Geophysics for Geotechnical Engineers


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A basic introduction to available geophysical test methods for the use of Geotechnical engineers presented at the USACE Infrastructure Conference in Atlanta, June 2011.

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Geophysics for Geotechnical Engineers

  2. 2. EVOLUTION OF GEOLOGY The earliest writing on Geology probably dates back to Theophrastus (372-287BC) who wrote a book on rocks called ‘Peri Lithion.” Abū Rayḥān al-Bīrūnī was perhaps the first person to document his observations about the earth and is credited with writing the first book on Geology. (A crater on the moon and the University in Tashkent are named after him).Will Durant in his History of Civilizationrecognized that al-Biruni worked on thehypothesis that the earth was asphere, revolved around the sun andspun on it axis. The term “geology” was introduced by Jean-Andrè Deluc in 1778. William Smith (1769-1839) produced the first geological map of England and Ireland.
  3. 3. GEOLOGY TODAYEarth science  Geography PaleoclimatologyEconomic geology  Geological modeling Paleontology Mining geology  Geometallurgy Micropaleontology Palynology Petroleum geology  Geomicrobiology PetrologyEngineering geology  Geomorphology Petro physicsEnvironmental geology  Geomythology Plate tectonicsGeoarchaeology  Geophysics SedimentologyGeochemistry  Glaciology Seismology Soil science Biogeochemistry  Historical geology Pedology (soil study) Isotope  Hydrogeology Speleology geochemistry  Meteorology StratigraphyGeochronology  Mineralogy BiostratigraphyGeodetics  Oceanography Chronostratigraphy Lithostratigraphy  Marine geology Structural geology Volcanology
  4. 4. GEOTECHNICAL ENGINEERING The credit for understanding of the concept of soil as an engineering material should rightfully belong to Coulomb, who soon after his graduation in 1761 used his knowledge of mechanics to apply to pressure exerted by soils.Karl Terzaghi of course has been credited with notonly coining the term soil mechanics, but also withrealizing the importance of understanding geology inunderstanding soil physical properties. As thesaying goes, the rest is history – of soil mechanics.No one is really sure when and why the termGeotechnical Engineering came to absorb soilmechanics, foundation design and anything elsethat has the word “soil” in it. Terzaghi’s wife Ruth, ageologist and his graduate student and ArthurCasagrande should be credited with connectingmechanics with the material.
  5. 5. MERGING GEOLOGY AND GEOTECHNICAL ENGINEERING• Geology and Geotechnical Engineering merge in many areas – soil and rock physical properties, site characterization, mineralogy and foundation design.• While Geotechnical engineers have refined their laboratory testing, in-situ testing and design techniques, the amalgamation of geophysics and geotechnical engineering has not taken a significant role in the practice of geotechnical engineering.• Geophysical methods should be the primary investigative tool for geotechnical engineers.
  6. 6. GEOPHYSICAL METHODSMETHOD MEASURED PARAMETERGround Penetrating Radar (GPR) Dielectric Constant (indicate the top of rock surface)Electromagnetic Frequency and Electrical Conductivity (lateral variation in soil and rock;Time Domain (EFT) differentiate soil types including contaminated soils)Very Low Frequency (VLF) ER Electrical Resistivity (apparent resistivity)Electrical Resistivity / Capacitively Electrical Resistivity (stratification/spacial differentiation)Coupled ResistivitySpontaneous Potential (SP) Electrochemical and Streaming potential (Seepage)Seismic Refraction Seismic velocity, shear modulus (rock rippability)Seismic Reflection Seismic velocity (Stratigraphy)Surface Wave Analysis Seismic velocity, dispersion (S-wave/stratigarphy, karst features)Microgravity Density (bedrock/karst)Magnetic Potential Magnetic susceptibility (minerals, buried objects)Thermal Imagery Surface temperature (seepage, karst)Radio-metrics Natural Gamma Radiation (ores, fracture)Cross-hole tomography Subsurface profiling, stratigraphy (karst)
  7. 7. GEOPHYSICS FOR GEOTECHNICAL ENGINEERS• Policy Development• Recruitment and Training• Data management and analysis• Risk Assessment and Mitigation• Consultation and Technical Reviews• Quality Assurance• Periodic Inspection and Periodic Assessment Support
  8. 8. RMC’s PROGRAM• Develop 1-, 5-, 10-, and 30-year infrastructure investment plans• Prioritize Issue Evaluations, Dam Safety Modification Reports, and Construction• Monitor progress and project management for dam safety projects• Support Senior Oversight Group and HQ efforts to manage funds and queues
  9. 9. HOW WE CAN SUPPLEMENT RMCRMC’s CURRENT CONCERNS OUR RESPONSE AND POTENTIALDam Safety Regulation and Procedures SWF has involved RMC in our DSMS RMC’sneed to define RMC Role role is evolving as we progressGeotechnical Issues dominate the SWF has one of the strongest staff supportPortfolio and expertise in this areaRisk Based Evaluation is needed SWF has the need to focus in this directionOrganizational Improvement needed We have expertise gathered from CoS, Border Protection, Force Protection, LEED and Design experienceExperienced Staff is Scarce We have surplus capacity from time to time and have a recruiting advantageExtensive outsourcing to A/E firms SWF has the potential to reduce A/E outsourcingPrioritizing and Implementation SWF is lower in priority as compared to NE and NW
  10. 10. A PLAN FOR SWF’s RMC PROGRAMWithin the first 30 days: Establish and staff the center Define roles and develop Position Descriptions Develop a 1-year and 5-year budget Establish program prioritiesWithin the first 90 days: Internal Recruitment and assign responsibilities for the internal team Prioritize projects and develop schedules (primarily DSMS and LRP projects) Match national resources and develop talent pool Detailed budgets for DSMS and LRP and funding support
  11. 11. SWF’s RMC PROGRAM PLANWithin the first 1 year: Get project teams working on specific DSMS and LRP projects Assist the Levee CoP in developing LSMS methods Develop detailed 5-year design plan for DSMS and LSMS Develop Remedial action plans and construction plans Write contracts for remedial works – standardize if possibleWithin the first 5 years: Set up Inspection Plans based on risk evaluation Assist Dam and Levee CoPs to develop practice standards Document strategies from lessons learned Identify10-year and 60-year needs and needed infrastructure improvements.
  12. 12. THANK YOU