强降雨条件下隧道洞口边坡开挖渗流特征以及支护方案研究

针对数值模拟软件难以模拟分析强降雨过程中隧道洞口边坡开挖渗流场分布的问题，依托某隧道洞口边坡工程，对FLAC^3D软件中的FISH语言进行二次开发，确定降雨渗透过程中不同饱和状态下土体渗透系数值并实时更新降雨入渗的边界条件，分析了不同降雨时长情况下不同支护方案隧道洞口边坡孔隙水压力、基质吸力分布以及安全稳定性。结果表明，历经24 h强降雨，原边坡和采用抗滑桩+锚索支护的边坡表面土体均达到饱和状态，即从坡脚至坡顶浸润线形成贯通；而采用台阶型放坡+锚杆支护的边坡仅在坡脚至边坡二级平台处的表面土体达到饱和状态；降雨过程中采用抗滑桩+锚索支护的隧道洞口边坡与原边坡安全系数的变化规律较为一致，安全系数均为先快速降低后逐渐趋于稳定，直至安全系数达到1.2;而采用台阶型放坡+锚杆支护的边坡安全系数降低幅度较小，其值基本保持在1.8以上；在选择隧道洞口边坡工程扩建方案时，从隧道洞口边坡工程开挖支护方案的安全系数、土方开挖量、总投资等多个角度考虑，抗滑桩+锚索支护方式优于台阶型放坡+锚杆支护方式。

Seepage Characteristics of Slope at Tunnel Entrance Under Heavy Rainfall and Its Support Scheme

It is difficult to simulate and analyze distribution of seepage field for the slope at the entrance of excavated tunnel during heavy rainfall. Aiming this problem, a slope project at a tunnel entrance was taken for study, and FISH language in the FLAC3D was redeveloped to determine the permeability coefficient of soil under different saturation state during rainfall infiltration, and the boundary conditions for rainfall infiltration were updated in real time. In addition, the pore water pressure, matrix suction distribution, as well as safety and stability of the slope at the tunnel entrance after different support schemes were all analyzed with different rainfall durations. The results showed that after 24 hours of heavy rainfall, the slope before and after a combined support including anti-slide piles and anchor cables all reached saturation state, that is, the saturation line ran through from the foot to the crest of the slope, while the slope, after benching and being supported with bolt, had its surface soil from the foot to the secondary platform of the slope under a saturated state. As for the slope at tunnel entrance supported by anti-slide pile combined with anchor cable, the variation law of its safety factor during rainfall was consistent with that of the slope without support treatment, showing that the factor of safety tended to be stable after an initial rapid decrease, and gradually reached 1.2. As for the slope after benching and being support with bolt, its factor of safety decreased a little and maintained above 1.8. It is concluded that the factor of safety, excavated earthwork quantity and total investment for the support scheme should be taken into consideration before starting a slope engineering at a tunnel entrance, and a combined support scheme including anti-slide pile and anchor cable is superior to the scheme including benching and support with bolt.