“Megaton” Cerenkov Detector - Excavation Kenneth Lande, Univ. of Pennsylvania 4200 mwe Depth

Brief DUSEL History 1) September 2000 –Homestake Mining Co. announces cessation of gold mining-Planning for Underground Laboratory begins immediately. 2) December 2000 – Bahcall Committee meets- Homestake Underground Lab presentation & recommendation (March 2001) 3) September st DUSEL Experiment Conference- Lead, SD- Megaton water Cerenkov Detector Array proposed. 4) March Megaton detector proposal presented to SAGENAP Panel (NSF/DOE)

5) April Barrick Gold Corporation Donates Mine to State of South Dakota 6) June 2006-T. Denny Sanford donates $70M to Laboratory 7) July 2007 – Final NSF selection of Homestake as site of DUSEL 8) May P5 panel rates Long Base Line Neutrino Beam (FNAL  DUSEL) + “Megaton” Detector Array at DUSEL as high priority.

First Evaluation of 100 kton excavation stability – fall ) In September 2001, a first survey of potential sites in the Homestake Mine for an array of 100kton chambers is carried out. (Karl Zipf-NIOSH & Kathy Hart-Chief Homestake Mine Geologist) 2) Rock samples of possible sites are collected & analyzed at the Spokane Labs of NIOSH (Bureau of Mines). 3) These data are used to design excavations & determine wall support as well as appropriate chamber separations. (NIOSH = U.S. Bureau of Mines)

Generalized Rock Stresses in the Homestake Mine  (vertical) = 28.3 h kPa (h in meters)  (horizontal–high) = h kPa  (horizontal-low) = h kPa (W. Pariseau – Bureau of Mines Report-1985) Note the very large difference in the stresses in the two horizontal directions.

YATES LABORATORY PROPERTIES E = 14,500,000 psi Tensile Strength = 1890 psi UCS = 28,800 psi!

MATERIAL PROPERTY REDUCTION – Modulus reduced 25% –Strengths reduced 50% –Cohesion = 30 deg.

C  Chlorine Solar Neutrino Detector XXXXX X 4850 Level

Rock Removal Tunnel (note- chambers & top of water are below tunnel & shaft entry level) – water cannot flood tunnel or shaft in case of containment failure

Steps needed to verify that initially selected site is satisfactory 1) Core rock in proposed chamber locations. 2) Measure stress/strain characteristics of rock cores 3) Using these data, redo the excavation modeling and, if necessary, revise construction specifics. 4) If rock strength measurements are satisfactory, then construct a small tunnel directly into the top of the first chamber and verify local rock conditions (including short cores -25 meters- throughout top region).

Coring Plan into Locations of Chambers 1-3

USE OF BORE HOLES 1) Measure strength characteristics of extracted cores. 2) Do a 3-D sonogram of the rock volume by installing sound generators/detectors in the bore holes. 3) Install fiber strain gauges in the bored holes and measure strains before, during and after excavation.