New pressure-yielding tunnel bottom structure and pressure-yielding construction method for expansive rock railway tunnels

Abstract

The present invention provides a new pressure-yielding tunnel bottom structure and pressure-yielding construction method for an expansive rock railway tunnel, belonging to the technical field of tunnel construction, and comprising an inner core, a core sleeve, a core cap, a gasket, and a sawtooth. The present invention carries out an overall planning and design of the core cap, the inner core, the gasket, the core sleeve, and the tunnel support structure according to the specific conditions of the tunnel engineering geological conditions, the hydrogeological conditions, and the economic budget, etc., which can ensure that the tunnel expansion force pressure-yielding device can play the maximum role, reduce the amount of arching of the tunnel bottom, and enhance the adaptability and matching between the support and the surrounding rock, thereby increasing the rigidity and strength of the overall structure of the tunnel. The method is simple to operate, low in cost, and easy to repair, which can greatly reduce the overall cost of the project and the cost of subsequent operation and maintenance. It can be applied to railway tunnels, highway tunnels, coal mine tunnels, etc., and can effectively reduce the amount of arching of the tunnel bottom and improve the stability and safety of the overall structure.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel construction, and in particular to a novel pressure-yielding tunnel bottom structure for an expansion rock railway tunnel and a pressure-yielding construction method. Background Art

[0002] Tunnel construction is particularly challenging in environments with larger cross-sections, higher speeds, greater burial depths, higher ground stresses, and more complex geological conditions. During construction and operation, some tunnels have experienced localized tunnel floor arching and cracking of the fill layer. High-speed rail tunnels generally utilize ballastless track technology, requiring a high-quality assessment of the tunnel floor construction before track slab laying. During operation, any occurrence of tunnel floor arching and other defects poses a significant risk to traffic safety. Generally, tunnel floor arching is primarily caused by plastic shear expansion. When the floor is composed of expansive soil minerals, the water content increases significantly, causing the floor to expand and deform, leading to arching. Tunnel floor arching can be classified into four types based on its failure mechanics: extrusion flow-type arching, water-expansion-type arching, shear dislocation-type arching, and flexural fold-type arching. Water-expanding tunnel floor arching occurs when certain minerals with significant hydrophilic components swell and soften upon contact with water, rapidly increasing in volume and causing significant deformation of the surrounding rock. The tunnel floor's expansive rock experiences triaxial compression, with the greater the expansion rate, the greater the ultimate expansion pressure. Once this ultimate expansion pressure exceeds the structural resistance of the tunnel floor, tunnel floor arching occurs. Furthermore, expansive rock presents significant engineering risks, both due to the complex changes it undergoes during engineering disturbances and due to the lack of clarity regarding its deformation patterns and constitutive relationships under external forces. Summary of the Invention

[0003] The object of the present invention is to provide a new pressure-releasing tunnel bottom structure and pressure-releasing construction method for an expansion rock railway tunnel, so as to solve at least one technical problem existing in the above-mentioned background technology.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] In one aspect, the present invention provides a novel pressure-yielding tunnel bottom structure for an expansive rock railway tunnel, comprising:

[0006] An inner core, and a core sleeve movably sleeved on the inner core;

[0007] A core cap is provided on the top of the inner core;

[0008] The core sleeve includes a sleeve body for movably inserting the inner core, one end of the sleeve body is connected to a gasket, and the other end of the sleeve body is connected to a pair of rod bodies on both sides, and the rod bodies are provided with a plurality of saw teeth;

[0009] The end of the inner core extending into the sleeve is tapered, and the middle of the sleeve is provided with a recessed portion recessed toward the inner core, so that when the inner core extends into the sleeve, the rod body is expanded under the action of the recessed portion.

[0010] In a second aspect, the present invention provides a railway tunnel pressure-releasing construction method using the novel pressure-releasing tunnel bottom structure of the expansive rock railway tunnel described above, comprising:

[0011] Measure the upper and lower lines of the reserved steel bars, and calculate the transverse excavation depth of the pre-excavated invert arch section based on the height difference between the baseline elevation and the invert arch excavation surface elevation;

[0012] arch wall and invert arch excavation;

[0013] Drilling and placement of expansion force relief devices;

[0014] Apply initial stress;

[0015] Initial support and secondary lining of inverted arch;

[0016] Backfill and pouring of the invert arch.

[0017] Preferably, the excavation of the arch wall and the inverted arch includes: the excavation of the inverted arch soil layer should be mainly manual excavation in combination with mechanical excavation. According to the different types of surrounding rock, when using upper and lower steps for excavation, the length of the excavation section should be controlled. For Grade V surrounding rock sections, the excavation length should be ≤3m, for Grade IV surrounding rock sections, the excavation length should be ≤5m, and for Grade III and above surrounding rock sections, the excavation length should be ≤10m.

[0018] Preferably, the drilling and placement of the expansion force pressure relief device include: drilling holes perpendicular to the centers of the corresponding circles of the tunnel bottom invert arches in sequence according to a preset construction sequence, and placing the expansion force pressure relief device into the holes.

[0019] Preferably, applying the initial stress includes: first, using a pile driver to hit the gasket so that the tip of the serrated rod portion of the core sleeve is deeply inserted into the surrounding rock; then using a pile driver or a manual hammer to hit the core cap of the inner core so that the height of the inner core is further reduced, so that the serrated portion of the core sleeve is completely inserted into the surrounding rock.

[0020] Preferably, the initial support and secondary lining of the inverted arch include: before installing each support structure, measuring the geometric dimensions of the base elevation to check whether it meets the design requirements, clearing out the loose ribs, debris and accumulated water in the foundation pit, and then laying a concrete leveling layer; then installing the inverted arch steel frame, and then carrying out the initial support construction of the inverted arch, installing the arch foot drainage pipe, tying the secondary lining steel bars, erecting the formwork, and pouring the inverted arch concrete.

[0021] Preferably, the installation of the inverted arch steel support must comply with the design and specification requirements, and must be welded firmly to the side wall arch frame; the protruding length of the embedded steel bars in the secondary lining side walls on both sides of the inverted arch should meet the requirements for welding with the circumferential secondary lining steel bars, and the joints should be staggered so that the number of steel bar joints in the same section is not more than 50% of the total number; the binding of the secondary lining steel bars of the inverted arch must ensure the spacing, and the layer spacing must be ensured by welding positioning steel bars.

[0022] Preferably, the backfilling and pouring of the inverted arch include: strictly verifying the concrete mix ratio before pouring the inverted arch, using a top formwork with reserved vibration holes to ensure that the concrete is vibrated and dense, and pouring the inverted arch concrete using pumped concrete.

[0023] Preferably, the location of the reserved settlement joints should be designed in advance before the construction of the inverted arch. The settlement joints should ensure that the secondary lining concrete, arch wall and inverted arch are disconnected in the same vertical plane, and the settlement joints should be processed as required.

[0024] The beneficial effects of the present invention are as follows: the tunnel inverted arch is subjected to the vertical load transmitted by the upper stratum and the deadweight of the structure through the arch foot, and the bottom is subjected to the upward stratum reaction force and expansion force of the lower foundation. Under the interaction of these multiple forces, the inverted arch and its filling are formed with large internal forces. In addition, the influence of long-term train operation causes the tunnel structure to generate large structural internal forces in both the horizontal and vertical directions.

[0025] Additional aspects and advantages of the present invention will be set forth in part in the following description, will become apparent from the following description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 This is a schematic diagram of the water-expandable tunnel bottom arch according to an embodiment of the present invention.

[0028] Figure 2 Schematic diagram of a pressure relief device for applying expansion force to the cross section of a high-speed railway double-track tunnel according to an embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram of the factory prefabrication state of the new pressure-releasing tunnel bottom structure according to an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram of the state of the novel pressure-releasing tunnel bottom structure after initial stress is applied according to an embodiment of the present invention.

[0031] Figure 5 Schematic diagram of the inner core structure of the novel pressure-yielding tunnel bottom structure according to an embodiment of the present invention.

[0032] Among them: 1-inner core; 2-core sleeve; 3-core cap; 4-sleeve body; 5-gasket; 6-rod body; 7-serration; 8-recessed part; 9-through hole. DETAILED DESCRIPTION

[0033] The embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention and are not to be construed as limiting the present invention.

[0034] Those skilled in the art will understand that unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs.

[0035] It should also be understood that terms, such as those defined in commonly used dictionaries, should be understood to have a meaning consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless as defined herein.

[0036] Those skilled in the art will appreciate that, unless otherwise stated, the singular forms "a," "an," "said," and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and / or groups thereof.

[0037] In the description of this specification, reference to the terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and integrate different embodiments or examples described in this specification, as well as features of different embodiments or examples, unless otherwise inconsistent.

[0038] In the description of this specification, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0039] In the description of this specification, the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings. They are only for the convenience of describing the present technology and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, they should not be understood as limiting the present technology.

[0040] Unless otherwise specified or limited, the terms "installed," "connected," "connected," and "disposed" should be understood broadly. 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 these terms in this technology based on specific circumstances.

[0041] To facilitate understanding of the present invention, the present invention is further explained below with reference to specific embodiments in conjunction with the accompanying drawings. However, the specific embodiments do not constitute a limitation on the embodiments of the present invention.

[0042] Those skilled in the art should understand that the drawings are merely schematic diagrams of embodiments, and the components in the drawings are not necessarily necessary for implementing the present invention.

[0043] Example

[0044] like Figures 1 to 5 As shown, in this embodiment, a new pressure-yielding tunnel bottom structure for an expansion rock railway tunnel is first provided, comprising: an inner core 1, and a core sleeve 2 movably sleeved on the inner core 1; a core cap 3 is provided on the top of the inner core 1; the core sleeve 2 comprises a sleeve body 4 for movably inserting the inner core 1, one end of the sleeve body 4 is connected to a gasket 5, and a through hole 9 is provided in the middle of the sleeve body 4 for the inner core 1 to extend into the sleeve body 4, and a gasket 5 is provided on each side of the through hole 9, and a pair of rod bodies 6 are connected to the end portions of the other end of the sleeve body 4, and a plurality of serrations 7 are provided on the rod bodies 6; the end of the inner core 1 extending into the sleeve body 4 is tapered, and the middle part of the sleeve body 4 is provided with a recessed portion 8 recessed toward the inner core 1, so that when the inner core 1 extends into the sleeve body 4, the rod body 6 is supported open by the action of the recessed portion 8.

[0045] After using the novel yielding tunnel floor structure for expansive rock railway tunnels provided in this embodiment, the tunnel invert is subjected to vertical loads transmitted through the arch foot from the upper strata and the deadweight of the structure, while the bottom is subjected to the upward stratum reaction force and expansion force from the lower foundation. Under the interaction of these multiple forces, large internal forces are generated within the invert and its filling. Coupled with the influence of long-term train operation, large structural internal forces are generated in the tunnel structure both horizontally and vertically.

[0046] Combined with attachment Figure 4 The new pressure-yielding tunnel bottom structure of this expansive rock railway tunnel is described in detail.

[0047] The new yield tunnel bottom structure consists of a core cap 3, an inner core 1, a gasket 5, and a core sleeve 2. The core cap 3, inner core 1, and gasket 5 are all made of ordinary steel, while the core sleeve is made of special steel with a high Poisson's ratio. Considering the 60cm spacing between each steel arch frame in the initial support and the use of 15-beam steel frames, the core cap is designed to have a diameter of 90cm and a thickness of 5cm. Taking into account the yield paths and evolution characteristics of expansion forces in different directions, the core sleeve consists of a serrated portion and a semicircular portion (i.e., the sleeve body, which, after the recess 8 is installed, has an overall gourd-shaped shape). It is 3m long and lubricated on its outer surface. The tunnel invert is subjected to vertical loads transmitted through the arch foot from the upper strata and the deadweight of the structure. The bottom is also subject to upward ground reaction and expansion forces from the underlying foundation. The interaction of these multiple forces generates significant internal forces within the invert and its filling. Combined with the effects of long-term train operation, this generates significant structural internal forces both laterally and longitudinally in the tunnel structure.

[0048] The principle underlying the present invention is as follows: As drilling proceeds ahead of the pre-embedded device, the reaction and expansion forces of the stratum at the tunnel bottom are somewhat relieved, transforming triaxial stress into biaxial stress. While tangential forces increase, radial forces are reduced. To resist and transmit these internal forces, the expansion force-relieving device embedded in the rock stratum is prestressed by a pile driver or manual hammering. This causes the serrated corners of the core sleeve 2 to open, allowing insertion into the rock stratum (the device has a total length of 3 meters and a borehole depth of 2 meters), ultimately lowering the inner core 1 by 30 cm. The core cap 3 and inner core 1, exposed outside the hole, undergo a series of primary support and secondary lining construction processes, including a concrete leveling layer, steel arch support, spray-mixing, secondary lining steel bars, formwork erection, and pouring of inverted arch concrete, followed by backfilling and pouring, before being anchored integrally to the tunnel structure. The core cap 3, inner core 1, gasket 5 and core sleeve 2 form an expansion bolt system together with the concrete and steel arch frame. The cyclic reciprocating loads from the upper strata and structure, the deadweight of the train, and the accumulation of bending moments in the longitudinal direction cause the cross section of the invert to be subjected to extremely large longitudinal compressive stress, which further resists and suppresses the expansion force at the invert at the tunnel bottom.

[0049] Each step of the present invention will be explained below:

[0050] 1. Factory prefabricated new pressure-relief tunnel bottom structure

[0051] Considering the 60cm spacing between each steel arch in the initial support and the use of 15 I-beams, the core cap was designed with a diameter of 90cm and a thickness of 5cm. Based on mechanical principles, the inner core was designed as a nail-shaped variable-section member with a maximum diameter of 80cm and a length of 2m. To cooperate with the core cap, the left and right gaskets are 90cm long, 50cm wide, and 5cm high, respectively. Considering the pressure-yielding paths and evolution characteristics of expansion forces in different directions, the core sleeve consists of a serrated portion and a semicircular part, with a total length of 3m, and the outer surface of the sleeve is lubricated.

[0052] 2. Measurement and layout

[0053] The upper and lower lines of the reserved steel bars need to be accurately measured. According to the height difference between the baseline elevation and the invert excavation surface elevation, the excavation depth of the pre-excavated invert section at every 1m interval should be calculated to ensure that the invert excavation depth meets the design requirements.

[0054] 3. Excavation of arch wall and inverted arch

[0055] Excavation of the inverted arch soil layer should primarily be done manually with mechanical excavation. Depending on the surrounding rock type, when using upper and lower bench excavation, the length of the excavation section must be controlled. Generally, for Grade V surrounding rock sections, the excavation length should be ≤3m; for Grade IV surrounding rock sections, the excavation length should be ≤5m; and for Grade III and above surrounding rock sections, the excavation length should be ≤10m. When surrounding rock conditions are favorable, the maximum excavation length should not exceed 15m. The junctions between the two corners of the tunnel floor and the side walls should be excavated smoothly to avoid stress concentration. Debris at the bottom of the side wall steel frame should be cleared to ensure a good connection with the inverted arch steel frame. In the case of expansive surrounding rock with significant deformation, anchor bolts should be pre-installed at the two corners of the bottom surface, or other reinforcement measures should be implemented before excavation.

[0056] 4. Drilling and placement

[0057] After the prefabricated new pressure-relieving tunnel bottom structure is delivered to the site, a drilling machine or a small pile driver is used to Figure 2 The construction sequence is A, B, C, D, and E. Five holes are drilled, each 2m deep and 0.9m in diameter, perpendicular to the center of the corresponding circle of the tunnel bottom arch. After drilling, ensure that there is no debris or debris in the hole before placing the pressure-yielding tunnel bottom structure into the hole.

[0058] 5. Apply initial stress

[0059] First, a pile driver is used to hit the left and right gaskets (3) so that the serrated tip of the core sleeve (4) is inserted into the surrounding rock to a depth of about 1 meter (the tip angle is 10 degrees, cos10 degrees = 0.98). Then, a pile driver or a manual hammer is used to hit the inner core (2) so that the height of the inner core (2) is further lowered by about 30 cm so that the serrated portion of the core sleeve (4) is completely inserted into the surrounding rock.

[0060] 6. Initial support and secondary lining of inverted arch

[0061] Before installing each supporting structure, the base elevation and geometric dimensions must be measured to check whether they meet the design requirements. Any loose ties, debris, and accumulated water in the foundation pit must be cleared, and then a concrete leveling layer must be laid. The inverted arch steel frame must then be installed, followed by the initial support of the inverted arch, the arch foot drainage pipe, the secondary lining steel bars, the formwork, and the pouring of the inverted arch concrete. The installation of the inverted arch steel support must comply with the design and specification requirements, and must be welded firmly to the side wall arch frame. The extended length of the embedded steel bars in the secondary lining side walls on both sides of the inverted arch must meet the requirements for welding with the circumferential secondary lining steel bars, and the joints must be staggered so that the number of steel bar joints in the same cross section does not exceed 50% of the total. The spacing between the secondary lining steel bars must be maintained, and the interlayer spacing must be ensured by welding positioning steel bars.

[0062] 7. Backfill and pouring of inverted arch

[0063] Before pouring the inverted arch, the concrete mix ratio should be strictly verified, and the top formwork with reserved vibration holes should be used to ensure that the concrete is vibrated and dense. The inverted arch concrete can be poured by pumping concrete. Before the inverted arch is constructed, the position of the reserved settlement joints should be designed in advance. The settlement joints should ensure that the secondary lining concrete, arch wall and inverted arch are disconnected in the same vertical plane, and the settlement joints should be handled as required to ensure construction quality. In areas where the surrounding rock does not change much, expansion joints should be set as few as possible or not at all to ensure that there are no drainage problems in the lining.

[0064] In summary, the novel pressure-yielding tunnel bottom structure for expansive rock railway tunnels of the present invention is rationally designed based on the actual conditions of the surrounding rock and support. The expansion force is yielded to a circumferential (tangential) expansion force. At the same time, the tunnel bottom is anchored on this basis to form a similar expansion bolt system structure. The combination of the two can greatly increase the stability of the tunnel bottom structure and effectively suppress tunnel bottom uplift. The core cap, inner core, gasket, core sleeve, and tunnel support structure can be generally planned and designed according to the specific conditions of the tunnel engineering geological conditions, hydrogeological conditions, and economic budget. This can ensure that the tunnel expansion force yielding device can play its maximum role, reduce the amount of tunnel bottom arching, and enhance the adaptability and matching between the support and the surrounding rock, thereby increasing the rigidity and strength of the overall tunnel structure. The method is simple to operate, low in cost, and easy to repair, greatly reducing the overall cost of the project and the cost of subsequent operation and maintenance. It can be applied to railway tunnels, highway tunnels, coal mine tunnels, etc., effectively reducing the amount of tunnel bottom arching and improving the overall structural stability and safety.

[0065] Although the above describes the specific embodiments of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solutions disclosed in the present invention without the need for creative work should be included in the scope of protection of the present invention.

Claims

1. A railway tunnel pressure relief construction method using a new pressure relief tunnel bottom structure for an expansive rock railway tunnel, characterized in that: include: Measure the upper and lower lines of the reserved steel bars, and calculate the transverse excavation depth of the pre-excavated invert arch section based on the height difference between the baseline elevation and the invert arch excavation surface elevation; arch wall and invert arch excavation; Drilling and placement of expansion force relief devices; Apply initial stress; Initial support and secondary lining of inverted arch; Backfill and pouring of inverted arch; The excavation of the arch wall and inverted arch includes: the excavation of the inverted arch soil layer should be mainly done by manual excavation combined with mechanical excavation. When using upper and lower steps for excavation according to the type of surrounding rock, the length of the excavation section should be controlled. For Grade V surrounding rock sections, the excavation length should be ≤3m; for Grade IV surrounding rock sections, the excavation length should be ≤5m; and for Grade III and above surrounding rock sections, the excavation length should be ≤10m. The placement of the drilling holes and the expansion force pressure relief device includes: drilling holes perpendicular to the centers of the corresponding circles of the tunnel bottom invert arches in sequence according to a preset construction sequence, and placing the expansion force pressure relief device in the holes; The initial stress application includes: first, using a pile driver to hit the gasket so that the tip of the serrated rod portion of the core sleeve is inserted deep into the surrounding rock; then using the pile driver or a manual hammer to hit the core cap of the inner core so that the height of the inner core is further lowered and the serrated portion of the core sleeve is completely inserted into the surrounding rock; The novel pressure-yielding tunnel bottom structure of the expansion rock railway tunnel includes: An inner core (1), and a core sleeve (2) movably sleeved on the inner core (1); A core cap (3) is provided on the top of the inner core (1); The core sleeve (2) comprises a sleeve body (4) for movably inserting the inner core (1), one end of the sleeve body (4) is connected to a gasket (5), and the other end of the sleeve body (4) is connected to a pair of rod bodies (6) on both sides, and the rod bodies (6) are provided with a plurality of saw teeth (7); The end of the inner core (1) extending into the sleeve (4) is tapered, and a recessed portion (8) recessed toward the inner core (1) is provided in the middle of the sleeve (4), so that when the inner core (1) extends into the sleeve (4), the rod (6) is stretched open under the action of the recessed portion (8).

2. The method according to claim 1, characterized in that The initial support and secondary lining of the inverted arch include: before installing each support structure, measuring the geometric dimensions of the base elevation to check whether it meets the design requirements, clearing out the loose slag, debris and accumulated water in the foundation pit, and then laying the concrete leveling layer; then installing the inverted arch steel frame, and then carrying out the initial support construction of the inverted arch, installing the arch foot drainage pipe, tying the secondary lining steel bars, erecting the formwork, and pouring the inverted arch concrete.

3. The method according to claim 2, characterized in that The installation of the inverted arch steel support must comply with the design and specification requirements, and must be firmly welded to the side wall arch frame; the protruding length of the embedded steel bars in the secondary lining side walls on both sides of the inverted arch should meet the requirements for welding with the circumferential secondary lining steel bars, and the joints should be staggered so that the number of steel bar joints in the same section is not more than 50% of the total. The binding of the secondary lining steel bars of the inverted arch must ensure the spacing, and the layer spacing must be ensured by welding positioning steel bars.

4. The method according to claim 1, wherein Backfill and pouring of the inverted arch include: the concrete mix ratio should be strictly verified before pouring the inverted arch, the top formwork with reserved vibration holes should be used to ensure that the concrete is vibrated and dense, and the inverted arch concrete should be poured with pumped concrete.

5. The method according to claim 4, characterized in that Before the construction of the inverted arch, the location of the reserved settlement joints should be designed in advance. The settlement joints should ensure that the secondary lining concrete, arch wall and inverted arch are disconnected in the same vertical plane, and the settlement joints should be handled as required.

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