Abstract：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.
