Model test on interaction between colluvial slope and underpass tunnel under rainfall

In order to master the creep deformation law of colluvial slope and the stress deformation characteristics of tunnel lining structure under rainfall, the response physical model test of seepage and stress deformation characteristics of tunnel slope parallel system is carried out by using earth pressure cells, strain gauges, dial indicators and hygrometers. The test results indicate that rainfall infiltration depth decreases with increasing slope height and distance from the slope surface. The existence of the tunnel will affect the seepage path of rainwater, accelerating infiltration and increasing peak moisture content on the slope above the tunnel, while decelerating infiltration and reducing peak moisture content on the slope below the tunnel. The slope deformation is positively correlated with the change rate of water content. Slope deformation is concentrated during rapid water content increase, with vertical displacements at the slope top, middle, and foot accounting for 89.6%, 96.4%, and 98.9% of the total, respectively. The earth pressure increment at the tunnel top due to slope deformation correlates positively with the tunnel’s buried depth in the colluvial body, with an average increase of 24% per 15 cm. The earth pressure increment at the bedrock end is approximately 2.4 times that at the entrance end, while the increment at the tunnel bottom is smaller than that at the top. The tunnel exhibits the following stress and deformation characteristics: compression at the top, tension at the bottom, overall sinking, local downward bending with the central position as the inflection point, and abrupt strain changes at the bedrock-colluvial layer junction due to shear stress. These characteristics resemble the stress mode of a beam structure with one end hinged and one end anchored. It is recommended to incorporate anti-seepage measures such as sprayed concrete, shallow grouting, or slope ecological protection on the upper slope of the tunnel during the design and construction of similar tunnels. Reinforcement treatment should be implemented in the tunnel entrance area, the middle section with significant deformation, and the rock-soil junction.