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Geotechnical Investigation

Geotechnical Investigation. Step 1 - Gather Existing Information Structure Data Bridge, building, road, wall, etc. Type - stories, loads, materials, etc Known Soil Data Your own knowledge of the area Geologic or other maps Other people Aerial photos. Geotechnical Investigation.

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Geotechnical Investigation

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  1. Geotechnical Investigation • Step 1 - Gather Existing Information • Structure Data • Bridge, building, road, wall, etc. • Type - stories, loads, materials, etc • Known Soil Data • Your own knowledge of the area • Geologic or other maps • Other people • Aerial photos

  2. Geotechnical Investigation • Step 2 - Field Investigation • Site Recon -Before you move any equipment to site, visit the site • A visual inspection can tell you a lot: • Site access • existing structures • evidence of old structures • environmental hazards • non-engineered fill • sinkholes • topography • condition of nearby structures

  3. Geotechnical Investigation • Step 2 - Field Investigation - cont’d • Subsurface Investigation • Test Pits - holes dug with a backhoe • Borings • Solid Flight • Hollow Stem • Rotary Wash

  4. Geotechnical Investigation • Step 2 - Field Investigation - cont’d • Borings used to obtain samples at various depths • Samples needed depend on project • Most common method of sampling is the • Standard Penetration Test - SPT • Recall SPT is 140 lb hammer dropped 30”

  5. Geotechnical Investigation • Borings - cont’d • Drill rig – Hollow Stem Auger - SPT

  6. Geotechnical Investigation • Borings - cont’d • Drill rig – Hollow Stem Auger - SPT

  7. Geotechnical Investigation • Borings - cont’d • Drill rig – Hollow Stem Auger - SPT

  8. Geotechnical Investigation • Borings – cont’d • # of borings project dependent • For a building, will typically start with corners and in the middle • Based on what is found, more borings can be drilled as needed to define areas of concern or to obtain additional data

  9. Geotechnical Investigation • Borings – cont’d • Layout depends on footprint too • Depth depends on anticipated soil conditions and foundation type • We want to be sure we sample all soil potentially influenced by the foundation system

  10. Geotechnical Investigation • Borings – What are we looking for? • Soil classification • Soft compressible soils • Competent foundation soils • Bedrock • Ground water • Any other subsurface that could affect the project

  11. Geotechnical Investigation • Step 3 – Laboratory Investigation • Most common tests include: • Plasticity (atterbergs) • Sieve • Moisture • Unit Weight • Proctor • Strength tests (unconfined, direct shear, etc.)

  12. Geotechnical Investigation • Step 4 – Design • The design process will take into account all data • Consider loads, soils, type and use of facility, etc. • GE often asks “what is needed” vs. what is calculated

  13. Geotechnical Investigation • Step 4 – Design – cont’d • Some of the main items conveyed to client: • Types of soils • Groundwater • Recommended foundation type or options plus design and construction criteria • Depth to bedrock • Excavatability • Soil compaction criteria • Slope recommendations • Retaining wall design • Boring and Lab test results

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