Dragload and downdrag performances of inclined pile group embedded in consolidating soil

Abstract

Abstract：The performance of inclined pile group embedded in consolidating soil under surcharge load was investigated by experiment in comparison with vertical pile group and single pile under the same conditions; dragload, downdrag, and layered soil settlement were measured. A three-dimensional numerical model was built via FLAC 3D software, and verified by the experimental results. Influence factors, such as consolidation time, pile spacing, and pile tilt angle were analyzed. The results show that dragload of inclined pile group increases with the increase of consolidation time and pile spacing or the decrease of pile tilt angle. Downdrag of inclined pile group increases with the increase of consolidation time, pile spacing and pile tilt angle.Inclined pile foundation is one of the common foundations used in engineering, such as infrastructure of bridge abutment and wharf. When the soils surrounding the pile settle more than the pile under surcharge load or groundwater table lowering conditions, negative skin friction (NSF) may occur. The development of dragload and downdrag in the pile could cause engineering problems like pile foundation failure or pile damage, difference settlement.Many researches have been carried out on dragload of vertical pile foundations through field tests (Fellenius [1] ), model tests (Toma et al [2] , Lee et al [3] , and Kong et al [4] ) and numerical simulations (Chow et al [5] , Lee et al [6] , Comodromos et al [7] , Hoque et al [8] , and Kong et al [9] ), and influence factors including pile arrangement, surcharge load, consolidation time, pile spacing, and pile positions, etc were analyzed. Some focused on downdrag of vertical pile group (Ng et al [10] and Lam et al [11] ). Only Shibata et al [12] and Kong et al [13] carried out model tests on the dragload of inclined pile group and analyzed the influence factors including surcharge load, consolidation time, and asphalt coating. But the downdrag of inclined pile group, the influence of pile tilt angle and pile spacing have not been considered.Hence, model tests on inclined pile group (2×2, S=4d, 15°, where S is pile spacing and d is the diameter of pile) and single pile (15°) embedded in consolidating soil under surcharge load were carried out in this study. Vertical pile group and single pile were also tested under the same conditions for comparative analysis. Three-dimensional numerical analysis on dragload and downdrag of inclined pile group embedded in consolidating soil was made with FLAC 3D[14] . The influence factors were analyzed.