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

Abstract

To provide a construction method of an underground structure allowing cost to be reduced and usability to be expanded by making a precast concrete side wall thinner and preventing damage of the precast concrete side wall even upon large overburden.SOLUTION: A construction method comprises steps of: at construction sites on both side wall parts, installing a precast concrete side wall 2 to be a body structure in the ground, in which steel material 5 is placed as core material in place of main reinforcement as well as soil retention steel material 5B is formed for resistance in a lateral direction against soil-water pressure and the like by extending the steel material 5 upward from an upper end surface; constructing a top cap 3 to be a body part between the precast concrete side walls 2, 2 after excavating and removing the ground down to a position where the top cap between the precast concrete side walls 2, 2; and finishing a shallower part of the top cap through refilling therein in advance.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for constructing underground structures such as semi-underground road tunnels, underground parking lots, bicycle parking lots, utility tunnels, subways, and underpasses. [Background technology]

[0002] The applicant proposed a method for constructing an underground structure with a large earth covering 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 as the main structure in the ground, the precast concrete side walls being provided with a plurality of temporary steel materials detachably protruding upward for lateral resistance such as soil and water pressure, 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 between the precast concrete side walls, the method for constructing an underground structure having at least both side walls, a top plate, and a bottom plate ... This method for constructing underground structures consists of the following steps: a first step of pouring concrete into the lower part of the top plate, bonding and integrating it with the precast concrete side walls, and completing the top plate, which will be the main structure; a second step of excavating the ground deeper than the top plate, surrounded by the precast concrete side walls and the top plate, and finally excavating to the construction depth of the bottom plate; and a third step of pouring concrete in the bottom plate construction area between the precast concrete side walls, bonding and integrating it with the precast concrete side walls, and constructing the bottom plate, which will be the main structure.

[0003] According to this method of constructing underground structures, in underground structures with a large amount of soil covering, it is possible to absorb construction errors in the side walls, minimize the scale and duration of ground occupation required for construction, keep the impact on the surrounding environment to a necessary minimum, facilitate transportation and on-site work, and ensure structural strength, among other benefits. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2011-122386 A Summary of the Invention [Problem to be solved by the invention]

[0005] 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. As a result, the costs of manufacturing and transporting the precast concrete side walls increase, and there were concerns that the applicability of this construction method would decrease.

[0006] Furthermore, in the method of constructing underground structures described in Patent Document 1 above, temporary steel materials are provided on the upper end surface of the precast concrete side wall so as to protrude upward, and these precast concrete side walls and temporary steel materials are either bolted to insert fittings 52 embedded to a predetermined depth from the upper end surface of the precast concrete side wall 50 via base plates 53 provided at the ends of the temporary steel materials 51, as shown in Figure 20, or are detachably provided by splicing the temporary steel materials 51 via splice plate 56 to steel material 55 embedded to a predetermined depth from the upper end surface of the precast concrete side wall 50 and having a support plate 54 or stud (not shown) provided at its embedded tip, as shown in Figure 21.

[0007] However, when temporary steel members protruding upward from the upper end surface of a precast concrete sidewall are installed in this manner, if the soil covering becomes large, excessive stress will be concentrated at the fixed parts of the temporary steel members relative to the precast concrete sidewall, which could cause the precast concrete sidewall to crack or suffer other damage.

[0008] Therefore, the main object 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. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention according to claim 1 provides a method for constructing an underground structure having at least two side walls, a top plate, and a bottom plate, comprising: At the construction sites of the both side walls, Natural ground side Instead of main reinforcement, steel is placed as the core material, A T-shaped steel is used as the steel material, and the T-shaped steel is arranged so that a flange portion faces the outer surface side of the precast concrete side wall and a web portion protrudes inward, a first step in which precast concrete side walls that form the main structure are erected in the ground, with the steel material extending upward from the upper end surface to form a steel portion for a retaining wall for lateral resistance to soil and water pressure, etc., and the ground is excavated and removed up to the position where the top plate between the precast concrete side walls will be constructed, and then the top plate portion that will form the main structure is constructed between the precast concrete side walls and backfilled 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 to a construction depth of the bottom plate; At the bottom plate construction site In this case, when connecting the bottom slab and the precast concrete side wall, the main reinforcement bars of the side wall 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. After the reinforcement of the bottom slab is arranged to the mechanical joint, a form is arranged and concrete is poured. The precast concrete side walls are joined together and integrated. While A method for constructing an underground structure is provided, comprising a third step of constructing a bottom slab that will become the main structure.

[0010] In the invention described in claim 1, the precast concrete side wall is Natural ground side Because the structure uses steel as the core material instead of main reinforcement, the cross-sectional area of ​​the steel is increased compared to conventional reinforced concrete structures that use deformed steel bars as the main reinforcement, and the bending strength of the precast concrete as a whole is increased. As a result, it is possible to make the precast concrete components thinner and lighter, reducing costs, and it can also be used for underground structures at great depths, expanding the applicability of this construction method.

[0011] In addition, the steel material used as the core material of the precast concrete members extends upward from the upper end surface and forms a steel section 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 large soil and water pressure is applied to the steel section for the earth retaining wall from the lateral direction, the steel material extending continuously from the core material can ensure continuous resistance in the depth direction, preventing damage such as cracks in the precast concrete members.

[0012] Precast concrete sidewall So, As a core material to replace the main reinforcement on the natural ground side where tensile stress is dominant Made of T-shaped wire By using steel, the bending strength of the precast concrete side walls is increased, making it possible to more reliably make the precast members thinner and lighter.

[0013] before Record T The flanges of the steel sections face the outer surface of the precast concrete sidewall, and the webs are positioned so that they protrude inward, so that the center of gravity of the steel material is closer to the outer surface of the precast concrete sidewall than when H-shaped steel is used, and so for the same cross-sectional area, the effective height is greater, which is advantageous in terms of design. Also, because the bending strength is greater than that of conventional reinforced concrete structures using deformed steel bars, the need for support using braces during internal excavation can be simplified. Furthermore, in the production of precast concrete sidewalls, the base slab constructed from cast-in-place concrete can be used as a support for the concrete structure. Department and A large number of mechanical joints are installed as the joints in the concrete structure. In this case, compared to when H-shaped steel is used as the steel material, there is no interference between the steel material and the mechanical joints, and it is possible to arrange the mechanical joints at a specified pitch, which improves the filling properties of the concrete.

[0014] According to claim 2 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 and a bottom plate, comprising the steps of: The construction sites of the side walls are as follows: Natural ground side Instead of main reinforcement, steel is placed as the core material, A T-shaped steel is used as the steel material, and the T-shaped steel is arranged so that a flange portion faces the outer surface side of the precast concrete side wall and a web portion protrudes inward,a first step of erecting precast concrete side walls, which will form the main structure, into the ground, with the steel material extending upward from the upper end surface to form a retaining wall steel portion for lateral resistance such as soil and water pressure, and erecting precast concrete intermediate walls or intermediate columns, which will form the main structure, into the ground, with steel material instead of main reinforcement being placed as core material at the construction site of the intermediate walls or intermediate columns, with the steel material extending upward from the upper end surface to form a retaining wall steel portion for lateral resistance such as soil and water pressure, excavating and removing the ground up to the position where the top plate between these spans will be constructed, constructing the top plate portion, which will form the main structure, between the precast concrete side walls, and backfilling 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; At the bottom plate construction site In this case, when connecting the bottom slab and the precast concrete side wall, the main reinforcement bars of the side wall 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. After the reinforcement of the bottom slab is arranged to the mechanical joint, a form is arranged and concrete is poured. The precast concrete side walls and the precast concrete intermediate walls or intermediate columns are joined and integrated. While A method for constructing an underground structure is provided, comprising a third step of constructing a bottom slab that will become the main structure.

[0015] The invention described in claim 2 above is a construction method for an underground structure having intermediate walls or intermediate columns between side walls. When intermediate walls or intermediate columns are present between side walls, it is possible to excavate the ground for constructing the top plate between the side walls and then construct the top plate, but in this case, the scale of excavation will be large and the aboveground occupation period will be long. Therefore, by constructing each span separated by both side walls and intermediate walls or intermediate 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 part below the top plate by backfilling, it is possible to shorten the aboveground occupation period.

[0016] Claim 3 As the present invention, the precast concrete side walls and / or the precast concrete intermediate walls or intermediate columns are provided with a plurality of steel piles protruding downward from the lower end surfaces for vertical bearing capacity and lateral resistance such as soil and water pressure.、2 A method for constructing an underground structure as described above is provided.

[0017] The above claims 3 In the described invention, a plurality of steel piles are provided on the precast concrete side walls and / or precast concrete intermediate walls or intermediate columns so as to protrude downward from the bottom end surface 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.

[0018] Claim 4 As the present invention related to the above, the precast concrete side wall and / or the precast concrete intermediate wall or intermediate column has a film attached or a release agent applied at least to the inner wall surface side. 3 A method for constructing an underground structure as described above is provided.

[0019] The above claims 4 In the described invention, 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. During construction, the surface of the precast concrete members becomes dirty with muddy water or soil cement, so the inner wall surface can be easily finished neatly by peeling off the film after the construction is completed or by applying a release agent so that it can be easily washed away.

[0020] Claim 5 The present invention relates to Natural ground side Instead of main reinforcement, steel is placed as the core material, A T-shaped steel is used as the steel material, and the T-shaped steel is arranged so that a flange portion faces the outer surface side of the precast concrete side wall and a web portion protrudes inward,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 the precast concrete side walls are provided with a plurality of steel piles protruding downward from the lower end surface for vertical bearing capacity and lateral resistance such as soil and water pressure, a top plate portion provided at the upper portion between the precast concrete side walls, and a bottom plate portion provided at the lower portion between the precast concrete side walls and constructed of cast-in-place concrete. A structure constructed by the method for constructing a structure according to claim 1. An underground structure is provided.

[0021] Claim 6 The present invention relates to a method for constructing a structure having one or more precast concrete intermediate walls or intermediate columns between the precast concrete side walls, and wherein the precast concrete intermediate walls or intermediate columns have steel materials arranged as core materials instead of main reinforcement, and the steel materials extend 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 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. 5 An underground structure as described is provided. Effect of the Invention

[0022] As described above in detail, according to the present invention, by making the precast concrete side walls thinner, it is possible to reduce costs and expand applicability, and it is also possible to prevent damage to the precast concrete side walls even when there is a large amount of soil covering. [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a vertical cross-sectional view showing an underground structure 1A according to the present invention. [Diagram 2] This is the construction procedure for underground structure 1A (part 1). [Diagram 3] 1 shows a precast concrete side wall 2, 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. [Figure 4]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. [Diagram 5] 5 is a view taken along the line VV in FIGS. 3 and 4. FIG. [Figure 6] This is a bending moment diagram of a box culvert. [Figure 7] A cross-sectional view of the precast concrete side wall 2 at the bottom slab joint. [Figure 8] 1 is a cross-sectional view showing a main portion of an example of a waterproof structure between precast concrete side walls 2, 2. FIG. [Figure 9] Construction procedure for underground structure 1A (part 2). [Figure 10] Construction procedure for underground structure 1A (part 3). [Figure 11] Construction procedure for underground structure 1A (part 4). [Figure 12] 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. [Figure 13] 2 is a cross-sectional view of a main portion showing the joint structure between a precast concrete side wall 2 and a top slab 3. FIG. [Figure 14] Construction procedure for underground structure 1A (part 5). [Figure 15] Construction procedure for underground structure 1A (part 6). [Figure 16] Construction procedure for underground structure 1A (part 7). [Figure 17] Construction procedure for underground structure 1A (part 8). [Figure 18] 4 is a longitudinal cross-sectional view of a main portion showing the joint with the bottom plate portion 4. FIG. [Figure 19] A vertical cross-sectional view showing an underground structure 1B according to a second embodiment. [Figure 20] 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. [Figure 21] 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. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0025] [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 material instead of main reinforcement, and the steel materials 5 extend upward from the upper end surface to form a retaining wall steel material section 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 capacity and lateral resistance such as soil and water pressure, a top slab portion 3 provided at the upper portion between the precast concrete side walls 2, 2, and a bottom slab portion 4 provided at the lower portion between the precast concrete side walls 2, 2 and constructed of cast-in-place concrete.

[0026] Below, the underground structure 1A will be described in detail in accordance with the construction sequence.

[0027] (1st 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.

[0028] First, as shown in FIG. 2, excavation is carried out at the side wall construction site using an excavator for erecting the precast concrete side wall 2, and then the precast concrete side wall 2 is erected.

[0029] As shown in Figures 3 to 5, the precast concrete side wall 2 has steel materials 5, 5... arranged as core material instead of main reinforcement, and the steel materials 5 are arranged extending upward from the upper end surface and function as a retaining wall steel material section 5B for lateral resistance such as soil and water pressure until the top plate section 3 is constructed.The precast concrete side wall 2 is provided with a plurality of steel piles 6, 6... protruding downward from the lower end surface to provide vertical bearing capacity and lateral resistance such as soil and water pressure.

[0030] The steel material 5 is formed continuously from 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.

[0031] As shown in Figure 5, the steel material 5 is preferably arranged in place of the main reinforcements arranged on the ground side of the precast concrete side wall 2 and on the inside of the structure, and it is preferable to arrange reinforcing bars made of deformed steel bars on the inside of the structure.

[0032] By placing the steel material 5 as a core material instead of the main reinforcement on the natural ground side, in a box culvert structure such as the underground structure 1A according to the present invention, the strength of the side wall where tensile stress predominates can be increased as shown in Fig. 6, and the cross-sectional area of ​​the steel material increases and the bending strength increases for the same cross-sectional area compared to a reinforced concrete structure using deformed steel bars. As a result, the precast concrete side wall 2 can be made thinner and lighter, and it can be used for underground structures at great depths, expanding the applicability of this construction method.

[0033] Moreover, the steel material 5 is extended to a length that reaches the ground above the upper end surface of the precast concrete side wall 2, and a plate material such as a steel sheet pile is installed on the natural ground side, so that it can be used as an earth retaining wall. In order 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 divided from the core steel material part 5A as shown in Fig. 3, or a structure in which the ends of the divided steel material are spliced ​​and joined together by a splice plate 7 at a position protruding above the upper end surface of the precast concrete side wall 2 as shown in Fig. 4.

[0034] In this way, the steel 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 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 large soil and water pressure is applied to the retaining wall steel section 5B from the lateral direction, the steel 5 extending continuously from the core material can ensure continuous resistance in the depth direction, preventing damage such as cracks in the precast concrete side wall 2.

[0035] The steel material 5 may be any known shaped 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 Fig. 5, the T-shaped steel should be arranged so that the flange portion 5f faces the outer surface side (the natural ground side) of the precast concrete side wall 2 and the web portion 5w protrudes inward.

[0036] By arranging the steel material 5 consisting of a 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 an H-shaped steel is arranged with its flange portion facing the outer surface of the precast concrete side wall 2, so that for the same cross-sectional area, the effective height is greater in the case of using a T-shaped steel, which is advantageous in terms of design.

[0037] 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.

[0038] Furthermore, in the manufacture of the precast concrete side wall 2, mechanical joints 8, 8... are installed at the positions corresponding to the arrangement of the main reinforcement bars as joints with the bottom slab 4 and top slab 3 constructed by on-site poured concrete, as shown in FIG. 7. A ), when H-shaped steel is used as the steel material, the mechanical joints 8 may interfere with the flanges of the H-shaped steel and may not be able to be positioned to correspond to the main reinforcement, resulting in the spacing between adjacent mechanical joints 8, 8 becoming too close. B ), when T-shaped steel is used as the steel material 5, the steel material 5 and the mechanical joints 8 can be arranged at approximately equal intervals in positions corresponding to the main reinforcement without interfering with each other, resulting in good concrete filling properties.

[0039] It is desirable that at least the inner wall surface of the precast concrete side wall 2 be provided with a film or coated with a release agent.

[0040] As shown in Figure 3, the precast concrete side wall 2 and the steel pile 6 are fixed by bolts via base plates 6a provided at the ends of the steel piles 6 to insert fittings 9 buried to a specified depth from the bottom end surface of the precast concrete side wall 2, or, although not shown, the steel piles 6 are detachably attached by being spliced ​​via a splice plate to steel material that is buried to a specified depth from the bottom end surface of the precast concrete side wall 2 and has a bearing plate or stud provided at the embedded tip.

[0041] When erecting the structure, a predetermined 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 any restrictions, but it is particularly preferable to use the suitable water-stopping structure disclosed in JP 2011-122386 A. The waterproof structure of the precast concrete side wall 2 disclosed in the publication, as shown in Figure 8, is such that on the opposing sides of adjacent precast concrete side walls 2A, 2B, a space 11 is formed which is sealed off from the surroundings by engagement between a first-side connector metal fitting 10A embedded in the side of one precast concrete side wall 2A and a second-side connector metal fitting 10B embedded in the side of the other precast concrete side wall 2B, and within this sealed space 11, opposing grooves 12 are formed in the precast concrete side walls 2A, 2B along the longitudinal direction of the members, a waterstop plate 13 is inserted and installed spanning between these grooves 12, 12, and grout material 14 is filled into the sealed space 11.

[0042] Once the above steps have been completed, the ground between the retaining wall steel parts 5B, 5B protruding 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 enables the construction of the top plate part 3 in the next step.

[0043] Once excavation is complete, a top plate 3 is constructed between the precast concrete side walls 2, 2, as shown in Figure 11. The top plate 3 can be constructed by a precast method in which a precast concrete top plate is erected, or by a cast-in-place method using cast-in-place concrete.

[0044] When the top plate 3 is constructed by the precast method, the joint with the precast concrete side wall 2 is preferably performed in a rod jointing manner, for example, as shown in Fig. 12(A), in which an anchor rod 21 is buried in the upper part of the precast concrete side wall 2 and a screw coupler 22 is provided on the upper part of the anchor rod 21, 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 coupler 22, and connected to the screw coupler 22, and then the upper part is fastened. Alternatively, as shown in Fig. 12(B), in order to absorb construction errors, 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, and mortar is injected into the sleeves 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 construction errors of the top plate 3 can be absorbed by this portion.

[0045] In addition, a method of constructing the top plate 3 by the on-site casting method involves, for example, arranging the side wall main reinforcing bars 27, 27... on the upper surface or upper part of the side of the precast concrete side wall 2 and providing a mechanical joint 28 at their tips, joining a mechanical joint 30 attached to the tip of the top plate main reinforcing bar 29 to this mechanical joint 28 to arrange the reinforcement of the top plate 3, then setting formwork and pouring concrete, as shown in Figure 13.

[0046] 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 material 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 Fig. 12, a fitting part 31 that can fit with the retaining wall steel material part 5B is provided in the precast concrete top plate 3 along the vertical direction, and after the precast concrete top plate 3 is installed while fitting the retaining wall steel material part 5B into this fitting part 31, the gap between the retaining wall steel material part 5B and the fitting part 31 is filled with mortar.

[0047] Once the top plate 3 has been installed as described above, as shown in Figure 14, the portion of the steel material 5B for the retaining wall that protrudes above the top plate 3 is removed by gas cutting or the like, and then the area is backfilled to release the aboveground area.

[0048] (2nd process) Once the shallower portion of the top plate 3 has been completed in advance in 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.

[0049] (3rd step) 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, as shown in Figure 17. The bottom slab 4 and the precast concrete side walls 2 are joined, for example, as shown in Figure 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 these mechanical joints 34 to arrange the reinforcement of the bottom slab 4, followed by setting up formwork and pouring concrete.

[0050] Next, as a final finishing step, if a film has been applied beforehand to the inner wall surface of the precast concrete side wall 2, this is peeled off to expose the clean concrete surface. If a stripping agent has been applied, dirt such as muddy water and soil cement is removed by spraying with jet water or cleaning with a brush.

[0051] [Second embodiment example] In the above example, the top plate portion 3 and the bottom plate portion 4 are bridged between the two side walls 2, 2. However, as shown in Figure 19, it is also possible to create an underground structure 1B in which the two side walls 2, 2 are separated by a precast concrete intermediate wall or intermediate column 15. The construction procedure is basically the same as in the first embodiment described above. However, in cases where there is no construction yard, etc., a stepwise construction may be performed in which steel materials are placed as core materials instead of at least a portion of the main reinforcement bars, and an intermediate wall 15 is used in which the steel materials extend upward from the upper end surface to provide lateral resistance such as soil-water pressure. In the first step, the top plate 3 of the left span portion between the left side wall 2 and the intermediate wall 15 is constructed first, and only the retaining wall steel material 5B of the left side wall 2 is removed and backfilled. 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 steel materials do not extend upward from the upper end surface may be placed, and the left span portion and the right span portion may be constructed simultaneously.

[0052] Furthermore, in the third step, when pouring concrete into the bottom 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 bottom slab so that the poured concrete can be reinforced continuously without interruption in the precast concrete intermediate wall or intermediate column 15.

[0053] [Other examples] (1) In the above embodiment, 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.

[0054] (2) In the above embodiment, both the precast concrete side wall 2 and the precast concrete intermediate wall or intermediate column 15 are provided with a plurality of steel piles 6 protruding downward from their lower end surfaces, but the steel piles 6 may be eliminated and the entire embedded length may be made of precast concrete members.

[0055] (3) In the above-described 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 retaining wall steel materials 5B for lateral resistance to soil and water pressure, etc. However, depending on soil and water pressure, etc., one or more steel materials 5 may be allowed to extend upward from the upper end surface, and the remaining steel materials 5 may not be allowed to extend upward. [Explanation of symbols]

[0056] 1A, 1B... Underground structure, 2... Precast concrete side wall, 3... Top slab, 4... Bottom slab, 5... Steel material, 5A... Core steel material, 5B... Retaining wall steel material, 6... Steel pile

Claims

1. 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.

2. 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.

3. 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.

4. A 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.

5. An underground structure constructed by the method of constructing a structure as described in claim 1, characterized in that the structure comprises precast concrete side walls having a steel core material in place of the main reinforcement on the ground side, a T-shaped steel being used as the steel material, the T-shaped steel being arranged so that its flange portion faces the outer surface of the precast concrete side wall and its web portion protrudes inward, the steel material extending upward from its 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 protruding downward from its lower end surface for vertical bearing capacity and lateral resistance such as soil and water pressure, a top slab portion provided at the upper portion between the precast concrete side walls, and a bottom slab portion provided at the lower portion between the precast concrete side walls and constructed of cast-in-place concrete.

6. 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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