A Modified Expanded Clay as a Yielding Material in Deep Mechanized Tunnel Boring

Abstract

This paper investigates the use of a modified expanded clay as a yielding fill material in the overcut behind the segmental lining. In order to match the stress-strain curves of the ideal yielding material, expanded clay of different sizes and different clay mixed components were tested. Both of the field tests and numerical calculation were conducted to evaluate the behaviour of liner in deep tunnel when the modified expanded clay was backfilled. The safety of the liner was assessed. The results show that the non-modified expanded clay offers a linear behaviour up to a deformation of 25% to 40%, and with an average limit compressive strength between 1 MPa to 5 MPa. By adding a certain percentage of polystyrene to the expanded clay, the limit compressive strength and the linear deformation phase can be modified. Polystyrene reduces the stiffness and offers a yielding section in the deformation phase, which makes the expanded clay close to an ideal yielding material. Through modification of the expanded clay, the limit compressive strength can be adjusted to an approximately 55% compressive strain. The results of field tests and numerical simulation verified the use of the modified expanded clay as a yielding material in deep tunnels.