Note: Descriptions are shown in the official language in which they were submitted.
1 337893
This invention relates to apparatus for the
production of underground structures, especially piles.
While the invention is particularly concerned with
the production of piles, the principles may also be
applied to the production of ground anchors or other
underground structures. An important difference between
piles and ground anchors is that piles are usually load
bearing generally vertical structures set into the
ground, whereas ground anchors are generally anchoring
stays in the ground by means of masses which are stable
against stresses and strains on the stay with various
lateral and vertical components.
Many of the considerations in producing ground
anchors and piles and other underground structures are
somewhat similar. For example, when injecting grout for
such structures into the ground, control of the amount,
the direction and the spread of the grout is of especial
importance.
Examplary U.S. patents which disclose means in which
especial attention is given to the control of the amount
of a fluid for underground injection are U.S. Patent No.
4,378,997 to Kasama et al, issued April 15th 1983, U.S.
Patent No. 3,698,196 to Janowski issued October 15th 1972
and U.S. Patent No. 3,699,687 to Bourland issued October
24th 1972 These patents all disclose capsules which may
be ruptured to release their contents into their
immediate surroundings for, respectively, breaking up the
surroundings, filling cracks with swellable foam or
anchoring purposes.
The use of such rupturable capsules may be suitable
when a generally multi-directional unconfined splash of
*
- 1 3378~3
material is required or for generally providing pressure
to force fluid into existing cracks or crevices.
However, for the provision of generally vertical piles,
which may be provided with thickened bulbous base
S portions, considerably more control is required.
Where the use of conventional mechanical pile
drivers is contra-indicated, or as an alternative from
such use, it is known to form a bore into the ground,
insert an injection tube into the bore and inject grout
to form a pile through the tube.
One problem with this type of method involves the
provision of non return injection valves for the injection
tubes so that the grout can be flushed non-returnably from
the tube into the ground whereafter the tube may be
withdrawn and reused.
A number of U.S. patents such as No. 3,984,988 to
Portier issued October 12th 1976, No. 4,545,702 to Sano et
al issued October 8th 1985 and No. 4,710,063 to Faktus et
al issued December 1st 1987 concern structures of non
return valves for such injection tubes.
U.S. Patent No. 4,426,175 to Lin issued January 17th
1984, French patent No. 2,552,462 to Acaplast, Societe
Anonyme and Russian patent No. 600,245 all disclose
apparatus in which grout is not released into the
surroundings from the injection tube when pressure is
built up sufficiently to burst rupturable valves in the
injection openings. Means is provided to seal the bore
above the valved part of the tube so that pressure will
not escape up the bore. No provision is made to
stabilise the surroundings of the bore into which grout
is to be injected to control the spread of grout.
1 337893
U.S. patent No. 3,494,134 to Jorge issued February
10th 1970 discloses means for setting a stay or rod into
the ground as a ground anchor in which precautions are
taken to first proved establishment of grout around the
stay or rod and thereafter fill the bore with grout which
may penetate to into the walls of the bore where they
are, by chance, of a nature to allow such penetration.
No stabilisation of the environment of the walls of the
bore is attempted.
U.S. patent No. 1,386,876 to Dupeuble issued June 7th
1981 discloses an apparatus using an injection tube with
non-return valves for anchoring the rods. This apparatus
again involves sealing the bore to prevent back flow of
grout and then injecting grout into the lower part of the
bore and to fill the tube which surrounds the tie rods.
The whole of the tube remains in the ground.
Some of the previous techniques of providing
underground structures by injection of grout have been
"one shot" processes. This involves the establishment
of a plug in the borehole above the injection region and
then simply injecting grout into the lower part of the
borehole, allowing any natural seepage into its walls.
An improved "two-shot" process may also be used in which,
after a structure formed by a one shot process has been
allowed to set, a second injection through the same
injection tube is performed, cracking open the first
structure at least at its base and injecting grout
therethrough to form a bulb on root system. When the
second grouting sets, second stage grout bonds with the
broken first grout. Efficient non-return valves have
been very important in such processes. Even so it has
been difficult to achieve consistent results. Moreover,
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the more sophisticated non-return valves add expense to
the apparatus. Such a two-stage process is described in
an article entitled "Pieux-Aiguilles" published by
Soletanche, 7, Rue de Logelbach, Paris 17.
An attempt has now been made to provide apparatus
and a method for grout injection into bore holes,
especially for the production of piles. Important
considerations were the desirability of stabilising the
environment in the immediate vicinity of grout injection,
and the provision of relatively inexpensive apparatus
without the need for sophisticated non-return valves.
Thus according to the invention we provide apparatus
for use in the production of a structure anchored in the
ground comprising a first stage grout injection sheathing
tube having first orifices therethrough adapted for the
passage of fluid grout therethrough, the first orifices
being distributed over at least a lower part of the tube;
a second stage grout injection tube adapted for the
introduction of pressurised grout locatable substantially
coaxially within said first stage sheathing tube and
having second orifices therethrough distributed over a
lower part;
an elongate pod of resiliently deformable material
releasably enclosing the lower part of the second stage
tube, the pod having longitudinal lines of weakness in a
sidewall rupturable to form corresponding longitudinal
slits, and adapted to, under pressure of grout from the
second orifices, rupture to allow the passage of
pressurised fluid grout into the lower part of first
stage injection tube and through the first orifices
thereof.
1 337893
- 5 -
According to the invention we also provide a process
for the production of a structure anchored in the ground
comprising:
introducing into a borehold, a first stage grout
injection sheathing tube having first orifices
therethrough adapted for the passage of fluid grout, the
first orifices being distributed over at least a lower
part of the tube;
introducing co-axially said first stage tube, a
second stage grout injection tube adapted for the
introduction of pressurised grout said second stage tube
having second orifices therethrough distributed over a
lower part thereof, the lower part of the second stage
tube being releasably enclosed by an elongate pod of
resiliently deformable material, the pod having
longitudinal lines of weakness in the sidewall rupturable
to burst open to form corresponding longitudinal slits
under pressure of grout from the orifices of the second
stage injection tube, to allow the further passage of
pressurised grout at least into the lower part of first
stage injection tube;
introducing into the first stage injection sheathing
tube, fluid first stage grout at a pressure to fill the
tube and inject it through the first orifices into
surrounding environment;
allowing said grout to set;
introducing into the second stage injection tube,
second stage fluid grout and injecting it under pressure
through the second orifice to rupture the lines of
weakness in the pod and crack the first stage grout, and
flow through the first orifices; and
B~ ~
i
1 337893
allowing the second stage grout to set releasing the
second stage tube from the pod and withdrawing it
therefrom.
The apparatus used in the process of the inventions
may have the advantage that only first stage injection
tube and the pod are left in the ground. The first stage
injection tube makes a useful reinforcement for the
resulting pile and the pod may be relatively inexpensive.
An embodiment of the invention will now be described
with reference to the drawings in which:
Figure 1 is a sectional diagramatic sketch of one
form of apparatus according to the invention located in a
borehole;
Figure 2 is a view similar to Figure 1 after a first
stage introduction of grout;
Figure 3 is a section of Figure 2 on the line III-
III of Figure 2;
Figure 4 is a view similar to Figure 2 after a
second stage injection of grout;
Figure 5 is a section of Figure 4 on the line V - V
of Figure 4; and
Figure 6 is a view similar to Figure 1 of the
resulting pile.
The drawings show a borehole 10 in which a pile is to
be located. A first stage injection tube 12 having a cap
1 337893
~_ 29 above ground level 23 is inserted into the borehole
10. Grout to be dispensed into the borehole 10 through
tube 10 may be under low pressure, for example, it may be
introduced by pouring. However, conveniently it is
introduced through primary grout injection tube 21. The
tube 10 has means for dispensing grout into the borehole
12 at least at the lower end and preferably over, its
length. The means for dispensing grout may be first
orifices 14, as shown, or may be rupturable diaphragms
or orifices provided with non-return valves. However,
simple orifices 14 are sufficient and any rupturable
diaphragms or non-return valves should be suitable to
dispense grout unto the borehole 10 under quite low
pressures.
lS A second stage injection tube 20 has second orifices
22 for the injection of pressurised grout only at its
lower end portion 24.
A pod 26 comprising a tubular portion 28 of greater
diameter and coextensive with the lower end portion 24 of
the second stage injection tube 20 has a closed lower end
30 and means for releasable connection to the injection
tube 20 at its upper end. The means for connection with
the injection tube 20 may be a conventional pipe reducer
32, its smaller end being adapted for screw threaded
engagement with a screw-threaded portion 34 of injection
tube 20 above the lower portion 24. Figures 1 to 3 of
the drawings show the pod 26 with the smaller end of the
pipe reducer 32 engaged with screw-threaded portion 34
of tube 20. The wider end of the pipe reducer 32 is
connected to the tubular portion 28 of the pod 26 by any
convenient means, for example, by a solvent joint.
The pod 26 may conveniently comprise an outer sheath
1 337893
_ 25 of flexible plastic having longitudinal lines 6
weakness or slits 36 at least partially therethrough.
The outer sheath 25 of pod 26 may be made of
flexible deformable plastics material such as polyvinyl
chloride and the longitudinal slits 36 may be only in the
outer surface of its side wall. Thus, the slits 36 need
not extend completely through the side wall but form
weakened portions adapted to rupture under the influence
of pressurised grout. For supporting the flexible sheath
25, an inner support pod 27 may be provided comprising a
cylinder of longitudinally corrugated, perforated metal,
for example, steel.
In operation first stage injection tube 12 is lowered
down borehole 10 and second stage injection tube 20 is,
with pod 26 engaged thereon, lowered down tube 12.
Primary grout 38 is injected under low presure
through or even poured into first stage tube 12. The
grout 38 flows down the tube and is injected into the
borehole 10 through orifices 14. There may be seepage 39
of grout 38 beyond the walls of borehole 10. This will
depend upon the structure of the soil, the compaction of
the borehole walls and the pressure of grout 38.
Grout 38 also acts to exert pressure to compress pod
26 so that it tends to assume the somewhat flattered oval
form shown in Figure 3. Since the slits 36 are in the
sheath 25 surface of tubular portion 28, this flattening
action tends to close the slits firmly guarding against
any tendency of grout 38 to burst inwardly into the pod
26 through slits 36. The longitudinal corrugations of
support pad 27 are an aid against undue deformation of pad
27 during application of primary grout 38.
1 337893
Grout 38, 39 is allowed to set to form a pile
structure. The pile structure within the borehole 10 will
tend toward constant cross section of which corresponds
to the diameter of the borehole 10. The structure is
reinforced by the embedment of first stage injection tube
12 therein. Seepage 39 extends outwardly of the borehole
10 where the soil structure allows it and may provide
some additional anchoring force. Except where
particular crevices or soil weakness or mud areas exist,
the cross section of the whole pile structure including
seapage 39 will probably be generally constant from the
bottom of tube 12 to ground level.
The process, thus far, is not totally dissimilar to
previous one step processes with a notable exception
that, no attempt is necessarily made to provide
non-return valves for orifices 14 and first stage
injection tube 12 is embedded into the structure as
reinforcement.
When grout 38 has been given the opportunity to set
grout 40 is injected under pressure through second stage
injection tube 20. The resultant action at the bottom of
borehole 10 is that pressurized grout 40 re-expands pod 26
to expand the support pad 27 and burst open the slits 36
of flexible outer sheath 25 as shown in Figures 4 and 5.
The surrounding set grout 38 in tube 12, borehole 10 and
seepage 39 may crack and break under the strain opening
crevices to orifices 14. The bottom part of tube 12 may
splay out as shown in Figure 4 to form a strong anchor in
the ground. At a preset pressure of grout 40, which is
determined by the size, and depth of slits 36, the
material of tubular portion 28 and the strength of set
grout 38, the slits 36 rupture. Thus pod 26 bursts open
1 337893
to release second stage grout 40 into the bottom part of
tube 12 and through orifices 14 in the bottom part of
tube 12 to spread outwardly to extend beyond the limits
of seepage 39. The spread of grout 40 may be as a root
system 42 as shown in Figure 4 or it may form a bulb
surrounding the bottom of tube 11.
In any case the presence of seepage 39 and set grout
38 in tube 12 and borehole 10 tends to direct the spread
of grout 40 downwardly as well as outwardly to form a
root system 42 for the resulting pile.
As grout 40 sets, it bonds with previously set grout
38 to form a cohesive structure.
Burst point of pod 26 may be consistent, resulting in
a root system 42 of consistent size and shape for each
configuration of tube 12. The grout 40 may be applied in
consistent amount by using water pressure or other
pressure to force a set amount of grout 40 through
injection tube 20. Either while grout 40 is still wet or
if water is used to force the grout through the tube 20.
The pressure in tube 20 may be relieved after
injection of an appropriate amount of grout 40. The
tubular portion 28 will then be compressed against lower
portion 24 of tube 20 thus having some tendency to seal
orifices 22 against return of grout 40. At this stage,
either while grout 40 is still wet or if water is used to
force the grout through the tube 20, ~he tube 20 may be
unscrewed from the pipe reducer 32 and withdrawn for
reuse leaving tube 12 and ruptured pod 26 in place in a
substantial rooted pile structure.
