极端降雨对黄土沟壑区隧洞施工力学效应影响分析

黄土地区输水隧洞的建设中，降雨入渗极大影响着输水隧洞围岩稳定性。本文利用非饱和渗流理论和数值模拟方法研究了极端降雨条件入渗与黄土沟壑区隧洞的开挖扰动耦合影响下围岩的变形和渗流场演变规律，通过Plaxis3D模型对降雨入渗下新奥法施工过程中围岩力学特性、初期支护过程进行流固耦合分析。结果显示，降雨等级越高，围岩孔隙水压力变化幅度越大，对围岩的稳定性越不利；降雨入渗与开挖扰动会加速土层中渗流场和应力场的重分布过程；基于沟道的汇水特性，隧洞围岩含水率在最初5~10 d呈台阶式增长，拱顶、拱腰和拱趾处的最大变形为17.8 mm、28.2 mm、24.6 mm，最大剪切应力为175.3 kPa、182.5 kPa、150.6 kPa，降雨结束约15~20 d围岩变形速率逐渐减小收敛至特定值，但围岩的应力持续增加，为避免围岩发生塑性变形，故可在15~20 d进行二次衬砌支护。本次研究结果可对极端降雨期黄土沟壑地区隧洞施工安全控制提供参考。

Analysis of the effect of extreme rainfall on the mechanical effect of tunnel construction in loess gully area

In the construction of water transmission tunnels in loess areas, rainfall infiltration greatly affects the stability of the water transmission tunnel envelope. In this paper, the unsaturated seepage theory and numerical simulation method are used to study the deformation and seepage field evolution of the surrounding rock under the coupling effect of extreme rainfall infiltration and excavation disturbance of the tunnel in loess gully area, and the flow-solid coupling analysis is carried out by Plaxis3D model on the mechanical characteristics of surrounding rock and the initial support process during the construction of New Austria method under rainfall infiltration. The results show that the higher the rainfall level, the greater the change of pore water pressure in the surrounding rock, and the more unfavorable to the stability of the surrounding rock; rainfall infiltration and excavation disturbance will accelerate the redistribution process of seepage and stress field in the soil layer; based on the water catchment characteristics of the trench, the water content of the tunnel surrounding rock shows a stepwise increase in the first 5-10 d, and the maximum deformation at the vault, arch waist and arch toe are 17.8 mm, 28.2 mm, 24.6 mm and 21.1 mm, The maximum shear stress is 175 kPa, 182 kPa, 150 kPa, and the deformation rate of the surrounding rock gradually decreases and converges to a specific value about 15~20 d after the end of rainfall, but the stress of the surrounding rock continues to increase, and in order to avoid plastic deformation of the surrounding rock, the secondary lining support can be carried out at 15~20 d. The results of this study can provide reference for the safety control of tunnel construction in loess gully area during extreme rainfall period.