Tunnel soft surrounding rock excavation and shotcrete construction method

Abstract

The application relates to the technical field of tunnel construction, and particularly discloses a tunnel soft surrounding rock excavation and shotcrete construction method, which solves the technical problems of over-excavation, serious shotcrete overconsumption and low construction efficiency in the existing tunnel soft surrounding rock excavation. The method determines the excavation conditions through comprehensive geological prediction in advance, combines standard calculation with on-site actual comparison and selection of drill-and-blast design schemes, dynamically adjusts drill-and-blast parameters, simultaneously controls shotcrete construction from the aspects of section treatment, raw materials, mix proportion, shotcrete construction and rebound material recycling, and realizes drill-and-blast excavation precision and shotcrete high efficiency. The application effectively reduces the concrete over-square rate and rebound rate, reduces the over-excavation amount, improves the explosive utilization rate and construction footage, saves the construction cost, improves the overall quality of tunnel excavation and support, has environmental protection and promotion values, is suitable for the tunnel construction scene of Triassic sandstone interbedded mudstone and other soft surrounding rocks, and has extremely high popularization and application values.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, specifically to a method for excavating weak surrounding rock and spraying concrete in tunnels. Background Technology

[0002] In tunnel construction, the lithology of weak surrounding rock sections is extremely complex, commonly found in Triassic strata. Sandstone interbedded with mudstone, and alternating layers of mudstone and sandstone are prevalent, leading to uneven rock mass strength and poor stability. These sections exhibit highly developed joints and fissures, resulting in fractured rock masses with significantly reduced integrity, making them prone to deformation or collapse during construction. Furthermore, they are often accompanied by adverse geological problems such as landslides and fault fracture zones, further increasing construction risks. When using conventional blasting excavation, the weak surrounding rock and low blast resistance easily lead to large over-excavation and poor cross-sectional profile control, resulting in uneven excavation surfaces and increased support difficulties. This not only causes severe overconsumption of shotcrete and significant material waste but also drastically increases construction costs, impacting the project's economic benefits. Meanwhile, existing construction methods often use fixed drilling and blasting parameters, failing to dynamically adjust them according to real-time conditions of the surrounding rock, such as lithological changes and fracture distribution. This not only results in low explosive utilization and poor blasting effects but also limits cyclic advance and slows down construction progress. In the shotcrete construction stage, there is a lack of systematic control over the quality of raw materials, mix design, and construction technology. For example, improper cement-aggregate ratios and unstable spraying pressure lead to high concrete rebound rates, causing not only material waste and environmental pollution but also affecting the density and strength of the support structure. This weakens the quality and efficiency of support construction and may even lead to safety hazards later on.

[0003] To address the aforementioned issues, existing technologies often only optimize individual drilling and blasting parameters or concrete spraying processes, such as adjusting explosive quantities or improving spraying equipment. They lack a comprehensive, integrated solution covering the entire process from advanced geological prediction, drilling and blasting design, drilling and blasting construction, concrete spraying, to construction data feedback. This fragmented approach fails to fundamentally solve the core problems of over-excavation and excessive concrete consumption in soft rock excavation, because each stage of construction is interconnected. Any optimization in one area can be offset by deficiencies in other areas. For example, drilling and blasting designs that fail to incorporate geological prediction may exacerbate rock disturbance, while mismatched concrete spraying can waste prior efforts. Therefore, it is difficult to balance construction efficiency and project quality, often leading to cost overruns and project delays. A systematic approach is urgently needed to integrate technical and management elements to achieve refined and adaptive construction. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for tunnel excavation and shotcrete construction in soft surrounding rock, which enables dynamic optimization of construction parameters and full-process quality control, saves construction costs, and improves the overall quality of tunnel excavation and support.

[0005] To achieve the above objectives, the present invention provides a method for excavating tunnels in weak surrounding rock and constructing with shotcrete, comprising the following steps: Step S1: Advanced Geological Comprehensive Prediction Based on the advanced geological forecast provided by the design institute, a preliminary analysis of the lithology ahead of the tunnel is conducted. After confirming the safety of the surrounding rock ahead, a specialist conducts a geological sketch of the tunnel face to observe the rock orientation and the development of joints and fissures. The focus is on confirming the presence of triangular joints, vertical joints, and large slip layers to determine the safe construction conditions at the tunnel face. During manual excavation, the difficulty of drilling and the color and state of the drilling fluid are used to help determine the lithology ahead. Based on the above information, the basic parameters such as blasting method, drilling equipment (machine / manual), blast hole spacing, and initial charge are determined.

[0006] Step S2: Comparison and Determination of Drilling and Blasting Design Schemes Two drilling and blasting design schemes were developed: Scheme 1 involved calculations based on the "Engineering Blasting Technical Guidelines" to determine the drilling and blasting parameters; Scheme 2 involved inviting blasting professionals to develop drilling and blasting parameters based on their experience. Comparing the two schemes in terms of cycle advance and operability, the scheme with a larger cycle advance and better suitability for on-site construction was selected as the final drilling and blasting design scheme. In this invention, Scheme 1 has a cycle advance of 3.3m, and Scheme 2 has a cycle advance of 2.4m. Scheme 1 is preferred, and the arch frame spacing is determined to be 1m.

[0007] Step S3: Precise control of drilling and blasting parameters (1) Control of advanced support parameters: Three-arm drilling is used to construct advanced small guide pipes and pipe roofs. The construction angle is controlled to be no more than 9° by the equipment instrument panel. The spacing and construction position of the pipe roofs are dynamically adjusted according to the degree of rock fragmentation and the distribution of slip layers to reduce over-excavation of the arch crown. (2) Adjustment of peripheral hole parameters: The original design of 0.6m peripheral hole spacing at the arch is adjusted to 0.4m, and the charge is reduced. The peripheral hole spacing at other positions remains unchanged. The convergence and insertion angle of the peripheral hole and the bottom plate drilling angle are dynamically adjusted according to the real-time situation of the surrounding rock. (3) Optimization of blasting process: water pressure blasting is used for the perimeter holes to reduce the amount of explosives used and reduce the disturbance of the surrounding rock; in view of the safety requirements of gas tunnels, detonating cords are abandoned and double detonators are used to ensure the safety and reliability of blasting. (4) Comparison of excavation methods: The minimum angle of mechanical excavation is adjusted to 9°, and the over-excavation phenomenon is obvious. Therefore, it is recommended to combine manual excavation with drilling and blasting parameters to improve the excavation accuracy.

[0008] Step S4: Dynamic adjustment of drilling and blasting parameters Based on the surrounding rock and joint development at the construction site, a targeted drilling and blasting plan is developed for each cycle to achieve dynamic optimization of drilling and blasting parameters: (1) For surrounding rock with well-developed joints and fissures and localized point-like water discharge, the perimeter boreholes converge 20cm to the excavation outline, and boreholes without external insertion angle are used. (2) For surrounding rock with relatively well-developed joints and good overall rock mass, the perimeter boreholes converge 15cm to the excavation outline, and boreholes are drilled at an external insertion angle of 9-10°. (3) Based on the influence of the unit rock mass explosive consumption on the rock fragmentation size, blast hole utilization rate, cross section profile quality and surrounding rock stability, the single hole charge is adjusted in real time according to different rock strata and joint development conditions, taking into account both blasting effect and surrounding rock protection.

[0009] Step S5: Full Process Control of Shotcrete Construction (1) Over- and under-excavation section treatment: After the blasting and slag removal is completed, the measurement is immediately organized to scan the over- and under-excavation section, accurately analyze the over- and under-excavation amount of the arch crown, arch waist, side wall and arch foot, treat only the under-excavation position, and then carry out the risk removal and erection to avoid the over-excavation expansion caused by excessive treatment. At the same time, the drilling and blasting parameters adjustment measures are formulated according to the scanning data. (2) Raw material quality control: Ordinary silicate cement is selected, and an appropriate amount of accelerator is added to accelerate the setting speed of concrete and reduce shrinkage; the mud content of sand does not exceed 3%, and the fineness modulus does not exceed 2.6; the particle size of coarse aggregate does not exceed 10mm to ensure that the raw materials are suitable for wet spraying process. (3) Mix ratio optimization: control the ratio of bone ash to ashes to be ≤1:4, and the amount of cement to be ≤390kg / m³. 3 To avoid excessive rebound due to insufficient cement or hardening shrinkage due to excessive cement; the sand content should be controlled at 50%, and the water-cement ratio should be 0.4 to 0.45 to effectively reduce concrete rebound and surface dust, and improve the flatness of the support surface; (4) Wet spraying construction control: The nozzle is kept perpendicular to the surface of the initial support, the spraying distance is controlled at 0.7-1.3m, the air pressure is adjusted to 0.5-0.6Mpa, and the air pressure, blast hole spacing and excavation angle are adjusted in coordination to control the concrete rebound rate within 20%. (5) Rebound material treatment: Collect, weigh and analyze the rebound material during the shotcrete construction, calculate the rebound rate, analyze the causes of rebound (such as nozzle angle, air pressure, mix ratio, etc.), formulate targeted solutions, and optimize subsequent construction parameters.

[0010] Step S6: Complete workflow management of construction data Each cycle collects construction data such as mileage sections, construction locations, designed concrete volume, actual volume, excess volume, explosive usage, explosive consumption per unit, over-excavation, under-excavation, and concrete rebound rate, and establishes a construction data ledger; analyzes the correlation between data, such as the correlation between over-excavation and excess concrete volume, explosive usage and over-excavation, and shotcrete process parameters and rebound rate, and feeds the analysis results back to the drilling and blasting parameter adjustment and concrete shotcrete construction stages, forming a complete process management of data collection, analysis, optimization, and construction, and continuously improving construction accuracy.

[0011] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The method of this invention reduces the problem of over-excavation in tunnel excavation from the source by accurately predicting geological conditions in advance, dynamically optimizing drilling and blasting parameters, and adapting the excavation method to control the excavation. The over-excavation of key parts such as the arch crown, arch foot, and bottom slab is reduced by an average of 17.8-35cm. Combined with the fine control of the entire process of shotcrete, the concrete over-cubic-meter rate is reduced by 32.1%-45.1%, the rebound rate is reduced by 2%-2.5%, and the rebound material is collected, analyzed, and reused in compliance with regulations, further reducing material waste. In actual construction, approximately 10m³ of concrete can be saved per cycle. 3 Based on the industry's standard unit price, each cycle directly saves more than 6,000 yuan in material costs, significantly reducing the overall construction cost of tunnel sections with weak surrounding rock. (2) The method of the present invention implements differentiated drilling and blasting parameter adjustments for different surrounding rock conditions (joint development, point water discharge, sandstone interbedded with mudstone, etc.), and precisely controls the convergence value, insertion angle and charge amount of blast holes in key parts such as peripheral holes, arch foot holes and bottom holes. At the same time, it strictly controls the construction deviation of blast holes and charge standards, reduces the disturbance of blasting to weak surrounding rock, and improves the quality of tunnel cross-section contour forming. The shotcrete process implements full-chain control from raw materials, mix ratio, construction technology to forming and testing, ensuring that the flatness and thickness of the initial support surface meet the design requirements, so that the support structure is closely attached to the surrounding rock, enhances the synergistic stability of the surrounding rock and the support system, and fundamentally reduces the safety hazards of construction in weak surrounding rock sections. (3) The method of the present invention selects drilling and blasting design schemes based on the on-site operability of each cycle of advance. The selected optimal scheme is more suitable for the on-site construction conditions and avoids the work delay caused by unreasonable advance. The utilization rate of explosives is improved by dynamically optimizing drilling and blasting parameters, reducing ineffective operations such as drilling and charging, and reducing the delay of processes such as spraying and repair caused by excessive concrete consumption. The excavation method with manual labor as the main method and mechanical labor as the auxiliary method is suitable for the construction characteristics of soft surrounding rock, taking into account the excavation accuracy and work efficiency. The connection between each process is smooth, and the overall construction and excavation efficiency of the tunnel in the soft surrounding rock section is improved, effectively shortening the construction period. (4) The method of the present invention requires a comprehensive survey of the working conditions of the surrounding rock at the tunnel face before each drilling and blasting cycle, to formulate a targeted drilling and blasting plan and dynamically adjust the parameters, and at the same time establish a construction data ledger, and feed the data analysis results back to the drilling, blasting and concrete spraying links, forming a complete construction process management of survey, design, construction, analysis and optimization. For typical weak surrounding rock designs such as Triassic sandstone interbedded with mudstone, mudstone-dominated or sandstone-dominated, the parameters can be flexibly adjusted according to the actual situation of different tunnels such as lithology, joint development, and slip distribution, adapting to various weak surrounding rock tunnel construction scenarios, and having universality for promotion across the entire line; (5) The method of the present invention is designed for gas tunnel construction scenarios. It abandons the method of setting up a blasting network with double detonators connected by detonating cords, avoids the safety hazards of using detonating cords, and improves the safety of blasting construction. The peripheral holes adopt water pressure blasting technology, which reduces the amount of explosives used and reduces the dust generated by blasting. Combined with the wind pressure control and dust suppression in the shotcrete process, it improves the construction environment in the tunnel. The dynamic control of the advanced support angle and the spacing of the pipe roof effectively prevents construction risks such as soft surrounding rock slippage and collapse. It comprehensively protects the construction safety of workers from process design to on-site construction. (6) The method of the present invention has established clear quantitative standards and operational requirements for each construction step, such as the pre-support angle not exceeding 9°, the water-cement ratio of shotcrete controlled at 0.4 to 0.45, and the verticality / angle deviation of the blast hole controlled within the specified range. At the same time, a practical quantitative evaluation table for drilling and blasting schemes has been designed to transform the vague construction requirements into quantifiable, detectable, and executable standards. The establishment and closed-loop management of construction data ledgers realize the full collection, analysis, and application of construction data for each cycle, promote the transformation of tunnel soft surrounding rock construction from experience-based management to standardized and digital management, and improve the level of refinement of construction management. (7) The method of the present invention verifies the rhythm matching of excavation advance and support procedures during the drilling and blasting scheme screening stage, ensuring that the excavation advance is coordinated with the arch spacing and shotcrete efficiency, avoiding equipment and personnel idleness caused by untimely support due to excessive advance or insufficient advance; the coordinated adjustment of drilling and blasting parameters and shotcrete parameters reduces the problem of over-spraying and re-spraying of concrete due to irregular excavation cross-section, making the excavation and support procedures form an organic whole, improving the utilization efficiency of construction resources such as equipment, personnel and materials, and reducing ineffective consumption. Attached Figure Description

[0012] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart of the construction method of the present invention; Figure 2 Image 1 shows the working face of the construction example in Embodiment 7 of the present invention; Figure 3 Image 2 shows the working face of the tunnel in the construction example of Embodiment 7 of the present invention; Figure 4 This is a geological sketch of the surrounding rock at the working face in the construction example of Embodiment 7 of the present invention; Figure 5 This is a drilling and blasting design scheme diagram for a construction example in Embodiment 7 of the present invention; Figure 6 This is a chart showing the over-excavation and under-excavation control data of the construction example in Embodiment 7 of the present invention; Figure 7 This is a specific construction image of the construction example in Embodiment 7 of the present invention; Figure 8 This is a dynamic adjustment diagram of the drill-and-blast design in Embodiment 7 of the present invention; Figure 9 This is the dynamic adjustment table for the drill-and-blast design in Embodiment 7 of the present invention; Figure 10 This is the second specific construction image of the construction example in Embodiment 7 of the present invention; Figure 11 This is a construction control diagram for shotcrete in the construction example of Embodiment 7 of the present invention; Figure 12 This is a table and graph showing the collection and analysis of shotcrete rebound material in the construction example of Embodiment 7 of the present invention; Figure 13 This is a construction diagram of the shotcrete rebound material collection in the construction example of Embodiment 7 of the present invention. Detailed Implementation

[0013] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0014] To make the objectives, process conditions, and advantages of the present invention clearer, the present invention will be further described in detail with reference to the following embodiments. However, the embodiments of the present invention are not limited thereto. Various substitutions and modifications can be made based on common technical knowledge and conventional means in the art without departing from the above-described technical concept of the present invention, and all such substitutions and modifications should be included within the scope of the present invention. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0015] Example 1: This embodiment provides a method for excavating tunnels in weak surrounding rock and constructing shotcrete, the process of which is as follows: Figure 1 As shown, it includes the following steps: Step S1: Conduct advanced geological prediction analysis and perform geological hand-drawn sketches of the tunnel face to determine the blasting method and basic borehole parameters; Step S2: Determine the arch spacing and initial drill-and-blast parameters based on the practicality of each cycle of advance; Step S3: Perform precise control of drilling and blasting operation parameters; Step S4: Based on the surrounding rock and joint development at the construction site, develop a targeted drilling and blasting plan for each drilling and blasting cycle and dynamically optimize the drilling and blasting parameters. Step S5: Implement meticulous control over the entire process of shotcrete construction. Step S6: Collect construction data for each drilling and blasting cycle, establish a construction data ledger, analyze the correlation between data, and feed the analysis results back to the drilling and blasting parameter adjustment and concrete spraying construction stages to achieve complete process management of construction data.

[0016] Example 2: Based on the above embodiments, this embodiment further defines the specific process of step S1 as follows: Step S11: Based on the advanced geological forecast document issued by the design institute, analyze the lithology, rock layer distribution and geological structure of the surrounding rock in front of the tunnel, and preliminarily confirm that the surrounding rock in front has the conditions for safe excavation. Step S12: Arrange for a specialist to conduct on-site survey and observation of the working face, complete a geological sketch of the working face, clarify the rock orientation and the degree of joint and fracture development, and at the same time confirm whether there are triangular joints, vertical joints and large slip layers at the working face, and determine the on-site safe construction conditions of the working face. Step S13: During the manual excavation stage, the changes in drilling resistance, drilling speed, and the color, turbidity, and flow rate of the drilling flushing fluid are used to help determine the lithology and integrity of the surrounding rock in front of the tunnel face. Step S14: Based on the comprehensive analysis and judgment results, determine the basic drilling parameters for tunnel excavation, including blasting method, drilling equipment type, initial spacing of blast holes, and initial charge per hole.

[0017] Example 2: Based on the above embodiments, this embodiment further defines the specific process of step S2 as follows: Step S21: Develop at least several candidate drill-and-blast design schemes; Step S22: Use the on-site operability of each cycle of advance as the core evaluation index to comprehensively compare and select each drill-and-blast design candidate scheme; Step S23: Select the optimal drill-blast design candidate scheme as the on-site construction execution scheme, determine the standard value of the arch spacing for tunnel excavation based on the scheme, and extract the initial drill-blast parameters from the scheme.

[0018] The specific process of comprehensively comparing and selecting each drill-and-blast design candidate scheme in step S22, with the on-site operability of each cycle of advance as the core evaluation index, is as follows: quantitatively screening each drill-and-blast design candidate scheme through three dimensions: on-site construction condition matching, work efficiency feasibility, and process connection adaptability. The on-site construction condition matching judgment candidate scheme determines whether the drilling depth and blast hole layout density corresponding to each cycle of advance are compatible with the operating capacity of the existing excavation equipment and the tunnel face construction space of the project, and excludes schemes where the equipment cannot reach the designed drilling depth or the tunnel face space cannot meet the blast hole layout requirements. The feasibility calculation of the work efficiency of the candidate schemes is based on the theoretical total working hours of each process of drilling, charging, blasting and slag removal in a single cycle under the theoretical advance of each cycle. The schemes with theoretical total working hours not exceeding the working hours quota are compared with the project's established single-cycle construction time quota. The process connection adaptability verification candidate scheme theoretically matches the rhythm of each cycle of excavation advance with subsequent support processes (such as arch frame erection and shotcrete), ensuring that the excavation advance is coordinated with the arch frame spacing and support operation efficiency, and avoiding schemes that cause untimely support due to excessive advance or idle work due to excessive advance.

[0019] The following is a quantitative evaluation table of the on-site operability of the drill-and-blast design scheme for each cycle of advance: Evaluation subject: Candidate schemes for drill-and-blast design for tunnel excavation in weak surrounding rock (Scheme 1, Scheme 2, etc.) Key evaluation metric: On-site practicality of advance per cycle Evaluation dimensions: compatibility with on-site construction conditions, feasibility of work efficiency, and adaptability of work process connections. Evaluation criteria: The full score is 100 points. A score of ≥70 points is considered passing the practical assessment, and a score of <70 points is considered failing. Passing solutions will proceed to the next stage of comprehensive evaluation. A score of <20 points in any single dimension will result in the solution being deemed failing the practical assessment. Table 1. Scoring Table for Candidate Schemes of Drilling and Blasting Design for Excavation in Tunnel with Weak Surrounding Rock

[0020] Form completion and instructions: ①Evaluation team: The evaluation team consists of the project's technical manager, construction worker, blasting engineer, and supervising engineer. They score independently and take the average score as the final score. ② Data Basis: All scores must be based on the project's existing construction resources (equipment, personnel), construction organization design, actual geological / spatial conditions at the working face, and written documents of the drilling and blasting design plan. Subjective assumptions are prohibited. ③ Application of results: This evaluation form is the core basis for screening drilling and blasting design schemes. Only schemes that pass the practical test can enter the subsequent comprehensive comparison and selection stage. Unqualified schemes are directly eliminated without further evaluation of indicators. ④ Dynamic adjustment: If the project construction resources (equipment, personnel) and the geological conditions of the working face change, the quantitative indicators in the evaluation criteria should be adjusted in a timely manner to ensure that the evaluation results are consistent with the actual situation on site.

[0021] The initial drilling and blasting parameters extracted in step S23 include the blast hole layout, the initial spacing of blast holes in each part, the initial charge amount, and the detonator connection method.

[0022] Example 3: Based on the above embodiments, this embodiment further defines the specific process of precisely controlling the drilling and blasting construction parameters in step S3 as follows: Step S31: Control of advanced support parameters. Three-arm drilling is used to construct advanced small guide pipes and pipe roofs. The construction angle is monitored and controlled in real time through the equipment instrument panel to not exceed 9°. At the same time, the construction spacing and layout of the pipe roofs are dynamically adjusted according to the degree of fracture of the surrounding rock at the working face and the distribution of slip layers. Step S32: Precisely adjust the peripheral hole parameters, adjust the spacing of the peripheral holes of the arch from the original design value to 0.4m and reduce the corresponding charge amount at the same time. The spacing of the peripheral holes in other positions (including sidewalls, bottom plate, etc.) remains unchanged at the original design of 0.6m. The convergence value of the peripheral hole, the insertion angle and the drilling angle of the bottom plate are dynamically adjusted according to the real-time status of the surrounding rock. Step S33: Optimize and control the blasting process. Use hydraulic blasting for the perimeter holes to reduce the amount of explosives used and reduce disturbance to the surrounding rock. For the gas tunnel construction scenario, abandon the detonating cord and use a double detonator connection to complete the blasting network layout to ensure the safety of blasting construction. Step S34: Excavation method adaptation control. Compare the over-excavation effect of mechanical excavation and manual excavation. If there is still obvious over-excavation when the minimum adjustment angle of mechanical excavation is 9°, prioritize the use of manual excavation combined with mechanical assistance, and further optimize the drilling and blasting foundation parameters based on the excavation effect.

[0023] The specific process of step S34 is as follows: S341: Conduct a comparative test on the over-excavation effect of mechanical excavation and manual excavation. Under the same drilling and blasting foundation parameters and the same surrounding rock section, adjust the drilling angle of mechanical excavation to a minimum of 9° for trial excavation, and record the over-excavation amount and over-excavation area of ​​each part of the arch crown, arch waist, sidewall and arch foot after mechanical excavation. S342: In the same section, drilling, charging and blasting operations are carried out by manual excavation. The over-excavation amount and over-excavation area of ​​each part are recorded after manual excavation. The over-excavation data of the two excavation methods are compared to determine whether there is an obvious over-excavation problem in mechanical excavation. S343: If it is determined that there is obvious over-excavation in mechanical excavation, then the excavation operation mode of manual excavation as the main method and mechanical assistance shall be adopted. The core process of the working face shall be completed by manual labor (such as the positioning of blast holes, control of drilling angle, charging and sealing of holes, etc.), and the auxiliary process shall be completed by machinery (such as slag removal, relocation of drilling equipment, etc.). S344: During the operation mainly based on manual excavation, the excavation effect of each part is observed in real time, the actual over-excavation data is recorded, and the drilling and blasting basic parameters (such as blast hole spacing, charge amount, drilling angle, etc.) are optimized in reverse based on the excavation effect to achieve coordinated optimization of excavation method and drilling and blasting parameters.

[0024] Example 4: Based on the above embodiments, this embodiment further defines the specific process of step S4 as follows: S41: Based on the actual working conditions of the surrounding rock determined by the survey, formulate a single-cycle drilling and blasting plan, make differentiated adjustments to the parameters of the surrounding boreholes, and set requirements for borehole construction and charging for different surrounding rock conditions. S42: Based on the rock fragmentation characteristics under different surrounding rock conditions, and taking into account the impact of unit rock mass explosive consumption on rock fragmentation size, borehole utilization rate, cross-sectional profile quality and surrounding rock stability, the single-hole charge of each part of the borehole is dynamically adjusted. Different charge standards are adopted for sandstone and mudstone sections. S43: Simultaneously optimize and adjust the drilling angle, blast hole spacing, and charge amount of the bottom plate holes and holes around the arch foot. Based on the actual situation of the bottom plate bulging and arch foot over-excavation, fine-tune the drilling insertion angle and charge amount to avoid aggravating local over-excavation.

[0025] The specific process of step S41 is as follows: For working conditions where the surrounding rock has developed joints and fissures and there are localized point-like water outflows, the peripheral boreholes are converged 20cm to the excavation outline and vertical drilling without external insertion angle is adopted. During drilling, the verticality deviation of the boreholes is controlled to be no more than 0.5°, and the deviation of the borehole depth from the design depth is controlled within ±5cm. In addition, the amount of explosives charged in the peripheral boreholes is reduced by 20% to 30% compared with the conventional working conditions, and waterproof explosive rolls are used for the entire section. For working conditions where the surrounding rock joints are relatively well-developed and the rock mass has good integrity, the peripheral boreholes are converged to the excavation outline by 15cm and boreholes are drilled at an external insertion angle of 9-10°. The deviation of the external insertion angle of the boreholes is no more than 1°, the deviation of the angle consistency between boreholes is controlled within ±0.5°, and the deviation of the borehole depth from the design depth is controlled within ±8cm. In this type of working condition, the amount of explosives charged in the peripheral boreholes is adjusted according to the rock mass integrity grade. When the rock mass integrity coefficient is ≥0.4, the amount of explosives is kept at the conventional standard, and when the rock mass integrity coefficient is <0.4, the amount of explosives is reduced by 10% to 15%.

[0026] In step S42, the charge amount per borehole in each location is dynamically adjusted, with the explosive consumption per unit rock mass as the core control indicator. This is combined with the rock lithology and joint development level to implement graded and quantitative adjustments. Specific requirements are as follows: The control benchmark for explosive consumption per unit rock mass is determined based on the rock mass integrity coefficient at the tunnel face. When the rock mass integrity coefficient is ≥0.4, the benchmark value for explosive consumption per unit rock mass is controlled between 0.8 and 1.0 kg / m. 3 When the rock mass integrity coefficient is <0.4, the benchmark value for explosive consumption per unit rock mass should be controlled between 0.6 and 0.8 kg / m. 3 ; For sandstone strata, which are hard and difficult to break, the single-hole charge amount is determined by increasing the consumption amount benchmark value of the corresponding rock mass integrity coefficient by 10% to 15%. The upper limit of the increase in charge amount for slotted holes and auxiliary slotted holes is taken, while the lower limit of the increase in charge amount for peripheral holes is taken. For mudstone sections, the rock is relatively soft and easily disturbed by blasting, resulting in over-excavation. The single-hole charge amount is determined by reducing the consumption amount benchmark value of the corresponding rock mass integrity coefficient by 15% to 20%. The upper limit of the reduction range of the charge amount of the holes around the arch crown and arch foot is taken, and the lower limit of the reduction range of the charge amount of the holes in the bottom plate is taken. If the working face is a sandstone-mudstone interbedded layer, the explosive consumption per unit rock mass is calculated by weighting the proportion of rock layer distribution. For the explosive charge at the interface between sandstone and mudstone, the average value of the adjusted explosive charge of adjacent rock layers is taken, and the deviation of the explosive charge at the interface is controlled within ±0.1 kg / hole. After adjusting the charge amount, it is necessary to take into account the rock fragmentation size, blast hole utilization rate and surrounding rock stability, to ensure that the rock fragmentation size after blasting is suitable for the operation requirements of the slag removal equipment, the blast hole utilization rate is not less than 85%, and there are no new cracks or significant expansion of slip layer in the surrounding rock at the working face after blasting.

[0027] In step S43, the drilling angle, blast hole spacing, and charge quantity of the bottom plate holes and holes around the arch foot are simultaneously optimized and adjusted. Targeted control is implemented based on the characteristics of local over-excavation at the working face and the distribution of structural stress. Specific requirements are as follows: Optimization and adjustment of boreholes around the arch foot: If there is severe over-excavation with an over-excavation depth of ≥20cm on one or both sides of the arch foot, the borehole insertion angle of the corresponding arch foot perimeter holes will be reduced by 2° to 3° compared with the original design, the spacing between blast holes will be reduced to 0.3 to 0.35m, and the charge amount will be reduced by 15% to 20% compared with the conventional value in the same location; if there is only slight over-excavation or no over-excavation at the arch foot, the borehole insertion angle will be maintained at 9° to 10°, the spacing between blast holes will be 0.4m, and the charge amount will be matched with the standard value of rock mass integrity coefficient; Bottom plate hole optimization and adjustment: If the bottom plate of the working face has a heave height ≥10cm or an over-excavation depth ≥15cm, adjust the bottom plate hole drilling angle to a downward 1°~2° slight downward angle, reduce the hole spacing from the original design 0.6m to 0.4~0.5m, and reduce the charge by 10%~15%; if the bottom plate is excavated and formed flat, keep the bottom plate holes horizontal, the hole spacing is as designed, and the charge is adjusted to match the lithology of the bottom plate rock mass. Coordination and matching requirements: After the parameters of the arch foot and bottom plate holes are adjusted, they must be coordinated with the drilling and blasting parameters of the holes around the working face and the tunneling holes. The deviation of the row spacing between the blast holes should be controlled within ±5cm. The gradient transition of the charge amount should not be abrupt. Avoid blasting stress concentration caused by local parameter differences, which may lead to new over-excavation or surrounding rock instability. Dynamic verification requirements: After the parameter adjustment is implemented in a single cycle of drilling and blasting, the excavation and forming effect of the arch foot and bottom plate should be measured immediately, and the over-excavation and uplift data should be recorded. If the local problems are not improved, the drilling angle, spacing and charge amount should be further fine-tuned in the next cycle until the excavation and forming of the arch foot and bottom plate meet the design requirements.

[0028] Example 5: Based on the above embodiments, this embodiment further defines the specific process of step S5 as follows: S51: Over- and under-excavation section pretreatment control. After the blasting and muck removal is completed, the over- and under-excavation scanning detection of the tunnel face and excavation section is carried out immediately to accurately obtain the over-excavation, under-excavation, and over- and under-excavation area of ​​each part of the arch crown, arch waist, side wall and arch foot. Only the under-excavated parts are targeted for repair. After the treatment is completed, the tunnel face hazard removal and arch frame erection operations are carried out. S52: Quality control of shotcrete raw materials. Strictly screen the raw materials used in shotcrete, select ordinary Portland cement and add appropriate accelerator, control the mud content of sand to ≤3% and fineness modulus to ≤2.6, select graded aggregate with particle size ≤10mm for coarse aggregate, and conduct performance tests on all raw materials before they enter the site. Only after the tests are qualified can they be put into use. S53: Optimization and control of shotcrete mix proportions; precise design of concrete mix proportions according to performance requirements, controlling aggregate-to-cement ratio ≤ 1:4 and cement content ≤ 390 kg / m³. 3The sand content is 50%, the water-cement ratio is controlled in the range of 0.4 to 0.45, and after the mix proportion is determined, a test spray is carried out for verification. The optimal mix proportion is optimized and adjusted according to the rebound rate, setting speed and surface smoothness of the test spray. S54: Wet spraying construction process control. Wet spraying process is used for concrete spraying operations. The nozzle is kept perpendicular to the surface of the initial support. The spraying distance is 0.7 to 1.3 m. The spraying air pressure is controlled at 0.5 to 0.6 MPa. At the same time, the spraying parameters are adjusted in conjunction with the on-site excavation section, the spacing of the blast holes and the drilling angle to control the concrete rebound rate to within 20%. S55: Rebound material collection, analysis and processing. Collect and weigh all concrete rebound materials during the shotcrete process, calculate the actual rebound rate, analyze the causes of high rebound rate, and formulate targeted improvement measures for nozzle operation, mix ratio and spraying air pressure. At the same time, mix qualified rebound materials into new materials in proportion for reuse to reduce material waste. S56: Shotcrete forming quality inspection. After the concrete is shotcreted, the flatness and thickness of the initial support surface are comprehensively inspected. Any unqualified parts are promptly re-shotcreted to ensure that the quality of the shotcrete support meets the design and specification requirements.

[0029] Example 6: Based on the above embodiments, this embodiment further defines the specific process of step S6 as follows: S61: Full collection of construction data. For each drilling and blasting cycle, collect all dimensions of construction data according to a unified standard, including basic information such as mileage section and construction location; drilling and blasting parameters such as blast hole layout, charge amount for each part, drilling angle, and explosive consumption; over-excavation and under-excavation parameters such as over-excavation amount, over-excavation area, and under-excavation amount for arch crown / arch waist / sidewall / arch foot; concrete spraying parameters such as design volume, actual volume, over-excavation volume, rebound rate, raw material ratio, and spraying process parameters; and process time parameters such as operation time for each process of drilling, blasting, slag removal, and shotcreting. S62: Establish a construction data ledger. Classify, organize, and input the collected full-dimensional data according to the number of cycle operations to establish a standardized construction data ledger. The ledger is equipped with a data traceability module to associate the corresponding cycle's working face photos, geological sketches, cross-section scanning reports, and drilling and blasting design drawings to achieve a one-to-one correspondence between the data and the on-site construction data. S63: Data correlation analysis. Using comparative analysis and correlation analysis methods, we can explore the inherent correlation between construction data. We will focus on analyzing the correlation between drilling and blasting parameters and over-excavation, charge amount and explosive utilization rate, shotcrete process parameters and concrete rebound rate, and over-excavation and concrete over-volume. We will quantify the impact of each parameter on construction quality, material consumption and work efficiency, and locate the key points for parameter optimization in construction. S64: Analysis results feedback application. The key points, optimization directions and quantitative adjustment suggestions of parameter optimization obtained from data correlation analysis are fed back to the drilling and blasting parameter adjustment stage and the concrete spraying construction stage, respectively. This serves as the core basis for the formulation of drilling and blasting plans and the control of construction parameters for the next drilling and blasting cycle, so as to achieve targeted optimization of construction parameters. S65: Closed-loop management of construction data. After completing the construction data collection for the next drilling and blasting cycle, compare the construction data before and after optimization to verify the implementation effect of parameter adjustment. If the optimization effect does not meet expectations, conduct data correlation analysis again and adjust the optimization suggestions. This forms a complete process management system for construction data, including data collection, ledger establishment, analysis and mining, feedback optimization, and effect verification, to achieve continuous dynamic optimization of construction parameters.

[0030] Example 7: This embodiment provides an engineering example of using the construction method described in this invention, as follows: The tunnel's exit section is characterized by Triassic sandstone interbedded with mudstone, exhibiting well-developed joints and fissures. The rock mass is generally fractured, strongly weathered, and of poor integrity, with some severe and large slip layers. The tunnel face condition is as follows. Figure 2 , Figure 3 As shown, conventional blasting excavation was used in the early stages, resulting in significant over-excavation and severe overconsumption of shotcrete. The construction method of this invention was then employed, with the specific steps as follows: Advanced geological assessment: Based on the advanced geological forecast analysis from the design institute, the lithology ahead is sandstone interbedded with mudstone, with no adverse geological hazards; a specialist will conduct a geological sketch of the working face, such as... Figure 4 As shown, local slip layers were found at the working face, but no triangular joints or vertical joints were found. During manual drilling, based on the drilling resistance and the turbidity of the flushing fluid, it was determined that the surrounding rock ahead was moderately fractured. Therefore, a drilling method combining manual and mechanical drilling was adopted, with an initial blast hole spacing of 0.5m and shallow hole blasting.

[0031] Comparison of drill-and-blast design schemes: Scheme 1, calculated according to the "Technical Guidelines for Engineering Blasting," has a cycle advance of 3.3m and an arch frame spacing of 1m; Scheme 2, designed by a PhD student from Southwest University, has a cycle advance of 2.4m. After comparison, Scheme 1 is preferred. Figure 5 As shown, the final drill-and-blast design scheme was determined.

[0032] Control of drilling and blasting operation parameters, such as Figure 6 As shown: A three-arm drilling rig was used to construct the advanced small guide pipe, with a controlled angle of 8°. Based on the slippage situation on the left side of the face, the spacing of the pipe roof on the left side was adjusted from 0.8m to 0.6m; the spacing of the boreholes around the arch was adjusted to 0.4m, and the charge was reduced by 20%, while the spacing of the boreholes around the sidewalls and bottom slab remained at 0.6m; hydraulic blasting was used for the peripheral boreholes, with double detonators connected to avoid the use of detonating cords; purely mechanical excavation was abandoned, and manual finishing of the blast holes was adopted to reduce over-excavation. The construction operation was as follows: Figure 7 As shown.

[0033] Dynamic adjustment of drilling and blasting parameters, such as Figure 8 , Figure 9 As shown: The joints at the working face are relatively well-developed, and the overall integrity of the rock mass is generally poor. The perimeter boreholes will be converged 15cm to the excavation outline, and the outward angle will be adjusted to 9°. Based on the interbedded sandstone and mudstone, the single-hole charge in the sandstone section will be increased by 10%, and the single-hole charge in the mudstone section will be reduced by 15%, ensuring blasting effectiveness while minimizing disturbance to the surrounding rock. Construction operations are as follows: Figure 10 As shown.

[0034] Shotcrete construction control, such as Figure 11 As shown: After blasting and muck removal, a cross-sectional scan revealed a local over-excavation of 0.5m at the arch crown, with no under-excavation at the sidewalls. Only the under-excavated areas were treated before scaffolding was erected. The shotcrete raw materials used were P.O42.5 ordinary Portland cement, with the addition of a quick-setting accelerator. The sand had a mud content of 2.5%, a fineness modulus of 2.5, and a coarse aggregate particle size of 8mm. The mix design was an aggregate-to-cement ratio of 1:3.8 and a cement content of 380kg / m³. 3 The soil composition is 50% sand and the water-cement ratio is 0.42. During wet shotcreting, the nozzle is perpendicular to the initial support surface, the spraying distance is 1.0m, the air pressure is 0.55Mpa, and the concrete rebound rate is controlled at 18%. Rebound material is collected, weighed, and analyzed. Figure 12 , Figure 13 As shown, the excessive rebound in some areas was caused by nozzle angle deviation. In subsequent construction, operator training should be strengthened to ensure accurate nozzle angle.

[0035] Complete workflow management of construction data: This cycle mileage is PK16+631.2~+628.8, with a designed concrete volume of 17.89m³. 3 The actual volume is 45m³. 3 The over-cubic-meter rate was reduced by 35% compared to before optimization, the amount of explosive used was 192 kg, and the explosive consumption per cubic meter was 0.80 kg / m³. 2 The average over-excavation at the arch crown was 20cm, a 40% reduction compared to before optimization. The data was entered into the ledger and analysis showed that the over-excavation at the arch crown was still caused by local slippage. The next cycle will further densify the small guide pipes at the arch crown and optimize the charge amount.

[0036] The construction method of this invention has the following advantages. (1) It saves on concrete consumption and the time required for the process due to excessive consumption.

[0037] (2) Increased the advance rate and increased the utilization rate of explosives.

[0038] (3) The use of water pressure blasting has played a role in environmental protection.

[0039] (4) Improved the overall excavation and support quality.

[0040] The solution is currently performing well and has great potential for wider application. It improves construction quality, increases construction efficiency, reduces the amount of concrete used, and thus saves costs.

[0041] Main advantages (1) It saves on concrete consumption and the time required for the process due to excessive consumption.

[0042] (2) Increased the advance rate and increased the utilization rate of explosives.

[0043] (3) The use of water pressure blasting has played a role in environmental protection.

[0044] (4) Improved the overall excavation and support quality.

[0045] Economic analysis

[0046] The table above shows that after controlling over-excavation and under-excavation, the concrete over-excavation rate decreased by 32.1%-45.1%; the concrete rebound rate decreased by 2%-2.5%; and the average over-excavation was reduced by 17.8-35 cm. Approximately 10 m³ is saved per cycle. 3 The cost is 637.48 yuan per cubic meter, and the cost savings per cycle is 6374.8 yuan.

[0047] Social benefit analysis The minor improvements to the excavation and shotcrete construction of the weak surrounding rock were showcased and discussed at a seminar within the project section. These improvements received unanimous praise from the project management, supervision, and design units. The improvements were then implemented across the entire weak surrounding rock section, yielding positive social benefits.

[0048] Although embodiments of the invention have been shown and described, those skilled in the art will understand 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 claims and their equivalents.

Claims

1. A method for excavating and spraying concrete in soft surrounding rock of a tunnel, characterized in that, Includes the following steps: Step S1: Conduct advanced geological prediction analysis and perform geological hand-drawn sketches of the tunnel face to determine the blasting method and basic borehole parameters; Step S2: Determine the arch spacing and initial drill-and-blast parameters based on the practicality of each cycle of advance; Step S3: Perform precise control of drilling and blasting operation parameters; Step S4: Based on the surrounding rock and joint development at the construction site, develop a targeted drilling and blasting plan for each drilling and blasting cycle and dynamically optimize the drilling and blasting parameters. Step S5: Implement meticulous control over the entire process of shotcrete construction. Step S6: Collect construction data for each drilling and blasting cycle, establish a construction data ledger, analyze the correlation between data, and feed the analysis results back to the drilling and blasting parameter adjustment and concrete spraying construction stages to achieve complete process management of construction data.

2. The method for excavation and shotcrete construction of tunnels in weak surrounding rock according to claim 1, characterized in that, The specific process of step S1 is as follows: Step S11: Based on the advanced geological forecast document issued by the design institute, analyze the lithology, rock layer distribution and geological structure of the surrounding rock in front of the tunnel, and preliminarily confirm that the surrounding rock in front has the conditions for safe excavation. Step S12: Arrange for a specialist to conduct on-site survey and observation of the working face, complete a geological sketch of the working face, clarify the rock orientation and the degree of joint and fracture development, and at the same time confirm whether there are triangular joints, vertical joints and large slip layers at the working face, and determine the on-site safe construction conditions of the working face. Step S13: During the manual excavation stage, the changes in drilling resistance, drilling speed, and the color, turbidity, and flow rate of the drilling flushing fluid are used to help determine the lithology and integrity of the surrounding rock in front of the tunnel face. Step S14: Based on the comprehensive analysis and judgment results, determine the basic drilling parameters for tunnel excavation, including blasting method, drilling equipment type, initial spacing of blast holes, and initial charge per hole.

3. A method for excavation and shotcrete construction in soft surrounding rock of a tunnel according to claim 1 or 2, characterized in that, The specific process of step S2 is as follows: Step S21: Develop at least several candidate drill-and-blast design schemes; Step S22: Use the on-site operability of each cycle of advance as the core evaluation index to comprehensively compare and select each drill-and-blast design candidate scheme; Step S23: Select the optimal drill-blast design candidate scheme as the on-site construction execution scheme, determine the standard value of the arch spacing for tunnel excavation based on the scheme, and extract the initial drill-blast parameters from the scheme.

4. The method for excavation and shotcrete construction of tunnels in weak surrounding rock according to claim 3, characterized in that, The specific process of comprehensively comparing and selecting each drill-and-blast design candidate scheme in step S22, with the on-site operability of each cycle of advance as the core evaluation index, is as follows: quantitatively screening each drill-and-blast design candidate scheme through three dimensions: on-site construction condition matching, work efficiency feasibility, and process connection adaptability. The on-site construction condition matching judgment candidate scheme determines whether the drilling depth and blast hole layout density corresponding to each cycle of advance are compatible with the operating capacity of the existing excavation equipment and the tunnel face construction space of the project, and excludes schemes where the equipment cannot reach the designed drilling depth or the tunnel face space cannot meet the blast hole layout requirements. The feasibility calculation of the work efficiency of the candidate schemes is based on the theoretical total working hours of each process of drilling, charging, blasting and slag removal in a single cycle under the theoretical advance of each cycle. The schemes with theoretical total working hours not exceeding the working hours quota are compared with the project's established single-cycle construction time quota. The process connection adaptability verification candidate scheme theoretically matches the rhythm of each cycle of advance with the subsequent support process, ensuring that the excavation advance, the arch spacing, and the support operation efficiency are coordinated, avoiding schemes that cause untimely support due to excessive advance or idle work due to excessive advance.

5. The method for excavation and shotcrete construction of tunnels in weak surrounding rock according to claim 3, characterized in that, The initial drilling and blasting parameters extracted in step S23 include the blast hole layout, the initial spacing of blast holes in each part, the initial charge amount, and the detonator connection method.

6. A method for excavation and shotcrete construction in soft surrounding rock of a tunnel according to claim 1 or 2, characterized in that, The specific process for precisely controlling the drilling and blasting parameters in step S3 is as follows: Step S31: Control of advanced support parameters. Three-arm drilling is used to construct advanced small guide pipes and pipe roofs. The construction angle is monitored and controlled in real time through the equipment instrument panel to not exceed 9°. At the same time, the construction spacing and layout of the pipe roofs are dynamically adjusted according to the degree of fracture of the surrounding rock at the working face and the distribution of slip layers. Step S32: Precisely adjust the perimeter hole parameters, adjust the perimeter hole spacing of the arch from the original design value to 0.4m and simultaneously reduce the corresponding charge amount, while keeping the perimeter hole spacing of the other positions unchanged at the original design of 0.6m, and dynamically adjust the perimeter hole convergence value, external insertion angle and bottom plate drilling angle according to the real-time status of the surrounding rock. Step S33: Optimize and control the blasting process. Use hydraulic blasting for the perimeter holes to reduce the amount of explosives used and reduce disturbance to the surrounding rock. For the gas tunnel construction scenario, abandon the detonating cord and use a double detonator connection to complete the blasting network layout to ensure the safety of blasting construction. Step S34: Excavation method adaptation control. Compare the over-excavation effect of mechanical excavation and manual excavation. If there is still obvious over-excavation when the minimum adjustment angle of mechanical excavation is 9°, prioritize the use of manual excavation combined with mechanical assistance, and further optimize the drilling and blasting foundation parameters based on the excavation effect.

7. The method for excavation and shotcrete construction of tunnels in weak surrounding rock according to claim 6, characterized in that, The specific process of step S34 is as follows: S341: Conduct a comparative test on the over-excavation effect of mechanical excavation and manual excavation. Under the same drilling and blasting foundation parameters and the same surrounding rock section, adjust the drilling angle of mechanical excavation to a minimum of 9° for trial excavation, and record the over-excavation amount and over-excavation area of ​​each part of the arch crown, arch waist, sidewall and arch foot after mechanical excavation. S342: In the same section, drilling, charging and blasting operations are carried out by manual excavation. The over-excavation amount and over-excavation area of ​​each part are recorded after manual excavation. The over-excavation data of the two excavation methods are compared to determine whether there is an obvious over-excavation problem in mechanical excavation. S343: If it is determined that there is obvious over-excavation in mechanical excavation, then the excavation operation mode of manual excavation as the main method and mechanical assistance shall be adopted, with manual completion of the core process of the working face and mechanical completion of the auxiliary process; S344: During the operation mainly based on manual excavation, the excavation forming effect of each part is observed in real time, the actual over-excavation data is recorded, and the drilling and blasting foundation parameters are optimized in reverse according to the excavation effect to achieve the coordinated optimization of excavation method and drilling and blasting parameters.

8. A method for excavation and shotcrete construction of tunnels in weak surrounding rock according to claim 1 or 2, characterized in that, The specific process of step S4 is as follows: S41: Based on the actual working conditions of the surrounding rock determined by the survey, formulate a single-cycle drilling and blasting plan, make differentiated adjustments to the parameters of the surrounding boreholes, and set requirements for borehole construction and charging for different surrounding rock conditions. S42: Based on the rock fragmentation characteristics under different surrounding rock conditions, and taking into account the impact of unit rock mass explosive consumption on rock fragmentation size, borehole utilization rate, cross-sectional profile quality and surrounding rock stability, the single-hole charge of each part of the borehole is dynamically adjusted. Different charge standards are adopted for sandstone and mudstone sections. S43: Simultaneously optimize and adjust the drilling angle, blast hole spacing, and charge amount of the bottom plate holes and holes around the arch foot. Based on the actual situation of the bottom plate bulging and arch foot over-excavation, fine-tune the drilling insertion angle and charge amount to avoid aggravating local over-excavation.

9. A method for excavating and spraying concrete in weak surrounding rock of a tunnel according to claim 8, characterized in that, The specific process of step S41 is as follows: For working conditions where the surrounding rock has developed joints and fissures and there are localized point-like water outflows, the peripheral boreholes are converged 20cm to the excavation outline and vertical drilling without external insertion angle is adopted. During drilling, the verticality deviation of the boreholes is controlled to be no more than 0.5°, and the deviation of the borehole depth from the design depth is controlled within ±5cm. In addition, the amount of explosives charged in the peripheral boreholes is reduced by 20%~30% compared with the conventional working conditions, and waterproof explosive rolls are used for the entire section. For working conditions where the surrounding rock joints are relatively well-developed and the rock mass has good integrity, the peripheral boreholes are converged to the excavation outline by 15cm and boreholes are drilled at an external insertion angle of 9-10°. The deviation of the external insertion angle of the boreholes is no more than 1°, the deviation of the angle consistency between boreholes is controlled within ±0.5°, and the deviation of the borehole depth from the design depth is controlled within ±8cm. In this type of working condition, the amount of explosives charged in the peripheral boreholes is adjusted according to the rock mass integrity grade. When the rock mass integrity coefficient is ≥0.4, the amount of explosives is kept at the conventional standard, and when the rock mass integrity coefficient is <0.4, the amount of explosives is reduced by 10%~15%.

10. The method for excavation and shotcrete construction of tunnels in weak surrounding rock according to claim 1, characterized in that, The specific process of step S5 is as follows: S51: Over- and under-excavation section pretreatment control. After the blasting and muck removal is completed, the over- and under-excavation scanning detection of the tunnel face and excavation section is carried out immediately to accurately obtain the over-excavation, under-excavation, and over- and under-excavation area of ​​each part of the arch crown, arch waist, side wall and arch foot. Only the under-excavated parts are targeted for repair. After the treatment is completed, the tunnel face hazard removal and arch frame erection operations are carried out. S52: Quality control of shotcrete raw materials. Strictly screen the raw materials used in shotcrete, select ordinary Portland cement and add appropriate accelerator, control the mud content of sand to ≤3% and fineness modulus to ≤2.6, select graded aggregate with particle size ≤10mm for coarse aggregate, and conduct performance tests on all raw materials before they enter the site. Only after the tests are qualified can they be put into use. S53: Optimization and control of shotcrete mix proportion. The concrete mix proportion is precisely designed according to performance requirements, controlling the aggregate ratio to be ≤1:4, the cement content to be ≤390kg / m³, the sand content to be 50%, and the water-cement ratio to be controlled within the range of 0.4~0.

45. After the mix proportion is determined, a test spray is conducted for verification. The optimal mix proportion is then optimized and adjusted based on the rebound rate, setting speed, and surface smoothness of the test spray. S54: Wet shotcrete construction process control. Wet shotcrete process is used for concrete spraying operations. The nozzle is kept perpendicular to the surface of the initial support. The spraying distance is 0.7~1.3m. The spraying air pressure is controlled at 0.5~0.6Mpa. At the same time, the spraying parameters are adjusted in conjunction with the on-site excavation section, the spacing of the blast holes and the drilling angle to control the concrete rebound rate to within 20%. S55: Rebound material collection, analysis and processing. Collect and weigh all concrete rebound materials during the shotcrete process, calculate the actual rebound rate, analyze the causes of high rebound rate, and formulate targeted improvement measures for nozzle operation, mix ratio and spraying air pressure. At the same time, mix qualified rebound materials into new materials in proportion for reuse to reduce material waste. S56: Shotcrete forming quality inspection. After the concrete is shotcreted, the flatness and thickness of the initial support surface are comprehensively inspected. Any unqualified parts are promptly re-shotcreted to ensure that the quality of the shotcrete support meets the design and specification requirements.

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