Evaluation of Bored Piles Load Capacity in Rock Bearing. (Dept. C)

Rock socketed bored piles are particularly advantageous for conditions in which rock is near the ground surface underlying weak layers. This paper aims to predicate the ultimate capacity of bored piles supported in rock using analytical and mathematically based graphical approaches. Data-base of pile load tests from three projects constructed in Abu-Dhabi city in UAE were used, and Finite Element Analysis using 2-D Plaxis axisymmetric model has been developed to simulate the behaviour of such piles. The ultimate load predicted from the FEM method is compared with that estimated from the theoretical approaches. The pile working load with the corresponding settlements estimated from the theoretical approaches based on reasonable factor of safety were evaluated based on the results of pile load tests. From this study it was found that, the results of pile ultimate load estimated from the static formula were closer to those predicted by the FEM, compared with those calculated by modified Chin and Hansen methods. Under the ultimate load settlement was about 2.3% of pile diameter. While the socket length of a pile into rock is an important factor, the strength and R.Q.D. of rock seem to be the most significant parameters even for lesser socket length. The limiting displacement, after which the applied axial load is shared between the side resistance and the base resistance, has found to vary between 0.3% to 1.1% of rock socketed pile length, depending on the rock strength and R.Q.D.