Tunnels and their stability mechanisms

Tunnels and their stability mechanisms

Introduction

What’s a Tunnel Made of?

Mechanism of Tunnel Stability in the Ground

Tunnel is a thin walled closed excavated cross section and according to peck’s theory, tunnel get stability in a ground through deformation of its shape and/or support from surrounding ground makes it stable (Fig.1). After excavation a loosened zone is created and stress redistributes outside the loosened zone due the formation of ground arch (Fig.2), only few part of ground which is present in loosened zone, imparts load on the support or lining because of this arch action. Trapdoor experiment (Laboratory experiment) reveals this stress redistribution phenomenon. Figure 3 shows that ground will deform upon loading in order to attain stability. This is important to realize that if tunnel supporting pressure will be less, than tunnel will deform more so in case of urban area tunneling, strong lining is required. Fenner-Pacher curve can also be seen to understand the ground stability which explains relationship between supporting pressure and displacement of excavated surface (Fig. 4).