Experimental Study on Pile Group Efficiency in Various Types of Soil Using a Small–Scale Physical Model

Abstract

A testing program of static pile load was conducted using a small-scale model to investigate some factors influencing pile group efficiency. Natural sandy and clay soils were put into a soil tank. The test piles have a small size with two different lengths. The studied types of soil include sand soil, sand-clay alternating layers’ soil, and clay soil. There were a total of thirty-six tests with various spacing to diameter ratios (S/d) and length to diameter ratios (L/d). In sandy soil, the group efficiency η was always greater than 1, in which there was a slight decrease in the group efficiency η when (L/d) increased and η decreased to 1 when (S/d) increased. In clay soil, η was always less than 1; however, when (L/d) increased, η increased significantly. Thus, the effect of the pile length should be considered for pile in clay soil, where η increased when (S/d) increased, which is clearly opposite to that of sandy soil. With the same parameters including the number of piles, pile dimensions, and (S/d) and (L/d) ratios, the order in term group efficiency η was obtained as follows: sand soil, sand-clay soil, and clay soil.