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Site Conditions and Geotechnical Data Presentation Outline

This presentation provides an overview of the geologic conditions at the SLAC site, including historical data, LCLS investigation, and future work. It covers the geologic overview, groundwater elevation contours, geotechnical investigation results, and tunneling memorandum summaries.

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Site Conditions and Geotechnical Data Presentation Outline

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  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 1950’s • 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 • Phase 1 • Summer 2003, Rutherford & Chekene • 5 soil borings • Sample Analyses • Dry Density • Moisture Content • Unconfined Compression • Consolidated Undrained Triaxial • Petrographic Analysis • Slake Durability • 2 Reports Produced • “Geotechnical Data Report” • “Tunneling Memorandum”

  7. LCLS Boring Locations 5 A B C D E 6 1 2 3a,b 4

  8. Phase 1 Analytical Results

  9. 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

  10. LCLS Geotechnical Investigation, cont. • Phase 2 • Satisfy requirements iterated by Jacobs Engineering “SLAC Geotechnical Investigation and Report Needs List”, 2/4/04 • Summer 2004, Rutherford & Chekene • 7 soil borings in locations chosen to complete geographical coverage • Additional sample analysis • In-Situ Testing • Geophysical/Shear wave velocity measurement • Pressure meter testing/ insitu deformation modulus • Background vibration measurement • Report due October 2004

  11. Phase 2 Summary • Subsurface conditions similar to conditions encountered in Phase 1 • Sample analyses - Same parameters as Phase 1, plus • Particle size analysis with hydrometer • Shrink/swell expansion pressure • Cerchar abrasion • Creep • R-value • Corrosion potential • Shear wave velocity ~1,800 feet/sec Compression wave velocity ~4,100 feet/sec • Deformation parameter varied from 1,000 bars to 12,500 bars, indicating interbedded layers of soft and hard rock

  12. Future Work • Develop detailed geologic cross section through the LCLS alignment – 1/05 • Establish site-specific earthquake spectra – 1/05 • Perform probabilistic site response analyses – 2/05 • Support structural engineering effort – ongoing • Produce Geotechnical Baseline Report – FY05

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