FCE 311 GEOTECHNICAL ENGINEERING

APPLICATIONS IN GEOTECHNICAL ENGINEERING

Department of Civil & Construction Engineering

University of Nairobi

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;

• 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)

The phase relationships are defined with a Phase DiagramV = 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 ofSaturation = S = -------- 100%

Void Ratio = e = ------------

Total Unit Wt. = = -------

Dry Unit Wt. = d = -------

Water Content = w = --------- 100%

Specific Gravity = Gs = -----------

Traditional Areas of Geotechnical Engineering

– Site Investigation

–Compaction

–Consolidation

– Slope Stability

–Retaining Walls

– Foundations

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.

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

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

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.

Borehole Drilling

• Drilling Rig

• Continuous Hollow Stem Augers With Removable Drill Rod And Center Head

Borehole Logs

Typical Soil Profile

• Soil Profile

– Airport Runway, 4 Borings

Soil Types

–Organic Clay

– Sandy Silt

– Sandy Clay

–Gravelly Clay

–High PlasticityClay

CompactionRalph 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

Compaction

3-5 Samples ofsoil wetted to different watercontents

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

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

CutCut 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)

Fill•Filled soil is spread (Scraper, Dozer) andCompacted

Cut and Fill – How Much?

Survey

Pick Centerline

Draw Topo

Determine Sections

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