Ground grouting reinforcement method for unfavorable geological sections in subway tunnels

Abstract

This invention discloses a ground grouting reinforcement method for adverse geological sections in subway tunnels. Through comprehensive investigation of soil and rock properties, groundwater level, groundwater permeability coefficient, and depth of adverse geological sections, the distribution and depth of grouting holes are designed according to different geological conditions. Grouting fluids containing specific proportions of components are prepared for sand, clay, and rock. Based on the soil and rock type, the grouting volume, pressure, and speed per hole are rationally set. Multiple detection methods, such as ground-penetrating radar scanning, are used to evaluate the effect, and supplementary grouting is performed in areas that do not meet the standards. For special adverse geological conditions, such as flowing sand layers, expansive clay, and fault fracture zones, corresponding auxiliary measures and grouting methods are adopted. This method effectively improves the pertinence, scientific rigor, and adaptability of grouting reinforcement, ensures tunnel construction safety and long-term stable operation, reduces engineering costs, and improves the accuracy and reliability of reinforcement.

Description

Technical Field

[0001] This invention relates to the field of tunnel grouting technology. More specifically, this invention relates to a method for ground grouting reinforcement of unfavorable geological sections in subway tunnels. Background Technology

[0002] With the rapid development of urban rail transit, the scale of subway tunnel construction continues to expand. During tunnel construction, traversing various adverse geological conditions is an unavoidable challenge, posing numerous serious difficulties to the project.

[0003] Sandy soil, a common type of unfavorable geological condition, has low interparticle cohesion, large pores, and good connectivity. Especially under conditions of high groundwater levels and high permeability, sandy soil is highly prone to quicksand, leading to water and sand inrush during tunnel excavation. This seriously endangers construction safety and may even cause major accidents such as ground subsidence. Currently, due to the lack of standardized grouting fluids, the preparation of grouting fluids in sandy soil areas relies heavily on the subjective experience of engineers. This makes it difficult to accurately control the composition and properties of the grout based on the characteristics of the sandy soil, groundwater level, and permeability under complex hydrogeological conditions. In such cases, the grout is easily diluted and washed away by rapidly flowing groundwater, failing to form a stable and effective reinforcement zone in the sandy soil layer. The reinforcement effect falls far short of expectations, significantly increasing project risks.

[0004] Clay, due to its fine particles and low porosity, undergoes significant volume changes with variations in moisture content. Expansive clay, in particular, expands when wet and shrinks when dry. This characteristic exerts immense pressure on tunnel lining structures, leading to cracking and deformation, severely impacting the tunnel's normal use and structural safety. Traditional reinforcement methods for clay, such as simple cement grouting, lack standardized grouting solutions and cannot adequately address the complex physical properties of clay and factors like groundwater levels. Consequently, they are insufficient to effectively suppress clay expansion and contraction deformation, and even reinforced clay can still cause serious damage to the tunnel structure, shortening its service life.

[0005] While rock strata are relatively stable, rocks with well-developed fissures can weaken the integrity and strength of the rock mass. During tunnel excavation, this can easily lead to problems such as collapses and water inrushes. Similarly, due to the lack of standardized grouting fluids, it is impossible to scientifically prepare grout based on rock characteristics, groundwater level, and permeability when facing complex rock fissure networks. This makes it difficult for the grout to evenly fill the fissures, resulting in insufficient reinforcement in some areas and significantly affecting the stability of the surrounding rock. Even for relatively intact blocky rocks, the lack of standardized grouting fluids makes it difficult to effectively improve their adhesion to the lining, thus making enhancing overall stability a challenging problem.

[0006] Furthermore, unfavorable geological sections are often accompanied by complex groundwater levels and infiltration conditions. High groundwater levels increase soil saturation and reduce soil strength; high permeability accelerates groundwater flow, further exacerbating the adverse effects of unfavorable geological conditions on tunnel construction and structure. Existing surface grouting reinforcement methods, lacking standardized grouting fluids, have numerous shortcomings when comprehensively considering factors such as soil and rock properties, groundwater levels, and permeability coefficients. They cannot comprehensively and efficiently address the problems caused by unfavorable geological sections, not only delaying project progress but also significantly increasing project costs and potentially posing safety hazards for subsequent operation. Therefore, developing a method that can fully consider multiple geological factors, accurately design grouting parameters, and effectively improve grouting reinforcement effects is of crucial practical significance for subway tunnel construction. Summary of the Invention

[0007] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0008] Another objective of this invention is to provide a ground grouting reinforcement method for unfavorable geological sections in subway tunnels. This method comprehensively considers multiple factors, resulting in excellent grouting performance. Through geologically differentiated grouting fluid schemes and dynamic adaptation of grouting parameters, it solves the problem of insufficient reinforcement by traditional grouting methods in sandy, clay, and rock strata, thus ensuring the safety of tunnel construction and structure. To achieve these objectives and other advantages according to the present invention, a ground grouting reinforcement method for unfavorable geological sections in subway tunnels is provided, comprising: S1. Survey the soil and rock properties, groundwater level H, groundwater permeability coefficient K, and depth of unfavorable geological sections in the subway tunnel section; S2. Design the distribution of grouting holes based on the soil and rock characteristics surveyed in step S1, and design the hole depth based on the depth of the adverse geological section and the tunnel burial depth. S3. Prepare grouting fluid based on the soil and rock properties, groundwater level, and groundwater permeability coefficient measured in step S1. S4. Grouting reinforcement is carried out according to the grouting hole distribution designed in step S2; In step S3, the grouting fluid includes component A and component B: if the unfavorable geological section is sandy soil, component A and component B are a prepolymer containing isocyanate groups and a sand-fixing agent, respectively; if the unfavorable geological section is clay, component A and component B are epoxy resin and a curing agent, respectively; if the unfavorable geological section is rock, component A and component B are cement and water glass, respectively.

[0009] Traditional methods rely on experience to prepare grout, failing to comprehensively consider dynamic parameters such as groundwater level and permeability coefficient, leading to unstable grouting results. This implementation method dynamically adapts grouting based on soil and rock characteristics, groundwater level, and groundwater permeability coefficient, achieving precise matching of grout performance with hydrogeological conditions and avoiding grout waste or insufficient reinforcement.

[0010] In particular, sandy soil particles are loose and highly permeable, making it easy for traditional grouts (such as cement grout) to be diluted and washed away by groundwater, failing to form an effective solidified body and leading to the risk of water and sand inrush. This implementation method uses a combination of isocyanate-based prepolymer and sand-stabilizing agent, allowing the grout to remain stably in highly permeable sand layers, effectively suppressing sand flow and preventing tunnel collapse. Clay expands when it comes into contact with water and shrinks when it loses water; traditional cement grouting cannot suppress its volume change, leading to cracking of the lining structure. This implementation method uses epoxy resin and a curing agent, forming a flexible-rigid composite after curing, reducing lining structure deformation and extending the tunnel's service life. In rocks with well-developed fissures, traditional grouts are difficult to fill fissures evenly, leaving weak areas even after reinforcement. This implementation method uses a cement + water glass two-component grout, which has strong permeability and high density of the solidified rock, significantly improving the overall stability of the surrounding rock.

[0011] In the aforementioned technical solution, the S1 survey stage comprehensively assesses the characteristics of the soil and rock, groundwater level, groundwater permeability coefficient, and depth of adverse geological sections, providing detailed information for subsequent precise design and greatly enhancing the relevance and scientific rigor of the grouting reinforcement scheme. In the S2 grouting hole design step, the distribution pattern is rationally designed based on the soil and rock characteristics, such as rectangular arrangements for sand, ring arrangements for clay, and quincunx arrangements for rocks, ensuring uniform grout diffusion and improving reinforcement uniformity. The hole depth is determined by combining the depth of adverse geological sections and the tunnel burial depth, ensuring the grouting depth effectively covers adverse geological sections and penetrates into stable strata, enhancing the stability of the tunnel structure. In the S3 grout preparation stage, the grout components are specifically adjusted according to different geological and hydrological conditions. For example, the ratio of isocyanate-based prepolymer to sand-fixing agent and the composition of the sand-fixing agent are adjusted based on the groundwater level and permeability coefficient; appropriate ratios of epoxy resin and curing agent, and cement and water glass are respectively used for clay and rock, ensuring the grout performance matches various geological conditions and improving the reinforcement effect. Ultimately, during the S4 grouting reinforcement process, the scientific design of each step in the early stage enabled the grouting to be carried out accurately and efficiently, effectively enhancing the stability of the soil in the adverse geological section, reducing the risks of water inrush and collapse, ensuring the safety of subway tunnel construction and long-term stable operation, while reducing project costs and subsequent maintenance workload.

[0012] Preferably, when the unfavorable geological section in step S3 is sandy soil, the mass ratio of the isocyanate-containing prepolymer to the sand-stabilizing agent and the composition of the sand-stabilizing agent are prepared according to the different groundwater levels H and groundwater permeability coefficient K, as follows: When H≤3m and K≥1.5×10 -3At a speed of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 2~2.3:1, and the sand-fixing agent comprises 48~50% water (solvent by mass), 38~40% sodium silicate (modulus 3.0~3.3), 4~8% polyacrylamide (degree of hydrolysis 25~35%), 2~4% potassium aluminum sulfate (accelerator), and 0.1~1% sodium dodecylbenzenesulfonate. When H≤3m and K<1.5×10 -3 At a speed of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 1.5~1.8:1. The sand-fixing agent comprises 42~45% water (solvent), 34~36% potassium silicate (modulus 2.6~2.8), 8~10% dibutyl phthalate (plasticizer), 10~12% ethanol (diluent), 2~4% triethanolamine (accelerator), and 0.1~0.4% polyether-modified polysiloxane (defoamer). When H>3m and K≥1.5×10 -3 At a speed of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 1.1~1.3:1, and the sand-fixing agent comprises 48~50% water (solvent), 36~38% aluminum iron silicate, 3~6% dibutyltin disilicate (catalyst), 3~5% metakaolin (reinforcing agent), and 0.3~0.8% sodium hexametaphosphate (dispersant). When H > 3m and K < 1.5 × 10 -3 At a speed of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 1:1. The sand-fixing agent comprises 42-45% solvent by mass, 45-48% of a compound of metakaolin and silicate cement, 6-8% quartz sand, 0.5-1% nano silica, and 0.6-1% tartaric acid as a retarder. In the compound of metakaolin and silicate cement, the mass ratio of metakaolin to silicate cement is 4:5, and the particle size of the quartz sand is 0.1-0.3 mm.

[0013] In the above technical solution, the ratio of isocyanate-based prepolymer and sand-stabilizing agent is precisely controlled according to different groundwater levels and groundwater permeability coefficients, and the composition of the sand-stabilizing agent is meticulously designed. This is applicable when the groundwater level is less than or equal to 3m from the ground surface and the groundwater permeability coefficient is greater than or equal to 1.5 × 10⁻⁶. -3At a flow rate of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 2-2.3:1. The sand-fixing agent comprises 48-50% water (by mass), 38-40% sodium silicate (modulus 3.0-3.3), 4-8% polyacrylamide (degree of hydrolysis 25-35%), 2-4% potassium aluminum sulfate (accelerator), and 0.1-1% sodium dodecylbenzene sulfonate. The high proportion of isocyanate-containing prepolymer reacts rapidly with the sand-fixing agent components such as sodium silicate and polyacrylamide to form a robust gel structure. Sodium silicate rapidly solidifies under the action of the potassium aluminum sulfate accelerator, and polyacrylamide strengthens the gel network structure, effectively resisting groundwater erosion, preventing the grout from being diluted and washed away, ensuring rapid and effective consolidation of sand in a high-permeability environment, improving sand stability, reducing the risk of water and sand inrush, and ensuring construction safety. When the groundwater level is less than or equal to 3m from the ground surface and the groundwater permeability coefficient is less than 1.5×10⁻⁶, the sand-fixing agent is suitable for applications where... -3 At a flow rate of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-stabilizing agent is 1.5~1.8:1. The sand-stabilizing agent comprises 42~45% water (solvent by mass), 34~36% potassium silicate (modulus 2.6~2.8), 8~10% dibutyl phthalate (plasticizer), 10~12% ethanol (diluent), 2~4% triethanolamine (accelerator), and 0.1~0.4% polyether-modified polysiloxane (defoamer). Under the action of the plasticizer dibutyl phthalate and the diluent ethanol, the potassium silicate enhances the flexibility and fluidity of the sand-stabilizing agent, allowing it to diffuse better into the pores of low-permeability sand. The accelerator triethanolamine accelerates the reaction process, enabling the sand-stabilizing agent to fully react with the isocyanate-containing prepolymer, forming a stable solidified body, effectively reinforcing the sand, improving its bearing capacity, and meeting the grouting reinforcement requirements in low-permeability environments. When the groundwater level is greater than 3m below the ground surface and the groundwater permeability coefficient is greater than or equal to 1.5×10⁻⁶, the sand-stabilizing agent is suitable for applications where the groundwater level is greater than 3m below the ground surface and the groundwater permeability coefficient is greater than or equal to 1.5×10⁻⁶. -3 At a flow rate of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-stabilizing agent is 1.1~1.3:1. The sand-stabilizing agent comprises 48~50% water (solvent), 36~38% aluminum ferrosilicon, 3~6% dibutyltin dibutylsilicate (catalyst), 3~5% metakaolin (reinforcing agent), and 0.3~0.8% sodium hexametaphosphate (dispersant). Under the action of the dibutyltin dibutylsilicate catalyst, the aluminum ferrosilicon reacts with the isocyanate-containing prepolymer to generate a high-strength solidified material. Metakaolin enhances structural stability, and sodium hexametaphosphate ensures uniform dispersion of all components, enabling the slurry to effectively fill the pores of the sand even in a high-permeability environment, enhancing the sand strength and ensuring the reinforcement effect. When the groundwater level is greater than 3m below the ground surface and the groundwater permeability coefficient is less than 1.5×10⁻⁶, the sand-stabilizing agent is suitable for applications where the groundwater level is greater than 3m below the ground surface and the groundwater permeability coefficient is less than 1.5×10⁻⁶. -3At a flow rate of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 1:1. The sand-fixing agent comprises 42-45% solvent by mass, 45-48% of a compound of metakaolin and silicate cement, 6-8% quartz sand, 0.5-1% nano-silica, and 0.6-1% tartaric acid as a retarder. In the compound of metakaolin and silicate cement, the mass ratio of metakaolin to silicate cement is 4:5, and the particle size of the quartz sand is 0.1-0.3 mm. Under the synergistic effect of quartz sand and nano-silica, the metakaolin and silicate cement compound forms a high-strength and high-stability solidified body. The tartaric acid retarder ensures that the grout has sufficient workable time. In a low-permeability and low-water-level environment, it effectively reinforces the sand and improves the overall performance of the sand, providing a stable foundation for subway tunnel construction.

[0014] Preferably, when the unfavorable geological section in step S3 is clay: If the groundwater level is less than or equal to 3 meters from the ground surface, and the groundwater permeability coefficient is greater than or equal to 1.5 × 10⁻⁶... -3 cm / s, using E-44 type epoxy resin and ethylenediamine curing agent, with a mass ratio of 8:1; If the groundwater level is 3m or less below the ground surface and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, using E-51 type epoxy resin and diethylenetriamine curing agent, with a mass ratio of 10:1.2; If the groundwater level is more than 3 meters below the ground surface and the groundwater permeability coefficient is greater than or equal to 1.5 × 10⁻⁶, then... -3 cm / s, using E-44 type epoxy resin and m-phenylenediamine curing agent, with a mass ratio of 9:1; If the groundwater level is greater than 3m below the ground surface and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, using E-51 type epoxy resin and polyamide curing agent in a mass ratio of 12:1.

[0015] In the above technical solution, the groundwater level is less than or equal to 3m from the ground surface, and the groundwater permeability coefficient is greater than or equal to 1.5×10⁻⁶. -3 At a groundwater level of cm / s, considering the high groundwater level and high groundwater permeability coefficient leading to dilution and loss of the epoxy resin grout, it is necessary to accelerate the curing speed and enhance the consolidation effect. Therefore, E-44 type epoxy resin and ethylenediamine curing agent are selected. The relatively high proportion of curing agent can promote rapid cross-linking and curing of the epoxy resin, reducing the adverse effects of groundwater on the grout. The mixed grout should be used as soon as possible to prevent premature curing. When the groundwater level is less than or equal to 3m from the ground surface and the groundwater permeability coefficient is less than 1.5×10⁻⁶, [further action is needed]. -3At a flow rate of cm / s, the scouring effect of groundwater on the grouting fluid is relatively weak. However, the clay has small pores, requiring better fluidity to ensure grout diffusion. Therefore, E-51 epoxy resin and diethylenetriamine curing agent are selected. The relatively appropriate ratio of diethylenetriamine curing agent ensures curing effect while reducing the viscosity of the grouting fluid to a certain extent, thus improving fluidity. When the groundwater level is greater than 3m below the ground surface and the groundwater permeability coefficient is greater than or equal to 1.5×10⁻⁶, the grouting fluid is further improved. -3 At a groundwater permeability of cm / s, the dilution effect of groundwater is relatively small due to the low groundwater level. However, the high groundwater permeability coefficient still requires ensuring the curing speed and strength. Therefore, E-44 type epoxy resin and m-phenylenediamine curing agent are used. The m-phenylenediamine curing agent enables the epoxy resin to form a high-strength aggregate, which is suitable for environments with high groundwater permeability. When the groundwater level is greater than 3m below the ground surface and the groundwater permeability coefficient is less than 1.5 × 10⁻⁶ cm / s, the curing speed and strength are still required. -3 At a speed of cm / s, the impact of groundwater is relatively small. The focus is on ensuring the reinforcement effect and durability of the clay. Therefore, E-51 type epoxy resin and polyamide curing agent are selected. The polyamide curing agent can give the epoxy resin good flexibility and adhesion, and is compatible with the characteristics of the clay.

[0016] In the above technical solution, taking E-44 epoxy resin and ethylenediamine curing agent as an example, the preparation method is as follows: First, pour the calculated amount of E-44 epoxy resin into a mixing container and stir at a speed of 150~200 r / min to ensure the epoxy resin is in a uniform flow state. Next, slowly add the ethylenediamine curing agent while continuously stirring to ensure uniform dispersion of the curing agent. The addition time should be controlled within 3~5 minutes. After the addition is complete, continue stirring for 10-15 minutes to ensure thorough mixing and form a uniform and stable grouting solution. The mixed grouting solution should be used as soon as possible, preferably within 1.5 hours, to prevent premature curing.

[0017] Preferably, the unfavorable geological section in step S3 is rock: If the groundwater level is less than or equal to 3 meters from the ground surface, and the groundwater permeability coefficient is greater than or equal to 1.5 × 10⁻⁶... -3 cm / s, using 42.5 grade silicate cement and water glass with a modulus of 2.8~3.0, with a volume ratio of 1:0.8; If the groundwater level is 3m or less below the ground surface and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, using 32.5 grade silicate cement and water glass with a modulus of 2.4~2.6, with a volume ratio of 1:0.6; If the groundwater level is more than 3 meters below the ground surface and the groundwater permeability coefficient is greater than or equal to 1.5 × 10⁻⁶, then... -3 cm / s, using 42.5 grade silicate cement and water glass with a modulus of 2.6~2.8, with a volume ratio of 1:0.7; If the groundwater level is greater than 3m below the ground surface and the groundwater permeability coefficient is less than 1.5×10 -3 For the flow rate of cm / s, 32.5 grade silicate cement and water glass with a modulus of 2.2~2.4 are selected, with a volume ratio of 1:0.5.

[0018] In the above technical solution, the groundwater level is less than or equal to 3m from the ground surface, and the groundwater permeability coefficient is greater than or equal to 1.5×10⁻⁶. -3 At a groundwater flow rate of cm / s, under conditions of high groundwater level and high groundwater permeability, cement grout is easily diluted and washed away by groundwater, leading to reduced strength of the cementitious mass and poor grouting effect. To address this, it is necessary to increase the amount of water glass to accelerate the cement setting speed and enhance its erosion resistance. Therefore, 42.5 grade silicate cement and water glass with a modulus of 2.8~3.0 are selected. A higher proportion of water glass can promote rapid hardening of the cement, forming a solidified body with a certain strength in a short time, effectively resisting the erosion effect of groundwater. When the groundwater level is less than or equal to 3m below the ground surface and the groundwater permeability coefficient is less than 1.5×10⁻⁶, the grouting effect is improved. -3 At a flow rate of cm / s, the scouring effect of groundwater on the grouting fluid is relatively weak, but the rock fissures may be quite small. Therefore, the grouting fluid needs to have good fluidity and injectability. Thus, 32.5 grade silicate cement and water glass with a modulus of 2.4~2.6 are selected. A suitable proportion of water glass ensures that the cement grout has sufficient time to diffuse in the rock fissures and also provides a certain degree of strength gain later on. When the groundwater level is greater than 3m below the surface and the groundwater permeability coefficient is greater than or equal to 1.5×10⁻⁶, the grouting fluid is suitable for applications where the groundwater level is greater than 3m below the surface and the groundwater permeability coefficient is greater than or equal to 1.5×10⁻⁶. -3 At a permeability of cm / s, the lower groundwater level reduces the dilution effect of groundwater on the grout. However, the high permeability coefficient still requires the grout to solidify rapidly to fill rock fissures. Therefore, 42.5 grade silicate cement and water glass with a modulus of 2.6~2.8 are selected. The volume ratio of the two ensures that the cement grout has a certain diffusion capacity while utilizing water glass to accelerate the solidification speed, adapting to the high permeability environment. When the groundwater level is greater than 3m below the ground surface and the groundwater permeability coefficient is less than 1.5×10⁻⁶, the grout's performance is further improved. -3 When the groundwater flow rate is low, the focus is on ensuring the long-term strength and stability of the reinforced rock. Therefore, 32.5 grade silicate cement and water glass with a modulus of 2.2 to 2.4 are selected. The lower proportion of water glass can fully hydrate the cement and form a stone body with high strength and good durability.

[0019] In the above technical solution, taking 42.5 grade silicate cement and water glass with a modulus of 2.8~3.0 as an example, the preparation method is as follows: Accurately measure the cement and water glass according to the design ratio. Slowly pour the cement into the mixing bucket, add an appropriate amount of water, and stir at a speed of 200~250 r / min for 3~5 minutes to fully disperse the cement and form a uniform cement slurry. Then, while continuing to stir, slowly add the water glass, controlling the addition time to 2~3 minutes, to ensure that the water glass is evenly mixed into the cement slurry. After the addition is completed, continue stirring for 5~8 minutes to allow the cement and water glass to fully react and mix. The mixed slurry should be used as soon as possible, preferably within 30~40 minutes to complete the grouting operation, to avoid premature solidification of the slurry affecting the grouting effect.

[0020] Preferably, in step S2, the distribution of grouting holes is designed according to the characteristics of the soil and rock, specifically as follows: If the unfavorable geological section is sandy soil, the grouting holes are arranged in a rectangular shape, with a spacing of 1.5~2.0m between the grouting holes; If the adverse geological section is clay, the grouting holes are arranged in a ring, and multiple layers of ring grouting holes are set around the perimeter of the subway tunnel. The spacing between the inner two layers of grouting holes is 0.8~1.0m, and the spacing between the outer layers of grouting holes is 1.2~1.5m. If the unfavorable geological section is rock, the grouting holes are arranged in a quincunx pattern with a spacing of 1.0 to 3.0 m. For rocks with well-developed fissures, the spacing is 1.0 to 2.0 m, and for relatively intact blocky rocks, the spacing is 2.0 to 3.0 m.

[0021] In the above technical solution, if the unfavorable geological section is sandy soil, the grouting holes are arranged in a rectangular pattern with a spacing of 1.5~2.0m. This fully utilizes the good diffusion properties of the grout in the sandy soil to achieve uniform reinforcement and ensure that the sandy soil in the entire area is effectively treated. If the unfavorable geological section is clay, the grouting holes are arranged in a ring, with multiple layers of ring-shaped grouting holes around the perimeter of the subway tunnel. The spacing between the inner two layers of grouting holes is 0.8~1.0m, and the spacing between the outer layers is 1.2~1.5m. The ring arrangement can form a continuous reinforcement ring around the tunnel, effectively constraining the deformation of the soft clay and improving its bearing capacity. If the adverse geological section is rock, the grouting holes are arranged in a quincunx pattern with a spacing of 1.0 to 3.0 meters. For rocks with well-developed fissures, the spacing is 1.0 to 2.0 meters, and for relatively intact blocky rocks, the spacing is 2.0 to 3.0 meters. The quincunx arrangement allows the grout to cross-penetrate in different directions, filling fissures in different directions, improving the overall strength and impermeability of the rock, and enhancing the reinforcement effect.

[0022] Preferably, in step S2, the grouting hole depth is designed based on the depth of the adverse geological section and the tunnel burial depth, specifically as follows: If the depth of the unfavorable geological section is less than 1 / 3 of the tunnel burial depth, the grouting hole depth is designed to penetrate the unfavorable geological section and enter the lower stable stratum by 0.5~1.0m; If the depth of the unfavorable geological section is greater than or equal to 1 / 3 of the tunnel depth but less than 2 / 3 of the tunnel depth, the grouting hole depth is designed to penetrate the unfavorable geological section and enter the lower stable stratum by 1.1~1.5m; If the depth of the unfavorable geological section is greater than or equal to 2 / 3 of the tunnel burial depth, the grouting hole depth is designed to penetrate the unfavorable geological section and enter the lower stable stratum by 1.6~2.0m.

[0023] In the above technical solutions, when the depth of the adverse geological section is less than 1 / 3 of the tunnel burial depth, if the adverse geological section is sandy soil, the grouting hole depth needs to penetrate the adverse geological section and enter the lower stable stratum by 0.5~1.0m to ensure thorough reinforcement of the sandy adverse geological section and prevent instability of the surrounding soil due to the characteristics of sandy soil. If the adverse geological section is clay, it also needs to penetrate the adverse geological section and enter the stable stratum by 0.5~1.0m. Due to the characteristics of clay, penetration reinforcement can effectively control its deformation, form a continuous reinforcement area, constrain clay deformation, and improve bearing capacity. If the adverse geological section is rock, the grouting hole depth should penetrate the adverse geological section and enter the stable rock by 0.5~1.0m. However, for special geological conditions, such as fractured rock, the influence range of the fractures also needs to be considered. In actual operation, the depth should be appropriately increased to ensure that the grout can fully fill the fractures. For blocky rock, the grouting hole depth should ensure effective anchoring and reinforcement, and the depth into the stable rock can also be appropriately increased.

[0024] In the above technical solutions, when the depth of the adverse geological section is greater than or equal to 1 / 3 but less than 2 / 3 of the tunnel depth, if the adverse geological section is sandy soil, the grouting hole depth should penetrate the adverse geological section and enter the lower stable stratum 1.0~1.5m to enhance the reinforcement effect of the sandy soil and prevent tunnel safety from being affected by sand seepage. If the adverse geological section is clay, the grouting hole depth should generally penetrate the adverse geological section and enter the lower stable stratum 1.0~1.5m to ensure effective reinforcement of the clay and control its impact on the tunnel. However, for particularly soft clay, the depth needs to be adjusted appropriately according to the compressibility and deformation of the clay. If the adverse geological section is rock, the grouting hole depth should generally penetrate the adverse geological section and enter the lower stable stratum 1.0~1.5m. However, for special geological conditions, such as fractured rock, the extension of the fractures and the reinforcement range should be further considered, and the depth should be reasonably increased.

[0025] In the above technical solutions, when the depth of the adverse geological section is greater than or equal to 2 / 3 of the tunnel burial depth, if the adverse geological section is sandy soil, the grouting hole depth should penetrate the adverse geological section and enter the lower stable stratum 1.5~2.0m to fully reinforce the sandy soil and reduce its adverse effects on the tunnel. If the adverse geological section is clay, the grouting hole depth should penetrate the adverse geological section and enter the lower stable stratum 1.5~2.0m. However, for particularly soft clay, the long-term stability of the clay and its impact on the tunnel structure need to be considered, and the depth should be adjusted appropriately. If the adverse geological section is rock, the grouting hole depth generally penetrates the adverse geological section and enters the lower stable stratum 1.5~2.0m. However, for special geological conditions, such as fractured rock, the integrity of the rock and the distribution of fractures need to be further considered, and the depth should be adjusted appropriately.

[0026] Preferably, when performing grouting reinforcement in step S4, the grouting volume per hole is as follows: When the adverse geological section is sandy soil or rock, the grouting material volume per hole is Q1=πnHR 2 (1+a)b; When the adverse geological section is clay, the single-hole grouting volume Q2=kcSH / (1+d); Where R is the grout diffusion radius, m, and is taken as 1 / 2 of the grouting hole spacing; H is the grouting hole depth, in meters; n represents the porosity of the soil and rock mass, expressed as % for sandy soil (25-40%) and rock (3-15%). 'a' is the slurry loss coefficient, which is taken as 0.2~0.5; b is the filling density correction factor, 1.2~1.5 for sand and 1.0~1.3 for rock; S represents the area affected by grouting in a single hole, in meters. 2 Take the product of the distances between adjacent grouting holes; c is the natural bulk density of clay, in kN / m³ 3 Take 16~20; k is the grout replacement rate, which is taken as 0.15~0.25; d is the clay compression coefficient, which is taken as 0.1~0.3.

[0027] In the above technical solution, the grouting volume calculation is linked with geotechnical physical parameters (porosity, unit weight), engineering parameters (grouting hole depth, spacing) and process characteristics (loss, replacement rate) to achieve precise quantitative control of the grouting volume.

[0028] Preferably, during grouting reinforcement in step S4, the grouting pressure and grouting speed are set according to the characteristics of the soil and rock in the adverse geological section: If the unfavorable geological section is sandy soil, the grouting pressure is 0.3~0.6MPa and the grouting speed is 25~40L / min; If the unfavorable geological section is clay, segmented grouting shall be adopted. The grouting pressure of the first segment shall be 0.4~0.8MPa and the grouting speed shall be 15~25L / min. The grouting pressure of each subsequent segment shall increase by 0.1~0.2MPa and the grouting speed shall decrease by 5~8L / min. If the unfavorable geological section is rock, for rock with developed fissures, the grouting pressure is 1.2~2.5MPa and the grouting rate is 8~15L / min. For relatively intact blocky rock, the grouting pressure is 0.8~1.5MPa and the grouting rate is 5~10L / min.

[0029] Preferably, the grouting effect should be tested after grouting is completed in step S4. If the radar velocity of the grouting area increases by less than 15% or if there are areas of continuous abnormal reflection, it is determined to be an area that does not meet the standards and additional grouting is required. Unconfined compressive strength was tested by core drilling. If the unfavorable geological section was sandy soil, the unconfined compressive strength was greater than 1.2 MPa; if the unfavorable geological section was clay, the confined compressive strength was greater than 0.8 MPa; and if the unfavorable geological section was rock, the unconfined compressive strength was greater than 3.5 MPa. The groundwater permeability coefficient was measured, and after reinforcement, the groundwater permeability coefficient decreased by at least two orders of magnitude compared to the original groundwater permeability coefficient.

[0030] Preferably, when the adverse geological section is sandy soil, if it is a flowing sand layer, freezing pipes are installed along the axis of the subway tunnel to maintain the freezing temperature at -25~-30℃ until the strength of the grout reaches 70~75% of the preset value; When the unfavorable geological section is clay, if it is expansive clay, then when grouting in step S4, layered grouting shall be adopted, with each layer not exceeding 0.5m in thickness and the interval between layers being greater than 4h. When the unfavorable geological section is a fault fracture zone, a quick-setting liquid is injected to form a water-stopping curtain before grouting in step S4. The quick-setting liquid includes sulfoaluminate cement, nano-silica and calcium chloride in a mass ratio of 10:1:0.5.

[0031] In the above technical solution, the present invention further proposes an innovative solution for grouting reinforcement under extreme geological conditions, forming a complete risk response system.

[0032] Preferably, when the adverse geological section is sandy soil, if it is a flowing sand layer, the total grouting volume is... ; When the unfavorable geological section is clay, and if it is expansive clay, the grouting volume for each layer should be determined when using layered grouting. ; Where N is the number of frozen tubes; D i Where is the diameter of the freezing pipe, in meters (m); T represents the freeze time, in days; L i The length of the frozen section is in meters (m). ρ i The porosity reduction coefficient after the sand layer freezes is taken as 0.6~0.8; h is the layer thickness, in meters, ranging from 0.3 to 0.5 meters. P max P min This is the grouting pressure limit value for this layer, in MPa; v represents the average grouting speed, in L / min; K1 and K2 are the groundwater permeability coefficients before and after grouting, in cm / s.

[0033] In the above technical solution, the present invention further introduces a dynamic correction mechanism for special working conditions. First, the formula for flowing sand layer couples the parameters of the freezing pipe with the time variable to reflect the influence of phase change on the grouting volume. Second, the formula for expansive clay reflects the nonlinear relationship between grouting efficiency and the degree of formation improvement through the logarithmic relationship of groundwater permeability coefficient, so that the grouting volume can meet the reinforcement requirements while avoiding resource waste, forming a complete quantitative control system.

[0034] The present invention has at least the following beneficial effects: Firstly, the ground grouting reinforcement method for unfavorable geological sections in subway tunnels provided by this invention, through investigation of soil and rock characteristics, groundwater level, groundwater permeability coefficient and depth of unfavorable geological sections, accurately designs grouting schemes for different soil and rock characteristics, effectively improving the pertinence and scientific nature of grouting reinforcement, realizing the relative standardization of ground grouting reinforcement for unfavorable geological sections in subway tunnels, and comprehensively improving the treatment effect of unfavorable geological sections. Secondly, in sandy soil sections with poor geological conditions, this invention precisely designs the ratio of isocyanate-containing prepolymer to sand-fixing agent and the composition of sand-fixing agent based on groundwater level and groundwater permeability coefficient. This allows the grouting liquid to quickly and effectively solidify sand under different hydrological conditions, enhance sand stability, improve resistance to sand flow, significantly reduce the risk of water and sand inrush, and ensure construction safety. Thirdly, the present invention also rationally designs the distribution of grouting holes according to different soil and rock characteristics, with rectangular arrangement for sand, ring arrangement for clay and plum blossom arrangement for rock, to ensure uniform diffusion of grouting liquid, fully fill the voids and cracks in soil and rock, improve the uniformity and integrity of reinforcement, and enhance the overall bearing capacity of poor geological sections. Fourth, this invention establishes the relationship between the depth of the poor geological section and the tunnel burial depth, precisely designs the grouting hole depth, and ensures that the grouting depth can effectively cover the poor geological section and penetrate into the stable strata, forming a solid reinforcement foundation, providing reliable support for the tunnel, and enhancing the stability of the tunnel structure. Fifth, based on the type of rock and soil, the present invention adopts a reasonable single-hole grouting volume calculation formula to accurately control the grouting volume, which ensures that the rock and soil are fully filled and reinforced, avoids grout waste, and effectively controls the project cost while improving the reinforcement effect. Sixth, this invention scientifically sets the grouting pressure and grouting speed according to the characteristics of the soil and rock in the adverse geological section, so as to ensure that the grout can spread smoothly in different soil and rock and guarantee the reinforcement quality. Among them, the segmented grouting of clay can adapt to the characteristics of clay, improve the reinforcement effect, and ensure the efficiency and safety of grouting construction. Seventh, this invention employs multiple detection methods, such as ground-penetrating radar scanning, core drilling to test unconfined compressive strength, and groundwater permeability coefficient measurement, to comprehensively and accurately evaluate the grouting effect. Grouting is promptly added to areas that do not meet the standards to ensure that the reinforced sections with poor geological conditions meet the engineering requirements and to guarantee the long-term safe and stable operation of the tunnel. Eighth, this invention further addresses special adverse geological conditions, such as the use of freezing pipes to assist in the treatment of mobile sand layers, layered grouting of expansive clay, and the injection of quick-setting liquid into fault fracture zones to form a water-stopping curtain, effectively solving special geological problems and further improving the adaptability and effectiveness of this method under complex geological conditions. Ninth, this invention provides scientific formulas for calculating the total grouting volume and the layered grouting volume for flowing sand layers and expansive clay layers, respectively, to accurately guide grouting construction, ensure that the grouting volume meets the engineering requirements, and improve the accuracy and reliability of grouting reinforcement under special geological conditions.

[0035] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the ground grouting reinforcement method described in this invention. Detailed Implementation

[0037] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can implement it based on the description.

[0038] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0039] This invention provides a method for ground grouting reinforcement of unfavorable geological sections in subway tunnels, the specific process of which is as follows: Figure 1 As shown, the following are several specific embodiments of the present invention.

[0040] Example 1 (Sandy Soil with Unfavorable Geological Conditions) The subway tunnel passes through a section of sandy soil with poor geological conditions. The groundwater level is 2.5m below the surface, and the groundwater permeability coefficient is 2.0×10⁻⁶. -3 cm / s. Through geological drilling, geophysical exploration and other exploration methods, the characteristics of the soil and rock in this area were determined to be a poor geological section of sandy soil, specifically medium and coarse sand with a porosity of 30%. The depth of the poor geological section is 8m, and the tunnel burial depth is 25m.

[0041] Based on the characteristics of the soil and rock, a rectangular arrangement of grouting holes is adopted, with a hole spacing of 1.8m. According to the depth of the adverse geological section and the tunnel burial depth, the grouting hole depth is designed to penetrate the adverse geological section and enter the lower stable stratum by 1.2m, that is, the grouting hole depth is 9.2m.

[0042] Because the groundwater level and permeability coefficient of the unfavorable geological section of the subway tunnel meet the conditions of high water level and high permeability, the grouting fluid includes a prepolymer containing isocyanate groups and a sand-fixing agent, wherein the mass ratio of the prepolymer containing isocyanate groups to the sand-fixing agent is determined to be 2.2:1. The sand-fixing agent composition includes 50% water (solvent fraction), 39% sodium silicate (modulus 3.2), 6.9% polyacrylamide (degree of hydrolysis 30%), 4% potassium aluminum sulfate (accelerator), and 0.1% sodium dodecylbenzenesulfonate.

[0043] When performing grouting reinforcement, the amount of grout injected per hole is determined by the formula Q1=πnHR. 2 The calculation is performed using (1+a)b, where R is 0.9m, H is 9.2m, n is 30%, a is 0.3, and b is 1.4. The grouting volume per hole is then calculated. The grouting pressure under no-load conditions is 0.5MPa, and the grouting rate is 30L / min.

[0044] After grouting, ground-penetrating radar was used to scan the grouting area. The radar wave velocity increased by more than 15%, and no areas of continuous reflection anomalies were found. Core sampling of the boreholes tested the unconfined compressive strength, which reached 1.5 MPa, meeting the requirement of greater than 1.2 MPa. Groundwater permeability was measured and decreased by more than two orders of magnitude compared to the original value, indicating good grouting results.

[0045] Example 2 (Clay-prone geological section) The subway tunnel section passes through a clay-rich geological area, with the groundwater level 4 meters below the surface and a groundwater permeability coefficient of 1.0 × 10⁻⁶. -3 cm / s. Investigation determined it to be a section of poor clay geological conditions, specifically soft clay, with a natural bulk density of 18 kN / m³. 3 The compression coefficient is 0.2. Meanwhile, the depth of the unfavorable geological section is 12m, and the tunnel burial depth is 30m.

[0046] Based on the soil and rock characteristics, a ring-shaped arrangement is adopted, with multiple layers of annular grouting holes set around the perimeter of the subway tunnel. The spacing between the inner two layers of grouting holes is 0.9m, and the spacing between the outer layers of grouting holes is 1.3m. According to the depth of the adverse geological section and the tunnel burial depth, the grouting hole depth is designed to penetrate the adverse geological section and enter the lower stable stratum by 1.3m, that is, the grouting hole depth is 13.3m.

[0047] Due to the moderate groundwater level and relatively low groundwater permeability in the unfavorable geological section of the subway tunnel, epoxy resin and curing agent were selected as the grouting fluid. Given the small pores and poor permeability of the soft clay, and the need to enhance the adhesion and curing effect of the grouting fluid to fill the clay pores and inhibit its deformation, E-44 type epoxy resin was selected, with ethylenediamine as the curing agent, and the mass ratio of the two was 8:1.

[0048] When performing grouting reinforcement, the amount of grout for a single hole is calculated using the formula Q2=kcSH / (1+d), where S is the product of the distances between adjacent grouting holes, k is taken as 0.2, c is 18kN / m³, and d is 0.2. Segmented grouting is adopted, with the initial grouting pressure at 0.6MPa and the grouting rate at 20L / min. For each subsequent segment, the grouting pressure increases by 0.15MPa, and the grouting rate decreases by 6L / min.

[0049] Ground-penetrating radar scans showed no abnormalities, and core drilling tests revealed an unconfined compressive strength of 1.0 MPa, which is greater than 0.8 MPa. The groundwater permeability coefficient was significantly reduced, meeting the reinforcement requirements.

[0050] Example 3 (Unfavorable geological conditions) The subway tunnel section encountered a section with poor geological conditions characterized by well-developed fissures in the rock. The groundwater level was 3.5m below the surface, and the groundwater permeability coefficient was 1.8×10⁻⁶. -3 cm / s. The exploration determined that the rock porosity was approximately 8%, the depth of the unfavorable geological section was 10m, and the tunnel burial depth was 28m.

[0051] Based on the characteristics of the soil and rock, a quincunx pattern was adopted, with a hole spacing of 1.5m. The grouting hole depth was designed to penetrate the unfavorable geological section and enter the lower stable stratum by 1.4m, that is, the grouting hole depth is 11.4m.

[0052] Prepare cement and water glass grouting solution.

[0053] The grouting volume per hole is calculated according to formula Q1, the grouting pressure is 1.8MPa, and the grouting speed is 12L / min.

[0054] Ground-penetrating radar showed that the grouting area was uniform, and core drilling tests showed an unconfined compressive strength of 4.0 MPa, which is greater than 3.5 MPa. The groundwater permeability coefficient decreased significantly, achieving the desired reinforcement effect.

[0055] Example 4 (Unfavorable geological conditions) The subway tunnel contains a relatively intact section of blocky rock with poor geological conditions. The groundwater level is 5m below the surface, and the groundwater permeability coefficient is 0.8×10⁻⁶. -3 cm / s. The survey determined that the rock porosity was 5%, the depth of the unfavorable geological section was 9m, and the tunnel depth was 26m.

[0056] Based on the characteristics of the soil and rock, the grouting holes are arranged in a quincunx pattern with a spacing of 2.5m. The grouting hole depth is designed to penetrate the unfavorable geological section and enter the lower stable stratum by 1.5m, that is, the grouting hole depth is 10.5m.

[0057] Prepare cement and water glass grouting solution.

[0058] The grouting volume per hole was calculated, the grouting pressure was 1.2 MPa, and the grouting rate was 8 L / min. All test indicators met the requirements, and the grouting reinforcement effect was good.

[0059] Example 5 (Poor Geological Section with Flowing Sand Layer) The subway tunnel section has a section with poor geological conditions, including a layer of flowing sand. The groundwater level is 2m below the ground surface, and the groundwater permeability coefficient is 3.0×10⁻³cm / s.

[0060] Freezing pipes were installed along the subway tunnel axis to maintain a freezing temperature of -28℃. The total grouting volume was calculated according to formula Q3, and other grouting parameters were set based on the high water level and high permeability conditions of the sandy soil section. The grouting effect was good and met the project requirements.

[0061] Example 6 (Unfavorable geological section with expansive clay) The subway tunnel traverses a section of expansive clay with unfavorable geological conditions. The groundwater level is 3 meters below the surface, and the groundwater permeability coefficient is 1.2 × 10⁻³ cm / s. Layered grouting was employed, with each layer 0.4 meters thick and a 5-hour interval between layers. The grout volume for each layer was calculated using a formula, and other grouting parameters were set based on the clay characteristics. Testing showed a significant reinforcement effect, effectively inhibiting clay expansion.

[0062] Example 7 (Fault Fracture Zone) The subway tunnel section passes through a fault fracture zone with unfavorable geological conditions. The groundwater level is 4.5m below the surface, and the groundwater permeability coefficient is 2.5×10⁻³cm / s. Before grouting, a quick-setting liquid composed of sulfoaluminate cement, nano-silica, and calcium chloride in a mass ratio of 10:1:0.5 was injected to form a water-stop curtain. Subsequent grouting parameters were set according to the development of fractures in the unfavorable rock geological section. Test results show that the grouting reinforcement effect is good and meets the requirements for tunnel construction and operation.

[0063] The number of devices and processing scale described herein are for simplification of the invention. Applications, modifications, and variations of the ground grouting reinforcement method for unfavorable geological sections in subway tunnels according to this invention will be readily apparent to those skilled in the art.

[0064] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and the specific embodiments shown and described herein.

Claims

1. A method for ground grouting reinforcement of unfavorable geological sections in subway tunnels, characterized in that, include: S1. Survey the soil and rock properties, groundwater level H, groundwater permeability coefficient K, and depth of unfavorable geological sections in the subway tunnel section; S2. Design the distribution of grouting holes based on the soil and rock characteristics surveyed in step S1, and design the hole depth based on the depth of the adverse geological section and the tunnel burial depth. S3. Prepare grouting fluid based on the soil and rock properties, groundwater level, and groundwater permeability coefficient measured in step S1. S4. Grouting reinforcement is carried out according to the grouting hole distribution designed in step S2; In step S3, the grouting fluid includes component A and component B: if the adverse geological section is sandy soil, component A and component B are a prepolymer containing isocyanate groups and a sand-fixing agent, respectively; if the adverse geological section is clay, component A and component B are epoxy resin and a curing agent, respectively; if the adverse geological section is rock, component A and component B are cement and water glass, respectively. When the unfavorable geological section in step S3 is sandy soil, the mass ratio of the isocyanate-containing prepolymer to the sand-stabilizing agent and the composition of the sand-stabilizing agent are prepared according to the different groundwater levels H and groundwater permeability coefficient K, as follows: When H≤3m and K≥1.5×10 -3 At a speed of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 2~2.3:1, and the sand-fixing agent comprises 38~40% sodium silicate, 4~8% polyacrylamide, 2~4% potassium aluminum sulfate, and 0.1~1% sodium dodecylbenzenesulfonate by mass fraction. When H≤3m and K<1.5×10 -3 At a speed of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 1.5~1.8:1, and the sand-fixing agent comprises 34~36% potassium silicate, 8~10% dibutyl phthalate, 10~12% ethanol as a diluent, 2~4% triethanolamine, and 0.1~0.4% polyether-modified polysiloxane by mass fraction. When H>3m and K≥1.5×10 -3 At a speed of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 1.1~1.3:1, and the sand-fixing agent comprises 36~38% by mass of aluminum iron silicate, 3~6% by mass of dibutyltin dimethyl silicate, 3~5% by mass of metakaolin, and 0.3~0.8% by mass of sodium hexametaphosphate; When H > 3m and K < 1.5 × 10 -3 At a speed of cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-fixing agent is 1:

1. The sand-fixing agent comprises 45-48% by mass of a compound of metakaolin and silicate cement, 6-8% by mass of quartz sand, 0.5-1% by mass of nano-silica, and 0.6-1% by mass of tartaric acid. In the compound of metakaolin and silicate cement, the mass ratio of metakaolin to silicate cement is 4:5, and the particle size of the quartz sand is 0.1-0.3 mm.

2. The ground grouting reinforcement method for unfavorable geological sections in subway tunnels as described in claim 1, characterized in that, In step S2, the distribution of grouting holes is designed according to the following rules based on the soil and rock characteristics: If the unfavorable geological section is sandy soil, the grouting holes are arranged in a rectangular shape, with a spacing of 1.5~2.0m between the grouting holes; If the adverse geological section is clay, the grouting holes are arranged in a ring, and multiple layers of ring grouting holes are set around the perimeter of the subway tunnel. The spacing between the inner two layers of grouting holes is 0.8~1.0m, and the spacing between the outer layers of grouting holes is 1.2~1.5m. If the unfavorable geological section is rock, the grouting holes are arranged in a quincunx pattern. For rocks with developed fissures, the spacing between grouting holes is 1.0~2.0m, and for relatively intact blocky rocks, the spacing between grouting holes is 2.0~3.0m.

3. The ground grouting reinforcement method for unfavorable geological sections in subway tunnels as described in claim 2, characterized in that, In step S2, the grouting hole depth is designed based on the depth of the adverse geological section and the tunnel burial depth, specifically as follows: If the depth of the unfavorable geological section is less than 1 / 3 of the tunnel burial depth, the grouting hole depth is designed to penetrate the unfavorable geological section and enter the lower stable stratum by 0.5~1.0m; If the depth of the unfavorable geological section is greater than or equal to 1 / 3 of the tunnel depth but less than 2 / 3 of the tunnel depth, the grouting hole depth is designed to penetrate the unfavorable geological section and enter the lower stable stratum by 1.1~1.5m; If the depth of the unfavorable geological section is greater than or equal to 2 / 3 of the tunnel burial depth, the grouting hole depth is designed to penetrate the unfavorable geological section and enter the lower stable stratum by 1.6~2.0m.

4. The ground grouting reinforcement method for unfavorable geological sections in subway tunnels as described in claim 3, characterized in that, When performing grouting reinforcement in step S4, the grouting volume per hole is as follows: When the adverse geological section is sandy soil or rock, the grouting material volume per hole is Q1=πnHR 2 (1+a)b; When the adverse geological section is clay, the single-hole grouting volume Q2=kcSH / (1+d); Where R is the grout diffusion radius, m, and is taken as 1 / 2 of the grouting hole spacing; H is the grouting hole depth, in meters; n represents the porosity of the soil and rock mass, expressed as % for sandy soil (25-40%) and rock (3-15%). 'a' is the slurry loss coefficient, which is taken as 0.2~0.5; b is the filling density correction factor, 1.2~1.5 for sand and 1.0~1.3 for rock; S represents the area affected by grouting in a single hole, in meters. 2 Take the product of the distances between adjacent grouting holes; c is the natural bulk density of clay, in kN / m³ 3 Take 16~20; k is the grout replacement rate, which is taken as 0.15~0.25; d is the clay compression coefficient, which is taken as 0.1~0.

3.

5. The ground grouting reinforcement method for unfavorable geological sections in subway tunnels as described in claim 1, characterized in that, When performing grouting reinforcement in step S4, the grouting pressure and grouting speed are set according to the characteristics of the soil and rock in the adverse geological section: If the unfavorable geological section is sandy soil, the grouting pressure is 0.3~0.6MPa and the grouting speed is 25~40L / min; If the unfavorable geological section is clay, segmented grouting shall be adopted. The grouting pressure of the first segment shall be 0.4~0.8MPa and the grouting speed shall be 15~25L / min. The grouting pressure of each subsequent segment shall increase by 0.1~0.2MPa and the grouting speed shall decrease by 5~8L / min. If the unfavorable geological section is rock, for rock with developed fissures, the grouting pressure is 1.2~2.5MPa and the grouting rate is 8~15L / min. For relatively intact blocky rock, the grouting pressure is 0.8~1.5MPa and the grouting rate is 5~10L / min.

6. The ground grouting reinforcement method for unfavorable geological sections in subway tunnels as described in claim 1 or 5, characterized in that, After grouting is completed in step S4, the grouting effect needs to be tested. If the radar velocity of the grouting area increases by less than 15% or if there are areas of continuous abnormal reflection, it is determined to be an area that does not meet the standards and additional grouting is required. Unconfined compressive strength was tested by core drilling. If the unfavorable geological section was sandy soil, the unconfined compressive strength was greater than 1.2 MPa; if the unfavorable geological section was clay, the confined compressive strength was greater than 0.8 MPa; and if the unfavorable geological section was rock, the unconfined compressive strength was greater than 3.5 MPa. The groundwater permeability coefficient was measured, and after reinforcement, the groundwater permeability coefficient decreased by at least two orders of magnitude compared to the original groundwater permeability coefficient.

7. The ground grouting reinforcement method for unfavorable geological sections in subway tunnels as described in claim 1, characterized in that: When the adverse geological section is sandy soil, if it is a flowing sand layer, freezing pipes are installed along the axis of the subway tunnel to maintain the freezing temperature at -25~-30℃ until the strength of the grout reaches 70~75% of the preset value; When the unfavorable geological section is clay, if it is expansive clay, then when grouting in step S4, layered grouting shall be adopted, with each layer not exceeding 0.5m in thickness and the interval between layers being greater than 4h. When the unfavorable geological section is a fault fracture zone, a quick-setting liquid is injected to form a water-stopping curtain before grouting in step S4. The quick-setting liquid includes sulfoaluminate cement, nano-silica and calcium chloride in a mass ratio of 10:1:0.

5.

8. The ground grouting reinforcement method for unfavorable geological sections in subway tunnels as described in claim 7, characterized in that: When the unfavorable geological section is sandy soil, if it is a flowing sand layer, the total grouting volume Q3 = ; When the adverse geological section is clay, if it is expansive clay, and layered grouting is used, the grouting volume for each layer is Q4 = 0.5h. ; Where N is the number of frozen tubes; D i Where is the diameter of the freezing pipe, in meters (m); T represents the freeze time, in days; L i The length of the frozen section is in meters (m). ρ i The porosity reduction coefficient after the sand layer freezes is taken as 0.6~0.8; h is the layer thickness, in meters, ranging from 0.3 to 0.5 meters. P max P min This is the grouting pressure limit value for this layer, in MPa; v represents the average grouting speed, in L / min; K1 and K2 are the groundwater permeability coefficients before and after grouting, in cm / s.

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