Patent Publication Number: US-6902352-B2

Title: Soft ground improvement system

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus for improving soft ground, which is used in civil engineering works, and more particularly to an apparatus for improving soft ground, in which composite slurry including cement is introduced in an injection rod inserted in the ground and is vigorously discharged from the injection rod by air under a high pressure to cause a hardening agent to easily and evenly infiltrate the soil, thereby improving the soft ground. 
   2. Description of the Prior Art 
   In general, a method of improving soft ground is extensively known in the art, in which a monitor inserted in a bore formed in the ground is rotated and retracted upward while discharging a liquid-phase hardening agent, such as cement milk, into the bore, thereby providing a pile-shaped solid body in the bore of the ground. 
   According to the above-mentioned conventional method of improving the soft ground, because properties of the ground are uneven, an infiltrating region of the hardening agent does not have a uniform shape, as shown in FIG.  7 . 
   In the conventional method of improving the soft ground, an injection rod  5  is inserted into the ground, and water and air, or cement slurry and air, which are pressurized under a predetermined pressure, are horizontally discharged from nozzles  2  and  3 , as shown in FIG.  8 . For this reason, when the improved construction is undertaken in the soft layer of the ground, a discharging distance of the water and air, or cement slurry and air cannot be controlled, thereby causing an infiltrating range of the liquid or slurry to be excessively enlarged, or causing the liquid or slurry to rise along the soft layer. In addition to this, excessive slime is generated from the soft layer, higher costs are incurred due to excessive charging of the material. Furthermore, when the improved construction is undertaken in a clay layer, a compressive strength of the resulting solid body is lowered. 
   In the improved construction shown in  FIG. 8 , the liquid and slurry are discharged from the nozzles  2  and  3  such that the discharging direction of the liquid and slurry defines the right angle with respect to the direction of the liquid and slurry being introduced into the injection rod  5 . Accordingly, since a pressure of the liquid and slurry is lowered at the inflection point, the efficiency of the improved construction is deteriorated. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an apparatus for improving the soft ground, which discharges water and hardening agent from nozzles under a high pressure in a direction which is inclined downward rather than horizontally, so as to finely cut soil of the ground and to excavate a uniform bore in the ground, thereby achieving a solid body having a desired strong uniform shape, regardless of conditions of the soil. 
   In order to accomplish the above object, the present invention provides an apparatus for improving soft ground, including an injection rod having an injection pipe into which fluid is introduced, and an outer casing disposed around the injection pipe with an air feeding path therebetween, one or more injection holders coupled to an outer surface of the outer casing to be positioned at different levels and to be inclined downward, and a bit coupled to a lower end of the injection rod, and having jet holes, which are inclined downward and in which inclined jet nozzles are inserted, and a cutting water nozzle provided at its center. 
   The injection holders may be coupled to the injection pipe and the outer casing to be horizontally positioned. 
   Each of the injection holders may include a tubular connecting holder coupled to the injection pipe through the outer casing, a flange disposed under a lower end of the connecting holder and having a plurality of air guide holes, a nozzle fitted in the flange, a jet guide holder having an upper space in which the nozzle fitted in the flange is received, and a drain hole having a diameter smaller than that of the space and connected to the space, in which a snap ring is partially embedded in an inner surface of the jet guide holder to support an upper end of the flange), with a check rubber ring disposed under the flange in the space, and a support cap interposed between the flange and the check rubber ring to support the check rubber ring, and a protection pipe threadedly coupled to the jet guide holder at its one end and coupled to the outer casing at the other end. 
   The apparatus may further include a check packing provided under the flange in the space of the jet guide holder. 
   The nozzle fitted in the flange may include an arched concave surface and an inclined surface at its upper end. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a schematic view showing a ground improvement work using an injection rod according to the present invention; 
       FIG. 2  is a cross-sectional view showing a substantial part of the injection rod of  FIG. 1 ; 
       FIG. 3  is an exploded perspective view showing injection holders according to the present invention; 
       FIG. 4  is a vertical cross-sectional view of the injection holder; 
       FIG. 5  is a cross-sectional view showing a substantial part of the injection rod according to another embodiment of the present invention, in which injection holders are horizontally mounted on an injection rod; 
       FIG. 6  is a cross-sectional view showing a cylindrical solid body formed in the ground by the apparatus according to the present invention; 
       FIG. 7  is a cross-sectional view showing a solid body formed in the ground by a prior art; and 
       FIG. 8  is a schematic view showing a prior art apparatus for improving soft ground, which horizontally discharges liquid. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   This invention will be described in further detail by way of example with reference to the accompanying drawings. 
     FIG. 1  is a schematic view showing a ground improvement work using an injection rod according to the present invention,  FIG. 2  is a cross-sectional view showing a substantial part of the injection rod of  FIG. 1 ,  FIG. 3  is an exploded perspective view showing injection holders according to the present invention,  FIG. 4  is a vertical cross-sectional view of the injection holder,  FIG. 5  is a cross-sectional view showing a substantial part of the injection rod according to another embodiment of the present invention, in which injection holders are horizontally mounted on an injection rod, and  FIG. 6  is a cross-sectional view showing a cylindrical solid body formed in the ground by the apparatus according to the present invention. 
   As shown in  FIGS. 1 through 6 , an apparatus for improving soft ground, according to the present invention comprises an injection rod  20  including an injection pipe  10  into which fluid is introduced, an outer casing  12  disposed around the injection pipe  10  with an air feeding path  14  therebetween, a bit  30  coupled to a lower end of the injection rod  20 , and one or more injection holders  40  mounted on an outer surface of the outer casing  30  to be inclined downward. 
   The one or more injection holders  40  are mounted on predetermined positions of the outer casing  30  of the injection rod  20  such that the one or more injection holders  40  are positioned at different levels and extended outward and downward. 
   Each of the injection holders  40  includes a tubular connecting holder  42 , which passes through the outer casing  12  and is connected to the injection pipe  10 , a flange  46  joined to a lower end of the connecting holder  42  and having a plurality of air guide holes  44 , and a nozzle  50  fitted in the central hole of the flange  46 . 
   The nozzle  50  is integrally fitted in the flange  46 , and is disposed in a space  52  formed in a jet guide holder  90 . The jet guide holder  90  is provided with a snap ring  54 , which is partially embedded in an inner surface of the jet guide holder  90 , so as to prevent the flange  46  from being separated from the jet guide holder  90 . 
   The jet guide holder  90  further includes a drain hole  56  at its lower portion, which has a diameter smaller than that of the space  52  and is continuously connected to the space  52 . 
   The jet guide holder  90  is provided at its outer surface with a threaded region, on which a protection pipe  96  mounted on the outer casing  12  is threadedly coupled. 
   A check packing  92  is provided under the flange  46  in the space  52  of the jet guide holder  90 , so as to allow fluid to flow in a direction but checking the flow in the reverse direction. 
   Furthermore, a check rubber ring  84  is disposed under the flange  46  in the space  52  of the jet guide holder  90 . A support cap  86  is interposed between the flange  46  and the check rubber ring  84  to support the check rubber ring  84 . Thus, the fluid is prevented from flowing in the reverse direction even when a discharging action of pressurized air and fluid is stopped. That is, when the discharging action of the pressurized air and fluid is undesirably stopped during the pressurized air and fluid discharging process, the check rubber ring  84  is in close contact with the check packing  92  in the space  52 . The support cap  86  in the above state further compresses the check rubber ring  84  on the check packing  92 , thus closing the air guide holes  44  of the flange  46 . Therefore, even though an unexpected situation, such as the breakdown of a hardening agent shifting pump, is caused, it is possible to prevent soil placed in the drain hole  56  of the jet guide holder  90  from undesirably flowing into the air guide holes  44  of the flange  46 . 
   The nozzle  50 , which is fitted in the flange  46 , is provided at its upper end with an arched concave surface  98  and an inclined surface  98   a  to allow cement slurry to be smoothly introduced into the nozzle  50 , thus preventing clogging and reduction a central hole of the nozzle  50 . 
   The bit  30  is joined to a lower end of the injection rod  20 . The bit  30  includes jet holes  60  and  60   a , which are inclined downward, and in which inclined jet nozzles  70  and  70   a  are inserted. The bit  30  further includes a cutting water nozzle  74  at its center. 
   In an operation of improving soft ground by the apparatus according to the present invention, a target ground is uniformly excavated by water get discharged from the bit  30  joined to the lower end of the injection rod  20 , and composite slurry (mixture of cement, reinforcing agent and quick setting agent) is injected into the excavated bore of the ground to form a cylindrical solid body, as shown in FIG.  1 . During the ground improvement operation, the apparatus is coupled to a mixing plant and an air compressor, with a high pressure pump provided on a feed line between the apparatus and the mixing plant to pump the composite slurry from the mixing plant to the apparatus. 
   More specifically, the connecting holder  42  is first connected to the injection pipe  10  of the injection rod  20  to be inclined downward. Subsequently, the flanges  46  and the nozzle  50  are integrally inserted into the space  52  of the jet guide holder  90 , and the flange  46  is supported by the snap rings  54 . When the jet guide holder  90  is threadedly coupled to an end of the protection pipe  96  with the other end being welded to the outer casing  12 , the nozzle  50  is inserted into the lower end of the connecting holder  42 . At this point, the injection holder  40  is assembled in the airtight condition by the sealing performance of the check packing  92 . 
   In such a manner, one or more injection holders  40  are mounted on the injection rod  20  to be positioned at different levels and to be inclined downward. 
   Highly pressurized water is supplied into the injection pipe  10  of the injection rod  20 , while pressurized air is supplied into the air-feeding path  14 . 
   The pressurized water and air are introduced into the injection holder  40 . At this point, the pressurized air is introduced into a gap between the protection pipe  96  and the connecting holder  42 , and the pressurized water is introduced into the connecting holder  42  and then discharged through the nozzle  50 . 
   While the pressurized water is discharged through the nozzle  50 , the pressurized air is introduced into the space  52  of the jet guide holder  90  through the air guide holes  44 . Accordingly, since the pressurized air is added to the pressurized water, which is discharged through the nozzle  50 , the pressurized water is more vigorously discharged through the drain hole  56  with the aid of the pressurized air. 
   The pressurized water, which is introduced in the injection pipe  10 , is also discharged to be inclined downward through the inclined jet nozzles  70  and  70   a  fitted in the jet holes  60  and  60   a , and vertically discharged through the cutting water nozzle  74  mounted on the center of the bit  30 . 
   When the pressurized water is discharged through the nozzles under a pressure of 200 kg/cm 2 , the discharging distance of the pressurized water is 1.5 m in the case of the present invention while the discharging distance of the pressurized water is 1 m in the case of a prior art. 
   When the excavating operation is completed, composite slurry and air are discharged through the nozzle in the same manner as that of the pressurized water and air. At this time, the composite slurry is supplied into the injection pipe  10  of the injection rod  20  while the pressurized air is supplied into the air-feeding path  14 . Thereafter, the composite slurry and the pressurized air are discharged to the outside through the same paths, thereby forming a solid body. 
   The finished solid body is shaped into a stable structure having a uniform external diameter, as shown in FIG.  6 . 
   According to the present invention, since the top end of the nozzle  50  is provided with the arched concave surface  98  and the inclined surface  98   a , composite slurry including cement, which is under the influence of the high pressure, is gently guided to the end of the nozzle  50  by the arched surface  98 , and quickly introduced into the nozzle  50  by the inclined surface  98   a . Therefore, it is possible to prevent clogging of the nozzle and to achieve a desirable discharging state of the composite slurry. 
   In addition, since the check packing  92  is provided between the flange  46  and the jet guide holder  90 , to allow outflow of fluids while preventing back flow of fluids, it is possible to prevent undesirable contaminants such as soil and cement from flowing into the apparatus. 
     FIG. 5  is a cross-sectional view showing an apparatus according to another embodiment of the present invention. In this embodiment, injection holders  40  are horizontally mounted on the injection rod  20 . Since the apparatus according to this embodiment has the same functions as those of the previous embodiment, the detailed description of the apparatus is omitted. 
   As described above, the present invention provides an apparatus for improving soft ground, which is capable of providing a uniform solid body regardless of soil conditions of the target ground by evenly excavating a bore and discharging hardening agent by control of nozzles. According to the present invention, since soil is crushed into minute particles in the excavating operation, injection material efficiently infiltrates the soil. In addition, since composite slurry is solidified as soon as it is discharged from the nozzles, it is possible to prevent undesirable material from flowing out of the ground surface. Furthermore, the apparatus according to the present invention has additional advantages in that working property is excellent, the improving efficiency for the soft ground is enhanced, and a construction period is shortened. 
   Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.