Pre-Excavation Rock Evaluation1) Goal- Excavate the largest possible safe

and stable detector chamber

2) Procedure• a) measure characteristics of the rock

mass-governed by the underground stress state and the geomechanical and fluid-flow properties of the rock mass.

• b) based on those measurements, model the excavation & the necessary rock wall and roof supports + internal mounting connections

Rock Characterization1) Obtain samples of the rock by coring

2) Evaluate the cores - compressive strength, joints, invasive materials

3) Utilize the core holes to:

a) examine & test the rock surface of the holes,

b) explore the region of rock between core holes-

c) Set up long term stress and motion sensors

What is Already Known?• The Yates member of the Poorman formation

appears very strong and has minimal joints. It was not extensively explored because it does not contain gold.

• This is the section of rock that houses the Davis cavity (chlorine solar neutrino detector)– stable for over 40 years.

• 2001 preliminary study conclusions & recommendations

2001 Excavation Study• One location, known as site 3, looked particularly attractive. It was

in the Yates member of the Poorman formation on the 4850 ft level and adjacent to the existing chlorine solar neutrino detector. Unfortunately, at that time it was not possible to obtain rock cores from the interior of the rock formations and only surface rocks were collected. Based on these an evaluation of large excavations was carried out. At that time, in 2001, we set the baseline excavation as a 50-meter diameter by 50-meter high vertical cylinder. The RQD (Rock Quality Designation) of site 3 was initially evaluated as 100 and then downgraded to 85 to adjust for the possibility that there are unknown joints in that rock. The unconfined compressive strength of that rock sample was 186 MPa.

• As a comparison, the Kamioka Mine rock at the location of the Super Kamiokande excavation (40-meter diameter by 40 meter high cylinder with an additional 18 meter high domed roof) has a

• RQD = 84 and unconfined compressive strength of 149 MPa (Nakagawa et al., 1997; Yamatomi et al., 1999).

Boltable, Gasketed, Reinforced Concrete Segments

Cable Bolt Lengths – from Barton

2009 Proposal & Plan Penn, Wisconsin, Stanford, Clemson

1) Drill core holes, extract oriented cores – measure unconstrained rock strength-LBL

2) View inside of core holes with a televiewer

3) Examine each hole & structure between holes with an acoustic array – reflection & transmission

4) Measure constrained rock strength by hydro-fracture

5) Install fiber optic sensors to monitor changes in stress & movement – before, during & after excavation

U.S.G.S.Example ofcomparison of Optical, acoustic and thermal televiewer outputs – West Virginia water system

Televiewer Specifications

• Diameter: 50mm

• Length: 1.51m including natural-gamma option

• Radial Resolution: 720 pixels/360°

• maximum vertical Resolution: 1mm

• Sensor type: CCD 768x494 elements

• Orientation: Any

• Lighting: Internal ‘white’ LEDs; • external for diameters up to 300mm (12in). External lighthead for larger

diameters available.

3D Virtual Core Display3D Virtual Core Display

Cased Hole InspectionCased Hole Inspection

Optical Fiber Stress SensorBragg Grating Technology