Pile Foundation
Content
There are many reasons a geotechnical engineer would recommend a deep foundation over a
shallow foundation, but some of the common reasons are very large design loads, a poor soil at
shallow depth, or site constraints (like property lines). There are different terms used to describe
different types of deep foundations including the pile (which is analogous to a pole), the pier (which
is analogous to a column), drilled shafts, and caissons. Piles are generally driven into the ground in
situ; other deep foundations are typically put in place using excavation and drilling. The naming
conventions may vary between engineering disciplines and firms. Deep foundations can be made
out of timber, steel, reinforced concrete and prestressed concrete.
Contents
[hide]
1 Driven foundations
o
1.1 Pile foundation systems
o
1.2 Monopile foundation
2 Drilled piles
o
2.1 Under reamed piles
o
2.2 Augercast pile
o
2.3 Pier and grade beam foundation
o
2.4 Drilled Pier vs. Drilled Pile
3 Speciality piles
o
3.1 Micropiles
o
3.2 Tripod piles
o
3.3 Sheet piles
o
3.4 Soldier piles
o
3.5 Suction Piles
o
3.6 Adfreeze Piles
o
3.7 Vibrated stone columns
4 Piled walls
o
4.1 Secant piled walls
o
4.2 Slurry walls
5 Deep mixing/mass stabilization techniques
6 Classification of pile with respect to type of material
o
6.1 Timber
o
6.2 Steel
o
6.3 Prestressed concrete piles
o
6.4 Composite piles
7 See also
8 Notes
9 References
10 External links
Driven foundations[edit]
Pipe piles being driven into the ground
Illustration of a hand-operated pile driver in Germany after 1480.
Prefabricated piles are driven into the ground using a pile driver. Driven piles are
either wood, reinforced concrete, or steel. Wooden piles are made from the trunks of tall trees.
Concrete piles are available in square, octagonal, and round cross-sections (like Franki Piles). They
are reinforced with rebar and are often prestressed. Steel piles are either pipe piles or some sort of
beam section (like an H-pile). Historically, wood piles used splices to join multiple segments end-toend when the driven depth required was too long for a single pile; today, splicing is common
with steel piles, though concrete piles can be spliced with mechanical and other means. Driving
piles, as opposed to drilling shafts, is advantageous because the soil displaced by driving the piles
compresses the surrounding soil, causing greater friction against the sides of the piles, thus
increasing their load-bearing capacity. Driven piles are also considered to be "tested" for weightbearing ability because of their method of installation; thus the motto of the Pile Driving Contractors'
Association is "A Driven Pile...Is a Tested Pile!".[1]
Pile foundation systems[edit]
Foundations relying on driven piles often have groups of piles connected by a pile cap (a large
concrete block into which the heads of the piles are embedded) to distribute loads which are larger
than one pile can bear. Pile caps and isolated piles are typically connected withgrade beams to tie
the foundation elements together; lighter structural elements bear on the grade beams, while heavier
elements bear directly on the pile cap.[citation needed]
Monopile foundation[edit]
A monopile foundation utilizes a single, generally large-diameter, foundation structural element to
support all the loads (weight, wind, etc.) of a large above-surface structure.
A large number of monopile foundations[2] have been utilized in recent years for economically
constructing fixed-bottom offshore wind farms in shallow-water subsea locations.[3] For example,
the Horns Rev wind farm from 2002 in the North Sea west of Denmark utilizes 80 large monopiles of
4 metres diameter sunk 25 meters deep into the seabed, [4] while the Lynn and Inner Dowsing Wind
Farm off the coast of England went online in 2008 with over 100 turbines, each mounted on a 4.7metre-diameter monopile foundation in ocean depths up to 18 metres of water.[5]
The typical construction process for a wind turbine subsea monopile foundation in sand includes
driving a large hollow steel pile, of some 4 m in diameter with approximately 2-inch-thick walls, some
25 m deep into the seabed, through a 0.5 m layer of larger stone and gravel to minimize erosion
around the pile. A "transition piece (complete with pre-installed features such as boat-landing
arrangement, cathodic protection, cable ducts for sub-marine cables, turbine tower flange, etc.)" is
attached to the now deeply driven pile, the sand and water are removed from the centre of the pile
and replaced with concrete. An additional layer of even larger stone, up to 0.5 m diameter, is applied
to the surface of the seabed for longer-term erosion protection. [3]
Drilled piles[edit]
A pile machine in Amsterdam, theNetherlands.
Also called caissons, drilled shafts, drilled piers, Cast-in-drilled-hole piles (CIDH piles) or Castin-Situ piles. Rotary boring techniques are larger diameter piles than any other piling method and
permit pile construction through particularly dense or hard strata. Construction methods depend on
the geology of the site. In particular, whether boring is to be undertaken in 'dry' ground conditions or
through water-logged but stable strata - i.e. 'wet boring'.
For end-bearing piles, drilling continues until the borehole has extended a sufficient depth
(socketing) into a sufficiently strong layer. Depending on site geology, this can be a rock layer, or
hardpan, or other dense, strong layers. Both the diameter of the pile and the depth of the pile are
highly specific to the ground conditions, loading conditions, and nature of the project. [citation needed]
Drilled piles can be tested using a variety of methods to verify the pile integrity during installation.
Under reamed piles[edit]
Underreamed piles have mechanically formed enlarged bases that have been as much as 6 m in
diameter. The form is that of an inverted cone and can only be formed in stable soils. The larger
base diameter allows greater bearing capacity than a straight-shaft pile. [citation needed]
These pile are suited for expansive soils which are often subjected to seasonal moisture variations,
as also filled up ground and loose or soft strata. They are used in normal ground condition also
where economics are favorable. [6][full citation needed]
Augercast pile[edit]
An augercast pile, often known as a continuous flight augering (CFA) pile, is formed by drilling into
the ground with a hollow stemmed continuous flight auger to the required depth or degree of
resistance. No casing is required. A cement grout mix is then pumped down the stem of the auger.
While the cement grout is pumped, the auger is slowly withdrawn, conveying the soil upward along
the flights. A shaft of fluid cement grout is formed to ground level. Reinforcement can be installed.
Recent innovations in addition to stringent quality control allows reinforcing cages to be placed up to
the full length of a pile when required. A typical reinforcing cage will consist of 4 to 8 bars from #5 to
#8 bars typically 1/3 the length of the pile with longitudinal circular ties spaced along the length of the
cage. Where tension loads are present it is typical to see a single full length bar placed at the center
of each pile.
Augercast piles cause minimal disturbance, and are often used for noise and environmentally
sensitive sites. Augercast piles are not generally suited for use in contaminated soils, due to
expensive waste disposal costs. In cases such as these however a displacement pile may provide
the cost efficiency of an augercast pile and minimal environmental impact. In ground containing
obstructions or cobbles and boulders, augercast piles are less suitable as refusal above the design
pile tip elevation may be encountered. In certain cases drill motors that produce more torque and
horsepower may be able to mitigate these events.[citation needed]
Pier and grade beam foundation[edit]
In drilled pier foundations, the piers can be connected with grade beams on which the structure sits,
sometimes with heavy column loads bearing directly on the piers. In some residential construction,
the piers are extended above the ground level and wood beams bearing on the piers are used to
support the structure. This type of foundation results in a crawl space underneath the building in
which wiring and duct work can be laid during construction or re-modelling. [7]
Drilled Pier vs. Drilled Pile[edit]
There is a difference between the terms "drilled pier" and "drilled pile".
Drilled Pier
Consists of concrete and a rebar cage
CSL testing is performed
May or may not have permanent/temporary casing
Drilled Pile
Consists of concrete, a pile, and may or may not have a rebar cage
CSL tests are not typically performed
May or may not have permanent/temporary casing
Speciality piles[edit]
Micropiles[edit]
Micropiles, also called mini piles, are often used for underpinning. They are also used to create
foundations for a variety of project types, including highway, bridge andtransmission tower projects.
They are especially useful at sites with difficult or restricted access, or with environmental sensitivity.
[8][9]
Micropiles are made of steel with diameters of 60 to 200 mm. Installation of micropiles through
top soil, sand and cobblestones overburden and into soil rock can be achieved using Air Rotary or
Mud Rotary drilling, impact driving, jacking, vibrating or screwing machinery.[10]
Tripod piles[edit]
The use of a tripod rig to install piles is one of the more traditional ways of forming piles. Although
unit costs are generally higher than with most other forms of piling, [citation needed]it has several advantages
which have ensured its continued use through to the present day. The tripod system is easy and
inexpensive to bring to site, making it ideal for jobs with a small number of piles.
Sheet piles[edit]
Sheet piles are used to restrain soft soil above the bedrock in this excavation
Sheet piling is a form of driven piling using thin interlocking sheets of steel to obtain a continuous
barrier in the ground. The main application of sheet piles is in retaining walls and cofferdams erected
to enable permanent works to proceed. Normally, vibrating hammer, t-crane and crawle drilling are
used to establish sheet piles.[citation needed]
Soldier piles[edit]
A soldier pile wall using reclaimed railway sleepers as lagging.
Soldier piles, also known as king piles or Berlin walls, are constructed of wide flange steel H
sections spaced about 2 to 3 m apart and are driven prior to excavation. As the excavation
proceeds, horizontal timber sheeting (lagging) is inserted behind the H pile flanges.
The horizontal earth pressures are concentrated on the soldier piles because of their relative rigidity
compared to the lagging. Soil movement and subsidence is minimized by maintaining the lagging in
firm contact with the soil.[citation needed]
Soldier piles are most suitable in conditions where well constructed walls will not result in
subsidence such as over-consolidated clays, soils above the water table if they have some
cohesion, and free draining soils which can be effectively dewatered, like sands. [citation needed]
Unsuitable soils include soft clays and weak running soils that allow large movements such as loose
sands. It is also not possible to extend the wall beyond the bottom of the excavation and dewatering
is often required.[citation needed]
Suction Piles[edit]
Suction piles are used underwater to secure floating platforms. Tubular piles are driven into the
seabed (or more commonly dropped a few metres into a soft seabed) and then a pump sucks water
out at the top of the tubular, pulling the pile further down.
The proportions of the pile (diameter to height) are dependent upon the soil type: Sand is difficult to
penetrate but provides good holding capacity, so the height may be as short as half the diameter;
Clays and muds are easy to penetrate but provide poor holding capacity, so the height may be as
much as eight times the diameter. The open nature of gravel means that water would flow through
the ground during installation, causing 'piping' flow (where water boils up through weaker paths
through the soil). Therefore suction piles cannot be used in gravel seabeds. [citation needed]
Adfreeze Piles[edit]
Adfreeze Piles supporting a building in Barrow, Alaska, United States
In high latitudes where the ground is continuously frozen, adfreeze piles are used as the primary
structural foundation method.
Adfreeze piles derive their strength from the bond of the frozen ground around them to the surface of
the pile.[citation needed]
Adfreeze pile foundations are particularly sensitive in conditions which cause the permafrost to melt.
If a building is constructed improperly, it will heat the ground below resulting in a failure of the
foundation system.[citation needed]
Vibrated stone columns[edit]
Vibrated stone columns are a ground improvement technique where columns of
coarse aggregate ("stone") are placed in soils with poordrainage or bearing capacity to improve the
soils.[11]
Piled walls[edit]
Sheet piling, by a bridge, was used to block a canal in New Orleans, United States after Hurricane
Katrina damaged it.
These methods of retaining wall construction employ bored piling techniques - normally CFA or
rotary. They provide special advantages where available working space dictates that basement
excavation faces be vertical. Both methods offer technically effective and cost efficient temporary or
permanent means of retaining the sides of bulk excavations even in water bearing strata. When
used in permanent works, these walls can be designed to accommodate vertical loads in addition
to moments and horizontal forces.Construction of both methods is the same as for foundation
bearing piles. Contiguous walls are constructed with small gaps between adjacent piles. The size of
this space is determined by the nature of the soils.
Secant piled walls[edit]
Secant pile walls are constructed such that space is left between alternate 'female' piles for the
subsequent construction of 'male' piles. Construction of 'male' piles involves boring through the
concrete in the 'female' piles hole in order to key 'male' piles between. The male pile is the one
where steel reinforcement cages are installed, though in some cases the female piles are also
reinforced.
Secant piled walls can either be true hard/hard, hard/intermediate (firm), or hard/soft, depending on
design requirements. Hard refers to structural concrete and firm or soft is usually a weaker grout mix
containing bentonite.
All types of wall can be constructed as free standing cantilevers, or may be propped if space and
sub-structure design permit. Where party wall agreements allow, ground anchors can be used as tie
backs.
Slurry walls[edit]
A slurry wall is a barrier built under ground using a mix of bentonite and water to prevent the flow of
groundwater. A trench that would collapse due to the hydraulic pressure in the surrounding soil does
not collapse as the slurry balances the hydraulic pressure.
Deep mixing/mass stabilization techniques[edit]
These are essentially variations of in situ reinforcements in the form of piles (as mentioned above),
blocks or larger volumes.
Cement, lime/quick lime, flyash, sludge and/or other binders (sometimes called stabilizer) are mixed
into the soil to increase bearing capacity. The result is not as solid as concrete, but should be seen
as an improvement of the bearing capacity of the original soil.
The technique is most often applied on clays or organic soils like peat. The mixing can be carried out
by pumping the binder into the soil whilst mixing it with a device normally mounted on an excavator
or by excavating the masses, mixing them separately with the binders and refilling them in the
desired area. The technique can also be used on lightly contaminated masses as a means of
binding contaminants, as opposed to excavating them and transporting to landfill or processing.
Classification of pile with respect to type of material [edit]
Timber[edit]
As the name implies, timber piles are made of wood.
Historically, timber has been a plentiful, locally available resource in many areas. Today, timber piles
are still more affordable than concrete or steel. Compared to other types of piles (steel or concrete),
and depending on the source/type of timber, timber piles may not be suitable for heavier loads.
A main consideration regarding timber piles is that they should be protected
from rotting above groundwater level. Timber will last for a long time below the groundwater level.
For timber to rot, two elements are needed: water and oxygen. Below the groundwater level,
dissolved oxygen is lacking even though there is ample water. Hence, timber tends to last for a long
time below groundwater level. In 1648 the Royal Palace of Amsterdam was constructed on 13659
timber piles that still survive today since they were below groundwater level. Timber that is to be
used above the water table can be protected from decay and insects by numerous forms of wood
preservation using pressure treatment (alkaline copper quaternary (ACQ), chromated copper
arsenate (CCA), creosote, etc.).
Splicing timber piles is still quite common and is the easiest of all the piling materials to splice. The
normal method for splicing is by driving the leader pile first, driving a steel tube (normally 60–100 cm
long, with an internal diameter no smaller than the minimum toe diameter) half its length onto the
end of the leader pile. The follower pile is then simply slotted into the other end of the tube and
driving continues. The steel tube is simply there to ensure that the two pieces follow each other
during driving. If uplift capacity is required, the splice can incorporate bolts, coach screws, spikes or
the like to give it the necessary capacity.
shallow foundation, but some of the common reasons are very large design loads, a poor soil at
shallow depth, or site constraints (like property lines). There are different terms used to describe
different types of deep foundations including the pile (which is analogous to a pole), the pier (which
is analogous to a column), drilled shafts, and caissons. Piles are generally driven into the ground in
situ; other deep foundations are typically put in place using excavation and drilling. The naming
conventions may vary between engineering disciplines and firms. Deep foundations can be made
out of timber, steel, reinforced concrete and prestressed concrete.
Contents
[hide]
1 Driven foundations
o
1.1 Pile foundation systems
o
1.2 Monopile foundation
2 Drilled piles
o
2.1 Under reamed piles
o
2.2 Augercast pile
o
2.3 Pier and grade beam foundation
o
2.4 Drilled Pier vs. Drilled Pile
3 Speciality piles
o
3.1 Micropiles
o
3.2 Tripod piles
o
3.3 Sheet piles
o
3.4 Soldier piles
o
3.5 Suction Piles
o
3.6 Adfreeze Piles
o
3.7 Vibrated stone columns
4 Piled walls
o
4.1 Secant piled walls
o
4.2 Slurry walls
5 Deep mixing/mass stabilization techniques
6 Classification of pile with respect to type of material
o
6.1 Timber
o
6.2 Steel
o
6.3 Prestressed concrete piles
o
6.4 Composite piles
7 See also
8 Notes
9 References
10 External links
Driven foundations[edit]
Pipe piles being driven into the ground
Illustration of a hand-operated pile driver in Germany after 1480.
Prefabricated piles are driven into the ground using a pile driver. Driven piles are
either wood, reinforced concrete, or steel. Wooden piles are made from the trunks of tall trees.
Concrete piles are available in square, octagonal, and round cross-sections (like Franki Piles). They
are reinforced with rebar and are often prestressed. Steel piles are either pipe piles or some sort of
beam section (like an H-pile). Historically, wood piles used splices to join multiple segments end-toend when the driven depth required was too long for a single pile; today, splicing is common
with steel piles, though concrete piles can be spliced with mechanical and other means. Driving
piles, as opposed to drilling shafts, is advantageous because the soil displaced by driving the piles
compresses the surrounding soil, causing greater friction against the sides of the piles, thus
increasing their load-bearing capacity. Driven piles are also considered to be "tested" for weightbearing ability because of their method of installation; thus the motto of the Pile Driving Contractors'
Association is "A Driven Pile...Is a Tested Pile!".[1]
Pile foundation systems[edit]
Foundations relying on driven piles often have groups of piles connected by a pile cap (a large
concrete block into which the heads of the piles are embedded) to distribute loads which are larger
than one pile can bear. Pile caps and isolated piles are typically connected withgrade beams to tie
the foundation elements together; lighter structural elements bear on the grade beams, while heavier
elements bear directly on the pile cap.[citation needed]
Monopile foundation[edit]
A monopile foundation utilizes a single, generally large-diameter, foundation structural element to
support all the loads (weight, wind, etc.) of a large above-surface structure.
A large number of monopile foundations[2] have been utilized in recent years for economically
constructing fixed-bottom offshore wind farms in shallow-water subsea locations.[3] For example,
the Horns Rev wind farm from 2002 in the North Sea west of Denmark utilizes 80 large monopiles of
4 metres diameter sunk 25 meters deep into the seabed, [4] while the Lynn and Inner Dowsing Wind
Farm off the coast of England went online in 2008 with over 100 turbines, each mounted on a 4.7metre-diameter monopile foundation in ocean depths up to 18 metres of water.[5]
The typical construction process for a wind turbine subsea monopile foundation in sand includes
driving a large hollow steel pile, of some 4 m in diameter with approximately 2-inch-thick walls, some
25 m deep into the seabed, through a 0.5 m layer of larger stone and gravel to minimize erosion
around the pile. A "transition piece (complete with pre-installed features such as boat-landing
arrangement, cathodic protection, cable ducts for sub-marine cables, turbine tower flange, etc.)" is
attached to the now deeply driven pile, the sand and water are removed from the centre of the pile
and replaced with concrete. An additional layer of even larger stone, up to 0.5 m diameter, is applied
to the surface of the seabed for longer-term erosion protection. [3]
Drilled piles[edit]
A pile machine in Amsterdam, theNetherlands.
Also called caissons, drilled shafts, drilled piers, Cast-in-drilled-hole piles (CIDH piles) or Castin-Situ piles. Rotary boring techniques are larger diameter piles than any other piling method and
permit pile construction through particularly dense or hard strata. Construction methods depend on
the geology of the site. In particular, whether boring is to be undertaken in 'dry' ground conditions or
through water-logged but stable strata - i.e. 'wet boring'.
For end-bearing piles, drilling continues until the borehole has extended a sufficient depth
(socketing) into a sufficiently strong layer. Depending on site geology, this can be a rock layer, or
hardpan, or other dense, strong layers. Both the diameter of the pile and the depth of the pile are
highly specific to the ground conditions, loading conditions, and nature of the project. [citation needed]
Drilled piles can be tested using a variety of methods to verify the pile integrity during installation.
Under reamed piles[edit]
Underreamed piles have mechanically formed enlarged bases that have been as much as 6 m in
diameter. The form is that of an inverted cone and can only be formed in stable soils. The larger
base diameter allows greater bearing capacity than a straight-shaft pile. [citation needed]
These pile are suited for expansive soils which are often subjected to seasonal moisture variations,
as also filled up ground and loose or soft strata. They are used in normal ground condition also
where economics are favorable. [6][full citation needed]
Augercast pile[edit]
An augercast pile, often known as a continuous flight augering (CFA) pile, is formed by drilling into
the ground with a hollow stemmed continuous flight auger to the required depth or degree of
resistance. No casing is required. A cement grout mix is then pumped down the stem of the auger.
While the cement grout is pumped, the auger is slowly withdrawn, conveying the soil upward along
the flights. A shaft of fluid cement grout is formed to ground level. Reinforcement can be installed.
Recent innovations in addition to stringent quality control allows reinforcing cages to be placed up to
the full length of a pile when required. A typical reinforcing cage will consist of 4 to 8 bars from #5 to
#8 bars typically 1/3 the length of the pile with longitudinal circular ties spaced along the length of the
cage. Where tension loads are present it is typical to see a single full length bar placed at the center
of each pile.
Augercast piles cause minimal disturbance, and are often used for noise and environmentally
sensitive sites. Augercast piles are not generally suited for use in contaminated soils, due to
expensive waste disposal costs. In cases such as these however a displacement pile may provide
the cost efficiency of an augercast pile and minimal environmental impact. In ground containing
obstructions or cobbles and boulders, augercast piles are less suitable as refusal above the design
pile tip elevation may be encountered. In certain cases drill motors that produce more torque and
horsepower may be able to mitigate these events.[citation needed]
Pier and grade beam foundation[edit]
In drilled pier foundations, the piers can be connected with grade beams on which the structure sits,
sometimes with heavy column loads bearing directly on the piers. In some residential construction,
the piers are extended above the ground level and wood beams bearing on the piers are used to
support the structure. This type of foundation results in a crawl space underneath the building in
which wiring and duct work can be laid during construction or re-modelling. [7]
Drilled Pier vs. Drilled Pile[edit]
There is a difference between the terms "drilled pier" and "drilled pile".
Drilled Pier
Consists of concrete and a rebar cage
CSL testing is performed
May or may not have permanent/temporary casing
Drilled Pile
Consists of concrete, a pile, and may or may not have a rebar cage
CSL tests are not typically performed
May or may not have permanent/temporary casing
Speciality piles[edit]
Micropiles[edit]
Micropiles, also called mini piles, are often used for underpinning. They are also used to create
foundations for a variety of project types, including highway, bridge andtransmission tower projects.
They are especially useful at sites with difficult or restricted access, or with environmental sensitivity.
[8][9]
Micropiles are made of steel with diameters of 60 to 200 mm. Installation of micropiles through
top soil, sand and cobblestones overburden and into soil rock can be achieved using Air Rotary or
Mud Rotary drilling, impact driving, jacking, vibrating or screwing machinery.[10]
Tripod piles[edit]
The use of a tripod rig to install piles is one of the more traditional ways of forming piles. Although
unit costs are generally higher than with most other forms of piling, [citation needed]it has several advantages
which have ensured its continued use through to the present day. The tripod system is easy and
inexpensive to bring to site, making it ideal for jobs with a small number of piles.
Sheet piles[edit]
Sheet piles are used to restrain soft soil above the bedrock in this excavation
Sheet piling is a form of driven piling using thin interlocking sheets of steel to obtain a continuous
barrier in the ground. The main application of sheet piles is in retaining walls and cofferdams erected
to enable permanent works to proceed. Normally, vibrating hammer, t-crane and crawle drilling are
used to establish sheet piles.[citation needed]
Soldier piles[edit]
A soldier pile wall using reclaimed railway sleepers as lagging.
Soldier piles, also known as king piles or Berlin walls, are constructed of wide flange steel H
sections spaced about 2 to 3 m apart and are driven prior to excavation. As the excavation
proceeds, horizontal timber sheeting (lagging) is inserted behind the H pile flanges.
The horizontal earth pressures are concentrated on the soldier piles because of their relative rigidity
compared to the lagging. Soil movement and subsidence is minimized by maintaining the lagging in
firm contact with the soil.[citation needed]
Soldier piles are most suitable in conditions where well constructed walls will not result in
subsidence such as over-consolidated clays, soils above the water table if they have some
cohesion, and free draining soils which can be effectively dewatered, like sands. [citation needed]
Unsuitable soils include soft clays and weak running soils that allow large movements such as loose
sands. It is also not possible to extend the wall beyond the bottom of the excavation and dewatering
is often required.[citation needed]
Suction Piles[edit]
Suction piles are used underwater to secure floating platforms. Tubular piles are driven into the
seabed (or more commonly dropped a few metres into a soft seabed) and then a pump sucks water
out at the top of the tubular, pulling the pile further down.
The proportions of the pile (diameter to height) are dependent upon the soil type: Sand is difficult to
penetrate but provides good holding capacity, so the height may be as short as half the diameter;
Clays and muds are easy to penetrate but provide poor holding capacity, so the height may be as
much as eight times the diameter. The open nature of gravel means that water would flow through
the ground during installation, causing 'piping' flow (where water boils up through weaker paths
through the soil). Therefore suction piles cannot be used in gravel seabeds. [citation needed]
Adfreeze Piles[edit]
Adfreeze Piles supporting a building in Barrow, Alaska, United States
In high latitudes where the ground is continuously frozen, adfreeze piles are used as the primary
structural foundation method.
Adfreeze piles derive their strength from the bond of the frozen ground around them to the surface of
the pile.[citation needed]
Adfreeze pile foundations are particularly sensitive in conditions which cause the permafrost to melt.
If a building is constructed improperly, it will heat the ground below resulting in a failure of the
foundation system.[citation needed]
Vibrated stone columns[edit]
Vibrated stone columns are a ground improvement technique where columns of
coarse aggregate ("stone") are placed in soils with poordrainage or bearing capacity to improve the
soils.[11]
Piled walls[edit]
Sheet piling, by a bridge, was used to block a canal in New Orleans, United States after Hurricane
Katrina damaged it.
These methods of retaining wall construction employ bored piling techniques - normally CFA or
rotary. They provide special advantages where available working space dictates that basement
excavation faces be vertical. Both methods offer technically effective and cost efficient temporary or
permanent means of retaining the sides of bulk excavations even in water bearing strata. When
used in permanent works, these walls can be designed to accommodate vertical loads in addition
to moments and horizontal forces.Construction of both methods is the same as for foundation
bearing piles. Contiguous walls are constructed with small gaps between adjacent piles. The size of
this space is determined by the nature of the soils.
Secant piled walls[edit]
Secant pile walls are constructed such that space is left between alternate 'female' piles for the
subsequent construction of 'male' piles. Construction of 'male' piles involves boring through the
concrete in the 'female' piles hole in order to key 'male' piles between. The male pile is the one
where steel reinforcement cages are installed, though in some cases the female piles are also
reinforced.
Secant piled walls can either be true hard/hard, hard/intermediate (firm), or hard/soft, depending on
design requirements. Hard refers to structural concrete and firm or soft is usually a weaker grout mix
containing bentonite.
All types of wall can be constructed as free standing cantilevers, or may be propped if space and
sub-structure design permit. Where party wall agreements allow, ground anchors can be used as tie
backs.
Slurry walls[edit]
A slurry wall is a barrier built under ground using a mix of bentonite and water to prevent the flow of
groundwater. A trench that would collapse due to the hydraulic pressure in the surrounding soil does
not collapse as the slurry balances the hydraulic pressure.
Deep mixing/mass stabilization techniques[edit]
These are essentially variations of in situ reinforcements in the form of piles (as mentioned above),
blocks or larger volumes.
Cement, lime/quick lime, flyash, sludge and/or other binders (sometimes called stabilizer) are mixed
into the soil to increase bearing capacity. The result is not as solid as concrete, but should be seen
as an improvement of the bearing capacity of the original soil.
The technique is most often applied on clays or organic soils like peat. The mixing can be carried out
by pumping the binder into the soil whilst mixing it with a device normally mounted on an excavator
or by excavating the masses, mixing them separately with the binders and refilling them in the
desired area. The technique can also be used on lightly contaminated masses as a means of
binding contaminants, as opposed to excavating them and transporting to landfill or processing.
Classification of pile with respect to type of material [edit]
Timber[edit]
As the name implies, timber piles are made of wood.
Historically, timber has been a plentiful, locally available resource in many areas. Today, timber piles
are still more affordable than concrete or steel. Compared to other types of piles (steel or concrete),
and depending on the source/type of timber, timber piles may not be suitable for heavier loads.
A main consideration regarding timber piles is that they should be protected
from rotting above groundwater level. Timber will last for a long time below the groundwater level.
For timber to rot, two elements are needed: water and oxygen. Below the groundwater level,
dissolved oxygen is lacking even though there is ample water. Hence, timber tends to last for a long
time below groundwater level. In 1648 the Royal Palace of Amsterdam was constructed on 13659
timber piles that still survive today since they were below groundwater level. Timber that is to be
used above the water table can be protected from decay and insects by numerous forms of wood
preservation using pressure treatment (alkaline copper quaternary (ACQ), chromated copper
arsenate (CCA), creosote, etc.).
Splicing timber piles is still quite common and is the easiest of all the piling materials to splice. The
normal method for splicing is by driving the leader pile first, driving a steel tube (normally 60–100 cm
long, with an internal diameter no smaller than the minimum toe diameter) half its length onto the
end of the leader pile. The follower pile is then simply slotted into the other end of the tube and
driving continues. The steel tube is simply there to ensure that the two pieces follow each other
during driving. If uplift capacity is required, the splice can incorporate bolts, coach screws, spikes or
the like to give it the necessary capacity.
