Two dimensional experimental study for the behaviour of surface footings on unreinforced and reinforced sand beds overlying soft pockets

Abstract

This paper presents results of a comprehensive investigation undertaken to quantify the efficiency of using reinforcement layers in order to enhance the bearing capacity of soils that are characterised by the existence of localised soft pockets. Small-scale model experiments using two dimensional tank were conducted with beds created from well graded sand with mean particle size of 300 μm but prepared with different dry densities. A relatively softer material was embedded at predetermined locations within the sand beds so as to represent localised soft pockets. Various arrangements of soil reinforcement were tested and compared against comparable tests but without reinforcement. In total 42 tests were carried out in order to study the effect of the width and depth of the soft pocket, the depth of one reinforcing layer and the length and number of reinforcing layers on the soil bearing capacity. The results show clearly that the ultimate bearing capacity reduces by up to 70% due to the presence of a soft pocket. It was also noted that the proximity of the soft pocket also influenced the bearing capacity. Reinforcing the soil with a single layer or increasing the length of reinforcement is not as effective as was anticipated based on previous studies. However, bearing capacity increased significantly (up to 4 times) to that of unreinforced sand when four layers of reinforcement were embedded. The results suggest that rupture of the bottom reinforcement layer is imminent in heavily reinforced sand beds overlying soft pockets and therefore its tensile strength is critical for successful reinforcement.