JP7633891B2 - Method for constructing underground structure, underground structure, and precast concrete side or intermediate wall/column therefor - Google Patents

Description

The present invention relates to methods for constructing underground structures such as semi-underground road tunnels, underground parking lots, bicycle parking lots, utility tunnels, subways, and underpasses.

The applicant proposed a method for constructing an underground structure with a large soil cover in the following Patent Document 1. Specifically, the method for constructing an underground structure having at least both side walls, a top plate, and a bottom plate includes forming an embedded portion in which insert metal fittings or steel materials are embedded from the upper end surface to a predetermined depth in the construction portion of the both side walls, and erecting precast concrete side walls that form the main structure in the ground and that are provided with a plurality of temporary steel materials that are detachably attached so as to protrude upward to provide lateral resistance such as soil and water pressure, and then excavating and removing the ground up to the position where the top plate is to be constructed between the precast concrete side walls, and then excavating and removing the ground up to the position where the top plate is to be constructed, and then excavating and removing the ground between the precast concrete side walls, avoiding the embedded portions of the insert metal fittings or steel materials. This method of constructing an underground structure consists of a first step in which concrete is poured into the lower part of the precast concrete wall, and the top plate, which will be the main structure, is completed in advance by connecting and integrating it with the precast concrete side walls; a second step in which the ground is excavated below the top plate, which is surrounded by the precast concrete side walls and the precast concrete wall, and finally to the construction depth of the bottom plate; and a third step in which concrete is poured between the precast concrete side walls in the construction area of the bottom plate, and the bottom plate, which will be the main structure, is constructed by connecting and integrating it with the precast concrete side walls.

This method of constructing underground structures has the following advantages: it is possible to absorb errors in the construction of side walls in underground structures with a large soil cover, it is possible to minimize the amount of ground occupied by the construction work and its duration, it is possible to keep the impact on the surrounding environment to a minimum, it is possible to facilitate transportation and on-site work, and it is possible to ensure the strength of the structure.

JP 2011-122386 A

When constructing underground structures at great depths underground, the precast concrete side walls are subjected to large soil and water pressures, so the thickness of the precast concrete side walls must be increased. This increases the costs of manufacturing and transporting the precast concrete side walls, and there are concerns that the applicability of this construction method will decrease.

In the method for constructing an underground structure described in Patent Document 1, temporary steel materials are provided on the upper end surface of the precast concrete side wall so as to protrude upward. As shown in FIG. 20, the precast concrete side wall and the temporary steel materials are fixed by bolts via base plates 53 provided at the ends of the temporary steel materials 51 to insert metal fittings 52 embedded to a predetermined depth from the upper end surface of the precast concrete side wall 50, or as shown in FIG. 21, the temporary steel materials 51 are attached and detached by splicing them via splice plates 56 to steel materials 55 embedded to a predetermined depth from the upper end surface of the precast concrete side wall 50 and having bearing plates 54 and studs (not shown) at the embedded end.

However, if temporary steel members protruding upward from the top end surface of the precast concrete sidewall are installed in this manner, when the soil cover becomes large, excessive stress is concentrated at the fixed part of the temporary steel member to the precast concrete sidewall, which may cause the precast concrete sidewall to crack or suffer other damage.

The main objective of the present invention is to reduce costs and expand applicability by making the precast concrete side walls thinner, while also preventing damage to the precast concrete side walls even when there is a large soil covering.

In order to solve the above problems, the present invention relates to a method for constructing an underground structure having at least two side walls, a top plate, and a bottom plate, comprising:
a first step of erecting precast concrete side walls that will form the main structure in the ground , the precast concrete side walls having a flange portion facing the outer surface of the precast concrete side walls and a web portion protruding inward, the precast concrete side walls extending upward from their upper end surfaces to form a retaining wall steel portion for lateral resistance to soil and water pressure, and excavating and removing the ground up to a position where a top plate will be constructed between the precast concrete side walls, and then constructing a top plate portion that will form the main structure between the precast concrete side walls and backfilling the ground to complete the portion shallower than the top plate in advance;
A second step of excavating the ground below the top plate surrounded by the precast concrete side walls and the top plate, and finally excavating the ground to a construction depth of the bottom plate;
The present invention provides a method for constructing an underground structure, which comprises the steps of: when joining the bottom slab and the precast concrete side wall at the bottom slab construction site, the side wall main reinforcing bars are arranged in advance from the lower part of the precast concrete side wall toward the bottom slab side, and a mechanical joint is provided at the tip of the reinforcing bars; after the bottom slab is reinforced relative to this mechanical joint, formwork is installed and concrete is poured to construct the bottom slab, which will become the main structure, while joining and integrating it with the precast concrete side wall.

In the invention described in claim 1 above, the precast concrete side walls are constructed in such a way that steel material is placed as the core material instead of the main reinforcement on the ground side . This increases the cross-sectional area of the steel material compared to conventional reinforced concrete structures using deformed steel bars as the main reinforcement, and increases the bending strength of the precast concrete as a whole. As a result, it is possible to make the precast concrete members thinner and lighter, thereby reducing costs and making it possible to accommodate underground structures at great depths, thereby expanding the applicability of this construction method.

In addition, the steel material used as the core material of the precast concrete member extends upward from the upper end surface to form a steel portion for the earth retaining wall that can be used as an earth retaining wall during construction. Therefore, even if there is a large amount of soil covering and a large soil and water pressure is applied to the steel portion for the earth retaining wall from the side, the steel material extending continuously from the core material ensures continuous resistance in the depth direction, preventing damage such as cracks in the precast concrete member.

In the precast concrete side walls, by using steel material consisting of T-shaped steel bars as the core material instead of the main reinforcement on the ground side where tensile stress is dominant, the bending strength of the precast concrete side walls is increased, making it possible to more reliably make the precast members thinner and lighter.

The flange of the T -shaped steel faces the outer surface of the precast concrete side wall, and the web is arranged to protrude inward, so that the center of gravity of the steel material is closer to the outer surface of the precast concrete side wall than when H-shaped steel is used, and therefore the effective height is larger for the same cross-sectional area, which is advantageous in design. In addition, the bending strength is larger than that of conventional reinforced concrete structures using deformed steel bars, so that the support by struts during internal excavation can be simplified. Furthermore, in the production of precast concrete side walls, many mechanical joints are installed as joints with the bottom slab constructed by on-site poured concrete. In this case, compared to when H-shaped steel is used as the steel material, the mechanical joints can be arranged at a specified pitch without interference between the steel material and the mechanical joints, and the concrete filling property is improved.

According to a second aspect of the present invention, there is provided a method for constructing an underground structure having both side walls, an intermediate wall or intermediate column between both side walls, a top plate portion, and a bottom plate portion, comprising the steps of:
a first step of erecting precast concrete side walls that will form a main structure in the ground for each span separated by the side wall portions and the intermediate wall or column between the side walls, in which steel material is placed as a core material in place of main reinforcement on the ground side of the construction portion of the side walls, T-shaped steel is used as the steel material, and the flange portion of the T-shaped steel is arranged so that it faces the outer surface of the precast concrete side wall and the web portion protrudes inward, and the steel material extends upward from the upper end surface to form a steel material portion for a retaining wall for lateral resistance such as soil and water pressure, and erecting precast concrete intermediate walls or intermediate columns that will form a main structure in the ground for each span separated by the side wall portions and the intermediate wall or column, in which steel material is placed as a core material in place of main reinforcement in place of main reinforcement and the steel material extends upward from the upper end surface to form a steel material portion for a retaining wall for lateral resistance such as soil and water pressure, excavating and removing the ground up to a position where a top plate will be constructed between the spans, constructing a top plate portion that will form the main structure between the precast concrete side walls, and backfilling the ground to complete the portion shallower than the top plate portion in advance;
A second step of excavating the ground below the top plate surrounded by the precast concrete side walls and the top plate, and finally excavating the ground to a construction depth of the bottom plate;
The present invention provides a method for constructing an underground structure, which comprises the steps of: when joining the bottom slab and the precast concrete side walls at the bottom slab construction site, first, arranging the main reinforcement bars of the side wall from the lower part of the precast concrete side wall toward the bottom slab, and providing a mechanical joint at the tip of the reinforcement bar; after arranging the reinforcement bars of the bottom slab relative to this mechanical joint, setting formwork and pouring concrete to construct the bottom slab, which will become the main structure, while joining and integrating the precast concrete side walls and the precast concrete intermediate walls or intermediate columns.

The invention described in claim 2 above is a construction method for underground structures with intermediate walls or columns between side walls. When intermediate walls or columns are present between side walls, it is possible to excavate all of the ground in which the top plate between the side walls will be constructed, and then construct the top plate, but in this case, the scale of excavation will be large and the aboveground occupation period will be extended. Therefore, by constructing each span separated by both side walls and intermediate walls or columns between both side walls in the following order, erecting precast concrete members, excavating the ground up to the top plate construction position, constructing the top plate, and completing the shallower portion below the top plate by backfilling, it is possible to shorten the aboveground occupation period.

As the present invention of claim 3 , there is provided a method for constructing an underground structure as described in either claim 1 or 2, wherein the precast concrete side walls and/or precast concrete intermediate walls or intermediate columns are provided with a plurality of steel piles protruding downward from their lower end surfaces for vertical bearing capacity and lateral resistance such as soil and water pressure.

In the invention described in claim 3 , a plurality of steel piles are provided to protrude downward from the bottom end surface of the precast concrete side walls and/or precast concrete intermediate walls or intermediate columns in order to provide vertical bearing capacity and lateral resistance such as soil and water pressure. It is possible to use precast concrete members for the entire embedded length, but in this case, not only will the excavation depth of the building groove be deeper, but the cost of the precast members will increase, causing a longer construction period and increased construction labor and costs. Therefore, by providing a plurality of steel piles at the bottom end, the building groove can be made shallow, and these steel piles can ensure sufficient vertical bearing capacity and lateral resistance such as soil and water pressure.

As a fourth aspect of the present invention, there is provided a method for constructing an underground structure according to any one of claims 1 to 3 , wherein the precast concrete side walls and/or precast concrete intermediate walls or intermediate columns have a film attached or a release agent applied to at least the inner wall surface side.

In the invention described in claim 4 , a film is applied or a release agent is applied to at least the inner wall surface of the precast concrete side walls and/or the precast concrete intermediate walls or intermediate columns. Since muddy water and soil cement adhere to the surface of the precast concrete members during construction and become dirty, the inner wall surface can be easily finished neatly by peeling off the film after the work is completed or by applying a release agent so that it can be easily washed away.

According to a fifth aspect of the present invention, there is provided an underground structure constructed by the method for constructing a structure as described in the first aspect, characterized in that steel material is arranged as a core material instead of main reinforcement on the ground side, T-shaped steel is used as the steel material, the flange portion of the T-shaped steel is arranged so that it faces the outer surface of the precast concrete side wall and the web portion protrudes inward, the steel material extends upward from the upper end surface to form a steel part for a retaining wall for lateral resistance such as soil and water pressure, and a plurality of steel piles are provided so as to protrude downward from the lower end surface for vertical bearing force and lateral resistance such as soil and water pressure, a top plate portion provided at the upper part between the precast concrete side walls, and a bottom plate portion provided at the lower part between the precast concrete side walls and constructed of cast -in-place concrete.

As the present invention of claim 6 , there is provided an underground structure as described in claim 5, which has one or more precast concrete intermediate walls or intermediate columns between the precast concrete side walls, and in which steel material is arranged as a core material instead of main reinforcement in the precast concrete intermediate walls or intermediate columns, and the steel material extends upward from the upper end surface to form a steel portion for a retaining wall for lateral resistance such as soil and water pressure, and a plurality of steel piles are provided to protrude downward from the lower end surface for vertical bearing force and lateral resistance such as soil and water pressure.

As explained above in detail, the present invention makes it possible to reduce costs and expand applicability by making the precast concrete side walls thinner, and also makes it possible to prevent damage to the precast concrete side walls even when they are covered with a large amount of soil.

A vertical cross-sectional view showing an underground structure 1A according to the present invention. This is the construction procedure (part 1) for underground structure 1A. 1 shows a precast concrete side wall 2, where (A) is a vertical cross-sectional view of the side surface and (B) is a vertical cross-sectional view of the front surface. 1A and 1B show a precast concrete side wall 2 according to a modified example, in which (A) is a vertical cross-sectional view of the side surface, and (B) is a vertical cross-sectional view of the front surface. 3 and 4 as seen from the line VV. This is a bending moment diagram of a box culvert. A cross-sectional view of the precast concrete side wall 2 at the bottom slab joint. This is a cross-sectional view of a main portion showing an example of a waterproof structure between precast concrete side walls 2, 2. This is the construction procedure (part 2) for underground structure 1A. This is the construction procedure (part 3) for underground structure 1A. This is the construction procedure (part 4) for underground structure 1A. 2 is a cross-sectional view showing a main portion of the joint between a precast concrete side wall 2 and a precast concrete top slab 3. FIG. 2 is a cross-sectional view showing a main portion of the joint structure between a precast concrete side wall 2 and a top plate 3. FIG. This is the construction procedure for underground structure 1A (part 5). This is the construction procedure (part 6) of underground structure 1A. This is the construction procedure (part 7) of underground structure 1A. This is the construction procedure for underground structure 1A (part 8). A longitudinal cross-sectional view of the essential parts showing the joint with the bottom plate portion 4. A vertical cross-sectional view showing an underground structure 1B relating to a second embodiment example. 1A and 1B show a fixing structure of a conventional temporary steel material 51, in which (A) is a vertical cross-sectional view of the side surface and (B) is a vertical cross-sectional view of the front surface. 1A and 1B show a fixing structure of a conventional temporary steel material 51 according to a modified example, in which (A) is a vertical cross-sectional view of the side surface, and (B) is a vertical cross-sectional view of the front surface.

The following describes in detail the embodiments of the present invention with reference to the drawings.

[First embodiment]
In Figures 1 to 3, underground structure 1A comprises precast concrete side walls 2 in which steel materials 5, 5... are arranged as core materials instead of main reinforcement, the steel materials 5 extending upward from the upper end surface to form a retaining wall steel material portion 5B for lateral resistance such as soil and water pressure, and a plurality of steel piles 6, 6... are provided so as to protrude downward from the lower end surface for vertical bearing force and lateral resistance such as soil and water pressure, a top plate portion 3 provided at the upper portion between the precast concrete side walls 2, 2, and a bottom plate portion 4 provided at the lower portion between the precast concrete side walls 2, 2 and constructed of cast-in-place concrete.

Below, the underground structure 1A will be described in detail in accordance with the construction sequence.

(First step)
The first step is to construct the top plate 3, which will be the main structure, between the precast concrete side walls 2, 2, and to complete the portion shallower than the top plate by backfilling. This first step will be described in detail with reference to Figs. 2 to 14.

First, as shown in FIG. 2, excavation is performed at the side wall construction site using an excavator to construct the precast concrete side wall 2, and then the precast concrete side wall 2 is erected.

As shown in Figures 3 to 5, the precast concrete side wall 2 is made of steel materials 5, 5... that are arranged as core materials instead of main reinforcement, and the steel materials 5 extend upward from the upper end surface. Until the top plate 3 is constructed, they function as the steel material section 5B for the retaining wall to provide lateral resistance such as soil and water pressure, and are equipped with multiple steel piles 6, 6... that protrude downward from the lower end surface to provide vertical support and lateral resistance such as soil and water pressure.

The steel material 5 is formed by continuously forming a core steel material section 5A embedded in the precast concrete side wall 2 and a retaining wall steel material section 5B extending upward from the upper end surface of the precast concrete side wall 2.

As shown in Figure 5, the steel material 5 is preferably arranged in place of the main reinforcement bars arranged on the ground side of the precast concrete side wall 2 and on the inside of the structure, and reinforcing bars made of deformed steel bars are preferably arranged on the inside of the structure.

By placing the steel material 5 as a core material in place of the main reinforcement on the natural ground side, in a box culvert structure such as the underground structure 1A of the present invention, the strength of the side wall where tensile stress predominates can be increased as shown in Figure 6, and compared to a reinforced concrete structure using deformed steel bars, the cross-sectional area of the steel material increases, and the bending strength increases for the same cross-sectional area. As a result, the precast concrete side wall 2 can be made thinner and lighter, and it can also be used for underground structures at great depths, expanding the applicability of this construction method.

The steel material 5 is extended above the upper end surface of the precast concrete side wall 2 to a length that reaches the ground above, and a plate material such as a steel sheet pile is installed on the ground side, so that it can be used as an earth retaining wall. To extend the steel material 5 above the upper end surface of the precast concrete side wall 2, it may be a continuous piece of steel material without being separated from the core steel material portion 5A as shown in Figure 3, or it may be structured such that the ends of the separated steel material are spliced together with a splice plate 7 at a position protruding above the upper end surface of the precast concrete side wall 2 as shown in Figure 4.

In this way, the steel material 5 used as the core material of the precast concrete side wall 2 extends upward from the upper end surface of the precast concrete side wall 2 to form the retaining wall steel material section 5B that can be used as an earth retaining wall during construction. Therefore, even if there is a large amount of soil covering and a large soil and water pressure is applied to the retaining wall steel material section 5B from the side, the steel material 5 extending continuously from the core material ensures continuous resistance in the depth direction, preventing damage such as cracks in the precast concrete side wall 2.

The steel material 5 can be any known steel material, such as a T-shaped steel, an H-shaped steel, an I-shaped steel, or a channel steel, but it is particularly preferable to use a T-shaped steel. As shown in Figure 5, the T-shaped steel should be arranged so that the flange portion 5f faces the outer surface (ground surface) of the precast concrete side wall 2 and the web portion 5w protrudes inward.

By arranging the steel material 5 made of T-shaped steel in the above-mentioned orientation, the center of gravity of the steel material is closer to the outer surface of the precast concrete side wall 2 compared to when the H-shaped steel is arranged so that the flange portion faces the outer surface of the precast concrete side wall 2, so for the same cross-sectional area, the effective height is greater in the case of T-shaped steel, which is advantageous in terms of design.

In addition, since the bending strength is greater than that of conventional reinforced concrete structures using deformed steel bars, support using braces during internal excavation can be simplified.

Furthermore, in the production of the precast concrete side walls 2, mechanical joints 8, 8... are installed in correspondence with the positions of the main reinforcement as shown in Figure 7, at the joints with the bottom slab 4 and top slab 3 constructed with cast-in-place concrete. At that time, when H-shaped steel is used as the steel material, as shown in Figure 7( A ), the mechanical joints 8 may interfere with the flanges of the H-shaped steel and not be able to be positioned in positions corresponding to the main reinforcement, resulting in the spacing between adjacent mechanical joints 8, 8 becoming too close together. However, when T-shaped steel is used as the steel material 5, as shown in Figure 7( B ), the steel material 5 and the mechanical joints 8 do not interfere with each other, and they can be positioned at approximately equal intervals in positions corresponding to the main reinforcement, resulting in good concrete filling properties.

It is desirable to apply a film or a release agent to at least the inner wall surface of the precast concrete side wall 2.

As shown in FIG. 3, the precast concrete side wall 2 and the steel pile 6 are fixed by bolts via a base plate 6a provided at the end of the steel pile 6 to an insert metal fitting 9 buried to a specified depth from the bottom end surface of the precast concrete side wall 2, or, although not shown, the steel pile 6 is removably attached by splicing it via a splice plate to a steel material buried to a specified depth from the bottom end surface of the precast concrete side wall 2 and equipped with a bearing plate or stud at the tip of the buried side.

When erecting the structure, a specified water-stopping structure is provided at the joint surface between the precast concrete side walls 2, 2. Any known water-stopping structure can be used without restriction, but it is particularly preferable to use the suitable water-stopping structure disclosed in JP 2011-122386 A. The water-stopping structure of the precast concrete side wall 2 disclosed in the publication is as shown in FIG. 8, in which a space 11 is formed on the opposing sides of adjacent precast concrete side walls 2A and 2B by the engagement of a first-side metal joint 10A embedded in the side of one precast concrete side wall 2A with a second-side metal joint 10B embedded in the side of the other precast concrete side wall 2B. In this closed space 11, opposing concave grooves 12 are formed in the precast concrete side walls 2A and 2B along the longitudinal direction of the members, and a water stop plate 13 is inserted and installed across these concave grooves 12, 12, and the closed space 11 is filled with grout material 14.

Once the above steps have been completed, the ground between the retaining wall steel parts 5B, 5B that protrude above the precast concrete side wall 2 and between the precast concrete side walls 2, 2 is excavated and removed, as shown in Figure 9. When excavating the ground, struts 20 are erected between the retaining wall steel parts 5B, 5B as necessary, as shown in Figure 10. The excavation depth is set to a level that exposes the top of the precast concrete side wall 2 and allows the construction of the top plate part 3 in the next step.

Once excavation is complete, the top plate 3 is constructed between the precast concrete side walls 2, 2, as shown in Figure 11. The construction of the top plate 3 can be done using a precast method in which a precast concrete top plate is erected, or a cast-in-place method using cast-in-place concrete.

When constructing the top plate 3 by the precast method, it is desirable to adopt a rod connection method in which an anchor rod 21 is buried in the upper part of the precast concrete side wall 2 and a screw-type coupler 22 is provided on the upper part of the anchor rod 21, as shown in FIG. 12(A), and after the precast concrete top plate 3 is installed, a rod 24 is inserted through a sleeve 23 previously buried in the corresponding position of the screw-type coupler 22, and connected to the screw-type coupler 22, and then the upper part is fastened. Or, as shown in FIG. 12(B), a sleeve method is adopted in which reinforcing bars 26, 26 protruding from the upper surface of the precast concrete side wall 2 are inserted into sleeves 25, 25 buried in the precast concrete top plate 3 to absorb construction errors, and then mortar is injected into the sleeve 25 to join them. The inner diameter of the sleeve 25 is made slightly larger than the outer diameter of the reinforcing bar 26, and this part can absorb construction errors in the top plate 3.

In addition, the method of constructing the top plate 3 using the on-site casting method involves, for example, placing the side wall main reinforcing bars 27, 27... on the top surface or upper part of the side of the precast concrete side wall 2 in advance, providing mechanical joints 28 at their tips, joining mechanical joints 30 attached to the tips of the top plate main reinforcing bars 29 to the mechanical joints 28, reinforcing the top plate 3, setting up formwork, and pouring concrete, as shown in Figure 13.

Here, it is preferable to strengthen the bond between the precast concrete side wall 2 and the top plate 3 by placing the top plate 3 on the upper surface of the precast concrete side wall 2 and embedding the retaining wall steel part 5B, which protrudes upward from the upper end surface of the precast concrete side wall 2, in the top plate 3. For example, when erecting the precast concrete top plate 3 as shown in Figure 12, a fitting part 31 that can fit with the retaining wall steel part 5B is provided in the precast concrete top plate 3 along the vertical direction, and after installing the precast concrete top plate 3 while fitting the retaining wall steel part 5B into this fitting part 31, the gap between the retaining wall steel part 5B and the fitting part 31 is filled with mortar.

Once the top plate 3 has been installed as described above, as shown in Figure 14, the retaining wall steel section 5B that protrudes above the top plate 3 is removed by gas cutting or the like, and then backfilling is performed to release the aboveground area.

(Second step)
Once the shallower portion of the top plate 3 has been completed in advance by the above-mentioned first step, the ground deeper than the top plate 3, surrounded by the precast concrete side walls 2, 2 and the top plate 3, is excavated as shown in Figure 15, and finally excavation is performed up to the construction depth of the bottom plate 4. As shown in Figure 16, the excavation is supported by struts 32, 32 as necessary, and the excavated soil is discharged, for example, by leaving part of the top plate 3 open, lifting it to the ground with a bucket (crane), and transporting it away by a dump truck or the like.

(Third process)
Once excavation to a specified depth (construction depth of the bottom slab 4) is completed, concrete 33 is poured into the bottom slab construction area and the precast concrete side walls 2, 2 are joined and integrated together, as shown in Fig. 17. The bottom slab 4 and the precast concrete side walls 2 are joined, for example, as shown in Fig. 18, by arranging side wall main reinforcing bars 33 from the lower part of the precast concrete side wall 2 toward the bottom slab 4 side, providing mechanical joints 34 at their tips, and joining mechanical joints 36 attached to the tips of bottom slab main reinforcing bars 35 to the mechanical joints 34 to arrange the reinforcement of the bottom slab 4, followed by setting up formwork and pouring concrete.

As a final finishing touch, if a film has been applied to the inner wall surface of the precast concrete side wall 2, this is removed to expose the clean concrete surface. If a stripping agent has been applied, muddy water, soil cement, and other contaminants are removed by spraying with jet water or cleaning with a brush.

[Second embodiment]
In the above example, the top plate portion 3 and the bottom plate portion 4 are bridged between the both side walls 2, 2. However, as shown in Figure 19, it is also possible to create an underground structure 1B in which the both side walls 2, 2 are separated by a precast concrete intermediate wall or intermediate column 15. The construction procedure is basically similar to that of the first embodiment described above. However, in cases where there is no construction yard, etc., a stepwise construction may be carried out in which a steel material is placed as a core material instead of at least a part of the main reinforcement, and an intermediate wall 15 in which the steel material extends upward from the upper end surface for lateral resistance such as soil-water pressure is used, and the top plate 3 of the left span portion between the left side wall 2 and the intermediate wall 15 is constructed in advance in the first step, and only the retaining wall steel material 5B of the left side wall 2 is removed and backfilled, and then the right span portion between the intermediate wall 15 and the right side wall 2 is excavated and the top plate 3 is constructed, and the retaining wall steel material 5B of the intermediate wall 15 and the right side wall 2 is removed and backfilled. Alternatively, in cases where there is a construction yard, etc., a normal intermediate wall in which the steel material does not extend upward from the upper end surface may be arranged, and the left span portion and the right span portion may be constructed simultaneously.

In addition, in the third step, when pouring concrete into the base slab 4, it is desirable to position the lower end surface of the precast concrete intermediate wall or intermediate column 15 above the lower surface of the base slab so that the poured concrete can be continuously reinforced without interruption in the precast concrete intermediate wall or intermediate column 15.

[Other examples]
(1) In the above example, the ground is excavated and removed up to the position where the top plate between the precast concrete side walls 2, 2 is to be constructed, and then the top plate portion 3 is constructed. However, if the excavated portion will be left open for a long period of time, a covering plate may be installed to seal the excavated portion, and the top plate portion 3 may be constructed while successively replacing this covering plate.

(2) In the above embodiment, both the precast concrete side walls 2 and the precast concrete intermediate walls or intermediate columns 15 are equipped with multiple steel piles 6 that protrude downward from their lower end faces, but the steel piles 6 may be eliminated and the entire embedded length may be made of precast concrete members.

(3) In the above embodiment, as shown in Figures 3 and 4, all of the core materials (steel materials 5) arranged in the precast concrete side wall 2 extend upward from the upper end surface to form the retaining wall steel materials 5B for lateral resistance to soil and water pressure, etc. However, depending on soil and water pressure, etc., every other steel material 5 may extend upward from the upper end surface by one or more, and the remaining steel materials 5 may not extend upward.

1A, 1B... Underground structure, 2... Precast concrete side wall, 3... Top plate, 4... Bottom plate, 5... Steel, 5A... Core steel, 5B... Retaining wall steel, 6... Steel pile

Claims (6)

A method for constructing an underground structure having at least two side walls, a top plate, and a bottom plate, comprising the steps of:
a first step of erecting precast concrete side walls that will form the main structure in the ground , the precast concrete side walls having a flange portion facing the outer surface of the precast concrete side walls and a web portion protruding inward, the precast concrete side walls extending upward from their upper end surfaces to form a retaining wall steel portion for lateral resistance to soil and water pressure, and excavating and removing the ground up to a position where a top plate will be constructed between the precast concrete side walls, and then constructing a top plate portion that will form the main structure between the precast concrete side walls and backfilling the ground to complete the portion shallower than the top plate in advance;
A second step of excavating the ground below the top plate surrounded by the precast concrete side walls and the top plate, and finally excavating the ground to a construction depth of the bottom plate;
A method for constructing an underground structure, characterized in that, when joining the bottom slab and the precast concrete side wall at the bottom slab construction site, the side wall main reinforcement bars are first arranged from the lower part of the precast concrete side wall toward the bottom slab and a mechanical joint is provided at the tip of the reinforcement bars, and after the bottom slab is reinforced relative to this mechanical joint, formwork is installed and concrete is poured to construct the bottom slab, which will become the main structure, while joining and integrating it with the precast concrete side wall. A method for constructing an underground structure having two side walls, an intermediate wall or intermediate column between the two side walls, a top plate and a bottom plate, comprising the steps of:
a first step of erecting precast concrete side walls that will form a main structure in the ground for each span separated by the side wall portions and the intermediate wall or column between the side walls, in which steel material is placed as a core material in place of main reinforcement on the ground side of the construction portion of the side walls, T-shaped steel is used as the steel material, and the flange portion of the T-shaped steel is arranged so that it faces the outer surface of the precast concrete side wall and the web portion protrudes inward, and the steel material extends upward from the upper end surface to form a steel material portion for a retaining wall for lateral resistance such as soil and water pressure, and erecting precast concrete intermediate walls or intermediate columns that will form a main structure in the ground for each span separated by the side wall portions and the intermediate wall or column, in which steel material is placed as a core material in place of main reinforcement in place of main reinforcement and the steel material extends upward from the upper end surface to form a steel material portion for a retaining wall for lateral resistance such as soil and water pressure, excavating and removing the ground up to a position where a top plate will be constructed between the spans, constructing a top plate portion that will form the main structure between the precast concrete side walls, and backfilling the ground to complete the portion shallower than the top plate portion in advance;
A second step of excavating the ground below the top plate surrounded by the precast concrete side walls and the top plate, and finally excavating the ground to a construction depth of the bottom plate;
A method for constructing an underground structure, characterized in that, in connecting the bottom slab and the precast concrete side walls at the bottom slab construction site, the side wall main reinforcement bars are arranged in advance from the lower part of the precast concrete side wall toward the bottom slab, and a mechanical joint is provided at the tip of the reinforcement bars, and after the bottom slab is reinforced relative to this mechanical joint, formwork is arranged and concrete is poured to construct the bottom slab, which will become the main structure, while connecting and integrating the precast concrete side walls and the precast concrete intermediate walls or intermediate columns. A method for constructing an underground structure as described in claim 1 or 2, wherein the precast concrete side walls and/or precast concrete intermediate walls or intermediate columns are provided with a plurality of steel piles protruding downward from their lower end surfaces for vertical bearing capacity and lateral resistance such as soil and water pressure. The method for constructing an underground structure according to any one of claims 1 to 3 , wherein the precast concrete side walls and/or the precast concrete intermediate walls or intermediate columns have a film attached or a release agent applied to at least the inner wall surface side. 2. An underground structure constructed by the method of constructing a structure as described in claim 1, characterized in that the precast concrete side walls are provided with a top plate portion provided at the upper part between the precast concrete side walls, and a bottom plate portion provided at the lower part between the precast concrete side walls and constructed of cast-in-place concrete, the top plate portion being provided at the upper part between the precast concrete side walls, and the bottom plate portion being provided at the lower part between the precast concrete side walls and constructed of cast -in-place concrete. 6. An underground structure as described in claim 5, having one or more precast concrete intermediate walls or intermediate columns between the precast concrete side walls, in which steel material is arranged as a core material instead of main reinforcement, the steel material extends upward from the upper end surface to form a steel portion for a retaining wall for lateral resistance such as soil and water pressure, and a plurality of steel piles are provided to protrude downward from the lower end surface for vertical bearing force and lateral resistance such as soil and water pressure.

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