DISCONTINUUM ANALYSIS OF A HIGHWAY TUNNEL

R.CHITRA ¹ , MANISH GUPTA ¹ and A.K.DHAWAN ²

¹ Senior Research Officer, Central Soil and Materials Research Station, New Delhi, India
(rchita@nic.in )

² Director, Central Soil and Materials Research Station, New Delhi, India

Tunnels are conveyance systems, used in the transportation sector for conveyance of highway and railway traffic. They also serve as a means of conveyance of water in irrigation and hydroelectric power projects. During construction of tunnels variation of strata is often encountered. This poses various problems in tunnelling. Historically tunnelling projects have suffered significant cost and time overrun on account of variation in geological formation. Variation in strata may lead to various problems like tunnel caving in, water seepage and many more. Also, the decision regarding the support system required for various strata is critical to ensure trouble free construction.

The proposed tunnel alignment encounters mainly fresh and hard Quartz-Mica Schist with a few prominent sheared rock zones. The geological set up of the area indicates that folds are not present in the rock bed and the general dip ranges from 15 to 30 . Generally the alignment runs more or less favourable to the strike of the foliation of the rock. The proposed tunnel runs through high overburden depths upto 1900 m covered with steep slopes, dense forest and perennial snow. Among the sections tried, the horse shoe section is found to be the most suitable section for such conditions of high in-situ stress and...