T013 Foundation types

Mind Map by , created over 6 years ago

M007 & T013 Mind Map on T013 Foundation types, created by alison_patey0437 on 04/28/2013.

Created by alison_patey0437 over 6 years ago
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T013 Foundation types
1 Types of foundation
1.1 Shallow
1.1.1 Spread foundation
1.1.2 mat/ raft foundation
1.1.3 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
1.2 Deep
1.2.1 piling
1.2.2 piled walls
1.2.3 Diaphragham walls
1.2.4 cassions
1.2.5 used: when the underlying soil has unstable bearing capcacity Foundations extend to transfer load to more app bearing stratum rick or dense soils
1.3 Factor 2 consider when selecting foundations
1.3.1 pattern & size of building load
1.3.2 Subsurface & g.water conditions
1.3.3 impact on adj properties
1.3.4 BR req.
1.3.5 construction method & risk
2 Advantages of shallow foundations
2.1 affordable cost
2.2 simple construction
2.3 doesn't need expertise
3 shallow foundation
3.1 spread footings
3.1.1 an enlargement @ bottom of column/ bearing wall - spreads the load over large soil area
3.1.2 footing must be placed below the depth of frost penetration layer to avoid ground heave frostline = 305mm
3.1.3 common as cheap & ease of construction
3.1.4 used in small- medium sized structures
3.1.5 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
3.2 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
3.3 Raft fondations
3.3.1 the bdg is essentially put on one large footing
3.3.2 flat concrete slab - heavily reinforced may b stiffened with ribs/ beams
3.3.3 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
3.3.4 advantage: reduce differential settlement as concrete resists the movement
3.3.5 Used: when soil is prone 2 diff settlement - the strenght of the raft will subdue issues e.g. expansive soils create diff settlement
3.3.6 used: structural loads r erractic and create diff settlement
3.3.7 used: when lateral loads are not uniformly distributed
3.3.8 used: when uplift leads r more than footings can cope with
3.3.9 when bottom of structure is below the g.water table - e.g. hydrostatic uplift
4 Deep foundations
4.1 ext through unsuitable soil 2 transfer bdg load to more appropriate bearing stratum
4.2 piles
4.2.1 what is it? a slender structural member either concrete/steel/wood installed in ground to transfer bdg loads
4.2.2 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
4.2.3 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
4.2.4 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
4.2.5 when to choose which type of pile? pile type avilable Locvation & type of structure (magnitude of load) g. conditions (soil type) cost durability
4.2.6 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
4.3 piers
4.3.1 its a vertical bridge support
4.3.2 a foundation 4 carrying very heavy structural load
4.3.3 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
4.4 cassions
4.4.1 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
4.5 compensated foudation

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