Roadway surrounding rock fracturing ring construction outer self-bearing ring and near surface yielding support ring cooperative control method

Abstract

A cooperative control method for an outer self-bearing ring and a near-surface yielding support ring for roadway surrounding rock fracturing ring construction belongs to the technical field of mineral exploitation, and comprises the following steps: exploring a fracturing target rock stratum conforming to physical and mechanical parameters around a roadway; determining characteristic parameters of a surrounding rock loosening circle, and further determining a near-surface yielding support circle range; the pulse fracturing drilling length is determined according to the target fracturing rock stratum, and the pulse fracturing weakening circle range is obtained; weakening the rock stratum outside the yielding support ring in a pulse fracturing manner to form a pulse fracturing weakening ring, and meanwhile, transferring the high support stress of the surrounding rock in the pulse fracturing weakening ring to the far-field hard rock stratum to construct a self-bearing ring outside the far-field surrounding rock; a near-surface yielding support ring is constructed in an active and passive yielding support mode, and a buffer area is formed between the yielding support ring and the pulse fracturing weakening ring; through a cooperative control mode of roadway surrounding rock fracturing weakening, far-field surrounding rock self-bearing and near-surface surrounding rock yielding supporting, large deformation control over the surrounding rock of the deep well soft rock roadway is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of mineral mining, and specifically refers to a method for coordinated control of an outer self-bearing ring and a near-surface yielding support ring in constructing a tunnel surrounding rock fracturing ring. Background Art

[0002] As my country's coal mining gradually develops deeper, the high-altitude stress environment has a significant impact on the surrounding rock of the tunnel. Under the deep high-altitude stress environment, the tunnel surrounding rock shows large deformation phenomena such as rheology and structural instability, which are specifically manifested as "large deformation of the tunnel surrounding rock, long duration, and serious damage to the support structure", which seriously affects the safe and efficient production of underground mines.

[0003] Under deep mining conditions, geostress, mining impact and mechanical properties of the surrounding rock near the surface are the main factors restricting the control of the tunnel surrounding rock. Under the dual constraints of high geostress and weak surrounding rock, the physical properties of the tunnel surrounding rock deteriorate and the strength decays. At the same time, the tunnel surrounding rock induces crack expansion under the action of deviatoric stress and gradient stress, causing the tunnel surrounding rock to deteriorate in the plastic zone, flow, and fracture, resulting in continuous large deformation of the tunnel surrounding rock. Specifically, it manifests as discontinuous deformation such as expansion and shear expansion of the surrounding rock in the shallow area around the tunnel, and continuous deformation dominated by plastic deformation caused by the tunnel under high stress.

[0004] Under high ground stress environment, some tunnels are severely deformed without being affected by mining. Traditional tunnel surrounding rock reinforcement supports control tunnel deformation by increasing the bearing capacity of the near-surface surrounding rock. However, the high ground stress of deep mining exceeds the bearing capacity of the tunnel surrounding rock, resulting in large rheological deformation of the soft rock tunnel. It is worth noting that the anchor support system did not fail during the tunnel repair, indicating that the anchored surrounding rock of the tunnel underwent overall extrusion deformation, showing typical large rheological deformation characteristics of soft rock. Under deep mining conditions, the sum of the surrounding rock bearing capacity increased by traditional reinforced support and the original rock bearing capacity is less than the ground stress, which is the mechanical essence of large deformation of the surrounding rock.

[0005] The main technology for controlling the surrounding rock of deep mining tunnels is to strengthen support, including: bolt support, cable support, shotcrete support, U-shaped steel support, single hydraulic prop, etc. The traditional tunnel surrounding rock strengthening support technology can effectively enhance the bearing capacity of the surrounding rock in the mining environment with low shallow ground stress, thereby achieving tunnel surrounding rock control. However, due to the prominent characteristics of high ground stress in deep mining, soft rocks are often more prone to plastic deformation and rheological deformation. It is difficult to effectively control the large deformation of the surrounding rock in deep mining by only using traditional strengthening support measures to improve the bearing capacity of the tunnel near the surface surrounding rock. The resistance of the support system is often unable to match the deformation of the rock mass under the action of high ground stress, which leads to aggravated deformation of the tunnel and failure of the support system.

[0006] Therefore, the traditional tunnel surrounding rock strengthening support technology cannot fundamentally curb the deformation of tunnel surrounding rock under deep mining conditions, which leads to high maintenance frequency and cost of tunnels, and has a serious impact on mine safety production. It is necessary to jointly control the surrounding rock deformation from the perspective of improving the tunnel stress environment and strengthening the surrounding rock bearing capacity. It is urgent to propose a safe, reliable and effective deep soft rock large tunnel surrounding rock control technology. Summary of the invention

[0007] In view of the above situation, in order to overcome the defects of the prior art, an embodiment of the present invention provides a method for coordinated control of an outer self-bearing ring and a near-surface yielding support ring for constructing a tunnel surrounding rock fracturing ring, which at least partially solves the above technical problems.

[0008] The technical solution adopted by the embodiment of the present invention is as follows: a method for coordinated control of an outer self-bearing ring and a near-surface yielding support ring for constructing a tunnel surrounding rock fracturing ring, comprising the following steps:

[0009] Explore the target rock formations for fracturing that meet the physical and mechanical parameters around the tunnel;

[0010] Determine the characteristic parameters of the surrounding rock loosening zone, and then determine the range of the near-surface yielding support ring;

[0011] Determine the pulse fracturing drilling length according to the target fracturing rock formation and obtain the pulse fracturing weakening zone range;

[0012] The pulse fracturing method is used to weaken the rock formation outside the pressure support ring to form a pulse fracturing weakening circle to achieve the purpose of energy absorption. At the same time, the high support stress of the surrounding rock in the pulse fracturing weakening circle is transferred to the hard rock formation in the far field to construct a self-supporting circle outside the far field surrounding rock.

[0013] A near-surface yielding support ring is constructed through active and passive yielding support methods, and a buffer zone is formed between the yielding support ring and the pulse fracturing weakening zone.

[0014] Furthermore, exploration holes are set in the roof, side and bottom plates of the surrounding rock near the tunnel to determine the rock properties of the tunnel near the surface, and its physical and mechanical parameters are tested indoors; the nearby rock formations with high strength, good integrity, high rigidity and large thickness are identified as key rock formations, which serve as the target rock formations for subsequent pulse fracturing.

[0015] Furthermore, the characteristic parameters of the surrounding rock loosening zone include the loosening zone radius, the loosening zone thickness, the maximum loosening stress, the stress distribution in the loosening zone and the range of the surrounding rock plastic zone in the loosening zone;

[0016] The range of the near-surface yielding support ring is 5m to 10m larger than the range of the surrounding rock loosening zone.

[0017] Furthermore, the number of boreholes was calculated based on the radial main fracture extension range of 15 m in a single borehole;

[0018] A buffer distance of 15m-30m is provided between the pulse fracturing weakening zone and the near-surface yielding support ring.

[0019] Further, the pulse weakening configuration is: when the target rock formation is a single layer and the thickness is ≤10m, a radial pulse hydraulic fracturing network is formed by sequentially carrying out pulse hydraulic fracturing on each borehole, wherein the parameters of the pulse fracturing are: pulse frequency 5Hz~10Hz, displacement 80L / min~120L / min, and pulse waveform sine wave;

[0020] When the target rock layer has multiple layers or a single layer with a thickness greater than 10m, multiple pulse fracturing is performed in sequence on each borehole in the same thick hard rock layer by a backward staged pulse fracturing method, wherein the backward distance of the backward staged pulse fracturing method is 5m to 10m.

[0021] Furthermore, for soft rocks such as mudstone that soften when exposed to water, the amount of water used for fracturing is controlled, the total liquid volume is read in real time throughout the fracturing process, and fracturing is stopped immediately when the test threshold is reached; the fracturing return water is drained to the designated drainage ditch through a dedicated drainage pipeline.

[0022] Furthermore, the construction of the near-surface yielding support ring includes:

[0023] Initial yielding support: Use yielding anchors to support the surrounding rock near the tunnel surface, then lay anchor nets on the top plate and both sides and spray concrete;

[0024] Secondary support: The tunnel is reinforced with anchor cables, which together with the primary support system form a coupled anchoring structure. A retractable U-shaped steel arch frame with reserved deformation is laid on the entire section of the tunnel and concrete is sprayed.

[0025] Furthermore, in the tunnels prone to bottom heave, the construction of a near-surface pressure-yielding support ring also includes constructing a composite reverse bottom arch structure: the bottom plate tensile stress is converted into annular compressive stress through the arc-shaped reverse bottom arch structure, and the cracks in the bottom plate surrounding rock are filled with a graded grouting process to form a "flexible buffer-rigid load-bearing" composite structure.

[0026] Furthermore, the ultimate tensile strength σ of the yield anchor u Dynamically match the surrounding rock rheological rate with the elongation δ, and adapt in stages according to the ground stress gradient, that is, σ u and δ with ground stress σ v and the compressive strength of the surrounding rock near the surface σ c The ratio σ v / σ c Increase with rise.

[0027] Furthermore, the reserved deformation of the retractable U-shaped steel arch is determined by the following method:

[0028] First, after fracturing, the scope of the fracturing weakening zone was determined by drilling peek and numerical simulation method, and the radius R of the pulse fracturing weakening zone was obtained. f ;

[0029] Secondly, the core was taken in situ by drilling, and the elastic modulus E0 of the surrounding rock of the pulse fracturing weakening zone before fracturing, the elastic modulus E1 of the surrounding rock of the pulse fracturing weakening zone after fracturing, and the initial ground stress σ of the near-surface yielding support ring were tested in the laboratory. v0 ,pass:

[0030]

[0031] The surrounding rock weakening modulus reduction coefficient η is calculated based on the above calculation results:

[0032]

[0033] The effective stress σ transferred to the near-surface yielding support ring is calculated v1 , where D is the distance from the outer edge of the pulse fracturing weakening zone to the side of the tunnel;

[0034] Then the effective stress σ v1 The surrounding rock strength σ of the near-surface yielding retaining ring c The ratio H is obtained by:

[0035]

[0036] Calculate and then set the reserved deformation U of the retractable U-shaped steel arch according to the H classification.

[0037] The beneficial effects achieved by the present invention using the above structure are as follows:

[0038] (1) The present invention actively regulates the surrounding rock stress field through pulse fracturing weakening technology, transfers the high bearing stress of the near-surface surrounding rock to the hard rock layer in the far-field deep, and constructs a far-field surrounding rock self-bearing ring; then, the "external self-bearing ring-near-surface yielding support ring" collaborative control system is used, the outer ring relies on stress redistribution to achieve rock self-bearing, and the inner ring cooperates with yielding support methods such as prestressed yielding anchor rods, laying buffer layers and retractable U-shaped steel arch frames to produce controllable deformation in the near-surface surrounding rock, achieve local pressure relief, and optimize the adaptability of the support system to the surrounding rock deformation;

[0039] (2) The present invention aims to solve the problem of large deformation of surrounding rock caused by the three-way contradiction of "high ground stress - weak bearing capacity of surrounding rock - rigid support system" in deep well soft rock tunnels. By coupling stress environment optimization and reconstruction of surrounding rock-support mechanical relationship, the present invention takes stress environment optimization and deformation coordination control as the core, and breaks through the adaptability bottleneck of traditional rigid support system under the dual constraints of high ground stress and weak bearing capacity of soft rock.

[0040] (3) The present invention significantly enhances the self-stabilizing ability of the surrounding rock and the dynamic response characteristics of the support system by establishing a coordinated mechanism of "external self-bearing-internal pressure-yielding regulation", achieving the integrated goals of rheological suppression, deformation control and cascade prevention and control of instability risks, and providing a reference for surrounding rock control in deep soft rock tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flow chart of the steps of the coordinated control method of the outer self-bearing ring and the near-surface yielding support ring in the construction of the surrounding rock fracturing ring;

[0042] Figure 2 It is a schematic diagram of the coordinated control method of the outer self-bearing ring and the near-surface yielding support ring for the surrounding rock fracturing ring of a single soft rock tunnel in a deep well;

[0043] Figure 3 It is a schematic cross-sectional diagram of a coordinated control method for constructing an external self-bearing ring and a near-surface yielding support ring for surrounding rock fracturing rings of multiple system tunnels at the same mining level;

[0044] Figure 4 It is a schematic plan view of a coordinated control method for constructing an external self-bearing ring and a near-surface yielding support ring for surrounding rock fracturing rings of multiple system tunnels at the same mining level;

[0045] In the figure:

[0046] 1-soft rock formation with low bearing capacity, 2-hard rock formation with high bearing capacity, 3-soft rock tunnel, 4-near-surface yielding support ring, 5-pulse fracturing weakening ring, 6-pulse fracturing crack network, 7-pulse fracturing borehole, 8-yielding anchor rod, 9-concrete spraying layer, 10-reserved deformation of retractable U-shaped steel arch frame, 11-original section of tunnel, 12-grouting anchor rod, 13-retractable U-shaped steel arch frame, 14-buffer zone, 15-far-field surrounding rock self-bearing ring, 16-support pressure distribution curve;

[0047] 1-1-weak rock layer where the tunnel to be protected is located, 1-2-coal mining seam, 3-1-return air tunnel, 3-2-track tunnel, 3-3-gangue transportation tunnel, 3-4-belt conveyor transportation tunnel, 3-5-working face track tunnel, 3-6-working face transportation tunnel, 3-7-working face, 3-8-goaf, 5-1-midpoint of the line connecting the two furthest distances in the tunnel to be protected, 5-2-long axis length of the pulse fracturing weakening zone, 5-3-pulse fracturing The short axis length of the punch fracturing weakened zone, 16-1-the area of ​​increased bearing pressure of the near-surface surrounding rock yielding support ring, 16-2-the area of ​​decreased bearing pressure of the near-surface surrounding rock yielding support ring, 16-3-the area of ​​increased bearing pressure in the buffer zone, 16-4-the area of ​​decreased bearing pressure of the pulse fracturing weakened zone, 16-5-the area of ​​increased bearing pressure of the far-field surrounding rock self-bearing ring, 16-6-the area of ​​decreased bearing pressure of the far-field surrounding rock self-bearing ring, 16-7-the area of ​​original rock stress of the far-field surrounding rock.

[0048] The accompanying drawings are used to provide further understanding of the embodiments of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0050] In the description of the embodiments of the present invention, it should be understood that terms such as "up", "down", "front", "back", "left", "right", "top", "bottom", "inside" and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as limiting the present invention.

[0051] The technical problem to be solved by the present invention is: how to control the surrounding rock deformation of the soft rock tunnel 3 under high ground stress environment, transfer the supporting stress of the tunnel surrounding rock, and ensure the long-term service of the deep well soft rock tunnel 3.

[0052] Under deep mining conditions, the sum of the surrounding rock bearing capacity increased by traditional reinforced support and the original rock bearing capacity is less than the ground stress, resulting in large deformation phenomena such as rheology and structural instability in the tunnel surrounding rock. Traditional tunnel surrounding rock reinforcement support technology cannot fundamentally curb the deformation of tunnel surrounding rock under deep mining conditions, which leads to high maintenance frequency and cost of tunnels, and has a serious impact on mine safety production. Therefore, deep mining faces the problem of surrounding rock control in soft rock tunnels under high ground stress environment.

[0053] like Figure 1 In view of the above problems, the present invention provides a method for coordinated control of an outer self-bearing ring and a near-surface yielding support ring for constructing a tunnel surrounding rock fracturing ring, comprising the following steps:

[0054] S1. Survey the rock properties of the tunnel to determine the key rock strata: construct top and bottom plate exploration holes in the roof, side and bottom plates of the surrounding rock near the tunnel to be protected to determine the rock properties of the tunnel near the surface, and test its physical and mechanical parameters indoors; determine the rock strata with high strength, good integrity, high rigidity and large thickness as the key rock strata, which will be used as the target rock strata for subsequent pulse fracturing.

[0055] S2. Determine the loose zone of the tunnel surrounding rock: Through the methods of acoustic wave detection technology, borehole peeping and geological radar, obtain the empirical values ​​of the characteristic parameters of the loose zone of the surrounding rock, including the radius of the loose zone, the thickness of the loose zone, the maximum loose stress, the stress distribution in the loose zone and the range of the plastic zone of the surrounding rock in the loose zone, so as to provide a basis for determining the range of the near-surface yield support ring 4.

[0056] S3. Determine the range of pulse fracturing weakening zone 5: determine the length of pulse fracturing borehole 7 (i.e., borehole) according to the target fracturing rock layer of the surrounding rock near the surface of the roadway, and then obtain the diameter of pulse fracturing weakening zone 5. According to the radial main crack extension range of a single pulse fracturing borehole 7 of about 15m, the number of pulse fracturing boreholes 7 is calculated. The pulse fracturing weakening zone 5 forms a whole circle with the roadway as the center; the pulse fracturing weakening zone 5 and the near-surface yielding support ring 4 form a certain buffer distance to prevent the pulse fracturing cracks from extending to the support area and causing the support system to fail, which is optimal. The selected buffer distance is 15m to 30m; for the development tunnel or the soft rock tunnel 3 with a straight-line distance of less than 50m and parallel axes, it is manifested as an elliptical pulse fracturing weakening zone 5, the center of which is the midpoint of the line connecting the farthest tunnels to be protected, and the length of the major axis is the sum of the radius of the line connecting the farthest tunnels to be protected and the near-surface yield support ring 4 of a single tunnel and the buffer zone distance between the near-surface yield support ring 4 and the pulse fracturing weakening zone 5; the vertical range of the pulse fracturing weakening zone 5 cannot exceed the coal seam or the adjacent coal seam to be mined.

[0057] Soft rock tunnel 3 includes return air tunnel 3-1, rail tunnel 3-2, gangue transport tunnel 3-3, belt conveyor transport tunnel 3-4, working face rail tunnel 3-5, working face transport tunnel 3-6, working face 3-7 and goaf 3-8.

[0058] S4. Determine the range of the near-surface yield support ring 4: the range of the near-surface yield support ring 4 is 5 to 10 meters larger than the range of the loosened surrounding rock zone of the tunnel measured in step S2; for the tunnels that have been affected by mining, the range of the loosened surrounding rock zone measured in the tunnel shall prevail; for the tunnels that have not been affected by mining, the empirical value of the loosened surrounding rock zone of the tunnels whose adjacent working faces have been affected by mining or the tunnels with similar conditions in step S2 shall be used as the basis for calculation.

[0059] S5. Constructing the pulse fracturing weakening circle 5 of the outer rock formation: The rock formation outside the near-surface bearing circle is weakened by pulse fracturing, and a certain range of weak structure is formed by generating a pulse fracturing fracture network 6. On the one hand, it absorbs the high dynamic load of the initial mining and periodic breaking of the roof, and at the same time transfers the high bearing stress of the near-surface yield support circle 4 to the "far-field surrounding rock self-bearing circle 15", giving full play to the bearing capacity of the far-field hard rock formation, and utilizing the advantage of higher strength of the far-field surrounding rock under the triaxial stress state, to optimize the stress environment of the near-surface surrounding rock of the tunnel.

[0060] S51, drilling and pulse fracturing: construct fracturing holes on the roof, side and floor of the tunnel, carry out pulse hydraulic fracturing on each hole in turn, and absorb the elastic energy released by the roof rupture by forming a radial pulse hydraulic fracture network 6. At the same time, transfer the near-surface surrounding rock support stress within the pulse fracturing weakening zone 5 to the far-field hard surrounding rock outside the weakening zone to construct a self-bearing zone outside the far-field surrounding rock. Use the high self-bearing capacity of the far-field surrounding rock as the main way to resist ground stress, and optimize the stress environment of the soft rock tunnel 3.

[0061] S52: Borehole sealing: The pulse fracturing borehole 7 is grout-sealed to prevent the fracturing cracks from closing under the action of ground stress, causing the fracturing fluid to flow back to the soft rock layer that swells and softens when it encounters water, thereby reducing the strength and normal stress of the fracture surface of the near-surface soft surrounding rock, causing the surrounding rock loosening zone to expand again.

[0062] S6. Construct a near-surface yielding support ring 4 for the entire section of the tunnel: construct a near-surface yielding support ring 4 through active and passive yielding support methods to adapt to the stable plastic deformation of the surrounding rock while strengthening the bearing capacity of the near-surface surrounding rock.

[0063] S61, anchor net spraying initial yielding support: use high strength, high toughness, high prestressed yielding anchor rod 8 to support the surrounding rock near the surface of the tunnel, then lay anchor nets on the top plate in turn and spray concrete on the top plate and the side of the tunnel.

[0064] S62, retractable U-shaped steel arch frame 13 and prestressed anchor cable secondary support: After the primary deformation of the surrounding rock tends to be stable, secondary support is carried out on the surrounding rock to provide the final support strength and stiffness for the tunnel. High prestressed anchor cables are used to reinforce the tunnel support, and together with the primary support system in step S61, a coupled anchoring structure is formed to enhance the reinforcement support effect; secondly, a retractable U-shaped steel arch frame 13 with reserved deformation is laid on the entire section of the tunnel and concrete is sprayed.

[0065] S63. Construct a flexible buffer-rigid load-bearing composite anti-bottom arch structure: For tunnels prone to bottom heave, the tensile stress of the bottom plate is converted into annular compressive stress through an arc-shaped anti-bottom arch structure, and the cracks in the surrounding rock of the bottom plate are filled with a graded grouting process to form a "flexible buffer-rigid load-bearing" composite structure to suppress the amount of bottom heave. First, low-pressure grouting is used to fill large-scale cracks to form a low-modulus flexible buffer zone, and the deformation energy generated by the bottom heave is absorbed through plastic deformation; secondly, high-pressure grouting is used to split and penetrate the micro-cracks of the bottom plate to form a high-modulus rigid load-bearing area, and the concrete as a whole forms a concrete spray layer 9.

[0066] In a further implementation of this embodiment, in step S2, for the tunnels not affected by mining, the determination of the empirical values ​​of the characteristic parameters of the surrounding rock loosening zone in step S2 is carried out in different working face tunnels affected by mining in the same mining area of ​​the mine.

[0067] In a further implementation of this embodiment, in step S2, the geological radar is an optimal non-destructive detection technology for the loose zone of the tunnel. By comparing and verifying different detection technologies, an accurate range of the loose zone of the surrounding rock is obtained, providing a basis for determining the range of the subsequent yield support ring.

[0068] In a further implementation of the present embodiment, in step S51, if the key rock formation determined in step S1 has multiple layers or a single layer with a large thickness (greater than 10m), the backward staged pulse fracturing technology is adopted to perform multiple pulse fracturing in the same thick hard rock formation to enhance the weakening effect of the high-integrity thick hard rock formation, and the preferred backward distance is 5 to 10m.

[0069] In a further implementation of this embodiment, in step S51, the preferred parameters of pulse fracturing are: pulse frequency 5-10 Hz, displacement 80-120 L / min, and pulse waveform sinusoidal wave.

[0070] In a further implementation of the present embodiment, in step S51, for soft rocks such as mudstone that soften when exposed to water, the following measures are taken to control the water dripping problem on the borehole and the roof: strictly control the amount of water used for fracturing, read the total liquid volume in real time throughout the fracturing process, and stop fracturing immediately when the test threshold is reached; drain the fracturing return water through a dedicated drainage pipeline to a designated drainage ditch to avoid direct discharge into the tunnel to cause short-term local water accumulation, thereby eliminating interference with production activities.

[0071] In a further implementation of this embodiment, in step S51, the outer boundary of the self-supporting ring outside the far-field surrounding rock is taken as a boundary that is 5% higher than the original rock stress.

[0072] In a further implementation of this embodiment, in step S61, if the tunnel has been deformed by dynamic pressure and static pressure, expansion and bottoming are first performed so that the net cross-sectional dimensions of the tunnel after support can be restored to the original designed cross-sectional dimensions.

[0073] In a further implementation of this embodiment, in step S61, the high-strength, high-toughness, high-prestressed yield anchor 8 adopts a constant resistance anchor, which provides constant resistance as the surrounding rock deforms and can generate significant plastic sliding energy absorption, thereby avoiding failure of the support system due to excessive deformation.

[0074] In a further implementation of this embodiment, in step S61, when spraying the concrete pressure layer, a certain thickness of concrete is first sprayed, a buffer layer is laid on the outside of the concrete layer to attenuate stress waves and absorb energy, and another layer of concrete is sprayed on the outside of the buffer layer. The preferred buffer layer material is closed-cell aluminum foam.

[0075] In a further implementation of the present embodiment, in steps S61 and S62, the high-strength, high-toughness, high-prestressed yield anchor 8 and anchor cable are made of strong and tough alloy materials, the initial prestress is applied in stages according to the ground stress gradient, the anchor can be retracted based on the expansion range of the plastic zone of the surrounding rock, and the sliding energy consumption is triggered when the load reaches the preset yield threshold to avoid brittle failure caused by stress concentration.

[0076] In a further implementation of this embodiment, in steps S61 and S62, the ultimate tensile strength σ of the high-strength, high-toughness, high-prestress yield anchor 8 is u Dynamically match the surrounding rock rheological rate with the elongation δ, and adapt in stages according to the ground stress gradient, that is, σ u and δ with ground stress σ v and the compressive strength of the surrounding rock near the surface σ c The ratio σ v / σ c Increase with the increase; high strength, high toughness and high prestressing force make the elongation δ and ultimate tensile strength σ of the pressure anchor 8 u Dynamic balance according to the inverse proportional function relationship.

[0077] In a further implementation of this embodiment, in step S62, the reserved deformation amount 10 of the retractable U-shaped steel arch is determined by the following method:

[0078] First, after fracturing, the scope of the fracturing weakening zone is determined by drilling and the radius R of the pulse fracturing weakening zone is obtained. f ;

[0079] Secondly, the core was taken in situ by drilling, and the elastic modulus E0 of the surrounding rock of the pulse fracturing weakening zone before fracturing, the elastic modulus E1 of the surrounding rock of the pulse fracturing weakening zone after fracturing, and the initial ground stress σ of the near-surface yielding support ring were tested in the laboratory. v0 ,pass:

[0080]

[0081] The surrounding rock weakening modulus reduction coefficient η is calculated based on the above calculation results:

[0082]

[0083] The effective stress σ transferred to the near-surface yielding support ring is calculated v1 , where D is the distance from the outer edge of the pulse fracturing weakening zone to the side of the tunnel;

[0084] Then the effective stress σ v1 The surrounding rock strength σ of the near-surface yielding retaining ring c The ratio H is obtained by:

[0085]

[0086] The reserved deformation U of the retractable U-shaped steel arch frame is calculated and then set according to the H classification. If the deformation rate exceeds the threshold, the reserved deformation is adaptively adjusted according to the stress release demand.

[0087] Example 1

[0088] like Figure 2 As shown, for the surrounding rock control of a single soft rock tunnel 3 in a deep well, the present invention provides a method for collaboratively controlling the outer self-bearing ring and the near-surface support ring of the tunnel surrounding rock fracturing ring. The specific implementation steps are as follows:

[0089] Step S1, survey the lithology of the tunnel to determine the key rock layer: for the tunnel to be protected 3, excavate in the soft rock layer 1 with low bearing capacity (that is, the soft rock layer 1-1 where the tunnel to be protected is located), and there may be hard rock layers 2 with strong bearing capacity above and below it, and construct top and bottom plate exploration holes in the top plate, side plate and bottom plate of the surrounding rock near the tunnel to be protected to determine the lithology of the surrounding rock near the tunnel surface, and test its physical and mechanical parameters indoors; determine the rock layer with high strength, good integrity, high rigidity and large thickness as the key rock layer, as the target rock layer for subsequent pulse fracturing.

[0090] Step S2, determination of the loose zone of the surrounding rock of the tunnel: by means of acoustic detection technology, borehole peep and geological radar, the empirical values ​​of the characteristic parameters of the loose zone of the surrounding rock are obtained, including the radius of the loose zone, the thickness of the loose zone, the maximum loose stress, the stress distribution in the loose zone and the range of the plastic zone of the surrounding rock in the loose zone, so as to provide a basis for determining the range of the near-surface yield support ring 4. For the tunnels not affected by mining, the empirical values ​​of the characteristic parameters of the loose zone of the surrounding rock are determined in the tunnels of different working faces in the same mining area of ​​the mine that have been affected by mining.

[0091] The geological radar is an optimal non-destructive detection technology for the loose zone of the tunnel. By comparing and verifying different detection technologies, the accurate range of the loose zone of the surrounding rock can be obtained, providing a basis for the subsequent determination of the range of the yield support ring.

[0092] Step S3, determine the range of the pulse fracturing weakening zone 5: determine the length of the pulse fracturing borehole 7 according to the target fracturing rock layer of the near-surface surrounding rock of the tunnel, and then obtain the diameter of the pulse fracturing weakening zone 5, and calculate the number of pulse fracturing boreholes 7 according to the radial main crack extension range of about 15m of a single pulse fracturing borehole 7. The pulse fracturing weakening zone 5 forms a whole circle with the tunnel as the center; the pulse fracturing weakening zone and the near-surface yield support ring form a buffer zone 14 to prevent the pulse fracturing cracks from extending to the support area and causing the support system to fail. The preferred length of the buffer zone 14 is 15m to 30m.

[0093] Step S4, determine the range of the near-surface yield support ring 4: the range of the near-surface yield support ring 4 is 5 to 10 meters larger than the range of the loosened surrounding rock circle of the tunnel measured in step S2; for the tunnel that has been affected by mining, the range of the loosened surrounding rock circle measured in the tunnel shall prevail; for the tunnel that has not been affected by mining, the empirical value of the loosened surrounding rock circle of the tunnel whose adjacent working face has been affected by mining or the tunnel with similar conditions in step S2 shall be used as the basis for calculation.

[0094] Step S5, constructing a pulse fracturing weakening circle 5 of the outer rock formation: weakening the rock formation outside the near-surface bearing circle through pulse fracturing, and forming a weak structure in a certain range by generating a pulse fracturing network 6. On the one hand, it absorbs the high dynamic load of the initial mining and periodic breaking of the roof, and at the same time transfers the high bearing stress of the near-surface yield support ring 4 to the far-field surrounding rock self-bearing circle 15, giving full play to the bearing capacity of the far-field hard rock formation, and utilizing the advantage of higher strength of the far-field surrounding rock under the triaxial stress state, to optimize the near-surface surrounding rock stress environment of the tunnel.

[0095] Step S51, drilling and pulse fracturing: construct fracturing boreholes 7 on the tunnel roof, tunnel side and floor, carry out pulse hydraulic fracturing on each borehole in turn, absorb the elastic energy released by the roof break by forming a radial pulse hydraulic fracture network 6, and at the same time transfer the near-surface surrounding rock supporting stress in the pulse fracturing weakening circle 5 to the far-field hard surrounding rock outside the weakening circle to construct a far-field surrounding rock outer self-bearing circle 15, and use the high self-bearing capacity of the far-field surrounding rock as the main way to resist ground stress, so as to achieve the optimization of the stress environment of the soft rock tunnel 3.

[0096] If the key rock layer determined in step S1 has multiple layers or a single layer with a large thickness (greater than 10m), the backward staged pulse fracturing technology is used to perform multiple pulse fracturing in the same thick hard rock layer to enhance the weakening effect on the high-integrity thick hard rock layer. The preferred retreat distance is 5 to 10m.

[0097] The preferred parameters for pulse fracturing are: pulse frequency 5-10 Hz, displacement 80-120 L / min, and pulse waveform sinusoidal.

[0098] For soft rocks such as mudstone that soften when exposed to water, the following measures are taken to control the water dripping problem between the borehole 7 and the roof: strictly control the amount of water used for fracturing, read the total liquid volume in real time during the entire fracturing process, and stop fracturing immediately when the test threshold is reached; guide the fracturing return water to the designated drainage ditch through a dedicated drainage pipeline to avoid direct discharge into the tunnel to cause short-term local water accumulation, thereby eliminating interference with production activities.

[0099] The outer boundary of the self-supporting ring 15 outside the far-field surrounding rock is taken as 5% higher than the original rock stress.

[0100] Step S52: Borehole sealing: The pulse fracturing borehole 7 is grout-sealed to prevent the fracturing cracks from closing under the action of ground stress, causing the fracturing fluid to flow back to the soft rock layer that swells and softens when it encounters water, thereby reducing the strength and normal stress of the fracture surface of the near-surface soft surrounding rock, causing the surrounding rock loosening zone to expand again.

[0101] Step S6, constructing a near-surface yielding support ring 4 for the entire section of the tunnel: constructing a near-surface yielding support ring 4 through active and passive yielding support methods to adapt to the stable plastic deformation of the surrounding rock while strengthening the bearing capacity of the near-surface surrounding rock.

[0102] Step S61, anchor net spraying initial yielding support: Use high-strength, high-toughness, high-prestress yielding anchor rods 8 to support the surrounding rock near the tunnel surface, then lay anchor nets on the top plate in turn and spray concrete on the top plate and tunnel side 9. If the tunnel has been deformed by dynamic pressure and static pressure, first expand the side and lay the bottom, so that the net cross-sectional size of the tunnel after support can be restored to the original design cross-sectional size 11.

[0103] When spraying the concrete pressure relief layer 9, a certain thickness of concrete is first sprayed, a buffer layer is laid on the outside of the concrete layer to attenuate stress waves and absorb energy, and another layer of concrete is sprayed on the outside of the buffer layer. Among them, the preferred buffer layer material is closed-cell foam aluminum.

[0104] The high-strength, high-toughness, high-prestressed yield anchor 8 and anchor cable are made of strong and tough alloy materials. The initial prestress is applied in stages according to the ground stress gradient. The yield anchor 8 can be reduced based on the design of the expansion range of the plastic zone of the surrounding rock, and triggers sliding energy consumption when the load reaches the preset yield threshold to avoid stress concentration leading to brittle failure. The high-strength, high-toughness, high-prestressed yield anchor 8 uses a constant resistance anchor, which provides constant resistance as the surrounding rock deforms and can produce significant plastic sliding energy absorption to avoid failure of the support system due to excessive deformation.

[0105] The ultimate tensile strength σ of the high-strength, high-toughness, high-prestressed anchor rod 8 is u Dynamically match the surrounding rock rheological rate with the elongation δ, and adapt in stages according to the ground stress gradient, that is, σ u and δ with ground stress σ v and the compressive strength of the surrounding rock near the surface σ c The ratio σ v / σ c Increase with the increase; high strength, high toughness and high prestressing force make the elongation δ and ultimate tensile strength σ of the pressure anchor 8 u Dynamic balance according to the inverse proportional function relationship.

[0106] Step S62, retractable U-shaped steel arch frame 13 and prestressed anchor cable secondary support: After the primary deformation of the surrounding rock tends to be stable, secondary support is carried out on the surrounding rock to provide the final support strength and stiffness for the tunnel. High prestressed anchor cables are used to reinforce the tunnel support, and together with the primary support system in step S61, a coupled anchoring structure is formed to enhance the reinforcement support effect; secondly, a retractable U-shaped steel arch frame 13 with reserved deformation is laid on the entire section of the tunnel and concrete 9 is sprayed.

[0107] The reserved deformation 10 of the retractable U-shaped steel arch is determined by the following method:

[0108] First, after fracturing, the scope of the fracturing weakening zone is determined by drilling and the radius R of the pulse fracturing weakening zone is obtained. f ;

[0109] Secondly, the core was taken in situ by drilling, and the elastic modulus E0 of the surrounding rock of the pulse fracturing weakening zone before fracturing, the elastic modulus E1 of the surrounding rock of the pulse fracturing weakening zone after fracturing, and the initial ground stress σ of the near-surface yielding support ring were tested in the laboratory. v0 ,pass:

[0110]

[0111] The surrounding rock weakening modulus reduction coefficient η is calculated based on the above calculation results:

[0112]

[0113] The effective stress σ transferred to the near-surface yielding support ring is calculated v1 , where D is the distance from the outer edge of the pulse fracturing weakening zone to the side of the tunnel;

[0114] Then the effective stress σ v1 The surrounding rock strength σ of the near-surface yielding retaining ring c The ratio H is obtained by:

[0115]

[0116] The reserved deformation U of the retractable U-shaped steel arch frame is calculated and then set according to the H classification. If the deformation rate exceeds the threshold, the reserved deformation is adaptively adjusted according to the stress release demand.

[0117] Step S63, constructing a flexible buffer-rigid load-bearing composite anti-bottom arch structure: For the roadway that is prone to bottom drum, lay a warp and weft grid made of welded steel bars, drive a self-drilling hollow internal grouting anchor rod 12 on the bottom plate and inject grout, convert the bottom plate tensile stress into annular compressive stress through the arc-shaped anti-bottom arch structure, and use a graded grouting process to fill the cracks in the surrounding rock of the bottom plate to form a "flexible buffer-rigid load-bearing" composite structure to suppress the amount of bottom drum. First, low-pressure grouting is used to fill large-scale cracks to form a low-modulus flexible buffer zone, and the deformation energy generated by the bottom drum is absorbed through plastic deformation; secondly, high-pressure grouting is used to split and penetrate the micro-cracks of the bottom plate to form a high-modulus rigid load-bearing area.

[0118] Through the coordinated control method of the outer self-bearing ring and the near-surface yielding support ring constructed by the above-mentioned tunnel surrounding rock fracturing ring, stress transfer occurs in the tunnel surrounding rock, and the support pressure distribution curve 16 sequentially experiences from the near-surface to the far-field: the near-surface surrounding rock yielding support ring support pressure increase area 16-1, the near-surface surrounding rock yielding support ring support pressure decrease area 16-2, the buffer zone support pressure increase area 16-3, the pulse fracturing weakening ring support pressure decrease area 16-4, the far-field surrounding rock self-bearing ring support pressure increase area 16-5, the far-field surrounding rock self-bearing ring support pressure decrease area 16-6, and the far-field surrounding rock original rock stress area 16-7.

[0119] Example 2

[0120] like Figure 3 and Figure 4 As shown in the figure, for the surrounding rock control of multiple soft rock system tunnels at the same mining level, the near-surface yielding support ring and support pressure curve of a single tunnel are referenced Figure 2 The method for coordinated control of the outer self-bearing ring and the near-surface yielding support ring of the tunnel surrounding rock fracturing ring provided by the present invention has the following specific implementation steps:

[0121] Step S1, survey the lithology of the tunnel to determine the key rock layer: for the tunnel 3 to be protected, it is excavated in the soft rock layer 1 with low bearing capacity, and there may be hard rock layers 2 with strong bearing capacity above and below it. Top and bottom plate exploration holes are constructed in the top plate, side plate and bottom plate of the surrounding rock near the tunnel to be protected to determine the lithology of the surrounding rock near the tunnel surface, and its physical and mechanical parameters are tested indoors; the rock layer with high strength, good integrity, high rigidity and large thickness is determined as the key rock layer, which is used as the target rock layer for subsequent pulse fracturing.

[0122] Step S2, determining the loose zone of the tunnel surrounding rock: by means of acoustic wave detection technology, borehole peeping and geological radar, obtain empirical values ​​of characteristic parameters of the loose zone of the surrounding rock, including the radius of the loose zone, the thickness of the loose zone, the maximum loose stress, the stress distribution in the loose zone and the range of the plastic zone of the surrounding rock in the loose zone, so as to provide a basis for determining the range of the near-surface yield support ring 4.

[0123] For tunnels not affected by mining, the empirical values ​​of characteristic parameters of the surrounding rock loosening zone are determined in tunnels of different working faces that have been affected by mining in the same mining area of ​​this mine.

[0124] The geological radar is an optimal non-destructive detection technology for the loose zone of the tunnel. By comparing and verifying different detection technologies, the accurate range of the loose zone of the surrounding rock can be obtained, providing a basis for the subsequent determination of the range of the yield support ring.

[0125] Step S3, determine the range of the pulse fracturing weakening circle 5: determine the length of the pulse fracturing borehole 7 according to the target fracturing rock layer of the surrounding rock near the surface of the roadway, and then obtain the diameter of the pulse fracturing weakening circle 5, and calculate the number of pulse fracturing boreholes 7 according to the radial main crack extension range of a single pulse fracturing borehole 7 of about 15m. The pulse fracturing weakening circle 5 forms a whole circle with the roadway as the center; the pulse fracturing weakening circle and the near-surface pressure support ring form a buffer zone 14 to prevent the pulse pressure cracks from extending to the support area and causing the support system to fail. The preferred length of the buffer zone 14 is 15m to 30m; for the development of roadways or areas with a short straight-line distance The soft rock tunnel 3 with a length of 50m and parallel axes is shown as an elliptical pulse fracturing weakening zone 5, the center of which is the midpoint 5-1 of the line connecting the return air tunnel 3-1 and the belt conveyor transport tunnel 3-4, which are the farthest apart in the tunnels to be protected. The long axis length 5-2 of the pulse fracturing weakening zone is the sum of the radius of the near-surface yield support ring of a single tunnel and the near-surface yield support ring and the pulse fracturing weakening zone buffer zone 14; the determination of the short axis length 5-3 of the pulse fracturing weakening zone should take into account that the vertical fracturing range cannot exceed the coal seam or the adjacent coal seam 1-2 to be mined.

[0126] Step S4, determine the range of the near-surface yield support ring 4: the range of the near-surface yield support ring 4 is 5 to 10 meters larger than the range of the loosened surrounding rock circle of the tunnel measured in step S2; for the tunnel that has been affected by mining, the range of the loosened surrounding rock circle measured in the tunnel shall prevail; for the tunnel that has not been affected by mining, the empirical value of the loosened surrounding rock circle of the tunnel whose adjacent working face has been affected by mining or the tunnel with similar conditions in step S2 shall be used as the basis for calculation.

[0127] Step S5, constructing a pulse fracturing weakening circle 5 of the outer rock formation: weakening the rock formation outside the near-surface bearing circle through pulse fracturing, and forming a weak structure in a certain range by generating a pulse fracturing network 6. On the one hand, it absorbs the high dynamic load of the initial mining and periodic breaking of the roof, and at the same time transfers the high bearing stress of the near-surface yield support ring 4 to the far-field surrounding rock self-bearing circle 15, giving full play to the bearing capacity of the far-field hard rock formation, and utilizing the advantage of higher strength of the far-field surrounding rock under the triaxial stress state, to optimize the near-surface surrounding rock stress environment of the tunnel.

[0128] Step S51, drilling and pulse fracturing: construct fracturing boreholes 7 on the tunnel roof, tunnel side and floor, carry out pulse hydraulic fracturing on each borehole in turn, absorb the elastic energy released by the roof break by forming a radial pulse hydraulic fracture network 6, and at the same time transfer the near-surface surrounding rock supporting stress in the pulse fracturing weakening circle 5 to the far-field hard surrounding rock outside the weakening circle to construct a far-field surrounding rock outer self-bearing circle 15, and use the high self-bearing capacity of the far-field surrounding rock as the main way to resist ground stress, so as to achieve the optimization of the stress environment of the soft rock tunnel 3.

[0129] If the key rock layer determined in step S1 has multiple layers or a single layer with a large thickness (greater than 10m), the backward staged pulse fracturing technology is used to perform multiple pulse fracturing in the same thick hard rock layer to enhance the weakening effect on the high-integrity thick hard rock layer. The preferred retreat distance is 5 to 10m.

[0130] The preferred parameters for pulse fracturing are: pulse frequency 5-10 Hz, displacement 80-120 L / min, and pulse waveform sinusoidal.

[0131] For soft rocks such as mudstone that soften when exposed to water, the following measures are taken to control the water dripping problem between the borehole 7 and the roof: strictly control the amount of water used for fracturing, read the total liquid volume in real time during the entire fracturing process, and stop fracturing immediately when the test threshold is reached; guide the fracturing return water to the designated drainage ditch through a dedicated drainage pipeline to avoid direct discharge into the tunnel to cause short-term local water accumulation, thereby eliminating interference with production activities.

[0132] The outer boundary of the self-supporting ring 15 outside the far-field surrounding rock is taken as 5% higher than the original rock stress.

[0133] Step S52: Borehole sealing: The pulse fracturing borehole 7 is grout-sealed to prevent the fracturing cracks from closing under the action of ground stress, causing the fracturing fluid to flow back to the soft rock layer that swells and softens when it encounters water, thereby reducing the strength and normal stress of the fracture surface of the near-surface soft surrounding rock, causing the surrounding rock loosening zone to expand again.

[0134] Step S6, constructing a near-surface yielding support ring 4 for the entire section of the tunnel: constructing a near-surface yielding support ring 4 through active and passive yielding support methods to adapt to the stable plastic deformation of the surrounding rock while strengthening the bearing capacity of the near-surface surrounding rock.

[0135] Step S61, anchor net spraying initial yielding support: Use high-strength, high-toughness, high-prestress yielding anchor rods 8 to support the surrounding rock near the tunnel surface, then lay anchor nets on the top plate in turn and spray concrete on the top plate and tunnel side 9. If the tunnel has been deformed by dynamic pressure and static pressure, first expand the side and lay the bottom, so that the net cross-sectional size of the tunnel after support can be restored to the original design cross-sectional size 11.

[0136] When spraying the concrete pressure relief layer 9, a certain thickness of concrete is first sprayed, a buffer layer is laid on the outside of the concrete layer to attenuate stress waves and absorb energy, and another layer of concrete is sprayed on the outside of the buffer layer. Among them, the preferred buffer layer material is closed-cell foam aluminum.

[0137] The high-strength, high-toughness, high-prestressed yield anchor 8 and anchor cable are made of strong and tough alloy materials. The initial prestress is applied in stages according to the ground stress gradient. The yield anchor 8 can be reduced based on the design of the expansion range of the plastic zone of the surrounding rock, and triggers sliding energy consumption when the load reaches the preset yield threshold to avoid stress concentration leading to brittle failure. The high-strength, high-toughness, high-prestressed yield anchor 8 uses a constant resistance anchor, which provides constant resistance as the surrounding rock deforms and can produce significant plastic sliding energy absorption to avoid failure of the support system due to excessive deformation.

[0138] The ultimate tensile strength σ of the high-strength, high-toughness, high-prestressed anchor rod 8 is u Dynamically match the surrounding rock rheological rate with the elongation δ, and adapt in stages according to the ground stress gradient, that is, σ u and δ with ground stress σ v and the compressive strength of the surrounding rock near the surface σ c The ratio σ v / σ c Increase with the increase; high strength, high toughness and high prestressing force make the elongation δ and ultimate tensile strength σ of the pressure anchor 8 u Dynamic balance according to the inverse proportional function relationship.

[0139] Step S62, retractable U-shaped steel arch frame 13 and prestressed anchor cable secondary support: After the primary deformation of the surrounding rock tends to be stable, secondary support is carried out on the surrounding rock to provide the final support strength and stiffness for the tunnel. High prestressed anchor cables are used to reinforce the tunnel support, and together with the primary support system in step S61, a coupled anchoring structure is formed to enhance the reinforcement support effect; secondly, a retractable U-shaped steel arch frame 13 with reserved deformation is laid on the entire section of the tunnel and concrete 9 is sprayed.

[0140] The reserved deformation amount 10 of the retractable U-shaped steel arch is determined by the following method:

[0141] First, after fracturing, the scope of the fracturing weakening zone is determined by drilling and the radius R of the pulse fracturing weakening zone is obtained. f ;

[0142] Secondly, the core was taken in situ by drilling, and the elastic modulus E0 of the surrounding rock of the pulse fracturing weakening zone before fracturing, the elastic modulus E1 of the surrounding rock of the pulse fracturing weakening zone after fracturing, and the initial ground stress σ of the near-surface yielding support ring were tested in the laboratory. v0 ,pass:

[0143]

[0144] The surrounding rock weakening modulus reduction coefficient η is calculated based on the above calculation results:

[0145]

[0146] The effective stress σ transferred to the near-surface yielding support ring is calculated v1 , where D is the distance from the outer edge of the pulse fracturing weakening zone to the side of the tunnel;

[0147] Then the effective stress σ v1 The surrounding rock strength σ of the near-surface yielding retaining ring c The ratio H is obtained by:

[0148]

[0149] The reserved deformation U of the retractable U-shaped steel arch frame is calculated and then set according to the H classification. If the deformation rate exceeds the threshold, the reserved deformation is adaptively adjusted according to the stress release demand.

[0150] Step S63, constructing a flexible buffer-rigid load-bearing composite anti-bottom arch structure: For the roadway that is prone to bottom drum, lay a warp and weft grid made of welded steel bars, drive a self-drilling hollow internal grouting anchor rod 12 on the bottom plate and inject grout, convert the bottom plate tensile stress into annular compressive stress through the arc-shaped anti-bottom arch structure, and use a graded grouting process to fill the cracks in the surrounding rock of the bottom plate to form a "flexible buffer-rigid load-bearing" composite structure to suppress the amount of bottom drum. First, low-pressure grouting is used to fill large-scale cracks to form a low-modulus flexible buffer zone, and the deformation energy generated by the bottom drum is absorbed through plastic deformation; secondly, high-pressure grouting is used to split and penetrate the micro-cracks of the bottom plate to form a high-modulus rigid load-bearing area.

[0151] Through the coordinated control method of the outer self-bearing ring and the near-surface yielding support ring constructed by the above-mentioned tunnel surrounding rock fracturing ring, stress transfer occurs in the tunnel surrounding rock, and the support pressure distribution curve 16 sequentially experiences from the near-surface to the far-field: the support pressure increase area 16-1 of the near-surface surrounding rock yielding support ring, the support pressure decrease area 16-2 of the near-surface surrounding rock yielding support ring, the support pressure increase area 16-3 of the buffer zone, the support pressure decrease area 16-4 of the pulse fracturing weakening zone, the support pressure increase area 16-5 of the far-field surrounding rock self-bearing ring 15, the support pressure decrease area 16-6 of the far-field surrounding rock self-bearing ring, and the far-field surrounding rock original rock stress area 16-7.

[0152] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that many changes, modifications, substitutions and variations can be made to the embodiments without departing from the principles and spirit of the invention.

[0153] The present invention and its embodiments are described above, and such description is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. In short, if ordinary technicians in the field are inspired by it, without departing from the creative purpose of the embodiments of the present invention, they can design a structure and embodiment similar to the technical solution without creativity, which should belong to the protection scope of the present invention.

Claims

1. A method for coordinated control of an outer self-bearing ring and a near-surface yielding support ring for constructing a tunnel surrounding rock fracturing ring, characterized in that: The following steps are involved: Explore the target rock formations for fracturing that meet the physical and mechanical parameters around the tunnel; Determine the characteristic parameters of the surrounding rock loosening zone, and then determine the range of the near-surface yielding support ring; Determine the pulse fracturing drilling length according to the target fracturing rock formation and obtain the pulse fracturing weakening zone range; The pulse fracturing method is used to weaken the rock formation outside the pressure support ring to form a pulse fracturing weakening circle to achieve the purpose of energy absorption. At the same time, the high support stress of the surrounding rock in the pulse fracturing weakening circle is transferred to the hard rock formation in the far field to construct a self-supporting circle outside the far field surrounding rock. A near-surface yielding support ring is constructed through active and passive yielding support methods, and a buffer zone is formed between the yielding support ring and the pulse fracturing weakening zone.

2. The method for coordinated control of the outer self-bearing ring and the near-surface yielding support ring for constructing the tunnel surrounding rock fracturing ring according to claim 1 is characterized in that: Exploration holes are set in the top plate, side plate and bottom plate of the surrounding rock near the tunnel to determine the rock properties of the tunnel near the surface, and its physical and mechanical parameters are tested indoors; the nearby rock formations with high strength, good integrity, high rigidity and large thickness are identified as key rock formations and used as the target rock formations for subsequent pulse fracturing.

3. The coordinated control method of the outer self-bearing ring and the near-surface yielding support ring for constructing the tunnel surrounding rock fracturing ring according to claim 1 is characterized in that: The characteristic parameters of the surrounding rock loosening zone include the loosening zone radius, the loosening zone thickness, the maximum loosening stress, the stress distribution in the loosening zone and the range of the surrounding rock plastic zone in the loosening zone; The range of the near-surface yielding support ring is 5m to 10m larger than the range of the surrounding rock loosening zone.

4. The method for coordinated control of the outer self-bearing ring and the near-surface yielding support ring for constructing the tunnel surrounding rock fracturing ring according to claim 1 is characterized in that: The number of boreholes was calculated based on the radial main fracture extension range of 15 m in a single borehole; A buffer distance of 15m-30m is provided between the pulse fracturing weakening zone and the near-surface yielding support ring.

5. The method for coordinated control of the outer self-bearing ring and the near-surface yielding support ring for constructing the tunnel surrounding rock fracturing ring according to claim 1 is characterized in that: The pulse fracturing weakening configuration is: when the target rock layer is a single layer and the thickness is ≤10m, a radial pulse hydraulic fracturing network is formed by sequentially carrying out pulse hydraulic fracturing on each borehole, wherein the parameters of the pulse fracturing are: pulse frequency 5Hz to 10Hz, displacement 80L / min to 120L / min, and pulse waveform sine wave; When the target rock layer has multiple layers or a single layer with a thickness greater than 10m, multiple pulse fracturing is performed in sequence on each borehole in the same thick hard rock layer by a backward staged pulse fracturing method, wherein the backward distance of the backward staged pulse fracturing method is 5m to 10m.

6. The method for coordinated control of the outer self-bearing ring and the near-surface yielding support ring for constructing the tunnel surrounding rock fracturing ring according to claim 1 is characterized in that: For soft rocks such as mudstone that soften when exposed to water, the amount of water used for fracturing is controlled, the total liquid volume is read in real time during the entire fracturing process, and fracturing is stopped immediately when the test threshold is reached; the fracturing return water is drained to the designated drainage ditch through a dedicated drainage pipeline.

7. The method for coordinated control of the outer self-bearing ring and the near-surface yielding support ring for constructing the tunnel surrounding rock fracturing ring according to claim 1 is characterized in that: The construction of the near-surface yielding support ring includes: Initial yielding support: Use yielding anchors to support the surrounding rock near the tunnel surface, then lay anchor nets on the top plate and both sides and spray concrete; Secondary support: The tunnel is reinforced with anchor cables, which together with the primary support system form a coupled anchoring structure. A retractable U-shaped steel arch frame with reserved deformation is laid on the entire section of the tunnel and concrete is sprayed.

8. The method for coordinated control of the outer self-bearing ring and the near-surface yielding support ring for constructing the tunnel surrounding rock fracturing ring according to claim 7 is characterized in that: The construction of the near-surface yielding support ring in the tunnel prone to bottom heave also includes constructing a composite reverse bottom arch structure: the bottom plate tensile stress is converted into annular compressive stress through the arc-shaped reverse bottom arch structure, and the cracks in the bottom plate surrounding rock are filled with a graded grouting process to form a "flexible buffer-rigid load-bearing" composite structure.

9. The method for coordinated control of the outer self-bearing ring and the near-surface yielding support ring for constructing the tunnel surrounding rock fracturing ring according to claim 7 is characterized in that: The ultimate tensile strength σ of the yield anchor u Dynamically match the surrounding rock rheological rate with the elongation δ, and adapt in stages according to the ground stress gradient, that is, σ u and δ with ground stress σ v and the compressive strength of the surrounding rock near the surface σ c The ratio σ v / σ c Increase with rise.

10. The method for coordinated control of the outer self-bearing ring and the near-surface yielding support ring for constructing the tunnel surrounding rock fracturing ring according to claim 7, characterized in that: The reserved deformation of the retractable U-shaped steel arch is determined by the following method: First, after fracturing, the scope of the fracturing weakening zone is determined by drilling and the radius R of the pulse fracturing weakening zone is obtained. f ; Secondly, the core was taken in situ by drilling, and the elastic modulus E0 of the surrounding rock of the pulse fracturing weakening zone before fracturing, the elastic modulus E1 of the surrounding rock of the pulse fracturing weakening zone after fracturing, and the initial ground stress σ of the near-surface yielding support ring were tested in the laboratory. v0 ,pass: The surrounding rock weakening modulus reduction coefficient η is calculated based on the above calculation results: The effective stress σ transferred to the near-surface yielding support ring is calculated v1 , where D is the distance from the outer edge of the pulse fracturing weakening zone to the side of the tunnel; Then the effective stress σ v1 The surrounding rock strength σ of the near-surface yielding retaining ring c The ratio H is obtained by: Calculate and then set the reserved deformation U of the retractable U-shaped steel arch according to the H classification.

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