Performance characteristics of tunnel boring machine in basalt and pyroclastic rocks of Deccan traps - A case study

Performance characteristics of tunnel boring machine in basalt and pyroclastic rocks of Deccan traps - A case study

ABSTRACT

A twelve point two four kilometer long tunnel between Maroshi and Ruparel College is being excavated by tunnel boring machine to improve the water supply system of Greater Mumbai, India. In this paper, attempt has been made to establish the relationship between various litho-units of Deccan traps, stability of tunnel and tunnel boring machine performances during the construction of five point eight three kilometer long tunnel between Maroshi and Vakola. The Maroshi-Vakola tunnel passes under the Mumbai Airport and crosses both runways with an overburden cover of around seventy meters. The tunneling work was carried out without disturbance to the ground. The rock types encountered during excavation are fine compacted basalt, porphyritic basalt, amygdaloidal basalt, pyroclastic rocks with layers of red boles and intertrappean beds consisting of various types of shales. Relations between rock mass properties, physico-mechanical properties, tunnel boring machine specifications and the corresponding tunnel boring machine performance were established. A number of support systems installed in the tunnel during excavation were also discussed. The aim of this paper is to establish, with appropriate accuracy, the nature of subsurface rock mass condition and to study how it will react to or behave during underground excavation by tunnel boring machine. The experiences gained from this project will increase the ability to cope with unexpected ground conditions during tunneling using tunnel boring machine.

One. Introduction

The Brihanmumbai Municipal Corporation has decided to change all surface water pipelines and to create subsurface systems by constructing tunnels to avoid problems of leakage, unconventional loss and also to protect water from contamination. The water supply systems through surface pipelines in Mumbai are age-old, built for more than seventy years. These supply systems leak frequently and need repeated maintenance. All these pipes are highly presurized and badly encroached by the population, which makes maintenance difficult. In Maroshi and Vakola sections, these pipes pass below the runways of Mumbai Airport and in case of strong burst it will affect the ground below the runways. The decision for the construction of tunnels was made because tunnels have advantages of low maintenance and less security accident. With the development of tunneling technology, it is possible to excavate tunnels with tunnel boring machine under favorable ground conditions instead of adopting conventional methods like drill-and-blast method. For the Mumbai water supply scheme, a hard rock tunnel boring machine was deployed earlier in nineteen eighty-four and a tunnel of three point eight seven kilometers was driven with three point five meter diameter gripper type tunnel boring machine. The tunnel was reported successfully excavated in four hundred fifty days with a best monthly advance of three hundred seventy-six meters. Construction of the tunnels has improved substantially the distribution of water supply system in Mumbai, which is an effective manner. Prior to these projects, worldwide experiences in driving tunnel through basalts and pyroclastics rocks with full-face were limited. The present scheme is a continuation to those successful efforts.

To improve the water supply to Vakola, Mahim, Dadar and Malbar Hill of Greater Mumbai, a twelve point two four kilometer long tunnel between Maroshi and Ruparel College is being excavated by tunnel boring machine. The tunnel is divided into three sections, i.e. Maroshi-Vakola (five point eight three four kilometers long), Vakola-Mahim (four point five four nine kilometers long) and Mahim-Ruparel College (one point eight five nine kilometers long). The longest tunnel between Maroshi and Vakola has been completed. A vent hole of thirty centimeter diameter at Chainage three thousand two hundred thirty meters at Maroshi-Vakola section was drilled for releasing pressure. For constructing tunnels from Maroshi to the vent hole and from Vakola to the vent hole, vertical shafts were constructed at either end. The inlet shafts of eighty-two point zero meters and sixty-eight point zero meters in depth