A numerical study on behavioural characteristics of cut and cover tunnel

Abstract

More than 68% of the Korean Peninsula is mountainous area. In some cases where the tunnelling can be hardly taken into consideration for road and/or railway constructions, full excavation used to be applied, thereby leading to steep slopes inevitably which may impact natural environment. That is, the steep slopes cause the following environmental problems; destruction of natural spectacle, disruption of ecological pathway of animals and plants, structural instability due to slope failures, etc. In order to overcome these problems, the environment-friendly cut and cover tunnelling construction technology has been alternatively taken into consideration to form Eco-bridge on the construction sites for protection of the ecological system. In the cut and cover method, earth pressure acting on cut and cover tunnel lining varies depending on geological factors such as cut slope angle, distance between the concrete lining and cut slope, embankment slope angle, etc. Design of cut and cover tunnels is performed by considering field conditions such as earth pressure, self-weight, temperature load, earthquake, etc. Among the conditions, earth pressure acting on lining is taken into account by self-weight of embankment and in general, structural analysis of the tunnel lining used to be carried out to estimate the earth pressure without consideration of geological aspects. In this study, for economical and reasonable design of cut and cover tunnels, a basic research was numerically performed by using a FE package of PLAXIS 2D Ver. 7.2, in which considered variation of earth pressure with respect to the following geological factors: interaction between concrete lining and embankment; grade of cut slope; distance between cut slope and concrete lining; berm, coefficient of lateral earth pressure, etc. However, the influence of distance between cut slope and concrete lining, grade of cut slope, and embankment slope location on the behaviour of cut and cover tunnels are only presented in this paper. Coefficients of correlations between embankment volume and maximum axial force, and maximum shear force appear relatively high and increase proportionally as embankment volume increases. However, coefficients of correlations between embankment volume and maximum bending moment and horizontal and vertical displacement appear relatively low. Therefore, it is concluded that behaviors of cut and cover tunnel are significantly influenced by not only embankment volume but also geological and field conditions. Coefficients of correlations between embankment volume and Mmax, Smax, Amax and displacements are high. Therefore, it is concluded that volume of embankment slope above the height of 1.5 D is considered as self weight on the cut and cover tunnel lining. If eccentric load that induces the unbalanced distribution of bending moment, is not reasonably considered, structural safety could not be evaluated reasonably. (A). Reprinted with permission from Elsevier. For the covering abstract see ITRD E124500.