EP0404703A1 - Foundation piles, methods, tools and devices for the construction of these piles - Google Patents

Abstract

The invention relates to foundation piles and to methods, tools and machines for the construction of these piles. A pile according to the invention comprises a cooperating casing (1) which is composed of prefabricated reinforced-concrete or prestressed-concrete tubular elements (1a, 1b, etc.) which have an outside diameter of between 300 and 500 mm and a thickness of the order of 80 to 100 mm, which are joined end-to-end by means of resin-sealed connecting bars (3) and which have radial channels (2). It comprises, furthermore, a filling (4) of concrete, cement grout, sand, etc., which is injected under pressure into the surrounding earth by way of the channels (2). To drive the casing elements into the ground, an auger is used which passes inside the casing and which carries a cutting tool at its end. One application is the construction of foundation piles in current civil engineering works and buildings. <IMAGE>

Description

The present invention relates to new foundation piles and methods. tools and machines for the construction of these piles.

The technical sector of the invention is that of the construction of piles intended to serve as a foundation for common works.

In the field of common pile foundations, that is to say piles having to support loads between 400 and 2000 K.N, two categories of piles are used to date.

A first category is that of injected micropiles having a diameter of less than 200 mm.

The micropiles are obtained by drilling techniques used in the mining or petroleum fields

In a first phase, a borehole is dug with a drill bit and this hole is fitted with perforated casing.

In a second phase, a cement grout is injected inside the casing and this grout passes through the perforations in the casing and penetrates into the surrounding land.

Thanks to this injection, the micropiles have the advantage of very good friction between the pile and the ground.

By cons, they have the disadvantage of low inertia, hence the risk of buckling and low resistance to horizontal forces. It is not possible to economically build piles with a diameter greater than 200 mm by drill bit techniques, which would entail the construction of very expensive drilling tools.

A second category of common piles are traditional beaten and molded piles with a diameter greater than or equal to 0.4 m.

A machine is known, used for the construction of traditional piles, which comprises a vertical auger and which is moved along a vertical mast and which is rotated at low speed, so that it penetrates into the ground as a Once the auger is pressed down to the bottom of a pile, we pull up with jacks while sending a concrete slurry through the hollow auger shaft.

As the auger rises, it carries with it a cylindrical core of ground in the manner of a corkscrew and the vacuum which is thus created is filled with concrete grout.

This technique makes it possible to obtain piles of large diameter which are not likely to buckle. However, it presents difficulties of implementation in unstable ground. In addition, since the concrete is poured in place as the core is removed, it is not possible to control the quality of the concrete filling of the well.

The friction characteristics between the ground and a traditional pile are less good than those of the injected piles.

The numerous disorders occurring on traditional piles have led to demand quality controls and to limit the admissible stresses in the concrete poured in place at working rates of the order of 5 to 6 MPa, that is to say less than half the theoretical work rate.

The objective of the present invention is to provide new foundation piles intermediate between the micropiles and the traditional piles, which combine the advantages of these, that is to say which allow to set up during digging a reinforced or prestressed concrete casing collaborating in the bearing capacity of the pile, to fill it in whole or in part, using concrete, cement grout, sand ... where elimination of the risk of landslides or cavities in the filling material, inject a cement grout into the surrounding soil to improve lateral friction and obtain piles with a diameter sufficient to avoid the risk of buckling and armed piles which resist horizontal forces well .

This objective is achieved by means of foundation piles which include:
- a concrete casing, composed of tubular elements of reinforced concrete or prestressed concrete, having an external diameter, of the order of 300 to 800 mm and a thickness of the order of 80 to 150 mm, which elements include radial channels
- and if necessary a cement grout which forms a core poured over at least part of the interior of said casing and which is injected under pressure into the surrounding lands through said radial channels.

Advantageously, the prefabricated tubular elements have, at their two ends, vertical reservation holes and two superimposed elements are assembled end to end by connecting bars, which are engaged in two facing holes and which are sealed with a polymerizable resin. .

A method of constructing a foundation pile according to the invention comprises the following operations:
- Tubular elements in reinforced concrete or in prestressed concrete are prefabricated in the factory, having an external diameter of the order of 300 to 800 mm and a thickness of the order of 80 to 100 mm and comprising radial channels;
- said elements are lowered one by one vertically into the ground by cutting by means of an auger which is engaged inside the prefabricated elements, which carries at its end a retractable cutting tool and which is rotated at a speed sufficient to remove the cuttings;
- when an element is fully sunk into the ground, the auger is removed and a second tubular element is erected on the first, then the auger is lowered inside the two elements and the havage is continued;
- And, when the prefabricated casing is in place, we proceed either to the filling using concrete, cement grout, sand, or we put in it an inflatable obturator at an intermediate level and we inject , in the zone located inside the casing and below said obturator, a cement grout which penetrates into the surrounding lands through said radial channels to form an anchorage in the ground.

A tool for implementing a method according to the invention comprises a vertical shaft which is rotated by a mobile rotation table along a vertical mast and which carries a helical screw forming an auger, and said shaft carries at its end, a collapsible cutting tool, which fits in the folded position inside a circle having a diameter less than the internal diameter of said prefabricated tubular elements and which has, in the working position, a greater external diameter with external diameter said prefabricated tubular elements.

According to a preferred embodiment, the cutting tool comprises a metal blade which is located below the lower end of said helical screw and which pivots around a vertical articulation axis eccentric relative to the axis of said auger.

The invention results in new foundation piles having an external diameter of the order of 300 mm to 800 mm.

The piles according to the invention are intermediate between the micropiles and the traditional beaten and molded piles.

The piles according to the invention have the following advantages: in unstable ground, the holding of the ground is ensured by the precast concrete elements which act as collaborating casing.

The piles according to the invention can pass through relatively hard layers of ground using a drilling tool comprising destructive cutters allowing the crossing of these terrains.

The reinforced concrete tubular elements are prefabricated in the factory and can be prestressed, which ensures good reliability of the qualities of the concrete.

The filling in concrete, cement grout, sand ... or grout injected under pressure is carried out away from the lost casing, which allows a homogeneous filling.

The admissible working constraints both in the prefabricated casing and in the filling with concrete grout are 8 MPa.

The piles according to the invention make it possible to inject cement grout through the casing into the host soil and to obtain a coefficient of lateral friction of the pile which is two to four times higher than that of piles driven or molded in place .

As a result, the piles according to the invention can withstand a limit unit friction identical to that of the micropiles.

The piles according to the invention can withstand high horizontal forces thanks to the reinforcements of the prefabricated casing and to the connecting bars between tubular elements.

If necessary, the resistance to horizontal forces can be increased by adding a reinforcement in the central part of the pile before filling it with a cement grout. It is even possible to exert the post prestressing by means of a tie rod central tensioned.

• La figure 1 est une coupe verticale d'un pieu selon l'invention passant par l'axe zzl de celui-ci.
• La figure 2 est une vue en élévation d'un chantier de construction d'un pieu selon l'invention.
• La figure 3 est une coupe verticale à grande échelle de l'extrémité inférieure d'un pieu et de l'outil de forage.
• La figure 4 est une vue de dessous de l'outil de forage en position de travail et en position repliée.

The following description refers to the appended drawings which represent, without any limiting character, an embodiment of a pile according to the invention.

• Figure 1 is a vertical section of a pile according to the invention passing through the axis zzl thereof.
• Figure 2 is an elevational view of a pile construction site according to the invention.
• Figure 3 is a large-scale vertical section through the lower end of a pile and the drilling tool.
• Figure 4 is a bottom view of the drilling tool in the working position and in the folded position.

Figure 1 shows a stake intended as a foundation for a structure.

This pile comprises a casing 1 which is composed of tubular elements 1a, 1b, etc., of reinforced concrete or of prestressed concrete which are prefabricated in the factory. Each tubular element has an outside diameter of the order of 400 mm, which can vary for example between 300 and 800 mm, a thickness of the order of 80 to 150 mm, an inside diameter of the order of 200 to 600 mm. and a length of the order of 5 to 6 meters.

Figure 1 shows, by way of illustration, a pile comprising two elements 1a, 1b superimposed. The number of elements can be higher.

The elements 1a, 1b being prefabricated in the factory, are manufactured with care and it is possible to calculate the resistance of the pile by taking into account 75% of the maximum rate of stress that the reinforced concrete can support.

The prefabricated elements 1a, 1b have small radial channels 2 which pass right through them and which are distributed over their entire height.

The tubular elements 1a, 1b have, on their upper edge and on their lower edge, vertical reservation holes which face two by two when two elements are superimposed. These high-strength steel connecting bars 3 are placed in these holes and sealed with a quick-setting polymerizable resin.

The tubular elements 1a, 1b can be dimensioned so as to withstand the entire load that each pile must support.

In some cases, we can take into account the central section filled with cement grout to define the load that the pile can support.

In order to improve the friction of the pile with the surrounding soil and to reduce the force exerted on the lower end of the pile, each pile has, over part of its height, a cement grout 4 which fills the inside the casing 1 and which penetrates into the surrounding land by passing through the small radial channels 2.

Alternatively, the casing 1 can be filled with cement grout over its entire height, if necessary.

FIG. 2 represents a pile according to the invention during the driving in of a first concrete element 1a.

It brings to the site where the piles are to be established, the tubular elements 1a, 1b prefabricated in the factory and sinking equipment mounted on a vehicle 5 which carries a mast 6 shown in dotted lines in the folded position and in solid lines in the vertical position of job.

The mast 6 has a total height which may correspond to the height of the pile. It can be made up of several sections which are gradually put in place.

The sinking equipment further comprises a tool comprising a hollow vertical shaft 7 which is rotated by a rotation table 8 movable along the mast 6 and which carries a helical screw 9 forming an auger and, at its lower end , a cutting tool 10. The external diameter of the screw 9 is less than the internal diameter of the prefabricated elements 1a, 1b.

To drive a first prefabricated element la into the ground, it is placed vertically on the ground, then engages inside the latter the auger 9 and the cutting tool 10 which is in the folded position. When the tool 10 comes into contact with the ground, the speed of rotation of the table is increased to reach a speed sufficient for the auger to remove the cuttings from the upper end of the element 1a. Under the effect of centrifugal force and friction of the ground, the tool 10 automatically occupies a position in abutment where its external diameter is slightly greater than the external diameter of the element la, so that it digs beneath it a cutting groove and the element la s gradually sinks into the ground following tool 10.

When a first element la has been driven into the ground, the rotation table 8 is rotated in the opposite direction, which has the effect of automatically folding the cutting tool 10 whose external diameter is then less than the internal diameter of the element la and then the rotation table and the auger are raised sufficiently high to be able to place a second prefabricated element 1b vertically above the first element la. Before putting the element 1b in place, vertical bars 3 are engaged in the vertical holes reserved at the upper end of the element 1a then the vertical holes reserved at the lower end of the element 1b are fitted onto these bars and the bars are sealed with a polymerizable resin.

The hollow shaft 7 and the auger 9 can be composed of several sections which are assembled end to end as the casing sinks into the ground.

Once the casing is in place, the auger is removed, the inside of the casing is cleaned and the concrete, cement grout or sand is filled. As a variant, one or more inflatable shutters of any known type are placed inside the casing 1, which are lowered to a determined level which has been chosen to constitute the head of the anchoring zone of the casing.

Then injected into the interior of the tubing located below the inflatable obturator a sufficiently fluid cement grout so that it passes through the radial channels 2 of the casing and penetrates into the strata or cracks of the surrounding lands.

This cement slurry injection ensures a good bond between the pile and the ground both from the point of view of the force at the tip of the pile, as well as the lateral friction of the pile. This injection also provides a good mechanical connection between the various concrete elements 1a, 1b.

Figure 3 is an elevational view of the lower end of the tool in the cutting position.

We see in this figure a first prefabricated element in reinforced concrete la which carries, advantageously at its lower end, a metal shoe 11 comprising a cylindrical skirt 12 which surrounds the external periphery of the element 1a and a frustoconical skirt 13 which diverges towards the low. Shoe 11 is optional. It facilitates the downward gravity movement of the casing and it facilitates the folding of the lifting tool when raising the auger.

We see in Figure 3 the hollow shaft 7 which carries at its periphery a helical screw 9 forming an auger intended for the evacuation of waste upwards.

The lower end of the hollow shaft 7 carries fixed peaks 14, distributed around its periphery which dig in the ground a pilot hole having a diameter slightly greater than the diameter of the shaft 7.

A little above its lower end, the shaft 7 carries a fixed metal blade 15 whose external diameter is substantially equal to the external diameter of the helical screw 9.

Advantageously, the blade 15 is helical and it extends the helical screw 9.

Advantageously, the leading edge of the blade 15 is equipped with peaks 15a.

Between the lower end of the helical screw 9 and the fixed blade 15 is mounted a cutting tool 10 comprising a blade 16 whose leading edge 17 carries peaks 18.

The blade 16 is articulated around a vertical axis 19 which is eccentric relative to the axis zzl of the shaft 7.

Advantageously, the blade 16 is slightly helical to facilitate the removal of the cuttings.

Figure 4 is a bottom view of the lower end of the tool on which there is shown in solid lines the working position of the cutting tool 10 and in dotted lines the folded position of the same tool.

This figure shows the eccentric axis 19 around which the blade 16 of the cutting tool pivots. We see that this blade 16 has the general shape of a portion of the crown which is delimited by an external arc of a circle 16₁ whose diameter is equal to the external diameter of the helical screw 9 and by an internal arc of circle 16₂, the diameter is equal to the outer diameter of the hollow shaft 7. The two arcs 161 and 162 are parallel. They extend over about a semicircle. They have a common center 0 which is located at a distance from the pivot axis 19 equal to the eccentricity e of the axis 19 relative to the axis zzl of the shaft 7, so that the center 0 moves on a circle centered on axis 19 and passing through axis zzl.

When the cutting tool 10 is in the folded position shown in dotted lines, the internal edge 16₂ envelops half of the periphery of the hollow shaft 7 and the external edge 16₁ coincides with the projection of the external periphery of the helical screw 9.

When the hollow shaft 7 is rotated clockwise, which is the direction of evacuation of the earth, the reaction of the ground on the peaks 18 and on the blade 16 automatically rotates the latter around axis 19 counterclockwise. The blade 16 has a heel 20 which is located beyond the axis 19 and which bears against the shaft 7 thus blocking the blade 16 in the working position shown in solid lines in FIG. 4.

In this position, the peaks 18 and the blade 10 dig into the ground a circular cut limited by a circle C2 which is the circle tangent to the blade 16. The diameter of the circle C2 is slightly greater than the external diameter of the prefabricated casing elements.

When one has finished driving a casing element into the ground, the direction of rotation of the hollow shaft 7 is reversed and the auger is raised. The pivoting blade 16 rubs against the metal shoe 13 or against the lower end of the concrete element la in the case where there is no metal shoe and the friction exerts on the blade 16 a thrust which makes it pivot automatically this clockwise until it is pressed against the shaft 7 in the position shown in dotted lines in FIG. 4.

We see that in this position, the entire cutting tool is located inside the circle C1 and can therefore go back up inside the casing.

The peaks 14, 16. 18 have cutting edges made of a hard material, for example example made of tungsten carbide or any other material commonly used to make drilling or rock drilling tools.

As a variant, the cutting tool 10 may consist of two blades 16. each occupying half of the circular section C1 in the folded position, the two axes 19 being diametrically opposite.

Claims (8)

1. Method for constructing a foundation stake, characterized in that it comprises the following operations:
- tubular elements (1a, 1b) are made of reinforced concrete or prestressed concrete, having an external diameter of the order of 300 to 800 mm and a thickness of the order of 80 to 150 mm and comprising radial channels ( 2);
- said elements (1a, 1b) are lowered one by one vertically into the ground by cutting by means of an auger (7, 9) which is engaged inside the prefabricated elements, which carries a cutting tool at its end (10) retractable and which is rotated at a speed sufficient to remove the cuttings;
- when an element (1a, 1b) is fully sunk into the ground, the auger (7, 9) is removed and a second tubular element (1) is erected on the first, then the auger (7, 9) is lowered inside the two elements and drilling and cutting are continued simultaneously;
- and, when all the prefabricated elements are in place, they are filled with concrete, with cement or sand grout, or one or more inflatable obturators are placed in them, at an intermediate level, and injected, in the area inside the casing and below said obturators, a cement grout (4) which penetrates into the surrounding lands through said radial channels to form an anchorage in the ground. 2. Tool for implementing a method according to claim 1 of the type comprising a vertical shaft (7) which is rotated by a rotation table (8) movable along a vertical mast (6) and which carries a helical screw (9) forming an auger, characterized in that said shaft carries at its end, a folding cutting tool. which fits in the folded position inside a circle (C1) having a diameter less than the internal diameter of said prefabricated tubular elements and which has, in the working position, an external diameter greater than the external diameter of said prefabricated tubular elements. 3. Tool according to claim 2, characterized in that said cutting tool comprises a metal blade (16), which is located below the lower end of said helical screw (9) and which pivots about a vertical articulation axis (19) eccentric with respect to the axis of said auger. 4. Tool according to claim 3, characterized in that the outer edge (16₁) and the inner edge (162) of said blade are parallel arcs of circle having a common center (0), which is located at a distance (e ) of said articulation axis equal to the distance between the axis of said auger and said articulation axis (19) of said blade. 5. Tool according to claim 4, characterized in that said internal edge (16₂) has a radius equal to the radius of the shaft (7) of said auger and said external edge (16₁) has a radius equal to the external diameter of said helical screw (9). 6. Tool according to any one of claims 2 to 5, characterized in that said vertical shaft (7) carries, at its end, peaks (14), distributed around its periphery and a fixed blade (15) which extends the lower end of said helical screw and whose leading edge is equipped with spikes (16). 7. Machine for implementing a method according to claim 1, characterized in that it comprises a tool according to any one of claims 2 to 6. 8. Foundation pile constructed by a method according to claim 1, characterized in that it comprises a concrete casing (1). which is composed of one or more superimposed tubular elements (1a, 1b), which are prefabricated in reinforced concrete or in prestressed concrete and which have an external diameter of the order of 300 to 800 mm, a thickness of the order of 80 to 150 mm and an internal diameter such that said auger (7, 9) can pass through said casing, and said tubular elements include radial channels (2) through which a cement grout is injected into the surrounding lands .

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