考虑卸荷劣化的边坡二次开挖稳定性分析

Stability analysis of excavation process of high-steep slope considering unloading deterioration effect

摘要

既有道路改扩建时，如何防止二次开挖导致的边坡失稳和防护失效是一个关键的问题。岩土体的开挖过程会对既有边坡造成二次扰动，同时开挖卸荷作用会导致岩土体材料强度参数的改变，这种改变往往对边坡稳定性不利。既有规范延续传统设计理念，将岩土体视为理想弹塑性材料，未考虑边坡岩土体材料卸荷劣化效应，这与工程实际情况不符。基于FLAC^3D软件进行二次开发，设计并开发了边坡开挖过程中岩土体材料卸荷劣化效应的嵌入程序，并结合具体工程实例开展了考虑卸荷导致岩土体强度参数劣化效应的高陡边坡开挖全过程稳定性数值分析。结果表明，考虑卸荷劣化效应后，边坡在开挖过程中的潜在破坏模式及安全系数变化过程均出现明显差异。卸荷劣化效应使新边坡坡面处的岩体参数大幅降低，导致在边坡开挖后期，边坡在新坡面局部范围内出现了浅层滑坡破坏；相比与不考虑卸荷劣化效应的理想弹塑性边坡模型，考虑卸荷劣化效应后，边坡的安全系数出现不同比例的减小，二者之间的差距最大可以达到20%左右。研究成果可为高陡边坡开挖设计和施工过程中的稳定性控制提供参考和理论依据。

Abstract

Instability and improper protection of the secondary excavation about the slope is one of the key challenges during the reconstruction and expansion of the existing road. The excavation of rock and soil will cause secondary disturbance to the existing slope. Variations in strength parameters of rock and soil materials is found as a result of the excavation unloading. This unfavorable condition often cause the stability of the slope. Adopting the traditional design concept, the existing codes treats rock and soil as ideal elastic-plastic materials without considering the unloading deterioration effect of slope rock and soil materials. However, this practice is not consistent with practical projects. In this paper, based on the secondary development of FLAC^3D, the embedded program for unloading deterioration effect of rock and soil materials during the slope excavation is developed and realized. Then, the stability analysis of high-steep slope for the processing considering the deterioration of rock and soil mass parameters caused by unloading is performed. The result show that the maximum unloading amount in the slope excavation process can reach about 90%. After considering the unloading deterioration effect, the potential failure mode and safety factor change process of the slope during the excavation process are quite different. The unloading deterioration effect greatly reduces the rock mass parameters of the new slope, resulting in the failure of shallow landslides in the local area of the new slope in the later stage of slope excavation; compared with the ideal elastic-plastic slope model without considering the unloading deterioration effect, after considering the unloading deterioration effect, the safety factor of the slope decreases in different proportions, and the gap between them can reach about 20%.The research on the excavation of high and steep slopes considering the effect of unloading degradation can provide a reference and theoretical basis for the excavation design and stability control of high and steep slopes during construction.

关键词

高陡边坡 / 改扩建 / 卸荷劣化 / 稳定性分析 / 数值计算

Key words

high-steep slope / reconstruction and extension project / unloading degradation / stability analysis / numerical calculation

基金资助

深圳市综合交通与市政工程设计研究总院有限公司科技开发项目(RD201909)