Physical Modeling of Shallow Tunnels in Loose Granular Soils with a Sloping Ground Surface

The prediction of the surface settlement and ground displacement due to the underground excavation is a key factor for the stabilization and planning to control probable incidents. Due to the real condition and natural modeling materials, physical modeling has critical role in this area. In this research, a series of physical model tests was conducted to study the influence of tunnel depth on the ground deformation and ground surface settlement in a loose sandy ground. Particle Image Velocimetry (PIV) technique was used, as a non-destructive image processing technique, to measure the ground deformation and surface settlement during the tunneling process. The results show that in case of a sloping ground surface, the settlement trough is asymmetric and the deformed zone and ground settlement in extended upward the slope. Although the maximum surface settlement still appeared along the crown of the tunnel, its value increased up the 25%, compared to a horizontal ground surface with a tunnel at the same depth. The deformed areas in the models were divided into two district portions; the deformed zone close to the tunnel and the deformed zone close to the ground surface. In the deformed zone close to the tunnel, in general, the dip of the boundary increased with an increase of the tunnel depth. Moreover, the lower side boundary was about 10 degrees steeper that the upper side boundary. In the deformed zone close to the ground surface, the deformed boundary has an inclination of 54 degrees for all the models, independent of the tunnel depth. .