Analysis of bearing capacity of bored piles from bi-directional load test: A case study in Quang Ngai province

The paper presents the vertical bearing capacity of bored piles from the bi-directional load test (O-Cell method) at the Tra Khuc dam-bridge project in Quang Ngai province. The dam structure was supported by approximately 400 bored piles with the diameter of D1200mm and the length of 27 m to 50 m. The ground includes the sand, clay and weathered rock layers with the SPT index (N30) from 8 to 80. The pile's tips were socketed in the granite layer with the average compressive strength of 18.6 MPa. Two test piles with the length of 29.1 m (T1N) and 42.75 m (T8N) were conducted O-Cell test. The side friction of soil layers and pile tip resistance were analyzed. The axial strain obtained from strain gages were used to analyze the axial load distribution along the depth of the pile. The test results show that the side resistance of the piles in the weathered rock mixed is 77.14 kPa for the pile T1N and 72.34 kPa for the pile T8N (approximately 50% of the total side resistance) which are not the ultimate shaft resistance of the piles in this layer. As its’ advantages, the bi-directional load test could be applied widely in the narrow site or on river condition in Vietnam