Experimental study of a shallow strip footing on geogrid-reinforced sand bed above a void

Underground voids located in the failure zone of a structure's footing decrease the bearing capacity and increase the settlement of the footing. This paper presents results from laboratory-model tests of strip footings supported by reinforced sand beds above a continuous void to investigate the potential benefits of using a replaced reinforced sand layer to bridge the void. The parameters studied in this testing programme include the relative density of the replaced sand, the void embedment depth and the number of reinforcement layers below the footing base. The results demonstrate that the bearing pressure and footing settlement significantly improved as the three parameters above were increased due to arching of the soil mass overlying the void. With unreinforced sand, the undesirable structural effects of the void can be eliminated only by using sand with a relative density of 72% for a void embedded at a depth of around 3.5-4 times the void's diameter (D). The effects of voids embedded at depths of 3D and 2D can be mitigated using four layers of reinforcement at relative densities of 57 and 72%, respectively.