Construction of Udhampur-Srinagar-Baramulla Broad gauge railway line is one of the mega projects undertaken by Indian Railways to establish a dependable transportation in the state of Jammu and Kashmir. In engineering terminology, it is a challenging project, negotiating breakthroughs against the complex Himalayan geology. The project which has been operational over last 12 years, stretch by stretch, is in advance stage of construction.

The purpose of the prestigious project is to connect the Kashmir valley to the mainland of the state of the country. On the date owing to the hurdles of the tuff terrain, the transport of this part is totally dependent on the surface transport, i.e., through a road which connects NH-1A from Delhi to Srinagar. The altitude of the region varies from 500.00 to 1700.00, ranging through Udhampur to Katra-Reasi-Sangaldan-Banihal-Quazikund-Ananthnag-Srinagarand Baramulla. The main features of this project are its Pirpanjal Tunnel and T-48 & 49 tunnels which cover the maximum length of tunneling through thick hostile geological conditions, the total length being 138km. Details of Pirpanjal tunnels are shown in Fig-1.

The contract for construction of Pir Panjal (T-80) has been awarded to HCC. The scope of Pir Panjal contract-the second longest transportation tunnel in India and third in Asia covers the construction of 11.2km long tunnel; this is the third longest railway tunnel in India, next only to Pir Panjal. The fast track nature of the job impinged upon us a responsibility to complete the job within the stipulated time, come what may. Hey presto, we have completed, in all respects, the Pir Panjal tunnel track and made it operational for movement of passenger trains. In this paper the author wants to highlight the difficulties faced in the highly complicated and adverse geological conditions and also on the spot solution adopted. There will be space above and below an extract. If the body text resumes after the extract, it should be styled using the normal style.

Geology Along The Tunnel Alignment

The tunnel alignment is traversing through the complex geological setup of Pir Panjal Mountain Range of lower Himalayas. It constitutes of soft ground and both medium hard to very hard strata. Both the portals have been constructed in soft ground consisting of glacio-fluvial deposits mainly boulders and gravels of variable size & shape in the matrix of silty clay in a variable proportions. The length of soft ground tunnelling is about 1250m having a thickness of overburden 2-3m at portal end and an average 30-40m.The medium hard to hard rock constitute a major portion of the tunnelling medium comprising Andesite & Basalt, Agglomeratic Shale, Quartzite, Shale, Tuff & Agglomerates, Limestone and Siliceous Limestone. Thickness of overburden ranges from 150m to an average of 500 m and a maximum up to 1100m.

The Pir Panjal Range is dominated with the folding leading to different dipping directions of the strata. Shearing of strata is very common along bedding and contact zones. Contacts between the litho-units are often faulted with thick fault gauge. The general strike of bedding is 130-3100 dipping either side with an average dip amount of 70-850. Other than bedding, three sets of medium to closely spaced joints with minor to thick clay filling have been observed resulting into frequent wedge formations at crown and sliding of blocks from walls and face. Locally strata is highly crushed and sheared and very unfavorable for tunnelling.

Construction Plan And Geotechnical Design

The shape of main tunnel is modified horse shoe shape and the alignment is straight along 1.90 with an increasing gradient of 1 % from either side towards central portion. It is a single tube twin tunnel of 6.29m clear height and a carriage width of 7.59m having single rail track and a service road. At every 250m there is maintenance niche, at every 500m truck turning niche and five MVS niches. The adit will used be as an emergency exit and supply and shaft for ventilation in future. Austrian standard for rock classification system has been adopted for Geotechnical Design which involves -

Step 1: Determination of Rock Mass Type (RMT)
Step 2: Determination of Rock Mass Behavior Type (BT)
Step 3: Determination of Excavation and Support
Step 4: Establishment of Construction Plan
Step 5: Determination of Excavation Classes

Step 1 – Determination of Rock Mass Types: The first step starts with a description of the basic geologic architecture and proceeds by defining geotechnically relevant key parameters for each ground type. The key parameters Values and distributions are determined from available information and/or estimated with engineering and geological judgment; values are constantly updated as pertinent information is obtained. Rock Mass Types (RMT) is then defined according to their key parameters.

The number of Rock Mass Types elaborated depends on the project specific geological conditions and on the stage of the design process.

Similar litho-units having similar composition, strength, structural & hydraulic conditions has been placed into the following 12 different Rock Mass Types -Table 1.

Step 2 – Determination of Rock Mass Behavior Types (BT): The second step involves evaluating the potential rock mass behaviors considering each rock mass type and local influencing factors, including the relative orientation of relevant discontinuities to the excavation, ground water conditions, stress situation, etc. This process results in the definition of project specific Behavior Types (BT).

The rock mass behavior has to be evaluated for the full cross sectional area without considering any modifications including the excavation method or sequence and support or other auxiliary measures. The rock mass behavior types form the basis for determining the excavation and support methods as well as assist in evaluating monitoring data during the excavation.

Step 3 – Determination of the Excavation and Support: Based on the defined project specific behavior types, different excavation and support measures are evaluated and acceptable methods are determined. The System Behavior is a result of the interaction between the rock mass behavior and the selected excavation and support schemes. The evaluated System Behavior has to be compared to the defined requirements. If the system behavior does not comply with the requirements, the excavation and/or support scheme has to be modified until compliance is obtained.

Step 4 – Geotechnical Repor t-Baseline Construction Plan: Based on steps 1 through 3 the alignment is divided into ‘homogeneous’ regions with similar excavation and support requirements. The baseline construction plan indicates the excavation and support methods available for each region, and contains limits and criteria for possible variations or modifications on site.

Step 5 – Determination Of Excavation Classes: Excavation Classes are defined based on the evaluation of the excavation and support measures. After evaluation of RMT & BT; round length, excavation method and the support system was decided resulting into excavation class for each round of excavation and accordingly construction plan was established.

Based on different geo-mechanical and ground behavior project was estimated in rock class I-VIII. Different support measures were as shown in Table 2.

Difficulties In Constrction And On The Spot Solutions Adopted

The USBRL line consists of a total length of 273.00 KM which the Indian Railway has divided into a number of sections to accelerate the works on various fronts. The Tunnel no-80 which connects Quazikund city in north and Banihal City in the South has been further divided into two packages namely Pirpanjal VA and Pirpanjal VB, in order to start the work from two ends.

The Pirpanjal VA consisting of 6.13 KM Tunnel and an Adit of 774.00 M and Pirpanjal VB consisting of 4.70 KM and Vertical Shaft of 55.00 M and a cross passage of 37 M, have been awarded to M/S Hindustan Construction Co. Ltd. as per the terms and conditions of the Indian Govt. Contract system.

The tunnel alignment passes through complex geological strata. It constitutes soft ground and soft to very hard rock, and owing to its location in the high altitude it also records a heavy snow fall in winter, October to March, for almost 6 months. The tunneling was carried out by NATM method using heading and benching by drill blast. Also used were the Road headers and tunnel excavators during the fast track execution. Unique and ubiquitous heavy ingress of water, high over burden and bad Himalayan geology are perpetually encountered.

Heavy Ingress Of Water In Major Portion Of Tunnel Length Varying From 10.0 LPS To 280.0 LPS

During tunneling from the Adit towards the north portal, heavy seepage, from the starting end of the tunnel, i.e. about 2750.00m south, was faced. The seepage varies from 25.00 liters per second to 280.00 liter per second, leading to face -collapse and cavity formation and to creating hurdles in the application of shotcrete and other primary supports. The non application of primary supports in this situation frequently causes a halt, and going ahead without supports is against the safety norms and the adopted methodology in various rock classes. The seepage is mainly from the crown and face, i.e., between SPL to SPL where working with electrical equipment and manpower is one of the major challenges. To overcome the difficulties, we have adopted the following innovations:

*Fig. 3: Typical Cross Section of Rock Class V, VII and VIII*

Stopping Heading Progress and Switching to Benching Excavation till Draining the Water from Face: We used heading and benching methodology for progressing the tunnel as per the standard methodology to suit the site conditions and eventually, we have advanced about 500.00 M in heading and then switched over to benching. As per the planning, we made a truck turning niche at every 500m interval to facilitate the turning facilities to all tunneling equipments in some special cases; however, we had to stop the heading before completion of the standard length due to heavy seepage of water. To apply the primary supports during such situations, we had to stop heading excavation after drilling additional longer and larger drainage holes of 50mm to 104 mm and up to the length of 15 to 30.0m in the face as well as in supported walls and crowns to drain out the water in advance before reaching the origin of seepage. Consequently, the pressure which is present in the walls and face was released to some extent and also special care was taken also to drain out the water. Some time we also fixed PVC/ MS/Hoses in the drainage holes and diverted water from sensitive areas like crown and face to avoid collapses due to erosion of bad rock/soil. As a result, we continued tunneling without stoppage of mining and then switched over to benching till the time water seepage reduces, thereby ensuring tunnel safety and safety of tunneling crew.

After successful drain out of major water from the ground, by allowing water to come out from ground, proceeding again with tunneling in heading, special care was taken while applying primary lining by diverting water through channels or through conduits in drilled holes in order to avoid rebound of shotcrete and filling voids perfectly with rock contact. Furthermore, innovations like inserting grout pipes in the primary lining for contact/ consolidation- grouting after reduction of seepage from surface were also made-so that a perfect contact could be ensured between primary lining and rock. It was also ensured that pressure- relief-holes were made to release the pressure between primary lining and the rock soon after the application of primary supports along the periphery up to the depth of 300 to 400mm before proceeding to next round of excavation.

After completion of the Adit junction, the main tunnel in critical drive (MTS-2) was excavated, 574 with the heading and benching method where only the heading was completed. Here a hard and very strong quartzite was encountered with medium to widely spaced some open joints. Minor seepage started from 572m and some drainage holes were drilled to control the seepage. Then the next successive blast was taken to advance the main tunnel. Heavy water ingress started from the face and the crown, measuring around 280 l/sec. Seeing the impossibility to excavate through such heavy ingress of water, it was decided to stop the heading excavation and first complete the benching.

Heavy water ingress inside tunnel was due presence of open joints, heavy snowfall over the project, presence of perennial stream across the tunnel and formation of aquifer around the tunnel and regular recharge of aquifer through the stream. Situation tackled by stopping the heading and starting the benching and face work was discontinued for 3 months to drain the water. Due to this water discharge reduced and measured around 110L/sec. Drainage hole 120mm dia. and 25m long were drilled systematically with an spacing of 1.5m from 570m supported face (in periphery).Water ingress was recorded in all drainage holes and perforated 76dia SDR were inserted in drainage holes to avoid collapse and choking of drilled holes, this resulted almost dry and workable face. Further 25m long probe holes were drilled on left and right side of the face and the process was repeated for systematic drilling of drainage holes and probe holes. This on the spot solution resulted successful completion of the project.

*Fig. 5: Snow Fall at Site and Heavy Water Ingress in T-80*

Rock Bursting Due To High Over Burden

This was very challenging to excavate through a very good rock with very high overburden. It was noticed several time that heavy sounds were coming from the face and crown of the advancing face with sudden and violent failure of rock mass. Sometimes supported rounds were also damaged due to the failure of rock mass and portion was rectified with great difficulties. Executing team with all crew members was always feared about any miss happenings but this was the result of team work where all problems were left behind to complete the project without any miss happenings. Problem started with the start of massive andesite.

Reason for the rock bursting was due to presence of hard and massive andesite, brittle nature of rock mass and widely to very widely spaced discontinuous joints. These joints were very tight without observed openings. Over burden in this area was between 900 to 1100m and due to high overburden vertical stresses were in the range of 240 to 300Mpa and strength of rock mass was 100-150Mpa. Sudden release of stored stress were observed. Situation was tackled by increasing support elements, thickness of primary lining (shotcrete) and installation of pre supporting elements (fore poles) by drilling 120mm wide 6m long, 20-30 numbers holes in the periphery and face area to accommodate the stored stresses. Regular face sealing was done after proper scaling of face with heavy hammer. In addition to these 4 to 6 numbers 20m long drainage holes in the both walls of face and 8 to 12 nos. 2m long pressure relief holes were drilled to keep face under control. Special care was taken to monitor the sign of failure very closely on regular basis and minimum workers were deployed at face for ensuring ease of evacuation. Ambulance and recovery vans with all supports were kept ready to tackle any situation and encouraging the will of the workers. This on the spot solution resulted successful completion of the project. It is suggested that research and developments are required to detect the phenomena well in advance.

3.3 Excavation in Weak Rock (Shale)

While the South portal side team was tackling the rock bursting in a hard and very good rock, the team of North Portal was executing through the weak rock mass (Shale) which was another challenge in the North Portal drive. Top heading was in progress at tunnel meter 3400 and it was noticed that behind 200m cracks in the early supported rounds were developed which were increasing day by day with wider openings although deformation was stabilized during the course of excavation and deformation re started and reached in alarming conditions with several mm closure of tunnel and was continuously increasing slowly. After taking into consideration of safety of work and man power it was decided to come back and re strengthen the early supported rounds.

Squeezing condition was due to presence of weak rock mass (Shale), high over burden ranging 700-900m with UCS of rock between 25-35Mpa and vertical stresses in the range of 180-240Mpa. Strength of rock was very low in comparison to the active vertical stress. Presence of water through the strata which again reduced the strength of the rock mass in the new environment. Due to high stress strength ratio in the incompetent strata squeezing started with alarming recorded deformations.

Situation was tackled carefully by increasing support elements and thickness of primary lining (shotcrete). Support system changed from class V from class IV and additionally 9-10 SD rock anchors were installed with proper grouting. Two layer wire mesh and additional shotcrete was done with additional drainage holes 8-10 numbers with a length of 12-20m in each rounds. Contact grouting and check holes completed over the whole length of shale strata with additional weep holes 6-8numbers of 1.5m in each round. Excavation of bench and invert was done by placing a longitudinal drainage layer below the invert, excavating 300mm x 300mm x 300mm ditch and placing 160mm perforated Upvc pipe covered with geotextile and filled with 20mm coarse aggregates. This drainage system was again connected through the lateral collector drain where water was collected into the ditch and regular de-watering through the sub-miscible pumps.

Adequate stand by pumps were installed with sufficient capacity to drain the water. Finally base was dry and deformation was stopped. For closing the invert ring backfilling the invert was done with a good and suitable filling material. Regular 3D observation and re supporting the strata with longer (12m) SD rock bolts and doing proper grouting. After stabilization re- excavation of the filled invert was done. Repairing of the damaged layer of shotcrete and wire mesh in the invert portion was done by placing of suitable water stopper and backfilling the invert with concrete as per the design. Re-mining and rectification works in the crown and periphery to get the minimum thickness of the final lining. Close and regular 3D monitoring of the whole stretch was ensured. After stabilization final lining was completed. This on the spot solution has resulted successful completion of the project.

Project Roads

The project is linked through 200km long Jammu-Srinagar National highway up to Banihal and thereafter through the same highway up to Qazigund after crossing Jawahar Tunnel. The National Highway traffic is badly affected during the winters and the rains due to permanent slides near Udhampur and Nasari. Mostly one way traffic is permitted over more than four months in a year, due to which transportation of construction materials, diesel and other essential material supplies is heavily affected, and the cost also escalates. Moreover the project approach roads are very slide prone, and most of the time, the road remains blocked due to mass movement of hill slope debris. During the monsoon the road would be washed away at several places and also get blocked because of the landslides and also because of sinking tendency of various stretches which stand already detached from the mountain slope. Not only a considerable time was lost due to poor roads but a few accidents also occurred during construction. We suffered a setback due to the break in the supply chain and the work stopped for a longer period. The same was restored by putting manifold all efforts and equipments and manpower.

Fig. 6: Condition of Project Approach Road at Different Locations During Rainfall

Muck Management

The major activity taken up during construction of the tunnel is disposal of excavated material or spoils. This material, if disposed off into nearby water bodies, insidiously increases water turbidity, thereby causing adverse effect on aquatic flora and fauna. For the success of any underground project, muck dumping yards are the key facility.

Therefore at every location, a separate dumping yard was required to accommodate the huge quantity of excavated tunnel muck. As this area is undulating and there is steep slope. And of course a very limited land for muck disposal is available. There are no approach roads either. Due to unavailability of the dumping area and the approach road at all location, adverse effect on the progress was recorded.

To acquire the land from the local inhabitants on lease, clients and district administration was liaison. Stability was ensured at steeper locations by properly protecting the same in benches, providing base drainage and surface protection against erosion. The excavated material was also tested at reputed labs for reutilization as coarse and fine aggregates, and the left out material was used for developing the job facilities, play grounds and other project infrastructures.

Conclusion

(i) Most of the problems in the Himalayan tunneling can be attributed to the lack of knowledge of the geology ahead of the face. These problems have resulted in loss of time and costs overrun; which eventually deprives the country of the project benefits. It is essential that detailed exploration work be carried out before the start. And exploration ahead of face should be undertaken on a continuous basis.

(ii) Proper, wide and good, roads should be made before the start of the project to facilitating speedy and safe working. Proper safety arrangements by implementing safety plan for the project should be made for ensuring safety of the precious human life.

(iii) Selection of proper equipments is very important for speedy and successful completion of a Project. NATM Technology is the best and safe soft ground conditions and recommended to be implemented widely at different Himalayan location for infrastructure projects.'

(iv) Proper construction planning of each activity of this railway Tunnel paved way for faster construction.

(v) Never ignore the streams which are flowing near the tunnel and specially if crossing the tunnels. Systematic Probe holes and drainage holes even if there is no discharge from the face.

(vi) Team work, proper co-ordination/co-operation and dedication of HCC engineers have been the formulae to bring the project into proper shape and achieving successful completion of the project.

Acknowledgements

Author is thankful to Northern Railways and IRCON International for their support and cooperation during execution of the works.

References