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(11) | EP 0 921 234 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Method and device for arranging a pile in a ground |
| (57) The invention relates to a method for arranging a pile (3) with a widened foot (4)
in a ground (2), comprising the steps of:
carrying into the ground (2) a tube (5) with a diameter substantially corresponding with that of the pile (3) for arranging, opening the tube (5) on the underside, introducing a material (11) forming the pile (3) into the ground (2) through the tube (5), urging the material (11) in its plastically deformable state with force laterally into the ground (2) on the underside of the tube (5) in order to form the widened foot (4), and removing the tube (5) from the ground (2) while forming the body of the pile (3). The material under the tube (5) can herein be urged laterally into the ground (2) by exerting a constant pressure force thereon. A pile (3) with widened foot (4) can thus be placed in the ground (2) in vibration-free manner. The invention further relates to a device for performing this method. For vibration-free urging of the material (11) into the ground (2) this device can be provided with a ram (7) displaceable to a position below the tube. |
[0001] The invention relates to a method for arranging in a ground in substantially vibration-free manner a slender, upright element, in particular a pile with a widened foot.
[0002] The use of a foundation pile in order to support a construction being built on a soft ground is generally known. Such a foundation pile is generally carried into the soft ground over a length such that the bottom end thereof comes to rest on a stable ground layer. A problem which occurs here is that the permissible load on the pile is generally considerably higher than the bearing capacity of the supporting ground layer on which this pile comes to rest. An average foundation pile thus has a maximum permissible load of about 150 to 200 kgf/cm2 (14.7 to 19.6 Mpa), while the bearing strength of a sandy ground is for instance only in the order of 50 kgf/cm2 (4.9 Mpa). This has the consequence that such a foundation pile is in fact used extremely inefficiently because it can only be loaded to a quarter or a third of its strength.
[0003] It has therefore already been proposed to provide such foundation piles with a widened foot, whereby the pressure force from the pile can be distributed over a larger area in the bearing layer and a larger load can thus be taken up. Such a widening will in practice consist of a doubling of the diameter of the pile on its underside, since the bearing surface area is after all quadrupled thereby. Such a foundation pile with widened foot is already known under the name of "Franki pile", which is formed in practice by arranging in the ground a temporarily closed tube which is open on the underside and into which is cast a concrete mass which, when earthmoist, is struck out of the tube by means of a piledriving operation to form the widened foot. The rest of the pile is then formed and the reinforcement arranged, wherein the tube is pulled upward out of the ground.
[0004] A drawback of the known method of forming the "Franki pile" is that the pile-driving of the widened foot is not in all cases practical or even permitted. This is particularly the case when the pile is placed in a built-up and/or residential area.
[0005] The invention therefore has for its object to provide a method of the above described type wherein this drawback does not occur. This is achieved according to the invention by a method comprising the steps of:
carrying into the ground in substantially vibrationfree manner a tube with a diameter substantially corresponding with that of the element for arranging,
opening the tube at least on the underside, introducing a material forming the element into the ground through the tube,
urging the material in its plastically deformable state with force laterally into the ground on the underside of the tube in order to form the widened foot, and
removing the tube from the ground while forming the body of the element.
[0006] By thus urging the material as plastic concrete mass in particular laterally into the ground, the pile can be formed practically without any vibration at all. This in contrast to the known method, wherein material is forced into the ground by means of pile-driving of earth-moist material, i.e. by a dynamic operation.
[0007] The plastically deformable material under the tube is preferably urged laterally into the ground by exerting a constant or gradually changing pressure force thereon in mechanical manner. The widened foot is thus formed in a virtually static process, whereby vibrations and the drawbacks associated therewith are avoided. For exerting of the pressure force use can be made of a ram gradually displaceable to a position below the tube at low speed or of a pressure pump connected to the tube.
[0008] The invention also relates to a device for performing the above described method. Such a device is provided according to the invention with:
at least one tube with a diameter substantially corresponding with that of the element for arranging,
means for carrying the tube into a ground in substantially vibration-free manner,
means for introducing a material forming the element into the tube,
means for urging the material with force laterally into the ground under the tube, and
means for removing the tube from the ground.
[0009] The means for lateral displacement of the plastically deformable material are preferably mechanical means which are adapted to exert a constant or gradually changing pressure force on the material. These means can be formed by a ram uniformly displaceable at relatively low speed to a position below the tube or by a closable inner tube functioning as such. The means for lateral displacement of the plastically deformable material can however also be formed by a pump placed above ground with which the material is pressed into the tube under pressure.
[0010] The invention will now be elucidated on the basis of a number of embodiments, wherein reference is made to the annexed drawings, in which:
figure 1 shows a partly cut-away schematic perspective view of a part of a first embodiment of the device for forming a pile with widened foot, which is provided with a separate ram,
figure 2 shows a view corresponding with figure 1 of an alternative embodiment of the device with a closable inner tube functioning as ram,
figure 3 shows a view corresponding with figures 1 and 2 of a second alternative embodiment wherein a closable inner tube likewise functions as ram,
figure 4 is a view corresponding with the foregoing figures of a third alternative embodiment with a pressure pump instead of a ram, and
figure 5 shows schematically the most important steps of the method according to the invention.
[0011] A device 1 for arranging in a ground 2 an upright, slender element, in particular a pile 3 with a widened foot 4, comprises an outer tube 5 for arranging in the ground 2, the diameter of which substantially corresponds with the diameter of the pile 3 to be formed. Device 1 further comprises means (not shown here) for carrying tube 5 into ground 2, for instance a drilling gear or screw installation.
[0012] Lowered into outer tube 5 in the shown example is an inner tube 6 in which a ram 7 is movable up and downward to a position under tubes 5, 6. This ram 7 can for instance be formed by a very heavy block suspended from a cable 8, but can also take the form of a pressing element which is pushed downward by one or more hydraulic jacks or by means of hydrostatic pressure. This pressing downward takes place gradually and uniformly at a relatively low speed which may lie between 1 and 100 m/min, preferably between 2 and 50 m/min and more preferably between 5 and 20 m/min. In the shown example ram 7 is pressed downward at a speed of about 10 m/min.
[0013] A seal 9 is arranged between ram 7 and the inner wall of inner tube 6 in order to prevent concrete mass escaping between ram 7 and inner tube 6 when pressure is exerted thereon. Formed between outer tube 5 and inner tube 6 is an annular space 10 into which the material 11 from which pile 3 must be formed is cast or pumped as according to arrow S. Into this annular space 10 is also lowered the reinforcement 12 which imparts to the pile 3 part of its final strength. The annular space 10 is closable by a closing member 13 or - if the material 11 of the pile is pumped - optionally by a valve on the material pump.
[0014] Outer tube 5 is carried into the ground 2 until it encounters a bearing ground layer 14. The material 11 is subsequently cast or pumped into annular space 10 and the space closed by member 13. Tube 5 is then raised in its entirety through a determined height, wherein the space left behind is simultaneously filled with the material (fig. 5A). Using ram 7 pressure is then exerted on material 11 while it is still plastically deformable. Material 11 is driven laterally outward with force by ram 7 which is pressed gradually downward to a position below outer tube 5. The surrounding ground 2 is herein pressed aside so that a foot 4 is formed which protrudes outside outer tube 5. Ram 7 is moved reciprocally, wherein the space formed thereby is repeatedly filled with material 11 (fig. 5C, D). Because material 11 is still very soft during the up and downward movement of ram 7, this movement does not result in shocks or vibrations in the ground 2.
[0015] Once the foot 4 has been formed the outer tube 5 is gradually withdrawn from ground 2, while a constant, optionally hydrostatic pressure is exerted on the supplied concrete mass 11, whereby the body of pile 3 is formed. When the whole pile 3 is finally formed the tubes 5 and 6 will therefore stand above the ground 16.
[0016] In an alternative embodiment of the device 21 (figure 2) inner tube 6 is likewise fixed relative to outer tube 5 but the annular space 10 formed therebetween is not used for supplying material 11. Use is made for this purpose of a second tube 27 which is further located inside inner tube 6 and which functions simultaneously as ram. Reinforcement 12 is also placed in this movable ram tube 27. In the shown embodiment ram tube 27 is closable at the top by means of a closing member 23. It is also possible - if use is made of a material pump - to use a valve on the pump instead. For exerting a pressure force on the plastically deformable material 11 the ram tube 27 is closed by means of member 23 and thereafter pressed downward. As a result of closing member 23 the material present in ram tube 27 cannot escape, whereby an increasing pressure is built up as ram tube 27 moves downward. Outer tube 5 therefore only serves here to form a cavity of the desired diameter. The speed at which ram tube 27 is pressed downward otherwise corresponds with the above stated speeds of ram 7 of the first embodiment.
[0017] In a second variant of device 31 (figure 3) no separate inner tube 6 is present but ram tube 27 is received for direct displacement in outer tube 5. This variant otherwise operates just as the first alternative shown in figure 2.
[0018] Instead of a ram displaceable in tube 5, use can also be made for exerting a pressure force of a pump 37 placed above ground 16, whereby material 11 is delivered under pressure into outer tube 5 via a conduit 42 (figure 4). Because this embodiment does not require any components movable in tube 5, it is structurally simpler. It should be remembered here that tube 5 will often extend some tens of metres into the ground 2. Pump 37 will on the other hand require a relatively high capacity.
[0019] With the devices as described above and shown in the figures it is possible to arrange a pile 3 with a widened foot 4 in a soft ground 2 in wholly or practically vibration-free manner. Use is herein made of the insight that the material 11 of the pile can be easily placed under pressure in static or practically static manner as long as it is plastically deformable, whereby no striking or pile-driving operations are required.
[0020] Although the method and device according to the invention are described above withe reference to a number of embodiments, it will be apparent to the skilled person that it is not limited thereto. The slender, upright body does not therefore have to form a pile but can also function for instance as drainage column. Concrete or mortar is then not used here as material but gravel or sand which can be blown or pressed downward under pressure into outer tube 5.
carrying into the ground in substantially vibrationfree manner a tube with a diameter substantially corresponding with that of the element for arranging,
opening the tube at least on the underside, introducing a material forming the element into the ground through the tube,
urging the material in its plastically deformable state with force laterally into the ground on the underside of the tube in order to form the widened foot, and
removing the tube from the ground while forming the body of the element.
at least one tube with a diameter substantially corresponding with that of the element for arranging,
means for carrying the tube into a ground in substantially vibration-free manner,
means for introducing a material forming the element into the tube,
means for urging the material with force laterally into the ground under the tube, and
means for removing the tube from the ground.