GROUP CAPACITY AND EFFICIENCY OF FULL FRICTION PILES ON VERY SOFT SOIL

Abstract

This study was conducted by loading on full-friction piles in very soft clay. The test piles
comprised of square concrete piles of 20 cm x 20 cm, with 11.5 m and 17.5 m long. The pile groups consisted
of 2x2 piles and 3x3 piles, with the distance between piles from 3 to 5 times pile diameter. The loading tests
were conducted on single piles (2 tests), on individual piles within a group of piles (5 tests), and on a group of
piles (4 tests). The results showed that the loading capacity of a single pile, in general, was higher than the
capacity of individual pile within a group of piles; and yet, the capacity of individual pile within any group of
piles was higher for the pile at the edges of the group than for the pile at the center of the group. Furthermore,
since the loading capacity of any group of piles was always less than the capacity of single pile multiplied by
the number of piles, the pile group efficiency factor was found to range from about 50% to 70%. Finally, the
group of longer piles was found to yield lower efficiency factors than those of shorter piles.