U.S. patent application number 14/911749 was filed with the patent office on 2016-07-07 for method and device for producing a foundation element in the ground.
This patent application is currently assigned to BAUER Spezialtiefbau GmbH. The applicant listed for this patent is BAUER MASCHINEN GMBH, BAUER Spezialtiefbau GmbH. Invention is credited to Stefan Michael FINKENZELLER, Paul SCHELLER, Manfred SCHWEIGER, Patrik WENZL.
Application Number | 20160194848 14/911749 |
Document ID | / |
Family ID | 48998447 |
Filed Date | 2016-07-07 |
United States Patent
Application |
20160194848 |
Kind Code |
A1 |
FINKENZELLER; Stefan Michael ;
et al. |
July 7, 2016 |
METHOD AND DEVICE FOR PRODUCING A FOUNDATION ELEMENT IN THE
GROUND
Abstract
The invention relates to a method and to a device for creating a
foundation element in the ground, wherein ground material is
removed by means of a drilling tool and a borehole is created, into
which a pile pipe and a curable medium are introduced. The borehole
is created having a boring diameter that is greater than an outside
diameter of the pile pipe by a specified amount, wherein an annular
space is formed between a borehole wall and an outer face of the
pile pipe. The removed ground material is conveyed in an interior
of the pile pipe, while the annular space is kept substantially
free of removed ground material. The curable medium is introduced
into the annular space in order to anchor the pile pipe in the
ground.
Inventors: |
FINKENZELLER; Stefan Michael;
(Reichertshofen, DE) ; SCHWEIGER; Manfred;
(Hilgertshausen-Tandern, DE) ; SCHELLER; Paul;
(lsmaning, DE) ; WENZL; Patrik; (Stadtbergen,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BAUER Spezialtiefbau GmbH
BAUER MASCHINEN GMBH |
Schrobenhausen
Schrobenhausen |
|
DE
DE |
|
|
Assignee: |
BAUER Spezialtiefbau GmbH
Schrobenhausen
DE
BAUER Maschinen GmbH
Schrobenhausen
DE
|
Family ID: |
48998447 |
Appl. No.: |
14/911749 |
Filed: |
June 20, 2014 |
PCT Filed: |
June 20, 2014 |
PCT NO: |
PCT/EP2014/063006 |
371 Date: |
February 12, 2016 |
Current U.S.
Class: |
405/244 |
Current CPC
Class: |
E21B 7/208 20130101;
E02D 13/04 20130101; E02D 7/28 20130101; E02D 7/06 20130101; E02D
13/00 20130101 |
International
Class: |
E02D 7/28 20060101
E02D007/28; E02D 13/00 20060101 E02D013/00; E21B 7/20 20060101
E21B007/20; E02D 7/06 20060101 E02D007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 14, 2013 |
EP |
13180333.0 |
Claims
1. Method for producing a foundation element in the ground, in
particular in a bed of a body of water, in which ground material is
removed by means of a drilling tool (20) and a borehole is
produced, into which a pile tube (10) and a hardenable medium are
introduced, characterized in that the borehole is produced with a
drilling diameter which is, by a specified amount, larger than an
external diameter of the pile tube (10), wherein an annular space
(8) is formed between a borehole wall (5) and an external face of
the pile tube (10), in that the removed ground material is conveyed
into an internal space (14) of the pile tube (10) while the annular
space (8) is kept substantially free of removed ground material,
and in that the hardenable medium is fed into the annular space (8)
in order to anchor the pile tube (10) in the ground.
2. Method according to claim 1, characterized in that the removed
ground material is mixed with a fluid, in particular water, which
is fed into a lower area of the borehole.
3. Method according to claim 2, characterized in that the removed
and mixed ground material is conveyed at least partially through
the pile tube (10) out of the borehole.
4. Method according to claim 1, characterized in that the drilling
tool (20) is driven in a rotating manner by means of a drill rod
(26) which is arranged inside the pile tube (10), and in that via
the drill rod (26) fluid is fed into the lower area of the borehole
and/or removed ground material is discharged from the borehole.
5. Method according to claim 1, characterized in that the
hardenable medium is fed into a lower area of the annular space
(8).
6. Method according to claim 1, characterized in that the
introduction of the pile tube (10), the removal of the ground
material, the feeding-in of the fluid and/or the feeding-in of the
hardenable medium take place simultaneously.
7. Method according to claim 1, characterized in that for removal
of ground material inside the pile tube (10) a drilling means (50)
is secured on the pile tube (10) which has a drive means (52) for
driving the drilling tool (20) in a rotating manner.
8. Method according to claim 1, characterized in that after
anchoring the pile tube (10) in the ground, removed ground material
remains inside the pile tube (10).
9. Method according to claim 4, characterized in that after sinking
of the borehole the drill rod (26) is separated from the drilling
tool (20) at the lower end of the pile tube (10), wherein the
drilling tool (20) remains in the ground as a lost drilling tool
(20).
10. Device for producing a foundation element in the ground, in
particular according to claim 1, comprising a drilling means (50)
with a drilling tool (20) for removing ground material below a pile
tube (10) which can be introduced into the ground as part of the
foundation element, characterized in that for the production of a
borehole the drilling tool (20) is designed with a drilling
diameter which is, by a specified amount, larger than an external
diameter of the pile tube (10), wherein an annular space (8) is
formed between the borehole wall (5) and an external face of the
pile tube (10), in that the annular space (8) is separated from the
interior of the pile tube (10) and in that a supply means (30) for
a hardenable medium is provided, wherein the supply means (30)
leads into the annular space (8).
11. Device according to claim 10, characterized in that the
drilling means (50) has a rotary drive for driving the drilling
tool (20) in a rotating manner and in that the rotary drive (54) is
designed for introduction into the pile tube (10) and for being
secured in the pile tube (10).
12. Device according to claim 11, characterized in that the
drilling tool (20) is driven in a rotating manner via a drill rod
(26) by the rotary drive (54) and in that between the drilling tool
(20) and the drill rod (26) a mixing means (40) is provided for
crushing and/or mixing the ground material removed by the drilling
tool (20) with a supplied fluid, in particular water.
Description
[0001] The invention relates on the one hand to a method for
producing a foundation element in the ground, in particular in the
bed of a body of water, in which ground material is removed by
means of a drilling tool and a borehole is produced, into which a
pile tube and a hardenable medium are introduced, in accordance
with the preamble of claim 1.
[0002] The invention furthermore relates to a device for producing
a foundation element in the ground, comprising a drilling means
with a drilling tool for removing ground material below the pile
tube which can be introduced into the ground as part of the
foundation element, in accordance with the preamble of claim
10.
[0003] A generic method and a generic device can be taken from EP 2
322 724 A1. By means of an underwater drilling arrangement a
pile-shaped foundation element is introduced into the bed of a body
of water. On the tubular foundation element a drilling means is
fixed which removes ground below the tubular foundation element and
produces a borehole. The removed ground material can be pumped out
of the tubular foundation element and a settable suspension can be
introduced into the tube.
[0004] The load-bearing capacity of such a foundation element
depends to a considerable degree on the skin friction with respect
to the surrounding ground. Particularly in the case of a bed of a
body of water this may result in a relatively low friction factor
so that the foundation element has to be introduced into the ground
at a corresponding depth and thus in a laborious manner.
[0005] From WO 2010/015799 A2 a method for underwater foundation
can be taken, in which a borehole is produced initially. Into this
a foundation tube with a smaller diameter can be introduced which
is embedded on its internal and external face into a hardenable
cement mass. This cement mass then hardens together with the tube
element to form the foundation element.
[0006] In the described method the removed ground material is
ejected from the borehole into the surrounding water. This can
constitute an environmental impact. Moreover, a large amount of
cement mass is required to form the foundation element. The
handling of large amounts of cement underwater can also lead to an
undesirable environmental impact.
[0007] The invention is based on the object to provide a method and
a device for producing a foundation element in the ground, in
particular in a bed of a body of water, with which a foundation
element with a high load-bearing capacity can be produced
efficiently and at the same time in an environmentally friendly
manner as possible.
[0008] The object is achieved on the one hand by a method having
the features of claim 1 and on the other hand by a device having
the features of claim 10. Preferred embodiments of the invention
are stated in the respective dependent claims.
[0009] The method according to the invention is characterized in
that the borehole is produced with a drilling diameter which is, by
a specified amount, larger than an external diameter of the pile
tube, wherein an annular space is formed between a borehole wall
and an external face of the pile tube, in that the removed ground
material is conveyed into an internal space of the pile tube while
the annular space is kept substantially free of removed ground
material, and in that the hardenable medium is fed into the annular
space in order to anchor the pile tube in the ground.
[0010] The invention is based on the finding that in order to
achieve a high load-bearing capacity the foundation element is
anchored in the surrounding ground by means of a hardenable medium,
in particular a cement mass. To obtain this high load-bearing
capacity is it not vital that the entire pile tube is filled with
the hardenable medium or mass. In fact, the hardenable medium is
substantially only fed into the external annular space formed
between the external face of the pile tube and the borehole wall of
the borehole that is larger by a defined amount. As a result, a
connecting shell is formed that anchors the pile tube in the
surrounding ground with a high friction factor. The consumption of
hardenable medium can thus be reduced considerably which is on the
one hand economical and on the other hand environmentally friendly.
On completion of the method hardenable medium can be fed into the
base area of the pile tube, whereby a stable pile base is formed. A
central area located above preferably remains free of hardenable
medium.
[0011] In this process, the ground material removed by the drilling
tool does not have to be discharged completely from the borehole.
In fact, it is possible that at least a part of the removed ground
material remains inside the pile tube. Within the meaning of the
invention the drilling tool is to be understood not only as a
drilling tool driven in a rotating manner but, in principle, also
as a cutter-like drilling tool, a drilling tool effecting removal
through high-pressure injection, a combination of these drilling
tools or another ground-removing tool.
[0012] A preferred embodiment of the method according to the
invention resides in the fact that the removed ground material is
mixed with a fluid, in particular water, which is fed into a lower
area of the borehole. If the removed ground material is adequately
liquefied through crushing and mixing with a liquid it can largely
rise upwards inside the pile tube without additional conveying
means, such as a conveyor flight. Basically, it is also possible
that the ground material thus put into a flowable state is pumped
away by a pumping means. In certain cases the fluid can also
contain a hardenable medium.
[0013] In this process, it is preferred that the removed and mixed
ground material is conveyed at least partially through the pile
tube out of the borehole. Insofar as permitted and environmentally
compatible, in underwater drilling the ground material can be
released via a discharge piece into the surrounding water. By way
of a corresponding line the removed ground material can also be
conveyed ashore or to a vessel. In this connection it is of
advantage that the removed ground material is not contaminated with
the hardenable medium. This permits an easy disposal.
[0014] According to a preferred embodiment provision is made in
that the drilling tool is driven in a rotating manner by means of a
drill rod which is arranged inside the pile tube, and in that via
the drill rod fluid is fed into the lower area of the borehole
and/or removed ground material is discharged from the borehole. For
this purpose, a hollow drill rod can be used that has one or
several outlet openings in its lower area for the supply of a
fluid, more particularly water. The fluid can also be supplied
under pressure, thereby contributing to the ground removal and/or
the mixing of the removed ground material.
[0015] Furthermore, according to an embodiment variant of the
invention provision is made in that the hardenable medium is fed
into a lower area of the annular space. To this end, one or several
supply lines can be provided along the pile tube, in particular
along the internal face of the pile tube. These lines lead into a
lower area of the annular space so that the annular space produced
can be filled up from below with the hardenable medium, more
particularly a cement mass.
[0016] Provision can also be made for further openings around the
circumference of the pile tube and along the axial height of the
pile tube. The pile tube is, on the whole, designed with a lower
annular shoulder such that the annular space is sealed tightly
against the internal space of the pile tube, in which the removed
ground material is accommodated. In this way, it prevents
contamination of the internal removed ground material with the
hardenable medium. At the same time, the hardenable medium is used
sparingly and efficiently to fill the annular space. It should be
noted that ground material can infiltrate from the borehole wall or
to a certain extent also from the borehole bottom into the annular
space or that such an infiltration can, at least, never be
completely ruled out. However, from a quantitative viewpoint the
hardenable medium is supplied to such an extent that even if ground
material infiltrates, a sufficient hardening of the anchoring shell
around the pile tube is reached. Of major importance is the fact
that the hardenable medium cannot infiltrate into the interior of
the pile tube and thus lead to an undesirable contamination of the
removed ground material in the internal space of the pile tube.
[0017] A particularly efficient method is attained according to the
invention in that the introduction of the pile tube, the removal of
the ground material, the feeding-in of the fluid and/or the
feeding-in of the hardenable medium take place simultaneously. All
in all, a rapid sinking of the borehole and a speedy construction
of the foundation element can thus be achieved.
[0018] Furthermore, according to an embodiment of the invention it
is preferred that for removal of ground material inside the pile
tube a drilling means is secured on the pile tube which has a drive
means for driving the drilling tool in a rotating manner. The
drilling means capable of being secured on the pile tube can have a
support frame for example which can be secured by tensioning or
clamping means on the pile tube and in which a drive means or a
rotation motor for driving a drill rod is accommodated. The
drilling means can be secured, for example, inside an internal
cross section of the pile tube, thereby allowing the drilling means
and the pile tube to be sunk jointly. It is also possible to
provide a telescopic drill rod or to support the drill rod in an
axially adjustable manner with respect to the support frame so that
an independent axial feed motion of the drilling tool and the pile
tube can take place.
[0019] According to the invention an especially economical method
variant is attained in that after anchoring the pile tube in the
ground, removed ground material remains inside the pile tube.
Hence, the removed ground material is not or not entirely
discharged from the pile tube. In fact, the removed ground material
which can be crushed and, as the case may be, mixed with liquid
remains inside the pile tube. Solidification of this material
filling is not necessary since the load-bearing capacity of the
foundation element primarily depends on the skin friction. In this
way, the costs for the discharge of the ground material and an
environmental impact possibly involved therewith can be avoided.
Since the ground material is not contaminated with hardenable
medium it does not constitute an environmental impact e.g. on
underwater foundation elements even in the long term.
[0020] To produce the borehole with a larger diameter a specific
drilling tool with radially extendable removal teeth can basically
be used. Such a drilling tool can be folded in radially after
sinking of the borehole and withdrawn upwards through the pile tube
with a smaller diameter. With regard to the use of cost-intensive
special-purpose vessels for underwater drilling operations an
economical alternative resides in the fact that after sinking of
the borehole the drill rod is separated from the drilling tool at
the lower end of the pile tube, wherein the drilling tool remains
in the ground as a lost drilling tool. Hence, a simple inflexible
drilling tool can be used which remains in the ground as a lost
drill bit on the underside of the foundation element.
[0021] The object stated at the beginning is furthermore achieved
by a device which is characterized in that for the production of a
borehole the drilling tool is designed with a drilling diameter
which is, by a specified amount, larger than an external diameter
of the pile tube, wherein an annular space is formed between the
borehole wall and an external face of the pile tube, in that the
annular space is separated from the interior of the pile tube, and
in that the supply means for a hardenable medium is provided,
wherein the supply means leads into the annular space. With this
device the afore-described method can be carried out and the stated
advantages can be accomplished.
[0022] Due to the continuous tube body of the pile tube and in
particular due to an enlarged diameter, for instance by way of a
shoulder, at the lower end of the pile tube the annular space on
the external face of the pile tube is separated, as far as the
process is concerned, from the interior of the pile tube. In this
way, the achievement is made that no hardenable medium can pass
from the external annular space into the interior of the pile tube.
Likewise, ground material can also be prevented from infiltrating
into the annular space. However, this poses no problem as long as
the strength of the formed connecting mortar in the annular space
is not significantly affected. Through a clear separation an
efficient use of the hardenable medium in the annular space and the
avoidance of contamination of the removed ground material in the
interior of the pile tube are ensured. The supply means leads
solely into the annular space but not into the interior of the pile
tube.
[0023] Basically, the drilling tool can be operated in a
conventional manner by a drilling device located outside the
borehole, for instance on a drilling vessel. According to the
invention it is preferred that the drilling means has a rotary
drive for driving the drilling tool in a rotating manner and that
the drill drive is designed for introduction into the pile tube and
for being secured in the pile tube. By way of a suitable tensioning
means the drill drive can be secured inside the pile tube. The
drilling means can also be part of an underwater drilling unit that
can be lowered into the body of water.
[0024] According to a further embodiment of the invention provision
is made in that the drilling tool is driven in a rotating manner
via a drill rod by the drill drive and in that between the drilling
tool and the drill rod a mixing means is provided for crushing
and/or mixing the ground material removed by the drilling tool with
a supplied fluid, in particular water. The drilling tool and the
mixing means can be operated simultaneously and can in particular
be driven in a rotating manner. The supply of the hardenable medium
takes place simultaneously with the operation of the drilling tool.
Moreover, with the removal of ground material and the corresponding
axial feed motion of the drilling tool the pile tube is also
lowered into the ground. The mixing means can have mixing paddles
or mixing blades that additionally crush the removed ground
material and mix it with a supplied fluid so that the removed
ground material reaches an overall flowable state.
[0025] In particular, the mixing means can also have eccentrically
arranged mixing elements, whereby the mixing and crushing effect
can be enhanced.
[0026] In the following the invention is described further by way
of preferred embodiments illustrated schematically in the drawings,
wherein show:
[0027] FIG. 1 a schematic side view of a device according to the
invention;
[0028] FIG. 2 a longitudinal section of the device of FIG. 1;
[0029] FIG. 3 an enlarged cross-sectional view according to section
A-A of FIG. 1; and
[0030] FIG. 4 an enlarged detailed illustration of the lower area
according to FIG. 2.
[0031] According to FIGS. 1 and 2 a device 1 pursuant to the
invention has a pile tube 10 which is substantially formed of a
cylindrical base body 12. At the lower end of the cylindrical base
body 12 a sleeve-shaped shoulder 16 with a larger diameter is
designed which accommodates a mixing space 18.
[0032] Inside an internal space 14 of the pile tube 10 a drilling
means 50 is arranged. The drilling means 50 can be clamped against
the internal face of the pile tube 10. The pile tube 10 itself can
be arranged in a known manner on a drilling unit, more particularly
an underwater drilling unit. By way of the drilling unit, not
shown, the pile tube 10 can be driven in a torque-proof or also in
a rotating manner. During operation of the drilling means 50 the
pile tube 10 is stationary and, once a section of the borehole has
been produced, it can then be moved axially downwards into the
borehole.
[0033] From the drilling means 50 a drill rod 26 extends axially
downwards to the free end of the pile tube 10. Below the pile tube
10 a drilling tool 20 is arranged on the drill rod 26. The drilling
tool 20 has a conveyor flight 24, at the lower end of which,
starting from a central pilot bit 22, several radially arranged
removal teeth 23 are located along cutting edges.
[0034] Between the drilling tool 20 and the drill rod 26 a mixing
means 40 is interposed which is explained in greater detail
hereinafter in conjunction with FIGS. 3 and 4.
[0035] The drill rod 26 has an inner drive shaft 28 and an outer
drive shaft 38 surrounding the latter concentrically. The inner
drive shaft 28 is driven in a rotating manner by a rotary drive 54
of a drive means 52, whereby the torque is transmitted from the
inner drive shaft 28 to the drilling tool 20. Independent of this,
the outer drive shaft 38 can be driven by a mixing drive 56 with a
different direction of rotation and/or rotational speed. At the
lower end of the outer drive shaft 38 a mixing means 40 is
provided, through which removed ground material is mixed with
supplied fluid.
[0036] Furthermore, the inner drive shaft 28 and the outer drive
shaft 38 can be designed as hollow tube elements so that these can
be used for introducing a fluid into the borehole, as will be set
out in detail hereinafter.
[0037] By means of the drilling tool 20 a borehole with a drilling
diameter is produced which approximately corresponds to the
external diameter of the sleeve-shaped shoulder 16 at the lower end
of the pile tube 10. In this way, the pile tube 10 can be followed
down into the borehole without any considerable amounts of removed
ground material being able to flow past the external circumference
of the sleeve-shaped shoulder 16 in the upward direction.
[0038] Compared to the sleeve-shaped shoulder 16 with a larger
diameter the cylindrical base body 12 of the pile tube 10 has a
smaller diameter so that an annular space 8 is formed between the
external face of the cylindrical base body 12 and a borehole wall
5. By way of a supply means 30 a hardenable medium, in particular a
cement mass, can be fed into the annular space 8 that can be filled
therewith. For this purpose, the supply means 30 has a line 32 that
extends from a pump, not shown, along an internal face of the
cylindrical base body 12 of the pile tube 10. By way of an elbow 34
the supply line 32 leads into the annular space 8, as can be taken
from FIG. 4 in particular.
[0039] With reference to FIGS. 3 and 4 the lower end area of the
device 1 and the pile tube 10 is described in greater detail. Via a
radial annular plate 17 the sleeve-shaped shoulder 16 is connected
in a fluid-tight manner to the external circumference of the
cylindrical base body 12 of the pile tube 10. As a result, the
annular space 8 formed between the borehole wall 5 and the external
circumference of the continuous cylindrical base body 12 is sealed
off tightly against an internal space 14 of the pile tube 10.
[0040] Below the sleeve-shaped shoulder 16 the drilling tool 20,
having the same external diameter, is arranged with conveyor
flights 24 and a pilot bit 22. The drilling tool 20 is driven in a
rotating manner by the inner drive shaft 28. Ground material is
removed and conveyed upwards by the conveyor flights 24 into a
mixing space 18 designed inside the sleeve-shaped shoulder 16. In
the mixing space 18 a mixing means 40 is arranged. In the
illustrated embodiment the mixing means 40 comprises three
plate-shaped inner mixing elements 42 which are arranged at the
same angular distance in relation to each other and are mounted on
the inner drive shaft 28 so as to rotate therewith.
[0041] Moreover, the mixing means 40 comprises three plate-shaped
outer mixing elements 44 which are also arranged such that they are
offset by 120.degree. in relation to each other and are connected
in a torque-proof manner to the outer drive shaft 38. An outer
mixing element 44 has an upper radial bar 46 and a lower radial bar
47 which are firmly connected to each other by way of an axial
connecting element 45. The lower radial bar 47 is supported in a
rotatable manner with respect to the inner drive shaft 28. On an
internal face of the connecting element 45 a radially inward
projecting shear plate 48 is arranged.
[0042] Through a relative rotation of the inner mixing elements 42
and the outer mixing elements 44, which rotate in opposite
directions in particular, the removed ground material conveyed by
the conveyor flights 24 is crushed further and mixed with liquid
that is fed via fluid lines 58 in the interior of the drill rod 26.
The fluid lines 58 are in particular arranged in the intermediate
space between the inner drive shaft 28 and the outer drive shaft 38
and have laterally-directed radial outlet openings as well as
downward-directed ones for the injection of liquid. At the same
time, liquid can be fed directly downwards via the remaining
annular space between the two drive shafts. The mixing and
liquefying of the removed ground material is additionally enhanced
by a radially inward projecting annular protrusion 60, through
which the removed ground material is forced radially inwards into
the mixing space 18. Through the effect of the conveyor flights 24
and the supply of liquid the ground material thus crushed and mixed
is displaced upwards into the internal space 14 of the pile tube
10.
[0043] Separated tightly from the internal space 14 is the annular
space 8 between the borehole wall 5 and the cylindrical base body
12. Basically, the separation of these two process spaces can be
enhanced further in that the pressure in both process spaces is
controlled by controlling the respective filling levels. Via the
supply line 32 and the elbow 34 a hardenable medium is fed into the
annular space 8 at the lower end thereof. The hardenable medium, in
particular a cement mass, hardens after sinking of the borehole and
introduction of the pile tube 10 into the borehole so that a solid
connecting shell is created thereby between the borehole wall 5 and
the pile tube 10 so as to form the foundation element.
[0044] A pressure in the internal space 14 can be controlled via a
filling level of the removed and mixed ground material in the
internal space 14. In particular, the filling level can be set by
means of a pump, not shown. Basically, the pressure in the internal
space 14 can be higher than in the annular space 8, whereby a
leakage of the hardenable medium from the annular space 8 into the
internal space 14 is prevented in a particularly reliable manner.
This ensures that the removed ground material in the internal space
14 is not contaminated with hardenable medium thus necessitating
its disposal at high costs. By preference, the pressure in the
annular space 8 is higher than in the internal space 14, whereby an
infiltration of ground material into the annular space 8 is
counteracted.
[0045] After the connecting shell in the annular space 8 has
hardened, crushed and/or liquefied ground material can remain in a
non-hardened state in the internal space 14 of the pile tube 10.
For, even in the case of an underwater foundation, the loosened
ground material, which is not contaminated with hardenable mass,
does not constitute an environmental impact. To form the foundation
element the pile tube 10 and the drilling tool 20 remain in the
ground while the drill rod 26 is recovered together with the mixing
means 40.
* * * * *