Two-Layer Reinforced Foundation Soils Loaded to Failure

Geosynthetic reinforcement has been successfully applied in slopes and retaining walls for three decades. Although reinforcement for foundation soils has been a subject of studies, no generally-accepted methods for design of reinforced foundation soils are available. Laboratory experiments reveal that the collapse mechanisms of foundation soils with strips of reinforcement have features similar to the mechanisms of unreinforced soils. A recent development will be presented where the kinematic approach of limit analysis is used to arrive at the bearing capacity of reinforced foundation soils. Two modes of foundation soil collapse are distinguished: the first one is associated with reinforcement slip, and the second one occurs due to tensile failure of the reinforcement. Limit analysis is applied to both cases, but only the second case yields the strict upper bound to the limit loads. The slip mode requires assumption of the stress distribution on the reinforcement, which relaxes the strict nature of the limit analysis method. The solution for uniform soils reinforced with geosynthetics was developed recently, and the method is now extended to two-layer foundation soils where a reinforced granular fill is overlying soft/weak deposits. The solution obtained for the increase in the foundation soil bearing capacity can be used as a guideline in design. A chart is presented to facilitate the use of the preliminary results. In addition to numerical assessment of the increase in bearing capacity, the analysis indicates the effective length of reinforcement and its placement (depth and spacing).