Application of ShearWave Velocity to the Building Code Nevada Seismological Laboratory, University o

1
Application ofShear-Wave Velocityto the
Building CodeNevada Seismological Laboratory,
University of Nevada, RenoNevada Great Basin
Community Velocity Model WorkshopJanuary 14, 2008

• Robert H. Sydnor
• Engineering Geologist
• Fair Oaks, California
• CEG 968, LM-AEG, LM-SSA, LM-AGU, M-ASTM, M-ASCE,
  M-EERI

2
Applications of Shear-Wave Velocityin
Engineering Geology and Applied Geophysics

• Classification of Geologic Subgrade ? Class B,
  C, D
• Default Method for Ground Motion ? coefficients
  Fa, Fv
• Soil-Structure Interaction ? coefficient Vso
• Rippability of Rock ? deeply?? weathered
  granitic rock
• Liquefaction Analysis ? Vs proxy for N1(60)
  see Andrus Stokoe (2000)
• Remediation of Liquefaction ? Acceptance Criteria
  for Improved Ground
• Reclassify the Subgrade after Remediation ?
  from D ? C ?
• Complicated Geologic Subgrade ? mine tailings
  landfills
• Reconnaissance for Drilling Program ? borehole
  spacing depth

3
3 Conceptual Map-Scales for Shear-Wave Velocity

• Regional Maps ? Statewide
• 1500,000 to 11 million-scale ? deep
  sedimentary basins
• Combined with regional fault model and PSHA
  results in derivative map of
• strong ground-motion for statewide seismic-safety
  planning
• By Seismologists Regional Geologists
• For Seismic Safety Planners Insurance
  Actuaries Decision-Makers General Public
• City County Scale Maps ? Sedimentary Basins
• 124,000 to 1100,000-scale regional seismic
  surveys earthquake studies
• By Seismologists Engineering Geologists
  Petroleum Geophysicists (proprietary data)
• For Seismologists (basin-edge effects
  deep-basin effects), Seismic Hazard Zoning Maps
  Seismic Safety Planners, Insurance
  Actuaries local government officials
• Project-Level Specific Work ? Single Parcel
• 1120 to 11200-scale highly detailed
  combined with subsurface exploration specific
  shear-wave measurements (crosshole, seismic
  cone, ReMi, hammer-seismics)
• By Engineering Geologists Engineering
  Geophysicists Geotechnical Engineers
• For Building Code applications for Structural
  Engineers -- earthquake ground-motion design
  soil-structure interaction

4
Research Funding and Priority
Needsat various Map-Scales for Shear-Wave
Velocity

• Regional Maps ? limited funding
• 1500,000 to 11 million-scale ? Deep
  Sedimentary Basins
• Funded by Congressional appropriations via
  NEHRP, NSF, SCEC, USGS, Academia
• Awarded to Academia State Geological
  Surveys U.S. Geological Survey National Labs,
  etc.
• City County Scale Maps ? greatest need for
  funding
• 124,000 to 1100,000-scale
  regional seismic surveys earthquake studies
• Funded by NEHRP grants via USGS, NSF, SCEC
  California Earthquake Authority
• Awarded to Academia for thesis work, State
  Geological Surveys USGS, National Labs, etc.
• Stakeholders Consulting Geotech Firms
  Insurance Actuaries County City Engineers
  Planners

(continued)
5
Research Funding and Priority
Needsat various Map-Scales for Shear-Wave
Velocity(continued)

• Project-Level Specific Work ? high costs for
  Bldg. Permit
• 1120 to 11200-scale highly detailed
  combined with subsurface exploration
• Specific Shear-Wave Measurements (crosshole,
  seismic cone, ReMi, hammer-seismics)
• Funded by Bank Loans via Owners of Large
  Structures
• e.g., high-rise buildings, dams, power-plants,
  bridges, hospitals, hotels, schools
• Proprietary Funds new robust Software new
  Geophysical Equipment
• by High-Technology Firms Drilling Companies
• reliable shear-wave velocity at lower cost
• Awarded to Private consulting geotechnical
  firms
• (engineering geologists geotechnical
  engineers)
• Stakeholders Structural Engineers who design
  the important facilities
• using the International Building Code
  ASCE Standard 7-05 and
• General Public - who expect seismic-safety
  for important structures

6
Predicaments, Weaknesses, Drawbackswith the
Building Code

• ? Expensive to Purchase
• Not online no quick downloads not on Google or
  Wikipedia
• Costly to purchase - hundreds of dollars
• ? Limited Availability
• Not in most Public Libraries Not in many
  University Libraries
• Many small geotechnical consulting firms have No
  Copy of current Code
• Not available for photocopying at the counter of
  local Building Departments
• ? Tedious to Read
• Obtuse Dry Format Unfriendly for Beginners
  Students No Short Cuts
• Vexatious Cross-References - to yet Another
  Section of Code
• 95 does not apply to Seismology, Geology, or
  Geotechnical Engineering
• No Flow-Charts, No Logic Trees, No Markov Chains
  to explain tedious pathway
• ? Collateral References to ASCE Standard 7-05
• Purchase yet another expensive book.
  Cannot read IBC without ASCE 7-05

7
Strengths Benefits of the 2006 International
Building Code 2007 California Building Code

• Contains Modern Seismology Concepts
• Continues to rely Probabilistic Seismic Hazard
  Analysis
• New coefficient for Long-Period transition
  period, TL
• Reno Great Basin TL 6 Berkeley Los
  Angeles TL 8
• San Francisco Sacramento TL 12
• Is compatible with USGS, CGS, and UNR
  seismology websites
• Eliminates old Seismic Zones 3 4 focuses on
  real ground-motion
• Retains Emphasis on Average Shear-Wave Velocity
  Vs30m
• Introduces term Maximum Considered Earthquake
• MCE 2 chance of exceedance in 50 years.
• Statistical return period of 2,475 years with
  deterministic cap
• Collateral References to ASCE Standard 7-05
• ASCE Standard 7-05 contains
  useful Commentary not found in 2006 IBC

8
Insights for Use of Vs30m

• Depending on Geologic Complexity and Tectonic
  Geomorphology, there may be 2 different
  subgradeson a large parcel that is to be
  developed.
• Architects and some Structural Engineersseem
  focused on one flat-land campus.However, larger
  parcels near the break-in-slopetypically have
  both thick alluvium and soft rock.
• ? Two different Vs30m
• ? Two different levels for MCE ground-motion

9
Current ASTM Standards forEngineering
Geophysics Vs30m

• ASTM Standard D-4428M-07 (K.H. Stokoe,
  Univ. Texas, Austin)
• Cross-Hole Seismic Testing, 11 pages
• ASTM Standard D-6429-99 (2006)
• Guide for Selecting Surface Geophysical
  Methods, 11 pages
• ASTM Standard D-7128-05
• Guide for Using the Seismic-Reflection Method
• for Shallow Subsurface Investigations, 25
  pages
• New ASTM Standard is needed for ReMi method.
• cost-effective, non-invasive, no boreholes, no
  VibroSeis trucks

10
Suggestions for Applied Researchregarding
Shear-Wave Velocity

• 30 meter or 100-foot Depth of Subgrade
• There is no geophysical basis for the
  convenient depth of 100 feet.
• Computer modeling of Strong Ground-Motion, plus
• insights from existing downhole Strong-Motion
  Accelerometer arrays
• might yield a different depth than 100 feet.
• Most boreholes in alluvium are typically 50
  feet for 4 reasons
• Typical limits of Liquefaction are 50 feet ( ?
  increasing overburden pressure)
• lt50 foot limit for Boussinesq pressure bulb for
  typical 1 to 2-story buildings
• Drill Stem on most Drilling Rigs is 65 feet
• Drilling Costs the practical efficiency of two
  50-foot boreholes vs one 100-ft.

11
Suggestions for Applied Researchregarding
Shear-Wave Velocity

• Regional Map of the Great Basin showing Basement
  Contours
• Historic Example from California
• Smith, Merritt B., 1964,Map showing
  distribution and configuration of basement rocks
  in California U.S. Geological Survey Oil Gas
  Map OM-215, two map sheets, 44?63 inches in
  size, scale 1500,000
• This was prepared as a petroleum exploration map,
  and has useful comprehensive statewide coverage.
  How do deep sedimentary basins amplify
  earthquake ground motion? OM-215 is 44 years
  old, but the historic insights may be a good
  example for theGreat Basin.