In the last few decades, many hydropower projects have been built in Vietnam. Most of the hydropower projects have tunnels with different length and width, constructed in different geological conditions, ranging from excellent rock mass quality in hard granitic rock environment to poor quality sedimentary rock formations, fracture/weakness zones, and etc. With thick vegetation and weathering cover, the amount of geological information during pre-construction phase is normally limited, so the tunnel design may involve lot of uncertainties, such as rock mass quality, groundwater, weakness zones, and rock stress. The uncertainties may require special competence and experience in rock engineering to deal with. With a unique profile, SINTEF Building and Infrastructure (SINTEF) utilises its vast competence and experience in both hydropower and rock mechanics to effectively assist several hydropower project owners in dealing with the uncertainties, and SINTEF holds a good reputation within the hydropower industry in the country. The SINTEF services so far in Vietnam can be categorised in several groups:

  1. Geological mapping for rock mass evaluation and recommendation of rock support;

  2. Rock stress measurement;

  3. Due diligence;

  4. Working as advisor on special rock engineering issues;

Limited information in pre-construction phase means that estimation of the rock support is often preliminary based on different constructed projects with similar rock mass conditions. During construction, geological conditions are well exposed, and the rock mass can be evaluated in great details. In this situation, it is wise to carry out a detailed rock engineering evaluation in the tunnel in order to obtain the most appropriate rock support measures. SINTEF has successfully carried out such rock engineering services for several hydropower tunnels in Vietnam, and recommended appropriate rock support solutions. In two hydropower project, we proposed to change a tunnel from full concrete lining to an unlined tunnel.

As mentioned in the welcome message of the conference that " The goal of Workshop is to promote the exchange, transfer of knowledge and experience on Rock Mechanics and Rock Engineering for sustainable development of this field in Vietnam", in this paper, we present our experience in carrying out our services for different hydropower tunnels. Rock engineering challenges, technical and economical values added to the projects as well as benefits bringing to the project owners are also presented. This paper is an updated version of a publication in 2013 (Trinh and Grøv, 2013).

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