Investigating polymeric foam materials as compressible layer for tunnelling in squeezing ground conditions

Abstract

Installation of a compressible layer between primary support and secondary lining is a feasible solution to decrease damage of the secondary lining induced by the time-dependent deformation in the squeezing tunnel. Laboratory tests and numerical analysis were conducted to investigate the feasibility of the polymeric foam for the compressible layer in a squeezing tunnel. The PU (Polyurethane) foam (density 70 kg/m3–100 kg/m3) and PE (Polyethylene) foam (density 90 kg/m3–130 kg/m3) are chosen as candidate filling materials of the compressible layer. The stress-strain curves of the candidate materials show a clear stress plateau stage, and the deformation capability and stress of the plateau stage can meet the requirements of the compressible layer. PU foam with density 80 kg/m3 is finally selected due to its energy absorption capability for the compressible layer. The performances of the PU foam compressible layer under uniform and nonuniform squeezing deformation are simulated, the results show that the stress and failure zone of the secondary lining can be clearly decreased by the PU foam compressible layer, and the tension stress of secondary lining induced by non-uniform tunnel deformation can be avoided. The mechanical performance of the PU foam indicates the feasibility of using polymeric foam as the compressible layer in squeezing ground conditions.