Tunnel forepoling method

Abstract

The invention discloses a tunnel forepoling method, and relates to the technical field of tunnel forepoling, the tunnel forepoling method comprises the following steps: identifying fracture distribution, fracture zone position and scale in a tunnel rock mass, and obtaining geological information of the rock mass in front of a tunnel face; obtaining construction parameters according to the geological information; according to the construction parameters, drilling, pipe shed mounting, steel strand inserting and tensioning and grouting in the surrounding rock are conducted, and a reinforcing area is formed; and stability monitoring is conducted on the reinforced area, and the reinforced area serves as a tunnel advance support. According to the method, the three-dimensional geomechanical model is constructed through multi-source geological detection to guide construction parameter optimization, precise construction control and real-time stability monitoring are combined, and the problems of inaccurate geological information, extensive parameter design and monitoring deficiency in a traditional supporting technology are solved; the reliability of the forepoling structure is improved, the construction risk is reduced, and the engineering cost is saved.

Description

Technical Field

[0001] This invention relates to the field of tunnel pre-support technology, and in particular to a method for tunnel pre-support. Background Technology

[0002] Tunnel engineering, as an important component of modern transportation infrastructure construction, plays a crucial role in mountainous highways, urban subways, and water conservancy and hydropower projects. However, tunnel construction often encounters complex geological conditions, particularly adverse geological environments such as fractured rock masses, fracture zones, and weak strata, posing severe challenges to construction safety and project quality.

[0003] Traditional tunnel pre-support technology is difficult to adapt to the reinforcement needs under different geological conditions, and the reinforcement effect is limited, resulting in high safety risks in tunnel construction. Summary of the Invention

[0004] The main objective of this invention is to propose a method for tunnel pre-support, which aims to improve the effect of tunnel pre-support reinforcement and enhance the safety of tunnel construction.

[0005] To achieve the above objectives, the present invention proposes a method for tunnel pre-support, the method comprising: Identify the distribution of fractures, the location and scale of fracture zones in the tunnel rock mass, and obtain geological information of the rock mass in front of the tunnel face; Based on the geological information, construction parameters are obtained; According to the construction parameters, drilling, pipe roof installation, steel strand insertion and tensioning, and grouting into the surrounding rock are carried out to form a reinforced zone; The stability of the reinforced area is monitored, and the reinforced area is used as the advance support for the tunnel.

[0006] In one embodiment, the step of identifying the distribution of fractures, the location and scale of fracture zones in the tunnel rock mass, and obtaining geological information of the rock mass ahead of the tunnel face includes: The geological radar was used to scan along the tunnel excavation axis to obtain the dielectric constant distribution information of the tunnel rock mass and to preliminarily delineate the geological anomaly zone. In the geologically anomalous area, a multibeam ultrasonic detector is used for cross-detection to obtain wave velocity field and attenuation coefficient field data in the tunnel rock mass; Based on the dielectric constant distribution information of the tunnel rock mass and the wave velocity field and attenuation coefficient field data in the tunnel rock mass, a three-dimensional geomechanical model including fracture orientation, fracture zone boundary and rock mass strength index is constructed to obtain the geological information of the rock mass in front of the tunnel face.

[0007] In one embodiment, the step of obtaining construction parameters based on the geological information includes: The average spacing of fractures in the rock mass within a preset range outside the tunnel outline is extracted from the three-dimensional geomechanical model, and the circumferential spacing of the pipe roof is set to 0.8 to 1.2 times the average spacing of the fractures.

[0008] In one embodiment, the step of obtaining construction parameters based on the geological information further includes: Based on the geological information, grouting parameters are obtained; the grouting parameters include the grout mix ratio, which is composed of the following components in parts by mass: 100 parts cement, 15-25 parts silica fume, 35-45 parts water, 0.5-1.5 parts water-reducing agent, and 2-5 parts bentonite.

[0009] In one embodiment, the steps of drilling, installing pipe roofs, threading and tensioning steel strands, and grouting into the surrounding rock to form a reinforced zone, according to the construction parameters, include: A drilling guide frame is erected at the tunnel face, and a total station is used to calibrate the design inclination and azimuth of each hole on the guide frame; A hydraulic rock drilling rig is used to drill holes under the guidance of a guide frame. The drilling trajectory is monitored in real time during the process to ensure that the deviation from the design trajectory is less than 2% of the hole depth. After connecting the pipe roof segments with threaded sleeves, insert them into the drill holes to ensure that the deviation between the pipe roof axis and the drill hole axis is less than 5mm. The steel strand is passed through the inside of the installed pipe roof, and its rear end is fixed to the stable rock mass behind it by anchors. The front end is connected to the tensioning equipment to apply a prestress of 0.6MPa to 0.8MPa to the steel strand. The grout is injected into the surrounding rock through the grouting holes pre-embedded in the pipe roof using a CNC grouting pump. The grouting process adopts a pressure control mode, with an initial pressure of 0.3 MPa, which is then increased stepwise to 0.8 MPa at a rate of 0.1 MPa / min and stabilized for 10 minutes to form the reinforced zone.

[0010] In one embodiment, the grout is injected into the surrounding rock through grouting holes pre-embedded in the pipe roof using a CNC grouting pump. The grouting process adopts a pressure control mode, with an initial pressure of 0.3 MPa, followed by a stepwise increase to 0.8 MPa at a rate of 0.1 MPa / min, and then a pressure stabilization period of 10 minutes. After the step of forming the reinforced zone, the method of tunnel pre-support further includes: Grouting is terminated when the grouting pressure reaches 0.8 MPa and the grouting flow rate remains less than 5 L / min for 2 minutes during the pressure stabilization period.

[0011] In one embodiment, the step of performing stability monitoring on the reinforced area and using the reinforced area as the tunnel pre-support includes: Strain sensors and displacement sensors are embedded in the pipe roof and surrounding rock mass to collect stress and deformation data in real time. When the stress change rate exceeds 5 kPa / h or the displacement rate exceeds 2 mm / h, an early warning signal is issued to monitor the stability of the reinforced area. The reinforced area is used as the advance support for the tunnel.

[0012] In one embodiment, prior to the step of using the reinforced zone as the tunnel pre-support, the tunnel pre-support method further includes: Some of the excavated soil generated during tunnel excavation is crushed and screened to a particle size of less than 50mm, and then backfilled into the stable space formed by the reinforced area to balance the ground pressure or serve as the foundation for subsequent construction platforms.

[0013] In one embodiment, the grout is injected into the surrounding rock through grouting holes pre-embedded in the pipe roof using a CNC grouting pump. The grouting process adopts a pressure control mode, with an initial pressure of 0.3 MPa, followed by a stepwise increase to 0.8 MPa at a rate of 0.1 MPa / min, and then a pressure stabilization period of 10 minutes. Before the step of forming the reinforced zone, the method of tunnel pre-support further includes: Add 1% to 3% of a quick-setting agent by mass of cement to the slurry.

[0014] In one embodiment, the quick-setting agent is a powder of sodium aluminate and calcium hydroxide compounded in a mass ratio of 2:1.

[0015] The technical solution of this invention constructs a three-dimensional geomechanical model through multi-source geological exploration to guide the optimization of construction parameters. Combined with precise construction control and real-time stability monitoring, it solves the problems of inaccurate geological information, coarse parameter design, and lack of monitoring in traditional support technologies. It achieves the acquisition of geological information and three-dimensional visualization modeling, providing a reliable basis for setting support parameters. During construction, positioning and process control ensure the quality of pipe roof installation, and the synergistic effect of prestressed steel strands and optimized grouting technology enhances the overall stability of the rock mass. The real-time monitoring system can promptly identify abnormal states in the reinforced area, effectively preventing the risk of support structure failure. This method forms a complete technical chain of geological exploration, parameter optimization, directional construction, and real-time monitoring, solving the systemic defects of traditional advanced support technologies, improving the reliability of advanced support structures, reducing construction risks, and saving project costs. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0017] Figure 1 This is a flowchart illustrating an embodiment of the tunnel pre-support method provided by the present invention.

[0018] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0022] Tunnel engineering, as an important component of modern transportation infrastructure construction, plays a crucial role in mountainous highways, urban subways, and water conservancy and hydropower projects. However, tunnel construction often encounters complex geological conditions, particularly adverse geological environments such as fractured rock masses, fracture zones, and weak strata, posing severe challenges to construction safety and project quality.

[0023] Traditional tunnel pre-support technology suffers from the following technical problems: First, the acquisition of geological information is not precise enough. Existing technologies typically employ single detection methods, such as drilling or simple geophysical exploration, which are insufficient to accurately identify the distribution patterns of fractures, the precise location and scale of fracture zones in the rock mass ahead of the tunnel face. This results in a lack of reliable geological basis for support design, easily leading to under- or over-support. Second, the determination of support parameters lacks scientific basis. Traditional methods often rely on construction experience to set key parameters such as pipe roof spacing and grouting pressure, failing to make fine adjustments based on specific geological conditions. This leads to unsatisfactory support effects, wasting materials and potentially posing safety hazards. Third, the precision of construction process control is low. In key processes such as pipe roof installation, steel strand tensioning, and grouting, the lack of precise construction control methods and real-time monitoring means makes it difficult to ensure the accurate positioning and construction quality of each component, affecting the overall support effect. Furthermore, existing grouting material formulations are limited and cannot adapt to the reinforcement needs under different geological conditions. Traditional grouting fluids often use fixed proportions, failing to optimize and adjust them according to the characteristics of the rock mass. This results in inconsistent grouting effects, especially in highly permeable fractured rock masses, where ordinary grouting fluids are prone to leakage, limiting their reinforcement effect. Finally, there is a lack of an effective stability monitoring system. After traditional support is completed, there is often a lack of systematic real-time monitoring methods, making it impossible to detect stress changes and deformations in the support structure in a timely manner. This makes it difficult to provide early warnings of potential hazards, posing a significant risk to tunnel construction safety.

[0024] To address this technical problem, this invention proposes a method for tunnel pre-support.

[0025] Please see Figure 1 In one embodiment of the present invention, the method for tunnel pre-support includes: Step S10: Identify the distribution of fractures, the location and scale of fracture zones in the tunnel rock mass, and obtain geological information of the rock mass in front of the tunnel face; Step S20: Obtain construction parameters based on the geological information; Step S30: According to the construction parameters, drilling, pipe roof installation, steel strand insertion and tensioning, and grouting into the surrounding rock are carried out to form a reinforced zone; Step S40: Perform stability monitoring on the reinforced area and use the reinforced area as the tunnel advance support.

[0026] The process involves several key steps: Identifying fracture distribution within the tunnel rock mass involves using ground-penetrating radar (GPR) and ultrasonic cross-detection to obtain data on the rock mass's dielectric constant and wave velocity field. This can be achieved using a multi-beam ultrasonic detector to construct a three-dimensional geomechanical model. Obtaining construction parameters based on geological information involves extracting rock mass characteristic data from the three-dimensional model to generate pipe roof spacing and grouting parameters. This can be achieved using the average fracture spacing analysis method to ensure the support parameters match the geological conditions. Drilling and installing the pipe roof involves precise drilling using guide frame positioning and trajectory monitoring. This can be achieved using a hydraulic rock drilling rig with total station calibration to ensure the accuracy of the pipe roof installation position. Inserting and tensioning prestressed steel strands within the pipe roof involves installing prestressed steel strands within the pipe roof. This can be achieved using anchor fixing combined with CNC tensioning equipment to provide active support force. Grouting the surrounding rock to form a reinforced zone involves injecting optimized grout using a pressure-controlled mode. This can be achieved using a CNC grouting pump with staged pressurization to fill rock fractures and enhance overall integrity. Stability monitoring refers to the real-time data collection by embedding sensors within the reinforced structure. Specifically, it can be achieved by linking strain sensors and displacement sensors for monitoring, and is used to assess the safety status of the support structure.

[0027] More specifically, the dielectric constant distribution was first obtained by scanning along the tunnel axis using ground-penetrating radar to preliminarily delineate geological anomaly areas. Subsequently, multi-beam ultrasonic cross-detection was conducted in the anomaly areas to collect wave velocity and attenuation coefficient data. Based on the multi-source detection data, a three-dimensional geomechanical model including fracture orientation and fracture zone boundaries was constructed to provide data support for parameter generation. According to the rock mass characteristic parameters extracted from the model, the circumferential spacing of the pipe roof and the grouting material mix ratio were dynamically set. During the drilling phase, guide frame positioning and real-time trajectory monitoring were used to ensure drilling accuracy. After the pipe roof was installed, steel strands were inserted and prestressed to form an active support system. During grouting, the grout diffusion range was controlled by staged pressurization to ensure the grout fully filled the rock mass fractures. After the reinforced zone was formed, a sensor network was deployed to monitor stress and strain data in real time; an early warning mechanism was activated when the monitored values ​​exceeded the threshold.

[0028] Compared to existing technologies, traditional methods rely on single detection methods, leading to insufficient accuracy in geological models. This solution, however, constructs a three-dimensional geomechanical model through multi-source data fusion, significantly improving the accuracy of geological information. Existing technologies, using empirical parameters, are prone to unstable support effects. This solution dynamically generates construction parameters based on geological characteristics, achieving precise adaptation of the support system. Conventional construction lacks process control, resulting in component positioning deviations. This solution ensures construction accuracy through dual control of directional positioning and trajectory monitoring. Traditional grouting materials with fixed proportions are difficult to adapt to complex geology. This solution uses adjustable-component grout to improve material adaptability. Existing technologies lack effective monitoring and early warning mechanisms. This solution establishes an active safety protection system through real-time data acquisition and analysis.

[0029] The technical solution provided by this invention utilizes multi-source geological exploration to construct a three-dimensional geomechanical model to guide the optimization of construction parameters. Combined with precise construction control and real-time stability monitoring, it solves the problems of inaccurate geological information, coarse parameter design, and lack of monitoring in traditional support technologies. This achieves the acquisition of geological information and three-dimensional visualization modeling, providing a reliable basis for setting support parameters. During construction, positioning and process control ensure the quality of pipe roof installation, and the synergistic effect of prestressed steel strands and optimized grouting technology enhances the overall stability of the rock mass. The real-time monitoring system can promptly identify abnormal states in the reinforced area, effectively preventing the risk of support structure failure. This method forms a complete technical chain of geological exploration, parameter optimization, directional construction, and real-time monitoring, solving the systemic defects of traditional advanced support technologies, improving the reliability of advanced support structures, reducing construction risks, and saving project costs.

[0030] For ease of understanding, a specific implementation method is shown here: In a soft rock tunnel project, the tunnel mainly traverses highly weathered mudstone strata. The rock mass is fractured, easily softened by water, and has an extremely short self-stabilization time. The method of this invention is used for advanced support.

[0031] First, step S10, geological information acquisition, was performed. At the tunnel face, a 100MHz ground-penetrating radar was used to scan a 30-meter area ahead, with a scan line spacing of 1 meter. After data analysis, a low-resistivity anomaly was found in the section from K5+120 to K5+135. Subsequently, two intersecting boreholes were deployed in this area using a multibeam ultrasonic detector. The acquired radar velocity data was fused and inverted with the ultrasonic velocity and attenuation data to generate a three-dimensional geomechanical model of this section. The model clearly shows that there is a fractured mudstone interlayer with a dip angle of approximately 60° and a thickness of approximately 2.5 meters in this section, with an average fracture spacing of 380 mm calculated by the software.

[0032] Next, step S20, determining the support parameters, is performed. Based on the above model, the core support area is determined to be within a 120° range of the tunnel arch. According to the average crack spacing of 380mm, the circumferential spacing of the pipe roof is determined to be 400mm (approximately 1.05 times). The pipe roof diameter is selected as 159mm, and the length is determined to be 15 meters to ensure passage through the fractured zone. The grout mix proportion is determined as follows: 100 parts by weight of PO 42.5 cement, 20 parts by weight of silica fume, 40 parts by weight of water, 1.0 part by weight of polycarboxylate superplasticizer, and 3 parts by weight of sodium bentonite.

[0033] Next, proceed with step S30, the support structure construction step. A steel guide frame is precisely installed at the working face, and a total station (e.g., Leica TS60) is used to lay out the 15° external angle for each hole. A three-arm hydraulic drilling rig is used to drill to a depth of 15.2 meters, and the depth deviation is checked with an inclinometer; it is less than 0.2%. 3-meter-long Φ159mm seamless steel pipes are connected using threaded sleeves and pushed into the hole section by section. A straightedge is used to check the overall straightness during installation. Then, Φ15.2mm high-strength steel strands are threaded into the pipe roof, and the rear end is anchored to the supported stable section's grating steel frame. A 700kN tension (approximately equivalent to 0.7MPa prestress) is applied to the front end with a jack and locked. Finally, a CNC grouting pump (e.g., Zhejiang Yanxiang ZYB-70 / 80D) is connected, and the pre-mixed composite grout is injected through the grouting holes on the pipe roof. Grouting must be strictly controlled according to the pressure program: start from 0.3 MPa, increase the pressure by 0.1 MPa per minute, and stabilize the pressure after reaching 0.8 MPa. If the flow rate is observed to be consistently below 5 L / min for 2 minutes, grouting of that hole should be stopped.

[0034] Finally, step S40, utilizing the support system, was executed. Surface strain gauges were welded onto the pipe roof of the supported section, and multi-point displacement gauges were embedded in the surrounding rock, with data lines connected to the tunnel entrance monitoring center. Real-time data showed that after the reinforcement ring was formed, the deformation rate of the surrounding rock stabilized below 0.5 mm / h, far below the warning value. The mudstone and slag generated during tunnel excavation were crushed by a jaw crusher and passed through a 50 mm vibrating screen before being used to backfill the loose slag space under the tunnel floor, effectively reducing the amount of slag transported by 20%.

[0035] In an embodiment of the present invention, the step of identifying the distribution of fractures, the location and scale of fracture zones in the tunnel rock mass, and obtaining geological information of the rock mass in front of the tunnel face includes: Step S11: Use ground-penetrating radar to scan along the tunnel excavation axis to obtain the dielectric constant distribution information of the tunnel rock mass and preliminarily delineate the geological anomaly zone; Step S12: In the geologically anomalous area, a multi-beam ultrasonic detector is used for cross-detection to obtain wave velocity field and attenuation coefficient field data in the tunnel rock mass. Step S13: Based on the dielectric constant distribution information of the tunnel rock mass and the wave velocity field and attenuation coefficient field data in the tunnel rock mass, construct a three-dimensional geomechanical model including fracture orientation, fracture zone boundary and rock mass strength index to obtain the geological information of the rock mass in front of the tunnel face.

[0036] Among them, ground-penetrating radar (GPR) refers to instruments that utilize the propagation characteristics of electromagnetic waves in a medium for geological exploration. Specifically, it can be implemented using a pulse radar system combining transmitting and receiving antennas. It obtains information on the dielectric constant distribution by receiving the time delay and amplitude changes of reflected electromagnetic waves. Multibeam ultrasonic detectors are acoustic wave detection devices with multiple transmitting and receiving units. Specifically, they can be implemented using arrayed piezoelectric transducers. They acquire data on the wave velocity field and attenuation coefficient field within the rock mass by emitting ultrasonic beams at different angles and receiving reflected signals. Three-dimensional geomechanical models are digital geological models that integrate multi-source detection data. Specifically, they can be constructed using finite element mesh generation and parameter inversion algorithms. The structural characteristics of the rock mass are reconstructed by coupling dielectric constant, wave velocity, and attenuation coefficient data.

[0037] More specifically, ground-penetrating radar continuously scans along the tunnel axis, quickly identifying regions with abnormal dielectric constants by analyzing the differences in the propagation speed of electromagnetic waves in different media. Multi-beam ultrasonic detectors are deployed within these abnormal regions for multi-angle cross-detection, utilizing the reflection and diffraction phenomena of ultrasonic waves at fracture interfaces to obtain the wave velocity distribution and energy attenuation characteristics in different directions within the rock mass. The dielectric anomaly boundary of the ground-penetrating radar is spatially matched with the wave velocity gradient variation region detected by ultrasonic waves. A three-dimensional interpolation algorithm is used to generate spatial distribution data including fracture strike and dip angle. Combined with attenuation coefficient field data, rock mass strength parameters are calculated, ultimately establishing a three-dimensional geological model reflecting the geometry and mechanical properties of the fracture zone.

[0038] This application addresses the issue of insufficient data accuracy caused by the reliance on single methods in traditional geological exploration, enabling precise identification of fracture distribution and fracture zone characteristics in the rock mass ahead of the tunnel face. Through cross-validation of multi-source detection data and 3D modeling, the spatial extent of geological anomaly areas can be accurately delineated, providing a reliable geomechanical basis for subsequent pipe roof spacing setting and grouting parameter optimization. The established rock mass strength index distribution model can guide the stress analysis of the support structure, effectively avoiding insufficient or excessive support.

[0039] In an embodiment of the present invention, the step of obtaining construction parameters based on the geological information includes: Step S21: Extract the average spacing of fractures in the rock mass within a preset range outside the tunnel outline from the three-dimensional geomechanical model, and set the circumferential spacing of the pipe roof to 0.8 to 1.2 times the average spacing of the fractures.

[0040] The pre-defined range outside the tunnel outline refers to the rock mass area extending outward from the outer edge of the tunnel's designed cross-section. Specifically, this range can be defined using a three-dimensional coordinate system, within a space of 0.5 to 3 meters from the tunnel axis. This range covers the loosened zone area required for support. The average fracture spacing refers to the average distance between adjacent fracture surfaces calculated using a three-dimensional geomechanical model. This can be achieved by statistically sampling the fracture network in the model using spatial interpolation algorithms. The circumferential spacing refers to the arc length distance between the centerlines of adjacent pipe roofs along the tunnel circumference, which can be precisely determined using a total station measurement and positioning system.

[0041] More specifically, in the completed three-dimensional geomechanical model, the boundary of the tunnel excavation impact zone is first delineated, and the spatial coordinate data of all fracture surfaces within this zone are extracted. By calculating the spacing distribution after the normal direction of each fracture surface is projected onto the tunnel cross-section, a weighted average method is used to obtain the average fracture spacing value characterizing the degree of rock mass fracturing. Based on this value, the pipe roof layout scheme is dynamically adjusted. When the average fracture spacing is large, the upper limit value is used to form a sparse layout; when the fractures are densely developed, the lower limit value is used to form a dense layout, so that the support structure formed by the pipe roof can effectively cross the weak area between adjacent fractures.

[0042] Compared with existing technologies, traditional methods typically determine pipe roof layout based on empirical formulas or fixed spacing tables, without considering the spatial heterogeneity of actual geological conditions. This scheme achieves adaptive matching between support parameters and rock mass structure by directly linking pipe roof spacing with measured fracture characteristics, overcoming the problems of support blind spots or resource waste that may be caused by empirical methods.

[0043] Through the above technical solution, this application solves the defect of traditional support parameter determination methods lacking geological basis, enabling pipe roof layout to accurately adapt to rock mass conditions with different degrees of fracture development, while ensuring effective support coverage of fractured areas and optimizing material usage, thereby improving the safety and economy of the advanced support system.

[0044] In an embodiment of the present invention, the step of obtaining construction parameters based on the geological information further includes: Step S22: Obtain grouting parameters based on the geological information; the grouting parameters include grout mix ratio, which is composed of the following components in parts by mass: 100 parts cement, 15-25 parts silica fume, 35-45 parts water, 0.5-1.5 parts water-reducing agent, and 2-5 parts bentonite.

[0045] Cement refers to the basic component of the cementitious material, which forms a hardened body through a hydration reaction. Ordinary Portland cement can be used to achieve this, providing the basic strength of the grout. Silica powder refers to silica powder with a particle size in the micrometer range, which can be obtained through the recycling and processing of industrial by-products. It acts as an active admixture, filling the gaps between cement particles and improving the grout's fluidity and permeability. Water is the medium used to regulate the grout's fluidity. Drinking-grade water is used, and the water-cement ratio is controlled within the range of 35 to 45 parts per unit area to balance the grout's pumpability and hardened mechanical properties. Water-reducing agent refers to a surfactant-type chemical additive, specifically polycarboxylate-based polymers, which adsorb onto the surface of cement particles to form a dispersed structure, reducing the amount of mixing water and increasing the grout's density. Bentonite refers to a clay mineral with montmorillonite as its main component, specifically sodium-based bentonite. Its water absorption and swelling properties regulate the grout's viscosity, enhancing its retention capacity in fractured rock masses.

[0046] More specifically, during construction in fractured zones or areas with well-developed fissures, the penetration and diffusion radius of the grout is controlled by adjusting the amount of silica fume. When the rock mass permeability coefficient is high, an upper limit of 25 parts of silica fume is used to improve the grout fluidity. In loose sedimentary strata, the viscosity of the grout is increased by adding bentonite to 5 parts to prevent excessive grout loss. The amount of water-reducing agent is dynamically adjusted according to the formation water content, with a lower limit of 0.5 parts used in areas with high groundwater levels to avoid excessive dilution of the grout. The water-cement ratio is controlled according to the graded control of rock mass fissure opening. For millimeter-wide fissures, 45 parts of water are used to ensure sufficient grout filling, while 35 parts of water are used in micro-fissure areas to ensure grout consolidation strength.

[0047] Compared to existing technologies, traditional grouting materials use a fixed ratio of cement and water, making it impossible to adjust the component ratio according to geological conditions. Conventional grouts are prone to loss or insufficient penetration in fractured rock masses. This solution, however, utilizes the synergistic effect of silica fume and bentonite to ensure effective diffusion in highly permeable formations while maintaining appropriate viscosity in loose formations. Existing technologies use a fixed amount of a single water-reducing agent, resulting in rigid grout performance. This solution achieves precise matching of grout performance to formation conditions by dynamically adjusting the ratio of water-reducing agent to water.

[0048] Through the above technical solution, this application can precisely adjust the fluidity, setting time, and consolidation strength of the grout according to the degree of formation fracture development and rock mass permeability. It forms a fully permeable network reinforcement structure in rock masses with wide fractures, and achieves dense filling in areas with micro-fractures, avoiding material waste caused by ineffective grout diffusion. Through the synergistic effect between components, it ensures both the bond strength between the grout and the surrounding rock and controls the effective range of the grout under complex geological conditions, overcoming the technical shortcomings of traditional single-formulation grouting materials with poor adaptability.

[0049] In an embodiment of the present invention, the steps of drilling, installing pipe roofs, inserting and tensioning steel strands, and grouting into the surrounding rock to form a reinforced zone, according to the construction parameters, include: Step S31: Install a drilling guide frame at the tunnel face and use a total station to calibrate the design inclination and azimuth of each hole on the guide frame; Step S32: Drill a hole using a hydraulic rock drill under the guidance of a guide frame. During the process, monitor the drilling trajectory in real time to ensure that its deviation from the designed trajectory is less than 2% of the hole depth. Step S33: After connecting the pipe roof segments with threaded sleeves, insert them into the drill holes to ensure that the deviation between the pipe roof axis and the drill hole axis is less than 5mm. Step S34: Pass the steel strand through the inside of the installed pipe roof, fix its rear end to the stable rock mass behind it with anchors, connect the front end to the tensioning equipment, and apply a prestress of 0.6MPa to 0.8MPa to the steel strand. In step S35, the grout is injected into the surrounding rock through the grouting holes pre-embedded in the pipe roof using a CNC grouting pump. The grouting process adopts a pressure control mode, with an initial pressure of 0.3 MPa, which is then increased stepwise to 0.8 MPa at a rate of 0.1 MPa / min and stabilized for 10 minutes to form the reinforced zone.

[0050] Among them, the drilling guide frame refers to the support structure used to fix the drilling position, which can be implemented using a steel frame with adjustable clamps, and its function is to provide a spatial positioning reference for drilling operations. Total station calibration refers to determining the spatial coordinates of the hole position using optical measuring instruments, which can be implemented using a reflecting prism with an angle measuring module, and its function is to eliminate angle deviations caused by manual calibration. The hydraulic rock drilling rig refers to the mechanical equipment that drills using hydraulic power, which can be implemented using a multi-joint robotic arm with a drill rod propulsion system, and its function is to achieve high-precision drilling trajectory control. The threaded sleeve connection refers to the pipe connection method using internal and external threads, which can be implemented using precision-machined steel sleeves, and its function is to ensure the coaxiality between pipe roof segments. The steel strand tensioning equipment refers to the device used to apply prestress, which can be implemented using a hydraulic jack with a force sensor, and its function is to form an active support system. The CNC grouting pump refers to the equipment that controls the grouting pressure through a program, which can be implemented using a servo motor-driven plunger pump with a pressure feedback system, and its function is to achieve controllable grout diffusion range.

[0051] More specifically, the drilling guide frame provides a clear spatial reference for each drilling location, and the high-precision calibration of the total station eliminates the cumulative errors caused by traditional manual layout. The hydraulic rock drilling rig operates under the constraint of the guide frame, and with the help of a real-time trajectory monitoring system, it can promptly correct deviations in the drilling direction. Pipe roof segments are mechanically connected using threaded sleeves, which, compared to traditional welding, maintains connection strength while improving installation accuracy. After the steel strands pass through the pipe roof, they are anchored at the rear end to form a fixed support point, and the prestress applied by the front tensioning equipment is evenly distributed along the entire length of the steel strands. The CNC grouting pump performs grouting operations according to a preset pressure curve. The initial low-pressure stage achieves grout penetration and filling, the stepped pressure increase process promotes the diffusion of grout to more distant fractures, and the pressure stabilization stage ensures sufficient grout consolidation.

[0052] Compared with existing technologies, traditional methods rely on manual measurement for borehole positioning, leading to accumulated angle deviations; the drilling process lacks real-time trajectory monitoring, making it prone to offset; pipe roof connections use on-site welding, posing a risk of thermal deformation; steel strand tensioning is largely controlled by empirical values, resulting in uneven stress distribution; and grouting pressure control relies on manual adjustment, making it difficult to achieve precise pressure gradients. This solution integrates optical measurement, mechanical guidance, real-time monitoring, and automatic control technologies to construct a systematic construction accuracy assurance system.

[0053] Through the above technical solutions, this application effectively improves the accuracy of borehole positioning, ensures the coaxiality of pipe roof installation, achieves uniform distribution of prestress in steel strands, and optimizes the grouting pressure control process, thereby significantly improving the overall stability and bearing capacity of the reinforced area.

[0054] In an embodiment of the present invention, the grout is injected into the surrounding rock through grouting holes pre-embedded in the pipe roof using a CNC grouting pump. The grouting process adopts a pressure control mode, with an initial pressure of 0.3 MPa, followed by a stepwise increase to 0.8 MPa at a rate of 0.1 MPa / min, and then a pressure stabilization period of 10 minutes. After the step of forming the reinforced zone, the method of tunnel pre-support further includes: Step F10: When the grouting pressure reaches 0.8MPa and the grouting flow rate is less than 5L / min for 2 minutes during the pressure stabilization period, the grouting is terminated.

[0055] The grouting flow rate being less than 5 L / min for 2 minutes refers to the volume of grout injected into the rock mass continuously recorded per unit time using an electromagnetic flowmeter. This flow rate threshold reflects that the pores of the rock mass have reached saturation due to grout filling, which can be achieved using a flow monitoring device with time integration function. A flow rate decay to this level indicates that the fracture space has been fully filled.

[0056] More specifically, the grouting process begins with an initial pressure of 0.3 MPa to allow the grout to smoothly penetrate the surface fissures of the rock mass. As the grouting pressure is increased in steps from 0.1 MPa / min to 0.8 MPa, the grout gradually permeates into the deep fissure network under pressure. When the pressure stabilizes at 0.8 MPa, if the flow rate monitoring data shows that the grout injection rate is less than 5 L / min for two consecutive minutes, it indicates that the space within the rock mass is nearing saturation, and the grouting operation is immediately stopped. This control method objectively judges the completion of grout diffusion through the dynamic coupling relationship between pressure and flow rate.

[0057] Compared to existing technologies, traditional methods rely solely on the experience of construction personnel or a single pressure index to determine the grouting endpoint. This can easily lead to grouting being stopped before shallow fissures are completely filled, or excessive grouting causing grout to leak into non-target areas. This solution establishes a dual criterion of pressure gradient enhancement and flow rate attenuation monitoring, forming a quantifiable termination standard that effectively overcomes errors caused by subjective judgment.

[0058] Through the above technical solution, this application solves the technical problem of the difficulty in accurately controlling the termination time in traditional grouting processes, and realizes the uniform diffusion and effective filling of grout in fractured rock masses. This control method avoids insufficient reinforcement strength caused by premature grouting cessation, and also prevents material waste caused by excessive grouting, ensuring the formation of a dense load-bearing structure in the reinforced zone.

[0059] In an embodiment of the present invention, the steps of performing stability monitoring on the reinforced area and using the reinforced area as the tunnel pre-support include: Step S41: Strain sensors and displacement sensors are installed in the pipe roof and surrounding rock mass to collect stress and deformation data in real time. When the stress change rate exceeds 5 kPa / h or the displacement rate exceeds 2 mm / h, an early warning signal is issued to monitor the stability of the reinforced area. Step S42: Use the reinforced area as the tunnel pre-support.

[0060] Among them, strain sensors are devices used to measure stress changes within the pipe roof and rock mass, specifically fiber optic grating sensors or resistance strain gauges, which reflect the structural stress state by capturing micro-strain signals in real time. Displacement sensors are devices used to monitor rock mass deformation, specifically laser rangefinders or inductive displacement gauges, which assess the stability of the reinforced zone by continuously recording displacement data. Early warning signals are alarm commands triggered based on preset thresholds, which can be implemented through linkage between the data acquisition system and audible and visual alarm devices, automatically activating the early warning mechanism when monitored parameters exceed critical values.

[0061] More specifically, after the pipe roof is installed, strain sensors are installed at intervals along its axial direction, while displacement sensors are installed at key locations in the surrounding rock mass, forming a monitoring network covering the reinforced area. The stress and displacement data collected by the sensors are uploaded to the data processing center in real time via wired or wireless transmission. After filtering and normalization, the data is compared with preset thresholds. When the stress change rate exceeds 5 kPa / h, it indicates a risk of stress concentration or sudden load change within the rock mass; when the displacement rate exceeds 2 mm / h, it indicates plastic deformation or slippage instability in the rock mass. Once these two abnormal conditions trigger an early warning signal, construction personnel can immediately suspend excavation and take measures such as reinforcing grouting or adding supports to prevent support structure failure.

[0062] Compared to existing technologies, traditional methods rely on manual inspections and periodic measurements, which cannot achieve continuous monitoring and have a delayed response. This solution constructs a real-time feedback mechanism through a dual-parameter sensor network, combined with dynamic threshold early warning standards, which can accurately capture early mechanical anomalies in the support system. Compared to traditional single-point monitoring methods, it improves data coverage density and enhances monitoring timeliness, providing a quantitative basis for the stability assessment of the support structure.

[0063] Through the above technical solution, this application solves the problem of the lack of effective real-time monitoring methods after the traditional tunnel support is completed. By using automated data acquisition and intelligent early warning mechanisms, it significantly improves the efficiency of identifying abnormal states of the support structure, reduces the risk of tunnel collapse caused by stress mutation or deformation accumulation, and ensures the safety of the construction process.

[0064] In an embodiment of the present invention, prior to the step of using the reinforced zone as the tunnel pre-support, the method for tunnel pre-support further includes: Step P10: After crushing and screening the excavated soil generated during tunnel excavation to a particle size of less than 50mm, it is backfilled into the stable space formed by the reinforced area to balance the ground pressure or serve as the foundation for subsequent construction platforms.

[0065] Crushing and screening to a particle size of less than 50 mm refers to controlling the particle size of the slag and soil within a specific range through mechanical crushing and grading processes. This can be achieved by using a jaw crusher and a vibrating screen in combination. This particle size range ensures that the backfill material has a uniform gradation distribution, avoiding excessive porosity in the backfill body due to excessively large aggregate particle size. Backfilling into the stable space formed by the reinforcement zone refers to transporting the treated slag and soil to the surrounding rock area surrounded by the reinforcement structure formed by pipe roof grouting. This can be achieved by using a belt conveyor in conjunction with a directional material placing device. The structural stability formed by the advanced support in this space provides a reliable bearing environment for the slag and soil backfill.

[0066] More specifically, the excavated soil generated during tunnel excavation is crushed and screened to form recycled aggregate with controllable particle size. This recycled aggregate is then injected into the enclosed space formed by the reinforced zone using a directional backfilling process. Under its own weight, the backfill generates a uniform compressive stress distribution, forming a mechanical coupling with the surrounding rock of the reinforced zone, effectively counteracting the deformation trend caused by the release of the original ground stress. Simultaneously, the compacted surface of the backfill can serve as a working platform for construction machinery, and its load-bearing capacity is ensured through aggregate gradation optimization and layered compaction. This technical solution achieves the dual goals of ground pressure control and construction resource integration through material recycling.

[0067] Compared to existing technologies, traditional methods typically involve transporting excavated soil off-site for disposal, which not only increases transportation costs but also leads to the risk of subsidence in the surrounding strata due to stress redistribution. This solution, however, eliminates the environmental pressure caused by excavated soil accumulation by backfilling in situ, actively regulates the stress state of the strata using the mechanical properties of the backfill, and provides a stable working surface foundation for subsequent construction processes.

[0068] Through the above technical solutions, this application effectively solves the problem of ground pressure imbalance caused by improper disposal of excavated soil during tunnel construction. By controlling particle size and using directional backfilling technology, the resource utilization of excavated soil is realized, which reduces the turnover cost of construction materials while maintaining the stability of the surrounding rock, and provides a reliable working platform support for continuous tunnel excavation.

[0069] In an embodiment of the present invention, the grout is injected into the surrounding rock through grouting holes pre-embedded in the pipe roof using a CNC grouting pump. The grouting process adopts a pressure control mode, with an initial pressure of 0.3 MPa, followed by a stepwise increase to 0.8 MPa at a rate of 0.1 MPa / min, and then a pressure stabilization period of 10 minutes. Before the step of forming the reinforced zone, the method of tunnel pre-support further includes: Step E10: Add 1% to 3% of a quick-setting agent by mass of cement to the slurry.

[0070] The accelerator is a chemical additive that accelerates the hydration reaction of cement. Specifically, it can be achieved by mixing sodium aluminate and calcium hydroxide in a 2:1 mass ratio. This ratio, through the synergistic reaction of aluminate and calcium ions, forms a stable crystalline network structure in the grout. The addition range of 1% to 3% of the cement mass refers to the mass ratio of the accelerator to the cement. This ratio, determined through experimental verification, ensures sufficient penetration time of the grout in the cracks while preventing blockage of the grouting pipes due to premature solidification.

[0071] More specifically, during the grouting process, sodium aluminate and calcium hydroxide react in a hydration environment to form ettringite crystals. These crystals form a three-dimensional network structure within the grout, causing the grout viscosity to exhibit a gradient increase characteristic. In the initial grouting stage, the grout maintains a low viscosity to fully penetrate the rock fractures; as time progresses, the crystal network gradually densifies, the grout viscosity increases, and it eventually solidifies. By controlling the proportion of the quick-setting agent, a dynamic balance is achieved between the grout's penetration depth and solidification time in the fractured rock mass. This avoids excessive grout loss due to highly permeable rock masses and prevents grouting interruptions caused by excessively rapid solidification.

[0072] In some specific embodiments, the preparation process of the quick-setting agent includes mixing sodium aluminate powder and calcium hydroxide powder evenly in a dry environment, and then controlling the particle size by using an air jet mill to ensure that the powder particle size is less than 50 micrometers in order to improve the reactivity.

[0073] Compared to existing technologies, traditional methods typically employ single-component accelerators or fixed-ratio systems, making it difficult to adapt to grouting requirements under varying geological conditions. For example, conventional aluminate accelerators tend to cause premature grout solidification in fractured rock masses, while simply adding retarder components reduces reinforcement strength. This solution achieves dynamic adjustment of grout rheological properties through the synergistic chemical effect of a compound system, overcoming the contradiction between permeability and setting rate inherent in traditional materials.

[0074] Through the above technical solution, this application effectively solves the problems of easy loss of grout and uncontrollable solidification in highly permeable fractured rock masses, enabling the grout to quickly form a reinforced structure with load-bearing capacity after fully filling the rock mass fissures, and significantly improving the overall stability of the advanced support system.

[0075] In an embodiment of the present invention, the quick-setting agent is a powder of sodium aluminate and calcium hydroxide compounded in a mass ratio of 2:1.

[0076] Sodium aluminate is a sodium salt compound containing aluminate ions, specifically produced using industrial-grade sodium aluminate powder. It reacts with cement hydration products to form ettringite crystals, accelerating slurry setting. Calcium hydroxide is an alkaline inorganic compound, specifically produced using slaked lime powder. It promotes the dissolution of sodium aluminate by adjusting the slurry's pH, while simultaneously activating the active components of silica fume to participate in the secondary hydration reaction. The 2:1 mass ratio refers to the feed ratio of sodium aluminate to calcium hydroxide, achieved through precise weighing and mechanical mixing of the two powders. This ratio ensures a synergistic effect between the setting accelerator and the alkaline activator, preventing excessive calcium hydroxide from causing slurry expansion and cracking.

[0077] More specifically, sodium aluminate powder and calcium hydroxide powder are mixed in a predetermined ratio and then uniformly incorporated into the cement-based grouting material. Sodium aluminate rapidly releases aluminate ions upon contact with water, reacting with calcium ions in the cement to form needle-like ettringite crystals, creating an early-strength framework. The dissolution of calcium hydroxide increases the alkaline environment of the grout, promoting the complete dissolution of sodium aluminate and accelerating the reaction of active silica in the silica fume with calcium hydroxide to form hydrated calcium silicate gel. When the two components are mixed in a 2:1 ratio, the setting-accelerating effect of sodium aluminate and the alkaline activating effect of calcium hydroxide are balanced, avoiding both excessively short setting time due to the use of sodium aluminate alone and grout volume instability caused by excessive calcium hydroxide. The powdered form allows the accelerator to be uniformly dispersed during the dry mixing stage, ensuring that all reactions occur simultaneously during the grouting process.

[0078] Compared to existing technologies, traditional accelerators often use single-component or fixed-ratio composite formulations, making it impossible to adjust the reaction rate according to geological conditions. However, the dynamic blending of sodium aluminate and calcium hydroxide allows for adjustment of the grout setting gradient based on differences in rock permeability. Compared to accelerator systems using only sodium aluminate, this approach extends the pumpable time of the grout through the alkaline activation effect of calcium hydroxide; and compared to conventional calcium-based accelerators, the high reactivity of sodium aluminate enables the grout to rapidly form an erosion-resistant structure within fractured rock masses.

[0079] Through the above technical solution, this application solves the problem of easy grout loss in high-permeability formations using traditional grouting materials. The gradient coagulation characteristics formed by the synergistic effect of sodium aluminate and calcium hydroxide allow the grout to preferentially coagulate within the permeability channels, forming a flow barrier. Subsequent grout injection continuously fills the fine fractures behind the barrier. The composite structure of ettringite crystals and hydrated calcium silicate gel enhances the impermeability and mechanical strength of the reinforced body, effectively meeting the reinforcement needs of rock masses with different degrees of fracture development.

[0080] For ease of understanding, another specific implementation method is shown here: In another section of the tunnel with abundant water and soft rock, groundwater is plentiful. To prevent the grout from being diluted and washed away by the water, a fast-setting grout must be used.

[0081] When determining the slurry mix ratio, an additional 2% quick-setting agent was added based on the above formula, which was made by dry mixing sodium aluminate powder and calcium hydroxide powder on site at a mass ratio of 2:1.

[0082] In the grouting process, the grout is thoroughly mixed in a mixer and then rapidly injected through a grouting pump. Due to the addition of a quick-setting agent, the initial setting time of the grout is controlled to approximately 12 minutes through testing. This allows the grout to solidify rapidly after being injected into rock fissures, effectively resisting groundwater erosion and ensuring the grouting consolidation effect in water-rich strata. Other grouting parameters and process controls are the same as in the above embodiments.

[0083] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. A method for advance support of tunnels, characterized in that, The method of tunnel pre-support includes: Identify the distribution of fractures, the location and scale of fracture zones in the tunnel rock mass, and obtain geological information of the rock mass in front of the tunnel face; Based on the geological information, construction parameters are obtained; According to the construction parameters, drilling, pipe roof installation, steel strand insertion and tensioning, and grouting into the surrounding rock are carried out to form a reinforced zone; The stability of the reinforced area is monitored, and the reinforced area is used as the advance support for the tunnel.

2. The method for tunnel pre-support as described in claim 1, characterized in that, The steps for identifying the distribution of fractures, the location and scale of fracture zones in the tunnel rock mass, and obtaining geological information of the rock mass in front of the tunnel face include: The geological radar was used to scan along the tunnel excavation axis to obtain the dielectric constant distribution information of the tunnel rock mass and to preliminarily delineate the geological anomaly zone. In the geologically anomalous area, a multibeam ultrasonic detector is used for cross-detection to obtain wave velocity field and attenuation coefficient field data in the tunnel rock mass; Based on the dielectric constant distribution information of the tunnel rock mass and the wave velocity field and attenuation coefficient field data in the tunnel rock mass, a three-dimensional geomechanical model including fracture orientation, fracture zone boundary and rock mass strength index is constructed to obtain the geological information of the rock mass in front of the tunnel face.

3. The method for tunnel pre-support as described in claim 2, characterized in that, The steps for obtaining construction parameters based on the geological information include: The average spacing of fractures in the rock mass within a preset range outside the tunnel outline is extracted from the three-dimensional geomechanical model, and the circumferential spacing of the pipe roof is set to 0.8 to 1.2 times the average spacing of the fractures.

4. The method for tunnel pre-support as described in claim 3, characterized in that, The steps for obtaining construction parameters based on the geological information also include: Based on the geological information, grouting parameters are obtained; the grouting parameters include the grout mix ratio, which is composed of the following components in parts by mass: 100 parts cement, 15-25 parts silica fume, 35-45 parts water, 0.5-1.5 parts water-reducing agent, and 2-5 parts bentonite.

5. The method for tunnel pre-support as described in claim 4, characterized in that, The steps for forming the reinforced zone, based on the aforementioned construction parameters, include drilling, installing the pipe roof, threading and tensioning the steel strands, and grouting the surrounding rock. A drilling guide frame is erected at the tunnel face, and a total station is used to calibrate the design inclination and azimuth of each hole on the guide frame; A hydraulic rock drilling rig is used to drill holes under the guidance of a guide frame. The drilling trajectory is monitored in real time during the process to ensure that the deviation from the design trajectory is less than 2% of the hole depth. After connecting the pipe roof segments with threaded sleeves, insert them into the drill holes to ensure that the deviation between the pipe roof axis and the drill hole axis is less than 5mm. The steel strand is passed through the inside of the installed pipe roof, and its rear end is fixed to the stable rock mass behind it by anchors. The front end is connected to the tensioning equipment to apply a prestress of 0.6MPa to 0.8MPa to the steel strand. The grout is injected into the surrounding rock through the grouting holes pre-embedded in the pipe roof using a CNC grouting pump. The grouting process adopts a pressure control mode, with an initial pressure of 0.3 MPa, which is then increased stepwise to 0.8 MPa at a rate of 0.1 MPa / min and stabilized for 10 minutes to form the reinforced zone.

6. The method for tunnel pre-support as described in claim 5, characterized in that, The grout is injected into the surrounding rock through grouting holes pre-embedded in the pipe roof using a CNC grouting pump. The grouting process adopts a pressure control mode, with an initial pressure of 0.3 MPa, followed by a stepwise increase to 0.8 MPa at a rate of 0.1 MPa / min, and then a pressure stabilization period of 10 minutes. After forming the reinforced zone, the method of tunnel pre-support further includes: Grouting is terminated when the grouting pressure reaches 0.8 MPa and the grouting flow rate remains less than 5 L / min for 2 minutes during the pressure stabilization period.

7. The method for tunnel pre-support as described in claim 6, characterized in that, The steps of conducting stability monitoring on the reinforced area and using the reinforced area as the tunnel pre-support include: Strain sensors and displacement sensors are embedded in the pipe roof and surrounding rock mass to collect stress and deformation data in real time. When the stress change rate exceeds 5 kPa / h or the displacement rate exceeds 2 mm / h, an early warning signal is issued to monitor the stability of the reinforced area. The reinforced area is used as the advance support for the tunnel.

8. The method for tunnel pre-support as described in claim 7, characterized in that, Before using the reinforced zone as the step of tunnel pre-support, the tunnel pre-support method further includes: Some of the excavated soil generated during tunnel excavation is crushed and screened to a particle size of less than 50mm, and then backfilled into the stable space formed by the reinforced area to balance the ground pressure or serve as the foundation for subsequent construction platforms.

9. The method for tunnel pre-support as described in claim 6, characterized in that, The grout is injected into the surrounding rock through grouting holes pre-embedded in the pipe roof using a CNC grouting pump. The grouting process adopts a pressure control mode, with an initial pressure of 0.3 MPa, followed by a stepwise increase to 0.8 MPa at a rate of 0.1 MPa / min, and then a pressure stabilization period of 10 minutes. Before the step of forming the reinforced zone, the method of tunnel pre-support also includes: Add 1% to 3% of a quick-setting agent by mass of cement to the slurry.

10. The method for tunnel pre-support as described in claim 9, characterized in that, The quick-setting agent is a powder made by compounding sodium aluminate and calcium hydroxide in a mass ratio of 2:1.

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