In Situ Testing of Soft Soil at a Case Study Site with the Self-Boring Pressuremeter

摘要

The Changi East Reclamation Project in the Republic of Singapore involves improvement of marine clay by means of installation of prefabricated vertical drains and subsequent preloading. The in situ testing site was located in the Northern area of the project where the thickest compressible marine clay layers existed. The in situ testing site comprises of a vertical drain area where vertical drains were installed at 1.5 m square spacing and an adjacent control area without vertical drains. Both areas were preloaded with the same magnitude of preload over and above of proposed finished level. In situ tests were carried out using the self-boring pressuremeter test (SBPT) to determine especially the undrained shear strength and overconsolidation ratio of the marine clay together with some other geotechnical parameters prior to reclamation and after 23 month of preloading. In situ dissipation tests were also undertaken with the SBPT to provide a means of evaluating the in situ coefficient of consolidation due to horizontal flow (c_h) and horizontal hydraulic conductivity (k_h) of Singapore marine clay at Changi. Degree of consolidation was assessed 23 months after preloading using SBPTs data. The SBPT test indicates that the degree of consolidation of the vertical drain area had attained a degree of consolidation of about 80 % while the control area had attained a degree of consolidation of about 20-30 %. The c_h determined by the SBPT prior to reclamation is noted to be an order of magnitude greater than the laboratory data. The k_h results from SBPT in the Singapore marine clay are in the 10~(-9) to 10~(-11) m/s range.