EP0317458A1 - Process and apparatus for laying a foundation by creating a solid mass constituted by the soil itself - Google Patents

Abstract

PCT No. PCT/FR88/00549 Sec. 371 Date Jun. 21, 1989 Sec. 102(e) Date Jun. 21, 1989 PCT Filed Nov. 8, 1988 PCT Pub. No. WO89/04402 PCT Pub. Date May 18, 1989.The present invention provides a method and apparatus for making a foundation by creating a block constituted by the ground itself, the method being characterized in that at least one deep anchor point is established by using anchor means (1/3) buried underground by pile-driving, which means (3) extend in the anchoring position up to the surface of the ground in order to project beyond the surface; a slab (10) is placed on the surface, the slab including at least one opening for passing extensions from the anchor means; and traction is exerted on the slab in order to presetress the ground by using means situated above the slab (10) to put the anchor means under tension until an in-service force is obtained suitable for holding the structure to be built on the surface.

Description

The present invention relates to a method and a device for implementing a foundation by creating a solid mass formed by the soil itself.

The technical sector of the invention is that of foundations for works made on the surface, such as electrical pylons, antennas or other similar works.

Currently, such structures are anchored in the ground in foundations generally made using concrete, reinforced concrete or prestressed concrete foundations. Another means of implementing such foundations is to make anchor points by means of piles or groups of driven piles.

The types of foundations used industrially are based on the following bases:
- Either make heavy foundations, a concrete block for example, embedded or in the ground. The tensile force on this type of solid in the case of a non-embedded solid must remain less than the weight of the foundation if we want it to maintain its effectiveness.

In the case of a bed embedded in the ground, the tensile force must remain lower than the sum of the following data: weight of the bed, weight of the earth above the bed, resulting on the bed of the lateral friction forces , sucking on the massif. It is noted in the case of an embedded solid that a major drawback, the rupture of the concrete solid, can occur if the following eventuality occurs: tensile force on the concrete greater than the weight of the foundation but less than the conjugation of the lateral friction and suction forces.

In addition, a massive weight must work in its central third, if differential settlement occurs, there may be tilting of the massif.
- Either place beaten or bored piles.

In such foundations, the risks of differential settlements are very minimal or even nonexistent, however such foundations resist resistance to lateral forces (cyclic or not) for which the risks of heaving remain certain.

The present invention aims to remedy the drawbacks of foundations currently used industrially and which have just been mentioned.

The objective to be achieved is to create foundations by creating a massif made up of the soil itself.

A loaded foundation induces a settlement of ground.

If the service loads of the work carried out on the surface, involve tensile forces, the behavior of the foundation poses a problem of behavior in view of the poor, if not non-existent tensile strength of the soil.

The objective of the present invention is achieved by the method for implementing a foundation by creating a solid mass constituted by the soil itself, according to which method:
- At least one deep anchoring point is made using anchoring means which are driven into the ground by threshing, which means extend in the anchoring position towards the ground surface to extend beyond of this surface;
- a slab is placed on the surface which has at least one opening for the passage of the extensions of said anchoring means,
- And a traction is exerted on this slab to prestress the ground by means of tensioning said anchoring means located above said slab until the service force necessary to maintain the structure to be achieved is obtained. area.

According to a preferred embodiment of said method, a deep anchoring point is produced, so as to obtain an underground effect of a ground stop by anchoring means capable of being placed in a position substantially parallel to the surface of the ground and where is disposed said slab.

According to the method, a direct evaluation and control of the soil stress is obtained by using a slab whose face brought into contact with the ground has an area equal to a multiple or an integer sub-multiple of the square meter.

For the implementation of this method, a device is used which is characterized by the fact that it is made up of anchoring means comprising at least one anchoring line extending towards the surface of the ground to extend beyond of this surface, which anchor line is passed through a reserved opening in a slab bearing on the ground, which anchor line is connected to means for its tensioning, which are supported on said slab to put the soil in prestress under the effect of a traction exerted on the slab in the direction of the anchor point.

In such a device, the anchoring means of which consist of an anchor comprising a rigid body comprising at least one end for attacking the ground and another end comprising an anvil to which a driving force is applied by threshing, which anchor further comprises a fin articulated about an axis transverse to said body and having a limited angle of movement of the order of 45 °, at least one anchoring line connected to said body at at least one point located between said end of attack and the center of gravity of the anchor body, said articulated fin being located opposite the attack end and whose pivot axis is offset from the median plane of the anchor body in which plane is located the threshing axis, in which the anchoring line is constituted by at least one tie rod connected to a fixing member pivoting about a transverse axis located in said median plane of the body of the anchor, which pulling is rigid and is made pa r a rod or a tube comprising connection means for aligning several tie rods as a function of the depth of insertion of the anchor into the ground, so that the last tie rod extends beyond the level of the ground for allow tensioning of the anchor line.

In the position of driving the anchor into the ground, the aligned tie rods, which constitute the anchor line, have their axis located substantially in the median plane of the body of the anchor and are located substantially in the center of the anvil. .

To drive the anchor into the ground, the anvil is struck by means of open or closed cross-section profiles which surround the anchor line and which extend above the ground surface to be subjected to the action of threshing means.

Preferably, the slab has, on its upper face, a metal plate comprising an orifice situated to the right of the orifice of the slab, which is of a diameter greater than that of the slab to allow adjustments on two axes x / y.

According to one embodiment, the means for tensioning the anchoring line consist of a frame bearing on said metal plate of the slab and comprising a conical housing whose generatrices of the wall converge towards the anchoring means at a point located on the axis of the tie rods constituting the anchor line whose last tie rod, which crosses the slab, extends into said conical housing and is threaded at its end to cooperate with a locking nut acting on corners placed in the conical housing and around the two tie rods by means of a ring inserted between the corners and the locking nut.

The periphery of the tie rod coming into contact with the locking corners is ridged or has micro-threads to increase the anchoring of the corners on the tie rod.

Said conical housing is reserved in a moving part, guided vertically on said frame, which moving part is supported on elastic means which surround the tie rod and which are inserted between said moving part and the bottom of the frame.

According to another embodiment, the means for tensioning the anchor line consist of a beam to which is fixed the last tie rod which passes through the slab and the metal plate, which beam is located above the slab and the plate and is subjected to the action of at least two jacks located on either side of the tie rod and resting on the metal plate which covers the slab.

Said beam comprises, in the middle, a ring comprising a conical orifice whose generatrices of the wall converge on the side of the anchoring point on a point situated on the axis of the tie rod and the fixing of the tie rod to the beam is carried out by locking corners distributed around the tie rod and arranged in the annular space existing between the tie rod and the conical orifice.

The metal plate which covers the slab has a boss comprising a conical orifice coaxial with the orifice of the slab and whose generatrices of its wall converge on the side of the anchoring point on a point located on the axis of the tie rod and the support in tension of the anchoring line is obtained by locking wedges distributed around the tie rod and arranged in the annular space existing between the tie rod and the conical orifice of said boss so as to cancel the pressure of the fluid of the hydraulic circuit leading to said cylinders.

The periphery of the tie rods brought into contact with the locking corners is ridged or has micro-threads to increase anchoring the corners on the tie rod.

The principle of prestressing makes it possible to shift the service efforts of the works carried out on the surface towards the compressions and to remain there so as to work only in the field of stable compressions.

In a foundation made by a pre-stressed soil mass, a predetermined holding point is placed at a certain depth in the ground. This holding point constitutes an anchor on which, from the surface, it is taken up again by means of a steel plate covering a concrete slab, or else by a steel plate or simply a concrete slab.

The soil mass located below the slab, after stressing, has different mechanical characteristics from those existing before stressing. It is from these new mechanical characteristics that the strength of the massif as a foundation is determined.

Under the slab resting on the ground by stiffening, on the anchor, a network of iso-stresses is distributed in the ground affecting part of the neighboring land. The volume, including the weight of the earth affected by these iso-stresses, is therefore much greater than that directly covered by the slab and thus is capable of constituting a massif.

For the holding of foundations, the disadvantages previously mentioned and inherent in the use of concrete masses embedded or not and with piles or groups of piles driven into the ground, disappear for the implementation of prestressed foundations because:
- the elimination of differential settlement, the concept of support effort in the central third disappears, the work being done in line with the foundation;
- the elimination of the risk of loosening of the massif requested by lateral loads if we consider the importance of the massif mobilized by iso-stresses.

The advantages mentioned above are explained by the fact that the mechanical behavior of the soil can be controlled and modulated by a more or less significant stiffening of the soil on a deep anchor point, so as to always remain below the limits of the creep of the ground, elastic mechanical means installed on the surface will always allow the variation of the forces involved to be taken up again.

According to the method for producing a pre-stressed soil mass, a vertical tension is exerted downwards on a plate (or slab) placed on the ground. This tension is obtained by the stiffening of an anchoring line fixed by one of its ends to a deep anchoring point to benefit from the underground effect of the ground stop and at its other end for example by tightening a bolt on the last element of the tie rod which constitutes said anchor line and which crosses the plate (or slab) placed on the surface.

The underground effect of the floor stop can be obtained either by, for example, a plate-shaped anchor or by the articulated element anchoring device having a bent shape, which has been the subject of a patent application. French registered under No 84 07281.

The junction between the underground floor stop device and the surface plate is made by means of tie rods constituted by a cable, a rod or a tube (or sets of rods or tubes) sized for the required force. The resumption of the effort on the tie is made by means of a system of claw corners or other equivalent means to avoid slippage.

In order to improve the non-slip performance of the blocking device, it is possible, for example, to provide micro-threads on the last tie emerging from the slab bearing on the ground in the area of contact with the corners.

According to the invention, the surface plate is dimensioned in such a way that an evaluation and direct control of the soil stress can be obtained during the tensioning of the tie rod. To obtain this evaluation, the plate (or the plate and the concrete slab) is made so that its surface is a multiple or an integer sub-multiple of the square meter.

The underground anchor is installed by threshing.

The stress recovery rod or tube is integral with the underground anchor.

The anchor line, consisting of a cable, a rod or a tube (or sets of rods and tubes) is put in place by means of false pile drivers constituted by tubes or profiles, in U for example, during threshing, at the same time as the anchoring. Once the underground anchor is positioned at the required depth, the pile drivers are removed. The rod or tube (or drill string or tube) that connects the underground anchor to the plate (and / or the surface slab) is gripped by the means described above by tightening the bolt or by other means comprising cylinders with pneumatic or hydraulic operation until the service force imposed by the structure produced is obtained. area. Elastic means, such as springs or Belleville washers for example can be incorporated on the surface at the upper end of the head tie to compensate or take up the forces.

The method according to the invention offers the advantage of being able to predetermine the holding capacity of the mass of land under stress and of improving it by stiffening more or less the surface plate (and / or slab) at its point. underground anchor. Indeed, throughout the threshing, knowing the master-couple at the sinking of the underground anchoring system, that is to say the contours of the cross sections to the axis of movement of the anchor line , we can, by knowing the threshing energy at each strike, determine the bearing capacity of the ground at each level of the anchoring. Furthermore, the surface plate (and / or slab) pulled towards the ground by the stiffening of the anchor line makes it possible, thanks to its compaction, to assess the stress of the ground on the surface. These two possibilities combined make it possible to correctly identify the possibilities of holding pre-stressed soil masses.

• - La figure 1 est une vue en coupe schématique d'un dispositif d'ancrage d'un pied de pylone électrique.
• - La figure 2 est une vue en élévation d'une ancre utilisée dans le dispositif de la figure 1.
• - La figure 3 est une vue de l'ancre de la figure 2 suivant la flèche F.
• - La figure 4 est une vue en élévation coupe à plus grande échelle d'un pied de pylone de la figure 1 illustrant un exemple de moyens pour la mise en tension de la ligne d'ancrage.
• - La figure 5 est une vue en élévation coupe d'un autre exemple de moyens pour la mise en tension de la ligne d'ancrage.

The following description refers to the accompanying drawings which illustrate, without any limiting nature, exemplary embodiments of a device according to the invention for the use of pre-stressed soil masses.

• - Figure 1 is a schematic sectional view of an anchoring device for an electric pylon base.
• - Figure 2 is an elevational view of an anchor used in the device of Figure 1.
• - Figure 3 is a view of the anchor of Figure 2 along arrow F.
• - Figure 4 is a sectional elevation view on a larger scale of a pylon foot of Figure 1 illustrating an example of means for the tensioning of the anchor line.
• - Figure 5 is a sectional elevation view of another example of means for tensioning the anchor line.

The anchor 1 (Figures 2 and 3) which is used in the device according to the invention is for example of the type of that described in French patent 84 07281. It is specified here that other similar anchoring means can find their application for the implementation of the method according to the invention.

Such an anchor 1 comprises a rigid body comprising a conical or pyramidal part 1a₁, the lower part of which ends with a leading end of the ground 1a₂. Its upper part 1a₃ is of a circular or square cross section and comprises an anvil 1a₄ intended to be struck by driving forces obtained by threshing and by means of tubular elements or by U-shaped profiles 2, which surround an anchor line 3 fixed to a pivoting part 4 around an axis transverse to the anchor 1.

The pivot axis 4a of the part 4 is located between the end 1a₂ and the center of gravity of the anchor and in the plane of symmetry of the body 1a.

Opposite the leading end of the ground 1a₂, the anchor 1 comprises an articulated element 5 forming a kind of fin, which is pivotally mounted on the body 1a around an axis 5a transverse to the anchor and offset with respect to the plane of symmetry of the body la in which the pivot axis 4a of the part 4 is also located. The articulated element 5 is designed to have a limited angular movement of the order of 45 °.

In the plane where said articulation axis of the part 4 is located, the anchor 1 comprises a plate 6 projecting symmetrically with respect to the body 1a (FIG. 2) and comprising a rectangular part 6a, extending approximately from the axis pivot 5a of the articulated element 5 to the pivot axis 4a of the part 4, the cross section of the anchor at this location constituting the master torque of the anchor. The plate 6 is extended towards the leading end of the ground 1a₂ by a symmetrical profiled part 6b to promote the penetration of the anchor into the ground, which part 6b is delimited by a series of edges 6b₁ / 6b₂ / 6b₃ / 6b₄ which converge at different angles on the axis of symmetry XX₁ of the anchor.

The plate 6 is stiffened by gussets 7/8 fixed on either side of the plate 6 forming deflectors and which converge on the axis of symmetry of the anchor XX₁ to promote the penetration of the anchor into the ground .

In the insertion position of the anchor 1, the anchor line 3 is located in the axis XX₁ of the anchor 1.

In this position, the anchor line and the intermediate threshing elements 2, or false threshing piles, are substantially coaxial when these are formed by tubes.

Referring now to Figure 1 of the drawing which represents the anchoring of a pylon foot 9, which rests on the ground by means of a reinforced concrete slab 10, covered with a plate for example of steel 11, which slab and plate 10/11 are crossed by the anchor line 3.

This consists of tie rods, for example in the form of tubes 3a / 3b connected by a connection sleeve 12.

FIG. 4 represents, on a larger scale, a pylon foot 9 and the means for tensioning the anchoring line to put the soil in prestress.

The slab 10 has an orifice 10a, located to the right of an orifice 11a, of larger diameter, and reserved in the plate 11 which covers the upper face of the slab and to which plate is fixed the pylon foot 9. The difference the diameter of the orifices 10a / 11a allows adjustments to be made in X / Y of the plate 11 relative to the slab 10. Said pylon is in an inclined position and is constituted by a tubular element and has a manhole 9a to access the interior.

The upper end of the tube 3b is passed through the holes 10a / 11a and extends inside the pylon foot 9 through a device for tensioning the anchor line. This device consists of a frame 13 bearing on the metal plate 11 and comprising a movable part 14 itself comprising a conical housing 15 in which the tube 3 has passed. The generatrices of the wall of said housing converge towards the anchor 1 at a point situated on the axis of the anchor line 3. The movable part 14 is supported on elastic means 15, for example Belleville washers, inserted between said movable part 14 and the bottom of the frame 13.

The upper end 3b₁ of the tube 3b is threaded and cooperates with a nut 17. In the conical housing 15 are arranged locking corners 18 distributed around the tube 3b, for example three in number and arranged at 120 °. A ring 19 disposed between the nut 17 and the corners 18 is connected to the latter by means of studs or other similar members 20.

The tensioning of the anchor line 3 and correlatively, the prestressing of the ground is obtained by screwing the nut 17. When tensioning the anchoring line 3, the anchor pivots around the axis 4a, the fin 5 around the axis 5a until it comes to rest at the ground stop in a substantially parallel or ground position as shown in the drawing in FIG. 1.

The periphery of the zone of the tie formed by the tube 3b brought into contact with the locking corners is ridged or has micro-threads to increase the anchoring of the corners in said tie.

The prestressing of the ground is obtained by tightening more or less the nut 17 as that was previously exposed.

Another embodiment of the means for tensioning the anchor line 3 is shown in Figure 5 of the drawing.

These means consist of a beam 21 having in its middle a ring 22 comprising a conical orifice 22a whose generatrices of the wall converge towards the anchoring point on a point located on the axis of the tie rod 3b. The tie rod 3b is fixed to the beam 21 by locking corners 23, for example three in number and arranged at 120 °, distributed around the tie rod and arranged in the annular space existing between the tie rod 3b and the conical orifice 22a.

According to this embodiment, the metal plate 11, which covers the slab 10 has a boss 24 comprising a conical orifice 24a coaxial with the orifice 10a of the slab and whose generatrices of its wall converge towards the anchoring point on a point located on the axis of the tube 3b.

The tensioning of the anchor line is for example obtained by means of two cylinders 25/26, for example single acting and hydraulically operated. The tensioning of the anchoring line 3 is obtained for example by three locking corners 27 distributed at 120 ° around the tube 3b and arranged in the annular space existing between the tube and the conical orifice 24a.

After the locking corners have been inserted and anchored in the tube 3b, the pressure in the hydraulic circuit is reduced until the operating pressure is canceled.

As for the device described with reference to FIG. 4, the periphery of the zones of the tubes 3b brought into contact with the locking corners 23/27 is striated or includes micro-threads for increase the anchoring of the corners in the tube. Also, the parts of the corners 18/23/27, brought into contact with the tubes can be serrated to further increase the embedding of the corners at the periphery of the tube.

The method and the device according to the invention and, among other applications, can be used to stiffen clays or marls saturated or supersaturated with water or else to produce stable foundations in sand deserts.

It will be noted that with regard to the anchor line 3, the rigid elements (tie rods, tubes or the like) may be replaced by suitable cables.

Claims (15)

1. Method for implementing a foundation by creating a solid mass constituted by the soil itself, characterized by the following operations:
- At least one deep anchoring point is made using anchoring means (1/3) which are driven into the ground by threshing, which means (3) extend in the anchoring position towards the surface of the soil to extend beyond this surface;
- a slab (10) is placed on the surface which has at least one opening (10a) for the passage of the extensions of said anchoring means (3),
- And a traction is exerted on this slab (10) to prestress the ground by means of tensioning said anchoring means located above said slab (10) until obtaining the service force necessary to maintain the structure to be produced on the surface. 2. Method according to claim 1, characterized in that one carries out a deep anchor point, so as to obtain an underground effect of ground stop by anchoring means (1) capable of being put in a position substantially parallel to the surface of the ground where said slab (10) is arranged. 3. Method according to any one of claims 1 or 2, characterized in that one obtains a direct evaluation and control of the soil stress by using a slab (10) whose face brought into contact with the ground is d '' an area equal to a multiple or an integer sub-multiple of the square meter. 4. Device for implementing the method according to any one of claims 1 to 3, characterized in that it consists of anchoring means comprising at least one anchoring line (3) extending towards the ground surface to extend beyond this surface, which anchor line is passed through a hole (10a) reserved in a slab (10) bearing on the ground, which anchor line (3) is connected to means for its tensioning, which are supported on said slab (10) to put the soil in prestress under the effect of a traction exerted on the slab (10) in the direction of the anchor point. 5. Device according to claim 4, the anchoring means of which consist of an anchor (1) comprising a rigid body 1 (a) comprising at least one end for attacking the ground (1a₂) and another end comprising an anvil (1a₄) on which a driving force is applied by threshing, which anchor (1) further comprises a fin ( 5) articulated around a transverse axis (5a) to said body (1a) and having a limited angle of movement of the order of 45 °, at least one anchoring line (3) connected to said body (1a) at at least one point (4) located between said leading end (1a₂) and the center of gravity of the anchor body, said articulated fin (5) being located opposite the leading end (1a₂) and whose pivot axis (5a) is offset relative to the median plane of the body of the anchor (1) in which plane is located the threshing axis, characterized in that the anchoring line (3) is constituted by at least one tie (3a / 3b) connected to a fixing member (4) pivoting about a transverse axis (4a), located in said median plane of the body of the anchor, which tie (3a / 3b) is rigid and is made up killed by a rod or a tube comprising connection means to be able to align several tie rods as a function of the depth of insertion of the anchor (1) in the ground, so that the last tie rod (3b) extends to the -behind the ground level to allow the tensioning of the anchor line (3). 6. Device according to any one of claims 4 or 5, characterized in that in the position of driving the anchor (1) into the ground, the tie rods (3a / 3b) aligned which constitute the anchor line (3) have their axis located substantially in the median plane of the body of the anchor (1) and are located substantially at the center of the anvil (1a₄). 7. Device according to claim 5, characterized in that the anvil (1 to 4) is struck by means of profiles (2) with open or closed cross-section which surround the anchor line (3) and which extend above the ground surface to be subjected to the action of the threshing means. 8. Device according to any one of claims 4 to 7, characterized in that the slab (10) comprises, on its upper face, a metal plate (11) having an orifice (11a) located in line with the orifice of the slab, which is of a diameter greater than that (10a) of the slab to allow adjustments along two axes (x / y). 9. Device according to any one of claims 4 to 8, characterized in that the means for tensioning the anchor line (3) consist of a frame (13) bearing on said metal plate (11) of the slab (10) and comprising a conical housing (15) whose generatrices of the wall converge towards the means of anchoring (1) on a point located on the axis of the tie rods constituting the anchoring line (3) whose last tie rod (3b) which crosses the slab (10) extends into said conical housing (15) and is threaded at its end (3b₁) to cooperate with a locking nut (17) acting on corners (18) placed in the conical housing (15) and around the tie rod (3b) by means of a ring (19) inserted between the corners and the locking nut (17). 10. Device according to claim 9, characterized in that the periphery of the tie rod (3b) brought into contact with the locking corners (18) is striated or has micro-threads to increase the anchoring of the corners (18) on the tie rod (3b). 11. Device according to any one of claims 9 and 10, characterized in that the conical housing (15) is reserved in a movable part (14), guided in the vertical direction on said frame (13), which movable part ( 14) is supported on elastic means (16) which surround the tie rod (3b) and which are inserted between said movable part (14) and the bottom of the frame (13). 12. Device according to any one of claims 4 to 8, characterized in that the means for tensioning the anchor line (3) consist of a beam (21) to which the last tie is fixed (3b) which crosses the slab (10) and the metal plate (11), which beam (21) is located above the slab (10) and the plate (11) and is subjected to the action of at least two jacks (25/26) located on either side of the tie rod (3b) and resting on the metal plate (11) which covers the slab (10). 13. Device according to claim 12, characterized in that said beam (21) comprises in its middle a ring (22) having a conical orifice (22a) whose generatrices of the wall converge on the side of the anchoring point on a point located on the axis of the tie rod (3b) and in that the fixing of said tie rod to the beam (21) is carried out by locking corners (23) distributed around the tie rod (3b) and arranged in the annular space existing between the tie rod (3b) and the conical orifice (22a). 14. Device according to any one of claims 12 or 13, characterized in that the metal plate (11) which covers the slab (10) has a boss (24) comprising a conical orifice (24a) coaxial with the orifice (10a) of the slab (10) and whose generatrices of its wall converge on the side of the anchoring point on a point located on the axis of the tie rod (3b) and in that the tensioning of the anchor line (3) is obtained by locking wedges (27) distributed around the tie rod (3b) and arranged in the annular space existing between the tie rod (3b) and the conical orifice (24a) of said boss (24) so as to cancel the pressure of the fluid in the hydraulic circuit leading to said jacks. 15. Device according to any one of claims 12 to 14, characterized in that the periphery of the zones of the tie rod (3b) brought into contact with the locking corners (18/23/27) is striated or comprises micro-threads for increase the anchoring of the corners on the tie rod (3b).

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