EP0131562B1 - Method for casting piles by means of a drive-out screw - Google Patents

Description

The present invention relates to a method for sinking by means of a discharge screw, concrete piles molded into the ground and provided with an enlarged seat.

It finds its main application in the vibration-free and noise-free production of concrete foundation piles, as supporting elements for buildings and bridges in the vicinity of existing constructions.

A device for making a foundation stake in a laterally repressible soil is already known from Belgian Patent No. 747,807. Screw piles are shaped using a steel tube, provided at the base with a drilling tool. This is screwed into the ground using a drilling table comprising a pushing mechanism which drives down the steel tube.

The soil is compressed laterally by the screw so that (from the point of view of soil mechanics, these piles are entirely identical to beaten piles formed in the ground) an area of compacted ground forms around the pile, comparable to what happens with the piles molded into the ground. With the screw pile, the soil is not moved but only compressed laterally.

. When the desired depth is reached, a steel frame is placed in the tube using a crane; then concrete is poured into the tube and the tank. Then rotate in the opposite direction, up the tube. The lower part of the screw comes off and remains as an abandoned part in the ground.

As the tube is unscrewed, the concrete slides, under the effect of static pressure and / or the force of gravity, into the formed cavity which regularly fills with reinforced concrete.

In another known embodiment, a helical flange is welded to the screw; this flange therefore only serves to provide the drilling crew with the necessary vertical reaction.

With the drilling crew, screw piles with a propeller-shaped barrel were produced.

The helical shape gives the pile a higher resistance to friction, but due to the too small thickness (taken into account when calculating the useful range on the bearing layer) of the screw formed in the ground, we do not hold not take into account the helical shape for the dimensioning of the load limit by lateral friction. Hitherto, only the diameter of the pile shaft (without screws) has been taken into account for the calculation of the lift by lateral friction.

The present invention aims to deeply improve the above embodiment. It makes it possible to produce a screw pile having better resistance to friction and, consequently, a higher breaking load.

The invention relates to a method for producing a screw pile in the ground by means of an assembly consisting of a tube and a drilling head comprising a helical screw, the diameter of said drilling head increasing up to to the desired diameter of the pile shaft. Along this diameter, a solid helix-shaped flange is welded on a revolution. At its lower part, the screw is provided with a free drilling point provided with unidirectional stops, which is screwed to the required depth, using a rotation table with pressure mechanism.

A characteristic feature consists in applying to the above-mentioned crew, when screwing up, a sufficient tensile force to make the upward displacement of the tube greater than that resulting from the rotation of the tube, taking into account of the screw pitch. An essential and different feature of the other embodiments consists in unscrewing the drilling head provided with a thread by applying said tensile force. There appears a free space in the shape of a helix, which has a section such that it can be taken into account for the calculation of the payload limit.

According to an important characteristic of the invention, there is a strong upward pull when unscrewing the discharge screw. By revolution, the translation is equal to the sum of the pitch of the screw and a predetermined difference of the pitch. Consequently, a free space in the form of a helix is formed, the height of which is equal to the sum of the thickness of the flange and the difference in pitch. The free space thus formed immediately fills with concrete under the influence of the above-mentioned gravity forces.

• la figure 1 est une vue en élévation latérale d'un dispositif de forage qui peut mettre en oeuvre le procédé suivant l'invention;
• la figure 2 est une vue latérale partiellement en coupe du trépan à refoulement et du tube;
• les figures 3 à 7 sont des couples transversales de l'ensemble de forage qui illustrent les diverses étapes pour mettre en place un pieu à vis dans le sol.

These features and other details of the invention will become apparent during the following detailed description, with reference to the attached drawings, which represent, by way of example, a specific embodiment and in which:

• Figure 1 is a side elevational view of a drilling device which can implement the method according to the invention;
• Figure 2 is a partially sectioned side view of the discharge drill bit and the tube;
• Figures 3 to 7 are transverse couples of the drilling assembly which illustrate the various steps for setting up a screw pile in the ground.

In these drawings, the same reference notations designate identical or analogous elements.

Screw piles are concrete piles molded into the ground, made by pouring concrete into a borehole, obtained by a discharge screw.

As shown in FIG. 2, the discharge screw, which is designated as a whole by the reference notation 1, comprises an assembly consisting of a steel tube 2 and a drilling head 3.

The tube is made up of various steel tube elements which each have a length of 6 m for example. The tube elements are interconnected by identical coupling members.

The drill head is a piece of cast iron and manganese steel with a helical shape whose diameter increases in a spiral to a diameter equal to the desired diameter of the pile. On the cast iron part, a 51st propeller was welded along a revolution. This propeller 5 is made of manganese steel.

The drilling head 3 has at its lower part a free drilling point 6. The drilling point 6 is made of cast iron. During drilling, it forms the seal of the injection tube 2. This point 6 is driven by two unidirectional stops 7 in a direction of rotation. During unscrewing, the tip remains abandoned in the ground. The point has a cross section 8. Other forms are also possible.

The steel injection tube 2 is screwed into the ground by rotation about its median axis LL 'using a rotary drive mechanism or rotation table 9 and under the influence of a pressure mechanism 10.

The drive mechanism 9 comprises in the example chosen, four hydraulic motors 11 and a set of gears which actuates a drum 13.

The rotational movement is transmitted to the injection tube by means of continuous tongues 14 made of steel by rings with heavy rollers 16. The rings are joined together using pins 17 made of steel. In the event of wear, a ring can easily be replaced. The rotary drum 13 rests on the rotary table by means of thrust roller bearings.

The housing 20 of the rotary table with the cover 21 above forms a fixed part of the machine and is fixed with nuts 22 to the frame 19.

The pressure mechanism 10 consists of two thrust bearings 23, 24 which are both actuated by two main hydraulic cylinders 25, 26 upwards and downwards. The thrust bearings 23, 24 can communicate various combinations of movement to the injection tube 2. By driving in turn, the injection tube 2, either up or down, they impart a translational movement continuous to tube 2. The unsolicited thrust bearing returns at high speed to the starting point. Due to the fact that a rotational movement around the center line of the discharge screw is transmitted simultaneously, the drilling head 3 also moves continuously like a helix in the ground.

The thrust bearings 23, 24 can, if necessary, work together periodically. A periodic translation with double power is recommended for example for drilling hard layers of ground; but this double power is above all necessary at the start of the withdrawal of the drilling head; it is necessary at this moment, in fact, to exert a very significant traction on the tube in order to form an enlarged seat and the initial helical shape.

At least three steel guide rods 29 guide the translational movement of each thrust bearing 23, 24. The hydraulic cylinders 25, 26 are fixed at their upper part to the thrust bearings 23, 24 and at their lower part at chassis 19 by means of spherical hinges 30. This avoids bending stresses in the jacks.

The connection of the thrust bearings 23, 24 with the tube 2 is carried out using spring pawls 31, 32 which are supported on a discontinuous tab of the injection tube.

Each spring pawl 31, 32 has a very hard steel nose which is pushed into an opening 36 of the discontinuous tongue by a spring 35.

The flat gives the translational movement of the jack 25, 26 to the drill pipe. During the vacuum stroke, the oblique part slides on the discontinuous steel tongue.

Each pawl 31, 32 can be turned over in a jiffy, a half turn or a quarter turn, to modify the position and therefore the operation.

• - engrènement uniquement en montée;
• - engrènement uniquement en descente, par inversion d'un demi-tour;
• - position neutre selon laquelle le cliquet reste retiré par inversion d'un quart de tour.

There are three possible positions:

• - engagement only uphill;
• - meshing only when going downhill, by reversing a half-turn;
• - neutral position according to which the pawl remains removed by reversing a quarter turn.

The tube 2 is actuated by a rotating drum 13 and by the two thrust bearings 23, 24 moved downwards, at the same time or in turn, until the required resistance or depth is reached .

As soon as the tube is placed in the ground, a steel frame 37 is optionally brought into the injection tube.

When unscrewing the tube upwards, measures are taken to ensure a particular combination of upward translation and reverse rotation at the start of the operation. It is in this that the method according to the invention differs from all known working methods.

When unscrewing upwards, a very large tensile force is applied to the tube, so that the upward movement, at each revolution, is greater than the pitch of the propeller. A free space 38 is therefore formed in the form of a propeller, which immediately fills with concrete. The formation of this propeller by respecting a determined speed difference differs from all other working methods. It is therefore possible to form a helical element of determined size, over the entire length of the screw pile.

As the tube is removed, the drill hole formed immediately fills with concrete under high static pressure, while the steel frame 37 remains in place in the ground.

The width and thickness of the propeller section are determined by the adjustment of the tensile force so that they can be taken into account for the calculation of the pile payload.

The payload of a screw pile is determined by the admissible soil stress under the base of the pile and the lateral friction resistance to be taken into account. The surface of the pile base and the lateral surface are determined from the outside diameter of the screw pile made.

On the other hand, the payload is limited by the admissible stress of the concrete in the pile of the pile.

The steel frame can vary according to the stress or the prescriptions. It can be installed over the total length of the pile, which can include more than 20 m. In many cases, a 4 or 6 m head reinforcement is sufficient, which can be placed in fresh concrete after the pile has been made.

It is obvious that the invention is not limited to the aforementioned embodiment and that numerous modifications can be made to it without removing it from the scope of the claims.

Instead of being placed vertically, the piles can also be made obliquely.

Claims (3)

1. A process for sinking a screw pile into the ground by means of equipment consisting of a tube (2) and a drilling head comprising a helical screw (3), the diameter of the said drilling head increasing to the desired diameter of the shaft of the pile, and a free drilling point (6) with uni-directional stops (7), which drilling head is screwed to the depth required with the aid of a rotary table (9) with a pressure mechanism (10), characterized in that the above-mentioned equipment has applied to it, when it is being unscrewed back upwards, a tractive power sufficient to make the upward displacement of the tube greater than the displacement resulting from the rotation of the drilling head in view of the thread pitch, so that an empty space in the form of a helix appears, which space has a section such that it can be taken into account in the calculation of the load-bearing capacity.

2. A process according to claim 1, characterized in that when the drive screw is withdrawn upwards, at the time of unscrewing, each revolution covers a distance equal to the sum of the thread pitch and a predetermined difference of ascent, withdrawal being effected with great force, so that an empty space is created in the form of a helix whose height is equal to the sum of the thickness of the flange and the pitch difference and which is immediately filled with concrete.

3. A process according to claim 1 or claim 2, characterized in that the piles are positioned obliquely.

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