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 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

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

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”

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

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

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

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

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

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

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

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

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