A construction method for covering an underground large-span spherical reinforced concrete dome

Abstract

The present invention relates to the technical field of underground cavern covering construction, and particularly to a method for covering an underground large-span spherical reinforced concrete dome. The method involves the following steps: 1) dome excavation: using a circular excavation and reserved rock pillar method to excavate and support the dome cavern ring by ring; during the excavation of the dome inner ring and core columns, a 3-meter high platform is retained in the center of the cavern; 2) ring beam construction: 3) setting up a temporary working platform; 4) installing the outer and inner layers of dome reinforcement; first installing the outer layer reinforcement, then the inner layer reinforcement; 5) assembling load-bearing supports; 6) installing dome formwork and wooden boards; 7) support reinforcement: increasing the number of columns and adding inter-column supports; 8) concrete pouring and curing; 9) removing the formwork and support, and excavating the 3-meter high platform retained in the center of the cavern. The present invention enhances the overall stability of the support, reduces safety risks, and effectively ensures construction quality, progress, and the safety of construction personnel.

Description

Technical Field

[0001] The invention relates to the technical field of underground cavern covering construction, in particular to an underground large-span spherical crown-shaped reinforced concrete dome covering construction method. Background Art

[0002] With the rapid development of my country's economy, more and more underground projects have entered the planning and construction stage. As an important part of large vertical storage caverns, spherical dome covering has the characteristics of large volume, heavy weight, large formwork area, difficult forming control, and high construction cost. Since the dome covering is set close to the rock surface, construction workers can only stand under the dome to work. The construction requirements for steel bar binding, dome support system and formwork selection and support, curvature control, concrete pouring, formwork removal, etc. are very high. Due to the limited construction space in the cavern, large mechanical equipment cannot be used. It mainly relies on small machinery and manpower to carry out material handling, full-height frame erection, formwork assembly, concrete pouring and other tasks. The labor input is large, the construction efficiency is low, and it is difficult to guarantee the construction period. Conventional covering construction methods are not applicable, and there is currently little construction experience available in China. Therefore, a covering construction method suitable for underground large-span spherical domes is needed to provide technical support for the safe and efficient construction of the project. Summary of the Invention

[0003] The present invention aims to provide a construction method for covering an underground large-span spherical reinforced concrete dome, which can solve a series of technical difficulties arising during the construction of the spherical dome, effectively ensure the construction quality and progress, and reduce construction costs and safety risks.

[0004] In view of the shortcomings of existing construction technology, the technical solution adopted by the present invention is: a construction method for covering an underground large-span spherical crown reinforced concrete dome, comprising the following steps:

[0005] 1) Dome Excavation: The dome cavern is excavated and supported ring by ring using the circular excavation and reserved rock pillar method. During the excavation of the dome inner ring and core pillar, a 3m high platform is retained in the center of the cavern. The circular excavation and reserved rock pillar method, which reserves a rock pillar in the middle, first excavates a radial central pilot tunnel, then excavates and supports the dome using circular blasting in sequence. After each cycle of advance, timely support is provided and the surrounding rock is sealed as soon as possible. Finally, the central rock pillar is excavated.

[0006] 2) Ring beam construction: The dome is poured in two stages, i.e. the ring beam and dome concrete are poured separately; the construction joint is left at the boundary between the ring beam and the shell, 500mm away from the shell side;

[0007] 3) Set up a temporary working platform; lay geotextile and waterproof sheet;

[0008] 4) Install the outer and inner layers of the dome reinforcement; install the outer layer reinforcement first, then the inner layer reinforcement;

[0009] 5) Assemble the load-bearing bracket;

[0010] 6) Install dome formwork and wooden boards;

[0011] 7) Support reinforcement: increase the density of columns and add inter-column supports;

[0012] 8) Concrete pouring and curing;

[0013] 9) Remove the formwork and support, and dig out the 3m high platform retained in the center of the cavern.

[0014] Step 5) The radial main beams and load-bearing columns are prefabricated in the component processing plant and transported to the site before construction. Each bracket is assembled in the order of erecting the load-bearing columns first and then installing the radial main beams. After the first and second brackets are assembled, they are promptly connected together with connecting bars. Then, this is used as a stabilizing system to install other load-bearing brackets on both sides. After the outer ring load-bearing brackets are installed stably, the inner ring load-bearing brackets are installed in sequence until the entire bracket system is installed.

[0015] In step 5), to ensure the spherical forming effect of the dome, 5 rings of reinforcement beams are added close to the lower edge of the radial main beam, which are connected to the radial main beam with bolts. The reinforcement beams are all set at the top of the columns.

[0016] In step 6), to ensure the smoothness of the concrete surface, 6mm thick bamboo plywood and acrylic panels are used close to the concrete surface. 50mm×200mm wooden boards are placed under the panels as secondary ribs. They are arranged in a circular pattern, with the boards tightly attached to each other without leaving any gaps. The joints of the wooden boards are left on the radial main beam and firmly fixed with wire.

[0017] In step 8), the concrete pouring starts from the bottom pouring port of the formwork and is carried out from bottom to top, ring by ring, to ensure that the load on the dome is uniform at any time and to avoid eccentricity;

[0018] In step 9), the order of removing the formwork and supports is: starting from the center of the dome and removing them ring by ring outward.

[0019] The present invention provides a method for covering an underground large-span spherical reinforced concrete dome, which adopts the above technical solution and has the following beneficial effects:

[0020] 1. The present invention directly sets up the bracket on the reserved high platform, thereby reducing the height of the full-hall bracket, saving turnover materials, enhancing the overall stability of the bracket, and reducing safety risks.

[0021] 2. The present invention is easy to operate, requires less resource investment, and saves construction costs.

[0022] 3. The present invention can solve a series of technical problems that arise during the construction of a spherical reinforced concrete dome covering close to the rock surface, and effectively ensure the construction quality, progress and safety of construction workers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the planar division of the circular excavation of the dome cavern;

[0024] Figure 2 This is a cross-section of the circular excavation of the dome cavern;

[0025] Figure 3 It is a plan view of the support system;

[0026] Figure 4 It is a schematic diagram of the support system elevation;

[0027] In the figure, 1. load-bearing column; 2. load-bearing column; 3. radial main beam; 4. circular reinforcement beam; 5. sweeping rod; 6. construction joint. DETAILED DESCRIPTION

[0028] The present invention will be further described below with reference to the accompanying drawings and examples. It should be understood that the described examples are only a portion of the present invention, not the entire invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to fall within the scope of the claims.

[0029] like Figures 1 to 4 A method for covering an underground large-span spherical reinforced concrete dome comprises the following steps:

[0030] Step 1: Dome excavation; Figure 1 and Figure 2 As shown in the figure, the dome cavern adopts the method of circular excavation with reserved rock pillars, that is, a rock pillar V is reserved in the middle, radial middle pilot tunnel I is excavated first, and then II, III, and IV are excavated in sequence by circular blasting. After each cycle of excavation, initial support is provided in time and the ring is closed as soon as possible. Finally, the central rock pillar V is excavated. Figure 1 and Figure 2 Excavation is carried out in the order of Ⅰ→Ⅱ→Ⅲ→Ⅳ→Ⅴ→VI;

[0031] In order to reduce the height of the support and improve the overall stability of the support system, under the premise of ensuring the working space of the crawler down-the-hole drill, a 3m high platform VI is reserved in the center of the cavern and is not excavated temporarily. The support is directly set up on the high platform (see Figure 4 ), reducing safety risks. In step nine, the 3m high platform retained in the center of the cavern can be excavated.

[0032] Step 2: Ring beam construction: The dome structure is large and difficult to cast in one go. Therefore, the ring beam and dome concrete are cast separately (see Figure 4); that is, pour the ring beam and the dome concrete within the lowest 500mm range first, and then pour the remaining part of the dome. When tying the ring beam reinforcement, radial reinforcement of the dome should be reserved in advance. The reserved reinforcement length should not be less than the anchorage length, and the area of the connection joints in the same section should not exceed 50%;

[0033] Step 3: Set up a temporary working platform: The temporary working platform is constructed with Φ48×3.6 ordinary steel pipes, with a circumferential and radial spacing of 1.5m×1.5m for vertical poles and a horizontal pole pitch of 1.5m; the scaffolding is made of 50×200mm wooden boards; it is mainly used for laying geotextiles, laying waterproofing boards, tying dome reinforcement, setting up load-bearing supports, installing formwork, and pouring concrete;

[0034] Step 4: Install the outer and inner layers of dome reinforcement: During dome reinforcement construction, the dome reinforcement often sinks excessively due to its large span and low rise. The traditional approach is to embed hooks in the arch to control the sinking of the secondary lining reinforcement. However, using embedded hooks will damage the waterproof layer and cannot guarantee waterproofing. To address this construction technical challenge, Φ48×3.5mm ordinary steel pipes are used to temporarily support the outer layer of reinforcement, with a circumferential × radial spacing of 3.0×3.0m. The specific method is: "Dry"-shaped reinforcement is installed on the top of the steel pipe, with the spacing between the two horizontal bars equal to the concrete cover thickness. The outer layer of reinforcement is installed on the first bar, and the inner layer of reinforcement is installed on the second bar. The steel pipe column is supported at the position of the second layer of horizontal reinforcement. After the concrete is poured, the "Dry"-shaped reinforcement is not removed. After the formwork is removed, the exposed steel bar heads are cut with a grinding wheel cutter. Electric welding and gas cutting are strictly prohibited.

[0035] Step 5: Prefabrication and installation of radial main beams and columns: The full-height bracket is the support system for the entire dome structure during the concrete pouring period; the construction requirements of the full-height bracket are:

[0036] (1) Material unloading: Due to the narrow construction area, large machinery cannot enter. Materials such as steel bars, formwork, wood boards, steel sections, and steel pipes are mainly handled and installed manually, which is labor-intensive and time-consuming, and the construction efficiency is low. To facilitate manual handling, when the height of the load-bearing columns or the length of the radial main beam are large, they should be manufactured in sections and assembled on site. If the length is greater than 8m, it should be divided into three sections. If it is less than 8m, it can be divided into two sections. If it is less than 4m, it can be left undivided. Ensure that the weight of each section does not exceed 80kg.

[0037] (2) Component production: The radial main beams and circumferential reinforcement beams are enlarged at a ratio of 1:1, a steel frame processing platform is set up, and a processing mold is made according to the design line shape to ensure that the steel frame is consistent with the design line shape after forming.

[0038] (3) Installation of radial main beams: The radial main beams and load-bearing columns are prefabricated in the component processing plant and transported to the site before construction. Each bracket is assembled in the order of first erecting the load-bearing columns and then installing the radial main beams. After the first and second brackets are assembled, they are promptly connected together with connecting bars. Then, using this as a stable system, other load-bearing brackets are installed on both sides. When the outer ring load-bearing brackets are installed and stabilized, the inner ring load-bearing brackets are installed in sequence until the entire bracket system is installed.

[0039] (4) Installation of circumferential reinforcement beams: To ensure the spherical forming effect of the dome, five ring reinforcement beams (18# I-beams) are added close to the lower edge of the radial main beams. They are connected to the radial main beams with 2M20×60 bolts. The reinforcement beams are all set at the top of the columns.

[0040] (5) To facilitate the subsequent formwork installation, the columns are installed in two stages. The columns installed in the first stage are only used to bear the weight of the radial main beam, wooden boards and formwork. The specific number of columns installed is: there are at least two columns under each radial main beam. After all the dome formwork is installed in place, the remaining columns are installed.

[0041] (6) The load-bearing columns are all made of Ф108×6.0mm ordinary steel pipes with different heights. The circumferential × radial spacing of the outer ring load-bearing columns is approximately 0.9m×2.0m (only the spacing of the outermost columns is 0.9m×1.5m), and the circumferential × radial spacing of the inner ring load-bearing columns is approximately 0.9m×2.5m.

[0042] (6) 10mm thick connecting plates are welded to the top and bottom of the load-bearing columns. The top is connected to the radial main beam (I-beam) by 2M20×60 bolts, and the bottom is firmly fixed to the ground with Ф16 round steel to prevent the column from shifting.

[0043] (7) Horizontal supports between columns are made of Ø48×3mm ordinary steel pipes, and are welded to the columns. The weld thickness shall not be less than 5mm. Horizontal rods are set in both longitudinal and transverse directions. A horizontal sweeping rod is set in each direction 200mm above the ground to ensure that the free length of all columns is no more than 4.0m, reducing the calculated length of the compression rod, thereby ensuring the stability of the support system.

[0044] Step 6: Install the dome formwork and wooden boards. Since the dome cover is set close to the rock surface, construction workers can only stand under the dome to work, which makes construction extremely difficult. To solve this construction problem, the following methods can be used:

[0045] (1) The bottom formwork of the dome should not be too thick. 6mm thick bamboo plywood is sufficient. The bottom formwork is prefabricated on site using an enlarged sample and assembled in sections. It is laid ring by ring from the periphery to the center. The joints are sealed with tape to prevent leakage during concrete pouring and reduce the repair work of the joints and the top surface in the later stage. 50mm×200mm wooden boards are placed under the panel as secondary ribs. They are arranged in a ring direction. The boards are tightly attached to each other without leaving any gaps. The joints of the wooden boards are all left on the radial main beam (I-beam). The I-beam extension is connected with a 15mm thick connecting plate.

[0046] (2) When the bottom formwork is set up, pouring openings and vibrating openings are left on the dome, distributed in a plum blossom shape. Each window is equipped with a window cover. The window size is 400mm×400mm, and the window spacing is 3~4m, so that concrete can be poured, the vibrating rod can be extended to the bottom of the dome, and the concrete filling can be observed to be dense. After the concrete is poured to the vibrating opening, the formwork at the vibrating opening is closed and the concrete pouring of the upper part of the dome continues.

[0047] (3) Pre-buried Φ42mm grouting steel pipes are placed at the highest point of the dome formwork, with a spacing of 2 to 3m and arranged in a plum blossom shape.

[0048] Step 7: Strengthen the bracket.

[0049] (1) After all the dome formwork is installed, start installing the remaining load-bearing columns.

[0050] (2) Since the longer the free length of the load-bearing columns, the greater the possibility of buckling instability. Therefore, horizontal bars are set in both the longitudinal and transverse directions between the columns to ensure that the free length of all columns is no more than 4.0m, reducing the calculated length of the compression bars and thus increasing the stability of the support system. A horizontal sweeping bar is set in each direction at 200mm above the ground (see Figure 4 ).

[0051] Step 8: Concrete pouring. The dome concrete is self-compacting, forced into the formwork using a ground pump. Starting from the bottom pouring port of the formwork, concrete is poured ring by ring from bottom to top to ensure uniform loading on the dome at all times and avoid skewed loads.

[0052] While ensuring that no cold joints occur during construction, try to slow down the concrete pouring speed (control the pouring speed to about 0.6m high per hour to match the calculated working conditions) to reduce the lateral pressure of the concrete on the formwork, reduce the load on the support system, and thus reduce the verticality deviation caused by the displacement of the formwork system.

[0053] Covering concrete should be poured continuously and formed in one go, avoiding cold construction joints. If pauses are necessary, they should be placed before the previous layer of concrete begins to set, ensuring that the upper layer is poured. The maximum pause time should be determined by the concrete's setting time. Any pause exceeding the initial setting time should be treated as a construction joint.

[0054] During the concrete pouring process, full-time personnel are arranged to check the support conditions of steel pipes, top supports, and formwork at any time. Once there is looseness, displacement, bending or twisting, the pouring speed must be slowed down or stopped in time, and the support must be replaced or reinforced to ensure the appearance quality of the concrete and the personal safety of the construction workers.

[0055] Step 9: Remove the formwork and supports. Removal sequence: Start at the mid-span and work your way outwards, ring by ring. Strength control during formwork removal: The concrete strength at the time the formwork and supports are removed must meet design requirements, based on the compressive strength report of test blocks cured under the same conditions. For large-volume concrete, formwork removal must not only meet concrete strength requirements but also ensure that the temperature difference between the inside and outside of the concrete drops below 25°C. Otherwise, effective measures must be taken to prevent temperature cracks.

[0056] During the formwork removal process, if it is found that the actual structural concrete strength does not meet the requirements and there are quality problems that affect the structural safety, the formwork removal should be suspended. After proper processing and the actual strength reaches the requirements, the removal can be continued.

[0057] Main component parameter table

[0058] Serial number member Material Project volume Remark 1 load-bearing columns 16# I-beam 96 roots 2 Steel pipe column Ф108×6 steel pipe 1335m Ordinary steel pipe 3 Steel pipe column Ф300×6 steel pipe 4.05m Ordinary steel pipe 4 Steel pipe column inclined rod Ф48×3 steel pipe － Ordinary steel pipe 5 Circumferential horizontal rod Ф48×3 steel pipe － Ordinary steel pipe 6 Radial horizontal rod Ф48×3 steel pipe － Ordinary steel pipe 7 Radial main beam 16# I-beam 929m 8 Circumferential reinforcement beam 18# I-beam 197.8m 9 Circumferential secondary ridge 50mm×200mm wooden board 724m² Full Shop 10 template bamboo plywood 724m² Panel thickness 6mm

[0059] The invention solves a series of technical difficulties in covering construction of large-span spherical crown-shaped reinforced concrete domes in underground projects, ensures construction quality and progress, and reduces construction costs and safety risks.

Claims

1. A method for covering an underground large-span spherical reinforced concrete dome, characterized by: The following steps are involved: 1) Dome Excavation: The dome cavern is excavated and supported ring by ring using the circular excavation and reserved rock pillar method. During the excavation of the dome inner ring and core pillar, a 3m high platform is retained in the center of the cavern. The circular excavation and reserved rock pillar method, which reserves a rock pillar in the middle, first excavates a radial central pilot tunnel, then excavates and supports the dome using circular blasting in sequence. After each cycle of advance, timely support is provided and the surrounding rock is sealed as soon as possible. Finally, the central rock pillar is excavated. 2) Ring beam construction: The dome is poured in two stages, with the ring beam and dome concrete poured separately. A construction joint is left at the boundary between the ring beam and the shell, 500mm from one side of the shell. The ring beam and the dome concrete within the lower 500mm are poured first, followed by the remaining dome. When tying the ring beam reinforcement, radial reinforcement for the dome should be reserved in advance. The reserved reinforcement length should not be less than the anchorage length, and the joint area within the same section should not exceed 50%. 3) Set up a temporary working platform; lay geotextile and waterproof sheet; 4) Install the outer and inner layers of dome reinforcement; install the outer layer first, then the inner layer. Use Φ48×3.5mm ordinary steel pipes to temporarily support the outer layer of reinforcement, with a circumferential and radial spacing of 3.0×3.0m. Install "stem"-shaped reinforcement on top of the steel pipe, with the spacing between the two horizontal bars equal to the concrete cover thickness. The outer layer of reinforcement is installed on the first bar, and the inner layer of reinforcement is installed on the second bar. The steel pipe column is supported at the position of the second layer of horizontal reinforcement. Do not remove the "stem"-shaped reinforcement after pouring the concrete. After removing the formwork, cut the exposed steel bar heads with a grinding wheel cutter. Electric welding or gas cutting is strictly prohibited. 5) Assemble the load-bearing brackets. To ensure the spherical shape of the dome, five rings of reinforcement beams are added close to the lower edge of the radial main beams. Bolts are used to connect the reinforcement beams to the radial main beams. The reinforcement beams are all installed at the top of the columns. 6) Install the dome formwork and wooden boards. To ensure the smoothness of the concrete surface, 6mm thick bamboo plywood and acrylic boards are placed close to the concrete surface. 50mm x 200mm wooden boards are placed under the panels as secondary ribs. They are arranged in a circular pattern, with the boards tightly fitted together without any gaps. The joints of the wooden boards are left on the radial main beams and fixed firmly with wire. 7) Support reinforcement: increase the density of columns and add inter-column supports; 8) Concrete pouring and curing; 9) Remove the formwork and support, and dig out the 3m high platform retained in the center of the cavern.

2. The method for covering an underground large-span spherical reinforced concrete dome according to claim 1, characterized in that: Step 5) The radial main beams and load-bearing columns are prefabricated in the component processing plant and transported to the site before construction. Each bracket is assembled in the order of erecting the load-bearing columns first and then installing the radial main beams. After the first and second brackets are assembled, they are promptly connected together with connecting bars. Then, using this as a stabilizing system, other load-bearing brackets are installed on both sides. After the outer ring load-bearing brackets are installed stably, the inner ring load-bearing brackets are installed in sequence until the entire bracket system is installed.

3. The method for covering an underground large-span spherical reinforced concrete dome according to claim 1, characterized in that: In step 8), the concrete pouring starts from the bottom pouring port of the formwork and is carried out ring by ring from bottom to top to ensure that the load on the dome is uniform at any time and to avoid eccentricity.

4. The method for covering an underground large-span spherical reinforced concrete dome according to claim 1, characterized in that: In step 9), the order of removing the formwork and supports is: starting from the center of the dome and removing them ring by ring outward.

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