砂卵石复合地层条件下考虑山洪冲击力和局部冲刷的倾斜群桩承载性能研究

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

摘要

【目的】山洪沟中砂卵石复合地层广泛分布，在山洪冲击力和局部冲刷联合作用下，倾斜群桩承载性能演化机理尚不明确。为探究复杂地层条件对群桩承载性能的影响，对2×2倾斜群桩在不同工况下进行有限元模拟，得出了倾斜群桩受不同荷载的承载力变化曲线。【方法】考虑土体沿深度方向的不均匀性，采用Gibson土体模型，建立了考虑山洪冲击力、局部冲刷和桩土非线性接触的有限元数值分析模型，并采用现场试验数据验证了模型合理性。【结果】研究发现，在一定范围内增大基桩倾角可以减小群桩沉降量，提高群桩竖向承载力；当基桩倾角过大时，基桩进入下部卵石层深度显著减小，群桩沉降量增大，竖向承载力降低；砂卵石复合地层中下部卵石地层粒径大硬度高，在基桩倾角增大时群桩沉降增幅不明显；基桩倾角的增大可以有效提高群桩水平承载力；冲刷坑形成后，群桩沉降和水平位移明显增大，将导致群桩承载性能降低。【结论】结果表明：在下部为砂卵石层的复合地层条件下，倾斜群桩的承载能力并不完全是随着倾角增大而增大；随着倾角的增加，群桩对山洪冲击力的承载能力有明显增大。因此对于复合地层下的倾斜群桩需根据实际情况合理选择倾斜角度，使倾斜群桩在面对竖向荷载和山洪冲击时有良好的承载性能。

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.

关键词

砂卵石复合地层 / 倾斜群桩 / 承载性能 / 山洪冲击力 / 局部冲刷 / 沉降 / 水平位移 / 影响因素

Key words

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

基金资助

云南省基础研究专项面上项目(202301AT070396)

昆明理工大学自然科学研究基金(KKZ3202421107)

国家自然科学基金地区科学基金项目(42267020)