Lecture 6 - Lance Simms - COSC253 PDF

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Summary

Lance Simms - COSC253...

Description

9/20 Deep Foundation: Drilled Pier:  

Drilled into the earth with large auger belled (flared) at the bottom as necessary

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Diameter ranges from 12” – 18”

Belled Caissons:   

Practical only where the bell can be excavated in a cohesive soil that will remain solid Special “belling bucket” attachment used to bell bottom of caisson after shaft is drilled Belled for weight distribution

Socketed Caissons:   

Drilled into rock or hard stratum not belled at the bottom bearing capacity comes from end-bearing and friction between sides of caisson and rock

Piles: 

Used where drilled piers (caissons) are not practical

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Hammered or pressed into the earth

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classified as “end-bearing” or “friction” may be made of steel, wood, or precast concrete

Piles (end-bearing): 

forcibly driven until the tip encounters firm resistance (rock or strong soil)

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bearing capacity comes from end of pile driven to refusal

Piles (friction): 

used where no firm bearing layer can be reached

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Achieves load-bearing capacity through frictional resistance on surface of pile

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Driven to a predetermined depth or until a certain level of resistance is encountered

Pile Cap:  

Piles are typically driven close together in clusters a pile cap spreads load among clustered piles

Grade Beam: 

Spans between the pile caps or piers, to provide continuous support for the wall above

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reinforcing bars project from the tops of completed drilled piers gravel is being deposited between the piers, to form a base for concrete grade beams which will span between the piers

Minipiles (Pin Piles): 

made of steel pipe or bar 2 to 12 inches in diameter

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pressed or rammed into holes and grouted in place can be installed in short sections good choice when vertical clearance is limited

Helical Piles (Screw Piles):  

installed without hammering (augured into place) coupled end-to-end as drilling progresses

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no vibration/low noise

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good for work close to existing buildings

Seismic Base Isolation:  

used in areas of the country where earthquakes are common base isolators (elastomeric bearings) flex or yield to absorb a significant portion of movement during a seismic event

Underpinning:  

strengthening or stabilizing an existing foundation may be required when original foundation was improperly designed, when a change in use or addition increases foundation loads or when new construction could damage the foundation.

Sitework and Retaining Walls Retaining Walls: 

Hold back soil where an abrupt change in ground elevation occurs

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The wall must be strong enough to resist the forces of the earth and any groundwater may be made of masonry, wood, steel, precast concrete, or site cast concrete

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can fail by horizontal sliding, overturning, or undermining

9/22 Gabions: 

another form of earth retention utilizing corrosion-resistant wire baskets filled with

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cobble can also be used to resist or control erosion

Earth Reinforcement:   

AKA “Mechanically Stabilized Earth” can be fabric a reinforcing material is placed between each layer of fill or backfill is compacted in layers

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this layer is strengthening the soil often an economical alternative to retaining wall

Filling and Backfilling Filling: 

broad term to describe any placing of earth material

Backfilling: 

Refers more specifically to the replacement of earth material to restore it to finished level

Lifts: 

Filling or backfilling is placed and compacted in layers or “lifts” (thickness may range from 4 to 12 inches)

Filling and Proper Compaction:  

large open spaces allow fill to be compacted with heavy equipment Compacting fill or backfill in confined spaces often requires the use of small, wall-behind equipment

Key Terms:  

Site planRetaining wall-

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GabionEarth reinforcement-

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Filling-

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Backfilling lifts-...