EP1930506A1 - Load-testing element - Google Patents

Abstract

The device has a foot and or in the field of the founding element on a support cushion (1.1') and which consists of two separated sheets (2, 3 and 2', 3 ) which, at their edges have tensile and dense circulation. Tubes (4.4') have a slot (5) and arranged between the plates. The support cushion is filled and has is equipped with or without opening (15) for a concrete pipe inside the sheets.

Description

The invention describes a device for carrying out load tests on foundation elements in the ground.

In the foot area or along the shaft of a pile or a slot wall element devices according to the invention are installed before the concreting process. These divide the shaft into several sections.

After hardening of the concrete of the foundation elements, these devices are increased in volume by means of a liquid. This creates a hydraulic pressure.

During the increase in volume, the shaft portions are pushed apart vertically and thereby the vertical movements and deformations of the individual shaft sections are determined. This is usually done with extensometer rods or electrical transducers according to the prior art.

The displacements are then assigned to the respective force applied with the device.

About the size of the applied force between the shaft sections can be concluded on the existing skin friction and the peak pressure of the foundation element in the ground. The operation of this load test is for example in the DE 34 24 776 or the DE 34 07 938 described. For this purpose, hydraulic cylinders are installed in the foundation elements, in which a piston is extended.

A similar system is in the US 55 76 494 described.

These hydraulic cylinders are expensive to manufacture and relatively complicated to attach to the reinforcing baskets of the foundation elements. Another problem arises when these hydraulic cylinders are arranged in the pile shaft. In this case, the concreting process must be interrupted because the concreting pipe or the concreting hose can not be bypassed on the hydraulic cylinders.

In particular, in the production of foundation elements under water, the interruption of concreting can be very dangerous, since inhomogeneities in the concrete result when pulling out of the concreting tube and subsequent reinsertion of the concrete pipe can. This can lead to undesirable disturbances in the carrying behavior of the foundation element during the load test.

The continuous concreting process can be ensured by using hydraulic cylinders in the foundation element only by using a plurality of small hydraulic cylinders, which are arranged in a ring shape. This increases the cost of carrying out the experiment significantly and is associated with a large installation effort.

In addition, special control of the hydraulic cylinders is required to ensure that all pistons extend synchronously and do not tilt.

In the DE 10 2006 007 144 and in the GB 21 59 961 The expensive hydraulic cylinders are replaced by bellows-type devices (lifting cushions).

However, these bellows-type lifting cushions have the disadvantage that they tend to leak due to the many welds.

Another disadvantage of these bellows lifting cushion lies in the determination of the applied load. The force applied between the shaft portions is determined by multiplying the applied oil pressure by the pad area. However, since these lifting cushions deform insignificantly during inflation, the horizontal effective area of these inflatable cushions changes during inflation. Thus, the determination of the actually applied load is associated with certain measurement inaccuracies, since the real effective area is not known.

Also when using much more expensive hydraulic cylinder as in the US 55 76 494 described, can result inaccuracies in the determination of force. The hydraulic piston, which extends out of the cylinder, is sealed against the hydraulic fluid via special sealing rings and guided via support rings. Due to the inevitable friction, a certain part of the force is absorbed in the hydraulic cylinder, resulting in inaccuracies in the determination of the test load. leads.

The object of the invention is that the device is simpler and cheaper, that the risk of leaks in the system is reduced and that the force with which the individual shaft sections are pressed apart, can be determined as accurately as possible. In addition, an interruption of the concreting process should be avoided.

The solution of the problem is carried out according to the features of the claims.

The explanation of the invention is based on the FIGS. 1 to 8 ,

FIG. 1 shows a vertical section through a foundation element in the ground. The shaft is subdivided into sections 10, 11 and 12 by devices according to the invention. The devices according to the invention essentially consist of a lifting pad 1, 1 'and an independent force measuring device 6, 6', which is surrounded by a special annular space 8, 8 ', 8 ".

FIG. 2a shows a vertical section through an inventive lifting pad 1, as it is installed in the foot region of the shaft.

FIG. 2b shows a spatial representation of a lifting pad 1, which is cut vertically.

FIG. 3a shows a vertical section through a lifting pad 1 ', which is arranged in the shaft region and has an opening 15 in the middle for the passage of a concrete pipe or concreting hose.

FIG. 3b shows a vertical section through a spatial representation of a lifting pad 1 '.

FIG. 4 shows a vertical section through an embodiment of the invention for the lifting pad 1, in which the tube-like structure 4 is particularly formed.

FIG. 5 shows a vertical section through an embodiment variant according to the invention, in which the devices 1, 1 'according to the invention are attached to a reinforcing cage 29. Between the lifting cushions 1, 1 'and the associated force measuring devices 6, 6' additional contact pieces 7, 7 'are arranged here.

FIG. 6 shows a vertical section through the pile shaft of a foundation element, wherein a loading state is shown, in which the lifting cushions 1, 1 'are shown in an inflated state and in which the pile shaft elements 10, 11, 12 have already been pressed apart. In this load condition, cracks 21, 22 occur in the concrete of the shank.

FIG. 7 shows a vertical section through an embodiment according to the invention, in which the pressure measuring means 6, 6 'have direct contact with the surfaces of the lifting cushions 1, 1'.

FIG. 8 shows a vertical section through a foundation element, wherein on the inventive devices special power transmission bodies 30, 31, 32 are arranged in order to ensure an optimal force entry into the shaft sections.

The object is achieved with the device according to the invention in that the determination of the force between the individual shaft elements 10, 11, 12 is decoupled from the lifting process and that the force measurement is carried out so that the applied forces on the lifting cushion completely by separate force measuring devices 6, the sixth be directed. For this purpose, the force flow between the shaft elements 10, 11, 12 is controlled by specially designed annular spaces 8, 8 ', 8 "around the force measuring devices 6, 6' and it is avoided that forces are bypassed via force bridges or annular spaces at the force measuring devices.

In the lifting cushions according to the invention, a distinction is made between foot-lifting cushions 1 and shaft-lifting cushions 1 '.

The Fußhubkissen be, as in FIGS. 2a and 2b represented, spaced-apart sheets 2, 3 connected to a circumferential tube-like structure 4.

The simplest and preferred embodiment for the tube-like structure 4 are slotted tubes with a circular cross-section or quadrangular cross-section. Circular closed rings are preferably produced from these pipes in the case of bored piles. On the side where these rings are connected to the spaced sheets 2, 3, these pipe sections are provided with through slots 5. The connection of the slotted tubes with the spaced sheets is preferably carried out by welding.

The slits 5 running along the tube winding have a preferred slot width of 5 to 15 mm.

The welding of this tube-like structure 4 to the spaced sheets 2, 3 has the advantage that when inflating this lift cushion both in the sheets 2, 3 and in the wall of the tube-like structure 4 essentially only tensile forces and thus the sheets in the optimum direction be charged. A kinking of the pipe wall can be avoided in this way, so that the entire system can be subjected to very high pressures, without causing damage. In addition, the Welds essentially stressed and less stressed by bending and shear forces or shear forces, which is also conducive to their stability.

Preferred diameters for the tube-like structures 4, 4 'are in a range of about 2 cm to about 10 cm. Preferred sheet thicknesses for both the spaced sheets 2, 3, 2 ', 3' and for the sheet metal wall of the tube-like structures 4, 4 'are in a range of a few millimeters. To select the sheet thickness for the spaced sheets 2, 3 and the wall thickness of the tube-like structure 4 as similar as possible is particularly advantageous. In this way, a uniform load throughout the system during inflation results.

The paths which the lifting cushions 1, 1 'according to the invention execute during the loading test in the axial direction of the shaft are within a preferred range of a few millimeters to several centimeters. To inflate the lifting cushions, these are connected to lines that lead to the earth's surface. The line connection is preferably carried out in the region of the tube-like structure 4, 4 'via welded joints, screw connections or press connections.

FIG. 2b shows a variant for the foot pad 1, in which the tube-like structure has a polygonal cross-section. In principle, all cross-sectional shapes are possible, but preferred are convex embodiments in which the cross section with respect to the welding points on the spaced sheets is curved outward. These forms are just the most suitable for absorbing tensile forces when the pipe cross-section bends from the smaller to the larger bending radius.

So that the concreting process for installation of the devices according to the invention need not be interrupted, the devices according to the invention for the shank are formed with openings 15. These openings 15 should be at least as large as the diameter of the concreting pipes or concreting hoses. Preferably, however, the diameter should be selected larger than the concreting diameter so that the liquid concrete can easily rise through this opening 15.

In the lifting cushion 1 'according to the invention for the shaft region, the spaced sheets 2', 3 'are provided with an inner hole. The substantially as washers looking sheets are at the inner edge and at the outer edge with tube-like structures 4 'tensile strength and tightly connected. Again, in principle any cross-sectional shapes for the tube-like structures are conceivable.

FIG. 4 shows a variant in which the tubular structure 4 is formed by the fact that in a strip-shaped metal strip in a partial region, a tube-like structure 4 is formed, which is bounded on both sides with flat surfaces 26. The ends of these surfaces are welded to the spaced sheets 2, 3 after the sheet metal strip has been joined into a ring.

In FIG. 3b In this case, a further embodiment is shown, in which the tube-like elements are not welded to the sheets 2 ', 3', but they are in this case formed as half-tubes to the sheets 2 ', 3'. In this way, the number of welds is reduced, because the two half-shells are connected to each other only over two welds 27, in contrast to otherwise four necessary welds. The molding of the half tubes is done by pressing, punching or pulling the sheets 2 ', 3' or 2, 3.

The lifting cushions 1, 1 'are inflated via hydraulic lines 9 from the earth's surface after hardening of the concrete in the foundation element with a liquid.

The greater the distance between the sheets 2, 3 or 2 ', 3' during inflation, the more influence this has on the size of the effective horizontal base of the lifting cushion 1, 1 ', since the diameters of the lifting pads change.

For this reason, it is expedient to carry out the force measurement between the shaft elements 10, 11, 12 by an independent force measuring system.

• Einmal wird die Verformung, insbesondere die Stauchung, an einem elastischen Material ermittelt und eine Kraft als Funktion dieser Verformung ermittelt. Dazu werden an dem elastischen Körper Weg- oder Dehnungsaufnehmer unterschiedlichster Weise befestigt, wie z. B. aufgeklebte Dehnmessstreifen, Schwingsaiten- oder elektronische Wegaufnehmer.
  Für den Grundkörper werden bevorzugt Stahlringe verwendet. Solche Kraftmesseinrichtungen werden vor dem Einbau kalibriert.

For this purpose, additional force measuring devices 6, 6 'are arranged below or above the lifting cushions 1, 1'. These are essentially designed so that they perform only very small compressions under load. That is, they are essentially not or only very little deformable. Such force measuring devices are known from the prior art. There are essentially two measuring principles for this:

• Once the deformation, in particular the compression, is determined on an elastic material and determines a force as a function of this deformation. For this purpose, Weg- or extensometers are attached to the elastic body of different ways, such. B. glued strain gauges, Schwingsaiten- or electronic transducer.
  For the body preferably steel rings are used. Such force measuring devices are calibrated prior to installation.

In hydraulically acting force measuring devices, a hollow body is filled with a substantially incompressible liquid. The force is determined as a function of the pressure inside. The hollow body consists of thin-walled sheets. These force measuring devices are calibrated before installation.

In the device according to the invention, force measuring devices according to the prior art are preferably arranged over the surfaces of the sheets 3, 3 'or 2, 2'.

The force with which the individual shaft sections 10, 11, 12 are pressed apart by the lifting cushions 1, 1 'is applied in the apparatus according to the invention essentially over the flat surface of the sheets 2, 2', 3, 3 'of the lifting cushions.

So that the force is not conducted past the pipe-like structures 4, 4 'and any concrete bridges to an unknown portion laterally past the force measuring devices 6, 6', the force measuring devices 6, 6 'with an outer annular space 8, 8' and an inner annular space. 8 This annular space must be designed in such a way that, in particular, it can transmit no vertical forces or forces parallel to the shaft axis, for this purpose an annular space is formed which is filled with a non-force-transmitting and thus yielding or yielding medium preferably of rubber or artificial elastomers with and without gas pores or of flexible synthetic foams with gas pores The pressure resistance of this medium is chosen so high that the annulus is not compressed by the concreting pressure.

A further embodiment for the non-force transmitting and yielding annular space 8, 8 ', 8 "is the filling with a gaseous medium.This gaseous medium is filled into deformable, tube-like sheaths which are connected to vent lines which lead to the earth's surface or one assumes that only very small forces can be transmitted via a gas cushion.

In another embodiment of the invention, the annular space 8, 8 ', 8 "is formed of flexible hoses filled with a non-hardening liquid and having a discharge line to the surface of the earth. opened and the liquid can escape without pressure.

In a preferred manner, the force-measuring devices 6, 6 'are made smaller in area or the same size as the entire base surface of the lifting pad 1, 1'.

The horizontal extent of the inner 8 "and outer annular space 8, 8 'with the non-force transmitting and yielding medium is chosen so that the horizontal surface of the force measuring device 6, 6' plus the horizontal surface of the annular space is at least as large as the entire base area 25, 25 'of the lifting cushions 6, 6' Only then is it ensured that no compressive forces are applied directly from the shaft elements 10, 11, 12 via still existing concrete bridges, for example above the tube-like structures 4, 4 ', from a shaft element to If this were the case, the determined forces would appear too small and lead to a false interpretation of the test result.

In FIG. 7 an embodiment of the invention is shown in which the force measuring devices 6, 6 'have direct contact with the sheets of the lifting pad 1, 1'.

So that the forces extend from one shaft section to the other shaft section directly through the force measuring devices, the annular spaces 8, 8 ', 8 "are arranged with a non-force-transmitting medium.

These annular spaces extend in the horizontal direction to the extent that they at least completely cover the tube-like structures 4, 4 '. In this way, no vertical force can be transmitted from one shaft section to the other in the region of the tube-like structures 4, 4 '.

The connection of lifting cushion and force measuring device via welding, gluing, screwing or concreting to the optionally roughened surface.

In a preferred embodiment, a disc-shaped or annular contact piece 7, 7 'is arranged non-positively between the support surfaces of the force measuring devices 6, 6' and the substantially planar sheets 2, 3, 2 ', 3'. These contact pieces facilitate the connection of the lifting cushion with the force measuring devices. The connection is made by gluing, screwing or welding. Thus, over these contacts 7, 7 'and 19, 19' in a simple manner to transmit larger tensile forces, such as occur during installation of the reinforcement basket in the hole. In this load condition heavyweight reinforcing cage parts are connected to each other tensile strength over the lifting cushion and the force measuring devices.

Preferably, these contact pieces 7, 7 'made of steel plates or pipe sections or steel formwork, which are filled with a pressure-resistant material such as concrete or cement paste.

In FIG. 5 and 6 Embodiments are shown with the devices according to the invention, which can be mounted or welded as a prefabricated element between the reinforcing cage sections. For this purpose, lifting cushion and force measuring device are sandwiched together and protected with sheets 17, 18, 17 ', 18', via which the tight connection of the individual reinforcing cage sections takes place.

The free space between the plates 17, 18, 17 ', 18' is filled with the non-force transmitting and yielding medium to form annular spaces 8, 8 ', 8 ".

In a preferred embodiment, the force measuring devices are manufactured in a similar construction as the lifting cushion and filled with an incompressible liquid. They thus act like a hydraulic force measuring device.

The force measuring device 6, 6 'is connected via pipes 14 or cable to the earth's surface. The volume of this force measuring device is kept constant and force changes can thus be read by changes in the fluid pressure at the earth's surface.

Another variant for the reading of forces in the hydraulically acting force measuring devices is that the fluid pressure is not determined by pressure gauge, but via electrical pressure transducers, which are either inside the force measuring devices or arranged in the supply line 14. In this case, the readings are made via an upwardly directed measuring cable.

Preferably, the disc-shaped contact pieces 7, 7 'in their horizontal extension shape and surface as possible chosen so that they correspond to the surfaces of the sheets 2, 3, 2', 3 ', as they exist between the tube-like structures 4, 4'.

In this way, the lifting cushions can develop their power best and the force input into the force measuring devices 6, 6 'leads to realistic and reproducible measurement results.

FIG. 8 shows a variant in which directly or indirectly power transmission body 30, 31, 32 are arranged. These power transmission bodies are already fastened before insertion of the measuring device into the bore on the devices according to the invention.

These power transmission bodies may be either conical or dome-shaped structures or consist of circumferential cross-sectional areas, such as. As triangles, trapezoids, parabolas, etc ..

Preferably, these power transmission bodies are made of concrete, which is made good formable by the addition of special additives. In addition to the individual structures, continuous, curved, rent-like structures can also be created.

For the loading devices on the shaft foot preferably rounded elements 32 are concreted.

The power transmission body 30, 31, 32 have the task that the forces from the individual Pfahlschaftabschnitten 10, 11, 12 are introduced in the most uniform manner possible in the inventive devices. This is of particular interest when it is to be feared that during concreting by a too small opening 15, no continuous, uniform homogeneity of the concrete between the individual shank sections can be achieved.

Claims (14)

Device for carrying out a load test on foundation elements in the ground with round or square cross sections, such as piles or slot wall elements, wherein devices are installed in the lower part or along the shaft of the foundation element, with which the shaft can be divided in its length and wherein by increasing the volume of this Devices the shaft parts are separated from each other and pressed apart and that it is closed on the applied forces in the devices on the male friction and peak pressure forces of the foundation element, characterized - That at least one lifting cushion (1,1 ') is arranged in the foot area and / or in the shaft region of the foundation element, which consists of two spaced sheets (2, 3 and 2', 3 '), which at its edges tensile strength and tight with a circumferential, tube-like structures (4,4 ') are connected - And that the tube-like structure (4,4 ') has a slot (5) which connects the interior of the tube-like structure with the space between the sheets (2, 3 or 2', 3 ') - And that the lifting cushion (1, 1 ') via filling lines (9) is connected to the earth's surface - And that the lifting cushion (1, 1 ') without or with openings (15) for the concreting inside the sheets (2', 3 ') is equipped. Device for carrying out a load test on foundation elements in the ground with round or square cross sections, such as piles or slot wall elements, wherein devices are installed in the lower part or along the shaft of the foundation element, with which the shaft can be divided in its length and wherein by increasing the volume of this Devices the shaft parts are separated from each other and pressed apart and that it is closed on the applied forces in the devices on the male friction and peak pressure forces of the foundation element, characterized - That in the foot region and / or in the shaft region of the foundation element at least one lifting pad (1,1 ') is arranged, which consists of two spaced sheets (2, 3 and 2 ', 3'), which are tensile at their edges and tightly connected to a circumferential, tube-like structure (4,4 ') - And that the tube-like structure (4,4 ') has a slot (5) which connects the interior of the tube-like structure with the space between the sheets (2, 3 or 2', 3 ') - And that under or above the lifting cushion (1, 1 ') directly or via contact pieces (7, 7') an additional, substantially non-deformable force measuring device (6, 6 ') is arranged, which determines the force between the shaft sections ( 10, 11, 12 ...) occurs when the inner volume of the lifting pad (1, 1 ') is increased by filling with a liquid - and that by arranging an outer and / or inner annular space (8, 8 ', 8 ") about the force measuring device (6, 6') from a non-force transmitting and yielding medium, a horizontal surface in the region of the force measuring device (6, 6 ') is formed which is at least as large as the base surface (25, 25 ') of the lifting pad (1, 1'), whereby the axial forces between the individual shaft sections (10, 11, 12 ...) completely by the force measuring device (6 , 6 '). Device according to claim 2, characterized in that - That the substantially non-deformable force measuring device (6, 6 ') is a metal body, plastic body or concrete body or composed of different materials body whose low compression by means of displacement sensors, such. B. on glued strain gauges, swing sides or electronic position transducer, is determined and that is closed on calibration attempts of the compression on the associated force. Device according to one of claims 2 to 3, characterized - That the substantially non-deformable force measuring device (6, 6 ') consists of a hollow sheet metal body which is filled with a constant amount of liquid and in which the force acting on this sheet metal body, on the fluid pressure in the interior and the base surface is determined. Device according to one of claims 2 to 4, characterized - That the substantially non-deformable force measuring device (6, 6 ') in construction similar to the lifting cushion (1,1'), but remains constant in volume during the load test. Device according to one of claims 2 to 5, characterized - That the substantially non-force transmitting and yielding material in the annular spaces (8, 8 ', 8 ") is natural or synthetic rubber with or without gas pores, plastic or foam in particular. Device according to one of claims 2 to 6, characterized - That the essentially non-force transmitting and yielding material in the annular spaces 8, 8 ', 8 "is a gas introduced into deformable casings or a liquid which can escape from the interior of the shaft by opening lines without pressure. Device for carrying out a load test on foundation elements in the ground with round or square cross sections, such as piles or slot wall elements, wherein devices are installed in the lower part or along the shaft of the foundation element, with which the shaft can be divided in its length and wherein by increasing the volume of this Devices the shaft parts are separated from each other and pressed apart and that it is closed on the applied forces in the devices on the male friction and peak pressure forces of the foundation element, characterized - That in the foot area and / or in the shaft region of the base element at least one lifting pad (1,1 ') is arranged, which consists of two spaced plates (2, 3 and 2', 3 '), which at its edges tensile strength and tight with a circumferential, tube-like structures (4,4 ') are connected - And that the tube-like structure (4,4 ') has a slot (5) which connects the interior of the tube-like structure with the space between the sheets (2, 3 or 2', 3 ') - And that under or above the lifting pad (1, 1 ') directly or via contact pieces (7, 7') an additional, substantially non-deformable force measuring device (6, 6 ') is arranged, which determines the force between the shaft sections (10, 11, 12 ...) occurs when the inner volume of the lifting pad (1, 1 ') is increased by filling with a liquid - and that by arranging an outer and / or inner annular space (8, 8 ', 8 ") about the force measuring device (6, 6') from a non-force transmitting and yielding medium, a horizontal surface in the region of the force measuring means (6, 6 ') is formed, which is at least as large as the base surface (25, 25 ') of the lifting pad (1, 1'), whereby the axial forces between the individual shaft sections (10, 11, 12 ...) completely by the force measuring means (6 , 6 '). - And that between lifting cushion (1, 1 ') and force measuring device (6, 6') disc-shaped contact disc (7, 7 ') are arranged non-positively with or without a hole, the area and shape of the surface of the sheets (2, 3 or 2 ', 3') between the circumferential, tube-like structures (4, 4 ') correspond. Device according to one of claims 1 to 8, characterized - That the tube-like structures (4, 4 ') are tubes with a round, oval or polygonal-like limited cross section, which have a slot (5) which extends over the entire development length and in that the tubular structures (4, 4') closed like a ring are. Device according to one of claims 1 to 9, characterized - That the tubular structures (4, 4 ') have shapes according to claim 9, which in the region of the opening (5) in areal elements (26) pass over which the sheets (2, 2' and 3, 3 ') non-positively and be connected tightly. Device according to one of claims 1 to 10, characterized - That the tube-like structures (4, 4 ') on the lifting cushion (1, 1') are formed by the tube-like structure (4, 4 ') as half shells by pressing, drawing or punching the sheets (2, 2' and 3, 3 ') are formed and that the half-shells by seams (27) are tightly and non-positively connected to each other. Device according to one of claims 1 to 11, characterized - That the lifting cushion (1, 1 ') in plan are circular, quadrangular or polygonal-like limited and are equipped with or without opening (15) for carrying out a concrete pipe or concreting hose. Device according to one of claims 1 to 12, characterized - That between force measuring device (6, 6 ') and lifting cushion (1, 1') disc-shaped or annular contact pieces (7, 7 ') are non-positively disposed, which consist of steel, concrete or combinations thereof, such. As steel rings or steel formwork, which are filled with mortar, concrete or cement paste. Device according to one of claims 1 to 13, characterized - That the lifting cushion (1, 1 ') directly or indirectly with power transmission bodies (30, 31, 32) are equipped.

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