Patent Publication Number: US-2010116358-A1

Title: Dust-removal managing pit

Description:
TECHNICAL FIELD 
     The present invention relates to a dust-removal managing pit provided in connection with a water storage tank for storing water, sewers and the like buried under the ground and for removing dust from water supplied to the water storage tank, sewers and the like. 
     BACKGROUND ART 
     Such a facility for effectively using rainwater has been known that a water storage tank buried under the ground for storing rainwater in the water storage tank. This facility is configured such that rainwater falling on a roof or a rooftop of a house or on the ground is collected by a gutter or a groove, the collected water is introduced to an inflow pipe, and the water is supplied to the water storage tank through the inflow pipe so as to be stored inside the tank. Also, in such a facility, water discharge means such as a pump capable of extracting water stored inside from above the ground is provided so that the water stored inside can be extracted and used by the water discharge means. 
     Also, such a facility to avoid occurrence of so-called flood has been known that a water storage tank is buried under the ground and excess rainwater is temporarily stored in the water storage tank so as to prevent the excess rainwater from flowing to the surface of the ground. With this facility, if rainwater flowing in a river on the ground surface is raised to a predetermined level or more, excess rainwater is temporarily stored in the water storage tank through an inflow pipe and the water storage tank buried under the ground is constructed such that the temporarily stored rainwater can permeate the peripheral soil. Therefore, the facility is configured such that the rainwater temporarily stored in the water storage tank leaks out to the soil around the water storage tank during fine weather after that so as to form a space inside for storing rainwater again, and a space which can temporarily store a predetermined amount of rainwater during rain after that is prepared all the time. 
     As a water storage tank used in these facilities and which can be installed under the ground relatively easily, such a facility has been known that is formed by excavating a place to form an underground water storage tank, by arranging a sheet at the underground lowermost center portion of the excavated area, and by laminating a water retaining material made of sand, sand gravel, split stone, plastic molded body and the like on the center portion. As a sheet in this case, an impermeable sheet through which rainwater cannot penetrate is used for the purpose of reuse of rainwater, and a permeable sheet, which allows penetration of rainwater, is used for the purpose of avoiding occurrence of flood. After that, the periphery of the sheet is raised, the periphery of the water retaining material is surrounded by the sheet, and by placing an end portion of the sheet on the upper face of the water retaining material so as to wrap the water retaining material with the sheet, the water storage tank is formed. In this underground water storage tank, water is stored in a gap between water retaining materials made of sand, sand gravel, split stone, plastic molded body and the like. 
     In this type of water storage tank buried under the ground, it is known that a dust-removal managing pit is provided since rainwater falling on a roof or a rooftop of a house or on the ground or water flowing in a river is collected (See Patent Document 1, for example). That is, it is difficult to clean the inside of the water storage tank buried under the ground, and a relatively large amount of dust is contained in the rainwater falling on a roof or a rooftop of a house or on the ground or water flowing in a river. Thus, a dust-removal managing pit for removing a dust from water supplied to the water storage tank is provided in connection with the water storage tank so that the dust contained in the water is removed before the water is supplied to the water storage tank in order to avoid such a situation that the inside of the water storage tank is filled with dusts. In this dust-removal managing pit, water supplied from an inflow pipe is temporarily stored therein, the dust contained in the water is precipitated inside, and the water after the dust has been removed is supplied to the water storage tank through a water supply pipe. 
     Patent Document 1: WO2006/001139A1 (claim  11 , FIG. 18) 
     DISCLOSURE OF INVENTION 
     Problem to be Solved by the Invention 
     However, with the prior-art dust-removal managing pit, since the water supplied from the inflow pipe needs to be temporarily stored in the managing pit, the managing pit itself becomes long in the vertical direction, a depth to bury the managing pit becomes relatively deep, and a removal work if the dust precipitated inside the managing pit is accumulated takes labor, which are nonconformities and makes management difficult. 
     Also, it is also examined if this type of dust-removal management pit is provided beside a road and used for a road for guiding rainfall on the road to a sewer, and if the pit is provided beside a road, it is required that inflowing soil or dust is removed from water relatively easily so as to prevent clogging of a permeable layer provided consecutively to the dust-removal managing pit and to prevent the soil or dust from flowing into a sewer. 
     The present invention has an object to provide a dust-removal managing pit in which soil or dust is separated from inflowing water and the soil or dust is prevented from flowing into a water storage tank, a permeable pit, a sewer and the like. 
     The present invention has another object to provide a dust-removal managing pit that is easily cleaned and can be easily managed. 
     Means for Solving Problem 
     An invention according to claim  4  is, as shown in  FIG. 1 , characterized in that the present invention is provided with an upper pit  22  having a bottom and buried so that its upper end is exposed to the surface of the ground and to which an inflow pipe  20   a  is connected and a cylindrical lower vertical pit  23  having its upper part connected to the upper pit  22  for having water supplied from the inflow pipe  20   a  flow down from an upper-end opening portion, an upper end of the lower vertical pit  23  is provided so as to penetrate a bottom wall  22   a  of the upper pit  22 , while a peripheral wall  22   b  of the upper pit  22  is provided so as to surround the upper end of the lower vertical pit  23 , a peripheral groove  33  for precipitating solid substances contained in water supplied from the inflow pipe  20   a  and flowing into the upper-end opening portion of the lower vertical pit  23  is formed between the upper-end periphery of the lower vertical pit  23  penetrating the bottom wall  22   a  and the peripheral wall  22   b,  a drain pipe  36  for draining water in the peripheral groove  33  is connected to the peripheral groove  33 , and a bottom face of the peripheral groove  33  is formed with inclination with respect to a horizontal plane so that the water in the peripheral groove  33  flows into the drain pipe  36  by lowering the side to which the drain pipe  36  is connected. 
     With the dust-removal managing pit described in claim  4 , since the peripheral groove  33  for precipitating the solid substances contained in water is formed, dusts constituted by the solid substances can be removed from the water flowing down to the lower vertical pit  23  by the peripheral groove  33 . Thus, contamination by dusts on the inside of a water storage tank  10 , a sewer and the like to which water is supplied through the lower vertical pit  23  can be prevented, for example. Also, if the dust-removal managing pit is provided in a groove or the like beside a road shown in  FIG. 6 , inflowing soil or dusts can be separated from water, and clogging of a permeable layer provided consecutively to the dust-removal managing pit can be prevented. 
     Here, the peripheral groove  33  is formed between the upper-end periphery of the lower vertical pit  23  penetrating the bottom wall  22   a  of the upper pit  22  and the peripheral wall  22   b  of the upper pit  22  and is located at a relatively shallow position. Thus, if dusts precipitated in the peripheral groove  33  are accumulated, removal of dusts in the peripheral groove  33  is relatively easy. 
     On the other hand, the lower vertical pit  23  is vertically long and its buried depth can be relatively deep, but since the water having dusts precipitated in the peripheral groove  33  flows down into the lower vertical pipe  23 , an amount of dusts accumulated inside the lower vertical pipe  23  is extremely reduced than before, and a cleaning frequency of the inside of the lower vertical pipe  23  is decreased. Therefore, a management burden of the dust-removal managing pit of the present invention including the upper pit  22  and the lower vertical pipe  23  can be reduced from that of the prior-art managing pit. 
     Though the peripheral groove  33  is a portion for precipitating solid substances contained in water, if the entire peripheral groove  33  is filled with solid substances, it becomes difficult to remove the solid substances to become dusts from water flowing into the lower vertical pit  23 . With the dust-removal managing pit described in claim  4 , since the drain pipe  36  is connected to the peripheral groove  33 , water in the peripheral groove  33  can be drained together with the solid substances precipitated therein to the outside of the peripheral groove  33  through the drain pipe  36 , and by connecting the drain pipe  36  to a sewer pipe, the solid substances can be made to flow into the sewer pipe together with the water. As a result, a situation that the peripheral groove  33  is filled with the solid substances can be effectively avoided. 
     An invention according to claim  5  is, in the invention according to claim  4  and moreover as shown in  FIG. 2 , characterized in that the inflow pipe  20   a  and the drain pipe  36  are connected at opposing positions, respectively, in the peripheral wall  22   b  of the upper pit  22 , and an inner face of the peripheral wall  22   b  is formed with curvature or inclination so that a width inside the peripheral wall  22   b  from the inflow pipe  20   a  side toward the drain pipe  36  side is decreased. 
     With the dust-removal managing pit described in claim  5 , the water in the peripheral groove  33  can be quickly guided to the drain pipe  36  together with the solid substance precipitated therein, and a situation that the solid substances remain in the peripheral groove  33  can be effectively avoided. 
     An invention according to claim  6  is, in the invention according to claim  4  or  5 , characterized in that a grit tank  37  communicating with the peripheral groove  33  is provided adjacently to the upper pit  22 , and the drain pipe  36  is connected to the peripheral groove  33  through the grit tank  37 . 
     With the dust-removal managing pit described in claim  6 , since the drain pipe  36  is connected to the peripheral groove  33  through the grit tank  37 , solid substances constituting dusts precipitated in the peripheral grove  33  can be moved from the peripheral groove  33  and precipitated in the grit tank  37 . As a result, unnecessary solid substances are prevented from flowing into the drain pipe  36 , and a situation that the peripheral groove  33  is filled with the solid substances can be avoided for a relatively long time. 
     An invention according to claim  7  is, in the invention according to claim  6 , characterized in that a regulating valve  38  that can adjust a water amount flowing into the drain pipe  36  from the grit tank  37  is provided in the grit tank  37 . 
     With the dust-removal managing pit described in claim  7 , by regulating the water amount flowing into the drain pipe  36  from the peripheral groove  33  by the regulating valve  38  to a water amount or less flowing into the upper pit  22  from the inflow pipe  20   a,  the amount of water flowing down from the upper-end opening portion of the lower vertical pit  23  through the peripheral groove  33  into the lower vertical pit  23  can be adjusted to be increased/decreased. 
     An invention according to claim  8  is, in the invention according to any one of claims  4  to  7 , characterized in that a mesh plate  34  constituted so as to cover the upper-end opening portion of the lower vertical pit  23  and the peripheral groove  33  and capable of filtering water supplied from the inflow pipe  20   a  and leading to the peripheral groove  33  is provided on the upper pit  22 . 
     In the dust-removal managing pit described in claim  8 , since the mesh plate  34  is provided, relatively large dusts that can be trapped by the mesh plate  34  from the water supplied from the inflow pipe  20   a  can be removed from the water leading to the peripheral groove  33 . Thus, an amount of the relatively large dusts contained in the water flowing into the lower vertical pit  23  after that can be further decreased. 
     An invention according to claim  9  is an under-ground water storage system provided with a water storage tank  10  buried under the ground and the dust-removal managing pit  20  described in any one of claims  4  to  8 , provided in connection with the water storage tank  10  so that water flowing down from the upper-end opening portion of the lower vertical pit  23  is supplied to the water storage tank  10 . 
     EFFECT OF THE INVENTION 
     With the dust-removal managing pit of the present invention, since the peripheral groove is formed between the periphery of the upper end of the lower vertical pit penetrating the bottom wall and the peripheral wall for precipitating solid substances contained in water supplied from the inflow pipe and flowing into the upper-end opening portion of the lower vertical pit, dusts constituted by the solid substances contained in the water flowing into the lower vertical pit can be reduced, and dusts can be removed from the water supplied to a water storage tank, a penetration pit, a sewer and the like with a high probability. Here, the peripheral groove is formed between the periphery of the upper end of the lower vertical pit penetrating the bottom wall of the upper pit and the peripheral wall of the upper pit and is located at a relatively shallow position. Therefore, if dusts precipitated in the peripheral groove are accumulated, cleaning thereof is relatively easy. On the other hand, the lower vertical pit is vertically long and its buried depth can be relatively deep, but since the water having dusts precipitated in the peripheral groove flows down into the lower vertical pipe, an amount of dusts accumulated inside the lower vertical pipe becomes smaller than before, and a cleaning frequency of the inside of the lower vertical pipe is decreased. Therefore, a management burden of the dust-removal managing pit of the present invention including the upper pit and the lower vertical pipe can be reduced from that of the prior-art managing pit. 
     In this case, by providing the mesh plate covering the upper-end opening portion of the lower vertical pit and the peripheral groove and constructed capable of filtering water supplied from the inflow pipe and leading to the peripheral groove on the upper pit, an amount of relatively large-sized 20 dusts contained in the water flowing down to the lower vertical pit after that can be further reduced, and by connecting the drain pipe to the peripheral groove, a situation that the peripheral groove is filled with solid substances can be effectively avoided. Also, by forming the 25 bottom face of the peripheral groove with inclination with respect to the horizontal plane with the side to which the drain pipe is connected is lower so that the water in the peripheral groove flows down into the drain pipe, and by forming the inner face of the peripheral wall with curvature or inclination so that a width inside the peripheral wall of the upper pit from the inflow pipe side toward the drain pipe side is decreased, water in the peripheral groove can be quickly guided to the drain pipe together with the solid substance precipitated therein, and a situation that the solid substances remain in the peripheral groove can be effectively avoided. 
     Also, by providing the grit tank communicating with the peripheral groove adjacently to the upper pit and by connecting the drainpipe to the peripheral pipe through the grit tank, solid substances constituting dusts precipitated in the peripheral grove can be moved from the peripheral groove and precipitated in the grit tank, and unnecessary solid substances are prevented from flowing into the drain pipe, and a situation that the peripheral groove is filled with the solid substances can be avoided for a relatively long time. Also, by providing the regulating valve that can adjust a water amount flowing into the drain pipe from the peripheral groove, the amount of water flowing down from the upper-end opening portion of the lower vertical pit through the peripheral groove can be adjusted to be increased/decreased by regulating the water amount discharged from the peripheral groove with the regulating valve. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a sectional view illustrating a configuration of a dust-removal managing pit of an embodiment of the present invention; 
         FIG. 2  is an A-A line sectional view of  FIG. 1 ; 
         FIG. 3  is a sectional view corresponding to  FIG. 1  illustrating a configuration of another dust-removal managing pit in which a lower end of a lower vertical pipe is connected to a water storage tank; 
         FIG. 4  is a sectional view corresponding to  FIG. 1  illustrating a configuration of still another dust-removal managing pit in which a grit tank is brought into close contact with ah upper pit; 
         FIG. 5  is a B-B line sectional view of  FIG. 4 ; and 
         FIG. 6  is a sectional view illustrating a configuration of a dust-removal managing pit of another embodiment of the present invention. 
     
    
    
     EXPLANATIONS OF LETTERS OR NUMERALS 
     
         
           10  water storage tank 
           20  dust-removal managing pit 
           20   a  inflow pipe 
           22  upper pit 
           22   a  bottom wall 
           22   b  peripheral wall 
           23  lower vertical pit 
           33  peripheral groove 
           34  mesh plate 
           36  drain pipe 
           37  grit tank 
           38  regulating valve 
       
    
     BEST MODE(S) FOR CARRYING OUT THE INVENTION 
     A best mode for carrying out the present invention will be described below based on the attached drawings. 
     As shown in  FIG. 1 , a dust-removal managing pit  20  in this embodiment is provided by being connected to a water storage tank  10  in illustration. The water storage tank  10  is buried under the ground, and this water storage tank  10  stores rainwater falling on a roof or a rooftop of a house or on the ground inside so that the water stored inside is extracted by water discharge means, not shown, so as to be reused. The water storage tank  10  exemplified in  FIG. 1  is formed by covering an assembly constituted by combining a plurality of water retaining materials  12  with an impervious sheet  14 . As the water retaining material  12  in this embodiment, a plastic molded body  12  molded by a die is used. The water retaining material  12  made of the plastic molded body is formed in a truncated pyramid shape, disposed laterally and longitudinally and then, laminated thereon so as to obtain an assembly of the water retaining materials  12 . On the other hand, the impervious sheet  14  covering these water retaining materials  12  is an impervious sheet made of synthetic rubber, synthetic resin and the like, and nonwoven cloth for protection is usually overlapped on both sides thereof. 
     The water storage tank  10  is formed by arranging the impervious sheet  14  in an excavated spot, the water retaining materials  12  are disposed laterally and longitudinally as well as vertically at the center portion so as to obtain an assembly and then, by raising the periphery of the impervious sheet  14  and surrounding the periphery of the assembly of the water retaining materials  12  with the impervious sheet  14 , and by further placing an end portion of the impervious sheet  14  on an upper face of the water retaining materials  12  so as to wrap the assembly of the water retaining materials  12  with the impervious sheet  14 . Here, if the single impervious sheet  14  does not have a size to wrap the assembly of the water retaining materials  12 , a plurality of the impervious sheets  14  are prepared and thermally deposited at end edges thereof so as to integrate them and to obtain a sufficient size to wrap the assembly of the water retaining materials  12  and also to obtain the impervious sheet  14  which prevents water leakage at the deposited portions. The water storage tank  10  constituted as above is capable of storing water in a gap between the water retaining materials  12 . 
     The dust-removal managing pit  20  of the present invention provide by being connected to the water storage tank  10  is provided with an upper pit  22  having a bottom and buried so that its upper end is exposed to the surface of the ground and to which an inflow pipe  20   a  is connected and a lower vertical pit  23  having its upper part connected to the upper pit  22 . The lower vertical pit  23  is connected to the water storage tank  10 . Here, the inflow pipe  20   a  connected to the upper pit  22  leads water falling on a roof or a rooftop of a house or on the ground and collected to the upper pit  22 . 
     The upper pit  22  is provided with a bottom wall  22   a  and a peripheral wall  22   b.  The peripheral wall  22   b  is formed with a size that can surround the upper end of the lower vertical pit  23 , and the inflow pipe  20   a  is connected to the peripheral wall  22   b.  On an upper edge of the peripheral wall  22   b,  a stepped portion  22   c  on which the periphery of a lid plate  24  is seated is formed, and by seating the periphery of the lid plate  24  on the stepped portion  22   c,  the lid body  24  closing an upper-end opening portion of the upper pit  22  capable of opening is provided on the upper pit  22 . 
     On the bottom wall  22   a  of the upper pit  22 , a hole  22   d  corresponding to an upper-end outline of the lower vertical pit  23  is formed, and the upper end of the lower vertical pit  23  is inserted through the hole  22   d,  and the upper end of the lower vertical pit  23  is provided penetrating the bottom wall  22   a  of the upper pit  22 . That is, the upper end of the lower vertical pit  23  is provided penetrating the bottom wall  22   a  of the upper pit  22  so that a peripheral groove  33  is formed between the periphery of the upper end of the lower vertical pit  23  and the peripheral wall  22   b.  Then, the peripheral groove  33  formed in the periphery of the upper end of the lower vertical pit  23  and inside the upper pit  22  is configured to temporarily store water supplied from the inflow pipe  20   a  and flowing into the upper-end opening portion of the lower vertical pit  23  and precipitate solid substances contained in the water. 
     Also, to the peripheral groove  33 , one end of the drain pipe  36  with the other end connected to a sewer pipe, not shown, is connected. This drainpipe  36  is to have water in the peripheral groove  33  flow into the sewer pipe, and for the drainpipe  36  in this embodiment, a so-called porous pipe in which a plurality of small holes  36   a  are formed on the periphery is used. The drain pipe  36  made up of the porous pipe is buried under the ground, penetrates water inflowing from the peripheral groove  33  to the ground around it and has excess water flow into the sewer pipe, not shown. 
     Also, in the upper pit  22  in this embodiment, a grit tank  37  communicating with the peripheral groove  33  is provided adjacently. The grit tank  37  in  FIG. 1  is a so-called penetration-type pit having a lid  37   c  in which a plurality of through small holes  37   b  capable of transmitting water formed in a bottom portion and is buried along with the upper pit  22  with a predetermined interval from the upper pit  22 , and the upper pit  22  and the grit tank  37  are connected to a connection pipe  37   a.  The peripheral groove  33  formed inside the upper pit  22  communicates with the grit tank  37  through the connection pipe  37   a,  and one end of the drain pipe  36  is connected to the grit tank  37 . As a result, the drain pipe  36  is configured to be connected to the peripheral groove  33  through the grit tank  37 . The inflow pipe  20   a  and the drain pipe  36  are connected at opposing positions in the peripheral wall  22   b  of the upper pit  22 , respectively, and the drain pipe  36  is connected at a position lower than the inflow pipe  20   a.  An upper face of the bottom wall  22   a  constituting the bottom face of the peripheral groove  33  is formed with inclination with respect to the horizontal plane with the side to which the drain pipe  36  is connected is lower so that water in the peripheral groove  33  flows down into the drain pipe  36  through the connection pipe  37   a  and the grit tank  37 . 
     Also, as shown in  FIG. 2 , the inner face of the peripheral wall  22   b  is formed with curvature or inclination so that the width of the inside of the peripheral wall  22   b  extending from the inflow pipe  20   a  side to the drain pipe  36  side through the connection pipe  37   a  is decreased. In  FIG. 2 , an example is shown in which a corner portion at both sides of the peripheral wall  22   b  to which the drain pipe  36  is connected is formed with curvature in an arc state around the lower vertical pipe  23 . 
     Returning to  FIG. 1 , on a side wall to which the drain pipe  36  of the grit tank  37  is connected, an adjusting valve  38  constituted capable of adjusting a water amount flowing into a sewer pipe from the peripheral groove  33  by increasing/decreasing a sectional area of the drain pipe  36  is provided. By adjusting the water amount flowing from the peripheral groove  33  into the sewer pipe to a water amount or less flowing from the inflow pipe  20   a  to the upper pit  22  by the adjusting valve  38 , the water amount flowing down from the upper-end opening portion of the lower vertical pit  23  into the lower vertical pit  23  through the peripheral groove  33  is configured capable of being increased/decreased. 
     On the other hand, the lower vertical pit  23  is cylindrical and is configured such that its upper part is connected to the upper pit  22  and water supplied form the inflow pipe  20   a  to the upper pit  22  flows down from the upper-end opening portion through the peripheral groove  33 . The lower vertical pit  23  supplies water flowing down from the upper-end opening portion to the water storage tank  10 , and in this embodiment, after the flowing-down water is stored inside, the stored water is supplied through a vertical pipe  27  and a water supply pipe  26  to the water storage tank  10  present around them. 
     The vertical pipe  27  and the water supply pipe  26  in this embodiment are constructed by extrusion-molded pipes made of vinyl chloride having a circular section.  FIG. 1  shows a case in which the water supply pipes  26  are extended horizontally and provided on the lower vertical pit  23  at two spots with a predetermined interval in a vertical direction, and an upper end of the vertical pipe  27  is connected to an end portion of the water supply pipe  26  opened inside the lower vertical pit  23  through a so-called L-shaped pipe  28 . In this way, the lower vertical pit  23  and the water storage tank  10  are connected to each other by the water supply pipe  26  for supplying the water stored inside the lower vertical pit  23  to the water storage tank  10 , and a bellows  26   a  for absorbing relative positional fluctuation of the lower vertical pit  23  and the water storage tank  10  is provided on the water supply pipe  26 . 
     On the other hand, the vertical pipe  27  has its lower end opened facing the bottom portion of the cylindrical lower vertical pit  23  with a bottom and is configured such that the water stored inside the lower vertical pit  23  advances and rises from the lower end of the vertical pipe  27  and reaches the water supply pipe  26  from the upper end, flows horizontally through the inside of the water supply pipe  26  and is supplied to the inside of the water storage tank  10  located in the periphery of the lower vertical pit  23 . That is, it is configured such that the water stored inside the lower vertical pit  23  is supplied to the water storage tank  10  through the vertical pipe  27 . A check valve, not shown, is provided in this vertical pipe  27 , the check valve allowing flow of water from inside the lower vertical pipe  23  to the water storage tank  10  when a water level inside the lower vertical pipe  23  is at a water level inside the water storage tank  10  or more and prohibits the flow of the water in the water storage tank  10  into the lower vertical pipe  23  when the water level inside the lower vertical pipe  23  is less than the water level in the water storage tank  10 . 
     Also, into the upper pit  22 , a mesh plate  34  is inserted through the upper-end opening portion opened by removing the lid body  24 . This mesh plate  34  is provided inside the upper pit  22  with inclination so that the inflow pipe  20   a  side is located lower and is configured to cover the upper-end opening portion of the lower vertical pit  23  and the peripheral groove  33  in an inclined state. And this mesh plate  34  is constructed capable of filtering water supplied from the inflow pipe  20   a  and leading to the peripheral groove  33 , and the water in the peripheral groove  33  having passed through the mesh plate  34  leads to the upper-end opening portion of the lower vertical pit  23 . 
     In the dust-removal managing pit  20  configured above, water supplied from the outside through the inflow pipe  20   a  flows down to the upper pit  22 , flows down from the upper-end opening portion of the lower vertical pit  23  is stored inside thereof, and then, supplied to the water storage tank  10  through the vertical pipe  23  and the water supply pipe  26 . Here, since the peripheral groove  33  is formed in the periphery of the upper end of the lower vertical pit  23  inside the upper pit  22 , the peripheral groove  33  precipitates solid substances contained in water supplied from the inflow pipe  20   a  and flowing into the upper-end opening portion of the lower vertical pit  23 . Thus, an amount of dusts contained in the water flowing down from the upper-end opening portion of the lower vertical pit  23  is decreased, the dusts are removed from the water supplied to the water storage tank  10 , and a situation that the inside is filled with dusts can be avoided. 
     In this embodiment, since the mesh plate  34  covering the upper-end opening portion of the lower vertical pit  23  and the peripheral groove  33  and constructed capable of filtering water supplied from the inflow pipe  20   a  and leading to the peripheral groove  33  is provided on the upper pit  22 , the mesh plate  34  removes relatively large dusts that can be captured from the water supplied from the inflow pipe  20   a  and leading to the peripheral groove  33 . Thus, an amount of relatively large dusts contained in the water flowing into the lower vertical pit  23  after that is decreased, and the amount of dusts can be further decreased from the water supplied to the water storage tank  10 . 
     Also, though the peripheral groove  33  is a portion for precipitating solid substances contained in water, if the entire peripheral groove  33  is filled with solid substances, it becomes difficult to remove the solid substances to become dusts from water flowing into the lower vertical pit  23 . However, with this dust-removal managing pit, since the drain pipe  36  which has the water in the peripheral groove  33  flow together with the solid substances precipitated therein into a sewer pipe through the drain pipe  36  is provided, a situation that the peripheral groove  33  is filled with the solid substances can be effectively avoided. Particularly in this embodiment, the grit tank  37  communicating with the peripheral groove  33  is provided adjacently to the upper pit  22 , and the drain pipe  36  is connected to the peripheral groove  33  through the grit tank  37 , the solid substances constituting the dust precipitated in the peripheral groove  33  can be moved from the peripheral groove  33  and precipitated in the grit tank  37 . As a result, the unnecessary solid substances are prevented from flowing into the drain pipe  36  and into the sewer pipe, not shown, through the drain pipe  36 , and a situation that the peripheral groove  33  is filled with the solid substances can be avoided for a relatively long time. 
     Also, in this embodiment, the bottom face of the peripheral groove  33  is formed with inclination with respect to the horizontal plane with the side to which the drain pipe  36  is connected is lower so that water in the peripheral groove  33  flows into the drain pipe  36  by lowering the side to which the drain pipe  36  is connected, and the inner face of the peripheral wall  22   b  is formed with curvature so that the width inside the peripheral wall  22   b  from the inflow pipe  20   a  side to the drain pipe  36  side is decreased, the water in the peripheral groove  33  can be quickly guided together with the solid substances precipitated therein to the drain pipe  36 , and a situation that the solid substances remains in the peripheral groove  33  can be effectively avoided. Since the adjusting valve  38  that can adjust the water amount flowing from the peripheral groove  33  into the drain pipe  36  through the grit tank  37  is provided in the grit tank  37 , the amount of water flowing into the lower vertical pit  23  and supplied to the water storage tank  10  can be adjusted by the adjusting valve  38 . 
     On the other hand, soils and the like precipitated inside the peripheral groove  33  and the lower vertical pit  23  can be cleaned by removing the lid body  24  from the upper pit  22  so as to open the upper-end opening portion by using means which vacuums the bottom portion of the peripheral groove  33  and the lower vertical pit  23  through the opening portion. Similarly, even with the mesh plate  34  which captured relatively large dusts, they can be cleaned by removing the mesh plate  34  from the upper-end opening portion opened by removing the lid body  24  from the upper pit  22 . Moreover, even the solid substances and the like precipitated in the grit tank  37  can be cleaned by removing the lid  37   c  so as to open its upper end and by using means which vacuums the bottom portion. Thus, by cleaning the mesh plate  34 , by removing precipitated soils and the like from the bottom portion of the peripheral groove  33  and the lower vertical pit  23 , and by removing precipitated solid substances and the like from the bottom portion of the grit tank  37 , the dust-removal managing pit  20  of the present invention can be managed appropriately. 
     Here, the peripheral groove  33  is formed between the periphery of the upper end of the lower vertical pit  23  penetrating the bottom wall  22   a  of the upper pit  22  and the peripheral wall  22   b  of the upper pit  22  and is located at a relatively shallow position. Thus, cleaning is relatively easy if dusts precipitated in the peripheral groove  33  are accumulated. On the other hand, the lower vertical pit  23  is vertically long and its buried depth can be relatively deep, but since the water having dusts precipitated in the peripheral groove  33  flows down into the lower vertical pipe  23 , an amount of dusts accumulated inside the lower vertical pipe  23  is reduced than before, and a cleaning frequency of the inside of the lower vertical pipe  23  is decreased. Therefore, a management burden of the dust-removal managing pit of the present invention including the upper pit  22  and the lower vertical pipe  23  can be reduced from that of the prior-art managing pit. 
     In the above-mentioned embodiment, the lower vertical pit  23  is provided in the vicinity of the side portion of the water storage tank  10  but it may be installed upright inside the water storage tank. 
     Also, in the above-mentioned embodiment, the water storage tank  10  with the purpose of reuse of rainwater is used in explanation, but a water storage tank may be formed by covering an assembly of the water retaining materials  12  with an impervious sheet allowing transmission of rainwater and used as a water storage tank with the purpose of avoiding occurrence of flood. 
     Also in the above-mentioned embodiment, the corner portion on both sides of the peripheral wall  22   b  to which the drain pipe  36  is connected is formed with curvature in an arc state around the lower vertical pipe  23 , but the inner face of the peripheral wall  22   b  may be inclined so that the width of the inside of the peripheral wall  22   b  is decreased as long as remaining of dusts in the corner portion can be prevented. 
     Also, in the above-mentioned embodiment, the case configured such that the water stored in the lower vertical pipe  23  is supplied to the water storage tank  10  through the vertical pipe  27  and the water supply pipe  26  has been described, but it may be so configured that water in the lower vertical pit  23  is supplied to the water storage tank  10  only by the water supply pipe  26 , and as shown in  FIG. 3 , it may be so configured that the lower end of the lower vertical pipe  23  is directly connected to the water storage tank  10  so that the water flowing down from the upper-end opening portion is directly supplied to the water storage tank  10 . Here, reference numeral  41  in  FIG. 3  denotes a so-called elbow member provided at the lower end of the lower vertical pipe  23  for directly connecting the lower end to the water storage tank  10 , and reference numeral  42  denotes a bellows provided between the elbow member  41  and the water storage tank  10  for absorbing fluctuation of the position inbetween. 
     Also, in the above-mentioned embodiment, the case configured such that the grit tank  37  is buried with a predetermined interval from the upper pit  22 , and the upper pit  22  and the grit tank  37  are connected to each other by the connection pipe  37   a  has been described, but as shown in  FIGS. 4 and 5 , the grit tank  37  may be brought into close contact with the upper pit  22 . By bringing the grit tank  37  into close contact with the upper pit  22 , they can be integrated before they are buried. Also, by matching communication holes  22   e  and  37   e  formed therein with each other, the connection pipe  37   a  and its connection work, which were required in the above-mentioned embodiment, are no longer needed, and the burying work can be facilitated. Here, reference numeral  41  in  FIG. 4  denotes a sewer pipe, and above the drain pipe  36 , an overflow pipe  42  is provided in parallel with the drain pipe  36 . The drain pipe  36  and the overflow pipe  42  in the figure are usual ones without small holes formed in the periphery, and a case in which the water in the grit tank  37  is made to flow into the sewer pipe  41  without permeating the ground is shown, in which a large diameter pipe as compared with the drain pipe  36  is used as the overflow pipe  42 . This overflow pipe  42  prevents exposure of water to the surface of the ground by having the excess water flow into the sewer pipe  41  if a flow rate of the drain pipe  36  is limited by the adjusting valve  38  or a hole diameter of the drain pipe  36  is not sufficient and the flow rate is limited and the water level in the grit tank  37  is raised. 
     Also, through holes  22   f  and  37   f  are formed in the upper pit  22  and the grit tank  37 , respectively, above the communication holes  22   e  and  37   e  in  FIG. 4 , and the through holes  22   f  and  37   f  prevents water containing solid substances from flowing down through the upper-end opening portion of the lower vertical pit  23  by having excess water flow into the grit tank  37  from the peripheral groove  33  if the flow rate of the water flowing from the peripheral groove  33  into the grit tank  37  through the communication holes  22   e  and  37   e  is limited. 
     Also, in the grit tank  37  in  FIG. 4 , a basket  37   d  for collecting solid substances and the like inflowing from the peripheral groove  33  is provided inside. With this basket  37   d,  by removing the lid  37   c  of the grit tank  37  so as to open the upper end and by taking out the basket  37   d,  solid substances precipitated in the grit tank  37  can be taken out of the grit tank  37 , and its cleaning work can be further facilitated. 
     Moreover, in the above-mentioned embodiments, though the inner facer of the peripheral wall  22   b  is formed with curvature or inclination and the width of the inside of the peripheral wall  22   b  from the inflow pipe  20   a  side to the drain pipe  36  side is decreased, it may be so configured that, as shown in  FIG. 5 , the width of the inside of the peripheral wall  22   b  is made constant without decreasing the width, and the upper pit  22  and the grit tank  37  are connected to each other at plural spots. Here, in  FIG. 5 , the case in which the grit tank  37  is brought into close contact with the upper pit  22  is shown, in which the holes  22   e  and  37   e  are formed two each in them, and they are matched with each other so as to connect the upper pit  22  and the grit tank  37  at the two spots. 
     In  FIG. 6 , another embodiment of the present invention is shown. The same reference numerals as those in the above embodiment denote the same portions in the figure, and repeated description will be omitted. 
     As shown in  FIG. 6 , the dust-removal managing pit  20  in this embodiment is for road and is provided in a side ditch for guiding rainfall on the road to a sewer, and the inflow pipe  20   a  connected to the upper pit  22  is configured to guide the water falling on the road and collected to the upper pit  22 . Also, the lid body  24  closing the upper-end opening portion of the upper lid  22  capable of opening is a meshed article and is configured so as to introduce rainwater falling on the road and flowing along the surface into the upper pit  22 . The mesh plate  34  is inserted into the upper pit  22  and is configured to cover the upper-end opening portion of the lower vertical pipe  23  and the peripheral groove  33  in an inclined state. 
     The upper end of the lower vertical pit  23  is inserted through the hole  22   d  of the upper pit  22 , and the upper end of the lower vertical pit  23  is provided penetrating the bottom wall  22   a  of the upper pit  22  so that the peripheral groove  33  is formed between the periphery of the upper end of the lower vertical pit  23  and the peripheral wall  22   b  of the upper pit  22 . The lower vertical pit  23  is cylindrical and is configured such that water supplied from the inflow pipe  20   a  flows down from the upper-end opening portion through the peripheral groove  33 . And this lower vertical pit  23  is a porous pipe with a relatively large diameter having a plurality of small holes  23   a  formed in the periphery and a lower end thereof opened, and the lower vertical pit  23  is configured such that by being buried under the ground, water flowing from the upper-end opening portion through the peripheral groove  33  permeates the peripheral ground through the small holes  23   a  and the lower-end open end. 
     On the other hand, the grit tank  37  constituting the dust-removal managing pit  20  is provided in close contact with the upper pit  22 , and they are provided in close contact with each other in a state in which the relatively large holes  22   e  and  37   e  formed therein are matched with each other. In the grit tank  37 , the basket  37   d  for collecting solid substances and the like inflowing from the peripheral groove  33  is provided inside and is configured such that the solid substances and the like precipitated in the grit tank  37  can be taken out by removing the lid  37   c  so as to open its upper end and by taking out the basket  37   d  from the upper-end opening portion. 
     Then, to the grit tank  37 , one end of the drain pipe  36  with the other end connected to a sewer pipe, not shown, is connected, and the drain pipe  36  is configured to be connected to the peripheral groove  33  through the grit tank  37 . As the drain pipe  36  in this embodiment, a porous pipe in which a plurality of small holes  36   a  are formed on the periphery is used. By being buried under the ground, the drain pipe  36  made by a porous pipe is configured to permeate water inflowing from the peripheral groove  33  through the grit tank  37  into the peripheral ground, while excess water is made to flow into the sewer pipe, not shown. 
     The dust-removal managing pit  20  constituted as above is provided in a side ditch beside a road, and rainfall on the road flows into the upper pit  22  through the inflow pipe  20   a  and lead to the peripheral groove  33 . Also, from the upper-end opening portion of the upper pit  22 , rainwater falling on the ground and flowing along its surface flows down while relatively large dusts are removed by a mesh-state article, which is the lid body  24  of the upper pit  22 , and leads to the peripheral groove  33 . In the peripheral groove  33 , solid substance contained in water supplied from the inflow pipe  20   a  and the upper-end opening portion of the upper pit  22  are precipitated, and the water from which the solid substances are removed is made to flow down from the upper-end opening portion of the lower vertical pit  23  and to permeate the peripheral ground from the small holes  23   a  and the lower-end open end around it. As a result, the water from which the solid substances are removed can be made to flow down from the upper-end opening portion of the lower vertical pit  23 , and a situation that the inside of the lower vertical pit  23  is filled with dusts can be avoided. 
     In the grit tank  37  provided adjacently to the upper pit  22 , the solid substances constituting the dusts precipitated in the peripheral groove  33  are moved from the peripheral groove  33  and precipitated in the grit tank  37  so as to prevent inflow of the unnecessary solid substances into the drain pipe  36  and a sewer pipe, not shown, through the drain pipe  36  and to avoid a situation that the peripheral groove  33  is filled with the solid substances for a relatively long time. As a result, a situation that soils and dusts are removed from the inflowing water and the soils and dusts flow into the sewer can be avoided. 
     On the other hand, soils and the like precipitated inside the peripheral groove  33  and the lower vertical pit  23  can be cleaned by removing the lid body  24  and using means for vacuuming the bottom portions thereof through the upper-end opening portion. Similarly, the lid body  24  and the mesh plate  34  which captured relatively large dusts can be cleaned in a removed state. Moreover, the solid substances precipitated in the grit tank  37  can even be cleaned by removing the lid  37   c  so as to open the upper end and using means for vacuuming the bottom portion. Here, the peripheral groove  33  is located at a relatively shallow position, and the lower vertical pit  23  is relatively short, and cleaning thereof becomes relatively easy. Therefore, a management burden of the dust-removal managing pit of the present invention including the upper pit  22  and the lower vertical pipe  23  can be reduced from that of the prior-art managing pit. 
     INDUSTRIAL APPLICABILITY 
     The dust-removal managing pit of the present invention can be used by being connected to a water storage tank buried under the ground for storing water, a sewer and the like and can remove dusts from water supplied to the water storage tank, the sewer and the like.