Large-span tunnel expanding excavation construction technology

Abstract

The invention relates to a large-span tunnel expanding excavation construction process, which belongs to the technical field of tunnel construction, and comprises the following steps of: 1, backfilling sandbags at the lower part of a main hole of a tunnel part needing expanding excavation to form steps, and marking a plurality of forcible entry points on the inner surface of a second lining of the expanding excavation part; secondly, a main grouting pipe is inserted into the outside of the second lining of the expanding excavation part for grouting; thirdly, a plurality of auxiliary grouting pipes are inserted in the direction from the forcible entry point of the second lining to the outside of the second lining for grouting, and meanwhile the second lining is preliminarily excavated at the forcible entry point; 4, starting from the forcible entry point, carrying out secondary lining forcible entry on the upper step, carrying out expanding excavation according to the inner contour of the target structure, and constructing a primary support after the expanding excavation is completed; 5, starting from the forcible entry point, carrying out secondary lining forcible entry on the lower step, carrying out expanding excavation according to the inner contour of the target structure, and carrying out primary support after the expanding excavation is completed; the construction safety is considered while the construction efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction, and in particular relates to a large-span tunnel expansion construction process. Background Art

[0002] With economic development, the existing transportation infrastructure is likely to face the problem of insufficient capacity and need to be expanded. For example, when the number of lanes in a tunnel facility is small and new emergency parking lanes and other structures need to be added, the tunnel needs to be expanded and excavated.

[0003] Due to the particularity of the tunnel's deep geological structure, when constructing the existing structure of the tunnel, it is necessary to dismantle the existing structure and re-excavate. The excavation process will have an impact on the surrounding geological environment, and the dismantling of the existing structure will lead to a decrease in the supporting capacity. Under the combined effect of the two, there is a probability that the existing structure will collapse. For this reason, Chinese patent CN110593909A discloses a tunnel secondary lining replacement construction method, including: performing lining reinforcement operations on the secondary lining to be replaced; setting an isolation shock-absorbing groove at the junction of the dismantled and undismantled areas; before dismantling the secondary lining, making an isolation groove in the dismantling area and the reserved area, and cutting off all the secondary lining concrete and steel bars; before dismantling the lining, radial grouting reinforcement is performed on the surrounding rock behind the arch wall; dismantling the secondary lining, dismantling the reinforced arch, and retaining the initial support; if If the thickness of the secondary lining is less than 2 / 3 of the original design, the primary support is replaced, and the original primary support is broken and excavated in three steps, and then the secondary lining is restored. After the length of the secondary lining or primary support replacement reaches 12m, the secondary lining concrete is re-applied in time, and the secondary lining is applied at a rate of 10.5m / 1 group; if the thickness of the secondary lining is greater than 2 / 3 of the original design, the secondary lining is directly restored; it solves the problem of high safety risk in the replacement construction of the tunnel secondary lining by radial grouting reinforcement of the surrounding rock behind the arch wall before removing the lining; however, in the above scheme, it is necessary to grout around the secondary lining first, and then to demolish the secondary lining. At this time, grouting and demolition need to be carried out in two steps, and the construction efficiency is low. Therefore, a large-span tunnel expansion construction process is needed to improve construction efficiency while taking into account construction safety. Summary of the invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a large-span tunnel excavation construction process, which has the characteristics of improving construction efficiency while taking into account construction safety.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A large-span tunnel excavation construction process comprises the following steps:

[0007] Step 1: Backfill sandbags at the lower part of the main tunnel of the tunnel section that needs to be expanded to form steps, and mark several demolition points on the inner surface of the secondary lining of the expanded section;

[0008] Step 2: Use the main grouting pipe to insert into the outside of the second lining of the expanded part for grouting;

[0009] Step 3: Use several auxiliary grouting pipes to insert along the breaking point of the secondary lining to the outside of the secondary lining for grouting, and at the same time, perform preliminary excavation of the secondary lining at the breaking point;

[0010] Step 4: Starting from the demolition point, the secondary lining of the upper step is demolished, and the excavation is carried out according to the inner contour of the target structure. After the excavation is completed, the initial support is applied;

[0011] Step 5: Starting from the demolition point, demolish the secondary lining of the lower step, and expand the excavation according to the inner contour of the target structure. After the excavation is completed, apply initial support.

[0012] As a preferred technical solution of the present invention, the step three also includes: before the grouting is completed, pulling out the auxiliary grouting pipe.

[0013] As a preferred technical solution of the present invention, the step one also includes: measuring the span L of the expanded tunnel part; the step three also includes: step three: using an auxiliary grouting pipe to insert into the breaking point of the second lining, and insert it to the outside of the second lining, grouting, and adjusting the grouting amount to G, G=L / L0×G0, L0 and G0 are pre-calculated constants.

[0014] As a preferred technical solution of the present invention, the step three further comprises: applying a vibrator outside the auxiliary grouting pipe, and applying vibration to the auxiliary grouting pipe during the grouting process of the auxiliary grouting pipe.

[0015] As a preferred technical solution of the present invention, the step three further comprises: increasing the power of the vibrator when the span of the expanded tunnel portion exceeds a threshold value, and reducing the power of the vibrator when the span of the expanded tunnel portion is below the threshold value;

[0016] As a preferred technical solution of the present invention, the step three also includes: adjusting the power of the vibrator to p, where p = f(L) × p0, f(L) = Log(1.8x-0.8)+1.1, x = L / L0, 0.5L0≤L≤1.5L0;

[0017] As a preferred technical solution of the present invention, the step 4 further includes: before the demolition, setting the number of demolition points a for one-time demolition, where a=L0 / L×a0;

[0018] As a preferred technical solution of the present invention,

[0019] The beneficial effects of the present invention are:

[0020] (1) By dividing a number of demolition points at the secondary lining, drilling holes at the demolition points, inserting auxiliary grouting pipes and then grouting at the demolition points, the structural strength is weakened by the combined effect of the drilling holes at the demolition points and the pressure applied to the secondary lining by the grouting, and grouting is completed in the soil layer near the demolition points of the secondary lining, which additionally reinforces the soil layer near the demolition points. At the same time, during the grouting process, the secondary lining structure near the demolition points is further demolished, further weakening the structural strength near the demolition points of the secondary lining, reducing the construction time cost of subsequent demolition of the secondary lining, improving construction efficiency, and taking into account construction safety;

[0021] (2) By adjusting the grouting amount of the auxiliary grouting to the outside of the secondary lining according to the span data, when the tunnel span is large, the bearing capacity of the soil layer is poor, and the area of ​​the secondary lining is large, the grouting amount of the soil layer outside the secondary lining is increased to achieve more sufficient grouting of the vault to strengthen the soil layer, and at the same time, the squeezing force of the cement slurry on the secondary lining is more fully utilized to achieve the pre-demolition of the secondary lining; when the tunnel span is small, the grouting amount of the soil layer outside the secondary lining is reduced to ensure construction efficiency;

[0022] (3) The vibration of the auxiliary grouting pipe is transmitted to the demolition point of the secondary lining through the vibrator, which further reduces the structural strength of the demolition point, reduces the construction time of the subsequent demolition of the secondary lining, and improves the construction efficiency. At the same time, the vibration increases the density and uniformity of the cement slurry in the auxiliary grouting pipe, improves the grouting effect, and ensures safety;

[0023] (4) By adjusting the vibrator power according to the tunnel span, when the span is high and a higher vibration power is needed to assist the mud in the grouting pipe to form or to pre-break the secondary lining more fully, the vibration power is increased to assist the compaction of the mud and pre-break the secondary lining more fully. When the power span is low and a higher vibration power is not needed to assist the mud in the grouting pipe to form or to pre-break the secondary lining fully, the vibration power is reduced to save energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0025] Figure 1 This is a schematic diagram of the structure of the tunnel after sandbag backfilling of the present invention;

[0026] Figure 2 It is a structural schematic diagram of the grouting process of the present invention;

[0027] Description of main component symbols:

[0028] In the figure: 1. tunnel; 11. secondary lining; 2. main grouting pipe; 21. auxiliary grouting pipe; 3. sandbag. DETAILED DESCRIPTION

[0029] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0030] See also Figure 1-2 , a large-span tunnel excavation construction process, comprising the following steps:

[0031] Step 1: Backfill sandbags 3 at the lower part of the main hole of the tunnel 1 that needs to be expanded to form a step, and mark several demolition points on the inner surface of the secondary lining 11 of the expanded part;

[0032] Specifically, in this scheme, tunnel 1 is a single-hole four-lane tunnel 1 with a clear width of 18.25m and a clear height of 5.0m;

[0033] In this scheme, the step method is adopted for the expansion and excavation. Since the expansion and excavation is carried out on the basis of the existing tunnel 1, it is impossible to first excavate the earthwork of the upper half of the target position of the tunnel 1 to form a step like the traditional tunnel 1 excavation method. Therefore, the main hole of the existing tunnel 1 that needs to be expanded is first determined, and the sandbags 3 are backfilled in the lower part of the main hole of the existing tunnel 1 until the sandbags 3 form a platform close to half the height of the main hole. At this time, the plane formed by the ground of the main hole of the existing tunnel 1 and the sandbags 3 constitutes two steps. The plane formed by the sandbags 3 is the upper step, and the ground of the main hole of the existing tunnel 1 is the lower step.

[0034] Subsequently, during the expansion construction, the secondary lining 11 of the existing tunnel 1 needs to be demolished before the soil layer outside the secondary lining 11 can be excavated. Therefore, according to the construction plan, the operator marks several demolition points on the inner surface of the secondary lining 11 with paint or other tools, which are used to indicate the starting position of demolition during subsequent demolition.

[0035] After step 1 is completed, proceed to step 2:

[0036] Before demolition, the demolition force of the secondary lining 11 will be transmitted to the soil structure outside the secondary lining 11, and the existing secondary lining 11 structure will cause the supporting capacity to decrease. Under the combined effect of the two, there is a probability that the existing structure will collapse. To avoid such a situation, in step 2, the main grouting pipe 2 is inserted into the outside of the expanded secondary lining 11 for grouting;

[0037] Specifically, the outer part of the second lining 11 of the expanded part refers to the rock layer and soil layer on the side of the second lining 11 of the expanded section of the existing tunnel 1 away from the tunnel 1. During grouting, a 3.5m long φ42 small pipe is used for radial support and cement slurry is injected. The small pipes are arranged in a plum blossom shape with a spacing of 1m×1m. The water-cement ratio of the cement slurry is 1:1, and the grouting pressure is 0.5-1.0MPa. After the grouting is completed, the grouting effect is sampled;

[0038] After completing step 2, proceed to step 3:

[0039] In a general scheme, it is necessary to first grout around the secondary lining 11, and then to demolish the secondary lining 11. At this time, the grouting and demolishing need to be performed in two steps in sequence, and the construction efficiency is low. In the grouting process, the secondary lining 11 can be initially demolished by penetrating the grouting pipe. For this purpose, step three: a plurality of auxiliary grouting pipes 21 are inserted along the demolishing point of the secondary lining 11 to the outside of the secondary lining 11 to perform grouting, and at the same time, the secondary lining 11 is initially excavated at the demolishing point;

[0040] Specifically, the operator first drills holes in the secondary lining 11 at several demolition points of the secondary lining 11, so that the holes penetrate into the rock layer and soil layer to be grouted, and then inserts the auxiliary grouting pipes 21 along the several holes, and then the auxiliary grouting pipes 21 grout the soil layer;

[0041] The auxiliary grouting pipe 21 includes an upper pipe and a lower pipe, each of which has an outlet. The upper pipe and the lower pipe are arranged in such a way as to ensure that when the auxiliary grouting pipe 21 is inserted into the borehole, the upper pipe faces away from the secondary lining 11, and the lower pipe faces the secondary lining 11;

[0042] When in use, after the auxiliary grouting pipe 21 is inserted, cement slurry is sprayed out from the upper pipe and the lower pipe at the same time, poured into the soil layer outside the secondary lining 11, and the grouting in the soil layer outside the secondary lining 11 is completed. At the same time, cement slurry is continuously sprayed toward the lower pipe of the secondary lining 11. After the cement slurry fills the gaps in the soil layer, it continuously applies pressure to the surrounding structure under the action of hydraulic pressure. This part of the pressure forms a force acting on the demolition point of the secondary lining 11 from the outside of the secondary lining 11. Since the demolition point has been drilled, a structural weakness is formed. At this time, under the action of grouting, the structural strength of the secondary lining 11 near the demolition point is weakened, and the grouting of the soil layer and the rock layer is completed at the same time, and the pre-demolition of the secondary lining 11 is achieved, which reduces the construction time cost of the subsequent demolition of the secondary lining 11 and improves the construction efficiency.

[0043] At the same time, since the secondary lining 11 is initially demolished and the secondary lining 11 plays a partial role in bearing the surrounding soil layers, during the demolition process, the bearing capacity of the surrounding soil layers near the demolition point of the secondary lining 11 decreases. At this time, the auxiliary grouting pipe 21 for grouting at the demolition point performs additional grouting on the soil layers near the demolition point, thereby improving the strength of the soil layers near the demolition point and reducing the probability of the soil layers near the demolition point collapsing into the tunnel 1, thereby reducing the probability of soil layer collapse caused by the reduction of the structural strength of the demolition point of the secondary lining 11;

[0044] During the above process, the operators simultaneously carry out preliminary excavation of the secondary lining 11 around the demolition point, use a drilling rig to drill holes with a depth of 10 to 50 cm around the demolition point, or use a hydraulic hammer to shallowly demolish the secondary lining 11 around the demolition point, further reducing the structural strength of the secondary lining 11 near the demolition point, achieving pre-demolition of the secondary lining 11, reducing the construction time cost of subsequent demolition of the secondary lining 11, and improving construction efficiency;

[0045] By dividing a number of demolition points at the secondary lining 11, drilling holes at the demolition points, inserting the auxiliary grouting pipe 21 and then grouting at the demolition points, the structural strength is weakened under the combined effect of the drilling at the demolition points and the pressure applied to the secondary lining 11 by the grouting, and the grouting is completed in the soil layer near the demolition points of the secondary lining 11, and the soil layer near the demolition points is additionally reinforced. At the same time, during the grouting process, the secondary lining 11 structure near the demolition points is further demolished, further weakening the structural strength near the demolition points of the secondary lining 11, reducing the construction time cost of the subsequent demolition of the secondary lining 11, improving the construction efficiency, and taking into account the construction safety;

[0046] After completing step 3, proceed to steps 4 and 5;

[0047] Step 4: Starting from the demolition point, the second lining 11 of the upper step is demolished, and the excavation is carried out according to the inner contour of the target structure. After the excavation is completed, the initial support is applied;

[0048] Specifically, the secondary lining 11 structure at the upper step and above is defined as the upper part. Starting from the vault of the existing tunnel 1, the upper secondary lining 11 structure is dismantled from top to bottom in sections in a progressively stronger direction. After the dismantling is completed, the tunnel 1 at the upper step is excavated according to the target form after the excavation. At the same time, step five is executed, starting from the demolition point, the secondary lining 11 of the upper step is demolished, and the excavation is carried out according to the inner contour of the target structure. After the excavation is completed, initial support is applied. The execution order of steps four and five refers to the existing tunnel 1 step construction method.

[0049] Optionally, in step three, before the grouting is completed, the auxiliary grouting pipe 21 is pulled out. After the auxiliary grouting pipe 21 is pulled out, a structural cavity is formed at the drilled hole at the demolition point, and at this time, the drilled hole is not filled with the auxiliary grouting pipe 21, and the structural strength at the demolition point is further reduced, thereby further reducing the construction time cost of subsequent demolition of the secondary lining 11 and improving construction efficiency.

[0050] During the process of inserting the auxiliary grouting pipe 21 into the second lining 11 along the demolition point for grouting, for tunnels 1 with different spans, when the span of the tunnel 1 is small, the total area of ​​the second lining 11 is small, and the time consumed for demolition is short. For the arch part of the tunnel 1 with a smaller span, the distance from the side wall is closer. At this time, the existing structure of the tunnel 1 can bear more pressure from the outer soil layer during demolition, and there is no need to excessively utilize the squeezing effect of cement slurry to pre-break the second lining 11, thereby reducing the duration of the grouting process and ensuring construction efficiency. Therefore, for tunnels 1 with smaller spans, in the grouting steps in steps 2 and 3, there is no need to grout too much to reinforce the soil layer.

[0051] For a tunnel 1 with a larger span, the total area of ​​the second lining 11 is larger, and the demolition takes a longer time. The distance between the arch part and the side wall is farther. At this time, the existing structure of the tunnel 1 cannot withstand the pressure of the outer soil layer during demolition to a large extent. Therefore, for a tunnel 1 with a larger span, in the grouting steps in steps 2 and 3, more sufficient grouting is required to reinforce the soil layer, and at the same time, the squeezing force of the cement slurry on the second lining 11 needs to be more fully utilized to achieve the pre-demolition of the second lining 11; for this purpose, in step 1, the span L of the expanded tunnel 1 part is measured; at the same time, step 3 also includes: using the auxiliary grouting pipe 21 to insert the demolition point of the second lining 11, and insert it outside the second lining 11, grouting, and adjusting the grouting amount to G, G=L / L0×G0, L0 and G0 are pre-calculated constants;

[0052] When the measured span value L is large, more sufficient grouting is required to reinforce the soil layer, and at the same time, the squeezing force of the cement slurry on the second lining 11 needs to be more fully utilized to achieve the pre-breakout of the second lining 11. At this time, the value of G=L / L0×G0 is large. When the grouting amount is adjusted to G, the grouting amount of the outer soil layer of the second lining 11 is increased when the span of the tunnel 1 is large; similarly, when the measured span value L is small, there is no need for too sufficient grouting to reinforce the soil layer, the duration of the grouting link is reduced, and there is no need to excessively utilize the squeezing effect of the cement slurry to pre-breakout the second lining 11. At this time, the value of G=L / L0×G0 is small. When the grouting amount is adjusted to G, the grouting amount of the outer soil layer of the second lining 11 is reduced when the span of the tunnel 1 is small;

[0053] By adjusting the grouting amount of the auxiliary grouting to the outside of the secondary lining 11 according to the span data, when the span of tunnel 1 is large, the bearing capacity of the soil layer is poor, and the area of ​​the secondary lining 11 is large, the grouting amount of the soil layer outside the secondary lining 11 is increased, and the vault is more fully grouted to strengthen the soil layer. At the same time, the squeezing force of the cement slurry on the secondary lining 11 is more fully utilized to achieve the pre-demolition of the secondary lining 11; when the span of tunnel 1 is small, the grouting amount of the soil layer outside the secondary lining 11 is reduced, taking into account the construction efficiency.

[0054] In order to further improve the pre-demolition effect of the auxiliary grouting pipe 21 on the secondary lining 11, step three also includes: applying a vibrator outside the auxiliary grouting pipe 21, and applying vibration to the auxiliary grouting pipe 21 during the grouting process of the auxiliary grouting pipe 21. In this embodiment, a vibrator is arranged outside each auxiliary grouting pipe 21. When the auxiliary grouting pipe 21 is grouting, the vibration is transmitted to the demolition point of the secondary lining 11 through the auxiliary grouting pipe 21, thereby further reducing the structural strength of the demolition point, reducing the construction time cost of subsequent demolition of the secondary lining 11, and improving construction efficiency. At the same time, the vibration improves the density and uniformity of the cement slurry in the auxiliary grouting pipe 21, thereby improving the grouting effect and ensuring safety.

[0055] When the span of the tunnel 1 is small, the existing structure of the tunnel 1 can bear more pressure from the outer soil layer during demolition, and does not need to be reinforced too much, and does not need to pre-demolish the secondary lining 11 too much, thereby saving construction energy consumption. When the span of the tunnel 1 is large, it is necessary to fully reinforce the soil layer and pre-demolish the secondary lining 11 more fully. To this end, in the above step 3: when the span of the expanded tunnel 1 exceeds the threshold, the power of the vibrator is increased, and when the span of the expanded tunnel 1 is less than the threshold, the power of the vibrator is reduced;

[0056] Specifically, the power of the vibrator is p, where p = f(L) × p0, f(L) = Log(1.8x-0.8)+1.1, x = L / L0, 0.5L0≤L≤1.5L0, when L is less than 0.5L0 or greater than 1.5L0, L = 0.5L0 or L = 1.5L0;

[0057] When the value of L is low, there is no need for excessively high vibration power to assist the slurry forming in the grouting pipe 21 or to pre-break the second lining 11. At this time, the value of f(L)=Log(1.8x-0.8)+1.1 is low, and the value of p=f(L)×p0 is low. When the vibrator power is adjusted to p, the power of the vibrator is reduced when the span is low. When the value of L is high, the vibration power needs to be increased to assist the slurry forming in the grouting pipe 21 or to pre-break the second lining 11. At this time, the value of f(L)=Log(1.8x-0.8)+1.1 is low, and the value of p=f(L)×p0 is low. When the vibrator power is adjusted to p, the power of the vibrator is reduced when the span is low.

[0058] By adjusting the vibrator power according to the span of the tunnel 1, when the span is high and a higher vibration power is needed to assist the mud formation in the grouting pipe 21 or to perform a more sufficient pre-breakout of the second lining 11, the vibration power can be increased to assist the compaction of the mud and at the same time perform a more sufficient pre-breakout of the second lining 11. When the power span is low and a higher vibration power is not needed to assist the mud formation in the grouting pipe 21 or to perform a sufficient pre-breakout of the second lining 11, the vibration power can be reduced to save energy.

[0059] Since, during demolition, if too much secondary lining 11 is removed at one time, especially the secondary lining 11 located at the upper step, there is a probability that the bearing capacity of the tunnel 1 on the soil layer will be drastically changed, increasing the probability of collapse of the tunnel 1, the secondary lining 11 needs to be demolished in sections or batches. Therefore, step 4 also includes: before demolition, setting the number of demolition points a of a single demolition batch, and demolishing the demolition points of the part of the tunnel 1 that needs to be expanded in batches, where a=L0 / L×a0;

[0060] Specifically, a number of demolition points in a single demolition batch are close to each other, a number of demolition points in a single demolition batch form a rectangular array, and the rectangular array formed by a number of demolition points in a single demolition batch does not contain demolition points of other batches;

[0061] When the value of L is high, it means that the span is large. At this time, the redundancy of the bearing capacity of the soil layer of tunnel 1 is low, and the area of ​​the secondary lining 11 to be demolished in a single time needs to be reduced. At this time, the value of a=L0 / L×a0 is low. At this time, when the number of demolition points in a single demolition batch is set to a, the area of ​​the secondary lining 11 to be demolished in a single batch is reduced, thereby reducing the probability of collapse and improving safety. When the value of L is low, it means that the span is small. At this time, the redundancy of the bearing capacity of the soil layer of tunnel 1 is high, and there is no need to appropriately increase the area of ​​the secondary lining 11 to be demolished in a single batch. At this time, when the number of demolition points in a single demolition batch is set to a, the area of ​​the secondary lining 11 to be demolished in a single batch is increased, thereby improving construction efficiency.

[0062] By setting the number of demolition points in a single demolition batch to be negatively correlated with the span, the area of ​​the second lining 11 demolition in a single batch is reduced when the span is large, thereby reducing the probability of collapse and improving safety. When the span is small, the area of ​​the second lining 11 demolition in a single batch is increased, thereby improving construction efficiency.

[0063] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A large-span tunnel excavation construction process, characterized in that: The following steps are involved: Step 1: Backfill sandbags at the lower part of the main tunnel of the tunnel section that needs to be expanded to form steps, and mark several demolition points on the inner surface of the secondary lining of the expanded section; Step 2: Use the main grouting pipe to insert into the outside of the second lining of the expanded part for grouting; Step 3: Use several auxiliary grouting pipes to insert along the breaking point of the secondary lining to the outside of the secondary lining for grouting, and at the same time, perform preliminary excavation of the secondary lining at the breaking point; Step 4: Starting from the demolition point, the secondary lining of the upper step is demolished, and the excavation is carried out according to the inner contour of the target structure. After the excavation is completed, the initial support is applied; Step 5: Starting from the demolition point, demolish the secondary lining of the lower step, and expand the excavation according to the inner contour of the target structure. After the excavation is completed, apply initial support.

2. A large-span tunnel excavation construction process according to claim 1, characterized in that: The step three also includes: before the grouting is completed, pulling out the auxiliary grouting pipe.

3. A large-span tunnel excavation construction process according to claim 1, characterized in that: The step one also includes: measuring the span L of the expanded tunnel section; the step three also includes: step three: using an auxiliary grouting pipe to insert into the breaking point of the second lining, and inserting to the outside of the second lining, grouting, and adjusting the grouting amount to G, G=L / L0×G0, L0 and G0 are pre-calculated constants.

4. A large-span tunnel excavation construction process according to claim 3, characterized in that: The step three also includes: applying a vibrator outside the auxiliary grouting pipe, and applying vibration to the auxiliary grouting pipe during the grouting process of the auxiliary grouting pipe.

5. A large-span tunnel expansion construction process according to claim 4, characterized in that: The step three also includes: increasing the power of the vibrator when the span of the expanded tunnel section exceeds a threshold value, and reducing the power of the vibrator when the span of the expanded tunnel section is below the threshold value.

6. A large-span tunnel excavation construction process according to claim 4, characterized in that: The step three also includes: adjusting the power of the vibrator to p, where p=f(L)×p0, f(L)=Log(1.8x-0.8)+1.1, x=L / L0, 0.5L0≤L≤1.5L0.

7. The large-span tunnel excavation construction process according to claim 3 is characterized in that: The step 4 also includes: before demolition, setting the number a of demolition points of a single demolition batch, and demolishing the demolition points of the tunnel part that needs to be expanded in batches, where a=L0 / L×a0.

Images