The Pir Panjal railway tunnel is the first major tunnel in India to be constructed using NATM and has had to overcome labour strikes, equipment failures, horrendous weather and topographical conditions to remain on schedule. Despite drilling and blasting through very heterogeneous rock conditions with frequent changes of mass and fractured rock and with high water inflow the work is progressing without prolonged delays.

The design and construction method is keeping the project on track by allowing fast reaction to varying geology and the installation of initial support measures needed in a young rock mass such as the Himalayas. The tunnel is driven from several faces using drill & blast and road heading with immediate installation of primary support.

About 77 per cent of top heading has been completed. Considering the difficult geology, extreme weather in winter and the hostile conditions of the area the overall performance is satisfactory.

Railway development
The Pir Panjal Railway Tunnel is part of the New Broad Gauge (1.676m) Railway line of the Jammu-Kashmir Rail Link Project from Udhampur to Srinagar and Baramulla.

The tunnel across the Pir Panjal mountain range, which forms the border of Jammu and the Kashmir Valley, is one of the key structures of this new line. As a base tunnel between the Banihal valley and the Kashmir Valley it will provide a safe connection throughout the year. After its completion, the tunnel will have a total length of about 11km and will be the longest railway tunnel in India. It is located between the proposed railway stations Banihal (Jammu) in the south and Qazigund (Kashmir) in the north.

To meet client Northern Rail’s standard safety requirements for long tunnels, a 3m wide path will run alongside the single track for emergency and maintenance access. The main tunnel will be 10960m long. The project includes a 774m long access tunnel (adit) and a 55m deep access shaft with a 30m long connecting cross passage.

Tunnel design
The inner tunnel profile was designed to fit a single track railway, an overhead catenary system and the 3m wide access road beside the track. By using an outer (primary) and an inner (secondary) lining with variable thickness depending on the geotechnical conditions, and an invert for soft ground and very poor rock strata, the theoretical excavation section varies between 65m2 and 80m2. Special cross sections are required for the maintenance, equipment and truck turning niches.

The theoretical excavation section of the adit is between 50m2 and 65m2. The inner clearance profile was developed considering movement of heavy construction equipment and use for emergency access during operation.

The excavation diameter of the shaft is 12m, and was developed from the estimated clearance profile with consideration for providing access for heavy construction equipment through the shaft.

Connection structures of the adit and the shaft, which are used for the start of main tunnel driving, are perpendicular to the tunnel axis and have an enlarged cross section. While the width is the same as the adit the roof is about 1m higher than the main tunnel. The maximum theoretical excavation area of this cross passage is about 95m2.

The Geoconsult – RITES JV has designed two separate tunnel linings; a primary or outer lining and secondary or inner lining. The primary lining provides safe support during the construction, while the secondary lining will provide support for the lifetime of the tunnel. Thickness and layout of the outer and the inner lining depend on the geotechnical conditions and vary along the tunnel.

Construction program
The construction sequence was broken into two projects; the early works and the main tunnel works. The early works included the installation of the primary support of the adit, shaft and the 600m long soft ground section from the north portal. The Geoconsult – RITES JV prepared these in separate packages so construction could start ahead of the main tunnel construction. The main tunnel was tendered in two packages, separated in driving from the south portal and adit intersection towards north and driving from the shaft cross passage towards south (see Figure 1).

The use of an interim adit and a shaft has reduced the maximum driving length of the main tunnel to 7600m. In addition the potential risk of delays in the more than 500m long soft ground sections at both portals could be avoided in the critical driving path.

Construction follows a cyclical sequence of excavation and support installation of the outer lining with a delayed installation of the inner lining. For easier control of the water and for a higher advance rate an upward gradient is preferable and was considered in the program in particular where high water inflow was expected.

According to the original program installation of the inner lining should be carried out after completion of driving works in the respective sections. Installation of the inner lining is by casting the invert arch / side beams with in situ concrete and following casting of the crown with in situ concrete using movable shutters. After reconsidering the program inner lining installation is carried out concurrently with tunnel driving.

Early works
The early works were awarded in July 2004. Site preparation works like access roads, excavation and support installation of portal cuts started in November 2004. The actual driving of the adit and shaft started in May 2005. Driving of the main tunnel from the north portal started in August 2005.

The slow progress experienced in site preparation was due to insufficient planning, lack of winter experience, poor equipment, problems with material supply and severe weather conditions. Security and labour problems aggravated the conditions. Because of the heavy snow fall in the winter of 2004/05 the site was closed for several months. Preparation works, which were started but not completed before the winter, were destroyed to a great extent. After remobilization of the site repair and rectification of many works were required.

Underground driving started in April and May 2005 at the shaft and the adit, and in August from the north portal. The shaft was completed within four months and the connecting cross passage was finished in March 2006. The construction of the adit needed 23 months which is an average driving rate of about 35 m/month. The main tunnel drive from the north portal required 15 months which is about 42m/month.

Both drives of the early works encountered difficult geotechnical conditions. The main tunnel from the north was in soft ground over its total length and round length was limited to 1m. After a learning period of two to three months top heading driving speed increased to 50 – 60m per month, which is about two rounds per day. During the winter period 2005/06 construction came to a complete stand still and started again slowly before increasing the progress to an average of more than 90m per month or three or more rounds per day.

The adit was driven in soft ground for about 30m and subsequently in shale and quartzite. Very weak and good rock conditions changed frequently and several fault zones with crushed material and heavy water inflow were encountered. The conditions were aggravated by the 10 per cent down gradient requiring continuous dewatering. After a learning period with slow progress of almost a year average driving rates of 50 – 80m/month and peak rates over 100m/month could be achieved over the summer season from May to November, while the progress at the start of the works and during winter was extremely slow with frequent stops.

Reasons for the slow progress can be summarised as follows:

• In generally difficult geological conditions combined with no experience by the contractor of the construction method and long learning period.

• Poor quality of the equipment and poor maintenance. Because of the small contract values only old equipment was used.

• Accordingly frequent breakdowns common and performance in drilling, blasting, shotcrete spraying and installation of other support measures were slow.

• Insufficient and inadequate tools.

• Lack of tool kit for emergency situations.

• Poor drilling performance and inadequate blasting technology. Low quality of electric detonators.

• Problems with dewatering in Case of high water inrush and downward drive due to lack of standby pumps, cable extension and power.

• Severe weather conditions combined with poor maintenance of construction site (construction road) and inexperience with such conditions.

• Blockage of the highway from Jammu to Srinagar by landslides during bad weather conditions and associated problems with supply of construction material and spare parts combined with inadequate planning for supply of construction material and spare parts.

• Road closure in winter and interruption of connection between construction sites in north and south.

• Non availability and/or poor performance of communication facilities (telephone, fax, internet, cell phones).

• Hostile conditions and security problems in Kashmir area.

• Labour strike and labour unrest.

The main tunnel
The main tunnel drive from the south portal started in April 2006 after five month of site preparation including portal cutting and installation of Slope support. In July 2009 the main tunnel drive from the south portal reached the counter drive which was excavated from the adit at tunnel meter 1961.5. The top header drive has an average driving rate of 50m per month. Encountered geology included about 550m of soft ground, followed by about 390m of highly weathered and fractured limestone with sandstone intercalations, bands of quartzite with thick clay fillings and volcanic dyke, followed by some 1020m of very strong slightly fractured and weathered quartzite with clay and shale intercalations. All ranges from wet to dripping and flowing water were encountered in the rock with water inflow up to 10l/sec.

A counter drive was started from the adit towards the south in September 2007. In June 2009 the face was stopped for the breakthrough at tunnel meter 788.5. This drive has an average progress rate of 36m per month. The slower rate is due to the fact that this drive, which was not on a critical path, has not been continuously driven. Encountered rock for the first 380m was mainly shale with quartzite bands during the first 80m. Shale was highly to moderately fractured. The encountered rock for the next 100m was shale and limestone and changed completely for about a further 80m to limestone, followed by argillaceous limestone for about 70m. The argillaceous limestone was highly to moderately unweathered with sheared rock mass and with volcanic Dyke/Sill. The following about 160m of the encountered rock was grey quartzite alternating with a band of black shale. Quartzite was very strong to strong, unweathered and highly to moderately fractured. Water conditions were dripping with local flowing.

After completion of the adit another drive towards the north could be started in March 2007. In early December 2009, 2210m of header drive were completed, which is an average driving rate of 67m/month. Encountered rocks included about 320m quartzite and shale layers of varying thickness between 10m and 40m, followed by shale with quartzite bands for about 260m, and quartzite and fault breccia for about 70m, grained quartzite with shale bands and breccia for about 480m. Quartzite was highly fractured and water ingress was high. In general water flow was between 20l/sec and 60l/sec. The highest water inflow was 160l/sec. Further encountered rock was agglomeratic shale for about 700m, followed by green andesite with quartz as inclusion and with locally weak zones. The agglomeratic shale was moderately laminated, fractured and fine grained with a water flow from damp to seeping. The andesite was very strong unweathered and blocky with a water flow from dry to dripping.

After completion of the shaft cross passage and preparation for driving, excavation of the main tunnel towards the south started in July 2006. For about six months, until full completion and handover of soft ground section of the main tunnel north, the shaft was used for material and equipment supply and muck removal. By early December 2009, 2670m of heading drive was completed which gave an average progress rate of 65m/month. Encountered rock was very weak and highly weathered shale for about 50m, highly fractured quartzite with shale intercalations and frequent shear zones for about 150m, weathered limestone with frequent shear zones for about 80m, quartzite with shale bands for about 100m and from about tunnel meter 390 for about 1860m limestone of varying degree of weathering with shale intercalations and occasional shear zones. Karstic features were expected for this limestone section, but besides clay coating and clay filling in the joints and fractured rock in some areas only minor karst features were found. The further rock encountered from tunnel metre 2245 was quartzite with shale and limestone intercalation, gauge material, clay filling and shear planes. The encountered quartzite was strong to weak, slightly to highly weathered, fine grained, highly fractured and bedded. Water conditions were generally from wet to seepage flow of several litres per second. Maximum water inflow was in the order of 50 and 60l /sec.

In comparison to the early works construction progress has increased in all drives, which is mainly due to improvement of the main construction equipment and provision of tools and tool kit which allows faster reaction and control in case of changing rock conditions. Provision of new construction equipment included Boomer drillrig, heavy tunnel excavator with movable head in all direction, a large loader with side tipping shovel for unloading, and robitic nozzle for shotcrete spraying.

However, idling periods and stand stills are still on the high side, because of break down, missing spare parts and frequent tire failure. A major impact to works can also be attributed again to severe weather conditions, the hostile situation of the work site, labour strikes and similar conditions which are outside of the control of the contractor and Ircon.

More than 9200m (about 77 per cent) of underground driving of the Pir Panjal tunnel is complete. More than 8200m or almost 75 per cent of the main tunnel heading drive has been finished. For the tunnel section between adit and shaft, which is on the critical path, about 4900m are driven and about 2700m are still remaining. From recent progress rates the final break through could be possible in early 2011.

Uncertainties remain with regard to the security situation in Kashmir and associated interruption of the work. Other uncertainties are related to rock mass conditions in fault zones and at the higher overburden. Present overburden is close to 600m at the south drive and about 440m at the north drive. Particular uncertainty is related to the highest overburden of more than 1000m and in the shale, where squeezing rock conditions may occur. It is fair to say that under the given conditions at the work site and in comparison to other tunnels of the Jammu-Kashmir-Railway project Pir Panjal Tunnel achieved a good overall progress and work standard.

The south portal was excavated in alluvial deposits and slope debris Fig 1- Schematic Layout of Underground Structures Fig 2-Longitudinal Section The north portal with a view of the foothills the tunnel cuts through