Abstract
The ultimate bearing capacity (qp) estimated by SPT N-value (N) for cast-in-place concrete piles supported by cohesionless soils was investigated by analyzing the published vertical loading test results. Following findings were obtained. (i) It is better to separate the effects of the confining stress and soil density on both qp and N. (ii) It is more rational to classify the cohesionless bearing stratum into sandy soils and gravelly soils in estimating their bearing capacity. (iii) A qp/σv’–N1 correlation based on the Terzaghi's theory well fits to the vertical loading test results for both sandy and gravelly soils where N1 is a normalized SPT N-value by the effective overburden stress (σv’). The qp/σv’–N1 correlation is better than qp–N correlation. (iv) By modifying the Yamaguchi's theory, a qp/σv0’0.75–N1 correlation derived in the present study shows better fit to the results of vertical loading test of cast-in-place concrete piles supported by both sandy and gravelly soils.
