Investigation of the behaviour and the design for piles subject to ground heave

Abstract

: Abstract The High Speed Two (HS2) mainline crosses deep cuttings in Charmouth Mudstone. Deep excavations cause significant stress changes in the ground which inevitably result in ground heave. However, there is a dearth of research and design guidance currently available for piles subject to ground heave induced by deep excavation in Charmouth Mudstone. In this paper, the geology and properties of Charmouth Mudstone, as revealed in in-situ and laboratory tests, are discussed. Preliminary pile load tests with bi-directional load cells, strain gauge and extensometer measurements were carried out to investigate the pile behaviour in Charmouth Mudstone. The t-z method in conjunction with interpretation of preliminary pile load test data have been used to analyse the displacement and the induced stress in the pile subject to excavation-induced heave. The parameters of the t-z curves were derived from the pile load test results. The analyses show that the pile behaviour is dependent on slippage along the pile-soil interface and the specific t-z curve for Charmouth Mudstone. Finite Element analysis is carried out to demonstrate that a simplified t-z analysis with an appropriate chosen t-z curve for Charmouth Mudstone can capture the vertical heave response reasonably well for the purpose of engineering design. The study and the conclusions made in this paper provide a viable method about pile heave design which are applicable to the wider industry.