JP2008133645A - Method of constructing underground water storage tank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely and efficiently construct an underground water storage tank without using special materials by smoothly settling a box while maintaining a stable attitude even if the ground is extremely soft. <P>SOLUTION: This method of constructing an underground water storage tank comprises the steps of so forming pile holes 9a vertically in a ground E into which the box 3 is to be settled at intervals along the circumferential direction of the lower end of the box 3 that they reach the position deeper than the lower end of the settled box 3, filling the pile holes 9a with crushed stone mixture 9b to form crushed stone piles 9, assembling the box 3 by bringing its lower end into contact with the upper ends of the crushed stone piles 9, and settling the box 3 in the ground E by excavating the ground E inside the box 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a construction method of an underground water storage tank in which an underground water storage tank used as a fire prevention water storage tank, a water receiving tank, or the like is submerged in the ground by a submerged method.

Conventionally, a box formed in a cylindrical shape is dug into the ground by excavating the ground inside, and then a bottom plate is constructed at the bottom of the box, and a top plate is disposed at the top of the box A method of constructing an underground water tank by backfilling is generally known. And, in the case where the ground at the construction site of the underground water storage tank is soft ground where there is almost no earth bearing strength, a subsidence prevention body that obtains a reaction force from the ground is disposed on the ground on the outer peripheral side of the box, A plurality of long screw rod members arranged at intervals along the circumferential direction of the box are held by the settlement prevention body with nuts screwed thereto, and the lower end of the screw rod member is By connecting to an auxiliary ring provided at the lower end of the box and excavating the ground inside the box, the holding position of the long bar member in the sinking prevention body is moved by loosening the nut to move the box. A construction method in which a body is set in the ground is known (see, for example, Patent Document 1).
JP 2000-352085 A

The construction method of the underground water tank is that the box is supported by the subsidence prevention body that obtains a reaction force from the ground even if the ground is soft, and is accurately set to a predetermined depth while stably controlling its posture. However, since the weight of the box is added to the ground at the outer peripheral portion of the box through the sinking prevention body, the ground value is N or zero. However, it sinks without being able to support the sinking prevention body, wraps around the inside of the box from the lower end of the box, and sinks the box in the ground while maintaining its posture stably. You may not be able to.
In addition, it takes time and effort to sink the box by moving the holding positions of the plurality of screw rod members with respect to the sinking prevention body while loosening the nut, and the sinking work cannot be performed efficiently. There is a problem that equipment such as a body and a screw rod member is required, and there is a considerable amount of labor for incidental work such as installation and removal at the site.

  The present invention has been made in view of the above circumstances, and it is not necessary to use special equipment, and even in extremely soft ground, the box is smoothly laid while maintaining a stable posture, An object of the present invention is to provide a method for constructing an underground water tank that can reliably and efficiently construct an underground water tank.

The present invention is characterized by the following points in order to solve the above problems.
That is, in the construction method of the underground water storage tank according to claim 1 of the present invention, the box formed in a cylindrical shape is arranged vertically on the ground, and the ground inside the box is excavated, It is a construction method of an underground water tank that sinks a box in the ground,
A plurality of pile holes arranged at intervals along the circumferential direction of the lower end of the box so as to reach a position deeper than the set depth of the lower end of the box on the ground on which the box is to be set. After the pile hole is filled with crushed stone to form the crushed stone pile, the lower end is brought into contact with the upper end of the crushed stone pile, and the box is assembled. It is characterized by excavating the ground.

  Further, in the construction method of the underground water storage tank according to claim 2, the pile hole is arranged so that its outer peripheral side is inscribed in the outer peripheral circle of the box, and the diameter is determined from the thickness of the wall of the box. It is characterized by being set large.

According to the present invention, the following excellent effects can be obtained.
That is, according to the construction method of the underground water storage tank according to claim 1, while supporting the lower end of the box by a plurality of crushed stone piles installed in the ground so as to reach a position deeper than the set depth of the box, Since the box can be gradually subsided by the collapse of the crushed stone from the upper end side of the crushed stone pile to the inside of the box, even if the ground on which the box is to be installed is extremely soft, the box Can be smoothly laid down to a predetermined depth while maintaining a stable posture, and an underground water storage tank can be reliably constructed. And the underground water storage tank built in the ground can suppress secular subsidence and inclination displacement as small as possible by the crushed stone pile left under the box.
Further, as in the prior art, it is not necessary to use special equipment such as a sinking prevention body installed on the outer periphery of the box to be set up or a screw rod member for hanging the box on the settling prevention body. There is no need to carry out the box lowering operation and the installation and removal of the equipment at the site, and the underground water tank can be constructed efficiently.

  Moreover, according to the construction method of the underground water tank according to claim 2, an appropriate diameter of the crushed stone pile can be set according to the outer diameter of the box and the thickness of the wall, and when excavating the ground inside the box The collapse from the upper part of the crushed stone pile can be promoted appropriately, and the box can sink smoothly.

Next, a construction method of an underground water storage tank according to an embodiment of the present invention will be described with reference to the accompanying drawings.
First, the underground water tank 1 constructed by the underground water tank construction method according to an embodiment of the present invention will be described. As shown in FIG. 1 and FIG. 2, the underground water tank 1 has a plurality of arc-shaped segments 2 arranged in the circumferential direction and the axial direction, and adjacent segments are connected by bolts, nuts, or the like. And a box 3 formed in a cylindrical shape, and an auxiliary segment ring 4 formed by joining a plurality of arc-shaped auxiliary segments in the circumferential direction is connected to the lower end of the box 3. Underwater concrete 5a and discarded concrete 5b are constructed over the auxiliary segment ring 4 and the lower end of the box 3 (lower box 3a), and a bottom plate 6 having a water collecting pit 6a is provided on the discarded concrete 5b. Furthermore, a top plate 8 having a manhole 7 is provided on the top of the box 3 (upper box 3b), and is installed in the ground E.
The bottom slab 6 is overcoated with a waterproof mortar 6b.

  The lower half of the lower box 3a is a friction cut part 3c having a diameter larger than the outer diameter of the upper half and the outer diameter of the upper box 3b by a predetermined dimension, The diameter of the outer periphery of the auxiliary segment ring 4 is the same as the diameter of the outer periphery of the box 3 (friction cut portion 3c). Further, below the box 3 (auxiliary segment ring 4), a plurality of crushed stone piles 9 having a predetermined length in which the axial direction is directed to the axial direction of the underground water storage tank 1 (direction perpendicular to the ground E). However, it is installed in the ground E at a predetermined interval in the circumferential direction of the lower end portion of the box 3.

  The crushed stone pile 9 is formed by filling a crushed stone mixture 9b in which sand is added to a crushed stone having a predetermined particle size into a pile hole 9a having a circular cross section formed by excavating the ground E, and is compacted. The auxiliary segment ring 4 (box) having a diameter d slightly larger than the wall thickness e of the auxiliary segment ring 4 (friction cut portion 3c of the box 3) and an inner circumferential circle h of the pile hole 9a having a diameter D. It is arranged in the circumferential direction of the box 3 so as to be inscribed in the outer circumferential circle S of 3). As the crushed stone in the crushed stone mixture 9b, in addition to what is formed by crushing natural stone, incinerated ash, coal ash or the like of waste is mixed with a binder and solidified to form artificially crushed stone. Similarly, the sand in the crushed stone mixture 9b is not limited to naturally obtained sand, but artificially formed sand can be used.

Hereinafter, the construction method of the underground water tank 1 will be described with reference to FIGS.
First, the ground E where the underground water tank 1 is to be constructed is slightly larger than the diameter (outer diameter) of the box 3 of the underground water tank 1 and has a predetermined depth (for example, a depth slightly deeper than the height of the manhole 7). A circular pit 10 is excavated. Then, a plurality of (with equal intervals in the circumferential direction of the outer circumference circle S along a circle corresponding to the outer circumference circle S of the box 3 (friction cut portion 3c) to be installed inside the pit 10 ( In the illustrated example, 20 pile holes 9a are excavated perpendicularly to the ground E using a drilling machine such as an earth auger having a diameter corresponding to the diameter d of the pile hole 9a (FIG. 3, FIG. 4). In this case, it is preferable that each pile hole 9a is excavated to a depth that reaches the formation where a predetermined earth strength can be obtained, with the tip thereof being below the lower end of the box 3.

Next, by repeating the work of filling and compacting the crushed stone mixture 9b prepared in advance in each pile hole 9a excavated as described above, the crushed stone mixture 9b is densely filled in the entire length of each pile hole 9a. The formed crushed stone pile 9 is constructed and formed (see FIG. 4).
After that, on the ground E in the pit 10, a plurality of arc-shaped auxiliary segments 4 a are arranged at the upper end of the crushed stone pile 9 so that the outer peripheral wall is along the outer peripheral circle S, The auxiliary segment rings 4 are assembled by joining the adjacent ones in the direction with bolts and nuts (see FIG. 4).

  Next, the arc-shaped segment 2 prepared in advance at the construction site is lifted by a heavy machine such as a truck crane, moved onto the auxiliary segment ring 4, and placed on the auxiliary segment ring 4. . Then, another segment 2 is placed next to the segment 2 placed on the auxiliary segment ring 4 first, the joining surfaces in the circumferential direction of the segments 2 and 2 are brought into contact with each other, and the bolts and nuts provided on the joining surfaces It connects by the 1st fastening part 11a by such as. Such assembling work of the segments 2 is repeated to connect the segments 2 in the circumferential direction to complete the lower box 3a on the auxiliary segment ring 4 (see FIG. 4). At that time, the lower box 3a is connected to the auxiliary segment ring 4 by bolts, nuts or the like.

  Further, in the same manner as when the lower box 3a is assembled, the segments 2 are sequentially placed on the upper end of the lower box 3a, and the adjacent ones in the circumferential direction are connected by the fastening portion 11a. The upper box 3b is formed. In that case, the position of the joint surface between the segments 2 and 2 in the upper box 3b is the segment 2 in the circumferential direction of the box 3 with respect to the position of the joint surface between the segments 2 and 2 in the lower box 3a. Shift by half of the circumferential length of. Then, the segments 2 and 2 of the lower box 3a and the upper box 3b are connected to each other by a second fastening portion 11b such as a bolt and a nut provided on the joint surface in the axial direction (see FIG. 5). ). Thereby, the boxes 3a and 3b are supported by the upper end of the crushed stone pile 9 arranged in a ring shape along the outer circumference circle S and the ground between them through the auxiliary segment ring 4. It becomes.

  As described above, when the connection of the upper box 3b is completed on the lower box 3a, the inside of the lower box 3a (auxiliary segment ring 4) is formed by an excavating machine such as a club bucket or a backhoe. The ground E is excavated evenly in the circumferential direction and discharged out of the boxes 3a, 3b. At that time, the crushed stone pile 9 supported vertically by the ground around the pile hole 9a loses support from the inside of the box 3a due to discharge of the ground inside the box 3a. Due to the action of the load of the ring 4 and the boxes 3a and 3b, the upper crushed stone mixture 9b in the pile hole 9a collapses into the box 3a. As a result, the auxiliary segment ring 4 and the boxes 3a, 3b are supported by the crushed stone pile 9 and gradually sink while maintaining a horizontal state by their own weight (see FIG. 5).

  In this way, the box 3 in which the lower box 3a and the upper box 3b are integrated together is sunk together with the auxiliary segment ring 4, and the upper end of the upper box 3b is the surface of the ground E. When the box 3 sinks to a predetermined depth (near the bottom of the pit 10), excavation of the ground inside the lower box 3a (auxiliary segment ring 4) by the excavating machine is stopped. After this, underwater concrete 5a is constructed inside the auxiliary segment ring 4 and the lower part of the lower box 3a, and then the concrete 5b is disposed thereon, and the bottom plate 5 is attached to the bottom of the lower box 3a. After construction, top coat 6b with waterproof mortar.

Finally, after installing the top plate 7 on the upper end of the upper box 3b, the earth and sand are backfilled in the pit 10, and the upper end of the manhole 7 of the box 3 is the ground E as shown in FIG. The construction work for installing the underground water tank 1 in the ground E is completed so as to be substantially flush with the surface.
Since the underground water tank 1 installed in this way is stably supported uniformly in the circumferential direction of the box 3 by the plurality of crushed stone piles 9 remaining in the ground below the box 3, Even if the installed ground E is soft ground, secular settlement can be suppressed as small as possible.

  As explained above, in the construction method of the underground water storage tank according to the embodiment, the box 3 formed in a cylindrical shape is vertically arranged on the ground E, and the ground E inside the box 3 is arranged. A method of constructing an underground water storage tank in which the box 3 is sunk in the ground by excavation, and is along the circumferential direction of the lower end of the box 3 on the ground E on which the box 3 is to be sunk. A plurality of pile holes 9a arranged at intervals are provided so as to be perpendicular to the ground E so as to reach a position deeper than the set depth of the lower end of the box 3, and the pile hole 9a is filled with a crushed stone mixture 9b. After compacting and forming the crushed stone pile 9, the lower end is brought into contact with the upper end of the crushed stone pile 9 via the auxiliary segment 4 to assemble the box 3, and then the ground E inside the box 3 is attached. It is configured to drill.

Therefore, according to the construction method of the underground water storage tank according to the embodiment, the lower end portion of the box 3 is provided by the plurality of crushed stone piles 9 installed in the ground E so as to reach a position deeper than the settling depth of the box 3. The box 3 can be gradually subsided by the collapse of the crushed stone mixture 9b from the upper end side of the crushed stone pile 9 to the inside of the box 3, while supporting the ground E. Even if it is extremely soft, the box 3 can be smoothly laid down to a predetermined depth while maintaining a stable posture, and the underground water storage tank 1 can be reliably constructed. And the underground water tank 1 built in the ground E can suppress aged subsidence and inclination displacement as small as possible by the crushed stone pile 9 left under the box 3.
Further, unlike the conventional case, it is not necessary to use special equipment such as an anti-sag body installed on the outer periphery of the box 3 to be set up or a long bar member that suspends the box 3 on the set-up prevention body. Further, the operation of lowering the box 3 with the equipment and the additional work such as installation and removal of the equipment on the site are unnecessary, and the underground water storage tank 1 can be efficiently constructed with reduced cost.

  Moreover, according to the construction method of the underground water storage tank according to the embodiment, the pile hole 9a is arranged so that the outer peripheral side thereof is inscribed in the outer peripheral circle S of the box 3 (friction cut portion 3c), Since the diameter d is set to be larger than the wall thickness e of the box 3 (friction cut part 3c), an appropriate crushed stone according to the outer diameter of the box 3 and the wall thickness. The diameter d of the pile 9 can be set, the collapse from the upper part of the crushed stone pile 9 can be appropriately promoted during excavation of the ground inside the box 3, and the box 9 can be smoothly settled.

In addition, in the construction method of the underground water storage tank according to the embodiment, the wall E in the box 3 (friction cut part 3c) is slightly larger than the wall thickness e on the ground E along the circumferential direction of the box 3. Although the 20 crushed stone piles 9 having the diameter d are installed to support the box 3, the diameter d and the number of the crushed stone piles 9 are not limited to the above, and the box 3 (friction cut portion 3c). ) In accordance with the diameter D, weight, etc., other arbitrary diameters, and a plurality other than 20. And since the said crushed stone pile 9 was formed by filling the crushed stone mixture which mixed the sand with the pile hole 9a crushed stone, when the space part of the crushed stone is filled with sand, it will be compacted firmly and a strong crushed stone pile will become. However, when the ground has viscosity and is not extremely soft, it can be formed only with crushed stone without mixing the sand.
Further, when the ground E does not have special adhesiveness, the friction cut portion 3c of the lower box 3 can be omitted. Further, when the ground around the lower box 3a after the installation of the underground water storage tank 1 is not particularly soft, the ground E on the outer peripheral side of the lower box 3a wraps around into the box 3a from below. Since there is no fear, the auxiliary segment ring 4 for preventing the ground E from entering the lower box 3a when the bottom plate 6 is constructed can be omitted.

Moreover, in the underground water tank construction method according to the embodiment, the pit 10 having a predetermined depth is provided in the ground E so that the box 3 can be configured at a low position inside the pit 10. Although it is not necessary to use a heavy machine such as a large crane that lifts the segment 2 constituting the box 3 high, it can be omitted depending on the size of the underground water storage tank 1 and the situation at the construction site.
Although the example in the case of constructing the underground water storage tank 1 in which the box 3 is connected in two stages up and down is shown, the present invention is not limited to this, and the box 3 is connected in one or more stages up and down. This can also be applied to the construction of underground water tanks.

It is the top view which showed a part of underground water tank constructed by applying the construction method of the underground water tank concerning one embodiment of the present invention in a cross section. It is the side view which similarly showed a part with the longitudinal cross-section. It is a top view which shows the installation method of the crushed stone pile in the construction method of the underground water tank which concerns on one embodiment of this invention. It is a longitudinal cross-sectional view which similarly shows the installation method of a crushed stone pile. It is a longitudinal cross-sectional view which similarly shows the sedimentation method of the box in an underground water tank. It is a longitudinal cross-sectional view which shows the state at the time of completion of settling of the box in a similar underground water tank.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Underground water tank 2 Segment 3 Box 3a Lower box 3b Upper box 4 Auxiliary segment ring 6 Bottom plate 7 Manhole 8 Top plate 9 Crushed stone pile 9a Pile hole 9b Crushed stone mixture 10 Pit D of auxiliary segment ring (box) Diameter of outer circumference d Diameter of pile hole E Ground e Thickness of wall of auxiliary segment ring (friction cut of box) S Circle of outer circumference of auxiliary segment ring (box)

Claims (2)

A method for constructing an underground water tank in which a box formed in a cylindrical shape is arranged vertically on the ground, and the box is submerged in the ground by excavating the ground inside the box,
A plurality of pile holes arranged at intervals along the circumferential direction of the lower end of the box so as to reach a position deeper than the set depth of the lower end of the box on the ground on which the box is to be set. After the pile hole is filled with crushed stone to form the crushed stone pile, the lower end is brought into contact with the upper end of the crushed stone pile, and the box is assembled. A method for constructing an underground water tank, characterized by excavating the ground.   The said pile hole is arrange | positioned so that the outer peripheral side may be inscribed in the outer periphery circle of the said box, The diameter is set larger than the thickness of the wall part of the said box, It is characterized by the above-mentioned. How to build an underground water tank.

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