Stress of Piles and Lateral Load Sharing Ratio Between Piles and Raft Evaluated From Seismic Observation on Piled Raft Foundation

Abstract

Seismic observation on piled raft foundation subjected to unsymmetrical earth pressure was performed since after the 2011 off the Pacific Coast of Tohoku Earthquake. Accelerations of building, dynamic sectional forces of piles and dynamic earth pressures on both sides of an embedded foundation and beneath a raft were observed at 235 seismic events including an earthquake magnitude of Me7.1. The maximum acceleration of 32.2 cm/s 2 was observed on building foundation. Based on the seismic record, it is confirmed that a lateral inertial force of the building is related to shear forces and bending moments of piles, and lateral resistant force beneath the raft. It was also found that lateral load sharing ratio of piles was estimated about 10 to 20 % of the inertial force of building from observed record. The load sharing ratio between piles and raft and bending moments of pile could be approximately explained by simplified theoretical equations.

Horizontal Loading Tests on Disconnected Piled Rafts and a Simplified Method to Evaluate the Horizontal Bearing Capacity

“…A series of horizontal loading tests on piled raft models was conducted by [20]; in which a horizontal load was applied to the connected piled raft to discuss the pile bending moment and the shear force of the raft. Hamada et al [13,14] carried out static cyclic lateral loading tests on large-scale piled raft foundations and found that most of the lateral force was carried by raft friction when there was large contact earth pressure beneath the raft, and piles experienced pulling forces from the raft, behaving like anchors at large deformations. Sawada et al [15] carried out a series of static horizontal loading tests by using a geotechnical centrifuge and found that the horizontal resistance of the pile part in the piled raft is higher than those observed in the pile group due to the raft base contact pressure.…”