Lightweight solidified soil leaking stoppage material

Abstract

The invention discloses a solidified soil light leaking stoppage material which is prepared by the technical means of introducing partially hydrolyzed polyacrylamide and a calcium-based cross-linking agent into a solidified soil system which takes shield muck (containing certain clay minerals) as a main raw material, and taking the partially hydrolyzed polyacrylamide and the calcium-based cross-linking agent as clay expansion excitants. The clay particles are triggered to generate controllable and violent physical and chemical volume expansion in the plastic stage of the material by utilizing the interspersing effect of a macromolecular chain and a clay mineral sheet layer and the cross-linking effect of calcium ions, so that a large number of uniform and stable micropore structures are formed inside. According to the present invention, the clay is adopted as the main body, the sulphoaluminate cement clinker and the nanometer nucleating agent are cooperatively used, and the mechanism of generating hydration products such as needle-rod-shaped ettringite by using the rapid hydration characteristic of the sulphoaluminate cement clinker and the nanometer nucleating agent is utilized, such that the penetrable three-dimensional gelling micro-skeleton is rapidly constructed when the clay particle expansion process tends to be stable, and the skeleton can effectively anchor and lock the porous structure formed after the expansion;

Description

Technical Field

[0001] This invention relates to the field of engineering construction resource recycling technology, and more specifically, to a lightweight sealing material for solidified soil. Background Technology

[0002] The construction of shield tunnels generates a large amount of excavated soil, which is currently mainly considered construction waste and typically disposed of by transporting it to landfills. This method not only incurs high transportation and site occupancy fees, increasing the economic cost of the project, but also leads to a series of problems such as land resource depletion, dust pollution, and potential ecological and environmental impacts. Therefore, promoting the resource utilization of shield tunnel excavated soil and reducing its off-site disposal is clearly necessary to reduce project costs and alleviate environmental pressure. Summary of the Invention

[0003] To achieve the resource utilization of tunnel boring machine (TBM) excavated soil, this invention provides a lightweight, solidified soil sealing material. This material introduces partially hydrolyzed polyacrylamide and calcium-based crosslinking agents into a solidified soil system primarily composed of TBM excavated soil (containing certain clay minerals). These partially hydrolyzed polyacrylamide and calcium-based crosslinking agents act as clay expansion activators. Utilizing the interpenetration of their polymer chains with clay mineral layers and the crosslinking effect of calcium ions, controllable and intense physicochemical volume expansion of clay particles is triggered during the material's plasticity stage, resulting in a large number of uniform and stable microporous structures within the material. Combined with sulfoaluminate cement clinker and nano-nucleating agents, the rapid hydration characteristics of these materials generate hydration products such as needle-shaped ettringite. This rapidly constructs a pervasive three-dimensional cementitious microframework when the clay particle expansion process stabilizes. This framework effectively anchors and locks in the porous structure formed after expansion.

[0004] The technical solution of this invention is as follows: A lightweight sealing material for solidified soil comprises 100-150 parts of pretreated shield tunnel slag, 5-15 parts of cementitious material, 0.5-3 parts of clay expansion activator, 0.1-1.0 parts of fluidizing agent, and 30-60 parts of mixing water. The pretreated shield tunneling excavated soil contains at least 8% clay minerals, including montmorillonite and illite, and the moisture content of the pretreated shield tunneling excavated soil is adjusted to 40%–60%. The cementing material is sulfoaluminate cement clinker or rapid-hardening sulfoaluminate cement; The clay expansion activator includes partially hydrolyzed polyacrylamide and calcium-based crosslinking agent. The mass ratio of partially hydrolyzed polyacrylamide to calcium-based crosslinking agent is: partially hydrolyzed polyacrylamide: calcium-based crosslinking agent = (1:1) to (1:2). The degree of hydrolysis of partially hydrolyzed polyacrylamide is 20% to 30%, and the calcium-based crosslinking agent is calcium chloride or calcium nitrate. The fluidizing agent is a lignin sulfonate water-reducing agent.

[0005] All proportions in this invention are by weight.

[0006] This invention utilizes the reaction between clay expansion activator and clay minerals in slag soil to induce controllable physicochemical expansion during the plastic stage of the slurry. At the same time, it relies on cementing materials to rapidly form a micro-skeleton to stabilize the expansion structure, thereby achieving a material dry density of 900-1100 kg / m³ and a 28-day compressive strength of not less than 2.0 MPa.

[0007] Pretreated tunnel boring machine (TBM) slag serves as the primary filler aggregate. When clay minerals react with clay expansion activators, some hydrolyzed polyacrylamide molecules adsorb onto the surface of the clay minerals. Under the action of calcium ions provided by calcium-based crosslinking agents, this triggers intense water absorption and expansion of the clay particles, along with crosslinking reactions between particles. These clay minerals undergo physicochemical expansion, inducing controllable and significant volume expansion, directly leading to a reduction in material density and achieving a lightweight effect. Simultaneously or subsequently, the cementitious material undergoes a hydration reaction, rapidly generating hydration products such as ettringite and alumina. These hydration products intertwine to form a robust network microskeleton structure. This network microskeleton structure encapsulates and stabilizes the porous structure generated by the expansion, preventing its collapse and thus endowing the material with the necessary mechanical properties, ensuring its compressive strength.

[0008] From a microstructural perspective, the material, after solidification, comprises a network-like microframework formed by ettringite and alumina gel generated from the hydration of sulfoaluminate cement, and stable, multi-scale pores formed by the chemically activated expansion of clay minerals. This microframework effectively binds and fixes the expanded clay aggregates and slag particles, forming a stable composite structure that supports the pores.

[0009] The aforementioned lightweight sealing material for solidified soil contains partially hydrolyzed polyacrylamide with a molecular weight of 8 million to 18 million.

[0010] The aforementioned lightweight, solidified soil sealing material, and the pretreatment process for tunnel boring machine (TBM) excavation soil include: Mechanical dewatering treatment was carried out on the original shield tunneling slag to obtain mud cake with a moisture content of no more than 30%. The mud cake is air-dried or oven-dried to reduce its moisture content to below 15%, and then crushed to obtain dry slag. The dry slag is screened through a drum screen or vibrating screen to remove coarse particles and impurities with a particle size greater than 10mm, and the slag powder is obtained after screening. After screening, add mixing water to the slag powder and mix it evenly by mechanical stirring, so that the moisture content of the slag is precisely adjusted to the target range of 40% to 60%. After adjusting the moisture content, the clay mineral content of the slag soil is tested to ensure that the total mass ratio of montmorillonite and illite is not less than 8%. If the test result is too low, an appropriate amount of bentonite or kaolin is added to the slag soil for mixing and adjustment until the total clay mineral content requirement is met, thus obtaining the pretreated shield slag soil.

[0011] The above-mentioned lightweight soil-stabilizing sealing material, and the on-site activation method of the clay expansion activator include: Partially hydrolyzed polyacrylamide powder is slowly added to a portion of the mixing water to prepare a stock solution of a specific mass concentration; The calcium-based crosslinking agent is dissolved separately in the remaining mixing water to prepare a solution of a specific mass concentration; In the on-site mixing process, the polyacrylamide stock solution is first premixed with dry materials such as slag and cementitious materials, and then calcium-based crosslinking agent solution is added in the final stage to trigger the expansion reaction.

[0012] The aforementioned lightweight sealing material for solidified soil also contains 0.5 to 2.0 parts of a nano-nucleating agent, which is nano-silica or nano-silica fume with a specific surface area of ​​not less than 15,000 m² / kg and an average particle size of not more than 100 nanometers.

[0013] Nanonucleating agents are adsorbed onto the surface of cementitious material particles and clay minerals, providing a large number of hydration nucleation sites, significantly accelerating the crystallization process of sulfoaluminate cement hydration products, especially ettringite, thereby strengthening and accelerating the formation of cementitious microskeleton, and more effectively locking the pore structure generated during the expansion stage.

[0014] The aforementioned lightweight waterproofing material for solidified soil also contains 0.1 to 0.5 parts of a retarding plasticizer, which is calcium saccharide or sodium citrate.

[0015] Retarding plasticizers are used to moderately slow down the hydration reaction rate of cementitious materials, controlling the initial setting time within the range of 90 to 180 minutes. This ensures that the clay expansion activator has sufficient time to complete full volume expansion, avoids premature formation of the microskeleton which would inhibit the expansion effect, and achieves temporal coordination between the expansion process and strength development.

[0016] The above-mentioned lightweight sealant for solidified soil includes the following on-site mixing and pouring process: Step S1. Premixing slurry: The pretreated shield tunnel slag, cementitious material, fluidizing agent and pre-prepared partially hydrolyzed polyacrylamide solution are put into a forced mixer and stirred for a certain period of time to form a uniform matrix slurry. Step S2. Triggering expansion: The pre-prepared calcium-based crosslinking agent solution is rapidly added to the matrix slurry under rapid stirring. After stirring for a period of time, the volume of the slurry expands significantly and the fluidity temporarily increases. Step S3. Pumping and pouring: Immediately transport the expanded slurry to the backfill area behind the subway station lining using a mud pump. Utilize the self-leveling properties of the slurry to fill the gaps. The pouring process is continuous, progressing gradually from low to high positions.

[0017] Furthermore, during the expansion process triggered in step S2, the slurry temperature is monitored in real time and controlled between 10°C and 35°C. If the ambient temperature is below 10℃, preheat the mixing water and raw materials; If the ambient temperature is higher than 35℃, use cooling water for mixing or change the construction to nighttime.

[0018] By controlling the temperature of the slurry, the expansion reaction rate of clay minerals and the hydration rate of cementitious materials are kept in the optimal matching range, thereby obtaining a uniform and stable lightweight structure.

[0019] The aforementioned lightweight sealing material for solidified soil partially replaces hydrolyzed polyacrylamide with an equal mass of hydroxypropyl methylcellulose or methylcellulose. The replacement ratio is 20%-50% of the total mass of the partially hydrolyzed polyacrylamide, and the viscosity range of the hydroxypropyl methylcellulose or methylcellulose is 20,000 to 60,000 mPa·s.

[0020] Hydroxypropyl methylcellulose or methylcellulose can induce volume expansion through interaction with clay minerals and calcium ions, while further enhancing the water retention and viscosity of the slurry and reducing bleeding and segregation.

[0021] The aforementioned lightweight soil-stabilizing and leak-sealing material is used in lightweight composite roadbeds. The structure of the lightweight composite roadbed includes: A sand and gravel cushion layer located on top of the foundation; Geogrid reinforcement layer laid on top of the subbase; The lightweight backfill layer is formed by the solidified soil slurry formed by the solidified soil lightweight sealing material backfilled on the reinforced layer and solidified. And, the pavement structure layer located above the lightweight backfill layer; A waterproof geomembrane and a graded crushed stone leveling layer are installed between the lightweight backfill layer and the pavement structure layer.

[0022] According to the above-described solution, the beneficial effects of this invention are as follows: 1. The material of this invention relies on the chemical reaction that occurs inside the material. By utilizing the reaction between the clay expansion activator and the clay minerals in the slag, controllable volume expansion is induced during the plastic stage of the slurry, thereby forming a large number of uniform and stable microporous structures inside the material. These closed pores replace part of the solid material, resulting in a very low dry density. For engineering scenarios such as backfilling behind subway station linings and roadbed filling, it can effectively reduce the additional load on the original foundation or surrounding structure below, and is particularly suitable for soft soil foundations or structural areas that are sensitive to loads.

[0023] 2. The material of the present invention maintains its mechanical properties while reducing density. It utilizes the products such as ettringite and alumina gel generated after the hydration of sulfoaluminate cement to form a strong network microframework during the hydration reaction of these hydration products. The network microframework can effectively wrap and stabilize the pore structure generated by the expansion reaction, preventing it from collapsing under stress, thereby forming a stable composite structure in which the framework supports the pores, thus taking into account both lightweight and high strength. Detailed Implementation

[0024] To make the technical problems, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] A lightweight sealing material for solidified soil comprises 100-150 parts of pretreated shield tunneling slag, 5-15 parts of cementitious material, 0.5-3 parts of clay expansion activator, 0.1-1.0 parts of fluidizing agent, and 30-60 parts of mixing water. The pretreated shield tunneling slag contains at least 8% clay minerals, including montmorillonite and illite, and the moisture content of the pretreated slag is adjusted to 40%-60%. The cementitious material is sulfoaluminate cement clinker or rapid-hardening sulfoaluminate cement. The clay expansion activator comprises partially hydrolyzed polyacrylamide and a calcium-based crosslinking agent, with a mass ratio of partially hydrolyzed polyacrylamide to calcium-based crosslinking agent of (1:1) to (1:2). The degree of hydrolysis of the partially hydrolyzed polyacrylamide is 20%-30%, and the calcium-based crosslinking agent is calcium chloride or calcium nitrate. The fluidizing agent is a lignin sulfonate water-reducing agent.

[0026] Tunnel boring machine (TBM) excavated soil originates from construction waste generated during TBM tunnel construction. During collection, it is crucial to avoid piles of excavated soil containing large rocks, metal debris, or toxic and harmful components. Priority should be given to freshly discharged, uncontaminated excavated soil from the construction site to ensure the basic purity of the raw materials. The collected raw TBM excavated soil must undergo immediate pretreatment. First, mechanical dewatering equipment such as plate and frame filter presses is used for dewatering, controlling the dewatering pressure at 0.6-1.0 MPa. The dewatering time is adjusted according to the initial moisture content of the excavated soil, ultimately obtaining a mud-cake-like excavated soil with a moisture content not exceeding 30%. During the dewatering process, the filter cloth of the filter press must be cleaned regularly to prevent clogging and maintain dewatering efficiency.

[0027] After dehydration, the mud cakes are transferred to a well-ventilated and dry drying area for air drying, or sent to a low-temperature drying equipment for processing. The drying temperature is controlled below 60℃ to prevent high temperature from damaging the activity of clay minerals in the slag. Natural air drying or low-temperature drying gradually reduces the moisture content of the mud cakes to below 15%.

[0028] After the mud cake reaches the target moisture content, it is crushed using a jaw crusher. The crushed and dried slag needs to be screened through a drum screen or vibrating screen with a screen aperture of 10mm. During the screening process, the slag is continuously stirred to remove coarse particles, gravel and other impurities with a particle size greater than 10mm, so as to obtain uniformly sized slag powder.

[0029] Subsequently, a measured amount of mixing water is slowly added to the sieved slag powder, and mechanical mixing is carried out using a horizontal mixer. The mixing speed is controlled at 150-200 r / min, and the mixing time is not less than 10 minutes to ensure that the slag and water are fully and evenly mixed. The moisture content of the slag is precisely adjusted to the target range of 40% to 60%. During the adjustment process, the moisture content needs to be sampled and tested multiple times. The moisture content is measured by drying and weighing method to ensure that the moisture content deviation does not exceed ±2%.

[0030] After the moisture content is adjusted, the clay mineral content of the slag is tested. The total mass ratio of montmorillonite and illite is determined by X-ray diffraction. If the test result is less than 8%, an appropriate amount of bentonite or kaolin is added to the slag. During the addition process, the mixture is stirred and tested until the total clay mineral content meets the requirement of not less than 8%. Finally, the pretreated shield tunnel slag that meets the standard is obtained. The pretreated slag needs to be stored in a sealed silo with a moisture-proof layer at the bottom to avoid fluctuations in moisture content.

[0031] The cementitious material is selected from sulfoaluminate cement clinker or rapid-hardening sulfoaluminate cement, ensuring that the initial setting time of the cement does not exceed 45 minutes, the final setting time does not exceed 10 hours, the 3-day compressive strength is not less than 15MPa, and the hydration heat release rate meets the technical requirements for rapid hydration to generate ettringite.

[0032] The partially hydrolyzed polyacrylamide in the clay swelling activator must be an industrial-grade product with a molecular weight between 8 million and 18 million and a degree of hydrolysis of 20% to 30%. The molecular weight should be verified by gel permeation chromatography, and the degree of hydrolysis should be determined by titration to ensure that the parameters meet the standards. The calcium-based crosslinking agent should be industrial-grade calcium chloride or calcium nitrate with a purity of not less than 95%, free from obvious lumps and impurities. It must be stored separately after purchase to avoid contact with acidic substances.

[0033] The fluidizing agent is a lignin sulfonate water-reducing agent, which is required to have a water reduction rate of not less than 10%, effectively improve the fluidity of the slurry and not affect the hydration reaction of the cementitious materials. When purchasing, its pH value should be tested to be between 7 and 9, and it should have no obvious odor or sediment.

[0034] The nanonucleating agent is selected from nano-silica or nano-silica with a specific surface area of ​​not less than 15000m² / kg and an average particle size of not more than 100 nanometers. Key parameters are detected by BET specific surface area analyzer and laser particle size analyzer to ensure that it can provide sufficient hydration nucleation sites.

[0035] The retarding plasticizer should be industrial-grade calcium sugar or sodium citrate with a purity of not less than 90%. Its retarding effect should be verified by testing to ensure that the initial setting time of the cementitious material can be controlled within the range of 90-180 minutes.

[0036] The mixing water should be clean tap water free of impurities or filtered natural water. The water quality must meet the relevant requirements in the "Standard for Water Used in Concrete", with chloride ion content not exceeding 200 mg / L and sulfate content not exceeding 270 mg / L. Avoid using wastewater containing oil, organic matter or heavy metal ions to prevent affecting the hydration reaction and mechanical properties of the materials.

[0037] After all raw materials are procured and delivered to the construction site, they must be sorted and stacked, with clear signs indicating the material name, specifications, quantity, and date of arrival. Chemical agents must be stored in a cool, ventilated dedicated warehouse equipped with moisture-proof, fire-proof, and explosion-proof facilities, avoiding direct sunlight and high-temperature environments. Cementing materials and pre-treated shield excavated soil must be covered with rain shelters to prevent them from getting damp and clumping.

[0038] After raw materials arrive on site, they undergo rigorous inspection. Pre-treated tunnel boring machine (TBM) slag requires sampling and testing for clay mineral content, moisture content, and particle size distribution. At least three samples are required for each batch to ensure a total montmorillonite and illite content ≥8%, a moisture content between 40% and 60%, and a particle size all less than 10mm. Cementitious materials require testing for stability, setting time, and strength development. Stability is tested using the boiling method, setting time is determined using a Vicat apparatus, and strength testing requires the preparation and curing of standard specimens. Partially hydrolyzed polyacrylamide requires testing for molecular weight, degree of hydrolysis, and dissolution rate. The dissolution rate must ensure complete dissolution without precipitation within 30 minutes in water at 20℃. Calcium-based crosslinking agents require testing for purity and solubility to ensure rapid and complete dissolution in water without residual impurities. Fluidizing agents require testing for water reduction rate and compatibility with other materials. The water reduction effect is verified through a paste fluidity test to ensure no abnormal coagulation occurs after mixing with cementitious materials. Nanonucleating agents need to be tested for specific surface area, particle size distribution, and activity to ensure good dispersibility and no obvious agglomeration. Retarded plasticizers need to be tested for their retarding effect and impact on strength, verified through setting time and strength tests to ensure the initial setting time meets requirements and does not significantly reduce the material's 28-day compressive strength. All test results must be recorded and archived. Unqualified raw materials are strictly prohibited from use; suppliers must be contacted immediately for returns and exchanges.

[0039] The selection of the on-site mixing area must meet construction requirements. Priority should be given to sites that are close to the pouring area, flat, firm, and easily accessible. The site must be hardened, with a 10-15cm thick layer of C20 concrete laid to ensure it can support the weight of the mixing equipment and raw materials, preventing settlement during construction. The mixing area must have a drainage slope of no less than 3%, and drainage ditches should be dug around it to ensure timely drainage of rainwater and prevent water accumulation from affecting construction.

[0040] Ambient temperature control is one of the key parameters for on-site mixing. The entire mixing and pouring process must maintain the ambient temperature between 10℃ and 35℃. High-precision temperature sensors are installed on-site to monitor the ambient temperature in real time, every 15 minutes, and the data is recorded. If the ambient temperature is below 10℃, the mixing water and all solid raw materials must be preheated. The mixing water is preheated using an electric heater, with the preheating temperature controlled between 20℃ and 30℃. The preheated water must be stored in an insulated water tank to prevent rapid temperature drop. Solid raw materials, such as pretreated tunnel boring machine excavated soil and cementitious materials, can be insulated by covering them with insulating blankets or setting up heated sheds to ensure that the raw material temperature does not fall below 10℃. If the ambient temperature is above 35℃, cooling water must be used for mixing. Cooling water can be prepared by adding ice or using refrigeration equipment, with the temperature controlled between 5℃ and 15℃. Simultaneously, a sunshade should be erected in the mixing area to block direct sunlight and reduce the impact of ambient temperature on the slurry. Alternatively, the construction time can be adjusted to nighttime to utilize the lower nighttime temperatures for mixing and pouring.

[0041] Dust control facilities must be installed in the mixing area. Spray dust suppression devices should be installed in the slag storage area and around the mixing equipment to regularly spray water mist and control dust dispersion. Operators must wear dust masks and other protective equipment. Wastewater generated during construction must be collected in a sedimentation tank, treated by sedimentation, and then discharged to avoid polluting the surrounding soil and water bodies.

[0042] The mixing equipment selected is a forced twin-shaft mixer. The mixing capacity is determined according to the construction progress, generally a 1-2 m³ mixer is chosen to ensure that the continuous pouring needs are met. The mixer must be equipped with a variable frequency speed control device to achieve medium-low speed mixing of 150-250 r / min and fast mixing of 300-400 r / min, meeting the speed requirements of different mixing stages. Before use, the mixer must be fully debugged, checking the installation and tightness of the mixing blades to ensure that the blades are not loose, the wear does not exceed the design allowable range, and the mixing shaft rotates flexibly without jamming. During debugging, a no-load test must be performed for no less than 10 minutes to check whether the equipment operating noise and motor temperature are normal. At the same time, the mixing time control device should be calibrated to ensure accurate mixing time. A backup mixer and generator must be provided on site to prevent the main equipment failure or sudden power outage from affecting the construction progress. The backup equipment must be the same model as the main equipment and be in a ready-to-start state.

[0043] The on-site activation of the clay expansion activator should be carried out in advance. First, a partially hydrolyzed polyacrylamide stock solution should be prepared. According to the mass concentration requirement of 0.5%-2.0%, the partially hydrolyzed polyacrylamide powder and the corresponding proportion of mixing water should be accurately weighed. The mixing water should be poured into the mixing tank, the stirring device should be turned on, and the stirring speed should be controlled at 200-300 r / min. Then, the partially hydrolyzed polyacrylamide powder should be slowly sprinkled into the water to avoid the powder from clumping. Continue stirring for no less than 30 minutes until the powder is completely dissolved and a uniform and transparent stock solution is formed. After the stock solution is prepared, it should be allowed to stand for 10-15 minutes. It can be used after checking that there is no sediment.

[0044] The calcium-based crosslinking agent solution is prepared separately. Weigh the calcium-based crosslinking agent and the remaining mixing water according to the mass concentration requirement of 5%-15%. Add the calcium-based crosslinking agent to the water and stir until completely dissolved to form a clear solution. During the preparation process, pay attention to stirring evenly to avoid excessively high local concentrations that may affect the reaction effect.

[0045] The partially hydrolyzed polyacrylamide stock solution and the calcium-based crosslinking agent solution should be stored separately in sealed plastic or stainless steel containers. The storage time should not exceed 24 hours. If the storage time is exceeded, the solution should be prepared again to prevent deterioration and affect the expansion effect.

[0046] On-site mixing is carried out in the order of premixing and triggered expansion. First, each raw material is accurately weighed according to the design ratio: 100-150 parts of pretreated shield tunneling slag, 5-15 parts of cementitious material, and 0.1-1.0 parts of fluidizing agent. If the formula contains 0.5-2.0 parts of nano-nucleating agent and 0.1-0.5 parts of retarding plasticizer, these must also be accurately weighed. Weighing is done using an electronic weighing scale with an accuracy of not less than 0.1 kg. The weighing process must be supervised and recorded by a designated person to ensure the accuracy of the ratio. All the weighed dry materials are put into a forced mixer. The mixer is turned on and dry-mixed at a speed of 150-200 r / min for 1-2 minutes to ensure that the dry materials are fully mixed and uniform, avoiding local material agglomeration.

[0047] After dry mixing, slowly add a portion of the pre-prepared hydrolyzed polyacrylamide stock solution to the mixer, while simultaneously adding an appropriate amount of mixing water. Adjust the mixer speed to 150-250 r / min and continue mixing for 3-5 minutes to form a uniform matrix slurry. During mixing, observe the slurry state to ensure there are no obvious lumps or segregation, and that the slurry has uniform fluidity. If the slurry fluidity is insufficient, appropriately increase the amount of fluidizing agent, but do not exceed the design upper limit of 0.1-1.0 parts. If the slurry is too thin, a small amount of pretreated shield tunneling slag can be added to adjust it. Based on experience, ensure that the matrix slurry reaches a suitable fluidity state.

[0048] After premixing and pulping, quickly add the pre-prepared calcium-based crosslinking agent solution to the mixer, and simultaneously increase the mixer speed to 300-400 rpm, stirring rapidly for 1-2 minutes. During this process, closely observe the volume change and state of the slurry. Under normal circumstances, a significant expansion of the slurry volume can be observed, with a temporary increase in fluidity, forming a uniform porous slurry. During the expansion process, the slurry temperature must be monitored in real time by measuring the temperature using a temperature sensor inserted inside the slurry, ensuring that the slurry temperature is controlled between 10℃ and 35℃. If the slurry temperature is below 10℃, stop adding the calcium-based crosslinking agent solution and preheat the slurry appropriately until the required temperature is reached before continuing the operation. If the slurry temperature is above 35℃, add a small amount of cooling water to cool it down, or stop stirring until the temperature drops to the control range before proceeding with subsequent steps.

[0049] After mixing, pumping and pouring must begin immediately without delay to prevent the slurry from setting prematurely during transport. A hydraulic mud pump should be used, with a pumping pressure controlled between 1.5-2.5 MPa. The pump pipe should be a wear-resistant rubber or steel pipe with a diameter of 100-150 mm. The pipe connections must be secure, and gaskets should be used to seal the joints to prevent slurry leakage. Before pumping, the pump pipe must be rinsed with clean water to ensure the inner wall is clean and smooth, reducing resistance to slurry transport. Then, pour the mixed slurry into the hopper and start the mud pump. The pumping speed should be controlled at 0.5-1.0 m³ / min, maintaining a uniform pumping speed to avoid slurry segregation or pipe blockage due to excessive speed.

[0050] If the pouring area is the backfill area behind the subway station lining, it should start from the bottom of the lining and be poured continuously from low to high. The self-leveling properties of the grout should be used to fully fill the gaps between the lining and the surrounding rock. During the pouring process, a designated person should observe the pouring area to ensure that the grout is fully filled without voids or dead corners. If any areas are found to be incompletely filled, the pump pipe position should be adjusted promptly for additional grouting. The pouring process must be continuous and should not be interrupted. If a stop is necessary due to special circumstances, the stop time should not exceed 30 minutes. If the stop exceeds 30 minutes, the poured grout must be cleaned up and the pouring process restarted to prevent the formation of cold joints.

[0051] If the material is used for lightweight composite subgrade construction, it must be constructed sequentially according to the subgrade structure layers. First, a sand and gravel cushion layer is laid on top of the foundation. This layer uses well-graded crushed stone and medium sand, with a particle size range of 5-31.5mm. The thickness is determined according to design requirements, generally 10-20cm. After laying, it is compacted using a vibratory roller, with 4-6 compaction passes, achieving a compaction degree of not less than 95%. After compaction, the surface of the cushion layer is smooth, without significant settlement or loosening. Next, a geogrid reinforcement layer is laid on top of the sand and gravel cushion layer. The geogrid used is a biaxially oriented plastic geogrid with a tensile strength of not less than 20kN / m. During laying, ensure the geogrid is flat and wrinkle-free, with an overlap length of not less than 20cm between adjacent geogrids. The overlaps are secured with high-strength nylon ropes at intervals not exceeding 50cm to prevent geogrid displacement during construction.

[0052] After the geogrid reinforcement layer is laid, the lightweight backfill layer is poured. The pouring method is the same as that for subway station backfilling, using continuous pumping. Pouring proceeds from one end of the roadbed to the other, and the pouring thickness is controlled according to design requirements. Generally, it is poured in two layers, each no more than 30cm thick. After the first layer is poured, the second layer is poured before the slurry initially sets, ensuring a tight bond between the two layers. After the lightweight backfill layer is poured, its surface needs to be covered with geotextile for moisture retention and curing. The curing time should be no less than 7 days. During the curing period, the geotextile should be kept moist to prevent the slurry surface from losing water too quickly and causing cracks.

[0053] After the lightweight backfill layer is completely cured, a waterproof geomembrane is laid on it. The waterproof geomembrane is selected as a high-density polyethylene geomembrane with a thickness of not less than 1.5 mm. When laying, it starts from one end and is laid horizontally along the roadbed. The overlapping length between adjacent membrane sheets is not less than 15 cm. The overlapping part is welded by a hot-melt welding machine, with the welding temperature controlled at 200 - 230 °C and the welding speed of 1 - 2 m / min. After welding, inflation detection needs to be carried out. The inflation pressure is 0.15 - 0.2 MPa. If there is no pressure drop after maintaining for 5 minutes, the welding is qualified. A graded crushed stone leveling layer is laid on the waterproof geomembrane. The particle size range of the graded crushed stone is 5 - 20 mm, and the laying thickness is 5 - 10 cm. After laying, it is leveled by a grader and lightly compacted by a vibratory roller for 2 - 3 passes to ensure that the surface flatness deviation of the leveling layer does not exceed 5 mm, providing a good foundation for the subsequent construction of the road surface structure layer.

[0054] If hydroxypropyl methylcellulose or methylcellulose is used to partially replace partially hydrolyzed polyacrylamide during the construction process, the replacement ratio needs to be strictly controlled between 20% - 50%. Before replacement, experimental verification needs to be carried out. Make specimens according to the ratio after replacement, and test indexes such as the expansion rate, water retention, bleeding, and compressive strength and dry density after curing of the slurry to ensure that all indexes meet the design requirements. The preparation and mixing process of the material after replacement is the same as the original plan, but the mixing time needs to be appropriately extended by 1 - 2 minutes to ensure that the replaced material is fully mixed with other components evenly. At the same time, strengthen the observation of the slurry state and adjust the mixing parameters in a timely manner to ensure the construction quality.

[0055] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A lightweight, solidified soil sealing material, characterized in that, It includes 100-150 parts of pretreated shield tunneling slag, 5-15 parts of cementitious material, 0.5-3 parts of clay expansion activator, 0.1-1.0 parts of fluidizing agent, and 30-60 parts of mixing water; The pretreated shield tunneling excavated soil contains at least 8% clay minerals, including montmorillonite and illite, and the moisture content of the pretreated shield tunneling excavated soil is adjusted to 40%–60%. The cementing material is sulfoaluminate cement clinker or rapid-hardening sulfoaluminate cement; The clay expansion activator includes partially hydrolyzed polyacrylamide and calcium-based crosslinking agent. The mass ratio of partially hydrolyzed polyacrylamide to calcium-based crosslinking agent is: partially hydrolyzed polyacrylamide: calcium-based crosslinking agent = (1:1) to (1:2). The degree of hydrolysis of partially hydrolyzed polyacrylamide is 20% to 30%, and the calcium-based crosslinking agent is calcium chloride or calcium nitrate. The fluidizing agent is a lignin sulfonate water-reducing agent.

2. The lightweight, solidified soil sealing material according to claim 1, characterized in that, Partially hydrolyzed polyacrylamide has a molecular weight of 8 million to 18 million.

3. The lightweight, solidified soil sealing material according to claim 1, characterized in that, The pretreatment process for tunnel boring machine (TBM) excavation includes: Mechanical dewatering treatment was carried out on the original shield tunneling slag to obtain mud cake with a moisture content of no more than 30%. The mud cake is air-dried or oven-dried to reduce its moisture content to below 15%, and then crushed to obtain dry slag. The dry slag is screened through a drum screen or vibrating screen to remove coarse particles and impurities with a particle size greater than 10mm, and the slag powder is obtained after screening. After screening, add mixing water to the slag powder and mix it evenly by mechanical stirring, so that the moisture content of the slag is precisely adjusted to the target range of 40% to 60%. After adjusting the moisture content, the clay mineral content of the slag soil is tested to ensure that the total mass ratio of montmorillonite and illite is not less than 8%. If the test result is too low, an appropriate amount of bentonite or kaolin is added to the slag soil for mixing and adjustment until the total clay mineral content requirement is met, thus obtaining the pretreated shield slag soil.

4. The lightweight, solidified soil sealing material according to claim 1, characterized in that, The on-site activation methods for clay expansion activators include: Partially hydrolyzed polyacrylamide powder is slowly added to a portion of the mixing water to prepare a stock solution of a specific mass concentration; The calcium-based crosslinking agent is dissolved separately in the remaining mixing water to prepare a solution of a specific mass concentration; In the on-site mixing process, the polyacrylamide stock solution is first premixed with dry materials such as slag and cementitious materials, and then calcium-based crosslinking agent solution is added in the final stage to trigger the expansion reaction.

5. The lightweight, solidified soil sealing material according to claim 1, characterized in that, It also contains 0.5 to 2.0 parts of nano-nucleating agent, which is nano-silica or nano-silica with a specific surface area of ​​not less than 15,000 m² / kg and an average particle size of not more than 100 nanometers.

6. The lightweight, solidified soil sealing material according to claim 1, characterized in that, It also contains 0.1 to 0.5 parts of a retarding plasticizer, which is calcium saccharide or sodium citrate.

7. The lightweight, solidified soil sealing material according to claim 1, characterized in that, The on-site mixing and pouring process of materials includes: Step S1. Premixing slurry: The pretreated shield tunnel slag, cementitious material, fluidizing agent and pre-prepared partially hydrolyzed polyacrylamide solution are put into a forced mixer and stirred for a certain period of time to form a uniform matrix slurry. Step S2. Triggering expansion: The pre-prepared calcium-based crosslinking agent solution is rapidly added to the matrix slurry under rapid stirring. After stirring for a period of time, the volume of the slurry expands significantly and the fluidity temporarily increases. Step S3. Pumping and pouring: Immediately transport the expanded slurry to the backfill area behind the subway station lining using a mud pump. Utilize the self-leveling properties of the slurry to fill the gaps. The pouring process is continuous, progressing gradually from low to high positions.

8. The lightweight, solidified soil sealing material according to claim 7, characterized in that, During the expansion process triggered in step S2, the slurry temperature is monitored in real time and controlled between 10℃ and 35℃. If the ambient temperature is below 10℃, preheat the mixing water and raw materials; If the ambient temperature is higher than 35℃, use cooling water for mixing or change the construction to nighttime.

9. A lightweight, solidified soil sealing material according to claim 1, characterized in that, Partially hydrolyzed polyacrylamide is partially replaced with an equal mass of hydroxypropyl methylcellulose or methylcellulose, with a replacement ratio of 20%-50% of the total mass of partially hydrolyzed polyacrylamide. The viscosity range of hydroxypropyl methylcellulose or methylcellulose is 20,000 to 60,000 mPa·s.

10. A lightweight, solidified soil sealing material according to claim 1, characterized in that, The material is used in lightweight composite roadbeds, the structure of which includes: A sand and gravel cushion layer located above the foundation; Geogrid reinforcement layer laid on top of the subbase; The lightweight backfill layer formed by the solidified soil slurry of any one of the solidified soil lightweight plugging materials of claims 1-9, which is backfilled on top of the reinforced layer, is produced after solidification. And, the pavement structure layer located above the lightweight backfill layer; A waterproof geomembrane and a graded crushed stone leveling layer are installed between the lightweight backfill layer and the pavement structure layer.