FR2845705A1 - Pylon foundation reinforcing procedure uses concrete blocks connected to outside plate anchors by tensioned cables - Google Patents

Abstract

The reinforcing procedure for a pylon's foundations, comprising a concrete block with a sole (5) below it for each of the pylon's feet and a socket (6) above it with fixings for the foot, uses a plate anchor (11) situated below and outside the sole and connected to the block by a cable with a tensioner (18). The depth and width of the plate anchor are in a ratio of at least 7 : 1. In one version of the procedure each block can be fitted with at least one horizontal beam (19) to which the ground anchors are attached.

Description

The invention relates to a method for reinforcing foundations.

of a pylon.

  The invention can be used either to reinforce the foundations during the installation of the pylon, or to reinforce the existing foundations of an old pylon. The base of a pylon foot is usually rigidly

  fixed on fittings anchored in a concrete block made in an appropriate excavation. In the case of a monopod pylon, a single foundation block is made, and in the case of a pylon which has several 10 feet, each foot is fixed on its own block.

  The pylons involved in the process according to the invention can be used for any purpose, in particular for supporting antennas, or for

  support for electricity transmission lines.

  The dimensioning of the foundations of a pylon is calculated in such a way that the foundations do not tip over, in the case of pylons

  monopods, or are not torn off, in the case of pylons comprising several feet, under the action of torques due in particular to the forces of the wind. When the pylons support cables for transporting energy, these torques can be very high when the wind blows in a direction perpendicular to the direction of the cables supported.

  However, the sizing of the current pylon foundations was established on the basis of statistical data concerning the prevailing winds in a territorial region or the maximum wind speeds measured during previous storms, and by applying a limited safety multiplier not to increase

  unnecessary construction costs of foundations.

  During the exceptional storms that hit France in December 1999, a large number of pylons were cut down, and their reconstruction was extremely expensive and took a lot of time. Storms of this intensity may still have

  place and it is desirable that they do not cause the same damage.

  There is therefore a need to consolidate the foundations of the pylons which have resisted. This can obviously be achieved by resizing the foundations and building new power lines in place of the old ones. But it takes a lot of time, is very expensive and creates environmental problems. It has also been proposed to realize new means

  for anchoring the pylons by means of piles which cross the existing foundations, and the number, arrangement and sizes of which are calculated in such a way that these feet can withstand alone the expected pullout forces, the anterior foundation does not no longer playing this role.

  The carrying out of this work requires heavy machinery which is forced to take appropriate paths, to reach the site, which, in many cases, requires the creation of these paths, thus striking

  the costs and can create nuisances in the environment.

  We could also rig the pylons, but this would be a catastrophic solution for the environment and would create many legal problems, since the majority of the pylons are installed in fields and the owners of these pylons have no property rights or

  of use only over a very limited space around said pylons.

  The object of the invention is to overcome these problems by proposing a method for reinforcing foundations, in particular existing foundations, which is easy to implement, which respects the immediate environment of the pylons, which does not deteriorate the current capacities at tearing of existing foundations, but which adds capacity

  complementary against the tearing of the assembly.

  The invention therefore relates to a method for reinforcing the foundations of a pylon having at least one foot, said foundations comprising, for each pylon foot, a reinforced concrete block buried in the ground, said block having in its lower part a sole, and above said sole a chimney fitted with fittings for the

  fixing the base of said pylon foot.

  The method according to the invention is characterized in that at least one anchoring device of the type is installed in the ground, in an area situated below the bed and outside the vertical of the sole. plate and by the fact that one connects said device to said massive by

a stretched cable.

  The plate type anchoring device has been known for a long time and is used in particular for guying structures. This device is in the form of a plate or shovel articulated in its median zone on a rod, and is driven into the ground by pneumatic means, the plate tending to return perpendicular to the

  rod when a traction is exerted on the latter.

  The anchoring device is preferably installed, the plate 5 of which has a width B given at a depth H such that the ratio between said depth H and said plate width B is at least equal to 7.

  With this ratio, the terrain located above the anchoring device can undergo significant cyclic stresses while remaining within the

  domain of reversible strain constraints.

  Very advantageously, the mass is fitted with at least one horizontal beam buried in the ground and the cable is hooked to said beam. In the case of a monopod pylon, it can be understood that this arrangement prevents tilting of the pylon, because the torque 15 generated by the wind is counterbalanced by an inverse torque generated by the tension of a connecting cable d '' an anchoring device

judiciously arranged.

  In all cases, this arrangement makes it possible to separate the area of ground where the anchoring device is located from the underlying areas of the sole which are normally subjected to compressive stresses.

due to the weight of the massif.

  Preferably, the horizontal beam is located at a depth at least equal to 80 cm. This arrangement makes it possible to return the land overlying its normal use, for cultivation for example, and makes it possible to reinforce the massif without carrying out excessive excavations which

  could reduce the adhesion capacity of the bed in the ground.

  When the method according to the invention is applied to a pylon

  monopod, we equip the chimney of the massif with at least two horizontal beams which extend in opposite directions, and the cables 30 are fixed to the end of said beams.

  When the method according to the invention is applied to a pylon having four feet, delimiting a quadrangular surface, is equipped, according to a first embodiment, each solid chimney of two horizontal beams perpendicular to each other and which extend 35 towards the of said quadrangular surface parallel to the sides

of said surface.

  According to a second embodiment of the application of the method according to the invention to a pylon having four feet delimiting a quadrangular surface, the chimneys of two adjacent massifs are connected in pairs by a horizontal beam and each of said beams is connected by a cable stretched to at least one plate anchoring device. In this case, each cable is advantageously arranged substantially vertically. This arrangement reduces the footprint

  on the ground, during reinforcement work.

  If necessary, the beams of a pair of parallel beams are connected to at least two plate anchoring devices by cables whose fixing points on said beams share these at intervals

substantially equal.

  Other advantages and characteristics of the invention will emerge

  on reading the following description given by way of example and with reference to the appended drawings in which:

  Figure 1 is a side view of a massif supporting a pylon base and reinforced by the method according to the invention; Figure 2 is a top view of the massif of Figure 1; Figure 3 is a top view of a pylon having four feet 20 of which the foundation blocks have been reinforced according to a first embodiment of the method of the invention; Figure 4 is a side view of a massif of the pylon of Figure 3; Figure 5 is a top view of a support block of a monopod pylon; Figure 6 is a side view of the support frame of a monopod pylon; FIG. 7 is a side view of the foundations of a four-foot pylon, reinforced according to a second embodiment of the invention; and FIG. 8 is a top view of the support blocks of the

  four-legged pylon shown in Figure 7.

  FIG. 3 shows a square arrangement of four concrete blocks referenced la to id serving as support for the respective feet of a quadripod pylon with a vertical axis 2. The base 3 of each pylon foot is anchored in a block in concrete or is fixed to anchored fittings

  in said concrete block, bearing the general reference 1.

  As seen in Figures 1 and 4, the concrete block 1 has a bottom flange 5 surmounted by a chimney 6 of which 5 the upper end 7 emerges above the surface of a self 8. Depending on the loads of pylon to support, the sole 5 is buried more or less deeply in the ground 8 and the underside 9 of the sole 5 can be at a depth of 2.80 m, for example, for pylons

  supporting electric current transfer lines.

  The forces directed upwards necessary to tear off the block 1 are equal to the sum of the weight of the block 1, the weight of the cone

  of terrain surmounting the sole 5 and characteristics of the soil.

  These efforts can reach 200 tonnes and the object of the invention is to propose a method of reinforcing each block 1 which would make it necessary to increase the tearing efforts of the block 1 by approximately 10%. The reference 10 (Figure 4) indicates a cone of revolution around the axis of the massif 1 in which the soil is subjected to stresses

generated by the massif 1.

  According to the invention, the block 1 is reinforced by at least one anchoring device 11 with a plate disposed in an anchoring zone 12 situated under the sole 5, outside the cone 10 and outside a vertical cylinder 13 surrounding the sole 5, so that the stresses of the ground by the anchoring devices 11 are not disturbed by the anchoring of the block 1 in the ground 8. The anchoring zone 12 is preferably spaced of the vertical cylinder 13 by a distance at least equal to the sum of the half-diameter of the cylinder 13 and the half-diameter

  of the plate 14 of the anchoring device 11.

  The plate anchoring devices 11 used can be devices which are commonly found on the market and in particular under the brands Stingray and MANTA RAY and do not require further explanation. It suffices to know that these devices 11 comprise a plate 14 in the form of a shovel articulated on a rod 15 and are commonly used for guying. The rod of the anchoring device 35 It obviously includes means for hanging

  the end of a cable or a stay cable.

  The rod 15 of the plate anchoring device 11 is connected to the

solid 1 by a tensioned cable 16.

  The upper end 17 of the cable 16 is fixed by means of a tensioner 18 to the free end 18a of a horizontal beam 19 secured to a breastplate 20 rigidly fixed on the chimney

6 of massif 1.

  The horizontal beam 19 is arranged under the surface of the ground 8 to

  a depth which is at least equal to 80 cm so that, after the reinforcement works of the massif 1, the land surrounding the pylon can be reused for its normal use.

  This depth is at least equal to the depth reached

by plowing machines.

  The excavations necessary around the massif 1 to install the

  breastplate 20 and the beam 19 are thus of low importance compared to the 15 sheets which were necessary during the initial realization of the solid mass 1.

  The angle A formed by the cable 16 and the vertical is between 0 and 400 and is preferably less than or equal to 30. This angle can also be zero. The vertical component of the tension of cable 16 is equal to the value of the tension multiplied by the cosine of angle A. For a tension of 20 tonnes, the vertical component is 17,320 daN if

the angle is 300.

  It is easily understood that if the pylon is monopod, as it is mounted in FIGS. 5 and 6, the torque exerted by the vertical component of the tension of the cable 16 makes it possible to avoid the tilting of the pylon, because this torque is proportional to the length of the beam

  horizontal 19. In this case, the breastplate 20 will advantageously comprise two, three or four beams 19, regularly distributed around the axis 2 of the pylon. The forces exerted by the wind on the pylon are taken up by the anchoring device or devices 11 placed in the wind, while the cables 30 disposed in the wind tend to relax.

  In Figure 3, we see that the mass la to id are each

  reinforced by two plate anchoring devices 11 disposed outside the quadrangular surface defined by the four massifs, in median vertical planes, of the corresponding massif, these vertical planes being parallel to the ribs of the quadrangular surface.

  As shown in Figure 2, the breastplate 20 of

  each block 1 comprises two horizontal beams 19a and 19b, perpendicular to each other, at the ends of which are hung the upper ends of two cables 16a and 16b. The cables 16a and 16b 5 extend in the vertical median planes of the horizontal parts 19a and 19b.

  The foundations of the quadripod pylon shown in Figure 3

  thus comprise on each side of the support polygon of the pylon, two anchoring devices 11 whose cables are substantially parallel 10 between them.

  The breastplate 20 is mounted on the chimney 6 in such a way

  that the fittings anchored in the chimneys or the base of the corresponding foot of the pylon can take up the torques and the forces transmitted by the beams 19a and 19b, by means of judiciously jointed ribs 15.

  Figures 7 and 8 show a second embodiment of the invention applied to the support blocks la, lb, lc, ld of a pylon

  large with four feet.

  The support blocks, each comprising a base 5 and 20 a chimney 6, are interconnected two by two by horizontal beams referenced 19a, 19b, 19c, 19d each having at their end plates 30a and 30b rigidly fixed on the faces vis-à-vis the chimneys 6a, 6b of these two massifs by appropriate fixing means. The plate anchoring devices 11 are here arranged substantially under the horizontal beams and are connected to the latter by cables 16 substantially vertical, and tension adjustment systems. The number of cables 16 connected to each horizontal beam is a function of the length of the beam and of the additional forces 30 desired against the tearing. In the case where a beam is connected to a single plate device 11, the point of attachment 31 of the cable 16 on the beam 19 is located in the middle zone of the beam. In the case where a beam 19 is connected to two plate anchoring devices 11, the fixing points 31a and 31b are distant from the adjacent plates 30a and 30b by a length substantially equal to one third of the length of the beam 19 A beam can also be connected to more than two anchoring devices 11,

  the fixing points then sharing the beam at equal intervals.

  The beams 19 can be I-beams, or any other type of beam whose section is configured to generate a small deflection under a large transverse force. With this second embodiment applied to a pylon having four feet, the footprint of the reinforcement systems is

  limit to the support polygon of the pylon.

  The beams 19 are also placed in the ground 8 at a depth of preferably 0.80 meters, and the excavations are filled in at the end of the installation. Means for detecting the position of the tensioners or manholes may optionally be provided on the surface of the ground above the tensioners to facilitate the subsequent operations of

  cable tension check and readjustment 16.

  Figure 8 shows the support blocks of a pylon having four feet and whose support polygon is rectangular. The lift polygon could obviously be square. In FIG. 8, the beam 19a is connected to two anchoring devices 11 and the beam 19c parallel to the previous one is connected only to a single anchoring device with a plate 11. But this beam 19c could obviously be connected to two plate anchoring devices 11, and in practice two parallel beams will be connected to the same number of anchoring devices to

plate 11.

Claims (9)

  1. Method for reinforcing the foundations of a pylon having at least one foot, said foundations comprising, for each foot of 5 pylons, a reinforced concrete block (1) buried in the ground (8), said block having in its part lower a sole (5), and above said sole a chimney (6) fitted with fittings for fixing the base of said pylon foot, characterized in that it is installed in the ground, in an area 10 located below the block and outside the vertical of the sole (5), at least one anchoring device (11) of the plate type and by the fact that said plate device is connected (11 ) massive audit by a stretched cable (16). 2. Method according to claim 1, characterized in that the anchoring device (11) is installed, the plate of which has a width B given at a depth H such that the ratio between said depth H   and said plate width B is at least equal to 7.   3. Method according to any one of claims 1 or 2,   characterized by the fact that the block (1) is fitted with at least one horizontal beam (19) buried in the ground and by the fact that the cable is hooked (16) to said beam (19).   4. Method according to claim 3, characterized in that the   cable (16) makes an angle A with the vertical at most equal to 400.   5. Method according to any one of claims 1 to 4, 25 applied to a monopod pylon, characterized in that one equips the   chimney (6) of the block (1) of at least two horizontal beams (19a, 19b) which extend in opposite directions, and by the fact that the   cables (16) are fixed to the end of said beams (19a, 19b).   6. Method according to any one of claims 1 to 4, 30 applied to a pylon having four feet, delimiting a surface   quadrangular, characterized by the fact that each chimney (6) is fitted with solid masses of two horizontal beams (19a, 19b) perpendicular to each other and which extend towards the outside of said surface   quadrangular parallel to the sides of said surface.   7. Method according to any one of claims 1 to 4,   applied to a pylon having four feet delimiting a quadrangular surface, characterized in that one connects two by two the chimneys (6a, 6b) of two adjacent solid masses (la, lb) by a horizontal beam (19a) and by the fact that each of said beams is connected by   a cable (16) stretched to at least one plate anchoring device (11).   8. Method according to claim 7, characterized in that   each cable (16) is arranged substantially vertically.   9. Method according to one of claims 7 or 8, characterized by   the fact that at least the beams (19a, 19c) of a pair of parallel beams are connected to at least two plate anchoring devices (11) by 10 cables (16) including the fixing points (31a, 31b) on said beams   share these in roughly equal intervals.