Investigation of blast fractures from mechanized charging with emulsion during tunnelling
A quality factor that can decrease the need for rock reinforcement and maintenance in underground facilities is limitation of blast damage in the tunnel contour. This is usually required for underground constructions with a long operation time, such as public tunnels for transport or underground repositories for nuclear waste. A project was initiated by the Swedish Nuclear Fuel and Waste Management Co (SKB) and Forcit Sweden AB to investigate the extent of blast damage from emulsion explosives. This paper presents results from investigations conducted in the framework of the project at two tunnel sites in Sweden, Äspö Hard Rock Laboratory (HRL) and a wastewater tunnel under construction in Kista. The tunnels were excavated with the same technology for mechanized charging but with different purposes and quality requirements. At Äspö HRL the investigation was conducted in two experimental tunnels at the -410 m level. During construction, these tunnels were subjected to requirements on smooth blasting and contour quality and the construction process was documented to a high level of detail compared to conventional tunnels, including follow up on charge concentration with the aid of registered data from the drilling and charging logs.