Study on tunnelling induced ground deformation in reinforced soils

Abstract

Intuitively, tunnel-vertical-reinforcement interaction should be similar to tunnel-pile interaction because of similarities in their relative stiffnesses. However, piles are usually restrained at the top and connected to rigid beams which have high flexural rigidity. The deflection of the pile may not therefore follow that of the soil during movement. Likewise, negative skin friction would be significant on piles which are rigidly supported (e.g. Chen et al. 1999). Vertical reinforcements are free-floating columns which possibly can limit the soil flow and surface settlements during tunnel collapse. The reinforcements do not carry any axial load and, small diameter rods can be extracted and possibly reused when the tunnel face is passed by the reinforcements. The purpose of this paper is to examine the influence of vertical reinforcements on settlement trough due to tunnelling in model sand beds. The model tests have been conducted at the Indian Institute of Technology Bombay (IITB) Geotechnical Centrifuge (see Fig. 1). Details of the IITB centrifuge and its operation are available in Chandrasekaran (2001). All dimensions in the figures are in mm unless otherwise stated.