Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to a founda-
tion pile which is set into a hole excavated below to
a permafrost level in the ground, comprising a pre-
fabricated plastic pipe which constitutes a permanent
formwork for the cast concrete pile, and including a
second pipe coaxially surrounding the plastic pipe
such that an annular space is formed between the two
pipes,
Piles of the above type are used as founda-
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tions to support buildings, installations and the
like. Even though the piles are installed below
the permafrost level, the permafrost still exercises
a lifting effect on the piles in winter. Erost heave
is a well known phenomenon, and occurs because as the
moist ground mass free~es, it expands upward in the
direction of least resistance. As the frozen ground
mass expands and moves upward, it pulls the piles up
with lt. The ground mass at the bottom end of the
plles, which is below the permafrost level, slides
into the space thus vacated beneath the lower end
of the pile, with the result that the pile remains
permanently in the heaved position.
Norwegian Patent Publication No. 115,378
discloses a method of constructing columns for house
foundations, utilizing a prefabricated, permanent
formwork for a cast concrete pile, where the material
of the formwork, e.g., plastic, has the property that
it does not adhere to the hardened concrete. The idea
is that the frozen earth will exert pressure on the
formwork pipe and lift it independent of the concrete
pile. However, the external pressure on the pipe is
of very great magnitude, and the pipe must be extremely
strong in order to be able to withstand the pressure.
US patent No. 3.630.037 dlsclosed a plle
coaxially surrounded by an elastic, compressible sleeve
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whose diameter is such that an annular space is
formed between the pile and the sleeve. The
I annular space is sealed at both ends and filled
with a non-freezing liquid. The idea is that when
the earth freezes, it can expand inward toward the
pile, in that the antifreeze liquid is pressed out
of the annular spaceu There is thus no significant
pressure against the pile itself. However, this type
of arrangement is quite expensive, and will be very
vulnerable to leaks in the fluid system.
j The purpose of the present invention is
! to provide an arrangement for piles set into the
ground whereby the effects of frost heave are eli-
minated insofar as is possible, and the pile is
inexpensive to produce and robust in use, such that
no speciaL maintenance or supervision is required.
This is achieved according to the invention
by a pile structure for installation in a hole
excavated below the permafrost level in the ground,
j comprislng a prefabricated plastic pipe as a penma-
! nent formwork for the cast concrete pile, and includ-
ing a second pipe coaxially surrounding the plastic
pipe such that an annular space is formed between
the two pipes, the inven~ion being characterized in
j ~ that the annular space between the two coaxlal pipes
! is filled by a sleeve of elastic material, preferably
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plastic foam (pore plastlc), the sleeve being slide-
able relative to at least one of the pipes, and
preferably, relative to both pipes.
In a preferred embodiment of the invention,
the sleeve in the annular space is dimensioned such
that it exerts a pressure against the adjacent pipe
walls of the two pipes.
According to the invention, a foot on the
pile is obtained in a simple manner, in that the outer
pipe extends a distance beyond the lower end of the
inner pipe, while the sleeve terminates at the same
depth as the inner pipe, such that when the pile is
cast, a foot having the same diameter as the internal
diameter of the outer pipe is obtained. The sleeve
can advantageously be made of polyurethane foam. A
practical material for the two pipes is hard poly-
etylene.
The invention will be described ln more
detail in the following with reference to the drawings,
j where
` ~ Figure 1 shows a conventional pile cast below
the permafrost level, under summer conditions.
Figuxe 2 shows the pile of Figure 1 under
winter conditions.
¦ Figure 3 shows a pile made in accordance
! with the lnvention, under summer conditions. -~
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Figure 4 shows the pile of Figure 3 under
¦ winter conditions.
! On Figure 1, a conventional pile 1 has been
- dug down or cast in the ground 2 to a depth below the
permafrost level 3. The pile is shown under summer
conditions and is not affected by heaving.
On Figure 2, the pile of Figure 1 has been
affected by frost heave, and it can be seen that the
ground mass has been pressed upwards, forming a small
mound 4 around the pile 1. The direction of force is
! also shown by the arrows 5. Once the pile has been
raised, sand and gravel will have a tendency to slide
down into the space 6 vacated at the bottom of the pile,
such that the pile remains permanently in the heaved
position.
¦ Figure 3 shows the pile of the invention. It
comprises a formwork pipe 7 of a plastic material, e.g.,
hard polyethylene. A second plastic pipe 8, also pre-
ferably of hard polyethylene, is disposed coaxially
outside the pipe 7. The internal diameter of the pipe
8 is such that an annular space 9 ls formed between the
inner pipe 7 and outer pipe 8. As can be seen on the
drawlng, the lower end of the outer plpe 8 projects a
distance beyond the lower end of the plastic pipe 7.
¦ In the annular space 9 between pipes 7 and 8, a sleeve
1 10 of polyurethane foam has been inserted. The sleeve
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is dimensioned such that it is force-fitted between
the exterior of pipe 7 and the interior of pipe 8.
The lower end of the sleeve 10 is at the same depth
as the pipe 7. As seen on Figure 3, the pipe 8 and
sleeve 10 can be terminated a distance below the top
of the inner pipe 7, such that an offset 11 is formed.
The offset 11 is flush with the ground level 12. The
unit, comprising the pipe 7, sleeve 10 and pipe 8,
is positioned in a hole 13 in the ground, and concrete
is poured into the upper opening of the pipe 7. Because
the inner pipe 7 and sleeve 10 do not extend down as
far as the lower end of the outer pipe 8, a foot 14
will be formed during the casting.
Flgure 4 shows the pile of the invention
under winter conditions. The f~rces in the frozen earth
operate in a more horizontal direction (shown) by the
arrows 15) and cause very little lifting 16 of the
ground. The reason or this ls that the earth can
expand in a horizontal direction, compressing the
elastic sleeve 10 and pipe 8 in toward the pipe 7.
Because the earth freezes first at the surface 12, the
upper portion of the pipe 8 will be compressed into a
somewhat conical shape~ the cone pointing upward. In
this way, a heave effect is further reduced, in that
one obtalns a downwardly-directed component of force.
The concrete pile 17 will thus remain unaffected by
the frost heave.
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