The present invention is directed to a process for producing a pile in the earth with a pipe, the pipe being provided internally with a conduit, which emerges on the bottom side of the pipe, for feeding pile-forming, hardening material into the earth, the process comprising the introduction of the pipe into the earth, the removal of said pipe from the earth and, as the pipe is withdrawn, the filling of the space thus created with the pile-forming, hardening material.
In the prior art, numerous processes are known for the making of piles. A distinction must be drawn between reinforced and non-reinforced piles. For the production of reinforced piles, all sorts of pipe constructions are brought into the earth and, once the desired depth has been reached, the reinforcement is put in place and concrete poured or vice versa. The production of such concrete piles is a lengthy process which takes minutes to tens of minutes. Piles obtained in this way generally have a diameter greater than 20 cm. A known problem with such piles, especially with loose earth layers, is the risk of bulging as the pipe is vibrated or driven out, resulting from the difference in specific weight between the concrete and the surrounding earth. Vibration or shaking of the pipe as it is removed is necessary for the compaction of the concrete.
On the other hand, it is known to produce so-called foam concrete piles in the earth. A steel pipe is first placed in the soil down to the bearing layer, after which a plastics pipe may be placed therein which is subsequently filled with foam concrete, after which the steel pipe is removed. No reinforcement is used. Foam concrete of relatively low specific weight is used to combat the bulging effect.
The piles which are provided with reinforcements, which piles are known from the prior art, have a high bearing capacity. The structures lying thereon are of relatively heavy construction so as to bridge the large distance between the different piles of high bearing capacity. Foam concrete piles are often used to stabilize the earth. For foundation applications, these are not suitable.
A process for producing a pile in the earth with a pipe is know from WO 93/16236. The process which is known herefrom comprises in sequence the following steps: the driving into the earth of a pipe having a closed pointed end, the lowering of a reinforcement into the driven-in pipe, the filling of the pipe driven into the earth and the withdrawal of this pipe from the earth only after the pipe has been filled, the pointed bottom end of the pipe being able to swing open so as to leave the pile-forming material behind in the earth. The pipes in question have a diameter between 150 and 300 mm.
DE 3612437 discloses a pipe being introduced in the soil by vibration. Centrally a tube is provided. Before introduction the open end of the tube at the extrimity of the pipe is closed off by a cup shaped cover and at reachting the lowest point of introduction of the pipe followed by retraction cover 8 remains at the lower end of the hole so that the pipe becomes opened. A similar closing off and opening mechanism for concrete material to be pumped through a pipe is shown in U.S. Pat. No. 4,152,089 wherein a penetration plate 42 is pushed in advance of a pipe introduced in the soil and remains at the lower end of the bore provided.
The object of the present invention is to provide a process for producing a pile in the earth, which process can be realized relatively quickly. That is to say the number of maneuvers needed to arrive at the pile should be kept to an absolute minimum, thereby enabling a large number of piles to be put in place in one day, whereby hitherto used foundation methods can be substantially improved.
This object is achieved in the above-described process in that the conduit, as the pipe is introduced into the earth, is closed off on the bottom side of the pipe by means of a shut-off valve and is full of pile-forming material, and in that, immediately after this pipe reaches its lowest point, the shut-off valve is opened and the pile-forming material is pumped via the conduit, as the pipe is withdrawn, into the underlying space which is thereby created, and that the formed pile has a diameter less than 25 cm, such as 20 cm, and that the pumped pile-forming material contains no solid constituents of more than 16 mm in diameter.
Preferably, the pipe is moved down to the bearing layer and not introduced into the bearing layer as is customary with driven piles and the like. The pile can also however be moved down into the bearing layer. The pile according to the invention has a relatively small diameter-and a correspondingly low bearing capacity. As an example, a value between 10 and 15 tonnes is given compared to 50-200 tonnes for conventional driven piles. In the piles according to the invention, it is not however necessary to apply a reinforcement. However, a reinforcement can very easily be provided, for example a reinforcement of fibres, for example steel fibres, mixed into the pile-forming material. Work can proceed especially quickly, because at the instant at which the pipe reaches the lowest point it is immediately withdrawn again, whereupon the opening which is left is directly filled with the pile-forming material. This pile-forming material can be any material known in the prior art, but it is essential that it compacting concrete mortar. These mortars consist of a mixture of cement, fly ash or other fine parts and water. The liquid mortar can have a strength classification which is known in the prior art, for example B15 or B25. Liquid mortar does not need to be compacted, thereby obviating the need to shake or vibrate the pipe as it is lifted, as well as preventing bulging.
The fact that the conduit is already full of pile-forming material as the pipe is introduced into the earth means that, as soon as the lowest point is reached, the pipe can start to be withdrawn and, at the same time, the space vacated as the pipe withdraws can start to be filled with pile-forming material. When the lowest point is reached, the pipe is therefore already full to the bottom with pile-forming, hardening material, thereby allowing an extra filling step to be omitted, so that a considerable time saving is achieved through the direct withdrawal of the pipe and the immediate filling of the space in the earth.
It has been shown that the pile according to the invention can be produced within 1 minute. During the first 30 seconds of this minute, the pipe is moved downwards and during the following 30 seconds the pipe is withdrawn as the cavity created is filled with the pile-forming material. Directly after the removal of the pipe, a reinforcement bar or some reinforcement might possibly be applied. The piles made with the invention are relatively short and are generally less than 15 metres in length, though piles of up to 25 meters in length are also conceivable.
The pipe can be introduced in any way which is known in the prior art. Preference is given to vibration and more especially to high-frequency vibration. High-frequency vibration has been shown reliably to prevent damage to surrounding structures. Moreover, it is possible to move especially quickly with the pipe through soft layers of earth.
The pipe can be closed off in any way during the downward motion, the shut-off valve being preferably located close to the bottom side of the pipe, so that the pipe is already filled with pile-forming material. This increases the speed of the process and at the same time prevents air having to be forced out of the pipe as the pile-forming material is introduced. This can be achieved with a valve disc which is known in the prior art and which is clamped on the front of the pipe. Once the lowest point has been reached and the pipe withdrawn, such a disc is left in the earth. It is also possible to reduce this disc to a plug which is fitted to the outlet opening of the conduit for the pile-forming material. All this is dependent upon the design of the closure for the pile-forming material. This can be a grid valve consisting of two plates sliding one over the other, each provided with openings, where in a first position these openings are situated in line and in the second position these openings cover each other to form a seal. This is an especially simple shut-off valve which can easily be operated from ground level. Other shut-off valves are also possible however. As an example, a so-called tube valve is cited. This is a shut-off valve in which part of the passage is delimited by a flexible wall surrounded by an annular chamber. Through the introduction of (air) pressure into such a chamber, the parts of the flexible wall are forced one against the other and the passage is closed. A shut-off valve of this type has the advantage over the above-described grid valve that when it is open a relatively large passageway is present. This is of benefit in connection with cleaning and installation of the above-stated plug. It is also possible to use ball valves, in which case the above-described base comprises a conical part which closes off the bottom side of the pipe to be placed in the earth. When the lowest point is reached, the base is disconnected and the pipe moves away from the cone, after which material transport can immediately take place. As indicated above, the invention allows a pile to be produced especially quickly. It is thereby possible fully to revise foundation methods. According to the invention, it is no longer proposed to use a limited number of high-load-bearing piles with a heavy structure on top, but rather it is proposed to provide a large number of piles according to the invention on a relatively small surface area. It is consequently no longer necessary to place a heavy structure on the piles, since the weight placed on a floor or the like is transmitted evenly into the earth as a result of the large number of piles. According to an advantageous embodiment of the invention, at least 5 piles per 10 m2 and according to a preferred embodiment at least one pile per m2 are present in such a structure. As a result of the fast way of making the piles, considerable savings are shown to accrue by comparison with the prior art. These savings apply to the provision of the piles according to the invention compared with piles according to the prior art. Added to this is the benefit of the lighter construction which is allowed by the use of a large number of piles.
With the invention, any sort of foundation is obtainable. Floors of commercial buildings are herein envisaged, though bodies of dykes, roadbeds, etc. are also envisaged.
Because the diameter of the pile made according to the invention is less than 25 cm, the diameter of the pipe which is placed in the earth will also be less than 25 cm. The pump for pumping the material from which the pile is made can be any pump which is known in the prior art but preferably comprises a hose pump. Apart from the reliability thereof, this has the advantage that the quantity of material which is metered per revolution is accurately known. In certain soil conditions, this is of importance. In such cases, it is essential that precisely the right quantity of material is introduced into the earth when the pipe is removed. If too little material is introduced, then a constriction arises in the pile to be made. If too much material is introduced, then an inadmissible thickening arises. By feeding the speed of withdrawal of the pipe to a computing device or the like, the pump speed is able to be controlled such that the volume which is left upon the withdrawal of the pipe is always perfectly regulated. This regulation can also, of course, work the other way round, that is to say that if the pump speed is constant the speed of withdrawal is controlled. A combination of the two is also possible. The pile-making process according to the invention is so simple that it can largely be automated. A device which drives the pipe into the earth can be accurately controlled by means of a GPS system. Since, apart from the vibration block, no other special structures are necessary, the device for introducing the pipes can be made in relatively light construction. This means that such a device can move over the building site without a large number of special measures having to be taken. It is in any event not necessary to erect on the building site heavy steel planking and the like, which planking results in hold-ups and logistical problems.
Since the piles realised with the above-described process have a limited bearing capacity, such as 10-15 tonnes per pile, compared with the piles known in the prior art, it is possible without many special measures to test these piles for strength after the material concerned has hardened. Indeed, based on a safety factor of 2, the strength of a pile can already easily be determined if an approximately 30-tonne load is applied. A 30-tonne weight can be relatively simply applied using a mobile installation, without resorting to tie piles or large reaction weights which are used in the testing of other piles.
Through the performance of such tests, the safety factor can also be adjusted downwards.
By withdrawing the pipe from the earth at a speed greater than 0.5 m/s, such as 0.67 m/s, the likelihood of so-called bulging of the pile to be formed is reduced. If the withdrawal speed is such, then a pile of relatively constant cross-sectional size is realizable. In particular, it is herein advantageous if the speed of withdrawal of the pipe is greater than 1 m/s. The so-called bulging of the pile to be formed can be further reduced according to the invention by withdrawing the pipe from the earth without it being vibrated.
In order to minimize bulging on the one hand and constriction of the pile to be formed on the other hand and to obtain a pile of the most constant possible cross-sectional shape, according to the invention it is advantageous if the pump capacity and/or the speed of withdrawal of the pipe is/are controlled such that the space which is created beneath the pipe upon its withdrawal is essentially immediately filled with the pile-forming, hardening material.
For the purpose of facilitating the introduction of the pipe into the earth, according to the invention it is advantageous if, as the pipe is placed in the earth, water is injected at high pressure into the earth beneath the pipe such that the earth beneath the pipe is fluidized.
According to the invention, the pipe can be brought into the earth by the application of a compression force to the pipe and/or by vibration of the pipe. The application of a compression force to the pipe in order to drive it into the earth is denoted indeed as xe2x80x9cpull-downxe2x80x9d. It is especially advantageous in this context if the pipe is driven into the outermost top layer of the earth by the sole application of a compression force, this for the purpose of preventing vibrations in this top layer, which is generally relatively loose.