Support structure and construction method for high ground stress tunnel in grade ii-iii hard rock

Abstract

This invention discloses a support structure and construction method for high-stress tunnels in Class II-III hard rock in the field of initial support technology for tunnel engineering. The tunnel is divided into multiple sections based on each cycle of excavation. These sections include steel-framed sections, which contain steel frames and anchor bolts, and are sealed with shotcrete. There are also non-steel-framed sections, which do not contain steel frames or anchor bolts, but are sealed with shotcrete. The steel-framed and non-steel-framed sections are arranged cyclically along the excavation direction. Multiple anchor bolts in the steel-framed sections are configured obliquely, so that the surrounding rock of the non-steel-framed section corresponds to the anchor bolts of two adjacent steel-framed sections. This changes the traditional steel-frame, full-anchor bolt support mode per cycle to "steel frame, anchor bolts across two cycles," reducing the amount of steel frames and anchor bolts by approximately 50%. The surrounding rock arch effect is fully utilized, using the rigid support points formed by adjacent supported sections to transfer the stress on the middle section of the surrounding rock to both sides, achieving overall stability.

Description

Technical Field

[0001] This invention relates to the field of initial support technology for tunnel engineering, specifically to an initial support method for newly constructed traffic tunnels under Class II-III hard rock and high ground stress conditions. It is particularly applicable to highway or railway tunnel projects where the surrounding rock has a certain self-stabilizing capacity but high ground stress levels and may experience stress relaxation. Specifically, it relates to a support structure and construction method for high ground stress tunnels in Class II-III hard rock. Background Technology

[0002] As tunnel engineering progresses to greater depths, even with hard and intact surrounding rock (Class II-III) under high ground stress, problems such as rock deformation can occur due to stress relaxation. In cases of favorable surrounding rock conditions and low ground stress, initial support is typically simple and efficient. For example, according to current construction guidelines, good surrounding rock conditions usually only require localized shotcrete or localized anchor bolt support (supplemented with localized steel mesh to prevent rockfall if necessary), indicating that high-quality surrounding rock does not require extensive, dense support. However, in deep-buried tunnels under high ground stress, due to concerns about tunnel deformation, the approach of weak surrounding rock support is often still used in medium to good surrounding rock conditions. To ensure safety, a "strong support, short advance" strategy is employed, meaning that each excavation cycle is immediately followed by the application of initial support combining anchor bolts, steel frames, and shotcrete to quickly seal the surrounding rock into a ring. While this continuous deployment of the entire support system improves the safety factor in practice, it also leads to high costs and long construction periods.

[0003] The closest existing implementation to this invention is the conventional New Austrian Tunneling Method (NATM) initial support: Each excavation cycle typically involves an advance of 1-2 meters, followed by the installation of system anchor bolts (mostly radial anchor bolts perpendicular to the excavation face), the setting up of steel frames (grid arch frames or I-beam arch frames), and the sealing with shotcrete. The anchor bolts are generally full-length bonded (cement mortar anchor bolts or resin anchor bolts), with the spacing designed according to the surrounding rock grade. The spacing of the steel frames is equal to the advance (usually one steel frame per cycle), and the shotcrete thickness depends on the surrounding rock and design requirements. The characteristic of this approach is that a complete initial support system is completed in each cycle, ensuring timely support for any newly exposed surrounding rock. This approach can suppress excessive rock relaxation and collapse risk in high-stress hard rock tunnels, but because it does not fully consider the bearing capacity of the hard surrounding rock itself, its support element configuration is often conservative.

[0004] In practice, the closest approach to cost savings is to increase the spacing between supports or locally thicken the lining. However, these methods do not deviate from the scope of "full-ring continuous support," thus limiting their cost-saving effects. In summary, traditional solutions lack effective measures for support optimization, resulting in high construction costs and tight schedules. It is necessary to explore new support layout methods to improve economy and efficiency. Summary of the Invention

[0005] To overcome the problems of high cost and long construction period of initial support for Class II-III surrounding rock under high ground stress environment, the present invention provides a support structure and construction method for high ground stress tunnels in Class II-III hard rock.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] Support structure for Class II-III hard rock tunnels with high ground stress, used for initial support during tunnel construction. The tunnel is divided into multiple sections based on each cycle of excavation, including steel frame sections, which are equipped with steel frames and anchor bolts and are sealed with shotcrete, and non-steel frame sections, which are not equipped with steel frames and anchor bolts but are sealed with shotcrete.

[0008] The tunnels with steel frames and those without steel frames are arranged cyclically along the excavation direction. In the tunnels with steel frames, multiple anchor bolts are configured at an angle, so that the surrounding rock corresponding to the tunnels without steel frames contains anchor bolts from two adjacent tunnels with steel frames.

[0009] This application effectively reduces the amount of steel frames and anchor bolts by approximately 50% by changing the traditional pattern of steel frame and full anchor bolt support per cycle to "steel frame and anchor bolts across two cycles". The structure formed between alternating support sections resembles an arch bridge: adjacent support sections with steel frames act as the main supporting "piers", while the middle section without steel frames and anchor bolts relies on the arch effect of the side support sections and its own shotcrete to cross the high ground stress area. The surrounding rock arch effect is fully utilized here—using the rigid fulcrum formed by adjacent supported sections, the stress on the surrounding rock in the middle section is transferred to both sides, achieving overall stability. This support system design is based on the premise that Class II-III surrounding rock has temporary stability, and through interval support, each support unit is both independently stressed and mutually coordinated.

[0010] In some embodiments, the inclined anchor bolts in the steel frame section of the tunnel are inclined at 10°-20° relative to the normal of the surrounding rock surface, and the inclination direction is the tunnel extension direction.

[0011] In some embodiments, multiple anchor bolts located at the same circumferential position within a steel-framed tunnel section are configured to radiate outward from the same center.

[0012] In some embodiments, a steel mesh is provided between the shotcrete seal and the surrounding rock in the steel frameless section of the tunnel.

[0013] In some embodiments, the single-cycle advance for Class II surrounding rock is 1.5m-2m, and the single-cycle advance for Class III surrounding rock is 1.0m-1.5m.

[0014] In some embodiments, the shotcrete in the frameless tunnel section contains an accelerator.

[0015] In some embodiments, the steel frames in adjacent steel-framed tunnel sections are welded together by connecting bars.

[0016] In some embodiments, the length of the anchor bolt inserted into the adjacent non-steel-framed section of the tunnel exceeds half the length of the non-steel-framed section.

[0017] In some embodiments, the area in a tunnel with a steel frame where the anchor bolts extend beyond half the length of an adjacent tunnel without a steel frame corresponds to a surrounding rock thickness greater than or equal to 1m.

[0018] The present invention also provides a support construction method for tunnels with high ground stress in Class II-III hard rock, which includes tunnel construction with steel frame section and tunnel construction without steel frame section, and the construction of tunnel with steel frame section and tunnel construction without steel frame section are carried out alternately in a cycle;

[0019] Construction of tunnels with steel frames: Excavate the tunnel in the current cycle, spray some concrete to seal the rock surface, install steel frames and anchor bolts, and ensure that the anchored sections penetrate into the surrounding rock of the previous and next sections respectively. After the anchor bolts are installed, spray concrete to the design thickness.

[0020] Construction of tunnel sections without steel frames: Excavate the tunnel in the current cycle and spray concrete to the design thickness in one go.

[0021] The beneficial effects of this invention are:

[0022] By changing the traditional pattern of steel frame and full anchor bolt support per cycle to "steel frame and anchor bolts spanning two cycles," the amount of steel frame and anchor bolts used is effectively reduced by about 50%. The structure formed between alternating support sections resembles an arch bridge: adjacent support sections with steel frames act as the main supporting "piers," while the middle section without steel frames and anchor bolts relies on the arch effect of the side support sections and its own shotcrete to cross the high-stress area. The surrounding rock arch effect is fully utilized here—using the rigid fulcrum formed by adjacent supported sections, the stress on the surrounding rock in the middle section is transferred to both sides, achieving overall stability. This support system design is based on the premise that Class II-III surrounding rock has temporary stability, and through interval support, each support unit is both independently stressed and mutually coordinated. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the support structure for high ground stress tunnels in Class II-III hard rock provided by the present invention.

[0024] Figure 2 for Figure 1 A schematic diagram illustrating the formation of a plastic arch in a tunnel section without a steel frame.

[0025] Figure 3This is a schematic flowchart illustrating the support construction method for high ground stress tunnels in Class II-III hard rock provided by the present invention.

[0026] The markings in the diagram are: 1-anchor bolt, 2-concrete, 3-tunnel with steel frame, 4-tunnel without steel frame, 5-steel frame, 6-plastic arch. Detailed Implementation

[0027] The invention will be further described below with reference to the accompanying drawings.

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0029] Existing continuous support technology has the following main drawbacks and limitations:

[0030] 1. Redundant and inefficient support: For Class II-III hard rock surroundings, the traditional practice of installing complete anchor bolt-steel frame-shotcrete support per cycle often exceeds actual needs. While brief exposure of hard rock surroundings does not immediately lead to instability, installing a large number of support components still results in waste of materials and labor, and reduces construction speed.

[0031] 2. High cost and long construction period: Continuous strong support measures mean dense anchor bolts, one steel frame per cycle, and a large amount of shotcrete, directly leading to high support costs. At the same time, the frequent insertion of anchor bolt drilling and installation and steel frame assembly into each cycle slows down the tunneling progress and extends the construction period.

[0032] 3. Insufficient utilization of the self-supporting capacity of the surrounding rock: The existing design has not been optimized based on the actual mechanical performance of hard rock under high stress. The surrounding rock itself has a certain bearing capacity and arching effect, but the hard constraints of the continuous steel frame and anchor bolts may lead to insufficient attention to the self-supporting capacity of the surrounding rock, failing to utilize the arching bearing potential of the rock mass itself, and instead increasing construction interference.

[0033] 4. Limited Anchor Bolt Arrangement: Traditional anchor bolt systems are mostly installed perpendicular to the excavation profile, limiting the support range to the current cycle section where the anchor bolt is located. If attempts are made to increase the steel frame or anchor bolt spacing (skipping sections), the unsupported rock sections in the middle will lack anchoring constraints and are prone to loosening due to deep stress release, making this skip-section approach difficult to implement. Therefore, there are currently no reliable measures to solve the problem of reinforcing the deep rock mass of a section when "skipping a section without anchor bolts."

[0034] In summary, existing technologies for initial support of high-stress hard rock tunnels suffer from uneconomical design and lack of flexibility. The purpose of this invention is to address these shortcomings by proposing a new initial support structure and construction layout method. This method reduces unnecessary support component input while ensuring surrounding rock stability and construction safety, fully utilizing the bearing capacity of the hard rock itself, thus solving the technical problems of high cost and long construction period associated with traditional solutions. Furthermore, this invention aims to solve the problem of insufficient deep constraint of adjacent surrounding rock sections during segmented support through an innovative anchor bolt arrangement, thereby achieving a balance between safety and efficiency.

[0035] Overall Approach: The initial support technology proposed in this invention adopts the principle of "alternating deployment," that is, using two excavation cycles as a unit: in these two cycles, the complete set of initial support is implemented only in the first cycle, forming a tunnel with a steel frame section; in the second cycle, only shotcrete is applied without installing anchor bolts and steel frames, forming a tunnel without a steel frame section, and so on, alternating between the two (see...). Figure 1 (The diagram shows an alternating support layout). By changing the traditional pattern of steel frame and full anchor bolt support per cycle to "steel frame and anchor bolts across two cycles," the amount of steel frame and anchor bolts used is effectively reduced by about 50%. The structure formed between the alternating support sections resembles an arch bridge: adjacent support sections with steel frames act as the main supporting "piers," while the middle section without steel frames and anchor bolts relies on the two side support sections and its own shotcrete arch effect to cross the high ground stress area. The surrounding rock arch effect is fully utilized here—using the rigid fulcrum formed by adjacent supported sections, the stress on the surrounding rock in the middle section is transferred to both sides, achieving overall stability. This support system design is based on the premise that Class II-III surrounding rock has temporary stability, and through interval support, each support unit is both independently stressed and mutually coordinated.

[0036] The following is a detailed analysis in conjunction with the attached diagram, such as... Figures 1-3 As shown, the present invention provides a support structure and construction method for high ground stress tunnels in Class II-III hard rock.

[0037] This support structure is used for high ground stress tunnels in Class II-III hard rock. It is used for initial support during tunnel construction. The tunnel is divided into multiple sections based on each cycle of excavation. It includes a steel-framed section tunnel 3, which contains steel frames 5 and anchor bolts 1 and is sealed with shotcrete 2. It also includes a non-steel-framed section tunnel 4, which does not contain steel frames 5 and anchor bolts 1 and is sealed with shotcrete 2. The steel-framed section tunnel 3 and the non-steel-framed section tunnel 4 are arranged cyclically along the excavation direction. In the steel-framed section tunnel 3, multiple anchor bolts 1 are configured at an angle, so that the surrounding rock of the non-steel-framed section tunnel 4 is distributed with the anchor bolts 1 of two adjacent steel-framed section tunnels 3.

[0038] This application effectively reduces the amount of steel frames (5) and anchor bolts (1) used by approximately 50% by changing the traditional support pattern of 5 steel frames and 1 anchor bolts per cycle to "5 steel frames and 1 anchor bolts across two cycles". The structure formed between the alternating support sections resembles an arch bridge: the adjacent support sections with steel frames (5) act as the main supporting "piers", and the tunnel 4 without steel frames in the middle relies on the tunnels 3 with steel frames on both sides and its own shotcrete arch (2) to cross the high ground stress area. The surrounding rock arch effect is fully utilized here—using the rigid fulcrum formed by adjacent supported sections, the stress on the surrounding rock in the middle section is transferred to both sides, achieving overall stability. This support system design is based on the premise that Class II-III surrounding rock has temporary stability, and through interval support, each support unit is both independently stressed and mutually coordinated.

[0039] Reference Figure 2 As shown, this invention fully utilizes the self-supporting arch effect of the rock mass through alternating support arrangements: In the section of tunnel 4 without a steel frame, lacking anchor bolts 1 and steel frames 5, the plastic arch 6 formed by the plastic deformation of the surrounding rock transmits the pressure from the surrounding rock to the adjacent reinforced sections at both ends, as if a "natural arch" is erected between the two consolidated arch frames. The inclined anchor bolts 1 in the two side sections penetrate deep into the rock mass of the middle section, acting as "hidden" supports, internally constraining the displacement of the surrounding rock in the middle section, preventing excessive convergence or collapse even under high stress. In this system, adjacent support sections interact through the anchor bolts 1, surrounding rock, and concrete arch, resulting in a more coordinated and continuous overall stress distribution.

[0040] It is obvious that the absence of anchor bolts 1 in the steel frameless section of tunnel 4 means that anchor bolts 1 were not installed during the construction of this section. It is possible that the anchor bolts 1 in the adjacent steel frame section of tunnel 3 were inserted into the steel frameless section of tunnel 4 at an angle.

[0041] Steel Frame 5: The steel arch frame (or grid arch frame) is installed only in the first cycle of each support unit. The steel frame 5 type can use I-beams or steel arch frames, and its cross-sectional specifications are selected according to the original design.

[0042] In practice, anchor bolt type 1 can be a full-length bonded resin anchor bolt or a self-drilling hollow anchor bolt, with a diameter typically ranging from φ25mm to φ32mm. The length can be increased as needed to cover the deep surrounding rock of the adjacent steel-frame-less tunnel section 4, generally ranging from 3m to 5m. Figure 1 In the side view direction, i.e. the direction of the tunnel portal, consistent with existing technology, the anchor bolts 1 are arranged in a quincunx pattern, with a circumferential spacing of approximately 0.5m-1.2m along the arch and sidewall perimeter. In the direction of travel, i.e. the excavation direction (tunnel extension direction), a set of anchor bolts 1 is installed every two cycles, and a set of anchor bolts 1 contains multiple rows depending on its circumferential distribution. Figure 1 The anchor rod 1 shown is a row of anchor rods 1.

[0043] In some embodiments, the inclined anchor bolts 1 in the steel frame section tunnel 3 are configured to be inclined at 10°-20° relative to the normal of the surrounding rock surface, with the inclination direction being the tunnel extension direction.

[0044] The direction in which the tunnel extends is also the direction of tunnel excavation.

[0045] Some anchor bolts 1 are inclined in the direction of excavation (forward inclination), while others are inclined in the opposite direction (backward inclination), so that the direction in which the anchor bolts 1 are injected into the surrounding rock is different from each other (as if inserted radially with the tunnel centerline as the axis). By adjusting the inclination angle and length of the anchor bolts 1, the anchoring section of the anchor bolts 1 can be extended into the surrounding rock area of ​​the adjacent section without anchor bolts 1 (corresponding to the section of tunnel 4 without steel frame), thereby achieving the cross-over of the support range.

[0046] In this embodiment, multiple anchor bolts 1 located at the same circumferential position in the steel frame section of the tunnel 3 are configured to radiate outward from the same center, which facilitates implementation and provides a more balanced force distribution.

[0047] In this embodiment, a steel mesh is installed between the shotcrete 2 seal and the surrounding rock in the steel-frameless section of tunnel 4. The steel mesh is laid before the shotcrete 2 operation. The steel mesh can be anchored to the steel frame 5 or anchor rod 1 in the preceding steel-framed section of tunnel 3 to enhance the adhesion and integrity of the shotcrete 2.

[0048] As a preferred option, the single-cycle advance for Class II surrounding rock is 1.5m-2m, and for Class III surrounding rock it is 1.0m-1.5m.

[0049] In this embodiment, the concrete 2 sprayed in the steel frameless section of tunnel 4 contains an accelerator.

[0050] Considering the increased spacing of the steel frame 5 in the skip-segment arrangement, to prevent sagging or cracking due to excessive span in the sprayed layer, a quick-setting agent can be added to the shotcrete 2, and the layers can be sprayed in layers with timely curing to ensure the quality of the sprayed layer. Reinforcing the concrete with steel fibers or synthetic fibers can also be considered to improve the crack and shear resistance of the sprayed layer. In the case of steel fiber shotcrete, the reinforcing mesh can be simplified as needed.

[0051] In this embodiment, the steel frame 5 in the adjacent steel frame section of tunnel 3 is welded together with connecting bars.

[0052] To ensure continuity, the steel frames 5 are welded together using connecting bars and fixed to the arch foot rock mass using anchor pipes. In the circulation section without steel frames 5, although there is no rigid arch support, the adjacent steel frames 5 at both ends can transfer forces through the connecting bars and the surrounding rock arch. If necessary, temporary supports such as retractable columns can be added to the sections that skip steel frames 5 to help control the initial deformation (temporary supports are usually not needed when the surrounding rock is good).

[0053] In this embodiment, the length of the anchor bolt 1 inserted into the adjacent non-steel-framed tunnel 4 in the steel-framed section of tunnel 3 exceeds half the extension length of the non-steel-framed section of tunnel 4, thereby achieving cross-overlap of the support range.

[0054] The length direction here is also... Figure 1 The horizontal direction, that is, the direction in which the tunnel extends. It is obvious that... Figure 1 This illustrates the overlapping effect of the aforementioned support coverage areas. The area where anchor bolts 1 meet in the diagram does not indicate interference between anchor bolts 1; rather, there is a certain spatial relationship or design misalignment. This is based on the design location. Figure 1 The connection point of the anchor bolt 1 is half the extension length of the steel frameless tunnel 4. Here, the length of the anchor bolt 1 inserted into the adjacent steel frameless tunnel 4 in the steel framed tunnel 3 does not refer to the absolute length of the anchor bolt 1 inserted into the steel frameless tunnel 4, but rather to the component of the anchored section of the anchor bolt 1 inserted into the steel frameless tunnel 4 in the aforementioned length direction (tunnel extension direction). This ensures that when the anchor bolt 1 in the steel framed tunnel 3 is inserted into the adjacent steel frameless tunnel 4, its distribution range in the steel frameless tunnel 4 exceeds half in the length direction.

[0055] Furthermore, in the section of tunnel 3 with steel frame, the area where the anchor bolt 1 extends beyond half the length of the adjacent section of tunnel 4 without steel frame corresponds to a surrounding rock thickness greater than or equal to 1m.

[0056] The thickness direction here is also... Figure 1 In the longitudinal direction, along the thickness of the surrounding rock. The anchorage range of two adjacent sections supported by anchor bolt 1 overlaps by at least 1m within the intermediate section of tunnel 4 without a steel frame, ensuring that the deep surrounding rock in the intermediate section is also constrained by anchor bolt 1. Based on Figure 1 This refers to the fact that anchor bolt 1 extends vertically by 1m or more at the point of connection.

[0057] The present invention also provides a support construction method for tunnels with high ground stress in Class II-III hard rock, comprising the construction of a steel frame section 3 and a non-steel frame section 4, wherein the construction of the steel frame section 3 and the non-steel frame section 4 are carried out alternately in a cycle.

[0058] Construction of tunnel 3 with steel frame: Excavate the tunnel in the current cycle (drill and blast or mechanical excavation), spray some concrete 2 in a timely manner to seal the rock surface, install steel frame 5 (and install anchor pipes) and anchor rod 1, drill holes and install anchor rod 1 according to the design layout, wherein the inclination angle and length of anchor rod 1 should ensure that the anchored section penetrates into the surrounding rock of the previous segment and the next segment respectively, and after the anchor rod 1 is installed, spray concrete 2 to the design thickness.

[0059] In this embodiment, the anchor bolt 1 has an anchor plate at the locking end that is in close contact with the surface of the shotcrete 2. If necessary, a steel mesh is added between the anchor plate and the rock surface to improve the local support stiffness.

[0060] Based on the foregoing, during the construction of steel frame 5, it can be fixed to the previous steel frame segment 5 by welding connecting bars.

[0061] Construction of section 4 of the tunnel without steel frame: Excavate the tunnel in the current cycle and spray concrete to the design thickness in one go.

[0062] Based on the foregoing, a steel mesh can be laid before spraying concrete 2.

[0063] The excavation will proceed in the same cyclical manner, alternating between the steel-framed section 3 and the non-steel-framed section 4. During construction, it is crucial to ensure the timely and effective installation of the steel frame 5 and anchor bolts 1 in each steel-framed section of tunnel 3, and to ensure the shotcrete 2 is well-connected and tightly sealed at construction junctions to form a continuous support system. If the surrounding rock conditions change (weakening or significant deformation), strategies should be adjusted promptly, such as shortening segment lengths, installing support in each cycle, or reinforcing intermediate section support (by increasing the density of anchor bolts 1 or using temporary arches) to ensure safety.

[0064] Based on the above, shotcrete 2 was applied during the construction of both the steel-framed section 3 and the steel-frameless section 4. For the steel-framed section 3, the initial shotcrete thickness should reach about half of the design thickness to seal the surrounding rock surface. After the anchor bolts 1 and steel frame 5 are installed, the remaining thickness is shotcreted until the design requirements are met (generally a total thickness of 20cm-30cm; depending on the surrounding rock stress, the shotcrete layer can be appropriately thickened to 25cm-35cm to enhance rigidity when the span of steel frame 5 increases). For the steel-frameless section 4, shotcrete should be applied immediately after excavation to the design thickness and adhere tightly to the wall to quickly form a closed arched shell.

[0065] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A support structure for high ground stress tunnels in Class II-III hard rock, used for initial support during tunnel construction, wherein the tunnel is divided into multiple sections based on each cycle of excavation, including a steel frame section tunnel (3), wherein the steel frame section tunnel (3) is equipped with a steel frame (5) and anchor bolts (1), and is sealed with shotcrete (2), characterized in that, It also includes a section of tunnel without a steel frame (4), in which no steel frame (5) and anchor bolts (1) are installed, and it is sealed with shotcrete (2); The steel-framed section tunnel (3) and the non-steel-framed section tunnel (4) are arranged cyclically along the excavation direction. In the steel-framed section tunnel (3), multiple anchor bolts (1) are set at an angle, so that the surrounding rock corresponding to the non-steel-framed section tunnel (4) contains the anchor bolts (1) of two adjacent steel-framed section tunnels (3).

2. The support structure for a medium-high stress tunnel in grade II-III hard rock according to claim 1, characterized in that, The anchor rods (1) installed obliquely in the steel frame section tunnel (3) are inclined at 10°-20° relative to the normal of the surrounding rock surface, and the inclination direction is the tunnel extension direction.

3. The support structure for high ground stress tunnels in Class II-III hard rock according to claim 1, characterized in that, In the steel-framed section of the tunnel (3), multiple anchor bolts (1) located at the same circumferential position in the tunnel are arranged in a radiating pattern from the same center.

4. The support structure for a medium to high stress tunnel in grade II-III hard rock according to claim 1, characterized in that, In the section of the tunnel without a steel frame (4), a steel mesh is installed between the shotcrete (2) seal and the surrounding rock.

5. The support structure for high ground stress tunnels in Class II-III hard rock according to claim 1, characterized in that, For Class II surrounding rock, the single-cycle advance is 1.5m-2m, and for Class III surrounding rock, the single-cycle advance is 1.0m-1.5m.

6. The support structure for a medium to high ground stress tunnel in grade II-III hard rock according to claim 1, characterized in that, The concrete (2) sprayed in the steel frameless section of the tunnel (4) contains an accelerator.

7. The support structure for a high ground stress tunnel in a hard rock of grade II-III according to claim 1, characterized in that, The steel frame (5) in the adjacent steel frame section tunnel (3) is welded together with connecting bars.

8. The support structure for a medium to high stress tunnel in grade II-III hard rock according to any one of claims 1-7, characterized in that, In the steel-framed section of the tunnel (3), the length of the anchor bolt (1) inserted into the adjacent steel-frameless section of the tunnel (4) exceeds half the extension length of the steel-frameless section of the tunnel (4).

9. The support structure for a medium-high stress tunnel in grade II-III hard rock according to claim 8, characterized in that, In the section of the tunnel with steel frame (3), the area where the anchor bolt (1) extends beyond half the length of the adjacent section of the tunnel without steel frame (4) corresponds to a surrounding rock thickness greater than or equal to 1m.

10. A method for constructing a support structure for a high-stress tunnel in hard rock of grade II-III according to any one of claims 1-9, characterized in that, The construction includes the construction of tunnels with steel frame sections (3) and tunnels without steel frame sections (4), and the construction of tunnels with steel frame sections (3) and tunnels without steel frame sections (4) are carried out alternately in a cycle; Construction of the tunnel with steel frame section (3): Excavate the tunnel in the current cycle, spray part of concrete (2) to seal the rock surface, install steel frame (5) and anchor (1), wherein the inclination angle and length of the anchor (1) should ensure that the anchored section penetrates into the surrounding rock of the previous section and the surrounding rock of the next section respectively. After the anchor (1) is installed, spray concrete (2) to the design thickness. Construction of the tunnel without steel frame (4): Excavate the tunnel in the current cycle and spray concrete (2) to the design thickness in one go.

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