A tunnel section delay blasting excavation method with grading, layering and porosity linkage

Abstract

The application discloses a tunnel section delay blasting excavation method with grading, layering and porosity linkage, which comprises the following steps: according to the rock strength, integrity coefficient and underground water state of surrounding rock, a tunnel face is divided into several surrounding rock grading areas; an excavation section is divided into several excavation layers along the vertical direction, and the control surrounding rock grade corresponding to each excavation layer is determined; the representative porosity of the rock mass in each layer is measured, and the blast hole arrangement parameters and single-hole charge quantity of each layer are determined; according to the control surrounding rock grade and representative porosity of each excavation layer, the delay blasting time sequence of the blast holes in different positions in each layer is determined, and each blast hole is blasted according to the delay blasting time sequence; after blasting and ventilation, concrete is sprayed to close the rock surface, and a steel arch is installed. The application realizes fine design of blasting parameters and differential control of the section delay blasting time sequence, thereby effectively inhibiting the large deformation of soft rock, reducing the collapse risk, and improving the construction safety and efficiency.

Description

Technical Field

[0001] This invention relates to the field of tunnel blasting construction technology, and in particular to a method for segmented delayed blasting excavation of tunnels that links graded, layered, and porosity blasting. Background Technology

[0002] In tunnel construction, soft rock sections with large deformations present significant challenges to excavation technology, as they represent typical adverse geological conditions. Soft rock generally exhibits low strength, poor self-stabilization, and is easily softened by water. When disturbed by blasting excavation, the surrounding rock is prone to significant deformation, which can lead to support structure failure or even tunnel collapse. Therefore, developing safe and efficient blasting excavation methods is crucial for ensuring construction safety and project progress.

[0003] Current engineering practice primarily employs the drill-and-blast method to address this level of problem. Conventional measures include shortening the excavation depth, enhancing support strength, and accelerating the closure of exposed rock surfaces. In terms of blasting parameter design, common approaches include reducing the amount of explosive per blast, increasing the density of peripheral holes, and optimizing the detonation sequence to mitigate the impact of blasting vibrations on the surrounding rock. Support systems often rely on combinations of shotcrete, steel arches, and rock bolts, with the effectiveness of the support assessed through monitoring surrounding rock deformation. Some projects utilize pre-reserved core soil or sectional excavation methods, using unexcavated soil to form temporary supports to slow the deformation rate of the excavated section.

[0004] However, existing technologies have systemic shortcomings when dealing with large deformations in soft rock. First, blasting parameter design often adopts a uniform standard, failing to differentiate based on the surrounding rock grade in different areas of the tunnel face. Even on the same tunnel face, significant differences may exist in lithology, integrity, and porosity at different locations, but traditional methods lack a refined mechanism for adjusting blasting parameters for different surrounding rock grades. Second, existing methods fail to fully integrate surrounding rock grade classification, excavation stratification, and porosity. The surrounding rock grade determines the basic mechanical properties of the rock mass and the overall control strategy for blasting; excavation stratification determines the spatial distribution of blasting, transforming vertical geological differences into operable stratum control; and porosity directly affects the energy transfer efficiency and fragmentation effect of explosives—higher porosity makes it easier for blasting energy to dissipate along the pores, requiring smaller borehole spacing and lower single-hole charge to control the blasting effect. Current technologies lack a blasting excavation method that progressively refines and systematically integrates the classification of surrounding rock, the division of excavation layers, and the determination of porosity. Furthermore, traditional delayed-detonation schemes do not consider the combined influence of surrounding rock grade and porosity on the optimal delay time, often employing a fixed delay sequence. This leads to a mismatch between the blasting energy release and the fracturing characteristics of the surrounding rock, increasing surrounding rock disturbance. These shortcomings collectively result in prolonged construction periods, increased safety risks, and higher support costs in soft rock sections with large deformation. Summary of the Invention

[0005] The main objective of this invention is to propose a segmented delayed blasting excavation method for tunnels that links graded, layered, and porosity-based processes. This method aims to achieve refined design of blasting parameters and differentiated control of segmented delayed blasting sequences through a progressive and detailed approach of "surrounding rock grade determination - excavation layer division - porosity measurement." This will effectively suppress large deformations in soft rock, reduce the risk of collapse, and improve construction safety and efficiency.

[0006] To achieve the above objectives, the present invention provides a segmented delayed blasting excavation method for tunnels that links graded, layered, and porosity-based processes. The excavation method is executed cyclically, with each cycle including the following steps: S1, classify the surrounding rock level of the working face, and divide the working face into several surrounding rock level areas according to the rock strength, integrity coefficient and groundwater status of the surrounding rock. S2, divide the excavation section vertically into several excavation layers, and determine the control surrounding rock level corresponding to each excavation layer; S3, for each excavation layer, the representative porosity of the rock mass in that layer is measured, and the borehole layout parameters and single-hole charge amount are determined based on the porosity. S4. Based on the controlled surrounding rock level and representative porosity of each excavation layer, determine the delayed detonation sequence of blast holes at different locations within each layer, and use digital detonators to network and detonate each blast hole according to the delayed detonation sequence. S5, after blasting and ventilation, spray concrete mixed with early strength compensating shrinkage agent within a preset time to seal the rock surface, and install steel arch frame.

[0007] Preferably, step S1 specifically includes: After the tunnel face is exposed, the rock strength and rock mass integrity coefficient at different parts of the tunnel face are measured, and the groundwater seepage state at the tunnel face is observed. Based on the measured rock strength and rock mass integrity coefficient, the basic quality index (BQ) value of the rock mass in each part is calculated. Based on the basic rock mass quality index BQ value and groundwater seepage status, the surrounding rock levels of various parts of the working face are classified, and a surrounding rock level zoning map is formed by marking the working face; the surrounding rock levels include Class II, Class III, Class IV and Class V.

[0008] Preferably, step S2 specifically includes: The tunnel face is divided vertically into three layers: arch excavation layer, waist excavation layer, and bottom excavation layer. Based on the surrounding rock grade zoning map, the controlling surrounding rock grade in each excavation layer is determined. When there are two or more surrounding rock grades in the same excavation layer, the dominant surrounding rock grade in that layer is taken as the controlling surrounding rock grade of that layer. The thickness of each excavation layer is determined according to its corresponding controlled surrounding rock level: the single-layer excavation thickness of the layer containing Class II surrounding rock is 3.0 meters to 4.0 meters, the single-layer excavation thickness of the layer containing Class III surrounding rock is 2.5 meters to 3.5 meters, the single-layer excavation thickness of the layer containing Class IV surrounding rock is 2.0 meters to 3.0 meters, and the single-layer excavation thickness of the layer containing Class V surrounding rock is 1.5 meters to 2.5 meters.

[0009] Preferably, step S3 specifically includes: Within each excavation layer, rock core samples were collected from the crown, the two sides of the arch waist, and the center. The porosity of each sample was measured, and the arithmetic mean of the porosity of each sample was taken as the representative porosity of the excavation layer. Based on the representative porosity n, determine the borehole spacing a and the single-hole charge Q for this excavation layer: When n ≤ 5%, the borehole spacing a = 0.5~0.6 meters, and the charge per borehole Q = 0.6~0.8 kg; When 5% < n ≤ 10%, the borehole spacing a = 0.4~0.5 meters, and the single-hole charge Q = 0.4~0.6 kg; When 10% < n ≤ 15%, the borehole spacing a = 0.3~0.4 meters, and the charge per borehole Q = 0.25~0.4 kg; when n > 15%, the borehole spacing a = 0.25~0.35 meters, and the charge per borehole Q = 0.15~0.25 kg.

[0010] Preferably, step S4 specifically includes: Based on the control surrounding rock grade and representative porosity of each excavation layer, the millisecond delay time of the cut holes, auxiliary holes, peripheral holes and bottom holes in each excavation layer is determined respectively. For excavation layers where the surrounding rock grade is Class II or III and represents a porosity n≤5%: the cut hole delay is 0-10 milliseconds, the auxiliary hole delay is 25-40 milliseconds, the peripheral hole delay is 60-80 milliseconds, and the bottom hole delay is 100-130 milliseconds. For excavation layers controlling the surrounding rock grade IV or representing a porosity of 5% < n ≤ 10%: cut hole delay 0–15 ms, auxiliary hole delay 35–55 ms, peripheral hole delay 80–110 ms, and bottom hole delay 130–170 ms; For excavation layers controlling the surrounding rock grade V or representing a porosity of n > 10%: cut hole delay 0–20 ms, auxiliary hole delay 50–75 ms, peripheral hole delay 110–150 ms, and bottom hole delay 180–230 ms. The detonation sequence between different excavation layers is as follows: first detonate the arch excavation layer, then detonate the waist excavation layer, and finally detonate the bottom excavation layer. The time interval between detonations of adjacent layers shall not be less than 50 milliseconds.

[0011] Preferably, step S4 further includes: The detonation sequence for the same excavation layer is as follows: first detonate the cut hole, then detonate the auxiliary hole, then detonate the surrounding holes, and finally detonate the bottom hole; In the same type of blast hole, the hole-by-hole detonation method is adopted, and the detonation time interval between adjacent blast holes is 3 to 8 milliseconds; The detonation time of the holes around the arch is more than 50 milliseconds earlier than the detonation time of the holes around the sidewalls in the same row.

[0012] Preferably, step S5 specifically includes: After blasting, the ventilation system is activated to ensure that the air quality near the soft rock face meets the operational requirements within a preset time. Then, a wet spraying robot is used to spray C25 concrete mixed with an early strength compensating shrinkage agent onto the exposed surrounding rock surface. The dosage of the early strength compensating shrinkage agent is 8% to 10% of the total weight of cement and admixtures in the sprayed concrete, and the spraying thickness is 5 to 8 centimeters. After the initial setting of the shotcrete, install the steel arch frame, and drill two anchor holes with a downward inclination of 30 to 45 degrees at each of the left and right arch feet of each steel arch frame. An anchor pipe is installed in the anchor hole of the locking foot; a grouting pump is connected through the hollow channel of the anchor pipe, and pure cement grout with a water-cement ratio of 0.38 to 0.42 is injected. The grouting pressure is gradually increased to 1.0 MPa to 1.5 MPa and stabilized for 3 minutes; after the grout has initially set, a pad and nut are installed at the exposed end of the anchor pipe, and a torque wrench is used to apply a torque of 60 N·m to 80 N·m to the nut for tensioning.

[0013] Preferably, after step S5 is completed, the excavation method further includes a deformation monitoring and dynamic adjustment step: On the section where the initial support has been completed, concrete observation piles with precision reflectors are installed at five locations: the arch crown, the two sides of the arch waist, and the two sides of the sidewalls. Using a total station, a round of net clearance convergence measurement is carried out at 1 hour, 2 hours and 4 hours after the current excavation cycle blasting and ventilation is completed. If the cumulative net clearance convergence value measured at the 4th hour exceeds 15 mm, or if the convergence rate from the 2nd hour to the 4th hour does not show a decreasing trend, the deformation of the section is judged to be abnormal. If an abnormal deformation section appears in the excavation cycle, in the next adjacent excavation cycle, the spacing of the steel arches within the predetermined mileage range of that section will be reduced, the design length of the system anchor bolts will be increased, and the amount of explosives per hole will be reduced.

[0014] Preferably, after completing step S5, the excavation method further includes an invert arch construction step: In the area behind the working face by a certain safe step distance, the earth and rock of the invert arch section of the soft rock with large deformation is excavated to the design elevation, and C25 early strength concrete is sprayed with a wet spraying machine for preliminary sealing. After the initial shotcrete reaches the first preset strength, the invert arch connecting bars are tied, and the steel arch frame of the invert arch section is fastened to the side wall arch frame through connecting plates and high-strength bolts. Within 24 hours after the connection is completed, the first layer of inverted arch structure concrete is poured, with a thickness of 60% of the total design thickness. This layer of concrete is mixed with a high-efficiency early strength agent, and its 12-hour compressive strength is not lower than the second preset strength. After the strength of the first layer of concrete reaches the third preset strength as tested by test blocks under the same conditions, the second layer of concrete is poured immediately. Before pouring, a layer of steel mesh is laid on the arch surface of the invert, and finally the thickened reinforced concrete closed structure of the entire invert is completed.

[0015] Preferably, a preprocessing step is included before executing step S1 of the next cycle: A hydraulic breaker was used to mechanically break up the core soil remaining after the previous excavation cycle. The breaking sequence was from top to bottom and from both sides to the center. The broken material was then removed from the tunnel by a loader, so that the core soil was completely removed and the new tunnel face was fully exposed.

[0016] The technical solution of this invention achieves a refined understanding of the geological conditions of soft rock face from macroscopic to microscopic levels and allows for targeted design of blasting parameters through a progressive and detailed approach of "surrounding rock level classification, excavation layer division, and porosity measurement." The first level—surrounding rock level classification—divides the face into different levels based on the BQ classification method, providing a macroscopic framework and foundation for subsequent differentiated design. The second level—excavation layer division—combines different surrounding rock levels vertically, enabling blasting design to be layered and controlled according to geological differences at different heights, achieving spatial refinement from two-dimensional partitioning to three-dimensional layering. The third level—porosity measurement—further measures the microstructural characteristics of the rock mass within each layer, allowing for secondary fine-tuning of borehole spacing and single-hole charge quantity, achieving precise control from macroscopic layering to local refinement. These three levels, progressing from coarse to fine, form a complete "classification-layering-porosity" linkage control system. Based on this, the differentiated segmented delayed detonation sequence, determined comprehensively according to the surrounding rock grade and porosity, further optimized the release path and time distribution of blasting energy. Rapidly sprayed early-strength concrete and actively tensioned anchor pipes shortened the exposure time of the surrounding rock, providing timely and proactive support. These progressively advanced and synergistic technical features effectively suppressed large deformations in soft rock, ensuring tunnel construction safety and project progress. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the segmented delayed blasting excavation method for soft rock tunnels based on graded-layered-porosity linkage provided by the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] In existing tunnel construction, the excavation of soft rock sections with large deformations faces numerous challenges. Traditional methods fail to achieve progressive linkage control between surrounding rock classification, excavation layering, and porosity, and lack differentiated blasting parameters and segmented delayed detonation schemes for different surrounding rock classifications and porosities. To address this technical problem, this invention proposes a segmented delayed blasting excavation method for tunnels that links classification, layering, and porosity.

[0020] Please see Figure 1This invention provides a segmented delayed blasting excavation method for tunnels that links graded, layered, and porosity-based processes. The excavation method is executed repeatedly in cycles, each cycle including the following steps: S1, classify the surrounding rock level of the working face, and divide the working face into several surrounding rock level areas according to the rock strength, integrity coefficient and groundwater status of the surrounding rock. S2, divide the excavation section vertically into several excavation layers, and determine the control surrounding rock level corresponding to each excavation layer; S3, for each excavation layer, the representative porosity of the rock mass in that layer is measured, and the borehole layout parameters and single-hole charge amount are determined based on the porosity. S4. Based on the controlled surrounding rock level and representative porosity of each excavation layer, determine the delayed detonation sequence of blast holes at different locations within each layer, and use digital detonators to network and detonate each blast hole according to the delayed detonation sequence. S5, after blasting and ventilation, spray concrete mixed with early strength compensating shrinkage agent within 15 minutes to seal the rock surface and install steel arch frame.

[0021] Step S1 specifically includes: After the tunnel face is exposed, the rock strength at different parts of the tunnel face is determined by a rebound hammer or a point load tester, the rock mass integrity coefficient is determined by a ground-penetrating radar or a sonic tester, and the groundwater seepage status at the tunnel face is observed. Based on the measured rock strength and rock mass integrity coefficient, the basic quality index (BQ) value of the rock mass in each part is calculated. Based on the basic rock mass quality index BQ value and groundwater seepage status, the surrounding rock levels of various parts of the working face are classified, and a surrounding rock level zoning map is formed by marking the working face; the surrounding rock levels include Class II, Class III, Class IV and Class V.

[0022] Furthermore, the calculation of the basic rock mass quality index (BQ value) and the classification of surrounding rock grades shall refer to the BQ classification method in the "Engineering Rock Mass Classification Standard" (GB / T 50218). Taking the "Engineering Rock Mass Classification Standard" (GB / T 50218-1994) as an example, the formula for calculating the basic rock mass quality index (BQ value) is as follows: BQ = 90 + 3Rc + 250Kv; Where Rc is the uniaxial saturated compressive strength of the rock, and Kv is the rock mass integrity coefficient.

[0023] The method for classifying surrounding rock levels is as follows: when the BQ value is greater than 550, the area is designated as Class I surrounding rock zone; when the BQ value is between 451 and 550, it is designated as Class II surrounding rock zone; when the BQ value is between 351 and 450, it is designated as Class III surrounding rock zone; when the BQ value is between 251 and 350, it is designated as Class IV surrounding rock zone; and when the BQ value is less than or equal to 250, it is designated as Class V surrounding rock zone.

[0024] Step S2 specifically includes: The tunnel face is divided vertically into three layers: arch excavation layer, waist excavation layer, and bottom excavation layer. The arch excavation layer corresponds to the surrounding rock in the arch area, the waist excavation layer corresponds to the surrounding rock in the upper part of the side walls on both sides, and the bottom excavation layer corresponds to the surrounding rock in the lower part of the side walls and the invert arch area. Based on the surrounding rock grade zoning map, the controlling surrounding rock grade within each excavation layer is determined. Where two or more surrounding rock grades exist within the same excavation layer, the dominant surrounding rock grade within that layer is taken as the controlling surrounding rock grade. Dominant refers to the surrounding rock type occupying more than 50% of the area within that layer. The thickness of each excavation layer is determined according to its corresponding controlled surrounding rock level: the single-layer excavation thickness of the layer containing Class II surrounding rock is 3.0 meters to 4.0 meters, the single-layer excavation thickness of the layer containing Class III surrounding rock is 2.5 meters to 3.5 meters, the single-layer excavation thickness of the layer containing Class IV surrounding rock is 2.0 meters to 3.0 meters, and the single-layer excavation thickness of the layer containing Class V surrounding rock is 1.5 meters to 2.5 meters.

[0025] Step S3 specifically includes: Within each excavation layer, rock core samples were collected from the crown, the two sides of the arch, and the center. The porosity of each sample was determined using a helium porosimeter or nuclear magnetic resonance method. The arithmetic mean of the porosity of each sample was taken as the representative porosity of the excavation layer. Based on the representative porosity n, determine the borehole spacing a and the single-hole charge Q for this excavation layer: When n ≤ 5%, the borehole spacing a = 0.5~0.6 meters, and the charge per borehole Q = 0.6~0.8 kg; When 5% < n ≤ 10%, the borehole spacing a = 0.4~0.5 meters, and the single-hole charge Q = 0.4~0.6 kg; When 10% < n ≤ 15%, the borehole spacing a = 0.3~0.4 meters, and the charge per borehole Q = 0.25~0.4 kg; when n > 15%, the borehole spacing a = 0.25~0.35 meters, and the charge per borehole Q = 0.15~0.25 kg.

[0026] Step S4 specifically includes: Based on the control surrounding rock grade and representative porosity of each excavation layer, the millisecond delay time of the cut holes, auxiliary holes, peripheral holes and bottom holes in each excavation layer is determined respectively. For excavation layers where the surrounding rock grade is Class II or III and represents a porosity n≤5%: the cut hole delay is 0-10 milliseconds, the auxiliary hole delay is 25-40 milliseconds, the peripheral hole delay is 60-80 milliseconds, and the bottom hole delay is 100-130 milliseconds. For excavation layers controlling the surrounding rock grade IV or representing a porosity of 5% < n ≤ 10%: cut hole delay 0–15 ms, auxiliary hole delay 35–55 ms, peripheral hole delay 80–110 ms, and bottom hole delay 130–170 ms; For excavation layers controlling the surrounding rock grade V or representing a porosity of n > 10%: cut hole delay 0–20 ms, auxiliary hole delay 50–75 ms, peripheral hole delay 110–150 ms, and bottom hole delay 180–230 ms. The detonation sequence between different excavation layers is as follows: first detonate the arch excavation layer, then detonate the waist excavation layer, and finally detonate the bottom excavation layer. The time interval between detonations of adjacent layers shall not be less than 50 milliseconds.

[0027] Step S4 also includes: The detonation sequence for the same excavation layer is as follows: first detonate the cut hole, then detonate the auxiliary hole, then detonate the surrounding holes, and finally detonate the bottom hole; In the same type of blast hole, the hole-by-hole detonation method is adopted, and the detonation time interval between adjacent blast holes is 3 to 8 milliseconds; The detonation time of the holes around the arch is more than 50 milliseconds earlier than that of the holes around the sidewalls in the same row. Specifically, in tunnel blasting, the holes around the arch are the blast holes arranged along the designed excavation outline, while the holes around the arch specifically refer to the holes around the arch located on the outline of the arch.

[0028] Step S5 specifically includes: After blasting, the ventilation system is activated to ensure that the air quality near the soft rock face meets the operational requirements within 10 to 15 minutes. Then, a wet spraying robot is used to spray C25 concrete mixed with an early strength compensating shrinkage agent onto the exposed surrounding rock surface. The dosage of the early strength compensating shrinkage agent is 8% to 10% of the total weight of cement and admixtures in the sprayed concrete, and the spraying thickness is 5 to 8 centimeters. After the initial setting of the shotcrete, install the steel arch frame, and drill two anchor holes with a downward inclination of 30 to 45 degrees, a depth of 4.0 meters, and a diameter of 50 mm at the left and right arch feet of each steel arch frame. An anchor pipe is installed in the anchor pipe hole. The anchor pipe is a hot-rolled seamless steel pipe with a diameter of 42 mm, a wall thickness of 3.5 mm, and a tapered front end. A grouting pump is connected through the hollow channel of the anchor pipe to inject pure cement grout with a water-cement ratio of 0.38 to 0.42. The grouting pressure is gradually increased to 1.0 MPa to 1.5 MPa and stabilized for 3 minutes. After the grout has initially set, a pad and nut are installed at the exposed end of the anchor pipe. A torque wrench is used to apply a torque of 60 N·m to 80 N·m to the nut for tensioning.

[0029] After step S5 is completed, the excavation method further includes a deformation monitoring and dynamic adjustment step: On the section where the initial support has been completed, concrete observation piles with precision reflectors are installed at five locations: the arch crown, the two sides of the arch waist, and the two sides of the sidewalls. Using a total station, a round of net clearance convergence measurement is carried out at 1 hour, 2 hours and 4 hours after the current excavation cycle blasting and ventilation is completed. If the cumulative net clearance convergence value measured at the 4th hour exceeds 15 mm, or if the convergence rate from the 2nd hour to the 4th hour does not show a decreasing trend, the deformation of the section is judged to be abnormal. If an abnormal deformation section appears in the excavation cycle, in the next adjacent excavation cycle, the spacing of the steel arches within the predetermined mileage range of that section will be reduced (e.g., from 0.6 meters to 0.5 meters), the design length of the system anchor bolts will be increased (e.g., by 0.5 meters), and the charge per hole will be reduced (e.g., by 10% to 15%).

[0030] After completing step S5, the excavation method further includes an invert arch construction step: In the area behind the working face by a certain safe step distance, the earth and rock excavation of the invert arch section of the soft rock with large deformation is carried out to the design elevation, and a layer of C25 early strength concrete with a thickness of 8 cm to 10 cm is sprayed with a wet spraying machine for preliminary sealing. After the initial shotcrete strength reaches 5 MPa, the invert arch connecting bars are tied, and the steel arch frame of the invert arch section is fastened to the side wall arch frame through connecting plates and high-strength bolts. Within 24 hours of the connection being completed, the first layer of inverted arch structure concrete was poured, with a thickness of 60% of the total design thickness. This layer of concrete was mixed with a high-efficiency early-strength agent, and its 12-hour compressive strength was not less than 8 MPa. Once the strength of the first layer of concrete reaches 10 MPa as tested by test blocks under the same conditions, the second layer of concrete is poured immediately. Before pouring, a steel mesh with a diameter of 8 mm and a grid spacing of 20 cm × 20 cm is laid on the arch surface of the invert, thus completing the thickened reinforced concrete closed structure of the entire invert.

[0031] Before executing step S1 of the next loop, a preprocessing step is also included: A hydraulic breaker was used to mechanically break up the core soil remaining after the previous excavation cycle. The breaking sequence was from top to bottom and from both sides to the center. The broken material was then removed from the tunnel by a loader, so that the core soil was completely removed and the new tunnel face was fully exposed.

[0032] The following is a more specific example to illustrate this: At the start of each excavation cycle, the first step is to determine the surrounding rock grade. Construction workers use a rebound hammer to measure the rock strength at different locations on the working face and ground-penetrating radar to determine the rock mass integrity coefficient. Based on the BQ grading method in the "Engineering Rock Mass Grading Standard" (GB / T 50218-1994), the BQ values ​​for each location are calculated: BQ1 = 320 (Class IV), BQ at the waist = 280 (Class IV), and BQ3 at the bottom = 230 (Class V), thus forming a surrounding rock grade zoning map.

[0033] Next, proceed to step two – excavation layer division. Based on the surrounding rock grade zoning map, the working face is divided into arch excavation layer, waist excavation layer, and bottom excavation layer. According to the surrounding rock grade zoning map, the excavation thickness of each excavation layer is determined, resulting in the following correspondence: arch excavation layer (Grade IV, thickness 2.5m), waist excavation layer (Grade IV, 2.5m), and bottom excavation layer (Grade V, 2.0m).

[0034] Then, step three—porosity measurement and refinement of blasting parameters—was performed. A helium porosimeter was used to measure the porosity of multiple locations in the arch, waist, and bottom excavation layers, and the average value was used to calculate the representative porosity. The representative porosity of the arch excavation layer was 8%, the waist excavation layer was 9%, and the bottom excavation layer was 14%. Based on this, the blast hole parameters for each excavation layer were determined as follows: blast hole spacing of 0.45m and single-hole charge of 0.5kg for the arch excavation layer (8%); blast hole spacing of 0.45m and single-hole charge of 0.5kg for the waist excavation layer (9%); and blast hole spacing of 0.35m and single-hole charge of 0.3kg for the bottom excavation layer (14%).

[0035] The following step, step four—segmented delayed detonation—is then performed: For the arch excavation (Level IV, 8%), the detonation times for the blast holes are: cut holes 0–15 ms, auxiliary holes 35–55 ms, peripheral holes 80–110 ms, and bottom holes 130–170 ms; for the waist excavation (Level IV, 9%), the detonation times are: cut holes 0–15 ms, auxiliary holes 35–55 ms, peripheral holes 80–110 ms, and bottom holes 130–170 ms; for the bottom (Level V, 14%), the detonation times are: cut holes 0–20 ms, auxiliary holes 50–75 ms, peripheral holes 110–150 ms, and bottom holes 180–230 ms. The detonation sequence is: arch first, then waist, then bottom, with an interval of ≥50 ms. Holes of the same type are detonated sequentially, with an interval of 5 ms; peripheral holes in the arch are detonated 60 ms earlier than peripheral holes in the sidewalls.

[0036] Finally, proceed to step five: within 12 minutes after blasting and ventilation, spray C25 concrete (9% admixture, 6cm thickness) mixed with an early-strength shrinkage-compensating agent. After initial setting, install the steel arch frame. Drill anchor holes at the arch foot at a downward angle of 35°, 4.0m deep, install φ42 steel pipes, inject cement grout with a water-cement ratio of 0.40, and maintain a pressure of 1.2MPa for 3 minutes. After initial setting, install the pad nuts and apply a torque of 70N·m for tensioning.

[0037] After the initial support is completed, observation piles are installed, and a total station is used to measure the clearance convergence at the 1st, 2nd, and 4th hours. If the cumulative convergence value exceeds 15mm at the 4th hour or the convergence rate does not decrease, the deformation is judged to be abnormal. In the next cycle, the spacing of the steel arch frame within 5m before and after the fracture surface is adjusted from 0.6m to 0.5m, the anchor bolt length is increased by 0.5m, and the single-hole charge is further reduced by 10% to 15%.

[0038] Immediately after excavation of the invert arch section, spray an 8cm thick layer of C25 early-strength concrete to seal it; after the initial spray strength reaches 5MPa, tie the connecting bars to securely connect the invert arch steel frame to the side wall arch frame; within 24 hours, pour the first layer of invert arch concrete (60% of the total design thickness, mixed with high-efficiency early-strength agent, with a 12-hour strength ≥8MPa); after the first layer reaches a strength of 10MPa, lay φ8@20×20cm steel mesh and pour the second layer of concrete to complete the sealing.

[0039] After the current cycle ends and before the next cycle begins, a hydraulic breaker is used to break the core soil from top to bottom and from both sides towards the center, and the slag is immediately removed to fully expose the new working face. After entering the next excavation cycle, the surrounding rock grade is re-determined, the excavation layers are divided, and the porosity is measured. The blasting parameters are then updated based on the new measurement results.

[0040] Through the three-level progressive linkage control of "surrounding rock grade determination - excavation layer division - porosity measurement" and the synergistic cooperation of a series of technical features such as segmented delayed detonation and rapid active support, this tunnel blasting excavation method effectively solves the problems of large blasting disturbance and difficulty in controlling surrounding rock deformation during the construction of soft rock large deformation sections, and significantly improves construction efficiency and safety.

[0041] The above description is merely an exemplary embodiment of the present invention and does not limit the scope of protection of the present invention. Any equivalent structural transformations made based on the technical concept of the present invention and the contents of the specification and drawings of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of protection of the present invention.

Claims

1. A method for segmented delayed blasting excavation of tunnels based on graded-layered-porosity linkage, characterized in that, The excavation method is executed repeatedly in cycles, each cycle including the following steps: S1, classify the surrounding rock level of the working face, and divide the working face into several surrounding rock level areas according to the rock strength, integrity coefficient and groundwater status of the surrounding rock. S2, divide the excavation section vertically into several excavation layers, and determine the control surrounding rock level corresponding to each excavation layer; S3, for each excavation layer, the representative porosity of the rock mass in that layer is measured, and the borehole layout parameters and single-hole charge amount are determined based on the porosity. S4. Based on the controlled surrounding rock level and representative porosity of each excavation layer, determine the delayed detonation sequence of blast holes at different locations within each layer, and use digital detonators to network and detonate each blast hole according to the delayed detonation sequence. S5, after blasting and ventilation, spray concrete mixed with early strength compensating shrinkage agent within a preset time to seal the rock surface, and install steel arch frame.

2. The segmented delayed blasting excavation method for soft rock tunnels with graded-layered-porosity linkage as described in claim 1, characterized in that, Step S1 specifically includes: After the tunnel face is exposed, the rock strength and rock mass integrity coefficient at different parts of the tunnel face are measured, and the groundwater seepage state at the tunnel face is observed. Based on the measured rock strength and rock mass integrity coefficient, the basic quality index (BQ) value of the rock mass in each part is calculated. Based on the basic rock mass quality index BQ value and groundwater seepage status, the surrounding rock levels of various parts of the working face are classified, and a surrounding rock level zoning map is formed by marking the working face; the surrounding rock levels include Class II, Class III, Class IV and Class V.

3. The segmented delayed blasting excavation method for soft rock tunnels with graded-layered-porosity linkage as described in claim 2, characterized in that, Step S2 specifically includes: The tunnel face is divided vertically into three layers: arch excavation layer, waist excavation layer, and bottom excavation layer. Based on the surrounding rock grade zoning map, the controlling surrounding rock grade in each excavation layer is determined. When there are two or more surrounding rock grades in the same excavation layer, the dominant surrounding rock grade in that layer is taken as the controlling surrounding rock grade of that layer. The thickness of each excavation layer is determined according to its corresponding controlled surrounding rock level: the single-layer excavation thickness of the layer containing Class II surrounding rock is 3.0 meters to 4.0 meters, the single-layer excavation thickness of the layer containing Class III surrounding rock is 2.5 meters to 3.5 meters, the single-layer excavation thickness of the layer containing Class IV surrounding rock is 2.0 meters to 3.0 meters, and the single-layer excavation thickness of the layer containing Class V surrounding rock is 1.5 meters to 2.5 meters.

4. The segmented delayed blasting excavation method for soft rock tunnels with graded-layered-porosity linkage as described in claim 3, characterized in that, Step S3 specifically includes: Within each excavation layer, rock core samples were collected from the crown, the two sides of the arch waist, and the center. The porosity of each sample was measured, and the arithmetic mean of the porosity of each sample was taken as the representative porosity of the excavation layer. Based on the representative porosity n, determine the borehole spacing a and the single-hole charge Q for this excavation layer: When n ≤ 5%, the borehole spacing a = 0.5~0.6 meters, and the charge per borehole Q = 0.6~0.8 kg; When 5% < n ≤ 10%, the borehole spacing a = 0.4~0.5 meters, and the single-hole charge Q = 0.4~0.6 kg; When 10% < n ≤ 15%, the borehole spacing a = 0.3~0.4 meters, and the single-hole charge Q = 0.25~0.4 kg; When n > 15%, the borehole spacing a = 0.25~0.35 meters, and the charge per borehole Q = 0.15~0.25 kg.

5. The segmented delayed blasting excavation method for soft rock tunnels with graded-layered-porosity linkage as described in claim 4, characterized in that, Step S4 specifically includes: Based on the control surrounding rock grade and representative porosity of each excavation layer, the millisecond delay time of the cut holes, auxiliary holes, peripheral holes and bottom holes in each excavation layer is determined respectively. For excavation layers where the surrounding rock grade is Class II or III and represents a porosity n≤5%: the cut hole delay is 0-10 milliseconds, the auxiliary hole delay is 25-40 milliseconds, the peripheral hole delay is 60-80 milliseconds, and the bottom hole delay is 100-130 milliseconds. For excavation layers where the surrounding rock grade is IV or represents a porosity of 5% < n ≤ 10%: cut hole delay 0–15 milliseconds, auxiliary hole delay 35–55 milliseconds, peripheral hole delay 80–110 milliseconds, and bottom hole delay 130–170 milliseconds; For excavation layers where the surrounding rock grade is V or represents a porosity n > 10%: cut hole delay 0–20 ms, auxiliary hole delay 50–75 ms, peripheral hole delay 110–150 ms, and bottom hole delay 180–230 ms. The detonation sequence between different excavation layers is as follows: first detonate the arch excavation layer, then detonate the waist excavation layer, and finally detonate the bottom excavation layer. The time interval between detonations of adjacent layers shall not be less than 50 milliseconds.

6. The segmented delayed blasting excavation method for soft rock tunnels with graded-layered-porosity linkage as described in claim 5, characterized in that, Step S4 also includes: The detonation sequence for the same excavation layer is as follows: first detonate the cut hole, then detonate the auxiliary hole, then detonate the surrounding holes, and finally detonate the bottom hole; In the same type of blast hole, the hole-by-hole detonation method is adopted, and the detonation time interval between adjacent blast holes is 3 to 8 milliseconds; The detonation time of the holes around the arch is more than 50 milliseconds earlier than the detonation time of the holes around the sidewalls in the same row.

7. The segmented delayed blasting excavation method for soft rock tunnels with graded-layered-porosity linkage as described in claim 1, characterized in that, Step S5 specifically includes: After blasting, the ventilation system is activated to ensure that the air quality near the soft rock face meets the operational requirements within a preset time. Then, a wet spraying robot is used to spray C25 concrete mixed with an early strength compensating shrinkage agent onto the exposed surrounding rock surface. The dosage of the early strength compensating shrinkage agent is 8% to 10% of the total weight of cement and admixtures in the sprayed concrete, and the spraying thickness is 5 to 8 centimeters. After the initial setting of the shotcrete, install the steel arch frame, and drill two anchor holes with a downward inclination of 30 to 45 degrees at each of the left and right arch feet of each steel arch frame. An anchor pipe is installed in the anchor hole of the locking foot; a grouting pump is connected through the hollow channel of the anchor pipe, and pure cement grout with a water-cement ratio of 0.38 to 0.42 is injected. The grouting pressure is gradually increased to 1.0 MPa to 1.5 MPa and stabilized for 3 minutes; after the grout has initially set, a pad and nut are installed at the exposed end of the anchor pipe, and a torque wrench is used to apply a torque of 60 N·m to 80 N·m to the nut for tensioning.

8. The segmented delayed blasting excavation method for soft rock tunnels with graded-layered-porosity linkage as described in claim 1, characterized in that, After step S5 is completed, the excavation method further includes a deformation monitoring and dynamic adjustment step: On the section where the initial support has been completed, concrete observation piles with precision reflectors are installed at five locations: the arch crown, the two sides of the arch waist, and the two sides of the sidewalls. Using a total station, a round of net clearance convergence measurement is carried out at 1 hour, 2 hours and 4 hours after the current excavation cycle blasting and ventilation is completed. If the cumulative net clearance convergence value measured at the 4th hour exceeds 15 mm, or if the convergence rate from the 2nd hour to the 4th hour does not show a decreasing trend, the deformation of the section is judged to be abnormal. If an abnormal deformation section appears in the excavation cycle, in the next adjacent excavation cycle, the spacing of the steel arches within the predetermined mileage range of that section will be reduced, the design length of the system anchor bolts will be increased, and the amount of explosives per hole will be reduced.

9. The segmented delayed blasting excavation method for soft rock tunnels with graded-layered-porosity linkage as described in claim 1, characterized in that, After completing step S5, the excavation method further includes an invert arch construction step: In the area behind the working face by a certain safe step distance, the earth and rock of the invert arch section of the soft rock with large deformation is excavated to the design elevation, and C25 early strength concrete is sprayed with a wet spraying machine for preliminary sealing. After the initial shotcrete reaches the first preset strength, the invert arch connecting bars are tied, and the steel arch frame of the invert arch section is fastened to the side wall arch frame through connecting plates and high-strength bolts. Within 24 hours after the connection is completed, the first layer of inverted arch structure concrete is poured, with a thickness of 60% of the total design thickness. This layer of concrete is mixed with a high-efficiency early strength agent, and its 12-hour compressive strength is not lower than the second preset strength. After the strength of the first layer of concrete reaches the third preset strength as tested by test blocks under the same conditions, the second layer of concrete is poured immediately. Before pouring, a layer of steel mesh is laid on the arch surface of the invert, and finally the thickened reinforced concrete closed structure of the entire invert is completed.

10. The segmented delayed blasting excavation method for soft rock tunnels with graded-layered-porosity linkage as described in claim 1, characterized in that, Before executing step S1 of the next loop, a preprocessing step is also included: A hydraulic breaker was used to mechanically break up the core soil remaining after the previous excavation cycle. The breaking sequence was from top to bottom and from both sides to the center. The broken material was then removed from the tunnel by a loader, so that the core soil was completely removed and the new tunnel face was fully exposed.

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