Supporting structure for high ground stress tunnel in II-III grade hard rock and construction method

Abstract

The invention discloses a supporting structure for a high ground stress tunnel in II-III grade hard rock and a construction method, and belongs to the technical field of primary supporting of tunnel engineering. The tunnel is divided into multiple sections based on each cycle of excavation footage, steel frames and anchor rods are arranged in the tunnel with the steel frame section and the tunnel with the steel frame section, sprayed concrete is arranged for sealing, no steel frames and anchor rods are arranged in the tunnel with the steel frame-free section and the tunnel with the steel frame-free section, and sprayed concrete is arranged for sealing; the tunnels with the steel frame sections and the tunnels without the steel frame sections are circularly arranged in the excavation direction, and the anchor rods in the tunnels with the steel frame sections are obliquely arranged, so that the anchor rods in every two adjacent tunnels with the steel frame sections are distributed in surrounding rocks corresponding to the tunnels without the steel frame sections. A traditional mode of steel frame and full anchor rod supporting in each cycle is changed into a mode of steel frame and anchor rod spanning two cycles, and the using amount of steel frames and anchor rods is reduced by about 50%. The surrounding rock arching effect is fully applied, the stress of the surrounding rock of the middle section is transmitted to the two sides through rigid fulcrums formed by the adjacent supported sections, and overall stability is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of primary support for tunnel engineering, and more specifically to a method for primary support of newly constructed traffic tunnels in Class II-III hard rock and high geostress conditions. This method is particularly suitable for highway or railway tunnel projects where the surrounding rock has a certain degree of self-stabilization but high geostress levels, potentially leading to stress relaxation. Specifically, the invention relates to a support structure and construction method for tunnels in Class II-III hard rock and high geostress conditions. Background Art

[0002] As tunnel construction progresses to greater depths, even in high-in-situ stress environments with strong and intact surrounding rock (grades II-III), stress relaxation can lead to deformation and other problems. When surrounding rock conditions are good and in-situ stress is low, primary support is typically simpler and more effective. For example, according to current construction technical guidelines, good surrounding rock conditions typically require only localized shotcrete or anchor bolting (supplemented with localized steel mesh to prevent block fallout, if necessary), demonstrating that high-quality surrounding rock does not require extensive, strong support. However, in deep tunnels with high in-situ stress, concerns about tunnel deformation often necessitate weak support in moderate to good surrounding rock. To ensure safety, a "strong support, short advance" approach is adopted. This means that each excavation cycle is followed by primary support using a combination of anchor bolts, steel frames, and shotcrete to quickly close the surrounding rock into a ring. While this continuous deployment of a full set of support systems has improved safety in practice, it also comes with the challenges of high costs and extended construction times.

[0003] The current implementation method most similar to the present invention is conventional New Austrian Tunneling (NATM) primary support: Each excavation cycle typically involves 1-2 m of advance. Immediately following the excavation face, system anchors (mostly radial anchors perpendicular to the excavation face) are installed, followed by a steel frame (lattice arch or I-beam arch), which is then sealed with shotcrete. Anchors are generally full-length bonded (cement mortar or resin anchors), with spacing designed according to the surrounding rock grade. The steel frame spacing is equal to the advance (typically one steel frame per cycle), and the shotcrete thickness is determined by the surrounding rock and design requirements. This approach is distinguished by the completion of a complete primary support system with each cycle, ensuring that any newly exposed surrounding rock is promptly supported. This approach can mitigate the risk of excessive rock relaxation and collapse in hard rock tunnels with high in-situ stresses. However, because it fails to fully consider the inherent bearing capacity of the hard surrounding rock, the configuration of support elements is often conservative.

[0004] In practice, the closest approaches to cost savings are increasing support spacing or locally thickening the lining. However, these approaches fall within the realm of "full-circle continuous support," resulting in limited savings. In summary, traditional solutions lack effective measures for support optimization, placing significant pressure on construction costs and schedules. It is necessary to explore new support arrangements to improve cost-effectiveness and efficiency. Summary of the Invention

[0005] In order to overcome the problems of high initial support cost and long construction period for Class II-III surrounding rock in existing high ground stress environments, 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 the present invention to solve its technical problem is: This support structure is used for tunnels with medium to high ground stress in Class II-III hard rock. It is used for initial support during tunnel construction. The tunnel is divided into multiple sections based on the excavation progress per cycle. The sections include steel frame sections, which are equipped with steel frames and anchors and sealed with shotcrete, and non-steel frame sections, which are not equipped with steel frames and anchors and sealed with shotcrete. The steel frame section tunnel and the non-steel frame section tunnel are arranged cyclically along the excavation direction. The multiple anchor rods in the steel frame section tunnel are configured to be set obliquely, so that the anchor rods in the two adjacent steel frame section tunnels are distributed in the surrounding rock corresponding to the non-steel frame section tunnel.

[0007] This application effectively reduces the use of steel frames and anchor rods by about 50% by changing the traditional support mode of steel frames and full anchor rods per cycle to "steel frames and anchor rods spanning two cycles". The structure formed between the alternating support sections is similar to the span of an arch bridge: the support sections with adjacent steel frames act as the main supporting "piers", and the middle section without steel frames and anchor rods relies on the support sections on both sides and its own sprayed concrete arch to cross the high ground stress area. The surrounding rock arch effect is fully utilized here - the rigid fulcrum formed by the adjacent supported sections is used to transfer the force of the surrounding rock in the middle section to both sides to achieve overall stability. The design of this support system is based on the premise that the II-III grade surrounding rock has short-term stability. Through interval support, each support unit is independently stressed and coordinated with each other.

[0008] In some embodiments, the obliquely arranged anchor rods in the steel frame section tunnel are inclined by 10°-20° relative to the normal line of the surrounding rock surface, and the inclination direction is the tunnel extension direction.

[0009] In some embodiments, multiple anchor rods located at the same circumferential position in the tunnel with a steel frame section are arranged to diverge outward from the same center.

[0010] In some embodiments, a steel mesh is provided between the shotcrete seal and the surrounding rock in the tunnel without steel frame.

[0011] In some embodiments, the single-cycle footage of the Class II surrounding rock is 1.5m-2m, and the single-cycle footage of the Class III surrounding rock is 1.0m-1.5m.

[0012] In some embodiments, an accelerating admixture is added to the sprayed concrete in the tunnel without steel frame.

[0013] In some embodiments, the steel frames in adjacent tunnels with steel frame sections are welded via connecting ribs.

[0014] In some embodiments, the length of the anchor rods in the tunnel with steel frame section inserted into the adjacent tunnel without steel frame section exceeds half of the extended length of the tunnel without steel frame section.

[0015] In some embodiments, the surrounding rock thickness in the area where the anchor rods in the tunnel with steel frame section exceed half of the extension length of the adjacent tunnel without steel frame section is greater than or equal to 1 m.

[0016] The present invention also provides a support construction method for a tunnel with medium and high ground stress in Class II-III hard rock, which comprises tunnel construction with a steel frame section and tunnel construction without a steel frame section, wherein the tunnel construction with a steel frame section and the tunnel construction without a steel frame section are carried out alternately in a cycle; Tunnel construction with steel frame sections: excavate the tunnel with the current cycle advance, spray concrete partially to seal the rock face, install the steel frame and anchor bolts. The inclination and length of the anchor bolts should ensure that the anchoring sections penetrate deep into the surrounding rock of the previous and next sections respectively. After the anchor bolts are installed, spray concrete to the designed thickness; Tunnel construction without steel frame: excavate the tunnel with current cycle advance and spray concrete to the designed thickness in one go.

[0017] The beneficial effects of the present invention are: By changing the traditional support model of steel frames and full anchor bolts per cycle to "steel frames and anchor bolts spanning two cycles," the use of steel frames and anchor bolts can be effectively reduced by approximately 50%. The structure formed between the alternating support sections is similar to an arch bridge span: the adjacent support sections with steel frames act as the main supporting "piers," and the middle section without steel frames and anchor bolts relies on the support sections on both sides and its own shotcrete arch to cross the high ground stress area. The surrounding rock arch effect is fully utilized here—using the rigid support points formed by the adjacent supported sections to transfer the force of the surrounding rock in the middle section to both sides, achieving overall stability. This support system design is based on the premise that the II-III grade surrounding rock has short-term stability. Through interval support, each support unit is able to bear force independently and cooperate with each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic diagram of the support structure for a high ground stress tunnel in Class II-III hard rock provided by the present invention; Figure 2 for Figure 1 Schematic diagram of the state of plastic arch formation in the tunnel section without steel frame; Figure 3 A schematic flow chart of the support construction method for a high ground stress tunnel in Class II-III hard rock provided by the present invention.

[0019] The markings in the figure are: 1-anchor rod, 2-concrete, 3-tunnel section with steel frame, 4-tunnel section without steel frame, 5-steel frame, 6-plastic arch. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to the accompanying drawings.

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present 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 only used to explain the present invention and are not intended to limit the present invention.

[0022] The existing continuous support technology has the following main shortcomings and limitations: 1. Redundant support and inefficiency: For Grade II-III hard rock, the traditional practice of installing a complete anchor bolt-steel frame-shotcrete support system for each cycle often exceeds actual requirements. Even though the hard rock is briefly exposed and does not immediately cause instability, a large number of support components are still installed, resulting in waste of materials and labor, and slowing construction speed.

[0023] 2. High cost and long construction period: Continuous strong support measures meant dense anchor bolts, one steel frame per cycle, and large amounts of shotcrete, which directly led to high support costs. Furthermore, processes such as anchor bolt drilling and installation and steel frame assembly were frequently inserted into each cycle, slowing down excavation progress and extending the construction period.

[0024] 3. Underutilization of the surrounding rock's self-supporting capacity: Existing designs fail to optimize the actual mechanical behavior of hard rock under high stress. The surrounding rock itself possesses a certain bearing capacity and arching effect, but the rigid constraints of the continuous steel frame and anchors may result in insufficient emphasis on the surrounding rock's self-supporting capacity. This, in turn, increases construction disruptions due to the rock's inherent arching potential.

[0025] 4. Single anchor bolt arrangement: Traditional anchor bolts are mostly installed perpendicular to the excavation contour, limiting their support range to the current loop segment where the anchor bolts are located. If attempts are made to increase the spacing between the steel frames or anchor bolts (skip-segment support), the surrounding rock in the intermediate unsupported segments will lack anchoring constraints and easily loosen due to deep stress release, making this skip-segment solution difficult to implement. Therefore, there is currently no reliable solution to the deep reinforcement problem of the surrounding rock segment when skipping a segment without installing anchor bolt steel frames.

[0026] In summary, the existing technology has problems with the initial support of high-stress hard rock tunnels, such as uneconomical design and lack of flexibility. The purpose of the present invention is to propose a new initial support structure and construction layout method to address the above shortcomings. Under the premise of ensuring the stability of the surrounding rock and construction safety, it reduces the unnecessary investment in support components and gives full play to the bearing capacity of the hard rock surrounding rock itself, so as to solve the technical problems of high cost and long construction period of traditional solutions. At the same time, the present invention is committed to solving the problem of insufficient deep constraints on adjacent sections of surrounding rock during jump section support through innovative anchor arrangement methods, thereby achieving a balance between safety and efficiency.

[0027] Overall concept: The primary support technology proposed in this invention adopts the principle of "alternating arrangement", that is, two excavation cycles are used as a unit: in these two cycles, only in the first cycle, a full set of primary support is implemented to form a tunnel with a steel frame, and in the second cycle, only concrete is sprayed without installing anchors and steel frames to form a tunnel without steel frames, and this process is repeated alternately (see Figure 1 (See the diagram for the alternating support layout.) By changing the traditional support pattern of steel frames and full anchor bolts per cycle to "steel frames and anchor bolts spanning two cycles," the use of steel frames and anchor bolts is effectively reduced by approximately 50%. The structure formed between the alternating support sections resembles an arch bridge span: adjacent support sections with steel frames serve as the main supporting "piers," while the intermediate section without steel frames and anchor bolts relies on the support sections on both sides and the inherent shotcrete arch effect to span the high ground stress area. The surrounding rock arch effect is fully utilized here—using the rigid fulcrum formed by adjacent supported sections to transfer the forces in the central section of the surrounding rock to both sides, achieving overall stability. This support system design is based on the premise that the surrounding rock of Class II-III has short-term stability. Through spaced supports, each support unit is able to bear forces independently and coordinate with each other.

[0028] The following is a detailed analysis with reference to the accompanying drawings: Figure 1-Figure 3 As shown, the present invention provides a support structure and construction method for a high ground stress tunnel in grade II-III hard rock.

[0029] The support structure is used for high ground stress tunnels in grade II-III hard rock, and is used for initial support of tunnel construction. The tunnel is divided into multiple sections based on the excavation progress of each cycle, including a steel frame section tunnel 3, in which a steel frame 5 and anchor rods 1 are provided, and sprayed concrete 2 is provided for sealing. The tunnel also includes a non-steel frame section tunnel 4, in which no steel frame 5 and anchor rods 1 are provided, and sprayed concrete 2 is provided for sealing. The steel frame section tunnel 3 and the non-steel frame section tunnel 4 are arranged cyclically along the excavation direction, and multiple anchor rods 1 in the steel frame section tunnel 3 are configured to be obliquely set, so that the anchor rods 1 in the two adjacent steel frame section tunnels 3 are distributed in the surrounding rock corresponding to the non-steel frame section tunnel 4.

[0030] This application effectively reduces the usage of steel frames 5 and anchor rods 1 by about 50% by changing the traditional support mode of 5 steel frames and 1 full anchor rod per cycle to "5 steel frames and 1 anchor rod for two cycles". The structure formed between the alternating support sections is similar to the span of an arch bridge: the support sections with adjacent steel frames 5 act as the main supporting "piers", and the middle tunnel 4 without steel frame sections relies on the steel frame sections 3 on both sides and its own sprayed concrete arch 2 to cross the high ground stress area. The surrounding rock arch effect is fully utilized here - the rigid fulcrum formed by the adjacent supported sections is used to transfer the force of the surrounding rock in the middle section to both sides to achieve overall stability. The design of this support system is based on the premise that the II-III grade surrounding rock has short-term stability. Through interval support, each support unit is independently stressed and coordinated with each other.

[0031] Reference Figure 2 As shown, the present invention fully utilizes the self-supporting arch effect of the rock mass by alternating supports: the tunnel section 4 without steel frames lacks anchor rods 1 and steel frames 5. The plastic arch 6 formed by the plastic deformation of the surrounding rock transmits the surrounding rock pressure to the adjacent reinforced sections at both ends, as if a "natural arch" was erected between the two consolidated arches. The inclined anchor rods 1 in the sections on both sides penetrate deep into the rock mass of the middle section, playing a "hidden insertion" support role, constraining the displacement of the surrounding rock in the middle section from the inside, so that even under high stress, it will not experience excessive convergence or collapse. In this system, the adjacent support sections interact through the anchor rod 1-surrounding rock-concrete arch, and the overall force is more coordinated and continuous.

[0032] Obviously, the absence of anchor rods 1 in the tunnel section 4 without steel frame here means that no anchor rods 1 were set during the construction of this section, which does not rule out the possibility that the anchor rods 1 in the adjacent tunnel section with steel frame 3 are obliquely inserted into the tunnel section 4 without steel frame.

[0033] Steel frame 5: Steel arch frame (or grid arch frame) is only installed in the first cycle of each group of support units. The type of steel frame 5 can be I-beam or steel arch frame, and its cross-sectional specifications are selected according to the original design.

[0034] In practice, the anchor rod 1 type can be selected from full-length bonded resin anchor rods or self-propelled hollow anchor rods, etc., with a diameter of φ25mm-φ32mm. The length can be increased as needed to cover the deep surrounding rock of the adjacent non-steel frame tunnel 4, generally 3m to 5m. Figure 1 In the lateral direction (i.e., toward the tunnel portal), consistent with existing techniques, anchor bolts 1 are arranged in a plum blossom pattern, with circumferential spacing of approximately 0.5m-1.2m along the arch and sidewalls. In the direction of travel (i.e., the direction of excavation (tunnel extension)), a set of anchor bolts 1 is provided every two cycles, with each set comprising multiple rows depending on their circumferential distribution. Figure 1 The anchor rods 1 shown in FIG. 1 are a row of anchor rods 1 .

[0035] In some embodiments, the obliquely arranged anchor bolts 1 in the steel frame tunnel 3 are configured to be inclined by 10°-20° relative to the normal line of the surrounding rock surface, and the inclined direction is the tunnel extension direction.

[0036] The tunnel extension direction here is also the tunnel excavation direction.

[0037] Some anchor bolts 1 are tilted toward the excavation advance (forward tilt), while others are tilted in the opposite direction (backward tilt), causing the bolts 1 to penetrate the surrounding rock in different directions (as if inserted radially from the tunnel centerline). By adjusting the inclination and length of the anchor bolts 1, the anchoring section of the anchor bolt 1 penetrates into the surrounding rock area of ​​the adjacent section without anchor bolts 1 (corresponding to the steel frame-free tunnel section 4), thus achieving cross-overlapping of the support range.

[0038] In this embodiment, a plurality of anchor rods 1 located at the same circumferential position in the tunnel with a steel frame section 3 are arranged to diverge outward from the same center, which is convenient for implementation and provides relatively balanced force.

[0039] In this embodiment, a steel mesh is installed between the shotcrete 2 seal and the surrounding rock in the steel-free tunnel section 4. The steel mesh is laid before the shotcrete 2 is applied. The steel mesh can be anchored to the steel frame 5 or anchor rods 1 in the preceding steel-framed tunnel section 3, enhancing the adhesion and integrity of the shotcrete 2.

[0040] Preferably, the single-cycle footage of the Class II surrounding rock is 1.5m-2m, and the single-cycle footage of the Class III surrounding rock is 1.0m-1.5m.

[0041] In this embodiment, a quick-setting agent is added to the sprayed concrete 2 in the tunnel 4 without a steel frame.

[0042] Considering the increased time between steel frame 5 deployments, to prevent sagging or cracking in the sprayed layer due to excessive spans, an accelerator can be added to the sprayed concrete 2, sprayed in layers, and maintained promptly to ensure the quality of the sprayed layer. Steel fiber or synthetic fiber reinforced concrete can also be considered to improve the sprayed layer's resistance to cracking and shearing. In the case of steel fiber sprayed concrete, the reinforcement mesh can be simplified as needed.

[0043] In this embodiment, the steel frames 5 in the adjacent steel frame sections of the tunnel 3 are welded via connecting ribs.

[0044] To ensure continuity, the steel frames 5 are welded together using connecting bars and secured to the arch foot rock mass via locking anchor pipes. In loop sections without steel frames 5, while lacking rigid arch support, the connecting bars and the surrounding rock arch act together to transmit force. If necessary, temporary supports, such as retractable columns, can be added to sections where steel frames 5 are skipped to help control initial deformation. (Temporary supports are generally unnecessary if the surrounding rock is good.)

[0045] In this embodiment, the length of the anchor rod 1 in the steel frame section tunnel 3 inserted into the adjacent non-steel frame section tunnel 4 exceeds half of the extension length of the non-steel frame section tunnel 4, thereby achieving cross-overlap of the support action range.

[0046] The length direction here is Figure 1 The horizontal direction is the direction in which the tunnel extends. Figure 1 The cross-overlapping effect of the aforementioned support range is shown. The area where the anchor rods 1 meet in the figure does not mean that the anchor rods 1 interfere with each other. There is a certain front-to-back relationship or design misalignment. Based on the design position, Figure 1 The point where the anchor rods 1 meet is halfway along the extended length of the non-steel frame tunnel 4. The length of the anchor rods 1 inserted into the adjacent non-steel frame tunnel 4 in the steel frame tunnel 3 does not refer to the absolute length of the anchor rods 1 inserted into the non-steel frame tunnel 4. Rather, it refers to the length of the anchoring section of the anchor rods 1 inserted into the non-steel frame tunnel 4 in the aforementioned longitudinal direction (the tunnel extension direction). This ensures that when the anchor rods 1 in the steel frame tunnel 3 are inserted into the adjacent non-steel frame tunnel 4, their distribution range in the non-steel frame tunnel 4 exceeds halfway along the longitudinal direction.

[0047] Furthermore, the surrounding rock thickness in the area where the anchor rods 1 in the tunnel section 3 with steel frame exceed half of the extension length of the adjacent tunnel section 4 without steel frame is greater than or equal to 1 m.

[0048] The thickness direction here is Figure 1 The longitudinal direction of the surrounding rock thickness. The anchoring range of two adjacent sections with anchor rods 1 overlaps at least 1m in the middle section of tunnel 4 without steel frame, ensuring that the deep surrounding rock in the middle section is also constrained by anchor rods 1. Figure 1 , means that the anchor rod 1 will extend 1m or more in the vertical direction at the connected position.

[0049] The present invention also provides a support construction method for a high ground stress tunnel in grade II-III hard rock, which includes the construction of a steel frame tunnel section 3 and a non-steel frame tunnel section 4, and the construction of the steel frame tunnel section 3 and the non-steel frame tunnel section 4 are carried out in a cyclic alternating manner.

[0050] Construction of tunnel 3 with steel frame section: excavate the tunnel with the current cycle advance (drilling and blasting or mechanical excavation), spray some concrete 2 in time to seal the rock surface, install steel frame 5 (and set locking anchor pipe) and anchor 1, drill and install anchor 1 according to the designed layout, where the inclination angle and length of anchor 1 should ensure that the anchoring section penetrates into the surrounding rock of the previous segment and the next segment respectively. After the installation of anchor 1 is completed, spray concrete 2 to the designed thickness.

[0051] In this embodiment, an anchor plate is provided at the locking end of the anchor rod 1 to closely contact 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.

[0052] Based on the above, during the construction, the steel frame 5 can be welded and fixed to the previous segment steel frame 5 using connecting bars.

[0053] Construction of tunnel 4 without steel frame: excavate the tunnel with current cycle advance and spray concrete 2 times in one time to the designed thickness.

[0054] Based on the above, a steel mesh can be laid before spraying concrete 2.

[0055] Excavation will proceed in a cyclical manner, alternating between steel-framed tunnel sections 3 and non-steel-framed tunnel sections 4. During construction, timely and effective installation of the steel frame 5 and anchor bolts 1 in each steel-framed tunnel section 3 must be ensured, and shotcrete 2 must be well-connected and tightly sealed at the construction interface to form a continuous support system. If the surrounding rock conditions change (weakening or significant deformation), timely adjustments should be made to the strategy, such as shortening the segment length, installing support throughout each cycle, or strengthening the intermediate support (by increasing the number of anchor bolts 1 or temporary arches) to ensure safety.

[0056] Based on the above, concrete 2 shotcreting is performed during both the steel frame section 3 and the non-steel frame section 4. For the steel frame section 3, the initial shotcrete thickness should reach approximately half the designed 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 20-30 cm. Depending on the surrounding rock stress and the increased span of the steel frame 5, the shotcrete layer can be thickened to 25-35 cm to enhance rigidity). For the non-steel frame section 4, shotcrete should be sprayed immediately after excavation to the designed thickness, tightly adhering to the wall to quickly form a closed arch shell.

[0057] The above description is only 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 in the scope of protection of the present invention.

Claims

1. A support structure for a high ground stress tunnel in grade II-III hard rock, used for initial support of tunnel construction, wherein the tunnel is divided into multiple sections based on the excavation footage per cycle, and comprises a steel frame section tunnel (3), wherein the steel frame section tunnel (3) is provided with a steel frame (5) and anchor rods (1), and is sealed with sprayed concrete (2), and is characterized in that: It also includes a tunnel section without a steel frame (4), wherein the tunnel section without a steel frame (5) and anchor rods (1) are not provided, and is sealed with sprayed concrete (2); The steel frame section tunnel (3) and the non-steel frame section tunnel (4) are arranged cyclically along the excavation direction, and the plurality of anchor rods (1) in the steel frame section tunnel (3) are configured to be arranged obliquely, so that the anchor rods (1) in the two adjacent steel frame section tunnels (3) are distributed in the surrounding rock corresponding to the non-steel frame section tunnel (4).

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

3. The support structure for a tunnel with high ground stress in II-III hard rock according to claim 1, characterized in that: A plurality of anchor rods (1) located at the same circumferential position in a steel frame section tunnel (3) are arranged to diverge outward from the same center.

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

5. The support structure for a tunnel with high ground stress in grade II-III hard rock according to claim 1, characterized in that: The single-cycle footage of Grade II surrounding rock is 1.5m-2m, and the single-cycle footage of Grade III surrounding rock is 1.0m-1.5m.

6. The support structure for a tunnel with high ground stress in II-III hard rock according to claim 1, characterized in that: The concrete (2) sprayed in the tunnel (4) without steel frame is added with an accelerating agent.

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

8. The support structure for a tunnel with high ground stress in grade II-III hard rock according to any one of claims 1 to 7, characterized in that: The length of the anchor rod (1) in the steel frame section tunnel (3) inserted into the adjacent non-steel frame section tunnel (4) exceeds half of the extension length of the non-steel frame section tunnel (4).

9. The support structure for a tunnel with high ground stress in grade II-III hard rock according to claim 8, characterized in that: The area where the anchor rod (1) in the steel frame section tunnel (3) exceeds half of the extension length of the adjacent non-steel frame section tunnel (4) corresponds to a surrounding rock thickness greater than or equal to 1m.

10. A support construction method for a tunnel with high ground stress in II-III hard rock, characterized in that: It includes the construction of a tunnel section with a steel frame (3) and the construction of a tunnel section without a steel frame (4), and the construction of the tunnel section with a steel frame (3) and the construction of the tunnel section without a steel frame (4) are carried out alternately in a cycle; Construction of the tunnel with steel frame section (3): excavate the tunnel with the current cycle advance, spray concrete (2) to seal the rock face, install the steel frame (5) and anchor rods (1), wherein the inclination angle and length of the anchor rods (1) should ensure that the anchoring section penetrates into the surrounding rock of the previous section and the surrounding rock of the next section respectively. After the installation of the anchor rods (1), spray concrete (2) to the designed thickness; Construction of the tunnel section without steel frame (4): Excavate the tunnel with the current cycle advance and spray concrete (2) to the designed thickness in one go.

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