Bidirectional static loading tests on barrette piles. A case history from Ho Chi Minh City, Vietnam

Bi-directional static loading tests were conducted on two, strain-gage instrumented barrettes installed to 72 m depth in HoChiMinhCity, Vietnam. The barrettes were to support a 16 storey building with 5 basements. The soil profile comprised layers of medium coarse to fine sand, medium clay, firm to stiff clayey soil, and dense sandy silt. The region is experiencing an ongoing land subsidence affecting the upper about 40 m of soil and, on average in the city, the ground surface is currently settling 16 mm/year. The test records were processed by means of effective stress analysis to provide the axial pile force distribution, load transfer functions, and equivalent head-down load-movement curve. The analysis was then used to obtain the equivalent pile-head load-movement response adjusted to the planned 22 m deep basement excavation. Load transfer functions were back-calculated from the test records and indicate that the construction will show somewhat large load-transfer movement. However, because the neutral plane will be below the subsiding layers, below 40 m depth, downdrag is not expected to affect the building. The load response of the barrettes is compared to the results of a BD loading test on a 1.8 m diameter bored pile at an adjacent project.