Application of Shear-Wave Velocity to the Building Code by forrests

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									Application of Shear-Wave Velocity to the Building Code
Nevada Seismological Laboratory, University of Nevada, Reno Nevada Great Basin Community Velocity Model Workshop

January 14, 2008

Robert H. Sydnor
Engineering Geologist
Fair Oaks, California

Applications of Shear-Wave Velocity
in 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 Conceptual Map-Scales for Shear-Wave Velocity
Regional Maps ▬ Statewide
± 1:500,000 to 1:1 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
±1:24,000 to 1:100,000-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
± 1:120 to 1:1200-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

Research Funding $$$ and Priority Needs at various Map-Scales for Shear-Wave Velocity
Regional Maps ▬ limited funding
± 1:500,000 to 1:1 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
±1:24,000 to 1:100,000-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)

Research Funding $$$ and Priority Needs at various Map-Scales for Shear-Wave Velocity

Project-Level Specific Work ▬ high costs for Bldg. Permit
± 1:120 to 1:1200-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

Predicaments, Weaknesses, Drawbacks with the Building Code
♦ Expensive to Purchase ♦ Limited Availability
Not online; no quick downloads; not on Google or Wikipedia Costly to purchase - hundreds of dollars 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 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 Purchase yet another expensive book. Cannot read IBC without ASCE 7-05

♦ Tedious to Read

♦ Collateral References to ASCE Standard 7-05

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

Strengths & Benefits of the

 Eliminates old Seismic Zones 3 & 4 focuses on “real” ground-motion  Retains Emphasis on Average Shear-Wave Velocity Vs30m  Introduces term: Maximum Considered Earthquake  Collateral References to ASCE Standard 7-05
MCE = 2% chance of exceedance in 50 years. Statistical return period of 2,475 years; with deterministic cap
ASCE Standard 7-05 contains useful Commentary not found in 2006 IBC ASCE Standard 7-05 was written by an excellent seismology committee

 Allows for Site-Specific Calculation of Ground-Motion

▶ if you do not like the results of the default response spectra

Insights for Use of Vs30m
Depending on Geologic Complexity and Tectonic Geomorphology, there may be 2 different subgrades on a large parcel that is to be developed. Architects and some Structural Engineers seem focused on one flat-land campus. However, larger parcels near the break-in-slope typically have both thick alluvium and soft rock.   Two different Vs30m Two different levels for MCE ground-motion

Current ASTM Standards for Engineering Geophysics Vs30m
 ASTM Standard D-4428M-07
Cross-Hole Seismic Testing,
(K.H. Stokoe, Univ. Texas, Austin)

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
cost-effective, non-invasive, no boreholes, no VibroSeis trucks

 New ASTM Standard is needed for ReMi method.

Suggestions for Applied Research
regarding 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)
 <50 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.

Suggestions for Applied Research
regarding 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 1:500,000 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 the Great Basin.

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