Ground grouting reinforcement method for unfavorable geological section of subway tunnel section

Abstract

The invention discloses a ground grouting reinforcement method for an unfavorable geological section of a subway tunnel section. By comprehensively investigating rock and soil characteristics, underground water level, underground water permeability coefficient and unfavorable geological section depth, grouting hole distribution and hole depth are designed according to different geological conditions, and grouting liquid containing specific proportion components is prepared for sandy soil, clay and rock. And according to the rock-soil type, the single-hole grouting amount, the grouting pressure and the grouting speed are reasonably set, the effect is evaluated through multiple detection means such as geological radar scanning, and grouting is supplemented for the substandard area. For special unfavorable geology, such as a flowing sand layer, expansive clay, a fault fracture zone and the like, corresponding auxiliary measures and grouting modes are adopted. According to the method, the pertinence, scientificity and adaptability of grouting reinforcement are effectively improved, the safety and long-term stable operation of tunnel construction are guaranteed, the engineering cost is reduced, and the reinforcement accuracy and reliability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel grouting, and more particularly to a method for reinforcing a ground grouting section of a subway tunnel with poor geological conditions. Background Art

[0002] With the rapid development of urban rail transit, the scale of subway tunnel construction continues to expand. During tunnel construction, crossing various types of unfavorable geological sections is an unavoidable problem, which brings many severe challenges to the project.

[0003] Sandy soil, a common type of unfavorable geological condition, exhibits low inter-particle cohesion, large pores, and good connectivity. Especially under conditions of high groundwater levels and high permeability coefficients, sandy soil is prone to sand flow, leading to water and sand gushing during tunnel excavation, seriously endangering construction safety and potentially even causing major accidents such as ground collapse. Currently, due to the lack of standardized grouting fluids, the preparation of grouting fluids for sandy soils relies heavily on the subjective experience of engineers. This makes it difficult to precisely control the composition and properties of the grout based on sandy soil characteristics, groundwater levels, and permeability coefficients under complex hydrogeological conditions. Under these conditions, the grout is easily diluted and washed away by rapidly flowing groundwater, making it impossible to form a stable and effective reinforcement zone within the sandy soil layer. The reinforcement effect falls far short of expectations, significantly increasing project risks.

[0004] Due to its fine particles and low porosity, clay undergoes significant volume changes with changes in water content. Expansive clay, in particular, swells when exposed to water and contracts when dehydrated. This property exerts significant pressure on tunnel linings, leading to cracking and deformation, seriously impacting the tunnel's normal operation and structural safety. Traditional clay reinforcement methods, such as simple cement grouting, lack standardized grouting fluids and are unable to fully adapt to clay's complex physical properties and factors such as groundwater levels. Consequently, they struggle to effectively control clay expansion and contraction, and even after reinforcement, the reinforced clay can still cause serious damage to tunnel structures, shortening their service life.

[0005] While rock formations are relatively stable, well-developed fissures in rock can weaken the integrity and strength of the rock mass. During tunnel excavation, collapse and water inrush are common problems. Similarly, due to the lack of standardized grouting fluids, it's impossible to scientifically formulate grout based on rock properties, groundwater levels, and permeability coefficients when faced with complex rock fracture networks. This makes it difficult for the grout to evenly fill the fractures, resulting in insufficient reinforcement in some areas and significantly impacting the stability of the surrounding rock mass around the tunnel. Furthermore, for relatively intact block rock, the lack of standardized grouting fluids makes it difficult to effectively improve its adhesion to the lining, making enhancing overall stability a daunting challenge.

[0006] In addition, poor geological sections are usually accompanied by complex groundwater levels and groundwater permeability conditions. High groundwater levels will increase the degree of soil saturation and reduce soil strength; high permeability coefficients will accelerate the flow of groundwater, further exacerbating the adverse effects of poor geological conditions on tunnel construction and structure. Existing ground grouting reinforcement methods, due to the lack of standardized grouting fluids, have many defects when considering multiple factors such as geotechnical properties, groundwater levels, and permeability coefficients. The inability to comprehensively and efficiently solve the problems caused by poor geological sections not only delays the progress of the project, but also significantly increases the cost of the project and may even pose safety hazards to subsequent operations. Therefore, the development of a method that can fully consider multiple geological factors, accurately design grouting parameters, and effectively improve the grouting reinforcement effect is of vital practical significance for subway tunnel construction. Summary of the Invention

[0007] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0008] Another object of the present invention is to provide a ground grouting reinforcement method for poor geological sections of subway tunnels, which comprehensively considers multiple factors and has good grouting effect. By using geological classification grouting liquid schemes and dynamic adaptation of grouting parameters, the problem of insufficient reinforcement of traditional grouting methods in sand, clay, and rock formations is solved, ensuring tunnel construction and structural safety. In order to achieve these purposes and other advantages according to the present invention, a method for ground grouting reinforcement of a poor geological section of a subway tunnel is provided, comprising: S1. Survey the geotechnical properties, groundwater level H, groundwater permeability coefficient K and depth of the poor geological section of the subway tunnel; S2. Designing the distribution of grouting holes according to the geotechnical characteristics surveyed in step S1, and designing the depth of the grouting holes according to the depth of the unfavorable geological section and the buried depth of the tunnel; S3, preparing grouting fluid according to the rock and soil properties, groundwater level, and groundwater permeability coefficient surveyed in step S1; S4, performing grouting reinforcement according to the grouting hole distribution designed in step S2; Among them, the grouting liquid in step S3 includes component A and component B: if the poor geological section is sand, component A and component B are respectively an isocyanate-containing prepolymer and a sand-fixing agent; if the poor geological section is clay, component A and component B are respectively an epoxy resin and a curing agent; if the poor geological section is rock, component A and component B are respectively cement and water glass.

[0009] Traditional methods rely on empirical grouting to prepare the grout, failing to consider dynamic parameters like groundwater level and permeability, leading to unstable grouting results. This implementation dynamically adapts grouting based on geotechnical characteristics, groundwater level, and groundwater permeability, precisely matching grout properties with hydrogeological conditions and avoiding grout waste or insufficient reinforcement.

[0010] In particular, sand particles are loose and highly permeable, and traditional slurries (such as cement slurry) are easily diluted and washed away by groundwater, failing to form an effective reinforcement body and leading to the risk of water and sand gushing. This embodiment uses a combination of isocyanate-based prepolymers and sand-consolidating agents to allow the slurry to remain stably in the high-permeability sand layer, effectively suppressing sand flow and preventing tunnel collapse. Clay swells when exposed to water and shrinks when dehydrated, and traditional cement grouting cannot suppress its volume changes, leading to cracks in the lining structure. This embodiment uses epoxy resin and curing agent, which form a flexible-rigid composite after curing, reducing deformation of the lining structure and extending the service life of the tunnel. In rocks with developed fissures, traditional slurries are difficult to fill the cracks evenly, and weak areas still exist after reinforcement. This embodiment uses cement and water glass dual-liquid slurry, which has strong permeability and high stone body density, significantly improving the overall stability of the surrounding rock.

[0011] In the above technical solution, the S1 survey phase comprehensively assesses geotechnical properties, groundwater levels, groundwater permeability coefficients, and the depth of unfavorable geological sections, providing a detailed basis for subsequent precise design and significantly enhancing the targeted and scientific nature of the grouting reinforcement solution. In the S2 grouting hole design step, a rational distribution pattern is designed based on geotechnical characteristics, such as rectangular arrangements for sand, circular arrangements for clay, and plum blossom arrangements for rock. This ensures uniform grouting and improves reinforcement uniformity. Hole depth is determined based on the depth of the unfavorable geological section and tunnel burial depth, ensuring that the grouting depth effectively covers the unfavorable geological section and penetrates into stable strata, enhancing tunnel structural stability. In the S3 grouting fluid preparation phase, grouting fluid components are specifically adjusted based on different geological and hydrological conditions. For example, the ratio and composition of isocyanate-containing prepolymers and sand-consolidating agents for sand are adjusted based on the groundwater level and permeability coefficient. For clay and rock, the appropriate ratios of epoxy resin and curing agent, and cement and water glass, are respectively selected to ensure that the grouting fluid's performance is compatible with various geological conditions and enhance the reinforcement effect. Finally, during the S4 grouting reinforcement process, due to the scientific design of each step in the early stage, the grouting can be carried out accurately and efficiently, effectively enhancing the stability of the soil in the poor geological section, reducing the risks of water gushing 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 group-containing prepolymer to the sand-fixing agent and the composition of the sand-fixing agent are prepared as follows according to different conditions of the groundwater level H and the groundwater permeability coefficient K: When H≤3m and K≥1.5×10 -3cm / s, the mass ratio of the isocyanate group-containing prepolymer to the sand-consolidating agent is 2-2.3:1, and the sand-consolidating agent comprises 48-50% by mass of solvent water, 38-40% by mass of sodium silicate having a modulus of 3.0-3.3, 4-8% by mass of polyacrylamide having a degree of hydrolysis of 25-35%, 2-4% by mass of an accelerating setting agent, potassium aluminum sulfate, and 0.1-1% by mass of sodium dodecylbenzene sulfonate; When H≤3m and K<1.5×10 -3 cm / s, the mass ratio of the isocyanate group-containing prepolymer to the sand-consolidating agent is 1.5-1.8:1, and the sand-consolidating agent includes 42-45% by mass of solvent water, 34-36% by mass of potassium silicate with a modulus of 2.6-2.8, 8-10% by mass of dibutyl phthalate as a plasticizer, 10-12% by mass of ethanol as a diluent, 2-4% by mass of triethanol as an accelerator, and 0.1-0.4% by mass of polyether-modified polysiloxane as a defoamer; When H>3m and K≥1.5×10 -3 cm / s, the mass ratio of the isocyanate group-containing prepolymer to the sand-consolidating agent is 1.1-1.3:1, and the sand-consolidating agent comprises 48-50% by mass of solvent water, 36-38% by mass of aluminum ferrosilicate, 3-6% by mass of dibutyltin disilicate as a catalyst, 3-5% by mass of metakaolin as a reinforcing agent, and 0.3-0.8% by mass of sodium hexametaphosphate as a dispersant; When H>3m and K<1.5×10 -3 cm / s, the mass ratio of the isocyanate group-containing prepolymer to the sand-consolidating agent is 1:1, and the sand-consolidating agent includes 42-45% by mass of a solvent, 45-48% by mass of a compound of metakaolin and Portland cement, 6-8% by mass of quartz sand, 0.5-1% by mass of nano-silicon dioxide, and 0.6-1% by mass of a retarder, wherein the mass ratio of metakaolin to Portland cement in the compound of metakaolin and Portland 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-containing prepolymer and sand-fixing agent is precisely controlled according to the different conditions of groundwater level and groundwater permeability coefficient, and the composition of the sand-fixing agent is carefully designed. When the groundwater level is less than or equal to 3m from the ground and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3cm / s, the mass ratio of the isocyanate-containing prepolymer and the sand-fixing agent is 2~2.3:1. The sand-fixing agent includes 48~50% by mass of solvent water, 38~40% of sodium silicate with a modulus of 3.0~3.3, 4~8% of polyacrylamide with a hydrolysis degree of 25~35%, 2~4% of aluminum-based potassium sulfate as a quick-setting agent, and 0.1~1% of sodium dodecylbenzene sulfonate. The high proportion of isocyanate-containing prepolymer can react quickly with sand-fixing agent components such as sodium silicate and polyacrylamide to form a solid gel structure. Sodium silicate solidifies rapidly under the action of the aluminum-based potassium sulfate as a quick-setting agent, and polyacrylamide strengthens the gel network structure, effectively resisting the scouring of groundwater, preventing the slurry from being diluted and washed away, ensuring that the sand can be quickly and effectively consolidated in a high permeability environment, improving the stability of the sand, reducing the risk of water and sand gushing, and ensuring construction safety. When the groundwater level is less than or equal to 3m from the ground and the groundwater permeability coefficient is less than 1.5×10 -3 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 includes 42-45% by mass of solvent water, 34-36% of potassium silicate with a modulus of 2.6-2.8, 8-10% of dibutyl phthalate as a plasticizer, 10-12% of ethanol as a diluent, 2-4% of triethanol as a promoter, and 0.1-0.4% of polyether-modified polysiloxane as a defoamer. Under the action of the plasticizer dibutyl phthalate and the diluent ethanol, the potassium silicate enhances the flexibility and fluidity of the sand-fixing agent, allowing it to diffuse better in the pores of low-permeability sand. The promoter triethanol accelerates the reaction process, allowing the sand-fixing agent to fully react with the isocyanate-containing prepolymer to form a stable consolidated body, effectively reinforcing the sand, improving the bearing capacity of the sand, and meeting the needs of grouting reinforcement in low-permeability environments. When the groundwater level is greater than 3m from the ground and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3 cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-consolidating agent is 1.1-1.3:1. The sand-consolidating agent includes 48-50% by mass of solvent water, 36-38% of aluminum ferrosilicate, 3-6% of dibutyltin disilicate catalyst, 3-5% of metakaolin reinforcing agent, and 0.3-0.8% of sodium hexametaphosphate dispersant. Under the action of the dibutyltin disilicate catalyst, the aluminum ferrosilicate reacts with the isocyanate-containing prepolymer to form a high-strength consolidation product. The metakaolin enhances structural stability, and the dispersant sodium hexametaphosphate ensures uniform dispersion of the various components, allowing the slurry to effectively fill the sand pores in a highly permeable environment, enhance the sand strength, and ensure the reinforcement effect. When the groundwater level is greater than 3m from the ground and the groundwater permeability coefficient is less than 1.5×10 -3cm / s, the mass ratio of the isocyanate group-containing prepolymer and the sand consolidating agent is 1:1, and the sand consolidating agent includes 42-45% by mass of a solvent, 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-silicon dioxide, and 0.6-1% by mass of a retarder, wherein the mass ratio of metakaolin to silicate cement in the compound of metakaolin and silicate cement is 4:5, and the particle size of the quartz sand is 0.1-0.3 mm. The compound of metakaolin and silicate cement forms a high-strength and high-stability consolidated body under the synergistic effect of quartz sand and nano-silicon dioxide, and the retarder tartaric acid ensures that the slurry has sufficient operating time, thereby achieving effective reinforcement of the sand in a low-permeability and low-water-level environment, improving the overall performance of the sand, and 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 3m from the ground, and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3 cm / s, using E-44 epoxy resin and ethylenediamine curing agent, the mass ratio of the two is 8:1; If the groundwater level is less than or equal to 3m from the ground and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, using E-51 epoxy resin and diethylenetriamine curing agent, the mass ratio of the two is 10:1.2; If the groundwater level is greater than 3m from the ground and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3 cm / s, using E-44 epoxy resin and m-phenylenediamine curing agent, the mass ratio of the two is 9:1; If the groundwater level is greater than 3m from the ground and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, and E-51 epoxy resin and polyamide curing agent were selected with a mass ratio of 12:1.

[0015] In the above technical solution, when the groundwater level is less than or equal to 3m from the ground and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3 cm / s, considering that the high groundwater level and high groundwater permeability coefficient lead to the dilution and loss of epoxy resin slurry, it is necessary to accelerate the curing speed and enhance the consolidation effect. Therefore, E-44 epoxy resin and ethylenediamine curing agent are selected. The relatively high ratio of curing agent can promote the rapid cross-linking and curing of epoxy resin, reducing the adverse effects of groundwater on the slurry. The mixed grouting liquid 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 and the groundwater permeability coefficient is less than 1.5×10 -3cm / s, the scouring effect of the groundwater on the grouting fluid is relatively weak, but the clay pores are small, and better fluidity is needed to ensure the diffusion of the grouting fluid. Therefore, E-51 epoxy resin and diethylenetriamine curing agent are selected. The relatively moderate ratio of diethylenetriamine curing agent can not only ensure the curing effect, but also reduce the viscosity of the grouting fluid to a certain extent and improve the fluidity. When the groundwater level is greater than 3m from the ground and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3 cm / s, due to the low groundwater level, the dilution effect of groundwater is relatively small, but the high groundwater permeability coefficient still needs to ensure the curing speed and strength, so E-44 epoxy resin and m-phenylenediamine curing agent are used. The m-phenylenediamine curing agent can make the epoxy resin form a high-strength cohesive body, which is suitable for the environment with high groundwater permeability. When the groundwater level is greater than 3m from the ground and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, in this case, the impact of groundwater is small, and the focus is on ensuring the reinforcement effect and durability of the clay. Therefore, E-51 epoxy resin and polyamide curing agent are selected. The polyamide curing agent can give the epoxy resin better flexibility and adhesion, which 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 stirring container and stir at a speed of 150-200r / min to make the epoxy resin in a uniform flow state. Then, slowly add the ethylenediamine curing agent, stirring continuously during the addition process to ensure that the curing agent is evenly dispersed, and the addition time is controlled within 3-5 minutes. After the addition is completed, continue stirring for 10-15 minutes to fully mix the two to form a uniform and stable grouting liquid. The mixed grouting liquid should be used as soon as possible, and it is best to complete the grouting within 1.5 hours to prevent premature curing.

[0017] Preferably, when the unfavorable geological section in step S3 is rock: If the groundwater level is less than or equal to 3m from the ground, and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3 cm / s, using 42.5 grade Portland cement and water glass with a modulus of 2.8-3.0, with the volume ratio of the two being 1:0.8; If the groundwater level is less than or equal to 3m from the ground and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, use 32.5 grade Portland 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 greater than 3m from the ground and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3 cm / s, using 42.5 grade Portland 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 from the ground and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, 32.5 grade silicate cement and water glass with a modulus of 2.2~2.4 were selected, and the volume ratio of the two was 1:0.5.

[0018] In the above technical solution, when the groundwater level is less than or equal to 3m from the ground and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3 cm / s, in such an environment with high groundwater level and high groundwater permeability coefficient, cement slurry is easily diluted by groundwater erosion, resulting in reduced stone body strength and poor grouting effect. To deal with this situation, it is necessary to increase the amount of water glass to accelerate the setting speed of cement and enhance its anti-scouring ability. 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 the rapid hardening of cement and form a solid body with a certain strength in a short time, effectively resisting the scouring effect of groundwater. When the groundwater level is less than or equal to 3m from the ground and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, the scouring effect of groundwater on the grouting fluid is relatively weak, but the rock cracks may be relatively small, requiring the grouting fluid to have good fluidity and injectability. Therefore, 32.5 grade silicate cement and water glass with a modulus of 2.4-2.6 are selected. The moderate proportion of water glass can ensure that the cement slurry has enough time to diffuse in the rock cracks and provide a certain strength increase in the later stage. When the groundwater level is greater than 3m from the ground and the groundwater permeability coefficient is greater than or equal to 1.5×10 -3 cm / s, the groundwater level is low, which weakens the dilution effect of groundwater on the slurry. However, the high permeability coefficient still requires the slurry to solidify quickly to fill the rock cracks. 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 can ensure that the cement slurry has a certain diffusion capacity while using water glass to accelerate the solidification speed and adapt to the high permeability environment. When the groundwater level is greater than 3m from the ground and the groundwater permeability coefficient is less than 1.5×10 -3 cm / s, under the condition that the influence of groundwater is small, the focus is on ensuring the long-term strength and stability of the rock after reinforcement. Therefore, 32.5 grade silicate cement and water glass with a modulus of 2.2~2.4 are selected. The lower proportion of water glass can fully hydrate the cement and form a stone body with higher 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 designed ratio. Slowly pour the cement into the mixing bucket, add an appropriate amount of clean water, and stir at a speed of 200~250r / min for 3~5 minutes to fully disperse the cement to form a uniform cement slurry. Then, slowly add the water glass while continuing to stir, and control 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, and it is best to complete the grouting operation within 30~40 minutes to avoid premature solidification of the slurry and affect the grouting effect.

[0020] Preferably, in step S2, the distribution of grouting holes is designed according to the geotechnical characteristics, specifically: If the unfavorable geological section is sandy soil, the grouting holes are arranged in a rectangular shape, and the spacing between the grouting holes is 1.5~2.0m; If the unfavorable geological section is clay, the grouting holes are arranged in a ring shape, and multiple layers of ring grouting holes are set around 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 plum blossom shape, and the spacing between the grouting holes is 1.0~3.0m. For rocks with developed cracks, the spacing between the grouting holes is 1.0~2.0m, and for relatively complete blocky rocks, the spacing between the grouting holes is 2.0~3.0m.

[0021] In the above technical solution, 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 holes. This can fully utilize the good diffusibility of the grouting liquid in the sand to achieve uniform reinforcement and ensure that the sand in the entire area is effectively treated. If the unfavorable geological section is clay, the grouting holes are arranged in a circular shape, and multiple layers of circular 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. This circular arrangement can form a continuous reinforcement ring around the tunnel, effectively restraining the deformation of the soft clay and improving its bearing capacity. If the poor geological section is rock, the grouting holes are arranged in a plum blossom shape, and the spacing between the grouting holes is 1.0~3.0m. For rocks with developed cracks, the spacing between the grouting holes is 1.0~2.0m, and for relatively complete block rocks, the spacing between the grouting holes is 2.0~3.0m. The plum blossom shape arrangement can make the slurry cross-penetrate in different directions, fill cracks in different directions, improve the overall strength and impermeability of the rock, and enhance the reinforcement effect.

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

[0023] In the above technical solution, when the depth of the unfavorable geological section is less than one-third of the tunnel depth, if the unfavorable geological section is sandy soil, the grouting hole depth must penetrate the unfavorable geological section and enter the underlying stable stratum 0.5-1.0m. This ensures thorough reinforcement of the sandy unfavorable geological section and prevents instability of the surrounding tunnel soil due to the sandy soil's characteristics. If the unfavorable geological section is clay, the grouting hole depth must also penetrate the unfavorable geological section and enter the stable stratum 0.5-1.0m. Due to the characteristics of clay, penetration reinforcement can effectively control its deformation, forming a continuous reinforcement zone, constraining clay deformation, and improving bearing capacity. If the unfavorable geological section is rock, the grouting hole depth must not only penetrate the unfavorable geological section and enter the stable rock 0.5-1.0m. However, for special geological conditions, such as rock with developed fractures, the impact range of the fractures must also be considered. In actual operation, the depth should be appropriately increased to ensure that the grouting can fully fill the fractures. For massive rock, the grouting hole depth must ensure effective anchoring and reinforcement, and the depth of the stable rock can also be appropriately increased.

[0024] In the above technical solution, when the depth of the unfavorable geological section is greater than or equal to 1 / 3 but less than 2 / 3 of the tunnel burial depth, if the unfavorable geological section is sand, the grouting hole depth should penetrate the unfavorable geological section and enter the underlying stable stratum by 1.0-1.5m. This will enhance the reinforcement of the sand and prevent problems such as sand infiltration from affecting tunnel safety. If the unfavorable geological section is clay, the grouting hole depth should generally penetrate the unfavorable geological section and enter the underlying stable stratum by 1.0-1.5m. This will ensure effective reinforcement of the clay and control its impact on the tunnel. However, for particularly soft and rotten clay, the depth should be appropriately adjusted based on the clay's compressibility and deformation. If the unfavorable geological section is rock, the grouting hole depth should generally penetrate the unfavorable geological section and enter the underlying stable stratum by 1.0-1.5m. However, for special geological conditions, such as rock with developed fractures, the depth can be appropriately increased based on the extension of the fractures and the scope of reinforcement.

[0025] In the above technical solution, when the depth of the unfavorable geological section is greater than or equal to 2 / 3 of the tunnel burial depth, if the unfavorable geological section is sand, the grouting hole depth penetrates the unfavorable geological section and enters the lower stable stratum 1.5-2.0m, fully reinforcing the sand and reducing its adverse effects on the tunnel. If the unfavorable geological section is clay, the grouting hole depth penetrates the unfavorable geological section and enters the lower stable stratum 1.5-2.0m. However, for particularly soft and rotten 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 unfavorable geological section is rock, the grouting hole depth generally penetrates the unfavorable geological section and enters the lower stable stratum 1.5-2.0m. However, for special geological conditions, such as rock with developed fractures, the depth should be adjusted appropriately based on the integrity of the rock and the distribution of fractures.

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

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

[0028] Preferably, when grouting reinforcement is performed in step S4, the grouting pressure and grouting speed are set according to the rock and soil characteristics of 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 is used. The grouting pressure of the first segment is 0.4~0.8MPa and the grouting speed is 15~25L / min. The grouting pressure of each subsequent segment increases by 0.1~0.2MPa and the grouting speed decreases by 5~8L / min. If the unfavorable geological section is rock, for rocks with developed fractures, the grouting pressure is 1.2~2.5MPa and the grouting rate is 8~15L / min. For relatively complete blocky rocks, the grouting pressure is 0.8~1.5MPa and the grouting rate is 5~10L / min.

[0029] Preferably, after the grouting is completed in step S4, the grouting effect needs to be tested: Use geological radar to scan the grouting area. If the radar wave velocity increase is less than 15% or there are continuous reflection anomaly areas, it is determined to be a substandard area and additional grouting is required. The unconfined compressive strength is tested by coring holes. If the unfavorable geological section is sand, the unconfined compressive strength is greater than 1.2 MPa; if the unfavorable geological section is clay, the unconfined compressive strength is greater than 0.8 MPa; if the unfavorable geological section is rock, the unconfined compressive strength is greater than 3.5 MPa; The groundwater permeability coefficient was surveyed and it was found that the groundwater permeability coefficient after reinforcement decreased by at least 2 orders of magnitude compared with the original groundwater permeability coefficient.

[0030] Preferably, when the unfavorable geological section is sandy soil, if it is a mobile sand layer, a freezing pipe is set along the axis of the subway tunnel, and the freezing temperature is maintained at -25~-30℃ until the grouting strength reaches 70~75% of the preset value; When the unfavorable geological section is clay, if it is expansive clay, the grouting is performed in step S4 by layered grouting, with each layer of grouting 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 fluid is first injected to form a water-stop curtain before grouting in step S4. The quick-setting fluid includes sulphoaluminate cement, nano-silicon dioxide and calcium chloride in a mass ratio of 10:1:0.5.

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

[0032] Preferably, when the unfavorable geological section is sandy soil, if it is a flowing sand layer, the total grouting volume is ; When the unfavorable geological section is clay, if it is expansive clay, when using layered grouting, the grouting volume of each layer is ; Where N is the number of freezing pipes; D i is the diameter of the freezing pipe, m; T is the freezing time, days; L i is the length of the frozen segment, m; ρ i is the porosity reduction coefficient after the sand layer is frozen, which is 0.6~0.8; h is the layer thickness, m, ranging from 0.3 to 0.5 m; P max 、P min is the grouting pressure limit value of this layer, MPa; v is the average grouting speed, L / min; K1 and K2 are the groundwater permeability coefficients before and after grouting, cm / s.

[0033] In the above technical solution, the present invention further introduces a dynamic correction mechanism for special working conditions. First, the flowing sand layer formula couples the freezing pipe parameters and the time variable to reflect the influence of phase change on the grouting volume; second, the expansive clay formula reflects the nonlinear correlation between grouting efficiency and the degree of stratum improvement through the logarithmic relationship of the groundwater permeability coefficient, so that the grouting volume not only meets the reinforcement requirements but also avoids resource waste, forming a complete quantitative control system.

[0034] The present invention has at least the following beneficial effects: First, the ground grouting reinforcement method for poor geological sections in subway tunnels provided by the present invention accurately designs grouting schemes based on different rock and soil characteristics by surveying rock and soil properties, groundwater level, groundwater permeability coefficient, and the depth of poor geological sections. This effectively improves the pertinence and scientific nature of grouting reinforcement, achieves relative standardization of ground grouting reinforcement in poor geological sections in subway tunnels, and comprehensively improves the treatment effect of poor geological sections. Secondly, in areas with poor sandy soil geology, the present invention accurately designs the ratio of isocyanate-containing prepolymers to sand-consolidating agents and the composition of the sand-consolidating agents based on the groundwater level and groundwater permeability coefficient. This allows the grouting fluid to quickly and effectively consolidate sand under different hydrological conditions, enhance sand stability, and resist sand flow, significantly reducing the risk of water and sand gushing, thereby ensuring construction safety. Third, the present invention also rationally designs the distribution of grouting holes based on different rock and soil characteristics, with rectangular arrangement for sand, circular arrangement for clay, and plum blossom arrangement for rock, to ensure uniform diffusion of the grouting liquid, fully filling the rock and soil voids and cracks, improving the uniformity and integrity of the reinforcement, and enhancing the overall bearing capacity of the poor geological section; Fourthly, the present invention takes into account the relationship between the depth of the poor geological section of the foundation and the buried depth of the tunnel, and accurately designs the depth of the grouting holes to ensure that the grouting depth can effectively cover the poor geological section and penetrate into the stable stratum, forming a solid reinforced foundation, providing reliable support for the tunnel, and enhancing the stability of the tunnel structure; Fifth, the present invention adopts a reasonable single-hole grouting volume calculation formula based on the rock and soil type, accurately controls the grouting volume, ensures that the rock and soil body is fully filled and reinforced, avoids slurry waste, improves the reinforcement effect, and effectively controls the project cost; Sixth, the present invention scientifically sets the grouting pressure and grouting speed according to the rock and soil characteristics of the adverse geological section, ensuring that the slurry can be smoothly diffused in different rocks and soils while ensuring the reinforcement quality. The segmented grouting of clay can adapt to the characteristics of the clay, improve the reinforcement effect, and ensure the efficiency and safety of the grouting construction; Seventh, the present invention uses a variety of testing methods, such as geological radar scanning, core drilling testing of unconfined compressive strength, and survey of groundwater permeability, to comprehensively and accurately evaluate the grouting effect, and promptly supplement grouting in areas that do not meet the standards, ensuring that the reinforced unfavorable geological sections meet the engineering requirements and guaranteeing the long-term safe and stable operation of the tunnel; Eighth, the present invention further addresses special unfavorable geological conditions, such as using freezing pipes to assist in mobile sand layers, layered grouting of expansive clay, and injecting rapid-setting fluid into fault fracture zones to form a water-stop curtain, effectively solving special geological problems and further improving the adaptability and effectiveness of this method under complex geological conditions. Ninth, the present invention provides scientific calculation formulas for total grouting volume and layered grouting volume for mobile sand layers and expansive clay, respectively, accurately guides grouting construction, ensures that the grouting volume meets engineering requirements, and improves the accuracy and reliability of grouting reinforcement under special geological conditions.

[0035] Other advantages, objectives and features of the present invention will be reflected in part from the following description and will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic flow chart of the ground grouting reinforcement method of the present invention. DETAILED DESCRIPTION

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

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

[0039] The present invention provides a ground grouting reinforcement method for a poor geological section of a subway tunnel. The specific process is as follows: Figure 1 As shown, the following are several specific embodiments of the present invention.

[0040] Example 1 (sand soil poor geological section) The subway tunnel passes through a section of poor sandy soil. The groundwater level is 2.5m from the ground and the groundwater permeability coefficient is 2.0×10 -3 cm / s. Geological drilling, geophysical exploration, and other exploration methods determined the geotechnical characteristics of the area, which is a sandy and unfavorable geological section, specifically medium-coarse sand with a porosity of 30%. The depth of the unfavorable geological section is 8m, and the tunnel is buried at a depth of 25m.

[0041] According to the geotechnical characteristics, the grouting holes are arranged in a rectangular shape with a spacing of 1.8m. Based on the depth of the poor geological section and the buried depth of the tunnel, the grouting hole depth is designed to penetrate the poor geological section and enter the lower stable stratum 1.2m, that is, the grouting hole depth is 9.2m.

[0042] Because the groundwater level and permeability coefficient in the poor geological section of the subway tunnel meet the high water level and high permeability requirements, the grouting fluid consists of an isocyanate-containing prepolymer and a sand-consolidating agent, with a mass ratio of 2.2:1. The sand-consolidating agent consists of 50% water (solvent), 39% sodium silicate (modulus 3.2), 6.9% polyacrylamide (30% degree of hydrolysis), 4% potassium aluminum sulfate (accelerator), and 0.1% sodium dodecylbenzene sulfonate.

[0043] When grouting reinforcement is carried out, the amount of grouting material for a single hole is calculated according to the formula Q1=πnHR 2 The calculation is (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 calculated. The grouting pressure is 0.5MPa at no load, and the grouting rate is 30L / min.

[0044] After grouting was completed, geological radar was used to scan the grouting area. The radar wave velocity increased by over 15%, with no continuous reflection anomalies. Drilling and coring tests revealed unconfined compressive strength of 1.5 MPa, meeting the requirement of greater than 1.2 MPa. Surveys of groundwater permeability revealed a decrease of more than two orders of magnitude compared to the original value, demonstrating the effectiveness of the grouting.

[0045] Example 2 (Poor clay geological section) The subway tunnel passes through a section with poor clay geology. The groundwater level is 4m from the ground and the groundwater permeability coefficient is 1.0×10 -3 cm / s. The survey determined that the clay was a poor geological section and was soft clay with a natural bulk density of 18kN / m 3 , the compression coefficient is 0.2. At the same time, the depth of the bad geological section is 12m, and the tunnel burial depth is 30m.

[0046] Based on geotechnical characteristics, a circular arrangement was adopted, with multiple layers of grouting holes installed around the subway tunnel. The spacing between the inner two layers of holes was 0.9m, and the spacing between the outer layers was 1.3m. Based on the depth of the unfavorable geological section and the tunnel burial depth, the grouting holes were designed to penetrate the unfavorable geological section and reach 1.3m into the underlying stable strata, resulting in a grouting hole depth of 13.3m.

[0047] Due to the moderate groundwater level and relatively low groundwater permeability coefficient in the poor geological section of the subway tunnel, epoxy resin and curing agent are used as the grouting fluid. In view of the small voids and poor permeability of soft clay, and the need to enhance the adhesion and curing effect of the grouting fluid to fill the clay voids and inhibit its deformation, E-44 epoxy resin is selected and matched with ethylenediamine as the curing agent, with a mass ratio of 8:1.

[0048] During grouting reinforcement, the grouting volume per hole is calculated using the formula Q2 = kcSH / (1 + d), where S is the product of the spacing between adjacent grouting holes, k is 0.2, c is 18 kN / m³, and d is 0.2. Segmented grouting is used, with the initial grouting pressure at 0.6 MPa and a grouting rate of 20 L / min. The grouting pressure increases by 0.15 MPa and the grouting rate decreases by 6 L / min for each subsequent segment.

[0049] Geological radar scanning showed no abnormalities, and the unconfined compressive strength of the drill core test was 1.0 MPa, greater than 0.8 MPa. The groundwater permeability coefficient was significantly reduced, meeting the reinforcement requirements.

[0050] Example 3 (poor rock geology section) The subway tunnel section encountered a rock section with developed cracks and poor geological conditions. The groundwater level was 3.5m below the ground and the groundwater permeability coefficient was 1.8×10 -3 The survey determined that the rock porosity was approximately 8%, the depth of the unfavorable geological section was 10m, and the tunnel depth was 28m.

[0051] Based on the geotechnical characteristics, a plum blossom arrangement was adopted with a hole spacing of 1.5m. The grouting hole depth was designed to penetrate the poor geological section and enter the lower stable stratum 1.4m, that is, the grouting hole depth was 11.4m.

[0052] Prepare cement and water glass grouting liquid.

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

[0054] Geological radar showed that the grouting area was uniform, and the unconfined compressive strength of the drill core test was 4.0 MPa, greater than 3.5 MPa. The groundwater permeability coefficient decreased significantly, achieving the reinforcement effect.

[0055] Example 4 (poor rock geology section) The subway tunnel has a relatively complete block rock poor geological section, the groundwater is 5m below the ground, and the groundwater permeability coefficient is 0.8×10 -3 The survey determined the rock porosity to be 5%, the depth of the unfavorable geological section to be 9m, and the tunnel depth to be 26m.

[0056] Based on the geotechnical characteristics, the grouting holes are arranged in a plum blossom pattern with a spacing of 2.5m. The grouting holes are designed to penetrate the poor geological section and enter the lower stable stratum 1.5m deep, that is, the grouting hole depth is 10.5m.

[0057] Prepare cement and water glass grouting liquid.

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

[0059] Example 5 (Unfavorable geological section of mobile sand layer) There is a poor geological section of mobile sand layer in the subway tunnel section. The groundwater level is 2m from the ground 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°C. The total grouting volume was calculated using Formula Q3, and other grouting parameters were set based on the high water level and high permeability conditions in the sandy, unfavorable geological section. The grouting effect was excellent, meeting the project requirements.

[0061] Example 6 (Expanding Clay Unfavorable Geological Section) The subway tunnel section passes through a section of unfavorable expansive clay soil. The groundwater level is 3 meters below the surface, and the groundwater permeability coefficient is 1.2×10⁻³cm / s. Layered grouting was used, with each layer 0.4 meters thick and a 5-hour interval between layers. The grouting volume for each layer was calculated according to a formula, and other grouting parameters were set based on the clay's characteristics. Testing confirmed significant reinforcement results, effectively suppressing clay expansion.

[0062] Example 7 (Fault fracture zone) The subway tunnel section passes through a fault fracture zone with unfavorable geology. The groundwater level is 4.5 meters below the surface, and the groundwater permeability coefficient is 2.5×10⁻³cm / s. Before grouting, a quick-setting fluid composed of sulphoaluminate cement, nanosilica, and calcium chloride in a mass ratio of 10:1:0.5 was injected to form a water-stopping curtain. Subsequent grouting parameters were set based on the development of fractures in the unfavorable rock section. Test results indicate that the grouting reinforcement was effective, meeting the requirements for tunnel construction and operation.

[0063] The number of equipment and processing scale described here are used to simplify the description of the present invention. The application, modification and variation of the ground grouting reinforcement method for the poor geological section of the subway tunnel of the present invention will be obvious to those skilled in the art.

[0064] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the description and implementation methods. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and specific embodiments shown and described herein.

Claims

1. A ground grouting reinforcement method for a poor geological section of a subway tunnel, characterized in that: include: S1. Survey the geotechnical properties, groundwater level H, groundwater permeability coefficient K and depth of the poor geological section of the subway tunnel; S2. Designing the distribution of grouting holes according to the geotechnical characteristics surveyed in step S1, and designing the depth of the grouting holes according to the depth of the unfavorable geological section and the buried depth of the tunnel; S3, preparing grouting fluid according to the rock and soil properties, groundwater level, and groundwater permeability coefficient surveyed in step S1; S4, performing grouting reinforcement according to the grouting hole distribution designed in step S2; Among them, the grouting liquid in step S3 includes component A and component B: if the poor geological section is sand, component A and component B are respectively an isocyanate-containing prepolymer and a sand-fixing agent; if the poor geological section is clay, component A and component B are respectively an epoxy resin and a curing agent; if the poor geological section is rock, component A and component B are respectively cement and water glass.

2. The ground grouting reinforcement method for a poor geological section of a subway tunnel according to claim 1, characterized in that: When the unfavorable geological section in step S3 is sandy soil, the mass ratio of the isocyanate group-containing prepolymer to the sand-fixing agent and the composition of the sand-fixing agent are prepared as follows according to different conditions of the groundwater level H and the groundwater permeability coefficient K: When H≤3m and K≥1.5×10 -3 cm / s, the mass ratio of the isocyanate-containing prepolymer to the sand-consolidating agent is 2-2.3:1, and the sand-consolidating agent comprises 38-40% by mass of sodium silicate, 4-8% by mass of polyacrylamide, 2-4% by mass of potassium aluminum sulfate, and 0.1-1% by mass of sodium dodecylbenzenesulfonate; When H≤3m and K<1.5×10 -3 cm / s, the mass ratio of the isocyanate group-containing prepolymer to the sand-consolidating agent is 1.5-1.8:1, and the sand-consolidating agent comprises 34-36% by mass of potassium silicate, 8-10% by mass of dibutyl phthalate, 10-12% by mass of diluent ethanol, 2-4% by mass of triethanol, and 0.1-0.4% by mass of polyether-modified polysiloxane; When H>3m and K≥1.5×10 -3 cm / s, the mass ratio of the isocyanate group-containing prepolymer to the sand-consolidating agent is 1.1-1.3:1, and the sand-consolidating agent comprises 36-38% by mass of aluminum ferrosilicate, 3-6% by mass of dibutyltin disilicate, 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 cm / s, the mass ratio of the isocyanate group-containing prepolymer and the sand consolidating agent is 1:1, and the sand consolidating agent includes 45-48% by mass of a compound of metakaolin and Portland cement, 6-8% by mass of quartz sand, 0.5-1% by mass of nano-silicon dioxide, and 0.6-1% by mass of tartaric acid, wherein the mass ratio of metakaolin to Portland cement in the compound of metakaolin and Portland cement is 4:5, and the particle size of the quartz sand is 0.1-0.3 mm.

3. The ground grouting reinforcement method for a poor geological section of a subway tunnel according to claim 1, characterized in that: In step S2, the distribution of grouting holes is designed according to the following rules based on the geotechnical characteristics: If the unfavorable geological section is sandy soil, the grouting holes are arranged in a rectangular shape, and the spacing between the grouting holes is 1.5~2.0m; If the unfavorable geological section is clay, the grouting holes are arranged in a ring shape, and multiple layers of ring grouting holes are set around 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 plum blossom shape. For rocks with developed cracks, the spacing between the grouting holes is 1.0~2.0m, and for relatively complete massive rocks, the spacing between the grouting holes is 2.0~3.0m.

4. The ground grouting reinforcement method for a poor geological section of a subway tunnel according to claim 3, characterized in that: In step S2, the depth of the grouting holes is designed according to the depth of the unfavorable geological section and the buried depth of the tunnel, specifically: 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 underlying stable stratum 0.5~1.0m; If the depth of the unfavorable geological section is greater than or equal to 1 / 3 of the tunnel burial depth but less than 2 / 3 of the tunnel burial depth, the grouting hole depth is designed to penetrate the unfavorable geological section and enter the underlying stable stratum 1.1~1.5m; If the depth of the poor geological section is greater than or equal to 2 / 3 of the tunnel burial depth, the grouting hole depth is designed to penetrate the poor geological section and enter the underlying stable stratum 1.6~2.0m.

5. The ground grouting reinforcement method for a poor geological section of a subway tunnel according to claim 4, characterized in that: When grouting reinforcement is performed in step S4, the grouting amount of a single hole is as follows: When the unfavorable geological section is sand or rock, the single hole grouting material volume Q1=πnHR 2 (1+a)b; When the unfavorable geological section is clay, the single hole grouting volume Q2=kcSH / (1+d); Where R is the slurry diffusion radius, m, which is 1 / 2 of the grouting hole spacing; H is the depth of the grouting hole, m; n is the porosity of rock and soil, 25-40% for sand and 3-15% for rock; a is the slurry loss coefficient, ranging from 0.2 to 0.5; b is the correction factor for filling density, subtract 1.2~1.5 for sand and 1.0~1.3 for rock; S is the affected area of single hole grouting, m 2 , take the product of the spacing between adjacent grouting holes; c is the natural bulk density of clay, kN / m 3 , take 16~20; k is the replacement rate of the grouting body, which is 0.15~0.25; d is the compression coefficient of clay, which is between 0.1 and 0.

3.

6. The ground grouting reinforcement method for a poor geological section of a subway tunnel according to claim 1, characterized in that: When grouting reinforcement is performed in step S4, the grouting pressure and grouting speed are set according to the rock and soil characteristics of the unfavorable 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 is used. The grouting pressure of the first segment is 0.4~0.8MPa and the grouting speed is 15~25L / min. The grouting pressure of each subsequent segment increases by 0.1~0.2MPa and the grouting speed decreases by 5~8L / min. If the unfavorable geological section is rock, for rocks with developed fractures, the grouting pressure is 1.2~2.5MPa and the grouting rate is 8~15L / min. For relatively complete blocky rocks, the grouting pressure is 0.8~1.5MPa and the grouting rate is 5~10L / min.

7. The ground grouting reinforcement method for a poor geological section of a subway tunnel according to claim 1 or 6, characterized in that: After the grouting is completed in step S4, the grouting effect needs to be tested: Use geological radar to scan the grouting area. If the radar wave velocity increase is less than 15% or there are continuous reflection anomaly areas, it is determined to be a substandard area and additional grouting is required. The unconfined compressive strength is tested by coring holes. If the unfavorable geological section is sand, the unconfined compressive strength is greater than 1.2 MPa; if the unfavorable geological section is clay, the unconfined compressive strength is greater than 0.8 MPa; if the unfavorable geological section is rock, the unconfined compressive strength is greater than 3.5 MPa; The groundwater permeability coefficient was surveyed and it was found that the groundwater permeability coefficient after reinforcement decreased by at least 2 orders of magnitude compared with the original groundwater permeability coefficient.

8. The ground grouting reinforcement method for a poor geological section of a subway tunnel according to claim 1, characterized in that: When the unfavorable geological section is sandy soil, if it is a flowing sand layer, a freezing pipe is set along the axis of the subway tunnel and the freezing temperature is maintained at -25~-30℃ until the grouting strength reaches 70~75% of the preset value; When the unfavorable geological section is clay, if it is expansive clay, grouting is performed in step S4 by layered grouting, with each layer of grouting being no thicker than 0.5m and the interval between layers being greater than 4h; When the unfavorable geological section is a fault fracture zone, a quick-setting fluid is first injected to form a water-stop curtain before grouting in step S4. The quick-setting fluid includes sulphoaluminate cement, nano-silicon dioxide and calcium chloride in a mass ratio of 10:1:0.

5.

9. The ground grouting reinforcement method for a poor geological section of a subway tunnel according to claim 8, 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 unfavorable geological section is clay, if it is expansive clay, when using layered grouting, the grouting volume per layer is Q4=0.5h ; Where N is the number of freezing pipes; D i is the freezing pipe diameter, m; T is the freezing time, days; L i is the length of the frozen segment, m; ρ i is the porosity reduction coefficient after the sand layer is frozen, which is 0.6~0.8; h is the layer thickness, m, ranging from 0.3 to 0.5 m; P max 、P min is the grouting pressure limit value of this layer, MPa; v is the average grouting speed, L / min; K1 and K2 are the groundwater permeability coefficients before and after grouting, cm / s.

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