311 GEOTECHNICAL ENGINEERING

1. FCE 311 GEOTECHNICAL ENGINEERING
APPLICATIONS IN GEOTECHNICAL
ENGINEERING
Department of Civil & Construction Engineering
University of Nairobi

2. Soil:
– Is one of people’s oldest construction
material
– Is one of the most complex of the
standard construction materials
because of the variation in soil types
– Has been studied and analyzed for
hundreds of years, but;

3. • Is one of the more recent
disciplines in Civil
Engineering
– Karl Terzaghi (1983-
1963)
• Wrote
Erdbaumechanik
(1925)
• Published over 260
articles
• Taught at Harvard
(1932, 1935-1963)

4. The phase relationships are
defined with a Phase Diagram
V = Total Volume
Vs = Volume of Solids
Vv = Volume of Voids
Vw= Volume of Water
Va = Volume of Air
Gs = Specific Gravity
of Solids
W = Total Weight
Ws = Weight of Solids
Ww= Weight of Water
Wa = 0
Porosity = n = -------- 100%
Degree of
Saturation = S = -------- 100%
Void Ratio = e = ------------
Total Unit Wt. = γ = -------
Dry Unit Wt. = γd = -------
Water Content = w = --------- 100%
Specific Gravity = Gs = -----------

5. Traditional Areas of
Geotechnical Engineering
– Site Investigation
– Compaction
– Consolidation
– Slope Stability
– Retaining Walls
– Foundations

6. Site Investigation
• 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.

7. Site Investigation
– On Site Surveying, Borings and
Drilling, Bag Samples, etc.
– Laboratory Testing for Soil Properties
and Classification
– Produce a Report about the site for the
Owner
– Maybe develop a Foundation Design,
Retaining Structures, Embankments,
Cuts and Fills

8. Drilling Program
• 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

9. Drilling Program
• If the Upper Soils are Weak, a Deep
Foundation system must be developed.
• This investigation may also determine
where to find suitable fill material from
Borrow pits.

10. Borehole Drilling
• Drilling Rig
• Continuous Hollow
Stem Augers With
Removable Drill Rod
And Center Head

11. Borehole Logs

12. Typical Soil Profile
• Soil Profile
– Airport Runway, 4 Borings

13. Soil Types
– Organic Clay
– Sandy Silt
– Sandy Clay
– Gravelly Clay
– High Plasticity
Clay

14. Compaction
Ralph Proctor defined a standard
procedure to specify the required
density and water content of the soil
for Stable Embankments.
Duplicated compactive effort
available by compactors in 1927-
1931.
Test is consistent and reliable
It shows the relationship between
water content and dry unit weight

15. Compaction
3-5 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

16. 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

17. 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)

18. Fill
•Filled soil is spread
(Scraper, Dozer) and
Compacted

19. Cut and Fill – How Much?
Survey
Pick Centerline
Draw Topo
Determine Sections

20. Cut and Fill – How Much?
•Divide area into Grid
•Determine Elevations of
Natural and New Surface
•Determine Volume of Each
Section
•Sum for all Sections