水工隧洞钢筋混凝土衬砌外水压力取值方法研究

外水压力是隧洞衬砌承受的主要荷载之一，也是控制其建设与运行或检修过程中衬砌结构安全的关键因素。目前外水压力的取值仍然以经验公式为主，存在很大的局限性和不准确性。首先分析对比了衬砌外水压力的折减系数法、理论解析方法和数值分析方法几种取值方法，然后进行了不同渗透环境和衬砌支护条件下的衬砌外水压力计算。结果表明，随着围岩渗透性和衬砌厚度的增大，衬砌外表面的水压力越大；对于渗流数值计算，模型范围应取距离隧洞中心不小于30倍洞径；考虑渗流场的时间效应，开挖完成10 d后隧洞的渗流场趋于稳定，衬砌支护20 d后衬砌外侧水压力分布趋于稳定。

Study of external water pressure estimation method for reinforced concrete lining of hydraulic tunnels

The external water pressure is the key factor for lining structural safety in construction, operation and maintenance condition. The traditional method for external water pressure estimation is with empirical formula. However, the effects of geology, boundary, excavation and lining construction aren’t adequately taken into account; and the solution results have risks and uncertainties. This paper reviews the general methods for external water pressure estimation, such as discount coefficient method, theoretically analytical method and numerical analysis method. The numerical results compared with the analytical results under different permeability environment and lining support forms illustrate the viability of the numerical analysis method. The numerical model scope is discussed to reduce the calculation error. The evolution process of seepage field is captured along with the tunnel excavation and lining supporting. The results show that the external water pressure on lining increases with the increase of permeability of surrounding rock and the lining thickness. The distance from the tunnel center to the boundary should not be less than 30 times tunnel diameter. Considering the transient effect, the tunnel seepage field tends to be stable within 10 days after the excavation; the water pressure distribution tends to be stable within 20 days after the lining supporting.