Abstract

The purpose of this paper is to review the common approach for tunnelling support in Scandinavian crystalline rock based on experiences from underground facilities operated by the Swedish Nuclear Fuel and Waste Management Company (SKB). SKB operates both underground facilities for intermediate storage of spent fuel (CLAB) and final disposal of operational waste (SFR), as well as an underground research laboratory, (Äspö Hard Rock Laboratory). This paper compares and discusses the maintenance experiences from the SFR and Äspö HRL facilities. Both facilities are mainly excavated with the drill and blast method. The SFR facility has systematic support with rock bolts and shotcrete. The Äspö HRL was constructed with the aim of allowing as much exposure of the rock as possible, so the use of shotcrete is minimized; instead wire mesh is used selectively. The use of standard rock support measures commonly used in Scandinavian crystalline rock has been working well in both facilities. Clogging of seeping fractures caused by mineral precipitation is causing decreasing inflow over time in both facilities.

There are numerous case records from tunnelling projects in the Scandinavian shield showing the possibility for underground use in a competent geological environment. Construction problems are limited to faults or other causes for weak rock and occurrence of water in the fractured rock. The use of shotcrete and grouted, un-tensioned bolts is the normal rock support. In good rock conditions, especially when the demands on safety is low such as in access and service tunnels spot bolting and scaling during operation has been commonly applied. The general development of modern tunnels for infrastructure purposes such as highways and railroads has gradually increased the demands on durability and lifetime of rock support due to both serviceability and concern of the safety of the public.

The purpose of this paper is to review the common approach for tunnelling support in Scandinavian crystalline rock based on experiences from underground facilities operated by the Swedish Nuclear Fuel and Waste Management Company (SKB). SKB operates underground facilities for intermediate storage of spent fuel (CLAB) and final disposal of operational waste (SFR), as well as an underground research laboratory, (Äspö Hard Rock Laboratory). Experiences from the SFR facility and the Äspö HRL are compared. The SFR facility has systematic support with rock bolts and shotcrete. The Äspö HRL was constructed with the aim of allowing as much exposure of the rock as possible, so the use of shotcrete is minimized. The facilities have similar total length of the underground openings. Both facilities are located under the Baltic Sea. The most of the inflowing groundwater to both facilities is stagnant, very saline water. Brackish sea water and fresh groundwater contribute to the seepage in the upper parts of the facilities.

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