Patent Publication Number: US-2022213661-A1

Title: Ground improvement apparatuss and ground improvement method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2021-000677, filed on Jan. 6, 2021, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to a ground improvement apparatus and a ground improvement method which form an improved body having a rectangular cross section by applying the principle of Reuleaux triangle. 
     2. Related Art 
     As a ground improvement apparatus, there is a ground agitator described in Japanese Unexamined Patent Publication No. 2006-336427. The ground agitator includes a drive mechanism, a discharge mechanism, excavation cutters, and agitation blades. The driving mechanism includes a Reuleaux rotary shaft, a bearing, and a driving unit. The Reuleaux rotary shaft has a cross-section of a Reuleaux triangle shape. The bearing rotatably supports a portion of the Reuleaux triangle shape in a square shape having an outer width of the portion of the Reuleaux triangle shape as a side. The driving unit rotationally drives the Reuleaux rotary shaft. The driving mechanism is provided to be movable in an axial direction of the Reuleaux rotary shaft. The discharge mechanism discharges a sediment solidifying material from a distal end of the Reuleaux rotary shaft extended to a distal surface of the bearing. The excavation cutters are provided at the distal end of the Reuleaux rotary shaft and are formed within a range of the Reuleaux triangle shape in which a gravity center and directions of vertices are matched to the Reuleaux triangle shape of the Reuleaux rotary shaft by enlarging the Reuleaux triangle shape of the Reuleaux rotary shaft. The agitation blades are provided between the bearing of the Reuleaux rotary shaft and the excavation cutters and are formed in the same manner as the excavation cutters. 
     In the above ground agitator, the solidifying material is discharged from the distal end of the Reuleaux rotary shaft while excavating a substantially rectangular hole by rotation of the Reuleaux rotary shaft, and soil of the ground and the solidifying material are agitated and mixed by the agitation blades to form an underground continuous wall (improved body) having a rectangular cross section. 
     SUMMARY 
     In the above ground agitator, the entire apparatus is large in scale. Further, in the above ground agitator, the diameters of the Reuleaux rotary shaft and the bearing portion around the Reuleaux rotary shaft become large and thus the Reuleaux rotary shaft and the bearing portion become a large obstacle (load) when they penetrate into the ground, which makes it difficult to smoothly construct the improved body. 
     The disclosure is directed to a ground improvement apparatus and a ground improvement method which can make an outer pipe through which an inner pipe having a fixed sun gear is inserted small in diameter and can easily and reliably form an improved body having a substantially polygonal cross section. 
     A ground improvement apparatus in accordance with some embodiments includes: a double pipe including an outer pipe rotated by a driver and an inner pipe irrotationally arranged inside the outer pipe; an agitation shaft rotatably suspended via a connection member attached to a distal end of the outer pipe at a prescribed distance from the outer pipe so as to be parallel to the outer pipe; a sun gear fixed to a distal end of the inner pipe which is irrotational so as not to rotate; a planetary gear rotatably supported on an upper end side of the agitation shaft and configured to rotate while meshing with the sun gear which is irrotational; and an inverse rotation mechanism configured to mesh with the planetary gear and rotate the agitation shaft in a direction opposite to a rotation direction of the planetary gear. The agitation shaft includes agitation blades radially attached to the agitation shaft and is suspended on the connection member so as to rotate in synchronization with a rotation center of the inverse rotation mechanism. A ground at a location where the outer pipe is penetrated and a solidifying material discharged from a side of the agitation shaft are agitated and mixed with each other by the agitation blades with a trajectory of distal ends of the agitation blades drawing a substantially polygonal shape by rotation of the agitation shaft. 
     A ground improvement method in accordance with some embodiments includes: rotating an outer pipe of a double pipe by a driver; rotating an agitation shaft suspended via a connection member attached to a distal end of the outer pipe at a prescribed distance from the outer pipe so as to be parallel to the outer pipe; through rotation of the outer pipe, revolving a planetary gear around a sun gear and rotating the planetary gear, the sun gear being irrotational and fixed to a distal end of an inner pipe irrotationally arranged inside the outer pipe, the planetary gear being rotatably supported on an upper end side of the agitation shaft; and through revolution and rotation of the planetary gear, agitating and mixing a ground at a location where the outer pipe is penetrated and a solidifying material discharged from a side of the agitation shaft with each other by agitation blades radially attached to the agitation shaft, thereby forming an improved body having a substantially polygonal cross section. 
     According to the aforementioned configurations, an outer pipe through which an inner pipe having a fixed sun gear is inserted can be made small in diameter and an improved body having a substantially polygonal cross section can be easily and reliably formed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic configuration diagram illustrating a main part of a ground improvement apparatus according to a first embodiment. 
         FIG. 2  is a schematic configuration diagram of an interior of a connecting member attached to a distal end of an outer pipe of the ground improvement apparatus. 
         FIG. 3  is an explanatory diagram illustrating a dimensional relationship between a planetary gear and a sun gear fixed to a distal end of an inner pipe inserted into the outer pipe. 
         FIG. 4  is a schematic configuration diagram of an inverse rotation mechanism which reversely rotates the planetary gear and an agitation shaft. 
         FIGS. 5A to 5G  are explanatory diagrams of a substantially regular quadrangular trajectory drawn by distal ends of three agitation blades by rotation of the agitation shaft. 
         FIG. 6  is a schematic configuration diagram illustrating a main part of a ground improvement apparatus according to a second embodiment. 
         FIG. 7  is a schematic configuration diagram illustrating a main part of a ground improvement apparatus according to a third embodiment. 
         FIG. 8  is an explanatory diagram of a substantially regular hexagon trajectory drawn by distal ends of five agitation blades by rotation of an agitation shaft of a ground improvement apparatus according to a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the disclosed embodiments. It will be apparent, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are schematically shown in order to simplify the drawing. 
     Description will be hereinbelow provided for embodiments of the present invention by referring to the drawings. It should be noted that the same or similar parts and components throughout the drawings will be denoted by the same or similar reference signs, and that descriptions for such parts and components will be omitted or simplified. In addition, it should be noted that the drawings are schematic and therefore different from the actual ones. 
       FIG. 1  is a schematic configuration diagram illustrating a main part of a ground improvement apparatus according to a first embodiment of the disclosure,  FIG. 2  is a schematic configuration diagram of an interior of a connecting member  14  attached to a distal end  12   a  of an outer pipe  12  of the ground improvement apparatus,  FIG. 3  is an explanatory diagram illustrating a dimensional relationship between a planetary gear  16  and a sun gear  15  fixed to a distal end  13   a  of an inner pipe  13  inserted into the outer pipe  12 ,  FIG. 4  is a schematic configuration diagram of an inverse rotation mechanism  20  which reversely rotates the planetary gear  16  and an agitation shaft  17 , and  FIGS. 5A to 5G  are explanatory diagrams of a substantially regular quadrangular trajectory K drawn by distal ends  18   a  of three agitation blades  18  by rotation of the agitation shaft  17 . 
     As illustrated in  FIG. 1 , the ground improvement apparatus  10  includes a double pipe  11 , an agitation shaft  17 , a sun gear  15 , a planetary gear  16 , and an inverse rotation mechanism  20 . The double pipe  11  has a cylindrical outer pipe  12  and a cylindrical inner pipe (middle pipe)  13 . The outer pipe  12  is rotated by an auger motor  30 . The inner pipe  13  is arranged inside the outer pipe  12  so as to extend non-rotatably. The agitation shaft  17  is rotatably suspended via a connecting member  14  attached to a distal end  12   a  of the outer pipe  12  at a prescribed distance (for example, 77 mm) from the outer pipe  12  so as to be parallel to the outer pipe  12 . The sun gear  15  is fixed to a distal end  13   a  of the non-rotating inner pipe  13  so as not to rotate. The planetary gear  16  is rotatably supported on an upper end  17   b  side of the agitation shaft  17  and rotates while meshing with the non-rotating sun gear  15 . The inverse rotation mechanism  20  meshes with the planetary gear  16  and rotates the agitation shaft  17  in a direction opposite to a rotation direction of the planetary gear  16 . 
     The agitation shaft  17  is provided with three agitation blades  18  extending radially at 120° intervals. The agitation shaft  17  is suspended on the connecting member  14  so as to rotate via an agitation shaft fixing bearing  19  in synchronization with a rotation center O of the inverse rotation mechanism  20 . By rotation of the agitation shaft  17 , a trajectory K of distal ends  18   a  of the three agitation blades  18  draws a substantially regular quadrangular shape (substantially square shape). That is, a ratio of the number of teeth of the sun gear  15  to the number of teeth of the planetary gear  16  is 4 to 3 and the substantially regular quadrangular shape is formed by the trajectory K of the distal ends  18   a  of the three agitation blades  18  in accordance with the principle of Reuleaux triangle as illustrated in  FIGS. 5A to 5G . 
     As illustrated in  FIGS. 1 and 4 , the inverse rotation mechanism  20  includes an annular plate-shaped rack  21 , an inverse gear  22 , a reception gear  23 , and a bearing  25 . The rack  21  is formed on a lower surface periphery of the planetary gear  16 . The inverse gear  22  meshes with the rack  21 . The reception gear  23  is fixed to an upper end  17   b  of the agitation shaft  78  and an annular plate-shaped rack  24  with which the inverse gear  22  meshes is formed on an upper surface periphery of the reception gear  23 . The bearing  25  is interposed between the planetary gear  16  and the reception gear  23 . The inverse gear  22  is a pinion meshing with the rack  21  and the rack  24  of the reception gear  23 , however may be a bevel gear meshing with the rack  21  and the rack  24 . 
     The double pipe  11  of the ground improvement apparatus  10  moves up and down through a forced lifting and lowering device (not shown) along a leader (not shown) erected in front of a construction machine body, and the outer pipe  12  of the double pipe  11  is rotated by the auger motor (driver)  30 . When penetrating the outer pipe  12  of the double pipe into a ground (not shown), the ground improvement apparatus  10  discharges a slurry-like solidifying material (not shown) from a nozzle (not shown) as a discharge port provided on a distal end side of the agitation shaft  17 , and agitates and mixes, by the three agitation blades  18 , the ground at a location where the outer pipe  12  has been penetrated with the slurry-like solidifying material discharged from the agitation shaft  17  side, thereby improving the ground by forming an improved body R having a substantially regular quadrangular cross section. As illustrated in  FIG. 3 , for example, a radius R 1  of the sun gear  15  is set to 44 mm, a radius R 2  of the planetary gear  16  is set to 33 mm, a distance L from a center of the sun gear  15  to a center of the planetary gear  16  is set to 77 mm, and a radius of each agitation blades  18  is set to 500 mm. 
     According to the ground improvement apparatus  10  in accordance with the first embodiment, when the improved body R having a substantially square cross section is formed, first, the outer pipe  12  of the double pipe  11  is rotated by the auger motor  30 . By the rotation of the outer pipe  12 , the agitation shaft  17  suspended via the connecting member  14  attached to the distal end  12   a  of the outer pipe  12  at the prescribed distance from the outer pipe  12  so as to be parallel to the outer pipe  12  is rotated. That is, through the rotation of the outer pipe  12 , the planetary gear  16  rotatably supported on a side of the upper end  17   b  of the agitation shaft  17  via the inverse rotation mechanism  20  revolves around the non-rotating sun gear  15  fixed to the distal end  13   a  of the non-rotating inner pipe  13  arranged in the outer pipe  12 , and the planetary gear  16  itself also rotates. As a result, as illustrated in  FIGS. 5A to 5G , the distal ends  18   a  of the three agitation blades  18  radially attached to the agitation shaft  17  form the substantially regular quadrangular trajectory K. Thus, the ground at the location where the outer pipe  12  is penetrated and the slurry-like solidifying material discharged from the distal end side of the agitation shaft  17  are agitated and mixed with each other by the three agitation blades  18  to form the improved body R having a substantially regular quadrangular cross section. 
     In this way, the sun gear  15  and the planetary gear  16  with the ratio of the number of teeth of the sun gear  15  to the number of teeth of the planetary gear  16  being 4 to 3 are used and the improved body R having a substantially regular quadrangular cross section is formed by the three agitation blades  18 . As a result, the outer pipe  12  through which the inner pipe  13  to which the sun gear  15  is fixed is inserted can be reduced in diameter. Therefore, a large load is not applied when the outer pipe  12  is penetrated into the ground and the improved body R having an substantially regular quadrangular cross section can be smoothly, easily and reliably formed. 
     In the ground improvement apparatus  10  according to the first embodiment, the planar shape of the sun gear  15  is a perfect circle. Therefore, the improved body R formed by the ground improvement apparatus  10  has a round substantially regular quadrangular shape as illustrated in  FIGS. 5A to 5G . However, by changing the planar shape of the sun gear  15  to a shape that is not a perfect circle (for example, a gear or the like having a substantially regular quadrangular shape as a planar shape in which the four corners are removed and rounded), the cross-sectional shape of the improved body R can be made closer to an accurate regular quadrangular shape. In this case, since an inter-axis distance between the axes of the sun gear  15  and the planetary gear  16  is not constant, a variable mechanism (not shown) for varying the inter-axis distance is provided to keep the meshing between the sun gear  15  and the planetary gear  16 . 
       FIG. 6  is a schematic configuration diagram illustrating a main part of a ground improvement apparatus according to a second embodiment of the disclosure. 
     The ground improvement apparatus according to the second embodiment is different from the ground improvement apparatus according to the first embodiment in that, even when the distance between the center of the sun gear  15  and the center of the planetary gear  16  changes, meshing between the sun gear  15  and the planetary gear  16  is kept by utilizing the contraction/extension force of a spring (elastic body as a variable mechanism)  40  provided between the distal end  13   a  of the inner pipe  13  and a support shaft  16   a  of the planetary gear  16 . Since the other elements are the same as those of the first embodiment, the same elements are denoted by the same reference numerals and detailed descriptions thereof are omitted. 
     Specifically, the ground improvement apparatus according to the second embodiment supports the sun gear  15  and the planetary gear  16  by using the sun gear  15  having a rounded quadrangular shape similar to the trajectory drawn by the gravity center of the Reuleaux triangle when the Reuleaux triangle is rotated so as to draw a substantially square shape by the trajectory K of the vertices of the Reuleaux triangle, via the spring (variable mechanism)  40  which varies the inter-axis distance between the axes of the sun gear  15  and the planetary gear  16  so that the planetary gear  16  always meshes with the sun gear  15 . Thus, an improved body R having a substantially square cross section in which four sides are linear is formed. 
     In the ground improvement apparatus according to the second embodiment, even when the distance between the center of the sun gear  15  and the center of the planetary gear  16  is changed, the sun gear  15  and the planetary gear  16  are meshed with each other by the contraction/extension force of the spring  40 . Therefore, the improved body R can be formed by drawing the more complete regular square than that of the first embodiment by the distal ends  18   a  of the three agitation blades  18 . 
       FIG. 7  is a schematic configuration diagram illustrating a main part of a ground improvement apparatus according to a third embodiment of the disclosure. 
     The ground improvement apparatus according to the third embodiment is different from the ground improvement apparatus according to the first embodiment in that, even when the distance between the center of the sun gear  15  and the center of the planetary gear  16  changes, the sun gear  15  and the planetary gear  16  are meshed with each other by using a magnetic force between a magnet  41  provided on the distal end  13   a  of the inner pipe  13  and a magnet  16  provided on the support shaft  16   a  of the planetary gear  42 . Since the other elements are the same as those of the first embodiment, the same elements are denoted by the same reference numerals and detailed descriptions thereof are omitted. 
     Specifically, the ground improvement apparatus according to the second embodiment supports the sun gear  15  and the planetary gear  16  by using the sun gear  15  having a rounded quadrangular shape similar to the trajectory drawn by the gravity center of the Reuleaux triangle when the Reuleaux triangle is rotated so as to draw a substantially square shape by the trajectory K of the vertices of the Reuleaux triangle, via the magnets (variable mechanism)  41 ,  42  which vary the inter-axis distance between the axes of the sun gear  15  and the planetary gear  16  so that the planetary gear  16  always meshes with the sun gear  15 . Thus, an improved body R having a substantially square cross section in which four sides are linear is formed. 
     In the ground improvement apparatus according to the third embodiment, even when the distance between the center of the sun gear  15  and the center of the planetary gear  16  is changed, the sun gear  15  and the planetary gear  16  are meshed with each other by the magnetic force of the magnet  41  and the magnet  42  facing each other. Therefore, the improved body R can be formed by drawing the more complete regular square than that of the first embodiment by the distal ends  18   a  of the three agitation blades  18 . 
       FIG. 8  is an explanatory diagram of a substantially regular hexagon trajectory K drawn by distal ends  18   a  of five agitation blades  18  by rotation of an agitation shaft  17  of a ground improvement apparatus according to a fourth embodiment of the disclosure. 
     The ground improvement apparatus according to the fourth embodiment is different from the ground improvement apparatus according to the first embodiment in that a sun gear  15  and a planetary gear  16  with the ratio of the number of teeth of the sun gear  15  to the number of teeth of the planetary gear  16  being 6 to 5 are used and the trajectory K having a substantially regular hexagon shape is formed by the distal ends  18   a  of the five agitation blades  18 . Since the other elements are the same as those of the first embodiment, the same elements are denoted by the same reference numerals and detailed description thereof is omitted. 
     In the ground improvement apparatus according to the fourth embodiment, the improved body R having a substantially regular hexagonal cross section can be easily and reliably prepared by the five agitation blades  18  by using the sun gear  15  and the planetary gear  16  with the ratio of the number of teeth of the sun gear  15  to the number of teeth of the planetary gear  16  being 6 to 5. 
     In the above embodiments, the agitation blades  18  are radially attached to the agitation shaft  17 . However, an excavation bit may be attached to the distal end of the agitation shaft  17  to excavate the ground and form the improved body of the ground. 
     In the above embodiments, the agitation shaft  17  is provided with the discharge port for discharging the slurry-like solidifying material. However, a discharge port(s) for discharging the slurry-like solidifying material may be provided in the agitation blade(s)  18 . 
     Further, in the above embodiments, the sun gear  15  and the planetary gear  16  with the ratio of the numbers of their teeth being 4 to 3 are used and the improved body R having a substantially regular square cross section is formed by the three agitation blades  18 , or the sun gear  15  and the planetary gear  16  with the ratio of the numbers of their teeth being 6 to 5 are used and the improved body R having a substantially regular hexagonal cross section is formed by the five agitation blades  18 . However, the sun gear  15  and the planetary gear  16  with the ratio of the numbers of their teeth being 8 to 7 may be used and the improved body R having a substantially regular octagon cross section may be formed by the seven agitation blades  18 . 
     Embodiments of the present invention have been described above. However, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. 
     Moreover, the effects described in the embodiments of the present invention are only a list of optimum effects achieved by the present invention. Hence, the effects of the present invention are not limited to those described in the embodiment of the present invention.