DESCRIPTION SOIL IMPROVEMENT TOOL TECHNICAL FIELD [0001] The present invention relates to a soil improvement tool. More particularly, the present invention relates to a soil improvement tool to enable improvement of air permeability and water permeability of soil in which trees such as garden trees and street trees are planted. BACKGROUND ART [0002] Air permeability and water permeability deteriorate over time in the soil in which bases of trees such as garden trees and street trees are positioned because the soil has been trodden down or due to the growth of roots resulting from the growth of trees. Deterioration of air permeability and water permeability in the soil has a harmful effect on the growth of trees because supply of oxygen and water to plant roots runs short. [0003] In order to resolve such a situation, it is considered to dig up the soil in which bases of trees are positioned. However, in the case of excavation by stabbing the soil using a hard tool with a sharp point such as shovel, the tool may come into contact with a plant root and may cause damage to the roots, and in soil improvement work for street trees, it is also highly likely to damage objects buried under the soil such as various kinds of pipes for gas, electricity and water supply/sewage that are positioned in bases of the trees. [0004] Currently, soil treatments such as rhizome digging inspection and tree vigor 1 recovery work due to soil improvement are carried out through the gap of tree roots without causing damage by using a pneumatic soil treatment device as described in Patent Document 1 or more specifically, a pneumatic soil treatment device comprising an underground insertion tube with an injection nozzle which is provided at the tip division and inserted into the underground with the use of a side end thereof, a tapered shade body expanding outward to the tip end by being supported by an outer periphery surface in a position spaced away from the tip end of the underground insertion tube with a desired interval, and air supply means for supplying compressed air to the underground insertion tube, wherein the underground insertion tube is inserted into the underground and soil around the tube inserted into the underground is loosened by jetting compressed air at high pressure through the injection nozzle. [0005] Owing to soil improvement treatment with the use of such a pneumatic soil treatment device, the following effects are exhibited. 1) Soil density per unit area is reduced by making a hole in the soil and bringing the soil in the hole to the ground. 2) Soil improving material can be filled in a hole dug in the soil, which can realize continuous effects of soil improvement over a long period. 3) Jetted compressed air comes into contact with the soil to increase gaps on the surface of excavated soil, whereby enhancing absorption and air permeability. 4) Compressed air applied during work penetrates through the soil and therefore oxygen is supplied to the roots in the soil more easily. However, work with the use of the pneumatic soil treatment device described in this document is accompanied by sending compressed air with a pressure of 7 to 8 atmospheres constantly and continuously and results in a large amount of compressed air required in total so that a large-sized compressor whose weight is, for example, about one ton needs to be used, whereby lacking workability in taking care of tress 2 such as garden trees and street trees and transporting the compressor is not easy. High capability of soil discharge with a heavy splash of soil onto operators prevents a work progress and the whole body of operators gets dirty after work by the splash of soil, which is problematic. [0006] In addition, in such a pneumatic soil treatment device, the outer diameter of a nozzle is constant and thick as about 30 mm in the diameter and therefore it is difficult to insert the nozzle into the soil from the vicinity of roots in which large and small roots intersect with each other with high density and from gaps of base protection boards used for street trees or the like. Furthermore, due to a large weight of the device as a whole including a hose and a large amount of jetted air in the range of 3.5 to 4.0 m 3 /minute (or 3500 to 4000 1 per minute), it is difficult to operate and therefore may possibly damage a large root in combination with a large outer diameter of the nozzle. A damaged large root is often associated with decay which starts from the damaged area and causes damage to the tree itself as a result so that particular attention needs to be paid in soil improvement work. PATENT DOCUMENT [0007] Patent Document 1: JP-A-2006-22547 Patent Document 2: JP-A-62-138103 [0008] There is a need to provide a soil improvement tool which is suitably used for taking care of trees such as garden trees and street trees and makes it possible to improve air permeability and water permeability of soil. OBJECT [0008a] It is an object of the present invention to at least substantially satisfy the above need.
SUMMARY
[0009] An aspect of the present invention provides a soil improvement tool which has a nozzle with a jet port for compressed air at the tip division of a pipe connected to a compressed air supply device and excavates soil into the form of a hole by jetting compressed air through the jet port, wherein the nozzle is expanded to render the maximum outer diameter in the outer periphery of the nozzle in excess of the outer diameter of the pipe such that a value calculated from an equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) I area of the jet port of the nozzle" falls in 5 or more, and the nozzle is positioned substantially in line with the pipe which is oriented in an excavation direction in a substantially linear state. Here, the nozzle is preferably used in a detachable manner. [0010] The soil improvement tool uses the nozzle which is expanded to render the maximum outer diameter in the outer periphery thereof in excess of the outer diameter of the pipe such that a value calculated from the equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / area of the jet port of the nozzle" falls in 5 or more and positioned substantially in line with the pipe oriented in an excavation direction in a substantially linear state, so that excellent effects are exhibited such that an air gap corresponding to the difference between the maximum outer diameter of the nozzle and the outer diameter of the pipe can be easily formed on the side surface of the pipe above the nozzle in the soil, a passage to discharge compressed air jetted into the soil is ensured as a result, and efficiency of soil improvement work is enhanced significantly. Also, owing to a tapered shape at the end of the nozzle, a progress can be made in soil improvement work while avoiding plant roots and/or obstacles. [0011] Furthermore, with the use of the soil improvement tool, a high pressure of about 25 atmospheres can be applied instantly for use and therefore a total amount of compressed air to be used is reduced as a result, whereby treatment can be handled by using a smaller compressor (i.e. compressed air supply device) than pneumatic soil treatment devices that have been used conventionally. Accordingly, the soil improvement tool can be effectively used for taking care of garden trees and street trees. There are also effects such as a small splash of soil resulting from a short period of time required for air discharge and improvement of workability. Meanwhile, the nozzle whose maximum diameter is less than that of conventional soil improvement tools can be used and therefore the nozzle in the soil improvement tool is inserted from a gap of a base protection board, which is made of metal and difficult to move, to take forward work. [0012] In addition, because roots tend to be thick with the presence of a large number of roots in the vicinity of tree bases and be thinner with a smaller number of roots in areas separated farther away from the bases, if a nozzle positioned at the tip division of a pipe penetrating through the vicinity of a root is thick, penetration of the nozzle is impossible due to roots serving as obstacles and therefore the nozzle needs to be thin. Meanwhile, to meet the demand in work to make the nozzle thicker to handle thin roots that increase in areas separated farther away from the bases, the size of the nozzle can be changed as appropriate in accordance with the density of roots by using a detachable nozzle without replacing the pipe as a whole in a range from the vicinity of a tree base to its surrounding areas and machines to be prepared can be compact ones, which is effective. [0013] Thus, owing to compressed air supplied into the soil by using the soil improvement tool, along with significant reduction of labor and enhanced workability in comparison with conventional methods, it is possible to improve the quality of plants by enhancing oxygen concentration in the soil and improving the growth and productivity of plants, and prevent root rot of plants in a poorly drained land so that a role of deep plowing can be played in the present invention. BRIEF DESCRIPTION OF DRAWINGS [0013a] Preferred embodiments of the invention will be described hereinafter, by way of examples only, with reference to the accompanying drawings. [0014] Fig. 1 is a perspective view showing an embodiment of a nozzle provided in a soil improvement tool according to the present invention, wherein the nozzle is expanded to render the maximum outer diameter in the outer periphery of the nozzle in excess of the outer diameter of a pipe such that a value calculated from an equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) I area of an jet port of the nozzle" falls in 5 or more. Fig. 2 is a perspective view showing another embodiment of the nozzle provided in the soil improvement tool according to the present invention, wherein the nozzle is expanded to render the maximum outer diameter in the outer periphery of the nozzle in excess of the outer diameter of the pipe such that a value calculated from the equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / area of the jet port of the nozzle" falls in 5 or more.
Fig. 3 is a perspective view showing a groove which is further carved in the longitudinal direction in the embodiment shown in Fig. 2. Fig. 4 is a perspective view showing yet another embodiment of the nozzle provided in the soil improvement tool according to the present invention, wherein the nozzle is expanded to render the maximum outer diameter in the outer periphery of the nozzle in excess of the outer diameter of the pipe such that a value calculated from the equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / area of the jet port of the nozzle" falls in 5 or more. Fig. 5 is a perspective view showing a circular ring which is further fitted in the embodiment shown in Fig. 4. Fig. 6 is a perspective view showing a tip division of the soil improvement tool without having the nozzle. DESCRIPTION OF EMBODIMENTS [0015] A soil improvement tool according to the present invention is characterized by having a nozzle with a jet port for compressed air at the tip division of a pipe which is connected to a compressed air supply device, wherein the nozzle is expanded to render the maximum outer diameter in the outer periphery of the nozzle in excess of the outer diameter of the pipe such that a value calculated from an equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / area of a jet port of the nozzle" falls in 5 or more, and the nozzle is positioned substantially in line with the pipe oriented in an excavation direction in a substantially linear state. [0016] In the present invention, the nozzle refers to a machine part of a hollow tube used for determining a direction in which a fluid such as gas and liquid flows. The nozzle is used in a wide range in general to control characteristics of a fluid such as flow rate, flow speed, direction and pressure of a flowing substance. [0017] 7 A nozzle, having a jet port for compressed air, is used by being expanded to render the maximum outer diameter in the outer periphery of the nozzle in excess of the outer diameter of the pipe such that a value calculated from the equation of "circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / area of the jet port of the nozzle" falls in 5 or more. The jet port can be arranged at the tip end of the nozzle or on the side surface thereof, it is preferable to arrange the jet port at the tip end of the nozzle in soil excavation. Here, the jet port is a hole through which compressed air is forcibly discharged and refers to the smallest aperture area. Such a nozzle is used and positioned substantially in line with the pipe oriented in a soil excavation direction in a substantially linear state and it is therefore made easier to form an air gap corresponding to the difference between the maximum outer diameter of the nozzle and the outer diameter of the pipe in the soil on the side surface of the pipe above the nozzle inserted into the soil, whereby exhibiting excellent effects such that a passage to discharge compressed air which has been jetted into the soil is ensured and efficiency of soil improvement work is significantly enhanced. [0018] Accordingly, without the nozzle or if the maximum outer diameter in the outer periphery of the nozzle is the same as the outer diameter of the pipe, there is no air gap formed between the side surface of the pipe, which is inserted into the soil, and the soil and therefore it is difficult to ensure a discharge passage for compressed air jetted from the jet port of the nozzle in the soil to reach the ground, whereby resulting in reduction of soil discharge efficiency. Here, the nozzle is expanded at such a rate that a value calculated from the equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / area of the jet port of the nozzle" falls in 5 or more, preferably 10 or more. Here, a value obtained by subtracting an area calculated by the outer diameter of the 8 pipe from a circular area calculated by using the maximum outer diameter of the nozzle as a diameter refers to a sectional area of soil which can be excavated resulting from expansion of the nozzle, whereas an area calculated by using the outer diameter of the pipe refers to a sectional area of the pipe including a hollow tube and corresponds to, for example, a circular area calculated by using the outer diameter of a cylindrical pipe as a diameter. For example, in each of the embodiments shown in Figs. 3 to 5, a circular area calculated by using the maximum outer diameter of the nozzle as a diameter is different from a sectional area calculated by using the maximum outer diameter of the nozzle. [0019] Note that, Patent Document 2 describes a soil improvement work part in which compressed air is supplied from a gas feed pipe to an air spouting body having a nozzle of a pointed shape with an arrow-head-shaped tip division and compressed air is spouted upward from a jet hole opened upward in the nozzle, and discloses the nozzle in Fig. 1 in which the maximum outer diameter in the outer periphery of the nozzle exceeds the outer diameter of the gas feed pipe or the air spouting body. However, the nozzle fails to be positioned substantially in line with a pipe which is oriented in a soil excavation direction and continued to the ground in a substantially linear state as shown in the present invention, and there is completely no technical idea to form an air gap corresponding to the difference between the maximum outer diameter of the nozzle and the outer diameter of the pipe in the soil on the side surface of the pipe above the nozzle inserted into the soil. Accordingly, it is completely impossible to achieve excellent effects of the present invention such as ensuring a passage to discharge compressed air spouted into the soil and significantly enhancing efficiency of soil improvement work. [0020] It is also preferable to use a nozzle having a tapered shape at least in one end and 9 a nozzle which is more preferably used has a tapered shape at the end at which the nozzle is connected to the pipe. It is possible to take forward the soil improvement work while avoiding plant roots and/or obstacles by a nozzle having a tapered shape at the end. Accordingly, the tapered portion at the end of the nozzle connected to the pipe preferably has a sharp angle and it is particularly preferable to have an angle of 60 degrees or less. If the nozzle has a tapered shape in each end, a partial conical surface formed by side surfaces of the tapered portions has a vertical angle which is 120 degrees or less or preferably 90 degrees or less. Therefore, it is made easier to alleviate a situation where roots pushed aside by the tip division and the expanded portion of the nozzle return to original positions after the nozzle passed therethrough and become obstacles in pulling out the nozzle. Meanwhile, a digging force is reduced if the angle of the tapered part at the tip division of the nozzle is too sharp, so the angle is preferably 60 degrees or more. [0021] Embodiments of the present invention will be explained with reference to drawings. [0022] Fig. 1 is a perspective view showing a basic embodiment of the present invention, wherein a jet port 2 for compressed air is provided at the tip division of a pipe 1 which is connected to a compressed air supply device (not shown), and a nozzle 3 is expanded to render the maximum outer diameter in the outer periphery thereof in excess of the outer diameter of the pipe such that a value calculated from the equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / area of the jet port of the nozzle" falls in 5 or more. Although the jet port is positioned at the forefront of the nozzle in this embodiment, if the minimum inner diameter of the nozzle is present in the inside of the nozzle, a portion showing the minimum inner diameter of the nozzle 10 in the tip end direction of the nozzle serves as a jet port of the nozzle. Such an expanded portion formed to exceed the outer diameter of the pipe may be either solid or hollow and it is not limited to the present embodiment. The nozzle can be a columnar body or a cylindrical body with a circular, elliptical or polygonal cross section in the present embodiment and it is preferable to use a nozzle of a columnar body with a triangular or more polygonal cross section. For such a columnar body, a nut placed on the market can be used by being fitted into the outer periphery of the pipe at the tip division. [0023] An embodiment shown in Fig. 2 has a tapered shape with an acute angle in each end of the nozzle. That is, an expanded portion is formed into a chevron shape in which the diameter increases sequentially from the tip division of the nozzle 3 and then decreases sequentially in the longitudinal direction. [0024] An embodiment shown in Fig. 3 has one or a plurality of grooves 4 carved longitudinally in a chevron-shaped expanded portion as shown in the embodiment of Fig. 2. Formation of such grooves allows further reduction of resistance in insertion of the nozzle into the soil. [0025] In addition, an embodiment shown in Fig. 4 includes columnar bodies 5, 5', 5" and 5"' formed as expanded portions at the tip division of the nozzle and tip ends of the columnar bodies are extended beyond the jet port 2 of the nozzle. Such an embodiment enables improvement of a digging force in comparison with the embodiments shown in Figs. 1 to 3. Thus, the columnar bodies are provided for the purpose of loosening soil to excavate and the number of the columnar bodies is not particularly limited. Here, the columnar bodies for use preferably have pointed tip ends as shown in Fig. 4 in order to cut off roots coming into a space between the 11 columnar bodies. [0026] An embodiment shown in Fig. 5 is formed with a ring which is fitted into the columnar bodies 5, 5', 5" and 5' as shown in the embodiment of Fig. 4. The shape of the ring is not particularly limited as long as being fitted into the columnar bodies and may be circular or polygonal. Owing to the ring fitted into the columnar bodies, it is possible to expect further improvement of a digging force. Aside from the presence of the ring, the tip divisions of the columnar bodies as shown in the embodiment of Fig. 5 make it possible to gather soil in the vicinity of a jet port. [0027] The shape of the nozzle is not limited to these embodiments but it is preferable to use the nozzle shaped as shown in Fig. 4 for easiness of insertion into the soil. [0028] As a compressed air supply device, (compressed) air supply devices such as compressors placed in the market can be used in general without making any changes in a range from those with a common pressure of about 5 atmospheres to those with a high pressure of about 30 atmospheres. Here, for soil in which trees such as garden trees and street trees are planted or in greenhouses cultivating vegetables and fruits, it is preferable from the viewpoint of workability to use a light compressed air supply device of, for example, about 20 kg which can supply 150 to 80 L of compressed air per minute at a high pressure of about 10 to 25 atmospheres. [0029] The material of the pipe connected to the compressed air supply device is not particularly limited as long as having a substantially straight (linear) shape and a used pipe is made of a material which is strong enough to bear a high pressure applied from the inside and bear rubbing and shocks applied from the outside. The length and outer diameter of the pipe can also be set as appropriate depending on the situation of 12 soil subjected to improvement and a used pipe has, for example, a length of 90 to 160 cm and an outer diameter of about 6 to 10 mm. [0030] The nozzle having the jet port for compressed air is attached to the tip division of the pipe so as to be substantially in line with the pipe which is substantially linear. The nozzle can be fitted to the pipe by welding so as not to be detachable but it is preferably use a detachable fitting method such as, for example, screwing. By making the nozzle detachable, the size of the nozzle can be changed as appropriate according to the density of roots without exchanging the pipe as a whole in a range from the vicinity of tree bases to the periphery thereof and machine parts to be prepared can be compact ones. [0031] The pipe and the compressed air supply device are connected to each other by preferably interposing a plug such as ball cock for controlling discharge of compressed air in a tubular body such as a hose for example. [0032] The pipe disposed at the rear of the nozzle can be provided with a cover for suppressing scattering of soil which scatters in jet of compressed air and preventing scattering of spouted soil. For such a cover, it is possible to use a shade-shaped cover expanding to the direction of the nozzle or bowl-shaped cover having a flange directed to the tip division of the pipe, preferably use a bowl-shaped cover having a flange directed to the tip division of the pipe. It is possible in either shape to prevent scattering of soil to an upper area but soil which scatters laterally in the shade-shaped cover can be gathered around a hole into which the nozzle was inserted by using the bowl-shaped cover for preventing scattering of soil. [0033] Soil improvement work using the soil improvement tool in any of the above 13 configurations is carried out by sticking the nozzle into the soil, jetting compressed air using the compressed air supply device and loosening the soil in the vicinity of the jet port at the tip division of the nozzle, repeatedly. At this time, air discharged from the jet port is discharged to the ground by passing through the side surface of the pipe and loosened soil is partially blown up along with the air, whereby soil density in the underground can be reduced. EXAMPLES [0034] Next, examples of the present invention will be explained. [0035] Example 1 With the use of a soil improvement tool in which the nozzle as shown in the embodiment of Fig. 1 (prepared by setting the diameter of the jet port of the nozzle to 2.35 mm, the outer diameter of the pipe to 6.35 mm, the maximum outer diameter of the nozzle to 11.5 mm and a value calculated from the equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / sectional area of the jet port of the nozzle"=16.65) was set to be substantially in line with the pipe in a substantially linear state, soil improvement work was carried out through jet of compressed air with a pressure of 25 to 10 atmospheres using the air compressor EC1443H made by Hitachi Koki Co., Ltd., and the soil was excavated to a depth of 90 cm below the ground. When water is supplied to the tree on the next day of the work, it was confirmed that drainage was significantly improved in comparison with the condition observed before the work. [0036] Example 2 With the use of a soil improvement tool in which the nozzle as shown in the 14 embodiment of Fig. 3 (prepared by setting the diameter of the jet port of the nozzle to 2.50 mm, the outer diameter of the pipe to 9.0 mm, the maximum outer diameter of the nozzle to 15.0 mm and a value calculated from the equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / sectional area of the jet port of the nozzle"=23.04) was set to be substantially in line with the pipe in a substantially linear state, soil improvement work was carried out in the same manner as Example 1 and the soil was excavated to a depth of 50 cm below the ground. When water is supplied to the tree on the next day of the work, it was confirmed that drainage was significantly improved in comparison with the condition observed before the work. [0037] Example 3 With the use of a soil improvement tool in which the nozzle as shown in the embodiment of Fig. 3 (prepared by setting the diameter of the jet port of the nozzle to 2.50 mm, the outer diameter of the pipe to 9.0 mm, the maximum outer diameter of the nozzle to 20.0 mm and a value calculated from the equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / sectional area of the jet port of the nozzle"=51.04) was set to be substantially in line with the pipe in a substantially linear state, soil improvement work was carried out in the same manner as Example 1 and the soil was excavated to a depth of 50 cm below the ground. When water is supplied to the tree on the next day of the work, it was confirmed that drainage was significantly improved in comparison with the condition observed before the work. [0038] Example 4 With the use of a soil improvement tool in which the nozzle as shown in the embodiment of Fig. 4 (prepared by setting the diameter of the jet port of the nozzle to 15 2.50 mm, the outer diameter of the pipe to 9.53 mm, the maximum outer diameter of the nozzle to 15.0 mm and a value calculated from the equation of "(circular area calculated by using the maximum outer diameter of the nozzle as a diameter - area calculated by the outer diameter of the pipe) / sectional area of the jet port of the nozzle"=21.47) was set to be substantially in line with the pipe in a substantially linear state, soil improvement work was carried out in the same manner as Example 1 and the soil was excavated to a depth of 150 cm below the ground. When water is supplied to the tree on the next day of the work, it was confirmed that drainage was significantly improved in comparison with the condition observed before the work. [0039] Reference Example Soil improvement work was carried out for trees through gaps of base protection boards by using the nozzles as shown in the embodiments of Figs. 1, 3 and 4 and when the energy of the trees (or tree vigor) was observed five months later, it was confirmed that the tree vigor was obviously improved in comparison with the condition observed before the work. This means soil improvement can be efficiently carried out by using the soil improvement tool according to the present invention. INDUSTRIAL APPLICABILITY [0040] The soil improvement tool according to the present invention can be used for trees such as garden trees and street trees and can also be widely used in places in which plants extend their roots such as glasshouses for cultivating vegetables and fruits, greenhouses, plant pots and ridges in the field. REFERENCE SIGNS LIST [0041] 1 Pipe 2 Jet port 16 3 Nozzle 4 Groove 5, 5', 5", 5"' Columnar body 6 Ring 17