Overhead line iron tower foundation structure and construction method thereof

Abstract

The invention provides an overhead line iron tower foundation structure and a construction method thereof, and belongs to the technical field of overhead line iron towers, and the construction method comprises the following steps: a foundation pit is excavated, the bottom of the foundation pit is pretreated with acid liquor and alkali liquor in sequence, grouting is performed after heating and drying, a grouting cushion layer is obtained, and slurry adopted for grouting comprises silica fume, sodium hydroxide, an aluminum source and water; foundation bolts are inserted into the set positions of the grouting cushion layer, a reinforcing mesh is laid, concrete pouring is conducted, column foot connecting parts are installed on the foundation bolts, and the iron tower foundation structure is manufactured; and the foundation pit is filled with non-frost heaving soil to be compacted. The grouting cushion layer is prepared by grouting the bottom of the foundation pit, and the dense grouting cushion layer is formed after the slurry is injected into the soil layer pores, so that the porosity of the soil layer is reduced, the effective stress is increased, the strength and stability of the soil layer can be improved, and melting settlement deformation can be effectively resisted.

Description

Technical Field

[0001] This invention relates to the field of overhead line tower technology, specifically to an overhead line tower foundation structure and its construction method. Background Technology

[0002] In power transmission projects, a large number of overhead line towers are required. These towers serve as support components for the overhead laying of power lines. Installation involves first excavating a foundation pit, then pouring the foundation structure within the pit, and finally fixing the tower to the foundation. In permafrost regions, the strength of frozen soil depends on the ice binding soil particles together. Pouring the foundation structure directly into the pit results in a significant decrease in strength after the permafrost thaws, as the cohesion provided by the ice disappears. The soil in the thawed area undergoes consolidation settlement and uneven settlement under foundation loads, leading to severe subsidence or tilting of the tower base and threatening its stability.

[0003] Currently, constructing the foundation structure for overhead power line towers in permafrost regions typically requires installing pile foundations into deep, stable permafrost or non-permafrost layers, or laying insulation materials, ventilation pipes, and other structures near the foundation to prevent permafrost thawing. This process is quite challenging and makes it difficult to ensure the long-term safety and stability of the overhead power line towers in the extreme environment of permafrost. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides an overhead line tower foundation structure and its construction method, aiming to solve the problem that the construction of overhead line tower foundation structures in permafrost areas is difficult and it is difficult to ensure the long-term safety and stability of overhead line towers in the extreme environment of permafrost.

[0005] In a first aspect, embodiments of this application provide a construction method for the foundation structure of an overhead line tower, comprising the following steps:

[0006] S1. Excavate the foundation pit, pretreat the bottom of the foundation pit with acid and alkali solutions in sequence, heat and dry it, and then grout it to obtain a grouting cushion layer. The grout used includes silica fume, sodium hydroxide, aluminum source and water.

[0007] S2. Insert anchor bolts at the designated positions of the grouting cushion layer, lay steel mesh, pour concrete, and install column foot connectors on the anchor bolts to obtain the tower foundation structure.

[0008] S3. Fill the foundation pit with non-frost-susceptible soil and compact it.

[0009] In the technical solution of this application embodiment, the present invention first treats the soil layer at the bottom of the foundation pit with acid to decompose carbonates such as calcium carbonate in the soil layer, thereby increasing the porosity and specific surface area of ​​the soil layer, activating the soil layer, and improving the bonding strength between sand particles and grout. Then, it uses alkaline solution to adjust the pH of the soil layer to 8-10, which is beneficial to the gelation after subsequent grout injection. Grouting treatment is performed at the bottom of the foundation pit. After the grout is injected into the pores of the soil layer, a dense grouting cushion layer is formed, which reduces the porosity of the soil layer, increases the effective stress, and thus improves the strength and stability of the soil layer, effectively resisting melting settlement deformation.

[0010] In some embodiments, the pretreatment step in step S1 includes: injecting hydrochloric acid with a mass concentration of 5% to 10% into the bottom of the foundation pit, reacting for 3 to 5 hours, and then injecting sodium hydroxide solution with a mass concentration of 5% to 10% to adjust the pH of the soil layer at the bottom of the foundation pit to 8 to 10.

[0011] In some embodiments, the heating and drying in step S1 is carried out by hot air drying, so that the soil moisture content at the bottom of the foundation pit is 50% to 70%.

[0012] In the technical solution of this application embodiment, hot air drying can blow out the moisture in the soil, reduce the soil moisture content, increase the soil porosity, and facilitate the uniform injection of subsequent grout.

[0013] In some embodiments, the slurry includes 80-100 parts of silica sol, 10-15 parts of sodium hydroxide, 5-20 parts of aluminum source, 15-30 parts of silica fume, and 1-3 parts of PVP.

[0014] In the technical solution of this application embodiment, the silica sol in the grout of the present invention has strong permeability and can penetrate into the tiny gaps in the soil layer, which is beneficial for grouting. The silica sol generates SiO2 gel under the triggering of electrolytes, which can bind loose soil together, improve the compressive strength of the grouting cushion layer, and the grouting cushion layer after silica sol grouting has a low freeze-thaw rate, effectively preventing uneven settlement of the foundation and helping to maintain the long-term stability of the tower foundation. Sodium hydroxide, as a strong alkaline activator, provides a high pH environment to dissolve silica fume and aluminum hydroxide, which is beneficial for dispersing silica fume and aluminum hydroxide in the silica sol. Silica fume is used to provide highly active amorphous SiO2, which works synergistically with the silica sol to form the core of the silicon (aluminum) oxygen network framework. The aluminum source provides Al. 3+ By introducing aluminum oxide tetrahedra, the product is transformed from a pure silicon oxide network to a silicon aluminum oxide network, further enhancing the strength of the grouting layer; the gelation time of the silica sol can be adjusted by regulating the concentration of the aluminum source.

[0015] The soil layer at the bottom of the foundation pit is deep permafrost in the plateau region, which contains a large amount of calcium carbonate. In this invention, acid and alkali solutions are used to activate the soil layer in sequence, converting calcium carbonate into calcium hydroxide, which can provide Ca2+. This Ca2+ reacts with silica fume to generate CSH (hydrated calcium silicate) gel and CASH (aluminum-containing hydrated calcium silicate) gel, further improving the strength of the grouting cushion layer. At the same time, it can also stably provide OH- in the later stage of gel formation, preventing the pH value from dropping too quickly in the later stage, and allowing the gel to fully solidify.

[0016] In some embodiments, the mass concentration of the silica sol is 5% to 10%.

[0017] In some embodiments, the aluminum source includes at least one of aluminum hydroxide and sodium aluminate.

[0018] In some embodiments, the method for preparing the slurry includes: dispersing silica fume, aluminum hydroxide, and PVP in water to obtain a dispersion;

[0019] Mix silica sol and sodium hydroxide, then slowly add the dispersion solution while stirring at high speed to obtain a slurry.

[0020] In some embodiments, during the grouting process in step S1, the soil layer at the bottom of the foundation pit is heated to a temperature of 15~30°C using a heat pipe.

[0021] In the technical solution of this application embodiment, maintaining a high temperature during the grouting process is beneficial to the flow of grout and at the same time accelerates the curing efficiency of the grout.

[0022] In some embodiments, the non-frost-susceptible soil in step S3 includes graded gravel, crushed stone, and quicklime.

[0023] In the technical solution of this application embodiment, non-frost-susceptible soil is used to replace the strongly frozen soil around the tower foundation structure, which can ensure the stability of the soil layer around the tower foundation. Preferably, after the non-frost-susceptible soil is compacted, a waterproof layer can be laid on the non-frost-susceptible soil, and drainage ditches can be excavated around it to ensure the dryness of the tower foundation, reduce the moisture content of the non-frost-susceptible soil in the tower foundation part, and further reduce the freeze-thaw rate of the non-frost-susceptible soil.

[0024] Secondly, this application provides an overhead line tower foundation structure, which is manufactured using the above-mentioned construction method.

[0025] In some embodiments, a grouting pad layer is provided at the bottom of the foundation pit, and column foundations are provided at the four corners of the grouting pad layer. Multiple anchor bolts are provided inside the column foundations, and column base connecting parts are fixedly connected to the top of the anchor bolts.

[0026] Adjacent column foundations are fixedly connected by connectors, which include a concrete layer containing main reinforcement bars and stirrups. The two ends of the main reinforcement bars are fixedly connected to the two adjacent column foundations respectively.

[0027] The foundation pit is filled with non-frost-susceptible soil that has been compacted.

[0028] In the technical solution of this application embodiment, the excavation depth of the foundation pit can be greatly reduced by setting a grouting cushion layer, thereby reducing the amount of engineering work and concrete pouring. The column foundations are connected by connectors, making the four column foundations a whole, which improves the stability of the tower foundation structure.

[0029] The advantages of this application, which differ from existing technical solutions, include:

[0030] 1. This invention creates a grouting cushion layer by grouting at the bottom of the foundation pit. The grout, injected into the soil pores, forms a dense grouting cushion layer, reducing soil porosity and increasing effective stress, thereby improving soil strength and stability and effectively resisting melting settlement deformation. Casting the tower foundation structure on this grouting cushion layer significantly reduces the excavation depth, engineering volume, and concrete pouring volume. Connecting the column foundations with connectors integrates the four column foundations into a single unit, enhancing the stability of the tower foundation structure. Replacing the heavily frozen soil around the tower foundation with non-frost-susceptible soil ensures the stability of the soil layer surrounding the tower foundation.

[0031] 2. In the grout of this invention, the silica sol has strong permeability, allowing it to penetrate into the tiny cracks in the soil layer, which is beneficial for grouting. Under the triggering of electrolytes, the silica sol generates SiO2 gel, which can bind loose soil together, improving the compressive strength of the grouting cushion layer. Furthermore, the grouting cushion layer after silica sol grouting has a low freeze-thaw rate, effectively preventing uneven settlement of the foundation and contributing to the long-term stability of the tower foundation. Sodium hydroxide, as a strong alkaline activator, provides a high pH environment, dissolving silica fume and aluminum hydroxide, which facilitates their dispersion in the silica sol. Silica fume provides highly active amorphous SiO2, which synergistically forms the core of the silicon (aluminum) oxygen network framework with the silica sol. The aluminum source provides Al3+, introducing aluminum oxygen tetrahedra, transforming the product from a pure silicon oxygen network to a silicon aluminum oxygen network, further enhancing the strength of the grouting cushion layer.

[0032] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0034] Figure 1 This is a top view of the tower foundation structure in Embodiment 1 of this application;

[0035] Figure 2 This is a schematic cross-sectional view of the tower foundation structure in Embodiment 1 of this application.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1. Foundation pit; 2. Grouting cushion layer; 3. Column foundation; 31. Anchor bolts; 32. Column base connection; 4. Connecting parts; 5. Non-frost-susceptible soil. Detailed Implementation

[0038] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0039] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0040] I. Preparation Method

[0041] Example 1

[0042] A construction method for the foundation of an overhead power line tower includes the following steps:

[0043] S1. Excavate the foundation pit, inject 10% hydrochloric acid into the bottom of the pit, and after reacting for 3 hours, inject 10% sodium hydroxide solution to adjust the pH of the soil layer at the bottom of the pit to 8.

[0044] S2. Hot air drying is used to make the soil moisture content at the bottom of the foundation pit 50%.

[0045] S3. Disperse 30 parts silica fume, 5 parts aluminum hydroxide and 3 parts PVP in water to obtain a dispersion.

[0046] S4. Mix 80 parts of silica sol with a mass concentration of 10% and 10 parts of sodium hydroxide, then slowly add the dispersion liquid to it and stir at high speed to obtain a slurry.

[0047] S5. Grouting is carried out using the permeation grouting method. The grouting pipes are arranged in a quincunx pattern with a hole spacing of 1.5m, a grouting rate of 8L / min, a grouting pressure of 0.5MPa, and a grouting time of 10min. During grouting, heating pipes are used to maintain the soil temperature at 10~15℃. After stabilization for 4h, the grouting cushion layer is obtained. The grouting material used includes silica sol, sodium hydroxide, aluminum source, silica fume, and PVP.

[0048] S6. Insert anchor bolts at the designated positions in the grouting cushion layer, lay steel mesh, and pour concrete. Use frost-resistant concrete. Install column base connections on the anchor bolts to complete the tower foundation structure. Figures 1-2 As shown, the foundation structure of the iron tower includes a grouting cushion layer 2 set at the bottom of the foundation pit 1. Column foundations 3 are set at the four corners of the grouting cushion layer 2. Multiple anchor bolts 31 are set inside the column foundations 3. Column foot connecting parts 32 are fixedly connected to the top of the anchor bolts 31. Adjacent column foundations 3 are fixedly connected by connectors 4. The connectors 4 include a concrete layer, in which main reinforcement bars and stirrups are provided. The two ends of the main reinforcement bars are fixedly connected to two adjacent column foundations 3 respectively.

[0049] S7. Fill the foundation pit with non-frost-susceptible soil, which includes graded gravel, crushed stone and quicklime. The volume ratio of graded gravel to crushed stone is 7:3. The amount of quicklime added is 5% of the total weight of graded gravel and crushed stone. Compact the soil.

[0050] Example 2

[0051] A construction method for the foundation of an overhead power line tower includes the following steps:

[0052] S1. Excavate the foundation pit, inject 5% hydrochloric acid into the bottom of the pit, and after reacting for 5 hours, inject 5% sodium hydroxide solution to adjust the pH of the soil layer at the bottom of the pit to 10.

[0053] S2. Hot air drying is used to make the soil moisture content at the bottom of the foundation pit 70%.

[0054] S3. Disperse 15 parts silica fume, 20 parts aluminum hydroxide, and 1 part PVP in water to obtain a dispersion.

[0055] S4. Mix 100 parts of silica sol with a mass concentration of 5% and 15 parts of sodium hydroxide, then slowly add the dispersion liquid to it and stir at high speed to obtain a slurry.

[0056] S5. Grouting is carried out using the permeation grouting method. The grouting pipes are arranged in a quincunx pattern with a hole spacing of 1.5m, a grouting rate of 8L / min, a grouting pressure of 0.5MPa, and a grouting time of 10min. During grouting, heating pipes are used to maintain the soil temperature at 10~15℃. After stabilization for 4h, the grouting cushion layer is obtained. The grouting material used includes silica sol, sodium hydroxide, aluminum source, silica fume, and PVP.

[0057] S6. Insert anchor bolts at the designated positions of the grouting cushion layer, lay steel mesh, pour concrete, use antifreeze concrete, install column foot connection parts on the anchor bolts, and obtain the tower foundation structure.

[0058] S7. Fill the foundation pit with non-frost-susceptible soil, which includes graded gravel, crushed stone and quicklime. The volume ratio of graded gravel to crushed stone is 7:3. The amount of quicklime added is 5% of the total weight of graded gravel and crushed stone. Compact the soil.

[0059] Comparative Example 1

[0060] The difference between Comparative Example 1 and Example 2 is that no acid or alkali solution was used for pretreatment.

[0061] Comparative Example 2

[0062] The difference between Comparative Example 2 and Example 2 is that no heating and drying were performed after pretreatment with acid and alkali solutions.

[0063] Comparative Example 3

[0064] The difference between Comparative Example 3 and Example 2 is that the slurry does not contain an aluminum source.

[0065] Comparative Example 4

[0066] The difference between Comparative Example 4 and Example 2 is that the slurry does not contain silica fume.

[0067] II. Testing Methods

[0068] 1. Freeze-thaw cycle test: Soil samples were taken from a depth of 10-20 cm in the stabilized grouting layer. The soil samples were wrapped in plastic wrap to inhibit moisture evaporation, forming a specimen. The freezing temperature was set at -20℃ and the thawing temperature at 20℃. Each freezing and thawing cycle lasted 12 hours, with one freeze-thaw cycle completed every 24 hours. Each specimen underwent 6 freeze-thaw cycles. The volume of the specimen 12 hours after the last freezing was measured, and the rate of change of the frozen volume compared to the initial volume was calculated to obtain the frozen strain. Similarly, the volume of the specimen 12 hours after the last thawing was measured, and the rate of change of the thawed volume compared to the initial volume was calculated to obtain the thawed strain. Positive values ​​for both frozen and thawed strain indicate that the specimen underwent expansion deformation during the freezing or thawing phase, while negative values ​​indicate that the specimen underwent contraction deformation during the freezing or thawing phase.

[0069] 2. Unconfined compressive strength test: Refer to GB / T 50123-2019 "Standard for Geotechnical Testing Methods".

[0070] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0071] Freeze-thaw cycle tests and unconfined compressive strength tests were conducted on soil samples from the foundation pit before grouting (soil samples at a depth of 10~20cm), grouting cushion layers in Examples 1~2 and Comparative Examples 1~4. The test results are shown in Table 1 below.

[0072] Table 1

[0073] serial number Frozen body strain Melt strain Unconfined compressive strength (kPa) Soil samples from ungrouted foundation pits 5.3% -8.7% 352 Example 1 2.5% -1.2% 843 Example 2 1.1% -0.6% 1322 Comparative Example 1 3.8% -3.2% 658 Comparative Example 2 2.2% -0.8% 1084 Comparative Example 3 3.2% -2.1% 781 Comparative Example 4 3.3% -2.3% 964

[0074] As shown in Table 1, the freeze-thaw resistance of the grouted soil layer increased significantly. The absolute values ​​of the cumulative frozen and thawed strains after six freeze-thaw cycles were both relatively small, significantly lower than those of the ungrouted foundation pit soil sample. In Comparative Example 1, no acid or alkali pretreatment was used, resulting in low soil porosity and making grouting more difficult. Therefore, compared to Example 2, the absolute values ​​of both frozen and thawed strains increased significantly, and the unconfined compressive strength also decreased substantially, indicating that acid-alkali pretreatment of the soil can effectively improve the grouting effect. In Comparative Example 2, no heating and drying were performed, resulting in a decrease in freeze-thaw resistance and unconfined compressive strength compared to Example 2, indicating that excessive moisture content is detrimental to grouting. Comparative Example 3 did not add an aluminum source, and Comparative Example 4 did not add silica fume, leading to a decrease in freeze-thaw resistance and unconfined compressive strength compared to Example 2, indicating that both aluminum source and silica fume can improve the strength of the grouted cushion layer.

[0075] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A construction method for the foundation structure of an overhead power line tower, characterized in that, Includes the following steps: S1. Excavate the foundation pit, pretreat the bottom of the foundation pit with acid and alkali solutions in sequence, heat and dry it, and then grout it to obtain a grouting cushion layer. The grout used for grouting includes silica sol, sodium hydroxide, aluminum source, silica fume and PVP. S2. Insert anchor bolts at the designated positions of the grouting cushion layer, lay steel mesh, pour concrete, and install column foot connectors on the anchor bolts to obtain the tower foundation structure. S3. Fill the foundation pit with non-frost-susceptible soil and compact it.

2. The construction method for the foundation structure of overhead line towers according to claim 1, characterized in that, The pretreatment step in step S1 includes: injecting hydrochloric acid with a mass concentration of 5% to 10% into the bottom of the foundation pit, reacting for 3 to 5 hours, and then injecting sodium hydroxide solution with a mass concentration of 5% to 10% to adjust the pH of the soil layer at the bottom of the foundation pit to 8 to 10.

3. The construction method for the foundation structure of overhead line towers according to claim 1, characterized in that, The heating and drying process in step S1 uses hot air drying to make the soil moisture content at the bottom of the foundation pit 50%~70%.

4. The construction method for the foundation structure of overhead line towers according to claim 1, characterized in that, The slurry comprises, by weight, 80-100 parts silica sol, 10-15 parts sodium hydroxide, 5-20 parts aluminum source, 15-30 parts silica fume, and 1-3 parts PVP.

5. The construction method for the foundation structure of overhead line towers according to claim 1, characterized in that, The mass concentration of the silica sol is 5%~10%; The aluminum source includes at least one of aluminum hydroxide and sodium aluminate.

6. The construction method for the foundation structure of overhead line towers according to claim 1, characterized in that, The method for preparing the slurry includes: dispersing silica fume, aluminum hydroxide, and PVP in water to obtain a dispersion; Mix silica sol and sodium hydroxide, then slowly add the dispersion solution while stirring at high speed to obtain a slurry.

7. The construction method for the foundation structure of overhead line towers according to claim 1, characterized in that, During the grouting process in step S1, the soil layer at the bottom of the foundation pit is heated to a temperature of 15~30℃ using a heat pipe.

8. The construction method for the foundation structure of overhead line towers according to claim 1, characterized in that, The non-frost-susceptible soil mentioned in step S3 includes graded gravel, crushed stone, and quicklime.

9. A foundation structure for an overhead power line tower, characterized in that, It is prepared by the construction method described in any one of claims 1 to 6.

10. The overhead line tower foundation structure according to claim 9, characterized in that, It includes a grouting cushion layer set at the bottom of the foundation pit, with column-shaped foundations at the four corners of the grouting cushion layer, and multiple anchor bolts inside the column foundations, with column foot connecting parts fixedly connected to the top of the anchor bolts; The adjacent column foundations are fixedly connected by connectors, the connectors including a concrete layer, the concrete layer containing main reinforcement bars and stirrups, the two ends of the main reinforcement bars being fixedly connected to the two adjacent column foundations respectively; The foundation pit is filled with non-frost-susceptible soil.

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