Airing-free wet original soil matrix self-compacting backfill material and trench construction method thereof

Abstract

The invention discloses an airing-free wet original soil base self-compacting backfill material and a trench construction method thereof. The trench construction method comprises the following steps that a trench is excavated, and undisturbed soil is obtained while excavation is conducted; the undisturbed soil is pretreated to obtain wet original soil; after equipment in the groove is installed, wet original soil serves as a raw material to prepare a self-compacting backfill material, flowing slurry is obtained, and the slump expansion degree of the flowing slurry is larger than or equal to 550 mm; a self-compacting backfill material is fed into the groove, and self-compacting filling is achieved; 4 + / -0.5 min after pouring is completed, nano silicon dioxide sol with the solid content being 5%-8% is sprayed to the surface of the slurry in an atomized mode, and the dosage is 180-220 g / m < 2 >; the adaptability and the stability of groove backfilling operation under adverse weather conditions are improved, the construction process is simplified, the cost is reduced, and wide application prospects are achieved.

Description

Technical Field

[0001] This invention relates to the field of municipal underground pipeline engineering construction technology, and in particular to a self-compacting backfill material for wet original soil foundation that does not require drying and its trench construction method. Background Technology

[0002] In the construction and maintenance of urban municipal pipeline networks, backfilling the trenches after pipeline laying is a crucial process to ensure the safety of road structures and the long-term stability of pipelines. Currently, the mainstream backfilling techniques mainly include two categories: (1) Medium-coarse sand compaction backfill: Medium-coarse sand is purchased from outside and backfilled in layers and compacted. This method relies on natural sand and gravel resources. Under the background of the ban on river sand mining, the cost is high and the supply is unstable. In addition, it requires layered construction, which is not only complicated, but also makes it difficult to guarantee the compaction degree in actual construction.

[0003] (2) Ordinary self-compacting fluidized solidified soil (e.g., Chinese patent CN118561568A): This method involves mixing excavated soil with cementitious materials and then pumping the mixture backfill. However, this type of technology generally requires the original soil to be dried to a moisture content of 10–15%, and the mix ratio to be optimized under laboratory conditions. In areas such as the Yangtze River Basin, where there are 8–12 consecutive days of rainfall per year (≥3 days), construction is often forced to stop due to the inability to obtain dry sites or sudden rainfall, leading to public safety risks such as long-term road closures and sewage overflows.

[0004] More importantly, the slump expansion of existing self-compacting materials is usually less than 450mm, which makes it difficult to fully fill the triangular area at the bottom of the pipe and easily forms voids; at the same time, they lack early resistance to rainwater erosion and need to be reworked when there is rainfall of more than 30mm / h.

[0005] Therefore, the industry urgently needs a new backfilling technology that does not require drying, has super fluidity, and can be used stably in rainy conditions to overcome the bottleneck of construction during the rainy season. Summary of the Invention

[0006] This invention provides a self-compacting backfill material for wet original soil without drying and its trench construction method, aiming to solve the problems of construction difficulties and unstable quality caused by high moisture content original soil and rainwater in the prior art.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for constructing self-compacting backfill trenches in wet original soil without the need for sun drying includes the following steps: Excavate trenches and remove undisturbed soil during the excavation process; The original soil was pretreated to obtain wet original soil; After the equipment in the trench is installed, self-compacting backfill material is prepared using wet soil as raw material to obtain a flowing slurry with a slump expansion ≥550mm. Self-compacting backfill material is fed into the trench to achieve self-compacting filling; 4±0.5 minutes after pouring, atomize and spray nano-silica sol with a solid content of 5%~8% onto the surface of the slurry, at a dosage of 180~220g / m³. 2 ; After atomization, cover with a high-density polyethylene rainproof film with a thickness of 0.10~0.20mm for 8±1 minutes; The construction will be completed after at least 10 hours by removing the membrane.

[0008] Preferably, the pretreatment of the undisturbed soil includes the following steps: Remove tree roots, weeds, and hard objects with a particle size >25mm from the original soil. The original soil after removal is crushed and sieved through a 20mm square-hole sieve to obtain wet original soil; The wet soil is temporarily stored after being covered with tarpaulin or HDPE film.

[0009] Preferably, the preparation of the self-compacting backfill material includes the following steps: Mix the wet soil, silicate cement, aluminate cement, water-reducing agent, retarder, silica sol and water to form a fluid slurry, and stir for 2 to 4 minutes.

[0010] Preferably, the surface compressive strength of the grout is ≥0.4MPa within 10 hours after the grout is poured, and the porosity of the triangular area at the bottom of the pipe is ≤1%.

[0011] Preferably, the method is applicable to working conditions where the rainfall intensity does not exceed 30 mm / h.

[0012] Under the same inventive concept, a self-compacting backfill material for wet soil foundation without drying is provided for backfilling in the above-mentioned self-compacting backfill trench construction method for wet soil foundation without drying. By weight, it includes the following materials: 68-78 parts wet soil, 8-12 parts silicate cement, 4-7 parts aluminate cement, 1.5-2.2 parts modified polycarboxylate superplasticizer, 0.4-0.6 parts molasses retarder, 3-5 parts nano silica sol with a solid content of 5%-8%, and 6-10 parts water.

[0013] Preferably, the wet soil has a natural moisture content of 18% to 28%, is silty clay or clayey silt, has a liquid limit of 38% to 48%, and a plastic limit of 18% to 25%.

[0014] Preferably, the mass ratio of aluminate cement to silicate cement is (0.4~0.7):1.

[0015] Preferably, the modified polycarboxylate superplasticizer has C14-C18 alkyl hydrophobic groups grafted onto its molecular backbone.

[0016] Preferably, the mass ratio of the molasses retarder to the aluminate cement is (9~14):1.

[0017] The beneficial effects of this invention are: (1) This invention provides a self-compacting material suitable for trench backfilling and its construction method, aiming to solve the problems of construction difficulties and unstable quality caused by rainwater in the prior art. The self-compacting material is made of wet soil, aluminate cement, modified water-reducing agent, molasses retarder, nano SiO2 sol and appropriate amount of water. Under rainfall conditions, a dense and hydrophobic hard shell layer (thickness of about 0.6-1.2 mm) can be quickly formed on the surface, while the interior still maintains good fluidity, ensuring construction efficiency and quality under complex weather conditions. (2) In terms of method, the original soil is first pretreated, including removing impurities, crushing and screening through a 20 mm sieve; then, all components are mixed evenly in a specific ratio and pumped into the trench; then, atomized nano-SiO2 sol is sprayed within 4±0.5 minutes after pouring to enhance surface hardness; finally, HDPE rainproof film is covered after 8±1 minutes until hardening is completed. By strictly implementing the emergency protection sequence of atomization + film covering, it is guaranteed that the road can be opened to traffic after 10 hours. The experimental results show that when the aluminate cement and molasses ratio is in the range of 9:1 to 14:1, the ideal surface hard shell thickness (0.6–1.1 mm) can be obtained, and the high fluidity of the internal slurry (≥480 mm slump spread) can be guaranteed. (3) This invention not only improves the adaptability and stability of trench backfilling operations under adverse weather conditions, but also simplifies the construction process and reduces costs, and has broad application prospects. Detailed Implementation

[0018] The following describes and verifies the embodiments. It should be emphasized that all embodiments of the present invention are feasible.

[0019] As a preferred embodiment 1, a method for constructing a self-compacting backfill trench for wet original soil without sun exposure includes the following steps: Excavate trenches and remove undisturbed soil during the excavation process; The original soil was pretreated to obtain wet original soil; After the equipment in the trench is installed, self-compacting backfill material is prepared using wet soil as raw material to obtain a flowing slurry with a slump expansion ≥550mm. Self-compacting backfill material is fed into the trench to achieve self-compacting filling; 4±0.5 minutes after pouring, atomize and spray nano-silica sol with a solid content of 5%~8% onto the surface of the slurry, at a dosage of 180~220g / m³. 2 ; After atomization, cover with a high-density polyethylene rainproof film with a thickness of 0.10~0.20mm for 8±1 minutes; The road was opened to traffic 10 hours later after the membrane was removed.

[0020] The pretreatment of the undisturbed soil includes the following steps: Remove tree roots, weeds, and hard objects with a particle size >25mm from the original soil. The original soil after removal is crushed and sieved through a 20mm square-hole sieve to obtain wet original soil; Wet soil is temporarily stored after being covered with tarpaulin or HDPE film to control its moisture content stability.

[0021] To ensure pumping performance and mixing uniformity, necessary physical pretreatment of the excavated soil is still required, including: manual or mechanical removal of tree roots, plastic and other debris; simple crushing of soil clods larger than 25mm in diameter; and sieving through a 20mm square-hole sieve. Actual measurements show that silty clay from the Yangtze River basin with a moisture content of 18-28% is in a plastic state (liquid limit 38-48%, plastic limit 18-25%) and can be effectively treated by a vibrating screen or a spray-equipped drum screen without the need for a dedicated drying area.

[0022] The preparation of the self-compacting backfill material includes the following steps: Mix the wet soil, silicate cement, aluminate cement, water-reducing agent, retarder, silica sol and water to form a fluid slurry, and stir for 2 to 4 minutes.

[0023] The surface compressive strength of the grout is ≥0.4MPa within 10 hours after the grout is poured, and the porosity of the triangular area at the bottom of the pipe is ≤1%.

[0024] Suitable for emergency repairs of municipal sewage or rainwater pipelines, especially for emergency situations such as continuous rainfall, limited sand supply, or the need to restore traffic within 24 hours.

[0025] It should be emphasized that the "construction under rainfall conditions" described in this invention has clear technical boundaries: (1) Applicable only to working conditions where the rainfall intensity does not exceed 30 mm / h (equivalent to short-duration heavy rainfall or heavy rain level); (2) The emergency protection sequence of “atomizing nano-silica sol 4±0.5 minutes after pouring + covering with rainproof film 8±1 minutes” must be strictly followed; (3) Not applicable to areas with standing water in the trench, continuous heavy rain (24-hour rainfall > 50 mm) or extreme weather conditions.

[0026] This technology aims to solve the problem of construction interruption caused by intermittent rainfall or sudden moderate rain in municipal emergency repair projects, and significantly improves the resilience of construction during the rainy season, rather than replacing conventional sunny day operations or unconditionally supporting construction under rainfall of any intensity.

[0027] As a preferred embodiment 2, a self-compacting backfill material for wet original soil base that does not require drying is used for backfilling in the above-mentioned self-compacting backfill trench construction method for wet original soil base that does not require drying. By weight, it includes the following materials: 68-78 parts wet original soil, 8-12 parts silicate cement, 4-7 parts aluminate cement, 1.5-2.2 parts modified polycarboxylate superplasticizer, 0.4-0.6 parts molasses retarder, 3-5 parts nano silica sol with a solid content of 5%-8%, and 6-10 parts water.

[0028] The natural moisture content of the wet soil is 18%~28%, and it is silty clay or clayey silt with a liquid limit of 38%~48% and a plastic limit of 18%~25%.

[0029] The mass ratio of aluminate cement to silicate cement is (0.4~0.7):1.

[0030] The modified polycarboxylate superplasticizer has C14~C18 alkyl hydrophobic groups grafted onto its molecular backbone.

[0031] The mass ratio of the molasses retarder to the aluminate cement is (9~14):1.

[0032] As a more preferred embodiment 3, the modified polycarboxylate superplasticizer is prepared by the following method: (1) Dissolve methacrylic acid, polyethylene glycol monomethyl ether methacrylate and chain transfer agent in deionized water and remove oxygen by passing nitrogen gas. (2) Heat to 70~80℃, add initiator solution dropwise, react for 3~4 hours to obtain polycarboxylic acid backbone; (3) Cool to 40~50℃, add C14~C18 alkylamine, and carry out amidation reaction for 2~3 hours under the action of catalyst; (4) Adjust the pH to 6-7 to obtain a modified polycarboxylate superplasticizer with a solid content of 35%-45%.

[0033] As a preferred embodiment 4, the adaptability to the moisture content of the wet native soil was verified.

[0034] Experimental objective: To verify the workability, early strength, and rain erosion resistance of the material of this invention in the range of 18-28% natural moisture content in wet soil, and to confirm the boundaries of the "no-drying" technology.

[0035] Raw materials and equipment: Original soil: silty clay excavated from the trench of DN600 sewage pipe, with a liquid limit of 42.3%, a plastic limit of 21.5%, a pH of 6.1, and an organic matter content of 2.8%; Silicate cement: P·O42.5 grade (Huaxin Cement Co., Ltd.); Aluminate cement: CA-50 grade (Zhengzhou Great Wall Aluminum Cement); Modified polycarboxylate superplasticizer: prepared according to the method in Example 3, with a solid content of 40%; Molasses retarder: Commercially available Grade 1 molasses, solid content 78%; Nano silica sol: 6% solid content, average particle size 15nm (Zhejiang Yuda Chemical Co., Ltd.); Equipment: JS500 forced mixer, slump spread tester, YES-2000 electro-hydraulic servo pressure testing machine, artificial rainfall simulation device (rainfall intensity adjustable from 0 to 50 mm / h).

[0036] Experimental steps: After manually removing tree roots, weeds, and construction waste from the excavated soil, a jaw crusher is used to crush soil clods with a particle size greater than 25mm. After crushing, the material is screened through a 20mm square hole sieve to obtain wet soil that meets the requirements; The moisture content of the five groups of samples was adjusted to 16%, 18%, 23%, 28%, and 30% respectively (controlled by adding a small amount of water or short-term ventilation, without sun-drying or drying). Add the following ingredients to a mixer according to a fixed ratio (75 parts wet soil, 10 parts silicate cement, 5 parts aluminate cement, 1.8 parts modified polycarboxylate superplasticizer, 0.5 parts molasses retarder, 4 parts nano silica sol, and 8 parts water), and mix for 3 minutes. Determine the initial collapse spread and 30-minute retention rate; A cylindrical specimen with a diameter of 100×100mm was formed and cured in an environment of 20±2℃ for 10 hours. The surface compressive strength was determined by combining the rebound method with core drilling sampling. Take fresh slurry and spread it on a 300×300mm steel plate (simulating the bottom plate of the trench). Start the artificial rain device (rainfall intensity 30mm / h) and observe and record the formation time and integrity of the surface hard shell.

[0037] The test results are shown in Table 1: Table 1

[0038] Conclusion: When the moisture content of the undisturbed soil is controlled between 18% and 28%, the material exhibits high fluidity (≥560mm), sufficient early strength (≥0.39MPa), and excellent rainwater resistance (unbroken surface with no runoff). This range closely matches the natural moisture content of typical trench soil in the Yangtze River Basin, fully supporting the feasibility and rationality of using undisturbed trench soil directly for backfilling without moisture content adjustment in Examples 1 and 2.

[0039] As a preferred embodiment 5, the aluminate / molasses ratio window was verified.

[0040] Experimental objective: To determine the optimal mass ratio of aluminate cement to molasses retarder, and to achieve a synergistic control mechanism of "rapid surface hardening to resist rainwater + internal retarding to maintain flowability".

[0041] Experimental design: Other components were fixed (75 parts wet soil, 10 parts silicate cement, 8 parts water, etc.), and only the amount of molasses was adjusted so that the mass ratio of aluminate to molasses was 7:1, 9:1, 12:1, 14:1, and 16:1, respectively.

[0042] Test method: Surface hard shell performance: Immediately after pouring, start artificial rain at 30mm / h, scrape off the surface slurry of 0~2mm after 30 seconds, dry and weigh it, and measure the thickness using an optical microscope; Internal fluidity: Samples were taken from the center of the specimen 30 minutes after pouring to determine the slump spread; Strength development: The surface strength was measured using a rebound hammer after 10 hours, and core samples were drilled for compressive strength testing to verify the results.

[0043] The test results are shown in Table 2: Table 2

[0044] Conclusion: Only when the aluminate:molasses ratio is (9~14):1, the material simultaneously satisfies the following: (1) forming an effective protective hard shell of 0.6~1.2mm within 30 seconds; (2) maintaining high fluidity of ≥480mm inside; and (3) achieving a strength of ≥0.40MPa after 10 hours. This mixing ratio window is the core technical feature of this invention for achieving "construction in the rain," directly supporting the limitations in Example 2.

[0045] As a preferred embodiment 6, the structural necessity of the modified polycarboxylate superplasticizer was verified.

[0046] Experimental objective: To verify the key role of C14~C18 alkyl hydrophobic groups in the rainwater erosion resistance of materials.

[0047] Comparative sample preparation: Sample A (control group): Commercially available ordinary polycarboxylate superplasticizer, solid content 40%; Sample B: Grafted C8 alkyl polycarboxylate superplasticizer (homemade: C8 alkylamine replaced C16 alkylamine in step (3) of Example 3); Sample C (of the present invention): grafted C16 alkyl polycarboxylate superplasticizer (prepared according to the complete method of Example 3, using C16 alkylamine in step (3) of Example 3).

[0048] Experimental conditions: The moisture content of the wet soil was 25%, and the other components were the same and met the requirements of Example 2.

[0049] Test process: Three water-reducing agents were used to mix the backfill material. Immediately after mixing, spread the mixture onto a steel plate inclined at 3° (simulating the sidewall of a trench, 300×300mm in size). Activate the artificial rainmaking device (30mm / h, for 5 minutes); Observe the surface erosion pattern, collect the lost material, dry and weigh it, and calculate the loss rate; Measure the surface strength of the un-rinsed area after 10 hours.

[0050] The test results are shown in Table 3: Table 3

[0051] Mechanism analysis: Contact angle tests revealed that the C16 modified water-reducing agent increased the contact angle of the slurry surface from 65° to 102°, indicating that long-chain alkyl groups are enriched at the slurry-air interface to form a hydrophobic film, which significantly reduces the rainwater infiltration rate and thus protects the internal structure.

[0052] Conclusion: C14~C18 alkyl hydrophobic groups are essential structural features for achieving high rainwater resistance, proving the irreplaceable nature of the modified polycarboxylate superplasticizer structure prepared by the specific synthesis methods in Examples 2 and 3.

[0053] As a preferred embodiment 7, the sensitivity of atomization and coating timing was verified.

[0054] Experimental objective: To verify the accuracy of the "4±0.5 minutes atomization" + "8±1 minutes film covering" process window and its impact on backfill quality.

[0055] Experimental setup: Material (wet original soil moisture content 24%) was poured into a trench model 1.2m wide and 3.0m long. Four time series combinations were set up, as shown in Table 4: Table 4

[0056] Test items and methods: Uniformity of surface hard shell: The surface temperature field is scanned using an infrared thermal imager and combined with visual rating (excellent / good / poor). Pipe bottom triangular area filling density: The porosity of the pipe bottom area was calculated by using an industrial CT scanner to perform three-dimensional reconstruction of the pipe bottom area; 10-hour surface strength: measured using a ZC3-A rebound hammer, and three core samples were randomly drilled for compressive strength testing.

[0057] The test results are shown in Table 5: Table 5

[0058] Cause analysis: Atomization too early (<4min): The slurry has not yet initially solidified, and the nano-SiO2 sol is excessively diluted, resulting in an uneven hard shell; Applying the film too late (>9 min): Excessive evaporation of surface moisture causes early plastic shrinkage and forms microcracks.

[0059] Conclusion: "4±0.5min atomization" + "8±1min coating" is the only process window that can simultaneously ensure resistance to rainwater erosion and the density of filling in narrow spaces, directly supporting the precise timing of atomization and coating in Example 1.

[0060] As a specific example, 8: Project Overview: Emergency repair project for DN800 sewage pipe, construction period is from June 15 to 18, 2024. During this period, there was continuous rainfall (daily rainfall of 20-40 mm, maximum hourly intensity of 28 mm / h). The trench is 1.2 m wide and 2.8 m deep, located on a main urban road, and traffic needs to be restored within 24 hours.

[0061] Construction process: The excavation work was completed on the morning of June 15 (sunny day). The original soil was temporarily stockpiled on the north side of the trench and covered with HDPE rainproof film. Backfilling work was carried out from 14:00 to 16:00 on June 16, during which the rainfall intensity was 28mm / h; The original soil used was taken from below 50cm inside the stockpile. After rapid on-site testing, the moisture content was 25.3% (liquid limit 43.1%, plastic limit 22.0%). The mixture was prepared at a mobile mixing station according to the specified proportions in Example 2. HBT60 concrete pumps are used to pump the mixture into the trench, with a single construction length of 20m. Four minutes after pouring, atomize nano-SiO2 sol (200g / m³). 2 Cover with a 0.15mm HDPE rainproof film after 8 minutes; After 10 hours, the film was removed, and the rebound strength was 0.41 MPa, at which point traffic was allowed to resume.

[0062] Third-party testing results: Pipe bottom porosity: 0.9% (ground-penetrating radar detection); 24-hour settlement: 2.3 mm; Spring modulus: 186 MPa; No cracks, subsidence, or road surface damage were observed within 7 days.

[0063] Conclusion: The present invention was successfully implemented under real rainfall conditions, fully verifying the engineering feasibility, reliability and advanced nature of the materials and construction methods described in Examples 1-3.

Claims

1. A method for constructing a self-compacting backfill trench on a wet original soil foundation without the need for sun drying, characterized in that, Includes the following steps: Excavate trenches and remove undisturbed soil during the excavation process; The original soil was pretreated to obtain wet original soil; After the equipment in the trench is installed, self-compacting backfill material is prepared using wet soil as raw material to obtain a flowing slurry with a slump expansion ≥550mm. Self-compacting backfill material is fed into the trench to achieve self-compacting filling; 4±0.5 minutes after pouring, atomize and spray nano-silica sol with a solid content of 5%~8% onto the surface of the slurry, at a dosage of 180~220g / m³. 2 ; After atomization, cover with a high-density polyethylene rainproof film with a thickness of 0.10~0.20mm for 8±1 minutes; The construction will be completed after at least 10 hours by removing the film.

2. The method for constructing a self-compacting backfill trench for wet original soil foundation without sun drying, as described in claim 1, is characterized in that... The pretreatment of the undisturbed soil includes the following steps: Remove tree roots, weeds, and hard objects with a particle size >25mm from the original soil. The original soil after removal is crushed and sieved through a 20mm square-hole sieve to obtain wet original soil; The wet soil is temporarily stored after being covered with tarpaulin or HDPE film.

3. The method for constructing a self-compacting backfill trench on wet original soil without sun drying, as described in claim 1, is characterized in that... The preparation of the self-compacting backfill material includes the following steps: Mix the wet soil, silicate cement, aluminate cement, water-reducing agent, retarder, silica sol and water to form a fluid slurry, and stir for 2 to 4 minutes.

4. The method for constructing a self-compacting backfill trench for wet original soil foundation without sun drying, as described in claim 1, is characterized in that... The surface compressive strength of the grout is ≥0.4MPa within 10 hours after the grout is poured, and the porosity of the triangular area at the bottom of the pipe is ≤1%.

5. The method for constructing a self-compacting backfill trench for wet original soil foundation without sun drying, as described in claim 1, is characterized in that... The method is applicable to working conditions where the rainfall intensity does not exceed 30 mm / h.

6. A self-compacting backfill material for wet original soil foundations that does not require sun drying, used for backfilling in the trench construction method for self-compacting backfilling of wet original soil foundations as described in any one of claims 1 to 5, characterized in that, By weight, it includes the following materials: 68-78 parts wet soil, 8-12 parts silicate cement, 4-7 parts aluminate cement, 1.5-2.2 parts modified polycarboxylate superplasticizer, 0.4-0.6 parts molasses retarder, 3-5 parts nano silica sol with a solid content of 5%-8%, and 6-10 parts water.

7. The self-compacting backfill material for wet original soil foundation that does not require drying, as described in claim 6, is characterized in that... The natural moisture content of the wet soil is 18%~28%, and it is silty clay or clayey silt with a liquid limit of 38%~48% and a plastic limit of 18%~25%.

8. The self-compacting backfill material for wet original soil foundation that does not require drying, as described in claim 6, is characterized in that... The mass ratio of aluminate cement to silicate cement is (0.4~0.7):

1.

9. The self-compacting backfill material for wet original soil foundation without drying as described in claim 6, characterized in that, The modified polycarboxylate superplasticizer has C14~C18 alkyl hydrophobic groups grafted onto its molecular backbone.

10. The self-compacting backfill material for wet original soil foundation without drying, as described in claim 6, is characterized in that... The mass ratio of the molasses retarder to the aluminate cement is (9~14):1.

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