Soil compaction method using a laser scanner

Abstract

The disclosure relates to a method for compacting a soil, wherein: a) a ramming cycle is carried out several times on an impact area of the soil during which: a mass (16) is dropped on the impact area from a predetermined height (A); and after the impact of the mass (16) on the impact area, a point cloud is acquired using a laser scanner in order to obtain a radar image of at least the footprint (E) of the mass in the soil; b) at least one characteristic data of the soil compaction is determined from at least one of the radar images obtained at the end of the ramming cycles.

Claims

1. A method for compacting a soil, wherein: a) a ramming cycle is carried out several times on an impact area of the soil during which: a mass is dropped on the impact area from a predetermined height; and after the impact of the mass on the impact area, a point cloud is acquired using a laser scanner in order to obtain a radar image of at least a footprint of the mass in the soil and a lifting of the soil around the footprint; b) at least one of the volume of the footprint and the volume of the lifting of the soil around the footprint is determined from at least one of the radar images obtained at the end of the ramming cycles, wherein the repetition of the ramming cycles is stopped when the volume of the footprint or the volume of the lifting of the soil around the footprint has reached a predetermined threshold.

2. The method according to claim 1, wherein at least one of the volume of the footprint and the volume of the lifting of the soil around the footprint is determined at the end of each ramming cycle.

3. The method according to claim 2, wherein the evolution of at least one of the volume of the footprint and the volume of the lifting of the soil around the footprint is determined during the ramming cycles.

4. The method according to claim 1, wherein the volume of the footprint and the volume of the lifting of the soil around the footprint are determined at the end of each ramming cycle.

5. The method according to claim 4, wherein an effective volume is determined from the difference between the volume of the footprint and the volume of the lifting of the soil around the footprint.

6. The method according to claim 5, wherein the evolution, during the ramming cycles, of the effective volume is determined.

7. The method according to claim 5, wherein the repetition of the ramming cycles is stopped when the effective volume has reached a predetermined compaction threshold.

8. The method according to claim 1, wherein the predetermined height is determined from the volume of the footprint or from the volume of the lifting of the soil around the footprint.

9. The method according to claim 1, wherein, during step a), the acquisition of the radar image is carried out during the raising of the mass or when the mass has reached the predetermined height.

10. The method according to claim 1, wherein the radar image is a three-dimensional radar image.

11. A machine for the implementation of the method for compacting a soil according to claim 1, wherein said machine includes a mast, a mass suspended from the mast, a device for raising the mass after the impact of the mass on a soil impact area, and a laser scanner configured to acquire a point cloud in order to obtain a radar image of at least the impact area, wherein the laser scanner is mounted on the mast and comprises a 2D scanner pivotally mounted relative to the mast along a horizontal axis of rotation.

12. The machine according to claim 11, further including a drone equipped with the laser scanner.

13. A method for compacting a soil, wherein: a ramming cycle is carried out several times on an impact area of the soil during which: a mass is dropped on the impact area from a predetermined height; and after the impact of the mass on the impact area, a point cloud is acquired using a laser scanner in order to obtain a radar image of at least a footprint of the mass in the soil, the depth of the footprint is determined from the radar image; the predetermined height for the next mass drop is determined from the depth of the footprint.

14. A method for compacting a soil, wherein: a) a ramming cycle is carried out several times on an impact area of the soil during which: a mass is dropped on the impact area from a predetermined height; and after the impact of the mass on the impact area, a point cloud is acquired using a laser scanner in order to obtain a radar image of at least a footprint of the mass in the soil and a lifting of the soil around the footprint; b) the volume of the footprint and the volume of the lifting of the soil around the footprint are determined from at least one of the radar images obtained at the end of the ramming cycles, wherein an effective volume is determined from the difference between the volume of the footprint and the volume of the lifting of the soil around the footprint, and wherein the repetition of the ramming cycles is stopped when the effective volume has reached a predetermined compaction threshold.

15. The method according to claim 14, wherein the predetermined height is determined from the volume of the footprint or from the volume of the lifting of the soil around the footprint.

16. The method according to claim 14, wherein, during step a), the acquisition of the radar image is carried out during the raising of the mass or when the mass has reached the predetermined height.

17. The method according to claim 14, wherein the radar image is a three-dimensional radar image.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure will be better understood upon reading the following description of one embodiment of the disclosure given by way of non-limiting example, with reference to the appended drawings, in which:

(2) FIG. 1 illustrates the compaction method according to the disclosure, the mass being in the raised position;

(3) FIG. 2 illustrates the first impact in the soil and the formation of a footprint in the soil;

(4) FIG. 3 illustrates the raising of the mass;

(5) FIG. 4 illustrates the acquisition of the radar image of the footprint of the mass in the soil,

(6) FIGS. 5A to 5C schematize the evolution of the impact area after two ramming cycles;

(7) FIG. 6 is a sectional view of the impact area, taken in a vertical plane;

(8) FIG. 7 is an example of a surface generated from a radar image acquired at the end of a ramming cycle;

(9) FIG. 8 is an example of point clouds derived from a radar image;

(10) FIG. 9 is a curve showing the evolution of the volume of the footprint, of the lifting volume and of the effective volume during the ramming cycles;

(11) FIGS. 10A and 10B illustrate a first embodiment of the compacting machine according to the disclosure in which the laser scanner is mounted on the mast of the machine; and

(12) FIG. 11 illustrates a second embodiment of the compacting machine according to the disclosure in which the laser scanner is mounted on a drone.

DETAILED DESCRIPTION

(13) FIGS. 1 to 4 illustrate a machine 10 for the implementation of a soil compaction method 9, according to the present disclosure. This machine 10 includes a tracked carrier 12 provided with a mast 14. The machine 10 also includes a mass 16 whose upper face 16a is attached to the end of at least one cable 18. As schematized in FIG. 1, the cable 18 passes through the arrow 14a of the mast 14. A tensile force can be exerted on the cable 18 using the hoisting device 20 disposed on the carrier 12.

(14) In this non-limiting example, the mass weighs approximately 25 tons, and the machine 10 is configured to bring the mass to a predetermined height A comprised between 5 and 30 meters. The machine 10 is configured to drop the mass 16 on the soil 9. To do so, the tension exerted on the cable 18 is released, which causes the fall of the mass 16 on the soil from the predetermined height A. The cable released follows the mass 16 in its fall without however slowing it down.

(15) FIG. 1 illustrates the soil 9 before compaction, its surface T being substantially horizontal. This surface T constitutes a reference surface.

(16) FIGS. 1 to 4 illustrate a ramming cycle of a ramming sequence during which the mass 16 is first dropped on an area of the soil, called impact area Z, from the predetermined height A. It is understood that the mass 16 is released several times from a predetermined position in order to ram the impact area Z several times.

(17) The impact of the mass 16 on the soil impact area 9 has the effect of forming a crater or a footprint E in the soil 9 and, most often, a lifting area S located around the footprint E. It should be noted that the outskirts of the footprint may also have subsidence areas.

(18) As illustrated in FIG. 3, after the impact of the mass 16 on the soil 9, the mass 16 is raised by actuating the hoisting device 20, which causes traction on the cable 18. The mass 16 is therefore brought back towards its predetermined height A.

(19) According to the disclosure, after the impact of the mass 16 on the soil 9, a point cloud is acquired using a laser scanner 30 in order to obtain a radar image of at least the footprint E of the mass in the soil. In this non-limiting example, the laser scanner 30 is mounted on the mast 14. In this example, the radar image is acquired during the raising of the mass 16 and more specifically after the mass 16 has left the field of view of the laser scanner 30.

(20) After the mass 16 has returned to its predetermined height A, a second ramming cycle identical to the one just described is carried out. The same impact area (Z) mentioned above is therefore rammed again.

(21) All the ramming cycles carried out on the same impact area Z constitute a ramming sequence. After the ramming sequence, the operator moves the machine 10 in order to bring the mass 16 in line with another impact area in order to carry out the following ramming sequence, and so on.

(22) As can be seen in FIGS. 10A and 10B, the laser scanner 30 is rotatably mounted on the mast 14 about an axis of rotation R which, in this example, is substantially horizontal. The laser scanner 30 is pivoted about the axis of rotation R by means of a jack 32 fixed to the mast 14, on the one hand, and to the laser scanner 30, on the other hand.

(23) The actuation of the jack 32 has the effect of pivoting the laser scanner 30 over an amplitude α, on the order of 70 degrees.

(24) In this example, the laser scanner is a two-dimensional LIDAR type scanner. The pivoting of the laser scanner 30 about the axis of rotation R makes it possible to carry out a scanning in a vertical plane, whereby a three-dimensional radar image is acquired.

(25) According to the disclosure, at least one characteristic data of the compaction of the soil 9 is determined from at least one of the radar images obtained at the end of the ramming cycles.

(26) In this example, a first characteristic data of the soil compaction and a second characteristic data of the soil compaction are determined at the end of each ramming cycle.

(27) Without departing from the scope of the present disclosure, a single characteristic data of the soil compaction could be determined at the end of each ramming cycle.

(28) In this example, the first characteristic data of the soil compaction is the volume of the footprint VE, while the second characteristic of the soil compaction is the lifting volume VS.

(29) FIGS. 5A, 5B, 5C and 6 will help describing in more detail these first and second characteristic data of the soil compaction which are determined using radar images obtained by the laser scanner 30.

(30) FIG. 5A represents the condition of the soil before the ramming operations. The reference T illustrates the reference surface.

(31) FIG. 5B illustrates the impact area at the end of the first ramming cycle, which is also illustrated in FIG. 3.

(32) FIG. 5 represents for its part the impact area at the end of the second ramming cycle.

(33) In FIG. 5B, the references VE1, H1, VS1, L1 respectively represent the volume of the footprint, the depth of the footprint, the lifting volume and the lifting height at the end of the first ramming cycle.

(34) The references VE2, VS2, H2, L2 respectively represent the volume of the footprint, the lifting volume, the depth of the footprint E and the lifting height at the end of the second ramming cycle.

(35) The evolution during the first and second ramming cycles of these different values is schematized in FIG. 6 which illustrates the profile of the footprint in cross section in a vertical plane.

(36) FIG. 7 illustrates a radar image 12 obtained at the end of the second ramming cycle.

(37) FIG. 8 illustrates a point cloud coming from the radar images obtained at the end of the first and second ramming cycles. This point cloud then makes it possible, using algorithms known otherwise, to determine the volume VE1 of the footprint E, the depth H1 of the footprint E, the lifting volume VS1 and the lifting height L1 at the end of the first ramming cycle, as well as the volume VE2 of the footprint E, the depth H2 of the footprint E, the lifting volume VS2 and the lifting height L2 at the end of the second ramming cycle.

(38) Obviously, the same principle applies to carry out a mathematical processing for ramming sequences including a greater number of ramming cycles.

(39) According to the disclosure, the evolution of the characteristic data of the soil compaction is determined and followed during the ramming cycles.

(40) In this example, there will be more particularly an interest in the evolution during the ramming cycles of the first and second characteristic data of the soil compaction, constituted respectively by the volume of the footprint VE and the lifting volume VS. The evolution of these first and second characteristic data is illustrated on the curve in FIG. 9, where N corresponds to the number of cycles.

(41) In the mode of implementation described here, a characteristic value of the soil compaction VX is further determined from the first characteristic data of the soil compaction VE, VS. In this example, the characteristic value of the soil compaction VX is determined from the difference between the first and second characteristic data of the soil compaction, that is to say from the difference between the volume of the footprint VE and the lifting volume VS of the soil around the footprint E.

(42) There is therefore:
VX=VE−VS.

(43) This characteristic value of the compaction of the soil VX is called effective volume.

(44) According to the disclosure, the evolution of the characteristic value of the soil compaction VX during the ramming cycles is determined and followed.

(45) FIG. 9 also illustrates the evolution of the effective volume VX during the N ramming cycles.

(46) In this example, the repetition of the ramming cycles is stopped when their characteristic of the soil compaction VX has reached a predetermined compaction threshold V.sub.0. In this example, the compaction threshold is therefore a volume.

(47) Without departing from the scope of the present disclosure, the predetermined compaction threshold could be a constant, the ramming sequence being stopped when the slope of the curve of the effective volume VX is less than said constant.

(48) Indeed, it is observed that from a certain number of cycles, the curve of the effective volume presents a plateau which reflects the fact that the density of the soil hardly increases at all despite the continuation of the ramming cycles.

(49) In other words, the ramming cycles are stopped when the effective volume VX has reached this plateau. In this non-limiting example, the stopping of the ramming sequence at the end of the fifth ramming cycle have been schematized. Obviously, the number of ramming cycles will depend on some parameters such as the nature of the ground to be compacted, the mass 16, the predetermined height A, etc.

(50) FIG. 11 illustrates a second embodiment of the disclosure in which the laser scanner 30 is mounted on a drone 40.

(51) The drone 40 is also equipped with a device for transmitting the radar images, taken at the end of each cycle, to a computing unit (not illustrated here).