacity of weak soil. Many experimental and analytical studies have been performed to investigate the behaviour of reinforced granular beds for different soil types. Binquet and Lee [2] conducted tests on sand reinforced with metal strips. Shivashankar et al. [3] proposed that the improvement in bearing capacity of a reinforced granular bed is comprised of three components, namely, shear layer effect, confinement effect and surcharge effect. They proposed equations for computing the effect of each of these components. Kurian et al. [4] simulated reinforced soil systems with horizontal layers of reinforcement using a 3D nonlinear finite element programme. The results of numerical analysis were in good agreement with those obtained from model