EP1087062A2

EP1087062A2 - Pile joint and a method for implementation thereof

Info

Publication number: EP1087062A2
Application number: EP00120839A
Authority: EP
Inventors: Matti Numminen
Original assignee: Yit-Yhtyma Oyj
Current assignee: Yit-Yhtyma Oyj
Priority date: 1999-09-23
Filing date: 2000-09-25
Publication date: 2001-03-28
Anticipated expiration: 2020-09-25
Also published as: ATE402291T1; FI19992047A7; DE60039563D1; FI19992047L; EP1087062B1; EP1087062A3

Abstract

The present invention relates to an extension arrangement for piles (1,2) which are to be driven into the ground, wherein the upper end (3) of a lower pile (1) and the lower end (13) of an upper pile (2) are interconnected by a separate interconnecting portion (6) arranged axially at the ends (3,13) of said piles (1,2). Said interconnecting portion (6) is dimensioned to have such a fit that the lateral surfaces thereof will drift apart, due to a change in temperature, radially from the lateral surfaces of a counter-portion (3,13) which is axially in an overlying position therewith and connects thereto, while said lateral surfaces in a normal temperature, correspondingly, will press against each other. The present invention further relates to a method for extending piles (1,2) wherein the extension comprises outer and inner interconnecting portions (6;3,13) which are pushed into an overlying disposition. By means of a temperature difference said outer interconnecting portion (6) is expanded to be larger than said inner interconnecting portion (3,13), after which said outer (6) and said inner (3,13) interconnecting portions ar brought to move into said overlying position while the fitting clearance so provided prevails and then to clamp together in normal temperature.

Description

The present invention relates to an arrangement in accordance with the preamble of the independent claims, especially a joint arrangement for piles or the like pieces to be driven essentially vertically into the ground, wherein the upper end of a lower pile which is intended to be extended and the lower end of a an extension pile arranged in an opposed position in relation to said lower pile are interconnected by a separate joint piece made of metal and arranged at the ends of said piles axially with respect to the longitudinal axis of said ends. The invention further relates to a method for extending piles or the like pieces intended to be driven essentially vertically into the ground, wherein outer and inner connection portions intended to be axially pushed into a mutually overlapping position are used as a joint.

Traditionally one seeks to manufacture piles to be driven into the ground to a specific length so that there is no need for making any extensions in connection with the pile driving. One reason for this is especially the fact that any pile joints might have a harmful impact on the straightness of the pile and thus cause a risk for columnar deflection. In certain circumstances, however, piles have to be extended, and one seeks to make the extensions in such a manner that the joint is both strong and straight. Such conditions are, i.a., such pilings where the usable free space over the ground surface at the work site is limited, as in cellars or the like spaces under existing structures.

According to prior art such pile extensions comprise registering and fastening elements arranged at the ends of the piles, the purpose of said elements being the forming of a joint which is as straight as possible and wherein the load forces acting on the piles are directed straight in the pile direction downwards. The joint should also function so that it keeps the parts of the pile together and the pile straight also at that stage where the pile is pressed or rammed, i.e. driven, down into the ground. Especially ramming is a difficult stage with respect to the pile stresses, since therein striking forces are directed to the pile from above, counter strike forces ar directed from below and between there will, above all, act different resonance forces which are directed especially to any discontinuities in the pile, i.e. to the joints. Especially in a poorly load bearing ground there further will be the risk that the pile at least at some stage will tend to sink downwards by its own weight, in which case it even must be held by an upwards directed power. Thus, a pile joint must be capable of bearing at least some tensile force, despite the fact that the main load of a pile will be compression.

Thus, different pile joint arrangements are known, wherein mutually correspondingly shaped locking pieces are arranged at the ends of the piles. Here, however, the complex manufacture of especially the joint pieces or parts constitutes a problem, as well as the attachment of such parts to the corresponding pile end. A further problem is the fact that such parts must endure the loads which the pile driving causes on the respectively uppermost pile end. Such joint arrangements are, i.a., different threaded joints, machined conical joints and the like, wherein, respectively, the mutual correspondence in shape in the pieces to be interconnected is utilized. Besides the technical complexity the most serious drawback for such arrangements is the fact that they easily are battered at the work site and thus break so that the task of connecting them in work site conditions is difficult or impossible. Thus, handling them requires special care and special protecting measures, which, in the conditions prevailing at a building work site, often is difficult and inappropriate.

Such extensions are also known, which are produced by welding and which especially are used for metal piles. Especially in narrow spaces the establishment of such extensions in work site conditions is difficult and sometimes even constitutes a fire hazard. One known arrangement comprises a bushing or collar arranged at the end of the pile, which collar is partially positioned around the end of the underlying pile to be extended. In this case a cup-like collar is formed at the end of the pile, into which collar the end of the upper pile constituting the extension is forced or pressed in a tight fitting. On order to achieve a sufficient directional stability the fitting of the collar to the pile must be a tight press fitting.

For preventing such a collar from moving downwards on the lower pile during the connecting procedure the collar must further be fastened to said lower pile. In such cases when said lower pile is made of steel said fastening usually is done by welding. In such an arrangement, however, there remains the problem that the pile end is susceptible to damage. For this reason the pressing or driving of the pile into the ground requires the use of a separate extra piece which in narrow and low spaces causes, i.a., loss of effective working height. Performing the connection is also problematic as such since a pressing in opposite directions between the piles is required, the order of magnitude possibly being over 20 metric tons. The achievement of this in said spaces is also difficult, especially bearing in mind that merely the pressing of the upper pile into the collar mainly causes the lower pile to escape downwards, for which reason it must be separately held. Since bringing the end of the upper pile into the collar simultaneously induces a load on the collar walls and their deformation outwards, the fitting often remains inexact. At an inexact fitting it is difficult to achieve such a straightness of the joint which would completely eliminate the risk of columnar deflection. The risk is further increased if the pile is constituted of several rather short portions which subsequently are interconnected as discussed above.

In order to solve the above problems the arrangement according to the present invention has been developed, the characteristics of which being evident from the appended claims. There the tight press fit has been replaced with a temporary alternation, for the time of the interconnecting, of the radial measures of the parts which are interconnected, so that the lateral clearance between the parts is greater than the fit in the operative conditions. Favorably, the alternation is such that the opposite side surfaces of the connecting parts under normal conditions will press against each other with a considerable force. Thus, the arrangement according to the present invention is characterized especially by the arrangement of a piece favorably made of metal, which piece functions as an interconnecting portion which is dimensioned with such a tolerance that at least some of its lateral surfaces due to a change in temperature established in at least one portion of the connection will radially drift apart from corresponding lateral surfaces at a counter piece interconnecting therewith, where said lateral surfaces under normal temperature, correspondingly, will push against each other. Favorably, the arrangement comprises a metal sleeve having such a tolerance, with respect to said counter piece, that an expansion caused by a heating directed to the sleeve renders possible the introduction of the counter piece into the sleeve, but which, on the other hand, in normal temperature conditions will clamp its inner surface against the outer surface of said counter piece. The arrangement further comprises means for momentarily heating the sleeve in the vicinity of the pile end in order to achieve said expansion.

The method according to the present invention, on the other hand, is characterized by causing the inner dimensions of an outer interconnecting portion to expand, due to a difference in temperature, to be larger than the circumferential dimension of an inner interconnecting portion, by bringing said outer and inner interconnecting portions to move, within a mutually loose fit, in the axial direction of the pile into an overlapping position, after which the interconnected parts are brought to the normal temperature of the connection in order to remove the adaptation fit caused by the temperature difference and to tighten the pieces together.

In the method according to the present invention a sleeve favorably is used as said interconnecting portion, said sleeve being positioned around the ends of tube-shaped piles arranged in an opposite disposition, wherein the method comprises the mutual arrangement of the radial dimensions of the separate sleeve and the ends of said piles to be connected thereto from both sides, utilizing a temperature difference between said sleeve and said pile end(s), into each other for the time of implementing the connection or arranging said parts axially into said overlapping position. At this stage the inner diameter of said sleeve is larger than the outer diameter of the pile by an amount at least corresponding to an adaptation tolerance, after which said sleeve and said pile end(s) arranged, respectively, in axially overlapping disposition are brought into mutual constriction by bringing all said elements to normal temperature, i.e. mainly to that temperature in which the piles essentially will prevail.

The invention will now be described in more detail by reference to some favorable embodiments thereof as well as to the enclosed drawings sequentially describing the invention. In said drawings

Figure 1: in section discloses the end of a pile partially driven into the ground and intended to be extended,
Figure 2: in section discloses a pile end according to Figure 1, to which pile end a retention ring has been arranged,
Figure 3: in section discloses a sleeve like extension piece and schematically a heating arrangement therefor,
Figure 4: in section discloses a pile end to which an extension sleeve has been arranged,
Figure 5: in section discloses an extended tube pile still having the retention ring in place,
Figure 6: in section discloses an already extended pile which now can be driven deeper down,
Figure 7: in section discloses an alternative embodiment which especially can be used in connection with tubular piles, where an interconnecting piece constitutes a pin-like member which extends within the tubular end of the pile,
Figure 8: schematically discloses the cooling of a second portion of a pile extension,
Figure 9: in section schematically discloses the heating of the end of a pile to be extended, and
Figure 10: in section discloses a tube pile portion which has been extended in accordance with the above.

According to Figure 1 a pile 1 is brought down into the ground in a manner known per se, e.g., by driving or pressing with the aid of a jack. Especially in a situation where a restricted space is available over the working place said pile 1 must often be extended by the use of a second pile 2. Such a situation will occur, e.g., when the foundations of existing buildings are reinforced. In such a situation piles driven into the ground, e.g., all the way to the hard ground, must be divided into several relatively quite short portions. The entire pile formed by such portions will be the object of the same forces which would act on an entire pile. Additionally, special care must be taken with respect to the straightness of the pile entity, so that the pile not would deflect and in the worst case break.

Thus, according to Figure 1 said pile 1 or a part thereof will be brought by driving or pressing or some other manner into the ground so that the upper end 3 of said pile 1 still will remain over the ground surface 4. In certain situations the driving can also be extended deeper, but then the forming of the extension of the pile 1, i.e. the making of the connection between said pile 1 and said pile 2 in most case will be more difficult.

In a situations according to Figure 2 a retention ring 5 is arranged around the end 3 of said pile 1, the purpose of this mainly being the function as a retainer for the bushel or sleeve 6 included in the extension as an interconnecting portion and for preventing the movement thereof around the pile 1 to a depth which would render the connection instable. Simultaneously said retainer 5 can be used as a gripping point for preventing the pile 1 from sinking deeper by its own weight in such situations where such a ground layer extends at the lower end of the pile which layer does not bear the load caused by the pile's own weight. As such said retainer ring 5 favorably is constituted of two hinged ring portions, which at the side opposite to the hinge (not shown) comprise a clamping locking mechanism known per se (not shown) which appropriately facilitates an opening of the ring and its removal from around the pile also in a lateral direction.

According to the embodiment presented now an interconnecting sleeve 6 will be arranged, in the subsequent step, around the end 3 of said pile 1, as disclosed in Figure 4. Said sleeve 4 is dimensioned so that it firmly clamps with its lateral or inner surface 7 to the outer surface 8 of the end 3 of said pile 1 when it is arranged around said end 3 of said pile 1 in the normal temperature of the ground, i.e. in a temperature of a couple of centigrades plus. In order to position a sleeve 6 having a dimension as discussed the special method according to the present invention has been developed, wherein a temperature difference achieved mainly in an artificial manner is utilized so that the diameter of said sleeve 6 at the installation stage is clearly so much larger than the diameter of the end 3 of said pile 1 that the positioning and arrangement of the sleeve 6 around the end 3 of the pile 1 will be easy.

According to an especially favorable embodiment of the present invention a sufficient temperature difference is brought about in such a manner that said sleeve 6 is heated by means of a inductive heating arrangement 9 known per se, as disclosed in Figure 3. Here a usually relatively sparse loop inductive winding 12 arranged favorably at the end of coupling lines 11 is connected as the secondary winding of an inductive transformer 10 known per se. A high frequency pulsing electrical current fed into said winding 12 will bring about stray currents and thus vibrations in the annular sleeve 6 which favorably is made of a ferrous material and arranged within said winding, thus causing the sleeve 6 to warm intensely. Such an apparatus is relatively small in size and it is easy to handle also in narrow places. At the same time the fire hazard it may cause is moderate, since the heat effect expressly generates in the sleeve 6. The suitable temperature is in the order of 300 to 750 °C, favorably in the range of about 400 to 600 °C. Such a temperature brings about an expansion of the sleeve to such a size that it can be arranged around the end 3 of the pile 1 without problems, as disclosed in Figure 4. One considerable advantage of the inductive heating is also the fact that by adjusting the transformer's frequency the heating can be easily directed almost exclusively to the outer sleeve 6 or the like, while the inner structures like the pile itself hardly will be heated.

As such the deformation required by the arrangement according to the present invention is relative and temporary, i.e. the size of the piece itself will be restored to that which prevailed prior to the deformation caused by the temperature impact directed thereto. Thus, the mutual alignment of the parts can be performed at a wider clearance. A such, this general alignment principle is known in engineering industry but until now it has required such special arrangements which, used in building work site conditions, have been clearly inappropriate. Thus, even in difficult conditions piles have been extended in accordance with known technology so that the parts are brought together using brute force or specially shaped fittings. Contrary to this, according to the present invention the connection between the piles is made by bringing a bushel, a part of a tube, a sleeve 6 or the like portion to temporarily change its shape for the time of the adaptation and then to return to its original shape.

Instead of pressing the end 13 of a pile 2 constituting the extension by force into a sleeve which is separately fastened by welding to the pile to be extended, where said sleeve has a tight fit and where said sleeve will simultaneously suffer and change its shape to some extent, a technology known from other fields will now be used, in accordance with the present invention, in a new manner so that the actual diameter of the sleeve 6 is now enlarged for the time of making the connection. Thus, said sleeve 6 will not be forced by an axial movement of the parts to be wedged open to such an extent that it can accommodate the end 13 of the pile 2, but the expansion thereof will be accomplished by heating the sleeve 6 in accordance with the present invention. Here such axial forces are avoided, which forces are directed towards the sleeve 6 and which in most cases will break the sleeve to some extent, and due to which the joint after the connection will remain loose to some extent. On the opposite, due to the present invention such an extension will be achieved, wherein the outer sleeve by its own shrinking will snugly keep the pile ends by a radially directed force which, by means of an axial friction, will keep together the

ends

3, 13 of the pile. Simultaneously, said interconnecting piece 6 will straighten out any inclination by means of a radial force. Thus, a new way of extending poles has been disclosed, which is clearly faster, safer and also more useful in work site conditions than the pile extending technique used until now, due to the fact that any forceful axial pressing between the piles is rendered unnecessary.

As such the heating and attachment of said sleeve 6 can be made in one or two stages, depending on the case. In a one stage embodiment said sleeve 6 favorably is arranged in a cold state at the end 3 of the pile 1, suitably by means of an inclination 14 made suitably at the inner surface 7 thereof. Upon heating the sleeve 6 will fall down into position around the end 13 of the pile 1 all the way to the retention ring 5. After this the inductive 12 winding is removed and the lower end 13 of the pile 2 constituting the extension is arranged within the free upper end 15 of said sleeve 6. When the sleeve 6 is cooled down its diameter will decrease back to essentially the original size, in which case the diameter thereof will clamp around each one of said pile ends 3, 13 extremely forcefully from the outside. Due to the even shrinking said sleeve 6 will, in a self-centering manner, maintain its own direction and, simultaneously, take care of the mutual alignment of said

piles

1, 2, so that also the

extended pile entity

1, 2 will remain straight.

When the heating is performed in two stages the procedure will be essentially the same. The difference is that said sleeve 6 in connection with the first heating is brought around the end 3 of said first pile as a separate operation. After this said sleeve 6 may, if necessary, be cooled and thus grip the end 3 of pile 1. In the second stage a second heating of the sleeve 6 or the upper end of the sleeve is performed, said sleeve being in position on the end 3 of the lower pile 1, i.e., on the pile which is to be extended. Said induction winding 12 is then removed and the end 13 of said upper pile 2 is arranged within the extent 15 of the temporarily expanded sleeve 6, after which sleeve 6 may definitely cool down to normal i.e. to the ambient temperature.

The temperature difference required for the deformation due to a change in temperature for one or some parts can also be achieved by cooling instead of heating. As such a sufficient cooling of the end 3 of a pile 1 is a rather complicated operation especially for a pile which already is driven into the ground. The most favorable embodiment of the present invention is based on a condition where the fitting temperature for each piece differs from the normal temperature of the connection, i.e. the ambient temperature in the ground, by an amount of at least 300 °C, favorably more than 400 °C. Thus a sufficient change in temperature for one piece cannot normally be achieved only by cooling. The invention, on the other hand, also includes such an embodiment where one joint piece is heated and another, correspondingly, is cooled, in which case a sufficient total fitting clearance for the time of the joining operation is achieved on one hand by expanding an outer piece and, on the other hand, by shrinking an inner piece. This arrangement is appropriate especially in such an arrangement where the end 3 of a pile 1 as such constitutes said sleeve portion, as will be discussed in more detail below.

The inventive arrangement is especially favorable in connection with such piles 1 which are expressly round in section. Thus, the arrangement implemented in the manner described is especially suitable for extending tubular or the like piles made of metal and especially of steel. For tubular piles, however, such an arrangement can be used as well, wherein the

pile tubes

1, 2 as such constitute opposite sleeves. In this case a generally dowel-like member 17 suitably provided with a retaining flange 16 is arranged into the tubes, correspondingly, which member connects said tubes, as is disclosed in a general manner in Figure 7. Said dowel-like member 17 can be pushed into a pile tube 2 either so that the end 13 of said tube is heated in accordance with the above description as evident from Figure 9, in which case also the inner diameter of said tube 2 will grow and facilitate the insertion of a dowel 17a. The impact, i.e. the temporary expansion of the mutual clearance caused by the temperature difference can be increased by simultaneously cooling said dowel 17a. Here Figure 8 schematically discloses that an end provided with a dowel-like member 17 in accordance with the above, as disclosed in Figure 7, in itself is cooled in a suitable manner, e.g., by dipping said end into a vessel 18 containing fluid nitrogen. A dowel-like member which has been shrunk in this way is then especially easily insertable, as disclosed in Figure 9, into the structure of the tubular pile which has been expanded by heating. Here the result is a favorably entirely smooth joint, as disclosed in Figure 10. In the embodiment according to Figure 10 said dowel-like member 17 is tubular, as such, and thus the straightness of the pile can be checked via an

axial opening

19, 19a, 19b which extends continuously through the pile assembly 1-2.

One considerable advantage of the arrangement according to the present invention is the fact that all such machining work which requires some kind of precision, i.e. the forming of said sleeve 6 or said piece 17 corresponding thereto, as well as any other prefabrication can be performed in advance and under such conditions where the performance is easy. A such a rather coarse machining is enough even for the prefabrication, since the inventive arrangement in any case provides a tolerance which is exact enough for piles. At the actual installation work site only the alignment and the provision of the necessary temperature difference remains to be done. Thus, also the exact machining of the

ends

3, 13 of said

piles

1, 2 can be omitted, since the clearance provided by the temperature difference is clearly wider than the fitting required by prior art. In practice it is enough that the ends 3, 13 of said

piles

1, 2 are cut off fairly orthogonally, which, on the other hand, also can be done under work site conditions.

The same tolerance discussion applies for said sleeve 6 and, correspondingly, for the lateral dimension of the piles, i.e. the diagonal for round piles. Also here the temporary expansion of the fitting clearance achieved by the change of temperature will be so great that normal material used for piles, including any surface coarseness, will be well suited for interconnecting in accordance with the present invention without any further operations. In the same way also normal commercially available tube qualities can be used as material for the provision of said sleeve 6 to be arranged around the piles. However, in order to enhance the grip between said sleeve 6 and said

piles

1, 2 one or both of the

surfaces

7, 8 arranged in an opposite disposition may also include a roughening or the like (not shown), even though a sufficient grip in most cases will be achieved via the natural coarseness of the parts.

Since the arrangement according to the present invention in the first case will be realized by shrinking together such parts which have been radially expanded or shrunk, correspondingly, such an interconnection between the different parts will be achieved which in practice has both bending stiffness and resistance to torsion. Thus, the extension according to the present invention is suitable for the described piles which are driven mainly straight and additionally also for bored piles and other bore tubes or the like pieces which are rotated during the installation and which are intended to be mainly permanent.

Above an extension arrangement in accordance with the present invention has been described especially by referring to metal tube piles or solid piles having a round section. However, since the expansion due to temperature functions in the same manner regardless of the shape of said sleeve 6 no actual problems will araise in such cases either where the sectional shape of the piles to be extended is another. Thus, the arrangement can also be utilized, e.g., in connection with concrete piles having a quadratic sectional shape. When an annular sleeve 6 is used the shape of this sleeve is simply adapted to the sectional shape of the piles. In some cases in may, however, be appropriate to provide separate connecting pieces at the ends of the piles in connection with the molding of especially concrete piles in order to secure a sufficient fitting tolerance under all conditions.

Above some favorable embodiments of the present invention have been described, but for the professional in this field it is clear that the invention can be effected also in many other ways within the scope of the appended claims.

Claims

An extension arrangement for piles or the like pieces (1, 2) to be driven essentially in a vertical direction, wherein the upper end (3) of a lower pile (1) and the lower end (13) of an extending upper pile (2) to be arranged in an opposed position with respect thereto are interconnected by a separate interconnecting piece (6, 17) which is arranged at said ends (3, 13) of said piles (1, 2) axially with respect to the longitudinal axis of said piles, characterized in that said interconnecting piece (6, 17) is dimensioned to have such a tolerance that at least some lateral surfaces (7, 8) thereof, due to a change in temperature which is established in at least one part (6, 17; 3, 13) of the connection, will radially drift apart from corresponding lateral surfaces (8, 7) at a counterpiece (3, 13; 6, 17) arranged axially in an overlaying position and interconnecting therewith, while said lateral surfaces (7, 8) press against each other, correspondingly, in normal temperature conditions.
An arrangement as defined in claim 1, characterized in that said interconnecting piece is a metal sleeve (6) to be arranged around the pile, the fit of said sleeve (6) on the end (3, 13) of said pile (1, 2) being such that an expansion which is effected by a heating directed to said sleeve (6) will render possible the introduction of the end (3, 13) of at least one of said piles (1, 2) into the structure (15) constituted by said sleeve (6), but which, on the other hand, in a normal temperature will clamp with its inner surface (7) against the outer surface (8) of said pile (1, 2), the arrangement further comprising means (9) for temporarily heating said sleeve (6) at said pile end (3, 13) in order to achieve said expansion.
An arrangement as defined in claim 1 or 2, characterized in that said heating means (9) for creating the thermal expansion comprise an inductive transformer (10) and an inductive winding (12), said winding (12) being positionable, for the heating time, temporarily around the part (6, 3, 13) to be expanded.
An arrangement as defined in any one of claims 1 to 3, characterized in that the arrangement further comprises a retaining ring (5) which favorably temporarily can be arranged around the lower pile end (3).
An arrangement as defined in any one of claims 1 to 4, characterized in that the lateral surface (7, 8) of said interconnecting piece (6, 17) and/or at least one of said pile ends (3, 13), correspondingly, comprises a grip enhancing coarseness or the like formation, the radial extent of which being smaller than the total radial dimensional change which is due to the change of temperature in said interconnecting piece (6, 17) and/or said pile end (3, 13).
A method for the extending piles (1, 2) or the like pieces to be driven essentially vertically, in which method for the connection is used outer and inner interconnecting portions (6, 17; 3, 13) to be pushed into an axially mutually overlying disposition, characterized in bringing the inner diameter of said outer interconnecting portion (6; 3, 13) by means of a temperature difference relatively wider than the circumferential dimension of an inner interconnecting portion (3, 13; 17), bringing said outer (6; 3, 13) and said inner (3, 13; 17) interconnecting portion to move, within a mutual relatively loose fit, in the axial direction of the pile (1, 2) into said overlying disposition while the fitting clearance so provided prevails, after which said portions (6, 3, 13; 3, 13, 17) to be interconnected are brought to the normal temperature of the extension in order to remove the fitting clearance brought about by the temporary temperature difference between said portions (6, 3, 13; 3, 13, 17) and for clamping said portions (3, 6, 13, 17) together.
A method as defined in claim 6, characterized in that a sleeve (6) or the like arranged around the ends (3, 13) of said piles (1, 2) arranged in a mutually opposite disposition is used as said interconnecting portion, wherein said sleeve (6) with respect to its inner extent is brought to be larger than the outer extent of at least one of said pile ends (3, 13), after which said sleeve (6) is brought to shrink around said pile end (3, 13), suitably so that the expansion and, correspondingly, the subsequent shrinking is brought about by bringing said sleeve (6) to constitute the object of a temperature difference.
A method as defined in claim 7, characterized in that the expansion of said sleeve (6) from a shrinked mode corresponding to a normal temperature to an expanded mode for receiving the end (3, 13) of a pile (1, 2) is brought about by infrared or inductive heating said sleeve suitably to about 300 to 750 °C, favorably about 400 to 650 °C, after which the pile end(s) (3, 13) is/are installed within the extent of said sleeve (6) in an opposite disposition and said sleeve (6) is allowed to cool down to the normal ambient temperature.
A method as defined in any one of claims 6 to 8, characterized in that said temperature difference is provided both by heating (9) and actively cooling (18) the connection or portions (3, 6, 13, 17) included therein.
A method as defined in any one of claims 6 to 9, characterized in that the connection is effected in stages so that a separate interconnecting piece (6, 17) and one of said pile ends (3, 13) first are interconnected, after which said interconnecting piece (6, 17) thus connected and the other pile end (13) are connected as a separate operation.