EP3420143B1

EP3420143B1 - Electrically isolated and corrosion-resistant micropile or tie

Info

Publication number: EP3420143B1
Application number: EP16708211.4A
Authority: EP
Inventors: Giancarlo Rezzonico; Aurelio Muttoni; Franco LURATI; Miguel Fernandez Ruiz
Original assignee: Ecole Polytechnique Federale de Lausanne EPFL
Current assignee: Ecole Polytechnique Federale de Lausanne EPFL
Priority date: 2016-02-22
Filing date: 2016-02-22
Publication date: 2023-06-28
Anticipated expiration: 2036-02-22
Also published as: EP3420143A1; WO2017144941A1; PT3420143T

Description

FIELD OF THE INVENTION

The present invention relates to a micropile or tie that is used in construction of buildings or other structures for the anchoring of their structural parts in the ground. More particularly, it concerns a micropile or tie that is fully protected against corrosion.

BACKGROUND OF THE INVENTION

Micropiles or ties are generally composed of linear steel members covered by a cement mortar. The steel members may have different diameters and shapes and usually allow screwing or fixing of more elements in order to increase their length to the required one.
The steel members are introduced inside a hole drilled in the soil, masonry work, concrete or other materials. Thus, the micropiles or ties may carry compression or tension forces from one end to the other. The internal strength of the micropiles or ties essentially depends on their diameter. Without any particular protective action, the steel members are subjected to corrosion, which leads to a reduction of their diameter, and thus to their strength. Therefore, it has been found necessary to protect the steel members from corrosion.
In order to protect the micropiles or ties, different solutions have been proposed in the past.
One solution consists to inject a mortar between the steel member and the surface of the drilled hole. However, in this solution, a contact between the steel member and the soil may accidentally occur. Therefore, this solution does not warrant a full protection of the micropiles or ties.
One further solution consists to use stainless steel for the steel member. However, this solution is very expensive and not effective against stray currents.
The most common solution consists to arrange a protection duct, in plastics or steel, around the steel member and to inject a mortar inside said protection duct. Thereafter, this protected steel member is positioned inside the drilled hole and a mortar is injected between the duct and the drilled hole. However, this solution still presents two weaknesses. Firstly, the ends of the micropiles or ties, which are not covered by the duct, are not protected against corrosion. Secondly, the connecting regions between two adjacent steel members are not covered by the duct and/or by the mortar. Said regions may thus be subjected to corrosion.
Chinese Utility Model No. CN 202298615 U discloses a micropile or tie according to the preamble of claim 1.
Japanese Patent Publication No. JP 2007-332661 discloses a micropile or tie of the type comprising a linear element that is secured to a bearing/anchor plate acting as load-transfer element by means of a fixing nut, which fixing nut forms part of a head element that is located inside a head cap that is filled with a filler, such as grease. According to this document, the bearing/anchor plate is located outside of the head cap and the head cap is attached to the bearing/anchor plate by means of bolts and washers.
French Patent Publication No. FR 2 554 149 A1 discloses a traction rod for concrete works which is used for prestressing/tensioning purposes.
A first aim of the present invention is therefore to provide a micropile or tie, wherein the above mentioned drawbacks are avoided.
A second aim of the present invention is to provide a micropile or tie permitting a suitable transfer of loads from the structure to the steel member.

SUMMARY OF THE INVENTION

In this view, the present invention relates to a micropile or tie according to claim 1.
Important features of the micropile or tie of the present invention are further defined in dependent claims 2 to 13.
Thus configured, the micropile or tie of the present invention is fully protected against corrosion and electrically isolated.
Additionally, due to the shape and roughness of the cover surrounding the head element, the load transfer between the micropile or tie and the structure is assured.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will appear more clearly from the detailed description of several embodiments of the invention which is presented solely by way of non-restricted examples and illustrated by the attached drawings in which:

Figures 1(a), 1(b) and 1(c) are three longitudinal section views of a drilled hole and, thereinside, of a micropile according to a first embodiment of the present invention;
Figures 1(b1) and 1(b2) are longitudinal section views similar to Figure 1(b) but in an alternative embodiment of the present invention;
Figure 2 is an enlarged view of Figure 1(a);
Figure 3 is a view similar to Figure 2 but in a second embodiment of the present invention;
Figure 4 is a view similar to Figure 2 but in a third embodiment of the present invention;
Figure 5 is a view similar to Figure 3 but in a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In reference to Figures 1(a)-(c) , there is shown a drilled hole 1 formed in the ground 2. In this drilled hole is engaged a micropile 10. Spacers 3 are disposed along the drilled hole 1 to keep the micropile 10 distant from the lateral surface of the drilled hole 1. The hollow space between the micropile 10 and the lateral surface of the drilled hole 1 is filled with a hardening material, such as cement mortar.
The micropile 10 comprises two threaded steel rods, respectively a first rod 11 and a second rod 12, that are longitudinally spaced-apart and connected to each other through a coupling element 13. The coupling element 13 may advantageously include a threaded through-hole adapted to receive the lower end 11b of the first rod 11 and the upper end 12a of the second rod 12. The first rod 11, respectively the second rod 12, is positioned inside a first external plastic duct 14, respectively a second external plastic duct 15. These external ducts 14 and 15 are advantageously filled with a hardening material 16, such as cement mortar, before positioning the first and second rods 11, 12 surrounded by said external ducts 14, 15 inside the drilled hole 1. Thus configured, the first and second rods 11, 12 are electrically-isolated and corrosion-resistant along the length extending between their upper ends 11a, 12a and their lower ends 11b, 12b. So as to also protect the lower end 11b of the first rod 11 and the upper end 12a of the second rod 12 that are connected to the coupling element 13, an intermediate external plastic duct 19 may advantageously be disposed around said coupling element 13, said lower end 11b and said upper end 12a, said intermediate external duct 19 being sealed to the first and second external ducts 11, 12. This sealing operation can be done by different manner, such as by heating, screwing or gluing. As described in further detail in the following paragraphs, this intermediate external duct 19 may advantageously be filled with a hardening material, such as cement mortar, thus electrically isolating the portion of the micropile 10 extending between the lower end 11b and the upper end 12a. The first, second and intermediate external ducts 14, 15 and 19 may advantageously have a corrugated profile at their periphery.
The lower end 12b of the second rod 12 may advantageously be protected by a protection piece 17 threadly connected thereof and a cap 18 covering said protection piece 17 and sealed to the second external duct 15.
As shown in detail in Figure 2, the upper end 11a of the first rod 11 partially extends outside of the drilled hole 1 and outside of the first external duct 14 in the upper part of the micropile 10. Said upper end 11a is threadly connected to a head element 20. This head element 20 is positioned inside or embedded within the structure 5 that is supported on the ground 2. This head element 20 comprises three nuts 21 screwed on the first rod 11 and two supporting plates 23 disposed between two adjacent nuts 21 and blocked thereby. An additional reinforcing element 22, such as a helical metallic thread, may advantageously be included in the head element 20. The head element 20 is surrounded by a plastic cover 27, 28 so as to protect it against corrosion. Accordingly, the plastic cover 27, 28 is filled with a hardening material, such as cement mortar, before its sealing to the first external duct 14. In the embodiment shown in Figure 2, the plastic cover may advantageously have a conical shape, said conical shape assuring the load transfer between the micropile 10 and the structure 5. Furthermore, the plastic cover may comprise a lower part 27 and an upper part 28 sealed thereto, the lower part 27 being corrugated to improve the load transfer between the micropile 10 and the structure 5. The micropile 10 is electrically controlled by using a wire 25 that is electrically connected to the first rod 11 through one of the supporting plates 23, said wire permitting the measurement of the electric resistance of said first rod. The hardening material may advantageously be supplied to the intermediate external duct 19 through a first tube 24, said first tube having one end connected to a tank containing the hardening material and one other end positioned inside the intermediate external duct 19. In this case, a second tube 26 may be provided to ensure that the air and the hardening material in excess can be expelled from the intermediate external duct 19. Thus, this second tube 26 has one end positioned inside the intermediate external duct 19 and one other end positioned inside the plastic cover 27, 28.
In a further embodiment illustrated in Figures 1(b1) and 1(b2), the micropile 10 comprises an intermediate third rod 11' disposed between the first rod 11 and the second rod 12, said third rod 11' being connected to said first rod 11 through the first coupling element 13 and to the second rod 12 through a second coupling element 13'. This third rod 11' is positioned inside a third external duct 14' filled with the hardening material 16. A second intermediate external duct 19' is disposed around the second coupling element 13' and sealed to the second and third external ducts 15 and 14'. A hardening material is supplied to the second intermediate external duct 19' through first and second tubes 24 and 24' connected together via an intermediate tube 24", said first tube 24 having one end connected to a tank containing the hardening material and one other end positioned inside the first intermediate external duct 19 surrounding the first coupling element 13 and said second tube 24' having one end positioned inside said first intermediate external duct 19 and one other end positioned inside the second intermediate external duct 19'. The air and the hardening material is supplied to the first intermediate external duct 19 through a third tube 26' having one end positioned inside the second intermediate external duct 19' and one other end positioned inside said first intermediate external duct 19.
In further embodiments (not shown) of the present invention, the micropile 10 may comprise several intermediate rods between the first and second rods 11, 12. For each intermediate rod, the micropile may comprise an additional external duct surrounding this rod, an additional coupling element and an additional intermediate external duct surrounding this coupling element. Furthermore, the hardening material may be supplied to the intermediate external duct that surrounds the coupling element connecting the last intermediate rod to the second rod 12 through a first series of tubes fluidically connecting two consecutive intermediate external ducts, said tubes being connected together via a series of intermediate tube. The hardening material may be supplied to the other intermediate external ducts through a second series of tubes fluidically connecting two consecutive intermediate external ducts.
The embodiment illustrated in Figure 3 differs from the one of Figure 2 by the shape of the plastic cover. Indeed, the plastic cover of this embodiment comprises three successive portions 31, 32, 33, respectively a lower end and an upper end portions 31 and 33 having a conical shape and a cylindrical central portion 32 positioned therebetween. This plastic cover may be formed in two parts, a first part including the lower end portion 31 and the lower half of the central portion 32, and a second part including the upper end portion 33 and the upper half of the central portion 32. The two parts may be connected together through a sealing element, such as a shrinkable plastic film 34, disposed around the central portion 32. Furthermore, this embodiment comprises only one supporting plate 23.
The embodiment illustrated in Figure 4 differs from the one of Figure 3 by the fact that the central portion 32 of the plastic cover is corrugated, thus improving the load transfer between the head element 20 and the structure 5. Furthermore, this embodiment comprises two supporting plates 23.
The embodiment illustrated in Figure 5 differs from the one of Figure 3 by the fact that the micropile 10 comprises a single rod 11, without a coupling element 13 and a second rod 12. Thus, the hardening material is supplied to the plastic cover surrounding the head 20 by a single tube 35, having one end connected to the tank containing the hardening material and one other end positioned inside said plastic cover.
The above detailed description with reference to the drawings illustrates rather than limits the invention. There are numerous alternatives, which fall within the scope of the appended claims.
In particular, the micropile or tie of the present invention may have any orientation relative to the ground. In particular, the micropile or tie of the present invention may be horizontally orientated.

Claims

Micropile or tie (10) for connecting a structure (5) to a soil (2), the micropile or tie comprising:
- at least one linear metallic element (11),

- at least one external corrosion-protective duct (14), inside which is positioned the linear metallic element (11), said external duct being filled with a hardening material,

- a head element (20) connected to an upper end (11a) of the linear metallic element (11),
wherein the head element (20) is surrounded by a cover (27, 28; 31, 32, 33) for protection against corrosion, charaterized in that the cover (27, 28; 31, 32, 33) is sealed directly to the external duct (14), in that the head element (20) is threadly connected to the upper end (11a) of the linear metallic element (11), in that the cover (27, 28; 31, 32, 33) is filled with a hardening material, and in that the head element (20) further includes at least one supporting plate (23), located inside the cover (27, 28; 31, 32, 33) which is filled with the hardening material, to ensure the load transfer between the linear metallic element (11), the hardening material and the structure (5).
Micropile or tie (10) according to claim 1, wherein the cover (27, 28; 31, 32, 33) includes at least one corrugated portion (27, 32) improving the load transfer between the micropile or tie (10) and the structure (5).
Micropile or tie (10) according to any one of the preceding claims, wherein the cover (27, 28) has a conical shape.
Micropile or tie (10) according to claim 3, wherein the cover (27, 28) is defined by a corrugated conical face (27).
Micropile or tie (10) according to any one of claims 1-2, wherein the cover (31, 32, 33) has two conical end portions (31, 33) and a cylindrical central portion (32) positioned therebetween.
Micropile or tie (10) according to claim 5, wherein the central portion (32) of the cover is defined by a corrugated lateral face.
Micropile or tie (10) according to any one of the preceding claims, comprising at least two linear metallic elements (11, 12) threadly connected together through a coupling element (13), wherein each linear metallic element (11, 12) is protected by a separate external duct (14, 15) and the coupling element (13) is protected by an intermediate external duct (19) that is positioned between said separate external ducts (14, 15) and sealed thereto.
Micropile or tie (10) according to any one of the preceding claims, wherein the head element (20) further includes a reinforcing element (22) to improve the load transfer between the linear metallic element (11), the hardening material and the structure (5).
Micropile or tie (10) according to any one of the preceding claims, further comprising a wire (25) electrically connected to the linear metallic element (11) to measure the electric resistance thereof.
Micropile or tie (10) according to any one of the preceding claims, further comprising at least one first tube (35) adapted to fill the cover (31, 32, 33) with the hardening material, said first tube having one first end connected to a tank containing the hardening material and one second end positioned inside the cover.
Micropile or tie (10) according to claim 7, further comprising at least one first tube (24) adapted to fill a hollow space of the intermediate external duct (19) that surrounds the coupling element (13) with the hardening material, said first tube (24) having one first end connected to a tank containing the hardening material and one second end positioned inside said hollow space, and at least one second tube (26) having one first end positioned inside said hollow space and one second end positioned inside the cover (27, 28).
Micropile or tie (10) according to any one of the preceding claims, wherein the linear metallic element (11, 12) is made of steel.
Micropile or tie (10) according to any one of the preceding claims, wherein the hardening material is a cement mortar.