Just south of Oslo Central Station, the new high-speed Follo Line railway tunnels pass beneath the existing Ekeberg road tunnels. This paper presents the construction methods, numerical model, and monitoring program used to assess the stability of the E6 road tunnels during the excavation of the Follo Line tunnels only a few metres below. The construction of the Follo Line was approved subject to three conditions: (1) there should be no negative effect on the stability of the Ekeberg tunnels, (2) the traffic flow in the Ekeberg tunnels had to be maintained at all times and (3) any risk of instability in the existing tunnels must be detected beforehand, so that necessary precautionary actions could be taken in good time. To deal with the challenges, SINTEF developed a comprehensive analysis procedure, combining continuous rock stress measurements and displacement measurements with 2D and 3D numerical modelling. The rock stress change monitoring was used together with the numerical model to monitor the stability conditions in the Ekeberg tunnels as the Follo Line tunnels were excavated. This ensured that any risk of instability in the existing tunnels could be detected in advance to enable precautionary action to be taken. The successful completion of the new tunnels without any disturbance to the road tunnels shows that the procedure would be useful for dealing with similar applications in the future.

Reservoir-induced earthquakes are a challenging issue for hydropower, and have occurred at many sites around the world. However, each event is unique in itself and depends on the geo-tectonics and geo-hydrology of the area in which the event is situated. This article focuses on seismic events at the Song Tranh 2 hydropower project located in Quang Nam province, Vietnam. The construction of the 96 meter high Roller Compacted Concrete (RCC) dam of this project was completed in August 2011. Approximately one year after commissioning, the dam began experiencing a serious leakage problem through the dam body. In addition, a series of earthquakes occurred near the project area, and continued for several months. The high intensity and magnitude of the earthquakes caused damage to the project and promoted fear among the local people living in the downstream valley. The issues drew significant media attention and thousands of articles about this project were written within a short time. As a result, dam authorities have been subject to extreme public pressure.This paper describes the earthquake events and difficult situation that both the local population and authorities faced in its aftermath. In addition, we analyze seismic events qualitatively,using data and information on the water filling and drawdown processes. Our analysis provides an insight into these seismic events, as we reconstruct the earthquake scenarios and test a hypothesis of earthquake occurrence. Future earthquake activities are also predicted and compared.DOI: http://dx.doi.org/10.3126/hn.v15i0.11285HYDRO Nepal JournalJournal of Water, Energy and EnvironmentVolume: 15, 2014, JulyPage: 16-20

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