Foundations
Excavations
ARCH 330
Fall 2008
Yes, I was a stud.
The Function of a Foundation
Foundations
Foundation Engineering- Evaluating the ability to support a
given structural load and designing the substructure or
transition member needed to support the construction.
To transfer the structural loads safely into the ground.
This means dealing with forces and soil pressures. The
need for deep excavations.
Foundations
• Spread Footings
– Proper compaction under the footing
• Driven Piles
– Types of piles
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Wood
Concrete
Steel
Composite
-Pile Drivers
• Drop Hammer
• Mechanical- Hydraulic, diesel, steam
• Vibratory
• Caissons or Drilled Shafts
• Cofferdams
Review Plans & Specifications
• Consistency with geotechnical report
• Reduce confusion during construction
• Without Differing Site Conditions clause contractor
responsible
• Read the report in response to what is underground.
– Understand prescribed method, consistency with soils report
• Site Investigations
– Environmental restrictions
– Site conditions at each and every location
• The report has pertinent information- follow it.
• Compaction testing
– Understanding moisture content
– Proper proctor
Geotechnical Studies
Soils Report
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Buildings
Retaining Walls
Bridges
Roadways
Landslides
Forensic Investigations
Importance of Geotechnical
Studies
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Provide efficient foundations systems
Improve bid accuracy
Reduce change orders
Reduce long term problems
Geotechnical/Soils Reports
Recommendations
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Suitability of on site soil for structural fill
Bearing capacity
Foundation type
Lateral earth pressures
Pavements
Drainage
Seismic
Steps for Geotechnical Study
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Explore site conditions
Perform lab testing
Perform engineering analysis
Prepare report
Assist with plans and specifications
Construction observations
Soil Report
• Borings or test pits
• To lab for:
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Moisture content
Gradations
Proctor test
Consolidation, direct shear, triaxial
Pile & Pile Driving
• Site Investigation
– Type & weight of structure
– Soil properties
– Depth of stratum
– Variations of stratum depth
– Availability of piling type
– Availability of pile driver
– Availability of experience in driving pile
Pile & Pile Driving
(Site Investigation cont)
– Comparative placement cost
– EPA & OSHA regulations
– Depth of excavation for placement of
equipment ie building footing
– Location of piling ie river, lake, ocean
– Noise & Vibration
– Adjacent structures
Pile & Pile Driving
Piling Types
Wood Pile
Precast Concrete Pile
Steel H-Pile
Steel Pipe Pile
Composite Piles
(Please review page 571-594)
Pile & Pile Driving
• Pile Caps & Grade Beams
– Piles are clustered then caped
• Number of piles per cap are determined by the
load bearing capacity of the soil.
• From the cap comes a column or bent.
• Piles can be connected by grade beams
Pile & Pile Driving
Pile Drivers
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Drop Hammers
Single/Double-Acting Steam
Hydraulic
Diesel Hammers
Vibratory Pile Drivers
Caisson or Cofferdam
What’s the difference?
• Caisson- Boring or drilling a hole and filling
with concrete.
• Cofferdam- A temporary boxlike structure
used to hold back water or earth while
work is being done inside it.
EXCAVATION
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HORIZONTAL & VERTICAL LAYOUT
BEGIN EXCAVATION
SWELL AND SOIL TYPES
UNSUITABLE SOIL
STRUCTURAL FILL
SITE DRAINAGE
DEWATERING
COMPACTION
BACKFILL
SAFETY
MECHANICAL & ELECTRICAL
Excavation Wall Bracing
No matter what restraining system is used to
stabilize the sides of an excavation, the
walls will have to be braced against lateral
pressures exerted by the surrounding soil
and water.
• Shoring for trenches (trench boxes)
• Lateral forces surrounding the structure
– Slope back
– Different shoring systems
– Tiebacks (rock and earth)
Protection of Excavations
Lateral Forces
Deep Excavations
• Slope Back- Usually 2:1, The angle of repose at
which a soil material will stand without moving
• Interlocking Sheet Piling
• Steel Soldier Piles- H beam with lagging
• Concrete Slurry walls-Shotcrete (pneumatically
projected at high velocity onto a surface)
Other piling terminology
Battered pile- A pile driven somewhat at an
angle so as to resist horizontal forces.
Kelly bar- The equipment on the pile driver
that determines the height of the pile to
drive.
EXCAVATION
Terminology
In the industry terms can mean different things.
Toe- (1) Any protection from the base of a
construction or object to give it increased
bearing and stability. (2)That portion of sheeting
below the excavated material. (3) To drive a nail
at an oblique angle. (4) The junction between
the base metal and the face of a filled weld. (5)
The part of the base of a retaining wall that
projects beyond the face away from the retained
material.
Excavation
• Need for Deep Foundations
• Removing ground water or dewatering
• Amount of material to be removed
– Soil swell percentage
• For removal and replace
• Tons to cubic yards
• Protection of Excavation
– Sheet Piling
– Soldier Piles
– Concrete Slurry Walls
• Excavation Wall Bracing
– Slope back
– Shoring
– Tiebacks
Foundation Sequencing
Drive Piling- Excavate> >[Slope protection/shoring system]> Layout
Piles>Drive Piles>Cut off piles>Fine grade/Compact>Structural Fill>
Backfill to follow foundation system
Drilled Piling (concrete)- Excavate> >[Slope
protection/shoring system]>
Layout Piles>Auger piling>Fabricate
Cage>Set reinforcing cage>Pour concrete pile>Fine
grade/Compact>Structural Fill> Backfill to follow foundation system
Spread Footings-Excavate>[Slope protection/shoring
system]>Layout>Fine
foundation system
grade/Compact>Structural Fill>
Backfill to follow
EXCAVATION
EXCAVATION
• TABLE V:2-1. ALLOWABLE SLOPES.Soil
typeHeight/Depth ratioSlope angle Stable
RockVertical90°Type A¾:153°Type
B1:145°Type C1½:134°Type A (shortterm)½:163°(For a maximum excavation
depth of 12 ft)