Combination of O-Cell Test and Conventional Head-Down Test

O-cell tests were performed in Singapore on four bored piles in a residual soil and underlying weathered, highly fractured bedrock called the Bukit Timah Granite formation. Two of the piles were 1.2 m diameter, uninstrumented, and 28 m and 38 m long. The other two were strain-gage instrumented, 1.0 m diameter piles, both 37 m long. The latter tests combined the O-cell test with conventional head-down testing. Analysis of the test results indicated that the pile toe stiffness was low. The evaluation of the strain-gage data showed that the pile material modulus was a function of the induced strain. The desired axial working load was 10 MN, and the combined O-cell and head-down tests correlated to a head-down test with a maximum applied load of 38 MN, which, although smaller than the ultimate resistance of the piles, was taken as the capacity of piles constructed similar to the second set of test piles at the site.