Construction of a Cross-Passage for a Twin Tunnel system for Delhi Metro's CC-27 Project

R.G. Saini, Project Director, DMRC,L&T-SUCG JV CC-27, New Delhi, India.
Ishaan Uniyal, Student, Dept. of Civil Engineering, Thapar University, Punjab, India.

In this paper, construction of cross-passage for a twin tunnel system has been discussed along with problem encountered and solution adopted, by using a case history of cross passage in R.K Puram Station, being constructed by L&T-SUCG JV for CC27 of Delhi Metro. Work for the cross-passage commenced after the completion of the twin tunnel on account of ease and efficiency. Method employed for construction of the cross-passage and specifications of materials used have been reported in this paper. The paper also reports a solution adopted for mitigation of a major problem of water-logging encountered during the construction. Approach adopted to address the problem has also been reported in the paper. Efficacy of the procedure utilized and applicable conditions for same along with possible contributing factors have been indicated in the paper.

Introduction

Cross-passages are reinforced concrete structures built in between either two tunnels (as in case of twin tunnel systems) or a tunnel and the ground surface. They are provided to serve two primary purposes namely, emergency escape and maintenance work. In this paper, design, construction methodology and problem encountered during construction of one such structure has been described by analyzing case of a Cross-passage being constructed by L&T-SUCG JV for twin tunnels between R.K Puram and Munirka underground stations for project CC27 of 'Delhi MRTS Project of Phase-III'.

Project Background

The project consists of five underground metro stations (Hauz Khas, Vasant Vihar, Munirka, IIT and RK Puram), underground ramp at Shankar Vihar metro station (part of CC-27) and tunnel from end of this underground ramp to Hauz Khas metro station connecting the five underground stations listed above. Total tunnel drive length is 4.49 Km. Keeping strata of the soil in mind and time constraints, five Tunnel Boring Machines (TBM's) namely Okumura TBM, THI-1 TBM, Herrenknecht TBM, THI-2 TBM and Mitsubishi TBM were used for construction of the tunnels. Out of these, Okumura TBM is particularly suitable for tunneling in soft soil.

Of the total tunnel length under construction, part of the tunnel connecting R.K Puram station to Munirka station, is the subject of consideration in this paper. The tunnel extends 1.32km in length and has an internal diameter of 5.80m and external diameter of 6.35m.

As a standard practice, during construction of a tunnel system, depending upon length of the tunnel and soil characteristics, a pre-calculated number of cross-passages are planned. In the instant case, four cross passages numbered CP-12, CP-13, CP-14 and CP-15 are being constructed between the two stations with average gap of 400m between the cross passages. Soil type found in this region is called 'Delhi Silt' which contains silt and sand in varying proportions from 35% to 80%. It is lightly compacted, has only an insignificant proportion of clay and is largely non-plastic although its behavior is transitional. Absence of rocks and stones lends this soil easily to efficient utilization of Okumura TBM.

NBMCW June 2016