Patent Grant
10907317
The present disclosure relates to the field of constructing ground anchors, and in particular to the field of constructing anchoring tie-rods.
The disclosure is particularly applicable to fabricating anchoring tie-rods of medium capacity, made more particularly in soft earth.
Typically, an anchoring tie-rod is a device capable of transmitting the traction forces that are applied thereto to a layer of ground by bearing against a reaction mass constituting the structure that is to be anchored.
In general, an anchoring tie-rod is made up of:
In ground having mediocre mechanical capacities, such as soft earth, conventional bonding for anchoring tie-rods does not enable sufficient forces to be engaged to anchor the structure for anchoring correctly.
Also known are Documents CH 146 798 and U.S. Pat. No. 4,015,433, which describe anchors.
An object of the present disclosure is to solve the above-mentioned drawbacks by proposing a method of fabricating an anchor that provides better bonding of the reinforcement in the ground.
For this purpose, embodiments of the disclosure provide a method of constructing a ground anchor, wherein:
the method comprising:
Performing the method of the disclosure thus makes it possible to obtain a ground anchor that has a top portion with a first diameter and a bulb of substantially cylindrical shape having a second diameter that is greater than the first diameter.
Because of this difference in diameter between the top portion and the bulb, the bonding capacity of the ground anchor is significantly improved.
In addition, the use of a deployable mixer device makes it possible to guarantee the diameter of the bulb. By way of example, the boring machine may be a tool as described in Documents EP 1 878 833, EP 2 931 979, ES 2 402 975, or JP 11 222 846.
It is specified that the step of mixing the ground in place with the fluid may be performed while moving the boring tool along the boring axis in a first direction, in a second direction opposite to the first direction, or indeed in both directions. When the boring axis is vertical, the mixing step is performed during a stage of lowering and/or a stage of raising the boring tool.
Preferably, but not exclusively, the fluid is a binder, such that the bulb comprises a first material forming a mixture constituted by the ground in place mixed with the binder.
Also preferably, the step of introducing the boring tool into the ground is accompanied by injecting a boring fluid, e.g. water.
When the anchor is an anchoring tie-rod, it can be understood that the top portion constitutes the unbonded portion of the tie-rod, while the bulb constitutes the bonded portion of the tie-rod. The reinforcement is then fastened to an anchor head. The difference in diameter between the unbonded portion and the bonded portion significantly improves the bonding capacity of the tie-rod. In addition, the shoulder formed between the bulb and its top portion contributes advantageously to bonding the bulb in the ground.
Preferably, but not exclusively, the reinforcement is inserted into the bulb after withdrawing the boring tool.
Preferably, the second diameter is not less than twice the first diameter. Also preferably, the second diameter is not less than three times the first diameter. Also preferably, the second diameter is not less than four times the first diameter.
Preferably, the second diameter of the bulb is not less than 400 millimeters (mm), while the first diameter of the top portion lies in the range 100 mm to 300 mm.
Preferably, but not necessarily, the bulb presents a cylindrical portion terminated by a frustoconical portion connecting the cylindrical portion to the top portion.
The length of the bulb depends in particular on the force to be taken up by the anchor and on the characteristics of the terrain, and in particular on lateral friction.
In the disclosure, after the mixing step, the boring tool is withdrawn from the ground and then during the insertion step:
It can thus be understood that the reinforcement is covered with the bonding grout. In other words, the reinforcement is embedded in a volume of grout that extends at least inside the bulb. The volume of grout preferably extends also in the top portion.
The borehole is preferably made in the bulb while the first material is still fresh.
In an implementation, the reinforcement is a self-boring reinforcement that is constituted by the boring device that is used for making the borehole in the bulb.
In a first variant, the third diameter is less than the first diameter.
In an advantageous second variant, the third diameter is not less than the first diameter of the top portion. In this way, the first material that constitutes the top portion at the end of the mixing step is replaced by the bonding grout at the end of the filling step. An anchor is thus obtained that has a top portion (possibly wider than its initial top portion) that is constituted by the bonding grout, this top portion extending longitudinally in the bulb.
In this advantageous second variant, and when the anchor is an anchoring tie-rod, the bonding grout is selected to that the friction between the grout and the first material is greater than the friction between the grout and the ground, thereby making it possible in particular to reduce the length of the bonded portion in comparison with a conventional tie-rod.
Furthermore, the disclosure makes it possible to guarantee a large amount of friction between the reinforcement and the grout.
Preferably, the grout is a cement grout presenting a cement over water ratio (C/W) by weight of about 2. It may equally be a resin or any other settable substance. The lateral friction that is obtained is preferably of the order of 1 megapascal (MPa).
In an advantageous implementation, the boring machine further comprises a tubular element having a diameter and a bottom end, the mixer device being shaped to be capable of being received inside the tubular element when the mixer device is in the retracted position, the diametral span of the mixer device in the deployed position being greater than the diameter of the tubular element, the method comprising, during the step of introducing the boring tool into the ground:
The tubular element serves in particular to facilitate inserting the mixer device into the ground while it is in the retracted position. It also serves to support the terrain and guarantee the first diameter for the top portion.
Advantageously, after the mixing step, the mixer device in the retracted position is put into the tubular element, and then during the introduction step:
It can be understood that the tubular element serves both as a guide for facilitating insertion of the reinforcement into the ground, and also as a duct for delivering grout into the borehole. The tubular element serves to fill the borehole with the bonding grout from its bottom portion, thereby facilitating filling. The reinforcement is preferably a tube that is open at its bottom end in order to facilitate filling. It may also be a bar attached to a hose or to a tube with sleeves.
Advantageously, during the introduction step, the tubular element is introduced initially into the ground, and then the boring tool is introduced into the tubular element that has previously been introduced into the ground.
Or alternatively, during the introduction step, the tubular element together with the boring tool are introduced simultaneously into the ground, the mixer device being previously put in its retracted position and secured to the tubular element.
Preferably, the tubular element is withdrawn at the end of or during the insertion step.
In a variant, the step of filling with the bonding grout can be performed while the boring tool is being withdrawn.
In a preferred implementation, the boring tool has a tubular body extending along the longitudinal axis, and the mixer device has two deployable wings that are mounted to pivot relative to the tubular body, and the mixer device further comprises spring members arranged between the tubular body and each of the deployable wings, the spring members tending to bring the mixer device into the deployed position by pivoting the deployable wings.
As the boring tool, it is possible to use the tools described in EP 1 878 833, EP 2 931 979, ES 2 402 975, or indeed the tool described in JP 11 222 846.
Advantageously, the fluid is injected under pressure during the mixing step. An advantage is to assist in destructuring the ground and in mixing the grout with the ground. The pressure that is applied may lie in the range a few kilopascals (kPa) up to the high pressures used for jet-grouting, of the order of 60 MPa or more.
In another implementation of the disclosure, at the end of the mixing step and before the insertion step, the initial material of the bulb constituted by the mixture of the ground in place with the fluid is replaced by a bonding material. Preferably, the fluid is a drilling fluid, e.g. water, and the bonding material is a mortar. This variant can be performed advantageously in the presence of clayey ground. The replacement step preferably consists in injecting the filling material into the bulb while removing the initial material of the bulb. Also preferably, at the end of the mixing step, fluid injection is continued in order to remove the initial material, after which the mortar is injected.
Embodiments of the disclosure also provide a method of constructing a prestressed anchoring tie-rod in ground beside a reaction mass, by performing the method of the disclosure for constructing an anchor and wherein the introduction step includes a preliminary step of making a borehole in the reaction mass in which, after obtaining the anchor, a tie-rod head is placed between the reaction mass and the reinforcement, and then the reinforcement is put under tension.
The reaction mass may be a wall, a foundation raft or slab, or any other structure for anchoring.
Embodiments of the disclosure also provide a ground anchor, wherein, when considered from the surface of said ground, said anchor extends along a longitudinal axis and comprises in succession a top portion presenting a diameter, followed by at least one bulb presenting a diameter greater than the diameter of the top portion, the top portion and the bulb comprising at least a first material, and the anchor also comprises a reinforcement extending along the longitudinal axis in the top portion and in the bulb.
Advantageously, the first material is constituted by mixing the excavated ground with a binder. The proportions of ground and binder within the first material should be selected as a function of the type of terrain and of the target strength for the anchor. In a variant, the proportion of ground is less than 10%.
In the disclosure, the reinforcement is covered in a second material having a covering diameter that is less than the diameter of the bulb. Preferably, the covering diameter is not less than the diameter of the top portion. The second material is advantageously different from the first material.
Also preferably, the second material forms a cylindrical covering extending longitudinally in the bulb and in the top portion.
Advantageously, the second material is a bonding grout.
The reinforcement of the anchor preferably comprises a metal bar, a tube, or at least one strand.
Finally, embodiments of the disclosure provide an anchoring tie-rod comprising an anchor of the disclosure.
The disclosure can be better understood on reading the following description of implementations of the disclosure given as non-limiting examples, and with reference to the accompanying drawings, in which:
With reference to
In order to perform the method, there is provided a boring machine 10 of the kind described in EP 1 878 833 or EP 2 931 979. The boring machine 10, which is not described in detail herein, comprises a boring tool 12 that rotates about a longitudinal axis A. The means for driving the boring tool 12 in rotation are known from elsewhere and they are not described herein. The boring tool 12 is also provided with a deployable mixer device 14 that presents a retracted position as shown in
The boring tool 12 has a tubular body 16 extending along the longitudinal axis A; the mixer device 14 has two deployable wings 18 and 20 that are mounted to pivot relative to the tubular body 16 about a pivot axis X that is perpendicular to the longitudinal axis A. The mixer device also has spring members (not shown) that are arranged between the tubular body 16 and each of the deployable wings 18, 20. In known manner the spring members tend to urge the mixer device into the deployed position by pivoting the deployable wings about the axis X.
With reference to
The boring machine 10 also has a device 22 for injecting fluid under pressure into the ground. In this example, the fluid is a binder.
In this example, fluid is injected into the ground S via nozzles arranged in the tubular body 16 of the boring tool, in the proximity of the wings 18, 21.
In the first implementation of the method of the disclosure, an introduction step is performed of introducing the boring tool into the ground along a boring axis F that is parallel to the longitudinal axis A so as to form a top portion C having a height H1 and a first diameter D1. As shown in
In this example, the top portion C is substantially cylindrical in shape with a diameter D1. With reference to
The boring tool 12 also has a cutter member 13 that is arranged at the distal end of the tubular body 16 below the mixer device. This cutter member 13 is configured to bore into the ground S along the boring axis. After the mixer device has reached a depth greater than the height H1 of the top portion, a mixing step is performed during which the mixer device is taken to the deployed position by deploying the wings 18 and 20. Thereafter, the boring tool is driven in rotation together with the mixer device 14 in the deployed position while injecting the binder so as to perform in-situ mechanical mixing of the ground in place with the binder. During this mixing step, the boring tool is moved axially along the boring axis F so as to form a bulb B in the ground, under the top portion C.
As can be understood from
Alternatively, and without going beyond the ambit of the present disclosure, the wings could be deployed once the boring tool has reached the depth corresponding to the depth of the bottom portion of the bulb B. Under such circumstances, the bulb would be formed going upwards while raising the boring tool 12.
In preferred manner, the wings are deployed automatically, such that the bulb B is made going downwards by the mixer device being moved longitudinally while in the deployed position and by injecting fluid.
Without going beyond the ambit of the present disclosure, bulbs B of other shapes could be obtained depending on the type of boring tool used.
In accordance with the disclosure, an insertion step is then performed during which a reinforcement 30 is inserted into the bulb B after the boring tool 12 has been withdrawn from the ground. In this example, the reinforcement 30 is constituted by a metal bar that is inserted along the boring axis. Once the ground-and-binder mixture has hardened, the resulting ground anchor 100 extends along a longitudinal axis Z corresponding to the boring axis F.
With reference to
In this second implementation, the steps of introducing the boring tool into the ground and the mixing step are similar to those of the first implementation.
However the second implementation differs from the first implementation in that, after the mixing step, the boring tool is withdrawn from the ground and then, during the insertion step: a borehole K is made in the bulb B along the boring axis F before the ground-and-binder mixture hardens.
The borehole K presents a third diameter D3 that is less than the second diameter D2 of the bulb B. The borehole K is made using a boring device 40 of tubular shape having an open bottom end carrying cutter means 42. As shown in
Thereafter, after filling, the reinforcement 30 is inserted into the borehole K, as shown in
The grout is selected in such a manner that friction between the reinforcement and the grout is high, of the order of 1 MPa. It is also selected in such a manner that friction between the grout and the mixture resulting from mixing the ground with the binder is greater than the friction between said mixture and the ground surrounding the anchor.
In the example shown in
In the third implementation, the tubular element 50 is introduced into the ground along the boring axis F after previously placing the boring tool in the retracted position inside the tubular element 50. For this purpose, the boring tool 12 is secured to the tubular element 50 and the assembly constituted by the tubular element secured to the boring tool is introduced into the ground along the boring axis, as shown in
As shown in
With reference to
With reference to
After making the borehole K′, the boring tool 12 and the tubular element 50 are separated, and then the boring tool is withdrawn from the ground while leaving the tubular element 50 in the bulb B, as shown in
Thereafter, the reinforcement 30′ is inserted into the tubular element 50. In this example, the reinforcement 30′ is constituted by a tube that is open at its bottom end 30′a and at its top end 30′b.
After introducing the reinforcement 30′ into the tubular element 50, the tubular element 50 is filled with the bonding grout so as to fill the borehole K′. This filling is performed by injecting the bonding grout through the top end 30′b of the reinforcement 30′ so as to discharge the grout from the bottom end of the reinforcement. After the borehole K′ has been filled with the bonding grout, the tubular element 50 is withdrawn from the ground so as to obtain the anchor.
The reinforcement 30′ could equally well be a bar or a strand associated with an injection device such as a sleeve tube or more simply a hose. Without going beyond the ambit of the present disclosure, filling could equally well be performed during the step shown in
The anchoring tie-rod 300 is secured to a reaction mass 310 adjacent to the ground. In this non-limiting example, the reaction mass 310 is a vertical concrete wall.
To make the anchoring tie-rod 300, the above-mentioned introduction step comprise a preliminary step of boring the reaction mass 310. This boring is performed along a boring axis that slopes relative to the vertical axis such that the longitudinal axis Z of the anchoring tie-rod slopes relative to the vertical.
Thereafter, the anchor 200 is made by performing the method of the disclosure. When considered from the surface, the anchor 200 comprises in succession a top portion G followed by at least one bulb B that presents a diameter D2 greater than the diameter D3 of the top portion P. The top portion G extends over a height H1, while the bulb extends over a height H2. It is specified that the top portion G is for forming the unbonded portion of the anchoring tie-rod, while the bulb B forms the bonded portion of the anchoring tie-rod 300. In the unbonded portion, friction is reduced significantly by means of a device 203, such as a greased sheath, or a reinforcement covered in a non-stick coating.
With reference to
The anchor 200 also has reinforcement 30, specifically a metal bar of diameter D4 that extends in the axis Z in the top portion G and in the bulb B.
Furthermore, it can be understood that the cylindrical grout core covers the reinforcement 30 over more than two-thirds of its length. It can thus be understood that the bulb B is made out of a first material resulting from mixing the excavated ground with the binder and a second material, specifically the bonding grout, which surrounds the reinforcement 30, the first material surrounding the second material.
By way of example, the diameter D2 of the bulb B is equal to 600 mm, while the coefficient of friction between the first material and the ground is 80 kPa.
The diameter of the cylindrical core extending inside the bulb B and made of the second material presents a diameter D3 equal to 150 mm and a coefficient of friction between the first and second materials of about 320 kPa.
Finally, the diameter of the reinforcement 30 is 50 mm, and the coefficient of friction between the reinforcement and the second material is about 960 kPa.
After constructing the anchor 200, a tie-rod head 320 is mounted at the top end of the top portion G, this tie-rod head being secured to the reaction mass and to the reinforcement 30. After putting the tie-rod head 320 into position, the reinforcement 30 is put under tension so as to apply prestress to the anchoring tie-rod 300. Even though some features, concepts or aspects of the embodiments may be described herein as being a preferred (more or less) arrangement or method, or an advantageous arrangement or method, such description is not intended to suggest that such feature or features are required or necessary unless expressly so stated.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16 51052 | Feb 2016 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2017/050297 | 2/9/2017 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2017/137702 | 8/17/2017 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4015433 | Shibata | Apr 1977 | A |
| 4411557 | Booth | Oct 1983 | A |
| 4843785 | Sero | Jul 1989 | A |
| 5348424 | Tateyama | Sep 1994 | A |
| 9895729 | Perpezat et al. | Feb 2018 | B2 |
| 9976272 | Darson Balleur et al. | May 2018 | B2 |
| 20040244998 | Schellhorn | Dec 2004 | A1 |
| 20110243666 | Fox | Oct 2011 | A1 |
| 20190153692 | Han | May 2019 | A1 |
| Number | Date | Country |
|---|---|---|
| 146798 | May 1931 | CH |
| 1878833 | Jan 2008 | EP |
| 2634313 | Nov 2015 | EP |
| 2402975 | May 2013 | ES |
| H11222846 | Aug 1999 | JP |
| WO2016009143 | Jan 2016 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20190048550 A1 | Feb 2019 | US |
