Ground improvement device

Abstract

To enable a rotation speed of a rotary shaft of a ground improvement device to be favorably measured during construction by a ground improvement method.SOLUTION: A ground improvement device (1) in which a rotary shaft (14) is connected to a rotation drive device (18) and an agitation device (15) s provided on the rotary shaft (14) to improve a ground (2) by agitating and mixing sediment and a ground improving material in the ground (2) using the agitation device (15), calculates a rotation speed (rotation number per unit time) of the rotary shaft (14) based on a value of load current flowing through the rotation drive device (18). In particular, when the value of load current flowing through the rotation drive device (18) exceeds a specified value, the rotation speed of the rotary shaft (14) is calculated so that the rotation speed of the rotary shaft (14) gradually decreases depending on the value of load current. A range of the value of load current flowing through the rotation drive device (18) is divided into a plurality of sections and the rotation speed of the rotary shaft (14) depending on the value of load current is calculated by setting different gradual decrease rates for different sections.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a ground improvement device that improves the ground by stirring and mixing soil and soil improvement materials in the ground, using a rotating shaft that has a hollow outer shaft attached to the outside of an inner shaft in a double-tube configuration and an agitator connected to it. [Background technology]

[0002] Conventionally, ground improvement has been carried out for the purpose of strengthening weak ground or purifying contaminated ground.

[0003] The ground improvement device used in this ground improvement is configured so that a rotating shaft has a hollow outer shaft arranged in a double-tube shape outside the inner shaft, to which is connected a stirring device having an excavation body connected to the inner shaft and an inner stirring blade and an outer stirring blade connected to the outer shaft, and the rotating shaft is rotated by a rotary drive device.

[0004] In a ground improvement method using a ground improvement device, the ground is excavated using an excavation device, and a ground improvement material (such as a solidification agent or a purification agent) is discharged into the excavated ground, and the ground improvement material and the soil and sand are stirred and mixed in the ground using a stirring device, thereby improving the ground (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-161843 Summary of the Invention [Problem to be solved by the invention]

[0006] In the conventional ground improvement methods described above, soil improvement equipment is used to stir and mix soil and soil improvement materials inside the ground, making it difficult to directly check the condition of the ground with the naked eye, etc.

[0007] For this reason, with conventional ground improvement methods, the ground improvement equipment is equipped with a depth meter to measure the stirring and mixing position (depth), a flow meter to measure the discharge rate of the ground improvement material, an ammeter to measure the excavation resistance in order to check the supporting layer, etc., and a rotation sensor to measure the rotation speed of the rotating shaft (number of rotations per unit time), and it is necessary to indirectly confirm the state of the ground inside (degree of ground improvement) from the depth (change in depth per unit time: penetration and withdrawal construction speed), flow rate, excavation resistance, and rotation speed measured by these measuring instruments.

[0008] However, when excavating or mixing, the rotation sensor installed in the ground improvement device comes into contact with underground obstacles such as gravel or boulders, and the rotation drive device is subjected to significant vibrations via the mixing device or rotating shaft, which can cause malfunction or damage to either the contact sensor or the non-contact sensor, making it impossible to measure the rotation speed of the rotating shaft.

[0009] Therefore, in the present invention, it is possible to accurately measure the rotation speed of the rotation shaft of the ground improvement device during the execution of the ground improvement method. [Means for solving the problem]

[0010] In the present invention according to claim 1, in a ground improvement device in which a rotating shaft is connected to a rotary drive device and an agitator is provided on the rotating shaft, and the agitator is used to improve the ground by agitating and mixing soil and ground improvement material in the ground, the rotational speed of the rotating shaft (number of rotations per unit time) is calculated based on the load current value flowing through the rotary drive device.

[0011] In addition, in the present invention according to claim 2, in the present invention according to claim 1, when the load current value flowing through the rotary drive device exceeds a predetermined value, the rotation speed of the rotating shaft is calculated so that the rotation speed of the rotating shaft gradually decreases according to the load current value.

[0012] In addition, in the present invention according to claim 3, in the present invention according to claim 2, the range of the load current value flowing through the rotary drive device is divided into a plurality of sections, and the decrement rate is made different for each section to calculate the rotation speed of the rotating shaft according to the load current value.

[0013] Furthermore, in the present invention according to claim 4, in the present invention according to claim 2, the rotational speed of the rotating shaft according to the load current value is calculated by changing the decrement rate according to a signal for controlling the rotational speed of the rotary drive device.

[0014] Furthermore, in the present invention according to claim 5, in the present invention according to any one of claims 1 to 4, a hollow outer shaft is provided on the outside of an inner shaft in a double-tube shape as the rotating shaft, the inner shaft and the outer shaft are connected to a rotary drive device via a counter-rotating transmission, the inner shaft and the outer shaft are rotated in relatively opposite directions at a predetermined speed change ratio, and the rotation speed of either the inner shaft or the outer shaft is calculated based on the value of the load current flowing through the rotary drive device, and the rotation speed of the other shaft is calculated using the speed change ratio. [Effects of the Invention]

[0015] The present invention provides the following effects.

[0016] That is, in the present invention, in a ground improvement device in which a rotating shaft is connected to a rotary drive device and an agitator is provided on the rotating shaft, and the agitator is used to agitate and mix soil and ground improvement materials in the ground to improve the ground, the rotational speed of the rotating shaft (number of rotations per unit time) is calculated based on the load current value flowing through the rotary drive device.Therefore, even if a great deal of vibration is applied to the rotary drive device via the agitator or rotating shaft due to contact with underground obstacles such as stones during the construction of a ground improvement method, such as during excavation or agitation, the rotational speed of the rotating shaft of the ground improvement device can be measured accurately.

[0017] In particular, if the rotational speed of the rotating shaft is calculated so that it gradually decreases in accordance with the load current value when the load current value flowing through the rotary drive device exceeds a predetermined value, the rotational speed of the rotating shaft can be measured accurately.

[0018] Furthermore, if the range of the load current value flowing through the rotary drive device is divided into multiple sections and the decrement rate is varied for each section to calculate the rotational speed of the rotating shaft according to the load current value, the rotational speed of the rotating shaft can be measured even more accurately.

[0019] Furthermore, if the rotational speed of the rotating shaft corresponding to the load current value is calculated by varying the step-down rate in accordance with the signal for controlling the rotational speed of the rotary drive device, the rotational speed of the rotating shaft can be measured even more accurately.

[0020] Furthermore, when the rotating shaft is a double-tube structure in which a hollow outer shaft is provided outside the inner shaft, the inner shaft and the outer shaft are connected to a rotary drive device via a counter-rotating transmission, the inner shaft and the outer shaft are rotated in relatively opposite directions at a predetermined speed ratio, and the rotational speed of either the inner shaft or the outer shaft is calculated based on the value of the load current flowing through the rotary drive device, and the rotational speed of the other shaft is calculated using the speed ratio, it is possible to effectively measure the rotational speeds of both the inner shaft and the outer shaft simultaneously. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. [Figure 2] FIG. [Figure 3] Same plan view. [Figure 4] FIG. [Figure 5] FIG. 4 is an explanatory diagram showing a method for calculating a rotation speed. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, a specific configuration of the soil improvement device according to the present invention will be described with reference to the drawings.

[0023] As shown in Figures 1 to 3, the ground improvement device 1 is a device for excavating the ground 2 and stirring and mixing the excavated soil and sand with a ground improvement material (solidification material) to improve the strength and properties of the ground 2. This ground improvement device 1 has a support 4 erected at the front end of a heavy machine 3, and a ground improvement mechanism 5 attached to this support 4 so that it can be raised and lowered. A ground improvement material supply mechanism 6 is connected to this ground improvement mechanism 5 via a swivel joint 7. The ground improvement material supply mechanism 6 is configured to connect a ground improvement material storage tank 8 and a water tank 9 to a ground improvement material mixing plant 10, and to connect a ground improvement material discharge pump 11 to the ground improvement material mixing plant 10, so that the ground improvement material is supplied to the ground improvement mechanism 5.

[0024] The ground improvement mechanism 5 has a lifting support 12 attached to the front side of the support 4 so that it can be raised and lowered freely, a driver 13 attached to this lifting support 12, the base end (upper end) of a rotating shaft 14 extending in the vertical direction attached to the driver 13, and an agitator 15 connected in tandem to the tip end (lower end) of the rotating shaft 14.

[0025] The driving body 13 has an inner shaft 16 and an outer shaft 17 that constitute the rotary shaft 14 , and a rotary drive device 18 connected to the inner shaft 16 and the outer shaft 17 via a reversing transmission 19 .

[0026] The rotating shaft 14 is composed of an inner shaft 16 and an outer shaft 17, with their central rotation axes arranged coaxially. The outer shaft 17, which is also hollow and cylindrical and extends vertically, is provided on the outside of the inner shaft 16, which is hollow and cylindrical and extends vertically, in a double-tube configuration. The tip of the inner shaft 16 of the rotating shaft 14 protrudes downward further than the tip of the outer shaft 17. When the rotary drive device 18 is driven, the inner shaft 16 and the outer shaft 17 rotate in relatively opposite directions due to the action of a reversing transmission 19. The hollow part of the inner shaft 16 is connected to the ground improvement material supply mechanism 6 and serves as a flow path for discharging the ground improvement material into the ground 2.

[0027] Agitator 15 is interlocked and connected to the tip (lower end) of rotating shaft 14 via a seal rod 20 for preventing soil and soil improvement material from flowing in between inner shaft 16 and outer shaft 17 of rotating shaft 14. This agitator 15 is composed of agitator blade body 21 for agitating and mixing soil and soil improvement material, and an excavator body 22 for excavating ground 2.

[0028] The seal rod 20 is configured such that the outer side of the inner shaft 16, which protrudes from the lower end of the outer shaft 17, is covered at a distance by a pair of front and rear exterior bodies 23, 24 attached to the lower end of the outer shaft 17. A hollow space between the inner shaft 16 and the exterior bodies 23, 24 is provided with an inflow prevention body 25 for preventing the inflow of soil and soil improvement materials. The inflow prevention body 25 is formed by sandwiching grease-impregnated nonwoven fabric between multiple ring-shaped packings spaced apart vertically. The exterior bodies 23, 24 connected to the outer shaft 17 of the seal rod 20 rotate in the opposite direction relative to the inner shaft 16. At this time, the inflow prevention body 25 of the seal rod 20 functions as both a bearing and a seal.

[0029] The agitator blade body 21 has an inner blade shaft 26 interlocked with the inner shaft 16 of the rotating shaft 14, and an outer blade shaft 27 interlocked with the outer shaft 17 of the rotating shaft 14, with the central rotation axis arranged coaxially, and the hollow cylindrical outer blade shaft 27 extending vertically is provided outside the hollow cylindrical inner blade shaft 26 extending vertically in a double-tube shape. The hollow part of the inner blade shaft 26 is connected to the ground improvement material supply mechanism 6 via the inner shaft 16, and a discharge port for the ground improvement material is formed at the tip (lower end) of the inner blade shaft 26, etc., which serves as a flow path for discharging the ground improvement material into the ground 2.

[0030] The agitator blade body 21 also has an innermost agitator blade 28 that is arranged on the innermost side, an inner agitator blade 29 that is arranged on the outer periphery of that, and an outer agitator blade 30 that is arranged further on the outer periphery of that (outermost side).

[0031] The innermost agitating blade 28 has two flat innermost agitating blade pieces 31 attached to the outer peripheral surface of the tip of the outer blade shaft 27, facing radially outward at an interval of 180 degrees in the circumferential direction.

[0032] The inner agitator blade 29 has two inner agitator blade pieces 32 attached to the tip of the inner blade shaft 26 in a radial pattern facing outward at 180-degree intervals in the circumferential direction. Each inner agitator blade piece 32 is formed into a roughly U-shape in side view with the middle part bulging outward, consisting of an inner agitator blade upper piece 33 extending downward at an angle, an inner agitator blade middle piece 34 extending vertically downward, and an inner agitator blade lower piece 35 extending upward at an angle. The inner agitator blade lower piece 35 of each inner agitator blade piece 32 is attached to the tip of the inner blade shaft 26, and the inner agitator blade upper piece 33 is attached to an annular body 36, which is loosely fitted around the outer peripheral surface of the outer blade shaft 27 so as to be freely rotatable. Each inner agitating blade piece 32 has an agitating piece 37 attached to the outside of the inner agitating blade mid-portion piece 34 , and a connecting piece 38 attached between the inner agitating blade mid-portion piece 34 and the inner blade shaft 26 .

[0033] The outer agitator blade 30 has three outer agitator blade pieces 39 attached to the tip of the outer blade shaft 27 in a radial pattern facing outward at 120-degree intervals in the circumferential direction. Each outer agitator blade piece 39 is formed into a roughly U-shape in side view with the middle part bulging outward, consisting of an outer agitator blade upper piece 40 extending downward at an angle, an outer agitator blade middle piece 41 extending vertically downward, and an outer agitator blade lower piece 42 extending upward at an angle. The outer agitator blade upper piece 40 of each outer agitator blade piece 39 is attached to the base end of the outer blade shaft 27, and the outer agitator blade lower piece 42 is attached to an annular body 43, which is loosely fitted around the outer peripheral surface of the inner blade shaft 26 so as to be freely rotatable. Each outer agitating blade piece 39 has two agitating blades 44 attached inside the outer agitating blade mid-section piece 41, one above the other, sandwiching an agitating blade 37 attached outside the inner agitating blade mid-section piece 34 therebetween.

[0034] In the agitator blade body 21, the inner blade shaft 26 rotates as the inner shaft 16 of the rotating shaft 14 rotates, and the outer blade shaft 27 rotates in the opposite direction relative to the inner blade shaft 26 as the outer shaft 17 of the rotating shaft 14 rotates, and the inner agitator blade 29 rotates as the inner blade shaft 26 rotates, and the innermost agitator blade 28 and the outer agitator blade 30 rotate in the opposite direction relative to the inner agitator blade 29 as the outer blade shaft 27 rotates, and these innermost agitator blade 28, inner agitator blade 29 and outer agitator blade 30 agitate and mix the soil and ground improvement material inside the ground 2.

[0035] The excavating body 22 has two flat excavating wings 45 attached radially outward at an interval of 180 degrees in the circumferential direction to the outer peripheral surface of the tip of the inner blade shaft 26, and a plurality of excavating bits 46 detachably attached at intervals on the left and right to the lower part of each excavating wing 45. In the excavating body 22, the excavating wings 45, 45 rotate as the inner blade shaft 26 (inner shaft 16) rotates, and the excavating bits 46 excavate the ground 2.

[0036] In the ground improvement method using the above-mentioned ground improvement device 1, the ground improvement device 1 is moved to a predetermined position on the ground 2, the ground improvement mechanism 5 is lowered, and the excavation body 22 of the mixing device 15 excavates the ground 2 to a predetermined depth, and then the ground improvement material is discharged from the ground improvement material supply mechanism 6 into the ground 2, and the mixing blade body 21 of the mixing device 15 mixes and mixes the ground improvement material and the excavated soil and sand while the ground improvement mechanism 5 is raised and lowered, thereby forming improvement piles inside the ground 2.

[0037] In the present invention, as shown in Figure 4, the above-mentioned ground improvement device 1 is provided with a control device (computer) 47 for controlling the ground improvement mechanism 5 (e.g., rotary drive device 18, etc.) and the ground improvement material supply mechanism 6 (e.g., ground improvement material discharge pump 11, etc.), and the control device 47 appropriately drives and controls them.

[0038] This control device 47 is connected to various driving mechanisms such as the rotary drive device 18 and the ground improvement material discharge pump 11, as well as various measuring mechanisms such as a depth gauge 48 for measuring the stirring / mixing position (depth), a flow meter 49 for measuring the discharge amount of ground improvement material, and an ammeter 50 for measuring the load current flowing through the rotary drive device 18 to check the supporting layer, etc., and is also connected to various control signals such as a rotational speed switching signal 51 for switching the rotational speed of the rotary drive device 18, and a display device 52 for displaying various information.

[0039] In the present invention, it is not only possible to confirm that the load current has reached the supporting layer from the magnitude of the current value (load current value) of the load current flowing through the rotary drive device 18 measured using the ammeter 50, but also to measure (calculate) the rotational speed (number of rotations per unit time) of the rotating shaft 14 (inner shaft 16, outer shaft 17) during ground improvement work based on the load current value, and to confirm (manage) the condition inside the ground (degree of ground improvement) using that rotational speed, the stirring / mixing position (depth) measured using the depth meter 48, the penetration / pulling work speed (change in depth per unit time) measured using the depth meter 48, and the discharge amount of ground improvement material measured using the flow meter 49.

[0040] Here, the rotation speed of the rotary shaft 14 is calculated based on the load current value flowing through the rotary drive device 18 measured using an ammeter 50 as described below.

[0041] The rotating shaft 14 rotates at a constant rotational speed by passing a rated current at a rated voltage through the rotary drive device 18. However, when excavating, stirring, or mixing is performed inside the ground 2, the stirring blades 21 and excavation body 22 of the stirrer 15 rotating inside the ground 2 encounter resistance from soil and sand, soil improvement materials, etc., and as a result, a load current exceeding the rated current flows through the rotary drive device 18 while gradually increasing, making it unable to rotate at a constant rotational speed and causing the rotational speed to gradually decrease.

[0042] Therefore, preliminary tests were conducted in advance to measure the rotation speed of rotating shaft 14 and the value of the load current flowing through rotary drive device 18. Based on the results, an approximate correlation between the rotation speed of rotating shaft 14 and the value of the load current flowing through rotary drive device 18 was set, as shown in Figure 5, for example. The rotation speed of rotating shaft 14 was then calculated based on the value of the load current flowing through rotary drive device 18 using this correlation between the rotation speed of rotating shaft 14 and the value of the load current flowing through rotary drive device 18.

[0043] When approximately setting the correlation between the rotational speed of the rotating shaft 14 and the load current value flowing through the rotary drive device 18, if the load current value is less than a predetermined value (I1), the rotary drive device 18 will rotate at a constant rotational speed (N1).

[0044] When the load current value exceeds a predetermined value (I1), the rotation speed of the rotating shaft 14 is set to decrease linearly (gradually) at a constant decrease rate according to the load current value.

[0045] In this case, if the load current value exceeds a predetermined value (I1), the load current value flowing through the rotary drive device 18 is divided into multiple ranges (here, three ranges), and the decrement rate is set to be different for each range.

[0046] For example, when the load current value is equal to or greater than a first predetermined value (I1) and less than a second predetermined value (I2), the gradual decrease rate is set to K1%, when the load current value is equal to or greater than a second predetermined value (I2) and less than a third predetermined value (I3), the gradual decrease rate is set to K2%, and when the load current value is equal to or greater than a third predetermined value (I3) and less than a fourth predetermined value (I4), the gradual decrease rate is set to K3%. Here, the gradual decrease rate is set to decrease as the load current value increases.

[0047] In this way, an approximate correlation is set between the rotational speed of the rotating shaft 14 and the value of the load current flowing through the rotary drive device 18, and the control device 47 measures the value of the load current flowing through the rotary drive device 18 using the ammeter 50, and calculates the rotational speed of the rotating shaft 14 based on the load current value using the correlation between the rotational speed of the rotating shaft 14 and the value of the load current flowing through the rotary drive device 18.

[0048] The approximate correlation between the rotation speed of the rotating shaft 14 and the value of the load current flowing through the rotary drive device 18 as shown in Figure 5 may be set in advance for each of the inner shaft 16 and the outer shaft 17 that make up the rotating shaft 14. Alternatively, it is also possible to approximately set in advance a correlation between the rotation speed and the value of the load current flowing through the rotary drive device 18 for either the inner shaft 16 or the outer shaft 17, and calculate the rotation speed of one of the inner shaft 16 or the outer shaft 17 using the predetermined correlation based on the value of the load current flowing through the rotary drive device 18, and calculate (multiply) the rotation speed of the other of the outer shaft 17 or the inner shaft 16 using the gear ratio between the inner shaft 16 and the outer shaft 17 in the reversing transmission 19.

[0049] Furthermore, if the rotational drive device 18 has a structure in which the rotational speed of the rotating shaft 14 (inner shaft 16, outer shaft 17) can be changed and switched between multiple stages using the rotational speed switching signal 51, it is also possible to set a correlation between the rotational speed of the rotating shaft 14 and the load current value flowing through the rotational drive device 18, using different load current value sections and step-down rates for each rotational speed switching signal 51 (according to the rotational speed switching signal 51). Note that in the case of a continuously variable speed rotational drive device 18, it is also possible to use an inverter frequency signal as the rotational speed switching signal 51, and set a correlation between the rotational speed of the rotating shaft 14 and the load current value flowing through the rotational drive device 18, using different load current value sections and step-down rates depending on the magnitude of the frequency.

[0050] Furthermore, if the rotary drive device 18 is an electric motor or the like that is driven by power of a predetermined frequency, it is also possible to set a correlation between the rotational speed of the rotating shaft 14 and the load current value flowing through the rotary drive device 18 using load current value categories or decrement rates that differ depending on the power frequency.

[0051] As described above, the ground improvement device 1 has a rotating shaft 14 connected to a rotary drive device 18, a stirring device 15 attached to the rotating shaft 14, and uses the stirring device 15 to stir and mix soil and ground improvement material within the ground 2, thereby improving the ground 2.The device is configured to calculate the rotational speed (number of rotations per unit time) of the rotating shaft 14 based on the load current value flowing through the rotary drive device 18.

[0052] Therefore, in the ground improvement device 1 configured as described above, there is no need to install a rotation sensor such as a contact-type rotation sensor or a non-contact rotation sensor that may malfunction or be damaged by vibrations caused by contact with underground obstacles such as stones during excavation or mixing, etc. Even if a large amount of vibration is applied to the rotation drive device 18 via the mixing device 15 or the rotating shaft 14 due to contact with underground obstacles such as stones during the construction of the ground improvement method, such as excavation or mixing, the rotation speed of the rotating shaft 14 of the ground improvement device 1 can be measured accurately, and construction management can be carried out smoothly.

[0053] In addition, the above-mentioned ground improvement device 1 is configured to calculate the rotational speed of the rotating shaft 14 so that the rotational speed of the rotating shaft 14 gradually decreases according to the load current value when the load current value flowing through the rotary drive device 18 exceeds a predetermined value.

[0054] Therefore, in the soil improvement device 1 configured as described above, the rotation speed of the rotating shaft 14 can be measured accurately.

[0055] In addition, the above-mentioned ground improvement device 1 is configured to divide the range of the load current value flowing through the rotary drive device 18 into multiple sections, and calculate the rotation speed of the rotating shaft 14 according to the load current value by changing the decay rate for each section.

[0056] Therefore, in the soil improvement device 1 configured as described above, the rotation speed of the rotating shaft 14 can be measured more accurately.

[0057] In addition, the ground improvement device 1 is configured to calculate the rotational speed of the rotating shaft 14 according to the load current value by changing the decrement rate in accordance with a signal (rotational speed switching signal 51) for controlling the rotational speed of the rotary drive device 18.

[0058] Therefore, in the soil improvement device 1 configured as described above, the rotation speed of the rotating shaft 14 can be measured more accurately.

[0059] Furthermore, the ground improvement device 1 has a rotating shaft 14 in the form of a double tube, with a hollow outer shaft 17 provided outside the inner shaft 16, and the inner shaft 16 and the outer shaft 17 connected to a rotary drive device 18 via a reversing transmission 19, so that the inner shaft 16 and the outer shaft 17 rotate in relatively opposite directions at a predetermined gear ratio, and calculates the rotational speed of either the inner shaft 16 or the outer shaft 17 based on the load current value flowing through the rotary drive device 18, and also calculates the rotational speed of the other shaft using the gear ratio.

[0060] Therefore, in the ground improvement device 1 configured as described above, the rotation speeds of both the inner shaft 16 and the outer shaft 17 of the rotating shaft 14 can be measured simultaneously and satisfactorily. [Explanation of symbols]

[0061] 1 Soil improvement equipment 2 Soil 3 Heavy equipment 4 Posts 5 Ground improvement mechanism 6 Ground improvement material supply mechanism 7 Swivel joint 8 Ground improvement material storage tank 9 Water tank 10 Ground improvement material mixing plant 11 Ground improvement material discharge pump 12 Lifting support 13 driving body 14 rotating shaft 15 Stirring device 16 Inner shaft 17 outer shaft 18 rotary drive device 19 Reverse transmission 20 Seal rod 21 agitating blade body 22 excavation body 23,24 Exterior body 25 Inflow prevention body 26 Inner wing shaft 27 Outer wing shaft 28 Innermost stirring blade 29 Inner stirring blade 30 outer stirring blade 31 innermost stirring blade piece 32 Inner stirring blade piece 33 Inner stirring blade upper piece 34 Inner stirring blade middle piece 35 Inner stirring blade lower piece 36 Ring body 37 Stirring piece 38 Connection piece 39 Outer stirring blade piece 40 Upper part of outer stirring blade 41 Middle part of outer stirring blade 42 outer stirring blade lower piece 43 annular body 44 stirring piece 45 excavation blade 46 Drilling bit 47 Control device 48 Depth gauge 49 Flow meter 50 Ammeter 51 Rotation speed switching signal 52 Display device

Claims

1. A ground improvement device that connects a rotary shaft to a rotary drive device, provides an agitator on the rotary shaft, and uses the agitator to agitate and mix soil and soil improvement materials in the ground to improve the ground. A ground improvement device characterized by calculating the rotation speed (number of rotations per unit time) of a rotating shaft based on the load current value flowing through a rotary drive device.

2. The ground improvement device described in claim 1, characterized in that when the load current value flowing through the rotary drive device exceeds a predetermined value, the rotational speed of the rotating shaft is calculated so that the rotational speed of the rotating shaft gradually decreases according to the load current value.

3. The ground improvement device according to claim 2, characterized in that the range of the load current value flowing through the rotary drive device is divided into multiple sections, and the decrease rate is made different for each section to calculate the rotation speed of the rotating shaft according to the load current value.

4. A ground improvement device as described in claim 2, characterized in that the rotational speed of the rotating shaft corresponding to the load current value is calculated by changing the decay rate depending on the signal for controlling the rotational speed of the rotary drive device.

5. A ground improvement device as described in any one of claims 1 to 4, characterized in that as the rotating shaft, a hollow outer shaft is provided outside the inner shaft in a double-tube shape, the inner shaft and the outer shaft are connected to a rotary drive device via a counter-rotating transmission, the inner shaft and the outer shaft are rotated in relatively opposite directions at a predetermined speed ratio, the rotational speed of either the inner shaft or the outer shaft is calculated based on the load current value flowing through the rotary drive device, and the rotational speed of the other shaft is calculated using the speed ratio.

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