Tunnels - particularly transit and transport tunnels - are viewed as high risk, high damage potential targets because of the confined spaces and the numerous patronage present in a single location. We have recently seen many such malicious terrorist attacks in the world on underground transportation facilities, making safety precautions all the more necessary in today’s polarised world. In order to assess the risk and vulnerability and to analyse blast impacts on tunnel structures, engineers at WSP have developed a state-of- the-art approach known as TARIF. This approach has been successfully adopted on several tunnel projects.
TARIF includes five steps:
- Identify Threat
- Evaluate Assets
- Calculate Risk
- Analyse Impact
- Provide Fix
The steps for performing blast analysis for tunnels include: (1) determining the Design Threat Level(s) that should be adopted for the facility; (2) determining the structural vulnerability of the facility when subjected to internal and/or external explosions; (3) performing comprehensive analyses to consider a variety of explosive size, location, and delivery methods; (4) assessing blast induced over pressure on neighbouring facilities or adjoining structures; and (5) developing mitigation and protection measures.
A typical study and analysis will identify the damage level of the tunnel lining in the vicinity of the explosion, as well as the consequential damage in the liner of any adjacent tunnel or other subsurface infrastructure located close to the impacted tunnel. The analysis will also identify any potential of a local breach failure in the tunnel lining and the consequences of such a breach on the facility. Finally, our tunnelling experts will pin point any preventive, protective, and remedial measures that can be adopted to reduce the risks.
WSP in Action
Some of the recent projects where WSP has performed threat assessment and developed mitigation measures include:
- East Side Access in New York, United States
- Fort McHenry Tunnel in Maryland, United States
- Gateway Tunnels under the Hudson Yards, United States