Foundations and basements 1014 Building Technology Foundations and basements Things must go down before they go up

Why does it matter what’s underneath? 1014 Building Technology Why does it matter what’s underneath? Buildings are very, very heavy An estimate for a “typical” house in the USA is 320,000lb = 143 tons The weight of a building increases during course of construction The weight of a building varies as it is used The ground beneath must support this weight without moving

Most buildings are founded on undisturbed subsoil 1014 Building Technology Subsoil and bedrock If you go deep enough , you will hit bedrock, but you rarely build directly on it Most buildings are founded on undisturbed subsoil Never build on topsoil or peat Types of undisturbed subsoil Gravel Sand Clay All of the above

Must be firm, natural bed. Can be very strong if undisturbed 1014 Building Technology Gravel Must be firm, natural bed. Can be very strong if undisturbed Usually occur in flood plane areas

Must be undisturbed natural bed 1014 Building Technology Sand Finer than gravel Must be undisturbed natural bed Can be extremely strong if sand cannot be pushed sideways “Running sand” which is full of moving water, is very unsuitable to build on.

Very common, extremely fine grained powdered rock 1014 Building Technology Clay Very common, extremely fine grained powdered rock Can be very strong Can be “shrinkable”, changing volume with moisture content Can contain aggressive chemicals

Peat is soft, organic soil Never build on organic soils 1014 Building Technology Peat Peat is soft, organic soil Never build on organic soils Peat can occur beneath layers of otherwise stable soil Only a borehole down to bedrock will determine conclusively that there are no organic sub-soils

Foundation Footing Pile Raft Basement Names and terminology 1014 Building Technology Names and terminology Foundation Any sub-structure hidden in the ground Footing Strip or pad foundations just below walls and columns Pile Column-like foundations going deep into the subsoil Raft Wide, thin foundation spreading the weight of the building over the whole of its plan area Basement Underground room with walls and floors forming the foundations of the building above

Footings, more than just the bottom of a wall 1014 Building Technology Footings, more than just the bottom of a wall Basic principles of a “footing”, a wide base to a wall, (or a pad under a column): Calculate the weight of the building Establish the pressure the subsoil can support by testing Calculate the area needed to distribute the weight of the building at less than that pressure into the subsoil Pressure at base of plain wall, 2t/m2 Pressure at base of 1m wide footing 0.25t/m2 Load bearing strength of sub soil may be 1 t/m2 Ground level

Shallow strip vs. deep strip foundations 1014 Building Technology Shallow strip vs. deep strip foundations Deep strip, trench fill Shallow strip: subsoil concrete wall backfill 1.5 –2m

Shallow strip vs. deep strip foundations 1014 Building Technology Shallow strip vs. deep strip foundations Deep strip, trench fill Shallow strip: subsoil concrete Wide trench wall backfill 1.5 –2m

Shallow strip vs. deep strip foundations 1014 Building Technology Shallow strip vs. deep strip foundations Deep strip, trench fill Shallow strip: subsoil concrete Wide trench Little concrete wall backfill 1.5 –2m

Shallow strip vs. deep strip foundations 1014 Building Technology Shallow strip vs. deep strip foundations Deep strip, trench fill Shallow strip: subsoil concrete Wide trench Little concrete Brick layer must work in trench wall backfill 1.5 –2m

Shallow strip vs. deep strip foundations 1014 Building Technology Shallow strip vs. deep strip foundations Deep strip, trench fill Shallow strip: subsoil concrete Wide trench Little concrete Brick layer must work in trench Lots of fill wall backfill 1.5 –2m

Shallow strip vs. deep strip foundations 1014 Building Technology Shallow strip vs. deep strip foundations Deep strip, trench fill Shallow strip: subsoil concrete Wide trench Little concrete Brick layer must work in trench Lots of fill Narrow trench wall backfill 1.5 –2m

Shallow strip vs. deep strip foundations 1014 Building Technology Shallow strip vs. deep strip foundations Deep strip, trench fill Shallow strip: subsoil concrete Wide trench Little concrete Brick layer must work in trench Lots of fill Narrow trench Lots of concrete wall backfill 1.5 –2m

Shallow strip vs. deep strip foundations 1014 Building Technology Shallow strip vs. deep strip foundations Deep strip, trench fill Shallow strip: subsoil concrete Wide trench Little concrete Brick layer must work in trench Lots of fill Narrow trench Lots of concrete Brick layer works on surface wall backfill 1.5 –2m

Shallow strip vs. deep strip foundations 1014 Building Technology Shallow strip vs. deep strip foundations Deep strip, trench fill Shallow strip: subsoil concrete Wide trench Little concrete Brick layer must work in trench Lots of fill Narrow trench Lots of concrete Brick layer works on surface Little fill wall backfill 1.5 –2m

1014 Building Technology Digging foundations In reality, digging foundation trenches is a dirty, difficult and dangerous job.

Comparison of footings 1014 Building Technology Comparison of footings Soft, non-self supporting soils: wide strip footing best Firm self supporting soils: always use deep strip/trench fill Depth of foundation the same for both: down to below level of frost and water effects, where soil is strong enough to bear loads Maximum practical depth 2 m for footings

Raft foundation: stable but weak sub-soil near the surface 1014 Building Technology Raft foundations Raft foundation: stable but weak sub-soil near the surface subsoil concrete wall backfill topsoil

Raft foundation: stable but weak sub-soil near the surface 1014 Building Technology Raft foundations Raft foundation: stable but weak sub-soil near the surface subsoil concrete wall backfill topsoil

Raft foundation: stable but weak sub-soil near the surface 1014 Building Technology Raft foundations Raft foundation: stable but weak sub-soil near the surface subsoil Shallow excavation concrete wall backfill topsoil

Raft foundation: stable but weak sub-soil near the surface 1014 Building Technology Raft foundations Raft foundation: stable but weak sub-soil near the surface subsoil Shallow excavation Lots of reinforced concrete concrete wall backfill topsoil

Raft foundation: stable but weak sub-soil near the surface 1014 Building Technology Raft foundations Raft foundation: stable but weak sub-soil near the surface subsoil Shallow excavation Lots of reinforced concrete Little or no fill Walls built on raft Raft forms the ground floor structure concrete wall backfill topsoil

Basement retaining walls 1014 Building Technology Basement retaining walls Basement “foundation”: supports buildings and sides

Basement retaining walls 1014 Building Technology Basement retaining walls Basement “foundation”: supports buildings and sides Deep excavation: needs support

Basement retaining walls 1014 Building Technology Basement retaining walls Basement “foundation”: supports buildings and sides Deep excavation: needs support Raft forms the basement floor structure

Basement retaining walls 1014 Building Technology Basement retaining walls Basement “foundation”: supports buildings and sides Deep excavation: needs support Raft forms the basement floor structure Lots of reinforced concrete Basement walls must be reinforced and water proof

Basement retaining walls 1014 Building Technology Basement retaining walls Basement “foundation”: supports buildings and sides Deep excavation: needs support Lots of reinforced concrete Raft forms the basement floor structure Basement walls must be reinforced and water proof Ground floor suspended over basement

Basement retaining walls 1014 Building Technology Basement retaining walls Basement “foundation”: supports buildings and sides Deep excavation: needs support Lots of reinforced concrete Raft forms the basement floor structure Basement walls must be reinforced and water proof Ground floor suspended over basement External walls built on basement walls

Pile foundations: when you have to go deep 1014 Building Technology Pile foundations: when you have to go deep Ground beam: reinforced concrete, supported by the piles, not the ground subsoil Pile: steel, concrete or timber concrete wall backfill weak fill

Pile foundations: when you have to go deep 1014 Building Technology Pile foundations: when you have to go deep Ground beam: reinforced concrete, supported by the piles, not the ground subsoil Pile: steel, concrete or timber concrete wall backfill weak fill

Pile foundations: when you have to go deep 1014 Building Technology Pile foundations: when you have to go deep Ground beam: reinforced concrete, supported by the piles, not the ground subsoil Pile: steel, concrete or timber concrete wall backfill weak fill

Pile foundations: when you have to go deep 1014 Building Technology Pile foundations: when you have to go deep Ground beam: reinforced concrete, supported by the piles, not the ground subsoil Pile: steel, concrete or timber concrete wall backfill weak fill

Pile foundations: when you have to go deep 1014 Building Technology Pile foundations: when you have to go deep Ground beam: reinforced concrete, supported by the piles, not the ground subsoil Pile: steel, concrete or timber concrete wall backfill weak fill

Pile foundations: when you have to go deep 1014 Building Technology Pile foundations: when you have to go deep Ground beam: reinforced concrete, supported by the piles, not the ground subsoil Pile: steel, concrete or timber concrete wall backfill weak fill

Pile foundations: when you have to go deep 1014 Building Technology Pile foundations: when you have to go deep Ground beam: reinforced concrete, supported by the piles, not the ground subsoil Pile: steel, concrete or timber concrete wall backfill weak fill

End bearing: loads to the bottom Friction: loads to the sides 1014 Building Technology Types of pile End bearing: loads to the bottom Friction: loads to the sides Bored pile Driven pile

End bearing: loads to the bottom Friction: loads to the sides 1014 Building Technology Types of pile End bearing: loads to the bottom Friction: loads to the sides Bored pile Driven pile

End bearing: loads to the bottom Friction: loads to the sides 1014 Building Technology Types of pile End bearing: loads to the bottom Friction: loads to the sides Bored pile Driven pile

End bearing: loads to the bottom Friction: loads to the sides 1014 Building Technology Types of pile End bearing: loads to the bottom Friction: loads to the sides Bored pile Driven pile

Pile driver: hammers preformed piles directly into the sub soil 1014 Building Technology Piling rigs Pile driver: hammers preformed piles directly into the sub soil Bored piling rig: large auger screwed into sub soil to create deep hole for pile Pin piles, small scale driven piles; steel tubes hammered in and filled with concrete