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Hai Van tunnel back on track

Date: November 01, 2002

Construction of the US$250M, 6.3km long Hai Van Pass road tunnel in central Vietnam is back on schedule following the the successful remediation of the collapse last year (T&TI January 2002).
The bench and invert excavations are now virtually complete, ready for the main tunnel lining to start as T&TI went to press – as originally planned. The tunnelling works should be completed in 2003.

The project includes a 6.3km long, 90m2 tunnel section beneath the Hai Van massif with a parallel 16m2 evacuation tunnel.

Construction is predominantly through good quality granite by NATM. However, the first 100m at each portal is composed of highly weathered granite with erosion deposits covering the valley floors.

Tunnelling began in mid 2001 from both the North and South portals, but only progressed 30m from the South portal in the soft ground section of the main tunnel when a major collapse occurred.

A cross passage was then constructed in good rock from the progressing evacuation tunnel. This allowed construction to resume on schedule and left the soft ground section to be completed off the critical path.

The pilot tunnel broke through in April 2002, with breakthrough of the full top head-ing on 4 July 2002. Tunnel excavation is now progressing on all tunnel faces with advance rates of 120m-180m per month.

Problems were also encountered in the ventilation adit, where higher than expected water inflows were encountered in fault zones. This led to the delay of approximately 6 weeks. Remedial grouting works are currently being finalised.

The two tunnelling contracts were awarded in September 2000. The Hazama and Cienco 6 JV won the North section, while the Dong Ah and Song Da JV won the South section.

(Source: Tunnels and Tunnelling International)

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