A method for tunnel excavation based on deflection control of principal stress axes

Abstract

This invention belongs to the field of tunnel construction technology and discloses a tunnel excavation method based on principal stress axis deflection control. The method includes dividing the tunnel face to be excavated into a central tunnel and at least two side tunnels; excavating and supporting the central tunnel; determining the maximum shear stress of the surrounding rock based on the principal stress characteristic value of the axis deflection after excavation of the central tunnel and the initial drilling parameters of the stress relief hole group set before excavation of the side tunnels; obtaining the shear strength of the surrounding rock, determining the shear force ratio of the shear strength to the maximum shear stress, and iteratively adjusting the initial drilling parameters based on the shear force ratio; determining the drilling parameters corresponding to the shear force ratio that meets the preset requirements as the desired drilling parameters; drilling the stress relief hole group along the sidewall of the central tunnel towards the side tunnels according to the desired drilling parameters, and providing support after excavating the side tunnels. This invention eliminates redundant design and reduces the number of ineffective boreholes through quantitative design of the stress relief hole group, thereby reducing engineering costs and shortening the construction period.

Description

Technical Field

[0001] This invention discloses a tunnel excavation method based on principal stress axis deflection control, belonging to the field of tunnel construction technology. Background Technology

[0002] In tunnel and underground cavern engineering, sectional excavation technology (such as bench method, CRD method, etc.) effectively controls the stress concentration of the surrounding rock through layered and block construction, and has become the core construction method for excavation of soft strata and large cross-section caverns.

[0003] Stress relief technology creates a connected stress-relief space ahead of the tunnel face by pre-drilling to relieve pressure (such as high-pressure water jetting or blasting vibration), which promotes the transfer of concentrated stress to deeper rock strata, thereby reducing the risk of shear slippage in the abutment area caused by principal stress deflection. For strata prone to rockburst, peripheral hole-interval blasting can induce the development of a network of microfractures, enhance the stress wave superposition effect, and suppress sudden damage.

[0004] However, current stress relief design lacks theoretical support. The diameter, spacing, and layout of traditional advanced drilling rely heavily on engineering experience, which can easily lead to redundant holes (increasing costs and time) or insufficient holes (limited stress relief effect), resulting in an uncontrollable stress relief path. If the drilling direction does not match the direction of the principal stress, it may trigger a sudden energy release rockburst or insufficient stress relief, causing stress concentration at the arch shoulder. Summary of the Invention

[0005] The purpose of this invention is to provide a solution to the technical problems in the prior art. To achieve the above objective, this invention proposes a tunnel excavation method based on principal stress axis deflection control, the specific scheme of which is as follows:

[0006] A tunnel excavation method based on principal stress axis deflection control includes:

[0007] S1. Divide the tunnel face to be excavated into a central tunnel and at least two side tunnels;

[0008] S2. Excavate the central cavern and support the arch of the central cavern;

[0009] S3. Based on the principal stress characteristic value of the axial deflection after the excavation of the central cavern and the initial drilling parameters of the stress relief hole group set before the excavation of the side cavern, determine the maximum shear stress of the surrounding rock.

[0010] S4. Obtain the shear strength of the surrounding rock, determine the shear force ratio of the shear strength to the maximum shear stress, and iteratively adjust the initial drilling parameters according to the shear force ratio;

[0011] S5. Repeat S3 to S4 to determine the drilling parameters corresponding to the shear force ratio that meets the preset requirements as the desired drilling parameters.

[0012] S6. Drill a group of stress relief holes along the side wall of the central cavern toward the side cavern according to the desired drilling parameters, and provide support after excavating the side cavern.

[0013] Preferably, in S6, the two side chambers are excavated synchronously and symmetrically or asynchronously in sequence.

[0014] Preferably, S3 includes:

[0015] The principal stress characteristic values ​​include the maximum principal stress and the minimum principal stress;

[0016] The total area of ​​the borehole group is determined based on the initial drilling parameters;

[0017] Obtain the free surface area of ​​the side chamber, and determine the stress release amount based on the maximum principal stress, the total area of ​​the hole group, and the free surface area;

[0018] The maximum shear stress of the surrounding rock is calculated based on the stress release amount and the minimum principal stress.

[0019] Preferably, the drilling parameters include the borehole diameter and the number of boreholes.

[0020] Preferably, support is provided after the side chamber is excavated, including:

[0021] The side chambers were excavated using drilling and blasting methods or mechanical methods.

[0022] Support is provided after anchor bolts are installed in the stress relief hole group.

[0023] Preferably, the drilling direction of each borehole in the stress relief hole group is perpendicular to the outline of the cavern to be excavated.

[0024] Preferably, the depth of the stress relief hole group extends to a predetermined depth outside the outline of the cavern to be excavated.

[0025] Preferably, the maximum principal stress and the minimum principal stress are determined based on elasticity theory or stress monitoring.

[0026] Beneficial effects: This invention achieves graded and orderly release of elastic strain energy in shallow high-stress areas by quantitatively designing a group of stress-relieving holes and directionally controlling the stress-relieving path and rate. This effectively avoids rock bursts or collapses caused by sudden stress drops in traditional methods.

[0027] This invention determines the maximum shear stress of the surrounding rock by using the principal stress characteristic value after the excavation of the intermediate cavern and the drilling parameters of the set stress relief hole group. Based on the ratio of the shear strength of the surrounding rock to the maximum shear stress, the drilling parameters of the stress relief hole group are iteratively optimized, eliminating redundant design, reducing the number of invalid boreholes, reducing project costs and shortening the construction period.

[0028] The stress relief hole group of this invention has a dual function: after stress relief is completed, it transforms into anchor bolt installation channels, where anchor bolts are inserted and mortar is poured in, instantly forming a composite anchoring system. This solves the problem of rock mass disturbance caused by secondary drilling, strengthens the pull-out bearing capacity of the anchor bolts, and combines stress relief and permanent support into a single process, shortening the construction period and improving the coordinated deformation capacity of the support system. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the cavern zoning excavation and support structure in an embodiment of the present invention;

[0030] Figure 2 Figure I is a spatial schematic diagram of the side chamber in an embodiment of the present invention, and Figure II is a schematic diagram of the area of ​​the free surface of the side chamber and the total area of ​​the hole group.

[0031] In the diagram: 1. Upper middle pilot tunnel; 2. Upper left side pilot tunnel; 3. Upper right side pilot tunnel; 4. Lower left side pilot tunnel; 5. Lower middle pilot tunnel; 6. Lower right side pilot tunnel; 7. Thin layer of concrete; 8. Anchor bolt; 9. Steel mesh; 10. Shotcrete; 11. Stress relief hole group; 12. Stable surrounding rock zone; 13. Relaxed surrounding rock zone. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of the invention.

[0033] A tunnel excavation method based on principal stress axis deflection control includes:

[0034] S1. Divide the tunnel face to be excavated into a central tunnel and at least two side tunnels;

[0035] Specifically, in this embodiment, the working face of the tunnel to be excavated is divided into upper and lower stages for graded excavation, such as... Figure 1 As shown, the upper level specifically includes the upper central guide tunnel 1, which serves as the central cavern, and the upper left side guide tunnel 2 and the upper right side guide tunnel 3, which serve as the two side caverns. The lower level includes the lower left side guide tunnel 4, the lower central guide tunnel 5, and the lower right side guide tunnel 6.

[0036] It should be noted that the division of the tunnel face can be adjusted according to actual engineering needs. For example, in another embodiment, a five-zone pattern of central chamber, left chamber, right chamber, lower left chamber, and lower right chamber can be adopted. The key control element is that the top of the central chamber must be located at the center of the arch, while the tops of the two side chambers must correspond to the abutment area.

[0037] S2. Excavate the central cavern and support the arch of the central cavern;

[0038] Specifically, in this embodiment, after the tunnel face is divided, the upper and middle guide tunnel 1 is excavated by drilling and blasting or mechanical methods. During the excavation process, the outline line needs to be strictly controlled to avoid over-excavation and under-excavation.

[0039] After the excavation of the upper and middle pilot tunnel 1 is completed, initial support is implemented for the loosened rock zone 13 formed around the tunnel chamber according to the following steps: First, stress relief holes 11 are drilled on the arch rock surface of the tunnel chamber at preset intervals, lengths, and angles. Then, anchor bolts 8 are installed in the stress relief holes 11 and grouting is performed to reinforce them, completing the initial support. To enhance the support effect, a thin layer of concrete 7 is sprayed onto the arch to seal the rock surface and prevent weathering of the surrounding rock. To further improve the support strength, a steel mesh 9 can be added to the surface of the thin layer of concrete 7 and then sprayed with concrete 10 to the designed thickness to form a stable initial load-bearing arch structure.

[0040] Specifically, after the excavation and support of the upper and middle pilot tunnel 1 are completed, stress concentration occurs in the side cavern area. At this time, stress release is required, that is, the stress release hole group 11 is drilled. In order to avoid redundant hole layout or insufficient hole layout caused by previous experience-based hole layout, the drilling parameters of the stress release hole group 11 are determined based on the principal stress characteristic value of the principal stress axis deflection.

[0041] S3. Based on the principal stress characteristic value of the axial deflection after the excavation of the central cavern and the initial drilling parameters of the stress relief hole group 11 set before the excavation of the side cavern, determine the maximum shear stress of the surrounding rock.

[0042] Furthermore, the principal stress characteristic values ​​include the maximum principal stress and the minimum principal stress;

[0043] The maximum and minimum principal stresses of the axial deflection after the excavation of the intermediate cavern are determined based on elasticity theory or stress monitoring.

[0044] Specifically, determine the maximum principal stress of axial deflection after the intermediate cavern is excavated. and minimum principal stress Multiple methods can be employed. Based on elasticity theory, principal stress values ​​can be calculated through stress concentration effect analysis and Hooke's law. In practice, stress monitoring equipment can be used for real-time monitoring to obtain actual stress data. Furthermore, numerical simulation methods can be used to establish finite element models for calculation and analysis, or acoustic emission monitoring technology can be used to invert the stress state. For important projects, a comprehensive evaluation can be conducted by combining methods such as geomechanical analysis; if necessary, multiple methods can be used for cross-verification to improve the reliability of the results. In practical applications, appropriate methods or combinations of methods are usually selected based on the project characteristics, accuracy requirements, and site conditions.

[0045] The maximum shear stress of the surrounding rock is determined based on the maximum principal stress, the minimum principal stress, and the initial drilling parameters of the stress relief borehole group 11 before the excavation of the side cavern.

[0046] This includes: determining the total area of ​​the borehole group based on the initial drilling parameters;

[0047] Obtain the free surface area of ​​the side chamber, and determine the stress release amount based on the maximum principal stress, the total area of ​​the hole group, and the free surface area;

[0048] The maximum shear stress of the surrounding rock is calculated based on the stress release amount and the minimum principal stress.

[0049] Specifically, after determining the maximum and minimum principal stresses of the shaft deflection, the drilling parameters of the initial stress relief hole group 11 are set.

[0050] Drilling parameters include borehole diameter and number of boreholes. The total area B of the stress-relieving borehole group 11 drilled on the free surface is calculated based on the borehole diameter and number of boreholes. Figure 2 As shown, the free surface area A of the side chamber was then measured (i.e., the free surface area of ​​the side chamber and the middle chamber formed after the excavation of the upper and middle guide tunnel 1). Because drilling of the stress relief hole group 11 causes a sudden drop in the radial stress around the hole, it drives the original tangential principal stress... The stress is transferred to deeper layers; based on this mechanical mechanism, the stress release amount of stress relief hole group 11... It can be determined by the following relationship:

[0051]

[0052] In the formula:

[0053] A represents the total area of ​​the stress-relieving orifice group;

[0054] B represents the area of ​​the free surface of the side chamber;

[0055] This represents the original maximum principal stress in the tangential direction;

[0056] This indicates the amount of stress released by the stress relief hole group.

[0057] The above formula indicates the amount of stress relief. It is inversely proportional to the ratio of the opening area. Based on this principle, after stress regulation is completed through the stress relief hole group 11, the maximum shear stress of the surrounding rock can be calculated according to the Mohr's circle theory. The calculation formula is as follows:

[0058]

[0059] In the formula:

[0060] This represents the maximum principal stress after stress relief;

[0061] This represents the maximum shear stress in the surrounding rock;

[0062] This represents the original minimum principal stress in the tangential direction.

[0063] S4. Obtain the shear strength of the surrounding rock, determine the shear force ratio of the shear strength to the maximum shear stress, and iteratively adjust the initial drilling parameters according to the shear force ratio;

[0064] The shear strength of the surrounding rock is determined according to the Mohr-Coulomb criterion, and the specific formula is as follows:

[0065]

[0066] In the formula:

[0067] The shear strength of the surrounding rock;

[0068] The cohesion of the surrounding rock;

[0069] The internal friction angle of the surrounding rock;

[0070] This represents the normal stress acting on the shear plane.

[0071] The initial borehole parameters are iteratively optimized based on the ratio of shear strength to maximum shear stress to determine the ratio of shear strength to maximum shear stress. The initial drilling parameters are iteratively adjusted based on the shear strength ratio.

[0072] Specifically, when This indicates that the total area B of the currently designed borehole group can control the risk of shear failure, and the drilling parameters meet the requirements.

[0073] when Significantly lower than ,Right now If the value is greater than X, then the borehole diameter and / or the number of boreholes need to be reduced, where X is a preset safety factor that can be set according to the actual project requirements.

[0074] when If so, it is necessary to increase the borehole diameter and / or the number of boreholes to improve the pressure relief capacity and prevent slippage damage.

[0075] S5. Repeat S3 to S4 to determine the drilling parameters corresponding to the shear force ratio that meets the preset requirements as the desired drilling parameters.

[0076] S6. Drill a group of stress relief holes 11 along the side wall of the central cavern toward the side cavern according to the desired drilling parameters, and provide support after excavating the side cavern.

[0077] Specifically, in this embodiment, after determining the desired drilling parameters, namely the borehole diameter and the number of boreholes, stress relief holes 11 are drilled on the free surface of the upper left guide tunnel 2 toward the arch shoulder of the side chamber, according to the borehole diameter and drilling parameters.

[0078] In another embodiment, the method further includes real-time feedback of surrounding rock fracture signals through a microseismic monitoring system to regulate the drilling progress and location of the stress release hole group 11, thereby achieving directional regulation of the stress release rate and path of the surrounding rock, so that the elastic strain energy of the shallow high-stress zone can be released in stages and in an orderly manner.

[0079] The drilling direction of each borehole in the stress relief borehole group 11 is perpendicular to the outline of the cavern to be excavated. The depth of the boreholes in the stress relief borehole group 11 extends to a predetermined depth outside the outline of the cavern to be excavated. Specifically, the depth of the boreholes in the stress relief borehole group 11 extends to the surrounding rock stability zone 12 of the cavern. In this embodiment, each borehole extends 0.5m outside the outline.

[0080] In traditional tunnel construction, stress relief holes and support holes are set up independently, requiring secondary drilling which causes repeated disturbance to the surrounding rock. This not only reduces the utilization efficiency of the boreholes but also prevents the surrounding rock at the arch shoulder from being anchored in a timely manner by the support structure after stress relief. As a result, the deformation of the support system and the surrounding rock is difficult to coordinate, the axial force distribution of the anchor bolts is severely uneven, and it is difficult to cope with the continuous stress adjustment caused by the dynamic deflection of the principal stress axis, resulting in a significant deficiency in the synergistic bearing capacity.

[0081] To address the aforementioned issues, this embodiment provides support after excavating the side chamber, including: excavating the side chamber using drilling and blasting or mechanical methods; and providing support after installing anchor bolts 8 within the stress relief hole group 11.

[0082] Specifically, in this embodiment, the upper left guide tunnel 2 is excavated using either a drill-and-blast method or a mechanical method. After excavation, the stress relief hole group 11 is directly used as the installation channel for the anchor bolts 8. The anchor bolts 8 are immediately inserted into the hole group and then mortar is poured in for consolidation, fundamentally eliminating the disturbance of the surrounding rock caused by secondary drilling and significantly improving the ability of the support system to deform in tandem. After the anchor bolts 8 are installed, concrete is immediately sprayed to the designed thickness to quickly form the load-bearing arch structure in this area, ensuring that effective support can be obtained immediately after the stress of the surrounding rock is released.

[0083] It should be noted that the stress relief borehole group 11 is drilled, excavated, and supported by the two side chambers using either synchronous symmetrical or asynchronous sequential methods. If asynchronous sequential excavation is used, the construction time interval between the two side chambers must be strictly controlled, as excessively long intervals will weaken the overall stability of the tunnel.

[0084] In this embodiment, after completing the upper-level excavation, the lower middle guide tunnel 5, the lower left side guide tunnel 4, and the lower right side guide tunnel 6 are excavated and supported in sequence according to the step-by-step excavation sequence. Finally, the safe excavation and support of the entire tunnel are completed, effectively preventing shear collapse of the surrounding rock at the arch shoulder under the deflection of the principal stress axis.

[0085] This invention achieves graded and orderly release of elastic strain energy in shallow high-stress areas by quantitatively designing the stress release hole group 11 and directionally controlling the stress release path and rate, effectively avoiding rockburst or collapse accidents caused by sudden stress drop in traditional methods.

[0086] This invention determines the maximum shear stress of the surrounding rock by using the principal stress characteristic value after the excavation of the intermediate cavern and the drilling parameters of the set stress relief hole group 11. Based on the ratio of the shear strength of the surrounding rock to the maximum shear stress, the drilling parameters of the stress relief hole group 11 are iteratively optimized, eliminating redundant design, reducing the number of invalid boreholes, reducing project costs and shortening the construction period.

[0087] The stress relief hole group 11 of this invention has a dual function: after stress relief is completed, it transforms into anchor bolt 8 installation channels, where anchor bolts 8 are inserted and mortar is poured in, instantly forming the composite anchoring system. This solves the problem of disturbance to the rock mass caused by secondary drilling, strengthens the pull-out bearing capacity of the anchor bolts 8, and combines stress relief and permanent support into a single process, shortening the construction period and improving the coordinated deformation capacity of the support system.

[0088] The above description is merely a few embodiments of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any modifications or alterations made by those skilled in the art without departing from the scope of the technical solution of the present invention using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A method for tunnel excavation based on principal stress axis deflection control, characterized in that, include: S1. Divide the tunnel face to be excavated into a central tunnel and at least two side tunnels; S2. Excavate the central cavern and support the arch of the central cavern; S3. Based on the principal stress characteristic value of the axial deflection after the excavation of the central cavern and the initial drilling parameters of the stress relief hole group set before the excavation of the side cavern, determine the maximum shear stress of the surrounding rock. S4. Obtain the shear strength of the surrounding rock, determine the shear force ratio of the shear strength to the maximum shear stress, and iteratively adjust the initial drilling parameters according to the shear force ratio; S5. Repeat S3 to S4 to determine the drilling parameters corresponding to the shear force ratio that meets the preset requirements as the desired drilling parameters. S6. Drill a group of stress relief holes along the side wall of the central cavern toward the side cavern according to the desired drilling parameters, and provide support after excavating the side cavern.

2. The tunnel excavation method according to claim 1, characterized in that, In S6, two side chambers are excavated synchronously and symmetrically or asynchronously in sequence.

3. The tunnel excavation method according to claim 2, characterized in that, S3 includes: The principal stress characteristic values ​​include the maximum principal stress and the minimum principal stress; The total area of ​​the borehole group is determined based on the initial drilling parameters; Obtain the free surface area of ​​the side chamber, and determine the stress release amount based on the maximum principal stress, the total area of ​​the hole group, and the free surface area; The maximum shear stress of the surrounding rock is calculated based on the stress release amount and the minimum principal stress.

4. The tunnel excavation method according to claim 1, characterized in that, The drilling parameters include the borehole diameter and the number of boreholes.

5. The tunnel excavation method according to claim 1, characterized in that, Support is provided after the excavation of the side chambers, including: The side chambers were excavated using drilling and blasting methods or mechanical methods. Support is provided after anchor bolts are installed in the stress relief hole group.

6. The tunnel excavation method according to claim 1, characterized in that, The drilling direction of each hole in the stress relief hole group is perpendicular to the outline of the cavern to be excavated.

7. The tunnel excavation method according to claim 1, characterized in that, The stress relief hole group extends to a predetermined depth outside the outline of the cavern to be excavated.

8. The method according to claim 3, characterized in that, The maximum and minimum principal stresses are determined based on elasticity theory or stress monitoring.

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