One of the challenging and marvelous projects in Indian civil engineering history the pir panjal railway tunnel, India?s first longest Railway Tunnel (10.96 km) for transportation, was executed by HCC. A report...

The pir panjal railway tunnel is India?s first longest Railway Tunnel (10.96 km) for transportation. This outstanding tunnel is hundred per cent water proof and equipped with fire fighting system throughout the entire length of tunnel. The methodology adopted for construction of this tunnel is by New Australian Tunneling Method (NATM) where the geological stress from the surrounding rock is used to stabilise the tunnel hole. It is one of the challenging and marvelous projects in Indian civil engineering history. The tunnel is aligned straight from North to South for its length of10.96 km. The Pir Panjal Tunnel is a major part of Udhampur?Srinagar?Baramulla broad gauge rail line project. It is constructed in the rugged terrains of Pir Panjal pass in the state of Jammu & Kashmir. It connects the Bichleri valley at the south side with the Kashmir valley on the north side. The nearest town in south and north side is Banihal and Quazigund respectively. The quantum of work involves one million cum of underground excavation in the young Himalayan region with surprising geological challenges.

IRCON International Limited has taken up the job for construction of the project from Dharam to Baramulla section being an autonomous constructing agency for Indian Railways. The railway line rom Quazigund to Baramulla (119 km) was already completed by IRCON and it is operational to Public since October 2009. In order to accelerate the balance work, the total length between Dharam to Quazigund section was divided into six zones by IRCON and the contract was awarded to different agencies for early completion. The contract for Zone ? IV and V has been executed by HCC being one of the pioneer companies in construction and infrastructure development. HCC has eecuted more than 170 km of tunneling works at different location with different technical challenges and has completed majority of India?s landmark infrastructure projects in different sectors. The Pir panjal Tunnel project offered HCC an opportunity to accomplish one more feat to construct the India?s longest tunnel in the Young Himalayan Region.

Project overview

The entire project between Dharam? Quazigund section is a large project with different scope of work. The total length of the Dharam?Quazigund section is 56.54 km which comprises of 14 tunnels of total length of 44.50 km and 48 numbers of major and minor Bridges. In order to accelerate the overall construction the total length between laole to Quazigund was divided into 6 Zones. The civil works under Zone ? IV (km 142 to 152) and V (152+600 to 163+560) was awarded to HCC as a result of HCC?s vast experience in tunneling works, mostly in Himalayan region and the track record of executing more than 170 km of complex tunnels in India and around the world.

Details of Zone?V

The package under zone ? V is a single tunnel of 10.96 km (here it is called T-80); it is the India?s 1st longest tunnel and Asia?s second longest Tunnel. The major work of T-80 (excavation and lining) was divided into 4 separate contracts and out of 10.96 Km the excavation for 10.375 km and lining for 10.96 km was awarded to HCC.

1) Construction of Pir panjal tunnel from Ch 152+600 to 158+730 (Zone VA - 6.13 km) tunneling, lining works ? The work awarded to HCC.
2) Construction of Pir panjal tunnel from Ch 158+730 to 162+975 (Zone VB - 4.245 km) tunneling, (4.83 km) Lining Works  ? The work awarded to HCC
3) Construction of Pir panjal tunnel from Ch 162+975 to 163+560 (Zone VB - 585 m) in soft ground - The work was awarded to Gammon India
4) Construction of ADIT, Shaft with cross passage between ch 152 +000 to 164+000 of Pir panjal tunnel (Zone ?V) ? The work was awarded to HCC

The scope of VA project includes:

1) Construction of the main tunnel from Ch 152+600 to 158+730 (6.130 km) includes excavation, installation of support system, primary and secondary lining as per approved drawings.
2) Slope stabilisation and slope protection at the south portal approach as per approved drawings.
3) Construction of final portal structures from Ch 152+537.50 to 152+600 (62.5 m) including backfilling and other auxiliary works as per approved drawings.
4) Construction of 85m long remaining access tunnel section
5) Construction of the water proofing system and the concrete inner lining between Ch 152+600 to 158+730 (6.13 km).

The scope of VB project includes:

1) Construction of the Main Tunnel from Ch 158+730 to 162+975 (4.245 Km) includes excavation, installation of support systems, primary & secondary Lining as per approved drawings.
2) Construction of the water proofing system and the concrete inner lining between Ch 163+560 to 158+730 (4.83 km).
3) Construction of final portal structures between Ch 163+560 to 163+710 including backfilling and other auxiliary works as per approved drawings.

Construction method

The construction method adopted in Pir panjal tunnel is New Austrian Tunneling method (NATM) with latest technologies of 3D Monitoring system. The NATM was developed between 1957 and 1965 in Austria. The main contributors to the development of NATM were Ladislaus von Rabcewicz, Leopold M?ller, and Franz Pacher. The concept of NATM is, the surrounding soil or rock mass of a tunnel is integrated into overall support structure and the rock is activated to a load bearing ring around the tunnel.

Details of main tunnel

Based on the geological investigation the rocks between the tunnel portions are classified into eight types and accordingly the support system were designed by DDC. The excavation area of main tunnel is varying from 67 to 78 sq m based on the rock condition. The final finished cross sectional area is 48 sq m. The Whole length of T-80 was divided into four sections for execution purpose. The details are mentioned below,

1) Main tunnel south (MTS) ? 2,750 m
2) Main tunnel south 2 (MTS -2) ? 3,380 m
3) Main tunnel south towards X passage (MTXS) ? 4,220 m
4) Main tunnel North (MTN) ? 610 m

In order to accelerate the overall works and early completion, the excavation was started from three faces called,

(i) Drive from the south portal towards North
(ii) Drive through Adit towards North
(iii) Drive from North Portal towards South

Main tunnel south (MTS)

As mentioned above the total length of MTS is 2,750 m, It comprises of 650 m soft ground tunneling in the overburden of 20 to 40 m, it was a difficult task for execution as the portion was fully consists of soft clay soil with patches of hard strata in between the portion. The presence of village Cheril above the alignment of the tunnel added to the construction difficulties in tackling the ground conditions. The soft ground tunneling was done by sector excavation method with the help of Samboo (STE -280) Tunnel Excavator. The top part is excavated first followed by support measures. Thereafter, left part & right parts are excavated by following the complete support measures. Lastly the main support body (called central core) is excavated. The central core is the main support body to supports the surrounding soils to avoid collapse during excavation in side & top portion. The excavation in MTS was carriedout from two faces. The first 1,961m was excavated from south side and it is called MTS, the remaining portion 789m was excavated from ADIT and it is called MTS-1. The breakthrough of MTS & MTS ? 1 was achieved on 17 July 2009.

Details of access tunnel and shaft

The main purpose of providing ADIT and shaft is to shortening the critical length of drive and isolating difficult ground near portals. By providing an adit (south side) and a shaft (north side), the critical length is reduced to 7,600 m, against the total length of 10.96 km. The total length of ADIT is 772 m. It meets the main tunnel at ch 155+350 (2,750 m); the shaft is constructed in north portal at ch 162+950. The shaft is connected to the main tunnel with a cross passage of 38m. The shape of shaft is circular with a diameter of 12 m and depth of 56 m. It isolates the soft ground tunnel of 600m from the north end. The cross section of the adit and shaft also allow for construction convenience and ventilation during construction and operation.

Excavation methods

The total area of tunneling was excavated in three parts called top heading, benching and invert. The invert Excavation is applicable only in rock class ? V and above. The excavation was started on 25 and 27 April 2006 from VA and VB side. Based on the geological requirement there are 3 excavation techniques were adopted in Pir Panjal Tunnel.

a) Excavation by tunnel excavator
b) Excavation by road header
c) Excavation by drill and blast method

Tunnel excavator

This method was adopted in soft ground tunneling such as rock class VII and VIII; In this method tunnel face has to be excavated using a tunnel excavator SAMBOO STE 280. It has a rotating boom arrangement which makes it very convenient to use in restrained excavation in sectors. This equipment was very useful for successful completion of tunneling in soft ground of first 650m. The mucking was carried out with the help of side tilting wheel loader of make Liugong and 20 T Wagnor dumpers of make Atlas Copco.

Road header

The road header was used in north portal of the Pir panjal Tunnel where the usage of road header is effective and the unconfined compressive strength of rock is less than 100 Mpa. The road headeris equipped with a transversal cutting head (Picks) mounted on the end of a boom for excavation which is raised, lowered and slewed from side to side by hydraulic rams. The consumption of picks may vary from 0.025 to 0.3 per cum based on the varying UCS of rocks. The muck herein is accumulated in the apron in the equipment from where the same is loaded to the dumpers via the conveyor installed therein. The maximum & effective usage of road header is not much possible in Pir panjal Tunnel as the UCS of rocks is mostly higher than 100 Mpa which causes the reduction of road header performance and increase in consumption of picks. The overall utilisation of road header in Pir panjal tunnel was approximately 9 per cent of total excavation.

Drill and blast

In hard rock strata where both of the above mentioned excavation techniques were not much effective hence the drill and blast method was adopted to expedite the excavation. The blast holes were drilled in the face as per the drill pattern with a 2-boom hydraulic jumbo (L2C and L2D). Then the explosives are loaded in the drilled holes and blast was taken for breaking the face rock. The explosives used in Pir Panjal tunnel are power gel, Long delay detonators (LDD), Non electric detonators (NED), Dcord, 40 and 32 mm dia explosives for effective blasting. The NED is very useful in this project. The advantage of NED is safe working & the loading of NED can be done parallel to other activities. The mucking work is done with the help of side tilting wheel.

EQUIPMENT USED

? The major equipments and formwork used in the project are
? Tunnel excavator STE 280
? Cifa shotcrete machine
? 2 Boom hdraulic jumbo (Computerised L2C)
? Casagrande PG 175
? Side tilting wheel loader
? Road header
? Cifa gantry
? Invert bridge.

Longest Transportation Tunnel (10.96 Km) in India.

? Provision of ADIT and shaft for parallel working, and usage of same for ventilation, maintenance and emergency purposes.
? Provision of 3 m wide concrete road inside the tunnel throughout the length (10.96 km) for maintenance and emergency relief purpose. This road is constructed adjacent to the railway track.
? The total length of tunnel is water proofed.
? High mid point and sloping in both directions for drainage.
? The pir panjal tunnel passes 440.0 m (approx) below the existing Jawahar road tunnel (2.75 km).
? The alignment of Pir panjal tunnel crosses the NH ? 1A in three locations.
? First large scale use of NATM method in India.
? Usage of road headers adopted firstly in India for railway tunneling.
? Highest overburden of 1,100 m
? Usage of geotechnical Instruments for routine monitoring, assessing the stress redistribution and stabilisation before final lining.
? The total excavation quantity is of 11 lacks cum. rock bolting of 3,15,000 m.
? Progressed parallel activities (such as overt lining and excavation works) by introducing invert bridge.

CHALLENGES FACED

? Pir panjal tunnel project is a unique and pleasing project, but during execution of works following were the major challenges to be addressed.
? Change in geological condition / variation in anticipated rock class, occurrence of rock bursting while execution of works are mainly hindered the work.
? Excavation in soft ground.
? Restriction of blasting due to existence of villages over the alignment of tunnel.
? Excavation through heavy ingress of water
? Excavation in shear zones.
? Casting of invert lining inside the tunnel.
? Decrease in performance of road header