Interpretation of In Situ State Parameters of Piezocone Penetration Tests in High Pile Rebound Soils

Abstract

Abstract Cone penetrometer testing (CPT) was performed along with pile driving analysis (PDA) at six piling projects to determine typical soil characteristics encountered during excessive pile rebound. The PDA test was used to develop profiles of rebound versus elevation, while the CPT test was utilized to provide continuous variations of soil parameters with depth. In situ data from the CPT and PDA tests were matched based on depth and elevation, then averaged over four depth intervals ranging from 1B to 8B (B is the pile’s diameter). The results indicated that the rebound and non-rebound CPT data plots clustered in distinctive regions on the soil liquefaction assessment chart. The rebound data showed dilative behavior with state parameter values less than −0.125, while the non-rebound data exhibited contractive behavior, with larger state parameter values. Predictive models for estimating the magnitude of pile rebound in terms of normalized CPT data were thus developed using stepwise linear and nonlinear regression analyses. The results for these showed promising correlations between rebound, pore water pressure, cone tip resistance and state parameter predicted as a function of friction ratio. Additionally, the depth of soil layers underneath the pile’s toe was found to play a prominent role in controlling the extent and the amount of rebound. The CPT data as averaged over 4B and 8B intervals also showed a clear tendency to determine problematic pile rebound zones, though no such tendency was seen in data averaged over 1B and 2B intervals.