JP2011236613A - Shaft construction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shaft construction method allowing support strength of bottom slab to increase.SOLUTION: In this shaft construction method, excavated material 5 is thrown into an excavated hole 4 to a position lower than the top face 3d of a planned bottom slab 3. Concrete is then placed in the excavated hole 4 to form a continuous wall 2 and the excavated material laid in the lower end 2a side of the continuous wall 2 is removed. Thereby, a recess 13 is formed under the continuous wall 2. A reinforcement basket 14 is afterward inserted into the recess 13 and underwater concrete is placed in the bottom of a space S surrounded by the continuous wall 2. Thus, the underwater concrete flows into the recess 13 to construct the bottom slab 3 having a flange part 3a on the bottom of a shaft 1. By this shaft construction method, the recess 13 is easily prepared for forming the flange under the continuous wall 2, and the flange part 3a reinforced with the reinforcement basket 14 is easily constructed on the bottom slab 3.

Description

  The present invention relates to a shaft construction method used for tunnel construction and the like.

  Conventionally, there is JP-A-63-289195 as a technique in such a field. In the shaft described in this publication, a locking step portion is formed at the lower end of the underground continuous wall (continuous wall), and the end portion of the bottom plate is fitted into the locking step portion of the continuous wall. As a method for constructing a continuous wall provided with such a locking step portion, a variable excavation width excavator capable of changing the width of an excavation hole during excavation is used. By this excavator, excavation with a constant width is performed halfway, and when the planned depth is reached, the excavation width is narrowed to form an excavation hole. Thereafter, a reinforcing bar is built in the excavation hole, and concrete is placed in the excavation hole, so that a locking step portion can be formed at the lower end of the continuous wall.

JP 63-289195 A

  However, although the bottom plate is supported by the locking step formed at the lower end of the continuous wall, the contact area between the locking step and the bottom plate depends on the step size of the locking step, and the bottom plate When the pumping pressure of the groundwater to be pushed up is high, there is a possibility that the supporting strength of the bottom plate is insufficient.

  An object of this invention is to provide the construction method of the shaft which enabled the support strength improvement of the bottom slab.

The present invention is a method for constructing a shaft constructed by a continuous wall and a bottom slab,
Drilling an annular excavation hole to form a continuous wall;
A step of introducing a solid work to be drilled into the drilling hole to a position lower than the upper surface of the planned bottom plate,
Forming concrete walls by placing concrete in the excavation hole;
A process of discharging earth and sand in the continuous walls;
Removing the excavated object disposed on the lower end side of the continuous wall;
Inserting the reinforcing bar gago into the recess formed by removing the excavated object;
A step of placing underwater concrete at the bottom of the space surrounded by the continuous walls and forming a bottom plate having a flange portion formed by flowing the underwater concrete into the recess.

  In order to increase the support strength of the bottom plate of the shaft formed by this construction method, the bottom plate is supported by the lower end surface of the continuous wall, and in order to achieve this, the bottom plate has a flange for contacting the lower end surface Is provided. In shafts with such a structure, the groundwater pressure (lifting pressure) is resisted by the bottom plate weight, the weight of the continuous wall, and the frictional force between the outer peripheral surface of the continuous wall and the ground. Even if it is expensive, the bottom plate can be reliably supported. In constructing such a vertical shaft, a solid excavation object is put into the excavation hole to a position lower than the planned upper surface of the bottom slab. Thereafter, concrete is placed in the excavation hole to form a continuous wall, and the work to be excavated arranged on the lower end side of the continuous wall is eliminated. As a result, a recess is formed below the continuous wall. Thereafter, a reinforcing bar gago is inserted into the recess, and underwater concrete is placed at the bottom of the space surrounded by the continuous walls. As a result, the underwater concrete flows into the recess, and a bottom plate having a flange portion at the bottom of the shaft is constructed. When such a construction method is employed, a flange-forming recess can be easily created below the continuous wall, and a flange portion reinforced by a reinforcing bar can be easily constructed on the bottom plate.

Further, the reinforcing bars are equally divided in the circumferential direction of the shaft, and each reinforcing bar is preferably lowered in the vertical direction into the space surrounded by the continuous walls and then inserted into the recess in the horizontal direction. .
If such a method is employ | adopted, a reinforcing bar basket can be easily arrange | positioned in the recessed part formed under the continuous wall.

In addition, after the work to be excavated, the drainage pipe and the grout injection pipe reaching the excavation object are inserted into the excavation hole from above, and after placing underwater concrete to form the bottom plate, It is preferable to fill this gap with a grout material while discharging water accumulated in the gap between the flange portion of the formed bottom plate and the lower end of the continuous wall.
When underwater concrete is placed at the bottom of the space surrounded by the continuous walls, this underwater concrete flows into the recess. At this time, groundwater tends to accumulate in the upper part of the recess, and the underwater concrete is completely filled in the recess. It is difficult. Therefore, the grout material is filled into the gap while discharging the water accumulated in the gap between the flange portion of the bottom plate formed in the recess and the lower end of the continuous wall. As a result, there is no gap between the flange and the lower end of the continuous wall, so that the supporting force generated at the flange can be reliably transmitted to the lower end surface of the continuous wall, and the bottom plate can be supported securely. become.

In addition, it is preferable to insert a cooling pipe into the excavation hole from above after inserting the work to be drilled, freeze the boundary portion between the flange portion of the bottom plate and the lower end of the continuous wall, and stop the boundary portion.
By adopting such a method, it is possible to reliably avoid a situation in which groundwater leaks out from the boundary portion at the time of so-called dry-up, in which groundwater is drained from the shaft with a submersible pump or the like.

  According to the present invention, it is possible to build a shaft that enables the supporting strength of the bottom plate to be increased.

It is sectional drawing which shows one Embodiment of the shaft to which the construction method which concerns on this invention is applied. It is sectional drawing which shows the bottom part vicinity of a digging hole. It is sectional drawing which shows the excavation hole after crushed stone addition. It is sectional drawing which shows the state which laid the reinforcing bar in the excavation hole. It is sectional drawing which shows the state which cast concrete in the excavation hole. It is sectional drawing which shows the state which excavated the space enclosed by the continuous wall. It is sectional drawing which shows the state which has excluded the crushed stone. It is sectional drawing which shows the state which sunk the excavator in the water of the shaft. It is sectional drawing which shows the state which inserts a rebar basket in a recessed part. It is a top view which shows the reinforcing bar basket equally divided in the circumferential direction. It is sectional drawing which shows a bottom plate. It is sectional drawing which shows the state which injected the grout material in the space | gap of a bottom plate and a continuous wall. It is sectional drawing which shows the state which frozen the boundary part of a flange part and a continuous wall.

  Hereinafter, a preferred embodiment of a shaft construction method according to the present invention will be described in detail with reference to the drawings.

  As shown in FIG. 1, a vertical shaft 1 is surrounded by a cylindrical underground continuous wall (continuous wall) 2 made of concrete, and the bottom of the vertical shaft 1 is invaded by groundwater by a disk-shaped bottom plate 3 made of concrete. It is preventing.

  Further, a flange portion 3 a is provided at the outer peripheral end of the bottom plate 3 over the entire circumference, and an upper surface 3 b of the flange portion 3 a is in contact with a lower end surface 2 a of the continuous wall 2, and an outer peripheral surface 3 c of the bottom plate 3. Is in contact with the inner peripheral surface 2 b of the continuous wall 2. Thus, the support strength of the bottom plate 3 is increased by adopting the bottom plate 3 having an overhang structure by the flange portion 3a. In the shaft 1 having such a configuration, the weight of the bottom plate 3, the weight of the continuous wall 2, and the frictional force between the outer peripheral surface 2 c of the continuous wall 2 and the ground become resistance to the groundwater pressure (lifting pressure). Even if the groundwater pressure is high, the bottom plate 3 can be reliably supported, which makes it possible to reduce the thickness of the bottom plate 3, reduce the material cost, and shorten the construction period.

  Next, the construction method of the shaft 1 will be described.

  As shown in FIG. 2, the excavation hole 4 corresponding to the thickness of the continuous wall 2 is formed in the ground. Thereafter, as shown in FIG. 3, the solid object 5 is put into the excavation hole 4 to a position lower than the planned upper surface 3 d (see FIG. 1) of the bottom plate 3. Examples of the excavated object 5 include crushed stones, and the crushed stones 5 may be input as they are from above the excavation hole 4. However, by inserting the packed crushed stones 5 from above the excavation hole 4, Sexuality is improved. Since the crushed stone 5 is used to form the flange portion 3a (see FIG. 1), the crushed stone 5 is introduced into the excavation hole 4 until reaching a height corresponding to the thickness of the flange portion 3a.

  As shown in FIG. 4, after the crushed stone 5 is introduced, a reinforcing steel cage 6 that is used to reinforce the continuous wall 2 is built in the excavation hole 4. The rebar cage 6 is arranged over the entire circumference of the excavation hole 4, and a drain pipe 7 and a grout injection pipe 8 that reach the crushed stone 5 are inserted into the excavation hole 4 from above. A cooling pipe 9 is also inserted into the excavation hole 4 from above. A large number of drainage pipes 7, grout injection pipes 8 and cooling pipes 9 are arranged over the entire circumference of the excavation hole 4, the lower ends of the drainage pipes 7 and grout injection pipes 8 are opened, and the cooling pipe 9 has a full length. It is protected by a heat insulating material over the top and only the lower end of the cooling pipe 9 is exposed.

  After completing the installation of the reinforcing bar 6 or the like, the concrete wall 2 is formed by placing concrete in the excavation hole 4 as shown in FIG. Then, as shown in FIG. 6, the inner earth and sand enclosed by the continuous wall 2 is discharged | emitted until it reaches the planned depth. At this time, groundwater accumulates in the space S surrounded by the inner peripheral surface 2 b of the continuous wall 2.

  As shown in FIGS. 7 and 8, the excavator 10 having the rotatable drum cutter 10a is submerged in the water in the space S from above. The excavator 10 is lowered from the ground by the rod 11, and the drum cutter 10a is installed at a place where the crushed stone 5 is buried. Thereafter, the crushed stone 5 is gradually removed toward the back by the drum cutter 10 a while the rod 11 is gradually brought closer to the continuous wall 2. The crushed stone 5 discharged at this time is collected at the water inlet 12a of the submersible pump 12 fixed to the excavator 10, and is discharged to the ground through the pipe 12b. And if the width | variety of the drum cutter part 10a shall be 1 pitch, all the crushed stone 5 will be excluded over the perimeter, sending the excavator 10 to the circumferential direction 1 pitch at a time.

  As shown in FIG. 9 and FIG. 10, by removing the crushed stone 5, an annular recess 13 is formed below the continuous wall 2, and a reinforcing bar 14 is inserted into the recess 13. The reinforcing bar cage 14 is equally divided in the circumferential direction, and each reinforcing bar cage 14 is lowered vertically from the ground by the rod 16, and the reinforcing rod cage 14 is suspended at a position corresponding to the recess 13, and the rod 16 is connected. The steel bar 14 is inserted into the back of the recess 13 while gradually approaching the wall 2 in the horizontal direction. This operation is sequentially performed so that the entire circumference of the recess 13 is filled with the reinforcing bar cage 14. By inserting the reinforcing bar 14 as a unit into the recess 13, the reinforcing bar 14 can be easily disposed over the entire circumference of the recess 13 formed below the continuous wall 2.

  By adopting such a construction method, it is possible to easily create the flange forming recess 13 below the continuous wall 2 and to easily construct the flange portion 3a reinforced by the reinforcing bar 14 in the bottom plate 3. can do.

  As shown in FIG. 11, underwater steel basket 14 is hung with rod 16, underwater concrete 17 is placed at the bottom of space S surrounded by continuous wall 2, and underwater concrete 17 is poured into recess 13. A bottom plate 3 having a flange portion 3 a is formed at the bottom of the shaft 1.

  When the underwater concrete 17 is placed at the bottom of the space S surrounded by the continuous wall 2, the underwater concrete 17 flows into the recess 13, but at this time, groundwater tends to accumulate in the gap P formed at the top of the recess 13, It is difficult to completely fill the concave portion 13 with the underwater concrete 17.

  Therefore, after the underwater concrete 17 is hardened, the water accumulated in the gap P between the flange portion 3a of the bottom plate 3 formed in the recess 13 and the lower end of the continuous wall 2 is discharged by the drain pipe 7 while discharging the water. The gap P is filled with the grout material 20 by the grout injection pipe 8. As a result, the grout material 20 becomes a part of the flange portion 3a, and there is no gap P between the flange portion 3a and the lower end of the continuous wall 2, so that the ground material pressure (lifting pressure) is generated in the flange portion 3a. The supporting force can be reliably transmitted to the lower end surface 2a of the continuous wall 2, and the bottom plate 3 can be reliably supported.

  After hardening the grout material 20, the coolant is caused to flow into the cooling pipe 9 to freeze the boundary portion L between the flange portion 3 a of the bottom plate 3 repaired by the grout material 20 and the lower end surface 2 a of the continuous wall 2. Stop L. At this time, the frozen part R which closes the edge part of the boundary part L is formed also on the soil side. This freezing portion R can also reliably prevent the water from flowing into the boundary portion L.

  In this water stop state, so-called dry-up is performed by extracting groundwater from the shaft 1 with a submersible pump. At this time, since the boundary portion L is frozen, a situation in which groundwater leaks from the boundary portion L can be reliably avoided, and prolonged dry-up can be avoided.

  Then, after the completion of the dry-up, a concrete bottom plate (not shown) reinforced with reinforcing bars is placed on the bottom plate 3.

  It goes without saying that the present invention is not limited to the embodiment described above. In the shaft construction method according to the present invention, the planar shape of the shaft 1 is not limited to a circle, but an oval shape, a rectangle, or the like is applicable.

  DESCRIPTION OF SYMBOLS 1 ... Vertical shaft, 2 ... Connection wall, 3 ... Bottom plate, 3a ... Flange part, 4 ... Drilling hole, 5 ... Crushed stone (drilling object), 7 ... Drain pipe, 8 ... Grout injection pipe, 9 ... Cooling pipe, 13 ... concave part, 14 ... reinforcing bar cage, 17 ... underwater concrete, P ... gap, L ... boundary part.

Claims (4)

In the method of constructing a shaft constructed by a continuous wall and a bottom plate,
Excavating an annular excavation hole for forming the continuous wall;
Charging a solid work piece into the excavation hole to a position lower than the planned upper surface of the bottom slab;
Placing concrete in the excavation hole to form the continuous wall;
Discharging the earth and sand in the continuous wall;
Removing the work to be excavated disposed on the lower end side of the continuous wall;
Inserting a reinforcing bar gago into the recess formed by removing the excavated object;
Forming underwater concrete at the bottom of the space surrounded by the continuous wall, and forming the bottom plate having a flange portion into which the underwater concrete flows into the recess. How to construct a vertical shaft.   The reinforcing bar is equally divided in the circumferential direction of the shaft, and each reinforcing bar is lowered in the vertical direction into a space surrounded by the continuous wall and then inserted in the recess in the horizontal direction. The construction method of the shaft of Claim 1 characterized by these. After inserting the excavated material, a drain pipe and a grout injection pipe reaching the excavated material are inserted into the excavated hole from above,
After draining the underwater concrete to form the bottom plate, while discharging the water accumulated in the gap between the flange portion of the bottom plate formed in the recess and the lower end of the continuous wall, The shaft construction method according to claim 1 or 2, wherein the gap is filled with a grout material. After the work to be excavated, a cooling pipe is inserted into the excavation hole from above,
The construction method of the shaft according to any one of claims 1 to 3, wherein the boundary portion between the flange portion of the bottom plate and the lower end of the continuous wall is frozen to stop the boundary portion. .

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