Cone penetration test in clayey soil: Rate effect and application to pile shaft resistance calculations.

摘要

This research focuses on the evaluation of the factors affecting cone resistance measurement during cone penetration in saturated clayey soils and the application of the result to pile shaft capacity analysis. In particular, effects of drainage conditions around the cone tip were studied. In order to investigate the effects of drainage during cone penetration test, penetration tests were performed with various velocities in the field and in a calibration chamber and the obtained data were analyzed. For the field tests, two sites which have homogeneous clayey soil layers under the groundwater table were selected and CPTs were performed with various penetration rates. Penetration tests in calibration chamber were performed to investigate the transition points between undrained and partially drained, partially drained and fully drained conditions based on cone penetration rate and the coefficient of consolidation. A series of flexible-wall permeameter tests were conducted for various mixing ratios of clays and sands to obtain consolidation coefficient which is important to determine mixing ratios of chamber specimens. Nine piezocone penetration tests were conducted for different rates in calibration chamber specimen P1 (mixture of 25% clay and 75% Jumun sand) and eight penetration tests were carried out in calibration chamber specimen P2 (mixture of 18% clay and 82% Jumun sand). From the results of the penetration tests in the calibration chamber, a correlation between cone resistance and drainage condition was established. Cone factor was evaluated based on collected CPT data having appropriate soil parameters. The correlations between Nk and selected soil properties were examined and the new Nk correlation was proposed.; The new shaft capacity analysis method for piles driven in cohesive soil was proposed based on the suggested correlation between cone resistance and undrained shear strength and the alpha method. The alpha factor associated with the normalized cone resistance ratio and length effect was established based on statistical correlation based on 15 closed-ended pile load test results.