The Rohtang pass is a high-altitude road in the Indian Himalayas. It forms a treacherous section of the 479km Leh-Manali Highway between the town of Manali in Himachal Pradesh, and Leh in Jammu & Kashmir.

The pass’s forbidding elevation of 3,978m above sea level is only part of the issue. Winter weather shuts the road for half of the year, while its topography leaves it dangerously exposed to sudden snowstorms. These challenges to an isolated community in a strategically significant region were unacceptable to the Indian military’s Border Roads Organisation (BRO). BRO decided to circumvent the pass with a new tunnel, at the lower altitude of 3,100m.

Work on the now-famous Rohtang Tunnel began in 2010 and broke through in 2017, while construction should complete in 2019. The tunnel is an 8.8km single bore that will house two lanes of vehicular traffic. Its excavation profile was 13m high and 12.1m wide and was excavated from the north and south portals by drill and blast. The contractor, Strabag-Afcons JV, selected Atlas Copco (now Epiroc) WE3C and L2D boomers, Liebherr L944T crawler excavators and Meyco Potenza shotcreting units for the job.

The Seri Nala

The area along the tunnel alignment was virtually inaccessible due to mountains and snow, excepting the two portal sites. For this reason there are no adits to the tunnel, but it also made geological investigations from directly above impossible.

The areas above 4,500m remain covered in snow even during the summer and are difficult to access. What data could be obtained was gathered along a convenient stretch of the Manali-Leh Highway by the bank of the nearby River Chandra and other places. This was used to build a picture of the geology along the route.

The tunnel is located within the central crystalline group of rock. These units are collectively named ‘Vaikrita group’ and the zone represents an anticline that treads roughly along the axis of the Great Himalaya Range, extensively from the east to west of the entire range.

Geological studies indicated that the tunnel advancing from the southern portal would pass through quartzite-schist with various shear seams of phyllite and gneiss. It also passed through the Seri Nala fault zone (with conditions reaching their worst from Ch 2+049m to Ch 2+462m).

The rock mass within the zone consisted of decomposed rock fragments of phyllite, quartzitic phyllite, schist and river bed materials, with heavy ingress of cold water. The river bed materials, which included sand pockets and clays led to the frequent fall of loose materials and high water ingress, which lead to regular disruption. The miners’ reports were “characterised by constant collapse of face, extremely fractured and pulverised rock and very poor geological conditions, coupled with huge amounts of water ingress up to 127 litres per second”.

The conditions can only be described as atrocious. At one stage, progress was down to less than 1m per day. It took almost four years to excavate 0.41km. Although, once clear of the fault zone, this eventually rose as high as 217m in a month (April 2016). Total progress for 2016, the year the tunnellers were free of the fault, was 1,686m.

However, the teams were not there yet.

The difficulties increased monumentally when slurry began to flow heavily from the crown down the tunnel face (300m3). The flows of slurry and water caused such damage to the road inside the tunnel that a separate team employing specialist equipment was employed to undertake road maintenance.

Life without Rowa

The reduction in the ability of the crown to support a load meant that the contractor had to temporarily ditch its Rowa tunnelling system. This is a piece of equipment that features a mobile crusher, a conveyor system to rapidly remove spoil from the tunnel, a shotcrete pump and an electric overhead travelling crane for placing precast support members.

The Afcons engineers listed the benefits of the machine almost wistfully to Tunnels and Tunnelling, having had to do without: parallel activities without interruption, or reduced safety; eliminating unnecessary truck movements; reduction in the number of machines and pollution; reduced cycle time of all activities; less worker time in the tunnel; safer placement of precast members.

Then, tunnelling operations became awkward. The ventilation system was adequately designed to provide fresh air during excavation, assuming the Rowa system was in place. The increased traffic meant that an upgraded ventilation system had to be designed and installed to compensate for this. Higher capacity fans and ventilation ducts were installed, which increased the overall cost of ventilation to the contractor.

From about Ch 3+500m the temperature and humidity at the face became very high. It became extremely challenging to provide fresh air for the workers, with temperatures reaching 46°C. Oxygen levels became depleted due to the increased truck traffic and the workforce had to exit the tunnel at regular intervals for fresh air (and to attempt to control humidity levels).

Himalayan conditions

Away from the heat, humidity, water ingress and decomposed rock, site teams had to contend with other realities of work in the Himalayas. Aside from the occasional need for workers with alpine training to rescue soldiers that had become buried during avalanches, there were also project issues to face.

Between December to April each year, the area experiences heavy snowfall. Snow accumulates up to 10-12m deep and makes the routing of traffic on the approach road extremely difficult and dangerous due to risk of avalanches. To avoid complete suspension of work, snow removal and clearing equipment including cutters, loaders, salt spreaders and a sliding blade snow plough were needed. Even so, transportation companies were initially reluctant to make the trip in the winter months, and so there were delays to critical supplies reaching site.

The production and transportation of concrete in extremely cold weather was another key challenge undertaken by the engineers. The following measures were adopted to execute the work in hostile climatic conditions: hot (60°C) water was used to maintain the temperature of fresh concrete; sand and other aggregates were stored in covered sheds and then heated by steaming them, which removed lumps; conveyor belts were covered to avoid snow and rain mixing with the aggregates; transit mixtures are cleaned with hot water in winters prior to pouring of concrete in them so that the drum is not at a freezing level; the transit mixture is insulated during extreme weather conditions. Regular training also had to be conducted at the site to educate the team on concrete quality control and cold weather procedures.

As for the workers, office space and accommodation had to be constructed using puff panels to withstand the sub-zero temperatures. These buildings were also fitted with central heating. Medicines and other medical equipment had to be stockpiled to last a period of three months, while 30 days of food supplies for 400 (during the winter months) had to be held. A convenience store was maintained, with its stock geared towards winter needs, and an emergency office was also set up, which had work spaces for all departments.

A previous Tunnels and Tunnelling article noted that Rohtang was experiencing some problems related to industrial action, but Afcons says that these were an early issue that was since dealt with.

Final Toll

The project was delayed by a total of 4.5 years, primarily due to the challenges of the Seri Nala zone. The severity of the conditions took everyone by surprise, and for a while a change of alignment was considered to skirt around the section.

During the excavation of the tunnel through the Seri Nala, the cash flow of the contractor deteriorated due to low progress. Subsequent claims raised by the contractor for time and time-related costs were agreed by the client.

A difficult project became more painful than expected, but soon the Rohtang Pass will no longer keep local communities apart.