Construction method for bottom steel frame of tunnel primary support step

Abstract

The invention provides a tunnel primary support step bottom steel frame construction method which comprises the following steps: 1, constructing an upper step arch frame and a middle step arch frame, and supporting and compacting an arch foot by adopting a concrete cushion block; 2, the arch feet are covered with soil according to the elevation of a construction line; 3, leveling and tamping after the arch springing is covered; 4, performing concrete spraying construction on the arch frames of the upper step and the middle step; 5, excavating a middle step and a lower step, and carrying out arch frame construction on the middle step and the lower step; 6, welding a layer of densified reinforcing mesh between the two arch frames of the lower step, wherein the densified reinforcing mesh is positioned above the top ends of the connecting plates at the end parts of the arch frames; and 7, a baffle is arranged at the outer end of the connecting plate of the arch frame, and bolt holes in the connecting plate are isolated and protected. And when the next step is excavated, the piled soil covering the arch springing naturally falls off, a free working face or space is formed, construction operation is facilitated, and the baffle can isolate and protect bolt holes in the arch frame connecting plate.

Description

Technical Field

[0001] This application belongs to the technical field of tunnel construction. More specifically, it relates to a construction method for the steel frame at the bottom of the initial support of a tunnel step. Background Art

[0002] The bench method is one of the construction methods for tunnels and underground projects. It can be divided into the positive bench method and the reverse bench method. The reverse bench method is also called the middle diaphragm bench method. According to the length of the bench, there are three types: long bench, short bench, and ultra-short bench. In recent years, due to the design of large-section tunnels, there are also the three-bench temporary inverted arch method, the reserved core soil bench method, and even the multi-bench method.

[0003] When constructing using the three-bench temporary inverted arch method, the joints of the benches, the connection plates, and between two sets of steel arch frames are easily covered by shotcrete. Cleaning the sticky soil or debris at the bottom is time-consuming and laborious and difficult. During the excavation construction of the lower bench, the connection plate has a large area and there are many non-compacted areas behind it. During the inverted arch construction, a large amount of concrete residue needs to be cleaned. Using mechanical cleaning is likely to disturb the steel frame, and using manual cleaning is time-consuming and laborious, and there are potential safety and quality hazards. Summary of the Invention

[0004] To solve the above technical problems, the technical solution adopted in this application is: to provide a construction method for the steel frame at the bottom of the initial support of a tunnel step, including the following steps:

[0005] Step 1: Construct the arch frames of the upper and middle benches, and use concrete cushions to support and pad the arch feet firmly.

[0006] Step 2: Cover the arch feet with soil according to the construction line elevation.

[0007] Step 3: After covering the arch feet, level and tamp them to form a straight shotcrete line at the arch feet of the upper bench arch frame.

[0008] Step 4: Carry out shotcrete construction on the arch frames of the upper and middle benches.

[0009] Step 5: Excavate the middle and lower benches and carry out the construction of the arch frames of the middle and lower benches.

[0010] Step 6: Weld a layer of dense steel mesh between two sets of arch frames in the lower bench, and the dense steel mesh is located above the top of the connection plate at the end of the arch frame.

[0011] Step 7: Set baffles at the outer ends of the connection plates of the arch frames to isolate and protect the bolt holes on the connection plates.

[0012] Optionally, in Step 2, the construction line is located at a position 25 - 35 cm above the arch feet of the steel frame.

[0013] Optionally, in step 2, the width of the earth stacking coverage is 30 cm from the springing of the arch to the inner excavation surface, and the height is not less than 30 cm.

[0014] Optionally, in step 2, tunnel muck or rebound material is used to stack earth and cover the springing of the arch.

[0015] Optionally, in step 6, the reinforced steel mesh is welded with plain round steel bars with a diameter of 8 mm, and the mesh width of the reinforced steel mesh is 4 - 8 cm.

[0016] Optionally, in step 7, hooks are provided on the baffle, and the baffle is connected to the connecting plate through the hooks.

[0017] The beneficial effects of the construction method of the steel frame at the bottom of the initial support of the tunnel provided by this application are as follows: Compared with the prior art, before the construction method of this application is adopted, after the lower bench is excavated, it is necessary to manually use a pneumatic pick to chisel the sprayed concrete at the bottom of the steel frame of the upper process. It takes about 1 hour per cycle for two people; it is necessary to clean the bolt holes of the connecting plates at the ends of the arch frames, and there are gaps between the connecting plates that are not closely attached, making it difficult to install bolts and tighten nuts, and there will be a phenomenon of insufficient lap length of the local steel mesh. After adopting this method, the earth filling can be made from local materials, the operation is simple, it takes about 30 minutes per cycle for two people, and 0.5 hours can be saved per cycle, saving 40 yuan in labor costs per cycle. When the lower bench is excavated, the stacked earth covering the springing of the arch naturally falls off, forming a certain free operation surface or space, which is convenient for construction operations. The connecting plates at the outer ends of each arch frame are respectively hung with baffles to isolate and protect the bolt holes on the arch frame connecting plates. The operations such as bolt installation and steel mesh lap take a short time and are convenient to operate. The construction cycle time is reduced by 2 hours, and the cost is saved by 110 yuan per cycle. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is the front view of the earth stacking support at the springing of the upper and middle benches provided by the embodiment of the present application;

[0020] Figure 2 It is the side view of the earth stacking support at the springing of the upper and middle benches provided by the embodiment of the present application;

[0021] Figure 3 It is the front view of the bottom of the arch frame of the lower bench provided by the embodiment of the present application;

[0022] Figure 4The side view of the bottom of the lower-step arch frame provided by the embodiment of the present application;

[0023] Among them, the reference numerals in the figure are as follows:

[0024] 1. Arch frame; 2. Concrete cushion block; 3. Stacked soil; 4. Upper-step steel mesh; 5. Lower-step steel mesh; 6. Reinforced steel mesh; 7. Baffle; 8. Hook; 9. Connecting plate. Detailed implementation manners

[0025] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0026] It should be noted that when an element is referred to as "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0027] It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application 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 cannot be understood as a limitation to the present application.

[0028] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, "a plurality" means two or more unless otherwise specifically defined.

[0029] Please refer to Figures 1-4 , and now the construction method of the steel frame at the bottom of the tunnel initial support step provided by the embodiment of the present application will be described.

[0030] A construction method of the steel frame at the bottom of the tunnel initial support step includes the following steps:

[0031] Step 1: Construct the upper and middle step arch frames 1, and use the concrete cushion blocks 2 to support and pad the arch feet firmly;

[0032] Step 2: Cover the arch feet with stacked soil according to the construction line elevation;

[0033] Step 3: After the springing is covered, leveling and ramming are carried out to form a straight shotcrete line at the springing of the arch frame 1 on the previous bench.

[0034] Step 4: Shotcrete construction is carried out on the arch frames 1 of the upper and middle benches.

[0035] Step 5: Excavate the middle and lower benches and carry out arch frame construction for the middle and lower benches.

[0036] Step 6: Weld a layer of dense steel mesh 6 between two arch frames 1 on the lower bench, and the dense steel mesh 6 is located above the top of the connecting plate 9 at the end of the arch frame 1.

[0037] Step 7: Install a baffle 7 at the outer end of the connecting plate 9 of the arch frame 1 to isolate and protect the bolt holes on the connecting plate 9.

[0038] Before the construction method of the present application is adopted, after the middle and lower benches are excavated, it is necessary to manually use a pneumatic pick to chisel the shotcrete at the bottom of the steel frame of the upper process. It takes about 1 hour per cycle for two people. It is necessary to clean the bolt holes of the connecting plate 9 at the end of the arch frame 1, and there are gaps between the connecting plates 9 that are not closely attached. It is difficult to install bolts and tighten nuts, and there will be a phenomenon that the lap length of the local steel mesh is insufficient. After adopting the present method, the backfill soil 3 can be locally sourced, the operation is simple, it takes about 30 minutes per cycle for two people, and 0.5 hour can be saved per cycle, saving 40 yuan in labor costs per cycle. When excavating the next bench, the backfill soil 3 covering the springing naturally falls off, forming a certain free operation surface or space, which is convenient for construction operations. A baffle 7 is respectively hung on the connecting plate 9 at the outer end of each arch frame 1 to isolate and protect the bolt holes on the connecting plate 9 of the arch frame 1. The bolt installation and steel mesh lap take short time and are convenient to operate. The construction reduces the cycle time by 2 hours and saves 110 yuan in costs per cycle.

[0039] In some embodiments of the present application, in Step 2, the construction line is located at a position 25 - 35 cm above the springing of the steel frame. Optionally, the construction line is located 30 cm above the springing of the steel frame. In some other embodiments of the present application, the construction line can also be set at other heights according to the actual situation, and the present application does not make a limitation.

[0040] In some embodiments of the present application, in Step 2, the width of the backfill soil 3 covering is from 30 cm outward from the springing to the inner excavation surface, and the height is not less than 30 cm (greater than one steel mesh grid). In some other embodiments of the present application, the width of the backfill soil 3 covering can also adopt other dimensions, and the present application does not make a limitation.

[0041] In some embodiments of the present application, in step 2, tunnel muck or rebound material is used to cover the arch feet with soil. In some other embodiments of the present application, other materials can also be used to cover the soil according to the actual situation, such as fine sand, etc., which is not limited in the present application.

[0042] In some embodiments of the present application, in step 6, the reinforced steel mesh 6 is welded by plain round steel bars with a diameter of 8 mm, and the mesh width of the reinforced steel mesh 6 is 4 - 8 cm.

[0043] The reinforced steel mesh 6 can prevent a large amount of concrete from remaining behind the arch foot connecting plate 9 due to concrete spraying, increasing the cleaning difficulty. In some other embodiments of the present application, the reinforced steel mesh 6 can also be made of other types of steel bars, and the mesh width of the reinforced steel mesh 6 can also be of other sizes, which is not limited in the present application.

[0044] In some embodiments of the present application, before step 4, that is, before the shotcrete construction of the arch frame 1, a steel mesh sheet needs to be set between the arch frame 1 and the construction surface, including an upper bench steel mesh sheet 4 and a lower bench steel mesh sheet 5 arranged in sequence along the vertical direction, and the lap length of the upper bench steel mesh sheet 4 and the lower bench steel mesh sheet 5 is not less than 1 grid.

[0045] In some embodiments of the present application, in step 7, a hook 8 is provided on the baffle 7, and the baffle 7 is connected to the connecting plate 9 through the hook 8. By connecting the hook 8 with the connecting plate 9, it can be quickly installed, reducing the installation and disassembly time and improving the construction efficiency.

[0046] Before the construction without taking protective measures for the connecting plate 9, after the invert excavation, it is necessary to manually use a pneumatic pick to chisel the shotcrete at the bottom of the lower bench steel frame. It takes about 2 hours per cycle for two people, and the labor cost is 160 yuan per cycle. After taking protective measures for the connecting plate 9 with the baffle 7, the invert steel frame can be directly connected to the side wall steel frame after slightly cleaning, saving 2 hours per cycle and saving 160 yuan in labor costs per cycle; adding 2.7 kg of steel mesh per tunnel meter, with a cost of about 16 yuan per tunnel meter, increasing the cost by about 50 yuan per cycle; the externally attached baffle 7 can be reused without increasing costs. After taking protective measures for the connecting plate 9 with the baffle 7, the total construction cycle time is reduced by 2 hours, saving 110 yuan per cycle.

[0047] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for constructing a steel frame at the bottom of a tunnel primary support step, characterized in that: The following steps are involved: Step 1: Construct the arch frame of the upper and middle steps, and use concrete pads to support and cushion the arch feet; Step 2: Cover the arch foot with soil according to the construction line elevation; Step 3: After the arch foot is covered, level and compact it to form a straight line of shotcrete at the arch foot of the previous step; Step 4: Shotcrete the arches of the upper and middle steps; Step 5: Excavate the middle and lower steps and carry out the arch construction of the middle and lower steps; Step 6: Weld a layer of dense steel mesh between the two arch frames of the lower step, and the dense steel mesh is located above the top of the connecting plate at the end of the arch frame; Step 7: Set a baffle at the outer end of the connecting plate of the arch frame to isolate and protect the bolt holes on the connecting plate.

2. The method for constructing a steel frame at the bottom of the tunnel primary support step according to claim 1, characterized in that: In step 2, the construction line is located 25-35cm above the arch foot of the steel frame.

3. The method for constructing a steel frame at the bottom of a tunnel primary support step according to claim 1, characterized in that: In step 2, the width of the earth covering is 30 cm outward from the arch foot to the inner excavation surface, and the height is not less than 30 cm.

4. The method for constructing a steel frame at the bottom of a tunnel primary support step according to claim 1, characterized in that: In step 2, the arch foot is covered with soil using tunnel slag or rebound material.

5. The method for constructing a steel frame at the bottom of a tunnel primary support step according to claim 1, characterized in that: In step 6, the dense steel mesh is welded with smooth round steel bars with a diameter of 8 mm, and the mesh width of the dense steel mesh is 4-8 cm.

6. The method for constructing a steel frame at the bottom of the tunnel primary support step according to claim 1, characterized in that: In step 7, a hook is provided on the baffle, and the baffle is connected to the connecting plate through the hook.

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