Method for producing a reinforced structure in the ground

Abstract

Various methods of making a reinforced structure in the ground using a boring tool are provided. One of the methods includes providing a boring tool having a boring tube that can vibrate. The method also includes making a borehole in the ground using the boring tool while causing the boring tube to vibrate. Additionally, the method includes, when the boring tube has reached a predetermined depth, injecting a sealing grout into the boring tube that embeds the boring tube in the sealing grout. Further, the method includes detaching the boring tube from the boring tool, thereby providing a structure reinforced by the boring tube.

Claims

1. A method of making a reinforced structure in ground, said method comprising: calculating a target vibration frequency; providing a boring tool comprising a boring tube having a distal end that carries a cutter member and a vibrating device configured to vibrate the boring tube; making a borehole in the ground using the boring tool, wherein: making the borehole comprises vibrating the boring tube at the target vibration frequency, and boring the boring tube to a predetermined depth, the length of the boring tube is increased while the borehole is made, and the target vibration frequency is recalculated each time the length of the boring tube is increased; when the boring tube has reached the predetermined depth, injecting a sealing grout into the boring tube in order to embed the boring tube in the sealing grout; and after embedding the boring tube, detaching the boring tube from the boring tool, thereby obtaining a reinforced structure provided with a reinforcing element constituted by the boring tube.

2. The method according to claim 1, wherein the diameter of the cutter member is greater than the diameter of the boring tube.

3. The method according to claim 1, wherein, while injecting the sealing grout, the boring tube is caused to vibrate.

4. The method according to claim 1, wherein a centering device is fastened to the boring tube in order to ensure that the reinforcing element is centered in the borehole while the sealing grout is being injected.

5. The method according to claim 1, wherein the direction of the borehole is inclined relative to a vertical direction.

6. The method according to claim 5, wherein the direction of the borehole is inclined relative to the vertical direction by an angle that is strictly greater than 90.

7. A method of fabricating a micropile, wherein the steps of the method according to claim 1 are performed.

8. A method of fabricating an umbrella vault, wherein the steps of the method according to claim 1 are performed.

9. A method of making a reinforced structure in ground, said method comprising: providing a boring tool comprising a boring tube having a distal end that carries a cutter member and a vibrating device configured to vibrate the boring tube; calculating a target vibration frequency using a length of the boring tube, a propagation speed of compression waves in the boring tube, and a predetermined maximum frequency value; making a borehole in the ground to a predetermined depth using the boring tool while vibrating the boring tube; when the boring tube has reached the predetermined depth, injecting a sealing grout into the boring tube in order to embed the boring tube in the sealing grout; and after embedding the boring tube, detaching the boring tube from the boring tool, thereby obtaining a reinforced structure provided with a reinforcing element constituted by the boring tube.

10. A method of making a reinforced structure in ground, said method comprising: providing a boring tool comprising a boring tube having a distal end that carries a cutter member and a vibrating device configured to vibrate the boring tube; calculating a target vibration frequency equal to: Fmax, named the predetermined maximum frequency value, if Fmax<(V)/(2*L), where V is the propagation speed of compression waves in the boring tube and L is the length of the boring tube; or (n*V)/(2*L) if Fmax>(V)/(2*L), where n is an integer greater than or equal to 1 selected so that (n*V)/(2*L)<=Fmax and ((n+1)*V)/(2*L)>Fmax; making a borehole in the ground to a predetermined depth using the boring tool while causing the boring tube to vibrate at the target vibration frequency; when the boring tube has reached the predetermined depth, injecting sealing grout into the boring tube in order to embed the boring tube in the sealing grout; and after embedding the boring tube, detaching the boring tube from the boring tool, thereby obtaining a reinforced structure provided with a reinforcing element constituted by the boring tube.

11. A method of making a borehole using a boring tool, the boring tool comprising a boring tube, a distal end, and a vibrating device configured to vibrate the boring tube at more than one frequency, wherein making the borehole comprises: determining a first vibration frequency based on an initial length of the boring tube; drilling the boring tube into ground while vibrating the boring tube at the first vibration frequency using the vibrating device; increasing the length of the boring tube to a second length; determining a second vibration frequency based on the second length of the boring tube; drilling the boring tube into ground while vibrating the boring tube at the second vibration frequency using the first vibrating device; at a predetermined depth, embed the boring tube in the borehole by injecting sealing grout into the borehole from the distal end of the boring tool; and detaching the boring tube from the boring tool after embedding the boring tube in the borehole.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention can be better understood on reading the following description of embodiments of the invention given as non-limiting examples and with reference to the accompanying drawings, in which:

(2) FIG. 1A shows the boring step of the method of the invention;

(3) FIG. 1B shows the step of injecting a sealing grout into the boring tube;

(4) FIG. 1C is a longitudinal section view of a micropile obtained by performing the method of the invention;

(5) FIG. 2 is a longitudinal section view of a reinforced structure of an umbrella vault obtained by performing the method of the invention; and

(6) FIG. 3 is a diagram showing the method of optimizing the vibration frequency applied to the boring tube.

DETAILED DESCRIPTION OF THE INVENTION

(7) With reference to FIGS. 1A to 1C, there follows a description of a first implementation of the method of the invention in which a reinforced structure is made in ground S, said reinforced structure in this example being a micropile M.

(8) In accordance with the method of the invention, a boring tool 10 is provided that comprises a boring tube 12 made up of a plurality of tubular elements 12a, 12b, 12c, . . . . These tubular elements are fastened together end to end so as to constitute the boring tube 12.

(9) It can thus be understood that the length L of the boring tube 12 varies while making the borehole. More particularly, while making the borehole, as the boring tool penetrates further into the ground, new tubular elements are added to those already inserted into the ground in order to increase the length L of the boring tube 12.

(10) The boring tube 12 has a distal end 14. In the example of FIG. 1A, the boring direction is vertically downwards, such that the distal end in this example corresponds to the bottom end of the boring tube. The distal end carries a cutter member 16. As can be seen in FIG. 1A, the diameter D of the cutter member is preferably greater than the diameter d of the boring tube 12.

(11) In this example, the cutter member 16 is a fitting that is mounted on the distal end 14 of the boring tube 12.

(12) The boring tube 12 also has a proximal end 17 that is connected in this example to means 18 for driving the boring tube 12 in rotation and to means 20 for causing the boring tube 12 to vibrate.

(13) In this example, the means 18 for driving the boring tube 12 in rotation comprise a hydraulic motor.

(14) The means 20 for causing the boring tube to vibrate, specifically a vibration generator 20, serve to generate compression waves that are transmitted along the boring tube 12 from the proximal end 17 towards the distal end 14.

(15) In FIG. 1A, reference L designates the length of the boring tube 12. This length corresponds specifically to the distance between the means 20 for causing the boring tube 12 to vibrate and the distal end 14 of the boring tube 12, which distance corresponds essentially to the distance between the distal and proximal ends of the boring tube.

(16) In accordance with the invention, a borehole F is made in the ground S using the boring tool 10 by causing the boring tube to rotate about the vertical axis A by using the rotary drive means 18 and by causing it to vibrate by using the means 20 for causing the boring tube 12 to vibrate.

(17) While making the borehole, a boring fluid is injected into the boring tube so as to evacuate the debris excavated by the cutter member 16. As can be seen in FIG. 1A, the cutter member 16 has perforations 26 through which the boring fluid flows out from the boring tube prior to rising to the surface while flowing between the boring tube and the wall of the borehole F.

(18) Thereafter, as shown in FIG. 1B, when the boring tube 12 has reached the predetermined depth H, a sealing grout C is injected into the boring tube. This is a cement grout. The fact that the diameter D of the cutter member 16 is greater than the diameter d of the boring tube enables the boring tube to be substantially centered at its distal end 16. Furthermore, as can be seen in FIG. 1B, the boring tube 12 is provided with centering means 30 that are fastened along the boring tube 12.

(19) These centering means 30 serve in particular to center the boring tube 12 at the foot of the borehole F while the sealing grout is being injected so as to ensure that the boring tube is coated by the sealing grout. The centering means 30 are thus arranged to avoid the wall of the boring tube coming into contact with the terrain. In this example, the centering means 30 are in the form of fins that are fastened to the outside wall of the boring tube 12. The sealing grout C flows through the perforations 26 so that the boring tube 12 becomes embedded in the sealing grout C.

(20) In this example, while the sealing grout C is being injected, the boring tube 12 is caused to vibrate without being driven in rotation, thereby enhancing the flow of the sealing grout in the borehole F.

(21) After the sealing grout has been injected, the boring tube is adjusted to its final position, which is generally a little higher than the bored depth, and it is held in this position, with the boring tube 12 being detached from the boring tool 10. In other words, the boring tube 12 is left in the borehole filled with the sealing grout.

(22) In this example, before the sealing grout has set completely, fastener equipment 40, e.g. a short metal bar, is added to the top end of the borehole F, thereby obtaining a reinforced structure in the form of a micropile M having a reinforcing element that is constituted by the boring tool 12.

(23) FIG. 2 shows a reinforced structure 100 that is obtained by performing the method of the invention, in which the boring direction F is inclined relative to the vertical direction at an angle that is strictly greater than 90. In this example, an umbrella vault V is fabricated that is constituted by a plurality of rising reinforced structures 100.

(24) In a particularly advantageous aspect of the invention, while making the boreholes F and F as described above, it is desired to optimize the vibration frequency so as to maximize the boring energy that is transmitted by the boring tube 12. For this purpose, a target vibration frequency is calculated for application to the boring tube 12 by the vibration generator.

(25) The boring tube 12 is thus caused to vibrate at the target vibration frequency while making the various boreholes F, F. It can thus be understood that this target vibration frequency is a vibration frequency that is applied to the boring tube. Specifically, the vibration comprises compression waves that travel along the boring tube defining nodes and antinodes. These vibration waves cause the boring tube 12 to enter into resonance, or at least they are at a frequency close to its resonant frequency, thereby maximizing energy on the cutter member 16, with the effect of significantly increasing the efficiency of boring, and thus the overall efficiency of the method of the invention.

(26) Calculating the target vibration frequency begins with a step S100 during which the length L of the boring tube 12 is input manually or is determined automatically. It is assumed in this example that the boring tube is set into vibration over its entire length.

(27) Thereafter, on the basis of this length, the target vibration frequency is calculated during a step S102 on the basis of the length L of the boring tube, and of the propagation speed of the compression wave in the boring tube 12, which in this example is made of steel.

(28) Also preferably, the calculation makes use of a constant value that corresponds to the propagation speed of compression waves in the boring tube, which speed depends on the material from which the boring tube is made.

(29) In accordance with the invention, insofar as the length of the boring tube 12 increases while the borehole is being made because successive tubular elements 12a, 12b, . . . , are added, the target vibration frequency is recalculated each time the length of the boring tube is increased. This makes it possible to conserve an optimum vibration frequency throughout the duration of boring.

(30) The target vibration frequency calculated in this way is then displayed as a suggestion to the operator. In another implementation it may also be set as a setpoint to the vibration generator 20 during a step S104.

(31) In a manner that is preferred but not essential, the reference target frequency is equal to: Fmax (the predetermined maximum frequency value) if Fmax<(V)/(2*L), where V is the propagation speed of compression waves in the boring tube and L is the length of the boring tube; or (n*V)/(2*L) if Fmax>(V)/(2*L), where n is an integer greater than or equal to 1 selected so that (n*V)/(2*L)<=Fmax and ((n+1)*V)/(2*L)>Fmax.

(32) In the example below, V is equal to 5000 meters per second (m/s), and Fmax is equal to 130 Hz.

(33) L, the length of the borehole, is equal to the sum of the lengths of the tubular elements 12a, 12b, 12c, . . . . In this example, the tubular elements have the same unit length, namely a length of 3 m.

(34) The following table of results is obtained:

(35) TABLE-US-00001 No. of tubes L (m) 2L V/(2*L) n Target F (Hz) 5 15 30 167 130 (Fmax) 6 18 36 139 130 (Fmax) 7 21 42 119 1 119 8 24 48 104 1 104 9 27 54 93 1 93 10 30 60 83 1 83 11 33 66 76 1 76 12 36 72 69 1 69 13 39 78 64 2 128 14 42 84 60 2 120 15 45 90 56 2 112 16 48 96 52 2 104 17 51 102 49 2 98 18 54 108 46 2 93 19 57 114 44 2 88 20 60 120 42 3 126 21 63 126 40 3 120 22 66 132 38 3 114 23 69 138 36 3 108 24 72 144 35 3 105 25 75 150 33 3 99 26 78 156 32 4 128 27 81 162 31 4 124