Knowledge about the Excavation Damaged Zone (EDZ) is essential for underground construction design, underground facility layout, work environment issues and analysis of post-closure safety for a final repository for nuclear waste. The EDZ is defined as the zone around a tunnel where the damage is not reversible. The EDZ can be caused by the excavation method as well as by the actual strength – stress conditions.
SKB has chosen the Forsmark site for disposal of spent fuel. The site conditions include hard crystalline rock and fairly high stresses. However, analyzes prior to site selection found that the risk for stress induced development of an EDZ is limited. The aim of this paper is to outline the blast design concept and quality control measures to ensure that the excavation method fulfills the requirements. Strategies for blast design and QA/QC measures for tunnel excavation were applied during construction works for the Äspö HRL expansion 2012. This provided an opportunity to demonstrate methods for tunnel excavation and verify that requirements on minimizing the EDZ could be met during the construction of the planned Swedish final repository for spent fuel.
Within different R&D projects, the Swedish Nuclear Fuel and Waste Management Company, SKB have studied various aspects of a possible generated disturbed or excavation damaged zone (EDZ) around a deposition tunnel.
In 2011, SKB applied for a license to construct the final repository for spent nuclear fuel at Forsmark, Sweden. However some issues remain to be investigated and solved before the planned start of construction, one being related to the tentative development of a hydraulically connected EDZ.
The Äspö HRL expansion project included the excavation of two new access tunnels with several experimental tunnels on the 410m level. Several of these experimental tunnels were designed with dimensions similar to the deposition tunnels in a KBS-3 repository for spent fuel. The excavation works at Äspö HRL provided an opportunity to apply strategies for blast design and QA/QC measures in order to demonstrate and verify methods for tunnel excavation aiming at limiting the EDZ.
This paper presents the methods applied for limiting and controlling the EDZ with focus on the experimental tunnel TAS04, excavated on the 410 meter level at the Äspö HRL. The tunnel has dimensions according to the reference design for a deposition tunnel in the Swedish planned repository for spent fuel, Figure 1.
