Long and narrow deep cavity green low-carbon self-compacting backfill material and preparation and backfill method thereof

Abstract

The invention relates to a long and narrow deep cavity green low-carbon self-compacting backfill material and a preparation and backfill method thereof. A long and narrow deep-cavity fat groove is usually formed between a foundation pit enclosure structure of an open cut structure and a main body structure, and backfill materials of an existing long and narrow deep cavity are poor in self-compaction performance and prone to operation diseases during construction. The high-early-strength concrete is prepared from shield muck, a curing agent, an early-strength component, a water-retention healing component and water, the curing agent is a mixture of a gelling component and an alkali-activated component; the mass parts of the shield muck are 80-90 parts; 9 to 18 parts of a gelling component; 1.0 to 3.5 parts of an alkali-activated component; 0.5 to 1.0 part of an early strength component; 0.2 to 0.5 part of a water retention and healing component; and 10-20 parts of water. The grouting material has flowability and self-compaction performance and is suitable for long and narrow deep cavity backfill grouting construction, the engineering construction quality is thoroughly improved from the source, and operation diseases are reduced; and meanwhile, the emission of wastes is reduced, and the resource utilization of the shield waste slag and the industrial waste slag is realized.

Description

Technical Field

[0001] The invention relates to the technical field of underground engineering and geotechnical engineering materials, and in particular to a narrow and deep cavity green low-carbon self-compacting backfill material and a preparation and backfilling method thereof. Background Art

[0002] With the development of underground space, open-cut structures are more widely used in urban development, especially in rail transit construction projects. A narrow and deep cavity is usually formed between the open-cut foundation pit retaining structure and the main structure, which is usually backfilled with soil or concrete. However, it is difficult to use mechanical rolling for soil backfill, and its density is difficult to meet the design requirements, and the post-construction settlement is serious; concrete backfill cannot be vibrated, its density is greatly reduced, and the cost is high; the vibration caused by mechanical rolling and vibration and its construction process can easily damage the structural waterproof layer, thereby causing damage to the structural waterproof system, which is prone to diseases and is difficult to achieve the designed service life.

[0003] Therefore, there is an urgent need for a reasonable, green, environmentally friendly self-compacting backfill material suitable for narrow, long and deep cavities and a preparation and backfilling method thereof to reduce operational hazards. Summary of the invention

[0004] The purpose of the present invention is to provide a green, low-carbon, self-compacting backfill material for a narrow, long and deep cavity and a preparation and backfilling method thereof, so as to at least solve the problem that the existing backfill materials for narrow, long and deep cavities have poor self-compactness and are prone to operational defects during construction.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] Narrow and deep cavity green low-carbon self-compacting backfill material, including shield slag, curing agent, early strength component, water-retaining and healing component and water;

[0007] The curing agent is a mixture of a gelling component and an alkali-activated component;

[0008] The mass fractions are:

[0009]

[0010]

[0011] Furthermore, the shield slag is slag produced by earth pressure balance shield tunneling in sandstone and mudstone strata, and its particle size is 2 to 75 μm.

[0012] Furthermore, the gelling component is selected from mineral powder, steel slag or a combination of mineral powder and steel slag.

[0013] Furthermore, the alkali-activated component is selected from carbide slag, magnesium oxide, or a combination of carbide slag and magnesium oxide.

[0014] Furthermore, the early strength component is calcium sulfate.

[0015] Furthermore, the water-retaining and healing component is a combination of polyacrylamide and polyvinyl alcohol fibers.

[0016] The preparation method of the narrow and deep cavity green low-carbon self-compacting backfill material comprises the following steps:

[0017] Dry and crush the shield slag to obtain shield slag powder, and then sieve it;

[0018] Weigh shield slag powder, gelling component, alkali-activated component, early strength component and water-retaining healing component according to mass proportions;

[0019] The gelling component, the alkali-activated component, the early-strengthening component and the water-retaining and healing component are mixed and stirred to obtain a homogeneous mixed powder;

[0020] Transport shield slag powder and homogeneous mixed powder to the construction site and mix them evenly;

[0021] After mixing, add water for secondary mixing to obtain a green, low-carbon, self-compacting backfill material.

[0022] Furthermore, the moisture content after adding water and mixing twice is 10% to 20%.

[0023] The backfilling method of the narrow and deep cavity green low-carbon self-compacting backfill material is as follows:

[0024] The backfill material is pumped on site to the backfill area and backfilled from bottom to top.

[0025] Furthermore, the backfill area is a narrow and long deep cavity area with a length-to-width ratio greater than 100, a depth greater than 10m and a depth-to-width ratio greater than 10.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The invention mainly comprises shield slag and curing agent (gelling component and alkali-activated component), supplemented by early strength component and water-retaining healing component (polyacrylamide and polyvinyl alcohol fiber), and is mixed with water. The invention has fluidity and self-compactness, is suitable for backfilling and pouring construction of narrow and long deep cavities, and thoroughly improves the quality of engineering construction from the source, reduces operation hazards; at the same time, reduces the discharge of waste, realizes the resource utilization of shield slag and industrial waste slag, and has strong operability, high economic and social benefits, and wide application value, as follows:

[0028] The present invention uses shield tunneling slag as aggregate, which can solve the pollution problem of large amounts of shield tunneling slag that are difficult to dispose of. The shield tunneling slag is solidified by adding external curing agent materials to form solidified materials, which solves the difficulties in resource utilization caused by the high water content, high pollution, poor grading and other characteristics of the shield tunneling slag, expands the resource utilization scenarios of the shield tunneling slag, and increases the resource utilization rate of the shield tunneling slag.

[0029] The main aggregates (shield slag) and most of the materials in the external curing agent (granulated blast furnace slag, steel slag, carbide slag) of the present invention are bulk industrial solid wastes, which can solve the disposal problem of industrial solid wastes through resource utilization. Compared with traditional silicate cement building materials, it has the environmental and economic benefits of low energy consumption, low carbon emissions and low cost, and meets actual engineering needs.

[0030] The present invention can achieve strength control at different curing ages by controlling the dosage of each component, thereby meeting the strength and barrier requirements of building materials in different types of application scenarios. Applicable engineering scenarios include: contaminated site barrier materials, bottom lining materials, top covering materials, road subgrade materials, foundation reinforcement materials, backfill materials and soil improvement materials.

[0031] Under the conditions of environmental changes and external mechanical disturbances, the present invention can inhibit the formation of large cracks and form fine cracks within 100um after cracking. In addition, the gelling component and the alkali-excited component can undergo continuous hydration reaction to form a gelling product to achieve crack healing. The water-retaining healing component forms a hydrogel protective film, which can achieve the functions of inhibiting cracking and retaining water for healing.

[0032] The present invention has semi-rigid strength, long-term stability under acidic conditions, and can maintain high shear strength and compressive strength after multiple dry-wet cycles, with dry mass loss within 8% and strength loss within 15%. It can be applied to different types of environmental conditions, such as construction environments with strong seasonal fluctuations in groundwater and strong influences of regional climate.

[0033] The present invention has good anti-seepage performance, and can achieve a 28-day liquid permeability coefficient of less than 10 in an environment with high risk concentrations of heavy metals, inorganic salts and organic matter. -7 cm / s anti-seepage requirements (Technical Specifications for Vertical Barriers for Industrial Polluted Sites (HG / T 20715-2020)), which can be used as vertical barrier wall materials for polluted sites.

[0034] The present invention has good gas barrier properties and can keep the gas diffusion coefficient below 10 in a high-risk organic gas environment. -6 m 2 / s of gas barrier requirements, meeting the gas barrier requirements of the contaminated site covering barrier layer, and can be used as the bottom lining material and top covering material of the contaminated site.

[0035] The invention can effectively solidify inorganic and organic pollutants in shield slag. Under the acidic leaching conditions simulating acid rain, the concentration of leached pollutants still meets the fourth category standard of groundwater, is environmentally friendly, and will not pollute the surrounding environment. DETAILED DESCRIPTION

[0036] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below. The preferred embodiments of the present invention are given in the specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0037] In the description of this patent, it is necessary to understand that all the technical and scientific terms used have the same meanings as those generally understood by ordinary technicians in the field to which this patent belongs. When there is a contradiction, the definitions in this specification shall prevail. If not otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art, the reagents used in the examples are commercially available products, and the devices used in the examples are existing devices. The limitation of means, reagents or devices cannot be understood as a limitation of this patent, and the same type of means, reagents or devices for solving the same technical problems are within the scope of protection of this patent.

[0038] In the description of this patent, it is to be understood that when an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed separately. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0039] It should also be noted that although the order of steps is mentioned in the method description, in some cases, they may be performed in an order different from that shown here, and this should not be construed as a limitation on the order of the steps.

[0040] Embodiment 1:

[0041] The present embodiment provides a narrow and deep cavity green low-carbon self-compacting backfill material, which is a high water-stable building material. It uses shield slag as the main material and is mixed with a curing agent to improve its strength and barrier properties. It has the properties of waterproof, anti-seepage, anti-corrosion and gas barrier. It can reduce construction costs and carbon emissions while reusing solid waste materials. At the same time, the building materials of this embodiment can also be used as vertical barrier materials, bottom lining materials, top covering materials, road subgrade materials, foundation reinforcement materials, backfill materials and soil improvement materials for contaminated sites, and can be used in a variety of engineering scenarios.

[0042] This embodiment includes shield slag, curing agent, early strength component, water-retaining and healing component and water, and the curing agent is a mixture of a gelling component and an alkali-activated component.

[0043] Specifically, the following raw materials are included in parts by weight:

[0044]

[0045] Among them, shield slag is the slag produced by earth pressure balance shield tunneling in sandstone and mudstone strata, and its particle size is 2 to 75μm.

[0046] Liquid limit ≤25%, plastic limit ≤15%, plasticity index ≤10, liquid index ≤1, which is a low liquid limit clay with high water content; limiting particle size d60 ≤5mm, effective particle size d10 ≤0.25, and uniformity coefficient Cu ≥20, which is a poorly graded soil.

[0047] The gelling component is selected from mineral powder, steel slag or a combination of mineral powder and steel slag.

[0048] The ore powder is made of granulated blast furnace slag, grade S95 or S105, with a specific surface area of ​​not less than 0.28m 2 / g, wherein SiO2 content ≥ 20%, CaO content ≥ 20%;

[0049] The steel slag shall be electric furnace steel slag with a mesh size of not less than 200 after being subjected to magnetic separation and iron removal treatment and ground into powder in accordance with the provisions of the YB / T 022 standard, wherein the SiO2 content shall be ≥12% and the CaO content shall be ≥30%.

[0050] The alkali-activated component is selected from carbide slag, magnesium oxide, or a combination of carbide slag and magnesium oxide.

[0051] The carbide slag is a powder with a size of not less than 200 mesh and a CaO content of ≥ 60%;

[0052] The activity of activated magnesium oxide is between 90s and 100s, and the MgO content is ≥80%.

[0053] The early strength component is calcium sulfate, and the purity of calcium sulfate is ≥80%.

[0054] The water-retaining and healing component is a combination of polyacrylamide and polyvinyl alcohol fibers.

[0055] Polyacrylamide uses anionic polyacrylamide with a molecular weight of 8 million to 20 million;

[0056] The diameter of the polyvinyl alcohol fiber is 12 to 14 μm, the fiber length is 6 to 12 mm, the tensile strength is ≥1600 MPa, and the elastic modulus is ≥35 GPa.

[0057] The shield slag, the cementitious component, the alkali-activated component, the early-strength component and the water-retaining healing component are all in loose powder form.

[0058] The cementitious component contains a large amount of silicon and calcium elements, which are converted into silicon and calcium ions after being excited by the alkali-excited component, and then react with metal ions to produce volcanic ash reactions to form gel products including calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH), and can react with calcium sulfate in the early strength component to promote further hydration of the product to generate ettringite (AFt) material with high early strength. The polyacrylamide in the water-retaining and healing component can, on the one hand, combine with inorganic materials through hydrogen bonds and van der Waals forces to form an insoluble hydrogel film, effectively preventing water loss, and on the other hand, it can adsorb organic and inorganic pollutants in shield slag, reduce toxic leaching, improve the curing effect, and ensure environmental safety. The products can fill the pores of the material, provide strength support for the material, and increase the tortuosity of the internal channels of the material, thereby improving the material's anti-seepage and gas barrier properties. Polyvinyl alcohol fiber can effectively improve the interfacial adhesion inside the material, so that the material has a certain toughness and crack resistance. Under environmental changes and mechanical disturbances, the cementitious material will fill the cracks to form healing, thereby ensuring the integrity of the internal structure of the material.

[0059] The above materials have excellent performance in waterproofing, anti-seepage, anti-corrosion and gas barrier, and have toughness and crack resistance. They can be used as construction materials for various engineering applications, such as roadbed materials, foundation reinforcement materials, backfill materials and soil improvement materials. They are especially suitable for vertical barrier materials, bottom lining materials and top covering materials of contaminated sites. They have the following advantages:

[0060] First, this low-carbon building material uses shield slag as its main component, which can solve the disposal problem caused by the high water content and highly toxic leaching characteristics of shield slag.

[0061] Second, this low-carbon building material has semi-rigid mechanical strength and crack resistance, can inhibit cracking under environmental changes and mechanical effects, and undergo hydration and carbonization reactions in a short period of time to achieve self-healing.

[0062] Third, this low-carbon building material has long-term stability under acidic conditions and inorganic salt stress. After undergoing multiple stages of dry-wet cycles, the dry mass loss is controlled within 8% and the strength loss is controlled within 15%.

[0063] Fourth, the low-carbon building material has good anti-seepage performance, and can meet the 28-day liquid permeability coefficient of less than 10 in an environment with high risk concentrations of heavy metals, inorganic salts and organic matter. -7 cm / s anti-seepage requirement (Technical Specifications for Vertical Barriers for Industrial Polluted Sites (HG / T 20715-2020)).

[0064] Fifth, the low-carbon building material has good gas barrier properties and can keep the gas diffusion coefficient below 10 in a high-risk organic gas environment. -6 m 2 / s of air blocking requirement.

[0065] Sixth, this low-carbon building material can control the strength at different curing ages by controlling the dosage of each component, thereby meeting the strength requirements of building materials in different types of application scenarios.

[0066] Seventh, most of the solidifying materials of this low-carbon building material are bulk industrial solid waste, which can realize the resource utilization of solid waste.

[0067] Eighth, this low-carbon building material still meets the standard limit for Class IV groundwater in the "Groundwater Quality Standard" (GB / T 14848-2017) under acid leaching that simulates extreme acid rain conditions.

[0068] The following is the verification process of this embodiment, as shown below:

[0069] The specific content of each component is shown in Table 1.

[0070] Table 1 Specific implementation material dosage design scheme (dry mass ratio, dimensionless)

[0071]

[0072] Among them, the liquid and plastic limit properties of shield slag are shown in Table 2.

[0073] Table 2 Physical properties of shield slag

[0074] Shield muck density Dry density Porosity Moisture content Maximum dry density Physical property parameters <![CDATA[2.15g / cm 3 ]]> <![CDATA[1.68g / cm 3 ]]> 0.64 28.07％ <![CDATA[1.9g / cm 3 ]]> Shield muck Unevenness coefficient Cu Curvature coefficient Cc Liquid limit Plastic Limit Plasticity Index Physical property parameters 24.796 0.116 24.5％ 14.8％ 9.7％

[0075] The shield slag was tested for heavy metal and organic matter concentrations, where heavy metal analysis was conducted in accordance with the "Determination of Metal Elements in Solid Waste by Inductively Coupled Plasma Mass Spectrometry" (HJ 766-2015); organic pollutant analysis was conducted in accordance with the "Determination of Volatile Organic Compounds in Soil and Sediment by Purge and Trap / Gaseous Chromatography-Mass Spectrometry" (HJ 605-2011). The contamination of shield slag is shown in Table 3.

[0076] Table 3 Shield slag pollution

[0077] Pollutant indicators Pollutant concentration (mg / kg) First category land use screening value (mg / kg) Nickel (Ni) 20.2～40.8 150 Zinc (Zn) 9.1～13.5 none Arsenic (As) 0.6～5.2 20 Cadmium (Cd) 0.1～9.3 20 Lead (Pb) 420.8～511.9 400 Mercury (Hg) 0.05～0.21 8 Hexavalent chromium (Cr6+) 0.2～0.8 3 Volatile phenols 21.9～34.2 none Anionic surfactants 68.9～388.6 none

[0078] The following is a comparison example:

[0079] The control materials are commonly used materials for road subgrade, vertical barrier walls of contaminated sites and barrier layers covering contaminated sites, namely compacted clay and ordinary Portland cement-stabilized soil materials (cement grade 42.5, dosage 10%), among which compacted clay (CCL) is the traditional material for road subgrade and barrier layers covering contaminated sites, and ordinary Portland cement-stabilized soil (SC) is the main material for vertical barrier walls of contaminated sites. Compacted clay is set as control example 1 and ordinary Portland cement-stabilized soil is set as control example 2. The specific indicators of the clay used in the two are shown in Tables 4 and 5, respectively.

[0080] Table 4 Physical property parameters of compacted clay

[0081] Compacted clay proportion Optimum moisture content Maximum dry density Liquid limit Plastic Limit Plasticity Index Compaction Mixing moisture content Physical property parameters 2.73 27.6％ <![CDATA[1.7 g / cm 3 ]]> 57.4％ 27.9％ 29.5％ 96％ 30％

[0082] Table 5 Physical property parameters of clay in ordinary Portland cement-stabilized soil

[0083]

[0084] Among the mechanical indicators evaluated in actual engineering, unconfined compressive strength is one of the most important indicators, and it is a key indicator for judging whether the material meets the requirements of roadbed materials and whether it can serve effectively. Unconfined compressive strength specifically refers to the maximum axial stress that the material can withstand under the condition of unconstrained control on the side, which can quickly and accurately test the mechanical properties of the material. Among them, the roadbed base, surface cover, and bottom liner need to be compacted during the construction process, so the compaction degree of the sample needs to be controlled indoors, and the compaction degree of each embodiment and control example is controlled to be 96%; various backfill materials, foundation reinforcement, soil improvement, and vertical barriers do not need to be compacted during the construction process, only backfilling is required, so the backfill sample needs to be prepared directly indoors without controlling the compaction degree. Table 6 is the comparison results of the unconfined compressive strength of the cured compacted samples, and Table 7 is the comparison results of the unconfined compressive strength of the cured backfill samples. The results show that under the same in-situ soil and curing age, the results of curing by selecting the materials proposed in the present invention are better than those of curing by traditional cement materials.

[0085] Table 6 Unconfined compressive strength of compacted solidified soil samples

[0086]

[0087] Table 7 Unconfined compressive strength of cured backfill specimens

[0088]

[0089] In the service scenarios of roadbed base, surface cover, bottom liner, various backfill materials, foundation reinforcement, soil improvement and vertical barrier, attention should be paid to the stability of materials in case of water, which represents a key ability of whether the material can effectively maintain its own performance under the erosion of water. The ratio of the unconfined compressive strength of the sample after water immersion to the unconfined compressive strength of the sample under normal maintenance is set as the water stability coefficient (K r ), the larger the water stability coefficient, the better the water stability of the material; at the same time, the strength loss rate is defined, and the percentage of the ratio of the difference between the unconfined compressive strength of the same age under standard curing and the unconfined compressive strength of the sample after immersion in water to the unconfined compressive strength of the same age under standard curing is defined as the strength loss rate. In the present invention, the shield slag solidification backfill material is used for comparison, wherein the standard curing age is set to 28 days, and the sample after 14 days of standard curing is immersed in water for 14 days for direct comparison, and the water stability coefficient and strength loss rate are calculated by the following formula:

[0090]

[0091] in:

[0092] Kr is the water stability coefficient;

[0093] q ut is the unconfined compressive strength of the water-cured specimen, kPa;

[0094] q u0 is the unconfined compressive strength of the specimen maintained at constant temperature and humidity, kPa;

[0095] Δq t is the strength loss, %.

[0096] The water stability results of the materials of Examples 1-8 and Comparative Examples 1-2 are shown in Table 8. The results show that under the same in-situ soil and curing age, the results of selecting the green low-carbon building materials proposed in the present invention are better than those of traditional compacted clay and cement-solidified soil materials.

[0097] Table 8 Water stability of materials in various embodiments and comparative examples

[0098] Example Strength loss rate (%) Water stability coefficient 1 43.6 0.56 2 40.8 0.59 3 37.3 0.62 4 35.7 0.64 5 32.4 0.67 6 38.3 0.61 7 37.9 0.62 8 38.5 0.61 Comparative Example 1 58.3 0.41 Comparative Example 2 48.2 0.51

[0099] In order to further illustrate the excellent performance of the green and low-carbon building materials of the present invention, a dry-wet cycle test is used to evaluate the self-healing ability of low-carbon building materials after being affected by changes in the external environment. At the same time, the dry-wet cycle test can also effectively simulate the alternating dry and wet environment of low-carbon building materials during service, and can effectively evaluate the engineering performance of low-carbon building materials caused by changes in the external environment. It is also a relatively accelerated test, which can quickly and effectively evaluate the service performance of low-carbon building materials in the most extreme environment. Refer to American Society for Testing and Materials (ASTM) D4843-1988 standard test method for wetting and drying test of solid wastes. After curing the solidified slag material for 28 days, the quality is tested, and then the material is placed in water to soak for 24 hours. After the soaking is completed, it is placed in an oven at 60°C and heated for 24 hours. This process is level one, and this test will test the changes between levels 5 and 10. The calculation formula for the cumulative mass loss rate is as follows:

[0100] ML i =(m i -m0) / m0×100%

[0101] CML i =ML1+ML2+…+ML i

[0102] in:

[0103] ML i is the mass increase rate of the solidified shield slag sample after the i-th dry-wet alternating treatment;

[0104] CML i is the cumulative mass increase rate of the solidified shield slag sample after the 1st to the i-th dry-wet alternating treatment;

[0105] m0 is the mass of the solidified shield slag sample before the dry-wet alternating treatment;

[0106] m i is the mass of the solidified shield slag sample after the i-th dry-wet alternating treatment.

[0107] Table 9 shows the changes in the cumulative mass loss rate of the materials of Examples 1-8 and Control Examples 1-2 under the action of dry-wet cycles. The results of the Examples and Control Examples show that the low-carbon building materials of the present invention can effectively resist 10 dry-wet cycles, while the compacted clay materials and cement-based solidifying materials of the Control Example disintegrate and fail after 7 dry-wet cycles.

[0108] Table 9 Dry-wet cycle of materials in various embodiments and comparative examples

[0109] Example Level 5 cumulative mass loss rate (%) 10-level cumulative mass loss rate 1 14.2 33.5 2 13.9 29.1 3 13.3 27.8 4 12.8 26.6 5 11.4 25.7 6 13.8 28.7 7 13.5 29.3 8 14.3 28.6 Comparative Example 1 25.9 The sample disintegrated after level 7 Comparative Example 2 23.0 The sample disintegrated after level 7

[0110] In the surface covering, bottom lining and vertical barrier service scenarios, attention must be paid to the barrier performance of the material against contaminated groundwater, and the permeability coefficient is the key indicator for judging the barrier performance. In order to further evaluate the barrier performance of the material, groundwater from a petrochemical organic contaminated site in Yangzhou, Jiangsu was selected as the barrier solution. The specific pollution conditions in the solution are shown in Table 10. The permeability test used the flexible wall permeability test test method. After 28 days of standard curing of each case material, permeability tests were carried out using contaminated groundwater and tap water. According to the requirements of the "Technical Specifications for Vertical Barriers for Industrial Contaminated Sites" (HG / T 20715-2020), the permeability coefficient of cement-based vertical barrier materials under the action of tap water must be less than 10 -9 m / s, the permeability coefficient should be less than 10 under the action of pollutants -8 Table 11 shows the permeability coefficients of the materials in various embodiments and comparative examples under the action of tap water and contaminated liquid. The results show that the permeability coefficients of the solidified slag materials under the action of tap water and contaminated liquid are both less than 10 -9 m / s, however, cement-soil materials do not meet the index requirements.

[0111] Table 10 Groundwater pollution at a petrochemical contaminated site in Yangzhou, Jiangsu

[0112] Serial number Types of pollutants Concentration (mg / L) 1 benzene 2.66 2 Petroleum hydrocarbons 15 3 Ethylbenzene 1.22 4 Xylene 0.34 5 Toluene 0.612 6 phenol 0.023 7 aniline 51.217 8 Ethylene dichloride 5 9 Tetrachloroethylene 138 10 arsenic 60

[0113] Table 11 Permeability coefficient of each embodiment and reference example material after curing for 28 days

[0114] Example Tap water permeability coefficient (m / s) Permeability coefficient of contaminated liquid (m / s) 1 <![CDATA[3.3×10 -9 ]]> <![CDATA[8.4×10 -9 ]]> 2 <![CDATA[2.6×10 -9 ]]> <![CDATA[5.3×10 -9 ]]> 3 <![CDATA[1.2×10 -9 ]]> <![CDATA[2.4×10 -9 ]]> 4 <![CDATA[8.8×10 -10 ]]> <![CDATA[10.7×10 -10 ]]> 5 <![CDATA[5.3×10 -10 ]]> <![CDATA[6.1×10 -10 ]]> 6 <![CDATA[1.4×10 -10 ]]> <![CDATA[2.8×10 -10 ]]> 7 <![CDATA[1.5×10 -10 ]]> <![CDATA[3.2×10 -10 <!-- 9 -->]]> 8 <![CDATA[1.4×10 -10 ]]> <![CDATA[2.9×10 -10 ]]> Comparative Example 1 <![CDATA[7.5×10 -9 ]]> <![CDATA[5.2×10 -8 ]]> Comparative Example 2 <![CDATA[4.3×10 -9 ]]> <![CDATA[2.7×10 -8 ]]>

[0115] In the service scenarios of surface covering, bottom lining and vertical barrier, attention should be paid to the barrier performance of the material against soil gas. The existing national standards do not have clear requirements for the gas diffusion coefficient. In this implementation case, it is necessary to meet the international standard of gas diffusion coefficient less than 10 -6 m 2 / s requirement. The gas diffusion coefficient test device made by this project was used to conduct gas diffusion coefficient tests for the implementation cases and control cases, respectively, and oxygen was selected as the gas diffusion coefficient test gas. Table 12 shows the gas diffusion coefficients of the embodiments and control cases after 28 days of curing. By comparison, it can be seen that the gas diffusion coefficient requirements are met, and the gas diffusion coefficient of the low-carbon building material is about 1 order of magnitude lower than that of the CCL material and cement soil material.

[0116] Table 12 Gas diffusion coefficients of materials in various embodiments and comparative examples after curing for 28 days

[0117] Example <![CDATA[Diffusion coefficient of gas (m 2 / s)]]> 1 <![CDATA[3.9×10 -7 ]]> 2 <![CDATA[2.7×10 -7 ]]> 3 <![CDATA[1.2×10 -7 ]]> 4 <![CDATA[9.3×10 -8 ]]> 5 <![CDATA[6.8×10 -8 ]]> 6 <![CDATA[1.8×10 -7 ]]> 7 <![CDATA[1.1×10 -7 ]]> 8 <![CDATA[1.4×10 -7 ]]> Comparative Example 1 <![CDATA[6.9×10 -7 ]]> Comparative Example 2 <![CDATA[8.9×10 -7 ]]>

[0118] Environmental safety is one of the important properties of solidified materials. The pollution of shield slag itself is shown in Table 3 above. The toxic leaching test of the solidified shield slag sample was carried out in accordance with the relevant provisions of the "Solid Waste Leaching Toxicity Leaching Method Sulfuric Acid and Nitric Acid Method" (HJ / T299-2007). This test method can evaluate the environmental safety of solidified shield slag materials under the most unfavorable conditions of extreme acid rain erosion during service. Table 13 shows the leached pollutant indicators obtained by testing after toxic leaching tests after 28 days of solidification and curing of each embodiment. By comparing the concentrations of toxic leaching pollutants in each embodiment and the control example, it can be found that the toxic leaching indicators of each embodiment meet the standard limit of Class IV groundwater in the "Groundwater Quality Standard" (GB / T 14848-2017), but the control example cannot meet it.

[0119] Table 13 Toxicity leaching pollutant concentrations of various examples and reference examples

[0120]

[0121] In actual engineering construction, environmental economic benefits are factors that are subject to government supervision and key considerations by the construction party in engineering projects. Table 14 shows the unit price and net CO2 emissions of each component material in this implementation case, and Table 15 shows the economic cost and net CO2 emissions of each embodiment and control example material. Comparing the environmental economic benefits of each material in this implementation case, it can be found that this low-carbon green building material is superior to compacted clay and ordinary Portland cement-stabilized soil in terms of economic cost and carbon emissions.

[0122] Table 14 Unit price and net CO2 emissions of each component material

[0123] Material Name Unit price (CNY / t) <![CDATA[Net CO2 emissions (kg / t)]]> Shield muck 0 0 Mineral powder 200 0 Steel slag 50 0 Carbide slag 85 0 Magnesium Oxide 170 1400 Calcium sulfate 1700 277.8 APAM 9800 1137 PVA 15000 1021 Ordinary Portland cement (No. 42.5) 425 795 clay 1500 0.5

[0124] Table 15 Unit price and net CO2 emission of materials in various embodiments and comparative examples

[0125] Example Unit price (CNY / t) <![CDATA[Net CO2 emissions (kg / t)]]> 1 46.66 3.547 2 56.09 3.547 3 65.51 3.547 4 63.79 3.547 5 62.06 3.547 6 38.51 3.547 7 67.21 31.55 8 40.21 31.55 Comparative Example 1 1500 0.5 Comparative Example 2 1392.5 79.95

[0126] In summary, the present invention discloses a narrow and deep cavity green and low-carbon self-compacting backfill material. The green and low-carbon building material uses shield slag as the main material, and is added with an external curing agent to improve its strength and barrier properties. The resource utilization of solid waste materials reduces costs and carbon emissions, and can be applied to multiple application scenarios, including road subgrades, backfill materials, vertical barrier materials for polluted sites, and horizontal barrier materials for polluted sites. This green and low-carbon building material has the following excellent properties: most of the raw materials are bulk solid waste (shield slag, carbide slag, granulated blast furnace slag, steel slag), which can solve the problem of solid waste disposal. Compared with traditional silicate cement materials, it has low energy consumption, low carbon emissions and low cost environmental and economic benefits; it has semi-rigid strength and crack resistance, long-term stability under acidic conditions, and maintains its high shear strength and compressive strength characteristics after multiple stages of dry-wet cycles; it has good water retention, good anti-seepage performance and gas barrier performance; it has good environmental friendliness and can effectively solidify inorganic and organic pollutants; the mechanical properties and anti-seepage and air-tightness performance of the solidified slag can be controlled by controlling key parameters such as the dosage of the added curing agent, the distribution ratio of each group and the degree of compaction to meet the material requirements of different application scenarios.

[0127] Embodiment 2:

[0128] This embodiment provides a method for preparing a narrow and deep cavity green low-carbon self-compacting backfill material, comprising the following steps:

[0129] S1: drying and crushing the shield slag to obtain shield slag powder, and sieving it;

[0130] The shield slag was placed in a dryer at a temperature of 105°C, taken out after drying, and crushed with a soil crusher for 3 minutes to obtain shield slag powder.

[0131] S2: Weigh the shield slag powder, gelling component, alkali-activated component, early strength component and water-retaining healing component according to their mass fractions;

[0132] S3: mixing and stirring the gelling component, the alkali-activated component, the early strength component and the water-retaining and healing component to obtain a homogeneous mixed powder;

[0133] The mineral powder, steel slag, carbide slag or magnesium oxide, calcium sulfate, polyacrylamide and polyvinyl alcohol fiber are placed in a powder mixer, and are fully mixed and uniformly stirred to obtain a homogeneous mixed powder.

[0134] S4: transport the shield slag powder and homogeneous mixed powder to the construction site and mix them evenly;

[0135] S5: After mixing, add water and mix again to obtain a green, low-carbon, self-compacting backfill material.

[0136] The moisture content after adding water and mixing twice is 15%.

[0137] This building material preparation method is simple, fast, not restricted by engineering conditions, and has universal applicability.

[0138] Embodiment 3:

[0139] This embodiment provides a backfilling method of a narrow and deep cavity green low-carbon self-compacting backfilling material, the backfilling method is:

[0140] The backfill material is pumped on site to the backfill area and backfilled from bottom to top.

[0141] Among them, the backfill area is a narrow and deep cavity area with an aspect ratio greater than 100, a depth greater than 10m and a depth-to-width ratio greater than 10.

[0142] The above specific examples are used to illustrate the present invention, which are only used to help understand the present invention and are not used to limit the present invention. For those skilled in the art to which the present invention belongs, some simple deductions, modifications or substitutions can be made according to the idea of ​​the present invention.

Claims

1. Narrow and deep cavity green low-carbon self-compacting backfill material, characterized by: The backfill material includes shield slag, curing agent, early strength component, water retention and healing component and water; The curing agent is a mixture of a gelling component and an alkali-activated component; The mass fractions are: 80-90 parts of shield slag 9 to 18 parts of gelling component 1.0 to 3.5 parts of alkali excitation component Early strength component 0.5~1.0 part 0.2-0.5 parts of water-retaining and healing components 10-20 parts of water.

2. The narrow and deep cavity green low-carbon self-compacting backfill material according to claim 1 is characterized by: The shield slag is slag produced by earth pressure balance shield tunneling in sandstone and mudstone strata, and the particle size thereof is 2 to 75 μm.

3. The narrow and deep cavity green low-carbon self-compacting backfill material according to claim 1 is characterized by: The gelling component is selected from mineral powder, steel slag or a combination of mineral powder and steel slag.

4. The narrow and deep cavity green low-carbon self-compacting backfill material according to claim 1 is characterized by: The alkali-activated component is selected from carbide slag, magnesium oxide, or a combination of carbide slag and magnesium oxide.

5. The narrow and deep cavity green low-carbon self-compacting backfill material according to claim 1 is characterized by: The early strength component is calcium sulfate.

6. The narrow and deep cavity green low-carbon self-compacting backfill material according to claim 1 is characterized by: The water-retaining and healing component is a combination of polyacrylamide and polyvinyl alcohol fibers.

7. The method for preparing the narrow and deep cavity green low-carbon self-compacting backfill material according to claims 1-6 is characterized in that: The following steps are involved: Dry and crush the shield slag to obtain shield slag powder, and then sieve it; Weigh shield slag powder, gelling component, alkali-activated component, early strength component and water-retaining healing component according to mass proportions; The gelling component, the alkali-activated component, the early-strengthening component and the water-retaining and healing component are mixed and stirred to obtain a homogeneous mixed powder; Transport shield slag powder and homogeneous mixed powder to the construction site and mix them evenly; After mixing, add water for secondary mixing to obtain a green, low-carbon, self-compacting backfill material.

8. The method for preparing the narrow and deep cavity green low-carbon self-compacting backfill material according to claim 7, characterized in that: The moisture content after adding water and mixing twice is 10% to 20%.

9. A backfilling method for the narrow and deep cavity green low-carbon self-compacting backfill material according to claims 1-6, characterized in that: The backfill method is: The backfill material is pumped on site to the backfill area and backfilled from bottom to top.

10. The backfilling method of the narrow and deep cavity green low-carbon self-compacting backfilling material according to claim 9, characterized in that: The backfill area is a narrow and deep cavity area with an aspect ratio greater than 100, a depth greater than 10m and a depth-to-width ratio greater than 10.

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