Study on the interaction between squeezing ground and yielding supports with different yielding materials

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Segmental linings for tunnels are susceptible to overstress and damage when installed in squeezing ground. This paper investigates the effects of installing a type of yielding support behind the segmental lining by arranging compressible layer in the overcut. Two kinds of compressible layers (compressible concrete and expanded clay) were compared. A series of laboratory tests and numerical simulations were performed to study the interaction between the ground and these yielding supports. Different loading stresses were tested, and the corresponding rock pressure on the segmental lining, and internal force and deformation of the segmental lining were measured; additionally, the yielding of the added compressible layers was studied by analyzing the movement of the installed material. It was shown that different kinds of yielding materials result in different patterns of load transfer to the segmental lining. Under isotropic in-situ stress (k = 1), the yielding effect of compressible concrete is almost equal to that of expanded clay. However, under anisotropic in-situ stress (k ≠ 1), the segmental lining is more vulnerable to overstress when combined with compressible concrete, because the compressible concrete reduces hoop forces but markedly increases the bending moments in the liner. Expanded clay tends to move circumferentially towards areas with lower loads as well as compressing in the radial direction, thus resulting in a more isotropic load distribution on the liner overall.