Site Conditions and Geotechnical Data Presentation Outline

1
Site Conditions and Geotechnical
DataPresentation Outline

• Site Overview
• Historical Data
• LCLS Investigation
• Future Work

2
SLAC Site Geologic Overview

• Miocene Ladera Sandstone, overlain by Santa Clara
  Formation and native fill
• Very soft, very weakly cemented (by clay)
  sandstone, with strongly cemented (by calcium
  carbonate) thin interbedding locally
• Nearest major fault is the Peninsula Segment of
  the San Andreas Fault, 5 miles SW
• Groundwater is not expected at LCLS depths

3
Historical Geologic Data

• Numerous geologic studies at the site since the
  late 1950s
• 2 mile long Linac 1959
• Positron Electron Project (PEP) tunnel 1975
• Stanford Linear Collider - 1981
• SPEAR 1982
• Almost 200 boreholes drilled by 1994
• At least 32 geologic reports written by 1994

4
Geologic Map with LCLS Boring Locations
5
Groundwater Elevation Contours
LCLS Elev. 247.25
240 contour
180 contour
6
LCLS Geotechnical Investigation

• Two Phases
• Summer 2003 and Summer 2004
• Rutherford Chekene
• 12 soil borings
• Sample Analyses
• Dry Density
• Moisture Content
• Unconfined Compression
• Consolidated Undrained Triaxial
• Petrographic Analysis
• Slake DurabilityParticle size
• Shrink/swell expansion pressure
• Cerchar abrasion
• Creep
• R-value
• Corrosion potential
• In-Situ Testing
• Background vibration measurement

7
LCLS Boring Locations
5
A
B
C
D
E
6
1
2
3a,b
4
8
Analytical Results
9
Analytical Results cont.
10
Tunneling Memorandum Summary

• Tunneling will occur entirely in Ladera Sandstone
  Formation
• Tunneling condition categorized as fair to poor
  soft rock
• Suggested construction method roadheader
  excavation, followed by shotcreting
• Horseshoe tunnel cross section
• Stand open time and advance rate discussed

11
Future Work

• Support structural engineering effort ongoing
• Produce Geotechnical Baseline Report bids
  received, award planned 4/8/05