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