J S Rathore
The recent tunnel collapse in Silkyara-Barkot Tunnel(4.5 Km) in Uttarkashi, National Highway 134 in India, has raised serious concerns about the safety and resilience of infrastructure projects in the Himalayan region. The collapse has also highlighted the need for a more comprehensive understanding of the geology and geotechnical challenges associated with tunnelling in the Himalayas.
The Causes of the Collapse
A number of factors may have contributed to the Uttarkashi tunnel collapse, including:
* The presence of fractured or fragile rock formations
* Water seepage
* Landslide-prone young Himalayan rock system
* Lack of geological and geo-technical studies
* Improper study of shear zone and lack of timely rock support measures
* Failure to design an escape tunnel.
We must understand Himalayan geology is very complex, variable in nature and must be handled with precise geological and geotechnical investigation and shall be implement the robust design carefully and intelligently for every metre of excavation with proper tunnelling methodology as per NATM procedures. It is no more monotonous. Tunnelling in Himalaya has some regular history of excavation hazard mainly due to followings.
* Proceed Tunnelling in Himalayas without reasonable investigation both geology and hydro-geology.
* Try to excavate as fast as possible even at the cost of proper rock support is lacking, can be even delayed till rock yield?
* Word “RISK” and understanding it before hand is not in the dictionary of tunnelling in Himalayas.
* Risk will be handled after it caused failure resulting in cost increase, time delay but more importantly at expense of human moral and life.
* One of the reasons is that Indian Contract system does not allow to make provision of risk as it cannot be itemized and quantified in a classical way.
* Attempt to build in risk management as pert of contract has not produce any fruitful result mainly due to lack of understanding.
* There are ways to build risk even in item rate contract. Provided risk has been identified and quantified(?).
* No forensic study will be done in real sense to at least document the failure as a source of wisdom for future. Unfortunately, people try for shortcuts, but they are trapped, like Uttarkashi Silkyara Tunnel.
We must learn lessons from the past mistakes happened during tunnelling, road and dam construction in Himalayas. But unfortunately, we have short memory to understand the consequence. However, I must emphasise that the serious geological tunnelling risks shall be closely monitored and follow the national/ International safety norm and procedures set for tunnelling.
The Impact of the Tunnel Collapse:
The Uttarkashi tunnel collapse has had a devastating impact on the Infrastructure Projects as whole world is watching us and exposed glaring deficiencies in the execution of the Project.
What Needs to Be Done
In order to prevent future tunnel collapses, a number of measures need to be taken, including:
* Conducting thorough geological and geotechnical studies before starting any tunneling project
* Using appropriate tunneling methods for the specific geological conditions
* Implementing strict safety measures during construction
* Monitoring tunnels for signs of instability
* Adhering to International Tunnelling and Underground Space Association safety practices in tunnel construction, particularly regarding escape routes and contingency plans
The Way Forward to Ensure Safe Tunnel Construction
To ensure safe tunnel construction practices, particularly in the challenging Himalayan region, the following measures should be implemented:
* Detailed Geotechnical Studies: Prior to tunnel construction, comprehensive geotechnical studies must be conducted to assess the rock formation’s stability and identify potential hazards. This includes seismic refraction surveys, core sample analysis, and rock classification.
* Regular Monitoring by Specialist Geologists: Continuous monitoring by experienced geologists is essential throughout the construction process. Regular site visits, face log creation, and 3D mapping can help identify potential failures and determine rock stand-up time.
* Adequate Tunnel Support Systems: Supports such as shotcrete, rock bolts, steel ribs, and tunnel pipe umbrellas must be thoroughly tested and designed to withstand the specific rock conditions and anticipated loads.
* Instrumentation Monitoring: Implement instrumentation monitoring systems to track tunnel deformations, stress levels, and the behaviour of rock support systems. This data provides valuable insights for assessing stability of rock mass and making timely adjustments in rock support system.
* Safe Evacuation Arrangements: Develop and implement emergency evacuation plans, including the deployment of trained personnel and appropriate safety equipment. Construction companies should submit detailed safety plans as part of their project bids.
Reforms in Tunnel Construction Practices
Advocate for reforms in tunnel investigations, design, risk analysis, contracting, and construction procedures. Prioritize quality control of rock support systems and ensure proper utilization of monitoring data throughout the construction process shall Audit by Independent expert Tunnelling Geologist regularly.
We can greatly improve the safety of tunnel, road, and dam construction in the Himalayan regions, especially in Uttarakhand, Himachal Pradesh, J&K, and Northeastern region, where the mountains are relatively young, have fragile geology, and are tectonically very active. Sinking, landslides, and rockfalls can reduce the risk of future disasters. These comprehensive measures must be implemented by the Authorities NHAI, NHIDCL, BRO, NHPC, CVPP, PMGSY and PWD etc.
The author is Expert Tunneling Geologist, Ex-Director of Chenani Nashri Tunnel and Expert Committee member for tunnel Zone appointed by Govt. of India, Ministry of Road Transport and Highway (MORTH).
Follow our WhatsApp channel
