Method and device for driving piles

Abstract: The method, in which a ram (9) is dropped over a height in a tubular pile (8), provided with a foot, onto an impact face (11) situated in said tubular pile, in order to transfer the kinetic energy from the ram to the ground (13) near the tubular pile, for driving the tubular pile into the ground, is characterised in that the kinetic energy of the ram is transferred dispersed to the ground near the tubular pile. Devices for this are characterised in that means which can temporarily absorb a part of the kinetic energy of the ram are provided. These means can be spring elements (12), and can lie between ram and impact face or between impact face and the wall of the tubular pile. In particular, at least one spring element can be fastened to the ram at the bottom. In this case at least one spring element can have a linear, progressive, depressive or a combined action, and/or a pre-tension and/or a limit for limiting the lenght change can be provided in it. Such a spring element can also be made of rubber or plastic and/or can have a dampind effect. The tubular pile can be made in particular of steel or plastic.

Description: The present invention relates to a method and device for driving tubular piles, in which a ram is dropped over a height in a tubular pile, provided with a foot, onto an impact face situated in said tubular pile in the bottom part thereof, in order to transfer the kinetic energy from the ram to the ground near the tubular pile, for driving the tubular pile into the ground. Such a method is often used if the working space is not high enough to drive concrete piles, as is the case inside existing buildings, or where the access opening is small. Since the ram falls in a tubular steel pile, and since the tubular pile can be welded together in sections during pile driving, little working height is needed. A widened foot of steel or concrete is sometimes placed around the tubular pile. Instead of that, a widened foot is sometimes also driven out after the tubular pile has been driven into the ground. When the tubular pile is at the correct depth, it can be cut off at the correct height and filled with concrete, in which reinforcement can be provided. Driving a tubular steel pile is normally carried out by placing a plug of, for example, sand, gravel or concrete or a second steel plate in the bottom part thereof and dropping a solid metal ram, with a diameter generally lying between 80 and 500 mm and a weight generally lying between 100 and 4,000 kg, in the tube onto the ground, plug or plate, so that a force impulse is produced thereon (GB-A-1 474 379). The direct contact between ram and tubular pile, causing a very great peak force, is regarded as essential in this method, in order to make the use of a relatively small falling weight possible. This known method has the disadvantage that a part of the energy of the ram is not utilised for driving the tubular pile into the ground, but goes into the tubular pile itself and can lead there to undesirable plastic deformation if the wall thickness is small. When the ram falls at great speed the force impulse in fact within a very short time causes the build-up of a great tensile stress wave in the tubular pile. The object of the method according to the invention is to eliminate or reduce these disadvantages, through the fact that the kinetic energy of the ram is transferred more slowly to the ground near the tubular pile. The devices according to the invention are essentially characterised in that for this purpose means which temporarily absorb at least a part of the kinetic energy of the ram are provided. These energy-absorbing means can comprise at least one spring element. The use of such spring elements, against expectations, does not lead to a reduction in the amount of driving energy transferred to the ground, if the dimensions are correctly selected. It even turns out that transferred amount of driving energy is only to a small extent dependent on the spring constant. The advantage of dispersing the transfer is that a considerably smaller tensile stress wave is produced in the tubular pile. Because of this, a lower wall thickness of the tubular pile will suffice, which has a cost-saving effect and promotes easier handling. First calculations indicate that in the case of steel tubular piles even wall thicknesses of only 1 mm must be considered possible. A second advantage is that the vibration nuisance for the environment is reduced, which means that, amongst other things, the range of application of the method can be extended further. Due to the lower load of the tubular pile, it is also possible to apply a falling height which exceeds the current maximum of 2.5 m. As a result of this, it is possible to drive piles into harder ground or to use heavier piles or a lighter installation. Finally, the lower load of the tubular pile means that it is possible to use plastic tubular piles. In a first embodiment the spring element is fastened to the bottom of the ram, so that it can move simultaneously with the ram. For achieving the envisaged effect, namely dispersed transfer of the falling energy, using a spring element, this embodiment is found to be advantageous compared with another conceivable embodiment, in which the spring element is on the bottom of the tube. The use of a spring element which moves along with the ram can give rise to problems, but these are simple to eliminate. The first problem is connected with the replacement of a worn spring element. If, however, the spring element is made virtually maintenance-free, through the use of a strong, wear-resistant plastic, such as, for example, nylon, this spring element needs never or hardly ever be replaced. A second disadvantage is found in the fastening of the spring to the ram, since the ram undergoes great accelerations during the collision, and the fastening is then placed under great strain. This disadvantage is eliminated by selecting a spring element with a small spring constant, namely of the order of magnitude of the spring constant of the ground, so that the accelerations are reduced to an extent in which the spring element can be fixed without any problem to the ram. Advantages of this embodiment are that during the pile driving no additional operations are required compared with pile driving with the known devices in which there is no spring element, and that this embodiment, compared with a loose accessory, is safe in use. In addition, the spring element can be made more compact, since no separate bearing structure is needed. Another advantage is that the kinetic energy of the spring element during falling contributes to the pile driving energy transferred. The impact face at the bottom of the tubular pile is preferably made flat, and the diameter of the ram is adapted to the inside diameter of the tubular pile, for example with a play of 15 to 25 mm. In a further embodiment a spring element is disposed between the foot of the tubular pile and the wall of the tubular pile. This ensures that the kinetic energy of the ram is transferred in the first instance directly to the bottom near the tubular pile, and the tubular pile is subsequently pulled along by the spring. In an advantageous embodiment a flange is provided at the bottom of the ram, in which flange a plastic plug is provided, projecting downwards past the flange. In the embodiments mentioned each spring element can comprise, for example, a linear or degressively or progressively working tension or compression spring, and a spring which works degressively in one part of its range and progressively in another part thereof can also be used. The spring element can also be disposed under pretension, so that when the ram is going down, a certain force is exerted directly on the impact face when the spring element makes contact with the impact face. Without pre-tensioning, this force is built up from the value zero as the length of the spring element changes, while energy is stored in the spring element, which energy is not used for driving the tubular pile into the ground. A limit can also be provided to limit the length change of the spring element, so that when it goes down, after the limit is reached, the remaining kinetic energy of the ram is transferred to the tubular pile without further storage. Instead of this, the latter effect can also be reached approximately if a spring element which has very greatly increasing spring rigidity at a predetermined length change is used. Finally, the spring element can have a damping effect, for example for limiting the springing back of the ram. Through using the abovementioned measures, individually or in combination, the progression of the energy transfer from the ram to the tubular pile can be adapted to the pile driving situation. The invention will now be explained, by way of example, with reference to the drawing. In the drawing the following are shown schematically: Fig. 1 shows a device which operates according to the prior art, as indicated above; Fig. 2 shows an embodiment of a device according to claim 5; Fig. 3 shows an embodiment of a device according to claim 7; Fig. 4 shows another embodiment according to claim 7; Fig. 5 shows another embodiment according to claim 14; Fig. 6 shows embodiment according to claim 15. In the device according to Fig. 1, which shows the prior art, on each pile driving stroke ram 2 falls in tubular pile 1 onto an impact face 3 lying on top of a plug 4, in which case the ram 2 transfers its kinetic energy in pulse form to the tubular pile 1, as a result of which the latter is driven into the ground 5. The ram 2 is then raised by means of the hoisting wire 6. In the embodiment shown in Fig. 2 the ram 9 falls in the tubular pile 8 onto the impact face 10 of plug 11. The spring element 12 is fastened at the bottom to the ram 9 and when the ram 9 comes down onto the impact face 10 temporarily absorbs a part of the falling energy of the ram 9. This produces a dispersed transfer of the kinetic energy from the ram 9 to the ground 13 near the tubular pile 8. Fig. 3 shows an embodiment according to claim 7, in which a ram 25 falls onto an impact face 24 in the tubular pile 23. This impact face 24 is connected by means of a tension spring 26 to the wall of the tubular pile 23. The tubular pile 23 is shut off at the underside. Fig. 4 shows another embodiment according to claim 7, in which a ram 29 falls in the tubular pile 28 onto an impact face 30, forming part of the foot 31. This foot 31 is connected by means of a tension spring 32 to the tubular pile 28. Fig. 5 shows an embodiment according to claim 14. Here ram 34 falls in the tubular pile 33 onto impact face 37. A plastic plug 36 is fitted on the underside of the ram 34 in an annular flange 35, while the plug projects beyond the flange 35. The plug forms a progressive spring, due to the fact that when it is compressed it expands laterally until the flange prevents it, and length change is all that is now possible. Fig. 6 shows an embodiment according to claim 15, in which a ram falls in the tubular pile 39 onto impact face 42. Fixed at the bottom of the ram 40 is a plastic element 41, in the form of a solid semi-spherical element. This element 41 has a progressive spring action, through the fact that, viewed in the direction of fall, its cross-section narrows considerably.

Claims: Method for driving tubular piles, in which a ram (9; 25; 29; 34; 40) is dropped over a height in a tubular pile (8; 23; 28; 33; 39), provided with a foot, onto an impact face (10; 24; 30; 37; 42) situated in said tubular pile in the bottom part thereof, in order to transfer the kinetic energy of the ram to the ground (13) near the tubular pile, for driving the tubular pile into the ground, characterised in that the method comprises the use of energy-absorbing means (12; 26; 32; 36; 41) which temporarily absorb at least part of the kinetic energy of the ram such that the kinetic energy of the ram is transferred more slowly to the ground near the tubular pile. Device for carrying out the method according to claim 1, comprising a tubular pile (8; 23; 28; 33; 39) provided with a foot and an impact face (10; 24; 30; 37; 42) situated in said tubular pile in the bottom part thereof, and a ram (9; 25; 29; 34; 40) for dropping over a height in the tubular pile onto the impact face to transfer the kinetic energy of the ram to the ground near the tubular pile, for driving the tubular pile into the ground, characterised in that the device comprises energy-absorbing means (12; 26; 32; 36; 41) which temporarily absorb at least part of the kinetic energy of the ram such that the kinetic energy of the ram is transferred more slowly to the ground near the tubular pile. Device according to claim 2, characterised in that the energy-absorbing means are spring elements. Device according to claim 3, characterised in that at least one spring element is disposed between the ram and the impact face. Device according to claim 4, characterised in that at least one spring element is fastened to the ram at the bottom. Device according to claim 3, characterised in that at least one spring element (26; 32) is situated between the impact face (24; 30) and the wall of the tubular pile (23; 28). Device according to one of claims 3 - 6, characterised in that at least one spring element comprises a linear tension or compression spring. Device according to one of claims 3 - 6, characterised in that at least one spring element is composed of a progressive or degressive or combined degressive and progressive spring. Device according to one of claims 3 - 8, characterised in that at least one spring element has a pre-tension. Device according to one of claims 3 - 9, characterised in that at least one spring element at a predetermined length change shows a very great increase in spring rigidity. Device according to one of claims 3 - 9, characterised in that a limit which limits the length change of at least one spring element is provided. Device according to one of claims 3 - 11, characterised in that at least one spring element is made of rubber or plastic. Device according to claims 3 - 12, characterised in that a closed flange (35) is fixed at the bottom to the ram (34), between which a plastic plug (36) is fitted as the spring element and projects downwards past the flange (35). Device according to claims 3 - 12, characterised in that a plastic part whose cross section narrows in the direction of fall is fitted as the spring element (41). Device according to one of claims 3 - 14, characterised in that at least one spring element has a damping action. Device according to one of claims 2 - 15, characterised in that the tubular pile is a steel tubular pile. Device according to one of claims 2 - 18, characterised in that the tubular pile is a plastic tubular pile.

Inventors: DE WAAL VICTOR JAN, DE WAAL, VICTOR JAN
Applicants: WAAL TECHNOLOGY & CONSULTANCY, DE WAAL TECHNOLOGY & CONSULTANCY B.V.
Application year: 1992
Main classification: E02D7
IPC codes: E02D13