Soft soil roadbed curing agent for island-shaped permafrost region and application of soft soil roadbed curing agent

Abstract

The invention relates to a soft soil roadbed curing agent for an island-shaped permafrost region and application thereof, the soft soil roadbed curing agent is used for mixing the soft soil roadbed curing agent with undisturbed soil and compacting and molding, and the soft soil roadbed curing agent comprises the following raw materials in percentage: 50-60% of carbide slag, 20-30% of 525 Portland cement, 5-10% of nano silicon dioxide, 3-5% of plant ash, 3-5% of polyacrylamide and 3-5% of water glass. The soft soil roadbed curing agent disclosed by the invention is prepared from industrial waste residues which are widely distributed, easy to obtain, simple to activate, quick to process and low in cost, and can be used for remarkably shortening the solidification time of a roadbed, improving the compressive strength of the roadbed, reducing uneven frost heaving generated in an island-shaped permafrost region roadbed and improving the quality of the roadbed. The safety of railway operation is greatly improved, and the construction period is shortened.

Description

Technical Field

[0001] The present invention relates to the technical field of curing agents, and particularly relates to a soft soil subgrade curing agent for island permafrost regions and its application. Background Art

[0002] With the rapid development of high-speed railways, China is gradually forming the world's largest and fastest-operating high-speed railway network. The national high-speed railway network will inevitably cover a large area of severe cold island permafrost regions, including the Northeast, Northwest, and North China regions where permafrost is widely distributed. Compared with other countries at the same latitude, the construction environment of China's high-speed railways is harsh. In severe cold regions, the winter temperature is extremely low and the duration is long, which easily causes frost heaving deformation of the subgrade, resulting in track unevenness and seriously affecting the operation safety of high-speed railways, posing a huge challenge to China's high-speed railway construction technology.

[0003] In island permafrost regions, due to the large temperature difference, the soil in the permafrost area is relatively hard. The water in the soil precipitates, crystallizes, hardens, and expands at a lower temperature. In severe cases, it will cause cracking. When the season changes to summer, it will melt again, resulting in cracking of the base soil. Therefore, curing agents are usually used in the construction process. For example, the curing agent with the patent number CN101792670A provides a curing agent for island permafrost regions to solve the curing effect of the subgrade in island permafrost regions. However, the existing curing agents usually only play the role of increasing the conventional soil bearing capacity. The most important core factor for the soil in island permafrost regions is the excessive water content of the roadbed layer. At the insulation layer close to the outer layer, the water in the soil will condense and expand due to the low temperature, ultimately affecting the coverage of the insulation layer. Due to such deficiencies, the effect of the curing agent in the subgrade of island permafrost regions is poor, and it usually requires repeated construction and inspection to be applied, which not only prolongs the construction period but also wastes a lot of manpower and material resources. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a soft soil subgrade curing agent for island permafrost regions and its application, which overcomes the problems of large frost heaving sensitivity and long thawing period (up to 6 months) in island permafrost, and achieves a good curing and anti-freezing effect.

[0005] The present invention is realized by the following technical solutions: A soft soil subgrade curing agent for island permafrost regions, comprising the following raw materials in percentage: 50 - 60% carbide slag, 20 - 30% 525 Portland cement, 5 - 10% nano-silica, 3 - 5% plant ash, 3 - 5% polyacrylamide, 3 - 5% water glass.

[0006] According to the above technical solution, preferably, the carbide slag is made into slag powder with a particle size of 50 mm through drying, ultrafine grinding, and activation treatment. Among them, it is preferably to dry the carbide slag at 105 °C to remove the moisture in the carbide slag, decompose organic matter and volatile impurities, mix the sulfate as an activator with the carbide slag, the dosage of the sulfate is 2-8% of the mass of the carbide slag, add water and stir evenly, age for 2-7 days at room temperature, then wash the surface residual activator and impurities with distilled water, and finally filter and dry.

[0007] According to the above technical solution, preferably, the diameter of the nano-silica particles is 80 nm.

[0008] According to the above technical solution, preferably, the particle size of the polyacrylamide is 80 mesh.

[0009] According to the above technical solution, preferably, it includes the following raw materials in percentage: 55% carbide slag, 25% 525 Portland cement, 8% nano-silica, 4% polyacrylamide, 4% plant ash, and 4% water glass.

[0010] This application also discloses the application of a soft soil subgrade solidifying agent for island permafrost regions. Based on the above soft soil subgrade solidifying agent for island permafrost regions, the soft soil subgrade solidifying agent is mixed with undisturbed soil and compacted into shape. The specific steps are as follows: Prepare the soft soil subgrade solidifying agent according to the raw material ratio; Dry and crush the undisturbed soil through a sieve, and mix it with the soft soil subgrade solidifying agent, and add pure water and mix evenly; Compact and demold the mixed soft soil subgrade solidifying agent and undisturbed soil.

[0011] According to the above technical solution, preferably, when "drying and crushing the undisturbed soil through a sieve", the drying temperature is controlled at 105-110 °C, and the drying time is controlled within 24 h; Put the undisturbed soil into a ball mill, crush it for 4-5 minutes and then take it out, and pass it through a 0.5 mm sieve.

[0012] According to the above technical solution, preferably, when "mixing with the soft soil subgrade solidifying agent", the incorporation ratio of the soft soil subgrade solidifying agent is 10%.

[0013] The beneficial effects of the present invention are: (1) Low cost: The soft soil subgrade solidifying agent of the present invention makes full use of the industrial waste carbide slag for chemical reactions, does not require a large amount of earthwork to be transported out, and saves material costs and transportation costs.

[0014] (2) Strong integrity: The original soil forms a plate after being solidified by the soft soil subgrade solidifying agent. Under the action of vehicle load, the plate is stressed as a whole, and the upper load is evenly transmitted to the base layer, effectively improving the bearing capacity of the base layer and thus extending the service life of the base layer. The soft soil subgrade solidifying agent of the present invention has strong anti-seepage, anti-freezing and anti-pumping capabilities, can effectively treat soft ground, and enables the road surface base layer to have good overall stability.

[0015] (3) Short curing time, fast hardening, high compressive strength, good anti-freeze-thaw effect and stable performance; under standard curing conditions, when mixed according to the mass ratio of the solidifying agent accounting for 10% of the original soil in the frozen soil area, the unconfined compressive strength can reach 3 - 5 MPa in 3 days and 7 - 8 MPa in 7 days. When mixed according to the mass ratio of the solidifying agent accounting for 5% of the original soil in the frozen soil area, the compaction degree is 87%, the strength loss rate after 10 freeze-thaw cycles is 2.77%, and the strength loss rate after 25 freeze-thaw cycles is 6.87%.

[0016] (4) Strong environmental adaptability: The soft soil subgrade solidifying agent of the present invention replaces traditional cement with high energy consumption and high pollution, and achieves goals such as fast reaction, high strength and good durability. It can enable the solidified subgrade in the permafrost area to be solidified normally under the influence of complex environments such as wet-dry cycles and freeze-thaw cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the material ratio of the soft soil subgrade solidifying agent in Embodiment 1 of the present invention.

[0018] Figure 2 It is a schematic diagram of the solidification performance measurement of the original soil in the permafrost area in Embodiment 1 of the present invention.

[0019] Figure 3 It is a schematic diagram of the freeze-thaw strength loss measurement of the solidified soil in Embodiment 1 of the present invention.

[0020] Figure 4 It is a schematic diagram of the material ratio of the soft soil subgrade solidifying agent in Embodiment 2 of the present invention.

[0021] Figure 5 It is a schematic diagram of the solidification performance measurement of the original soil in the permafrost area in Embodiment 2 of the present invention.

[0022] Figure 6 It is a schematic diagram of the freeze-thaw strength loss measurement of the solidified soil in Embodiment 2 of the present invention.

[0023] Figure 7 It is a schematic diagram of the material ratio of the soft soil subgrade solidifying agent in Embodiment 3 of the present invention.

[0024] Figure 8 It is a schematic diagram of the solidification performance measurement of the original soil in the permafrost area in Embodiment 3 of the present invention.

[0025] Figure 9 It is a schematic diagram for measuring the freeze-thaw strength loss of solidified soil in Embodiment 3 of the present invention. Detailed implementation manners

[0026] In order to enable those skilled in the art of the present technology to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and the best embodiments. Based on the embodiments of the invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the scope of protection of the invention.

[0027] Based on the principle of natural mineral crystallization, the present application uses a variety of natural mineral materials without any environmental, soil, and groundwater pollution. Through fine grading, formulation, ultrafine grinding, and activation treatment, a soft soil subgrade solidifying agent is prepared. The carbide slag in the soft soil subgrade solidifying agent is dried, ultrafinely ground, and activated. Its main component is calcium hydroxide and also contains a small amount of alumina, which undergoes a hydration reaction with the water in the soil. In an alkaline environment, the carbide slag and plant ash undergo a pozzolanic reaction to generate a large amount of needle-like solidification products (C-S-H gel) and a small amount of ettringite, improving the compactness of the soft soil structure. The high specific surface area of nano-silica enables strong interaction between the solidifying agent molecules, enhancing the interaction force between the undisturbed soil and the solidifying agent. The active groups on the surface of nano-silica participate in the solidification reaction to form a dense cross-linked network structure, further improving the solidification effect of the soft soil subgrade. The high molecular weight on the molecular chain of polyacrylamide can form a polymer network structure with the surface of the undisturbed soil particles, thereby enhancing the adhesion between the undisturbed soil particles, effectively preventing the penetration of water in the undisturbed soil, and significantly improving the impermeability of the undisturbed soil. Sodium silicate can shorten the setting time of the cement in the solidifying agent. The silicic acid gel precipitated during the hardening of sodium silicate plugs the capillary pores of the undisturbed soil, thereby improving the pore structure of the undisturbed soil. At the same time, sodium silicate reacts with Ca(OH)2 in the carbide slag to generate hard calcium silicate gel to fill the pores of the undisturbed soil, increasing the compactness of the undisturbed soil and thus improving the frost resistance of the undisturbed soil.

[0028] The hydration reaction and main products of the soft soil subgrade solidifying agent of the present invention application with the soil are as follows:

[0029] Its function is to promote early strength.

[0030]

[0031] Its hydration reaction speed is the fastest and can effectively promote early setting.

[0032]

[0033] Example 1: The soft soil subgrade solidifying agent was prepared according to the material ratio in Figure 1 . In this example, the in-situ soil was taken from the highly frost-susceptible fluid plastic soft soil at Yichun West Station of the Harbin-Yichun High-Speed Railway. The corresponding soft soil subgrade solidifying agent was prepared according to the designed ratio, as shown in Figure 1 . The retrieved in-situ soil was dried in an oven with the temperature controlled at 105 - 110 °C for about 24 hours. The dried soil was taken out after being pulverized in a ball mill for 4 - 5 minutes and passed through a 0.5 mm sieve. The sieved in-situ soil was taken out, weighed, and mixed with 10% of the mass of the in-situ soil by the soft soil subgrade solidifying agent, and manually mixed until uniform. Pure water was added, and then manually mixed again to achieve a higher degree of uniformity as much as possible. The required amount of water was sprayed onto the soil material and mixed evenly. After standing for a while, it was put into a plastic bag and then placed in a closed container for at least 20 h to make the water content uniform. The above solidifying agent-in-situ soil sample was made into a standard size of a conventional triaxial apparatus with a height of 80 mm and a diameter of 39.1 mm. Through the compaction test, the optimal water content of the in-situ soil was 31.78%, and the maximum dry density was 1.926 g / cm 3 . The maximum wet density was calculated based on the maximum dry density and optimal water content of the soil sample, and then the mass required for each specimen was calculated. Before loading the sample, a layer of vaseline was evenly applied inside the static pressure mold, and a filter paper was placed at the bottom of the mold for easy demolding. Then the mixture was put into the static pressure machine in three layers for compaction. After each layer was compacted, a soil mixing knife was used to scrape the surface of the layer. After the compacted specimen was demolded, it was numbered and labeled, put into a plastic bag, and placed indoors for normal temperature curing until the designed age for the required unconfined compressive strength test. The average value of the strength of the solidified soil at this mixing ratio is shown in Figure 2 .

[0034] Meanwhile, according to the above method, the two groups of compacted specimens were demolded, numbered, and labeled, put into a plastic bag, and placed indoors for normal temperature curing until the designed age. One group of specimens was used to detect the compressive strength P q before freeze-thaw; the other group of specimens was used to detect the compressive strength P h after 25 cycles of repeated freeze-thaw. The specimens were placed in an automatic temperature-controlled freeze-thaw box. First, they were kept at a constant temperature of 1 °C for 12 h, then cooled uniformly to -40 °C in 12 h (with an average temperature drop of 3.42 °C per hour) and kept frozen at -40 °C for 12 h. Immediately afterwards, they were heated uniformly to 40 °C in 12 h (with an average temperature rise of 6.67 °C per hour) and kept thawed at 40 °C for 12 h. Such repeated 25 cycles of freeze-thaw. The strength loss rate P d of the solidified soil at this mixing ratio was calculated as shown in the following formula, and the test results are shown in Figure 3 .

[0035]

[0036] Example 2: According to Figure 4 the material ratio in, the soft soil subgrade solidifying agent was prepared. In this example, the undisturbed soil was taken from the flowing plastic soft soil with extremely high frost heaving sensitivity at Yichun West Station of the Harbin-Yichun High-Speed Railway. The corresponding soft soil subgrade solidifying agent was prepared according to the designed ratio, as shown in Figure 4 . The retrieved undisturbed soil was dried in an oven, with the temperature controlled at 105 - 110 °C and the time controlled for about 24 hours. After drying the water, the soil was put into a ball mill and crushed for 4 - 5 minutes and then taken out, and passed through a 0.5 mm sieve. The sieved undisturbed soil was taken out, weighed, and mixed according to 10% of the mass of the soft soil subgrade solidifying agent in the undisturbed soil, and manually mixed until uniform. Pure water was added, and then manually mixed again to try to achieve a higher degree of uniformity. The required amount of water was sprayed onto the soil material and mixed evenly. After standing for a while, it was put into a plastic bag, and then placed in a closed container for at least 20 h to make the moisture content uniform. The above solidifying agent-undisturbed soil sample was made into the standard size of a conventional triaxial apparatus with a height of 80 mm and a diameter of 39.1 mm. Through the compaction test, the optimum moisture content of the undisturbed soil was 31.78%, and the maximum dry density was 1.926 g / cm 3 . The maximum wet density was calculated based on the maximum dry density and optimum moisture content of the soil sample, and then the mass required for each specimen was calculated. Before loading the sample, a layer of vaseline was evenly smeared inside the static pressure mold and a filter paper was placed at the bottom of the mold to facilitate demolding. Then the mixture was put into the static pressure machine in three times for compaction. After each layer of compaction, a soil mixing knife was used to scrape the surface of the layer. After demolding the compacted specimen, it was numbered and labeled, put into a plastic bag, and placed indoors for normal temperature curing until the designed age for the required unconfined compressive strength test. The average value of the strength of the solidified soil at this mixing ratio is as shown in Figure 5 .

[0037] Meanwhile, according to the above method, the two groups of compacted specimens were demolded, numbered and labeled, put into a plastic bag, and placed indoors for normal temperature curing until the designed age. One group of specimens was used to detect the compressive strength P q before freeze-thaw; the other group of specimens was used to detect the compressive strength P h after 25 cycles of repeated freeze-thaw. The specimens were placed in an automatic temperature-controlled freeze-thaw box. First, they were kept at a constant temperature of 1 °C for 12 h, then cooled uniformly to -40 °C in 12 h (with an average temperature drop of 3.42 °C per hour) and kept frozen at -40 °C for 12 h. Immediately afterwards, they were heated uniformly to 40 °C in 12 h (with an average temperature rise of 6.67 °C per hour) and kept thawed at 40 °C for 12 h. Such repeated freeze-thaw cycles were carried out 25 times. The test results of the strength loss rate of the solidified soil at this mixing ratio are as shown in Figure 6 .

[0038] Example 3: According to Figure 7The soft soil subgrade solidifier is made according to the material ratio in this example. The original soil is taken from the flowing plastic soft soil with extremely high frost heave sensitivity at Yichun West Station of the Harbin-Yichun High-Speed Railway. The corresponding soft soil subgrade solidifier is prepared according to the design ratio, as shown in Figure 7 . The retrieved original soil is dried in an oven, with the temperature controlled at 105 - 110 °C and the time controlled at about 24 hours. After drying the moisture, the soil is put into a ball mill and crushed for 4 - 5 minutes, and then taken out and sieved through a 0.5 mm sieve. The sieved original soil is taken out, weighed, and mixed according to 10% of the mass of the original soil with the soft soil subgrade solidifier, and manually mixed until uniform. Pure water is added, and then manually mixed again to achieve a higher degree of uniformity as much as possible. The required amount of water is sprayed onto the soil material and mixed evenly. After standing for a while, it is put into a plastic bag and then placed in a closed container for at least 20 h to make the water content uniform. The above-mentioned solidifier - original soil sample is made into a standard size of a conventional triaxial apparatus with a height of 80 mm and a diameter of 39.1 mm. Through the compaction test, the optimal water content of the original soil is 31.78%, and the maximum dry density is 1.926 g / cm 3 . The maximum wet density is calculated based on the maximum dry density and optimal water content of the soil sample, and then the mass required for each specimen is calculated. Before loading the sample, a layer of vaseline is evenly applied inside the static pressure mold, and a filter paper is placed at the bottom of the mold for easy demolding. Then the mixture is put into the static pressure machine in three times for compaction. After each layer of compaction, a soil knife is used to scrape the surface of the layer. After demolding the compacted specimen, it is numbered and labeled, put into a plastic bag, and placed indoors for normal temperature curing until the design age for the required unconfined compressive strength test. The average value of the strength of the solidified soil at this mixing ratio is as shown in Figure 8 .

[0039] At the same time, according to the above method, the two groups of compacted specimens are demolded, numbered and labeled, put into plastic bags, and placed indoors for normal temperature curing until the design age. One group of specimens is used to detect the compressive strength P q before freeze-thaw; the other group of specimens is used to detect the compressive strength P h after 25 cycles of repeated freeze-thaw. The specimens are placed in an automatic temperature-controlled freeze-thaw box. First, they are kept at a constant temperature of 1 °C for 12 h, then cooled uniformly to -40 °C in 12 h (with an average temperature drop of 3.42 °C per hour) and kept frozen at -40 °C for 12 h. Immediately afterwards, they are heated uniformly to 40 °C in 12 h (with an average temperature rise of 6.67 °C per hour) and kept thawed at 40 °C for 12 h. Such repeated freeze-thaw cycles are carried out 25 times. The test results of the strength loss rate of the solidified soil at this mixing ratio are as shown in Figure 9 .

[0040] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A soft soil subgrade solidifying agent for island permafrost regions, characterized in that, It includes the following percentage of raw materials: 50-60% carbide slag, 20-30% 525 Portland cement, 5-10% nano-silica, 3-5% plant ash, 3-5% polyacrylamide, 3-5% water glass.

2. The solidifying agent for soft soil subgrade in island permafrost regions according to claim 1, characterized in that, The carbide slag is made into slag powder with a particle size of 50mm through drying, ultrafine grinding and activation treatment.

3. The solidifying agent for soft soil subgrade in island permafrost regions according to claim 1, wherein The diameter of the nano-silica particles is 80nm.

4. The soil stabilizer for soft soil subgrade in island permafrost regions according to claim 1, wherein The particle size of the polyacrylamide is 80 mesh.

5. The solidifying agent for soft soil subgrade in island permafrost regions according to any one of claims 1 to 4, characterized in that, It includes the following percentage of raw materials: 55% carbide slag, 25% 525 Portland cement, 8% nano-silica, 4% polyacrylamide, 4% plant ash, 4% water glass.

6. Application of a soft soil subgrade solidifying agent for island permafrost regions, based on the soft soil subgrade solidifying agent for island permafrost regions described in claims 1-5, characterized in that, Mix the soft soil subgrade curing agent with the undisturbed soil and compact it into shape. The specific steps are as follows: Prepare the soft soil subgrade curing agent according to the raw material ratio; Dry and crush the undisturbed soil through a sieve, mix it with the soft soil subgrade curing agent, and add pure water to mix evenly; Compact and demold the mixed soft soil subgrade curing agent and undisturbed soil.

7. The application of a soft soil subgrade solidifying agent for island permafrost regions according to claim 6, characterized in that, When "drying and crushing the undisturbed soil through a sieve", the drying temperature is controlled at 105-110°C and the drying time is controlled within 24h; Put the undisturbed soil into a ball mill, crush it for 4-5 minutes and then take it out, and pass through a 0.5mm sieve.

8. The application of a soft soil subgrade curing agent for island permafrost regions according to claim 6, characterized in that, When "mixing with the soft soil subgrade curing agent", the admixture ratio of the soft soil subgrade curing agent is 10%.

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