Soft rock geological cavern tunneling construction method

Abstract

The invention discloses a soft rock geological cavern tunneling construction method, belongs to the technical field of underground engineering tunnel construction, and aims to solve the safety risk problem caused by high surrounding rock deformation rate, insufficient supporting structure stability and dynamic adjustment lag in the tunnel construction process under the soft rock geological condition. According to the method, an upper pilot tunnel area, a middle pilot tunnel area and a lower pilot tunnel area are divided in the axial direction of a tunnel and excavated step by step, multiple layers of steel arches are sequentially installed, prestressed anchor rods are constructed, a real-time stress monitoring and early warning system is combined, the supporting force of adjustable hydraulic supporting rods is dynamically adjusted, and the deformation rate and the stress level of surrounding rock are controlled. According to the technical scheme, the method is characterized by comprising partition and layering excavation, steel arch and anchor rod collaborative supporting, stress monitoring point arrangement and a dynamic compensation mechanism. The method is mainly used for safe and efficient tunneling of the soft rock geological tunnel, the surrounding rock stability and the construction safety are remarkably improved through refined construction control and real-time feedback adjustment, and the method is suitable for tunnel engineering construction under the complex geological condition.

Description

Technical Field

[0001] The present invention relates to the technical field of underground engineering tunnel construction. More specifically, the present invention relates to a construction method for tunneling in soft rock geological tunnels. Background Art

[0002] When tunneling in soft rock geological conditions, the surrounding rock has low strength and poor self-stabilizing ability, and is prone to large deformations or even collapses, seriously threatening construction safety and project progress. Although the traditional step-by-step excavation method can control the disturbance of the surrounding rock in stages, the division of pilot tunnels and support parameters often adopt fixed designs, which are difficult to adapt to the rheological characteristics of soft rock and local geological mutations, resulting in uneven stress on the support structure and cumulative deformation, and ultimately causing distortion of steel arch frames or failure of anchor bolts. In addition, there is a lag in stress monitoring and support adjustment in the prior art. Usually relying on manual inspections or periodic data collection, it is difficult to capture the dynamic changes of the surrounding rock in a timely manner, resulting in delayed early warning and emergency response measures. For example, when the deformation rate of the surrounding rock suddenly increases, the traditional method needs to suspend construction and reinforce manually, which is not only inefficient but also may expand the risk due to untimely treatment.

[0003] The main reasons for the above problems mainly include: the non-homogeneity and time effect of soft rock are significant, the conventional support system lacks dynamic adaptability; the integration degree of the monitoring system is low, and the linkage between data feedback and the actuator is insufficient; the propulsion rhythm of each pilot tunnel and the support connection in the step-by-step excavation lack coordinated optimization, and stress concentration areas are easily formed. Especially in the excavation stage of the middle and lower pilot tunnels, the upper support structure may undergo secondary deformation due to subsequent construction disturbances. In the prior art, the connection method of multi-layer steel arch frames is single, and it is difficult to improve the overall stiffness. In addition, the arrangement angle and density of anchor bolts have a significant impact on the reinforcement effect of the surrounding rock, but the traditional design relies on empirical formulas and does not perform dynamic optimization in combination with real-time monitoring data, resulting in insufficient reinforcement in local areas. Summary of the Invention

[0004] An object of the present invention is to solve at least the above problems and provide at least the advantages described hereinafter.

[0005] Another object of the present invention is to provide a construction method for tunneling in soft rock geological tunnels, which is used for the safe and efficient tunneling of soft rock geological tunnels. Through refined construction control and real-time feedback adjustment, the stability of the surrounding rock and construction safety are significantly improved, and it is applicable to tunnel engineering construction under complex geological conditions.

[0006] To achieve these objects and other advantages in accordance with the present invention, there is provided a construction method for tunneling in soft rock geological tunnels, comprising the following steps: 1) Divide three pilot tunnel areas vertically along the heading face, where the height of the upper pilot tunnel area is 2.5 - 3.5 meters, the height of the middle pilot tunnel area is 2.0 - 2.5 meters, and the height of the lower pilot tunnel area is 1.8 - 2.2 meters; 2) The step-by-step excavation method is adopted. First, the upper pilot tunnel area is excavated, and the excavation footage range is controlled within 0.8 - 1.2 meters. After excavation, the first layer of steel arch is installed. After the installation of the first layer of steel arch is completed, the first group of prestressed anchor rods with a length of 3.5 - 4 meters are constructed at intervals of 0.8 - 1.5 meters along the circumferential direction of the tunnel. Secondly, after the upper pilot tunnel area is advanced by 5 - 8 meters, the middle pilot tunnel area is started to be excavated. After excavation, the second layer of steel arch is installed in the middle pilot tunnel area. The second layer of steel arch is welded and fixed with the first layer of steel arch by vertical connecting bars. After the installation of the second layer of steel arch is completed, the second group of prestressed anchor rods with a length of 3 - 3.5 meters are constructed at intervals of 2 - 3 meters along the circumferential direction of the tunnel. Finally, after the middle pilot tunnel area is advanced by 3 - 5 meters, the lower pilot tunnel area is started to be excavated. After excavation, the third layer of steel arch is installed in the lower pilot tunnel area. The third layer of steel arches are connected by cross bracing. After the installation of the third layer of steel arch is completed, the third group of prestressed anchor rods with a length of 2.5 - 3 meters are constructed at intervals of 3 - 4 meters along the circumferential direction of the tunnel. 3) Stress monitoring points are respectively set at the intersection of the first layer of steel arch and the second layer of steel arch, and at the intersection of the second layer of steel arch and the third layer of steel arch. Two groups of displacement sensors and one group of stress gauges are arranged at each stress monitoring point. When the circumferential displacement change rate monitored by the displacement sensor > 15 mm / 24 h or the stress value measured by the stress gauge > 70% of the design strength, the early warning system is automatically triggered. Within 4 hours after the early warning system is triggered, adjustable hydraulic support rods are symmetrically installed at a distance of 1.2 - 1.8 m from the inner side of the corresponding steel arch. After the installation is completed, the dynamic compensation mode is started, and data is real-time fed back through the pressure sensor. The supporting force of the adjustable hydraulic support rod is adjusted at a gradient of 5 kN / time until the circumferential displacement change rate drops to < 15 mm / 24 h and the stress value drops below 70% of the design strength.

[0007] Preferably, after step 3), the following step is further included: 4) After the dynamic compensation of the adjustable hydraulic support rod is completed, grouting reinforcement is carried out in sections and areas: Ultra-fine cement-based grouting materials with a particle size D50 ≤ 5 μm are used, and the slurry is prepared according to the water-cement ratio of 0.8:1. Grouting pipes are arranged at intervals of 1.2 m along the circumferential direction of the multi-layer steel arch. Grouting is carried out in two stages: In the first stage, low-pressure permeation grouting is carried out at 0.5 - 0.8 MPa until the grouting volume reaches 80% of the design value, and then the second stage of splitting grouting at 1.2 - 1.5 MPa is carried out after an interval of 12 hours. After grouting is completed, a stress monitoring box is installed at the tail of the grouting pipe to real-time feed back the co-deformation data of the surrounding rock-support structure.

[0008] Preferably, after step 4), the following step is further included: 5) Implement the coordinated deformation compensation of surrounding rock - support: Set a flexible buffer layer outside the grouting reinforcement area. Pour a circumferential isolation belt with a thickness of 300 mm of foamed concrete outside the flexible buffer layer, and reserve a 20 - mm deformation joint; Layout prestressed anchor cables longitudinally along the tunnel at an interval of 2 m. The tensile force of the anchor cables is applied in stages up to 150 kN and is connected to the first - layer steel arch, the second - layer steel arch, and the third - layer steel arch through articulated trays; Install a distributed optical fiber monitoring system, lay strain - sensing optical fibers along the entire length of the anchor cables to monitor the stress distribution of the anchor cables in real - time; Dynamically adjust the prestress of the anchor cables based on the monitoring data, with the adjustment amplitude ≤ 20 kN / time, and maintain the radius of the plastic zone of the surrounding rock ≤ 1.2D, where D is the tunnel diameter.

[0009] Preferably, step 2) specifically includes the following steps: S21. Adopt the step - by - step excavation method. First, excavate the upper pilot tunnel area. The upper pilot tunnel excavation adopts the layered staggered - distance method, and the excavation footage range is controlled within 0.8 - 1.2 m. After excavation, install the first - layer steel arch. The first - layer steel arch uses HW175 - type I - shaped steel, the longitudinal spacing of the first - layer steel arch is 0.4 - 0.6 m, and the web of the first - layer steel arch is provided with connection holes at an interval of 0.3 m; After the installation of the first - layer steel arch is completed, construct the first group of prestressed anchor rods with a length of 3.5 m at an interval of 0.8 m along the tunnel circumference. Each prestressed anchor rod in the first group of prestressed anchor rods forms an elevation angle of 15 - 25 degrees with the horizontal plane, and the end of each prestressed anchor rod is fixed to the first - layer steel arch through the connection hole. S22. After the upper pilot tunnel area advances 5 - 8 m, start the excavation of the middle pilot tunnel area. After excavation, install the second - layer steel arch in the middle pilot tunnel area. The second - layer steel arch is welded and fixed to the first - layer steel arch with Φ25 vertical connecting bars. The longitudinal spacing of the connecting bars is 0.8 m, and the weld height ≥ 10 mm to form a double - layer truss structure; After the installation of the second - layer steel arch is completed, construct the second group of prestressed anchor rods with a length of 3 - 3.5 m at an interval of 2 - 3 m. Each prestressed anchor rod in the second group of prestressed anchor rods forms an elevation angle of 15 - 18 degrees with the horizontal plane. S23. After the middle pilot tunnel area advances 3 - 5 m, start the excavation of the lower pilot tunnel area. After excavation, install the third - layer steel arch in the lower pilot tunnel area. The third - layer steel arches are connected by cross - braces. Among them, the cross - braces use Φ89×6 mm seamless steel pipes, the brace angle is 45° ± 5°, and triangular stiffening plates with a thickness of 12 mm are welded at the connection nodes. The third - layer steel arches are connected by cross - braces. After the installation of the third - layer steel arch is completed, construct the third group of prestressed anchor rods with a length of 2.5 - 3 m at an interval of 3 - 4 m along the tunnel circumference. Each prestressed anchor rod in the third group of prestressed anchor rods forms an elevation angle of 15 - 18 degrees with the horizontal plane.

[0010] Preferably, step 1) further includes: Dynamically adjust the height of the pilot tunnel according to the surrounding rock integrity coefficient. When the surrounding rock integrity coefficient < 0.4, the height of the upper pilot tunnel area is reduced to 2.2 - 2.8 meters, the height of the lower pilot tunnel area is increased to 2.0 - 2.3 meters, and a temporary invert is added in the middle pilot tunnel area; Embed distributed optical fiber monitoring pipes at the boundary of the pilot tunnels to monitor the strain rate of the surrounding rock at the interface in real time; Set up Φ42mm, L = 5m advanced small pipes at the top of the upper pilot tunnel area, arranged in a plum blossom shape with a spacing of 0.5 meters, and grout to form a pre - support arch shell.

[0011] Preferably, the grouting reinforcement also includes: integrating a micro - camera at the front end of the grouting pipe to observe the diffusion form of the grout in real time; applying a 0.5Hz low - frequency vibration wave synchronously during the grouting process to promote the penetration of the grout; spraying a quick - setting sealing layer on the grouting completion surface to form a waterproof isolation membrane.

[0012] Preferably, step 2) also includes: using a high - frequency plasma generator to radiatively modify the surrounding rock of the tunnel face before excavation to form a hardened shell layer with a compressive strength ≥ 35 MPa and a thickness of 2.0 ± 0.2 m; using a negative - pressure adsorption type muck transportation system, equipped with a cyclone separator for dust adsorption and dust removal, where the air volume of the negative - pressure adsorption system is 8000m³ / h.

[0013] Preferably, the low - frequency vibration wave application system is configured with a rheological parameter feedback module to collect the viscosity and thixotropy index of the grout in real time, and dynamically adjust the vibration frequency and energy density; the outer wall of the grouting pipe is provided with spiral guide vanes, the vane inclination angle is 30° ± 2°, and the pitch is 1.2 times the pipe diameter; the propagation direction of the low - frequency vibration wave forms an angle of 45° ± 5° with the main joint trend of the surrounding rock, and the loading angle is automatically calibrated after determining the spatial distribution of the main joints through geological radar scanning.

[0014] Preferably, a basalt fiber grid with an aperture of 50×50 mm is embedded between the flexible buffer layer and the circumferential isolation belt, a water - swelling rubber strip with a swelling rate ≥ 300% is filled in the deformation joint, and a graphene - based anti - slip coating with a friction coefficient ≥ 0.8 is coated on the surface of the isolation belt.

[0015] Preferably, the construction of the prestressed anchor cable includes: the free section of the prestressed anchor cable is wrapped with a shape - memory alloy sleeve, and temperature - triggered expansion forms multiple anchoring points; when the anchor cable is tensioned, low - temperature liquid nitrogen at - 196℃ is injected synchronously, and the tail of the anchor cable is connected to an electromagnetic damper to dissipate vibration energy in real time.

[0016] The present invention has at least the following beneficial effects: 1. The tunneling construction method for soft rock geology of the present invention significantly reduces the surrounding rock deformation rate by step-by-step excavation of the upper, middle, and lower pilot tunnels and installation of multiple layers of steel arch frames and prestressed anchor bolts, combined with real-time stress monitoring and dynamic compensation mechanism. The partitioned and layered excavation reduces the one-time disturbance range, and the coordinated support of the steel arch frame and the anchor bolt enhances the structural integrity. The stress monitoring points are linked with the early warning system, and the dynamic adjustment of the hydraulic support rods can be started within 4 hours when the deformation rate exceeds the limit, reducing the displacement rate below the safety threshold and effectively avoiding the risk of collapse.

[0017] 2. The tunneling construction method for soft rock geology of the present invention uses ultra-fine cement-based grouting materials for grouting in two stages. The low-pressure penetration ensures that the grout fully fills the cracks, and the high-pressure splitting enhances the bonding force between the surrounding rock and the support interface. A stress monitoring box is installed at the tail of the grouting pipe to provide real-time feedback of the coordinated deformation data and accurately evaluate the grouting effect. The ultra-fine material with a slurry particle size ≤ 5μm can penetrate micro-cracks, and the water-cement ratio of 0.8:1 optimizes the slurry fluidity, improves the reinforcement uniformity, and reduces the grouting blind area.

[0018] 3. The tunneling construction method for soft rock geology of the present invention combines a flexible buffer layer and a foamed concrete isolation belt with prestressed anchor cables to form a multi-level load transfer path. The tensile force of the anchor cables is applied in stages up to 150 kN and connected to the three-layer steel arch frame through articulated trays to ensure uniform load distribution to the support system. The distributed optical fiber monitoring system real-time tracks the stress distribution of the anchor cables and dynamically adjusts the prestress (amplitude ≤ 20 kN / time), restricting the radius of the plastic zone of the surrounding rock ≤ 1.2D and significantly suppressing the large deformation of the surrounding rock.

[0019] 4. In the tunneling construction method for soft rock geology of the present invention, the upper pilot tunnel uses HW175 type I-beams (longitudinal spacing 0.4 - 0.6 m), the middle pilot tunnel forms a double-layer truss by welding Φ25 vertical connecting bars, and the lower pilot tunnel uses Φ89×6 mm cross braces to improve the stiffness of each layer structure. The elevation angles of the anchor bolts are designed in layers (15° - 25° for the upper pilot tunnel, 15° - 18° for the middle pilot tunnel), optimizing the direction of the anchoring force, enhancing the targeted restraint on the surrounding rock deformation, and reducing the risk of local stress concentration.

[0020] 5. The tunneling construction method for soft rock geology of the present invention dynamically adjusts the height of the pilot tunnel according to the integrity coefficient of the surrounding rock (for example, when the coefficient < 0.4, the height of the upper pilot tunnel is reduced to 2.2 - 2.8 m), and a temporary inverted arch is added to balance the pressure in the middle pilot tunnel. The advanced small pipes (Φ42 mm, L = 5 m) are arranged in a plum blossom shape and grouted to form a pre-support arch shell to reinforce the surrounding rock in front of the heading face in advance and reduce the risk of collapse during the excavation stage. The distributed optical fiber monitoring pipes capture the strain rate at the interface in real time to provide data support for dynamic adjustment.

[0021] 6. The grouting pipe integrated with a micro camera in the tunneling construction method for soft rock geology of the present invention observes the diffusion form of the grout in real time, and combines with 0.5 Hz low-frequency vibration waves to promote the penetration of the grout, solving the problem of traditional grouting blind areas. After the spraying of the quick-setting sealing layer, a waterproof isolation membrane is formed to block the seepage path of groundwater. The synchronous application of vibration waves enhances the bonding force between the grout and the surrounding rock, and the low-frequency characteristics avoid disturbing the reinforced area, improving the grouting efficiency and quality.

[0022] 7. The tunneling construction method for soft rock geology of the present invention modifies the surrounding rock of the tunnel face by high-frequency plasma radiation, forming a hardened shell layer with a compressive strength ≥ 35 MPa and a thickness of 2.0 ± 0.2 m, significantly improving the self-stabilizing ability of the surrounding rock. The negative pressure adsorption type muck transportation system (air volume 8000 m³ / h) is combined with a cyclone separator, and the dust adsorption rate > 90%, improving the working environment and reducing occupational health hazards.

[0023] 8. The rheological parameter feedback module in the tunneling construction method for soft rock geology of the present invention real-time collects the viscosity and thixotropy index of the grout, dynamically adjusts the vibration frequency (0.5 Hz ± 0.1 Hz) and energy density to ensure the matching of grout penetration and rock joints. The spiral guide vanes (inclination angle 30° ± 2°) on the outer wall of the grouting pipe optimize the grout flow path, and the pitch is 1.2 times the pipe diameter, reducing the risk of pipe blockage. The propagation direction of the vibration wave forms an angle of 45° ± 5° with the main joints, and the loading angle is calibrated by a ground penetrating radar to enhance the diffusion effect of the grout along the joints.

[0024] 9. In the tunneling construction method for soft rock geology of the present invention, basalt fiber grids (aperture 50 × 50 mm) are embedded between the flexible buffer layer and the isolation belt to improve the shear strength; water-swelling rubber strips (swelling rate ≥ 300%) are filled in the deformation joints, and tightly seal the cracks after encountering water. A graphene-based anti-slip coating (friction coefficient ≥ 0.8) is coated on the surface of the isolation belt to reduce the relative slip between the surrounding rock and the structure, and at the same time enhance the waterproof performance and extend the durability of the support system.

[0025] 10. In the tunneling construction method for soft rock geology of the present invention, the shape memory alloy sleeve expands to form multiple anchoring points under temperature triggering, improving the biting strength between the anchor cable and the surrounding rock. When tensioning, liquid nitrogen at -196 °C is injected synchronously to cool and shrink the free section of the anchor cable, enhancing the efficiency of prestress application. The electromagnetic damper dissipates the vibration energy in real time, reducing the risk of fatigue damage of the anchor cable. The low-temperature liquid nitrogen can also locally reinforce the micro-cracks in the surrounding rock to form an auxiliary anchoring effect and extend the service life of the anchor cable.

[0026] Other advantages, objectives and features of the present invention will be partially reflected by the following description, and will also be understood by those skilled in the art through the research and practice of the present invention. Detailed implementation manners

[0027] The following provides a further detailed description of the present invention so that those skilled in the art can implement it with reference to the text of the specification.

[0028] It should be understood that terms such as "having", "comprising", and "including" used herein do not exclude the presence or addition of one or more other elements or their combinations.

[0029] The present invention provides a construction method for tunneling in soft rock geology, including the following steps: 1) Divide the heading face into three pilot tunnel areas in the vertical direction, where the height of the upper pilot tunnel area is 2.5 - 3.5 meters, the height of the middle pilot tunnel area is 2.0 - 2.5 meters, and the height of the lower pilot tunnel area is 1.8 - 2.2 meters; 2) Adopt the step-by-step excavation method. First, excavate the upper pilot tunnel area, and control the excavation footage range within 0.8 - 1.2 meters. After excavation, install the first layer of steel arch; after the installation of the first layer of steel arch is completed, construct the first group of prestressed anchor rods with a length of 3.5 - 4 meters at intervals of 0.8 - 1.5 meters along the tunnel circumference. Secondly, after the upper pilot tunnel area has advanced 5 - 8 meters, start excavating the middle pilot tunnel area. After excavation, install the second layer of steel arch in the middle pilot tunnel area. The second layer of steel arch is welded and fixed to the first layer of steel arch with vertical connecting bars. After the installation of the second layer of steel arch is completed, construct the second group of prestressed anchor rods with a length of 3 - 3.5 meters at intervals of 2 - 3 meters along the tunnel circumference. Finally, after the middle pilot tunnel area has advanced 3 - 5 meters, start excavating the lower pilot tunnel area. After excavation, install the third layer of steel arch in the lower pilot tunnel area. The third layer of steel arches is connected by cross braces. After the installation of the third layer of steel arch is completed, construct the third group of prestressed anchor rods with a length of 2.5 - 3 meters at intervals of 3 - 4 meters along the tunnel circumference; 3) Set stress monitoring points at the intersections of the first layer of steel arch and the second layer of steel arch, and at the intersections of the second layer of steel arch and the third layer of steel arch respectively. Two groups of displacement sensors and one group of stress gauges are arranged at each stress monitoring point; when the circumferential displacement change rate monitored by the displacement sensor > 15 mm / 24 h or the stress value measured by the stress gauge > 70% of the design strength, the early warning system is automatically triggered; within 4 hours after the early warning system is triggered, symmetrically install adjustable hydraulic support rods at a distance of 1.2 - 1.8 m from the inner side of the corresponding steel arch. After installation, start the dynamic compensation mode, and real-time feedback data through the pressure sensor, and adjust the supporting force of the adjustable hydraulic support rods in a gradient of 5 kN / time until the circumferential displacement change rate drops to < 15 mm / 24 h and the stress value drops below 70% of the design strength.

[0030] In the above technical solution, pilot tunnel division and step-by-step excavation: The height of the pilot tunnel can be adjusted according to the integrity coefficient of the surrounding rock. For example, when the integrity coefficient < 0.4, the height of the upper pilot tunnel can be reduced to 2.2 - 2.8 m, and the height of the lower pilot tunnel can be increased to 2.0 - 2.3 m. The excavation footage range can be controlled within 0.8 - 1.2 m, and the advancing distance is 5 - 8 m for the upper pilot tunnel and 3 - 5 m for the middle pilot tunnel. Laser rangefinders or total stations can be used as measuring tools and installed on the top and side walls of the tunnel face. For layered excavation, a multi-boom rock drill or a hydraulic excavator can be selected, and the advancing distance is marked by mileage stakes.

[0031] Installation of steel arch frames and construction of prestressed anchor bolts: The first layer of steel arch frames can use HW175 I-beams, with a longitudinal spacing of 0.4 - 0.6 m and a web connection hole spacing of 0.3 m. Anchor bolts can be Φ25 threaded steel bars, with a length of 3.5 - 4 m, an elevation angle of 15° - 25°, and the ends are fixed to the steel arch frames through connection holes. The second layer of steel arch frames can be welded to the first layer using Φ25 vertical connecting bars, with a weld height ≥ 10 mm to form a double-layer truss. Pneumatic anchor drills can be selected as the equipment for constructing anchor bolts, and ordinary Portland cement slurry can be selected as the grouting material. Cross diagonal braces can be Φ89×6 mm seamless steel pipes, with a diagonal brace angle of 45° ± 5°, and triangular stiffeners with a thickness of 12 mm are welded at the joints.

[0032] Stress monitoring and dynamic compensation: Displacement sensors can be resistive or fiber optic sensors and are arranged at the intersections of steel arch frames. Stress gauges can be vibrating wire sensors, with a measurement range covering 0 - 100% of the design strength. Adjustable hydraulic support rods can be double-acting hydraulic cylinders, with a stroke range of 1.2 - 1.8 m, and are installed symmetrically on the inner side of the steel arch frames. The dynamic compensation mode is achieved through a PLC control system, and pressure sensors provide real-time feedback of data, with an adjustment gradient of 5 kN / time. The warning threshold is set based on on-site surrounding rock test data, for example, the design strength reference value is determined through uniaxial compressive tests.

[0033] Technical effects: Through step-by-step excavation and dynamic adjustment of the pilot tunnel height, the disturbance range of the surrounding rock is reduced, and large-scale instability is avoided. The layered construction of steel arch frames and anchor bolts forms a collaborative support system, suppressing local stress concentration. The stress monitoring and the hydraulic support rods have a linkage response, controlling the surrounding rock deformation rate within 15 mm / 24 h and reducing the risk of collapse. The connection of cross diagonal braces and multi-layer steel arch frames enhances the structural integrity and is suitable for the complex geological conditions of soft rock tunnels.

[0034] In another technical solution, after step 3), the following steps are further included: 4) After the dynamic compensation of the adjustable hydraulic support rod is completed, grouting reinforcement is carried out in sections and partitions: Use ultrafine cement-based grouting material with a particle size D50 ≤ 5 μm, prepare the slurry according to the water-cement ratio of 0.8:1, and arrange grouting pipes at a circumferential spacing of 1.2 m along the multi-layer steel arch; Grouting is carried out in two stages: In the first stage, low-pressure infiltration grouting is carried out at 0.5 - 0.8 MPa until the grouting volume reaches 80% of the design value, and after a 12-hour interval, the second stage of 1.2 - 1.5 MPa splitting grouting is carried out; After grouting is completed, install a stress monitoring box at the tail of the grouting pipe to real-time feedback the co-deformation data of the surrounding rock-support structure.

[0035] In the above technical solution, the particle size D50 of the ultrafine cement-based grouting material can select commercially available products with ≤ 5 μm, the water-cement ratio is prepared according to 0.8:1, and the stirring time is ≥ 5 minutes until the slurry is uniform and free of lumps. The grouting pipe can select a PVC pipe with an outer diameter of 25 mm and an inner diameter of 20 mm, with a circumferential spacing of 1.2 m and a vertical insertion depth into the surrounding rock of 1.0 - 1.5 m. The front end of the grouting pipe can be integrated with a micro camera, the lens diameter is 8 mm, the protection level is IP68, and the real-time slurry diffusion image is transmitted through optical fiber. The micro camera uses the Python language to write an image processing program, and uses the OpenCV library for image preprocessing, including grayscale conversion, filtering and denoising, and binary processing. The slurry area is segmented by setting the HSV threshold of the slurry color (H: 0 - 30, S: 0 - 255, V: 0 - 255), the Canny edge detection algorithm is used to extract the slurry edge, the slurry diffusion radius and perimeter are calculated, and the diffusion uniformity is calculated by the formula "diffusion uniformity = 4π×(slurry area) / (perimeter²)". When the slurry diffusion radius is less than 90% of the design value or the diffusion uniformity is lower than 80%, the system automatically issues an alarm and prompts to adjust the grouting pressure or slurry ratio through the man-machine interface.

[0036] When arranging the grouting pipes, drill holes at a circumferential interval of 1.2 m along the steel arch, with a hole diameter of 30 mm. The outer wall of the grouting pipe in the hole is wound with a grout stop tape to prevent slurry backflow. The mixer can select a double-shaft forced type, with a capacity of 500 L, a rotation speed of 30 - 40 rpm, and the slurry consistency is controlled by a funnel viscometer, and the outflow time ≤ 25 seconds.

[0037] The low-pressure infiltration grouting pressure in the first stage can be set to 0.5 - 0.8 MPa, stop when the grouting volume reaches 80% of the design value, and the grouting rate is controlled at 8 - 10 L / min. The second stage of splitting grouting is carried out after a 12-hour interval, the pressure is increased to 1.2 - 1.5 MPa, the grouting rate is adjusted to 12 - 15 L / min, and it continues until the slurry returns at the hole mouth. During the grouting process, a 0.5 Hz low-frequency vibration wave can be applied synchronously, the power of the vibrator is 2.2 kW, and the amplitude is ±2 mm to promote the slurry to penetrate the cracks.

[0038] The grouting pump can be a hydraulically driven double-cylinder piston pump with a pressure fluctuation range of ±0.1 MPa. The grouting volume is monitored by an electromagnetic flowmeter with an accuracy of ±1%. The direction of the vibration wave application forms an angle of 45° ± 5° with the strike of the main joints of the surrounding rock. After determining the joint distribution through geological radar scanning, the loading angle is adjusted.

[0039] The stress monitoring box can be internally equipped with a resistance strain gauge type sensor with a measuring range of 0 - 10 MPa and an accuracy of ±0.5% FS. The monitoring box is installed at the tail of the grouting pipe, 0.3 - 0.5 m away from the grouting hole, and fixed to the web of the steel arch by expansion bolts. The data acquisition frequency is set to 1 Hz and sent to the control terminal through a wireless transmission module to generate a real-time collaborative deformation curve of the surrounding rock - support structure. The outer shell of the monitoring box can be made of 304 stainless steel with an IP67 protection level and filled with silicone sealant inside. Initial value calibration is required after installation to eliminate the influence of installation stress. If the monitoring data shows that the stress value in a certain area exceeds 70% of the design strength, the system automatically marks and triggers an audible and visual alarm to prompt manual recheck of the grouting saturation.

[0040] Technical effects: The staged grouting process takes into account both penetration filling and crack expansion, improving the uniformity of surrounding rock reinforcement; Low-frequency vibration-assisted grouting enhances the slurry diffusion radius and reduces blind spots; Real-time stress monitoring provides data support for dynamically adjusting support parameters and reduces the risk of structural failure.

[0041] In another technical solution, after step 4), the following step is further included: 5) Implement surrounding rock - support collaborative deformation compensation: Set a flexible buffer layer outside the grouting reinforcement area. Pour a circumferential isolation belt with a thickness of 300 mm of foamed concrete outside the flexible buffer layer, and reserve a 20 mm deformation joint; Layout prestressed anchor cables at a longitudinal spacing of 2 m along the tunnel. The tension of the anchor cables is applied in stages up to 150 kN and connected to the first-layer steel arch, the second-layer steel arch, and the third-layer steel arch through articulated trays; Install a distributed optical fiber monitoring system, lay strain sensing optical fibers along the entire length of the anchor cables, and monitor the stress distribution of the anchor cables in real time; Dynamically adjust the prestress of the anchor cables based on the monitoring data, with an adjustment range of ≤20 kN / time, and maintain the radius of the plastic zone of the surrounding rock ≤1.2 D, where D is the tunnel diameter.

[0042] In the above technical solution, the flexible buffer layer can adopt a basalt fiber grid with a grid aperture of 50×50 mm, a tensile strength of ≥150 MPa, and it fits the outer surface of the grouting reinforcement area. The circumferential isolation belt is cast with foamed concrete, with a thickness of 300 mm, a dry density of ≤600 kg / m³, and a compressive strength of ≥5 MPa. The width of the deformation joint is 20 mm, and it is filled with a water-swellable rubber strip inside, with a swelling rate of ≥300% and a Shore hardness of 40±5 HA. The surface of the isolation belt can be coated with a graphene-based anti-slip coating, with a friction coefficient of ≥0.8 and a coating thickness of 0.5~1.0 mm. The flexible buffer layer is installed outside the grouting reinforcement area and is continuously laid along the tunnel circumference. The circumferential isolation belt is formed by casting with a formwork, leaving a 20-mm deformation joint between it and the flexible buffer layer, and the rubber strip in the joint is fixed by a pressing strip. The surface coating is constructed by spraying process in two passes, with an interval of 2 hours.

[0043] The prestressed anchor cable can select the steel strand type, with a nominal diameter of 15.2 mm and an ultimate tensile strength of ≥1860 MPa. The anchor cables are arranged at a longitudinal spacing of 2 m along the tunnel, and the length of the free section is adjusted according to the radius of the plastic zone of the surrounding rock, with the length of the anchorage section being ≥5 m. The tension of the anchor cable is applied in three levels: the initial tension is 50 kN, the second level is 100 kN, and the final tension is 150 kN, with a holding time of ≥5 minutes for each level. The end of the anchor cable is connected to the steel arch by a hinged tray, the tray is made of Q345B steel, with a thickness of ≥20 mm, and the adjustable range of the hinged angle is ±10°. When installing the anchor cable, the drilling diameter needs to be ≥110 mm, and cement slurry is injected into the hole, with a water-cement ratio of 0.4~0.45. The tensioning equipment can select a hydraulic jack, and the tension is calibrated with a pressure sensor, with the error controlled within ±2%. An electromagnetic damper is installed at the tail of the anchor cable, with a damping coefficient of 0.15~0.25 N·s / mm, which is used to dissipate vibration energy.

[0044] The strain-sensing optical fiber can select the distributed fiber grating type, with a wavelength accuracy of ±0.1 nm and a measurement range of 0~5000 με. The optical fiber is helically wound along the entire length of the anchor cable surface, with a pitch of 50~80 mm, and is fixed with epoxy resin glue. The monitoring system continuously collects the wavelength shift of the optical fiber and converts it into stress data, with a sampling frequency of ≥10 Hz. When it is monitored that the local stress of the anchor cable exceeds 80% of the design value, the system triggers an early warning and starts a dynamic adjustment program. During adjustment, the hydraulic pump station adjusts the tension of the anchor cable at a rate of ≤20 kN / time, with an interval of ≥30 minutes for each adjustment, until the stress value drops back to the safety threshold. The optical fiber data is synchronously uploaded to the control terminal, and a stress distribution cloud map is generated through software to guide the adjustment direction and amplitude. The assembly position of the monitoring system is at the junction of the free section and the anchorage section of the anchor cable, and the optical fiber joint is encapsulated with a waterproof box, with an IP67 protection level.

[0045] Technical effects: The flexible buffer layer and the circumferential isolation belt can absorb the deformation energy of the surrounding rock and reduce the stress concentration of the support structure; the graded tensioning and dynamic adjustment of the prestress of the anchor cable can adapt to the rheological characteristics of soft rock and control the expansion of the plastic zone; the distributed optical fiber monitoring system realizes the real-time feedback of the stress distribution and improves the accuracy of the surrounding rock stability control.

[0046] In another technical solution, step 2) specifically includes the following steps: S21. Adopt the step-by-step excavation method. First, excavate the upper pilot tunnel area. The upper pilot tunnel is excavated using the layered staggering method, and the excavation footage range is controlled at 0.8 - 1.2 meters. After excavation, install the first layer of steel arch. The first layer of steel arch uses HW175 I-beam, and the longitudinal spacing of the first layer of steel arch is 0.4 - 0.6 meters. The web of the first layer of steel arch is provided with connection holes with a spacing of 0.3 meters; after the installation of the first layer of steel arch is completed, construct the first group of prestressed anchor rods with a length of 3.5 meters at intervals of 0.8 meters along the tunnel circumference. Each prestressed anchor rod in the first group of prestressed anchor rods forms an elevation angle of 15 - 25 degrees with the horizontal plane, and the end of each prestressed anchor rod is fixed to the first layer of steel arch through the connection hole. S22. After the upper pilot tunnel area advances 5 - 8 meters, start the excavation of the middle pilot tunnel area. After excavation, install the second layer of steel arch in the middle pilot tunnel area. The second layer of steel arch is welded and fixed to the first layer of steel arch with Φ25 vertical connecting bars. The longitudinal spacing of the connecting bars is 0.8 meters, and the weld height ≥ 10 mm to form a double-layer truss structure; after the installation of the second layer of steel arch is completed, construct the second group of prestressed anchor rods with a length of 3 - 3.5 meters at intervals of 2 - 3 meters. Each prestressed anchor rod in the second group of prestressed anchor rods forms an elevation angle of 15 - 18 degrees with the horizontal plane. S23. After the middle pilot tunnel area advances 3 - 5 meters, start the excavation of the lower pilot tunnel area. After excavation, install the third layer of steel arch in the lower pilot tunnel area. The third layer of steel arches is connected by cross braces. Among them, the cross braces use Φ89×6 mm seamless steel pipes, and the brace angle is 45° ± 5°. Triangular stiffeners with a thickness of 12 mm are welded at the connection nodes. The third layer of steel arches is connected by cross braces. After the installation of the third layer of steel arch is completed, construct the third group of prestressed anchor rods with a length of 2.5 - 3 meters at intervals of 3 - 4 meters along the tunnel circumference. Each prestressed anchor rod in the third group of prestressed anchor rods forms an elevation angle of 15 - 18 degrees with the horizontal plane.

[0047] In the above technical solution, the excavation footage of the upper pilot tunnel can be controlled within 0.8 - 1.2 m. The layered staggered distance method is adopted, and the excavation height of each layer is 0.5 - 0.7 m. The first layer of steel arch can use HW175 I-beam, with a longitudinal spacing of 0.4 - 0.6 m, the spacing of web connection holes is 0.3 m, and the hole diameter is 25 mm. When installing the steel arch, it can be positioned in cooperation with a hydraulic lifting device to ensure that the depth of the arch foot embedded in the surrounding rock is ≥ 200 mm. The length of the first group of prestressed anchor bolts is 3.5 m, the circumferential interval is 0.8 m, the elevation angle is 15° - 25°, and the end of the anchor bolt is fixed to the steel arch through the connection hole. The rod body of the anchor bolt can be made of HRB400 deformed steel bar with a diameter of 22 mm, and the torque of the supporting nut is 200 - 250 N·m. The anchor bolt grouting uses cement-based slurry, with a water-cement ratio of 0.45 - 0.5 and a grouting pressure of 0.3 - 0.5 MPa.

[0048] For the second layer of steel arch installed after the excavation of the middle pilot tunnel, the longitudinal spacing is aligned with that of the first layer. The connecting bars can use Φ25 round steel, with a longitudinal spacing of 0.8 m and a single length of 1.2 m. Both ends are welded to the flange of the steel arch. The weld height is ≥ 10 mm, E5015 electrodes are used, and the welding current is 120 - 150 A. The length of the second group of prestressed anchor bolts is 3 - 3.5 m, the circumferential interval is 2 - 3 m, the elevation angle is 15° - 18°, and the tail of the anchor bolt is connected to the steel arch through a U-shaped buckle.

[0049] When installing the steel arch, the verticality can be calibrated with the help of a laser locator, and the deviation is controlled within ±5 mm. After the connecting bars are welded, percussion inspection is required to ensure no false welding or slag inclusion. Before the anchor bolt grouting, the hole needs to be cleaned until the residue at the bottom of the hole is ≤ 50 mm, and the grouting saturation is verified by acoustic wave detection. For the cross bracing of the third layer of steel arch, Φ89×6 mm seamless steel pipes can be selected, the angle of the bracing is 45° ± 5°, and triangular stiffening plates with a thickness of 12 mm are welded at the joints. The side length of the stiffening plate is 150 mm, the weld height is ≥ 8 mm, and double-sided continuous welding is adopted. The length of the third group of prestressed anchor bolts is 2.5 - 3 m, the circumferential interval is 3 - 4 m, the elevation angle is 15° - 18°, and the grouting pressure of the anchorage section is increased to 0.6 - 0.8 MPa.

[0050] When installing the cross bracing, it can be pre-assembled into truss units on the ground and then hoisted into the tunnel in sections. An anti-rust coating is applied at the connection between the bracing and the steel arch, and the dry film thickness is ≥ 80 μm. The anchor bolt holes are drilled with a pneumatic down-the-hole drill, the hole diameter is 42 mm, and the drilling deviation is ≤ 2%.

[0051] Technical effects: The layered staggered excavation reduces the single-time exposed area of the surrounding rock and inhibits the deformation rate; The cooperative action of multiple layers of steel arches and anchor bolts enhances the overall support stiffness; The design of cross diagonal braces and stiffening plates effectively disperses local stress and avoids joint failure.

[0052] In another technical solution, step 1) further includes: Dynamically adjust the height of the pilot tunnel according to the surrounding rock integrity coefficient. When the surrounding rock integrity coefficient < 0.4, the height of the upper pilot tunnel area is reduced to 2.2 - 2.8 m, the height of the lower pilot tunnel area is increased to 2.0 - 2.3 m, and a temporary inverted arch is added in the middle pilot tunnel area; Embed a distributed optical fiber monitoring tube at the boundary of the pilot tunnels to monitor the strain rate of the surrounding rock at the interface in real time; Set up advanced small pipes with a diameter of Φ42mm and a length of L = 5m at the top of the upper pilot tunnel area, arranged in a plum blossom shape with a spacing of 0.5 m, and grout to form a pre - support arch shell.

[0053] In the above - mentioned technical solution, the height of the pilot tunnel is dynamically adjusted according to the surrounding rock integrity coefficient (the threshold is set to 0.4). When the surrounding rock integrity coefficient is lower than 0.4, the height of the upper pilot tunnel area can be reduced from the original design of 2.5 - 3.5 m to 2.2 - 2.8 m, and can be specifically adjusted to 2.2 m, 2.5 m or 2.8 m; the height of the lower pilot tunnel area is increased from the original design of 1.8 - 2.2 m to 2.0 - 2.3 m, for example, adjusted to 2.0 m, 2.1 m or 2.3 m. A temporary inverted arch is added in the middle pilot tunnel area. The inverted arch can use HW150 - type I - shaped steel with a longitudinal spacing of 0.6 - 1.0 m and is connected to the steel arch of the middle pilot tunnel through Φ22 bolts. The assembly position of the temporary inverted arch is at the bottom of the middle pilot tunnel, close to the excavation face, and is used to enhance the compressive capacity of this area. During construction, the surrounding rock integrity coefficient is obtained in real time through a geological radar. If the detected value is lower than 0.4 for three consecutive times, the instruction to adjust the height of the pilot tunnel is automatically triggered.

[0054] Embed a distributed optical fiber monitoring tube at the boundary of the pilot tunnels. The optical fiber monitoring tube can select an armored optical fiber sensor with an outer diameter of 8 mm and a length matching the interface of the pilot tunnels, such as a BOTDR - type distributed optical fiber. The monitoring tube is longitudinally arranged along the interface of the pilot tunnels with a spacing of 1.5 - 2.0 m and a buried depth in the surrounding rock of 0.3 - 0.5 m. During installation, first drill a hole with a diameter of 50 mm at the interface, and inject epoxy resin glue into the hole to fix the optical fiber monitoring tube. The monitoring tube collects the strain rate data of the surrounding rock at the interface in real time and uploads the data to the early warning system through an optical fiber demodulator. When the strain rate exceeds 5 με / min, the system automatically marks the abnormal area and prompts that the support needs to be strengthened. The assembly position of the optical fiber monitoring tube is at the junction of the upper pilot tunnel and the middle pilot tunnel, and the middle pilot tunnel and the lower pilot tunnel, and is continuously arranged along the tunnel circumference.

[0055] At the top of the upper pilot tunnel area, small pre - driven pipes with a diameter of Φ42mm and a length of 5m are set. The material of the small pipes can be selected as seamless steel pipe of Q345B, and the wall thickness of the pipe is 4mm. The pipes are arranged in a plum - blossom shape, with a circumferential spacing of 0.5m and a longitudinal spacing of 1.2 - 1.5m. During construction, a hydraulic drill is used to drill holes at an upward angle of 15° - 20°, and the drilling depth is 5.2m. After inserting the pipes, a cement - water glass double - liquid slurry is injected through a grouting pump. The water - cement ratio is 0.8:1, and the grouting pressure is 0.5 - 0.8MPa. After the grouting is completed, the slurry diffuses to form a pre - support arch shell with a thickness of 0.3 - 0.5m. The assembly position of the pipes is 0.2m outside the top contour line of the upper pilot tunnel and is welded and fixed to the steel arch. During the construction process, after every 10m of pipe grouting is completed, a ground - penetrating radar is used to detect the integrity of the arch shell. If a cavity area is found, supplementary grouting is carried out.

[0056] Technical effects By dynamically adjusting the height of the pilot tunnel, it can adapt to the local strength change of soft rock and reduce excavation disturbance; adding a temporary inverted arch enhances the stability of the middle pilot tunnel. The distributed optical fiber monitoring pipe realizes the real - time monitoring of the strain at the interface and improves the timeliness of abnormal response. The pre - support arch shell formed by grouting of the small pre - driven pipes effectively inhibits the collapse of the surrounding rock at the top and provides safety guarantee for the subsequent excavation. The overall scheme reduces the construction risk of the soft - rock tunnel through parametric adjustment and real - time monitoring.

[0057] In a certain expressway tunnel project, the integrity coefficient of the surrounding rock is 0.32. The height of the upper pilot tunnel is adjusted to 2.3m, and the height of the lower pilot tunnel is adjusted to 2.0m. A temporary inverted arch is added to the middle pilot tunnel, and the temporary inverted arch is cast with C30 concrete with a thickness of 30cm. During the construction process, through the monitoring of total station and convergence meter, the deformation rate of the surrounding rock is reduced from 15mm / d before adjustment to less than 3mm / d, and finally the tunnel forming quality is good.

[0058] In another technical solution, the grouting reinforcement also includes: integrating a micro - camera at the front end of the grouting pipe to observe the diffusion form of the slurry in real time; synchronously applying a 0.5Hz low - frequency vibration wave during the grouting process to promote the penetration of the slurry; spraying a quick - setting sealing layer on the grouting completion surface to form a waterproof isolation membrane.

[0059] In the above technical solution, a micro camera can be integrated at the front end of the grouting pipe. The diameter of the camera can be selected from 10 to 15 mm, the resolution is not less than 1080P, and the pressure resistance level is ≥1.5 MPa. The camera can be fixed at 20 to 30 mm from the front end of the grouting pipe and connected to an external display through a waterproof optical fiber. During construction, after the grouting pipe is inserted into the surrounding rock borehole, the camera takes real-time pictures of the slurry diffusion form, and the images are transmitted to the monitoring system. If the slurry diffusion radius is less than the designed value (for example, 0.8 meters), the system will automatically prompt to adjust the grouting pressure or the slurry ratio. The protective shell of the camera can be made of 316L stainless steel, with a wear-resistant ceramic coating on the surface. The assembly position is at the center of the axis of the front end of the grouting pipe to avoid interfering with the slurry flow.

[0060] During the grouting process, a low-frequency vibration wave of 0.5 Hz can be applied synchronously. The vibration wave energy density can be set to 50 to 80 J / m³. The vibration system can use an electromagnetic vibration generator, with an output frequency range of 0.3 to 0.7 Hz. The vibration head is connected to the outlet pipeline of the grouting pump through a flange. The vibration direction forms an angle of 45°±5° with the main joint trend of the surrounding rock, and the specific angle is automatically calibrated after scanning the main joint distribution with a ground-penetrating radar. When the vibration wave is applied, the grouting pressure is maintained at 0.5 to 0.8 MPa, and the vibration duration is 60% to 80% of the total grouting duration. The assembly position is at the connection section between the grouting pump and the grouting pipe. The bolt torque of the vibration head flange needs to reach 80 to 100 N·m to prevent loosening.

[0061] After the grouting is completed, a quick-setting sealing layer can be sprayed on the grouting completion surface. The thickness of the sealing layer is 2 to 3 mm, and the setting time is ≤30 seconds. The quick-setting material can use a sulfoaluminate cement-based waterproof coating, with 3% to 5% of nano-silica reinforcing agent added. The spraying equipment can use an airless spraying machine, with a nozzle diameter of 1.2 to 1.5 mm and a spraying pressure of 0.4 to 0.6 MPa. During construction, first spray in sections from the tunnel crown to the side walls on both sides, with each section length of 1.5 to 2.0 meters. Immediately after spraying, use a scraper to level the surface. The sealing layer needs to completely cover the tail of the grouting pipe and the surrounding rock fissures. The assembly position is 50 to 80 mm away from the outlet of the grouting pipe and evenly covers in the direction perpendicular to the axis of the grouting pipe.

[0062] Technical effects The integrated micro camera can visually monitor the slurry diffusion state and reduce the grouting blind area; the low-frequency vibration wave optimizes the slurry penetration path and improves the reinforcement uniformity; the quick-setting sealing layer effectively seals the surface fissures and enhances the waterproof performance. The synergistic effect of the three can improve the grouting reinforcement efficiency and reduce the risk of secondary deformation of the surrounding rock.

[0063] In another technical solution, step 2) further includes: before excavation, the surrounding rock of the heading face is radiatively modified by a high-frequency plasma generator to form a hardened shell layer with a compressive strength ≥ 35 MPa and a thickness of 2.0 ± 0.2 m; a negative-pressure adsorption type muck transportation system is adopted, and a cyclone separator is configured for dust adsorption and dust removal, where the air volume of the negative-pressure adsorption system is 8000 m³ / h.

[0064] In the above technical solution, the high-frequency plasma generator can select an industrial-grade device with an output frequency of 13.56 MHz, a power range of 30 - 50 kW, and the distance between the radiation head and the heading face is controlled within 0.5 - 1.0 m. The treatment time is adjusted according to the type of surrounding rock, 8 - 12 minutes for mudstone and 10 - 15 minutes for shale. The hardened shell layer formed after modification has a compressive strength ≥ 35 MPa, a thickness of 2.0 ± 0.2 m, and the surface flatness deviation ≤ 5 mm. The plasma generator can be installed on the front support of the tunnel boring machine, and the radiation head reciprocates horizontally along the heading face at a moving speed of 0.2 - 0.5 m / s. During the treatment process, the temperature of the shell layer is monitored in real time and controlled within the range of 80 - 120 °C to avoid thermal cracking of the surrounding rock. The edge of the hardened shell layer needs to overlap with the untreated area by 200 - 300 mm to prevent stress mutation.

[0065] The negative-pressure adsorption system can be configured with a centrifugal fan, with an air volume of 8000 m³ / h and a wind pressure ≥ 5000 Pa. The suction inlet is arranged 1.5 - 2.0 m behind the excavation face and is connected by a telescopic metal hose with a diameter of 300 mm. The muck is transported through a negative-pressure pipeline to the cyclone separator. The diameter of the separator is 1.2 m, the inlet flow rate is 18 - 22 m / s, and the dust capture efficiency ≥ 95%. The separated muck can be temporarily stored in a closed aggregate bin with a bin volume of 8 - 10 m³, and a hydraulic discharge door is provided at the bottom. The dust removal system can be additionally equipped with a bag filter with a filtration accuracy ≤ 5 μm, a backflush pressure of 0.4 - 0.6 MPa, and automatic ash cleaning once every 30 minutes. The fan motor is equipped with a frequency converter to dynamically adjust the speed according to the muck volume, and the power fluctuation range is ± 10%.

[0066] The thickness of the hardened shell layer can be detected by an ultrasonic thickness gauge with a probe frequency of 5 MHz and a measurement error of ± 0.05 m. The compressive strength test can be carried out by taking cores on the surface of the shell layer with a portable press. The core sample has a diameter of 50 mm and a height of 100 mm, and the loading rate is 1.0 MPa / s. The integrity of the shell layer can be verified by geological radar scanning with an antenna frequency of 100 MHz and a detection depth of 3.0 m. During the construction process, a comprehensive inspection is carried out every 5 m of advancement. If it is detected that the local shell layer thickness < 1.8 m or the compressive strength < 32 MPa, an epoxy resin reinforcement layer with a thickness ≥ 50 mm needs to be sprayed for reinforcement, and the curing time ≤ 2 hours. The detection data is entered into the construction management system in real time to generate a three-dimensional geological model to guide the adjustment of subsequent excavation parameters.

[0067] Technical effects: The hardened shell layer formed by plasma modification significantly improves the self-stabilizing ability of the tunnel face and reduces the stress on the support structure; The negative pressure adsorption system effectively controls the excavation dust concentration and improves the safety of the working environment; The real-time detection and dynamic reinforcement mechanism ensures the uniformity of the shell layer quality and reduces the risk of collapse.

[0068] In another technical solution, the low-frequency vibration wave application system is configured with a rheological parameter feedback module to collect the slurry viscosity and thixotropy index in real time, and dynamically adjust the vibration frequency and energy density; the outer wall of the grouting pipe is provided with spiral guide vanes, the vane inclination angle is 30°±2°, and the pitch is 1.2 times the pipe diameter; the propagation direction of the low-frequency vibration wave forms an angle of 45°±5° with the main joint trend of the surrounding rock, and the loading angle is automatically calibrated after determining the spatial distribution of the main joints through geological radar scanning.

[0069] In the above technical solution, the low-frequency vibration wave application system can be configured with a rheological parameter feedback module to collect the slurry viscosity and thixotropy index in real time. The slurry viscosity range can be set to 50 - 200 mPa·s, and the thixotropy index threshold is set to 1.2 - 1.8. The feedback module can integrate an online rotational rheometer with a sampling frequency of 10 Hz and is connected to the vibration controller through an RS485 communication interface. When the slurry viscosity exceeds 150 mPa·s or the thixotropy index is lower than 1.3, the system automatically increases the vibration frequency from 0.5 Hz to 0.6 - 0.7 Hz and adjusts the energy density from 50 J / m³ to 60 - 70 J / m³. The assembly position of the module is on the bypass branch pipe of the outlet pipeline of the grouting pump, 1.2 - 1.5 m away from the inlet of the grouting pipe, ensuring real-time monitoring of the slurry rheological properties.

[0070] The outer wall of the grouting pipe can be provided with spiral guide vanes, the vane inclination angle is 30°±2°, and the pitch is 1.2 times the pipe diameter (for example, when the pipe diameter is 80 mm, the pitch is 96 mm). The vanes can be formed by stamping 304 stainless steel with a thickness of 2 mm, and the surface is sandblasted to enhance adhesion. The guide vanes are continuously welded spirally along the outer wall of the grouting pipe, and the weld height is not less than 3 mm. The assembly position of the vanes covers 2 / 3 of the front length of the grouting pipe, and the rear 1 / 3 is a smooth pipe wall for inserting into the borehole. During construction, the guide vanes guide the slurry to spread along the spiral path by rotating the grouting pipe, reducing slurry backflow and improving the penetration uniformity.

[0071] The included angle between the propagation direction of the low-frequency vibration wave and the strike of the main joints of the surrounding rock can be set to 45° ± 5°. Before construction, the spatial distribution data of the main joints are obtained through ground-penetrating radar scanning. The scanning depth is 3 - 5 m, and the scanning spacing is 1 m. The system automatically calibrates the angle of the vibration head according to the scanning results, and the error is controlled within ±3°. The vibration head can be connected with a universal joint coupling, and the adjustment range is 0° - 90°, and the torque of the locking bolt is 50 - 60 N·m. The assembly position of the vibration head is located in the transition section between the grouting pipe and the vibration generator, 200 - 300 mm away from the flange of the grouting pipe, ensuring that the vibration energy is transmitted directionally to the target joint surface.

[0072] Through indoor grouting simulation experiments, grouting tests are carried out in the same geological model using slurries with different viscosities (100 mPa・s, 150 mPa・s, 200 mPa・s). When the slurry viscosity is 150 mPa・s, the vibration frequency is increased from 0.5 Hz to 0.6 Hz, the energy density is adjusted from 50 J / m³ to 60 J / m³, the penetration depth of the slurry is increased from 1.2 m to 1.5 m, and the permeability coefficient is increased from 0.01 cm / s to 0.015 cm / s.

[0073] Technical effects The rheological parameter feedback module adapts to the change of slurry performance by adjusting the vibration parameters in real time, avoiding the risk of pipe blockage; the spiral guide vanes optimize the slurry flow path and improve the grouting density; the calibration of the vibration wave propagation angle ensures that the energy acts efficiently on the weak surface of the surrounding rock, enhancing the reinforcement effect. The synergy of the three can improve the controllability of the grouting project and the overall stability of the surrounding rock.

[0074] In another technical solution, a basalt fiber grid with an aperture of 50×50 mm is embedded between the flexible buffer layer and the circumferential isolation belt, a water-swellable rubber strip with a swelling rate ≥ 300% is filled in the deformation joint, and a graphene-based anti-slip coating with a friction coefficient ≥ 0.8 is coated on the surface of the isolation belt.

[0075] In the above technical scheme, a basalt fiber mesh with an aperture of 50×50 mm can be embedded between the flexible buffer layer and the annular isolation zone. The monofilament diameter of the basalt fiber mesh can be selected from 0.8 to 1.2 mm, the tensile strength is ≥2000 MPa, and the allowable error of the mesh size is ±2 mm. The mesh can be made of plain weave and coated with epoxy resin on the surface to enhance corrosion resistance. During construction, the mesh is first cut into strips with a width of 300 to 400 mm, laid on the surface of the flexible buffer layer along the annular direction of the tunnel, and fixed with Φ3 stainless steel wire, with a wire spacing of 150 to 200 mm. The assembly position of the mesh is located at the junction of the flexible buffer layer and the isolation zone, 20 to 30 mm away from the edge of the deformation joint, and continuously covered in the direction perpendicular to the tunnel axis. After laying, the bonding strength between the mesh and the buffer layer is verified by a pull-out test, which is required to be ≥0.5 MPa.

[0076] The expansion joint can be filled with water-expandable rubber strips with an expansion rate of ≥300%. The cross-sectional size of the rubber strip can be selected as 20×15 mm, the hardness range is Shore A 50~60, and the expansion time is ≤2 hours. The material can be a composite formula of butyl rubber and super absorbent resin, and the volume expands to more than 3 times the original size after absorbing water. During installation, first cut the rubber strip into segments 5% longer than the length of the expansion joint, use a special adhesive to stick it to the bottom of the expansion joint, cut the joint at a 45° angle, and tap it with a mallet to compact it. The assembly position of the rubber strip is close to the inner wall of the expansion joint, and a 2~3 mm gap is reserved at the top to accommodate subsequent deformation. After construction, the sealing is verified by a water injection test, and the water seepage is required to be ≤0.1 L / m within 24 hours.

[0077] The surface of the annular isolation belt can be coated with a graphene-based anti-skid coating with a friction coefficient of ≥0.8. The coating thickness can be set to 0.2-0.3 mm, the drying time is ≤4 hours, and the adhesion level is ≥4B (tested by the cross-cutting method). The material can be an epoxy resin base material, mixed with 5%-8% graphene nanosheets and silicon carbide particles (particle size 50-80 μm). During construction, a high-pressure airless spraying device is used, the nozzle diameter is 1.0-1.2 mm, and the spraying pressure is 0.3-0.5 MPa. The coating is applied in two passes, the first pass is sprayed longitudinally, and the second pass is cross-covered horizontally. After curing, a uniform concave-convex texture is formed on the surface. The assembly position of the coating covers the exposed surface of the isolation belt, and the edge extends to 10-15 mm outside the deformation joint, without direct contact with the basalt fiber grid.

[0078] Technical Effects The basalt fiber grid enhances the interface shear resistance between the buffer layer and the isolation zone, reducing the risk of interlayer delamination; the water-swelling rubber strip inhibits the water seepage channel through active sealing, improving the long-term waterproof reliability; the graphene coating reduces the slip tendency of the rock mass through the high-friction surface. The synergistic effect of the three can improve the overall durability and deformation adaptability of the tunnel structure.

[0079] In another technical solution, the construction of prestressed anchor cables includes: the free section of the prestressed anchor cable is wrapped with a shape memory alloy sleeve, which expands due to temperature triggering to form multiple anchoring points; when the anchor cable is tensioned, low-temperature liquid nitrogen at -196°C is injected synchronously, and an electromagnetic damper is connected to the tail of the anchor cable to dissipate vibration energy in real time.

[0080] In the above technical solution, the shape memory alloy sleeve can be made of nickel-titanium alloy, with a phase change temperature of 35 - 45°C and a wall thickness of 1.5 - 2.0 mm. The sleeve is pre-processed into a contracted state, and its inner diameter is 2 - 3 mm smaller than the diameter of the free section of the anchor cable. When the temperature rises above 40°C during the tensioning process of the anchor cable, the expansion rate of the sleeve is ≥8%, forming 3 - 5 circumferential anchoring points with the surrounding rock hole wall, and the spacing is 0.8 - 1.2 m. The length of the sleeve covers 80% of the full length of the free section of the anchor cable, and both ends are sealed with heat shrinkable sleeves. During the assembly of the sleeve, it can be pre-sleeved on the free section of the anchor cable and fixed at both ends with stainless steel clamps. After temperature triggering, an infrared thermal imager is used to monitor the uniformity of the sleeve expansion, and the surface temperature difference is controlled within ±3°C. The pull-out resistance test of the anchoring points can be carried out by loading with a hydraulic jack up to 200 kN, and the displacement ≤2 mm is considered qualified.

[0081] The low-temperature liquid nitrogen storage tank can be of vacuum insulation structure, with a volume of 500 - 800 L and a working pressure of 0.8 - 1.2 MPa. The inner diameter of the liquid nitrogen injection pipeline is 10 mm, covered with a polyurethane insulation layer, and a copper nozzle with a diameter of 3 mm is set at the end. When injecting, the temperature of the liquid nitrogen is -196°C, the flow rate is controlled at 5 - 8 L / min, and the duration is 70% - 80% of the whole process of the anchor cable tensioning. The injection of liquid nitrogen and the tensioning action are synchronously controlled by a PLC. For every 50 kN increase in the tension force, the liquid nitrogen injection volume increases by 10%. The nozzle is installed 20 - 30 cm from the tail of the anchor cable, and the spraying direction forms an angle of 30° with the axis of the anchor cable. After the injection is completed, a thermistor is used to monitor the temperature rise rate in the hole, and it is required that the temperature does not drop below -50°C within 10 minutes. The low-temperature liquid nitrogen storage tank is equipped with a pressure safety valve (opening pressure 1.6 MPa) and a temperature monitoring device (accuracy ±0.5°C), and an independent storage room is set up. The ventilation and air change rate of the storage room is not less than 12 times / h. During transportation, a special low-temperature transport tanker is used, the vehicle speed does not exceed 50 km / h, and the transportation route avoids crowded areas. When constructing in a tunnel, the operators wear cold-proof clothing (low-temperature protection level of -196°C), protective gloves, and goggles. An oxygen concentration monitor is set up on-site. When the oxygen concentration is lower than 19.5%, the ventilation equipment is automatically started, and at the same time, warning lines and warning signs are set up to prevent unauthorized personnel from entering the construction area.

[0082] The electromagnetic damper can adopt an eddy current structure, with a damping coefficient of 0.2 - 0.3 N·s / mm and a maximum energy consumption power of ≥500 W. The damper housing is made of aluminum alloy, the internal coil resistance is ≤5 Ω, and it is fixed to the tail tray of the anchor cable by bolts. When the vibration frequency is monitored in real time, the acceleration sensor has a measurement range of 0 - 200 Hz, a sampling rate of ≥1 kHz, and the data is uploaded to the control terminal through the AD conversion module.

[0083] The damper is connected to the anchor cable by a universal joint, allowing a ±15° deflection. The vibration energy overrun threshold is set at 50 J, and when exceeded, the full-power mode of the damper is automatically activated. After each shift of construction, check the temperature rise of the damper, with the surface temperature ≤60°C, and verify through a vibration table simulation test that the energy consumption efficiency decay rate <5%.

[0084] Technical effects: The shape memory alloy sleeve forms multi-point anchoring through temperature-triggered expansion, enhancing the anti-slip ability; Injecting low-temperature liquid nitrogen reduces the temperature stress of the surrounding rock and inhibits the expansion of microcracks during the tensioning process; The electromagnetic damper effectively dissipates the construction vibration energy and reduces the prestress loss of the anchor cable.

[0085] Although the technical solution of the present invention has been disclosed above, it is not limited to only the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the embodiments shown and described herein.

Claims

1. A tunneling construction method for soft rock geology, characterized in that, It includes the following steps: 1) Divide the heading face into three pilot tunnel areas vertically. The height of the upper pilot tunnel area is 2.5 - 3.5 meters, the height of the middle pilot tunnel area is 2.0 - 2.5 meters, and the height of the lower pilot tunnel area is 1.8 - 2.2 meters; 2) Adopt the step - by - step excavation method. First, excavate the upper pilot tunnel area, and control the excavation footage within 0.8 - 1.2 meters. After excavation, install the first - layer steel arch. After the installation of the first - layer steel arch is completed, construct the first group of prestressed anchor rods with a length of 3.5 - 4 meters at intervals of 0.8 - 1.5 meters along the tunnel circumference. Secondly, after the upper pilot tunnel area has advanced 5 - 8 meters, start excavating the middle pilot tunnel area. After excavation, install the second - layer steel arch in the middle pilot tunnel area. The second - layer steel arch is welded and fixed to the first - layer steel arch with vertical connecting bars. After the installation of the second - layer steel arch is completed, construct the second group of prestressed anchor rods with a length of 3 - 3.5 meters at intervals of 2 - 3 meters along the tunnel circumference. Finally, after the middle pilot tunnel area has advanced 3 - 5 meters, start excavating the lower pilot tunnel area. After excavation, install the third - layer steel arch in the lower pilot tunnel area. The third - layer steel arches are connected by cross - diagonal braces. After the installation of the third - layer steel arch is completed, construct the third group of prestressed anchor rods with a length of 2.5 - 3 meters at intervals of 3 - 4 meters along the tunnel circumference; 3) Set stress monitoring points at the intersections of the first - layer steel arch and the second - layer steel arch, and the intersections of the second - layer steel arch and the third - layer steel arch respectively. Arrange two groups of displacement sensors and one group of stress gauges at each stress monitoring point. When the circumferential displacement change rate monitored by the displacement sensor > 15 mm / 24 h or the stress value measured by the stress gauge > 70% of the design strength, the early - warning system is automatically triggered. Within 4 hours after the early - warning system is triggered, symmetrically install adjustable hydraulic support rods at a distance of 1.2 - 1.8 m from the inner side of the corresponding steel arch. After installation, start the dynamic compensation mode, and real - time feedback data through pressure sensors, and adjust the support force of the adjustable hydraulic support rods in a gradient of 5 kN / time until the circumferential displacement change rate drops to < 15 mm / 24 h and the stress value drops below 70% of the design strength.

2. The soft rock geological tunnel excavation construction method according to claim 1, characterized in that, After step 3), it also includes the steps: 4) After the dynamic compensation of the adjustable hydraulic support rods is completed, implement zoned and segmented grouting reinforcement: Use ultra - fine cement - based grouting materials with a particle size D50 ≤ 5 μm, prepare the grout according to a water - cement ratio of 0.8:1, and arrange grouting pipes at intervals of 1.2 m along the circumference of the multi - layer steel arch. Grouting is carried out in two stages: In the first stage, low - pressure permeation grouting is carried out at 0.5 - 0.8 MPa until the grouting volume reaches 80% of the design value, and then, after a 12 - hour interval, the second - stage splitting grouting is carried out at 1.2 - 1.5 MPa. After grouting is completed, install stress monitoring boxes at the tails of the grouting pipes to real - time feedback the collaborative deformation data of the surrounding rock - support structure.

3. The soft rock geological tunnel excavation construction method according to claim 2, characterized in that After step 4), it also includes the steps: 5) Implement the coordinated deformation compensation of surrounding rock - support: Set a flexible buffer layer outside the grouting reinforcement area. Pour a circumferential isolation belt with a thickness of 300 mm of foamed concrete outside the flexible buffer layer, and reserve a deformation joint of 20 mm; Layout prestressed anchor cables at a longitudinal spacing of 2 m along the tunnel. The tensile force of the anchor cables is applied in stages up to 150 kN and is connected to the first - layer steel arch, the second - layer steel arch, and the third - layer steel arch through articulated trays; Install a distributed optical fiber monitoring system, lay strain - sensing optical fibers along the entire length of the anchor cables, and monitor the stress distribution of the anchor cables in real - time; Dynamically adjust the prestress of the anchor cables based on the monitoring data, with the adjustment amplitude ≤ 20 kN / time, and maintain the radius of the plastic zone of the surrounding rock ≤ 1.2 D, where D is the tunnel diameter.

4. The soft rock geological tunnel excavation construction method according to claim 1, characterized in that, Step 2) specifically includes the following steps: S21. Adopt the step - by - step excavation method. First, excavate the upper pilot tunnel area. The upper pilot tunnel excavation adopts the layered staggered - distance method, and the excavation footage range is controlled within 0.8 - 1.2 m. After excavation, install the first - layer steel arch. The first - layer steel arch uses HW175 - type I - beam. The longitudinal spacing of the first - layer steel arch is 0.4 - 0.6 m. The web of the first - layer steel arch is provided with connection holes at a spacing of 0.3 m; After the installation of the first - layer steel arch is completed, construct the first group of prestressed anchor rods with a length of 3.5 m at an interval of 0.8 m along the tunnel circumference. Each prestressed anchor rod in the first group of prestressed anchor rods forms an elevation angle of 15 - 25 degrees with the horizontal plane, and the end of each prestressed anchor rod is fixed to the first - layer steel arch through the connection hole. S22. After the upper pilot tunnel area advances 5 - 8 m, start the excavation of the middle pilot tunnel area. After excavation, install the second - layer steel arch in the middle pilot tunnel area. The second - layer steel arch is welded and fixed to the first - layer steel arch with Φ25 vertical connecting bars. The longitudinal spacing of the connecting bars is 0.8 m, and the weld height ≥ 10 mm to form a double - layer truss structure; After the installation of the second - layer steel arch is completed, construct the second group of prestressed anchor rods with a length of 3 - 3.5 m at an interval of 2 - 3 m. Each prestressed anchor rod in the second group of prestressed anchor rods forms an elevation angle of 15 - 18 degrees with the horizontal plane. S23. After the middle pilot tunnel area advances 3 - 5 m, start the excavation of the lower pilot tunnel area. After excavation, install the third - layer steel arch in the lower pilot tunnel area. The third - layer steel arches are connected by cross - braces. Among them, the cross - braces use Φ89×6 mm seamless steel pipes, and the brace angle is 45° ± 5°. Triangular stiffening plates with a thickness of 12 mm are welded at the connection nodes. The third - layer steel arches are connected by cross - braces. After the installation of the third - layer steel arch is completed, construct the third group of prestressed anchor rods with a length of 2.5 - 3 m at an interval of 3 - 4 m along the tunnel circumference. Each prestressed anchor rod in the third group of prestressed anchor rods forms an elevation angle of 15 - 18 degrees with the horizontal plane.

5. The soft rock geological tunnel excavation construction method according to claim 1, characterized in that Step 1) further includes: Dynamically adjust the height of the pilot tunnel according to the integrity coefficient of the surrounding rock. When the integrity coefficient of the surrounding rock < 0.4, the height of the upper pilot tunnel area is reduced to 2.2 - 2.8 m, the height of the lower pilot tunnel area is increased to 2.0 - 2.3 m, and a temporary inverted arch is added in the middle pilot tunnel area; Embed a distributed optical fiber monitoring tube at the pilot tunnel boundary to monitor the strain rate of the surrounding rock at the interface in real - time; In the upper pilot tunnel area, pre - advanced small pipes with a diameter of Φ42mm and a length of L = 5m are set at the top, arranged in a plum - blossom pattern with a spacing of 0.5m, and grouted to form a pre - support arch shell.

6. The soft rock geological tunnel excavation construction method according to claim 2, characterized in that The grouting reinforcement also includes: a micro - camera is integrated at the front end of the grouting pipe to observe the diffusion form of the grout in real - time; a low - frequency vibration wave of 0.5Hz is applied synchronously during the grouting process to promote the penetration of the grout; a quick - setting sealing layer is sprayed on the grouting completion surface to form a waterproof isolation film.

7. The tunneling construction method for soft rock geology caves as described in claim 1, characterized in that, Step 2) also includes: before excavation, a high - frequency plasma generator is used to radiatively modify the surrounding rock of the heading face to form a hardened shell layer with a compressive strength ≥35 MPa and a thickness of 2.0 ± 0.2 m; a negative - pressure adsorption type muck transportation system is adopted, and a cyclone separator is configured for dust adsorption and dust removal, where the air volume of the negative - pressure adsorption system is 8000m³ / h.

8. The soft rock geological tunnel excavation construction method according to claim 6, characterized in that, The low - frequency vibration wave application system is configured with a rheological parameter feedback module to collect the viscosity and thixotropy index of the grout in real - time, and dynamically adjust the vibration frequency and energy density; spiral guiding vanes are arranged on the outer wall of the grouting pipe, with a vane inclination angle of 30° for vibration wave application and a pitch of 1.2 times the pipe diameter; the propagation direction of the low - frequency vibration wave forms a 45° angle with the main joint trend of the surrounding rock, and the loading angle is automatically calibrated after determining the spatial distribution of the main joints through geological radar scanning.

9. The soft rock geological tunnel excavation construction method according to claim 3, characterized in that A basalt fiber grid with an aperture of 50×50 mm is embedded between the flexible buffer layer and the circumferential isolation belt, a water - swelling rubber strip with a swelling rate ≥300% is filled in the deformation joint, and a graphene - based anti - slip coating with a friction coefficient ≥0.8 is coated on the surface of the isolation belt.

10. The soft rock geological tunnel excavation construction method according to claim 3, characterized in that, The construction of the prestressed anchor cable includes: the free section of the prestressed anchor cable is wrapped with a shape - memory alloy sleeve, and temperature - triggered expansion forms multiple anchoring points; when the anchor cable is tensioned, low - temperature liquid nitrogen at - 196℃ is injected synchronously, and an electromagnetic damper is connected to the tail of the anchor cable to dissipate vibration energy in real - time.