Combined bearing structure suitable for extremely broken rock and construction method

Abstract

The invention discloses a combined bearing structure suitable for extremely fractured rock mass and a construction method. The structure sequentially comprises a supporting structure layer and a supporting structure layer from the inner wall of a roadway to the outside, wherein the supporting structure layer is composed of at least two supporting components which are mutually connected or independently arranged; the load buffer layer is located between the supporting structure layer and the surrounding rock, is composed of rock masses with internal surrounding rock loosening and fragmentation caused by roadway excavation, and is used for absorbing and dispersing impact energy caused by excavation and relieving direct impact of surrounding rock loosening on the supporting structure layer; the surrounding rock bearing layer is a main bearing layer of surrounding rock of the roadway; and the supporting structure layer, the load buffer layer and the surrounding rock bearing layer are connected through the connecting structure. The self-bearing capacity of the deep surrounding rock of the roadway is exerted, the shallow surrounding rock and the deep surrounding rock form a bearing combined structure through anchor rod supporting, and the supporting effect of the combined system is fully aroused; the bearing capacity of surrounding rock in a roadway roof area is enhanced, and the problems that a broken surrounding rock roadway is poor in stability and high in supporting cost are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of mine tunnel support, and in particular relates to a combined bearing structure suitable for extremely broken rock masses and a construction method thereof. Background Art

[0002] As underground mines gradually enter a new stage of deep mining, tunnel surrounding rocks face unprecedented challenges, the most prominent of which is the significant deformation of surrounding rocks caused by engineering disturbances under high stress environments. This deformation not only threatens the safety of the support structure, causing it to fail prematurely or even be destroyed, but also seriously restricts mining efficiency and engineering safety. Traditionally, the support system that relies on anchor rods as the core has alleviated the problems caused by broken surrounding rocks to a certain extent by introducing new support materials or increasing support strength, but these methods are essentially passive responses and have failed to effectively curb the root causes of surrounding rock deformation. Summary of the invention

[0003] The object of the present invention is to provide a combined bearing structure and a construction method suitable for extremely broken rock masses.

[0004] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is: a combined bearing structure suitable for extremely broken rock mass, the structure comprising, from the inner wall of the tunnel to the outside, a supporting structure layer, including at least two supporting members connected to each other or arranged independently;

[0005] The load buffer layer is located between the support structure layer and the surrounding rock of the roadway, including the loose and broken rock mass of the internal surrounding rock caused by the excavation of the roadway;

[0006] The surrounding rock bearing layer is the first bearing layer of the surrounding rock of the tunnel;

[0007] A connecting structure is used to connect the supporting structure layer, the load buffer layer and the surrounding rock bearing layer.

[0008] Furthermore, the connection structure includes anchor rods, which penetrate the support structure layer, the load buffer layer and the surrounding rock bearing layer from the inner wall of the tunnel to the outside;

[0009] The anchor rods are evenly arranged in a plurality in the circumferential direction, and a spacing is set between adjacent anchor rods.

[0010] Furthermore, the radius of the plastic zone is determined by the boundary between the surrounding rock bearing layer and the tunnel surrounding rock, and the length range of the anchor rod is determined by the radius of the plastic zone.

[0011] Furthermore, along the extension direction from the supporting structure layer to the surrounding rock bearing layer, the distance between adjacent anchor rods increases gradually.

[0012] Furthermore, a construction method for a combined bearing structure suitable for extremely broken rocks is provided, the construction method comprising: S1, calculating the plastic zone radius of the tunnel surrounding rock, and determining the boundary between the surrounding rock bearing layer and the original rock stress zone through the plastic zone radius;

[0013] S2, calculating the radial stress of the tunnel surrounding rock, and determining the boundary between the load buffer layer and the surrounding rock bearing layer according to the radial stress of the tunnel surrounding rock;

[0014] S3, calculating the tunnel top arch height, and calculating the arch top pressure according to the tunnel top arch height;

[0015] S4. Calculate structural parameters of the connection structure based on the radial stress of the tunnel surrounding rock and the vault pressure. The structural parameters include but are not limited to: the length of the anchor rods and the spacing between the anchor rods.

[0016] Further, the length of the anchor rod includes a first length L1, a second length L2, and a third length L3;

[0017] The second length L2 is less than or equal to the length of the radius of the plastic zone.

[0018] Furthermore, the method further comprises: S5, calculating the thickness T of the concrete spraying layer as:

[0019] Among them, T is the thickness of the sprayed layer, PV is the arch pressure, K is the safety factor, S is the side length of the contact surface between the arch and the concrete sprayed layer, and RT is the calculated tensile strength of the sprayed concrete.

[0020] Furthermore, the spacing La of the anchor rods in S4 is:

[0021] Where L a is the spacing of anchor rods, m; the anchoring force Q is determined by the pull-out test; γ' is the average load of the surrounding rock,

[0022] K is the safety factor of the anchor.

[0023] Furthermore, the combined bearing structure is an arched structure, wherein the arch of the supporting structure layer is a parabola, and the arch height of the supporting structure layer is equal to the arch height of the tunnel top;

[0024] The top arch bearing combined structure also includes: applying lateral restraint force at the arch foot of the arch structure.

[0025] Further, in S3, the tunnel top arch height b = a / f;

[0026] Among them, f is the Proctor coefficient, f=ccosφ / 5(1-sinφ), and a is half of the tunnel width.

[0027] Furthermore, the structural parameters in S4 also include the rod diameter of the anchor rod.

[0028] Where d is the diameter of the anchor rod; the anchoring force Q is determined by the pull-out test; σ t is the tensile strength of the rod material.

[0029] After adopting the above technical scheme, the present invention has the following beneficial effects compared with the prior art.

[0030] The present invention combines active support with the bearing structure of the surrounding rock itself to construct a top arch combined bearing structure suitable for extremely broken rock masses. By introducing active support systems, such as anchor rods, anchor cables, steel belts and other reinforcement elements, it not only increases the mechanical strength of the surrounding rock, but also promotes the redistribution of internal stress in the surrounding rock, forming a more continuous and stable bearing system. This combination of internal and external support allows the surrounding rock to more effectively share and resist external loads, thereby enhancing its overall bearing capacity. Compared with passive support methods that rely solely on high-cost materials, the present invention achieves improved support effects and relatively reduced support costs by optimizing support structures and material configurations. At the same time, due to the enhanced bearing capacity of the surrounding rock, the deformation and damage of the support structure are reduced, thereby extending the support period and reducing the frequency and cost of later maintenance and repairs.

[0031] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an improper limitation of the present invention. Obviously, the drawings described below are only some embodiments. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the accompanying drawings:

[0033] Figure 1 It is a cross-sectional view of a combined bearing structure suitable for extremely broken rock masses according to the present invention;

[0034] Figure 2 It is a top view of a combined bearing structure suitable for extremely broken rock masses according to the present invention;

[0035] Figure 3 It is a bearing mechanics model of the combined bearing structure of the present invention applicable to extremely broken rock masses;

[0036] Figure 4 Schematic diagram of the structure of the steel mesh of the combined bearing structure of the present invention applicable to extremely broken rock mass;

[0037] Figure 5 It is a schematic diagram of the steel belt structure of the combined bearing structure of the present invention applicable to extremely broken rock mass;

[0038] Figure 6 It is a flow chart of the method for constructing a combined bearing structure suitable for extremely broken rocks according to the present invention.

[0039] Description of the drawings: 1. Support structure layer; 11. Concrete spraying layer; 12. Steel mesh; 13. Steel belt; 14. Second concrete spraying layer; 15. Plastic zone radius; 2. Load buffer layer; 3. Surrounding rock bearing layer; 4. Connection structure; 41. Anchor rod; 5. Top arch bearing composite structure; 51. Arch foot; 6. Original rock stress zone.

[0040] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but are intended to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following embodiments are used to illustrate the present invention but are not used to limit the scope of the present invention.

[0042] In the description of the present invention, it should be noted that the directions or positional relationships indicated by terms such as “upper”, “lower”, “front”, “back”, “left”, “right”, “vertical”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0043] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] Example 1

[0045] A combined bearing structure suitable for extremely broken rocks, the structure comprising, from the inner wall of the tunnel to the outside, a supporting structure layer 1, comprising at least two supporting components connected to each other or independently arranged, for example: the supporting components include but are not limited to: a steel mesh 12, a steel belt 13, an anchor rod 41, a concrete spraying layer 11, a second concrete spraying layer 14 and other supporting components jointly supported, the supporting method of the supporting structure is: the steel mesh 12, the steel belt 13, the concrete spraying layer 11, and the second concrete spraying layer 14 are connected by the full-length bonding anchoring effect of the anchor rod 41; a load buffer layer 2, located between the supporting structure layer 1 and the tunnel surrounding rock, the distribution area of ​​the load buffer layer 2 is from the tunnel surface to the position where the shear stress value is less than the original rock stress, including the loose and broken rock mass of the internal surrounding rock caused by the excavation of the tunnel. In addition to bearing the deadweight load of the loose and broken rock mass in the load buffer layer 2, the support structure layer 1 should also bear the radial stress at the position where the tangential stress of the tunnel surrounding rock is less than the original rock stress. Since the tunnel surrounding rock stress has not been completely released when the support member is applied, the support structure layer 1 will also bear part of the surrounding rock radial stress. The support structure layer 1 is arched, the arch top is a parabola, and the arch top height is the tunnel top arch height.

[0046] In this embodiment, the combined bearing structure also includes a surrounding rock bearing layer 3, which is the first bearing layer of the tunnel surrounding rock. The surrounding rock bearing layer 3 is the main bearing key layer of the deep surrounding rock of the tunnel and is the plastic strengthening zone of the tunnel surrounding rock. The distribution area extends from the load buffer layer 2 to the deep part to the radius position of the plastic zone. According to the New Austrian Tunneling Method theory, the self-bearing capacity of the deep surrounding rock is fully utilized, and the shallow and deep surrounding rocks are formed into a bearing combined structure by applying an active support structure, so as to fully mobilize the supporting role of the combined system. This technical solution enhances the bearing capacity and anti-disturbance ability of the surrounding rock in the tunnel roof area, and solves the problems of poor stability of broken surrounding rock tunnels, high support costs, and high difficulty in repair construction.

[0047] In this embodiment, since the tunnel surrounding rock stress has not been completely released when the support components are applied, the support structure layer 1 can bear part of the surrounding rock radial stress while bearing the self-weight load of the loose and broken rock mass. As the surrounding rock stress is gradually released, the force of the support structure layer will gradually stabilize.

[0048] In a feasible implementation, the combined bearing structure further includes a connection structure 4, through which the support structure layer 1, the load buffer layer 2 and the surrounding rock bearing layer 3 are connected. The connection structure 4 includes an anchor rod 41, which penetrates the support structure layer 1, the load buffer layer 2 and the surrounding rock bearing layer 3 from the inner wall of the tunnel to the outside, and the anchor rods 41 are evenly arranged in a plurality in the circumferential direction, and a spacing is set between adjacent anchor rods 41.

[0049] In this embodiment, along the extending direction from the supporting structure layer 1 to the surrounding rock bearing layer 3, the distance between adjacent anchor rods 41 increases gradually.

[0050] The anchor rods 41 penetrate the support structure layer 1, the load buffer layer 2 and the surrounding rock bearing layer 3 from the inner wall of the tunnel to the outside, tightly connecting the three together to form a unified bearing system. This connection not only enhances the interaction between the layers, but also improves the stability and bearing capacity of the overall structure. The anchor rods 41 are evenly arranged in multiple circumferential directions, and a reasonable spacing is set between adjacent anchor rods 41, so that the support force can be evenly distributed in the entire surrounding rock area, avoiding local stress concentration and damage.

[0051] In this embodiment, the radius of the plastic zone is determined by the boundary between the surrounding rock bearing layer 3 and the tunnel surrounding rock, and the length range of the anchor rod 41 is determined by the radius of the plastic zone.

[0052] Example 2

[0053] A method for constructing a combined bearing structure suitable for extremely broken rocks, the method comprising: S1, calculating the plastic zone radius 15 of the tunnel surrounding rock, and determining the boundary between the surrounding rock bearing layer 3 and the original rock stress zone 6 through the plastic zone radius 15;

[0054] S2, calculating the radial stress of the tunnel surrounding rock, and determining the boundary between the load buffer layer 2 and the surrounding rock bearing layer 3 according to the radial stress of the tunnel surrounding rock;

[0055] S3, calculating the tunnel top arch height, and calculating the arch top pressure according to the tunnel top arch height;

[0056] S4. Calculate structural parameters of the connection structure 4 based on the radial stress of the tunnel surrounding rock and the vault pressure. The structural parameters include but are not limited to: the length of the anchor rods 41 and the spacing between the anchor rods 41 .

[0057] In a feasible implementation manner, the method further includes: S5, calculating the thickness T of the concrete spraying layer as:

[0058] Where T is the spray layer thickness, P V is the arch pressure, K is the safety factor, S is the side length of the contact surface between the arch and the concrete spraying layer, R T Calculate the tensile strength of shotcrete.

[0059] In this embodiment, the spacing La of the anchor rods in S4 is:

[0060] Where L ais the spacing of anchor rods, m; the anchoring force Q is determined by the pull-out test; γ' is the average load of the surrounding rock, K is the safety factor of the anchor.

[0061] In this embodiment, the combined bearing structure is an arched structure, wherein the arch of the supporting structure layer is a parabola, and the arch height of the supporting structure layer is equal to the arch height of the tunnel top;

[0062] The top arch bearing combined structure also includes: applying lateral restraint force at the arch foot of the arch structure.

[0063] In this embodiment, the surrounding rock bearing mechanical model of the combined bearing structure is as shown in the attached Figure 3 As shown in Figure 1, the radius of the plastic zone for the surrounding rock of the roadway in S1 is 15, i.e. R 0 is the boundary between the surrounding rock bearing layer 3 and the original rock, and the radius 15 of the plastic zone is obtained as: Where a is the radius of the circular hole,

[0064] K p =(1+sinφ) / (1-sinφ), q=2ctan(45+φ / 2), P o is the original rock stress, c is the cohesion, φ is the internal friction angle, and r is the distance from the calculation point to the center of the circle.

[0065] In this embodiment, the plastic zone radius R 0 After the determination, it is used in S4 to calculate the structural parameters of the connection structure 4, which include but are not limited to the length of the anchor rod 41. The length L of the anchor rod 41 is: L = L 1 +L 2 +L 3 ; Where, L is the total length of the support anchor; L 1 L is the length of the exposed end of the anchor rod 41 outside the surrounding rock bearing layer, i.e., the first length of the anchor rod 41, which depends on the anchor rod type and construction requirements. For example, the height and the length of the iron and wooden pads and nuts outside the rock layer should be considered for the steel anchor rod; 2 is the second length of the anchor rod 41, that is, the effective length of the combined bearing structure, which can be selected as the height of the load buffer layer 2. The second length L 2 The length of the plastic zone radius 15 is less than or equal to that of the plastic zone radius. For example, the natural pressure arch height or the top plate thickness within the plastic zone, the measured loose zone thickness, etc. are used; L 3The anchoring force of the anchor rod 41 is the length of the anchor into the stable rock formation. The design principle is that the anchoring force cannot be less than the load that the anchor rod body can bear. The anchoring force of the anchor rod 41 is composed of the bonding force between the rod body and the adhesive, the bonding force between the adhesive and the rock hole wall, or the friction resistance between the anchor rod and the rock wall. It can be calculated based on actual data, and the empirical value is generally not less than 300mm. The present invention mainly connects the remaining structures through the anchor rod. The anchor rod 41 of the present invention adopts a full-length anchoring form, such as a cement mortar anchor rod, a numerical anchor rod, etc.

[0066] In this embodiment, the radial stress σθ of the tunnel surrounding rock in S2 is: when the value of the tangential stress σθ is less than the original rock stress P o When: σ θ ≤P o ; then: From this we get r 0 is the boundary between the load buffer layer 2 and the surrounding rock bearing layer 3. And the radial stress at the boundary position is for:

[0067] In this embodiment, in S3, the combined bearing structure is an arch structure, wherein the arch of the supporting structure layer 1 is a parabola, and the arch height of the supporting structure layer 1 is equal to the arch height of the tunnel top; the tunnel top arch height b = a / f, wherein f is the Proctor coefficient, f = ccosφ / 5 (1-sinφ), and a is half of the tunnel width. Specifically: the top of the tunnel is an arch, satisfying the conditions that the bending moment at any point on the arch axis is zero and the horizontal thrust acting at the arch foot must be less than or equal to the maximum friction force generated by the vertical reaction force: After sorting, the arch axis equation is obtained: The coordinates of any point on the arch axis are (x, y), b is the arch height, σ v is the uniformly distributed load generated by the deadweight of the rock mass above the arch axis, T is the horizontal thrust of the balanced arch crown section, a is half the width of the tunnel, f is the Proctor coefficient, or rock strength coefficient, f = c cosφ / 5(1-sinφ); when x = a, the arch crown height can be obtained: b = a / f.

[0068] In this embodiment, in a rock mass with relatively stable side wall surrounding rock, the span of the natural arch is the span 2a of the chamber, and the total arch pressure is: Where A 1 =ab-A 2 , γ is the weight of the surrounding rock. To facilitate the calculation of the internal force of the supporting components, the parabolic top surrounding rock pressure can be approximated as a rectangular uniformly distributed surrounding rock pressure with an arch height of b (slightly safer), and the total top pressure is: The load concentration of loosening pressure is:

[0069] In this embodiment, the structural parameters of the connection structure 4 also include the thickness of the concrete spray layer 11 and the second concrete spray layer 14. The concrete spray layer has two most significant supporting functions. First, once the rock is exposed during construction, it can be sprayed and covered with concrete spray layer. In addition to playing a certain supporting role, it also seals the rock surface in time, isolates the adverse effects of water, moisture, and weathering on the rock mass, and prevents the strength of the rock mass from decreasing. In addition, the concrete spray layer of the present application is used in conjunction with the anchor rod 41 to overcome the weakness of the anchor rod 41 that is easily invalidated due to weathering and falling of fossils near the rock surface, so that the surrounding rock forms a whole. The radial stress σ of the tunnel surrounding rock calculated in S2 θ and the dome pressure P calculated in S3 V Calculate the thickness of the concrete spraying layer together. Specifically, the condition for the stability of the surrounding rock is that the shear resistance and bonding strength of the concrete spraying layer must be greater than the weight of the broken surrounding rock. Generally, the bonding strength of the concrete spraying layer is greater than the shear resistance, so the thickness of the spraying layer can be calculated according to the shear strength: Where, T is the spray layer thickness, m; P v is the arch pressure, N; K is the safety factor, which is 3; S is the side length of the contact surface between the arch and the shotcrete, m; R T is the calculated tensile strength of shotcrete, Pa.

[0070] In a feasible implementation manner, the spacing La of the anchor rods (41) in S4 is: Where L a is the spacing of anchor rods, m; the anchoring force Q is determined by the pull-out test; γ' is the average load of the surrounding rock, K is the safety factor of the anchor.

[0071] In S4, the breaking force of the anchor rod should not be less than the anchoring force. Generally, the required anchoring force can be determined first according to engineering conditions and experience, and then the rod diameter of the rod body is calculated: the structural parameters also include the rod diameter of the anchor rod 41 Where d is the diameter of the anchor rod, mm; the anchoring force Q, kN, is determined by the pull-out test; σ t is the tensile strength of the rod material, MPa.

[0072] In a feasible implementation manner, as shown in the attached Figure 4 As shown, the steel mesh 12 has a specification of 1000mm×2000mm and a mesh size of 100mm×100mm. It is welded with φ6mm steel bars. The overlap length between the mesh pieces is 100mm. The overlap can be tied with double strands of No. 14 iron wire, and the binding mesh size is 300mm×300mm.

[0073] In a feasible embodiment, the length of the steel belt 13 is the distance between two adjacent anchor rods 41, the width of the steel belt 13 is the same as the width of the steel mesh 12, and the steel belt 13 is welded with φ12mm round steel, wherein the lap length of the round steel of the steel belt 13 at the closed part is not less than 100mm, and reinforcing ribs are welded at the ends and the middle of the steel belt.

[0074] In this embodiment, the load buffer layer 2 is mainly composed of loose and broken rock. Under strong disturbance conditions, as an improvement, the load buffer layer 2 can be reinforced by grouting. The grouting liquid is used to bond the broken rock, improve the physical and mechanical properties and mechanical state of the surrounding rock, further enhance the bearing capacity of the surrounding rock itself, and cause the surrounding rock to produce an arching effect.

[0075] In this embodiment, the combined bearing structure provides sufficient lateral restraint at the arch foot 51 to maintain the overall stability of the arch structure. The greater the restraint provided, the stronger the bearing capacity and anti-disturbance ability of the surrounding rock in the tunnel roof area.

[0076] The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this patent can make some changes or modifications to equivalent embodiments of equivalent changes by using the technical content suggested above without departing from the scope of the technical solution of the present invention. The implementation scheme in the above embodiment can also be further combined or replaced. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the solution of the present invention.

Claims

1. A combined bearing structure suitable for extremely broken rocks, characterized in that: The structure includes, from the inner wall of the tunnel to the outside, the following: The supporting structure layer (1) comprises at least two supporting components which are connected to each other or arranged independently; A load buffer layer (2), located between the support structure layer (1) and the tunnel surrounding rock, including loose and broken rock mass caused by tunnel excavation; The surrounding rock bearing layer (3) is the first bearing layer of the surrounding rock of the tunnel; A connection structure (4), through which the support structure layer (1), the load buffer layer (2) and the surrounding rock bearing layer (3) are connected.

2. The combined bearing structure suitable for extremely broken rocks according to claim 1, characterized in that: The connection structure (4) comprises an anchor rod (41), and the anchor rod (41) respectively penetrates the support structure layer (1), the load buffer layer (2) and the surrounding rock bearing layer (3) from the inner wall of the tunnel to the outside; The anchor rods (41) are evenly arranged in a plurality in the circumferential direction, and a spacing is provided between adjacent anchor rods (41).

3. The combined bearing structure suitable for extremely broken rocks according to claim 2, characterized in that: The radius of the plastic zone is determined by the boundary between the surrounding rock bearing layer (3) and the tunnel surrounding rock, and the length range of the anchor rod (41) is determined by the radius of the plastic zone.

4. A method for constructing a combined bearing structure suitable for extremely broken rocks, characterized in that: The construction method is applicable to any one of the above rights 1-3; The construction method comprises: S1, calculating the plastic zone radius (15) of the tunnel surrounding rock, and determining the boundary between the surrounding rock bearing layer (3) and the original rock stress zone (6) through the plastic zone radius (15); S2, calculating the radial stress of the tunnel surrounding rock, and determining the boundary between the load buffer layer (2) and the surrounding rock bearing layer (3) through the radial stress of the tunnel surrounding rock; S3, calculating the tunnel top arch height, and calculating the arch top pressure according to the tunnel top arch height; S4. Calculate the structural parameters of the connection structure (4) based on the radial stress of the tunnel surrounding rock and the vault pressure. The structural parameters include but are not limited to: the length of the anchor rods (41) and the spacing between the anchor rods (41).

5. The method for constructing a combined bearing structure suitable for extremely broken rocks according to claim 4, characterized in that: The length of the anchor rod (41) includes a first length L1, a second length L2, and a third length L3; The second length L2 is less than or equal to the length of the plastic zone radius (15).

6. The method for constructing a combined bearing structure suitable for extremely broken rocks according to claim 5, characterized in that: The method further comprises: S5, calculating the thickness of the concrete spraying layer Where T is the spray layer thickness, P V is the arch pressure, K is the safety factor, S is the side length of the contact surface between the arch and the concrete spraying layer, R T Calculate the tensile strength of shotcrete.

7. The method for constructing a combined bearing structure suitable for extremely broken rocks according to claim 6, characterized in that: The spacing of the anchor rods (41) in S4 Where L a is the spacing of anchor rods; the anchoring force Q is determined by the pull-out test; γ' is the average load of the surrounding rock, K is the safety factor of the anchor.

8. The method for constructing a combined bearing structure suitable for extremely broken rocks according to claim 7, characterized in that: The combined bearing structure is an arched structure, wherein the arch top of the supporting structure layer (1) is a parabola, and the arch top height of the supporting structure layer (1) is equal to the arch top height of the tunnel; The top arch bearing combined structure further comprises: applying lateral restraining force at the arch foot (51) of the arch structure.

9. The method for constructing a combined bearing structure suitable for extremely broken rocks according to claim 8, characterized in that: The top arch height of the tunnel in S3 is b = a / f; Among them, f is the Proctor coefficient, f=ccosφ / 5(1-sinφ); a is half of the tunnel width.

10. The method for constructing a combined bearing structure suitable for extremely broken rocks according to claim 4, characterized in that: The structural parameters in S4 also include the rod diameter of the anchor rod (41) Where d is the diameter of the anchor rod; the anchoring force Q is determined by the pull-out test; σ t is the tensile strength of the rod material.

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