BEHAVIOUR OF ECCENTRICALLY LOADED SQUARE FOOTING WITH MICROPILES

Abstract

Micropiles are small diameter driven and grouted piles. These are ideal for building foundations on sites with poor ground conditions, sensitive surroundings, and restricted vertical clearance. These piles have been used effectively in many ground improvement applications to increase the bearing capacity and reduce settlement, particularly strengthening existing foundations. The improvement of bearing capacity of subgrade by utilization of horizontal reinforcement has shortcomings due to the need to remove in situ soil from site to the desired depth and introduction of reinforcement in horizontal layers and compaction of soil to the desired density. In this study, the possibility of increasing the bearing capacity of soil using micropile as vertical reinforcement is investigated. When the vertical reinforcement has been driven at the side of foundation, the reinforcing element resists the lateral displacement of soil underneath the footing and creates the sand confinement situation and improves the bearing capacity. The frictional resistance between the surface of pile and soil and associated group effects are also considered as one of the reasons for possible improvement. In this investigation laboratory tests were conducted for centrally as well as eccentrically loaded square footing with micropile as vertical reinforcement. The effect of diameter of micropile, the spacing between the micropile and distance of micropile from the edge of the footing on the bearing capacity improvement has been studied. The amount of reduction of settlement of foundation has also being studied. The percentage of bearing capacity improvement of eccentrically loaded footing is compared with that of centrally loaded footing. A numerical simulation was carried out using FLAC (Fast Lagrangian Analysis of Continua) 3D. The results obtained from the numerical simulations were compared with the experimental results. The agreement between observed and computed results is found to be reasonably good in terms of pressure-settlement and pressure-tilt characteristics of soil.