Acid-resistant horizontal seepage barrier structure and construction method using tailings sand as the main material

Abstract

This invention provides an acid-resistant horizontal seepage barrier structure using tailings sand as a substrate and its construction method. The seepage barrier structure, from bottom to top, includes an adsorption salt barrier layer, a condensation water barrier layer, and a capillary barrier layer. The condensation water barrier layer is composed of a mixture of tailings sand, silica sol, and tetraethyl orthosilicate. When the condensation water barrier layer is in an acidic environment, under H... + Under catalysis, the SiO2 precursor dehydrates and condenses to form a network-structured gel, which coats and connects the particles of tailings sand. The adsorption salt barrier layer is used to adsorb and block salts rising with capillary water in the soil beneath the seepage barrier structure. The condensation water barrier layer is the key layer for the seepage barrier structure to achieve its seepage prevention and water interception effect. The capillary barrier layer is used to impede some of the infiltrated water at the interface between the two soil layers above the seepage barrier structure. This invention utilizes industrial solid waste tailings sand, realizing the resource utilization of tailings sand. Its adaptability to strongly acidic environments makes it applicable to a wide range of scenarios.

Description

Technical Field

[0001] This invention relates to the fields of industrial solid waste management and environmental geotechnical technology, and in particular to an acid-resistant horizontal impermeable layer with tailings sand as the main material and its construction method. Background Technology

[0002] Landfill leaching primarily targets leachate, which is formed by the degradation of organic matter in waste, dissolved substances from municipal solids, and a mixture of rainwater and groundwater. Due to the diversity and complexity of waste components, the chemical composition of leachate is extremely complex, with a wide range of pollutant concentrations. Leachate exhibits a highly complex chemical composition, with organic pollutants, inorganic pollutants, and heavy metal ions coexisting, demonstrating strong comprehensive pollution characteristics.

[0003] Currently, the main materials used for horizontal seepage prevention are clay and HDPE membranes. When clay is used as a seepage prevention material, the thickness of the seepage prevention layer is generally controlled between 1.5m and 6m, depending on the pollution level of the environment. Excessive layer thickness leads to a huge amount of clay used, and there are significant limitations in the acquisition and construction of clay, resulting in high seepage prevention costs. When HDPE membrane is used as a seepage prevention material, it has excellent stability in general environments, but it will corrode and age in strongly oxidizing acidic environments. Long-term contact with aliphatic hydrocarbons, aromatic hydrocarbons, and halogenated hydrocarbons will also cause swelling or cracking. Therefore, when used in complex environments, corrosion allowance must be considered, and the membrane thickness must be increased to delay its aging process.

[0004] Utilizing industrial solid waste for seepage prevention and barrier purposes is beneficial for reducing the cost of seepage prevention systems and realizing the recycling of solid waste, showing great promise. Tailings sand is waste tailings from ore processing, with an average particle size between 0.05mm and 5mm. The composition of tailings sand varies depending on the type of ore and processing technology, but it can mainly be divided into inorganic substances such as silicon dioxide, various metal oxides, and residual organic reagents from ore beneficiation. Improper treatment may pose a potential threat to the environment. Silica is an inorganic compound with the chemical formula SiO2. Long-range ordered arrangement of silicon and oxygen atoms forms crystalline silica, while short-range ordered or long-range disordered arrangement forms amorphous silica. It is chemically stable and does not react with water. It possesses high fire resistance, high temperature resistance, a low coefficient of thermal expansion, high insulation, corrosion resistance, piezoelectric effect, resonance effect, and unique optical properties. Summary of the Invention

[0005] This invention addresses the problems of existing seepage barriers in strongly acidic environments, such as the need to consider corrosion allowances, large thicknesses, and high costs. It proposes an acid-resistant horizontal seepage barrier structure and construction method using tailings sand as the main material. The method uses waste tailings sand as the base material and utilizes an acidic environment to allow silica precursors to react in H... +Under catalysis, dehydration and condensation form an amorphous silica network structure, which coats and connects the pores of the seepage barrier to solve the problems of corrosion resistance and durability of the seepage barrier in strong acid environments.

[0006] To achieve the above-mentioned technical objectives, this invention provides an acid-resistant horizontal seepage-proof structure with tailings sand as the main material, characterized in that: the seepage-proof structure is provided from bottom to top with an adsorption salt barrier layer, a condensation water barrier layer, and a capillary barrier layer; the thickness of the adsorption salt barrier layer is 10cm to 30cm, and the laying material of the adsorption salt barrier layer is composed of tailings sand and kaolin mixed at a mass ratio of 4 to 6:1, wherein the tailings sand is selected as coarse tailings sand with a particle size of 5 to 8mm; the thickness of the condensation water barrier layer is 20cm. The thickness of the condensation waterproof layer is 10cm to 30cm. The material for laying the condensation waterproof layer is composed of tailings sand, silica sol, and tetraethyl orthosilicate. The tailings sand accounts for 80%-90% of the total weight of the condensation waterproof layer material, the silica sol accounts for 5%-10% of the total weight of the condensation waterproof layer material, and the tetraethyl orthosilicate accounts for 5-10% of the total weight of the condensation waterproof layer material. The thickness of the capillary barrier layer is 10cm to 30cm. The material for laying the capillary barrier layer is composed of tailings sand and alumina mixed in a mass ratio of 7-9:1.

[0007] A preferred technical solution of the present invention: the tailings sand of the condensation waterproof layer is composed of fine tailings sand of different particle sizes with a particle size not exceeding 2 mm. The particle size distribution of the fine tailings sand is as follows: fine tailings sand with a particle size less than 0.075 mm accounts for 10%-20% of the total weight of the tailings sand in the condensation waterproof layer material; fine tailings sand with a particle size of 0.075 mm-0.15 mm accounts for 10%-15% of the total weight of the tailings sand in the condensation waterproof layer material; and fine tailings sand with a particle size of 0.15 mm-0.15 mm accounts for 10%-15% of the total weight of the tailings sand in the condensation waterproof layer material. Fine tailings with a particle size of 0.25mm account for 5%-15% of the total weight of the condensation impermeable layer material; fine tailings with a particle size of 0.25mm-0.5mm account for 10%-20% of the total weight of the condensation impermeable layer material; fine tailings with a particle size of 0.5mm-1mm account for 15%-25% of the total weight of the condensation impermeable layer material; and fine tailings with a particle size of 1mm-2mm account for 20%-30% of the total weight of the condensation impermeable layer material.

[0008] The preferred technical solution of the present invention is that the tailings sand of the capillary septum is selected as medium sand with a particle size of 3-5mm.

[0009] This invention also provides a construction method for an acid-resistant horizontal seepage-proof structure using tailings sand as the main material. The specific operation steps of the construction method are as follows:

[0010] S1. In actual construction, the first step is to remove debris and level the area to be treated. Coarse tailings sand with a particle size of 5-8mm and kaolin are mixed and stirred evenly at a mass ratio of 4-6:1 to prepare the raw material for the adsorption and salt barrier layer. The mixed raw material is then spread evenly in the cleaned area to be treated. After spreading, the adsorption and salt barrier layer is compacted using tamping machinery. The thickness of the compacted salt barrier layer is 10cm-30cm.

[0011] S2. Select fine tailings sand with a particle size of no more than 2mm, silica sol, and tetraethyl orthosilicate, mix them evenly according to the mass ratio to prepare a condensation waterproof layer laying material. The fine tailings sand accounts for 80%-90% of the total weight of the condensation waterproof layer material, the silica sol accounts for 5%-10%, and the tetraethyl orthosilicate accounts for 5-10%. Spread the evenly mixed condensation waterproof layer material evenly on the compacted adsorption and salt barrier layer, and flatten and compact it. The thickness of the compacted condensation waterproof layer is 20cm-30cm.

[0012] S3. Mix medium-sized tailings sand with a particle size of 3-5mm and alumina at a mass ratio of 7-9:1 to prepare a capillary barrier layer laying material. Spread the capillary barrier layer laying material evenly on the compacted condensation waterproof layer. After spreading, the capillary barrier layer is properly leveled and compacted to complete the laying of the acid-resistant horizontal seepage prevention structure. The thickness of the compacted capillary barrier layer is 10cm-30cm.

[0013] S4. After 12 hours of laying, the upper soil can be piled on the acid-resistant horizontal seepage-proof structural layer.

[0014] The preferred technical solution of the present invention is as follows: In the fine tailings sand in step S3, tailings sand smaller than 0.075mm accounts for 10%-20% of the total weight of the condensation waterproof layer material, tailings sand of 0.075mm-0.15mm accounts for 10%-15% of the total weight of the condensation waterproof layer material, tailings sand of 0.15mm-0.25mm accounts for 5%-15% of the total weight of the condensation waterproof layer material, tailings sand of 0.25mm-0.5mm accounts for 10%-20% of the total weight of the condensation waterproof layer material, tailings sand of 0.5mm-1mm accounts for 15%-25% of the total weight of the condensation waterproof layer material, and tailings sand of 1mm-2mm accounts for 20%-30% of the total weight of the condensation waterproof layer material.

[0015] This invention provides an acid-resistant horizontal seepage barrier layer mainly composed of tailings sand. In the area requiring horizontal seepage prevention treatment, an adsorption salt barrier layer, a condensation water barrier layer, and a capillary barrier layer are sequentially arranged from bottom to top. The adsorption salt barrier layer is composed of a mixture of tailings sand and hydrophilic minerals. The tailings sand is selected as coarse tailings with a particle size of 5-8 mm. When the capillary water carrying salt in the lower soil rises through the coarse tailings salt barrier layer, some of the salt in the water undergoes a neutralization reaction and complexation reaction with the metal oxides in the tailings sand under the action of H+, forming complex precipitates that adhere to the pores of the coarse particles. Together with the crystal structure of the hydrophilic minerals, it adsorbs other metal ions, thereby preventing salt from moving upward to the condensation water barrier layer, affecting the SiO2 dehydration condensation reaction, and reducing the seepage resistance. The thickness of the polycondensation waterproof layer is 20cm-30cm. The polycondensation waterproof layer material is composed of tailings sand, silica sol, and tetraethyl orthosilicate. In the polycondensation waterproof layer, the SiO2 precursors of silica sol and tetraethyl orthosilicate undergo dehydration condensation reaction under the catalysis of H+ to form an amorphous silica network structure that covers and connects between the tailings sand particles, thereby improving the cohesiveness between particles and ensuring the porosity and permeability of the material in an acidic environment.

[0016] The capillary barrier layer has a thickness of 10cm-30cm and is mainly composed of a mixture of tailings sand and alumina. The tailings sand is selected as medium-sized tailings sand with a particle size of 3-5mm. On the one hand, based on the difference between the capillary barrier layer and the upper soil layer, the capillary barrier layer uses the capillary retraction effect to block and collect some of the pore water infiltrating from the upper soil layer at the interface between the capillary barrier layer and the upper soil layer, so as to realize the drainage of pore water. On the other hand, the alumina in the interlayer reacts with the acid in the infiltrated water, and the Al3+ produced enters the lower condensation barrier layer, combines with some Si-OH in the silica network structure, and forms Si-O-Al bonds, which improves the strength and ductility of the network structure.

[0017] The impermeable layer of the present invention incorporates silica sol, tetraethyl orthosilicate, etc., to address the problem of increased permeability caused by corrosion in general impermeable layers under strong acidic environments. When the impermeable layer is in an acidic environment, the SiO2 precursor undergoes dehydration condensation under the catalytic action of H+ to form a network structure, thereby effectively ensuring the porosity and permeability coefficient of the material and ensuring the impermeability function of the impermeable layer for a long time.

[0018] This invention utilizes industrial solid waste tailings sand to achieve resource utilization of tailings sand. It has the characteristics of adapting to strong acidic environments and can be applied in a wide range of scenarios. It solves the shortcomings of existing horizontal seepage prevention and barrier technologies, which are prone to corrosion of the seepage prevention materials in strong acidic environments, leading to the destruction of the seepage prevention structure and increased permeability. The designed seepage prevention layer is suitable for various application scenarios such as horizontal bottom sealing and seepage prevention and surface covering. Attached Figure Description

[0019] Figure 1The image shown is a scanning electron microscope (SEM) image of the polycondensation waterproof layer of the sample prepared in the example before acid immersion.

[0020] Figure 2 The image shown is a scanning electron microscope (SEM) image of the polycondensation waterproof layer of the sample prepared in the example after acid immersion. Detailed Implementation

[0021] The technical solutions of the present invention will be further described in detail below with reference to several embodiments. The technical solutions presented in the embodiments are specific implementations of the present invention and are not intended to limit the scope of the claimed invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0022] The following embodiments provide an acid-resistant horizontal seepage-proof structure with tailings sand as the main material, which consists of an adsorption salt barrier layer, a condensation water barrier layer, and a capillary barrier layer arranged sequentially from bottom to top. The thickness of the adsorption salt barrier layer is 10cm to 30cm, and the material for laying the adsorption salt barrier layer is a mixture of tailings sand and kaolin in a mass ratio of 5:1. The tailings sand is selected as coarse tailings sand with a particle size of 5-8mm. The thickness of the condensation water barrier layer is 20cm to 30cm, and the material for laying the condensation water barrier layer is a mixture of tailings sand, silica sol, and tetraethyl orthosilicate. The tailings sand accounts for 80%-90% of the total weight of the condensation water barrier layer material, the silica sol accounts for 5%-10% of the total weight of the condensation water barrier layer material, and the tetraethyl orthosilicate accounts for 5-10% of the total weight of the condensation water barrier layer material. The thickness of the capillary barrier layer is 10cm to 30cm, and the material for laying the capillary barrier layer is a mixture of tailings sand and alumina in a mass ratio of 8:1. The tailings sand in the condensation impermeable layer is composed of a blend of fine tailings sand with different particle sizes, each not exceeding 2 mm. The particle size distribution of the fine tailings sand is as follows: fine tailings sand with a particle size less than 0.075 mm accounts for 10%-20% of the total weight of the condensation impermeable layer material; fine tailings sand with a particle size of 0.075 mm-0.15 mm accounts for 10%-15% of the total weight of the condensation impermeable layer material; and fine tailings sand with a particle size of 0.15 mm-0.25 mm accounts for a certain percentage. Fine tailings sand accounts for 5%-15% of the total weight of the condensation impermeable layer material; fine tailings sand with a particle size of 0.25mm-0.5mm accounts for 10%-20%; fine tailings sand with a particle size of 0.5mm-1mm accounts for 15%-25%; and fine tailings sand with a particle size of 1mm-2mm accounts for 20%-30%. The tailings sand in the capillary barrier layer is selected as medium sand with a particle size of 3-5mm.

[0023] The specific construction method is as follows:

[0024] S1. In actual construction, the first step is to remove debris and level the area to be treated. Coarse tailings sand with a particle size of 5-8mm and kaolin are mixed and stirred evenly at a mass ratio of 5:1 to prepare the raw material for the adsorption and salt barrier layer. The mixed raw material is then spread evenly in the cleaned area to be treated. After spreading, the adsorption and salt barrier layer is compacted using tamping machinery. The thickness of the compacted salt barrier layer is 10cm-30cm.

[0025] S2. Select fine tailings sand with a particle size of no more than 2mm, silica sol, and tetraethyl orthosilicate, mix them evenly according to the mass ratio to prepare a condensation waterproof layer laying material. The fine tailings sand accounts for 80%-90% of the total weight of the condensation waterproof layer material, the silica sol accounts for 5%-10%, and the tetraethyl orthosilicate accounts for 5-10%. Spread the evenly mixed condensation waterproof layer material evenly on the compacted adsorption and salt barrier layer, and flatten and compact it. The thickness of the compacted condensation waterproof layer is 20cm-30cm.

[0026] S3. Mix medium-sized tailings sand with a particle size of 3-5mm and alumina at a mass ratio of 8:1 to prepare a capillary barrier layer laying material. Spread the capillary barrier layer laying material evenly on the compacted condensation waterproof layer. After spreading, the capillary barrier layer is properly leveled and compacted to complete the laying of the acid-resistant horizontal seepage prevention structure. The thickness of the compacted capillary barrier layer is 10cm-30cm.

[0027] S4. After 12 hours of laying, the upper soil can be piled on the acid-resistant horizontal seepage-proof structural layer.

[0028] The following example uses a municipal solid waste landfill in a humid climate zone. During the decomposition process, a large amount of acidic substances are produced, causing the soil environment to become acidic. It is necessary to perform seepage prevention treatment on a certain area of ​​the site before continuing to fill waste. A small-scale field test was conducted using the seepage prevention layer of this invention.

[0029] Example 1 provides an acid-resistant horizontal seepage-proof structure with tailings sand as the main material. The thickness of the adsorption salt barrier layer is 20cm, the thickness of the condensation water barrier layer is 20cm, and the thickness of the capillary barrier layer is 20cm. The condensation water barrier layer is composed of 90% tailings sand, 5% silica sol, and 5% tetraethyl orthosilicate.

[0030] The acid-resistant horizontal seepage barrier structure prepared in Example 1 was laid in an environment with pH = 7.0, and a permeability test was conducted. The test results showed that the permeability coefficient of the seepage barrier structure was 5.2 × 10⁻⁶. -9 m / s.

[0031] Example 2 provides an acid-resistant horizontal seepage-proof structure with tailings sand as the main material. The thickness of the structural layer is the same as that of Example 1. The difference is that the condensation waterproof layer is composed of 85% tailings sand, 5% silica sol and 10% tetraethyl orthosilicate.

[0032] The geomembrane structure of Example 2 was laid in an environment with pH = 7.0, and a permeability test was conducted. The test result showed that the permeability coefficient of the geomembrane structure was 4.9 × 10⁻⁶. -10 m / s.

[0033] Example 3 provides an acid-resistant horizontal seepage-proof structure with tailings sand as the main material. The thickness of the structural layer is the same as that of Example 1. The difference is that the condensation waterproof layer is composed of 80% tailings sand, 5% silica sol and 15% tetraethyl orthosilicate.

[0034] The geomembrane structure of Example 3 was laid in an environment with pH = 7.0, and a permeability test was conducted. The test result showed that the permeability coefficient of the geomembrane structure was 7.6 × 10⁻⁶. -10 m / s.

[0035] Table 1 shows a comparison of the permeability coefficient tests in Examples 1 to 3:

[0036] Table 1 compares the test data of Examples 1 to 3.

[0037]

[0038] By comparing the permeability coefficients of Examples 1-3 in Table 1, it can be seen that the permeability coefficient first decreases and then increases with the increase of the amount of tetraethyl orthosilicate added. This is to meet the requirement of 1×10⁻⁶ for the closure of sanitary landfills for municipal solid waste (GB51220-2017). -9 Considering the construction cost of the seepage prevention layer, it is recommended that the amount of tetraethyl orthosilicate added be 10% to achieve a better seepage prevention effect.

[0039] Example 4 provides an acid-resistant horizontal seepage-proof structure with tailings sand as the main material. The adsorption salt barrier layer is 20cm thick, the condensation water barrier layer is 20cm thick, and the capillary barrier layer is 20cm thick. The condensation water barrier layer is composed of 85% tailings sand, 5% silica sol, and 10% tetraethyl orthosilicate.

[0040] In Example 4, the impermeable structure layer was laid in an environment with pH=5 and a permeability test was conducted. The test result showed that the permeability coefficient was 3.8×10-10m / s, which met the requirements of the impermeable layer.

[0041] Example 5 provides an acid-resistant horizontal seepage barrier structure using tailings sand as the main material. The thickness of the structural layer and the material formulation are the same as in Example 4. The difference is that the seepage barrier layer in Example 5 is laid in an environment with a pH of 3.0. A permeability test was conducted on the seepage barrier structure in this environment, and the test result showed a permeability coefficient of 4.0 × 10⁻⁶. -10 m / s, which meets the requirements of the seepage prevention layer.

[0042] The permeation test data from Examples 2, 4, and 5 under different pH test environments were compared, and the comparison results are shown in Table 2:

[0043] Table 2 compares the permeability coefficients under different pH test conditions.

[0044]

[0045] By comparing the examples in Table 2, it can be seen that as the pH of the test environment decreases, the permeability coefficient exhibits a pattern of first decreasing appropriately and then stabilizing. Figure 1 The microstructure shown indicates that the geomembrane can maintain good permeability even in acidic environments.

[0046] In summary, the novel acid-resistant horizontal geomembrane of this invention uses tailings ore as the base material and constructs a geomembrane structure by adding materials such as silica sol, tetraethyl orthosilicate, and hydrophilic minerals in layers. Compared with existing clay layer geomembranes, it greatly reduces the thickness of the horizontal geomembrane and effectively improves the corrosion resistance of the horizontal geomembrane in highly acidic environments. Compared with HDPE membrane geomembranes, the main material is solid waste tailings, realizing the resource utilization of solid waste and reducing the construction cost of the geomembrane to a certain extent.

Claims

1. An acid-resistant horizontal seepage-proof structure using tailings sand as the main material, characterized in that: The seepage-proof structure comprises, from bottom to top, an adsorption salt barrier layer, a condensation water barrier layer, and a capillary barrier layer. The adsorption salt barrier layer has a thickness of 10cm to 30cm and is made of a mixture of tailings sand and kaolin at a mass ratio of 4 to 6:1, with the tailings sand being coarse tailings sand with a particle size of 5 to 8mm. The condensation water barrier layer has a thickness of 20cm to 30cm and is made of a mixture of tailings sand, silica sol, and tetraethyl orthosilicate, wherein tailings sand accounts for 80% to 90% of the total weight of the condensation water barrier layer material, silica sol accounts for 5% to 10%, and tetraethyl orthosilicate accounts for 5% to 10%. The capillary barrier layer has a thickness of 10cm to 30cm and is made of a mixture of tailings sand and alumina at a mass ratio of 7 to 9:

1.

2. The acid-resistant horizontal seepage-proof structure using tailings sand as the main material according to claim 1, characterized in that: The tailings sand of the condensation impermeable layer is composed of fine tailings sand of different particle sizes with a particle size not greater than 2 mm. The particle size distribution of the fine tailings sand is as follows: fine tailings sand with a particle size less than 0.075 mm accounts for 10%-20% of the total weight of the condensation impermeable layer material; fine tailings sand with a particle size of 0.075 mm-0.15 mm accounts for 10%-15% of the total weight of the condensation impermeable layer material; fine tailings sand with a particle size of 0.15 mm-0.25 mm accounts for 5%-15% of the total weight of the condensation impermeable layer material; fine tailings sand with a particle size of 0.25 mm-0.5 mm accounts for 10%-20% of the total weight of the condensation impermeable layer material; fine tailings sand with a particle size of 0.5 mm-1 mm accounts for 15%-25% of the total weight of the condensation impermeable layer material; and fine tailings sand with a particle size of 1 mm-2 mm accounts for 20%-30% of the total weight of the condensation impermeable layer material.

3. The acid-resistant horizontal seepage-proof structure using tailings sand as the main material according to claim 1, characterized in that: The tailings sand in the capillary septum is selected as medium sand with a particle size of 3-5 mm.

4. A construction method for an acid-resistant horizontal seepage-proof structure using tailings sand as the main material, characterized in that, The specific operational steps of the construction method are as follows: S1. In actual construction, the first step is to remove debris and level the area to be treated. Coarse tailings sand with a particle size of 5-8mm and kaolin are mixed and stirred evenly at a mass ratio of 4-6:1 to prepare the raw material for the adsorption and salt barrier layer. The mixed raw material is then spread evenly in the cleaned area to be treated. After spreading, the adsorption and salt barrier layer is compacted using tamping machinery. The thickness of the compacted salt barrier layer is 10cm-30cm. S2. Select fine tailings sand with a particle size of no more than 2mm, silica sol, and tetraethyl orthosilicate, mix them evenly according to the mass ratio to prepare a condensation waterproof layer laying material. The fine tailings sand accounts for 80%-90% of the total weight of the condensation waterproof layer material, the silica sol accounts for 5%-10%, and the tetraethyl orthosilicate accounts for 5-10%. Spread the evenly mixed condensation waterproof layer material evenly on the compacted adsorption and salt barrier layer, and flatten and compact it. The thickness of the compacted condensation waterproof layer is 20cm-30cm. S3. Mix medium-sized tailings sand with a particle size of 3-5mm and alumina at a mass ratio of 7-9:1 to prepare a capillary barrier layer laying material. Spread the capillary barrier layer laying material evenly on the compacted condensation waterproof layer. After spreading, the capillary barrier layer is properly leveled and compacted to complete the laying of the acid-resistant horizontal seepage prevention structure. The thickness of the compacted capillary barrier layer is 10cm-30cm. S4. After 12 hours of laying, the upper soil can be piled on the acid-resistant horizontal seepage-proof structural layer.

5. The construction method of an acid-resistant horizontal seepage-proof structure using tailings sand as the main material according to claim 4, characterized in that: In step S3, the tailings sand with a diameter less than 0.075mm accounts for 10%-20% of the total weight of the polycondensation waterproof layer material, the tailings sand with a diameter of 0.075mm-0.15mm accounts for 10%-15% of the total weight of the polycondensation waterproof layer material, the tailings sand with a diameter of 0.15mm-0.25mm accounts for 5%-15% of the total weight of the polycondensation waterproof layer material, the tailings sand with a diameter of 0.25mm-0.5mm accounts for 10%-20% of the total weight of the polycondensation waterproof layer material, the tailings sand with a diameter of 0.5mm-1mm accounts for 15%-25% of the total weight of the polycondensation waterproof layer material, and the tailings sand with a diameter of 1mm-2mm accounts for 20%-30% of the total weight of the polycondensation waterproof layer material.

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