When a tunnel is assumed to receive swelling pressure from rocks, it is necessary to estimate the swelling pressure properly and to set the external force condition for the tunnel's repair design. For the mountain tunnel under service in Fukushima prefecture, there was a deformation at the roadbed and the tunnel lining due to swelling rock. Therefore we developed a swelling-rock model based on onsite monitoring data and laboratory test data. The model was used to estimate the external forces for design. Several monitoring devices were installed in the site to obtain rock deformation data around the tunnel and evaluate the mechanism of swelling. In addition, swelling pressure tests using site materials were conducted to grasp the swelling characteristics of the rock. A numerical simulation model was made for the interaction between the swelling pressure of the rock and the tunnel structure using the rock deformation with the results of the tests The simulation model, which was made in consideration of past data, estimates the external forces, which are necessary for the reconstruction of tunnels in the future. This paper outlines the method of setting the swelling model by numerical analysis, the features of the model, and the results of applying it to a tunnel.
This tunnel was constructed through a mountain with an altitude of about 2000 meters to improve the convenience of local transportation in Fukushima Prefecture. It is 4 km long and serves some of the local arterial roads.
The geology around the tunnel consists of lava, volcanic clastic rocks and intrusive rocks associated with volcanic activity of the Quaternary period.
According to the observation data of tunnel face during the construction, basaltic crushed lava, basalt lavas, tuff gravel rock was confirmed. Especially basaltic self-crushed lava is susceptible to alteration by crushing and is a geologically vulnerable.
In this tunnel, uplift of the pavement surface was confirmed after service was started. After that, field surveys, onsite monitoring and laboratory tests were carried out, and one of the causes of the deformation was pointed out: in addition to progressive deterioration of the ground due to tunnel drilling, the influence of groundwater infiltration from the around tunnel and absorption swelling due to groundwater supply.
