TUNNELLING:

It is a highly specialized subject and trade of Civil Engineering and Mining Engineering. Engineering Geology plays a very important role in the planning, designing and construction of the tunnels, especially its safety, stability and durability. The following works are completely planned and carried out according to Geological Knowledge of the site:

• Type of temporary and permanent supports including Rock-Bolting
• Type of lining
• Type of Blasting or Tunnel Boring
• Type of Water-Sealing, etc

What is a Tunnel? A Tunnel is a longish and cylindrical usually horizontal structure built completely inside the ground having its all the entries and exits open to the open atmosphere, used for the following purposes:

 

Types of the Tunnels according to their use & purpose:

• Transportation Tunnels e.g. tunnels used for highways, railways and water-ways
• For Power-Generation
• Channelising the water through the mountain or earth, usually in dams
• Public Utility Tunnels e.g. tunnels used for water supply, sewage, storm-water, ducts and cables, pedestrians and cyclists, etc
• Mining Tunnels
• Storage Tunnels
• Tunnels used for scientific or military experimentation e.g. nuclear or conventional explosion or testing, or for radio-activity, germs, bacterial / anti-bacterial experimentation

Usually the tunnels pass through the soil, rock and water. Their investigation and designing through the said materials are quite different from each other. Tunnels passing under a river, stream or sea are entirely different from the other types of tunnels i.e. the tunnels made in the soil and rocks; hence the former types of tunnels are studied quite differently and separately  

Operation-Cycle for Tunnelling:

• Drilling and Blasting of the rock or hard strata
• Temporary Roof Supporting including Rock-Bolting
• Ventilation after drilling and blasting
• Mucking and disposal of the blasted material
• Shape-drilling, sawing and finishing
• Water-Sealing
• Providing the Permanent Support and lining if considered necessary
• Nowadays “Tunnel Boring Machine (TBM) – a recent German Technology” is used for making the main bore of the tunnel of any size desired. It makes a bore, sprays the water to aid in the boring as well as in settling the dust, collects the cutting (cut-material) and dispose of itself by a belt-conveyor system
• TBM has completely replaced the Blasting in the tunnels
• Blasting causes a lot of disturbance: weakening, fracturing, de-stabilization and fall of surrounding and above strata.