Geotechnical Investigations

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 - contd
• Subsurface Investigation
• Test Pits - holes dug with a backhoe
• Borings
• Solid Flight
• Hollow Stem
• Rotary Wash

4
Geotechnical Investigation

• Step 2 - Field Investigation - contd
• 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 - contd
• Drill rig Hollow Stem Auger - SPT

6
Geotechnical Investigation

• Borings - contd
• Drill rig Hollow Stem Auger - SPT

7
Geotechnical Investigation

• Borings - contd
• Drill rig Hollow Stem Auger - SPT

8
Geotechnical Investigation

• Borings contd
• 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 contd
• 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 contd
• 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