The Long-Baseline Neutrino Facility and associated Deep Underground Neutrino Experiment (LBNF/DUNE) will include constructing facilities above and below ground at Sanford Lab in Lead, S.D., and Fermilab in Batavia, Ill. But it is on the 4850 Level of Sanford Lab that construction could have the greatest impact on current experiments.
Work at Sanford Lab includes excavating three large caverns on the 4850 Level: two that will house neutrino detectors filled with 70,000 tons of liquid argon, and one that will house utilities. Approximately 800,000 tons of rock will be removed. To understand the impacts such an excavation will have on existing experiments, the LBNF project conducted a blast vibration study.
?We were primarily interested in how the blast energy moves through both the rock and the air in existing spaces to assess the potential impact on other experiments,? said Tracy Lundin LBNF Conventional Facilities project manager.
?The different collaborations, including those with the Majorana Demonstrator, the Black Hills State University Underground Campus, and CASPAR (Compact Accelerator System for Performing Astrophysical Research) had concerns about the excavation and its potential impact on their experiments,? said Mike Headley, executive director of the South Dakota Science and Technology Authority. ?The LBNF team has regularly consulted with the other collaborations on the blast vibration study plans and results, as well as approaches that can be taken to reduce the impacts the LBNF excavation might have on other experiments.?
Preparation for the test blast required drilling a pattern of holes into the rock and filling most of them with explosives that get triggered in a specific timed sequence by detonators. A set of holes in the center of the pattern, called the burn cut, is left empty. The pattern is designed such that energy from the blasts in the outer holes propagates radially inward toward the burn cut.
The initial study, done in December, successfully demonstrated how the energy moves through the rock mass. However, Lundin said, ?it did not provide a complete understanding of air blast overpressures and our ability to manage impacts on existing facilities and experiments.?
Two successive blasts done in March included a redesigned blast pattern, non-electronic detonators, and reinforced air control doors throughout the 4850 Level. Both were successful, informing the next LBNF blast designs. ?Doing the study in two phases allowed us to make improvements to the blast design and to mitigate impacts on current experiments,? Lundin said.
?The new blasting plans will allow LBNF to move forward as planned without harming other experiments,? Headley said.