High ground stress broken surrounding pressure large section tunnel interpenetration construction method
By using the stepped double-wall trench construction method and the YT28 drilling rig blasting technology, the safety and stability issues of tunnel intersection construction under high ground stress and fractured confining pressure were solved, and the effective transfer of surrounding rock stress and the improvement of construction efficiency were achieved.
Patent Information
- Application Number
- CN202611244448.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-17
- Publication Date
- 2026-11-06
AI Technical Summary
Under conditions of high ground stress and fractured confining pressure, during the construction of tunnels intersecting each other, the intersection line is a spatially twisted line, resulting in a large area of suspended surrounding rock, which is prone to roof collapse. Traditional construction techniques are complex and difficult to effectively control ground pressure, leading to safety hazards and construction difficulties.
The project employs a stepped double-walled trenching method, combined with the YT28 drilling rig's dense hole drilling and bottom-hole air cushion charging structure, and strictly controls the maximum charge blasting technology. By constructing small-section tunnels first, entry and exit trenches and excavated sections are formed to ensure that the steel arch supports the surrounding rock under positive pressure. A concrete steel frame is set in the secondary lining of the large-section tunnel to achieve smooth stress transfer in the surrounding rock.
It reduces the exposed space during construction, lowers the risk of rockfall, improves construction safety and structural stability, saves on engineering work and construction period, and adapts to the construction needs of different cross-section combinations.
Smart Images
Figure CN123044302A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of tunnel intersection construction, and more specifically to a method for tunnel intersection construction with large cross-section under high ground stress and fractured confining pressure. Background Technology
[0002] The overall top-level strategic positioning of the "15th Five-Year Plan" determines the national strategic development trend. With "safety and resilience, digital and intelligent upgrading, and release of spatial value" as the core, various underground projects will be upgraded from supporting infrastructure to the strategic foundation supporting China's modernization, and underground space will be upgraded from engineering attributes to strategic resources.
[0003] To open up access to Tibet and South Asia and achieve interconnectivity between Sichuan, Yunnan, and Guizhou, the Hengduan Mountains will inevitably become a core confluence area. Due to the limitations imposed by high mountain and canyon terrain, geological hazards, and ecological protection, major surface engineering projects must be carried out underground. With the implementation of strategies for mineral mining, hydropower development, pumped storage, compressed air storage, supercomputing, underground storage, inter-basin water transfer, high-speed rail, and highways in the Hengduan Mountains region, a massive number of underground power plants, tunnels, underground interconnections, and hubs will need to be constructed, inevitably leading to a large number of vast underground spaces converging.
[0004] Currently, regardless of whether a large-section tunnel is connected to a small-section tunnel, or vice versa, a large space will inevitably be exposed during the excavation process. If not supported in time, this can easily lead to roof falls or even collapses, which not only compromises safety but also makes it difficult to repair large areas of collapsed space. This is especially true in the Hengduan Mountains region, where not only is the compression intense but the rock mass is also fractured, making roof falls and collapses particularly severe.
[0005] 1. Current mainstream construction techniques for tunnel intersections When tunnels intersect, the intersection line is not a plane, but a spatial twisted line determined by mathematical functions of cylindrical surfaces of different sizes, causing the surrounding rock near the intersection to be suspended in mid-air. In the initial support of ordinary tunnels, the steel structure is located in a vertical plane perpendicular to the tunnel axis, and the force is clear. Therefore, the mechanical behavior of large-section tunnels intersecting in the Hengduan Mountains region is very complex, and ground pressure control is difficult.
[0006] (1) Mainstream construction method of penetrating from a large-section tunnel to a small-section tunnel Using any tunnel excavation method, it is necessary to cut away the primary support of the large-section tunnel along the intersection line, even if the secondary lining has already been cast. The surrounding rock in the demolition area will be exposed in large areas due to lack of support. In order to avoid collapse due to the excavation of the small-section tunnel, it is only possible to anchor the top plate at the intersection of the cut primary support tunnel and provide advance support for the small-section tunnel as much as possible along the perimeter of the intersection line.
[0007] A cantilever beam needs to be installed in advance at the point where a small-section tunnel penetrates into a large-section tunnel, so that the steel arch frame of the large-section tunnel can be erected on the cantilever beam. See Figure 2When constructing the secondary lining of a large-section tunnel, the junction outline is then poured.
[0008] Because the intersection line is not a planar curve but a twisted spatial line, the line formed by the cutting point at the intersection of the initial support steel frame of a large-section tunnel also forms a twisted spatial line, which is neither an arch structure nor a beam structure. (See...) Figure 1 , Figure 2 Therefore, the small-section tunnel corresponds to the large-section tunnel section. The surrounding rock pressure cannot be directly transmitted to the bottom slab. It can only be anchored, suspending the loose ring of the large-section tunnel on the arch. The small-section tunnel construction operation has to be exposed below it, and is threatened by extremely high risks of roof fall and collapse.
[0009] The entrance to a small-section tunnel requires a cantilevered roof to conform to a normal cross-section, but the surrounding rock of the arch at the intersection is extremely prone to collapse.
[0010] The smaller tunnel is constructed before the larger tunnel because the smaller tunnel has better rigidity and stronger resistance to damage. Therefore, it is more conducive to the stability of the entire tunnel system to excavate the larger tunnel later.
[0011] (2) Mainstream construction method of tunneling from small cross-section tunnel to large cross-section tunnel The small-section tunnel is opened up to reveal the large-section tunnel, and then the large-section tunnel is excavated from both ends in opposite directions. Currently, there are two options: uphill excavation and horizontal excavation.
[0012] The mainstream horizontal excavation method involves a small-section tunnel penetrating into the area of a large-section tunnel. Initial supports can be gradually removed and the roof excavated at one end in a small area until the normal large-section tunnel outline is reached. (See...) Figure 3 .
[0013] When a small-section tunnel enters a large-section tunnel, a cantilever beam needs to be installed in advance to facilitate the erection of the large-section tunnel's steel arch frame onto the cantilever beam. During the construction of the secondary lining of the large-section tunnel, it should be poured together to form its normal outline.
[0014] Horizontal excavation is the mainstream construction method. It has a simple concept, but the process is difficult and prone to roof collapse.
[0015] The mainstream construction method for uphill excavation involves excavating a small-section tunnel at an angle upwards to a point slightly higher than the top of the large-section tunnel. To prevent rockfall, a pilot tunnel support gantry is installed. After excavation to the designated position, a steel arch is installed under the pilot tunnel gantry, and any excess portion encroaching on the gantry is cut away. The large-section tunnel is then constructed in the opposite direction.
[0016] Near the intersection line, the steel arch frame of the large-section tunnel is supported on the cantilever beam of the small-section tunnel. The cantilever beam is pre-installed at the end where the small-section tunnel enters the large-section tunnel, and the steel arch frame of the large-section tunnel is erected on the cantilever beam. Figure 4 When constructing the secondary lining of a large-section tunnel, it is poured together to form a normal outline.
[0017] The uphill construction method is complex and involves numerous procedures. The dimensions of the rectangular pilot tunnel gantry vary at different locations, and the encroaching portion of the steel arch frame must be cut off after installation. For the large-section tunnel, the steel arch frame is first erected on supports, and then swapped after the cantilever beams are installed in the small-section tunnel. The cantilever beams then provide support for the large-section tunnel's steel arch frame. (See...) Figure 4 .
[0018] Near the intersection line, the pressure from the surrounding rock is transmitted to the cantilever beam via the beam. Because the cantilever beam's load-bearing points are located in the same vertical and horizontal plane, the steel arch frame of a large-section tunnel is easily pulled and collapsed under the distributed pressure. Therefore, anchor bolts are still required to suspend the ground pressure in large-section tunnels. Asymmetrical installation of the steel arch frame can easily generate eccentric pressure, resulting in torque and stress concentration, leading to deformation or damage to the cantilever beam.
[0019] Whether a small-section tunnel penetrates into a large-section tunnel, or a large-section tunnel penetrates into a small-section tunnel, the cantilever beams are distributed on the small-section tunnel arch frame perpendicular to it and are curved. Therefore, the steel arch frame of the large-section tunnel is erected on the cantilever beams, which is extremely difficult, complex, and complicated.
[0020] Small-section tunnels have greater rigidity and integrity than large-section tunnels. Therefore, if small-section tunnels are constructed first, they will have better resistance to construction disturbances such as blasting of subsequent tunnels. However, regardless of whether the large or small section tunnels are constructed first, the construction organization shall determine the order of construction. The implementation should be based on the characteristics of their respective construction technology and the control of mechanical behavior by ground pressure technology, and should select a scheme that is conducive to the stability of the surrounding rock, portal frame, and steel arch frame. Summary of the Invention
[0021] Therefore, to address the aforementioned shortcomings of existing methods, this invention provides a method for constructing intersecting tunnels with large cross-sections under high ground stress and fractured confining pressure. This technology belongs to the field of tunnel construction. It addresses the problems encountered in traditional intersecting construction, such as the spatially twisted intersection line, the large area of suspended surrounding rock leading to roof collapse, and the complex stress on the support structure.
[0022] This invention is implemented as follows: a method for constructing intersecting large-section tunnels under high ground stress and confined pressure is characterized by the following: To reduce exposed space and leverage the self-stabilizing properties of the surrounding rock, a stepped double-walled trench method is employed to enhance support for the surrounding rock near the intersection line. The method also utilizes a YT28 drilling rig to drill dense holes, a bottom-hole air cushion charging structure, and strict control of the maximum charge amount during blasting to minimize construction disturbance. The method includes both small-section tunnels penetrating into large-section tunnels and large-section tunnels penetrating into small-section tunnels. (1) A small-section tunnel penetrates into a large-section tunnel: For small-section tunnels, any excavation method can be used to excavate to the intersection line, either by filling with slag or by using existing steps as a platform. The platform should be as small as possible to meet the construction space requirements. Excavate the ramp step guide tunnel to the intersection line with the large-section tunnel, and then excavate over the top. The width should allow for the construction of the portal frame and reinforced steel arch frame of the small-section tunnel. According to the technical requirements of drilling and blasting, shoveling, or arch support, the narrowest and shortest upward-facing bench is used to excavate to the top of the large-section tunnel arch, forming an entrance and exit trench. Then, the large-section tunnel steel arch is installed, with one end supported on the portal frame of the small-section tunnel entrance and the other end connected to the steel arch on the top of the inclined guide tunnel. System anchor bolts and locking foot anchor bolts are also installed. The large-section tunnel is expanded backwards to both sides of the small-section tunnel. Excavation and support are carried out simultaneously, thus forming an access trench, which creates conditions for the backward excavation of the large-section tunnel. Along the middle of the large-section tunnel, the axial direction is reversed and the trench is sloped, thus forming a section trench; Then, the tunnel is excavated layer by layer, and the steel arch frame is extended as it is excavated. After the cross-section of the trench is expanded two or three times, a normal excavation cross-section is formed, and the small cross-section tunnel is fully excavated. If the cross-section of a small-section tunnel is too large, i.e. the curvature of the tunnel profile is too small and the space on both sides of the step is too low, making it unsuitable for operation, then both large and small-section tunnels adopt the trenching step method; the entrance and exit trenches are changed to excavated section trenches, and the excavation is carried out step by step, so that the initial support of the steel arch frame can be connected in time to ensure that the construction is carried out under the support. If the cross-section of the small-section tunnel is too small, the entire cross-section of the small-section tunnel can be pushed to the intersection line. The entrance of the small-section tunnel can be enlarged, and a reinforced steel arch frame can be constructed. At the same time, the tunnel portal frame can be constructed. Based on the position of the steel arch frame of the large-section tunnel, the steel structure of the portal frame of the small-section tunnel and the steel structure of the reinforced steel arch frame can be used to strengthen the vertical connection between them, so that the pressure of the initial support steel arch frame of the large-section tunnel can be directly transmitted. Then, the slag can be piled up to the intersection line, and the tunnel can be excavated from the break line into the trench of the large-section tunnel. When supporting the secondary lining of a large-section tunnel, the reinforcing steel frame of the small-section tunnel entrance is poured into the secondary lining together with the portal frame to achieve the design appearance requirements. A concrete steel frame can also be installed near the intersection line and poured into the secondary lining together. This method can also be used for tunnels with equal cross sections that intersect.
[0023] (2) From a large-section tunnel to a small-section tunnel: When a large-section tunnel penetrates into a small-section tunnel, the portal frame and reinforcing steel arch frame of the small-section tunnel need to be installed first to prepare conditions for the timely erection of the steel arch frame of the large-section tunnel on the portal frame of the small-section tunnel. This is the same as the construction of the steel arch frame of the large-section tunnel, the reinforcing initial support steel arch frame of the small-section tunnel, and the portal frame when the small-section tunnel penetrates into the large-section tunnel. Because large-section tunnels use the partial excavation method, it is necessary to excavate the pilot tunnel down to the intersection line in advance, pre-install the reinforcing steel arch and portal frame of the small-section tunnel entrance, and then backfill; if the large-section tunnel is pushed to the intersection line of the large and small tunnels using the partial excavation method, and then the reinforcing steel arch and portal frame of the small-section tunnel are constructed, it can only be extended. When supporting the secondary lining of a large-section tunnel, the reinforcing steel frame of the small-section tunnel entrance is poured into the secondary lining together with the portal frame to achieve the design appearance requirements; a concrete steel frame can also be installed near the intersection line and poured into the secondary lining together. When the large-section tunnel is excavated to the intersection position, the steel arch frame of the large-section tunnel can be directly erected on the portal frame of the small-section tunnel; once the small-section tunnel is exposed, construction can be carried out directly on the small-section tunnel.
[0024] The present invention has the following advantages: (1) Better mechanical properties: In normal tunnels, regardless of the size of the cross section, the cross section of the steel arch frame is subjected to normal pressure without torque, bending moment, or traction. Because the intersection area is an asymmetrical structure, the mainstream construction method directly uses straight beams, which will inevitably generate bending moment, torque, and traction, which will easily lead to the collapse of the surrounding rock near the intersection line. In order to ensure that the cross section of the steel arch frame near the intersection line of the large cross section tunnel is only subjected to normal pressure without torque, bending moment, or traction, this patent adopts a continuous gradual change of curvature and mutual tangential axis contact between the supporting steel structures to ensure that the confining pressure is transmitted along the steel structure in a normal pressure arch shape and that the stress of the surrounding rock is transmitted to the bottom plate of the tunnel. (2) Whether a large cross section tunnel penetrates into a small cross section tunnel or a small cross section tunnel penetrates into a large cross section tunnel, the construction is carried out through the intersection line to penetrate into the subsequent tunnel. First, the portal frame of the small cross section tunnel and its reinforced initial support steel arch frame are constructed to ensure that the high-pressure broken surrounding rock has a supporting structure. In large-section tunnels, each steel arch frame is aligned with the vertical steel structure connecting the portal frame and reinforcing steel arch frame in small-section tunnels to avoid stress concentration between the portal frame and the reinforcing steel arch frame. (See...) Figure 8 (3) Enter and exit the trench, dig a section of the trench, and provide strong support for the surrounding rock along the trench side, while ensuring that the steel arch frame of the arch top is directly on the ground. (4) In order to avoid collapse, the size of the trench excavation project can be reduced, the exposed area can be reduced, the gantry frame can be reduced, the amount of work can be reduced, and the construction period can be saved. Attached Figure Description
[0025] Figure 1 A schematic diagram of a twisted spatial intersection line; Figure 2 Schematic diagram of initial support cutting and anchoring for large-section tunnels; Figure 3 Schematic diagram of mainstream horizontal excavation methods; Figure 4 Schematic diagram of mainstream construction methods for slope excavation; Figure 5 Schematic diagram of a small-section tunnel climbing uphill and penetrating into a large-section tunnel; Figure 6Schematic diagram of the layout of a small-section tunnel penetrating into a large-section tunnel, including the entrance and exit trenches and the section trenches; Figure 7 Schematic diagram of confining pressure stress transfer in the intersection area; Figure 8 Schematic diagram of the spatial relationship between the support arch of the large-section tunnel and the portal frame and reinforcing steel arch of the small-section tunnel. Detailed Implementation
[0026] The following will be combined with the appendix Figures 1-8 This invention will be described in detail, and the technical solutions in the embodiments of this invention will be clearly and completely described. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.
[0027] This invention provides an improved method for constructing intersecting large-section tunnels under high ground stress and fractured confining pressure. The following is a detailed description of the method. Figures 5-8 Please provide a detailed explanation; The construction approach for intersecting large-section tunnels under high ground stress and confined pressure involves reducing exposed space and leveraging the self-stabilizing properties of the surrounding rock. A stepped double-walled trench method is adopted to enhance support for the surrounding rock near the intersection line. YT28 drilling rigs are used to drill dense holes, a bottom-hole air cushion charging structure is employed, and the maximum charge in a single blasting section is strictly controlled to minimize construction disturbance.
[0028] (1) A small-section tunnel penetrates into a large-section tunnel: For small-section tunnels, excavate to the intersection line using any excavation method, either by filling with slag or utilizing existing steps as a platform, keeping it as small as possible to meet construction space requirements. Excavate a ramp-slope pilot tunnel to the intersection line with the large-section tunnel. (See...) Figure 5 Then, excavate above the top, allowing for the construction of a small-section tunnel portal frame and reinforced steel arch frame. See [link / reference]. Figure 5 .
[0029] According to the technical requirements of drill-and-blast, shovel-loading, or arch support, the narrowest and lowest upward-facing bench excavation is adopted to the large-section tunnel arch. Then, the large-section tunnel steel arch is installed, with one end supported on the portal frame of the small-section tunnel entrance, and the other end connected to the steel arch on the top of the pilot tunnel. System anchor bolts and locking anchor bolts are then installed. See [link to documentation]. Figure 5 .
[0030] The large-section tunnel extends backwards to both sides of the small-section tunnel, with excavation and support occurring simultaneously, thus forming an access trench. This creates conditions for the backward excavation of the large-section tunnel. (See...) Figure 6 .
[0031] Along the middle of the large-section tunnel, the axial direction is reversed by a trench, and the sides of the trench are sloped, thus forming a section trench, see Figure 6.
[0032] Then, the tunnel is excavated layer by layer, with the steel arch frame being extended as it is excavated. After the cross-section of the trench is expanded two or three times, a normal excavation cross-section is formed, and the small cross-section tunnel is then fully excavated.
[0033] If the cross-section of a small-section tunnel is too large, i.e., the tunnel profile curvature is too small and the space on both sides of the step is too low, making it unsuitable for operation, then the trenching step method is adopted for both large and small-section tunnels. The access trench is changed to a segmented trench, and the excavation is carried out step by step. The initial support of the steel arch frame can be connected in time to ensure that the construction is carried out under the support.
[0034] If the cross-section of the small-section tunnel is too small, the entire cross-section of the small-section tunnel can be extended to the intersection line. The tunnel entrance can be enlarged, and a reinforcing steel arch frame can be constructed. Simultaneously, a tunnel portal frame should be built, based on the location of the large-section tunnel's steel arch frame. The vertical connection between the small-section tunnel's portal portal frame and its reinforcing steel arch frame should be reinforced with steel structures to ensure direct transmission of the confining pressure from the initial support steel arch frame of the large-section tunnel. Then, slag should be piled up to the intersection line, and the tunnel should be excavated from the break line towards the large-section tunnel into the trench. (See...) Figure 6 .
[0035] When supporting the secondary lining of a large-section tunnel, the reinforcing steel frame of the small-section tunnel entrance is poured into the secondary lining together with the portal frame to achieve the design appearance requirements. A concrete steel frame can also be installed near the intersection line and poured into the secondary lining together.
[0036] (2) From a large-section tunnel to a small-section tunnel: When a large-section tunnel penetrates into a small-section tunnel, the portal frame and reinforcing steel arch frame of the small-section tunnel need to be installed first to prepare conditions for the timely erection of the steel arch frame of the large-section tunnel on the portal frame of the small-section tunnel. This is the same as the construction of the steel arch frame of the large-section tunnel, the reinforcing initial support steel arch frame of the small-section tunnel, and the portal frame when the small-section tunnel penetrates into the large-section tunnel.
[0037] Because large-section tunnels use the partial excavation method, it is necessary to excavate the pilot tunnel down to the intersection line in advance, pre-install the reinforcing steel arch and portal frame of the small-section tunnel entrance, and then backfill. If the large-section tunnel is pushed to the intersection line of the large and small tunnels using the partial excavation method, and then the reinforcing steel arch and portal frame of the small-section tunnel are constructed, it can only be lengthened.
[0038] When supporting the secondary lining of a large-section tunnel, the reinforcing steel frame at the tunnel entrance of the small-section tunnel is poured together with the portal frame into the secondary lining to achieve the design appearance requirements. A concrete steel frame can also be installed near the intersection line and poured into the secondary lining together.
[0039] Once the large-section tunnel is excavated to the intersection point, the steel arch frame of the large-section tunnel can be directly erected on the portal frame of the small-section tunnel. Once the small-section tunnel is exposed, construction can begin directly on it.
[0040] The following is a detailed description of the features and advantages of the intersecting construction method for large-section tunnels under high ground stress and confining pressure proposed in this application: (1) Improved mechanical properties: In normal tunnels, regardless of cross-section size, the steel arch frame's crown section is subjected to normal pressure without torque, bending moment, or traction. Because the intersection area is an asymmetrical structure, the mainstream construction method directly uses straight beams, which inevitably generates bending moment, torque, and traction, easily leading to rockfall near the intersection line. To ensure that the steel arch frame's crown section near the intersection line of a large-section tunnel is only subjected to normal pressure without torque, bending moment, or traction, this patent adopts a continuous gradual change in curvature and tangential contact between the supporting steel structures, ensuring that the confining pressure propagates along the steel structure in a normal pressure arch shape and smoothly transmits the surrounding rock stress to the tunnel floor. See Figure 7 .
[0041] (2) Regardless of whether a large-section tunnel penetrates into a small-section tunnel or a small-section tunnel penetrates into a large-section tunnel, the construction should proceed through the intersection line to the subsequent tunnel. First, construct the portal frame of the small-section tunnel and its reinforced initial support steel arch frame to ensure that the high-pressure fractured surrounding rock has a supporting structure.
[0042] In large-section tunnels, each steel arch frame is aligned with the vertical steel structure connecting the portal frame and reinforcing steel arch frame in small-section tunnels to avoid stress concentration between the portal frame and the reinforcing steel arch frame. (See...) Figure 8 .
[0043] (3) Enter and exit the ditch, dig a section of the ditch, and provide strong support for the surrounding rock along the ditch side, while ensuring that the steel arch frame of the arch top is directly grounded, see Figure 5 , Figure 6 .
[0044] (4) To avoid collapse, the size of the trench can be reduced, the exposed area can be reduced, the gantry can be reduced, the amount of work can be reduced, and the construction period can be saved.
[0045] This invention provides a systematic solution to the long-standing technical challenges in the construction of large-section tunnels intersecting under conditions of high ground stress and fractured surrounding rock. It has the following engineering application value and socio-economic benefits.
[0046] I. Solving the Global Challenge of Tunnel Intersection Construction under Complex Geological Conditions. In my country's Hengduan Mountains, Sichuan-Yunnan-Guizhou region, and other areas, the geological conditions, including high mountain and canyon terrain, high ground stress, and fractured rock masses, constrain tunnel intersection construction. The intersection lines exhibit spatially distorted curves, with large areas of unexposed surrounding rock. Traditional construction methods are prone to major safety accidents such as roof falls and collapses. This invention employs a stepped double-walled trenching method, combined with YT28 drill bit micro-holes, a bottom-hole air-cushion charging structure, and strictly controlled maximum charge blasting technology. This effectively reduces construction disturbance, minimizes exposed space, and fully utilizes the self-supporting capacity of the surrounding rock, providing reliable technical support for tunnel intersection construction under high ground stress and fractured surrounding rock conditions.
[0047] II. Enhancing Structural Mechanical Performance and Engineering Safety. Traditional construction methods use straight beam supports in the intersection area, which inevitably generates bending moments, torques, and traction forces, easily leading to rockfall. This invention employs a support steel structure with continuously varying curvature. Through tangential axis contact, it ensures that the surrounding rock pressure propagates along the steel structure in a positive pressure arch shape, smoothly transferring the surrounding rock stress to the tunnel floor and avoiding unfavorable stress states under asymmetrical structures. Simultaneously, the small-section tunnel portal gantry and reinforced initial support steel arch are constructed first, while each large-section steel arch is connected to the vertical steel structure of the portal gantry along the same line, eliminating stress concentration and significantly improving the overall stability of the support system.
[0048] Third, reduce project costs and shorten the construction period. The strong support provided by the entry and exit trenches and the excavated sections ensures that the steel arch frame of the arch top is directly grounded, avoiding large-area suspended support. The trench excavation dimensions can be minimized, reducing the exposed area and eliminating the need for extensive installation and dismantling of temporary gantry frames and cantilever beams, reducing the workload by approximately 20% to 30%, saving materials and labor input, and shortening the construction cycle.
[0049] Fourth, this invention simultaneously covers two construction directions: "small cross-section penetrating into large cross-section" and "large cross-section penetrating into small cross-section," which can flexibly adapt to different cross-section combinations and construction organization requirements. With the advancement of the "15th Five-Year Plan" national underground space strategy, this technology can be widely applied to a large number of emerging underground space intersection projects such as underground power plants, pumped storage power stations, compressed air energy storage chambers, and transportation hubs. It has important strategic significance and a demonstrative and leading role in ensuring the safety of national major infrastructure construction and promoting the development and utilization of underground space resources.
[0050] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims
1. A method for high ground stress broken surrounding pressure large section tunnel interpenetrating construction, characterized in that ； In the construction of large-section tunnels with high ground stress and fractured confining pressure, in order to reduce the exposed space and give full play to the self-stabilization of the surrounding rock, a stepped double-wall trench method is adopted to strengthen the support of the surrounding rock near the intersection line. YT28 drilling rig is used to drill dense holes, bottom hole air cushion charging structure and strictly control the maximum amount of explosive in the blasting technology to reduce construction disturbance. This includes tunnels with small cross-sections penetrating into tunnels with large cross-sections, and tunnels with large cross-sections penetrating into tunnels with small cross-sections. (1) A small-section tunnel penetrates into a large-section tunnel: For small-section tunnels, any excavation method can be used to excavate to the intersection line, either by filling with slag or by using existing steps as a platform. The platform should be as small as possible to meet the construction space requirements. Excavate the ramp step guide tunnel to the intersection line with the large-section tunnel, and then excavate over the top. The width should allow for the construction of the portal frame and reinforced steel arch frame of the small-section tunnel. According to the technical requirements of drilling and blasting, shoveling, or arch support, the narrowest and shortest upward-facing bench is used to excavate to the top of the large-section tunnel arch, forming an entrance and exit trench. Then, the large-section tunnel steel arch is installed, with one end supported on the portal frame of the small-section tunnel entrance and the other end connected to the steel arch on the top of the guide tunnel. System anchor bolts and locking foot anchor bolts are also installed. The large-section tunnel is expanded backwards to both sides of the small-section tunnel. Excavation and support are carried out simultaneously, thus forming an access trench, which creates conditions for the backward excavation of the large-section tunnel. Along the middle of the large-section tunnel, the axial direction is reversed and the trench is sloped, thus forming a section trench; Then, the tunnel is excavated layer by layer, and the steel arch frame is extended as it is excavated. After the cross-section of the trench is expanded two or three times, a normal excavation cross-section is formed, and the small cross-section tunnel is fully excavated. If the cross-section of a small-section tunnel is too large, i.e. the curvature of the tunnel profile is too small and the space on both sides of the step is too low, making it unsuitable for operation, then both large and small-section tunnels adopt the trenching step method; the entrance and exit trenches are changed to excavated section trenches, and the excavation is carried out step by step, so that the initial support of the steel arch frame can be connected in time to ensure that the construction is carried out under the support. If the cross-section of the small-section tunnel is too small, the entire cross-section of the small-section tunnel can be pushed to the intersection line. The entrance of the small-section tunnel can be enlarged, and a reinforced steel arch frame can be constructed. At the same time, the tunnel portal frame can be constructed. Based on the position of the steel arch frame of the large-section tunnel, the steel structure of the portal frame of the small-section tunnel and the steel structure of the reinforced steel arch frame can be used to strengthen the vertical connection between them, so that the pressure of the initial support steel arch frame of the large-section tunnel can be directly transmitted. Then, the slag can be piled up to the intersection line, and the tunnel can be excavated from the break line into the trench of the large-section tunnel. When supporting the secondary lining of a large-section tunnel, the reinforcing steel frame of the small-section tunnel entrance is poured into the secondary lining together with the portal frame to achieve the design appearance requirements. A concrete steel frame can also be installed near the intersection line and poured into the secondary lining together. Tunnels of equal cross-section can also be connected in this way. (2) From a large-section tunnel to a small-section tunnel: When a large-section tunnel penetrates into a small-section tunnel, the portal frame and reinforcing steel arch frame of the small-section tunnel need to be installed first to prepare conditions for the timely erection of the steel arch frame of the large-section tunnel on the portal frame of the small-section tunnel. This is the same as the construction of the steel arch frame of the large-section tunnel, the reinforcing initial support steel arch frame of the small-section tunnel, and the portal frame when the small-section tunnel penetrates into the large-section tunnel. However, since large-section tunnels adopt the partial excavation method, it is necessary to excavate the pilot tunnel down to the intersection line in advance, pre-install the reinforcing steel arch and portal frame of the small-section tunnel entrance, and then backfill; if the large-section tunnel is pushed to the intersection line of the large and small tunnels by the partial excavation method, and then the reinforcing steel arch and portal frame of the small-section tunnel are constructed, it can only be lengthened, the strength is reduced, and the process is complicated. When supporting the secondary lining of a large-section tunnel, the reinforcing steel frame of the small-section tunnel entrance is poured into the secondary lining together with the portal frame to achieve the design appearance requirements. A concrete steel frame can also be installed near the intersection line and poured into the secondary lining. When a large-section tunnel is excavated to the intersection position, the steel arch frame of the large-section tunnel can be directly erected on the portal frame of the small-section tunnel. Once the small-section tunnel is exposed, construction can begin directly on it.