Gas tunnel grading fortification and comprehensive guarantee method

Abstract

The invention belongs to the technical field of tunnel and underground engineering construction safety protection, and discloses a gas tunnel grading fortification and comprehensive guarantee method which comprises the steps that gas content w, gas pressure P, surrounding rock gas permeability and geological stress data are collected before construction; establishing a grading rule according to the parameters and generating a risk partition map in combination with the tunnel section, wherein the map is updated once every 50-100m along with construction; in the construction stage, elimination-rotation-release-sealing fortification is carried out according to subareas, pre-pumping, channel guiding and discharging, three-level ventilation and composite seepage prevention and grouting isolation are carried out in a high-risk area, and spraying and grouting with different thicknesses are adopted in a medium-risk area and a low-risk area respectively; setting multiple parameter thresholds of concentration, flow and pressure in coal uncovering operation, and triggering emergency ventilation, extraction and plugging; in the operation stage, a double-layer anti-seepage system composed of a PVC coiled material and a grouting isolation belt is constructed, and grout is supplemented regularly; data are obtained through a monitoring system composed of a gas sensor, a stress meter and a displacement meter.

Description

Technical Field

[0001] This invention belongs to the field of tunnel and underground engineering construction safety protection technology, specifically a method for graded protection and comprehensive protection of gas tunnels. Background Technology

[0002] Gas hazards are a key factor restricting the safe construction and long-term operation of long tunnels. In current engineering practice, gas content and pressure are usually measured by drilling and sampling, and risk zoning is made in combination with local experience. However, such judgments often remain at a static stage and cannot reflect the dynamic changes in gas occurrence conditions during tunnel excavation due to the permeability of the surrounding rock and the evolution of ground stress. Once the risk zoning does not match the site conditions, it is easy to cause the anti-outburst measures to lag behind, resulting in serious safety hazards. As railway, highway and urban rail transit tunnels continue to extend into deeper and more complex strata, the above problems become more prominent when some sections pass through coal-bearing strata or gas-rich zones. The superposition of transportation functions and gas control needs further increases the safety risks.

[0003] In the construction prevention and control phase, existing methods often employ single approaches, such as pre-extraction of gas or simple ventilation and dilution. Different risk areas are often not differentiated, resulting in insufficient measures in high-risk areas and waste of resources in medium- and low-risk areas. At the same time, although some projects have attempted to combine extraction and grouting, they lack a systematic coordinated path of gas outburst suppression, drainage, ventilation, and sealing, making it difficult to form a closed prevention and control chain. Especially in high-risk areas, single measures are often insufficient to effectively block gas outbursts. For traffic tunnels, the construction organization is often more complex, and the ventilation system needs to take into account both personnel operations and equipment operating environment. If prevention and control measures are insufficient, it can easily affect the progress of the project and the realization of traffic functions.

[0004] During coal uncovering operations, existing safety control measures typically rely on single-parameter early warning of gas concentration. When gas flow or pressure rises rapidly but the concentration has not yet exceeded the standard, the early warning system may not be able to respond in time, resulting in untimely handling of abnormal gas surges. At the same time, there is a lack of linkage control between emergency ventilation, extraction, and sealing, making it difficult to guarantee response time and creating serious safety blind spots. If such a situation occurs in a traffic tunnel, it will directly threaten tunnel traffic safety and emergency evacuation conditions.

[0005] During the tunnel operation phase, most current solutions rely solely on the surrounding rock isolation layer formed by one-time grouting during construction. The lack of subsequent maintenance and reinforcement makes it difficult to maintain a long-term sealing effect. The inner lining often lacks a dedicated anti-seepage structure, allowing gas to slowly infiltrate during operation. Furthermore, existing monitoring systems typically only include gas sensors, paying insufficient attention to surrounding rock stress and lining deformation. This fails to reveal the risk evolution patterns under multi-factor coupling and lacks a mechanism for automatically adjusting ventilation volume and extraction load based on monitoring data. The lack of seamless control between the construction and operation phases not only affects structural safety for long-term traffic tunnel operation but may also lead to increased ventilation energy consumption and a deterioration of the traffic environment, highlighting the necessity of integrated safety control technology for both traffic and gas tunnels. Summary of the Invention

[0006] The purpose of this invention is to provide a method for graded defense and comprehensive protection of gas tunnels, so as to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for graded defense and comprehensive protection of gas tunnels, the specific steps of which are as follows: Risk parameter collection: Before tunnel construction, gas content w (unit m³ / t), gas pressure P (unit MPa), surrounding rock permeability coefficient, and real-time geological stress data along the route are collected as input parameters for risk assessment. Graded and zoned risk assessment: A graded and zoned risk assessment method is established based on the input parameters. When w < 2.0 m³ / t and P < 0.2 MPa, it is classified as a low-risk zone; when w ≥ 2.0 m³ / t and 0.2 ≤ P < 0.74, it is classified as a medium-risk zone; and when P ≥ 0.74 MPa, it is classified as a high-risk zone. A dynamically updated risk zoning map is constructed by combining the geological characteristics of the tunnel's longitudinal profile and cross section. The map is updated every 50–100 m as the construction progresses and is used to guide the fortification measures for each risk zone. Construction Phase Defense Measures: During the construction phase, based on the aforementioned risk zoning map, a coordinated defense measure of elimination-conversion-release-sealing will be implemented. Specifically: In high-risk areas, pre-drainage and proactive gas suppression will be implemented (pre-drainage time not less than 72 hours, drainage rate not less than 30%), drainage channels with a diameter not less than 300 mm will be set up, and a three-level ventilation system consisting of main ventilation, local ventilation, and emergency ventilation will be adopted, maintaining a pressure difference of 50–100 Pa. At the same time, an epoxy resin-based composite seepage barrier layer with a thickness of not less than 50 mm and an isolation ring with a grouting pressure of 0.8–1.2 MPa will be formed. In medium-risk areas, a polyurea spray coating with a thickness of 20–30 mm will be used, and grouting at normal pressure with a grouting pressure of 0.4–0.6 MPa will be applied. In low-risk areas, a single-layer polyurethane spray seepage barrier coating with a thickness of 10–15 mm will be used. Coal uncovering safety control: During coal uncovering operations, multiple parameter early warning thresholds are set. These thresholds include a gas concentration greater than or equal to 1.5%, a gas flow rate greater than or equal to 6 m³ / min, or a gas pressure greater than or equal to 0.74 MPa. When any threshold is triggered, the system automatically switches to emergency ventilation mode within 30 seconds and increases the air volume to 1.5 times the normal operating condition. At the same time, regional extraction and local sealing measures are activated within 5 minutes. The negative pressure of the extraction pump is not less than 15 kPa, and the sealing material is a quick-setting cement-based slurry. During the operation phase, a double-layer seepage prevention system is constructed, consisting of a PVC waterproof membrane (thickness not less than 1.5mm) for the inner wall of the tunnel lining and a grouting isolation strip for the surrounding rock. The membrane and the isolation strip are connected by a pre-embedded grouting pipe, and grouting is supplemented once every two years during the operation period through the grouting pipe to maintain a long-term sealing effect. Three-element coupling monitoring: A three-element coupling monitoring system is established, consisting of a gas sensor (sampling frequency not less than 1 time / minute), a surrounding rock stress gauge (measurement range 0–50MPa), and a lining displacement gauge (accuracy ±0.1mm). The sensors are deployed in groups every 30–50m along the longitudinal direction of the tunnel to collect real-time data on gas concentration, surrounding rock stress, and lining deformation. Dynamic control execution: The monitoring data is input into the dynamic control algorithm. The algorithm calculates the target ventilation volume allocation ratio and the operating load of the extraction pump based on the coupled model of "gas concentration-ventilation volume-surrounding rock permeability", and outputs control commands to drive the ventilation unit, extraction pump and anti-seepage grouting device, thereby forming an integrated closed-loop control in the construction and operation stages.

[0008] Preferably, the specific steps for collecting the risk parameters are as follows: Before tunnel construction, it is necessary to collect system parameters for the target section; First, the gas content w (unit: m³ / t) of the coal and rock mass is obtained by means of drilling sampling and gas desorption. At the same time, the gas pressure P (unit: MPa) of the coal and rock mass is measured by a gas pressure gauge, and the permeability coefficient k (unit: m²) of the surrounding rock is obtained by gas permeability testing. These parameters directly reflect the gas occurrence conditions of the coal and rock mass. While collecting gas parameters and surrounding rock permeability coefficients, geological stress monitoring points are set up, and stress gauges are used to record geological stress data σ (unit: MPa) at different depths along the tunnel axis, forming a monitoring curve that is dynamically updated as construction progresses. The w, P, k and σ data together serve as input parameters for risk classification, ensuring that the zoning evaluation results are supported by objective data.

[0009] Preferably, the specific steps of the hierarchical and zoning risk assessment are as follows: Based on the input parameters, risk classification rules are established. When the gas content w in the coal and rock mass is less than 2.0 m³ / t and the gas pressure P is less than 0.2 MPa, the corresponding section is classified as a low-risk zone; when the gas content w is greater than or equal to 2.0 m³ / t and the gas pressure P is in the range of 0.2–0.74 MPa, the corresponding section is classified as a medium-risk zone; when the gas pressure P is greater than or equal to 0.74 MPa, the corresponding section is classified as a high-risk zone. Risk grading is based on quantitative rules established from input parameters: ; In the formula: Indicates the risk level; It is a low-risk area; It is a medium-risk area; It is a high-risk area; This formula establishes a judgment standard based on gas content and gas pressure, which is different from the existing grading model that relies on experience. The risk level results are combined with the longitudinal profile and cross-sectional geological structure of the tunnel to generate a two-dimensional or three-dimensional risk zoning map. This map is updated every 50–100m as the construction progresses. The update is based on newly measured w, P, and σ data and recalculated to ensure that the zoning is consistent with the geological conditions. The updated map is used to accurately guide the fortification measures of each section, rather than being specified based on experience, which is different from the existing static zoning scheme.

[0010] Preferably, the specific steps for setting up fortification during the construction phase are as follows: During the construction phase, based on the aforementioned risk zoning map, pre-drainage and advanced gas suppression operations are carried out sequentially in high-risk areas. The pre-drainage time is no less than 72 hours and the extraction rate is no less than 30%. At the same time, a drainage channel with a diameter of no less than 300mm is set up, and a three-level ventilation system consisting of main ventilation, local ventilation and emergency ventilation is adopted to keep the pressure difference between the inside and outside of the tunnel within the range of 50-100Pa. This measure ensures that the gas is fully extracted and dispersed before coal seam exposure and excavation. During construction in high-risk areas, an epoxy resin-based composite anti-seepage layer with a thickness of not less than 50 mm needs to be formed on the inner wall of the lining. This layer is made of resin and non-woven fabric composite, and a grouting isolation ring is established in the surrounding rock with a grouting pressure of 0.8–1.2 MPa. In medium-risk areas, a 20–30 mm polyurea spray coating and 0.4–0.6 MPa atmospheric pressure grouting are used. Low-risk areas are treated with a 10–15 mm single-layer polyurethane spray. Different risk areas require different prevention and control measures to avoid the shortcomings of traditional one-size-fits-all or single sampling methods.

[0011] Preferably, the specific steps of the coal uncovering safety control are as follows: During coal uncovering operations, multiple parameter early warning thresholds are set, including: gas concentration C ≥ 1.5%, gas flow rate Q ≥ 6 m³ / min, or gas pressure P ≥ 0.74 MPa. The logical formula is as follows: ; when When this happens, emergency control is triggered, which avoids delays or misjudgments caused by single-parameter triggering; When the monitoring data reaches any threshold, the control program is triggered to switch to emergency ventilation mode within 30 seconds, increasing the air volume to 1.5 times that of normal operating conditions; and regional extraction and local sealing are initiated within 5 minutes. The linkage control between emergency ventilation and extraction / sealing is implemented by an embedded PLC control system, which includes: Monitoring unit: Gas concentration, gas flow and gas pressure sensors, sampling period ≤1s; Control unit: PLC controller and its I / O modules, with built-in time logic and threshold determination program; Communication unit: Connected to the ventilation fan frequency converter, extraction pump control cabinet and grouting actuator via RS-485 or CAN bus; Execution units: main ventilation fan, local ventilation fan, extraction pump, and quick-setting cement-based grouting pump; when any parameter is detected to reach the warning threshold, the PLC automatically sends a three-level control signal: Within 0–5 seconds, the frequency converter of the ventilation fan is triggered to increase the frequency, so that the air volume is increased to 1.5 times the normal operating condition within 30 seconds, thus achieving emergency ventilation; Simultaneously, the extraction command is issued, and the extraction pump starts within 15 seconds and establishes a negative pressure of ≥15kPa to achieve continuous extraction; The system starts the grouting control module via bus, and starts the quick-setting cement-based grouting pump within 300s (5 minutes) to inject grout into the preset sealing channel to achieve local sealing; The signal transmission delay between units is less than 200ms. The entire response process is automatically completed under the time logic control of PLC, forming an integrated linkage control chain of emergency ventilation-extraction-blocking. The extraction pump operates under a negative pressure of ≥15kPa. The sealing is done with a fast-setting cement-based grout, which is injected into the coal and rock fissures and drainage structure by the grouting pump and hardens rapidly to form a sealing layer. Unlike existing measures that rely solely on alarms and shutdowns, this method uses parameterized linkage to create an automatic response mechanism.

[0012] Preferably, the specific steps for seepage prevention during the operation phase are as follows: During the tunnel operation phase, a polyvinyl chloride (PVC) waterproof membrane is laid on the inner wall of the lining. The membrane is at least 1.5 mm thick and is ensured to be tightly bonded to the lining surface during installation. The membrane serves as an inner structural layer fixed to the lining surface, forming a continuous impermeable inner layer that isolates external moisture and gas from seeping into the tunnel. A grouting isolation zone is set between the surrounding rock and the lining, and the isolation zone is connected to the waterproof membrane layer through a pre-embedded grouting pipe; Every two years during the operation period, grout is injected into the isolation zone through grouting pipes. The grouting material seeps in along the existing channels and gradually forms a new sealing ring. This double-layer seepage prevention system ensures the continuity of seepage prevention from construction to operation, rather than relying solely on grouting during the construction period as is the case with the existing system.

[0013] Preferably, the specific steps of the ternary coupling monitoring are as follows: The monitoring system established inside the tunnel consists of three types of sensors; Gas sensor (sampling frequency ≥ 1 time / minute, monitoring concentration C); Surrounding rock stress gauge (range 0–50 MPa, monitoring stress σ); Lining displacement gauge (accuracy ±0.1mm, monitoring displacement Δu); Various sensors are deployed along the longitudinal direction of the tunnel at intervals of 30–50m. Each group includes a gas sensor, a stress gauge, and a displacement gauge. Each monitoring unit operates continuously after deployment to collect data on gas concentration, surrounding rock stress, and lining displacement. The collected data is then used as ternary coupled monitoring data for subsequent control. Unlike existing solutions that only deploy gas sensors, this solution provides a three-element coupled input, which more comprehensively reflects the tunnel's condition.

[0014] Preferably, the specific steps for performing the dynamic control are as follows: The monitoring data collected by the gas sensor, the surrounding rock stress gauge and the lining displacement gauge are input into the dynamic control algorithm. The algorithm is based on the coupling relationship model of gas concentration-ventilation volume-surrounding rock permeability. The calculation results of the algorithm include the target ventilation volume allocation ratio of various ventilation systems and the operating load parameters required by the extraction pump, wherein the operating load parameters include negative pressure value and flow rate value. The monitoring data is input into the control algorithm to establish the following model: ; In the formula: Target ventilation volume allocation (m³ / min); Pump load; Gas concentration; Surrounding rock stress; Lining displacement; Surrounding rock permeability (m²); Gas dynamic viscosity (Pa) s) Empirical coefficients are derived from regression fitting based on historical monitoring data. Based on the calculation results, corresponding control commands are generated. These commands are used to drive the ventilation units, extraction pumps, and anti-seepage grouting devices within the tunnel. The ventilation units then... Adjust the air volume ratio of main ventilation, local ventilation, and emergency ventilation; the extraction pump should be adjusted accordingly. Adjust the operating negative pressure and extraction flow rate; the anti-seepage grouting device executes grouting operations according to instructions to maintain continuous control measures during the construction and operation phases; This creates a closed-loop control system during the construction and operation phases, eliminating reliance on manual experience or single alarms.

[0015] The beneficial effects of this invention are as follows: 1. This invention establishes quantitative risk classification rules by collecting gas content, gas pressure, surrounding rock permeability, and ground stress parameters before construction, and generates dynamically updated zoning maps based on tunnel longitudinal and transverse profiles. This solves the problem of existing technologies relying solely on static data and experience for zoning, which cannot reflect the evolution of risks during construction. The zoning map is automatically updated every 50–100 meters, enabling accurate identification of different risk sections and providing precise basis for subsequent defense measures. This dynamic zoning mechanism achieves synchronous matching between risk identification and construction progress, effectively improving the scientific nature and pertinence of graded prevention and control.

[0016] 2. This invention proposes a coordinated defense path of gas extraction, conversion, release, and sealing. In high-risk areas, a combination of pre-extraction, proactive gas outburst mitigation, drainage channels, and multi-stage ventilation, along with a composite impermeable layer and grouting isolation ring, achieves systematic control of high-risk areas. In medium- and low-risk areas, differentiated spraying and grouting measures are implemented. Compared with traditional single ventilation or extraction methods, this coordinated approach organically combines gas extraction, drainage, dilution, and sealing to form a closed prevention and control chain. This effectively solves the technical problems of convergent defense measures and unreasonable resource allocation in different risk areas, thereby ensuring the continuity and integrity of the prevention and control system.

[0017] 3. This invention constructs a multi-parameter early warning and double-layer seepage prevention system, and combines a ternary coupled monitoring and dynamic control algorithm to achieve closed-loop control during the construction and operation phases. When any indicator of gas concentration, flow rate, or pressure exceeds the limit, the system triggers emergency ventilation within 30 seconds and coordinates extraction and sealing within 5 minutes, overcoming the problems of existing systems that rely on single concentration early warning and have delayed response. At the same time, during the operation phase, the double-layer structure of PVC roll material and grouting isolation strip and periodic grouting maintain long-term seepage prevention and sealing. The monitoring system collects three types of data: gas concentration, stress, and lining displacement, and outputs control commands through the coupled algorithm, achieving integrated safety assurance during the construction and operation phases. Attached Figure Description

[0018] Figure 1 This is a flowchart of the gas tunnel graded defense and comprehensive protection method of the present invention. 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] like Figure 1 As shown in the figure, this invention provides a method for graded defense and comprehensive protection of gas tunnels. The specific steps of this method are as follows: Risk parameter collection: Before tunnel construction, gas content w (unit m³ / t), gas pressure P (unit MPa), surrounding rock permeability coefficient, and real-time geological stress data along the route are collected as input parameters for risk assessment. Graded and zoned risk assessment: A graded and zoned risk assessment method is established based on the input parameters. When w < 2.0 and P < 0.2, it is classified as a low-risk zone; when w ≥ 2.0 and 0.2 ≤ P < 0.74, it is classified as a medium-risk zone; and when P ≥ 0.74, it is classified as a high-risk zone. A dynamically updated risk zoning map is constructed by combining the geological characteristics of the tunnel's longitudinal profile and cross section. The map is updated every 50–100m as the construction progresses and is used to guide the fortification measures for each risk zone. Construction Phase Defense Measures: During the construction phase, based on the risk zoning map, a coordinated defense measure of elimination-conversion-release-sealing will be implemented. Specifically: In high-risk areas, pre-drainage and proactive gas suppression will be implemented (pre-drainage time not less than 72 hours, drainage rate not less than 30%), drainage channels with a diameter not less than 300mm will be set up, and a three-level ventilation system consisting of main ventilation, local ventilation and emergency ventilation will be adopted, maintaining a pressure difference of 50–100Pa. At the same time, an epoxy resin-based composite seepage barrier layer with a thickness of not less than 50mm and an isolation ring with a grouting pressure of 0.8–1.2MPa will be formed. In medium-risk areas, a polyurea spray coating with a thickness of 20–30mm will be used and grouting at normal pressure with a grouting pressure of 0.4–0.6MPa will be used. In low-risk areas, a single-layer polyurethane spray seepage barrier coating with a thickness of 10–15mm will be used. Coal uncovering safety control: During coal uncovering operations, multiple parameter early warning thresholds are set. The thresholds include a gas concentration greater than or equal to 1.5%, a gas flow rate greater than or equal to 6 m³ / min, or a gas pressure greater than or equal to 0.74 MPa. When any threshold is triggered, the system will automatically switch to emergency ventilation mode within 30 seconds and increase the air volume to 1.5 times the normal operating condition. At the same time, regional extraction and local sealing measures will be activated within 5 minutes. The negative pressure of the extraction pump will not be less than 15 kPa, and the sealing material will be a quick-setting cement-based slurry. During the operation phase, a double-layer seepage prevention system is constructed, consisting of a PVC waterproof membrane (with a thickness of not less than 1.5 mm) for the inner wall of the tunnel lining and a grouting isolation strip for the surrounding rock. The membrane and the isolation strip are connected by a pre-embedded grouting pipe, and grouting is supplemented once every two years during the operation period through the grouting pipe to maintain a long-term sealing effect. Three-element coupled monitoring: A three-element coupled monitoring system is established, consisting of a gas sensor (sampling frequency not less than 1 time / minute), a surrounding rock stress gauge (measurement range 0–50MPa), and a lining displacement gauge (accuracy ±0.1mm). A set of sensors is deployed every 30–50m along the longitudinal direction of the tunnel to collect real-time data on gas concentration, surrounding rock stress, and lining deformation. Dynamic control execution: The monitoring data is input into the dynamic control algorithm. The algorithm calculates the target ventilation volume allocation ratio and extraction pump operating load based on the coupled model of "gas concentration-ventilation volume-surrounding rock permeability", and outputs control commands to drive the ventilation unit, extraction pump and anti-seepage grouting device, thereby forming an integrated closed-loop control in the construction and operation phases. Example

[0021] Taking a high-gas section of a long railway tunnel as an example, the tunnel has a length of 6km and passes through coal-bearing strata; Before construction, exploratory boreholes with a diameter of 42 mm were drilled every 80 m along the tunnel axis. The gas content of the coal samples was measured using a gas desorption instrument, with an average value of 2.5 m³ / t. A gas pressure gauge was used to measure a gas pressure of 0.65 MPa at a depth of 50 m. A steady-state gas permeability test yielded a surrounding rock permeability coefficient of 1.2 × 10⁻⁶. -14 m²; simultaneously, stress gauges are installed at the same location to record ground stress in the range of 12–18 MPa, and the collected w, P, k, and σ data are used as risk inputs.

[0022] According to the classification judgment rules, if w≥2.0 and 0.2≤P<0.74, it is judged as a medium-risk area. Combined with the longitudinal and transverse profiles of the tunnel, a zoning map is generated, and the parameters are re-measured every 50m of tunneling to update the map.

[0023] During the construction phase, a 25mm thick polyurea spray coating was applied to this section at a spraying rate of 2.5kg / m², supplemented by 0.5MPa atmospheric pressure grouting with a grout diffusion radius of 2m. For high-risk areas subsequently entered by tunneling, gas pre-drainage was carried out for 72 hours in advance with a drainage rate of ≥30%. At the same time, a 350mm diameter drainage channel was laid out. Construction ventilation used two main fans of 75kW, a local fan of 37kW, and an emergency fan of 22kW, with the pressure difference controlled at 80Pa. A 55mm epoxy resin-based composite anti-seepage layer was sprayed on the inner wall, and a 1.0MPa grouting isolation ring was formed in the surrounding rock.

[0024] During coal uncovering operations, gas concentration sensors are installed. When the concentration is ≥1.5% or the flow rate is ≥6m³ / min, the control system automatically increases the main ventilation volume to 1.5 times the normal value within 25 seconds, and activates the extraction pump (negative pressure 18kPa) and the quick-setting cement-based slurry sealing device within 4 minutes to quickly suppress the risk of sudden inrush.

[0025] After the tunnel enters operation, 1.5mm thick PVC rolls are laid on the inner wall of the lining, and hot welding is used to ensure the joints are sealed. The surrounding rock outside the lining is grouted to form an isolation zone, and grouting is supplemented every two years during the operation period through pre-embedded grouting pipes.

[0026] In the monitoring phase, monitoring groups are set up every 40m along the longitudinal direction of the tunnel. Each group includes a gas sensor (sampling frequency 1 time / minute), a stress gauge (range 0–50MPa), and a displacement gauge (accuracy ±0.1mm). The collected data is transmitted to the ground control center via optical fiber.

[0027] In the dynamic control phase, monitoring data is input into the control algorithm, which outputs ventilation volume allocation values ​​(main air volume 65%, local air volume 25%, emergency air volume 10%) and extraction pump load (negative pressure 20kPa, flow rate 8m³ / min). Control commands are sent to the ventilation unit, extraction pump, and grouting pump via PLC, realizing integrated closed-loop control during construction and operation.

[0028] The specific steps for collecting risk parameters are as follows: Before tunnel construction, it is necessary to collect system parameters for the target section; First, the gas content w (unit: m³ / t) of the coal and rock mass was obtained using drilling sampling and gas desorption methods. Simultaneously, the gas pressure P (unit: MPa) of the coal and rock mass was measured using a gas pressure gauge, and the permeability coefficient k (unit: m²) of the surrounding rock was obtained through gas permeability testing. These parameters directly reflect the gas occurrence conditions of the coal and rock mass. While collecting gas parameters and surrounding rock permeability coefficients, geological stress monitoring points are set up, and stress gauges are used to record geological stress data σ (unit: MPa) at different depths along the tunnel axis. A monitoring curve that is dynamically updated with the progress of construction is formed. The w, P, k and σ data are used together as input parameters for risk classification to ensure that the zoning evaluation results are supported by objective data.

[0029] The specific steps for hierarchical and zoned risk assessment are as follows: Based on the input parameters, risk classification rules are established. When the gas content w in the coal and rock mass is less than 2.0 m³ / t and the gas pressure P is less than 0.2 MPa, the corresponding section is classified as a low-risk zone; when the gas content w is greater than or equal to 2.0 m³ / t and the gas pressure P is in the range of 0.2–0.74 MPa, the corresponding section is classified as a medium-risk zone; when the gas pressure P is greater than or equal to 0.74 MPa, the corresponding section is classified as a high-risk zone. Risk grading is based on quantitative rules established from input parameters: ; In the formula: Indicates the risk level; It is a low-risk area; It is a medium-risk area; It is a high-risk area; This formula establishes a judgment standard based on gas content and gas pressure, which is different from the existing grading model that relies on experience. The risk level results are combined with the longitudinal profile and cross-sectional geological structure of the tunnel to generate a two-dimensional or three-dimensional risk zoning map. This map is updated every 50–100m as the construction progresses. The update is based on newly measured w, P, and σ data and recalculated to ensure that the zoning is consistent with the geological conditions. The updated map is used to accurately guide the fortification measures of each section, rather than being specified based on experience, which is different from the existing static zoning scheme.

[0030] The specific steps for setting up fortification during the construction phase are as follows: During the construction phase, based on the risk zoning map, pre-drainage and advanced gas suppression operations are carried out sequentially in high-risk areas. The pre-drainage time is no less than 72 hours and the extraction rate is no less than 30%. At the same time, a drainage channel with a diameter of no less than 300mm is set up, and a three-level ventilation system consisting of main ventilation, local ventilation and emergency ventilation is adopted to keep the pressure difference between the inside and outside of the tunnel within the range of 50-100Pa. This measure ensures that the gas is fully extracted and dispersed before coal seam exposure and excavation. During construction in high-risk areas, an epoxy resin-based composite anti-seepage layer with a thickness of not less than 50 mm needs to be formed on the inner wall of the lining. This layer is made of resin and non-woven fabric composite, and a grouting isolation ring is established in the surrounding rock with a grouting pressure of 0.8–1.2 MPa. In medium-risk areas, a 20–30 mm polyurea spray coating and 0.4–0.6 MPa atmospheric pressure grouting are used. Low-risk areas are treated with a 10–15 mm single-layer polyurethane spray. Different risk areas require different prevention and control measures to avoid the shortcomings of traditional one-size-fits-all or single sampling methods.

[0031] The specific steps for coal seam exposure safety control are as follows: During coal uncovering operations, multiple parameter early warning thresholds are set, including: gas concentration C ≥ 1.5%, gas flow rate Q ≥ 6 m³ / min, or gas pressure P ≥ 0.74 MPa. The logical formula is as follows: ; when When this happens, emergency control is triggered, which avoids delays or misjudgments caused by single-parameter triggering; When the monitoring data reaches any threshold, the control program is triggered to switch to emergency ventilation mode within 30 seconds, increasing the air volume to 1.5 times that of normal operating conditions; and regional extraction and local sealing are initiated within 5 minutes. The linkage control between emergency ventilation and extraction / sealing is implemented by an embedded PLC control system, which includes: Monitoring unit: Gas concentration, gas flow and gas pressure sensors, sampling period ≤1s; Control unit: PLC controller and its I / O modules, with built-in time logic and threshold determination program; Communication unit: Connected to the ventilation fan frequency converter, extraction pump control cabinet and grouting actuator via RS-485 or CAN bus; Execution units: main ventilation fan, local ventilation fan, extraction pump, and quick-setting cement-based grouting pump; When any parameter is detected to have reached the warning threshold, the PLC automatically sends a three-level control signal: Within 0–5 seconds, the frequency converter of the ventilation fan is triggered to increase the frequency, so that the air volume is increased to 1.5 times the normal operating condition within 30 seconds, thus achieving emergency ventilation; Simultaneously, the extraction command is issued, and the extraction pump starts within 15 seconds and establishes a negative pressure of ≥15kPa to achieve continuous extraction; The system starts the grouting control module via bus, and starts the quick-setting cement-based grouting pump within 300s (5 minutes) to inject grout into the preset sealing channel to achieve local sealing; The signal transmission delay between units is less than 200ms. The entire response process is automatically completed under the time logic control of PLC, forming an integrated linkage control chain of emergency ventilation-extraction-blocking. The extraction pump operates under a negative pressure of ≥15kPa. The sealing is done with a fast-setting cement-based grout, which is injected into the coal and rock fissures and drainage structure by the grouting pump and hardens rapidly to form a sealing layer. Unlike existing measures that rely solely on alarms and shutdowns, this method uses parameterized linkage to create an automatic response mechanism.

[0032] The specific steps for seepage prevention during the operation phase are as follows: During the tunnel operation phase, a polyvinyl chloride (PVC) waterproof membrane is laid on the inner wall of the lining. The membrane thickness is not less than 1.5 mm, and it is ensured to be tightly bonded to the lining surface during the membrane construction process. The membrane serves as an inner structural layer fixed to the lining surface, forming a continuous impermeable inner layer to prevent external water vapor and gas from seeping into the tunnel. A grouting isolation zone is set between the surrounding rock and the lining, and the isolation zone is connected to the waterproof membrane layer through a pre-embedded grouting pipe; Every two years during the operation period, grout is injected into the isolation zone through grouting pipes. The grouting material seeps in along the existing channels and gradually forms a new sealing ring. This double-layer seepage prevention system ensures the continuity of seepage prevention from construction to operation, rather than relying solely on grouting during the construction period as is the case with the existing system.

[0033] The specific steps of ternary coupling monitoring are as follows: The monitoring system established inside the tunnel consists of three types of sensors; Gas sensor (sampling frequency ≥ 1 time / minute, monitoring concentration C); Surrounding rock stress gauge (range 0–50 MPa, monitoring stress σ); Lining displacement gauge (accuracy ±0.1mm, monitoring displacement Δu); Various sensors are deployed along the longitudinal direction of the tunnel at intervals of 30–50m. Each group includes a gas sensor, a stress gauge, and a displacement gauge. Each monitoring unit operates continuously after deployment to collect data on gas concentration, surrounding rock stress, and lining displacement. The collected data is then used as ternary coupled monitoring data for subsequent control. Unlike existing solutions that only deploy gas sensors, this solution provides a three-element coupled input, which more comprehensively reflects the tunnel's condition.

[0034] The specific steps for implementing dynamic control are as follows: The monitoring data collected by the gas sensor, the surrounding rock stress gauge and the lining displacement gauge are input into the dynamic control algorithm. The algorithm is based on the coupling relationship model of gas concentration-ventilation volume-surrounding rock permeability. The calculation results of the algorithm include the target ventilation volume allocation ratio of various ventilation systems and the operating load parameters required by the extraction pump. The operating load parameters include negative pressure value and flow rate value. The monitoring data is input into the control algorithm to establish the following model: ; In the formula: Target ventilation volume allocation (m³ / min); Pump load; Gas concentration; Surrounding rock stress; Lining displacement; Surrounding rock permeability (m²); Gas dynamic viscosity (Pa) s); Empirical coefficients are derived from regression fitting based on historical monitoring data. Based on the calculation results, corresponding control commands are generated. These commands are used to drive the ventilation units, extraction pumps, and anti-seepage grouting devices within the tunnel. The ventilation units then... Adjust the air volume ratio of main ventilation, local ventilation, and emergency ventilation; the extraction pump should be adjusted accordingly. Adjust the operating negative pressure and extraction flow rate; the anti-seepage grouting device executes grouting operations according to instructions to maintain continuous control measures during the construction and operation phases; This creates a closed-loop control system during the construction and operation phases, eliminating reliance on manual experience or single alarms.

[0035] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for graded defense and comprehensive protection of gas tunnels, characterized in that: The specific steps of this method are as follows: Risk parameter collection: Before construction, data on gas content, pressure, permeability and ground stress are collected through drilling and stress monitoring as inputs for risk assessment; Graded and zoned risk assessment: The risk level is determined based on parameters such as gas content, gas pressure, surrounding rock permeability coefficient and geological stress, and a risk zoning map is generated in combination with the longitudinal and cross-sectional geological characteristics of the tunnel; the map is dynamically updated every 50-100 meters as the construction progresses, and is used to guide the construction control system or management personnel to implement corresponding defense measures in different sections. Construction phase protection measures: In high-risk areas, pre-extraction, drainage, and multi-stage ventilation are implemented, along with an epoxy resin-based composite seepage barrier layer with a thickness of not less than 50mm and a grouting isolation zone; in medium-risk areas, a 20–30mm thick polyurea spray coating is applied and grouting is carried out at a normal pressure of 0.4–0.6MPa; in low-risk areas, a 10–15mm thick polyurethane single-layer spray seepage barrier coating is applied to ensure differentiated implementation of protection measures for different risk levels. Coal exposure safety control: When exposing coal, set multi-parameter thresholds for concentration, flow rate and pressure. If the limit is exceeded, start emergency ventilation within 30 seconds and link extraction and sealing within 5 minutes. During the operation phase, a double-layer seepage prevention system is formed by PVC rolls and grouting isolation strips, and grouting is regularly replenished and maintained every two years by pre-embedded grouting pipes. Three-element coupling monitoring: gas sensors, stress gauges and displacement gauges are deployed every 30-50 meters along the tunnel to collect three types of data in real time: concentration, stress and lining displacement. Dynamic control execution: Monitoring data is input into a coupled algorithm to calculate ventilation volume and extraction pump load, and generate commands to drive ventilation, extraction and grouting to form a closed-loop control.

2. The method for graded defense and comprehensive protection of gas tunnels according to claim 1, characterized in that: The specific steps for collecting the risk parameters are as follows: The risk level is determined based on the gas content w, gas pressure P, surrounding rock permeability coefficient k, and geological stress σ collected before construction. The judgment results are overlaid with the longitudinal and cross-sectional geological structure data of the tunnel to generate a risk zoning map reflecting different risk sections. The map is updated every 50–100m as the construction progresses. The updated map is used to guide the construction control system or on-site management personnel to implement corresponding defense measures in each risk section.

3. The method for graded defense and comprehensive protection of gas tunnels according to claim 2, characterized in that: The specific steps of the hierarchical and zoning risk assessment are as follows: The input parameters obtained from the risk parameter collection are used to establish risk classification and determination rules: When the gas content w in the coal and rock mass is less than 2.0 m³ / t and the gas pressure P is less than 0.2 MPa, the corresponding section is classified as a low-risk zone. When the gas content w is greater than or equal to 2.0 m³ / t and the gas pressure P is in the range of 0.2–0.74 MPa, the corresponding section will be classified as a medium-risk area. When the gas pressure P is greater than or equal to 0.74 MPa, the corresponding section will be classified as a high-risk area. The risk level is combined with the geological characteristics of the tunnel's longitudinal profile and cross section to generate a risk zoning map. The map is to be updated every 50–100m as the construction progresses to ensure that the zoning results are consistent with the actual geological conditions. The updated zoning map is used to determine the specific defense measures required for different areas.

4. The method for graded defense and comprehensive protection of gas tunnels according to claim 3, characterized in that: The specific steps for setting up fortification during the construction phase are as follows: During the construction phase, based on the risk zoning map, pre-drainage and advanced gas suppression operations are carried out sequentially in high-risk areas. The pre-drainage time is no less than 72 hours and the drainage rate is no less than 30%. At the same time, a drainage channel with a diameter of no less than 300mm is set up, and a three-level ventilation system consisting of main ventilation, local ventilation and emergency ventilation is adopted to maintain the pressure difference between the inside and outside of the tunnel within the range of 50-100Pa in order to achieve timely gas dissipation. In high-risk areas, an epoxy resin-based composite anti-seepage layer with a thickness of not less than 50 mm is formed, and an isolation ring with a grouting pressure of 0.8–1.2 MPa is established. In medium-risk areas, a polyurea spray coating with a thickness of 20–30 mm and atmospheric pressure grouting with a grouting pressure of 0.4–0.6 MPa are used. In low-risk areas, a polyurethane single-layer spray anti-seepage coating with a thickness of 10–15 mm is used to ensure that the construction protection measures corresponding to different risk levels are implemented.

5. The method for graded defense and comprehensive protection of gas tunnels according to claim 4, characterized in that: The specific steps for coal uncovering safety control are as follows: During coal uncovering operations, a multi-parameter early warning threshold is set, including: gas concentration greater than or equal to 1.5%, gas flow rate greater than or equal to 6 m³ / min, or gas pressure greater than or equal to 0.74 MPa. When the monitoring data reaches any of the thresholds, the control program is triggered to switch the ventilation system to emergency ventilation mode within 30 seconds and increase the air volume to 1.5 times the normal operating air volume. Simultaneously with the activation of the emergency ventilation mode, regional extraction and local sealing measures are initiated within 5 minutes. The negative pressure of the extraction pump is set to no less than 15 kPa to ensure continuous extraction. The material used for local sealing is a fast-setting cement-based grout, which forms a sealing layer in coal and rock fissures or drainage structures through grouting.

6. The method for graded defense and comprehensive protection of gas tunnels according to claim 5, characterized in that: The specific steps for seepage prevention during the operation phase are as follows: During the tunnel operation phase, a polyvinyl chloride waterproof membrane is laid on the inner wall of the lining. The membrane is not less than 1.5mm thick and is kept in close contact with the lining surface during the membrane construction process. The membrane is fixed to the lining surface as an inner layer structure to form a continuous seepage-proof inner layer, which is used to isolate the seepage channels of external water vapor and gas into the tunnel. A grouting isolation zone is set between the surrounding rock and the lining. The isolation zone is connected to the waterproof membrane layer through a pre-embedded grouting pipe. During the operation period, grouting is carried out every two years through the grouting pipe. The grouting material enters the space between the surrounding rock and the isolation zone along the existing channel to form a new sealing ring, thereby maintaining the sealing performance of the isolation zone.

7. The method for graded defense and comprehensive protection of gas tunnels according to claim 6, characterized in that: The specific steps of the ternary coupling monitoring are as follows: A monitoring system is established inside the tunnel, which includes a gas sensor, a surrounding rock stress gauge, and a lining displacement gauge. The gas sensor has a sampling frequency of no less than once per minute to acquire gas concentration data inside the tunnel; the surrounding rock stress gauge has a measurement range of 0–50 MPa to record the stress on the surrounding rock; and the lining displacement gauge has a measurement accuracy of ±0.1 mm to monitor the deformation of the tunnel lining. The monitoring system is set up with a group of sensors along the longitudinal direction of the tunnel at intervals of 30–50m. Each group includes a gas sensor, a stress meter, and a displacement meter. Each monitoring unit operates continuously after deployment to collect data on gas concentration, surrounding rock stress, and lining displacement. The collected data is then used as ternary coupled monitoring data for subsequent control.

8. The method for graded defense and comprehensive protection of gas tunnels according to claim 7, characterized in that: The specific steps for implementing the dynamic control are as follows: The monitoring data collected by the gas sensor, the surrounding rock stress gauge and the lining displacement gauge are input into the dynamic control algorithm. The algorithm is based on the coupling relationship model of gas concentration-ventilation volume-surrounding rock permeability. The calculation results of the algorithm include the target ventilation volume allocation ratio of various ventilation systems and the operating load parameters required by the extraction pump, wherein the operating load parameters include negative pressure value and flow rate value. Based on the calculation results, corresponding control commands are generated. These commands are used to drive the ventilation units, extraction pumps, and anti-seepage grouting devices in the tunnel. The ventilation units adjust the air volume ratio of main ventilation, local ventilation, and emergency ventilation according to the commands. The extraction pumps adjust the operating negative pressure and extraction flow rate according to the commands. The anti-seepage grouting devices perform grouting operations according to the commands to maintain continuous prevention and control measures during the construction and operation phases.

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