Louis Berger Tunnelling Through Challenges

Kshitish Nadgauda, Senior VP & MD – Asia, Louis Berger
Kshitish Nadgauda, Senior VP & MD – Asia, Louis Berger, shares information on the challenges encountered during tunnelling in the mountainous terrains of J&K and in the busy streets of Mumbai.

Louis Berger has completed many challenging tunnel projects across the world; please share your experience in one of India’s strategically important tunnel projects.
In 2004, the National Highway Authority of India (NHAI) selected Louis Berger in a joint venture with LRP Consultants to prepare the feasibility study, detailed project report (DPR) and engineering designs for the four-laning of the Udhampur to Banihal section of National Highway 1A, now part of National Highway 44. The project would eventually include replacing the existing 41-km (25.5-mile) long mountain road stretch with the 9-km long (5.6-mile) Chenani-Nashri tunnel, which would become India’s longest roadway tunnel.

Chenani Nashri tunnel

The design and construction of the Chenani-Nashri tunnel was a challenge not only due to inclement weather conditions but also due to the sheer size and magnitude of the project, and the prevailing soil and rock conditions in the area. Additionally, preservation of the endangered chinar (maple) tree forest was a mandatory requirement.

Srinagar was connected to Jammu and the rest of India by the old National Highway 1A, a narrow two-lane highway passing through treacherous terrain and some of the steepest landscapes in the world. Widening and realignment of the highway, including with new all-weather tunnels through steep rock beds, was needed to improve safety, decrease travel time and minimize roadway closures during adverse weather conditions.

The 9km-long tunnel reduces the travel distance between Jammu and Srinagar, the state’s two largest cities, by 30 km (18.6 miles), cuts travel time by about two hours, and is anticipated to boost tourism and economic growth in the region. The highway realignment will also help preserve forests in the ecologically sensitive Patni Top area of the state.

Louis Berger overcame all the challenges by working closely and collaboratively with our client, the NHAI, the consultant, contractor and other stakeholders, and ensured successful delivery of the project, minimizing or avoiding delays, and within the original budget. Today, the Chenani-Nashri tunnel is widely acclaimed as India’s longest and safest roadway tunnel in the heart of the Himalayas.

What steps were taken to overcome the challenges while building the Chenani-Nashri tunnel?
The old National Highway 1A was a narrow two-lane highway passing through challenging and rugged terrain, with steep gradients. Widening and realignment of the highway, including new all-weather tunnels through steep rock beds, were needed to improve safety, decrease travel time and minimize closings during adverse weather conditions.

The two major challenges were the terrain and the type of rock in the mountains all the way from Udhampur to Banihal. Our team assessed the environmental and social impact of the project, including cultural properties, natural habitats and involuntary resettlement. In fact, during the design phase, since the team had to go through every parcel of land with precision, the expert teams had to walk multiple times along the 122km length over a period of 4 days to verify the compatibility of the design with the site conditions!

The team overcame these challenges by designing the alignment with great precision, with several iterations to ensure accuracy. We also had to ensure during the design phase that the hill cutting was optimized, and minimize the overall ecological impact, without disturbing the forests of rare Chinar (maple) trees.

Another challenge was the large number of monkeys along the stretch. So, we incorporated in the DPR monkey-crossing structures at required locations - this is unique to the Chenani Nashri project!

The design of bridges and viaducts was also challenging due to the necessity of tall piers on account of the mountainous terrain and the high-risk seismic zone. Due to the nature of the rock, it was essential to stabilize cut slopes to avoid landslides. Our geotechnical experts studied the type and nature of the rock along the 122km alignment to design unique slope stabilization measures. Wherever feasible, tunnel options were explored, and accordingly, small tunnels at 8 locations were designed.

What are the important considerations during the development phase of tunnel projects?
Foremost amongst the challenges encountered is the selection of the site and optimum (shortest) alignment with horizontal and vertical geometry befitting the importance and category of the project, and other design criteria. Establishing the location of tunnel portals can also be a challenging task. The design must also allow for smooth connectivity of approaches to the tunnel.

Perhaps the most challenging task is the assessment of site geology, collection of geological maps, and establishing and executing an adequate geotechnical investigation program to inform the design of the tunnel and to ensure that the design is optimum. Ground movement, ground deformation and building settlements have to be minimized. It is, therefore, also important to assess and establish the construction methodology and fronts for construction such that safety is ensured at all times, along with minimum cost and duration.
Today, India is probably the fastest growing market for tunnel construction. International construction techniques such as New Austrian Tunnelling method are being implemented, TBMs are being used, and international norms and fire safety codes along with evacuation preparedness are being followed.

For engineers, tunnelling in hilly areas means dealing with difficult terrain conditions, in-situ stresses, ingress of water and gases, geothermal gradient, high-level of seismicity, etc. What technical know-how does Louis Berger provide for such projects?
For the DPR of the Chenani-Nashri tunnel project, Louis Berger conducted the design of all proposed tunnels in accordance with the New Austrian Tunneling Method (NATM). The design included civil works, electro-mechanical works (ventilation) and lighting, as well as state-of-the-art Control Centres.

Geological investigation plays a vital role during the design and construction stages to decide a suitable construction method and support arrangement. The advanced investigation tests are been carried out according to terrain conditions such as electromagnetic geophysical surveys, hydraulic fracture test, flat jack test, stress relief techniques, strain recovery methods, borehole breakout method along with fault slip data analysis for measurement of residual stresses etc.

A laboratory is set up at site for routine investigations to compare the design assumptions and construction approach. Further fore-poling is carried out and cores are collected before excavation cycle to ensure expected geological scenarios and avoid unforeseen surprises.

How do you rate India in terms of its technology and expertise in tunnel construction?
Today, India is probably the fastest growing market for tunnel construction due to the large number of roadways, rail and metro rail projects that are being implemented on a phenomenal scale as never before. In addition, large water supply, sewerage and storm water drainage tunnels are also being constructed. As a result, there is a large number of international consultants and contractors specialized in tunnels, present in India.

International construction techniques such as NATM (New Austrian Tunnelling method) are being implemented. TBMs (tunnel boring machines) that are manufactured and imported across the globe are also being used. International norms and NFPA codes (National Fire Protection Association) for safety and evacuation during fire are being followed.

tunnel projects

What are the current tunnel projects being undertaken by Louis Berger? Please elaborate on one of them.
Besides the Chenani-Nashri tunnel, Louis Berger recently conducted the design review of a 46km long railway tunnel between Karad and Chiplun. We are also working in the capacity of PMC on the Mumbai-Pune Expressway. The augmentation project includes 10km long twin 4-lane tunnels along a new alignment of the expressway in the ghat section. In addition, we are part of the General Consultant consortium for the 33-km long Mumbai Metro Line 3 that is presently under construction. Apart from these projects in India, we have extensive tunnel design and construction experience on projects worldwide.

All tunnel projects have their unique and distinctive features and challenges. The tunnelling work for the 33km-long fully underground Mumbai Metro Line 3 project is no exception. This line extends from Cuffe Parade in South Mumbai to the Aarey Milk Colony in the western suburbs to the north. The underground alignment passes under a diverse set of developments including high-rise buildings, heritage structures, delegate buildings, residential and commercial developments including hutments and the Mithi River. The project includes 26 underground stations and one at-grade station.

The assessment of the geology and geotechnical profile of the underlying strata along the alignment was a significant challenge, since Mumbai comprises seven islands. The varying strata includes hard rock, shale, as well as backfilled soil. The tunnel boring machines were therefore designed to suit the ground conditions.

The survey of existing buildings that was conducted was also crucial to categorize the condition of buildings as good, moderate or severe. This was important to ensure the stability and integrity of structures during tunnel construction. Protection of heritage buildings is also of utmost importance. Instrumentation to measure ground deformation and vibrations was placed in this regard. In addition, mapping of existing utilities and then relocating them if impacted by the alignment also needs to be done carefully.

NBM&CW March 2020

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