Client: AFCONS Infrastructure Ltd.
Project: DESIGN OF TUNNEL PORTALS OF PANDOH TAKOLI ROAD TUNNEL PROJECT IN CHALLENGING GEOLOGY
Location: District Mandi, Himachal Pradesh

About AFCONS

Afcons Infrastructure Ltd. is a part of Shapoorji Pallonji Group, which is India’s leading engineering and construction conglomerate. Afcons is one of India’s top EPC companies having a presence in more than 22 countries.
Afcons is the first infrastructure company globally to win the Most Innovative Knowledge Enterprise (MIKE) Award in the Global Asia Pacific, and India category. It is also the winner of the Most Admired Knowledge Enterprise (MAKE) Award several times.

About the Project

The project consisted of Four Laning of NH 21 from End of Pandoh Bypass to Takoli Section, Himachal Pradesh, India. The Total Length (as per CA) was 20.695km inclusive of open sections and tunnels. Total four number Twin Tunnels and two number Single Tunnels were part of the package.

DMR Assignment

DMR was entrusted with the detailed design and construction-stage engineering support of three number critical portals and tunnels which were set up in varied geological setups. The first portal was designed in “Slate” in steep topography involving high cuts in the limited right of Way – ROW. The second portal was set up in deep overburden beside an active Nallah. The third portal was designed basically on a Nallah bed with a steep side cut in the overburden.

Challenges

• Design and construction sequence of large-diameter tunnels (~14m) in challenging geology with just 20m widths of the central pillar between both tubes
• Design of Twin Portal tunnels which were set up in approximately 35m deep overburden with limited lateral cover.
• The presence of residential buildings and agricultural fields just above the portal location demanded little to no disturbance to the existing topography
• Design of 70 m high cut slope in overburden in limited Right of Way – ROW

Value added by DMR

DMR was approached by AFCONS since the onboard international Design consultant for the project provided a design that was uneconomical and was difficult to execute. The complexity of the project was analyzed and experienced design engineers from DMR worked closely with AFCON team to develop a viable and economic solution for the design of the three portals and tunnels. DMR innovatively designed the portals in deep overburden without disturbing the existing topography. The possible modes of failure during the execution were taken well into account by DMR during the design stage. Additional support measures wherever required were promptly designed and recommended by DMR in view of the hiccups which were faced during the execution phase. Efficient use of Pipe-roofing (with grouting), lattice girders, shotcrete with wire mesh, and Self-drilling Anchors for tunneling in the overburden was specified and implemented. Instrumentation and monitoring data analysis ensured safe execution. RCC Lining design also demanded special considerations in view of difficult ground conditions.

Client Testimonial
DMR team provided unique solutions to seemingly unsolvable challenges associated with the portal development in the loose ground in this project. The terrain was difficult and we knew that safety measures needed to be faultless. The designs developed were adjusted to the local conditions at the site taking care of all possible situations. DMR team worked as a partner for AFCON to develop these critical components of the project from scratch.