Study on the influence of flash-flood impact and local scour on the load bearing performance of inclined pile group foundation in sand-gravel strata

Abstract

[Objective] Sand-gravel strata distribute widely in flash-flood-prone valleys. Under the combined action of flash-flood impact and local scour, the evolution mechanism of bearing capacity of inclined pile group is not clear at present. In order to explore the influence of complex geological formation conditions on the bearing capacity of pile group, finite element simulations of a 2×2 inclined pile group under different working conditions is carried out, and the bearing capacity curves of inclined pile group under different loads are obtained. [Methods] This study considers the heterogeneity of soil along the depth direction with Gibson soil model, and subsequently builds a finite element model taking the flash-flood impact, local scour, and nonlinear pile-soil interaction into account. The model is validated with published data of in-situ test. [Results] The result show that increase of the inclination of piles during an appropriate range could reduce the settlement and increase the vertical bearing capacity of the pile group; When the inclination of piles exceeds a certain value, the embedment depth of piles in the gravel stratum will decrease significantly, and consequently the pile group settlement will increase as a result of declined vertical bearing capacity; Due to the fact that the gravel stratum has a large particle size and high stiffness in comparison with the sandy stratum, the decrement of pile group settlement is not obvious when increasing the inclination of piles; The increase of inclination of piles could effectively improve the horizontal bearing capacity of pile group; The settlement and horizontal displacement of pile group increase significantly with respect to the formation of local scour hole, and consequently will lead to the deterioration of bearing performance of pile group. [Conclusion] After all, the bearing capacity of inclined pile group does not increase monotonically with the increase of inclination angle under the condition of composite strata with cobble at the bottom. With the increase of inclination angle, the bearing capacity of pile group subjected to the impact force of flash flood increases obviously. Therefore, the inclined pile group in sand-gravel strata should be designed with a reasonable inclination angle with regard to the engineering geological condition, with which the inclined pile group could attain expected bearing performance under the action of vertical load and flash flood.

Keywords

sand-gravel stratum / inclined pile group / bearing performance / flash-flood impact / local scour / settlement / horizontal displacement / influence factor