Upgrading Footings in Sand With Bored Piles

Abstract

Upgrading of extant shallow foundations by bored piles is examined by field tests. Tests include single piles in tension and compression, plate-load tests, and tests on groups consisting of a central plate and two adjacent piles. All tests are carried out in sand until bearing-capacity failure occurs. The effect of spacing between the plate and the piles on the ultimate load and load transfer is determined. By analysis of test results, a clear understanding of the interference between the shear zones of the test plate and the bored piles, and its effect on reducing the pile load capacity, is reached. The results indicate that the load-carrying capacity of shallow foundations can be substantially improved by bored piles. And if the piles are installed at a spacing of one-and-a-half to two times the diameter of the footing, no reduction in load due to interference of shear zones will occur. For closer spacing, the efficiency of the group depends on the size, depth, and spacing of its components.