This paper presents a case study of the effects of changed and severe geological conditions on trend of construction of lot number 1 of Qomroud Long Tunnel (QLT) of a 9 km tunnel that is under construction as part of Dez to Qomroud water conveyance tunnels project with total length of 55 km in west central Iran. The main objective of the project is water transfer from Dez highlands in west central Iran to adjacent watershed (Qomroud watershed) in central Iran as a long-term drink water-supplying plan. Drill and blast method was selected initially as construction method of the tunnel based on results from initial stage geological investigations. From initial stage geological investigations tunnel will path through medium to hard rocks. Construction of tunnel started from three faces simultaneously: main tunnel and access tunnels no. 1 and 2. The instability problems were encountered during excavation of the tunnels and construction of the tunnels was stopped. During excavation of main tunnel, medium to hard rocks replaced by weak and crushed rocks with different type and finally in Km 0+919 a heavy collapse occurred with flow of 1500 m3 of loose saturated fine-grained soil into the tunnel and a sinkhole with height of 28 m and area of 50 m2 had been created as a result of complete overburden lost. Following principal instabilities a complementary geotechnical investigations carried out. Medium to hard rocks in primary geological-geotechnical profiles replaced by weak to medium rocks with near to 1.50 km of fine-grained saturated soils. Results from new geological-geotechnical investigations presented in this paper and some geological-geotechnical considerations proposed to continue of construction of QLT1. It is concluded that early changed geological conditions tends to 2-3 years of delay in construction time and construction cost will reach to 2-3 times of initial contract.
|Publication status||Published - 2005|
|Event||Symposium on Long Tunnels: “Design, Construction and Operation of Long Tunnels” - , Thailand|
Duration: Nov 7 2005 → Nov 10 2005
|Conference||Symposium on Long Tunnels: “Design, Construction and Operation of Long Tunnels”|
|Period||11/7/05 → 11/10/05|