Bearing Capacity of Pile Group and Piled Raft Foundations on Sandy Soil

Abstract

This paper presents an experimental study to investigate the behavior of piled raft system in different types of sandy soil. A small scale “prototype” model was tested in a sand box with load applied to the foundation through a compression jack and measured by means of a load cell. The settlement was measured at the raft by means of dial gauges, three strain gauges were attached on piles to measure the strains and to calculate the load carried by each pile in the group by the strain indicator. Nine configurations of pile groups (1x2, 1x3, 1x4, 2x2, 2x3, 2x4, 3x3, 3x4 and 4x4) were tested in the laboratory as a free standing pile group (the raft is not in contact with the soil) and as a piled raft (the raft is in contact with the soil), in addition to tests for a raft (unpiled) with different sizes. Three different densities of sand were used for some tests.It is found that the piles work as settlement reducers effectively when the number of piles is greater than (6) than when the number of piles is less than (6). The settlement can be increased by about 8 times in (1x2) free standing pile group compared to the piled raft of the same size. The effect of piled raft in reducing the settlement vanishes when the number of piles exceeds (6). For piled rafts (3x3) and (4x4) embedded in loose, medium and dense sand; an increase in the ultimate capacity by about 93%, 96% and 98% is obtained when the group is enlarged from (3x3) to (4x4). This is attributed to increase in footing size (cap) and the increase of the number of piles in the group