KR20230089079A - Method for installing underground transmission line using industrial by-product backfill material - Google Patents

Abstract

The present invention relates to a method for installing an underground transmission line by using an industrial by-product as a backfill material. The industrial by-product used in the present invention uses at least any one of steelmaking slag, ferronickel slag, mine waste rock, and recycled aggregate as gravel. The method according to the present invention comprises: a step (a) of excavating a trench in which a transmission line is to be installed; a step (b) of laying gravel, which is an industrial by-product, on the floor of the trench; a step (c) of installing a plurality of rows of conduits in a height direction by repeating the process of arranging the conduits on the gravel and laying the gravel so that all conduits are submerged; and a step (d) of supplying high fluidity backfill to the trench in a state in which the installation of the conduit and gravel is finished to fill and cure the voids between the gravel. According to the present invention, it is possible to improve the economics by using the slag and the recycled aggregate, which are industrial by-products, as gravel and using the fly ash as the main material of the backfill material.

Description

Underground transmission line burial method using industrial byproducts as backfill materials {METHOD FOR INSTALLING UNDERGROUND TRANSMISSION LINE USING INDUSTRIAL BY-PRODUCT BACKFILL MATERIAL}

The present invention relates to a technology for installing a transmission line in the ground, and more particularly, to a structure and method for embedding a transmission line in the ground.

In recent years, transmission lines are buried in the ground, not in the ground, in consideration of electromagnetic wave problems and aesthetics. The first thing to consider in the underground burial of the transmission line is to easily discharge the heat generated from the transmission line. This is because transmission lines are damaged if the temperature rises above a certain level.

Conventionally, sand laying and water compaction were used to dissipate heat from transmission lines. 1 is a schematic longitudinal cross-sectional view for explaining a structure of a conventional open-cut transmission line buried underground. Referring to FIG. 1 , conventionally, a trench 1 is made by excavating the ground, sand 3 is laid on the bottom of the trench, and water is compacted. Power transmission pipes (2, mainly corrugated pipes) into which power transmission lines are inserted are arranged in one row on top of the sand compaction layer, and sand is again laid and water compacted so that the power transmission pipes 2 are submerged. The conduit 2 is installed in a plurality of rows as shown in FIG. 1 by repeating the above method. If the transmission line is installed under the road, the pavement layer 4 is finally laid and finished.

In the structure described above, since the transmission line is embedded in the sand and water is filled in the voids between the sands through water compaction, heat generated in the transmission line is easily transferred to the ground through the sand and water. In addition, it is necessary to be able to easily re-excavate the trench (1) at any time in terms of maintenance of the transmission line, and the sand laying and water compaction method has the advantage of easy re-excavation.

However, since the sand and water compaction structure must be compacted by manpower during the construction process, there is a problem in that construction is not easy when sufficient working space such as roads is not secured. In addition, there was a problem that the compacted sand collapsed when performing other excavation work such as sewage pipe repair work in the surrounding ground. Above all, since the transmission line is buried above the groundwater level, the water filled in the sand leaks out, resulting in a rapid decrease in thermal conductivity over time.

In order to solve the above problems, conventionally, a method of pouring and hardening CLSM (controlled low strength material), a filling material with low long-term strength and high fluidity, has been attempted in the trench, but since the conduit before inserting the transmission line is light, if CLSM is poured, the conduit is light. Because of this buoyancy, construction was very difficult.

The present invention is intended to solve the above problems, and an object of the present invention is to provide a transmission line underground burial structure and method that can easily discharge heat generated from the transmission line to the outside as well as easy construction and maintenance.

Meanwhile, other unspecified objects of the present invention will be additionally considered within the scope that can be easily inferred from the following detailed description and effects thereof.

An underground transmission line burial method according to the present invention for achieving the above object includes: (a) excavating a trench in which the transmission line is to be buried; (b) laying gravel on the bottom of the trench; (c) burying a plurality of rows of conduits along the height direction by repeating the process of arranging conduits on the gravel and laying gravel so that all of the conduits are submerged; and (d) supplying a high-flowability backfill material to the trench in a state in which the installation of the conduit and the gravel is completed to fill and harden the voids between the gravel.

According to the present invention, the gravel is any one or a mixture of steelmaking slag, ferronickel slag, mine waste rock, recycled aggregate, and preferably has a granularity of 3.5 or more.

In one example of the present invention, the high fluidity backfill material comprises 75 to 90 parts by weight of a filler containing fly ash and 5 to 10 parts by weight of a calcium aluminate-based or calcium sulfoaluminate-based binder binding the filler and bentonite. It consists of a main material mixed with 5 to 15 parts by weight of an anti-settling material and a hardening accelerator mixed with 0.1 to 0.5 parts by weight with respect to the main material, and the water ratio (W / M) mixed with the high fluidity backfill material is 30 to 100 Composition in the % (mass) range.

In one example of the present invention, it is preferable to further include unburned carbon powder mixed in the range of 1 to 3 parts by weight with respect to the main material to increase the thermal conductivity of the high fluidity backfill material.

In the underground transmission line burial method according to the present invention, gravel is laid in the trench to bury the conduit, and the gap between the gravel is filled with a high fluidity backfill material. In the present invention, slag and recycled aggregate, which are industrial by-products, are used as gravel, and fly ash is used as a main material for backfilling, thereby improving economic feasibility.

In addition, while using industrial by-products as materials, it has an advantage in that heat generated in transmission lines can be easily released to the outside because the heat transfer rate is excellent compared to the conventional sand-water compaction method or the method using a fluid filler.

The present invention has the advantage that construction is very simple and the construction period can be shortened by using gravel and high fluidity backfill material.

On the other hand, even if the effects are not explicitly mentioned here, it is added that the effects described in the following specification expected by the technical features of the present invention and their provisional effects are treated as described in the specification of the present invention.

1 is a schematic longitudinal cross-sectional view for explaining a structure of a conventional open-cut transmission line buried underground.
2 is a schematic flowchart of an underground transmission line burial method according to an example of the present invention.
3 is a schematic perspective view for explaining a spacer panel and a conduit used in one example of the present invention.
FIG. 4 is a schematic front view of a state in which the spacer panel shown in FIG. 3 is installed in a trench.
5 is a schematic side view of a state in which a first row of conduits and an injection pipe are disposed after laying a gravel layer in the lower portion of the trench.
6 is a schematic cross-sectional view along line AA of FIG. 5 .
7 is a schematic cross-sectional view of a state in which both the conduit and gravel are installed.
8 is a schematic cross-sectional view after filling the high fluidity backfill material and completing the pavement layer finishing.
※ It is revealed that the accompanying drawings are illustrated as references for understanding the technical idea of the present invention, and thereby the scope of the present invention is not limited.

In describing the present invention, a detailed description thereof will be omitted if it is determined that a related known function may unnecessarily obscure the subject matter of the present invention as it is obvious to those skilled in the art.

Hereinafter, a method for burying an underground transmission line according to an embodiment of the present invention will be described in more detail with reference to the accompanying drawings.

2 is a schematic flowchart of an underground transmission line burial method according to an example of the present invention, and FIG. 3 is a schematic perspective view for explaining a spacer panel and a conduit used in an example of the present invention. 4 is a schematic front view of a state in which the spacer panel shown in FIG. 3 is installed in a trench, and FIG. 5 is a schematic side view of a state in which one row of conduits and an injection pipe are disposed after laying a gravel layer in the lower portion of the trench.

Referring to the drawings, in the underground transmission line burial method according to an example of the present invention, the trench 10 is formed by first excavating the ground g. Since the transmission line is long, the trench 10 is divided and excavated for each section.

After the trench 10 is excavated, spacer panels 20 are installed on both sides or one side of the trench 10 along its length. The spacer panel 20 has a shape corresponding to the longitudinal section of the trench 10 in the shape of a thin plate. In the spacer panel 20, a plurality of through holes 21 are spaced apart from each other at regular intervals, and the conduit 30 is inserted into the through holes 21, respectively.

The spacer panel 20 serves two functions. The first is formwork. That is, after installing the gravel and the conduit in the trench 10, it acts as a formwork when the high fluidity backfill is placed. In the example shown in the figure, since the other side of the trench 10 is blocked, the spacer panel 20 is installed only on one side of the trench 10, but in another example, the spacer panel may be installed on both sides of the trench. When the spacer panel 20 is installed, an airtight space is formed inside the trench 10 so that the high fluidity backfill material is not lost. However, when the ground is unevenly excavated, a gap may occur between the spacer panel 20 and the ground, which is sealed through a separate finish.

The second function of the spacer panel 20 is to maintain a space between the plurality of conduits 30 . Since the conduit 30 is a material that can be bent, such as a corrugated pipe, after installing the conduit 30, the installation position of the conduit 30 can be changed when filling gravel or placing a high fluidity backfill material. Since heat is generated in the transmission lines installed inside the conduit 30, the transmission lines must be spaced apart from each other at a certain distance. In the present invention, since the conduit 30 is inserted into the through hole 21 of the spacer panel 20, the position of the conduit 30 can be fixed during construction.

After the spacer panel 20 is installed, gravel 40 is laid on the bottom of the trench 10 to form a gravel layer A as shown in FIG. 7 . The gravel used in this example may be any one of steelmaking slag, ferronickel slag, mine waste rock, and recycled aggregate, or a mixture thereof. In other words, industrial by-products are recycled into gravel. The particle size of the gravel may be about 10 to 25 mm. More precisely, the gravel used in this example has a coarseness factor (FM) of 3.5 or more. Since the granularity of the fine aggregate is in the range of 2.3 to 3.1, aggregates larger than the fine aggregate are used in the present invention. The reason for using gravel will be explained later.

After laying the gravel layer (A) on the floor, the first row of conduit 30 and the backfill material injection pipe 50 are installed. Three conduits 30 are installed in the first row. The number of conduits is generally four, but the number can be varied. As shown in FIGS. 5 and 6 , the conduit 30 is inserted into the through hole 21 of the spacer panel 20 and then placed on gravel.

In addition, in this example, the injection pipe 50 for injecting the backfill material is installed together with the conduit 30. That is, the injection tube 50 is installed by binding it to one of the conduit tubes in the first row, preferably the lower part of the conduit tube disposed in the center. The injection tube 50 is formed long along the conduit 30 and is made of a flexible material. The front end of the injection pipe 50 is blocked, and a plurality of through holes 51 are formed on the outer circumferential surface. The through holes 51 are continuously disposed along the longitudinal direction of the injection tube 50 . The high fluidity backfill material is supplied to the injection pipe 50 and then discharged through the through hole 51. In this example, the injection pipe 50 is installed by binding to the conduit 30, but in other examples, the injection pipe may be installed separately from the conduit.

After installing the injection pipe 50 and the first row of conduits 30, the gravel 40 is laid again so that they are all submerged. A second row of conduits is then installed over the freshly laid gravel. The conduit of the second row is also installed by inserting it into the through hole of the spacer panel. All conduits can be installed in the same way as above. In this example, since three rows of conduits are arranged, as shown in FIG. 7, three gravel layers (B, C, and D) are stacked on top of the gravel layer (A), respectively, and the conduit 30 is buried in each gravel layer. .

When the installation of the conduit and the laying of the gravel layer are completed, the high fluidity backfill material 60 is injected through the injection pipe 50. The backfill material is supplied to the lower portion of the trench 10 and filled to the upper portion. Since the backfill material has high fluidity, it quickly flows into the voids between the gravel and fills the voids between the gravel 40 in the trench. The backfill will be described later.

When the filling of the backfill material is completed, the upper part is finished without waiting for hardening. For example, in the case of a road, the pavement layer 70 may be formed. In this example, since the trench 10 is filled with gravel, pavement finishing can be performed even if the backfill material is not completely hardened. However, depending on the construction conditions, the pavement may be finished by waiting for the backfill material to harden.

Hereinafter, the high fluidity backfill material used in the present invention will be described.

The high fluidity backfill material used in this example includes a filler and a binding material that couples the filler. Hereinafter, for convenience of description, the filler and the binder are collectively referred to as the main material. And in the present invention, it may further include a mixture for supplementing the function of the main material.

First, filler can be understood as the concept of 'aggregate' in the field of cement. In this embodiment, fly ash is used as a filler. And as a binder for integrating the fillers, a calcium aluminate-based or calcium sulfoaluminate-based material is used in the present invention. For example, materials such as C ₁₂ A ₇ , C ₃ A, and CA may be used for the calcium aluminate type, and materials such as C ₄ A ₃ S may be used for the calcium sulfoaluminate type.

In conventional fillers, it is common to use a calcium silicate-based material as a binder, but in the present invention, there is an important feature in that a calcium aluminate-based or calcium sulfoaluminate-based binder is used. Explain in detail.

Calcium silicate-based materials (ordinary cement) develop strength while curing through hydration reactions in the form of reaction formulas (1) and (2) below.

2C ₃ S + 6H → C ₃ S ₂ H ₃ + 3Ca(OH) ₂ ... Scheme (1)

2C ₂ S + 4H → C ₃ S ₂ H ₃ + Ca(OH) ₂ ... Scheme (2)

Cementitious materials usually harden through a hydration process that reacts with water to form new minerals. Conventional CLSM also obtains a hardened body with appropriate strength by the hydration reaction of cement and the pozzolanic reaction between a large amount of slaked lime and fly ash, which is amorphous silica, generated during the cement hydration process. However, the hydration of calcium silicate minerals such as C ₃ S and C ₂ S, which mainly contribute to the development of strength during the hydration reaction of cement, takes several days to several weeks and is characterized by a slow process. Therefore, the early strength within a few hours after placement does not exceed 0.13 MPa required for backfilling materials. However, as the hydration reaction continues, the long-term strength is highly expressed at the age of 10 days or more. High long-term strength is an advantage in materials for bridges, buildings, and pavements, but low early strength and high long-term strength act as a major weakness in backfill materials. That is, if the early strength is low, the curing time is long, so air may increase. However, in the present invention, since the gravel is laid, the curing time is not a big problem. In addition, when the long-term strength is high, it is difficult to re-excavate the backfill material for maintenance of the pipeline.

In the present invention, all of these problems are solved by using a calcium aluminate-based or calcium sulfoaluminate-based binder.

CA + H → CAH ₁₀ ... Scheme (3)

C ₁₂ A ₇ + H → C ₂ AH ₈ + AH ₃ ... Scheme (4)

C ₄ A ₃ + 8CH ₂ + 6CH + 74H 3C ₆ A ₃ H ₃₂ ... Scheme (5)

Reaction formulas (3) and (4) above show the hydration reaction of the amorphous calcium aluminate-based binder. Equation (5) shows the hydration reaction of the calcium sulfoaluminate-based binder. Since the gastric hydration reaction takes place rapidly, the early strength is high. Therefore, the long-term strength stays at a level slightly higher than the early strength. For reference, in this example, the 28-day compressive strength is formed to 2.0 MPa or less. Compared to calcium silicate-based binders, calcium aluminate-based or calcium sulfoaluminate-based binders have weaker long-term strength, but serve as an advantage in backfilling materials.

In the present invention, among the main materials, the filler is blended in the range of 75 to 90 parts by weight and 5 to 10 parts by weight of the calcium aluminate-based or calcium sulfoaluminate-based binder. In addition, the main material includes 5 to 15 parts by weight of an anti-settling material containing bentonite. As will be described later, the backfill material used in the present invention has a very high water ratio in order to express high fluidity, but when the water ratio is high, a problem in which the material and water are separated may occur. Bentonite used as an anti-settling material can prevent material separation by increasing the viscosity when water and the main material are mixed.

On the other hand, in the present invention, while maintaining the advantages of the amorphous calcium aluminate-based or calcium sulfoaluminate-based binder, a mixing agent is used to enhance the function as a backfill material.

A hardening accelerator and unburned carbon powder are used as the mixture.

As the curing accelerator, carbonate-based materials such as sodium carbonate, sodium bicarbonate, and lithium carbonate may be used. The hardening accelerator is formulated in the range of 0.1 to 2% based on the weight of the main material.

Unburnt carbon content refers to carbon content that has not been burned in a thermal power plant, and is mainly contained in fly ash. Since the unburned carbon powder is a carbon material, it can increase the thermal conductivity of the main material. In the present invention, the unburned carbon powder is mixed and used in the range of 1 to 3 parts by weight with respect to the main material of the backfill material. Unburned carbon is mainly included in fly ash among by-products of thermal power plants. In general aggregates or civil engineering materials, material performance deteriorates when a large amount of unburned carbon is included, so it is common to remove unburned carbon. In the present invention, unburned carbon content separately separated from a thermal power plant may be used, or fly ash having a very high unburned carbon content may be used as it is. That is, in the case of fly ash used as the main material, it generally contains 2 to 3% by weight of unburned carbon. there is.

In addition, in one embodiment of the present invention, a fibrous mineral such as asbestos may be additionally mixed in order to increase the heat transfer rate of the backfill material. The fibrous mineral is formed long in one direction and has excellent heat transfer rate. It may be included in a ratio of 2 to 3% by weight relative to the main material.

The backfill material used in the present invention forms a paste by mixing water with all the materials using the main material and the mixing agent, but the water ratio (W / M) to the entire material is adjusted to 30 to 100% (mass) to increase fluidity . In the present invention, the high fluidity backfill material is expressed with a slump flow of 500 mm or more.

The underground transmission line burial method having the above configuration is characterized in that the heat generated from the transmission line can be well discharged to the outside along with the convenience and efficiency of construction. Important features of the present invention will be described in detail.

First, the convenience and efficiency of construction, which is the first feature of the present invention, will be described.

In the present invention, a method of laying gravel in the trench and filling the void with a high fluidity backfill material is selected. In the existing method of compacting sand, compaction was required, and there was a problem that the sand collapsed during re-excavation. The method developed to avoid the sand-water compaction method, that is, when the CLSM is filled after installing the conduit in the trench, it is very difficult to construct because the conduit rises due to buoyancy.

In the present invention, since the conduit is buried in the gravel, the conduit does not float due to buoyancy even when the high fluidity backfill is filled. Installation is simple as no water compaction is required. In addition, since gravel and high fluidity backfill material are used instead of sand, the trench does not collapse and maintains its original shape even when excavating the surrounding area. In addition, since the high fluidity backfill material has a weak long-term compressive strength, it has the advantage of being easy to re-excavate later.

Moreover, when CLSM was used in the past, the pavement layer could be finished when the CLSM was fully cured and had bearing capacity. However, in the present invention, since the gravel provides a supporting force, there is an advantage in that the construction period can be shortened as the pavement layer can be finished immediately without waiting for the curing of the high fluidity backfill material.

That is, in the present invention, by filling the trench with gravel to bury the conduit, and filling the space between the gravel with a high-flowability backfill material, there is an advantage in that construction can be simplified and the construction period can be shortened.

The second characteristic of the present invention, excellent heat transfer rate, will be described.

The heat transfer rate is determined by the properties of the material and the air gap.

In terms of materials, the present invention uses gravel and flexible backfill material, and the thermal resistance of a mixture of gravel and flexible backfill material is very low at 0.5K.m/W. That is, in the case of sand-water compaction, which has been widely used in the past, the thermal resistance is 0.6K.m/W when saturated with water, and 2.0K.m/W when dry, which is very high. It can be seen that the present invention has a better heat transfer rate in the sand-water compacted form than in the case where water is saturated. In addition, high fluidity concrete developed as a substitute for sand-water compaction exceeds 0.6K.m/W no matter how low the thermal resistance is.

In addition, even if the material has excellent heat transfer rate, when the material does not tightly fill the trench and voids are generated, a heat insulating layer is formed and the heat transfer rate is lowered. In the present invention, the backfill material is formed with high fluidity so that the backfill material can easily flow into the void between the gravel to suppress the occurrence of voids. In particular, in the present invention, the backfill material is not supplied from the top of the trench, but the injection pipe is placed at the bottom to supply the backfill material from the bottom to the top of the trench. The method of filling up from the bottom to the top can reduce the void generation rate more than the reverse method.

Further, in the present invention, the granulation ratio of gravel is maintained at 3.5 or more. If the granularity ratio is low, a large amount of fine aggregate is included, and the fine aggregate is interposed between the coarse aggregates, resulting in a low porosity. If the porosity is low, it is difficult to inject the high fluidity backfill material, which is disadvantageous in terms of workability, but it is not preferable because the rate of occurrence of voids is high. Therefore, in the present invention, the assembly rate of gravel is adjusted to 3.5 or more to improve workability and suppress the occurrence of voids as much as possible.

The protection scope of the present invention is not limited to the description and expression of the embodiments explicitly described above. In addition, it is added once again that the scope of protection of the present invention cannot be limited due to obvious changes or substitutions in the technical field to which the present invention belongs.

10 ... trench, 20 ... spacer panel
30 ... Conduit, 40 ... Gravel
50 ... injection pipe, 60 ... high fluidity backfill
70 ... pavement layer, g ... ground

Claims (5)

(a) excavating a trench in which a transmission line is to be buried;
(b) laying gravel on the bottom of the trench;
(c) burying a plurality of rows of conduits along the height direction by repeating the process of arranging conduits on the gravel and laying gravel so that all of the conduits are submerged; and
(d) supplying a high fluidity backfill material to the trench in a state in which the installation of the conduit and the gravel is completed to fill and harden the voids between the gravel;
The gravel is an underground transmission line burial method, characterized in that at least one of steelmaking slag, ferronickel slag, mine waste rock and recycled aggregate as an industrial by-product. According to claim 1,
A spacer panel is installed on one side or both sides of the trench,
The spacer panel is a panel having a shape corresponding to the longitudinal section of the trench,
A plurality of through holes spaced apart from each other by a certain distance are formed,
The underground transmission line burial method, characterized in that the plurality of conduits are each inserted into the through hole. According to claim 1,
When laying gravel at the bottom of the trench or installing the conduit disposed at the bottom of the plurality of rows, an injection pipe having a plurality of through holes formed on the outer circumferential surface is installed together to inject the high fluidity backfill material. So,
The underground transmission line burial method, characterized in that the high fluidity backfill material is filled from the bottom to the top of the trench and filled. According to claim 1,
The high fluidity backfill material includes 75 to 90 parts by weight of a filler containing fly ash, 5 to 10 parts by weight of a calcium aluminate-based or calcium sulfoaluminate-based binder for binding the filler, and 5 to 10 parts by weight of an anti-settling material containing bentonite. It consists of a main material formulated in 15 parts by weight and a hardening accelerator mixed in 0.1 to 0.5 parts by weight based on the main material,
The underground transmission line burial method, characterized in that the water ratio (W / M) mixed with the high fluidity backfill material is 30 to 100% (mass). According to claim 4,
An underground transmission line burial method characterized in that it further comprises a fibrous mineral mixed in a range of 1 to 3 parts by weight with respect to the main material to increase the thermal conductivity of the high fluidity backfill material.

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