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T013 Foundation types
Description
M007 & T013 Mind Map on T013 Foundation types, created by alison_patey0437 on 28/04/2013.
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m007 & t013
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alison_patey0437
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alison_patey0437
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Resource summary
T013 Foundation types
Types of foundation
Shallow
Spread foundation
mat/ raft foundation
used: when stable soil of good bearing capacity is near the surface.
foundations r placed directly below and transfer the bdg load directly 2 the supporting soil
Deep
piling
piled walls
Diaphragham walls
cassions
used: when the underlying soil has unstable bearing capcacity
Foundations extend to transfer load to more app bearing stratum rick or dense soils
Factor 2 consider when selecting foundations
pattern & size of building load
Subsurface & g.water conditions
impact on adj properties
BR req.
construction method & risk
Advantages of shallow foundations
affordable cost
simple construction
doesn't need expertise
shallow foundation
spread footings
an enlargement @ bottom of column/ bearing wall - spreads the load over large soil area
footing must be placed below the depth of frost penetration layer to avoid ground heave
frostline = 305mm
common as cheap & ease of construction
used in small- medium sized structures
Shape and sizes of spread footings
Square/ Pad
individual spread footing supporting columns & piers
use 1:2:4 concrete mix + reinforcement
reinforcement resists/carries tension loads
types
mass concrete 4 steel columns
reinforced concrete with slopping upper face
plain reinforced concrete
stepped reinforced concrete
accommodate sloping gradient + maintain required depth
Rectangular
used when obstructions prevent using pads
use when large movement r present
circle spread
used: flag poles; power lines etc
combined
support more than one column; maybe support interior loads as well as perimeter
useful when columns r 2 close 2gether 2 have own footings
continuous spread
continuous spread footings of foundation walls
ring spread
continuos footing in a circle
commonly used to support wall above ground or storage tanks
lowest part of shallow foundation are spread footings. ext laterally 2 distribute load an area so that it doesn't exceed the bearing capacity of soil
Raft fondations
the bdg is essentially put on one large footing
flat concrete slab - heavily reinforced
may b stiffened with ribs/ beams
used: when bearing capacity of soil is low compared to building loads
rule of thumb: if footing are going to spread the area of 50% of bdg footprint ; its economical 2 have a raft
advantage: reduce differential settlement as concrete resists the movement
Used: when soil is prone 2 diff settlement - the strenght of the raft will subdue issues
e.g. expansive soils create diff settlement
used: structural loads r erractic and create diff settlement
used: when lateral loads are not uniformly distributed
used: when uplift leads r more than footings can cope with
when bottom of structure is below the g.water table - e.g. hydrostatic uplift
Deep foundations
ext through unsuitable soil 2 transfer bdg load to more appropriate bearing stratum
piles
what is it?
a slender structural member either concrete/steel/wood
installed in ground to transfer bdg loads
when are they used?
when soil nr surface doesn't have enough bearing capacity 2 support bdg
settlement of soil exceeds tolerable limits
diff settlement - soil variability/ non-uniform structural loads
transfer of load in 2 ways:
end bearing pile
transmit load to firm layer of grounds e.g. rock; gravel; v. dense sand
friction pile
tranfer load to penetrable soil by means of friction/ cohesion between soil and embedded surface of pile
Types of piles
concrete
in-situ
form: driving cylindrical steel shells in 2 ground at desired depths
steel shell doesn't contribute to transfer cap.
steel shell: open a hole to facilitate construction of concrete pile like formwork
vigilant QM & construction practice 2 ensure integrity
cavity filled with concrete
Advantages
sustain hard driving
suits 4 marine environ
easily inspected
length can b changes
pre-cast
square/octagonol/circular x-sections
fab off-site & pre-stressed
problems with transporting some lenghts
higher capacity than timber
drilled shafts
steel
shapes
H piles
rolled steel sections
H: sometimes encase in concrete 2 pt at below water table
cylindrical
tapered
used when req penetrate boulder/ rock
welded sections up 2 70m
needs treatment from corrosion
timber
oldest form of pile
length dependent on tree size
usually used as frictional pile
can have a steel shoe and drive band 2 prevent spliting
susceptible to rot
cheaper but low capacity
composite
constructed of 2 materials e.g. timber & concrete upper so 2 prevent the portion above water from deteriorating
when to choose which type of pile?
pile type avilable
Locvation & type of structure (magnitude of load)
g. conditions (soil type)
cost
durability
Pile Construction
Displacement
soil is displace radially & virtically as pile shaft is driven or jack into the ground
drop hammer/ jack
types of displacement piles
pre-formed displacement piles
Precast concrete/ steel
driven & insitu displacement
2 forms
driving a temp steel casing with enclosed end 2 form void and fill with concrete. steel removed
the same as above but the steel tube is left in place
Helical insitu
created using a special type of auger
the soil is compacted as the auger is screwed into the ground
the auger has a hollow stem which concrete can b pumped. the auger is slowly unscrewed leaving in-stiu pile in place
method of installation
drop hammer/weight
common with displacement
diesel hammer
best 4 driving into granular non cohesive soils
vibration hammer
jacking
vibration free/ minimal noise
Non-displacement
soil is removed leaving a hole 2 b filled with concrete or pre-cast concrete piles dropped in 2 hole & grouted in
Auger drilled
types
small dia. in-situ
large in-situ
partially preformed
grout/concrete intruded piles
piers
its a vertical bridge support
a foundation 4 carrying very heavy structural load
things to consider
driling through wet /caving soils need 2 use temp steel casing. Use tremie & pump to remove water & place concrete. more exp and large dia. hole
reinforcement : hard 2 get to depth - use large bars vs. more bars
cassions
what is it?
prefab hollow box thats sunk into the ground & filled with concrete = foundation
common bridge/pier work
cassions can be floated to a location to be sunk in place
created by aurguing a deep hole in the ground; re-bar and concrete poured; normally bell shaped
compensated foudation
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