Multi-level O-cell tests were carried out on two strain-gauge instrumented bored piles at the Can Tho Bridge crossing the Hau (Bassac) River in the Vietnamese Mekong Delta. The soil profile consists of about 70 m thick soft, deltaic silty clay deposited on dense to compact sand. The test piles, 2.0 and 2.5 m in diameter, were installed into 87 and 98 m depth, respectively, by a combination of casing the upper length and using bentonite slurry to stabilize below the casing. The lower and upper O-cell assemblies in the two test piles were located 2.5 m through 3.0 m and 12 m through 15 m above the respective pile toe level, respectively. The tests were performed in four Stages and the maximum loads applied by the lower and upper O-cells were about 21 and 26 MN, respectively. The measurements indicated that the pile toe stiffness of Pile TP1 was very low. The fit of the q-z Ratio Function shows ratio exponents of 0.2 and 0.1 for Pile TP1 and TP2, respectively. The stress-movement curves at the strain gage level GL1 show no tendency toward an ultimate resistance. The evaluation of the strain-gauge data showed that the pile axial stiffness was a function of the induced strain, ranging from a stiffness of 103 through 85 GN. The average unit resistance of both pile shafts placed in dense sand layer is about 460 kPa.
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