Use of Tunnel Boring Machines (TBMs) in India with special reference to Parbati Hydroelectric Project (Stage -II)

摘要

Parbati Hydroelectric Project is a cascade development planned to be developed in three stages with an aggregate generating capacity of 2070 MW. Parbati Project Stage-ll first in the series is a run of the river scheme comprises of 85m high Concrete Gravity Dam and 31.501 km long HRT utilizing a gross head of 862m to generate 800MW of power. The project is of special importance as the longest reach of 9 km is being excavated with the use of TBM and 2 Nos inclined Pressure Shafts each about 2 km long are also being excavated with TBM. The total quantum of underground works involving tunneling shall be more than 56 km. The project lies in very complex geological goups like Larji group, Rampur group & Kullu group. The main troublesome stretches will be consisting of biotitic schist, carbonaceous phyllite and talc chlorite schist. The tunnel also passes under a high rock cover of more than 1000 m, which are generating rock burst conditions in competent rocks like quartzite. There is also a possibility of occurrence of hot springs. All types of geological formations of ages with shear zones to big thrust zones shall be encountered. The project involves a maze of tunnels and complex layout of entire scheme. The construction methodology being used is drilling & blasting, multidrifting and use of TBMs. Use of TBMs for blast free excavation in the world exists only for a period of about 30 years. In the international scenario most of the TBM tunnels have been driven in soft and medium hard rocks like chalk, dolomites, limestone, and clay stone and siltstone etc. Hard rock TBMs have driven very few kilometers in the world as compared top soft rocks. In India hard rock open type TBMs have worked successfully in western part of India but in Himalayan geology there is a case of failure also, therefore, the applicability of TBM in the Himalayan geology has been an area of debate for quite some time. However with the demand of fast track execution of the projects the need for fast execution of long reaches of tunneling have necessitated the use of TBM in the Himalayan geology also. Projects, which are situated in inner Himalayan region, have longer tunnels and environmental restrictions for blasting due to Eco development zone. With the thrust on the development of hydro power it has become necessary to execute projects in a tight schedule of 4 to 5 years; in this context, therefore, it has become necessary to switch over to TBMs for the excavation of tunnels. However conditions prevailing in the Himalayan geology as compared to western countries are quite different, therefore, certain modifications to suit Indian conditions are required to be incorporated at the design and manufacturing/ refurbishing stage of the TBM. The paper deals with the project features and various aspects of the use Tunnel Boring Machines with suggestions for modifications to be carried out in future TBMs to be used in India.