Support pressure for circular tunnels advanced below water bodies

摘要

The limiting support pressure required to be exerted by a support system for maintaining stability, of circular tunnel driven in granular soils below water bodies has been computed. The analysis was performed on the basis of lower bound theorem of plasticity in conjunction with finite elements and second order cone programming. The effect of anisotropy in both strength and hydraulic properties of granular soil on the magnitude of required support pressure has been examined. The required support pressure is defined in terms of non-dimensional factors normalized with respect to unit weight of soil and diameter of tunnel. The variation of support pressure for different combinations of strength and hydraulic properties of soil, height of water level above bed of water body, and diameter and cover of tunnel has been established. The magnitude of support pressure is observed to be substantially influenced by strength anisotropy of soil; whereas, the influence of hydraulic anisotropy is shown to be insignificant on the support pressure. Moreover, the support pressure is found to be increasing with increase in the height of water level and is found to be higher in the case of tunnel driven below water bodies than that advanced in dry soil.