JP2022010955A - Construction method of underground structure in acidic soil - Google Patents

Abstract

To provide a construction method of an underground structure in acidic soil, which enables construction of an underground structure completely shielded from acidic soil in acidic soil ground, and also enables construction of the underground structure with excellent workability.SOLUTION: When excavating the ground 2 of acid soil and constructing an underground structure made of reinforced concrete in the ground, a continuous seamless acid-resistant layer 8 by spraying acid-resistant mortar is formed on an inner surface 9a of an outer formwork 9 for constructing the underground structure to form the part of the underground structure facing the acid soil ground.SELECTED DRAWING: Figure 6

Description

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to construct an underground structure completely shielded from acidic soil in the ground of acidic soil, and in acidic soil capable of constructing the underground structure with excellent workability. Regarding the construction method of the underground structure to.

In urban ground, sulfate ions flow into groundwater from domestic wastewater, hydrogen sulfide is generated by biochemical metabolism by sulfate-reducing bacteria and sulfur-oxidizing bacteria, and sulfuric acid is generated from the generated hydrogen sulfide. , May show strong acidity.

Rain absorbs sulfur dioxide, nitrogen oxides, hydrocarbons, methane, carbon monoxide, etc. in the air, and becomes thinly acidic water that falls on the ground. Rainwater itself is weakly acidic, but hydrogen ions contained in it are accumulated in the ground, and the ground is acidified.

Excavation of ground containing a large amount of pyrite may acidify the groundwater. This is a result of rocks containing sulfide being oxidized by contact with oxygen and eluted in groundwater, and in hot spring areas and acidic bedrock areas, it shows strong acidity with a considerably low pH.

General cement-based materials are easily deteriorated by acidity such as sulfuric acid, and corrosion progresses in a short time. For example, when an underground structure made of reinforced concrete is constructed in strong acid soil, the hardened cement on the surface of the concrete exposed to strong acid becomes fragile due to the reaction with acid, loses its binding force, and is lost together with the aggregate. To go. By repeating this, the concrete becomes thin and the yield strength decreases.

In the ground of such acidic soil, it is desirable to construct the underground structure with acid-resistant concrete. However, acid-resistant concrete is more expensive than ordinary concrete because it is necessary to use various admixture materials to ensure workability in addition to acid-resistant admixtures (silica fume, blast furnace slag powder, etc.).

Patent Documents 1 and 2 are known regarding the construction of structures in consideration of acidic soil. In Patent Document 1, "Method for constructing acid-resistant sabo dam and foundation block", a foundation block made of resin concrete is laterally connected to a portion on the front surface side of the dam to be constructed, and the foundation block is connected on the back surface side. It is supported by a support member to form a formwork, and cast-in-place concrete is placed in the formwork to the upper end edge of the foundation block or its lower part to form a first-stage dam, and then by the same means as described above. The dams in the first and third stages are formed and constructed in sequence.

In the "corrosion-proof buried formwork" of Patent Document 2, the formwork body is methacrylic resin-based resin concrete, urethane resin-based resin concrete, epoxy resin-based resin concrete, vinyl ester resin-based resin concrete, epoxy resin-based resin concrete or vinyl ester resin. It is molded from any of the resin concrete, and a fixing means for fixing the concrete is provided on the inner surface of the formwork body, and the formwork body is provided with a transparent member penetrating the concrete inside.

Japanese Unexamined Patent Publication No. 8-338014 Japanese Unexamined Patent Publication No. 2000-17636

In both Patent Documents 1 and 2, as a measure against acidic soil, a formwork made of resin concrete is used to place cast-in-place concrete or concrete, and in Patent Document 1, blocks are connected. Then, it is decided to connect the so-called precast formwork body.

When forming a formwork by connecting blocks or precast formwork bodies in this way, a gap that becomes a seam is created between the blocks and between the formwork bodies, and the acidic soil is acidic through this gap. It is not possible to prevent the groundwater from seeping inside the formwork. For this reason, there is a problem that the concrete placed in the formwork is exposed to an acidic component and deteriorates.

In addition, the resin concrete block and precast formwork body are considerably heavier than the commonly used plate-shaped formwork, and surround the entire structure to be constructed to shield it from acidic soil. Arranging and stacking a large number of pieces in this way required a great deal of labor and time, and the workability was not good.

The present invention has been devised in view of the above-mentioned conventional problems, and it is possible to construct an underground structure completely shielded from acidic soil in the ground of acidic soil, and it has excellent workability. It is an object of the present invention to provide a method of constructing an underground structure in acidic soil capable of constructing the underground structure.

The method for constructing an underground structure in acidic soil according to the present invention is the above-mentioned method of constructing an underground structure made of reinforced concrete in the ground by excavating the ground of the acidic soil and facing the ground of the acidic soil. It is characterized by forming a continuous seamless acid-resistant layer by spraying acid-resistant mortar on the site of the underground structure.

An excavation process of excavating the ground of acidic soil to form a construction space of a size surrounding the underground structure to be constructed, and construction of the underground structure in the construction space facing the ground of acidic soil. The acid-resistant mortar is sprayed to form a seamless and continuous acid-resistant layer by using the inner surface of the outer form that is shielded from acidic soil as a spraying surface and the formwork step of installing the outer form for use. In the spraying process, on the inner surface side of the outer formwork, reinforcement arrangement of reinforcing bars and installation of a formwork for constructing an additional underground structure are performed, and the formwork is adhered to the acid-resistant layer and concrete is cast. A construction step for constructing an underground structure, a demolding step for removing the outer formwork from the underground structure, and a backfilling step for backfilling the surroundings of the underground structure having an acid-resistant layer. It is characterized by including (first embodiment).

An excavation process that excavates the ground of acidic soil to form a construction space of a size surrounding the underground structure to be constructed, and an underground structure including a reinforcing bar arrangement and an outer frame in the construction space. At least one of the frame process of installing the mold for construction, the construction process of placing concrete in the construction space to construct the underground structure, and the mold for constructing the underground structure. The acid-resistant mortar is sprayed to form a seamless and continuous acid-resistant layer by using the part of the underground structure facing the ground of the acidic soil as a spraying surface and the demolding step of demolding the outer mold. It is characterized by including a spraying step of forming and a backfilling step of backfilling the surroundings of the underground structure having the acid resistant layer (second embodiment).

An excavation process of excavating the ground of acidic soil to form a construction space of a size surrounding the underground structure to be constructed, and construction of the underground structure in the construction space facing the ground of acidic soil. The formwork process for installing the outer formwork for use and the continuous acid-resistant layer without seams by spraying the acid-resistant mortar with the inner surface of the outer formwork shielded from acidic soil as the spray surface. The spraying process to be formed, the reinforcement arrangement of the reinforcing bars and the installation of the formwork for constructing an additional underground structure are performed on the inner surface side of the outer-circumference formwork, and the concrete is poured by adhering to the acid-resistant layer. It is characterized by including a construction step of constructing the above-mentioned underground structure (third embodiment).

After the excavation step and before the formwork step, the waste concrete of the underground structure is constructed of acid-resistant concrete on the ground of the construction space, and the outer formwork or the outer form is formed on the waste concrete. It is characterized by installing the outer-circumferential throw-away form.

The acid-resistant mortar has latent water hardness with more than 40 to 50% by mass of Portland cement or blast furnace cement, 10 to 30% by mass of silica fume, which is an admixture having pozzolan reactivity and exhibiting initial strength. The blast furnace slag fine powder, which is an admixture that develops medium- to long-term strength, is composed of 20 to 25% by mass, and is composed of the Portland cement or blast furnace cement, the silica fume having the initial strength development, and the blast furnace having the medium- to long-term strength development. It is characterized by being prepared with an acid-resistant cement composition having a content of 100% by mass with slag fine powder.

The acid-resistant mortar has latent water hardness with more than 40 to 50% by mass of Portland cement or blast furnace cement, 10 to 30% by mass of silica fume, which is an admixture having pozzolan reactivity and exhibiting initial strength. A high-performance water reducing agent or fluidizing agent added in an amount of 20 to 25% by mass of blast furnace slag fine powder, which is an admixture exhibiting medium- to long-term strength, and 0.1 to 2% by mass based on the mass of the Portland cement or blast furnace cement. The admixture is 100% by mass of the Portland cement or blast furnace cement, the silica fume having the initial strength developing property, the blast furnace slag fine powder having the medium- to long-term strength developing property, and the admixture. It is characterized by being prepared with an acid resistant cement composition.

In the method of constructing an underground structure in acidic soil according to the present invention, it is possible to construct an underground structure completely shielded from acidic soil in the ground of acidic soil, and spraying acid resistant mortar. The underground structure can be constructed with excellent workability.

It is explanatory drawing explaining the reinforced concrete underground structure constructed in the ground of the acidic soil by the construction method of the underground structure in the acidic soil which concerns on this invention. It is explanatory drawing which shows the excavation process of 1st Embodiment of the construction method of the underground structure in the acidic soil which concerns on this invention. It is explanatory drawing which shows the state of constructing the waste concrete following the excavation process shown in FIG. It is explanatory drawing which shows the formwork process following the construction of the waste concrete shown in FIG. It is explanatory drawing which shows the spraying process following the formwork process shown in FIG. It is explanatory drawing which shows the construction process following the spraying process shown in FIG. It is explanatory drawing which shows the demolding process and backfilling process following the spraying process shown in FIG. It is explanatory drawing which shows after the completion of the excavation step-demolding step of the 2nd Embodiment of the construction method of the underground structure in the acidic soil which concerns on this invention. It is explanatory drawing which shows the completion of the spraying process, and the backfilling process which follow after the completion of the demolding process shown in FIG. It is explanatory drawing which shows after the completion of the excavation process-spraying process of the 3rd Embodiment of the construction method of the underground structure in the acidic soil which concerns on this invention. It is explanatory drawing which shows the completion of the construction process which follows after the completion of the spraying process shown in FIG.

Hereinafter, a preferred embodiment of the method for constructing an underground structure in acidic soil according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows an underground structure made of reinforced concrete constructed in the ground of acidic soil by the construction method according to the present invention, and FIG. 1 (A) is a side sectional view and FIG. 1 (B). Is a cross-sectional view taken along the line AA in FIG. 1 (A).

The underground structure 1 is constructed in a construction space 3 formed by excavating the ground 2 of acidic soil. The underground structure 1 has a pressure-resistant concrete 4 provided on the ground formed by excavation work under the construction space 3, a pressure-resistant plate 5 constructed on top of the waste concrete 4, and a pressure-resistant concrete 4. A plurality of columns (not shown) arranged around the plate 5 and an outer wall 6 provided between the columns, and a plurality of beams (not shown) erected between the columns facing each other and provided on the beams. It is composed of a ground floor 7 that closes the inside surrounded by the outer wall 6. The underground structure 1 is constructed by casting ordinary concrete in the field.

The outer surface of the outer wall 6 and the outer surface of the pillar facing the ground 2 of the acidic soil are hereinafter referred to as the outer circumference of the underground structure 1. The inner surface of the outer wall 6 and the inner surface of the pillars that do not face the acidic soil other than the outer circumference of the underground structure 1 are hereinafter referred to as the inner surface of the underground structure 1.

An acid-resistant layer 8 that surrounds the underground structure 1 without gaps and shields it from the surrounding acidic soil is continuously and seamlessly formed around the outer circumference of the underground structure 1. The acid-resistant layer 8 is continuously and seamlessly formed around the outer circumference of the underground structure 1 by spraying the acid-resistant mortar.

The discarded concrete 4 is constructed by casting acid-resistant concrete in the field. If the layer of acidic soil is shallow and the discarded concrete 4 is not affected by the acidic soil, the discarded concrete 4 may be constructed of ordinary concrete.

Acid-resistant mortar and acid-resistant concrete
(1) Portland cement or blast furnace cement with more than 40 to 50% by mass, 10 to 30% by mass of silica fume, which is an admixture having pozzolan reactivity and exhibiting initial strength, and medium- to long-term strength with latent hydrohardness. It is composed of 20 to 25% by mass of blast furnace slag fine powder, which is an admixture that expresses Prepared by adding sand and / or aggregate to the acid-resistant cement composition to be mass%, or
(2) Portland cement or blast furnace cement with more than 40 to 50% by mass, 10 to 30% by mass of silica fume, which is an admixture that has pozzolan reactivity and develops initial strength, and medium- to long-term strength with latent water hardness. 20 to 25% by mass of blast furnace slag fine powder, which is an admixture that expresses The acid-resistant cement composition, which is 100% by mass of Portland cement or blast furnace cement, silica fume having initial strength development, blast furnace slag fine powder having medium- to long-term strength development, and sand and admixture. / Or it is desirable to add aggregate to prepare.

These acid-resistant cement compositions (1) and (2) are inexpensive, generate less rebound and dust, and are suitable for spraying work.

In these acid-resistant cement compositions, silica fume and blast furnace slag fine powder consume calcium hydroxide produced by the hydration reaction of water and cement by the pozzolan reaction and the latent hydraulic reaction, so that it can be combined with sulfuric acid. Reduce the amount of dihydrate gypsum produced in the reaction to build acid resistance.

However, the acid-resistant mortar and the acid-resistant concrete are not limited to these cement compositions, and of course, other cement compositions may be used.

(First Embodiment) FIGS. 2 to 7 sequentially show procedures of a method of constructing an underground structure in acidic soil according to the first embodiment. In these figures, only a part of the construction part is shown.

When constructing an underground structure 1 made of reinforced concrete in the ground 2 of acidic soil, an excavation process is first carried out as shown in FIG.

The ground 2 of acidic soil is excavated to form a construction space 3 having a size surrounding the underground structure 1 to be constructed. In the excavation process, a slope 2a extending from the bottom to the top is formed in order to secure a work space for efficiently performing the formwork process described later with a minimum amount of excavated soil.

Next, as shown in FIG. 3, after the excavation process and before the subsequent formwork process, the discarded concrete of the underground structure 1 is placed on the ground formed by the excavation work under the construction space 3. 4 is constructed of acid-resistant concrete.

Next, as shown in FIG. 4, after the waste concrete 4 is constructed, the formwork process is carried out. In the construction space 3, the outer formwork 9 for constructing an underground structure is installed on the waste concrete 4 facing the ground 2 of the acidic soil.

The outer formwork 9 for constructing an underground structure means an outer wall 6 outer surface facing the ground 2 of acidic soil and an outer wall formwork and an outer formwork for forming a pillar outer surface. For the outer wall 6 and the pillar, the wall outer formwork and the pillar outer formwork are combined with the wall inner formwork and the pillar inner formwork (hereinafter referred to as an inner formwork 10 for constructing an underground structure, see FIG. 6). Then, the formwork for placing concrete is constructed. As all of these formwork, commonly used wooden or steel plate-shaped formwork is used.

The outer formwork 9 is supported in a state of standing on the waste concrete 4 at a position positioned by the positioning material 15 on the waste concrete 4 via a support material 11 temporarily provided at an appropriate position on the surrounding ground 2. The concrete. In the first embodiment, as will be described later, all the formwork including the outer formwork 9 for constructing the underground structure is later demolded as a temporary material.

Next, as shown in FIG. 5, the step of spraying the acid-resistant mortar is carried out. The acid-resistant mortar is sprayed onto the sprayed surface of the underground structure 1 facing the ground 2 of the acidic soil, that is, the outer circumference (outer wall outer surface and pillar outer surface) of the underground structure 1 as a spray surface. It is applied to form a seamless and continuous acid resistant layer 8 around the outer circumference of the.

In the first embodiment, since the underground structure 1 to be constructed is incomplete, the outer formwork 9 for constructing the underground structure that forms the outer circumference of the underground structure 1 instead of the outer circumference of the underground structure 1. With the inner surface 9a of the outer peripheral mold 9 shielded from the acidic soil as the spraying surface, acid-resistant mortar is sprayed on the spraying surface to form a seamless and continuous acid-resistant layer 8. .. The spraying work itself may be performed by a generally known method.

The surface of the acid-resistant layer 8 formed of the sprayed acid-resistant mortar has unevenness, and the adhesion to the ordinary concrete to be post-cast is good as it is. It is preferable to dispose an anchor 12 firmly fixed to the ordinary concrete to be cast, and therefore to the underground structure 1.

For example, a reinforcing bar or the like is used as the anchor 12, and the anchor 12 is inserted after the sprayed acid-resistant mortar is cured to some extent.

At this time, it is desirable that the thickness of the acid-resistant mortar sufficient to obtain the required acid-resistant action is secured between the tip of the anchor 12 to be inserted and the inner surface 9a (spraying surface) of the outer formwork 9. ..

Of course, acid-resistant mortar may be constructed using a quick-setting agent. When a quick-setting agent is not used, in order to prevent cracking due to temperature stress and drying shrinkage, it is recommended to sprinkle water and perform moist curing for 5 days or more at the time when condensation starts several hours after spraying. preferable. Even when a quick-setting agent is used, it is desirable to perform the same curing in order to prevent cracking and promote strength development.

After the acid-resistant layer is cured, the construction step of the underground structure 1 is carried out as shown in FIG. The underground structure 1 is an additional underground structure that forms the inside of the underground structure 1 by arranging the reinforcing bars of the underground structure 1 on the inner surface 9a side of the outer formwork 9 and sandwiching the reinforcing bars. An inner formwork 10 for construction is installed, and ordinary concrete constituting the underground structure 1 is placed between the outer formwork 9 and the inner formwork 10. Reinforcing bar arrangement work may be performed during curing of the acid-resistant mortar.

The ordinary concrete adheres to the acid-resistant layer 8 on the inner surface 9a of the outer formwork 9, and the acid-resistant layer 8 is integrated with the ordinary concrete of the underground structure 1. It is desirable to use the anchor 12 because the integration of the acid resistant layer 8 and the underground structure 1 is enhanced.

The placement of ordinary concrete also promotes the wet curing of the acid-resistant mortar of the acid-resistant layer 8.

After the curing and hardening of the ordinary concrete of the underground structure 1 is completed, the demolding step is carried out as shown in FIG.

In this demolding step, the unnecessary formwork including the outer formwork 9 is demolded from the underground structure 1. By demolding, the acid-resistant layer 8 is exposed facing the ground 2 of the acidic soil.

Subsequently, a backfilling step of backfilling around the underground structure 1 having the acid resistant layer 8 (indicated by an arrow B in the figure) is carried out.

It is desirable that the backfill soil to be backfilled in the space between the acid-resistant layer 8 and the slope 2a, which is used as the work space for the formwork process, on the waste concrete 4 is not acidic soil.

In the method for constructing an underground structure in acidic soil according to the first embodiment, the inner surface 9a of the outer peripheral mold 9 for forming the outer circumference of the underground structure 1 facing the ground 2 of the acidic soil is used as a spray surface for mortar. Since the acid-resistant mortar was sprayed on the sprayed surface to form a seamless and continuous acid-resistant layer 8 on the underground structure 1, the underground structure completely shielded from the acidic soil in the ground 2 of the acidic soil. 1 can be constructed, and the underground structure 1 can be constructed with excellent workability by spraying acid-resistant mortar as compared with the background technique of constructing blocks and mold bodies side by side.

Further, since the anchor 12 for fixing the acid-resistant layer 8 to the underground structure 1 is provided in the outer formwork 9, the acid-resistant layer 8 formed by spraying and the underground structure 1 can be firmly integrated. ..

(Second Embodiment) FIGS. 8 and 9 sequentially show the procedure of the method of constructing an underground structure in acidic soil according to the second embodiment. In these figures, only a part of the construction part is shown.

The second embodiment is different from the first embodiment in that the underground structure 1 is constructed in advance and the acid resistant layer 8 is later constructed.

After completing the excavation process and the construction of the discarded concrete 4, the formwork process is carried out.

In the second embodiment, in the formwork process, the reinforcing bars of the underground structure 1 are arranged on the waste concrete 4 in the construction space 3 so that the construction of the underground structure 1 can be completed in advance, and the reinforcing bars are interposed. Both the outer formwork 9 and the inner formwork 10 for constructing the underground structure are installed so as to be sandwiched between the two.

In the second embodiment, since both the inner loop and outer loop formwork 9 and 10 are used at the same time, the support material 11 from the ground 2 does not have to be used. Also in the second embodiment, all the formwork including the inner loop and outer loop formwork 9 and 10 are later demolded as temporary materials.

Next, the construction process of the underground structure is carried out. In the second embodiment, ordinary concrete is placed between the assembled inner loop and outer loop formwork 9 and 10, and the underground structure 1 is constructed in advance in the construction space 3.

Next, among the formwork for constructing the underground structure, at least the outer formwork 9 is demolded. As a result, as shown in FIG. 8, the outer circumference of the underground structure 1 is exposed facing the ground 2 of the acidic soil. The inner loop formwork 10 is also appropriately demolded before and after the phase.

Next, as shown in FIG. 9, the step of spraying the acid-resistant mortar is carried out. Similar to the first embodiment, the acid-resistant mortar is sprayed on the site of the underground structure 1 facing the ground 2 of the acidic soil, that is, the outer circumference (outer wall outer surface and pillar outer surface) of the underground structure 1 as a spray surface. It is sprayed on the surface to form a continuous seamless acid resistant layer 8 around the outer circumference of the underground structure 1. The acid-resistant mortar to be sprayed adheres to ordinary concrete around the outer circumference of the underground structure 1, and the acid-resistant layer 8 is integrated with the underground structure 1.

It is preferable to dispose an anchor 12 around the outer circumference of the underground structure 1 to firmly fix the acid-resistant layer 8 formed of the sprayed acid-resistant mortar to ordinary concrete, and therefore to the underground structure 1. .. It is desirable to use the anchor 12 because the integration of the acid resistant layer 8 and the underground structure 1 is enhanced.

After the curing / hardening of the ordinary concrete of the underground structure 1 and the curing / hardening of the acid-resistant layer 8 are completed, the backfilling around the underground structure 1 having the acid-resistant layer 8 is performed as in the first embodiment. Carry out the backfilling process.

In the second embodiment, the construction of the underground structure 1 is completed in advance, and then the spraying process is performed. Therefore, the construction space 3 to be secured around the underground structure 1 is larger than that in the first embodiment. As a result, the amount of excavated soil increases and the amount of backfill soil increases, but unlike the first embodiment, the spraying process can be completed only by treating the outer wall, and construction is easy and efficient according to the normal construction procedure. can do.

In the method of constructing an underground structure in acidic soil according to the second embodiment, the outer circumference of the underground structure 1 facing the ground 2 of the acidic soil is used as a spray surface of mortar, and the spray surface is sprayed with acid-resistant mortar to be underground. Since the continuous acid-resistant layer 8 is formed on the structure 1, the underground structure 1 completely shielded from the acidic soil can be constructed in the ground 2 of the acidic soil, and the block can be constructed. The underground structure 1 can be constructed with excellent workability by spraying acid-resistant mortar, as compared with the background technique of arranging the molds and the mold bodies side by side.

Of course, the second embodiment may also be constructed using a quick-setting agent.

(Third Embodiment) FIGS. 10 and 11 sequentially show a procedure of a method of constructing an underground structure in acidic soil according to the third embodiment. In these figures, only a part of the construction part is shown.

The third embodiment is different from the first embodiment in that the outer formwork for constructing the underground structure is the discard formwork 13.

As shown in FIG. 10, when the outer formwork 13 is used, it is not necessary to secure a work space in anticipation of the demolding process between the underground structure 1 to be constructed and the surrounding ground 2. Therefore, in the excavation process for forming the construction space 3, the ground 2 of the acidic soil is excavated almost vertically at the position where the outer formwork 13 is installed, and the construction is large enough to surround the underground structure 1 to be constructed. Space 3 is formed.

When the excavation depth is deep, it is preferable to excavate so that the slope has a predetermined slope so as to prevent the ground 2 from collapsing.

Next, as shown in FIG. 10, after the waste concrete 4 is constructed, a formwork step of installing the outer-circumference formwork 13 is carried out.

The outer-circumference formwork 13 is installed on the waste concrete 4 in the construction space 3 so as to face the ground 2 of the acidic soil and preferably hit the ground 2.

The outer-circumferential throw-away formwork 13 stands on the throw-away concrete 4 at a position positioned by the positioning material 15 on the throw-away concrete 4 via a formwork fall-preventing material 14 embedded at an appropriate position on the surrounding ground 2. Supported by.

Next, as shown in FIG. 10, the step of spraying the acid-resistant mortar is carried out in the same manner as in the first embodiment.

The acid-resistant mortar is sprayed onto the sprayed surface of the underground structure 1 facing the ground 2 of the acidic soil, that is, the outer circumference (outer wall outer surface and pillar outer surface) of the underground structure 1 as a spray surface. It is applied to form a seamless and continuous acid resistant layer 8 around the outer circumference of the.

In the third embodiment as well, as in the first embodiment, since the underground structure 1 to be constructed is incomplete, the underground structure is formed by molding the outer circumference of the underground structure 1 instead of the outer circumference of the underground structure 1. Acid-resistant mortar is sprayed on the sprayed surface using the inner surface 13a of the outer formwork 13 which is the inner surface 13a of the outer formwork for building a structure and is shielded from acidic soil as a spraying surface, and is continuous without seams. Acid resistant layer 8 is formed.

The surface of the acid-resistant layer 8 formed of the sprayed acid-resistant mortar has unevenness, and the adhesion to the ordinary concrete to be post-cast is good as it is. It is preferable to dispose an anchor 12 firmly fixed to the ordinary concrete to be cast, and therefore to the underground structure 1.

Also in this case, after the sprayed acid-resistant mortar has hardened to some extent, the anchor 12 is inserted, and at that time, it is necessary between the tip of the anchor 12 to be inserted and the inner surface 13a (spraying surface) of the outer-circumference mold 13. It is desirable to ensure that the thickness of the acid-resistant mortar is sufficient to obtain a sufficient acid-resistant effect.

An anchor 12 is provided in the outer formwork 13 to firmly fix the acid-resistant layer 8 formed of the sprayed acid-resistant mortar to the ordinary concrete to be post-cast, and therefore to the underground structure 1 again. It is preferable to keep it.

After that, after the acid-resistant layer 8 is cured, as shown in FIG. 11, the construction step of the underground structure 1 is carried out in the same manner as in the first embodiment.

In the underground structure 1, an inner formwork 10 for constructing an additional underground structure for forming the inner side of the underground structure 1 is installed on the inner surface 13a side of the outer formwork 13 and these formwork 10, 13 are installed. Reinforcing bars of the underground structure 1 are arranged between them, and ordinary concrete constituting the underground structure 1 is placed between the outer formwork 13 and the inner formwork 10.

The ordinary concrete adheres to the acid-resistant layer 8 on the inner surface 13a of the outer formwork 13, and the acid-resistant layer 8 is integrated with the ordinary concrete of the underground structure 1. It is desirable to use the anchor 12 because the integration of the acid resistant layer 8 and the underground structure 1 is enhanced.

With the above, the construction of the underground structure 1 is completed. In the third embodiment, since the outer-circumferential throw-away formwork 13 is used, it is not necessary to remove the mold from the outer-circumferentially throw-away formwork 13, and the backfilling step is also unnecessary.

For this reason, the work required for demolding can be omitted, and since the outer-circumference formwork 13 is provided against the ground 2, the amount of excavated soil can be reduced and the backfilling work can be eliminated, improving workability. can do.

In the method for constructing an underground structure in acidic soil according to the third embodiment, the inner surface 13a of the outer rotation discarding mold 13 for forming the outer circumference of the underground structure 1 facing the ground 2 of the acidic soil is used as the spray surface of the mortar. Since the acid-resistant mortar was sprayed on the sprayed surface to form a seamless and continuous acid-resistant layer 8 on the underground structure 1, the underground structure completely shielded from the acidic soil in the ground 2 of the acidic soil. The object 1 can be constructed, and the underground structure 1 can be constructed with excellent workability by spraying an acid-resistant mortar as compared with the background technique of constructing blocks and mold bodies side by side.

Further, by providing the anchor 12 for fixing the acid-resistant layer 8 to the underground structure 1, the acid-resistant layer 8 formed by spraying and the underground structure 1 can be firmly integrated.

The inner loop formwork 10 is demolded / removed after the curing / hardening of the ordinary concrete of the underground structure 1 is completed.

Of course, the third embodiment may also be constructed using a quick-setting agent.

In the description of the third embodiment, the outer formwork 13 is used, but a waterproof sheet or the like may be used as long as it is a member capable of shielding acidic soil and spraying acid-resistant mortar. Of course.

It goes without saying that the acid-resistant mortar of each of the above-described embodiments contains acid-resistant concrete. In this case, it is desirable that the acid-resistant concrete has a small grain size of the coarse aggregate, and it is preferable that the composition thereof can suppress rebound.

When the inner surface 9a of the outer form 9 is used as a spray surface as in the first embodiment, a release agent or the like is applied to the inner surface 9a so that the outer form 9 can be easily removed from the acid resistant layer 8. May be applied.

In the above embodiment, the case of a solid foundation structure provided with the pressure plate 5 as the underground structure 1 has been described, but it goes without saying that a pile foundation structure provided with an underground slab may be used.

1 Underground structure made of reinforced concrete 2 Ground of acidic soil 3 Construction space 4 Waste concrete 8 Acid-resistant layer 9 Outer formwork for underground structure construction 9a Inner surface of outer formwork 10 Inner formwork for underground structure construction 12 Anchor 13 Outer throw-away formwork for underground structure construction 13a Inner surface of outer-turn throw-away formwork B Backfilling

Claims (7)

When excavating the ground of acidic soil and constructing an underground structure made of reinforced concrete in the ground,
An underground structure into an acidic soil, characterized in that a continuous seamless acid-resistant layer is formed by spraying an acid-resistant mortar at a site of the underground structure facing the ground of the acidic soil. Construction method. An excavation process in which the ground of acidic soil is excavated to form a construction space of a size surrounding the underground structure to be constructed.
In the construction space, the formwork process of installing an outer formwork for constructing an underground structure facing the ground of acidic soil, and
A spraying step of spraying the acid-resistant mortar with the inner surface of the outer formwork shielded from acidic soil as a spraying surface to form a seamless and continuous acid-resistant layer.
Reinforcing bars are arranged on the inner surface side of the outer formwork, and a formwork for constructing an additional underground structure is installed. The construction process to build and
The demolding process of demolding the outer formwork from the underground structure,
The method for constructing an underground structure in acidic soil according to claim 1, further comprising a backfilling step of backfilling the surroundings of the underground structure having an acid-resistant layer. An excavation process in which the ground of acidic soil is excavated to form a construction space of a size surrounding the underground structure to be constructed.
In the above construction space, a formwork process for arranging reinforcing bars and installing a formwork for constructing an underground structure including an outer formwork,
In the construction space, the construction process of placing concrete to construct the underground structure and
Of the formwork for constructing the underground structure, at least the demolding step of demolding the outer formwork and the demolding process.
A spraying step of spraying the acid-resistant mortar to form a seamless and continuous acid-resistant layer using the portion of the underground structure facing the ground of the acidic soil as a spraying surface.
The method for constructing an underground structure in acidic soil according to claim 1, further comprising a backfilling step of backfilling the surroundings of the underground structure having an acid-resistant layer. An excavation process in which the ground of acidic soil is excavated to form a construction space of a size surrounding the underground structure to be constructed.
In the above construction space, the formwork process of installing an outer-circumferential formwork for constructing an underground structure facing the above-mentioned ground of acidic soil, and
A spraying step of spraying the acid-resistant mortar to form a seamless and continuous acid-resistant layer using the inner surface of the outer formwork shielded from acidic soil as a spraying surface.
Reinforcing bars are arranged and a formwork for constructing an additional underground structure is installed on the inner surface side of the outer-circumferential throw-away formwork, and the formwork is attached to the acid-resistant layer and concrete is poured to form the underground structure. The method for constructing an underground structure in acidic soil according to claim 1, further comprising a construction step for constructing. After the excavation step and before the formwork step, the waste concrete of the underground structure is constructed of acid-resistant concrete on the ground of the construction space, and the outer formwork or the outer form is formed on the waste concrete. The method for constructing an underground structure in acidic soil according to any one of claims 2 to 4, wherein the outer formwork is installed. The acid-resistant mortar has latent water hardness with more than 40 to 50% by mass of Portland cement or blast furnace cement, 10 to 30% by mass of silica fume, which is an admixture having pozzolan reactivity and exhibiting initial strength. The blast furnace slag fine powder, which is an admixture that develops medium- to long-term strength, is composed of 20 to 25% by mass, and is composed of the Portland cement or blast furnace cement, the silica fume having the initial strength development, and the blast furnace having the medium- to long-term strength development. The method for constructing an underground structure in acidic soil according to any one of claims 1 to 5, wherein the cement composition is prepared with an acid-resistant cement composition having 100% by mass of slag fine powder. The acid-resistant mortar has latent water hardness with more than 40 to 50% by mass of Portland cement or blast furnace cement, 10 to 30% by mass of silica fume, which is an admixture having pozzolan reactivity and exhibiting initial strength. A high-performance water reducing agent or fluidizing agent added in an amount of 20 to 25% by mass of blast furnace slag fine powder, which is an admixture exhibiting medium- to long-term strength, and 0.1 to 2% by mass based on the mass of the Portland cement or blast furnace cement. The admixture is 100% by mass of the Portland cement or blast furnace cement, the silica fume having the initial strength developing property, the blast furnace slag fine powder having the medium- to long-term strength developing property, and the admixture. The method for constructing an underground structure in acidic soil according to any one of claims 1 to 5, wherein the cement composition is prepared with acid-resistant cement.

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