Tunnel inverted arch lining fabricated steel bar design and construction method

Abstract

The invention relates to the technical field of tunnel lining construction, and discloses a tunnel inverted arch lining fabricated reinforcing steel bar design and construction method which comprises the steps of inverted arch lining fabricated reinforcing steel bar section division, inverted arch annular main reinforcing steel bar welding lap joint length and hook anchoring calculation, inverted arch lining fabricated reinforcing steel bar construction and the like. According to the tunnel inverted arch lining fabricated reinforcing steel bar design and construction method, inverted arch reinforcing steel bars are divided into three sections according to the stress characteristics of an inverted arch and prefabricated, the fabricated reinforcing steel bars of the three sections are hoisted to the designed positions to be connected during construction, and then the fabricated reinforcing steel bars of the three sections can be connected under the condition that the quality of the inverted arch lining is not affected. The problems of time and labor consumption and the like of steel bar field binding during inverted arch construction are solved, the tunnel inverted arch construction is simpler and more convenient, the construction period is shortened, and the engineering investment is greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel lining construction, and in particular to a tunnel invert lining assembled steel bar design and construction method. Background Art

[0002] The construction of secondary lining for tunnel invert excavation is generally to tie the invert reinforcement and pour concrete first, then do the invert backfill and road filling, and tie the upper lining reinforcement of the invert after the invert lining reaches a certain strength, and finally use the lining trolley to pour the upper lining concrete of the invert, so that the entire secondary lining structure is closed into a ring. The construction speed of the invert directly affects the timing of the lining structure closing into a ring after tunnel excavation, and then affects the stress and stability of the tunnel structure.

[0003] However, the current invert lining construction adopts the method of on-site binding of invert reinforcement and cast-in-place concrete, which is not only cumbersome and requires a lot of man-hours and engineering investment, but also lags behind the timing of closure of the lining structure, which has an adverse effect on the stability of the tunnel structure. Therefore, how to simplify the construction steps and increase the construction speed while ensuring the construction quality of the invert lining is of great engineering significance to tunnel construction. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a tunnel invert lining assembled steel bar design and construction method.

[0005] The technical solution adopted by the present invention is:

[0006] A method for designing assembled steel bars for tunnel invert lining comprises the following steps:

[0007] Step 1: Division of prefabricated steel bars in the invert lining:

[0008] Step 1.1, through the tunnel lining design drawings, calculate the secondary lining using the load structure method to obtain its bending moment distribution diagram;

[0009] Step 1.2, through the lining bending moment distribution diagram, find the position with the smallest bending moment of the inverted arch as the central reference point of the lap joint of the circumferential main reinforcement; according to the principle that the lap joint of the reinforcement should be as close as possible to the trisection point of the inverted arch, the lining reinforcement of the inverted arch can be divided into three sections in the circumferential direction;

[0010] Step 2, calculation of welding lap length and hook anchorage of the inverted arch annular main reinforcement:

[0011] Step 2.1, the welding lap length of the annular main reinforcement includes the determination of the anchorage length and the determination of the lap length correction coefficient;

[0012] Step 2.2, the design of the annular main reinforcement hook anchorage includes determining the minimum inner diameter of the hook and the length of the straight section of the hook.

[0013] Furthermore, in step 2.1, the correction coefficients of the anchorage length and lap length of the annular main reinforcement are determined as follows:

[0014] The anchorage length of the tensioned steel bars shall be calculated according to the following formula based on the anchorage conditions and shall not be less than 200 mm:

[0015] When the seismic resistance level is one to four, the formula is: a =ζ a l ab

[0016] When the seismic resistance level is non-seismic, the formula is used: l aE =ζ aE l abE

[0017] Where: l a is the anchorage length of the tensile reinforcement; a is the anchor length correction factor. When there are more than one item, it shall be calculated by multiplying them together, but it shall not be less than 0.6; l ab is the basic anchorage length of ordinary tensile reinforcement; l aE is the seismic anchorage length of the tensile reinforcement; aE l is the correction factor of seismic anchorage length of tensile reinforcement; abE It is the basic anchorage length of the tensile reinforcement for earthquake resistance;

[0018] The lap joint of the annular main reinforcement includes the inner lap joint of the annular main reinforcement and the outer lap joint of the annular main reinforcement. The inner lap length of the annular main reinforcement is the same as the outer lap length of the annular main reinforcement. They are calculated according to the following formula based on the percentage of the steel bar lap joint area in the same connection section, and should not be less than 300mm;

[0019] The inner lap length of the annular main reinforcement and the outer lap length of the annular main reinforcement are distributed on both sides of the central reference point of the annular main reinforcement lap joint, and the inner end point of the annular main reinforcement and the outer end point of the annular main reinforcement are used as the starting points;

[0020] The calculation formula is: l =ζ l (l a or aE )

[0021] Where: l l is the lap length of the annular tensile reinforcement; l a is the anchorage length of the annular tensile reinforcement; l aE is the seismic anchorage length of the tensile reinforcement; l It is the correction factor of lap length of hoop tensile reinforcement.

[0022] Furthermore, in step 2.2, the minimum inner diameter of the bend of the annular main reinforcement hook and the length of the straight section of the hook are determined as follows:

[0023] Circumferential main reinforcement hooks are provided at the inner ends of the circumferential main reinforcement and at the inner ends of the circumferential main reinforcement; the minimum inner diameter of the bending arc of the circumferential main reinforcement hook is determined based on the steel bar grade; the straight section length of the circumferential main reinforcement hook is determined according to the anchoring form.

[0024] A method for constructing assembled steel bars for tunnel invert lining, which is based on the above-mentioned method for designing assembled steel bars for tunnel invert lining, comprises the following steps:

[0025] Step 3, prefabricated reinforcement construction of invert lining:

[0026] Step 3.1, prefabrication of assembled steel bars for inverted arch lining: according to the division of the inverted arch steel bars into three sections in step 1 and the calculation of the welding lap length and hook anchorage of the inverted arch annular main bars in step 2, the annular main bars of the three sections of the inverted arch are prefabricated and assembled with the longitudinal distribution steel bars and stirrups;

[0027] Step 3.2, hoisting of prefabricated steel bars for invert lining: First, after the excavation of the invert, measure the elevation of the base of the invert, the size of the hole, etc., to check whether they meet the requirements; second, remove the slag, debris, and water in the foundation pit of the invert. If the tunnel section is designed with initial support, implement the initial support in time; then, lay out and install the positioning steel bars at the bottom and both sides of the invert; finally, install the positioning steel pipes at the positioning steel bars, and use the hoisting equipment to install the prefabricated steel bars of the three sections of the invert lining to the designed position of the invert;

[0028] Step 3.3, binding of prefabricated steel bars for inverted arch lining: connect the prefabricated steel bars of three sections of the same ring of inverted arch lining hoisted into place by transverse binding; at the same time, connect the prefabricated steel bars of two adjacent rings of inverted arch lining by longitudinal binding.

[0029] Furthermore, in step 3.1, closed stirrups arranged in plum blossom shape are arranged inside the prefabricated reinforcement of the inverted arch; the closed stirrups are within the length of the overlap section and clamp the upper and lower rows of circumferential main reinforcements with a spacing of 200 mm; at the same time, the upper and lower rows of longitudinal distribution reinforcements are clamped outside the length of the overlap section, and the spacing is relaxed to 600 mm; single-leg stirrups are no longer arranged where the closed stirrups are arranged within the length of the overlap section.

[0030] Furthermore, in step 3.2, when using lifting equipment to lift the prefabricated steel bars of the three sections of the invert lining, first install 4 rectangularly arranged positioning steel bars at the bottom and both sides of the invert foundation pit, and the insertion depth and exposed length should not be less than 250 mm; during lifting, install positioning steel pipes at the positioning steel bars, and complete the lifting of a ring of prefabricated steel bars for the invert lining by nesting the positioning steel bars inside the positioning steel pipes.

[0031] Furthermore, after the lap joint of the annular main reinforcement of one ring of the inverted arch lining is completed, the hoisting of the prefabricated steel bars of the next ring of the inverted arch lining and the connection of the annular main reinforcement are carried out along the tunnel face direction, and the longitudinal distribution steel bars of the two rings of the prefabricated steel bars of the inverted arch lining are connected. After the construction of the prefabricated steel bars of the inverted arch lining is completed, the inverted arch lining concrete is poured and the next construction process is carried out.

[0032] The beneficial effects of the present invention are:

[0033] The design and construction method of prefabricated steel bars for tunnel invert lining divides the invert steel bars into three sections according to the stress characteristics of the invert and prefabricates them. During construction, the prefabricated steel bars of the three sections are hoisted to the designed position for connection. This can solve the problems of time-consuming and labor-intensive on-site tying of steel bars during invert construction without affecting the quality of the invert lining, making the tunnel invert construction simpler, shortening the construction period, and significantly reducing the project investment.

[0034] The prefabricated steel bar design and construction method of the tunnel invert lining makes the tunnel invert construction faster and easier, reduces the adverse effect of the invert construction speed on the timing of closing and ringing of the lining structure after tunnel excavation, and thus improves the stability of the tunnel support structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flow chart of a design method and a construction method for assembled steel bars for tunnel invert lining according to the present invention;

[0036] Figure 2 It is a schematic diagram of dividing the three sections of the inverted arch lining steel bars of the present invention;

[0037] Figure 3 It is a structural schematic diagram of the inverted arch lining steel bar hook of the present invention;

[0038] Figure 4 It is a schematic diagram of the structure of the assembled steel bars on both sides of the invert lining of the present invention;

[0039] Figure 5 It is a schematic diagram of the structure of the assembled steel bars at the lower part of the invert lining of the present invention;

[0040] Figure 6 It is a schematic diagram of the arrangement of the closed stirrups inside the assembled steel bars of the inverted arch lining of the present invention;

[0041] Figure 7 It is a schematic diagram of the connection of the assembled steel bars for the inverted arch lining of the present invention;

[0042] Figure 8 and Fig. 9 It is a schematic diagram of the arrangement of the inverted arch positioning steel bars of the present invention;

[0043] In the figure: 1-the part with the smallest bending moment of the inverted arch, 2-the center reference point of the lap joint of the annular main reinforcement, 3-the inner lap length of the annular main reinforcement, 4-the outer lap length of the annular main reinforcement, 5-the hook of the annular main reinforcement, 6-the annular main reinforcement, 7-the longitudinal distribution reinforcement, 8-the stirrups, 9-the closed stirrups, 10-the positioning reinforcement. DETAILED DESCRIPTION

[0044] The following will be combined with the accompanying drawings of the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] Example 1

[0046] This embodiment provides a method for designing assembled steel bars for tunnel invert lining; Figure 1 As shown, the tunnel invert lining assembled reinforcement design method comprises the following steps:

[0047] Step 1: Division of prefabricated steel bars in the invert lining:

[0048] Step 1.1, through the tunnel lining design drawings, calculate the secondary lining using the load structure method to obtain its bending moment distribution diagram;

[0049] Step 1.2, such as Figure 2 As shown in the figure, through the lining bending moment distribution diagram, the part with the smallest bending moment of the inverted arch is found 1, such as the red line part in the figure, which is used as the center reference point 2 of the lap joint of the annular main reinforcement; according to the principle that the lap joint of the reinforcement should be as close as possible to the trisection point of the inverted arch, the lining reinforcement of the inverted arch can be divided into three sections in the annular direction.

[0050] Step 2, calculation of welding lap length and hook anchorage of the inverted arch annular main reinforcement:

[0051] Step 2.1, the welding lap length of the annular main reinforcement includes the determination of the anchorage length and the determination of the lap length correction coefficient.

[0052] Furthermore, in this embodiment, the method for determining the correction coefficient of the anchorage length and lap length of the annular main reinforcement is as follows:

[0053] The anchorage length of the tensioned steel bars shall be calculated according to the following formula based on the anchorage conditions and shall not be less than 200 mm:

[0054] When the seismic resistance level is one to four, the formula is: a =ζ a l ab

[0055] When the seismic resistance level is non-seismic, the formula is used: l aE =ζ aE l abE

[0056] Where: l a is the anchorage length of the tension reinforcement;

[0057] ζ a is the anchorage length correction factor, which shall be taken according to the provisions of Table 2. When there are more than one item, it shall be calculated by multiplying them together, but shall not be less than 0.6;

[0058] l ab It is the basic anchorage length of ordinary tension steel bars, which shall be taken according to the provisions of Table 1;

[0059] l aE is the seismic anchorage length of the tensile reinforcement;

[0060] ζ aE It is the correction factor of the seismic anchorage length of the tensile reinforcement, which is 1.15 for the first and second seismic resistance levels, 1.05 for the third seismic resistance level, and 1.00 for the fourth seismic resistance level;

[0061] l abE It is the basic earthquake-resistant anchorage length of the tensile reinforcement and shall be determined according to the provisions of Table 1.

[0062] Table 1 Basic anchorage length l of tensile reinforcement ab , l abE

[0063]

[0064]

[0065] For example, if the steel bar type is HPB300, the concrete strength grade is C25, and the seismic grade is designed to be level 1 or 2, then abE Take 39d.

[0066] Table 2 Correction coefficient ζ of anchorage length of tensile reinforcement a

[0067]

[0068] Note: When the thickness of the protective layer in the anchorage area is the middle value in the table, the value can be obtained by linear interpolation; d is the diameter of the anchor steel bar.

[0069] like Figure 2 As shown, the lap joint of the annular main reinforcement includes the inner lap joint of the annular main reinforcement and the outer lap joint of the annular main reinforcement. The inner lap length 3 of the annular main reinforcement and the outer lap length 4 of the annular main reinforcement are the same. They are calculated according to the following formula based on the percentage of the steel bar lap joint area in the same connection section, and should not be less than 300mm;

[0070] The inner lap length of the annular main reinforcement and the outer lap length of the annular main reinforcement are distributed on both sides of the central reference point 2 of the annular main reinforcement lap joint, and the inner end point of the annular main reinforcement and the outer end point of the annular main reinforcement are used as the starting points;

[0071] The calculation formula is: l =ζ l (l a or aE )

[0072] Where: l l is the lap length of the hoop tensile reinforcement;

[0073] l a is the anchorage length of the hoop tensile reinforcement;

[0074] l aE is the seismic anchorage length of the tensile reinforcement;

[0075] ζ l is the correction coefficient for the lap length of the annular tensile reinforcement. Since the inverted arch lining is a beam-type component, the value corresponding to the lap joint area percentage of 50% is taken according to Table 3.

[0076] Table 3 Correction coefficients for lap length of circumferential tensile reinforcement

[0077]

[0078] Step 2.2, the design of the annular main reinforcement hook anchorage includes determining the minimum inner diameter of the hook and the length of the straight section of the hook.

[0079] Further, such as Figure 2 As shown, in this embodiment, a circumferential main reinforcement hook 5 is provided at the inner end of the circumferential main reinforcement and the inner end of the circumferential main reinforcement; the specific structure of the circumferential main reinforcement hook 5 is as shown in FIG. Figure 3 As shown, Figure 3 In the figure, a is a 90° hook and b is a 135° hook.

[0080] The minimum inner diameter of the bend of the circumferential main reinforcement hook 5 and the length of the straight section of the hook are determined as follows:

[0081] The minimum inner diameter of the bend of the annular main reinforcement hook 5 is determined based on the steel bar grade, and the specific value is taken according to Table 4. The straight length of the annular main reinforcement hook 5 is determined according to the anchoring form, and the specific value is taken according to Table 5.

[0082] Table 4 Inner diameter D of the hook of steel bar

[0083]

[0084] Table 5 Forms and technical requirements of steel bar hooks

[0085]

[0086] Example 2

[0087] Based on the tunnel invert lining prefabricated steel bar design method provided in Example 1, this embodiment also proposes a tunnel invert lining prefabricated steel bar construction method; Figure 1 As shown, the tunnel invert lining assembled steel bar construction method comprises the following steps:

[0088] Step 3, prefabricated reinforcement construction of invert lining:

[0089] Step 3.1, prefabrication of prefabricated steel bars for invert lining: Figure 4 , Figure 5 and Figure 6 As shown, according to the division of the three sections of the inverted arch reinforcement in step 1 and the calculation of the welding lap length and hook anchorage of the inverted arch annular main reinforcement in step 2, the annular main reinforcement 6 of the three sections of the inverted arch is prefabricated and assembled with the longitudinal distribution reinforcement 7 and stirrups 8. Among them, the annular main reinforcement 6 is two groups of Φ22 steel bars, and the two Φ22 steel bars in each group are arranged at an interval of 200mm; the longitudinal distribution reinforcement 7 is connected to the annular main reinforcement 6, using Φ16 steel bars, and arranged at an interval of 200mm; the stirrups 8 are Φ8 steel bars installed on the distribution reinforcement 7 and arranged at an interval of 200mm.

[0090] Step 3.2, hoisting of prefabricated steel bars for invert lining: First, after the invert is excavated, measure the elevation of the invert base, the hole shape and dimensions, etc. to check whether they meet the requirements; secondly, clean up the slag, debris, and accumulated water in the invert foundation pit. If the tunnel section is designed with initial support, implement the initial support in time; then, Figure 8 and Fig. 9 As shown, the positioning steel bars 10 are laid out and installed at the bottom and both sides of the invert; finally, the positioning steel pipes, i.e., steel sleeves, are installed at the positioning steel bars 10, and the assembled steel bars of the three sections of the invert lining are installed to the designed position of the invert using lifting equipment.

[0091] Step 3.3, invert lining assembly reinforcement binding: Figure 7As shown, the prefabricated steel bars of three sections of the same ring inverted arch lining hoisted into place are connected by transverse binding; at the same time, the prefabricated steel bars of two adjacent ring inverted arch linings are connected by longitudinal binding.

[0092] Further, as the preferred technical solution of this embodiment; in step 3.1, in order to strengthen the stiffness of the assembled steel bar overlap section of the inverted arch lining and meet the lifting requirements, as Figure 4 , Figure 5 and Figure 6 As shown, this embodiment also arranges closed stirrups 9 in a plum blossom arrangement inside the inverted arch assembled reinforcement. The closed stirrups 9 are within the overlap section length and clamp the upper and lower rows of circumferential main reinforcements 6, with a spacing of generally 200 mm; at the same time, they clamp the upper and lower rows of longitudinal distribution reinforcements 7 outside the overlap section length, and the spacing can be relaxed, such as 600 mm. It is worth noting that the single-leg stirrups 8 are no longer arranged where the closed stirrups 9 are arranged within the overlap section length.

[0093] Further, as the preferred technical solution of this embodiment; such as 8 and Fig. 9 As shown, in step 3.2, when using the lifting equipment to lift the prefabricated steel bars of the three sections of the inverted arch lining, first install four rectangular positioning steel bars 10 at the bottom and both sides of the inverted arch foundation pit, and the insertion depth and exposed length should not be less than 250mm. During the lifting, the positioning steel pipe, i.e., steel sleeve, is installed at the positioning steel bar 10; by nesting the positioning steel bar 10 inside the positioning steel pipe, the lifting of a ring of prefabricated steel bars for the inverted arch lining can be completed.

[0094] like Figure 7 As shown in the figure, after the lap joint of the annular main reinforcement of one ring of invert lining is completed, the hoisting of the prefabricated steel bars of the next ring of invert lining and the connection of the annular main reinforcement can be carried out along the tunnel face direction, and the longitudinal distribution steel bars of the two rings of prefabricated steel bars of the invert lining can be connected. After the construction of the prefabricated steel bars of the invert lining is completed, the invert lining concrete can be poured and the next construction process can be carried out.

[0095] In summary, the design and construction method of prefabricated steel bars for tunnel invert lining divides the invert steel bars into three sections according to the stress characteristics of the invert and performs prefabrication and assembly. During construction, the prefabricated steel bars of the three sections are hoisted to the designed position for connection. This can solve the problems of time-consuming and labor-intensive on-site tying of steel bars during invert construction without affecting the quality of the invert lining, making the tunnel invert construction simpler, shortening the construction period, and significantly reducing the project investment. At the same time, it makes the tunnel invert construction faster and simpler, reduces the adverse effect of the invert construction speed on the timing of closing the lining structure into a ring after tunnel excavation, and thus improves the stability of the tunnel support structure.

[0096] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A design method for prefabricated reinforcement of tunnel invert lining. It is characterized in that The following steps are involved: Step 1: Division of prefabricated steel bars in the invert lining: Step 1.1, through the tunnel lining design drawings, calculate the secondary lining using the load structure method to obtain its bending moment distribution diagram; Step 1.2, through the lining bending moment distribution diagram, find the position with the smallest bending moment of the inverted arch as the central reference point of the lap joint of the circumferential main reinforcement; according to the principle that the lap joint of the reinforcement should be as close as possible to the trisection point of the inverted arch, the lining reinforcement of the inverted arch can be divided into three sections in the circumferential direction; Step 2, calculation of welding lap length and hook anchorage of the inverted arch annular main reinforcement: Step 2.1, the welding lap length of the annular main reinforcement includes the determination of the anchorage length and the determination of the lap length correction coefficient; Step 2.2, the design of the annular main reinforcement hook anchorage includes determining the minimum inner diameter of the hook and the length of the straight section of the hook.

2. The method for designing assembled reinforcement for tunnel invert lining according to claim 1, Features: In step 2.1, the correction coefficients for the anchorage length and lap length of the annular main reinforcement are determined as follows: The anchorage length of the tensioned steel bars shall be calculated according to the following formula based on the anchorage conditions and shall not be less than 200 mm: When the seismic resistance level is one to four, the formula is: a =ζ a l ab When the seismic resistance level is non-seismic, the formula is used: l aE =ζ aE l abE Where: l a is the anchorage length of the tensile reinforcement; a is the anchor length correction factor. When there are more than one item, it shall be calculated by multiplying them together, but it shall not be less than 0.6; l ab is the basic anchorage length of ordinary tensile reinforcement; l aE is the seismic anchorage length of the tensile reinforcement; aE l is the correction factor of seismic anchorage length of tensile reinforcement; abE It is the basic anchorage length of the tensile reinforcement for earthquake resistance; The lap joint of the annular main reinforcement includes the inner lap joint of the annular main reinforcement and the outer lap joint of the annular main reinforcement. The inner lap length of the annular main reinforcement is the same as the outer lap length of the annular main reinforcement. They are calculated according to the following formula based on the percentage of the steel bar lap joint area in the same connection section, and should not be less than 300mm; The inner lap length of the annular main reinforcement and the outer lap length of the annular main reinforcement are distributed on both sides of the central reference point of the annular main reinforcement lap joint, and the inner end point of the annular main reinforcement and the outer end point of the annular main reinforcement are used as the starting points; The calculation formula is: l =ζ l (l a or aE ) Where: l l is the lap length of the annular tensile reinforcement; l a is the anchorage length of the annular tensile reinforcement; l aE is the seismic anchorage length of the tensile reinforcement; l It is the correction factor of lap length of hoop tensile reinforcement.

3. The method for designing assembled reinforcement for tunnel invert lining according to claim 1, Features: In step 2.2, the minimum inner diameter of the bend of the annular main reinforcement hook and the length of the straight section of the hook are determined as follows: Circumferential main reinforcement hooks are provided at the inner ends of the circumferential main reinforcement and at the inner ends of the circumferential main reinforcement; the minimum inner diameter of the bending arc of the circumferential main reinforcement hook is determined based on the steel bar grade; the straight section length of the circumferential main reinforcement hook is determined according to the anchoring form.

4. A method for constructing assembled steel bars for tunnel invert lining, the method for constructing assembled steel bars for tunnel invert lining being based on the method for designing assembled steel bars for tunnel invert lining according to any one of claims 1 to 3, It is characterized in that The following steps are involved: Step 3, construction of prefabricated reinforcement for invert lining: Step 3.1, prefabrication of assembled steel bars for inverted arch lining: according to the division of the inverted arch steel bars into three sections in step 1 and the calculation of the welding lap length and hook anchorage of the inverted arch annular main bars in step 2, the annular main bars of the three sections of the inverted arch are prefabricated and assembled with the longitudinal distribution steel bars and stirrups; Step 3.2, hoisting of prefabricated steel bars for invert lining: First, after the excavation of the invert, measure the elevation of the base of the invert, the size of the hole, etc., to check whether they meet the requirements; second, remove the slag, debris, and water in the foundation pit of the invert. If the tunnel section is designed with initial support, implement the initial support in time; then, lay out and install the positioning steel bars at the bottom and both sides of the invert; finally, install the positioning steel pipes at the positioning steel bars, and use the hoisting equipment to install the prefabricated steel bars of the three sections of the invert lining to the designed position of the invert; Step 3.3, binding of prefabricated steel bars for inverted arch lining: connect the prefabricated steel bars of three sections of the same ring of inverted arch lining hoisted into place by transverse binding; at the same time, connect the prefabricated steel bars of two adjacent rings of inverted arch lining by longitudinal binding.

5. The method for constructing assembled steel bars for tunnel invert lining according to claim 4, Features: In step 3.1, closed stirrups in plum blossom arrangement are arranged inside the prefabricated reinforcement of the inverted arch; the closed stirrups are within the lap section length and clamp the upper and lower rows of circumferential main reinforcements with a spacing of 200 mm; at the same time, the upper and lower rows of longitudinal distribution reinforcements are clamped outside the lap section length, and the spacing is relaxed to 600 mm; single-leg stirrups are no longer arranged where closed stirrups are arranged within the lap section length.

6. The method for constructing assembled steel bars for tunnel invert lining according to claim 4, Features: In step 3.2, when using lifting equipment to lift the prefabricated steel bars of the three sections of the invert lining, first install 4 rectangular positioning steel bars at the bottom and both sides of the invert foundation pit. The insertion depth and exposed length should not be less than 250mm. During lifting, install positioning steel pipes at the positioning steel bars, and complete the lifting of a ring of prefabricated steel bars for the invert lining by nesting the positioning steel bars inside the positioning steel pipes.

7. The method for constructing assembled steel bars for tunnel invert lining according to claim 4, Features: When one ring of invert lining annular main reinforcement is overlapped, the next ring of invert lining prefabricated steel bars are hoisted and the annular main reinforcement is connected along the tunnel face direction, and the longitudinal distribution steel bars of the two rings of invert lining prefabricated steel bars are connected. After the construction of the invert lining prefabricated steel bars is completed, the invert lining concrete is poured and the next construction process is carried out.

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