Hybridoma Technology ( Production , Purification , and Application )
Soil investigation part2
1. SOIL INVESTIGATION &
FOUNDATION DESIGN
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2. FOUNDATIONS ON POOR SOIL
There are 2 ways to improve the strength
of the ground;
To excavate the ground until ground
capacity is reached.
Vibro- compaction of the soil- a vibrating
poker is used to make the ground more
dense.
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3. SUBSOIL SHRINKAGE
Shrinkage in the soil is caused by a number
of factors;
Extreme seasonal change
Vegetation
Trees
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4. Ground Heave
This is caused in a number of ways;
Water freezing in the ground which
results in the expansion of the ground
A high water table
The recent removal of trees or vegetation
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5. Excavations
Trenches over 1m deep require temporary
support
To stop trench collapse, timber supports-
shores or planks- are used to retain the
earth
On bigger projects sheet piling is used
All trenches should be checked with a CAT
scanner to detect an services
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6. Foundation Design
The design of foundations is covered by
document ‘A’ under Building Regs.
Strip foundations for example require a
minimum of 750mm in clay soils or 450mm
in others.
Most councils choose to go to 1m deep
Other factors include ‘dead’ and imposed
loads such as wind, snow, floors etc.
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7. Foundation Design
When designing a foundation, Engineers
concentrate on the unit of force (Kilonewtons )
rather than weight.
1 tonne is equal to 10 kilonewton
An average building load to a house is 120 tonnes
which exerts a force of 1200 kn to the ground
This number is then divided into the perimeter
length of the building eg. 30m which is then
divided into 1200kn. This formula will show how
much each metre run is carrying eg. 40kn
Depending on the soil, a design on the foundation
can be made
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8. Old Foundations
Prior to the 1875 Public Health Act most
houses were built on a wide brickwork base
which ‘corbelled in’ just before ground
level.
Brickwork was built in sand and lime to
allow for settlement in the ground
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9. PILING
Piling is used to transfer the load of the
building through weak or unstable soil to
ground of higher load bearing capacity
Vertical concrete piles are poured into the
ground by a crane mounted auger machine
which removes the soil and injects
concrete down a hollow stem.
A horizontal beam is then connected to the
to the top of the piles
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10. Strip Foundations
This is a strip of concrete which is under
all load bearing walls. The strip width and
depth depends on the building load and
nature of the ground
Strip foundations can be ‘stepped up’ with
sloping ground
Thickness of slab must NOT be less than
the ‘toe’ of the slab
The most economical option for builders
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11. Raft Foundations
This is a slab of concrete which supports the
building over a large area.
Tends to be used on ground of low bearing
capacity eg soft clays, loose sands etc.
Where differential movements are expected
Where subsidence due to mining is a possibility
No trenching required
Cheap and easy to construct
Less interference with sub soil water movement
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12. Pad Foundations
Pad foundations are used to support an individual
point load such as that due to a structural
column. They may be circular, square or
rectangular. They usually consist of a block or
slab of uniform thickness, but they may be
stepped or hunched if they are required to
spread the load from a heavy column. Pad
foundations are usually shallow, but deep pad
foundations can also be used.
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13. Summary
Strip foundations are suitable on;
Rock, gravel, dense sand or stiff clay
On soft clay or soft sandy clay, wider strip
foundations are required
Piled foundations are suitable for;
Shrinkable clays
Where the water table is high and where a firm
layer of ground is at a suitable depth
Where a firm layer of ground is at a considerable
depth
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14. Summary
Raft foundations are suitable on;
Grounds of low bearing capacity such as
soft clay or silt
In mining areas where subsidence is a risk
On deep areas of fill where piling would be
uneconomic
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Notas del editor
08/03/12 John Fox, College of North West London Soil Investigation & Foundation Design