Scaled model tests on segmental linings of shield tunnels under earth and water pressures

A series of 1g physical model tests were conducted to investigate the behaviour of staggered and non-staggered (NS) segmental linings of a shield tunnel under different soil pressures and external water pressures. Segmental joints were modelled by cutting a groove at joint locations. A loading frame was designed to apply vertical and horizontal earth pressures and a device was invented to simulate the water pressure on the segmental lining by creating negative air pressure inside a sealed shield-tunnel lining. It can be concluded that in a water-rich sandy cobble stratum with a high permeability, the increase of the external water pressure results in the increase of the axial force. However, the increasing pressure leads to the decrease of bending moment and eccentricity at the same time. Both the vertical stress and the at-rest lateral earth pressure coefficient can affect the internal force distribution of the segmental lining significantly. The staggered segmental lining has a bigger axial force, bending moment and eccentricity than the NS segmental lining. The results can be used to evaluate the bearing capacity of the segmental lining with different external water pressures, and other shield tunnels with different geometric dimensions could also use this method to simulate external water pressure.