外水压下大断面公路隧道衬砌结构受力特性模型试验

矿山法修建的山岭隧道有的情况下对地下水采取排导式处理方案。当衬砌背后来水量超出排水系统能力时，将引起衬砌背后外水压增高，甚至导致隧道衬砌结构破坏。自行研制了隧道衬砌外水压力模拟加载试验装置，该装置通过形成负压环境，利用隧道结构模型内外气压差来实现外水压的模拟。基于隧道-地层复合模拟试验平台，开展了外水压下大断面公路隧道衬砌结构受力特性的室内加载模型试验。结果表明：衬砌结构在水土压力共同作用下，轴力呈锥形分布，拱脚轴力大于仰拱和拱部；弯矩呈蝴蝶型分布，拱脚处承受外弯矩，仰拱及拱顶承受内弯矩；轴力、弯矩随水压增加大致呈线性增大，偏心距逐渐减小，拱脚位置具有最大的偏心距，为外水压下隧道衬砌结构受力的最不利位置；依托隧道工程三车道及加宽带衬砌结构产生渗透性裂缝的外水压力分别为330kPa和420kPa，开裂裂缝主要出现在左右拱脚区域的外侧及仰拱内侧，为受拉开裂破坏，且随着外水压的增加，裂缝的渗透性急剧增大。此研究可为大断面公路隧道排水型衬砌在外水压力作用下结构安全评估提供参考。

Scaled model test on mechanical characteristics of large cross-section highway tunnel lining under water pressure

In many mountain tunnels constructed by drilling and blasting method, ground water is drained out completely to avoid the action of water pressure. When ground water exceeds the capability of the drainage system behind the tunnel structure, water pressure on the tunnel lining may increase and cause structure damage in some cases. An apparatus is invented to simulate the water pressure on the tunnel structures, which creates negative pressure in the inner space of tunnel structures to simulate the external water pressure. Based on the tunnel-ground loading test platform, the behavior of highway tunnel structure with large section at different water pressure was tested. The results show that under high water pressure, the distribution of axial forces tend to be a cone conformation, that is, axis force in arch spring is larger than that in invert and arch. The distribution of moment appears as butterfly shape, that is, the arch spring is external bending moment and the invert and arch are internal bending moment. With the increase of water pressure, axial force and bending moment increase roughly linearly, while eccentricity decreases gradually. The arch spring is the most unfavorable position for the maximum eccentricity. Critical inner water pressure for the cracking of three-lane and four-lane lining structures are 24m and 36m respectively. Tension cracks mainly occur in the outside of left and right arch spring areas. In addition, permeability of the cracks increases with the water pressure. In general, the anti-hydraulic performance of four-lane tunnel is better than that of three-lane lining structure. The study can provide reference for the safety evaluation of large-section highway tunnels under water pressure.