In the first year of execution, the first few months were utilized for various administrative and preparatory works installation of equipment, establishment of site laboratory, etc.
In addition, a survey for the establishment of camp area and selection of staff to be employed at the site was carried out. Most of the tunnel excavation equipments like excavators, rock breakers, crawler dozers, wheel loaders, etc., were brought to the site.
The first tunnel blast took place on 29 August 2010 at South Portal. Along with the drilling and installation of Swellex rock bolts, erection of lattice girders and wire mesh as primary support for excavated surfaces started.
With the excavation of portals, avalanche gallery excavation also commenced along with dewatering system from portal area and ventilation system was made operational to remove the foul gases from inside the tunnel. The precast yard at Dhundi was also made operational for the casting of elements for Emergency Egress Tunnel (EET), Low Voltage (LV) ducts, High Voltage (HV) ducts.
The first blast at North Portal was taken on 04 October 2010 and activities of drilling, charging, blasting and muck clearance also commenced.
At the South Portal, the site installation, office complex, labour & staff accommodation were improved upon along with various tunnelling activities like tunnel drilling, charging, blasting with rock support along with commissioning of the ventilation system and drainage pipe.
Right of Way Association (ROWA) conveyor system installation activities like retaining wall for conveyor belt, drilling of hanger bolts were done.
Probe drilling for exploration of surface at the slope in front of the South Portal was done. At the North Portal, due to inclement weather conditions, site induction was delayed. After induction and preliminary activities, north portal was closed due to heavy snowfall.
At the South Portal, heading excavation up to Chainage 2+078 was achieved. During the month of April 2012, difficult geological conditions were encountered at heading excavation. The tunnel support between Chainage 1980 and Chainage 2+010 was additionally strengthened.
On 22 April 2012, heavy water ingress occurred and a major quantity of debris (940 cum) was deposited at the worksite. Preparations for the controlling of drainage water from the face were made and on 15 June 2012, the pipe roofing umbrella work started.
On 28 June 2012, the excavation of the heading started under the protection of pipe roof umbrella. Various measures like chemical grouting, excavation by segments was undertaken to achieve progress in the heading. Also, the ROWA conveyor system was installed to achieve speedy progress.
At the South Portal, on 05 February 2013, an avalanche caused heavy damage to site installations.
The Tunnel Seismic Profile (TSP) measurement was carried out during the month of March 2013 and results showed that rock class 7+ continues at least up to Chainage 2+220 with higher water ingress. Chemical grouting for face stabilization and consolidation was undertaken.
The severe collapse of tunnel crown portion between Chainage 7+255 and Chainage 7+200 occurred at 1345 hrs on 16 October 2013 due to which heading works were kept in suspension for some duration.
A trial blast was carried out on 07 November 2013. Additional rock profiles and 3D monitoring (twice a day) at the damaged portion was conducted till the site stabilised.
At the Southern side, heading excavation under pipe roofing system commenced in the month of January 2014. Due to severe cold conditions at South Portal, concrete works were stopped in January 2014 and heading works were hampered due to non-accessibility to the site because of heavy snowfall in the months February and March 2014.
During the month of March 2014 more than 100 incidents of small and big avalanches were recorded along the access road to South Portal.
At the North Portal, due to the closure of Rohtang Pass and severe winter conditions the site remained closed from January to April and mobilization of personnel started on 05 May 2014.
On 13 May 2014, a large avalanche struck at the North Portal and the whole tunnel entrance was covered with snow which caused an additional delay. Finally drilling, charging, blasting started on 25 May 2014. During the period from June to November end, heading excavation along with primary support was achieved till Chainage 6+523.25 and benching up to Chainage 7+962 (West side) and 7+951.5 (East side) was achieved.
At the South Portal, excavation for heading under pipe roofing system started from Chainage 2+407.15 onwards in month of Jan. The pipe roofs were grouted with micro fine cement.
During the month of March 2014, heavy convergence was noticed from Chainage 2+400 onwards and heading works were halted. Core drilling at the face and grouting in the crown portion was resorted to.
Excavation of the heading under pipe roofing was completed till Chainage 2+455.00. The ventilation slab cast for the entire year was 962.5 m.
At the North Portal, mobilization of personnel was done on 18 May 2015. Finally, drilling started in the month of June 2015. TSP and Water Penetration Test (WPT) were carried out for geology prediction. The production of precast elements started in July 2015 after operationalization of the plant.
The tunnel excavation up to Chainage 5+983.5 was achieved by end of November 2015. As regards, benching is concerned, drilling, charging, blasting up to Chainage 7+750.0 (West side) and Chainage 7+740.5 (East side) was achieved.
At the South Portal, excavation activities for heading started with Chainage 2+455.00. Ramp making for benching ahead of Seri Nala i.e., at Chainage 2+510 was constructed in March 2016 and benching beyond this Chainage started in April 2016.
At North Portal, mobilization of manpower was initiated on 26 April 2016 and excavation for heading started from Chainage 5+983.5 in May 2016. Working carrier, inner liner, rail line for the final arch lining was moved inside the tunnel in October 2016.
In the ensuing year, heading up to Chainage 5+419.00, Benching 1&2 up to Chainage 6+955 was achieved. Also, excavation and primary support i.e., shotcrete, rock bolting of EAC 15, FCDP 23, 24, 25, 26 was achieved.
At the South Portal, the main focus was on achieving a breakthrough with which Heading and Benching works for the year started from Chainage 4+129 and Chainage 3+145 respectively.
Heading breakthrough was finally achieved on14 October 2017. Works within Seri Nala such as sawtooth filling, survey works, reprofiling works, etc., were undertaken during November 2017. Total heading length of 1+124.2 m, Benching (West) of length 8+27.5, Benching (East) of length 1034.2 m was achieved.
At the North Portal, first heading blast was done on 25 May 2017 at Chainage 5+419.00. Total heading length of 341.3 m, Benching (West) of length 565.5 m and Benching (East) of length 516.95 m were achieved. EET was laid up to Chainage 6831.2. Arch lining for a length of 537 m and ventilation slab for 12.5 m was achieved.
At the South Portal, excavation of 2nd heading along with the installation of wire mesh, plastic sheet, and lattice girder, shotcrete inside Seri Nala was started in January 2018.
Due to the inflow of water inside Seri Nala, a dimpled membrane for channelizing the water and dewatering pipelines were installed. Rock bolts pull out tests were conducted.
Benching till Chainage 5+800 was considered from the South Portal, however the same was completed in April 2019 and beyond this chainage, benching was considered as part of the North Portal.
Since regular progress was achieved in Seri Nala, so periodic re-arrangement of the electrical, water supply line, dewatering pipes had to be made as per the progress of works.
Excavation for invert along with the installation of dimpled membrane, geotextile, 250 mm diameter pipes with filter gravel inside Seri Nala was initiated in the month of June 2018. Benching excavation except Seri Nala was completed in June 2018.
A temporary Bailey Bridge was constructed inside the tunnel to enable construction traffic and deep invert excavation work to go on simultaneously.
Excavation works for the South Portal were initiated in September 2018. Drilling and installation of support measures, SDA, Ground anchors as per design was carried out. Excavation for the portal location was completed in October 2018. Total progress in benching west and benching east achieved during the year was 707 m and 693.7 m respectively.
During the ensuing year, except for the Seri Nala portion, drainage pipe below invert level was completed at Chainage 5+388 and EET laying at Chainage 5+292.93. The total arch lining of 1700 m and casting of ventilation slab for 1125 m was achieved.
At the South Portal, during the year benching and deep invert excavation activities were confined only to the Seri Nala Zone as these were already completed in the rest of the tunnel. Excavation of benching in Seri Nala started from Chainage 2+210.
As regards deep invert activities are concerned, excavation started from Chainage 2+204.50 onwards. Since only in Seri Nala portion waterproofing system had been provided, so prior to placement of geotextile and PVC membrane, the smoothening layer of shotcrete, protection layer of concrete (50 mm) was done to avoid any sharp edges or undulations that may puncture the membrane in future.
Bailey Bridge had to be shifted at regular intervals as per the alignment of deep invert shutter, shifting of Emergency Escape Tunnel (EET) base slab. Excavation for slope protection works was undertaken in May along with the installation of double corrosion protection anchors in the Western face of the portal.
Excavation for slope protection works was undertaken in May along with the installation of double corrosion protection anchors in the Western face of the portal.
At the South Portal, arch lining for Seri Nala was completed on 06 January 2020. Ventilation slab concreting was completed on 07 February 2020.
Concreting of stairs, ground floor balance works, EET below building, works beyond the first floor were carried out in full swing since Apr2020. Reinforcement, concrete for the attic floor was done in June 2020 along with shuttering, reinforcement for grid C and D, for the sloping roof in June 2020. The building and PQC works were completed in the month of July 2020.
At the North Portal, work was halted due to extreme weather conditions and COVID-19 restrictions. Building works were restarted in April 2020 and concreting of ground floor, inverted beams on slab and other miscellaneous works were taken up on priority and the building was completed in July 2020. Construction of diesel tank was started in June 2020. Architectural works on the North Portal building with local touch were proposed and completed in the month of August 2020.