Double-hole double-arch tunnel variable three-line large-span single-hole tunnel rapid construction method

Abstract

The present application belongs to the technical field of tunnel construction, and specifically relates to a double-hole double-arch tunnel variable three-line large-span single-hole tunnel rapid construction method. The method comprises the following steps. S100: double-hole double-arch tunnel section is excavated and constructed; a middle partition wall is first constructed, then a left side pilot tunnel of a small hole of the double-hole double-arch tunnel is constructed, and finally a right side pilot tunnel of a large hole of the double-hole double-arch tunnel is constructed. S200: when the construction reaches a design junction of the double-hole double-arch tunnel section and the three-line large-span single-hole tunnel section, whether the geology of a front section is consistent with the design is ascertained according to advanced geological prediction. S300: if the geology of the front section is inconsistent with the design, the design parameters are changed; if the geology of the front section is consistent with the design, subsequent construction is carried out according to the design parameters. S400: tunnel vault subsidence and clearance change subsidence monitoring is carried out, and after the tunnel horizontal clearance change speed and the vault vertical displacement speed significantly decrease and stabilize, the three-line large-span single-hole tunnel section construction is carried out.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction, and in particular is a rapid construction method for converting a double-hole and double-arch tunnel into a three-line large-span single-hole tunnel. Background Art

[0002] With the acceleration of national railway infrastructure investment and construction, the road network is becoming increasingly dense, and the number of railway tunnels is increasing. Currently, my country's railway tunnel construction technology has made significant progress, with large-section tunnel excavation technology at the forefront domestically, and some achievements have even reached international advanced levels. However, there is currently little research, both domestically and internationally, on the cross-section transformation and construction method conversion technology used to transform large-section, double-hole, double-arch tunnels into three-line, long-span, single-hole tunnels. During this process, the stresses on the support structure change due to different excavation methods and the redistribution of ground stress after excavation, which can easily lead to tunnel collapse and cracking of the primary support structure. Consequently, these cross-section transformation and construction method conversion projects have low efficiency, slow progress, high safety risks, and high construction costs. Summary of the Invention

[0003] In order to solve the above problems, the present invention provides a rapid construction method for converting a double-hole and double-arch tunnel into a three-line large-span single-hole tunnel.

[0004] The present invention adopts the following technical solution: a rapid construction method for converting a double-hole and double-arch tunnel into a three-line large-span single-hole tunnel, comprising the following steps.

[0005] Excavation construction is underway at the S100~ double-hole, double-arch tunnel section; the middle partition wall is constructed first, followed by the left pilot pit of the small hole of the double-hole, double-arch tunnel, and finally the right pilot pit of the large hole of the double-hole, double-arch tunnel.

[0006] S200~When the construction reaches the designed junction of the double-hole and double-arch tunnel section and the three-line large-span single-hole tunnel section, it is necessary to determine whether the geology of the front section is consistent with the design based on the advanced geological forecast.

[0007] S300~If the geology of the front section is different from the design, the design parameters are changed; if the geology of the front section is the same as the design, subsequent construction is carried out according to the design parameters.

[0008] S400~Carry out tunnel vault sinking and clearance change settlement monitoring, and after the tunnel horizontal clearance change speed and vault vertical displacement speed have obviously decreased and stabilized, proceed with the construction of the three-line large-span single-hole tunnel section.

[0009] The specific construction steps of step S100 are:

[0010] S101~After the steps on the small hole of the double-arch tunnel are excavated and supported to the mileage of the designed intersection, the left pilot tunnel part ① is excavated by weak blasting, and then the initial support and temporary support are carried out around the left pilot tunnel part ①.

[0011] S102~ lags behind the upper part of the small tunnel pilot pit. After the excavation and support construction of the lower step of the small tunnel of the double-arch tunnel is completed, the lower part of the small tunnel pilot pit is excavated by weak blasting, and then the initial support and temporary support around the lower part of the small tunnel pilot pit are carried out. The left pilot pit is excavated by the step method, which is divided into upper and lower steps. The upper part of the left pilot pit is the upper step of the left pilot pit, and the lower part of the left pilot pit is the lower step of the left pilot pit.

[0012] S103~After excavation and support progress on the left pilot tunnel part ①, excavation and support below the left pilot tunnel part ①, the face construction is suspended, and excavation is continued after the small hole lining construction is completed; after the small hole lining construction is completed, excavation and support of the double side wall sections on the left pilot tunnel part ① and below the left pilot tunnel part ① are continued, and excavation and support of the left pilot tunnel part ① on the left pilot tunnel part ① is accumulated for a certain distance, and excavation and support below the small hole pilot tunnel part ① is suspended after a certain distance is accumulated.

[0013] The S104~ double-arch tunnel large hole is excavated using the three-step method, which is divided into upper step, middle step and lower step. The upper step and middle step of the double-arch tunnel large hole are excavated and supported to the designed intersection, and then the right side pilot pit part ② is excavated by weak blasting on both side walls. Then, the initial support and temporary support are implemented around the upper part of the right side pilot pit part ②. The upper part of the right side pilot pit part ② is the upper step of the right side pilot pit of the double side walls, and the lower part of the right side pilot pit part ② is the lower step of the right side pilot pit of the double side walls.

[0014] S105~ lags behind the right pilot pit ②. After the excavation and support construction of the steps under the large hole of the double-arch tunnel is completed, the right pilot pit ② is excavated by weak blasting, and then the initial support and temporary support around the right pilot pit ② are carried out.

[0015] S106~ lags behind the right pilot pit ②, and uses weak blasting to excavate the middle pilot pit ③ of the large hole, and then implements initial support around the middle pilot pit ③.

[0016] S107~According to the step method, the middle pilot pit section ④ and the middle pilot pit section ⑤ of the double side walls are excavated in sequence, and then the initial support of the invert arch is carried out. Among them, the pilot pit section ③ is the upper step of the middle pilot pit of the double side walls, the pilot pit section ④ is the middle step of the middle pilot pit of the double side walls, and the pilot pit section ⑤ is the lower step of the middle pilot pit of the double side walls.

[0017] S108~After the excavation and support of the left pilot tunnel part ① has accumulated a certain distance, the excavation and support of the left pilot tunnel part ① has accumulated a certain distance, the excavation and support of the right pilot tunnel part ② has accumulated a certain distance, the excavation and support of the right pilot tunnel part ② has accumulated a certain distance, the excavation and support of the middle pilot tunnel part ③ of the large tunnel has accumulated a certain distance, and the excavation and support of the middle pilot tunnel part ⑤ has accumulated a certain distance, the construction of the heading face will be suspended; after the lining construction of the double-arch large tunnel reaches the designed intersection, according to the monitoring measurement and analysis, after the initial support deformation is stable, the temporary steel frame of the double side walls will be dismantled in two cycles → the side wall foundation and invert arch of the middle pilot tunnel part ⑥ will be poured, among which part ⑥ is the tunnel side wall foundation and invert arch lining within the range of the double side walls.

[0018] S109~After the initial setting of the invert concrete, pour the invert filling section ⑦ to the designed height, and then excavate the construction faces of sections ①, ② and ③. Section ⑦ is the tunnel invert filling within the double side walls.

[0019] S110~According to the monitoring measurement and analysis, after the initial support converges, the lining template trolley is used to pour the 8th section of lining at one time, where the 8th section is the secondary lining of the inner section of the tunnel within the range of the double side walls.

[0020] In step S102, the distance lagging behind the left pilot pit ① is 3 to 5 meters.

[0021] In step S103, the distance of the upper excavation support of the left pilot tunnel ① is 10m; the distance of the lower excavation support of the left pilot tunnel ① is 5m.

[0022] In step S103, the upper excavation and support of the left pilot tunnel ① is accumulated to 20m, and the lower excavation and support of the left pilot tunnel ① is accumulated to 15m, and then the face construction is suspended.

[0023] In step S105, the distance lagging behind the right pilot pit ② is 3 to 5 meters.

[0024] In step S106, the distance behind the right pilot pit ② is 3 to 5 meters.

[0025] In step S108, the excavation and support of the left pilot tunnel part ① is accumulated to 30m, the excavation and support of the left pilot tunnel part ① is accumulated to 27m, the excavation and support of the right pilot tunnel part ② is accumulated to 22m, the excavation and support of the right pilot tunnel part ② is accumulated to 19m, the excavation and support of the middle pilot tunnel part ③ is accumulated to 14m, and the excavation and support of the middle pilot tunnel part ⑤ is accumulated to 6m, and then the face construction is suspended.

[0026] The cross-sectional width and height of the left and right guide pits on both side walls must be consistent with the width and height of the double-arch small holes.

[0027] Compared with the existing technology, the present invention makes full use of the characteristics of partial excavation of double tunnels and double arches and each small pilot tunnel on the double side walls of a large-span single tunnel is individually closed into a ring, determines a reasonable excavation sequence, excavation method and support parameters, optimizes the excavation section of the left and right pilot tunnels on the double side walls of the large-span single tunnel according to the excavation section size of each pilot tunnel of the double arches, ensures a smooth transition of the section change, optimizes the construction sequence of each small pilot tunnel between section changes and construction method conversions, and effectively avoids the changes in the stress of the support structure caused by different excavation methods and redistribution of ground stress after excavation during the section change and construction method conversion of large-section tunnels, making it easy for the tunnel to collapse and the primary support structure to crack. At the same time, the advanced geological prediction monitoring and measurement information technology is used to ensure the safety and quality during the section change and construction method conversion, improve the construction efficiency and accelerate the construction progress. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a cross-sectional diagram of the construction process of double-hole and double-arch excavation;

[0029] Figure 2 This is a cross-sectional diagram of the construction process of the three-line large-span single-hole double-side wall excavation;

[0030] Figure 3 This is the cross-sectional view of the construction of converting double-hole and double-arch to long-span single-hole and double-side wall;

[0031] Figure 4 This is the longitudinal section diagram of the double-hole and double-arch construction process;

[0032] Figure 5 This is the longitudinal section of the construction process S101 of converting double-hole and double-arch to long-span single-hole and double-side wall;

[0033] Figure 6 This is the longitudinal section of the construction process S102 of converting double-hole and double-arch into a long-span single-hole with double side walls;

[0034] Figure 7 This is the longitudinal section of the construction process S103 of converting double-hole and double-arch to long-span single-hole and double-side wall;

[0035] Figure 8 This is the longitudinal section of the construction process S104 of converting double-hole and double-arch into a long-span single-hole and double-side wall;

[0036] Figure 9 This is the longitudinal section of the construction process S105 of converting double-hole and double-arch into a long-span single-hole and double-side wall;

[0037] Figure 10 This is the longitudinal section of the construction process S106 of converting double-hole and double-arch into a long-span single-hole with double side walls;

[0038] Figure 11 This is the longitudinal section of the construction process S107 of converting double-hole and double-arch to long-span single-hole and double-side wall;

[0039] Figure 12 This is the longitudinal section of the construction process S108 of converting double-hole and double-arch into a long-span single-hole and double-side wall;

[0040] Figure 13 This is the longitudinal section of the construction process S109 of converting double-hole and double-arch to long-span single-hole and double-side wall;

[0041] Figure 14 This is the longitudinal section of the construction process S110 of converting double-hole and double-arch into a long-span single-hole and double-side wall;

[0042] In the picture, 1-small hole, 2-big hole, 3-middle partition wall. DETAILED DESCRIPTION

[0043] A rapid construction method for converting a double-hole double-arch tunnel into a three-line large-span single-hole tunnel, comprising the following steps: S100 to S101: Figure 1 As shown, excavation construction of the double-hole, double-arch tunnel section is carried out; the middle partition wall is constructed first, then the small hole (left pilot tunnel) is constructed, and finally the large hole (right pilot tunnel) is constructed; from S200 onwards, when the construction reaches the design intersection of the double-hole, double-arch tunnel section and the three-line large-span single-hole tunnel section, the geology of the front section is verified to be consistent with the design based on the advanced geological forecast; from S300 onwards, if the geology of the front section is different from the design, the design parameters are changed; if the geology of the front section is consistent with the design, subsequent construction is carried out according to the design parameters; from S400 onwards, the tunnel vault sinking and clearance change settlement monitoring is carried out, and the three-line large-span single-hole tunnel section is constructed after the tunnel horizontal clearance change speed and the vault vertical displacement speed have significantly decreased and stabilized.

[0044] The specific construction steps of step S100 are:

[0045] like Figure 4 As shown, after the upper steps of the small hole (left pilot tunnel) of the double-arch tunnel (S101) were excavated and supported to the mileage of the designed junction, the left pilot tunnel part ① of the double side walls was excavated by weak blasting, and then the initial support and temporary support were carried out around the upper part of the left pilot tunnel part ①.

[0046] like Figure 5 As shown, S102~ lags behind the upper section ① of the left pilot pit of the double sidewall by 3-5m. After the excavation and support construction of the lower bench of the small tunnel (left pilot pit) of the double-arch tunnel is completed, the lower section ① of the left pilot pit of the double sidewall is excavated by weak blasting. Then, initial support and temporary support are implemented for the lower section ① of the left pilot pit of the double sidewall. The small tunnel of the double-arch tunnel and the left pilot pit of the double sidewall are both excavated using the bench method, divided into upper and lower benches. The upper section ① of the pilot pit is the upper bench of the left pilot pit of the double sidewall, and the lower section ① of the pilot pit is the lower bench of the left pilot pit of the double sidewall. The upper and lower benches of the small tunnel of the double-arch tunnel correspond to the upper and lower sections ① of the left pilot pit of the double sidewall, respectively.

[0047] like Figure 6As shown, S103~, after the excavation and support progress of 10m on the left side pilot pit ① of the double side wall and 5m on the lower part of the pilot pit ①, the face construction was suspended, and the double side wall excavation was continued after the lining construction of the double arch small hole was completed; after the lining construction of the double arch small hole was completed, the excavation and support of the left side pilot pit ① of the double side wall section was continued, and the cumulative excavation and support of the pilot pit ① on the upper part of the pilot pit ① and the cumulative excavation and support of the pilot pit ① were 20m, and the cumulative excavation and support of the pilot pit ① were 15m, the face construction was suspended, and after the cumulative excavation and support progress of the right side pilot pit ② of the double side wall was 12m, the left side pilot pit ① of the double side wall and the lower part of the pilot pit ① were carried out.

[0048] like Figure 7 As shown, S104~ excavated and supported the upper and middle benches of the double-arch tunnel main tunnel (right pilot tunnel) to the designed intersection. Low-pressure blasting was used to excavate the upper right pilot tunnel section ②. Initial and temporary support were then implemented around the upper right pilot tunnel section ②. The double-arch tunnel main tunnel was excavated using a three-bench method, consisting of an upper bench, a middle bench, and a lower bench. The right pilot tunnel was excavated using both upper and lower benches. The upper right pilot tunnel section ② represents the upper bench of the double-sidewall right pilot tunnel, while the lower right pilot tunnel section ② represents the lower bench of the double-sidewall right pilot tunnel.

[0049] like Figure 8 As shown, S105~ lags behind the right pilot pit ② of the double side walls by 3 to 5 meters. After the excavation and support construction of the steps under the large hole of the double-arch tunnel is completed, the right pilot pit ② of the double side walls is excavated by weak blasting, and then the initial support and temporary support around the right pilot pit ② of the double side walls are carried out.

[0050] like Figure 9 As shown, S106~ lags behind the right pilot pit ② of the double side walls by 3 to 5 meters. The middle pilot pit ③ of the double side walls is excavated by weak blasting, and then initial support is applied around the pilot pit.

[0051] like Figure 10 As shown in Figure 107, the middle sections of the double sidewalls (Sections 4 and 5) were excavated sequentially using the bench method, followed by initial support for the inverted arch. The middle pilot pit of the double sidewalls was excavated using a three-bench method, consisting of an upper bench, a middle bench, and a lower bench. Section 3 of the pilot pit is the upper bench, Section 4 is the middle bench, and Section 5 is the lower bench.

[0052] like Figure 11As shown, to ensure that the step lengths at various locations in the tunnel excavation section meet the requirements of the Technical Specifications for Construction of Passenger and Freight Railway Tunnels (Q / CR 9653-2017) and the construction unit's tunnel excavation safety stepover requirements, S108~ completed a cumulative 30m of excavation and support work on the upper section ① of the left pilot tunnel and a cumulative 27m of excavation and support work on the lower section ① of the double side walls. The right pilot tunnel also completed a cumulative 22m of excavation and support work on the upper section ② and a cumulative 19m of excavation and support work on the lower section ②. The central pilot tunnel completed a cumulative 14m of excavation and support work on the lower section ③ of the central pilot tunnel and a cumulative 6m of excavation and support work on the lower section ⑤ of the pilot tunnel, before suspending face construction. After the lining of the double-arch tunnel (right pilot tunnel) reached the designed intersection, and based on monitoring, measurement, and analysis, and after the initial support deformation stabilized, the temporary steel frames of the double side walls of section D1K228+190-+196 were dismantled in two cycles. The sidewall foundation and invert arch of section ⑥ (D1K228+190-+196) were then poured. Part ⑥ is the tunnel side wall foundation and invert arch lining within the double side wall range.

[0053] like Figure 12 As shown in Figure 109, after the initial setting of the invert concrete, the invert filling section ⑦ was poured to the designed height. Then, the tunnel faces of the left pilot pit section ①, the right pilot pit section ②, and the center pilot pit section ③ of the double sidewall were excavated. Section ⑦ is the tunnel invert filling within the double sidewall area.

[0054] like Figure 13 As shown in Figure S110, based on monitoring, measurement, and analysis, after the initial support has converged, the lining formwork trolley is used to pour the 8th section of lining in one go. The 8th section is the secondary lining of the inner section of the tunnel within the double sidewalls.

[0055] In order to reduce tunnel collapse caused by sudden changes in surrounding rock stress concentration during excavation, the cross-sectional width and height of the left pilot tunnel part 1 and the right pilot tunnel part 2 of the double side walls must be consistent with the width and height of the double-arch small hole (left pilot tunnel). In this way, the cross-sectional changes when the construction method is changed can be smoothly transitioned. At the same time, the double-arch small hole excavation rig can be used to construct the advance support of the double side wall part ①, saving auxiliary materials and accelerating the construction progress.

[0056] When considering the change of section, try to choose a smooth transition of section. When the section change takes a sudden change, it is necessary to expand the section. When the expanded section is large, tunnel collapse accidents are prone to occur. Therefore, according to the cross-sectional size of the constructed double-arch small hole, the left and right pilot tunnel sections of the double side walls are divided. First, it is ensured that the surrounding rock stress does not suddenly change when the section changes, thereby ensuring the safety of excavation; second, the consistency of the front and rear sections allows the use of auxiliary equipment such as the original excavation rig to save costs and speed up the construction progress.

[0057] Based on the fact that the cross-sectional sizes of the double-arch small tunnel (right pilot tunnel) are consistent with those of the left pilot tunnel part 1 and the right pilot tunnel part 2 of the double side wall, the left pilot tunnel part 1 of the double side wall is optimized and determined as the pilot tunnel to ensure a smooth transition of the cross-sectional changes and reduce the safety risks when the cross-sectional changes are expanded. By utilizing the looping characteristics of the small pilot tunnels, the stability of the primary support structure is guaranteed under the redistribution of ground stress during the conversion of the construction method.

[0058] The present invention rationally arranges the construction sequence of each pilot tunnel, reduces the disturbance of the surrounding rock caused by the construction of adjacent pilot tunnels, and ensures that the construction personnel and equipment of each pilot tunnel are not idle. The advance pilot tunnel is used to reveal the surrounding rock conditions in front of the tunnel, providing a basis for other excavation construction on the double side walls.

[0059] In the step S300, the design change includes the change of advance support (the main change parameters are the change of Φ42 single-layer small conduit to Φ42 double-layer small conduit, the change of Φ42 single-layer small conduit to Φ60 medium pipe rack), the change of initial support (the main change parameters are the change of I18 steel frame to I20b steel frame, the change of I18 steel frame to I22b steel frame, the change of Φ22 locking foot anchor rod to Φ42 locking foot anchor pipe, the addition of strengthening measures such as temporary closure spraying of C20 concrete on the face of the palm).

[0060] In the aforementioned step S400, (1) Observation inside and outside the tunnel: geological description of the excavation surface is performed, including the lithology of the surrounding rock and the presence of water leakage; the initial support state is checked to see whether cracks, peeling and shear failures occur in the sprayed layer, and whether the steel support is compressed and analyzed. (2) Monitoring and measurement of arch crown sinking and clearance changes: the deformation rate of the initial support of the tunnel decreases significantly and tends to be moderate; the horizontal convergence is less than 0.2mm / d and the arch sinking speed is less than 0.15mm / d; when this occurs, the cross-section change and construction method conversion are performed.

[0061] Relying on the DRBRTJ-5 section of the Dali-Ruili Railway, Huataolin No. 1 Tunnel and Huataolin No. 4 Tunnel are built in parallel with each other, with a net construction distance of 35m. Huataolin No. 4 Tunnel is designed to be merged into Huataolin No. 1 Tunnel. The D1K228+170~+190 section of Huataolin No. 1 Tunnel and the freight line Huataolin No. 4 Tunnel form a double arch lining with a section width of 22m. The double arch excavation method is adopted, and the D1K228+190~+310 section is constructed using the double side wall pilot tunnel method. In view of the large excavation section, high risk of construction collapse, low work efficiency, large cost investment and high quality requirements in the section of section change and construction method conversion, our unit fully utilized the characteristics of double-hole and double-arch segmented excavation and the separate closure of each small pilot tunnel on the double side walls of the large-span single tunnel into a ring, determined a reasonable excavation sequence, excavation method and support parameters, optimized the excavation section of the left and right pilot tunnels on the double side walls of the large-span single tunnel according to the excavation section size of each pilot tunnel of the double-arch, ensured a smooth transition of the section change, and optimized the construction sequence of each small pilot tunnel between section change and construction method conversion. This effectively avoided the problems of collapse and cracking of the primary support structure caused by the different excavation methods and the redistribution of ground stress after excavation during the section change and construction method conversion of large-section tunnels. At the same time, the safety and quality of the section change and construction method conversion during the construction period were guaranteed by the use of advanced geological prediction monitoring and measurement information technology. Improved construction efficiency and accelerated construction progress. In order to further promote its application, a special construction method was summarized and formed.

Claims

1. A rapid construction method for converting a double-hole, double-arch tunnel into a three-line, large-span single-hole tunnel, characterized by: The following steps are included: S100~ Excavation construction of the double-hole, double-arch tunnel section begins; first, the middle partition wall is constructed, followed by the left pilot pit of the small hole of the double-hole, double-arch tunnel. The left pilot pit is excavated using the step method and is divided into an upper step and a lower step. Finally, the right pilot pit of the large hole of the double-hole, double-arch tunnel is excavated using the three-step method and is divided into an upper step, a middle step, and a lower step. In addition, at the designed intersection of the double-hole, double-arch tunnel section and the three-line long-span single-hole tunnel section, the cross-sectional width and height of the left and right pilot pits on both sides of the double wall must be consistent with the width and height of the double-arch small hole. The specific construction steps of step S100 are: S101~ After the upper bench of the small hole (1) of the double-arch tunnel is excavated and supported to the mileage of the designed intersection, the left pilot pit ① is excavated by weak blasting, and then the initial support and temporary support around the left pilot pit ① are implemented; S102~ lags behind the upper left pilot pit section ①. After the excavation and support construction of the lower step of the small hole of the double-arch tunnel is completed, the lower left pilot pit section ① is excavated by weak blasting. Then, the initial support and temporary support are carried out around the lower left pilot pit section ①. The left pilot pit is excavated using the step method, which is divided into an upper step and a lower step. The upper left pilot pit section ① is the upper step of the left pilot pit, and the lower left pilot pit section ① is the lower step of the left pilot pit. S103: Excavation and support progress is carried out on the left pilot pit section ①. After excavation and support is carried out on the left pilot pit section ①, face construction is suspended and excavation is resumed after the small hole lining construction is completed. After the small hole lining construction is completed, excavation and support of the double side wall section is continued on the left pilot pit section ① and on the left pilot pit section ①. Excavation and support are carried out on the left pilot pit section ① for a certain distance, and after excavation and support are carried out on the left pilot pit section ① for a certain distance, face construction is suspended. The S104~ double-arch tunnel main tunnel was excavated using a three-bench method, divided into an upper bench, a middle bench, and a lower bench. The upper and middle benches of the double-arch tunnel main tunnel were excavated and supported to the designed intersection. Then, weak blasting was used to excavate the upper portion of the right pilot pit ② on both sides. Initial and temporary supports were then implemented around the upper portion of the right pilot pit ②. The upper portion of the right pilot pit ② became the upper bench of the double-sidewall right pilot pit, and the lower portion of the right pilot pit ② became the lower bench of the double-sidewall right pilot pit. S105~ lags behind the right pilot pit section ②. After the excavation and support construction of the lower step of the double-arch tunnel is completed, the right pilot pit section ② is excavated by weak blasting, and then the initial support and temporary support around the right pilot pit section ② are implemented. S106~ lags behind the right pilot pit ②, and uses weak blasting to excavate the middle pilot pit ③ of the large hole, and then provides initial support around the middle pilot pit ③; S107~ Excavate the middle pilot pit section ④ and the middle pilot pit section ⑤ of the double sidewall in sequence using the step method, and then implement the initial support of the invert arch. The pilot pit section ③ is the upper step of the middle pilot pit of the double sidewall, the pilot pit section ④ is the middle step of the middle pilot pit of the double sidewall, and the pilot pit section ⑤ is the lower step of the middle pilot pit of the double sidewall. S108: After excavating and supporting the left pilot tunnel section ① for a certain distance, excavating and supporting the left pilot tunnel section ① for a certain distance, excavating and supporting the right pilot tunnel section ② for a certain distance, excavating and supporting the right pilot tunnel section ② for a certain distance, excavating and supporting the middle pilot tunnel section ③ for a certain distance, and excavating and supporting the middle pilot tunnel section ⑤ for a certain distance, face construction is suspended. After the lining of the double-arch tunnel is constructed to the designed intersection, and after the initial support deformation stabilizes based on monitoring measurement and analysis, the temporary steel frames of both side walls are removed in two cycles. The side wall foundation and invert arch of the middle pilot tunnel section ⑥ are poured. Section ⑥ is the tunnel side wall foundation and invert arch lining within the range of both side walls. S109~After the initial setting of the inverted arch concrete, pour the inverted arch filling section ⑦ to the designed height, then excavate the tunnel faces of sections ①, ②, and ③. Section ⑦ is the tunnel inverted arch filling within the double side walls. S110~ Based on monitoring, measurement and analysis, after the initial support has converged, the lining formwork trolley is used to pour the 8th section of lining at one time, where the 8th section is the secondary lining of the tunnel section within the double side walls; S200~When construction reaches the designed intersection of the double-hole and double-arch tunnel section and the three-line large-span single-hole tunnel section, verify whether the geology of the preceding section is consistent with the design based on the advanced geological forecast; S300~If the geology of the front section is different from the design, the design parameters are changed; if the geology of the front section is the same as the design, subsequent construction is carried out according to the design parameters; S400~Carry out tunnel arch crown sinking and clearance change settlement monitoring. When the tunnel horizontal clearance change rate is less than 0.2mm / d and the arch crown vertical displacement rate is less than 0.15mm / d, the construction of the three-line large-span single-hole tunnel section will be carried out.

2. The rapid construction method for converting a double-hole, double-arch tunnel into a triple-line, large-span single-hole tunnel according to claim 1 is characterized by: In the step S102, the distance lagging behind the left pilot pit portion ① is 3 to 5 meters.

3. The rapid construction method for converting a double-hole, double-arch tunnel into a triple-line, large-span single-hole tunnel according to claim 1 is characterized by: In step S103, the distance of the upper excavation support of the left pilot tunnel ① is 10m; the distance of the lower excavation support of the left pilot tunnel ① is 5m.

4. The rapid construction method for converting a double-hole, double-arch tunnel into a triple-line, large-span single-hole tunnel according to claim 1 is characterized by: In step S103, the face construction is suspended after the upper excavation and support of the left pilot tunnel ① is accumulated to 20m and the lower excavation and support of the left pilot tunnel ① is accumulated to 15m.

5. The rapid construction method for converting a double-hole, double-arch tunnel into a triple-line, large-span single-hole tunnel according to claim 1 is characterized by: In the step S105, the distance lagging on the right pilot pit ② is 3 to 5 meters.

6. The rapid construction method for converting a double-hole, double-arch tunnel into a triple-line, large-span single-hole tunnel according to claim 1 is characterized by: In the step S106, the distance behind the right pilot pit ② is 3 to 5 meters.

7. The rapid construction method for converting a double-hole, double-arch tunnel into a triple-line, large-span single-hole tunnel according to claim 1 is characterized by: In the step S108, the excavation and support on the left pilot pit ① is cumulatively 30m, the excavation and support on the left pilot pit ① is cumulatively 27m, the excavation and support on the right pilot pit ② is cumulatively 22m, the excavation and support on the right pilot pit ② is cumulatively 19m, the excavation and support on the middle pilot pit ③ is cumulatively 14m, and the excavation and support on the middle pilot pit ⑤ is cumulatively 6m, then the face construction is suspended.

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