Laboratory Investigation on Efficiency of Model Stone Column Groups


As in piles, the efficiency of a group (Eg) of stone columns is defined as the ratiobetween the capacity of the group to the capacity of each stone column in the groupmultiplied by single stone column capacity. In this paper, the group efficiency of 24 modelstone columns installed in soft clay is considered. These groups consist of 2, 3 and 4columns. The tests were conducted on stone columns with length to diameter ratio (L/D) of 6and 8. A laboratory setup was manufactured in which two proving rings were used tomeasure the total load applied to the soil-stone column system and the individual load carrieddirectly by the stone column. The foundation steel plates have 220 mm diameter and 5 mmthickness. These plates contain 1, 2, 3 and 4 holes, respectively. The spacing between allholes equals twice the stone column diameter (D), center to center.The stone column capacity is taken as the load corresponding to a settlement equalsto 50% of the diameter of stone column. The results illustrated that the group efficiencydecreases with increasing the number of stone columns, also the stone columns with L/D of(8) provided higher efficiency than those with L/D of (6).