7 applications in geotechnical engineering
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Transcript of 7 applications in geotechnical engineering
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