3.3.1 Shotcreting Video

3.3 Primary Shotcrete protection

•The primary stabilisation of the tunnel excavation is achieved by shotcrete.

•The shotcrete stabilises the excavated rock surface by filling the cracks produced in the rocks

•Primary shotcrete consists of M40A10 grade concrete. The shotcrete is sprayed throughout the excavation with the help of a computer operated machine called MYCO POTENZA.

•Along with shotcrete, an accelerator admixture is pumped so as to harden the shotcrete concrete immediately.

•If accelerator is not used, the shotcrete may not stick to the excavated surface.

•The accelerator commonly used is Sodium Silicate.

•The quantity of accelerator is kept 7% of the volume of shotcrete.

MYCO potenza for Shotcreting

3.2 De-fuming, Mucking and Scaling

• It takes about 30 minutes to expel the fumes out of the tunnel. All the workers and engineers are supposed to move out of the tunnel during this process.
• After De-fuming, mucking operation starts. Mucking is the operation of removing the blasted rock from the tunnel face.
• In Rohtang tunnel, a conveyor belt is used to convey the Muck out of the tunnel. The conveyor mechanism has been installed by ROWA Tunneling Logistics.
• The facilities are designed in such a manner, so that muck volume of 600 tons per hour can be effected.
• The removal of loose rock which has not been removed during blast is called as Scaling. Usually this operation is done using Hydraulic hammer.
  
   
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3.1 Drilling and blasting

•The face of the tunnel is made smooth with the help of hydraulic hammers.

•Holes of diameter 48mm to 51mm are drilled on the face of top heading or benching with the help of a machine called Boomer.

•The maximum length of the hole is kept 3m.

•The holes are filled with explosives and connected to a non electric detonator. The detonating mechanism is placed at least 500m distance from blast site.

•The detonator used for explosion is a non electric detonator and is commonly called as Shock Tube Initiator.

Boomer for hole drilling

Cortex tube for detonation purpose

Explosive

3. Tunneling Approach

The excavation of Rohtang Tunnel is done on the basis of NATM (New Austrian Tunnelling method). This method can be described as "Design as you monitor" approach, by providing support to the tunnel on the basis of Rock class. The NATM has following sequence:


1. Drilling and blasting.
2. De-fuming (it takes 30 minutes)
3. Mucking and scaling.
4.Primary shotcreting with M40 grade concrete.
5. Installation of square wire mesh throughout the tunnel.
6. Lattice girder installation.
7. Secondary shotcreting with M40 grade concrete reinforced with steel fibres.
8. Drilling holes for Rock bolts.
9. Inserting Rock bolts.
10. Cement grouting of Rock bolts.
11. Tunnel final lining with reinforced M35 grade concrete.


I'll explain each process in detail.

2. History of Rohtang Tunnel

Well we have introduced ourselves to Rohtang tunnel in the previous blog. Now we will discuss the history of the "Project Rohtang Tunnel".
In 1980's Indira Gandhi was on a visit to Lahaul Spiti. She addressed the problems faced by the people of Lahaul and Spiti during winters. Well, all of us know that Lahaul and spiti gets isolated from us during winters. Immediately, Indira Gandhi went to Delhi and she discussed the issue with the members of her party.
Finally, it was decided to excavate an all weather tunnel through the mountains of District Kullu and Lahaul-Spiti.
The Government of India handed over the responsibility to Ministry of Defence. Ministry of Defence handed over the task to BORDER ROADS ORGANISATION which is a specialized agency of Defence ministry for the construction of roads.
The site investigation was carried out between 1985 to 1988 and in the year of 1998, Atal Vihari Vajpeyi allotted the budget to the tunnel. Investigations and surveys were carried out further. The road from solang to dhundi (Where south portal is located) was constructed by BRO. Finally tenders were invited and the contract was awarded to AFCONS (an indian construction company) working jointly with STRABAG AG (An Austrian Construction company).
The work commenced on 5th November 2009. Initially, the overall budget of the project was 1458 crores but some geological faults doubled the cost of the project.
Moreover, these faults extended the date of completion of the project by 3 years.
Most likely, the tunnel will be open for traffic in 2019.

1. Introduction

Hi guys! My name is Pankaj Thakur. This is my first ever blog, so please don't go hard at me. I'm working as a trainee in Rohtang highway tunnel and I'm sharing some of the information based on that experience.


The south portal of Rohtang Tunnel is situated at Dhundi 25km North of Manali in Himachal Pradesh. The elevation of south portal is 3060m above MSL. The North portal is situated at Khoksar, Lahaul-spiti at an elevation of 3072m above MSL. The Overall length of the tunnel is 8.8km. The interesting fact is that Rohtang Tunnel on completion will be the longest tunnel in the world at an elevation more than 10000 feet.


An emergency Egress Tunnel has been provided just beneath the main tunnel for the sake of safety during fires, tunnel lining failures etc. Often, folks say that the egress tunnel is designed to carry a vehicle of SUV size. Absolutely no! This emergency tunnel is designed to carry humans only. Rather, the top of the egress tunnel supports massive weight of traffic running in the main tunnel, as the pavemnt of roadway is placed just over the Egress tunnel. The egress tunnel is 3.6m wide and 2.25m high and is connected to the main tunnel through stairs provided at an interval of 500m along the length of the tunnel.


Talking about the geometry of the main tunnel, the main tunnel is given "Modified Horseshoe shape", the radius of curved portion is 6m. The width of the roadway is 8m (two lane highway).