Steel frame interlocking composite support structure and construction method for small-spacing tunnel in complex geology

Abstract

The application discloses a complex geology small-pitch tunnel steel frame interlocking type composite supporting structure and a construction method, wherein the interlocking type composite supporting structure comprises initial supporting units arranged in left-hole tunnels and right-hole tunnels and a cross connection unit connecting the initial supporting units of the two tunnels; the cross connection unit comprises at least two groups of interlocking type connection assemblies, each group of the interlocking type connection assemblies is used for connecting the oppositely arranged initial supporting units in the left-hole tunnels and the right-hole tunnels; the interlocking type connection assembly comprises a transverse connecting rod, a left lock buckle mechanism and a right lock buckle mechanism, one end of the transverse connecting rod is connected with a steel frame of the left-hole tunnel through the left lock buckle mechanism, and the other end of the transverse connecting rod is connected with a steel frame of the right-hole tunnel through the right lock buckle mechanism. The steel frames of the left-hole tunnels and the right-hole tunnels are rigidly connected into a whole through the interlocking type connection assemblies by arranging the cross connection unit, and the overall rigidity and stability of the supporting system are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of engineering protection technology, specifically relating to an interlocking composite support structure and construction method for steel frames in tunnels with small clearances in complex geological conditions. Background Technology

[0002] Under complex geological conditions, the construction of tunnels with small clearances faces numerous challenges. Due to the small clearance between tunnels, the excavation of the two chambers significantly affects each other, which can easily lead to risks such as instability of the surrounding rock, excessive deformation of the tunnel structure, or even collapse.

[0003] Traditional tunnel support structures often struggle to effectively control complex stress environments and deformation characteristics, especially in challenging geological conditions such as weak, fractured surrounding rock, high ground stress, and water-rich strata. Single support methods, such as shotcrete, rock bolts, or steel frames, have limited overall stiffness and synergistic load-bearing capacity, making it difficult to form a robust support system to resist the deformation and pressure of the surrounding rock. Furthermore, the connection methods between the steel frame and the surrounding rock, and between the steel frame and itself, in existing support structures are not optimized, leading to unclear load transfer paths. This affects the overall stability and load-bearing capacity of the support structure, making it difficult to reliably guarantee construction safety and project quality. Therefore, developing a composite support structure and corresponding construction methods that can adapt to the characteristics of tunnels with small clearances in complex geological conditions, possessing high stiffness, strong synergy, and good load-bearing performance, has become an urgent technical problem to be solved in the field of tunnel engineering. Summary of the Invention

[0004] The present invention aims to solve the above problems. By setting a mid-span connection unit, the steel frames of the left tunnel and the right tunnel are rigidly connected into one body through interlocking connection components, so that the support structures of the two tunnels can jointly bear the surrounding rock pressure and deformation, which significantly improves the overall stiffness and stability of the support system.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The steel frame interlocking composite support structure for tunnels with small clearance in complex geology includes initial support units set in the left and right tunnels, as well as a mid-span connection unit connecting the initial support units of the two tunnels. The mid-span connection unit includes at least two sets of interlocking connection components. Each set of interlocking connection components corresponds to the initial support units set opposite to each other in the left tunnel and the right tunnel. Each set of interlocking connection components includes a transverse connecting rod, a left locking mechanism, and a right locking mechanism. One end of the transverse connecting rod is interlocked with the steel frame of the left tunnel through the left locking mechanism, and the other end is interlocked with the steel frame of the right tunnel through the right locking mechanism.

[0006] Furthermore, both the left and right locking mechanisms include a lock seat fixed to the web of the steel frame, a U-shaped lock groove formed on the lock seat, and a locking pin that cooperates with the U-shaped lock groove. The end of the transverse connecting rod is provided with a connecting ear plate that is adapted to the U-shaped lock groove. After the connecting ear plate is inserted into the U-shaped lock groove, it is locked by the locking pin.

[0007] Furthermore, the initial support units are arranged at intervals along the longitudinal direction of the tunnel. Each initial support unit includes a steel frame, a shotcrete layer, system anchors, and locking anchors. The steel frame is set close to the tunnel excavation outline, and the shotcrete layer is sprayed on its outer side.

[0008] Furthermore, the system anchor bolts are inserted into the surrounding rock at intervals along the circumferential direction of the steel frame, and their ends are fixedly connected to the steel frame.

[0009] Furthermore, the anchor bolt is installed at the arch foot of the steel frame and is obliquely embedded into the surrounding rock.

[0010] Furthermore, the lock seat is fixed to the center of the web of the steel frame by welding steel plate.

[0011] Furthermore, the transverse connecting rod comprises multiple connecting rod sections spliced ​​together sequentially. Each connecting rod section is made of low-alloy high-strength structural steel, and the sections are connected by flanges and high-strength bolts. Rubber sealing gaskets are provided between the flanges to accommodate slight longitudinal deformation of the tunnel and ensure tightness of the connection.

[0012] This invention also discloses a construction method using the above-mentioned steel frame interlocking composite support structure, the specific technical solution of which is as follows: The construction method of steel frame interlocking composite support structure for tunnels with small clearance in complex geological conditions includes the following steps: S1. Tunnel Excavation and Outline Finishing: The left and right tunnels are excavated in stages according to the designed excavation plan. After the excavation is completed, the tunnel outline is finished in a timely manner to ensure that the installation base of the steel frame is flat.

[0013] S2. Construction of the initial support unit: S2.1 Installation of steel frame: According to the design spacing, the steel frame is erected close to the tunnel excavation outline. The axis, elevation and mileage of the steel frame are ensured to be accurate by measurement and positioning. Adjacent steel frames are firmly connected by bolts. S2.2 Construction of anchor bolts: At the arch foot of the steel frame, anchor bolts are inserted obliquely according to the design angle and depth. The ends of the anchor bolts are welded and fixed to the steel frame to enhance the overturning resistance of the steel frame. S2.3 System Anchor Bolt Construction: Drill holes at intervals along the circumferential direction of the steel frame, insert system anchor bolts, and fix the ends of the anchor bolts to the steel frame with nuts or welding to form an integral load-bearing structure with the steel frame; S2.4 Shotcrete layer construction: Shotcrete is sprayed on the outside of the steel frame and the surface of the surrounding rock until the designed thickness is reached to form a shotcrete layer, which tightly binds the steel frame, system anchors and surrounding rock.

[0014] S3. Installation of mid-span connecting unit: After the initial support units of the left and right tunnels are completed and the shotcrete layer reaches the design strength, the mid-span connecting unit is installed.

[0015] S3.1 Lock seat installation: Fix the lock seats of the left and right locking mechanisms to the web plates of the steel frame that are set opposite to each other in the left and right tunnels, respectively, to ensure that the U-shaped lock groove openings of the lock seats are in the same direction and at the same horizontal height; S3.2, Positioning of the transverse connecting rod: Select a suitable number of connecting rod segments to splice them into a transverse connecting rod, and insert the connecting lugs at both ends of the transverse connecting rod into the U-shaped lock grooves of the left lock seat and the right lock seat respectively; S3.3 Locking pin: Pass the locking pin through the pin hole of the lock seat and the connecting ear plate to complete the detachable interlocking connection between the transverse connecting rod and the steel frame. Install at least two sets of interlocking connection components according to design requirements.

[0016] S4. Monitoring, Measurement and Adjustment: During and after construction, real-time monitoring and measurement of tunnel surrounding rock deformation and support structure stress are carried out. Based on the monitoring data, support parameters are adjusted in a timely manner or the mid-span connection unit is reinforced to ensure the safety and stability of the support structure.

[0017] Furthermore, in step S1, the tunnel excavation adopts micro-vibration controlled blasting or mechanical excavation, strictly controls the excavation cycle advance, and maintains a certain safe distance between the excavation faces of the left tunnel and the right tunnel to avoid excessive disturbance to the middle rock pillar caused by the simultaneous excavation of the two tunnels.

[0018] Furthermore, in step S1, during contour trimming, manual labor combined with machinery is used to remove dangerous rocks and loose surrounding rock, so that the tunnel excavation contour line meets the design requirements, and initial spraying is carried out to provide conditions for the precise installation of the steel frame.

[0019] Compared with the prior art, the advantages of the present invention are: the present invention has a simple structure and is easy to implement. By setting a mid-span connection unit between the initial support units of the left tunnel and the right tunnel, and using interlocking connection components to rigidly connect the steel frames of the two tunnels, a composite support system with overall stress is formed, which effectively improves the overall stiffness and cooperative stress performance of the support structure of tunnels with small clearance.

[0020] Meanwhile, the transverse connecting rod is made of multiple sections of low-alloy high-strength structural steel rods spliced ​​together and connected by flanges and high-strength bolts. The rubber sealing gaskets between the flanges not only ensure the tightness of the connection, but also adapt to the slight longitudinal deformation of the tunnel, further enhancing the stability and adaptability of the support structure.

[0021] Furthermore, in the initial support unit, the synergistic effect of the steel frame, shotcrete layer, system anchors, and locking anchors fully leverages their respective advantages. The shotcrete layer tightly integrates the steel frame, system anchors, and surrounding rock. The system anchors are inserted into the surrounding rock at circumferential intervals and fixed to the steel frame, effectively restraining the deformation of the surrounding rock. The locking anchors are obliquely inserted into the surrounding rock at the arch foot, significantly enhancing the overturning resistance of the steel frame. Together, they provide strong support for the tunnel surrounding rock. This composite support structure can well adapt to the stress environment and deformation characteristics of tunnels with small clearances under complex geological conditions. Especially in adverse geological sections such as weak and fractured surrounding rock, high ground stress, and water-rich strata, it can effectively control the instability of the surrounding rock and the deformation of the tunnel structure, reducing the risk of collapse. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the interlocking composite support structure of steel frame for tunnels with small clearance in complex geological conditions, provided by the present invention.

[0024] Figure 2 This is a schematic diagram of the transverse connecting rod of the interlocking composite support structure of steel frame for tunnels with small clearance in complex geological conditions provided by the present invention.

[0025] Figure label: 1. Left tunnel; 2. Right tunnel; 3. Initial support unit; 4. Lateral connecting rod; 5. Lock seat; 6. Locking pin; 7. Flange; 8. Connecting ear plate; 9. Locking foot anchor. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0028] In the description of this invention, it should be noted that if terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed, they are only for the convenience of describing this invention 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 invention.

[0029] Furthermore, the terms "first," "second," and "third" are used only for distinguishing descriptions and should not be interpreted as indicating or implying relative importance.

[0030] Furthermore, the use of terms such as "horizontal," "vertical," and "suspended" does not imply that the component must be absolutely horizontal or suspended, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0031] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; 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; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0032] It should be noted that, where there is no conflict, the features in the embodiments of the present invention can be combined with each other.

[0033] like Figures 1-2As shown, the steel frame interlocking composite support structure for a tunnel with small clearance in complex geology includes an initial support unit 3 installed in the left tunnel 1 and the right tunnel 2, and a mid-span connecting unit connecting the two initial support units 3. The mid-span connection unit includes at least two sets of interlocking connection components. Each set of interlocking connection components connects the initial support units 3 that are set opposite to each other in the left tunnel 1 and the right tunnel 2. Each set of interlocking connection components includes a transverse connecting rod 4, a left locking mechanism and a right locking mechanism. One end of the transverse connecting rod 4 is interlocked with the steel frame of the left tunnel 1 through the left locking mechanism, and the other end is interlocked with the steel frame of the right tunnel 2 through the right locking mechanism.

[0034] Compared to existing technologies, traditional small-clearance tunnel support structures often focus only on the support design within a single tunnel. The support systems of each chamber are relatively independent, lacking effective lateral connection measures. This makes it difficult for the two tunnels to form a unified load-bearing structure during excavation and operation. The intermediate rock column is prone to stress concentration and excessive deformation due to mutual disturbance between the two tunnels. Furthermore, the connection methods between the steel frame and the surrounding rock in existing support structures, as well as the connection strength between the steel frames, are insufficient. For example, some support structures use simple welding or bolt connections, resulting in weak collaborative load-bearing performance. Under complex geological conditions, this can easily lead to localized failure of the support structure, thereby increasing the risk of overall instability.

[0035] This invention, by setting a mid-span connecting unit, rigidly connects the steel frames of the left and right tunnels into a single unit through interlocking connection components. This breaks the limitations of traditional single-tunnel independent support, allowing the support structures of both tunnels to share the pressure and deformation of the surrounding rock, significantly improving the overall rigidity and stability of the support system. Simultaneously, the design of the interlocking connection components, such as the locking seat 5, U-shaped locking groove, connecting ear plate 8, and locking pin 6, enables a quick and reliable connection between the transverse connecting rod 4 and the steel frame. This not only facilitates installation but also ensures effective load transfer, avoiding the loosening or uneven stress problems that may occur in traditional connection methods. The transverse connecting rod 4, constructed from multiple sections of low-alloy high-strength structural steel and equipped with rubber sealing gaskets, further optimizes the adaptability and durability of the support structure, enabling it to better cope with various challenges under complex geological conditions.

[0036] Specifically, in this invention, both the left and right locking mechanisms include a lock seat 5 fixed to the web of the steel frame, a U-shaped lock groove opened on the lock seat 5, and a locking pin 6 that cooperates with the U-shaped lock groove. The end of the transverse connecting rod 4 is provided with a connecting ear plate 8 that is adapted to the U-shaped lock groove. After the connecting ear plate 8 is inserted into the U-shaped lock groove, it is locked by the locking pin 6.

[0037] The initial support units 3 are arranged at intervals along the longitudinal direction of the tunnel. Each initial support unit 3 includes a steel frame, a shotcrete layer, system anchors and locking anchors 9. The steel frame is set close to the tunnel excavation outline and is sprayed with a shotcrete layer on its outer side.

[0038] The system anchor bolts are inserted into the surrounding rock at intervals along the circumferential direction of the steel frame, and their ends are fixedly connected to the steel frame.

[0039] The anchor bolt 9 is installed at the arch foot of the steel frame and is inserted obliquely into the surrounding rock.

[0040] The lock seat 5 is fixed to the center of the web of the steel frame by welding steel plates. The transverse connecting rod 4 consists of multiple connecting rods spliced ​​together in sequence. Each connecting rod is made of low alloy high strength structural steel, and the rods are connected by flanges 7 and high-strength bolts. Rubber sealing gaskets are provided between the flanges 7 to accommodate slight longitudinal deformation of the tunnel and ensure tightness of the connection.

[0041] In practical use, the left tunnel 1 and the right tunnel 2 are first excavated in stages according to the designed excavation plan. Micro-vibration controlled blasting or mechanical excavation is adopted, and the excavation cycle advance is strictly controlled. At the same time, it is ensured that the excavation working faces of the left tunnel 1 and the right tunnel 2 maintain a certain safe distance to avoid excessive disturbance to the middle rock pillar caused by the simultaneous excavation of the two tunnels.

[0042] After excavation, the initial support unit 3 is constructed. Steel frames are erected close to the tunnel excavation outline according to the designed spacing. Measurements are used to ensure the accuracy of the steel frame's axis, elevation, and mileage. Adjacent steel frames are securely connected with bolts. Then, at the arch foot of the steel frame, anchor bolts 9 are obliquely inserted at the designed angle and depth. The ends of the anchor bolts are welded to the steel frame to enhance its overturning resistance. Next, holes are drilled circumferentially along the steel frame, and system anchor bolts are inserted. The ends of the anchor bolts are fixed to the steel frame with nuts or by welding, forming an integral load-bearing structure. Finally, shotcrete is sprayed onto the outside of the steel frame and the surrounding rock surface until the designed thickness is reached, forming a shotcrete layer that tightly binds the steel frame, system anchor bolts, and surrounding rock.

[0043] After the initial support unit 3 is completed and the shotcrete layer reaches the design strength, the mid-span connection unit is installed. First, the locking seats 5 of the left and right locking mechanisms are fixed at the center of the web of the steel frame opposite to each other in the left tunnel 1 and the right tunnel 2, respectively, to ensure that the U-shaped locking groove openings of the locking seats 5 are in the same direction and at the same horizontal height. Then, a suitable number of low-alloy high-strength structural steel connecting rods are selected and spliced ​​into transverse connecting rods 4 by flanges 7 and high-strength bolts. Rubber sealing gaskets are placed between the flanges 7. Then, the connecting ear plates 8 at both ends of the transverse connecting rods 4 are inserted into the U-shaped locking grooves of the left and right locking seats 5, respectively. Finally, the locking pins 6 are passed through the pin holes of the locking seats 5 and the connecting ear plates 8 to complete the detachable interlocking connection between the transverse connecting rods 4 and the steel frame. At least two sets of interlocking connection components are installed according to the design requirements.

[0044] Throughout the construction process and after completion, the deformation of the surrounding rock and the stress of the support structure are monitored and measured in real time. Based on the monitoring data, the support parameters are adjusted in a timely manner or the mid-span connection unit is reinforced to ensure the safety and stability of the support structure.

[0045] This invention also provides a construction method for the steel frame interlocking composite support structure for tunnels with small clearance in complex geological conditions, comprising the following steps: S1. Tunnel Excavation and Outline Trimming: The left tunnel 1 and right tunnel 2 are excavated in stages according to the designed excavation plan. After the excavation is completed, the tunnel outline is trimmed in a timely manner to ensure that the installation base of the steel frame is flat. S2, Construction of Initial Support Unit 3: S2.1 Installation of steel frame: According to the design spacing, the steel frame is erected close to the tunnel excavation outline. The axis, elevation and mileage of the steel frame are ensured to be accurate by measurement and positioning. Adjacent steel frames are firmly connected by bolts. S2.2 Construction of anchor bolt 9: At the arch foot of the steel frame, anchor bolt 9 is inserted obliquely according to the design angle and depth. The end of the anchor bolt is welded and fixed to the steel frame to enhance the overturning resistance of the steel frame. S2.3 System Anchor Bolt Construction: Drill holes at intervals along the circumferential direction of the steel frame, insert system anchor bolts, and fix the ends of the anchor bolts to the steel frame with nuts or welding to form an integral load-bearing structure with the steel frame; S2.4 Shotcrete layer construction: Shotcrete is sprayed on the outside of the steel frame and the surface of the surrounding rock until the designed thickness is reached to form a shotcrete layer, which tightly binds the steel frame, system anchors and surrounding rock.

[0046] S3. Installation of mid-span connection unit: After the initial support unit 3 of the left tunnel 1 and the right tunnel 2 is completed and the shotcrete layer reaches the design strength, the mid-span connection unit is installed.

[0047] S3.1 Installation of lock seat 5: Fix the lock seat 5 of the left locking mechanism and the right locking mechanism to the web of the steel frame that are set opposite to each other in the left tunnel 1 and the right tunnel 2 respectively, to ensure that the U-shaped lock groove opening direction of the lock seat 5 is consistent and at the same horizontal height; S3.2, Positioning of transverse connecting rod 4: Select a suitable number of connecting rod segments to splice together to form transverse connecting rod 4, and insert the connecting ear plates 8 at both ends of transverse connecting rod 4 into the U-shaped lock grooves of the left lock seat 5 and the right lock seat 5 respectively; S3.3 Locking pin 6: Lock pin 6 passes through the pin hole of lock seat 5 and connecting ear plate 8 to complete the detachable interlocking connection between transverse connecting rod 4 and steel frame. Install at least two sets of interlocking connection components according to design requirements.

[0048] S4. Monitoring, Measurement and Adjustment: During and after construction, real-time monitoring and measurement of tunnel surrounding rock deformation and support structure stress are carried out. Based on the monitoring data, support parameters are adjusted in a timely manner or the mid-span connection unit is reinforced to ensure the safety and stability of the support structure.

[0049] The construction method of this invention, through step-by-step implementation and close coordination of each process, ensures the construction quality and overall load-bearing performance of the support structure. During the tunnel excavation stage, strict control over the excavation method and cyclic advance, while maintaining a safe distance between the left and right working faces, effectively reduces disturbance to the intermediate rock pillar; contour trimming lays the foundation for the subsequent precise installation of the steel frame. In the initial support unit 3 construction, the accurate positioning of the steel frame, the stable installation of the anchor bolts 9, the circumferential arrangement of the system anchor bolts, and the timely application of the shotcrete layer form the first solid line of defense against the tunnel surrounding rock, fully leveraging the synergistic effect of each support component. The installation of the mid-span connecting unit is the key step in connecting the left and right tunnel support structures into a whole. The precise fixing of the locking seat 5, the reliable splicing of the transverse connecting rod 4, and the effective locking of the locking pin 6 ensure the effective transmission of force between the two tunnels, significantly improving the stability and deformation resistance of the entire support system. Finally, by monitoring and measuring the entire process and making dynamic adjustments based on the data, the safety and reliability of the support structure under complex geological conditions were further ensured, providing an efficient, safe, and economical solution for the construction of tunnels with small clearances in complex geological conditions.

[0050] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A steel frame interlocking composite support structure for tunnels with small clearances in complex geological conditions, characterized in that: It includes initial support units (3) installed in the left tunnel (1) and the right tunnel (2), as well as mid-span connecting units that connect the initial support units (3) of the two tunnels; The mid-span connection unit includes at least two sets of interlocking connection components. Each set of interlocking connection components corresponds to the initial support units (3) set opposite to each other in the left tunnel (1) and the right tunnel (2). Each set of interlocking connection components includes a transverse connecting rod (4), a left locking mechanism and a right locking mechanism. One end of the transverse connecting rod (4) is interlocked with the steel frame of the left tunnel (1) through the left locking mechanism, and the other end is interlocked with the steel frame of the right tunnel (2) through the right locking mechanism.

2. The steel frame interlocking composite support structure for complex geological tunnels with small clearance as described in claim 1, characterized in that, Both the left and right locking mechanisms include a lock seat (5) fixed on the web of the steel frame, a U-shaped lock groove opened on the lock seat (5), and a locking pin (6) that cooperates with the U-shaped lock groove. The end of the transverse connecting rod (4) is provided with a connecting ear plate (8) that is adapted to the U-shaped lock groove. After the connecting ear plate (8) is inserted into the U-shaped lock groove, it is locked by the locking pin (6).

3. The steel frame interlocking composite support structure for complex geological tunnels with small clearance as described in claim 1, characterized in that, The initial support units (3) are arranged at intervals along the longitudinal direction of the tunnel. Each initial support unit (3) includes a steel frame, a shotcrete layer, system anchors and locking anchors (9). The steel frame is set close to the tunnel excavation outline and the shotcrete layer is sprayed on its outer side.

4. The steel frame interlocking composite support structure for complex geological tunnels with small clearance as described in claim 1, characterized in that, The system anchor bolts are inserted into the surrounding rock at intervals along the circumferential direction of the steel frame, and their ends are fixedly connected to the steel frame.

5. The steel frame interlocking composite support structure for complex geological tunnels with small clearance as described in claim 1, characterized in that, The anchor bolt (9) is set at the arch foot of the steel frame and is obliquely implanted into the surrounding rock.

6. The steel frame interlocking composite support structure for tunnels with small clearance in complex geological conditions according to claim 2, characterized in that, The lock seat (5) is fixed to the center of the web of the steel frame by welding steel plate.

7. The steel frame interlocking composite support structure for tunnels with small clearance in complex geological conditions according to claim 2, characterized in that, The transverse connecting rod (4) includes multiple connecting rods spliced ​​together in sequence. Each connecting rod is made of low alloy high strength structural steel, and the rods are connected by flanges (7) and high strength bolts. Rubber sealing gaskets are provided between the flanges (7) to adapt to the slight longitudinal deformation of the tunnel and ensure the tightness of the connection.

8. A construction method for the steel frame interlocking composite support structure for complex geological tunnels with small clearance as described in any one of claims 1-7, comprising the following steps: S1. Tunnel excavation and contour trimming: The left tunnel (1) and right tunnel (2) are excavated in stages according to the design excavation plan. After the excavation is completed, the tunnel contour is trimmed in time to ensure that the installation base of the steel frame is flat. S2, Construction of the initial support unit (3): S2.1 Installation of steel frame: According to the design spacing, the steel frame is erected close to the tunnel excavation outline. The axis, elevation and mileage of the steel frame are ensured to be accurate by measurement and positioning. Adjacent steel frames are firmly connected by bolts. S2.2 Construction of anchor bolts (9): At the arch foot of the steel frame, anchor bolts (9) are inserted obliquely according to the design angle and depth. The ends of the anchor bolts are welded and fixed to the steel frame to enhance the overturning resistance of the steel frame. S2.3 System Anchor Bolt Construction: Drill holes at intervals along the circumferential direction of the steel frame, insert system anchor bolts, and fix the ends of the anchor bolts to the steel frame with nuts or welding to form an integral load-bearing structure with the steel frame; S2.4 Shotcrete layer construction: Shotcrete is sprayed on the outside of the steel frame and the surface of the surrounding rock until the designed thickness is reached to form a shotcrete layer, which tightly binds the steel frame, system anchors and surrounding rock. S3. Installation of mid-span connection unit: After the initial support unit (3) of the left tunnel (1) and the right tunnel (2) is completed and the shotcrete layer reaches the design strength, the mid-span connection unit is installed. S3.1, Lock seat (5) installation: Fix the lock seats (5) of the left and right locking mechanisms to the web plates of the steel frame that are set opposite to each other in the left tunnel (1) and right tunnel (2), respectively, to ensure that the U-shaped lock groove openings of the lock seats (5) are in the same direction and at the same horizontal height; S3.2, Positioning of the transverse connecting rod (4): Select a suitable number of connecting rods to splice into a transverse connecting rod (4), and insert the connecting ear plates (8) at both ends of the transverse connecting rod (4) into the U-shaped lock grooves of the left lock seat (5) and the right lock seat (5) respectively; S3.3, Locking pin (6): The locking pin (6) passes through the pin hole of the lock seat (5) and the connecting ear plate (8) to complete the detachable interlocking connection between the transverse connecting rod (4) and the steel frame. At least two sets of interlocking connection components are installed according to the design requirements. S4. Monitoring, Measurement and Adjustment: During and after construction, real-time monitoring and measurement of tunnel surrounding rock deformation and support structure stress are carried out. Based on the monitoring data, support parameters are adjusted in a timely manner or the mid-span connection unit is reinforced to ensure the safety and stability of the support structure.

9. The construction method of the steel frame interlocking composite support structure for tunnels with small clearance in complex geological conditions according to claim 8, characterized in that, In step S1, the tunnel excavation adopts micro-vibration controlled blasting or mechanical excavation, strictly controls the excavation cycle advance, and maintains a certain safe distance between the excavation working faces of the left tunnel (1) and the right tunnel (2) to avoid excessive disturbance to the middle rock pillar caused by the simultaneous excavation of the two tunnels.

10. The construction method of the steel frame interlocking composite support structure for tunnels with small clearance in complex geological conditions according to claim 8, characterized in that, In step S1, during contour trimming, manual labor combined with machinery is used to remove dangerous rocks and loose surrounding rock, so that the tunnel excavation contour line meets the design requirements, and initial spraying is carried out to provide conditions for the precise installation of steel frame.

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