Verification of pile design with bi-directional load testing

A large-scale pile testing programme, in-part comprising nineteen bi-directional load tests and forty-seven thermal integrity profile tests, was undertaken on 0.9m and 1.5m diameter bored piles up to 35m in length for the Victoria Park to Canning Level Crossing Removal Project, Western Australia. The bi-directional load tests were undertaken using Ougan Supercells, an assembly of cone-shaped hydraulic jacks, placed within each test pile at a level that would generate near equal and opposite upward and downward directed forces, facilitating shaft friction and end bearing measurements. The supercells were typically located within the bottom third of the test piles allowing pile behaviour at depth and at the pile base to be investigated. This paper discusses the interpretation of bi-directional load test data, pile-displacement behaviour and pile load distribution obtained in the tests carried out. Full mobilisation of pile capacity was observed in the lower test segment of a number of tests. Large displacement of the lower test segment allowed ultimate pile shaft friction and end bearing to be measured in very low strength Osborne Formation Siltstone and Shale. The significant displacement of the lower test segments was attributed to pile base disturbance during construction even though thorough base cleaning of the piles was undertaken. Pile constructability factors resulted in lower anticipated pile shaft friction as well as end bearing. Comparison is made between measured and estimated ultimate values from conventional rock uniaxial compressive strength-based methods for the Osborne Formation, and from cone penetration test-based method for the superficial formation.