Behavior of piled rafts overlying a tunnel in sandy soil

The present research presents experimental and finite element studies to investigate the behavior of piled raft-tunnel system in a sandy soil. In the experimental work, a small scale model was tested in a sand box with load applied vertically to the raft through a hydraulic jack. Five configurations of piles were tested in the laboratory. The effects of pile length (<i>L</i>), number of piles in the group and the clearance distance between pile tip and top of tunnel surface (<i>H</i>) on the load carrying capacity of the piled raft-tunnel system are investigated. The load sharing percent between piles and rafts are included in the load-settlement presentation. The experimental work on piled raft-tunnel system yielded that all piles in the group carry the same fraction of load. The load carrying capacity of the piled rafttunnel model was increased with increasing (<i>L</i>) for variable (<i>H</i>) distances and decreased with increasing (<i>H</i>) for constant pile lengths. The total load carrying capacity of the piled raft-tunnel model decreases with decreasing number of piles in the group. The total load carrying capacity of the piles relative to the total applied load (piles share) increases with increasing (<i>L</i>) and the number of piles in the group. The increase in (<i>L</i>/<i>H</i>) ratio for variable (<i>H</i>) distance and number of piles leads to an increase in piles share. ANSYS finite element program is used to model and analyze the piled raft-tunnel system. A three dimensional analysis with elastoplastic soil model is carried out. The obtained results revealed that the finite element method and the experimental modeling are rationally agreed.