Note: Descriptions are shown in the official language in which they were submitted.
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IMPROVEMENTS IN AND RELATING TO PILE FOUNDATIONS
Field of the Invention
The present invention concerns piles. More particularly, but not exclusively,
this invention concerns a pile within a bore and a method and a kit of parts
for
forming the same. The invention also concerns a building including a pile
within a
bore and a method of forming the same.
Background of the Invention
Piles are deep foundations providing support for buildings or other
structures.
They are typically long, narrow columns of reinforced concrete or steel. Prior-
art
piles include pre-cast concrete piles that are driven into the ground using a
pile-driver
and cast solid concrete piles that are formed by digging a bore in the ground
(typically
using an auger), pouring concrete directly into the hole and allowing it to
set.
WO 2008/047151 Al (City University) discloses a method of forming a pile
comprising: forming a bore in the ground to a required depth; disposing a
cylinder in
the bore; filling the bore with uncast concrete so that, on hardening, a cast
concrete
pile is formed in the bore, the pile having a longitudinal cavity permitting
access to
the pile along at least a portion of its length. The longitudinal cavity is
sufficiently
wide to allow access to the longitudinal cavity so that cast concrete can be
tested at a
time after construction.
The approach in WO 2008/047151 can be relatively time-consuming. There
also is a risk that voids or other faults will form in the pile when it is
cast
underground, as the bore in which it is cast can have unpredictable or
unhelpful wall
properties. Voids or other faults can result in weaknesses in the cast
concrete pile.
Although the longitudinal cavity provides some access for testing the cast
concrete,
there remains a risk that faults go undetected.
The present invention seeks to mitigate the above-mentioned problems.
Summary of the Invention
A first aspect of the invention provides a method of forming a pile within a
bore, the method comprising:
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stacking a plurality of hollow pile sections end-to-end within the bore to
form
a column, there being a gap between at least a part of an outside surface of
the column
and the surface of the bore;
filling the gap with a curable liquid material ; and
curing the liquid material.
A second aspect of the invention provides a method of constructing a building,
the method including forming a pile within a bore by the method of the first
aspect of
the invention.
A third aspect of the invention provides a pile within a bore, the pile within
a
bore having the features set out in claim 8 below.
A fourth aspect of the invention provides a building including a pile within a
bore according to the third aspect of the invention.
A fifth aspect of the invention provides a kit of parts having the features
set
out in claim 15 below.
It will of course be appreciated that features described in relation to one
aspect
of the present disclosure may be incorporated into other aspects of the
present
disclosure. For example, the method of the present disclosure may incorporate
any of
the features described with reference to the apparatus of the present
disclosure and
vice versa.
Description of the Drawings
Embodiments of the present disclosure will now be described by way of
example only with reference to the accompanying schematic drawings of which:
FIGS. la to lh are a sequence of side views of a pile being formed, according
to a
first embodiment of the present disclosure;
FIG. 2 is a perspective view of a pile section according to a second
embodiment of
the present disclosure;
FIG. 3 is a perspective view of a pile section according to a third embodiment
of
the present disclosure;
FIG. 4 is a perspective view of a pile section according to a fourth
embodiment of
the present disclosure;
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FIG. 5 is a side view of a pair of pile sections according to a fifth
embodiment of
the present disclosure;
FIG. 6 is a plan view of a pile section according to a sixth embodiment of the
present disclosure; and
FIG. 7 is a plan view of a pile section according to a seventh embodiment of
the
present disclosure;
Detailed Description
A first aspect of the invention provides a method of forming a pile within a
bore, the
method comprising:
stacking a plurality of hollow pile sections end-to-end within the bore to
form
a column,
there being a gap between at least a part of an outside surface of the
column and the surface of the bore;
filling the gap with a curable liquid material; and
curing the liquid material.
The pile sections may be tubular pile sections; thus, the column may be a
tube.
The pile sections are preferably concrete. The pile sections are preferably
pre-formed
(for example pre-cast) at a location remote from the location at which the
pile is to be
formed. The method may comprise the step of receiving the pile sections from a
remote location.
The surface of the bore will be understood to be the surface of the
surrounding
soil into which the bore is made (typically longitudinally and
circumferentially
extending).
The method may include the step of joining together a plurality of section
components to form each pile section. The section components are preferably
pre-
formed (for example pre-cast) at a location remote from the location at which
the pile
is to be formed. The method may comprise the step of receiving the plurality
of
section components from a remote location, and then joining together the
plurality of
section components to form each pile section.
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The curable liquid, when in place and cured, is preferably configured to
transfer the skin friction generated at the interface with the pile bore to
the interface
between the grout and the sections of the pile.
The curable liquid material may be grout. The grout may comprise reinforcing
material. Alternatively, the curable liquid material may be for example resin.
Advantageously, grout is not concrete. Providing a pile formed from a stack of
pile
sections and then filling the gap between the pile and the bore, with the
curable liquid,
has been found to be especially advantageous because it tends to be possible
to use on
a variety of soil types (whereas the pile in WO 2008/047151 tends to be
limited to use
of clay soils).
The method may include the step of pouring the curable liquid material
directly into the gap. The curable liquid material may be inserted under
relatively low
pressure.
The method may comprise the step of applying additional curable liquid
material after the previous liquid material has cured. The additional curable
liquid
material may be supplied at relatively high pressure, for example such that it
cracks
and percolates through the first cured material. This step may be advantageous
on
fine soils as it enables the additional curable liquid to percolate into the
soil. The
additional curable liquid material may be grout, preferably finer grout than
the first
curable liquid material.
The method may include the step of directing the curable liquid material into
the gap through channels in the sections. The stacking may include aligning
the
channels of one section with the channels of an adjacent section, such that
the liquid
material may flow from the channel in one section to the channel in an
adjacent
section. Alignment may be achieved visually but is more preferably achieved
via an
alignment arrangement (such as interlocking male and female members located at
a
common location on the opposing ends of the adjacent pile sections). The
adjacent
pile sections may be configured to be self-aligning (for example they may
comprise
suitable inclined surfaces to ensure correct alignment as the adjacent
sections are
stacked together).
The method may include the step of digging the bore, for example using an
auger.
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The method may include the step of forming impressions into the interior wall
of the bore.
The method may include lowering the pile sections into the bore sequentially,
for example one-at-a-time.
The column may have a length that is substantially the same as the depth of
the bore. The column may be shorter than the depth of the bore. The column may
for
example have a length that is between half the depth of the bore, and the full
depth of
the bore. Alternatively, the column may be longer than the depth of the bore.
The column may have a length that is more than three times its breadth.
The gap may be continuous. The gap may extend across the majority,
(preferably, all or substantially all) of the outside surface of the column
and the
surface of the bore. The gap may be substantially uniform around the outside
surface
of the column.
The curable liquid material may fill all or substantially all of the gap.
The method may comprise the step of installing a pile cap on the top of the
final pile section to close off the top of the stack of pile sections. The
method may
comprise the step of selecting the pile cap from a plurality of differently-
sized (more
preferably different length) pile caps. The pile caps may be pre-cast. This
may
ensure the correct height of the pile may be obtained (for example a
relatively short
cap can be provided if the stack of pile sections is relatively tall in the
bore, and
likewise a relatively long cap can be provided if the stack of pile sections
is relatively
short in the bore).
Before placing the stack of pile sections into the bore, the method may
comprise the step of initially installing a pile base piece in the base of the
bore, to
close off the base of the pile. The pile base piece may facilitate increased
end bearing
resistance of the pile. The pile base piece may be shaped to facilitate
increased end
bearing resistance of the pile.
A second aspect of the invention provides a method of constructing a building,
the method including forming a pile within a bore by the above-mentioned
method.
A third aspect of the invention provides a pile within a bore, comprising:
a column comprising a stack of a plurality of pile sections arranged end-to-
end within
the bore, and a cured material between at least a part of an outside surface
of the
column and the surface of the bore.
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The plurality of pile sections may include pile sections that have different
widths from each other. The column may taper in width, for example so that it
has a
smaller width at its base and a larger width at its top (or vice versa). Thus,
the pile
sections forming the column may increase in width with height up the column
(or vice
versa). The pile sections may have the same internal width (e.g. internal
diameter). A
taper in the column may be achieved by varying the thickness of the wall of
adjacent
pile sections. In embodiments comprising a channel configured to allow the
transport
of a curable liquid material along the length of the column, a channel in each
pile
section may be at the same spacing (e.g. radius) from the centre of the
column. That
spacing may be defined by the smallest width pile section.
The pile sections may be tubes. The tubes may have a constant inner width
along the height of the column (even in embodiments in which the outer width
of the
tubes is not the same along the height of the column, for example where the
tubes
forming the column increase in width with height up the column). The tubes may
have an internal width that is at least half their external width.
The pile sections may be circular in cross-section. The pile sections may be
polygonal in cross-section.
The pile sections may comprise elements (for example castellations) at each of
their axial ends, the axial end elements being sized and shaped to interlock
with the
corresponding axial end elements of another of the pile sections.
The pile sections may comprise a plurality of section components. Each pile
section may for example be made from between 2 and 10 section components. The
plurality of section components may be identical to each other. The section
components may be segments of an annulus. Providing section components in each
pile section may facilitate efficient transport of the components of the pile
(compared
to transporting fully assembled, or cast, pile sections).
Each pile section, and preferably each pile section component, may comprise
elements (for example, tongue-and-groove elements) at each axial end, sized
and
shaped to interlock with the corresponding elements of another of the pile
section/pile
section component. The method may comprise the step of j oining adjacent pile
sections together, for example with a fastener.
At least some of the pile sections may include a raised and/or indented
pattern
on their outer surfaces, i.e. a textured pattern. The pattern may be
irregular.
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Alternatively, the pattern may be a regular pattern of repeating shapes. Such
an
arrangement may facilitate effective binding of the curable liquid to the
outer surface
of the sections and/or increase the resistance between the outer surface of
the pile and
the cured liquid. At least some of the sections may include protrusions on
their outer
surface, which may be arranged in a regular pattern. The protrusions may be
dome-
shaped.
At least some of the sections may include channels configured to allow the
transport of a curable liquid material along the length of the column. The
channels
may be within the sections, for example entirely enclosed in the solid
material of the
sections (save at inlets and outlets). The channels may be wholly or partly on
the
surface of the sections, for example the channels may be exposed channels
running
along a face of the sections. The channels may comprise transport channels in
fluid
communication with outlet channels. The transport channels may be vertical.
The
outlet channels may be horizontal. The transport channels may be in fluid
communication with the outlet channels. There may, for example, be a
multiplicity,
for example 1 to 10, transport channels in each pile section. The transport
channels
may be at the same radial position in each pile section in the column.
The hollow pile sections may be concrete, for example pre-cast concrete. Use
of pre-cast concrete has the advantage that the pile sections (or the section
components) can be manufactured remotely from the site of the bore and then
transported to the bore for use. Manufacturing the pile sections (or the
section
components) as pre-cast concrete, before their use in the bore, has the
advantage that
quality checks can be carried out on them before their installation in the
ground. The
pile sections may be reinforced concrete.
A fourth aspect of the invention provides a building including a pile within a
bore, as described herein. The pile may be load-bearing within the building.
A fifth aspect of the invention provides a kit of parts for forming a pile
within
a bore, the kit comprising:
a plurality of pile sections, wherein
the plurality of pile sections are configured to be stacked end-to-end to
form a column,
the number of pile sections corresponds to a length of the column, said
length being equal to at least half of the depth of the bore; and
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a curable liquid material.
The invention will now be more fully understood and further advantages will
become apparent when reference is made to the following detailed description
of
embodiments of the invention, wherein like reference numerals denote similar
elements.
Figs. la to lh show in side view an example embodiment of the method of
forming a pile. In Fig. la, bore 110 has been excavated in the ground 10 using
an
auger (not shown), which has been operated by piling rig 100. Piling rig 100
includes
attachment point 102 that is used to attach various apparatus that is to be
lowered into
bore 110. (For example, the auger was attached to attachment point 102 during
the
digging of the bore 110).
In Fig. lb, impression-forming attachment 104 is attached to attachment point
102 and is lowered into bore 110. Impression-forming attachment 104 comprises
a
plurality of impression-forming elements 106 that are configured to form
impressions
in the interior wall of bore 110 when impression-forming attachment 104 is
actuated
to expand outwards in a radial direction. The actuation and expansion of
impression
forming attachment 104 is shown in Fig. lc. Impression forming elements 106
are
pressed into the wall of bore 110 to form impressions 112. Impression forming
attachment 104 is then withdrawn from bore 110 by piling rig 100 as shown in
Fig.
.. ld. The result of this operation as shown in Figs. lb to ld is that
impressions 112 are
formed in the wall of bore 110.
An advantageous effect of impressions 112 is that when the pile is finally
constructed, the skin friction between the pile and the bore is increased,
thereby
increasing the pull-out resistance and/or providing a piling structure that
better reacts
loads into the ground. However, this feature is not essential to the invention
and in
alternative embodiments of the present disclosure, the steps of Figs. lb to ld
may be
omitted, and substantially no impressions are formed in the wall of bore 110.
In Fig. le, pile section 200a has been attached to attachment point 102. Pile
section 200a is a hollow cylinder of prefabricated concrete. Piling rig 100
lowers pile
section 200a into bore 110 as indicated by directional arrow 105.
Successive pile sections 200b, 200c, 200d, 200e are attached to attachment
point 102 and lowered into bore 110 respectively in turn. As shown in Fig. lf,
each
successive pile section is stacked on top of the previous section to form
vertical
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column 250. Dashed line 202 indicated the continuous inner surface of hollow
column 250. The size of pile sections 200a-200e is selected such that when
pile
sections 200a-200e are stacked to form column 250, there is a gap 114 between
the
outer surface of column 250 and the inner surface of bore 110.
While column 250 has a length that is substantially the same as the height of
bore 110, in alternative embodiments of the present disclosure column 250 may
have
a length that is shorter than the height of the bore, for example, to leave
some space at
the top of bore 110 for other structural features in the construction. Indeed,
the length
of column 250 may correspond to between half the height of bore 110, and the
full
height of bore 110. In alternative embodiments of the present disclosure, the
length of
column 250 may correspond to a height greater than the height of bore 110.
Fig. lg shows that grout 260 is poured into gap 114. The insertion of grout
260 is indicated by directional arrow 113.
Fig. lh shows that grout 260 has filled gap 114, including impressions 112
within the wall of bore 110. This forms completed pile 270. In alternative
embodiments of the present disclosure, grout 260 may be an alternative curable
liquid
material, for example a resin. An advantage of grout is that it is light and
cheap, and
has relatively low viscosity (compared to more coarse materials such as
concrete).
Column 250 is formed of concrete and can bear the majority of the primary
longitudinal loads from any construction above. The grout is arranged to
transfer the
skin friction generated at the interface with the pile bore to the interface
between the
grout and the pre-cast sections of the pile (i.e. such that the loads can be
reacted/transferred from the pile to the surrounding soil).
In alternative embodiments of the present disclosure, pile sections 200a-200e
may comprise channels. Grout 260 is poured into the channels within column 250
to
achieve a uniform distribution of grout 260 across the entire length of column
250.
For example, Fig. 2 shows a perspective view of pile section 300 according to
an
embodiment of the present disclosure. Pile section 300 comprises vertical
channels
302 in fluid communication with horizontal channels 304 (shown in dashed lines
in
Figure 2). Vertical channels 302 are designed to allow for a vertical flow of
curable
liquid material through section 300. Horizontal channels 304 allow for the
curable
liquid material to flow out of pile section 300. In embodiments of the present
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disclosure, the curable liquid material would flow out of horizontal channels
304 and
into a gap (such as gap 114 in the embodiments of Figs. la-le).
In alternative embodiments of the present disclosure, vertical channel 302 is
not entirely enclosed in the solid material of pile section 300. Instead
vertical channel
302 may be an exposed channel running along the outside face of pile section
300.
Fig. 3 shows a perspective view of pile section 400 according to an
embodiment of the present disclosure. Pile section 400 comprises textured
pattern
402 on its exterior surface. Textured pattern 402 comprises protrusions that
extend
outwardly from the surface of pile section 400. These protrusions have the
effects of
increasing the friction between the outer surface of pile section 400 and any
grout that
may be in contact with it (such as grout 260 in the embodiments of Figs. la-
lh). In
embodiments of the present disclosure, textured pattern 402 may be irregular.
In
embodiments of the present disclosure, textured pattern 402 may be a regular
pattern
of repeating shapes.
Fig. 4 shows a perspective view of pile section 500 according to an
embodiment of the present disclosure. Pile section 500 comprises regular,
circular -
shaped protrusions 502 at regular intervals around the outer surface of pile
section
500. The function of protrusions 502 are similar to the function of textured
pattern
402 in the embodiment of Fig. 3. In alternative embodiments of the present
disclosure, protrusions 502 may be non-circular but may for example be any
other
regular shape, such as an oval, or square.
Fig. 5 shows a side view of a pair of pile sections 600a, 600b according to an
embodiment of the present disclosure. Each pile section 600a, 600b comprises a
castellations at an axial end. The castellations of first pile section 600a
are sized and
shaped to interlock with the castellations of second pile section 600b. This
is
achieved by the provision of female alignment portion 602a, and the provision
of
male alignment portion 602b. When first pile section 600a is brought together
with
second pile section 600b, the respective alignment portions fit within one
another and
prevents pile sections 600a, 600b from experiencing any radial or
circumferential
displacement. Advantageously, in embodiments in which pile sections 600a, 600b
comprise channels (such as those of Fig. 2), the castellations enable a more
straightforward alignment of the vertical channels of adjoining pile sections.
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Fig. 6 shows a plan view of pile section 700 according to an embodiment of
the present disclosure. Pile section 700 is composed of three equally sized
pre-cast
concrete section components 702, 704, 706. When the section components 702,
704,
706 are assembled together, they form a concrete cylinder that is pile section
700. To
facilitate alignment, each section component comprises protrusion 702b and
recess
702a at each end. Protrusion 702b interlocks with recess 704b of adjacent pile
section
704. Likewise, recess 702a interlocks with protrusion 704a of the same
adjacent pile
section 704. The protrusions and recesses ensure that once the pile sections
are in
position, the pile sections are only free to move in an axial direction, and
are fully
restricted in the radial and circumferential directions. Assembling the pile
section
from a plurality of section components allows the pile sections to be readily
transported (as section components, that can typically be stacked or otherwise
efficiently stored).
Fig. 7 shows a plan view of pile section 800 according to an embodiment of
the present disclosure. Pile section 800 is composed of five equally sized pre-
cast
concrete section components 802, 804, 806, 808, and 810. When the section
components 802, 804, 806, 808, and 810 are assembled together, they form a
hollow
concrete pentagon that is pile section 800.
Whilst the present invention has been described and illustrated with reference
to particular embodiments, it will be appreciated by those of ordinary skill
in the art
that the invention lends itself to many different variations not specifically
illustrated
herein. By way of example only, the pile sections need not necessarily be
circular
cylindrical. The pile sections may be other shapes such as polygonal. It may
be that
the section components of the pile sections are configured such that they can
form
different shaped/sized polygonal sections by altering the angle of the join
between
adjacent section components and/or by choosing differently sized section
components.
Where in the foregoing description, integers or elements are mentioned which
have known, obvious or foreseeable equivalents, then such equivalents are
herein
incorporated as if individually set forth. Reference should be made to the
claims for
determining the true scope of the present invention, which should be construed
so as
to encompass any such equivalents. It will also be appreciated by the reader
that
integers or features of the invention that are described as preferable,
advantageous,
convenient or the like are optional and do not limit the scope of the
independent
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claims. Moreover, it is to be understood that such optional integers or
features, whilst
of possible benefit in some embodiments of the invention, may not be
desirable, and
may therefore be absent, in other embodiments.
