Backfill material based on sandy high-fluidity silt and its preparation method and application

Abstract

The present invention provides a backfill material based on sandy high-fluidity silt, which includes: sandy silt, cement, anionic sodium polyalkylbenzene sulfonate, and water. Since the sandy silt has a small specific surface area, a small internal friction angle, and a weak particle-water-electricity system; when the particles come into contact with water molecules, there is less bound water film, and they exhibit high fluidity after encountering water; the addition of anionic sodium polyalkylbenzene sulfonate further reduces the cohesion and internal friction angle of the sandy silt, effectively improving the fluidity of the backfill material while ensuring strength. The prepared strength-controlled backfill material has good fluidity, self-compactness, and high unconfined compressive strength. It can effectively backfill narrow areas of ditches that are difficult to compact, meet the service requirements of flight zone backfill materials, reduce costs while ensuring performance, and has high economic value; and it recycles excavated and accumulated waste soil, with high social and environmental benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of municipal road engineering, and in particular to a strength-controllable backfill material for backfilling narrow working areas of foundation pits in sandy, highly fluid powdery soil areas, and a preparation method and application thereof. Background Art

[0002] With the rapid development of numerous infrastructure projects in my country, municipal road construction is advancing rapidly. The pace of municipal road renovation and expansion is accelerating across the country, leading to an increasing number of pipeline installations. During the backfilling of trenches created during pipeline excavation, the difficulty of compacting the narrow working surface significantly impacts the mechanical properties of the concrete and asphalt pavement above the pipelines. Due to the unique construction environment and complex structures, pipeline trench backfilling often cannot be compacted using heavy machinery, but instead relies on manual compaction with small compactors. This not only reduces construction efficiency but also fails to meet design expectations.

[0003] The Chinese invention patent application publication number CN108264292A discloses a controllable low-strength material made of construction waste and an application method. The raw materials used are recycled fine powder made from crushed brick-concrete construction waste and a gel material including cement, fly ash and recycled fine powder. Although the compressive strength of this controllable low-strength material made of construction waste is moderate, it can meet the strength required for the controllable low-strength material to be used as a backfill material. However, this controllable low-strength material has poor fluidity or insufficient strength due to high fluidity, and is only suitable for general roadbeds or green belt backfill areas. Moreover, due to its poor self-leveling properties, it is difficult to fill a narrow space with a working surface of only 1m wide or even narrower. At the same time, the preparation process of this controllable low-strength material requires secondary processing or purchase of construction waste, which not only increases the process of preparing raw materials, but also increases the material cost of the controllable low-strength material.

[0004] Furthermore, the excavation of various water supply and drainage pipelines, integrated pipeline corridors, and underpasses generates a significant amount of construction waste. Currently, this waste is often transported to designated locations for storage. This long-distance transportation not only increases project costs but also impacts the local environment and the city's appearance.

[0005] Therefore, it is necessary to design a backfill material for the narrow area of ​​the foundation pit that can fully utilize the engineering waste soil in the site and achieve controllable strength. Summary of the Invention

[0006] The purpose of the present invention is to provide a backfill material based on sandy high-fluidity silt and its preparation method and application. The backfill material uses the discarded sandy silt in the site as the main raw material and has controllable strength, and can be used for backfilling in narrow areas of foundation pits.

[0007] To achieve the above objectives, the present invention provides the following technical solutions:

[0008] One aspect of the present invention is to provide a backfill material based on sandy high-fluidity silt, which includes the following components and contents in parts by weight: 60-71 parts of sandy silt, 3-12 parts of cement, 0.1-0.5 parts of anionic sodium polyalkylbenzene sulfonate and 25-33 parts of water.

[0009] As a preferred technical solution, the backfill material based on sandy high-fluidity silt can also include the following components and their weight contents: 62-66 parts of sandy silt, 5-9 parts of cement, 0.2-0.3 parts of anionic sodium polyalkylbenzene sulfonate and 27-29 parts of water.

[0010] As a preferred technical solution, the backfill material can also include the following components and their weight contents: 60-64 parts of sandy silt, 5-8 parts of cement, 2-3 parts of fly ash, 0.2-0.3 parts of anionic sodium polyalkylbenzene sulfonate, and 27-29 parts of water.

[0011] Furthermore, in the sandy silt, the weight percentage of sand particles is 60-70%, the weight percentage of silt particles is 20-35%, and the weight percentage of clay particles is 0-5%.

[0012] Furthermore, the plastic limit index of the sandy silt is 9.2 to 9.7, and the liquid limit index is 0.47 to 0.72.

[0013] Furthermore, the shear strength parameters of the sandy silt are: cohesion of 11.0 to 20.0 KPa, and internal friction angle of 26.1 to 32.8°.

[0014] Furthermore, the permeability coefficient k of the sandy silt is 2.0E-04 to 3.5E-04 cm / s.

[0015] Furthermore, the compression modulus of the sandy silt is 5.50-22.97 MPa, and the standard penetration number is 3.0-35.0 blows.

[0016] Furthermore, the specific gravity γ of the sandy silt is 18.3-18.9 KN / m 3 ; Natural compaction degree: 79~88.1%.

[0017] Furthermore, the sandy silt may be mixed with 20% or less of silty clay.

[0018] Furthermore, the plasticity index of the silty clay is 10.2 to 21.5, and the liquid index is 0.1 to 0.9.

[0019] Furthermore, the silty clay has a cohesion of 22.0 to 44.0 KPa and an internal friction angle of 15.5 to 31.2°.

[0020] Furthermore, the compression modulus of the silty clay is 2.79-10.16 MPa, and the standard penetration number is 2.0-26.0 blows.

[0021] Furthermore, the permeability coefficient k of the silty clay is 2.0E-04 to 3.5E-04 cm / s.

[0022] Furthermore, the specific gravity γ of the silty clay is 18.3-18.9 KN / m 3 .

[0023] The sandy silt soil can be natural sandy silt soil in the site that meets the above indicators.

[0024] Furthermore, the cement is P·O42.5 cement.

[0025] Furthermore, the cement is one of ordinary Portland cement and sulphoaluminate cement, or a mixture of the two.

[0026] Furthermore, the anionic sodium polyalkylbenzenesulfonate is sodium dodecylbenzenesulfonate.

[0027] Furthermore, the fly ash is one of Class I fly ash and Class II fly ash, or a mixture of the two.

[0028] As an optimal technical solution, for applications in narrow backfill areas of roadbeds on highways and urban roads, the fluidity of the backfill material based on sandy high-fluidity silt can be controlled at 200-300 mm, the setting time is 6-8 h, and the 28-day immersion compressive strength is controlled at 0.40-0.80 MPa.

[0029] Highly fluid silt backfill material with sand is a type of backfill material with controllable strength and high fluidity. It can form a self-compacting structure by filling under its own weight. This backfill material eliminates the need for compaction, solving the problem of difficult backfilling. While ensuring project quality, it can also effectively reduce costs. Therefore, it is widely used in narrow backfill projects such as foundation pit pipelines and bridge abutment backs. Furthermore, this backfill material can utilize various industrial solid waste as raw materials, which is not only cost-effective and environmentally friendly, but also prevents environmental pollution.

[0030] Another aspect of the present invention is to provide a method for preparing the above-mentioned backfill material based on sandy high-fluidity silt, comprising the following steps:

[0031] S1. In the indoor test, in order to control the water consumption, the sandy silt and silty clay with uneven moisture content were first kept at a constant temperature of 105-110℃ to a constant weight, and then the agglomerated soil was broken up with a wooden hammer and sieved to remove particles with a particle size of 4.75mm or more for later use.

[0032] S2. Weigh a predetermined amount of sandy soil, cement, anionic sodium polyalkylbenzene sulfonate, and water and set aside. Clean the mixer by wiping and moistening the mixing pot and stirring blades with a damp cloth. Add the sandy soil and cement to the mixer, start the mixer, and dry mix for about 1 to 2 minutes at a stirring rate of 62±5 r / min. Then, add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly. Slowly add the sodium polyalkylbenzene sulfonate to the mixer during the stirring process for no more than 2 minutes. Continue stirring for about 2 minutes after all the sodium polyalkylbenzene sulfonate is added.

[0033] Furthermore, the sandy silt soil can be cleaned first, and plant roots and other organic impurities in the sandy silt soil can be removed, and then placed in a ventilated place to air dry.

[0034] Furthermore, in step S2, first weigh the sandy silt, then add cement, fly ash, and anionic sodium polyalkylbenzene sulfonate to the sandy silt and dry mix them evenly, and finally add water and mix them evenly.

[0035] Furthermore, in step S2, a cement slurry mixer is used for mixing; for large-scale construction, a concrete mixer can be used for mixing.

[0036] Another aspect of the present invention is to provide an application of the above-mentioned backfill material based on sand-containing high-fluidity silt in a backfill project in a narrow working area of ​​a foundation pit.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] (1) The present invention uses natural sandy silt in the site as the basic raw material, and mixes it evenly with cement, anionic sodium polyalkylbenzene sulfonate, and water, and can also add fly ash. At the same time, the usage ratio of each raw material is regulated to prepare a backfill material with controllable strength. The raw materials can be obtained on site, which can effectively reduce the cost of material preparation.

[0039] (2) The present invention makes full use of the waste soil generated during the excavation of foundation pits and pipelines, and utilizes the synergistic effect of various raw materials to prepare a backfill material with high fluidity, self-compacting, and certain early strength; the material has a relatively uniform texture, good fluidity, high strength, and a large compression modulus, and is a backfill material with excellent performance.

[0040] (3) The preparation process of the backfill material is simple, and the construction only requires mixing with a concrete mixer. It can be mixed and cast on site, which speeds up the construction progress, shortens the construction period, saves labor costs, and can meet the needs of large-scale production and construction on site, and has high application value.

[0041] (4) The backfill material utilizes the accumulated waste earth, which not only effectively reduces the preparation cost of the backfill material and has a high economic value; at the same time, the recycling of waste resources complies with the principle of resource utilization and harmless utilization of waste earth, and has good environmental benefits and social impact.

[0042] Compared with existing materials, the present invention has the following characteristics:

[0043] (1) The main raw material of the present invention is sandy silt that can be obtained on site. It does not require secondary crushing or compounding with solid waste such as waste residue and sludge. It can maximize the use of on-site resources, realize on-site processing of raw materials and prepare strength-controlled backfill materials.

[0044] (2) The strength-controlled backfill material prepared by the present invention has good fluidity, self-compacting and high unconfined compressive strength, and can effectively backfill narrow areas of trenches that are difficult to compact. The density and rebound modulus meet the requirements of foundation bearing, and the long-term settlement is less than that of ordinary silt (100% compaction).

[0045] (3) The application of fly ash improves the fluidity and density of the material. This is due to the morphological effect, micro-aggregate effect, and activity effect of fly ash. While filling the pores, it can effectively react with cement, soil, and water, not only forming a flowing self-compacting material with strong fluidity, high density, and high strength, but also reducing the amount of cement used, showing good application performance and excellent economic benefits.

[0046] (4) The application of sandy silt enables the mixture to exhibit excellent workability at lower water consumption. Since the mineral composition of sandy silt is quartz, albite and a small amount of calcite, it has a high sand content and a low clay content. Its particle size is larger than that of ordinary silt and clay, and the particles are rounded and have fewer edges and corners. These characteristics result in a small specific surface area of ​​the backfill material, a small internal friction angle, and a weak particle-water-electricity interaction system. When the particles come into contact with water molecules, there is less bound water film, and they exhibit high fluidity when in contact with water. At the same time, the mixture exhibits excellent workability at lower water consumption, and its strength does not decrease.

[0047] (5) The addition of anionic sodium polyalkylbenzene sulfonate further reduces the cohesion and internal friction angle of the sandy silt, making the material more fluid. After the addition of anionic sodium polyalkylbenzene sulfonate, it is adsorbed on the surface of the soil particles, and the surface of the sandy silt releases organic anions. The organic anions cannot form bridge chains between clay particles and cannot aggregate particles, thereby greatly reducing the cohesion and internal friction angle of the sandy silt modified by anionic sodium polyalkylbenzene sulfonate. In addition, the positive charge on the surface of the soil particles can adsorb organic anions, making the negative charge of the soil itself redundant and repelling like-charged anions, resulting in electrostatic repulsion. Therefore, the reduction in the cohesion and internal friction angle of the sandy silt modified by anionic sodium polyalkylbenzene sulfonate can make the mixture more fluid. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is the morphology of the backfill material obtained in the comparative example of the present invention;

[0049] Figure 2 This is the form of the backfill material obtained in the embodiment of the present invention;

[0050] Figure 3 7d compression modulus curves of ordinary compacted silt and the backfill material obtained in Example 3;

[0051] Figure 4 This is the compression deformation curve of ordinary compacted silt and the backfill material obtained in Example 3. DETAILED DESCRIPTION

[0052] The present invention is described in detail below with reference to specific embodiments. The embodiments of the present invention are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operating processes, but the protection scope of the present invention is not limited to the following embodiments.

[0053] Comparative Example 1 (ordinary silt)

[0054] This comparative example provides a backfill material based on ordinary silt.

[0055] The preparation method of the backfill material is as follows:

[0056] S1. In the indoor test, in order to control the water consumption, firstly cool the natural ordinary silt and silty clay with uneven moisture content to a constant weight at a temperature of 105-110℃, then use a wooden hammer to break up the agglomerated soil lumps, and sieve to remove particles with a particle size of 4.75mm or more, and set aside.

[0057] S2. First weigh 2200g of the prepared ordinary silt, 96g of cement, 11g of anionic sodium polyalkylbenzene sulfonate, and 965g of water and set aside; then clean the mixer by wiping and moistening the mixing pot and stirring blades with a damp cloth, then add the ordinary silt and cement to the mixer, start the mixer, and dry mix for about 1 to 2 minutes at a stirring rate of 62±5 r / min. Then, add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly. Slowly add it to the mixer during the stirring process for no more than 2 minutes. After all the ingredients are added, continue stirring for about 2 minutes.

[0058] The fluidity test is as follows:

[0059] First, prepare a Φ100mm×200mm moist and smooth cylinder and place it on a work platform (metal or glass plate can be used). Fill the cylinder with the mixture without vibrating or shaking, and scrape it flat. Slowly lift the cylinder vertically upward, and the lifting process takes about 2-4 seconds. Then, immediately use a ruler to measure the collapse expansion diameter of the mixture. When measuring, two mutually perpendicular diameters need to be tested, and the experimental results are averaged. After the material mixing is completed, the entire process of filling, lifting, and measuring must be completed within 90 seconds. The fluidity of the backfill material is measured in this way. After the fluidity meets the requirements, proceed to the next step.

[0060] The strength test specimens were prepared as follows:

[0061] The mixture was re-prepared according to the above method and loaded into a Φ100×200mm cylindrical compressive strength test mold and a Φ61.8×20mm ring knife compression test mold (the casting was slightly higher than the test mold), with 3 parallel specimens; after being placed indoors for 1 hour, the surface was scraped flat; after 48 hours, the specimens were demoulded and placed in a standard curing box (20℃±1℃, 100% RH) for continued curing until the age, at which point the sample preparation was completed.

[0062] Comparative Example 2 (ordinary silt)

[0063] This comparative example provides a backfill material based on ordinary silt.

[0064] The preparation method of the backfill material is as follows:

[0065] S1. In the indoor test, in order to control the water consumption, firstly cool the natural ordinary silt and silty clay with uneven moisture content to a constant weight at a temperature of 105-110℃, then use a wooden hammer to break up the agglomerated soil, and sieve to remove particles with a particle size of 4.75mm or more, and set aside.

[0066] S2. First, weigh 2200g of the prepared ordinary silt, 191g of cement, 11g of anionic sodium polyalkylbenzene sulfonate, and 957g of water and set aside; then clean the mixer by wiping and moistening the mixing pot and stirring blades with a damp cloth, then add the ordinary silt and cement to the mixer, start the mixer, and dry mix for about 1 to 2 minutes at a stirring rate of 62±5 r / min. Then, add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly. Slowly add it to the mixer during the stirring process for no more than 2 minutes. After all the ingredients are added, continue stirring for about 2 minutes.

[0067] The preparation of fluidity and strength specimens is similar to that of Comparative Example 1.

[0068] Comparative Example 3 (ordinary silt)

[0069] This comparative example provides a backfill material based on ordinary silt.

[0070] The preparation method of the backfill material is as follows:

[0071] S1. In the indoor test, in order to control the water consumption, firstly cool the natural ordinary silt and silty clay with uneven moisture content to a constant weight at a temperature of 105-110℃, then use a wooden hammer to break up the agglomerated soil, and sieve to remove particles with a particle size of 4.75mm or more, and set aside.

[0072] S2, first weigh 2200g of prepared ordinary silt, 292g of cement, 11g of anionic sodium polyalkylbenzene sulfonate, and 972g of water, and set aside; then clean the mixer, first wipe and wet the mixing pot and stirring blades with a damp cloth, then add ordinary silt and cement to the mixer, start the mixer, and dry mix for about 1 to 2 minutes at a stirring rate of 62±5r / min, then add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly, and slowly add it to the mixer during the stirring process, the time should not exceed 2 minutes, and continue stirring for about 2 minutes after all the addition is complete.

[0073] The preparation of fluidity and strength specimens is similar to that of Comparative Example 1.

[0074] Example 1:

[0075] This embodiment provides a backfill material based on sandy and highly fluid silt.

[0076] The preparation method of the backfill material is as follows:

[0077] S1. In the indoor test, in order to control the water consumption, the sandy silt and silty clay with uneven moisture content were first kept at a constant temperature of 105-110℃ to a constant weight, and then the agglomerated soil was broken up with a wooden hammer and sieved to remove particles with a particle size of 4.75mm or more for later use.

[0078] S2, first weigh 2200g of the prepared sandy silt, 96g of cement, 11g of anionic sodium polyalkylbenzene sulfonate, and 965g of water, and set aside; then clean the mixer, first wipe and wet the mixing pot and stirring blades with a damp cloth, then add the sandy silt and cement to the mixer, start the mixer, and dry mix for about 1 to 2 minutes at a stirring rate of 62±5r / min, then add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly, and slowly add it to the mixer during the stirring process, the time should not exceed 2 minutes, and continue stirring for about 2 minutes after all the addition is complete.

[0079] The fluidity test is as follows:

[0080] First, prepare a Φ100mm×200mm moist and smooth cylinder and place it on a work platform (metal or glass plate can be used). Fill the cylinder with the mixture without vibrating or shaking, and scrape it flat. Slowly lift the cylinder vertically upward, and the lifting process takes about 2-4 seconds. Immediately measure the collapse expansion diameter of the mixture with a ruler. When measuring, two mutually perpendicular diameters need to be tested, and the experimental results are averaged. After the material mixing is completed, the entire process of filling, lifting, and measuring must be completed within 90 seconds. The fluidity of the material is measured, and the next step is carried out after the fluidity meets the requirements.

[0081] The strength test specimens were prepared as follows:

[0082] The mixture was re-prepared according to the above method and loaded into a Φ100×200mm cylindrical compressive strength test mold and a Φ61.8×20mm ring knife compression test mold (the casting was slightly higher than the test mold), with 3 parallel specimens; after being placed indoors for 1 hour, the surface was scraped flat; after 47 hours, the specimens were demoulded and placed in a standard curing box (20℃±1℃, 100% RH) for continued curing until the age, at which point the sample preparation was completed.

[0083] Example 2:

[0084] This embodiment provides a backfill material based on sandy and highly fluid silt.

[0085] The preparation method of the backfill material is as follows:

[0086] S1. In the indoor test, in order to control the water consumption, the sandy silt and silty clay with uneven moisture content were first kept at a constant temperature of 105-110℃ to a constant weight, and then the agglomerated soil was broken up with a wooden hammer and sieved to remove particles with a particle size of 4.75mm or more for later use.

[0087] S2. Weigh 2200 g of sandy silt, 191 g of cement, 11 g of anionic sodium polyalkylbenzene sulfonate, and 957 g of water. Before stirring, wipe the mixing pot and stirring blades clean and wet them with a damp cloth. Add the sandy silt and cement to the mixer, start the mixer, and dry mix for about 1 to 2 minutes at a stirring rate of 62 ± 5 r / min. Then, add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly. Slowly add the sodium polyalkylbenzene sulfonate to the mixer during stirring for no more than 2 minutes. Continue stirring for about 2 minutes after all the sodium polyalkylbenzene sulfonate is added.

[0088] The fluidity test and strength specimen preparation are similar to those in Example 1.

[0089] Example 3:

[0090] This embodiment provides a backfill material based on sandy and highly fluid silt.

[0091] The preparation method of the backfill material is as follows:

[0092] S1. In the indoor test, in order to control the water consumption, the sandy silt and silty clay with uneven moisture content were first kept at a constant temperature of 105-110℃ to a constant weight, and then the agglomerated soil was broken up with a wooden hammer and sieved to remove particles with a particle size of 4.75mm or more for later use.

[0093] S2. Weigh 2200 g of sandy silt, 292 g of cement, 11 g of anionic sodium polyalkylbenzene sulfonate, and 972 g of water. Before stirring, wipe the mixing pot and stirring blades clean and wet them with a damp cloth. Add the sandy silt and cement to the mixer, start the mixer, and dry mix for about 1 to 2 minutes at a stirring rate of 62 ± 5 r / min. Then, add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly. Slowly add the sodium polyalkylbenzene sulfonate to the mixer during stirring for no more than 2 minutes. Continue stirring for about 2 minutes after all the sodium polyalkylbenzene sulfonate is added.

[0094] The fluidity test and strength specimen preparation are similar to those in Example 1.

[0095] Example 4:

[0096] This embodiment provides a backfill material based on sandy and highly fluid silt.

[0097] The preparation method of the backfill material is as follows:

[0098] S1. In the indoor test, in order to control the water consumption, the sandy silt and silty clay with uneven moisture content were first kept at a constant temperature of 105-110℃ to a constant weight, and then the agglomerated soil was broken up with a wooden hammer and sieved to remove particles with a particle size of 4.75mm or more for later use.

[0099] S2, weigh 2200g of sandy silt, 96g of cement, 110g of fly ash, 11g of anionic sodium polyalkylbenzene sulfonate, and 963ml of water, and set aside; then clean the mixer, first wipe and wet the mixing pot and stirring blades with a damp cloth, then add the sandy silt, cement, and fly ash to the mixer, start the mixer and dry mix for about 1 to 2 minutes at a stirring rate of 62±5r / min; then add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly, and slowly add it to the mixer during the stirring process, the time should not exceed 2 minutes, and continue stirring for about 2 minutes after all the ingredients are added.

[0100] The fluidity test and strength specimen preparation are similar to those in Example 1.

[0101] Example 5:

[0102] This embodiment provides a backfill material based on sandy and highly fluid silt.

[0103] The preparation method of the backfill material is as follows:

[0104] S1. In the indoor test, in order to control the water consumption, the sandy silt and silty clay with uneven moisture content were first kept at a constant temperature of 105-110℃ to a constant weight, and then the agglomerated soil was broken up with a wooden hammer and sieved to remove particles with a particle size of 4.75mm or more for later use.

[0105] S2, weigh 2200g of sandy silt, 195g of cement, 110g of fly ash, 11g of anionic sodium polyalkylbenzene sulfonate, and 977g of water, and set aside; then clean the mixer, first wipe and wet the mixing pot and stirring blades with a damp cloth, then add the sandy silt, cement, and fly ash to the mixer, start the mixer and dry mix for about 1 to 2 minutes at a stirring rate of 62±5r / min; then add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly, and slowly add it to the mixer during the stirring process, the time should not exceed 2 minutes, and continue stirring for about 2 minutes after all the ingredients are added.

[0106] The fluidity test and strength specimen preparation are similar to those in Example 1.

[0107] Example 6:

[0108] This embodiment provides a backfill material based on sandy and highly fluid silt.

[0109] The preparation method of the backfill material is as follows:

[0110] S1. In the indoor test, in order to control the water consumption, the sandy silt and silty clay with uneven moisture content were first kept at a constant temperature of 105-110℃ to a constant weight, and then the agglomerated soil was broken up with a wooden hammer and sieved to remove particles with a particle size of 4.75mm or more for later use.

[0111] S2, weigh 2200g of sandy silt, 297g of cement, 110g of fly ash, 11g of anionic sodium polyalkylbenzene sulfonate, and 991g of water, and set aside; then clean the mixer by first wiping and moistening the mixing pot and stirring blades with a damp cloth, then add the sandy silt, cement, and fly ash to the mixer, start the mixer and dry mix for about 1 to 2 minutes at a stirring rate of 62±5 r / min; then add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly, and slowly add it to the mixer during the stirring process for no more than 2 minutes. After all the ingredients are added, continue stirring for about 2 minutes.

[0112] The fluidity test and strength specimen preparation are similar to those in Example 1.

[0113] Performance testing:

[0114] The fluidity, unconfined compressive strength, compression deformation and modulus of the backfill materials obtained in Comparative Examples 1-3 and Examples 1-6 were tested to evaluate the working performance and mechanical properties of the prepared backfill materials in practical applications.

[0115] The fluidity test was carried out according to ASTM D6103, and the mold used was a cylinder with a diameter of 100 mm × 200 mm.

[0116] Unconfined compressive strength tests were conducted according to the "Testing Procedure for Stabilized Materials with Inorganic Binders for Highway Engineering," JTG E51-2009. The day before reaching the specified age, the specimens were immersed in water for one day and tested using a pavement material strength tester at a loading rate of 1 mm / min.

[0117] Compression tests were conducted in accordance with the "Cement-Soil Mix Design Code" (JGJ T233-2011). To address the worst-case scenario, the specimens were immersed in water on the final day of curing and then tested using a fully automatic oedometer. Because the deadweight load in the application area would not exceed 300 kPa, the maximum compression level was set at 400 kPa. Compression levels were 50, 100, 200, and 400 kPa, with a stability threshold of 1 hour for each level, requiring deformation to exceed 0.01 mm.

[0118] Table 1 Basic properties of backfill materials obtained from different comparative examples and examples

[0119]

[0120]

[0121] According to Table 1, among the backfill materials prepared with the same ash-water ratio and water-solid ratio, the fluidity of the backfill materials prepared by sandy silt in Examples 1 to 3 is 25 cm, and the fluidity of the backfill materials prepared by ordinary silt in Comparative Examples 1 to 3 is 15 cm. The state of the backfill materials can be referred to Figure 1 and Figure 2For narrow areas of foundation pits, the fluidity of the backfill material must be controlled at 20-30 cm to allow the material to self-compact and fill the entire area. Therefore, from a performance perspective, sand-coated silt improves the material's fluidity, offering significant advantages over ordinary silt. Furthermore, the strength of the backfill materials obtained in Examples 1-3 is similar to that of Comparative Examples 1-3. Examples 4-6 demonstrate that the addition of fly ash can improve the material's strength.

[0122] Table 2 Comparison of compression performance between ordinary compacted silt and Example 3

[0123]

[0124] From Table 2 and Figure 3 It can be seen that the 7d compression modulus of Example 3 is greater than that of ordinary silt (100% compaction degree), and the compression performance is better than that of silt. Figure 4 The total deformation curve of Example 3 is generally below the ordinary compaction deformation curve. That is to say, when Example 3 is applied to foundation pit backfill, the compression deformation caused by the superstructure load and additional load is smaller than the ordinary silt (96% compaction degree) used in the usual design, thus meeting the settlement deformation requirements of the foundation.

[0125] Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even when only a single embodiment is described with respect to specific features. The feature examples provided in the present disclosure are intended to be illustrative, not limiting, unless otherwise stated. In specific implementations, the technical features of one or more dependent claims may be combined with the technical features of the independent claims, depending on actual needs and where technically feasible, and the technical features from the corresponding independent claims may be combined in any appropriate manner rather than solely through the specific combinations listed in the claims.

[0126] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined by the claims.

Claims

1. A backfill material based on sandy high-fluidity silt, characterized in that: The invention comprises the following components: sandy silt, cement, anionic sodium polyalkylbenzene sulfonate, water and fly ash; The sandy silt soil is selected from natural sandy silt soil in the site that meets the following indicators: The sandy silt contains 60-70% by weight of sand particles, 20-35% by weight of silt particles, and 0-5% by weight of clay particles. The plastic limit index of the sandy silt is 9.2-9.7; the liquid limit index is 0.47-0.72; The shear strength parameters of the sandy silt are: cohesion of 11.0-20.0 KPa, internal friction angle of 26.1-32.8°; The permeability coefficient k of the sandy silt is 2.0E-04~3.5E-04 cm / s; The compression modulus of the sandy silt is 5.50-22.97 MPa, and the standard penetration number is 3.0-35.0 blows; The specific gravity γ of the sandy silt is 18.3-18.9 KN / m 3 ;Natural compaction degree: 79-88.1%; The sandy silt soil is mixed with silty clay in an amount less than or equal to 20% by weight; The plasticity index of the silty clay is 10.2-21.5, and the liquid index is 0.1-0.9; The silty clay has a cohesion of 22.0-44.0 KPa and an internal friction angle of 15.5-31.2°; The silty clay has a compression modulus of 2.79-10.16 MPa and a standard penetration test of 2.0-26.0 blows; The permeability coefficient k of the silty clay is 2.0E-04~3.5E-04 cm / s; The specific gravity γ of the silty clay is 18.3-18.9 KN / m 3 ; The fly ash is one of Class I fly ash and Class II fly ash, or a mixture of the two.

2. The backfill material according to claim 1, characterized in that The components are as follows in parts by weight: 60-71 parts of sandy silt, 3-12 parts of cement, 0.1-0.5 parts of anionic sodium polyalkylbenzene sulfonate, and 25-33 parts of water.

3. The backfill material according to claim 2, characterized in that: The components are as follows in parts by weight: 62-66 parts of sandy silt, 5-9 parts of cement, 0.2-0.3 parts of anionic sodium polyalkylbenzene sulfonate, and 27-29 parts of water.

4. The backfill material according to claim 1, characterized in that The components are as follows in parts by weight: 60-64 parts of sandy silt, 5-8 parts of cement, 2-3 parts of fly ash, 0.2-0.3 parts of anionic sodium polyalkylbenzene sulfonate, and 27-29 parts of water.

5. The backfill material according to claim 1, characterized in that: The cement is one of ordinary Portland cement and sulphoaluminate cement, or a mixture of the two.

6. A method for preparing a backfill material based on sandy high-fluidity silt according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. In the indoor test, to control the water consumption, first cool the sandy silt and silty clay with uneven moisture content to a constant weight at a temperature of 105-110°C. Then, use a wooden hammer to break up the lumps of soil and sieve to remove particles larger than 4.75 mm. Set aside. S2. First, weigh a predetermined amount of sandy silt, cement, anionic sodium polyalkylbenzene sulfonate, and water and set aside; then, clean the mixer by wiping and moistening the mixing pot and stirring blades with a damp cloth, then add the sandy silt and cement to the mixer, start the mixer, and dry mix for about 1 to 2 minutes at a stirring rate of 62±5 r / min. Then, add the anionic sodium polyalkylbenzene sulfonate to the water and mix evenly. Slowly add the sodium polyalkylbenzene sulfonate to the mixer during the stirring process for no more than 2 minutes. After all the sodium polyalkylbenzene sulfonate is added, continue stirring for about 2 minutes.

7. Use of the backfill material based on sandy high-fluidity silt according to any one of claims 1 to 5 in a backfill project in a narrow working area of ​​a foundation pit.

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