Tunnel support structure

Abstract

The application relates to a tunnel supporting structure, which comprises: an advanced supporting component arranged at an arch part of a tunnel; a primary supporting layer comprising a first supporting arch frame closed into a ring, the first supporting arch frame being arranged at the arch part, side walls and inverted arches of the tunnel; and a secondary supporting layer comprising a second supporting arch frame closed into a ring, the second supporting arch frame being arranged in the primary supporting layer in a sleeving manner; wherein the rigidity of the first supporting arch frame is greater than that of the second supporting arch frame, the variable-rigidity double-layer steel arch frame is used to implement echelon supporting, the double-layer supporting arch frame is adapted to the deformation of surrounding rock, the surrounding rock can bear a larger load, the load borne by the supporting arch frame is not too large, and the tunnel structure is prevented from being unstable and collapsing.

Description

Technical Field

[0001] This application relates to the field of plateau tunnel technology, and in particular to tunnel support structures. Background Technology

[0002] With the deepening implementation of the Western Development Strategy, infrastructure construction in areas such as transportation, water conservancy, and energy is accelerating in the complex geological regions of the west. However, the plateau region has unique regional geological and tectonic evolution conditions, and has been subjected to ductile-brittle strong shear mechanical forces in its geological history. It exhibits significant anisotropy, with high ground stress distribution, where horizontal tectonic stress is the principal stress, being prevalent, resulting in poor rock mass stability. Therefore, in the western plateau region, tunnel excavation can easily lead to tunnel structural instability and collapse, and the surrounding rock during tunnel construction is prone to large deformations. Utility Model Content

[0003] Therefore, it is necessary to provide a tunnel support structure to address the problem of large deformations in tunnels in high-altitude areas.

[0004] A tunnel support structure, comprising:

[0005] Advanced support components are installed in the arch of the tunnel;

[0006] The initial support layer includes a first support arch frame that is closed into a ring and supports the arch, sidewalls and invert of the tunnel.

[0007] The secondary support layer includes a second support arch frame that is closed into a ring, and the second support arch frame is fitted inside the initial support layer;

[0008] The stiffness of the first support arch is greater than that of the second support arch.

[0009] In some embodiments, the initial support layer includes a first concrete layer, the first support arch is embedded in the first concrete layer, and the secondary support layer includes a second concrete layer, the second support arch is embedded in the second concrete layer, and the second concrete layer is bonded to the first concrete layer.

[0010] In some embodiments, the tunnel support structure further includes self-drilling anchor bolts and locking anchor pipes. Both the self-drilling anchor bolts and the locking anchor pipes are connected to the first support arch and drilled into the surrounding rock corresponding to the first support arch. The self-drilling anchor bolts reinforce the surrounding rock and pull the first support arch and the surrounding rock corresponding to the first support arch into contact with it. The locking anchor pipes support the first support arch.

[0011] In some embodiments, the tunnel support structure further includes an anchoring assembly, which includes a prestressed anchor rod. The prestressed anchor rod is disposed in the arch and sidewall areas of the tunnel, and the prestressed anchor rod is grouted to anchor the surrounding rock in the arch and sidewall areas.

[0012] In some embodiments, the anchoring assembly includes a prestressed anchor cable disposed in the sidewall region, the prestressed anchor cable being grouted to anchor the surrounding rock in the sidewall region, and the anchoring force of the prestressed anchor cable being greater than the anchoring force of the prestressed anchor rod.

[0013] In some embodiments, the anchoring force of the prestressed anchor rod is ≥60KN, and the anchoring force of the prestressed anchor cable is ≥200KN.

[0014] In some embodiments, the advanced support assembly includes a central pipe roof and multiple small guide pipes. The central pipe roof includes multiple steel pipes arranged circumferentially along the arch. The small guide pipes are located between two adjacent steel pipes, and the central pipe roof and the small guide pipes grout the surrounding rock of the arch to form a first grouting semi-ring layer.

[0015] In some embodiments, the tunnel support structure further includes grouting pipes located at the sidewalls and the invert, for injecting grout into the surrounding rock at the sidewalls and the invert to form a second grouting semi-ring layer. The first grouting semi-ring layer and the second grouting semi-ring layer are connected to each other and closed into a ring.

[0016] In some embodiments, the first concrete layer comprises steel fiber reinforced concrete, and / or the second concrete layer comprises steel fiber reinforced concrete.

[0017] In some embodiments, the first support arch is made of HW200 material, and the second support arch is made of HW175 material.

[0018] In the aforementioned tunnel support structure, for high-stress fractured surrounding rock in plateau tunnels, a stepped support system using variable stiffness double-layer steel arches is employed. When using a combination of rigid and flexible support, the double-layer support arches adapt to the deformation of the surrounding rock to a certain extent, allowing the surrounding rock itself to change relatively stably and withstand a large load. After the double-layer support arches have stabilized, the load they bear will not be too large, which is more conducive to the long-term use and stability of the tunnel support structure. This effectively addresses the predicament of high horizontal tectonic stress, low self-bearing capacity of the surrounding rock caused by fractured rock mass, and high ground stress on the support structure in plateau tunnels, preventing tunnel structural instability and collapse. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating a tunnel construction method according to one embodiment of this application;

[0020] Figure 2 This is a cross-sectional schematic diagram of a tunnel support structure in one embodiment of this application;

[0021] Figure 3 This is a schematic diagram of the structure of the first support arch in a tunnel support structure according to an embodiment of this application;

[0022] Figure 4 This is a schematic diagram of the structure of the second support arch in the tunnel support structure according to one embodiment of this application;

[0023] Figure 5 This is a cross-sectional schematic diagram of the preset grouting area in one embodiment of this application;

[0024] Figure 6 for Figure 5 A schematic diagram of the grout stop wall in the preset grouting area.

[0025] Explanation of reference numerals in the attached drawings: 100, tunnel support structure; 10, initial support layer; 11, first support arch frame; 112, first main support arch frame; 114, first invert support arch frame; 30, secondary support layer; 32, second support arch frame; 42, self-drilling anchor bolt; 44, locking anchor pipe; 52, prestressed anchor bolt; 54, prestressed anchor cable; 60, grouting pipe; 70, grout stop wall; S, tunnel excavation outline; M, pre-set grouting area. Detailed Implementation

[0026] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0027] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0028] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0029] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0030] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0031] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0032] As described in the background section, the surrounding rock of tunnels in plateau regions is prone to large deformations. Using traditional tunnel excavation and support techniques can easily lead to problems such as initial support cracking, twisting, and continuous deformation. Therefore, it is necessary to clarify the mechanical evolution mechanism and geomechanical characteristics of the geological conditions in plateau regions, based on a thorough understanding of their geological evolution history, in order to propose more advanced tunnel construction technologies.

[0033] Through research, the inventors discovered that plateau regions exhibit unique regional geological and tectonic evolution patterns. Due to the subduction, compression, and uplift of tectonic plates, the strata in the tunnel site area underwent intense orogenic movements. The surrounding rock in the tunnel site area not only commonly exhibits foliation, flow cleavage, and leaf foliation, but also features characteristic structures such as ductile shear zones, en echelon vein structures, domino structures, neck structures, and asymmetric folds. This indicates that the surrounding rock was once buried at a depth of 10km-20km underground, where high temperature and pressure caused intense compression and shearing in a plastic state, forming the tectonic phenomena observed today. Later, through crustal uplift and peneplaining, the overlying rock mass was weathered and eroded, resulting in the tunnels we see today, with a burial depth of only 200m-600m.

[0034] This drastic change in burial depth causes a significant reduction in the confining pressure of the rock mass, resulting in unloading and a loosening of the rock mass. Furthermore, due to the development of platy and flow cleavage, the rock exhibits strong anisotropy. Specifically, in areas with deep tunnel burials, intact mountain bodies far from brittle faults, and where horizontal tectonic stress remains high, the rock mass is relatively intact, dense, and even impermeable, accumulating significant energy (high ground stress). Tunnel excavation disrupts the original stress balance, causing continuous compression deformation of the surrounding rock, which can easily lead to the collapse of the support structure and large deformation disasters. Conversely, in areas with shallower tunnel burials, or near brittle faults or joint zones, and where horizontal stress is low, unloading and weathering are more pronounced. The rock mass is already highly fractured and loose. After tunnel excavation, this fractured rock mass itself cannot stabilize. Once groundwater seeps in, it instantly turns into mud and rushes into the tunnel, causing mudslides and water inrushes.

[0035] To address the aforementioned technical problem of large deformations easily occurring in high-altitude tunnels, please refer to... Figures 1-4 In some embodiments of this application, a tunnel construction method is provided, comprising the following steps:

[0036] Step S200 involves setting a pre-set deformation allowance. This means designing a pre-set deformation allowance before tunnel excavation to allow for moderate deformation of the surrounding rock, preventing the support structure from collapsing due to rock displacement. This is especially important in high-altitude geological environments where brittle, highly shear-resistant surrounding rock may suddenly become unstable (e.g., rock bursts), necessitating sufficient buffer space. Furthermore, the pre-set deformation allowance must be appropriately sized; insufficient allowance will lead to rework due to encroachment, while excessive allowance will increase excavation costs.

[0037] Step S300: Pre-support is applied to the arch of the tunnel to stabilize the surrounding rock of the arch, prepare for subsequent tunnel excavation, and prevent the surrounding rock of the arch from collapsing after tunnel excavation.

[0038] In step S500, tunnel excavation begins. A closed-loop first support arch frame 11 is installed at the tunnel arch, sidewalls, and invert to form the initial support layer 10. Thus, after tunnel excavation, timely initial support is provided at the tunnel arch, sidewalls, and invert. The resulting closed-loop initial support layer 10 effectively absorbs and buffers pressure from multiple directions, providing excellent load-bearing capacity.

[0039] In step S700, if the deformation of the initial support layer 10 reaches the preset condition, a second support arch 32, forming a closed ring, is supported inside the initial support layer 10 to form a secondary support layer 30; if the deformation of the initial support layer 10 does not reach the preset condition, the second support arch 32 is not supported inside the initial support layer. In other words, after the initial support layer 10 is formed inside the tunnel, its deformation is observed. If the initial support layer 10 does not reach the preset condition after a period of deformation, it indicates that the initial support layer 10 can independently support the tunnel and stabilize it, and the second support arch 32 is not needed. If the initial support layer 10 reaches the preset condition after a period of deformation, it indicates that the deformation of the initial support layer 10 has reached its limit, and the initial support layer 10 cannot independently support the tunnel and stabilize it, requiring secondary support. In this case, the second support arch 32 is supported inside the initial support layer 10 to form the secondary support layer 30. In this way, an initial support layer 10 and a secondary support layer 30 are set in the tunnel section that requires secondary support, and only an initial support layer 10 is set in the tunnel section with small deformation that does not require secondary support. The entire construction process does not require the secondary support layer 30 to be supported in all tunnel sections, which makes the tunnel support construction more efficient and economically better.

[0040] Furthermore, when supporting the secondary support layer 30, the stiffness of the first support arch 11 is greater than that of the second support arch 32. In other words, the stiffness of the second support arch 32 used in the secondary support is less than that of the first support arch 11, meaning the flexibility of the second support arch 32 is greater than that of the first support arch 11. This combination of variable stiffness double-layer support arches allows for initial support through the more rigid first support arch 11, followed by further support through the more flexible second support arch 32. The greater flexibility of the second support arch 32 enables it to provide support with a certain deformation capacity even when the initial support layer 10 experiences significant deformation. This allows it to better adapt to the deformation of the surrounding rock and the initial support layer 10, reducing the risk of breakage due to excessive stiffness failing to effectively adapt to the deformation. Therefore, by combining the first support arch 11 and the second support arch 32 with different stiffnesses, it is possible to adapt to the deformation of the surrounding rock and provide effective support.

[0041] Especially for high-stress fractured surrounding rock in plateau tunnels, the use of variable stiffness double-layer steel arch frames for tiered support, combining rigid and flexible support, allows the double-layer support arch frames to adapt to a certain deformation of the surrounding rock. The surrounding rock itself can change relatively stably and can withstand a large load. After the double-layer support arch frames have stabilized, the load they bear will not be too large, which is more conducive to the long-term use and long-term stability of the tunnel support structure. This can effectively cope with the dilemma of high horizontal tectonic stress, low self-bearing capacity of the surrounding rock caused by fractured rock mass, and high ground stress on the support structure in plateau tunnels, and prevent tunnel structure instability and collapse.

[0042] Optionally, the first arch support frame 11 is made of HW200 material, and the second arch support frame 32 is made of HW175 material. Furthermore, before erecting the steel arch frames, surveyors will mark the positioning points, and the steel arch frames will be installed using an arch frame assembly trolley. The steel arch frames are pre-assembled outside the tunnel and then moved to the erected frame position at the tunnel face using the arch frame assembly trolley, where the remaining steel arch frames are installed. The mechanical fabrication and installation of the steel arch frames facilitates quality control and rapid positioning, shortening the structural closure time.

[0043] Furthermore, the preset conditions are that the deformation of the initial support layer 10 reaches a preset deformation value, and the deformation rate of the initial support layer 10 reaches a preset deformation rate. In other words, when both the deformation rate and deformation of the initial support layer 10 reach their respective preset values, it indicates that the deformation of the initial support layer 10 has reached its limit and requires the support of the second support arch 32. If the deformation rate of the initial support layer 10 reaches the preset rate, but the deformation of the initial support layer 10 does not reach the preset deformation value, it indicates that the deformation of the initial support layer 10 has not yet met the preset conditions. In this case, the deformation of the initial support layer 10 is relatively small and does not require secondary support; therefore, the second support arch 32 does not need to be installed. If the deformation of the initial support layer 10 has reached the preset deformation, but the deformation rate of the initial support layer 10 is less than the preset rate, then although the deformation of the initial support layer 10 has reached the preset deformation, the deformation rate of the initial support layer 10 is small, indicating that the initial support layer 10 has gradually stabilized. At this time, secondary support is not required, and a second support arch 32 is not required.

[0044] Optionally, the preset deformation amount ranges from 13cm to 17cm, and the preset deformation amount can be set to any one of 13cm, 14cm, 15cm, 16cm, and 17cm; the preset deformation rate ranges from 0.8mm / d to 1.2mm / d, and the preset deformation rate can be set to any one of 0.8mm / d, 0.9mm / d, 1mm / d, 1.1mm / d, and 1.2mm / d. For example, the preset deformation amount is 15cm, and the preset deformation rate is 1mm / d.

[0045] In some embodiments of SS, step S200 specifically involves determining the final deformation during the stabilization period of the support layer after the completion of the initial tunnel section's support, based on data detected at the construction site. When excavating a later tunnel with the same geological conditions as the initial tunnel section, a reserved deformation greater than the final deformation is set. Thus, based on the initial tunnel section with the same geological conditions, the reserved deformation of the later tunnel section is dynamically adjusted to ensure that the reserved deformation of the later tunnel section is always greater than the final deformation of the initial tunnel section. This ensures an appropriate amount of deformation is reserved, preventing insufficient reserved deformation leading to rework due to encroachment, or excessive reserved deformation increasing excavation costs.

[0046] Specifically, if the initial tunnel section is supported by a single layer, consisting only of the initial support layer 10, the final deformation of the initial tunnel section is determined based on the final deformation of the initial support layer 10. If the initial tunnel section is supported by a double layer, consisting of the initial support layer 10 and the secondary support layer 30, the final deformation of the initial tunnel section is determined based on the final deformation of the double support layer after the secondary support is completed.

[0047] For example, during the stabilization period of the support layer in the early tunnel section, the average convergence value on one side is between 20-30cm. The reserved deformation amount for the later tunnel section is temporarily set at 40cm (10cm for the initial support layer and 30cm for the secondary support layer). The subsequent tunnel sections will be dynamically adjusted based on on-site testing.

[0048] In some embodiments, step S300, which involves providing advance support to the tunnel arch, specifically includes:

[0049] Step S310: Multiple steel pipes are spaced apart along the circumference of the tunnel arch to form a central pipe shed, and a small guide pipe is set between each two adjacent steel pipes.

[0050] Step S330 involves grouting the surrounding rock of the tunnel arch using central pipe roofs and small guide pipes. This means that multiple central pipe roofs and small guide pipes are spaced and staggered within the tunnel arch. The central pipe roofs provide large-scale, high-strength rigid support, while the small guide pipes are driven into the gaps between adjacent central pipe roofs and grouted. The grout penetrates the surrounding rock and soil, cementing it into a unified whole. This transforms the discrete "pipe roof beams" into a continuous "reinforced arch," providing high-strength pre-support that meets the pre-support requirements of terrains with widespread high ground stress distribution in plateau regions.

[0051] Specifically, the pre-support pipe roof uses Φ60 steel pipes, with a single pipe length of 6m-9m, totaling 43 pipes per cycle, with a circumferential spacing of 0.3m and a longitudinal spacing of 6.0m. Φ42 small guide pipes, each 3.5m long, are inserted between adjacent steel pipes, with a total of 43 guide pipes per cycle, also with a circumferential spacing of 0.3m and a longitudinal spacing of 3.5m. In one specific embodiment, before drilling, surveyors mark the locations with paint. Pre-support small guide pipes are preferably drilled using a rock drilling rig, with an external insertion angle of 10°–15°; pre-support pipe roofs are drilled using a three-arm rock drilling rig, with an external insertion angle of 10°. The bottom of the drilling rig must be flat and stable. Before the construction of the pipe roof and small guide pipes, the working face is sealed with 5cm thick shotcrete. The pipe roof and small guide pipes are manufactured by a CNC intelligent machining center and inserted using a multi-arm drilling rig. After installation, the gaps at the borehole openings are sealed with plastic putty to prevent grout leakage. Before grouting the central pipe shed and small pipe shed, the steel pipes were labeled and statistically analyzed. For the Φ60 central pipe shed, the grout water-cement ratio was 0.7:1, and the grouting pressure was 0.8–1 MPa; for the Φ42 small pipe shed, the grout water-cement ratio was 0.7:1, and the grouting pressure was 0.8–1 MPa. Quick-connect grouting couplings were installed at the pipe ends, and a grout stop valve was used to prevent leakage after grouting was completed.

[0052] Understandably, in some other embodiments, if the surrounding rock stability is relatively good, only small guide pipes may be set, without setting the middle pipe roof, depending on the actual situation.

[0053] In some embodiments, step S500 specifically includes steps S510 and S530.

[0054] In step S510, the tunnel face is excavated to form the main body of the tunnel, and the first main support arch frame 112 is set at the arch and sidewalls of the main body of the tunnel; that is, while the main body of the tunnel is being excavated, the arch and sidewalls of the main body of the tunnel are supported in a timely manner through the first main support arch frame 112.

[0055] The tunnel main body is excavated using the micro-step method, with step lengths of 2m-3m. This short step length facilitates the rapid closure of the initial support steel frame, providing immediate support resistance to the surrounding rock and reducing localized deviatoric stress. Each excavation step is relatively short, minimizing disturbance to the surrounding rock and reducing stress release and plastic damage.

[0056] Specifically, when using the micro-step method for tunnel excavation, the upper step is excavated first, followed by the lower step, thus dividing the tunnel body into upper and lower steps for separate excavation. Optionally, the upper step excavation in a single operation should not exceed the spacing of two arch frames, and the lower step excavation in a single operation should not exceed the spacing of three arch frames. Furthermore, for elliptical sections, the upper step excavation height is 7.22m (considering a 30cm deformation allowance for the initial support and a 10cm deformation allowance for the secondary support layer), and the lower step excavation height is 2.53m; for circular sections, the upper step excavation height is 6.43m (considering a 30cm deformation allowance for the first layer of initial support and a 10cm deformation allowance for the second layer of initial support), and the lower step excavation height is 3.53m.

[0057] Furthermore, the specific steps for installing the first main support arch frame 112 at the arch and sidewalls of the tunnel body are as follows:

[0058] Step S512: Initial spraying of concrete onto the arch and sidewalls of the tunnel body;

[0059] Step S514: Support the first main support arch 112 in the area of ​​initial shotcrete, and drill self-drilling anchors 42 and locking anchors into the surrounding rock at the foot of the stepped arch. The self-drilling anchors 42 reinforce the surrounding rock and are connected to the first support arch 11 to pull the first support arch 11 into contact with the surrounding rock. The locking anchors are connected to the first main support arch 112 to support the first main support arch 112.

[0060] Step S516: Spray concrete at the first main support arch 112 to the designed thickness.

[0061] Thus, after the main tunnel excavation, initial shotcrete is promptly applied to the arch and sidewalls of the tunnel to stabilize the surrounding rock excavation face. After the initial shotcrete stabilizes the surrounding rock excavation face, self-drilling anchor bolts 42 can be quickly driven into the surrounding rock. Grouting occurs simultaneously with the driving of the self-drilling anchor bolts 42, rapidly reinforcing the fractured surrounding rock. Furthermore, the self-drilling anchor bolts 42 are connected to the first support arch frame 11, pulling the first support arch frame 11 into contact with the surrounding rock, providing effective support force. Additionally, locking anchor bolts can be driven into the surrounding rock, connected to the first support arch frame 11, to support and fix the arch foot of the first support arch frame 11. Optionally, steel fiber reinforced concrete is used for the initial shotcrete application, which has higher strength and can form a strong lock on the surrounding rock, further improving its stability. Specifically, after the main tunnel is excavated, steel fiber reinforced concrete is used in the initial shotcrete application. This seals the surrounding rock immediately after excavation, forming a "lock-and-key effect" that strongly locks key rock blocks and stabilizes the overall surrounding rock. At the same time, the steel fibers improve the tensile and shear strength of the shotcrete, providing higher support resistance for the surrounding rock.

[0062] Specifically, after the initial shotcrete application, self-drilling anchor bolts 42 are driven in to quickly reinforce the surrounding rock, simultaneously ensuring the first arch support frame 11 is tightly attached to the rock. Subsequently, when the shotcrete reaches half the thickness of the first arch support frame 11, locking anchor bolts are driven in at the arch foot to support and fix the first arch support frame 11. Finally, shotcrete is applied again to the designed thickness to cover and protect the first arch support frame 11. For example, the upper stepped arch foot is equipped with 4 Φ32 self-drilling anchor bolts 42 and 2 Φ60 locking anchor pipes 44, while the lower stepped arch foot is equipped with 4 Φ32 self-drilling anchor bolts 42.

[0063] Optionally, the concrete used in the sprayed concrete is steel fiber concrete, which has higher strength and can form a strong lock on the surrounding rock, further improving the stability of the surrounding rock.

[0064] In step S530, the invert arch at the bottom of the tunnel is excavated, and a first invert arch support arch frame 114 is installed at the invert arch. The first invert arch support arch frame 114 is connected to the first main support arch frame 112 to form the first support arch frame 11. Thus, after the invert arch at the bottom of the tunnel is excavated, the first invert arch support arch frame 114 is installed at the invert arch, and then the first invert arch support arch frame 114 is connected to the first main support arch frame 112. The first invert arch support arch frame 114 and the second invert arch support arch frame form a closed loop to form the first support arch frame 11. Specifically, during the initial support construction of the invert arch, before installing the first invert arch support arch frame 114, it is necessary to clean the loose debris at the base of the invert arch and remove the accumulated water to ensure that the first invert arch support arch frame 114 and the first main support arch frame 112 are tightly fitted and welded to form an integral force system, restore the triaxial stress state of the surrounding rock, and facilitate the rapid stabilization of the surrounding rock.

[0065] In some embodiments, during the excavation of the tunnel bottom invert, the single excavation length of the invert is less than or equal to 3m. This controls the scale of single excavation of the invert, rationally controls the stress release ratio of the surrounding rock, reduces the amplitude of deviatoric stress, thereby controlling plastic failure of the surrounding rock and protecting its integrity and self-supporting capacity. Specifically, the tunnel main body is excavated using the micro-step method, with a step length of 2m-3m; during the excavation of the tunnel bottom invert, the single excavation length of the invert is less than or equal to 3m. This controls the scale of single excavation of the upper step, lower step, and invert, rationally controls the stress release ratio of the surrounding rock, reduces the amplitude of deviatoric stress, thereby controlling plastic failure of the surrounding rock and protecting its integrity and self-supporting capacity. Furthermore, the length of a single excavation of the invert is no greater than the spacing between three steel frames and is less than or equal to 3m.

[0066] In some embodiments, when the first invert arch support arch frame 114 and the first main support arch frame 112 are connected to form the first support arch frame 11, the distance between the end of the first support arch frame 11 near the working face and the working face is less than or equal to 20m. That is, the distance between the position where the first support arch frame 11 is closed into a ring and the working face is relatively close. This allows the first support arch frame 11 to be closed into a ring in a short time to form an overall force system, quickly restore the triaxial force state of the surrounding rock, and facilitate rapid stabilization of the surrounding rock.

[0067] In some embodiments, step S521 is included after step S510.

[0068] In step S521, in the area where the first main support arch 112 is located, prestressed anchor bolts 52 are installed and grouting is performed in the surrounding rock of the arch, and prestressed anchor bolts 52 and prestressed anchor cables 54 are installed and grouting is performed in the surrounding rock of the sidewall. The installation of prestressed anchor bolts 52 at the arch and sidewall provides rapid active support to the surrounding rock, and the additional installation of prestressed anchor bolts 52 at the sidewall further enhances the support resistance of the sidewall area, enabling the tunnel surrounding rock to withstand the effects of high horizontal stress, reducing deviatoric stress, and thus preventing plastic failure of the surrounding rock. Through the combined beam effect, the stability of the surrounding rock is protected, preventing excessive deformation or collapse and roof fall disasters, thus solving the difficulty of high ground stress in plateau tunnels. Optionally, the anchoring force of the prestressed anchor bolts 52 is ≥60KN, and the anchoring force of the prestressed anchor cables 54 is ≥200KN, which can provide strong support for the surrounding rock. Alternatively, the prestressed anchor bolts 52 and / or prestressed anchor cables 54 are installed immediately after the working face, which can provide active support resistance to the surrounding rock in a short time.

[0069] In one specific embodiment, the prestressed anchor bolts 52 are installed using an integrated anchor-injection machine, closely following the working face. The prestressed anchor bolts 52 in the arch are 4m long, and the prestressed anchor bolts 52 in the sidewalls are 4.5m long, spaced 1.2m × 0.6m apart. The integrated anchor-injection machine drills Φ42 holes (45mm diameter), cleans the holes with high-pressure air, ensuring a hole position deviation of ±150mm and perpendicularity to the initial support face. K3550 resin roll anchoring agent (3 rolls / hole, 150cm anchoring length) is pushed through a PE pipe, and the integrated anchor-injection machine pushes and mixes the anchor (speed ≥300r / min, 10-15s). The anchor bolt insertion is ≥95% of the design length, and the exposed length is ≤15cm. The prestressing application function of the integrated anchor-injection machine is used to apply prestress to the anchor bolts. The prestress tension is not less than 60KN; anchors with a tension less than 60KN need to be re-installed. Grouting should use cement grout with a water-cement ratio of 0.35 to 0.45 (pressure 0.6 to 0.8 MPa, grouting stops when grout comes out of the vent pipe).

[0070] In one specific embodiment, the prestressed anchor cables 54 are arranged at 1.5m x 1.5m intervals in the sidewall. They can be installed using resin anchoring agent (layout → drilling → anchoring agent installation → anchor cable mixing → fittings → tensioning → grouting) or cement grouting (layout → drilling → grouting → anchor cable installation → fittings → tensioning). When a second-layer arch frame is not required, they follow the working face; when a second-layer arch frame is required, they follow the lower step. Optionally, the prestressed anchor cable 54 is an unbonded steel strand "bird's nest" anchor cable (anchor section of 3.2m, free section of 4.8m, 3 "bird's nest" structures @ 50cm, strength 1860MPS, effective length 8m, material cut to 8.5m and passing inspection).

[0071] Furthermore, in order to quickly achieve the tensioning conditions and rapidly form a strong support, a resin anchoring process is adopted.

[0072] Drilling is carried out using a multi-arm drill or an integrated anchor-injection machine with a Φ42mm drill bit, resulting in a hole diameter of approximately 45mm and a depth of approximately 8m. Before drilling, the anchor cable locations are laid out according to design requirements and marked with red paint, avoiding locations at the initial steel arch support. After drilling, an 8.5m long Φ25 PVC pipe is connected to a high-pressure air duct to promptly blow away rock powder and accumulated water from the hole until no more rock powder returns to the hole opening. An 8.5m long PVC pipe is also used for exploratory drilling to check for any hole collapse, ensuring smooth and efficient subsequent procedures. The anchoring agent is pushed to the bottom of the hole sequentially using the PVC pipe, with the final length of the anchoring agent controlled to 3.0m, requiring the insertion of 6 sections of anchoring agent. Anchor cable installation utilizes the anchor delivery device of the integrated anchor-injection machine. After manually driving the anchor cable 2m into the hole, connect the anchor injection machine to the free end of the anchor cable using an anchor cable mixer. The anchor cable is then fed to the edge of the resin anchoring agent via a friction pulley on the mixer. The mixer's feeding and mixing function is then activated, with a mixing speed of at least 300 rpm, driving the anchor cable to rotate at high speed and pushing it into the resin anchoring agent. After thoroughly mixing the anchoring agent for approximately 30 seconds and allowing it to settle for 5 minutes, install the anchor plate and anchorage. Before installing the anchor plate, fill any uneven areas on the initial support surface with anchoring agent to ensure the plate adheres tightly to the surrounding rock surface for effective prestressing application. The anchor plate dimensions should be at least 200mm × 200mm, with a thickness of 20mm. Tension the anchor cable using an anchor cable tensioning machine. The designed tension force of the anchor cable should be at least 200kN. A pneumatic anchor cable tensioning machine should be used, and tensioning should be performed after the accessories are installed. Before the anchor cable is formally tensioned, apply 10%-20% of the design tension load and tension the anchor cable 1-2 times to ensure tight contact at all parts and complete straightness of the steel strands. Then, tension the cable in five stages: 0.25, 0.5, 0.75, 1.0, and 1.1 times the design load. After each load application, maintain stability for at least 10 minutes. If the relative displacement is less than 1 mm within 10 minutes, the cable is considered stable; otherwise, continue monitoring until the displacement is less than 1 mm.

[0073] After tensioning, grouting can be performed on the free section of the anchor cable. The grouting pipe 60 is a φ20mm diameter flexible hose, 0.7m in length. After inserting 0.5m of the grouting pipe 60 into the grouting hole in the pad, grouting is performed. During the process, air inside the hole can be vented out through the vent hole in the pad. The grouting material is prepared according to a water-cement ratio of 0.35-0.45, and the cement strength grade is not lower than 42.5. Grouting is performed using a grouting pump at a pressure of 0.5-1 MPa until thick grout flows out of the hole, completing the grouting operation.

[0074] In some embodiments, step S521 is followed by step S523.

[0075] In step S523, grouting is performed ring by ring along the sidewall using grouting pipes 60 from the tunnel face to the tunnel entrance. This completes the installation of prestressed anchor bolts 52 and prestressed anchor cables 54 in the surrounding rock. After the surrounding rock is strongly supported, grouting is performed ring by ring on the sidewall area, starting from the area closer to the tunnel face and moving towards the tunnel entrance. The grout penetrates into the surrounding rock, further cementing the broken surrounding rock in the sidewall area into a whole, which can slow down the deformation rate of the surrounding rock and improve its self-supporting capacity. In addition, the arch area is grouted through pre-support grouting, and the sidewall area is grouted through grouting pipes 60, forming grout layers in both the tunnel arch and sidewall areas. The grout layers in the sidewall and arch areas are connected, improving the long-term strength of the surrounding rock and thus maintaining the long-term operational stability of the tunnel.

[0076] Furthermore, sidewall grouting can be carried out 15m after the working face, after the sidewall area has been initially stabilized, to release the initial deformation of the sidewall area. The surrounding rock in the grouting sidewall area will experience less deformation stress and the structure will be more stable.

[0077] Specifically, the grouting pipe 60 uses a steel perforated pipe. During construction using an anchor bolt trolley or multi-arm drilling rig, a φ42mm drill bit is used to drill the hole before inserting the grouting pipe. The grouting pipe is a steel perforated pipe with an outer diameter of φ42mm and a wall thickness of 3.5mm. The grouting pipe should be firmly embedded and have good grout-stopping measures. The grouting material is cement grout with a reference water-cement ratio of 0.7:1 and a grouting pressure of 0.8 MPa. After the pipe is inserted, the gap between the pipe wall and the hole opening is sealed with cement anchoring agent to a depth of at least 10cm. A 10-minute waiting period is required after sealing. The grouting direction is from the working face towards the tunnel opening, proceeding ring by ring, with each ring proceeding from bottom to top at intervals (1, 3, 5 → 2, 4, 6). A weighing scale is set up on site, and the weighing is carried out according to the 0.7:1 mix ratio. The grouting material is a 0.7:1 (water:cement) cement slurry. A grout stop valve is installed at each steel pipe opening to stop the grouting. The grouting machine is required to be equipped with a pressure gauge to facilitate the control of grouting pressure during the grouting process. The grouting pressure value is 0.8 MPa. After reaching the design pressure, the pressure is stabilized for 5 minutes before the grouting can be stopped.

[0078] In some embodiments, step S530 is followed by step S540.

[0079] Step 540: Along the tunnel face towards the tunnel entrance, grouting is performed ring by ring using grouting pipes 60 at the invert arch. A first invert arch support frame 114 is installed at the invert arch, which is connected to the first main support frame 112 to form a closed ring and an integrated load-bearing system. After restoring the triaxial stress state of the surrounding rock, grouting is performed ring by ring in the invert arch area starting from the area closer to the tunnel face towards the tunnel entrance. The grout penetrates into the surrounding rock, firmly connecting the surrounding rock in the invert arch area into a whole, which can slow down the deformation rate of the surrounding rock and improve its self-supporting capacity. In addition, the arch area is grouted through advance support, the sidewall area is grouted through grouting pipes 60, and the invert arch area is grouted through grouting pipes 60, so that grouting layers are formed in the tunnel arch, sidewalls, and invert arch areas. This full-ring grouting of the tunnel forms a closed ring grouting layer, which greatly improves the integrity and uniaxial compressive strength of the surrounding rock, and enhances the surrounding rock's resistance to plastic failure and its stability.

[0080] Specifically, Φ42×3.5mm steel pipes were used for grouting reinforcement of the tunnel bottom. The holes were 3m deep and spaced 1.5m×1.5m apart. Drilling was carried out by a multi-arm drilling rig (on both sides and in the middle of the trestle) and a pneumatic drill (at a 45° angle at the bottom of the trestle). The holes were avoided from the position of the first invert arch support frame 114. High-pressure air was used to clean the holes. Grouting was carried out within 1 hour after the first support arch frame 11 was closed into a ring. The water-cement ratio was 0.7:1 and the pressure was 0.8MPS. Grouting was carried out ring by ring, measured with a weighing scale, and the grout was stopped by a grout stop valve. The pressure was stabilized for 5 minutes after reaching the target pressure. The parameters were recorded and any abnormalities were reported.

[0081] To address the aforementioned issue of mudslides and water inrushes that are prone to occur in high-altitude tunnels, please refer to... Figures 5-6 In some embodiments, step S100 is included before step S200.

[0082] Step S110: A grout-stopping wall 70 is erected at the tunnel face, and the grout-stopping wall 70 is connected and fixed to the surrounding rock around the tunnel face. Specifically, a 2m thick grout-stopping wall 70 is constructed. During construction, a steel mesh is installed at the tunnel face, and mortar anchors are connected to the outside of the steel mesh. The steel mesh is then connected and fixed to the surrounding rock through the mortar anchors, and covered with concrete to form a reinforced concrete grout-stopping wall 70. In this way, the grout-stopping wall 70 is fixedly connected to the surrounding rock around the tunnel face. The mortar anchors are 2m long and embedded 1.5m into the rock mass.

[0083] In step S130, grout is injected into the pre-designated grouting area M of the surrounding rock behind the grout stop wall 70. The outer contour of the pre-designated grouting area M is formed by expanding the tunnel excavation contour S by a pre-designated width. This is equivalent to the pre-designated grouting area M covering and extending beyond the tunnel excavation area. In this way, when the tunnel is subsequently excavated within the grouting-reinforced pre-designated grouting area M, the surrounding rock around the excavated tunnel has been reinforced by grouting, which can effectively protect the tunnel, prevent high-head groundwater from suddenly flowing into the tunnel, and prevent mudslides and water inrush disasters.

[0084] For example, the outer contour of the pre-designed grouting area M is 6m-8m wider than the tunnel excavation contour S. The longitudinal length of the pre-designed grouting area M is 30m, with a total of 87 holes. The opening diameter of the grouting holes is not less than 108mm, and the final diameter is not less than 91mm. The grouting holes are arranged radially in an umbrella shape, with a grout diffusion radius of 2m and a hole-to-bottom spacing of not more than 3m. The grouting sequence is "from outside to inside, from bottom to top, with intermittent skipping holes." Figure 6 The order of the Chinese and English letters indicates the grouting sequence. Grout the outer ring first to prevent subsequent grout leakage outside the designated grouting area, and grout evenly from bottom to top with staggered holes. Use cement grout with a water-cement ratio of 0.5-1.0, or a cement-water glass grout. During grouting, a segmented approach can be used: the first segment is 3m, and the others are 5-8m. The grouting pressure for the first segment is 0.5-1.0MPa, and for the others 4.0-6.0MPa, or the grouting pressure for each segment is the hydrostatic pressure of that segment plus 2.0MPa.

[0085] In some embodiments, this application provides a tunnel structure manufactured using the tunnel construction method described in any of the above embodiments.

[0086] If the deformation of the initial support layer 10 reaches the preset condition, a second support arch 32, forming a closed ring, is installed inside the initial support layer 10 to form a secondary support layer 30. If the deformation of the initial support layer 10 does not reach the preset condition, the second support arch 32 is not installed inside the initial support layer. In other words, after the initial support layer 10 is formed in the tunnel, the deformation of the initial support layer 10 is observed. If the initial support layer 10 does not reach the preset condition after a period of deformation, it means that the initial support layer 10 can still independently support the tunnel, and the second support arch 32 is not needed. If the initial support layer 10 reaches the preset condition after a period of deformation, it means that the deformation of the initial support layer 10 has reached its limit, and secondary support is required. In this case, the second support arch 32 is installed inside the initial support layer 10 to form the secondary support layer 30. In this way, an initial support layer 10 and a secondary support layer 30 are set in the tunnel section that requires secondary support, and an initial support layer 10 is set in the tunnel section with small deformation that does not require secondary support. The entire construction process does not require the secondary support layer 30 to be supported in all tunnel sections, which makes the tunnel support construction more efficient and economically better.

[0087] Furthermore, when supporting the secondary support layer 30, the stiffness of the first support arch 11 is greater than that of the second support arch 32. In other words, the stiffness of the second support arch 32 used in the secondary support is less than that of the first support arch 11, meaning the flexibility of the second support arch 32 is greater than that of the first support arch 11. This combination of variable stiffness double-layer support arches allows for initial support through the more rigid first support arch 11, followed by further support through the more flexible second support arch 32. The greater flexibility of the second support arch 32 enables it to provide support with a certain deformation capacity even when the initial support layer 10 experiences significant deformation. This allows it to better adapt to the deformation of the surrounding rock and the initial support layer 10, reducing the risk of breakage due to excessive stiffness failing to effectively adapt to the deformation. Therefore, by combining the first support arch 11 and the second support arch 32 with different stiffnesses, it is possible to adapt to the deformation of the surrounding rock and provide effective support.

[0088] Especially for high-stress fractured surrounding rock in plateau tunnels, the use of variable stiffness double-layer steel arch frames for tiered support, with a combination of rigid and flexible support, allows the double-layer support arch frames to adapt to a certain deformation of the surrounding rock. The surrounding rock itself can change relatively stably and can withstand a large load. After the deformation of the double-layer support arch frames stabilizes, the load it bears will not be too large, which is more conducive to the long-term use and long-term stability of the tunnel support structure. This can effectively cope with the dilemma of low self-bearing capacity of the surrounding rock and high ground stress caused by high horizontal tectonic stress and fractured rock mass in plateau tunnels, and prevent tunnel structure instability and collapse.

[0089] In some embodiments, this application provides a tunnel support structure 100, including an advance support component, an initial support layer, and a secondary support layer 30. The advance support component is located at the tunnel arch to provide early support for the tunnel arch and prevent the surrounding rock of the tunnel arch from collapsing after subsequent tunnel excavation. The initial support layer 10 includes a closed-loop first support arch frame 11, which supports the tunnel arch, sidewalls, and invert, providing support for the tunnel surrounding rock through the closed-loop first support arch frame 11 and forming an integral force-bearing system, restoring the triaxial force state of the surrounding rock, which is conducive to the rapid stabilization of the surrounding rock.

[0090] The secondary support layer 30 includes a closed-loop second support arch frame 32, which is fitted inside the initial support layer 10. The stiffness of the first support arch frame 11 is greater than that of the second support arch frame 32. In other words, the stiffness of the second support arch frame 32 used in the secondary support is less than that of the first support arch frame 11, meaning that the flexibility of the second support arch frame 32 is greater than that of the first support arch frame 11. This combination of variable stiffness double-layer support arch frames allows for initial support through the more rigid first support arch frame 11, followed by further support through the more flexible second support arch frame 32. The greater flexibility of the second support arch frame 32 enables it to provide support with a certain deformation capacity even when the initial support layer 10 undergoes significant deformation. This allows it to better adapt to the deformation of the surrounding rock and the initial support layer 10, and it is less likely to break due to excessive stiffness failing to effectively adapt to the deformation of the surrounding rock and the initial support layer 10. Therefore, by combining the first support arch 11 and the second support arch 32 with different stiffnesses, it is possible to adapt to the deformation of the surrounding rock and provide effective support.

[0091] Especially for high-stress fractured surrounding rock in plateau tunnels, a tiered support system using variable stiffness double-layer steel arches is employed. The double-layer support arches, initially rigid and then flexible, adapt to the deformation of the surrounding rock, allowing for relatively stable internal changes and enabling the rock to withstand significant loads. Once the double-layer support arches have stabilized after deformation, the load they bear will not be excessive, which is more conducive to the long-term use and stability of the tunnel support structure. This effectively addresses the predicament of low self-supporting capacity of the surrounding rock and high ground stress in plateau tunnels caused by high horizontal tectonic stress and fractured rock mass.

[0092] Optionally, the first arch support frame 11 is made of HW200 material, and the second arch support frame 32 is made of HW175 material. Furthermore, before erecting the steel arch frames, surveyors will mark the positioning points, and the steel arch frames will be installed using an arch frame assembly trolley. The steel arch frames are pre-assembled outside the tunnel and then moved to the erected frame position at the tunnel face using the arch frame assembly trolley, where the remaining steel arch frames are installed. The mechanical fabrication and installation of the steel arch frames facilitates quality control and rapid positioning, shortening the structural closure time.

[0093] Furthermore, the initial support layer 10 includes a first concrete layer, with a first support arch 11 embedded within it. The secondary support layer 30 includes a second concrete layer, with a second support arch 32 embedded within it, and a second retarded concrete layer bonded to the first concrete layer. Thus, the hybrid structure of the first concrete layer and the first support arch 11 forms the initial support layer 10, and the hybrid structure of the second concrete layer and the second support arch 32 forms the secondary support layer 30. Furthermore, the first and second concrete layers are interlocked and bonded during spraying, resulting in a final double-layered support layer that is interconnected and fused into a single unit, leading to a more stable support effect.

[0094] Optionally, the first concrete layer includes steel fiber reinforced concrete, which has high compressive strength and improves the ability and stability of the surrounding rock to resist plastic failure; alternatively, the second concrete layer includes steel fiber reinforced concrete, which has high compressive strength and further improves the ability and stability of the surrounding rock to resist plastic failure.

[0095] In some embodiments, the tunnel support structure 100 further includes a self-drilling anchor bolt 42 and a locking anchor pipe 44. Both the self-drilling anchor bolt 42 and the locking anchor pipe 44 are connected to the first support arch frame 11 and drilled into the surrounding rock corresponding to the first support arch frame 11. The self-drilling anchor bolt 42 reinforces the surrounding rock and pulls the first support arch frame 11 and the surrounding rock corresponding to the first support arch frame 11 to fit together. The locking anchor bolt supports the first support arch frame 11.

[0096] In other words, after the main tunnel body is excavated, initial shotcrete is promptly applied to the arch and sidewalls of the tunnel body to cover and stabilize the surrounding rock excavation face. After the initial shotcrete stabilizes the surrounding rock excavation face, self-drilling anchor bolts 42 can be quickly driven into the surrounding rock. Grouting occurs simultaneously with the driving of the self-drilling anchor bolts 42, rapidly reinforcing the fractured surrounding rock. Furthermore, the self-drilling anchor bolts 42 are connected to the first support arch frame 11, pulling the first support arch frame 11 into contact with the surrounding rock, providing effective support force. Additionally, locking anchor bolts can be driven into the surrounding rock, connected to the first support arch frame 11, to support and fix the arch foot of the first support arch frame 11. Optionally, steel fiber reinforced concrete is used for the initial shotcrete application, as it has higher strength and can form a strong lock on the surrounding rock, further improving the stability of the surrounding rock. Specifically, after the main tunnel is excavated, steel fiber reinforced concrete is used in the initial shotcrete application. This seals the surrounding rock immediately after excavation, forming a "lock-and-key effect" that strongly locks key rock blocks and stabilizes the overall surrounding rock. At the same time, the steel fibers improve the tensile and shear strength of the shotcrete, providing higher support resistance for the surrounding rock.

[0097] Specifically, after the initial shotcrete application, self-drilling anchor bolts 42 are driven in to quickly reinforce the surrounding rock, simultaneously ensuring the first arch support frame 11 is tightly attached to the rock. Subsequently, when the shotcrete reaches half the thickness of the first arch support frame 11, locking anchor bolts are driven in at the arch foot to support and fix the first arch support frame 11. Finally, shotcrete is applied again to the designed thickness to cover and protect the first arch support frame 11. For example, the upper stepped arch foot is equipped with 4 Φ32 self-drilling anchor bolts 42 and 2 Φ60 locking anchor pipes 44, while the lower stepped arch foot is equipped with 4 Φ32 self-drilling anchor bolts 42.

[0098] Optionally, the concrete used in the sprayed concrete is steel fiber concrete, which has higher strength and can form a strong lock on the surrounding rock, further improving the stability of the surrounding rock.

[0099] In some embodiments, the tunnel support structure 100 further includes an anchoring assembly, which includes prestressed anchor rods 52. The prestressed anchor rods 52 are located in the tunnel arch and sidewall regions, and are grouted to anchor the surrounding rock in the arch and sidewall regions. Thus, drilling prestressed anchor rods 52 into the tunnel arch and sidewalls provides rapid active support to the surrounding rock, reduces deviatoric stress, and prevents plastic failure of the surrounding rock. Optionally, the anchoring force of the prestressed anchor rods 52 is ≥60KN, providing strong support to the surrounding rock.

[0100] In one specific embodiment, the prestressed anchor rods 52 in the arch are 4m long, and the prestressed anchor rods 52 in the sidewalls are 4.5m long, spaced 1.2m × 0.6m apart. A Φ42 hole (45mm diameter) is drilled using an integrated anchoring and grouting machine, with high-pressure air cleaning. The hole position deviation is ±150mm and the anchors are perpendicular to the initial support surface. K3550 resin roll anchoring agent (3 rolls / hole, 150cm anchoring length) is pushed through a PE pipe. The integrated anchoring and grouting machine pushes and mixes the anchors (speed ≥300r / min, 10-15s). The anchor rod insertion is ≥95% of the design length, and the exposed length is ≤15cm. The prestressing is applied to the anchor rods using the prestressing application function of the integrated anchoring and grouting machine. The prestressing tension is not less than 60KN; anchors with a tension less than 60KN need to be re-installed. Cement grout with a water-cement ratio of 0.35~0.45 is used for grouting (pressure 0.6~0.8MPS, grouting stops when grout exits the vent pipe).

[0101] Furthermore, the anchoring assembly also includes prestressed anchor cables 54, which are installed in the sidewall area. The prestressed anchor cables 54 are grouted to anchor the surrounding rock in the sidewall area, and the anchoring force of the prestressed anchor cables 54 is greater than that of the prestressed anchor rods 52. Thus, drilling prestressed anchor rods 52 into the arch and sidewalls provides rapid active support to the surrounding rock, and additionally drilling prestressed anchor cables 54 into the sidewalls further enhances the support resistance in the sidewall area. This allows the tunnel surrounding rock to withstand the effects of high horizontal stress, reduce deviatoric stress, and prevent plastic failure of the surrounding rock. Through the combined beam effect, it protects the stability of the surrounding rock, preventing excessive deformation, collapse, or roof fall disasters, thus solving the challenge of high ground stress in plateau tunnels. Optionally, the anchoring force of the prestressed anchor cables 54 is ≥200KN, providing strong support for the surrounding rock.

[0102] In one specific embodiment, the prestressed anchor cables 54 of the sidewall are arranged at 1.5m × 1.5m intervals. They can be installed using resin anchoring agent (layout → drilling → anchoring agent installation → anchor cable mixing → fitting → tensioning → grouting) or cement one-time grouting (layout → drilling → grouting → anchor cable installation → fitting → tensioning). When a second-layer arch frame is not required, they follow the working face; when a second-layer arch frame is required, they follow the lower step. Optionally, the prestressed anchor cables 54 are unbonded steel strand bird's nest anchor cables (anchor section of 3.2m, free section of 4.8m, 3 bird's nest structures @ 50cm, strength 1860MPS, effective length 8m, material cut of 8.5m and passing inspection).

[0103] In some embodiments, the advanced support component includes a central pipe roof and multiple small guide pipes. The central pipe roof includes multiple steel pipes arranged circumferentially along the arch, and the small guide pipes are located between two adjacent steel pipes. The central pipe roof and the small guide pipes grout the surrounding rock of the arch to form a first grouting semi-ring layer.

[0104] In other words, multiple steel pipes and multiple small guide pipes are interspersed in the tunnel arch. The central pipe shed formed by multiple steel pipes provides large-scale, high-strength rigid support. The small guide pipes are driven into the gaps between adjacent steel pipes and grout is injected. The grout penetrates into the surrounding rock and soil, cementing it into a whole. In this way, the discrete "pipe shed beams" are transformed into a continuous "reinforced arch", providing high-strength advance support and meeting the advance support needs of terrains with widespread high ground stress distribution in plateau areas.

[0105] Specifically, Φ60 steel pipes are used in the central pipe shed, with a single pipe length of 6m-9m, totaling 43 pipes per cycle, with a circumferential spacing of 0.3m and a longitudinal spacing of 6.0m. Φ42 small guide pipes, each 3.5m long, are inserted between adjacent steel pipes, with a total of 43 small guide pipes per cycle, also with a circumferential spacing of 0.3m and a longitudinal spacing of 3.5m. In one specific embodiment, before drilling, surveyors mark the locations with paint. The leading small guide pipes are drilled using a rock drilling rig with an external insertion angle of 10°–15°; the leading central pipe shed is drilled using a three-arm rock drilling rig with an external insertion angle of 10°. The bottom of the drilling rig must be flat and stable. Before the central pipe shed and small guide pipes are installed, the working face is sealed with 5cm thick shotcrete. The central pipe shed and small guide pipes are manufactured by a CNC intelligent machining center and inserted using a multi-arm drilling rig. After installation, the gaps at the borehole openings are sealed with plastic putty to prevent grout leakage. Before grouting the central pipe shed and small pipe shed, the steel pipes were labeled and statistically analyzed. The water-cement ratio of the grout for the Φ60 central pipe shed was 0.7:1, and the grouting pressure was 0.8~1MpS; the water-cement ratio of the grout for the Φ42 small pipe shed was 0.7:1, and the grouting pressure was 0.8~1MpS.

[0106] In some embodiments, the tunnel support structure 100 also includes grouting pipes 60, which are located at the sidewalls and inverts to inject grout into the surrounding rock at the sidewalls and inverts to form a second grouting semi-ring layer. The first and second grouting semi-ring layers are interconnected and closed into a ring. Thus, after the installation of prestressed anchor bolts 52 and prestressed anchor cables 54 is completed in the surrounding rock, and the surrounding rock is strongly supported, grouting is performed ring by ring from the area closer to the tunnel face towards the tunnel entrance, stabilizing and connecting the dispersed surrounding rock in the sidewall and invert areas into a whole through the grout penetrating into the surrounding rock. This can slow down the deformation rate of the surrounding rock and improve its self-supporting capacity.

[0107] In addition, the arch area is grouted with pre-support grouting to form a first grouting semi-ring layer, while the sidewall and invert arch areas are grouted with grouting pipe 60 to form a second grouting semi-ring layer. The first and second grouting semi-ring layers are interconnected and form a closed ring, which is equivalent to grouting the entire tunnel ring, forming a closed ring grouting layer. This greatly improves the integrity and uniaxial compressive strength of the surrounding rock, and enhances the surrounding rock's resistance to plastic failure and its stability. Optionally, the grouting pipe 60 is a steel perforated pipe.

[0108] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0109] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A tunnel support structure, characterized in that, include: Advanced support components are installed in the arch of the tunnel; The initial support layer includes a first support arch frame that is closed into a ring and supports the arch, sidewalls and invert of the tunnel. The secondary support layer includes a second support arch frame that is closed into a ring, and the second support arch frame is fitted inside the initial support layer; The stiffness of the first support arch is greater than that of the second support arch.

2. The tunnel support structure according to claim 1, characterized in that, The initial support layer includes a first concrete layer, and the first support arch is embedded in the first concrete layer. The secondary support layer includes a second concrete layer, and the second support arch is embedded in the second concrete layer, and the second concrete layer is bonded to the first concrete layer.

3. The tunnel support structure according to claim 2, characterized in that, The tunnel support structure also includes self-drilling anchor bolts and locking anchor pipes. Both the self-drilling anchor bolts and the locking anchor pipes are connected to the first support arch and drilled into the surrounding rock corresponding to the first support arch. The self-drilling anchor bolts reinforce the surrounding rock and pull the first support arch and the surrounding rock corresponding to the first support arch into contact. The locking anchor pipes support the first support arch.

4. The tunnel support structure according to claim 3, characterized in that, The tunnel support structure also includes an anchoring assembly, which includes a prestressed anchor rod. The prestressed anchor rod is located in the arch and sidewall areas of the tunnel, and the prestressed anchor rod is grouted to anchor the surrounding rock in the arch and sidewall areas.

5. The tunnel support structure according to claim 4, characterized in that, The anchoring assembly includes a prestressed anchor cable, which is disposed in the sidewall area. The prestressed anchor cable is grouted to anchor the surrounding rock in the sidewall area, and the anchoring force of the prestressed anchor cable is greater than the anchoring force of the prestressed anchor rod.

6. The tunnel support structure according to claim 5, characterized in that, The anchoring force of the prestressed anchor rod is ≥60KN, and the anchoring force of the prestressed anchor cable is ≥200KN.

7. The tunnel support structure according to any one of claims 2-6, characterized in that, The advanced support assembly includes a central pipe roof and multiple small guide pipes. The central pipe roof includes multiple steel pipes arranged at intervals along the circumference of the arch. The small guide pipes are located between two adjacent steel pipes. The central pipe roof and the small guide pipes grout the surrounding rock of the arch to form a first grouting semi-ring layer.

8. The tunnel support structure according to claim 7, characterized in that, The tunnel support structure also includes grouting pipes, which are located at the sidewalls and the invert arch to inject grout into the surrounding rock at the sidewalls and the invert arch to form a second grouting semi-ring layer. The first grouting semi-ring layer and the second grouting semi-ring layer are connected to each other and closed into a ring.

9. The tunnel support structure according to any one of claims 2-6, characterized in that, The first concrete layer comprises steel fiber reinforced concrete, and / or the second concrete layer comprises steel fiber reinforced concrete.

10. The tunnel support structure according to any one of claims 1-6, characterized in that, The material of the first support arch is HW200, and the material of the second support arch is HW175.

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