The study of cone penetration test in use of site investigation for Tsueng Kwan O – Lam Tin Tunnel Cross-bay link construction

Abstract

This Project has studied the use of cone penetration test (CPT) for ground investigation (GI) in Tsueng Kwan O area. The objective of this study was to find the effectiveness of CPT soil classification and explore the usefulness of CPT in shallow site investigation. The study of CPT would cover the following aspects: a) the review of past CPT studies in soil classification b) technically reliable compared to traditional site investigation method (borehole drilling and Standard Penetration Test) c) working time in project programme This study presented the results and findings from literature review on cone resistance to undrained shear strength, cone resistance to SPT N Value and soil classification scheme of CPT. This study would carry out field investigation on the comparison between CPT result and Drillhole data. It would also review the work programme among CPT and Drillhole. It was found that the undrained shear strength derived from cone resistance was generally higher than the undrained shear strength from Vane Shear Test. The N60 derived from cone resistance was generally similar with the N60 from SPT. The soil classification between Robertson 1990 and Jefferies 1993 were similar. However, they showed different normally consolidated results. From the study of project programme among CPT and drillhole, the time for carrying out a CPT was average 0.5 day. The time for carrying out a drillhole was average 6 days. The time for carrying out a CPT was faster compared to the time for carrying out a drillhole. Adopting CPT as the site investigation method would be valuable with a relatively short work duration compared to drilling a marine borehole. Borehole was the traditional site investigation method. But it was generally not reliable due to drilling errors and interferences, such as stress relief, swelling, compaction, base heaving, caving and piping. CPT data was relatively reliable compared to drilling a borehole. Dissipation data was not allowed to use in this study because the consolidation rate was not allowed to disclose to the public with the pre-reclamation stage of the Tseung Kwan O – Lam Tin Tunnel Cross-Bay Link construction. The study would be more comprehensive if the dissipation data could be allowed to use. The correlation result would be more representative if more CPT data and marine drillhole data could be allowed to use. The study could also be improved if more sites were added in the data analysis.