Pile Shaft Capacity from Cone Penetration Test Records Considering Scale Effects

Abstract

The cone penetration test (CPT) is used as a complementary approach for determining the bearing capacity of piles. Via direct CPT methods for pile capacity prediction, correlation coefficients smaller than unity are used to relate cone tip resistance and sleeve friction to pile toe and shaft capacities, respectively. For correlating CPT data to pile capacity, specific factors must be considered, such as diameter, penetration rate, partial embedment of pile toe into a hard layer, mechanism of plunging, failure zone, data processing, and stress–strain conditions. The aim of this paper is to investigate the role and significance of scale effects to establish a direct relation between CPT records and pile shaft capacity. A database has been compiled including 83 full-scale pile load tests and CPT records in order to calibrate and validate the proposed approach. The less-than-unity ratio of pile shaft capacity to cone sleeve friction (i.e., rs/fs) for most of the cases shows that shear stress in the soil surrounding the pile is smaller than in the soil around the cone. Therefore, the differences between pile and penetrometer penetration rate and geometry are considered as the major factors that cause lower shear strain in the soil around the pile. By considering the determinants, an analytical-practical procedure is proposed, from which the pile shaft capacity can be predicted using cone sleeve friction. This approach demonstrates better agreement with measured capacity by static loading test results (Rs) and less scatter than other current CPT methods, and it can be used as a complementary approach for determining pile shaft capacity.