Connecting Kashmir - Socio-Economic Growth and the Spirit of Resilience

2. Summary of challenges faced, solutions adopted and lessons learnt while tunneling through complex and difficult geology in Katra - Banihal section:

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2.1 Challenges / problems faced :

i) Survey work for fix the alignment: Due to not accessible the project sites, the final location survey work was very critical and challenging work for survey team.

ii) Heavy squeezing of tunnel profile and heaving of tunnel invert.

iii) Tunnel collapses and cavity formations.

iv) Tunneling through MBT (T-1): Gravity driven failure / Loose flow in zones comprising of fully saturated, crushed and sheared dolomite mixed with calcite, clay, and silt.

v) Complex geology and presence of localized shear zones.

vi) Huge Ingress of Water requiring continuous heavy dewatering arrangements: The most of the tunnel is in uprising gradient from P1 to P2. Due to reverse gradient from P2 side, multi stage dewatering using pumps (45 no's) of capacity amounting to 1620 HP was required 24 X 7. The huge ingress of water (more than 500 litre/sec) and dewatering made excavation most difficult and challenging.

vii) Presence of Methane gas (T-14): Tunnel mining through Subathu Formation (comprising of siltstone, shale, coal lenses), was highly challenging, time consuming and difficult task owing to very poor stand up time is very poor, and presence of methane gas (CH4 & H2S).

2.2 Solutions adopted :

i) Appointment of Detailed Design Consultants (DDCs) for tunnel design and technical guidance during tunnel construction.

ii) Adoption of elliptical / modified horse shoe tunnel profile in place of D-shape as elliptical / modified horse shoe profile is more efficient in disbursal of stresses.

iii) Adoption of state of the art NATM (New Austrian Tunneling Method) tunneling philosophy for execution of tunneling works instead of conventional rigid support system.

iv) Squeezing in D-shaped tunnel: Re-profiling the deformed portions by modifying D-shape to elliptical/modified horse shoe shape profile using NATM philosophy.