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The Konkan Railway of the Indian Railways services the west coast of India from Roha near Mumbai to Thokur near Mangalore in Karnataka. The railway line is 736 kms long on the western coast nestled along the Western Ghats and has been in service since January 1998. There are 91 tunnels on the route and 179 major bridges on the route. Natuwadi Tunnel is one of the major tunnels of Konkan Railway. It is 4389 metres long and is the second longest tunnel on the Konkan railway after Karbude Tunnel also on Konkan raiway. It spans two stations that fall on the line in Maharashtra; Karanjadi and Diwan Khavati.
The entire route of Konkan railway, with numerous tunnels and bridges, all along the west coast of the country, is one of the most beautiful train routes in India that traverses over amazing and diverse landscapes that are full of natural beauty.
The railway line of Konkan Railway is designed to run trains at a maximum speed of 160 kms per hour. For this speed to be achieved the track had to be kept level and curves to be minimum. Naturally many bridges and tunnels had to be constructed.
Natuwadi Tunnel was planned and constructed to create a straight and level line between Karanjadi and Diwan Khawati railway stations which fall in the Maharashtra section of the Konkan railway.
The Natuwadi Railway Tunnel joins Karanjadi and Diwan Khavati stations and is the second longest rail tunnel of Konkan Railway after Karbude tunnel. It starts just after Karanjadi station and ends just off Diwan Khavati station.
The length of this tunnel is about 4.3kms and was constructed in 1997. Construction of this tunnel was a challenge as the terrain as well as the weather, were the main issues that needed to be combated. Part of the excavation of the tunnel was through wet, soft and clayey soil. Special tunnel digging equipment had to be imported for the boring of the tunnel.
Another challenge for the Konkan Railway was the varying geographical and geological conditions. The landscape varied from the steep rocky slopes of the Western Ghats, many rivers and rivulets, sandy soil, soft clayey hills etc.
The Konkan Railway line was designed to run trains at a maximum speed of 160 kms per hour, hence the track had to be as straight and level with minimum curves and inclines. To achieve this condition a lot many bridges and tunnels had to be constructed in varying geographical terrain.
While some of the tunnel boring work was carried out by specially imported Swedish machines, where the soil was soft, loose and clayey, the excavation had to be done manually and took a lot of time and effort.
Sometimes just after the excavation process was complete, the tunnel would cave in and the process had to be repeated again. The inclement weather also made construction of the tunnels difficult.
Many safety measures had to be taken to ensure that the tunnels would be safe for rail traffic. Some of these were rock bolting, and shotcreting.
Rock bolting involved anchoring loose boulders to the parent rock by means of rock bolts. Wherever there was fairly weak quality of rocks, rock bolting was used. Rock bots were installed on the arched ceiling of the tunnel to strengthen the rock strata there.
Shotcreting was done to ensure that boulders and loose rocks do not fall in the tunnel. In this method a mixture of sand, cement and aggregate of around 12mm thickness is spread over the rock surface with the aid of shotcreting equipment. Synthetic polyester is added to the mixture to prevent cracks and improve cohesion or bonding. This method is cheaper and more effective than other strengthening methods.