Support system of hard rock giant span flat cavern and construction method thereof

Abstract

The invention relates to a supporting system of a hard rock giant span flat cavern and a construction method of the supporting system. The supporting system sequentially comprises a primary support, a secondary lining and a lattice girder system from outside to inside. The secondary lining comprises a giant span gradient arch cover structure of the arch part, an arch angle longitudinal hidden beam and a side wall secondary lining; the side wall secondary linings are located at the bottoms of the two transverse ends of the giant span gradient arch cover structure. The arch angle longitudinal hidden beam is connected between the transverse end part of the giant span gradual change arch cover structure and the top of the side wall secondary lining, and is longitudinally arranged and located on the hard surrounding rock; the lattice girder system is located on the inner side of the secondary lining. The gradient arch cover design of the arch part conforms to the cavern stress mode, the integrity and stability of the arch cover are enhanced, the hinging design of the side wall and the arch part is beneficial to the stability of the side wall structure, the lattice beam system can enable stress transmission to be more dispersed, the structural integrity is good, and the structure is suitable for construction of the hard rock giant span flat cavern.

Description

Technical Field

[0001] The present invention relates to the technical field of underground engineering construction, and in particular to a support system for a hard rock giant-span flat cavern and a construction method thereof. Background Art

[0002] With the rapid development of energy development, transportation construction, and the development and utilization of large urban underground spaces, demand for large-span, flat caverns in hard rock is increasing. These applications include underground powerhouses in pumped-storage power plants, underground stations, and large underground reservoirs. These caverns are characterized by large spans, flat cross-sections, and complex surrounding rock stress distribution. Especially in hard rock formations, despite the inherent strength of the rock mass, stress concentration zones are easily generated at the junction of the cavern arch and wall due to excavation unloading, ground stress release, and structural fractures. This makes it difficult for traditional support systems to effectively control surrounding rock deformation and stability.

[0003] At present, the initial support of hard rock cavern projects is generally constructed by combining sprayed anchor support and steel arch support. The secondary lining is cast-in-place concrete for the arch and side walls. However, its application in the support of large-span flat caverns has certain limitations: (1) The sprayed concrete structure has poor crack resistance and is prone to radial cracks due to bending tensile stress in the high-stress environment of hard rock, which weakens the integrity and waterproof performance; (2) The cavern has a large span and a large curvature radius, and it is difficult for the steel arch to fit tightly to the surrounding rock. After installation, "voids behind the frame" are likely to appear, resulting in uneven stress transfer and failure to form effective support; (3) A large stress concentration occurs at the junction of the secondary lining side wall and the arch, which is prone to cracking and damage of the concrete, and ultimately the overall failure of the structure.

[0004] Therefore, it is necessary to propose new support methods and measures for hard rock large-span flat caverns to ensure the safety of the cavern support structure. Summary of the Invention

[0005] The purpose of the present invention is to provide a support system and construction method for a hard rock large-span flat cavern, so as to solve the problem that the existing support method has limitations in the support construction of large-span flat caverns.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] Provide a support system for hard rock large-span flat caverns, the support system including primary support, secondary lining and lattice beam system from outside to inside;

[0008] The secondary lining includes a large-span gradual arch cover structure of the arch portion, longitudinal hidden beams at the arch angles, and a secondary lining of the side walls; the secondary lining of the side walls is located at the bottom of the transverse ends of the large-span gradual arch cover structure and is arranged vertically; the longitudinal hidden beams at the arch angles are the expanded arch angles of the large-span gradual arch cover structure, connected between the transverse ends of the large-span gradual arch cover structure and the top of the secondary lining of the side walls, and are arranged vertically and seated on the hard surrounding rock;

[0009] The lattice beam is located on the inner side of the secondary lining.

[0010] Furthermore, the initial support includes an anchor system and sprayed steel fiber concrete;

[0011] The scope of the sprayed steel fiber concrete includes the top of the large-span gradual arch cover structure, the outer side of the arch angle longitudinal hidden beam and the outer side of the secondary lining of the side wall;

[0012] The anchor rods are driven into the hard surrounding rock, and include prestressed long anchor rods with large spacing and short anchor rods with small spacing.

[0013] Furthermore, the top of the large-span gradual arch cover structure and the top of the arch angle longitudinal hidden beam are provided with the prestressed large-spacing long anchor rods, which are evenly arranged in the circumferential direction, and a plurality of the small-spacing short anchor rods are provided between the circumferentially adjacent prestressed large-spacing long anchor rods;

[0014] The outer side of the secondary lining of the side wall is provided with short anchor rods with small spacing.

[0015] Furthermore, the lattice beam system includes annular lattice beams and longitudinal lattice beams;

[0016] The scope of the annular lattice beam involves the bottom of the large-span gradual arch cover structure and the inner side of the secondary lining of the side wall;

[0017] The longitudinal lattice beams are arranged on the inner side of the secondary lining of the side wall and intersect with the annular lattice beams.

[0018] Furthermore, the lattice beam is a cast-in-situ reinforced concrete structure, and the annular lattice beam and the longitudinal lattice beam are cast in one piece.

[0019] Furthermore, the large-span gradually changing arch cover structure is a cast-in-place reinforced concrete structure whose thickness gradually increases from the arch top to the arch corner.

[0020] Furthermore, the transverse end of the large-span gradual arch cover structure is connected to the top of the secondary lining of the side wall via a hinged node, and the hinged node is located on the inner side of the longitudinal hidden beam of the arch angle.

[0021] Furthermore, the hinge node includes an upper support plate and a lower support plate, the bottom surface of the upper support plate is a convex cylindrical surface, the top surface of the lower support plate is a concave cylindrical surface, the convex cylindrical surface is embedded downwardly into the concave cylindrical surface, and a cylindrical slide plate is sandwiched between the two;

[0022] The upper support plate is connected to the upper large-span gradual arch cover structure through anchor bolts, and the lower support plate is connected to the lower side wall secondary lining through anchor bolts;

[0023] A flexible sealing material is also provided on the contact interface between the upper support plate and the lower support plate.

[0024] Furthermore, a horizontal bottom plate is provided at the bottom of the cave chamber, and the bottom plate is connected with the secondary lining of the side walls on both sides and is annularly closed.

[0025] In another aspect, a construction method for a support system for a hard rock large-span flat cavern is provided, the construction method comprising:

[0026] The cavern section is divided into the arch middle pilot tunnel, the side upper pilot tunnel, the arch reserved rock pillar, the lower pilot tunnel rock mass and the lower reserved rock platform; the side upper pilot tunnel is located on both sides of the arch middle pilot tunnel, the arch reserved rock pillar is located between the arch middle pilot tunnel and the side upper pilot tunnel, the lower pilot tunnel rock mass is located below the side upper pilot tunnel, and the lower reserved rock platform is located below the arch middle pilot tunnel and between the side upper pilot tunnels and the lower pilot tunnel rock mass on both sides;

[0027] Excavate the middle pilot tunnel of the arch and the upper pilot tunnel of the side. After the excavation is completed, install prestressed long anchor bolts with large spacing and short anchor bolts with small spacing, and construct sprayed steel fiber concrete.

[0028] Excavate the arch to reserve rock pillars. After excavation is completed, prestressed long anchors with large spacing and short anchors with small spacing are installed, and steel fiber concrete is sprayed.

[0029] A large-span gradient arch cover structure and longitudinal hidden beams at the arch corners are constructed in the arch part of the cave to form a stable arch-shaped bearing structure.

[0030] Continue excavating the lower pilot tunnel rock mass, installing short anchor bolts with small spacing, and spraying steel fiber concrete;

[0031] Excavate the lower part of the reserved rock platform and construct the secondary lining of the side wall. The secondary lining of the side wall and the large-span gradual arch cover structure are connected with hinged nodes.

[0032] Circumferential lattice beams and longitudinal lattice beams are constructed on the inner side of the secondary lining to form a stable lattice beam system;

[0033] Install the base plate and complete the construction.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The present invention provides a support system for a hard rock large-span flat cavern and a construction method thereof, which is suitable for supporting large-span flat caverns with a span of more than 35m, has strong bearing capacity, good stability, strong deformation resistance, and takes into account both safety and economy. This method installs long and short anchor rods with different spacings in the cavern. The long anchor rods anchor the deep stable rock mass, and the short anchor rods strengthen the shallow crushed area. Combined with the differential prestressing design, a three-dimensional load-bearing structure with "deep and shallow combination, tension and shear control" is formed; the use of sprayed steel fiber concrete can effectively control the radial cracks caused by bending tensile stress, ensuring the strength and waterproof performance of the concrete; the arch adopts a gradient arch cover structure, which conforms to the stress mode of the cavern arch. The design of the enlarged angle at the arch corner can effectively control the structural damage caused by stress concentration, ensuring safety while taking into account economy; the longitudinal hidden beam is set at the arch corner to provide a solid foundation for the arch cover, and at the same time, it can enhance the integrity of the arch cover and enable the stress to be dispersed and transmitted; the side wall and the arch are connected by hinges, which can avoid the excessive bending moment at the arch corner to be transmitted to the side wall, and at the same time can restrain the displacement of the side wall, which is beneficial to the stability of the side wall structure; the setting of the internal annular grid and longitudinal lattice beams of the secondary lining can further enhance the integrity of the structure, effectively avoiding local structural damage caused by excessive local stress and deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, without paying any creative work, they can also obtain drawings of other embodiments based on these drawings.

[0037] Figure 1 A cross-sectional view of the support system for a hard rock large-span flat cavern provided in an embodiment of the present invention.

[0038] Figure 2 A longitudinal section of the support system for a hard rock large-span flat cavern provided in an embodiment of the present invention.

[0039] Figure 3 A three-dimensional rendering of the support system for a hard rock large-span flat cavern provided in an embodiment of the present invention.

[0040] Figure 4 This is a diagram of step S2 of the method provided in an embodiment of the present invention.

[0041] Figure 5 This is a diagram of step S3 of the method provided in an embodiment of the present invention.

[0042] Figure 6 This is a schematic diagram of step S4 of the method provided in an embodiment of the present invention.

[0043] Figure 7 This is a schematic diagram of step S5 of the method provided in an embodiment of the present invention.

[0044] Figure 8 This is a schematic diagram of step S6 of the method provided in an embodiment of the present invention.

[0045] Figure 9 This is a diagram of step S7 of the method provided in an embodiment of the present invention.

[0046] Figure 10 A schematic diagram of the connection between the giant span gradual arch cover structure and the secondary lining of the side wall provided in an embodiment of the present invention.

[0047] The symbols in the figure are:

[0048] 1- Prestressed long anchor bolts with large spacing, 2- Short anchor bolts with small spacing, 3- Sprayed steel fiber concrete, 4- Large span gradual arch cover structure, 5- Longitudinal hidden beam at the arch corner, 6- Secondary lining of the side wall, 7- Articulated node, 8- Circumferential lattice beam, 9- Longitudinal lattice beam, 10- Bottom plate;

[0049] A-pilot hole in the middle of the arch, B-pilot hole in the upper part of the side, C-reserved rock pillar in the arch, D-pilot hole in the lower part of the side, E-reserved rock platform in the lower part;

[0050] 71-upper support plate, 72-lower support plate, 73-cylindrical slide plate, 74-anchor bolt, 75-flexible filling material. DETAILED DESCRIPTION

[0051] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0052] In the description of the present invention, it should be understood that the terms "up", "down", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0053] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "disposed" should be understood in a broad sense. For example, they may refer to fixed connection or disposition, detachable connection or disposition, or integral connection or disposition. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0054] It should also be noted that although the steps are described in order, in some cases they may be performed in an order different from that shown, and this should not be construed as limiting the order of the steps.

[0055] In a specific embodiment, the longitudinal direction of the chamber is defined as the longitudinal direction, and the direction perpendicular to the longitudinal direction is defined as the transverse direction (i.e. Figure 1 The outer side is defined as the side close to the surrounding rock, and the inner side is defined as the side close to the center of the cave.

[0056] Traditional support construction methods for hard rock caverns cannot be directly applied to large-span flat caverns. They have limitations in terms of structural crack resistance and supporting capacity. Stress concentration areas cannot be avoided in the structure, which can easily lead to defects such as concrete cracking.

[0057] To this end, the present invention provides a support system and construction method for large-span flat caverns in hard rock. In view of the characteristics of large-span flat caverns such as large spatial span, flat cross-section, and complex surrounding rock stress distribution, the construction structure and construction steps have been optimized and improved. It can be used for the support construction of large-span flat caverns with a span of more than 35m and a height of about 10m.

[0058] like Figure 1-3 The support system for a large-span, flat hard rock cavern according to the present invention comprises, from the outside inward, primary support, secondary lining, and a lattice beam system. The primary support comprises an anchor system and sprayed steel fiber concrete 3. The secondary lining, located inside the primary support, comprises a large-span, gradually changing arch cap structure 4, longitudinal hidden beams 5 at the arch corners, and secondary sidewall lining 6. The lattice beam system is located inside the secondary lining.

[0059] Specifically:

[0060] In the secondary lining, the side wall secondary lining 6 is located at the bottom of the transverse ends of the giant span gradient arch cover structure 4 and is arranged upright and longitudinally. The side wall secondary lining 6 is cast-in-place reinforced concrete with a thickness of 500mm and a concrete strength grade of not less than C40. The giant span gradient arch cover structure 4 adopts an enlarged arch angle design, and the arch angle longitudinal hidden beam 5 is the enlarged arch angle of the giant span gradient arch cover structure 4, which is connected between the transverse end of the giant span gradient arch cover structure 4 and the top of the side wall secondary lining 6, and is arranged longitudinally and directly located on the hard surrounding rock. The longitudinal hidden beam at the arch angle can provide a solid foundation for the arch cover, and at the same time can enhance the integrity of the arch cover so that the stress can be dispersed and transmitted to the surrounding rock.

[0061] During the initial support phase, the sprayed steel fiber concrete 3 covers the top of the large-span, tapered arch cap structure 4, the outside of the longitudinal hidden beams 5 at the arch angles, and the outside of the secondary lining 6 of the sidewalls. The use of sprayed steel fiber concrete effectively controls radial cracks caused by bending tensile stress, ensuring the concrete's strength and waterproof properties. The anchor system is driven into the hard surrounding rock and includes prestressed, long anchors 1 with large spacing and short anchors 2 with small spacing. In the present invention, the anchor system construction plan for different areas may vary:

[0062] (1) Arch combination scheme:

[0063] Prestressed long anchor rods 1 with large spacing are installed on the top of the giant span gradual arch cover structure 4 and the top of the longitudinal hidden beam 5 of the arch corner. They are evenly arranged in the circumferential direction. A plurality of short anchor rods 2 with small spacing are arranged between the circumferentially adjacent prestressed long anchor rods 1 with large spacing. The prestressed long anchor rods 1 with large spacing and the short anchor rods 2 with small spacing can be arranged in a plum blossom shape.

[0064] (2) Single sidewall solution:

[0065] Short anchor rods 2 with small spacing are provided on the outer side of the secondary lining 6 of the side wall.

[0066] This method uses anchor rods of varying lengths and spacing within the cavern. Long anchor rods anchor deep, stable rock mass, while short anchor rods reinforce shallow, fractured areas. Combined with a differentiated prestressing design, this creates a three-dimensional load-bearing structure that combines deep and shallow anchors, and independently controls tension and shear. Furthermore, the specific anchor rod construction plan can be flexibly adjusted based on the geological conditions and support requirements of the specific construction site, not limited to the two options described above. Anchor rod length and spacing can also be determined based on specific geological conditions.

[0067] The lattice beam system includes circumferential lattice beams 8 and longitudinal lattice beams 9. The beam cross-section is rectangular, with a cross-sectional width of 250 to 400 mm and a height of 400 to 500 mm. The range of the circumferential lattice beams 8 covers the bottom of the giant span gradual arch cover structure 4 and the inner side of the side wall secondary lining 6, that is, it extends circumferentially from the bottom of the left side wall to the bottom of the right side wall. The longitudinal lattice beams 9 are arranged on the inner side of the side wall secondary lining 6 and intersect with the circumferential lattice beams 8. Therefore, the lattice beam system of the arch portion includes longitudinal multi-ring arch beams, and the lattice beam system of the side wall is a planar beam network arranged in a lattice shape. The lattice beam system is a cast-in-place reinforced concrete structure. The circumferential lattice beams 8 and the longitudinal lattice beams 9 are cast in one piece and cast at the same time to form an integral structure. The lattice beam system can further enhance the integrity of the structure and avoid local damage to the structure due to excessive local stress and deformation.

[0068] The large-span tapered arch cover structure 4 is a cast-in-place reinforced concrete structure with a thickness that gradually increases from the arch crown to the arch corner. The thickness ranges from 900 to 1800 mm, and the concrete strength grade is not less than C40. The present invention adopts a tapered arch cover structure that conforms to the stress pattern of the cavern arch. The design of the expanded angle at the arch corner effectively controls the structural damage caused by stress concentration, ensuring safety while taking into account economic efficiency.

[0069] The lateral ends of the giant-span gradual-change arch cover structure 4 are connected to the top of the side wall secondary lining 6 via a hinged node 7, which is located on the inner side of the longitudinal hidden beam 5 of the arch angle. The hinged node 7 is a hinged support, including an upper support plate 71 and a lower support plate 72. The bottom surface of the upper support plate 71 is a convex cylindrical surface, and the top surface of the lower support plate 72 is a concave cylindrical surface. The convex cylindrical surface is embedded downward in the concave cylindrical surface, and a cylindrical slide 73 is sandwiched between the two to reduce contact friction. The upper support plate 71 is connected to the upper giant-span gradual-change arch cover structure 4 through anchor bolts 74, and the lower support plate 72 is connected to the lower side wall secondary lining 6 through anchor bolts 74. In addition, a flexible sealing material 75 is also provided on the contact interface between the upper support plate 71 and the lower support plate 72. The side wall and the arch are connected by a hinge, which can prevent excessive bending moment at the arch angle from being transmitted to the side wall, while at the same time restraining the displacement of the side wall, which is beneficial to the stability of the side wall structure.

[0070] A horizontal bottom plate 10 is provided at the bottom of the cavern, and the bottom plate 10 is connected with the secondary lining 6 of the side walls on both sides and is annularly closed.

[0071] like Figure 4-9 The above-mentioned support system construction method for a hard rock large-span flat cavern specifically includes the following steps:

[0072] S1: Divide the cavern section into zones.

[0073] Specifically, the cavern section is divided into the arch middle pilot tunnel A, the side upper pilot tunnel B, the arch reserved rock pillar C, the lower pilot tunnel rock mass D, and the lower reserved rock platform E. The side upper pilot tunnel B is located on either side of the arch middle pilot tunnel A, the arch reserved rock pillar C is located between the arch middle pilot tunnel A and the side upper pilot tunnel B, the lower pilot tunnel rock mass D is located below the side upper pilot tunnel B, and the lower reserved rock platform E is located below the arch middle pilot tunnel A and between the side upper pilot tunnels B on both sides and the lower pilot tunnel rock mass D. The bottom of the side upper pilot tunnel B is lower than the bottom of the arch middle pilot tunnel A and the arch reserved rock pillar C. The existing U-shaped structure with a downward opening ensures that the construction space on both sides is of equal size to the center, and that the construction efficiency and progress of the different pilot tunnels are consistent, steadily advancing cavern construction.

[0074] S2: Excavate the arch's central pilot tunnel A and the upper side pilot tunnel B. After excavation is complete, promptly implement initial support for the exposed surface. This includes installing prestressed, widely spaced, long anchor bolts 1, closely spaced, short anchor bolts 2, and spraying steel fiber concrete 3. Depending on the rock mass conditions, temporary support may be provided for the exposed surface of the reserved rock column.

[0075] S3: Excavate the arch's reserved rock pillar C. After excavation is complete, promptly implement initial support for the excavated free surface, including installing prestressed, widely spaced, long anchor bolts 1, closely spaced, short anchor bolts 2, and spraying steel fiber concrete 3. Depending on the rock mass, temporary support may be provided for the free surface of the intermediate reserved rock platform. The arch's central pilot tunnel A, the upper side pilot tunnel B, and the arch's reserved rock pillar C are interconnected and located in the upper portion of the cavern, creating a U-shaped space opening downward.

[0076] S4: A large-span gradual arch cover structure 4 and arch corner longitudinal hidden beams 5 are constructed in the arch part of the cavern to form a stable arch bearing structure.

[0077] S5: Continue excavating the lower pilot tunnel rock mass D. Provide timely initial support for the excavated free surface, including installing closely spaced short anchor bolts 2 and spraying steel fiber concrete 3. Depending on the rock mass conditions, temporary support may be provided for the free surface of the reserved intermediate rock platform. At this point, the two sides of the U-shaped space expand downward to the cavern floor.

[0078] S6: Excavate the reserved rock platform E at the lower part and construct the secondary lining 6 of the side wall. The secondary lining 6 of the side wall is connected to the large-span gradual arch cover structure 4 by using a hinged node 7.

[0079] The process of installing the articulated node 7 is as follows:

[0080] First, the upper support plate 71 is connected to the large-span gradual arch cover structure 4 by post-anchoring through anchor bolts 74;

[0081] Then, the lower support plate 72 is connected to the secondary lining steel bars of the side wall through anchor bolts 74, the lower support plate 72 is fixed, and the secondary lining 6 of the side wall is poured;

[0082] Finally, fill the gap between the upper and lower support plates with flexible sealing materials (rubber, silicone, etc.) to wrap the nodes to prevent dust and water vapor from invading the friction surface.

[0083] The hinged nodes 7 can be arranged longitudinally throughout or at intervals. The length of each segment and the longitudinal spacing need to be determined based on the actual bearing capacity calculation results.

[0084] At this time, the spaces where the middle guide tunnel A of the arch, the upper side guide tunnel B, the reserved rock pillar C of the arch, the lower guide tunnel rock body D and the lower reserved rock platform E are located are all connected, and the space inside the cave is all excavated.

[0085] S7: Circumferential lattice beams 8 and longitudinal lattice beams 9 are constructed on the inner side of the secondary lining to form a stable lattice beam system.

[0086] The circumferential lattice beams 8 and longitudinal lattice beams 9 are constructed simultaneously, starting from the bottom up, with the longitudinal lattice beams surrounding the side walls being constructed first, followed by the circumferential lattice beams surrounding the arches. Connecting steel bars can be pre-reserved between the arches and the side walls, allowing for direct, integrated casting in the formwork.

[0087] S8: Apply the base plate 10 and complete the construction.

[0088] Alternatively, the cavern can be divided longitudinally into multiple sections, with construction progressing gradually according to designated lengths. The pilot tunnels can also be staggered longitudinally, with temporary supports and bracing in place to ensure construction safety within the cavern.

[0089] In summary, the gradual arch cover design of the arch of the present invention conforms to the stress pattern of the cavern, enhances the integrity and stability of the arch cover, and takes into account safety and economy. The hinged connection design between the side wall and the arch is beneficial to the stability of the side wall structure. The design of the lattice beam system can make the stress transfer more dispersed and the structural integrity better. The combination of long and short anchor rods, combined with the differential prestressing design, can combine the shallow broken rock mass and the deep stable rock mass into an organic whole, forming a three-dimensional load-bearing structure with "deep and shallow combination, tension and shear control".

[0090] The above examples are used to illustrate the present invention, which are only used to help understand the present invention and are not intended to limit the present invention. Those skilled in the art can make several simple deductions, modifications or substitutions based on the concept of the present invention.

Claims

1. The support system for hard rock large-span flat caverns is characterized by: The support system includes, from outside to inside, initial support, secondary lining and lattice beam system; The secondary lining comprises a giant span gradual arch cover structure (4) of the arch portion, a longitudinal hidden beam at an arch angle (5) and a secondary lining (6) of the side wall; the secondary lining (6) of the side wall is located at the bottom of both transverse ends of the giant span gradual arch cover structure (4) and is arranged vertically; the longitudinal hidden beam at an arch angle (5) is an enlarged arch angle of the giant span gradual arch cover structure (4), connected between the transverse end of the giant span gradual arch cover structure (4) and the top of the secondary lining (6) of the side wall, and is arranged vertically and located on the hard surrounding rock; The lattice beam is located on the inner side of the secondary lining.

2. The support system for a hard rock large-span flat cavern according to claim 1 is characterized by: The initial support includes an anchor system and sprayed steel fiber concrete (3); The scope of the sprayed steel fiber concrete (3) involves the top of the large-span gradual arch cover structure (4), the outer side of the arch angle longitudinal hidden beam (5) and the outer side of the side wall secondary lining (6); The anchor rod system is driven into the hard surrounding rock and comprises prestressed long anchor rods (1) with large spacing and short anchor rods (2) with small spacing.

3. The support system for a hard rock large-span flat cavern according to claim 2 is characterized by: The top of the large-span gradual arch cover structure (4) and the top of the arch angle longitudinal hidden beam (5) are provided with the prestressed large-spacing long anchor rods (1), which are evenly arranged in the circumferential direction, and a plurality of the small-spacing short anchor rods (2) are provided between the circumferentially adjacent prestressed large-spacing long anchor rods (1); The outer side of the side wall secondary lining (6) is provided with the short anchor rods (2) with small spacing.

4. The support system for a hard rock large-span flat cavern according to claim 1 is characterized by: The lattice beam system comprises a circumferential lattice beam (8) and a longitudinal lattice beam (9); The range of the annular lattice beam (8) involves the bottom of the large-span gradual arch cover structure (4) and the inner side of the side wall secondary lining (6); The longitudinal lattice beam (9) is arranged on the inner side of the side wall secondary lining (6) and intersects with the annular lattice beam (8).

5. The support system for a hard rock large-span flat cavern according to claim 4 is characterized in that: The lattice beam is a cast-in-situ reinforced concrete structure, and the annular lattice beam (8) and the longitudinal lattice beam (9) are cast in one piece.

6. The support system for a hard rock large-span flat cavern according to claim 1 is characterized by: The large-span gradually changing arch cover structure (4) is a cast-in-situ reinforced concrete structure with thickness gradually increasing from the arch top to the arch corner.

7. The support system for a hard rock large-span flat cavern according to claim 1 is characterized by: The transverse end of the large-span gradual arch cover structure (4) is connected to the top of the side wall secondary lining (6) via a hinged node (7), and the hinged node (7) is located on the inner side of the arch angle longitudinal hidden beam (5).

8. The support system for a hard rock large-span flat cavern according to claim 7, characterized in that: The hinge node (7) comprises an upper support plate (71) and a lower support plate (72), the bottom surface of the upper support plate (71) being a convex cylindrical surface, the top surface of the lower support plate (72) being a concave cylindrical surface, the convex cylindrical surface being embedded downwardly into the concave cylindrical surface, and a cylindrical slide plate (73) being sandwiched between the two; The upper support plate (71) is connected to the upper large-span gradual arch cover structure (4) through anchor bolts (74), and the lower support plate (72) is connected to the lower side wall secondary lining (6) through anchor bolts (74); A flexible sealing material (75) is also provided on the contact interface between the upper support plate (71) and the lower support plate (72).

9. The support system for a hard rock large-span flat cavern according to claim 1, characterized in that: A horizontal bottom plate (10) is provided at the bottom of the cavern, and the bottom plate (10) is connected with the secondary linings (6) of the side walls on both sides in a circumferential direction and is closed.

10. A construction method for a support system for a large-span flat cavern in hard rock, characterized by: The construction method comprises: The cavern section is divided into the arch middle pilot tunnel (A), the side upper pilot tunnel (B), the arch reserved rock pillar (C), the lower pilot tunnel rock mass (D) and the lower reserved rock platform (E); the side upper pilot tunnel (B) is located on both sides of the arch middle pilot tunnel (A), the arch reserved rock pillar (C) is located between the arch middle pilot tunnel (A) and the side upper pilot tunnel (B), the lower pilot tunnel rock mass (D) is located below the side upper pilot tunnel (B), and the lower reserved rock platform (E) is located below the arch middle pilot tunnel (A) and between the side upper pilot tunnels (B) and the lower pilot tunnel rock mass (D) on both sides. Excavate the middle pilot hole (A) of the arch and the upper pilot hole (B) of the side. After the excavation is completed, install prestressed long anchor rods with large spacing (1) and short anchor rods with small spacing (2), and construct sprayed steel fiber concrete (3); Excavate the arch to reserve rock columns (C). After the excavation is completed, install prestressed long anchor rods with large spacing (1) and short anchor rods with small spacing (2), and construct sprayed steel fiber concrete (3); A large-span gradual arch cover structure (4) and arch angle longitudinal hidden beams (5) are constructed on the arch portion of the cave chamber to form a stable arch-shaped bearing structure; Continue excavating the lower pilot tunnel rock mass (D), installing short anchor bolts with small spacing (2), and constructing sprayed steel fiber concrete (3); Excavate the reserved rock platform (E) at the bottom, construct the secondary lining (6) of the side wall, and connect the secondary lining (6) of the side wall to the large-span gradual arch cover structure (4) with a hinged node (7); Circumferential lattice beams (8) and longitudinal lattice beams (9) are constructed on the inner side of the secondary lining to form a stable lattice beam system; Apply base plate (10) to complete the construction.

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