BEARING CAPACITY OF UNDER-REAM PILES IN WEAK SOILS

Abstract

The present study was carried out to study the bearing capacity. of single and multiple under-reamed piles in the weak soils covering a large portion of the Shriraagar Valley. The study include' full scale tests on 8 nos. 42 meter deep piles alongwith other field test and, an attempt has been made to be able .. compute the bearing capacity o.f these piles by simple field tests like the Dynamic cone penetration tests. The study has revealed that the bearing capacities computed from shear charac-teristics o•f un,dliscurbed samples, comparable values as found from actual load tosts are obtained. But, the existing relations, based on SPT values, estimate very high values. For this, suita-ble factors, that could be applied over the estimated values, have been worked out. While, computing the be ring capacity of under- reamed piles, it has been generally observed that the bearing part is much over-estimated. This could be due to the release of stresses in the zone around•.the bulbs due to cutting away of the soil. This may be particularly true when under-reaming is done in silty soils under water. Particular reference has been matte to the present practice where a tighter settlement criteria . in mo st codes for routine interpretation of load test on. piles is prescribed. On the basis of the present tests, it is found the the safe load tables, given in the Co ie (13:2911-Part 1, 196d) which is under revision, should be based on. 25 mm, and not 12 mm. settlement criteria.