The effect of suction on ground surface settlement for a tunnel

This paper addresses the physical modelling of a tunnel for saturated and unsaturated sand as well as tests in dry condition. A series of tests were conducted for a 50 mm diameter tunnel buried 25 mm into a poorly graded fine sand under different normal stresses: 0.78, 1.56, 2.34 and 3.31 kPa. Suction was controlled by means of the hanging column technique (HCT). Particle image velocimetry (PIV) was also utilised to obtain the vector displacement and compared with the results of the physical modelling. The results of the fully saturated sample showed that the sample experienced a sudden spatial collapse above and around the tunnel's crown. In addition, large displacement on top of the tunnel's crown was also observed for the fully dry case. However, the unsaturated sample did not experience any sudden collapse. This was attributed to the effect of the suction contribution on strength