Subsurface Investigation and Geotechnical Evaluation


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Subsurface Investigation and Geotechnical Evaluation

  1. 1. Atlantic Testing Laboratories Subsurface Investigation and Geotechnical Evaluation NYSCHSA January 22, 2013
  2. 2. Topics Designing a Subsurface Investigation Program Subsurface Investigation Methodologies Subsurface Investigation Log Review CPT Log Review Soil Classifications Engineering Properties of Soil Geotechnical Evaluation
  3. 3. Designing a Subsurface Investigation Determining the Number of Soil Borings  Former NYS Building Code  The Building Code of NYS 2002 (based on IBC 2000)  As a Rule of Thumb – 1 Boring for every 2,500 to 5,000 s.f. of building footprint
  4. 4. Seismic Site ClassificationDetermination Code does not require a 100 foot boring Calculate the average soil properties in the top 100 feet. (either soil shear wave velocity, Standard Penetration resistance, of soil undrained shear strength) Section 1615.1.1 allows the register design professional to assume based on knowledge of local geology
  5. 5. Seismic Site ClassificationDetermination Use table 1615.1.1 to determine Seismic Site Classification (class A, B, C, D, E, or F) Obtain the maximum considered earthquake ground motion of 0.2 sec spectral response (Ss) Obtain the maximum considered earthquake ground motion of 1 sec spectral response (S1)
  6. 6. Seismic Site ClassificationDetermination Can be obtained from the maps in the code, the CD prepared by ICC, or USGS web page Adjust Ss and S1 based on coefficients presented in Tables 1615.1.2(1) and 1615.1.2(2)
  7. 7. Seismic Site ClassificationDetermination Central New York sites typically fall into site class B, C, or D Glacial till and/or bedrock is often found at shallow depths. Exception is Onondaga Lake area, bedrock and/or glacial till in excess of 300 feet
  8. 8. Subsurface InvestigationMethodologies ConventionalSoil Borings Cone Penetration Testing (CPT) Geoprobe Test Pits
  9. 9. Conventional Drilling Hollow Stem Augers Flush Joint Casing Split Spoon Sampling Undisturbed Samples Bedrock Coring
  10. 10. Hollow Stem Augers Auger Flights around a center sampling tube Size refers to diameter of sampling tube Advantages  Quick  More Economical  Water not necessary  Ability to collect bulk samples
  11. 11. Flush Joint Casing Can be Driven or Spun-in the ground Advantages  Can be advanced through cobbles and boulder  Can be advanced to depths of around 300 feet  Provides a stable hole for special testing such as permeability testing
  12. 12. Split Spoon Sampling In accordance with ASTM D 1586 Sample for soil classification and future laboratory testing Retained in sealed glass jars
  13. 13. Undisturbed Samples In accordance with ASTM D 1587 Obtained from cohesive soils Returned to the laboratory for multiple analyses Provides accurate representation of in-situ conditions
  14. 14. Bedrock Coring In accordance with ASTM D 2113 Double tubed core barrel with a diamond cutting shoe Samples are returned for classification, RQD determination, and laboratory analysis
  15. 15. Cone Penetration Testing Pushes a “cone” with electronic sensors In accordance with ASTM D 3441 Determines:  Tip resistance  Side friction  Pore water pressure  Seismic shear wave velocity
  16. 16. Cone Penetration Testing Advantages  Rapid: Can advance 200 to 400 feet per day  Accurately determines to Seismic Site Classification  Replicates pile driving  Useful in cohesive and sand soils
  17. 17. Cone Penetration Testing Disadvantages  Not able to be pushed in dense soils or bedrock  No sample recovered, soil classifications relies on soil properties  Requires a large drill rig for reaction weight
  18. 18. Typical CPT Log
  19. 19. Cone Penetration Testing
  20. 20. GeoprobeData: Environmental Sampling, Soil Classification, Bedrock Profile, and Groundwater Elevation
  21. 21. Geoprobe
  22. 22. Test Pits Advantages  Good for fill sites  Groundwater information  Collect bulk samples Disadvantages  Limited depth  Cannot determine Seismic Site Classification
  23. 23. Subsurface Investigation LogReview Contain a wealth of information Soil types Soil consistency Groundwater information
  24. 24. Soil Classification Several Systems Used Burmister Unified Soil Classification System NYSDOT USDA
  25. 25. Burmister Soil Classification Visual-manual procedure Performed by the drillers in the field Soil classification verified in the laboratory
  26. 26. Burmister Soil ClassificationBOULDERS: > 12” Particle SizeCOBBLES: 3” – 12” Particle SizeGRAVEL: Course: 3” - 1” Sieve Size Medium: 1” – ½” Sieve Size Fine: ½” - #4 Sieve SizeSAND: Course: #4 - #10 Sieve Size Medium: #10 - #40 Sieve Size Fine: #40 - #200 Sieve SizeSILT: #200 Sieve (0.074 mm) to 0.005 mmCLAY: <0.005 mm Particle Size
  27. 27. Unified Soil Classification System In accordance with ASTM D 2487 and ASTM D 2488 ASTM D 2487 - laboratory analysis ASTM D 2488 - visual manual procedure performed in laboratory
  28. 28. Unified Soil Classification
  29. 29. Engineering Properties of Soil Natural Moisture Content Atterberg Limits  Liquid Limit  Plastic Limit  Plasticity Index Shear Strength Internal Friction Angle Consolidation Potential
  30. 30. Soil Property Uses Bearing Capacity Lateral Earth Pressures Slope Stability Frost Heave Potential
  31. 31. Geotechnical Evaluation Geotechnical Report Contents Optional Services Site Visit
  32. 32. Thank You
  33. 33. Question & Answer How deep can you drill with hollow stem augers?
  34. 34. Question & Answer In what type of soil conditions is a Shelby Tube most conducive?
  35. 35. Question & Answer Does a 100 foot boring need to be drilled to determine the seismic site classification?
  36. 36. Question & Answer True or False: Determining the groundwater table is extremely important.
  37. 37. Question & Answer What type of soil parameter does Cone Penetration Testing (CPT) determine that conventional soil borings can not?
  38. 38. Thank You