Straight-wall circular-arch underground chamber flat-top cross supporting method

Abstract

The invention relates to the field of underground tunnel engineering supporting, in particular to a straight wall circular arch underground chamber flat top cross supporting method. The structure stability problem is solved on the basis that the pipeline use space is met by adopting measures such as densification of the straight wall circular arch frame, reinforcement of the arch frame at the joint, cooperation of the pre-stressed anchor rod and the flat top steel support, reinforcement of the combined portal frame, reinforcement of the arch frame inclined strut and reinforcement of the portal frame inclined strut; the existing lagging jack does not need to be dismantled, secondary interference on the lagging jack is avoided, and redistribution of internal force of the lagging jack is also prevented; the first storage area and the second storage area are tunneled step by step and stage by stage; through the technology, the later use function is met, the safety of the channel structure is enhanced, and the construction efficiency is improved; monitoring and measuring results show that the accumulated maximum deformation settlement value is reduced by 30-40% compared with a conventional construction method, the structural safety is guaranteed, and the construction safety risk is reduced.

Description

Technical Field

[0001] The present invention relates to the field of support for underground tunnel engineering, and particularly to a support method for a flat-top cross of a straight-wall circular-arch underground chamber. Background Art

[0002] In recent years, the field of deep-buried underground artificial chambers has developed rapidly, and a large number of projects such as underground storage facilities, underground factories, and underground dispatching centers have been constructed. With the integrated development of comprehensive pipeline systems such as ventilation, strong and weak electricity, water supply and drainage, and fire protection, multiple pipelines cross and overlap at the chamber intersection, requiring a large spatial dimension. Due to the limitation of the vertical space hierarchical layout, the traditional non-uniform cross-section intersection structure has been difficult to meet the full-section pipeline integration requirements of modern projects. Engineering practice shows that the equal-height flat-top intersection has gradually become an important technical development direction due to its spatial utilization advantage, which poses higher requirements for the support system at the flat-top cross of the straight-wall circular-arch chamber. In the existing technical system, a non-uniform cross-section intersection structure can set a supporting beam in the low-section area to support the arch frame to form a stable mechanical transmission path. However, during the construction of an equal-height cross-section flat-top intersection, due to the geometric equal-height characteristic of the structure, the traditional supporting beam support system fails.

[0003] Although the small-section reverse excavation method commonly used in engineering can achieve cross-penetration, it is necessary to truncate the already constructed arch frame, which leads to three major technical defects: ① the integrity of the support system is damaged, causing stress redistribution imbalance; ② a local weakening area is formed at the truncated section of the arch frame; ③ multiple disturbances induce the expansion of the surrounding rock loose circle. The above problems seriously restrict the safe construction of deep-buried underground chamber groups, and there is an urgent need to develop a new support system. Summary of the Invention

[0004] The purpose of the present invention is to provide a support method for a flat-top cross of a straight-wall circular-arch underground chamber in view of the problems existing in the prior art that the small-section reverse excavation method commonly used in the through construction of the equal-height cross-section flat-top cross of the existing underground chamber requires truncating the already constructed arch frame, resulting in the integrity of the support system being damaged, causing stress redistribution imbalance, a local weakening area being formed at the truncated section of the arch frame, and multiple disturbances inducing the expansion of the surrounding rock loose circle.

[0005] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows: In the first aspect, the present invention provides a support method for a flat-top cross of a straight-wall circular-arch underground chamber, including the following steps: S1. Construct a straight-wall circular-arch passage. When the construction reaches a first set distance before the flat-top cross intersection, adjust the layout spacing of the steel arch frames, set encrypted steel arch frames, and set a strengthening arch frame at the connection between the passage and the flat-top cross intersection. The strengthening arch frame includes a flat-top steel support and a permanent support in the shape of an arch. The top of the permanent support is fixedly connected to the bottom of the flat-top steel support; S2. Before excavating the section at the flat-top crossroads position, set up advanced measures and grout for reinforcement on the surrounding rock within the upper bench of the tunnel, and install advanced support above the surrounding rock. S3. After the advanced support construction is completed, continue with the excavation of the tunnel. The excavation method is flat-top excavation, and the top height is the elevation of the circular arch top of the tunnel. After excavating the upper bench, conduct an initial shotcrete, and complete the initial support for the upper bench, including installing the flat-top steel support, prestressed anchor bolts, and temporary steel support for the upper bench. S4. After completing the initial support for 2 - 3 sets of arch frames in the upper bench, suspend the operation and start the construction of the diagonal bracing reinforcement for the arch frames of the strengthened arch frames. The two ends of the diagonal bracing of the arch frames are respectively connected to the cantilever of the flat-top steel support and the arch top of the permanent support to enhance the load-bearing capacity of the right-angle part of the initial support in the upper bench. S5. After completing the initial support for 5 - 7 sets of arch frames in the upper bench, start the construction of the lower bench and complete the initial support for the lower bench, including the temporary steel support for the lower bench. S6. After the initial support for the section at the flat-top crossroads position is completed, the upper bench and the lower bench continue to be constructed synchronously in the normal section for a second set distance and then suspend the operation, ensuring that the lower bench is at a second set distance from the flat-top crossroads position. S7. Construct combined gantries on both sides along the axial direction of the tunnel at the flat-top crossroads position. The combined gantry includes a gantry crossbeam, gantry diagonal braces, and an arch-shaped gantry frame. The top of the gantry frame is fixedly connected to the bottom of the gantry crossbeam, the top of the gantry crossbeam is fixedly connected to the bottom of the flat-top steel support, and the two ends of the gantry diagonal braces are respectively connected to the gantry crossbeam and the arch top of the gantry frame. S8. After the combined gantry is constructed, start the excavation of the first storage area with the same elevation section at the flat-top crossroads position. During the excavation of the first set distance, densify the layout spacing of the steel arch frames. Before excavation, remove the temporary steel support for the upper bench and the temporary steel support for the lower bench of the initial support of the cross-shaped flat-top within the range of the first storage area. S9. After the first storage area is excavated for the first set distance, start the excavation of the second storage area with the same elevation section at the flat-top crossroads position. During the excavation of the first set distance, densify the layout spacing of the steel arch frames. Before excavation, remove the temporary steel support for the upper bench and the temporary steel support for the lower bench of the initial support of the cross-shaped flat-top within the range of the second storage area.

[0006] Adopt a flat-top cross support method for a straight-wall circular-arch underground chamber according to the present invention. By adopting measures such as densifying the straight-wall circular-arch steel arches, strengthening the steel arches at the joints, coordinating the prestressed anchor rods and the flat-top steel supports, strengthening with combined gantries, and strengthening with inclined braces for the steel arches and gantries, on the basis of meeting the pipeline use space, the problem of structural stability is solved; viewed along the axial direction of the passage, permanent supports are set at the front and rear ends within the flat-top cross intersection to consolidate the corresponding flat-top steel supports, and temporary supports are set between the two permanent supports to support the corresponding flat-top steel supports. As the flat-top cross intersection is excavated, combined gantries are set in stages on both sides of the passage. After the combined gantries are formed, all the flat-top steel supports are supported, and the support system is transformed. At this time, the temporary supports can be removed to expose the tunneling faces of the first storage area and the second storage area. This does not require the removal of the existing steel arches, does not cause secondary interference to the steel arches, and also prevents the redistribution of the internal forces of the steel arches; the first storage area and the second storage area are excavated step by step in stages; through the above technologies, the later use functions are met, the safety of the passage structure is enhanced, and the construction efficiency is improved; according to the monitoring and measurement results, the cumulative maximum deformation settlement value is reduced by 30 - 40% compared with the conventional construction method, ensuring the structural safety and reducing the construction safety risk.

[0007] As a preferred technical solution of the present invention, the excavation of the passage is constructed by the small-dose blasting method.

[0008] As a preferred technical solution of the present invention, in step S1, the permanent support includes a top-step crown steel support, a top-step haunch steel support, and a bottom-step foot steel support that are connected in sequence from top to bottom.

[0009] As a further preferred technical solution of the present invention, lock-foot anchor rods are provided at the connection between the top-step crown steel support and the top-step haunch steel support, lock-foot anchor rods are provided at the connection between the top-step haunch steel support and the bottom-step foot steel support, and lock-foot anchor rods are provided at the bottom of the bottom-step foot steel support.

[0010] As a further preferred technical solution of the present invention, in step S2, the shape of the advanced support is adapted to the shape of the top-step crown steel support.

[0011] As a preferred technical solution of the present invention, in step S1, the cross-sectional dimension of the strengthened steel arch is larger than that of the steel arch.

[0012] As a preferred technical solution of the present invention, in step S7, the gantry frame includes gantry vertical beams and a gantry arch beam (14B). The top of the gantry vertical beam is connected to the end of the gantry cross beam. A joint is provided at the upper part of the gantry vertical beam. The top of the gantry arch beam (14B) is connected to the bottom of the gantry cross beam. The two ends of the gantry arch beam (14B) are respectively connected to the joint. The gantry inclined brace is connected between the gantry cross beam and the gantry arch beam (14B).

[0013] As a preferred technical solution of the present invention, in step S7, the combined portal frame adopts a double I-beam structure.

[0014] As a preferred technical solution of the present invention, real-time monitoring is used to ensure that the cumulative deformation of the initial support and the deformation rate after the arch frame is installed are controlled within the design threshold. After reaching the standard, the waterproof layer construction is carried out and the secondary lining operation is promoted simultaneously.

[0015] In a second aspect, the present invention further provides a straight-walled, round-arched, underground chamber flat-top cross-support system, comprising: A dense steel arch frame is provided within a first set distance between the passage connecting the flat-top cross intersection, the first storage area, and the second storage area; Prestressed anchor rods and flat-top steel supports, including a plurality of flat-top steel supports and a plurality of prestressed anchor rods, wherein the length direction of the flat-top steel supports is arranged transversely along the channel, the flat-top steel supports are arranged at intervals along the axial direction of the channel, and the prestressed anchor rods are tied and fixed in the surrounding rock on the flat top; Permanent support, the permanent support is arranged at the bottom of the flat-top steel support where the channel and the flat-top cross intersection meet, an arch brace is connected between the permanent support and the corresponding flat-top steel support, and the permanent support is arch-shaped and matches the cross-sectional shape of the channel; Temporary support, the remaining non-connected flat-top steel supports in the flat-top cross intersection are supported by the temporary support, and the temporary support is connected to the ends of the corresponding flat-top steel supports; Combined gantry, the combined gantry is respectively arranged at the junction of the first storage area and the flat-top cross intersection, and at the junction of the second storage area and the flat-top cross intersection, the combined gantry includes a gantry beam, a gantry brace and an arch-shaped gantry frame, the length direction of the gantry beam is arranged along the axial direction of the channel, the top of the gantry beam is connected to the bottom of all the flat-top steel supports, the top of the gantry frame is connected to the bottom of the gantry beam, the gantry brace is connected between the gantry beam and the gantry frame, and the shape of the gantry frame matches the cross-sectional shape of the first storage area and the cross-sectional shape of the second storage area.

[0016] Adopt a flat-top cross-support system for straight-wall circular-arch underground chambers described in the present invention. By taking measures such as densifying the straight-wall circular-arch frames, strengthening the frames at the joints, coordinating the prestressed anchor rods and flat-top steel supports, reinforcing with combined gantries, and strengthening with inclined braces of the frames and inclined braces of the gantries, on the basis of meeting the pipeline use space, the problem of structural stability is solved; looking along the axial direction of the passage, permanent supports are set at the front and rear ends within the flat-top cross intersection to consolidate the corresponding flat-top steel supports, and temporary supports are set between the two permanent supports to support the corresponding flat-top steel supports. As the flat-top cross intersection is excavated, combined gantries are set in stages on both sides of the passage. After the combined gantries are formed, all flat-top steel supports are supported, completing the transformation of the support system. At this time, the temporary supports can be removed to expose the excavation faces of the first storage area and the second storage area. This does not require the removal of the existing frames, has no secondary interference to the frames, and also prevents the redistribution of the internal forces of the frames; the first storage area and the second storage area are excavated step by step in stages; through the above technologies, the later use functions are met, the safety of the passage structure is enhanced, and the construction efficiency is improved; according to the monitoring and measurement results, the cumulative maximum deformation settlement value is reduced by 30 - 40% compared with the conventional construction method, ensuring the structural safety and reducing the construction safety risk.

[0017] In summary, due to the adoption of the above technical solutions, the beneficial effects of the present invention are: A flat-top cross-support method and support system for straight-wall circular-arch underground chambers described in the present invention. By taking measures such as densifying the straight-wall circular-arch frames, strengthening the frames at the joints, coordinating the prestressed anchor rods and flat-top steel supports, reinforcing with combined gantries, and strengthening with inclined braces of the frames and inclined braces of the gantries, on the basis of meeting the pipeline use space, the problem of structural stability is solved; looking along the axial direction of the passage, permanent supports are set at the front and rear ends within the flat-top cross intersection to consolidate the corresponding flat-top steel supports, and temporary supports are set between the two permanent supports to support the corresponding flat-top steel supports. As the flat-top cross intersection is excavated, combined gantries are set in stages on both sides of the passage. After the combined gantries are formed, all flat-top steel supports are supported, completing the transformation of the support system. At this time, the temporary supports can be removed to expose the excavation faces of the first storage area and the second storage area. This does not require the removal of the existing frames, has no secondary interference to the frames, and also prevents the redistribution of the internal forces of the frames; the first storage area and the second storage area are excavated step by step in stages; through the above technologies, the later use functions are met, the safety of the passage structure is enhanced, and the construction efficiency is improved; according to the monitoring and measurement results, the cumulative maximum deformation settlement value is reduced by 30 - 40% compared with the conventional construction method, ensuring the structural safety and reducing the construction safety risk. Description of the Drawings

[0018] Figure 1 It is a schematic diagram of the three-dimensional space of the cross intersection of equal-height cross-sections of the present invention; Figure 2 It is a schematic diagram of the truncation at the cross intersection of equal-height cross-sections of the present invention; Figure 3 Schematic diagram of the completed construction of the cross-section strengthening arch frame with equal height in the present invention; Figure 4 Schematic diagram of the completed combined gantry with equal height in the present invention; Figure 5 Schematic diagram of the layout of temporary support and crown support at the intersection in the present invention.

[0019] Markings in the figure: 1 - Passage; 2 - First storage area; 3 - Second storage area; 4 - Reinforced steel arch frame; 5 - Prestressed anchor bolt and flat-top steel support; 6 - Combined gantry; 7 - Advanced support; 8 - Permanent support, 8A - Steel support at the arch foot of the lower bench, 8B - Steel support at the arch waist of the upper bench, 8C - Steel support at the arch crown of the upper bench; 9 - Arch frame diagonal brace; 10 - Flat-top steel support; 11 - Gantry cross beam; 12 - Prestressed anchor bolt; 13 - Foot-locking anchor bolt; 14 - Gantry frame, 14A - Gantry vertical beam, 14B - Gantry arch beam; 15 - Gantry diagonal brace; 16 - Upper bench; 17 - Lower bench; 18 - Temporary support, 18A - Temporary steel support of the lower bench, 18B - Temporary steel support of the upper bench. Specific embodiments

[0020] The present invention will be further described in detail below in combination with test examples and specific embodiments. However, it should not be understood that the scope of the above-mentioned subject matter of the present invention is limited to the following embodiments. All technologies implemented based on the content of the present invention belong to the scope of the present invention.

[0021] In the description of the specific embodiments of the present invention, without special instructions, the expression terms of orientation or position relationship such as "upper", "lower", "left", "right", "center", "inner", "outer", etc. are all based on the orientation or position relationship shown in the drawings, or the orientation or position relationship when the invention product / device / equipment is usually used. These terms of orientation or position relationship are only for the convenience of describing the present invention scheme or simplifying the description in specific embodiments, facilitating technicians to quickly understand the scheme, rather than indicating or implying that a specific device / component / element must have a specific orientation, or be constructed and operated in a specific position relationship. Therefore, it should not be understood as a limitation to the present invention.

[0022] In addition, when terms such as "horizontal", "vertical", "hanging", "parallel" appear, it does not mean that the corresponding device / component / element is required to be absolutely horizontal or vertical or hanging or parallel, but it can be slightly inclined or deviated. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and it does not mean that the structure must be completely horizontal, but it can be slightly inclined. Or, it can be simply understood that the corresponding device / component / element is arranged in directions such as "horizontal", "vertical", "hanging", "parallel", etc., and can have an error / deviation of ±10% relative to the corresponding direction setting, more preferably an error / deviation within ±8%, more preferably an error / deviation within ±6%, more preferably an error / deviation within ±5%, more preferably an error / deviation within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still perform its function in the solution of the present invention.

[0023] In addition, when expressions such as "first", "second", "third", etc. appear in the terms, they are only used to distinguish the descriptions of the same or similar components, and should not be understood as emphasizing or implying the relative importance of specific components.

[0024] In addition, in the description of the embodiments of the present invention, "several", "multiple", "a number of" represent at least 2. It can be any situation such as 2, 3, 4, 5, 6, 7, 8, 9, etc., and even can be a situation exceeding 9.

[0025] In addition, in the description of the technical solution of the present invention, unless otherwise clearly specified / defined / limited, when terms such as "set", "installed", "connected", "coupled", "provided with", "laid", "arranged" appear, they should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection. It can be connection means commonly used in the art such as welding, riveting, bolting, threaded connection, etc. Such a connection can be a mechanical connection, an electrical connection or a communication connection; it can be directly connected, or indirectly connected through an intermediate medium, and can be the communication inside two components.

[0026] In the related art, due to the advantage of space utilization rate, the equal-height cross-section flat-top cross intersection of underground chambers can meet the demand for full-section pipeline integration. However, in the prior art, the small-section reverse excavation method commonly used for the through construction of the equal-height cross-section flat-top cross intersection requires truncating the already installed arch, which leads to three major technical defects: ① The integrity of the support system is damaged, causing stress redistribution imbalance; ② A local weakening area is formed at the truncated section of the arch; ③ Multiple disturbances induce the expansion of the surrounding rock loosening zone. The above problems seriously restrict the safe construction of deep-buried underground chamber groups, and there is an urgent need to develop a new support system. Therefore, the technical solution of this application is generated, and the following is elaborated in combination with Figures 1 to 5 to elaborate.

[0027] Example 1 As Figures 1 to 5 shown, a flat-top cross-supporting method for a straight-wall circular-arch underground chamber of the present invention includes the following steps: S1. Construct a straight-wall circular-arch passage 1 with a clear span of 5 m, a straight-wall section height of 4.5 m, and a springing height of 1 / 4 of the clear span. The excavation of the passage 1 is carried out by the two-step method of leaving a core soil and small-dose blasting; as Figure 1 and Figure 2 shown, when constructing to a first set distance (recommended value 10 m) before the flat-top cross-intersection, adjust the layout spacing of the steel arch frame I16, set the densified steel arch frame 4, and adjust the original spacing from 75 cm to 50 cm in the densified area.

[0028] As Figure 3 shown, a strengthening arch frame is provided at the connection of the passage 1 and the flat-top cross-intersection. The specification of the strengthening arch frame is I20, that is, the cross-sectional dimension of the strengthening arch frame is larger than that of the steel arch frame. The strengthening arch frame includes a flat-top steel support 10 and a permanent support 8 in the shape of an arch door; the permanent support 8 includes an upper-step arch-top steel support 8C, an upper-step arch-waist steel support 8B, and a lower-step arch-foot steel support 8A connected in sequence from top to bottom. The top of the upper-step arch-top steel support 8C is fixedly connected to the bottom of the flat-top steel support 10. A locking foot bolt 13 is provided at the connection of the upper-step arch-top steel support 8C and the upper-step arch-waist steel support 8B. The locking foot bolt 13 is provided at the connection of the upper-step arch-waist steel support 8B and the lower-step arch-foot steel support 8A. The locking foot bolt 13 is provided at the bottom of the lower-step arch-foot steel support 8A.

[0029] S2. Before excavating the section at the flat-top cross-intersection position, set advanced measures and grout for reinforcement on the surrounding rock within the upper step 16 of the passage 1, and set an advanced support 7 above the surrounding rock. As Figure 3 shown, the setting shape of the advanced support 7 conforms to the shape of the upper-step arch-top steel support 8C. The advanced support 7 uses a φ60 mm advanced middle pipe shed, 9 m per root, with an overlapping length of 3 m, a circumferential spacing of the pipe shed of 50 cm, and the external insertion angle of the pipe shed is controlled within 1° to 3°. After the construction is completed, verify the grouting effect by drilling and then carry out the excavation.

[0030] S3. After the construction of the advanced support 7 is completed, continue to excavate the passage 1. The excavation form is flat-top excavation, and the top height is the elevation of the circular arch top of the passage 1. The excavation distance per cycle is not greater than the spacing of 2 sets of arch frames. After excavating the upper step 16, it is closed with 5 cm thick shotcrete. As Figure 5As shown, the initial support for the upper bench is completed, including setting the flat-top steel support 10, the prestressed anchor bolt 12, and the temporary steel support 18B for the upper bench. The flat-top steel support 10 uses I18 type for strengthened support, with a spacing of 50 cm between the flat-top steel supports 10. The prestressed anchor bolt 12 ties the flat-top steel support 10 and is fixed on the flat top. The prestressed anchor bolt 12 is embedded in the surrounding rock. The top of the temporary steel support 18B for the upper bench is connected to the end of the flat-top steel support 10 by M30 high-strength bolts, and the bottom of the temporary steel support 18B for the upper bench is set on the lower bench 17.

[0031] S4. After completing the initial support of 2 - 3 sets (recommended value: 2 sets) of arch frames for the upper bench 16, suspend the operation. As Figure 3 shown, start the construction of strengthening the arch brace 9 of the arch frame. The arch brace 9 uses I18 steel. The two ends of the arch brace 9 are respectively connected to the cantilever of the flat-top steel support 10 and the arch-top steel support 8C of the upper bench, strengthening the load-bearing capacity of the right-angle part of the initial support for the upper bench 16.

[0032] S5. After the initial support for a distance of 5 - 7 sets (recommended value: 6 sets) of arch frames is completed in the construction of the upper bench 16, as Figure 5 shown, start the construction of the lower bench 17 and complete the initial support for the lower bench, including the temporary steel support 18A for the lower bench. The top of the temporary steel support 18A for the lower bench is connected to the bottom of the temporary steel support 18B for the upper bench by M30 high-strength bolts.

[0033] S6. After the initial support for the section at the flat-top cross-intersection position is completed, the upper bench 16 and the lower bench 17 continue to be constructed forward synchronously in the normal section for a second set distance (recommended value: 10 m) and then suspend the operation, ensuring that the lower bench 17 is at the second set distance from the flat-top cross-intersection position.

[0034] S7. Construct the combined gantry 6 on both sides along the axial direction of the passage 1 at the flat-top cross-intersection position. The combined gantry 6 uses a double-laced I-beam steel structure. As Figure 4 shown, the combined gantry 6 includes a gantry cross beam 11, gantry braces 15, and an arch-shaped gantry frame 14.

[0035] The top of the gantry frame 14 is fixedly connected to the bottom of the gantry cross beam 11, the top of the gantry cross beam 11 is fixedly connected to the bottom of the flat top steel support 10, and the two ends of the gantry diagonal brace 15 are respectively connected to the gantry cross beam 11 and the vault of the gantry frame 14; the gantry frame 14 includes gantry vertical beams 14A and gantry arch beams 14B, the top of the gantry vertical beam 14A is connected to the end of the gantry cross beam 11, a joint is provided on the upper part of the gantry vertical beam 14A, the top of the gantry arch beam 14B is connected to the bottom of the gantry cross beam 11, and the two ends of the gantry arch beam 14B are respectively connected to the joint, and the gantry diagonal brace 15 is connected between the gantry cross beam 11 and the gantry arch beam 14B.

[0036] The gantry cross beam 11 includes three units, the gantry vertical beam 14A includes one unit, the gantry arch beam 14B includes two units, and M30 high-strength bolts are used for connection between the gantry arch beam 14B and the gantry vertical beam 14A and between the gantry vertical beam 14A and the gantry cross beam 11. The gantry diagonal brace 15 is respectively welded to the gantry cross beam 11 and the gantry arch beam 14B.

[0037] S8. After the combined gantry 6 is constructed, the excavation of the first storage area 2 with an equal-height section at the flat-top crossroads position is started. During the excavation of the first set distance, the layout spacing of the steel arch frames is encrypted, and the arch frame spacing is 50 cm; before the excavation, the upper-step temporary steel support 18B and the lower-step temporary steel support 18A of the initial support of the cross-shaped flat top within the range of the first storage area 2 are demolished, and the demolition is carried out by mechanical means.

[0038] S9. After the first storage area 2 is excavated for the first set distance, the excavation of the second storage area 3 with an equal-height section at the flat-top crossroads position is started. During the excavation of the first set distance, the layout spacing of the steel arch frames is encrypted, and the arch frame spacing is 50 cm; before the excavation, the upper-step temporary steel support 18B and the lower-step temporary steel support 18A of the initial support of the cross-shaped flat top within the range of the second storage area 3 are demolished, and the demolition is carried out by mechanical means.

[0039] Among them, through real-time monitoring, it is ensured that both the cumulative deformation of the initial support and the deformation rate after the installation of the arch frames are controlled within the design thresholds. After reaching the standard, the waterproof layer construction is carried out and the secondary lining operation is promoted simultaneously. The said initial support includes steel arch frames, longitudinal connecting steel bars, system bolts, prestressed bolts, steel meshes and shotcrete.

[0040] The present embodiment describes a method for supporting a flat-top cross of a straight-walled, round-arched underground chamber, which solves the problem of structural stability on the basis of satisfying the space for pipeline use by adopting measures such as densification of straight-walled, round-arched arch frames, strengthening of arch frames at joints, coordination of prestressed anchor rods and flat-topped steel supports, reinforcement of combined portal frames 6, reinforcement of arch frame diagonal braces 9 and portal frame diagonal braces 15. From the axial direction of the channel 1, permanent supports 8 are arranged at the front and rear ends in the flat-topped cross intersection to consolidate the corresponding flat-topped steel supports 10, and temporary supports 18 are arranged between the two permanent supports 8 to support the corresponding flat-topped steel supports 10. Combined portal frames 6 are arranged in stages on both sides of the channel 1 as the flat-topped cross intersection is excavated. After the combined portal frame 6 is formed, it supports all the flat-top steel supports 10 and completes the transformation of the support system. At this time, the temporary support 18 can be removed to expose the excavation faces of the first storage area 2 and the second storage area 3. This does not require the removal of the existing arch frame, and there is no secondary interference to the arch frame, which also prevents the redistribution of the internal force of the arch frame; the first storage area 2 and the second storage area 3 are excavated step by step and stage by stage; through the above technology, the later use function is met, the safety of the channel structure is enhanced, and the construction efficiency is improved; according to the monitoring and measurement results, the cumulative maximum deformation and settlement value is reduced by 30~40% compared with the conventional method, which ensures the structural safety and reduces the construction safety risk.

[0041] Example 2 like Figures 1 to 5 As shown, the straight wall round arch underground chamber flat roof cross support system of the present invention comprises: A dense steel arch frame 4 is provided within a first set distance between the passage 1, the first storage area 2 and the second storage area 3 connecting the flat-top cross intersection; Prestressed anchor rods and flat-top steel supports 5, including a plurality of flat-top steel supports 10 and a plurality of prestressed anchor rods 12, wherein the length direction of the flat-top steel supports 10 is arranged transversely along the channel 1, the flat-top steel supports 10 are arranged axially at intervals along the channel 1, and the prestressed anchor rods 12 are tied and fixed in the surrounding rock on the flat top; Permanent support 8, the permanent support 8 is arranged at the bottom of the flat-top steel support 10 where the channel 1 is connected to the flat-top cross intersection, an arch brace 9 is connected between the permanent support 8 and the corresponding flat-top steel support 10, and the permanent support 8 is arch-shaped and matches the cross-sectional shape of the channel 1; Temporary support 18, the remaining non-connected flat-top steel supports 10 in the flat-top cross intersection are supported by the temporary support 18, and the temporary support 18 is connected to the ends of the corresponding flat-top steel supports 10; Combined gantry 6, the combined gantry 6 is respectively arranged at the connection between the first storage area 2 and the flat-top cross intersection, and at the connection between the second storage area 3 and the flat-top cross intersection. The combined gantry 6 includes a gantry cross beam 11, gantry diagonal braces 15 and an arch-shaped gantry frame 14. The length direction of the gantry cross beam 11 is arranged along the axis of the passage 1. The top of the gantry cross beam 11 is connected to the bottom of all the flat-top steel supports 10. The top of the gantry frame 14 is connected to the bottom of the gantry cross beam 11. The gantry diagonal braces 15 are connected between the gantry cross beam 11 and the gantry frame 14. The shape of the gantry frame 14 matches the cross-sectional shapes of the first storage area 2 and the second storage area 3.

[0042] For the flat-top cross intersection support system of the straight-wall circular-arch underground chamber described in this embodiment, by adopting measures such as densifying the straight-wall circular-arch frames, strengthening the frames at the joints, coordinating the prestressed anchor rods and flat-top steel supports, reinforcing with the combined gantry 6, and reinforcing with the arch diagonal braces 9 and gantry diagonal braces 15, on the basis of meeting the pipeline use space, the problem of structural stability is solved; looking along the axial direction of the passage 1, permanent supports 8 are arranged at the front and rear ends in the flat-top cross intersection to consolidate the corresponding flat-top steel supports 10, and temporary supports 18 are arranged between the two permanent supports 8 to support the corresponding flat-top steel supports 10. As the flat-top cross intersection is excavated, the combined gantry 6 is arranged in stages on both sides of the passage 1. After the combined gantry 6 is formed, it supports all the flat-top steel supports 10 to complete the transformation of the support system. At this time, the temporary support 18 can be removed to expose the excavation faces of the first storage area 2 and the second storage area 3. This does not require the removal of the existing frames, has no secondary interference to the frames, and also prevents the redistribution of the internal forces of the frames; the first storage area 2 and the second storage area 3 are excavated step by step in stages; through the above technologies, the later use functions are met, the safety of the passage structure is enhanced, and the construction efficiency is improved; according to the monitoring and measurement results, the cumulative maximum deformation settlement value is reduced by 30 - 40% compared with the conventional construction method, ensuring the structural safety and reducing the construction safety risk.

[0043] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for cross-supporting a flat-topped straight-walled, round-arched underground chamber, characterized in that: The following steps are involved: S1, constructing a straight-wall circular arch passage (1), when the construction reaches the first set distance before the flat-top cross intersection, adjusting the spacing of the steel arch frames, setting a dense steel arch frame (4), setting a reinforced arch frame at the junction of the passage (1) and the flat-top cross intersection, the reinforced arch frame comprising a flat-top steel support (10) and an arch-shaped permanent support (8), the top of the permanent support (8) being fixedly connected to the bottom of the flat-top steel support (10); S2. Before excavating the section at the flat-top cross intersection, advance measures are set for the surrounding rock within the upper step (16) of the passage (1) and grouting is performed for reinforcement, and advance support (7) is set above the surrounding rock; S3, after the construction of the advanced support (7) is completed, the excavation of the channel (1) is continued, the excavation form is a flat-top excavation, the top height is the elevation of the round arch top of the channel (1), and after the upper step (16) is excavated, the initial concrete spraying is carried out to complete the initial support of the upper step, including the installation of the flat-top steel support (10), the prestressed anchor rod (12) and the upper step temporary steel support (18B); S4, after completing the initial support of 2-3 arch frames of the upper step (16), the operation is suspended, and the reinforcement construction of the arch frame diagonal brace (9) of the reinforced arch frame is started, and the two ends of the arch frame diagonal brace (9) are respectively connected to the cantilever of the flat-top steel support (10) and the arch top of the permanent support (8); S5. After the initial support of 5 to 7 arches is completed for the upper step (16), the lower step (17) is started and the initial support of the lower step is completed, including the temporary steel support (18A) of the lower step. S6, after the initial support of the flat-top cross intersection section is completed, the upper step (16) and the lower step (17) continue to be constructed synchronously according to the normal section for a second set distance and then suspend the operation to ensure that the lower step (17) is at the second set distance from the flat-top cross intersection position; S7. A combined portal frame (6) is constructed on both sides of the axial direction of the passage (1) at the flat-top cross intersection. The combined portal frame (6) comprises a portal frame crossbeam (11), a portal frame diagonal brace (15) and an arch-shaped portal frame frame (14). The top of the portal frame frame (14) is fixedly connected to the bottom of the portal frame crossbeam (11). The top of the portal frame crossbeam (11) is fixedly connected to the bottom of the flat-top steel support (10). The two ends of the portal frame diagonal brace (15) are respectively connected to the portal frame crossbeam (11) and the arch of the portal frame (14); S8, after the construction of the combined portal frame (6) is completed, the excavation of the first storage area (2) with a cross section equal to the flat-top cross intersection position is started, and the spacing of the steel arch frames is increased within the first set distance of the excavation. Before the excavation, the temporary steel support (18B) of the upper step and the temporary steel support (18A) of the lower step of the initial support of the cross flat roof within the scope of the first storage area (2) are removed; S9. After the first storage area (2) is excavated for a first set distance, the excavation of the second storage area (3) with an iso-elevation cross section at the flat-top cross intersection is started. The spacing of the steel arch frames is increased within the first set distance of excavation. Before excavation, the upper step temporary steel support (18B) and the lower step temporary steel support (18A) of the initial support of the cross flat top within the second storage area (3) are dismantled.

2. The method for cross-supporting a flat roof of a straight-walled, round-arched underground chamber according to claim 1 is characterized in that: The channel (1) is excavated by using a small-dose blasting method.

3. The method for cross-supporting a flat roof of a straight-walled, round-arched underground chamber according to claim 1 is characterized in that: In step S1, the permanent support (8) includes an upper step arch top steel support (8C), an upper step arch waist steel support (8B) and a lower step arch foot steel support (8A) which are sequentially connected from top to bottom.

4. The method for cross-supporting a flat roof of a straight-walled, round-arched underground chamber according to claim 3 is characterized in that: A locking foot anchor rod (13) is provided at the connection between the upper step arch top steel support (8C) and the upper step arch waist steel support (8B), a locking foot anchor rod (13) is provided at the connection between the upper step arch waist steel support (8B) and the lower step arch foot steel support (8A), and a locking foot anchor rod (13) is provided at the bottom of the lower step arch foot steel support (8A).

5. The method for supporting a flat roof of a straight-walled, round-arched underground chamber according to claim 4 is characterized in that: In step S2, the configuration shape of the advanced support (7) matches the shape of the upper step arch steel support (8C).

6. The method for supporting a flat roof of a straight-walled, round-arched underground chamber according to claim 1, characterized in that: In step S1, the cross-sectional dimensions of the reinforced arch frame are greater than the cross-sectional dimensions of the steel arch frame.

7. The method for supporting a flat roof of a straight-walled, round-arched underground chamber according to claim 1, characterized in that: In step S7, the portal frame (14) includes a portal vertical beam (14A) and a portal arch beam (14B), the top of the portal vertical beam (14A) is connected to the end of the portal cross beam (11), the upper part of the portal vertical beam (14A) is provided with a joint, the top of the portal arch beam (14B) is connected to the bottom of the portal cross beam (11), the two ends of the portal arch beam (14B) are respectively connected to the joint, and the portal diagonal brace (15) is connected between the portal cross beam (11) and the portal arch beam (14B).

8. The method for supporting a flat roof of a straight-walled, round-arched underground chamber according to claim 1, characterized in that: In step S7, the combined door frame (6) adopts a double I-beam structure.

9. The method for supporting a flat roof of a straight-walled, round-arched underground chamber according to any one of claims 1 to 8, characterized in that: Through real-time monitoring, we ensure that the cumulative deformation of the initial support and the deformation rate after the arch installation are controlled within the design threshold. After reaching the standard, we will carry out the construction of the waterproof layer and promote the secondary lining operation simultaneously.

10. A straight wall, round arch, flat roof, cross support system for underground chambers, characterized in that: include: A dense steel arch frame (4) is provided within a first set distance between the passage (1) connecting the flat-top cross intersection, the first storage area (2), and the second storage area (3); Prestressed anchor rods and flat-top steel supports (5), comprising a plurality of flat-top steel supports (10) and a plurality of prestressed anchor rods (12), wherein the length direction of the flat-top steel supports (10) is arranged transversely along the channel (1), the flat-top steel supports (10) are arranged axially at intervals along the channel (1), and the prestressed anchor rods (12) are tied and fixed in the surrounding rock on the flat top; A permanent support (8), the permanent support (8) is arranged at the bottom of the flat-top steel support (10) where the channel (1) and the flat-top cross intersection meet, an arch brace (9) is connected between the permanent support (8) and the corresponding flat-top steel support (10), and the permanent support (8) is arch-shaped and matches the cross-sectional shape of the channel (1); Temporary support (18), the remaining non-connected flat-top steel supports (10) in the flat-top cross intersection are supported by the temporary support (18), and the temporary support (18) is connected to the ends of the corresponding flat-top steel supports (10); A combined portal frame (6), wherein the combined portal frame (6) is respectively arranged at the junction of the first storage area (2) and the flat-top cross intersection, and at the junction of the second storage area (3) and the flat-top cross intersection, the combined portal frame (6) comprises a portal frame cross beam (11), a portal frame diagonal brace (15) and an arch-shaped portal frame frame (14), wherein the length direction of the portal frame cross beam (11) is arranged axially along the passage (1), the top of the portal frame cross beam (11) is connected to the bottom of all the flat-top steel supports (10), the top of the portal frame (14) is connected to the bottom of the portal frame cross beam (11), the portal frame diagonal brace (15) is connected between the portal frame cross beam (11) and the portal frame (14), and the shape of the portal frame (14) matches the cross-sectional shape of the first storage area (2) and the cross-sectional shape of the second storage area (3).

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