Bidirectional Tests on Two Shaft-Grouted Barrette Piles in Mekong Delta, Vietnam

The piled foundation design of the 40-storey Exim Bank Building in Ho Chi Minh City, Vietnam, included bidirectional static loading tests on two shaft-grouted barrette piles tested in September 2013. The soil profile consisted of organic soft clay on silty sand with some gravel and silty clay. The cross-section area of the barrette piles, TP1 and TP2, was 2,800 mm by 800 mm. They were excavated to 65-m and 85-m depth, respectively, using grab-bucket excavation techniques with bentonite slurry and guide wall advanced ahead of the hole. For each pile, the bidirectional cell assembly was installed 16 m above the pile toe level and the reinforcing cage was instrumented with diametrically opposed vibrating wire strain-gages at three levels below and five (TP1) to eight (TP2) levels above the cell level. Shaft grouting was carried out along a 40-m length above the TP1 pile toe and along a 20-m length above the TP2 pile toe. The static loading tests were performed 23 and 25 days, respectively, after the piles had been concreted. Analysis of strain-gage records indicated Young's modulus values of about 27 GPa on the nominal cross section of the piles. Simulation of the measured load-movement response indicated that the shaft resistance response was hyperbolic. The test schedule was interrupted by unloading/reloading cycles, which disturbed the gage data and included uneven load-holding durations which exacerbated the analysis difficulty.