Classifications

• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D27/00—Foundations as substructures
  • E02D27/32—Foundations for special purposes
  • E02D27/50—Anchored foundations
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
  • E02D27/00—Foundations as substructures
  • E02D27/32—Foundations for special purposes
  • E02D27/42—Foundations for poles, masts or chimneys

Definitions

• the present invention relates to a device and a method of reinforcing the tearing of a tower foundation, intended more particularly for the reinforcement of an existing pylon foundation, called "superficial".
• superficial foundation is meant a shallow foundation that ensures the stability of the pylon by distributing the loads over a sufficiently large area of land.
• trellis-type pylons generally rest on a foundation consisting of four feet, that is, four individual concrete masses buried, at least partially, in the ground to balance the moments of overturning transmitted by the pylon. according to the laws of leverage. The evolution of the regulations concerning the stability of the structures leads to reinforcement if foundations of this type are too weak.
• the first is to pour a concrete block around the chord of the pylon or the unbaked part of the massif (if it exists), so as to increase the own weight of the foundation by adding the weight of said concrete block.
• the weight of this block is limited and only compensates for low QaI stress deficiency values, which are generally lower. at 20 kN.
• the second known method of reinforcement consists in reinforcing the foundation using micropiles mechanically linked to the pylon members and sunk deep into the ground to a deep substratum of good mechanical strength, such as a bedrock. This method is described in document FR 2 810 056.
• micropiles take up all the loads applied to the towers (the existing foundation is therefore not really used and is only useful for its own weight of concrete, which it brings to the whole).
• the lateral friction created between each micropile and the deep substratum makes it possible to compensate for high QaI deficits, greater than 1000 kN.
• QaI deficits greater than 1000 kN.
• the size of the micropiles, their technicality and the means necessary for their implementation make this second process very expensive.
• pylons are generally not located near roadways and it is often necessary to use heavy equipment in agricultural or steep terrain.
• the object of the invention is to propose a method of reinforcing the tearing out of a pylon foundation, which is economical, easy to implement, which requires means of execution of small dimensions and which is capable of compensating for pull-out deficits QaI "intermediate", that is to say of the order of the hundred kN and preferably remaining less than 1000 kN.
• the invention relates to a method of strengthening the tearing of a pylon foundation, said foundation comprising at least one solid which is buried in the ground of the foundation site and which has a section of greater area in a horizontal plane, characterized in that it comprises the following steps: - Digging a dig around said massif, at least above said section;
• a slab is made in the excavation, so that this slab is buried in the ground and disposed around said mass between said section and the ground surface, and that it exceeds the vertical projection of the periphery of said section;
• slab is meant in the present specification a mass of compact and solid material, of varying shape and thickness.
• a shapeable mixture comprising materials extracted from the soil of the site or external supply materials or a mixture of the two, and at least one binder, and this mixture is deposited in the excavation, said slab resulting from taking said mixture.
• the mixture is sufficiently manageable to be cast in the excavation.
• the nature of the materials and the proportions of binder that can be used to make this slab are a function of the effort deficit QaI to compensate.
• the method of the invention makes it possible to compensate for the QaI effort deficit by increasing the weight of the material requested during tearing; on the one hand, thanks to the weight of the slab and, secondly, in a complementary manner, thanks to the weight of a surrounding soil mass, in particular the floor above the slab, capable of being driven with said slab during tearing.
• the slab extends horizontally beyond the periphery of said section, so that it carries with it during tearing off a mass of soil, hereinafter referred to as additional mass, which would not have been driven in the absence of slab.
• the QaI effort deficit is also compensated by the increase in lateral friction between the reinforcement slab and the soil remaining in place.
• the slab is in direct contact with the soil of the site and it is necessary to make sure of the good lateral adhesion between the slab and the soil remained in place.
• the importance of these lateral friction is directly related to the intrinsic mechanical characteristics of the soil in place.
• to facilitate lateral adhesion it compact or vibrates said slab which, under the effect of compaction or vibration, tends to extend laterally.
• the lateral edges of the slab then exert a pressure against the surrounding ground, which reinforces the lateral adhesion and therefore the amplitude of the lateral friction during tearing.
• the materials used to cover the slab are compacted to ensure good lateral adhesion between these materials and the soil remaining in place.
• the method of the invention allows, in addition, to realize the slab directly on the foundation site and to overcome the transport of such a slab.
• the site for the implementation of the method of the invention remains reasonable because the excavation is shallow (the depth of this excavation is at most equal to the depth of the top of the section of larger horizontal section) and of limited width (generally the slab does not extend beyond the vertical projection of said section by more than two meters).
• this method does not require the use of particular or bulky equipment.
• the slab is in direct contact with the massif and surrounds it.
• a slab that surrounds the massif without being directly in contact with it such as a crown-shaped slab, could be envisaged, as long as it exceeds the vertical projection of the periphery of the section, and is likely to carry with it an additional mass of soil.
• the slab is not mechanically linked to the massif.
• the slab can adhere to the massif.
• This adhesion is not considered a mechanical bond within the meaning of the invention because the resistance of this bond by adhesion is very low compared to the deficit of QaI effort that one seeks to compensate.
• mechanical connection is meant to designate fixing systems by anchoring, clamping etc.
• the mixture used to make the slab is economical, it is used if the nature of the soil of the site allows it, at least a portion of the materials extracted from the soil of the site and, advantageously, only the materials extracted during digging of the excavation. In general, it is sought to use at least a portion of the materials extracted from the soil of the site during the digging of the excavation, to achieve said mixture and / or cover said slab. This saves the purchase of external materials, the transport of these materials and the evacuation of the extracted materials.
• ready-to-use concretes can be used. It is also possible to use less expensive materials, such as gravels, that is to say a natural or non-mixed mixture of pebbles or gravel, whose granularity is between 0 and 80 mm, and preferably between 0 and 40 mm.
• For the mixture used to make the slab is even more economical, it contains a small total proportion of binder, less than 15% by weight of the mixture. It is found that this proportion is sufficient to aggregate together the particles of the materials used, and thus obtain the desired slab. However, for the binder (s) to play their role correctly, it is advisable to choose a total proportion of binder greater than 3%.
• the binders used are, for example, hydraulic, hydrocarbon or synthetic binders.
• hydraulic binders include cements, slags, or lime.
• the proportion of the latter in the mixture is advantageously between 3 and 13% and preferably between 6 and 10% by weight (for example 8%). It will be noted that all the percentages by weight given in the present application are given for a dry mixture (without addition of water), unless otherwise specified.
• lime is used to neutralize the clays.
• the proportion of lime in the mixture is then between 1 and 4% by weight.
• the slab When the slab is made from external filler materials and has a sufficiently high mechanical strength and density relative to the surrounding soil, it can be sought to reduce the volume of the slab and thereby the volume of material extracted from the soil of the site. This allows, in addition, to use a large part, or all, of these materials extracted to cover the slab without the ground level above this slab is too high (too high a level constituting an inconvenience to the floor). access to the pylon, the installation of equipment around the pylon during any repairs or discomfort for the potential farmer of the land on which the tower is located) and thus to limit (or eliminate) costs related to evacuation of these materials.
• the layer of superficial ground that covers the slab contributes to strengthening the foundation.
• the mass of the ground covering the portion of slab that extends beyond the vertical projection periphery of said section constitutes an additional mass of materials (with respect to the ground mass that would be torn without the slab), solicited during the tearing off of the foundation.
• this layer of superficial terrain can be cultivated by the owner of the field on which the foundation is located.
• the towers are generally installed in cultivated or cultivable land, the latter advantage is not negligible.
• so as to leave a layer of soil sufficiently thick to be cultivable and heavy enough to participate in strengthening the foundation slab is buried at a depth of between 0.5 and 2 meters from the surrounding soil surface.
• the invention also relates to a reinforcing device for tearing off a pylon foundation, characterized in that it comprises a slab buried in the ground and arranged around the massif, between the section of larger horizontal section of the massive and the surface of the ground, this slab overflowing the vertical projection of the periphery of said section.
• said slab is made from a mixture comprising materials extracted from the soil of the site or external filler materials or a mixture of both, and at least one binder and this slab results from the taking of said mixture and is in direct contact with the soil of the site.
• FIG. 1 represents an example of an elevated pylon foundation mass
• FIG. 2 shows schematically, in top view, an example of tetrapod tower pylon with its four beds
• FIG. 3 represents a first embodiment of the device of the invention, according to the sectional plane III-III of FIG. 2;
• FIG. 4 represents a second embodiment of the device of the invention
• FIG. 5 represents a third embodiment of the device of the invention
• FIG. 6 represents a fourth embodiment of the device of the invention
• FIG. 7 represents a fifth embodiment of the device of the invention.
• FIG. 2 represents a tower foundation, for example of a trellis-type electrical pylon, comprising four solid masses 10, of the type of that represented in FIG. 1, arranged in a square around the pylon (not shown).
• the pylon is integral with this foundation and each massif plays the role of base in which the chord of the pylon is anchored.
• the massifs generally have several shoulders, or steps, and widen downwards, so that the lower section of the mass, also called sole 12, is the section of larger section in the horizontal plane.
• the sole 12 is of frustoconical shape and widens downwards. Note that for other types of massif, not described here, the section of larger horizontal section is an intermediate section, different from the lower section of the massif.
• the section of larger horizontal section corresponds to the lower end portion of the massif.
• the section of larger horizontal section is defined as the lower end portion of the solid mass.
• FIG. 3 represents a vertical section along the plane III-III (ie perpendicular to the surface T of the ground, itself considered as horizontal), perpendicular to the plane of symmetry S of the solid mass and which passes through the center of the sole 12 a massive 10.
• This device comprises a slab 20 disposed above the sole 12 of a solid 10 similar to that previously described.
• the periphery of the section of the massif 10 of larger horizontal section is, in the example, the periphery of the sole 12, is marked in section by the points B and B '(symmetrical with respect to the plane S).
• the vertical projections of the point B (BO on the lower and upper faces of the slab are respectively marked by the points C and E (C and
• the slab 20 has a cylindrical shape, but it could be frustoconical or have on its lateral edges at least one shoulder so as to reinforce the friction between its lateral edges and the ground around them.
• the outer periphery of this slab crosses the section plane of Figure 3 at points D and D 'for its upper face and points A and A' for its underside. Since the slab 20 projects beyond the vertical projection of the periphery of the sole 12, the points A, A ', D and D' lie outside the points C, C, E and E 'with respect to the plane S.
• the slab 20 is buried in the ground it is covered by a layer of so-called superficial ground.
• the upper face of this slab 20 (and points D, E, E 'and DO is below the surface T of the ground.
• G, F, F ', and G' denote the points situated at the surface T of the ground, vertically above the points D, E, E 'and D'.
• the slab 20 does not rest on the second shoulder 13 of the mass 10 because the ground located between the slab 20 and the shoulder 13 is sufficiently dense not to settle during the tearing of the solid, so that the slab 20 is immediately solicited during the lifting of the massif.
• the slab 20 is rested on this shoulder.
• the slab 20 is made from a mixture comprising materials extracted from the site (either during digging of the excavation or before if other earthworks operations have been carried out on this same site) and a mixture of two binders: lime and cement. The treatment of these materials with these binders provides a solid and compact block forming the slab 20.
• the slab 20 thus obtained has a higher density than that of the surrounding ground and therefore the slab's own weight makes it possible to increase the weight of material situated above the sole 12 and to improve the resistance to tearing off the foundation.
• the slab 20 has a higher tensile shear stress than that of the surrounding soil so that, in a tear-off situation, the vertical shear generated is exerted between the slab 20 and the surrounding soil, that is, at the side surface of the corresponding slab in FIG. 3 at lines AD and A'D '.
• this type of surface will be noted hereinafter M'D'D surface.
• the slab 20 overflows from the periphery of the sole 12 in vertical projection, it is the set of materials located above the slab, included inside the cylinder GDD'G ', and materials included in the inside the truncated cone ABB'A 'which are mobilized, and not just the materials located vertically of the sole 12, delimited by the cylinder FBB'F, as would be the case in the absence of slab.
• an additional mass of soil is mobilized whose weight opposes tearing off, this mass being located above the slab 20 and outside the periphery of the slab 20. outsole in vertical projection.
• this additional mass of soil is a ring of material between the surfaces FEE'F 'and GDD'G'.
• an additional mass of soil is mobilized between the ABB'A 'and CBB'C surfaces.
• the additional mass of materials requested is therefore a function of the distance DE (or CA) overflow of the slab 20 relative to the sole 12 and the depth DG (or FE) which is this slab.
• FIG. 4 represents another embodiment of the device of the invention, similar to that of FIG. 3, but which differs in the nature of the material constituting the slab 20.
• the slab 20 is made from serious treated, that is to say a mixture of serious and binder, and preferably from serious treated with hydraulic binders.
• a definition of the latter type of treated bass, accompanied by examples, is given in the French standard NF P 98-116 dating from February 2000.
• the serious mixture / binder is most often off-site, in a mixing plant but sometimes directly on the site, by means of a construction mobile mixer, for example a pulvimixer or a scooping bucket.
• the treated low are relatively cheap materials, which have a high density and good mechanical properties, in particular good shear strength.
• the thickness of the slab can be quite limited and, as in the example shown, the materials extracted during the digging of the excavation can then be removed or used to cover the slab, without the mound 26 formed vertically the massif is annoying because of its height which remains relatively low (preferably less than 50 cm).
• a reinforcing structure in the volume of the slab, like a metal or plasticized grid, a canvas, a geogrid, layers of geosynthetics, or a real metal frame around which the shapeable mixture is used.
• Figures 5, 6 and 7 show three other embodiments of the reinforcing device of the invention in which the slab 20 is a treated slab grave.
• this slab could be of a composition similar to that of the slab of FIG. 3 or even result from a mixture of materials extracted from the site, from the gravel and from at least one binder.
• the slab 20 is anchored in the ground by means of nails 28, which pass through it in the direction of the thickness. These nails pass through the outer edge of the slab 20, preferably the portion of the slab that projects beyond the vertical projection of the periphery of the sole 12 of the solid mass 10, and are oriented vertically as shown in FIG. 5 or are inclined as shown in Figure 7.
• the length of these nails 28 may vary and, as shown in Figure 6, the nails 28 can extend below the bed 10.
• the length of the nails 28 is limited.
• the nails 28 of the invention do not need to extend to a deep substratum. Moreover, they do not have to be mechanically linked to the pylon chord.
• the role of the nails 28 is twofold: first, they play a role of anchoring the slab 20, anchoring all the more marked that the nails are long, then they allow to mobilize by friction the volume of earth that surrounds (root effect), which again makes it possible to mobilize an additional mass of soil to oppose the uprooting of the solid mass 10.
• These nails 28 can be made by means of bars or metal tubes within which a grout of cement is optionally injected.
• the dimensions of the reinforcement devices described above they obviously depend on the dimensions of the foundations of the foundation to be reinforced, the loss of effort to pull out QaI to compensate, and the characteristics of the soil in which these devices are implanted.
• the soles 12 of the massifs 10 of lattice-type pylons generally have a width and a length of between 2 and 4 meters, while their depth is between 2.5 and 5 meters.
• the outer diameter of the lower section of the massif is a square of 2.35 m on the side while the cylindrical upper section of the massif has a diameter of 90 cm.
• the distance separating the bearing surface 12a from the sole 12 and the upper end of the section 14 is equal to 3.45 m and the solid mass 10 is generally not completely buried and protrudes from the ground surface T of a distance of 30 cm.
• the slab 20 overflows from the outer periphery of the sole 12, in vertical projection, with a distance of between 0.5 m and 1.5 m, preferably 1 m. Furthermore, when the slab 20 is buried, the top of the slab is generally located, at depth, between 0.5 m and 2 m of the surface T of the soil, preferably between 0.5 and 1 m and, for example , at 0.8 m, so that the thickness of the arable land layer is sufficient.
• the thickness of the slab meanwhile, is variable and depends on the material used, the presence of a possible reinforcing structure, and tearing efforts to resume.
• the top of the slab can be sloped to facilitate the flow of water.
• the structure of the reinforcement device of the invention being well understood, we will now describe an example of a method of installation of a device such as that shown in FIG. 3.
• the zone concerned located vertically above each massive 10 of the foundation to be reinforced, is cleared.
• we carry out a terrassing around the massif 10 so as to obtain a search of a depth of about 1.80 m with a lateral overhang of one meter relative to the outer periphery of the sole 12 of the massif 10.
• the first eighty centimeters of the soil of this area are stripped, sanded and stored on the site to be put back in place thereafter.
• the first centimeters of pickled soil are replaced in successive layers, for example by 20 cm thick layer, which is compacted, the fact of proceeding by successive layers provides better compaction.
• These compacting steps make it possible to restore the initial arrangement (in particular the density) of the soil layer situated above the slab and thus to increase the resistance to tearing off.
• This process simple and inexpensive to implement, has the merit of using machines commonly used in the field of building and public works, such as a mini excavator, lightweight compaction equipment and a mobile mixer site.

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• Engineering & Computer Science (AREA)
• General Engineering & Computer Science (AREA)
• General Life Sciences & Earth Sciences (AREA)
• Mining & Mineral Resources (AREA)
• Paleontology (AREA)
• Civil Engineering (AREA)
• Life Sciences & Earth Sciences (AREA)
• Structural Engineering (AREA)
• Foundations (AREA)
• Consolidation Of Soil By Introduction Of Solidifying Substances Into Soil (AREA)
• Working Measures On Existing Buildindgs (AREA)
• Investigation Of Foundation Soil And Reinforcement Of Foundation Soil By Compacting Or Drainage (AREA)
• Suspension Of Electric Lines Or Cables (AREA)
• Road Signs Or Road Markings (AREA)

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• 2004
  • 2004-08-12 FR FR0408837A patent/FR2874223B1/fr not_active Expired - Fee Related
• 2005
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