Areas of Geotechnics

O: 2/X-1/GTK/10

Traditional  Areas of Geotechnical Engineering

1. Site Investigation
2. Compaction
3. Consolidation
4. Slope Stability
5. Retaining Walls
6. Foundation

Site Investigation

1. To Properly Characterize a Site requires:
   - Literature Investigation to Determine
   - What Has Happened at the Site Before (Prior History)
   - What Investigations have been Made Near the Site
   - Geology, USDA Soil Profiles, Utility Crossings, etc.
2. On Site Surveying, Borings and Drilling, Bag Samples, etc.
3. Laboratory Testing for Soil Properties and Classification
4. Produce a Report about the site for the Owner
5. Maybe develop a Foundation Design, Retaining Structures, Embankments, Cuts and Fills

Drilling Program

1. The purpose of the Drilling Program is to determine the:
   - Thickness,
   - Lateral Extent, and
   - Physical Properties of Each Layer of Soil
   - Presence, Depth and Pressure of Water in the Soil
2. Coupled with the Topographic Survey, This provides a 3D view of the site and the soil underneath.
   If the Upper Soils are Weak, a Deep Foundation system must be developed.
3. This investigation may also determine where to find suitable fill material from Borrow pits.

Compaction
Ralph Proctor defined a standard procedure to specify the required density and water content of the soil for Stable Embankments.

1. Duplicated compactive effort available by compactors in 1927-1931.
2. Test is consistent and reliable
3. It shows the relationship between water   content  (w) and dry unit weight  (Gama d )

Samples of soil wetted to different water contents

• Each sample is compacted into the mold in 3 layers with 25 hammer blows per layer.
• Water content and Dry Unit Wt. determined for each sample.
• Peak is called Maximum Dry Unit Wt (Gamma-d Max) and Optimum Water Content

Contracts usually specify that the soil should be compacted to
A percentage of the Maximum Dry Unit Wt
     - Typically 95% for most fills
     - Sometimes 92% for landscaping
     - Sometimes 97-100% for fills requiring extra strength
B range of Water Contents around Optimum
     - Commonly 3 or 4% below and 2% above wopt.

Cut and Fill

If soil has to be moved around, you need to remove it (cut) at one location and, place it (Fill) at another location.

Economically, you want to design so that

• Minimize Volume
• Minimize Haul

Cut

• Cut soil is moved most easily by pushing it around (Short Haul)
  - Scraper
  - Wheeled (or Track) Bulldozer
  - Blade
• Lifting into a Dump Truck is much slower and expensive (usually Longer Haul)

 Cut and Fill, How Much ?

• Survey
• Pick Centerline
• Draw Topo
• Determine Sections

• Overlay Final Surface
• Draw Topo as Overlay
• Determine Section