A construction method for a large-span multi-arch tunnel entrance structure in a pass section

Abstract

The present invention relates to the technical field of tunnel engineering, and provides a construction method for a large-span arch tunnel entrance structure in a pass section, wherein a first pre-reinforced pile assembly and a second pre-reinforced pile assembly are constructed, a temporary slope is excavated to construct a middle guide tunnel, and then the middle guide tunnel is excavated. After the middle guide tunnel is connected, a middle partition wall is constructed in the middle guide tunnel, soil and rocks are backfilled to the bottom height of the protective arch, a protective arch located above the left tunnel and the right tunnel of the tunnel is constructed, an open tunnel section and an end wall type tunnel door are constructed, and soil is backfilled on the top of the protective arch to the designed height, and then the left tunnel and the right tunnel of the tunnel are synchronously constructed to the dark tunnel section. The present application can realize the synchronous construction of the left and right main tunnels of the arch tunnel, greatly reduce the construction procedures of the arch tunnel, and has high safety. At the same time, the slope is effectively reinforced to prevent the slope from sliding and collapsing during the excavation process. A design method for the protective arch is also provided, and the protective arch determined thereby can meet the structural requirements and improve the convenience of construction.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel engineering, and in particular to a construction method for a large-span multi-arch tunnel entrance structure in a pass section. Background Art

[0002] Nowadays, multi-arch tunnels are often used in highway projects with limited land use due to their advantage of occupying less space. In addition, due to the limitations of terrain and route selection, the tunnel entrances are inevitably located in locations with poor geology such as pass sections. In the existing technology, large-span multi-arch tunnels in pass sections are usually constructed by open hole construction or backfilling and excavation.

[0003] Among them, the open tunnel method is to use the open excavation method to excavate the mountain within the tunnel range with a gentle slope. Since the mountains on both sides of the pass are steep, the side slopes are often high. Therefore, this method requires the use of pile-sheet walls and anchor frame beams to reinforce the high slopes; the backfill and dark excavation plan adopts direct backfilling of soil in the pass section to ensure that the dark tunnel is covered with soil to a certain extent, and then the long pipe shed and radial grouting are used to reinforce the tunnel before excavation.

[0004] A large number of engineering examples show that the open tunnel scheme involves large-scale excavation during construction, which causes great damage to the original mountain and ecology, and the risk of side slope protection during construction and operation is extremely high. The backfill and dark excavation scheme artificially transforms the existing terrain. Affected by the limitations of the construction site and the poor geology of the valley section, the backfill and dark excavation scheme adopts direct backfilling in the pass section to ensure that the dark tunnel is covered with soil. The tunnel is reinforced by long pipe sheds and radial grouting before dark tunnel excavation. The main tunnel construction method generally adopts the side wall pilot method. The left and right main tunnel faces must be separated by no less than 20m, and the left and right main tunnels cannot be excavated simultaneously. Moreover, practice has shown that the backfill and dark excavation scheme is often prone to tunnel collapse and roof collapse during construction, and lining cracking during later construction and operation.

[0005] In view of this, it is necessary to propose a construction method for the entrance structure of a large-span multi-arch tunnel in a pass section to solve or at least alleviate the above-mentioned defects. Summary of the invention

[0006] The main purpose of the present invention is to provide a construction method for the entrance structure of a large-span multi-arch tunnel in a pass section, so as to solve the technical problems in the prior art that the open-cut method for the large-span multi-arch tunnel in the pass section requires large-scale excavation, and the direct backfilling and dark excavation scheme is difficult to ensure the safety of the tunnel structure and cannot achieve synchronous excavation of the left and right tunnels.

[0007] To achieve the above object, the present invention provides a construction method for a large-span multi-arch tunnel entrance structure at a pass section, comprising the following steps:

[0008] S1, constructing a first pre-reinforced pile assembly located outside the left tunnel and a second pre-reinforced pile assembly located outside the right tunnel; wherein the bottoms of the first pre-reinforced pile assembly and the second pre-reinforced pile assembly both extend downward below the tunnel arch bottom, and the tops of the first pre-reinforced pile assembly and the second pre-reinforced pile assembly both extend upward to the ground surface;

[0009] S2, excavating a temporary slope to construct a middle guide tunnel, and then excavating a middle guide tunnel extending in the extension direction of the tunnel, and after the middle guide tunnel is penetrated, constructing a middle partition wall extending in the extension direction of the tunnel in the middle guide tunnel;

[0010] S3, backfilling soil and rocks to the bottom height of the protective arch, and constructing the protective arch located above the left tunnel and the right tunnel; wherein the protective arch is connected between the first pre-reinforced pile assembly and the second pre-reinforced pile assembly;

[0011] S4, constructing an open tunnel section and an end wall type tunnel portal, and then backfilling the top of the arch to the designed height, and then synchronously constructing the left tunnel and the right tunnel to the dark tunnel section.

[0012] Preferably, the synchronous construction of the left tunnel and the right tunnel to the dark tunnel section in step S4 specifically includes the following steps:

[0013] S41: excavate the upper step rock and soil of the left tunnel and the right tunnel simultaneously, and then carry out the initial support corresponding to the upper step; the excavation advance of the upper step rock and soil per cycle is set to 0.5~1m;

[0014] S42, excavate the middle step rock and soil of the left tunnel and the right tunnel simultaneously, and then carry out the initial support corresponding to the middle step; the excavation advance of the middle step rock and soil is 1m per cycle, and the longitudinal distance between the excavation face of the upper step rock and soil and the excavation face of the middle step rock and soil is 5m;

[0015] S43, excavate the lower step rock and soil of the left tunnel and the right tunnel simultaneously, and then carry out the initial support corresponding to the lower step; the advance of each cycle of the lower step rock and soil is 1m, and the longitudinal distance between the excavation face of the middle step rock and soil and the excavation face of the lower step rock and soil is 3~5m;

[0016] S44, remove the temporary support of the middle guide tunnel located in the left tunnel and the temporary support located in the right tunnel;

[0017] S45, excavating the invert area and constructing the invert lining; wherein the longitudinal distance between the invert excavation face and the excavation face of the lower step rock mass is 6-9m;

[0018] S46, pouring of secondary lining in the arch wall area;

[0019] S47, loop steps S41 to S46 until the construction reaches the dark tunnel section.

[0020] Preferably, the guard arch includes a first connecting section, a first arch section, a second connecting section, a second arch section and a third connecting section which are connected in sequence along the transverse direction of the tunnel, wherein the first connecting section is connected to the first pre-reinforced pile assembly, the shape of the first arch section matches the shape of the left hole of the tunnel and is located at the top of the left hole of the tunnel, the second connecting section is overlapped on the top of the middle partition wall, the shape of the second arch section matches the shape of the right hole of the tunnel and is located at the top of the right hole of the tunnel, and the third connecting section is connected to the second pre-reinforced pile assembly.

[0021] Preferably, the longitudinal section design dimensions of the arch guard are obtained through the following design steps:

[0022] S31, treating the first pre-reinforced pile assembly, the second pre-reinforced pile assembly and the guard arch as equivalent to a rigid structure;

[0023] S32, obtaining a first potential sliding surface of a first slope corresponding to the first pre-reinforced pile assembly and a second potential sliding surface of a second slope corresponding to the second pre-reinforced pile assembly, and calculating a residual sliding force P1 of the first slope according to the first potential sliding surface, and calculating a residual sliding force P2 of the second slope according to the second potential sliding surface;

[0024] S33, calculating the equivalent horizontal load f1 per linear meter of the pile body of the first pre-reinforced pile assembly above the first potential sliding surface subjected to the residual sliding force P1, and the equivalent horizontal load f2 per linear meter of the pile body of the second pre-reinforced pile assembly above the second potential sliding surface subjected to the residual sliding force P2;

[0025] S34, based on collapse arch theory using formula q h =Q / L to obtain the vertical surrounding rock pressure q per meter of the arch h ; Wherein, Q is the deadweight of the soil covering the arch per linear meter, and L is the current transverse design dimension of the horizontal projection of the arch;

[0026] S35, obtain the vertical surrounding rock pressure q per meter at the top of the middle partition wall z ;

[0027] S36, obtain the horizontal surrounding rock pressure q per meter at the top of the middle partition wall e ;

[0028] S37, based on the equivalent horizontal load per linear meter f1, equivalent horizontal load per linear meter f2, vertical surrounding rock pressure per linear meter of the arch q h , vertical surrounding rock pressure per linear meter q z , horizontal surrounding rock pressure per meter at the top qe , using the finite element method to calculate the internal force of the rigid structure; wherein the internal force includes an axial force N and a bending moment M;

[0029] S38, perform structural safety verification according to the axial force N, bending moment M, the current design dimension b of the guard arch along the longitudinal direction of the tunnel, and the current design thickness h of the guard arch, and determine whether the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch meet the structural safety requirements; if so, use the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch as the longitudinal section design dimensions of the guard arch.

[0030] Preferably, the step S38 performs structural safety calculation according to the axial force N, the bending moment M, the current design size b of the guard arch along the longitudinal direction of the tunnel, and the current design thickness h of the guard arch, and determines whether the current design size b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch meet the structural safety requirements. Specifically, the steps include:

[0031] Use the load-bearing capacity calculation formula KNe≤R w bx(h o -x / 2)+R g A g '(h o -a') to check the bearing capacity of the rigid structure and determine whether the bearing capacity of the rigid structure meets the design requirements; where the safety factor K=2.0, e=M / N, e is the distance from the center of gravity of the steel bar to the point of action of the axial force, R w is the ultimate compressive strength of concrete, x is the height of the concrete compression zone, h o is the effective height of the section, R g is the standard value of tensile or compressive strength of steel bars, A g ' is the cross-sectional area of ​​the steel bar in the compression zone, a' is the distance from the center of gravity of the steel bar to the nearest edge of the cross section;

[0032] When the bearing capacity of the rigid structure meets the design requirements, it is determined that the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch meet the structural safety requirements.

[0033] Preferably, the method further comprises the steps of:

[0034] When the bearing capacity of the rigid structure does not meet the design requirements, it is determined that the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch do not meet the structural safety requirements, and the current design dimension b of the guard arch along the longitudinal direction of the tunnel or the current design thickness h of the guard arch are readjusted until the bearing capacity of the rigid structure meets the design requirements.

[0035] Preferably, the step S35 specifically includes the steps of:

[0036] Using the formula qz =2W / L z Get the vertical surrounding rock pressure per meter at the top of the middle partition wall q z ; Where W is the weight of the soil covering the triangular area between the arch and the middle partition wall, L z It is the horizontal projection dimension from the top of the first arched segment to the top of the second arched segment.

[0037] Preferably, the step S36 specifically includes the steps of:

[0038] Using the formula q e =λq h Get the horizontal surrounding rock pressure q per meter at the top of the middle partition wall e ; Where λ is the lateral static earth pressure coefficient.

[0039] Preferably, the first pre-reinforced pile assembly extends downward to a depth below the tunnel arch bottom of 0.3h. s1 , where h s1 is the height from the top of the first pre-reinforced pile assembly to the bottom of the tunnel arch; the depth of the second pre-reinforced pile assembly extending downward to below the bottom of the tunnel arch is 0.3h s2 , where h s2 It is the height from the top of the second pre-reinforced pile assembly to the bottom of the tunnel arch.

[0040] Preferably, a plurality of first steel pipes arranged at intervals in the circumferential direction of the first arch segment are inserted into the first arch segment, and a plurality of second steel pipes arranged at intervals in the circumferential direction of the second arch segment are inserted into the second arch segment, and both the first steel pipes and the second steel pipes extend in the extension direction of the tunnel.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] The invention provides a construction method for an entrance structure of a large-span multi-arch tunnel in a pass section, which comprises the following steps: constructing a first pre-reinforced pile assembly and a second pre-reinforced pile assembly, excavating a temporary slope to construct a middle guide tunnel, and then excavating the middle guide tunnel. After the middle guide tunnel is penetrated, a middle partition wall is constructed in the middle guide tunnel, soil and stone are backfilled to the bottom height of the protective arch, protective arches located above the left tunnel and the right tunnel are constructed, an open tunnel section and an end wall type tunnel portal are constructed, and soil is backfilled on the top of the protective arch to a designed height, and then the left tunnel and the right tunnel are synchronously constructed to a dark tunnel section.

[0043] This application can effectively resist the vertical and horizontal surrounding rock pressure by setting the first pre-reinforced pile assembly and the second pre-reinforced pile assembly on both sides of the tunnel, and setting the arch guard at the top of the tunnel, so as to achieve synchronous construction of the left and right main tunnels of the arch tunnel, greatly reduce the construction process of the arch tunnel, have high safety, improve the construction speed and convenience of the arch tunnel, and ensure the safety of tunnel construction and structural safety during operation; at the same time, the structure of this application can greatly reduce the excavation amount of the side slope, reflecting the concept of green and environmental protection of tunnel excavation. At the same time, the slope is also effectively reinforced to prevent the slope from sliding during the excavation process. This application also provides a design method for the arch guard, and the arch guard determined thereby can meet the structural requirements and improve the convenience of construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0045] Figure 1 It is a schematic diagram of a construction method in one embodiment of the present invention;

[0046] Figure 2 It is a flowchart of the specific steps of synchronously constructing the left tunnel and the right tunnel to the dark tunnel section in step S4 in one embodiment of the present invention;

[0047] Figure 3 It is a schematic elevation view of the overall structure in one embodiment of the present invention;

[0048] Figure 4 It is a schematic structural diagram of a protective arch in one embodiment of the present invention;

[0049] Figure 5 A schematic longitudinal section diagram of the overall structure of an embodiment of the present invention;

[0050] Figure 6 This is a schematic diagram of the main tunnel construction in one embodiment of the present invention;

[0051] Figure 7 The figure is a force diagram of the design process of the cross section of the arch in one embodiment of the present invention.

[0052] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments.

[0053] Description of Figure Numbers:

[0054] 110. First pre-reinforced pile assembly; 120. Second pre-reinforced pile assembly; 20. Guard arch; 210. First connecting section; 220. First arch section; 230. Second connecting section; 240. Second arch section; 250. Third connecting section; 260. First steel pipe; 270. Second steel pipe; 310. Left tunnel; 320. Right tunnel; 330. Upper step; 340. Middle step; 350. Lower step; 360. Inverted arch lining; 370. Secondary lining of arch wall area; 380. Middle guide tunnel; 390. Middle partition wall; 40. Open tunnel section; 50. End wall portal; 60. Concealed tunnel section; 710. First potential sliding surface; 720. Second potential sliding surface. DETAILED DESCRIPTION

[0055] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0056] The following will be combined with the drawings in 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.

[0057] In the present invention, the descriptions of "right part", "middle part", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "right part" and "middle part" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0058] Please refer to the attached Figures 1 to 7 In one embodiment of the present invention, a construction method for a large-span multi-arch tunnel entrance structure at a pass section includes the following steps:

[0059] S1, constructing a first pre-reinforced pile assembly 110 located outside the left tunnel 310 and a second pre-reinforced pile assembly 120 located outside the right tunnel 320; wherein the bottoms of the first pre-reinforced pile assembly 110 and the second pre-reinforced pile assembly 120 both extend downward below the tunnel arch bottom, and the tops of the first pre-reinforced pile assembly 110 and the second pre-reinforced pile assembly 120 both extend upward to the ground surface;

[0060] S2, excavating a temporary slope to construct a middle guide tunnel 380, and then excavating the middle guide tunnel 380 extending along the extension direction of the tunnel. After the middle guide tunnel 380 is connected, constructing a middle partition wall 390 extending along the extension direction of the tunnel in the middle guide tunnel 380;

[0061] S3, backfilling soil and rocks to the bottom height of the guard arch 20, and constructing the guard arch 20 located above the left tunnel 310 and the right tunnel 320; wherein the guard arch 20 is connected between the first pre-reinforced pile assembly 110 and the second pre-reinforced pile assembly 120;

[0062] S4, constructing the open tunnel section 40 and the end wall type tunnel portal 50, and then backfilling the top of the arch 20 to the designed height, and then synchronously constructing the left tunnel 310 and the right tunnel 320 to the dark tunnel section 60.

[0063] It should be noted that a pass in geography refers to a narrow, flat and relatively low place between two mountains, that is, a saddle-shaped col on a tall mountain ridge. The geology of the pass area is usually poor, and the slopes on both sides of the pass are prone to landslides during tunnel construction. The present application constructs a first pre-reinforced pile assembly 110 and a second pre-reinforced pile assembly 120 in the left tunnel 310 and outside the left tunnel 310, respectively. The bottom of the first pre-reinforced pile assembly 110 and the second pre-reinforced pile assembly 120 extend below the tunnel arch bottom, and the top extends to the ground surface, forming a continuous reinforcement structure from the ground surface to the bottom of the tunnel, which can reinforce and protect the steep mountains on both sides of the pass section, resist the bias of the mountains on both sides, make the tunnel structure evenly balanced in the horizontal direction, enhance the stability of the strata around the tunnel, and prevent strata collapse or landslides during subsequent tunnel excavation; excavate a temporary slope to create a construction space for the middle guide tunnel 380, and then excavate the middle guide tunnel 380 extending in the extension direction of the tunnel. After the middle guide tunnel 380 is connected, a middle partition wall 390 extending in the extension direction of the tunnel is constructed inside it. The middle guide tunnel 380 and the middle partition wall 390 provide a temporary support structure for subsequent tunnel excavation, thereby improving the stability and safety of tunnel construction.

[0064] Backfill the soil and rocks to the bottom height of the arch 20, and then construct the arch 20 located above the left tunnel 310 and the right tunnel 320. The arch 20 is connected between the first pre-reinforced pile assembly 110 and the second pre-reinforced pile assembly 120 to form a protective cover structure across the tunnel, which can effectively resist the upper unbalanced soil pressure and make the tunnel structure evenly balanced in the vertical direction. At the same time, the arch 20, as a lateral support for the first pre-reinforced pile assembly 110 and the second pre-reinforced pile assembly 120, can bear part of the horizontal load and form a joint force system.

[0065] The left tunnel 310 and the right tunnel 320 are constructed synchronously to the blind tunnel section 60 .

[0066] In the scheme of the present application, by respectively arranging the first pre-reinforced pile assembly 110 and the second pre-reinforced pile assembly 120 on both sides of the tunnel, and arranging the protective arch 20 on the top of the tunnel, it is possible to effectively resist the vertical and horizontal surrounding rock pressures, and enable the left and right main tunnels of the arch tunnel to be constructed synchronously, thereby greatly reducing the construction procedures of the arch tunnel, improving the construction speed and convenience of the arch tunnel, and ensuring the safety of tunnel construction; at the same time, the structure of the present application can greatly reduce the excavation amount of the side slope, reflecting the concept of green and environmental protection of tunnel excavation.

[0067] As a preferred embodiment, the synchronous construction of the left tunnel 310 and the right tunnel 320 to the dark tunnel section 60 in step S4 specifically includes the following steps:

[0068] S41, excavating the upper step 330 rock and soil of the left tunnel 310 and the right tunnel 320 simultaneously, and then applying the initial support corresponding to the upper step 330; wherein, the excavation advance of the upper step 330 rock and soil per cycle is set to 0.5-1m;

[0069] S42, excavating the rock mass of the middle step 340 of the left tunnel 310 and the right tunnel 320 simultaneously, and then carrying out the initial support corresponding to the middle step 340; wherein, the excavation advance of the rock mass of the middle step 340 is 1m per cycle, and the longitudinal distance between the excavation face of the rock mass of the upper step 330 and the excavation face of the rock mass of the middle step 340 is 5m;

[0070] S43, excavating the rock mass of the lower step 350 of the left tunnel 310 and the right tunnel 320 simultaneously, and then applying the initial support corresponding to the lower step 350; wherein, the advance of each cycle of the rock mass of the lower step 350 is 1m, and the longitudinal distance between the excavation face of the rock mass of the middle step 340 and the excavation face of the rock mass of the lower step 350 is 3-5m;

[0071] S44, removing the temporary support of the middle guide tunnel 380 located in the left tunnel 310 of the tunnel and the temporary support located in the right tunnel 320 of the tunnel;

[0072] S45, excavating the invert area and constructing the invert lining 360; wherein the longitudinal distance between the invert excavation face and the excavation face of the rock mass of the lower step 350 is 6-9m;

[0073] S46, pouring of secondary lining in arch wall area 370;

[0074] S47, loop steps S41 to S46 until the construction reaches the dark tunnel section 60.

[0075] In this embodiment, the tunnel excavation face is divided into three steps, namely, the upper part, the middle part and the lower part. Each step is excavated and the initial support construction is carried out respectively, which is conducive to controlling the stability of the excavation face and reducing the stratum disturbance. The left tunnel 310 and the right tunnel 320 of the tunnel are excavated and supported at the same time on each step, which improves the construction efficiency and shortens the construction period. In order to maintain the stability of the tunnel, the excavation faces between each step are set with a reasonable longitudinal spacing to ensure the safety during the construction process. After the excavation and support of the middle step 340 are completed, the temporary support in the middle guide tunnel 380 is removed to provide space for the excavation and secondary lining construction of the inverted arch area. After the excavation and initial support of all steps are completed, the secondary lining 370 of the arch wall area is constructed to improve the bearing capacity and durability of the tunnel. The above steps are cyclically carried out until the dark tunnel section 60 is constructed to complete the construction of the entire tunnel entrance structure.

[0076] This embodiment can realize the synchronous construction of the left tunnel 310 and the right tunnel 320, which significantly improves the construction efficiency and shortens the construction period.

[0077] As a preferred embodiment, the guard arch 20 includes a first connecting section 210, a first arch section 220, a second connecting section 230, a second arch section 240 and a third connecting section 250 which are connected in sequence along the transverse direction of the tunnel, wherein the first connecting section 210 is connected to the first pre-reinforced pile assembly 110, the shape of the first arch section 220 matches the shape of the left tunnel hole 310, and is located at the top of the left tunnel hole 310, the second connecting section 230 is overlapped on the top of the middle partition wall 390, the shape of the second arch section 240 matches the shape of the right tunnel hole 320, and is located at the top of the right tunnel hole 320, and the third connecting section 250 is connected to the second pre-reinforced pile assembly 120.

[0078] In this embodiment, the first connecting section 210 is connected to the first pre-reinforced pile assembly 110, and the third connecting section 250 is connected to the second pre-reinforced pile assembly 120, thereby forming a complete force system, thereby improving the overall structural strength. The surrounding rock or rock load can be effectively transferred to the stratum through the protective arch 20, the first pre-reinforced pile assembly 110, and the second pre-reinforced pile assembly 120, thereby optimizing the load transfer path and improving the bearing capacity of the structure.

[0079] Furthermore, the first pre-reinforcement pile assembly 110 includes a plurality of first pre-reinforcement piles arranged at intervals along the extension direction of the tunnel. Preferably, the interval between two adjacent first pre-reinforcement piles is 5 m, and the first pre-reinforcement piles extend 5 meters below the arch bottom of the left line of the tunnel. The tops of the first pre-reinforcement piles are flush with the ground surface, which effectively fixes the soil or rock around the tunnel, effectively enhances the stability of the tunnel structure, and prevents soil or rock slippage and collapse caused by tunnel excavation.

[0080] Furthermore, the second pre-reinforcement pile assembly 120 includes a plurality of second pre-reinforcement piles arranged at intervals along the extension direction of the tunnel. The second pre-reinforcement piles extend 5 meters below the arch bottom of the right line of the tunnel, effectively fixing the soil or rock around the tunnel, effectively enhancing the stability of the tunnel structure, and preventing soil or rock slippage and collapse caused by tunnel excavation.

[0081] As a preferred embodiment, the longitudinal cross-sectional design dimensions of the protective arch 20 are obtained through the following design steps:

[0082] S31, the first pre-reinforced pile assembly 110, the second pre-reinforced pile assembly 120 and the guard arch 20 are equivalent to a rigid structure; it should be noted that the structural calculation of the guard arch 20 generally regards the soil layer as an elastic foundation and complies with the Winkler assumption, and the pre-reinforced pile assembly and the soil below the sliding surface are simulated by a spring connecting rod that is only compressed. The connection between the guard arch 20 and the first pre-reinforced pile assembly 110 and the second pre-reinforced pile assembly 120 is simplified to a consolidation point, and the connection between the guard arch 20 and the middle partition wall 390 is simplified to a consolidation point.

[0083] S32, obtain the first potential sliding surface 710 of the first slope corresponding to the first pre-reinforced pile assembly 110, and the second potential sliding surface 720 of the second slope corresponding to the second pre-reinforced pile assembly 120, and calculate the residual sliding force P1 of the first slope according to the first potential sliding surface 710, and calculate the residual sliding force P2 of the second slope according to the second potential sliding surface 720; Specifically, the slope stability calculation can usually adopt the limit equilibrium method, and according to different assumptions about the inter-strip force, the Bishop method, the simple strip method, the transfer coefficient method and other landslide calculation theories can be adopted. The transfer coefficient method is used to analyze the landslide stability and calculate the residual sliding force P=TF (T is the slope sliding force, and F is the slope anti-sliding force). The specific slope calculation can be based on the slope stability calculation method of different sliding surface forms in Appendix A of the "Technical Code for Building Slope Engineering (GB 50330-2013)". Therefore, the residual sliding force P1 and the residual sliding force P2 can be obtained by the existing technology, which will not be repeated here.

[0084] S33, calculating the equivalent horizontal load f1 per linear meter of the pile body of the first pre-reinforced pile assembly 110 above the first potential sliding surface 710 subjected to the residual sliding force P1, and the equivalent horizontal load f2 per linear meter of the pile body of the second pre-reinforced pile assembly 120 above the second potential sliding surface 720 subjected to the residual sliding force P2;

[0085] like Figure 7As shown in the figure, the cantilever pile method is used according to the method of dealing with the soil in front of the pile above the potential sliding surface. During the calculation, the residual sliding force on the pile body above the sliding surface is applied to the pile as the design load. Its calculation mode is equivalent to the cantilever structure anchored at the bottom. In the calculation of pile structure, the soil layer is generally regarded as an elastic foundation and meets the Winkler assumption. The pile structure is simplified as an elastic foundation beam. The calculation principle of the Winkler elastic foundation beam is used. The concentrated force spring model of the pile and the rock and soil is adopted. The anti-sliding pile below the sliding surface and the soil are directly connected with a compression-only spring connecting rod to simulate the connection between the existing structure and the soil.

[0086] Preferably, the residual sliding force P1 and the residual sliding force P2 are equivalent to a triangular distribution, and the equivalent horizontal load f1 per linear meter is calculated using the formula f1=2P1 / L1, unit: kN / m, L1 is the upper pile length of the first potential sliding surface 710, unit: m, and the equivalent horizontal load f2 per linear meter is calculated using the formula f2=2P2 / L2, unit: kN / m, L2 is the upper pile length of the second potential sliding surface 720, unit: m.

[0087] S34, based on collapse arch theory using formula q h =Q / L to obtain the vertical surrounding rock pressure q per meter of arch 20 h , unit: KN / m; where Q is the deadweight of the soil overlying the guard arch 20, unit: kN, and L is the current transverse design dimension of the horizontal projection of the guard arch 20, unit: m;

[0088] S35, obtain the vertical surrounding rock pressure q per linear meter at the top of the middle partition wall 390 z , unit: KN / m;

[0089] Furthermore, the step S35 specifically includes the steps of:

[0090] Using the formula q z =2W / L z Get the vertical surrounding rock pressure q per meter at the top of the middle partition wall 390 z , unit: KN / m; where W is the deadweight of the soil covering the triangular area between the arch 20 and the middle partition wall 390, L z It is the horizontal projection dimension from the top of the first arched segment 220 to the top of the second arched segment 240 .

[0091] It should be noted that the triangular area is the area enclosed by the top of the middle partition wall 390, the top of the first arch section 220, and the top of the second arch section 240, according to Appendix G of the "Highway Tunnel Design Code, Volume 1, Civil Engineering" (JTG 3370.1-2018) (Calculation Method of Surrounding Rock Pressure of Continuous Arch Tunnels) The deadweight of the covering soil per linear meter.

[0092] S36, obtain the horizontal surrounding rock pressure q per meter at the top of the middle partition wall 390 e , unit: KN / m;

[0093] Furthermore, the step S36 specifically includes the steps of:

[0094] Using the formula q e =λq h Get the horizontal surrounding rock pressure q per meter at the top of the middle partition wall 390 e , unit KN / m; where λ is the lateral static earth pressure coefficient, and λ is the lateral static earth pressure coefficient, which can be determined in advance by the properties of the surrounding rock grade or by the compression instrument method or in-situ test method, and will not be elaborated here.

[0095] S37, based on the equivalent horizontal load per linear meter f1, equivalent horizontal load per linear meter f2, vertical surrounding rock pressure per linear meter q of arch 20 h , vertical surrounding rock pressure per linear meter q z , horizontal surrounding rock pressure per meter at the top q e The internal force of the rigid structure is calculated by the finite element method; wherein the internal force includes axial force N and bending moment M; wherein the axial force N is positive under compression and is perpendicular to the cross-section direction of the arch guard 20, and the unit is MN. For the bending moment M, the lower part of the cross-section of the arch guard 20 is under tension and the upper part is under compression, and it rotates counterclockwise along the axis of the cross-section of the arch guard 20, and the unit is MN·m.

[0096] According to the load combination (equivalent horizontal load f1 per linear meter, equivalent horizontal load f2 per linear meter, vertical surrounding rock pressure q per linear meter of arch 20 h , vertical surrounding rock pressure per linear meter q z , horizontal surrounding rock pressure per meter at the top q e ), the internal forces (axial force N and bending moment M) of the rigid structure are calculated using the finite element method.

[0097] S38, perform structural safety verification according to the axial force N, bending moment M, the current design dimension b of the guard arch along the longitudinal direction of the tunnel, and the current design thickness h of the guard arch, and determine whether the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch meet the structural safety requirements; if so, use the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch as the longitudinal section design dimension of the guard arch 20.

[0098] Furthermore, the step S38 performs structural safety calculation according to the axial force N, the bending moment M, the current design dimension b of the guard arch along the longitudinal direction of the tunnel, and the current design thickness h of the guard arch, and determines whether the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch meet the structural safety requirements. Specifically, the steps include:

[0099] Use the load-bearing capacity calculation formula KNe≤R w bx(h o -x / 2)+R g A g '(h o -a') to check the bearing capacity of the rigid structure and determine whether the bearing capacity of the rigid structure meets the design requirements; where the safety factor K=2.0, e=M / N, e is the distance from the center of gravity of the steel bar to the point of action of the axial force, unit: m, R w is the ultimate compressive strength of concrete, unit: MPa, x is the height of the concrete compression zone, unit: m, h o is the effective height of the cross section (i.e. the thickness of the arch 20), unit: m, R g It is the standard value of tensile or compressive strength of steel bar, unit: MPa, A g ' is the cross-sectional area of ​​the steel bars in the compression zone, unit: m 2 , a' is the distance from the center of gravity of the steel bar to the nearest edge of the section, unit: m.

[0100] When the bearing capacity of the rigid structure meets the design requirements, it is determined that the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch meet the structural safety requirements.

[0101] Furthermore, the method further comprises the steps of:

[0102] When the bearing capacity of the rigid structure does not meet the design requirements, it is determined that the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch do not meet the structural safety requirements, and the current design dimension b of the guard arch along the longitudinal direction of the tunnel or the current design thickness h of the guard arch are readjusted until the bearing capacity of the rigid structure meets the design requirements.

[0103] Use the load-bearing capacity calculation formula KNe≤R w bx(h o -x / 2)+R g A g '(h o -a') for verification. This formula takes into account the axial force N, bending moment M, cross-sectional dimensions, material strength (concrete bending compressive ultimate strength R w , Standard value of tensile or compressive strength of steel bars R g ) and reinforcement configuration (cross-sectional area of ​​reinforcement in compression zone A g', the position of the center of gravity of the steel bar a', etc.). The safety factor K is introduced into the formula to ensure that the structure has a certain safety reserve when bearing the design load. According to the verification results, judge whether the bearing capacity of the rigid structure meets the design requirements. If the verification results meet the requirements of the formula, that is, KNe is less than or equal to the value on the right side of the equation, then the bearing capacity of the rigid structure meets the design requirements. If the bearing capacity of the rigid structure does not meet the design requirements, it is necessary to readjust the current design dimension b of the guard arch along the longitudinal direction of the tunnel or the current design thickness h of the guard arch, and re-calculate until the design requirements are met.

[0104] By introducing the bearing capacity calculation formula and safety factor, it can be ensured that the rigid structure has a certain safety reserve when bearing the design load, thereby improving the safety of the design. By repeatedly checking and adjusting the design dimensions, it is possible to find a longitudinal section dimension that meets the design requirements and is relatively economical, thereby optimizing the structural design. Accurate calculation and adjustment during the design stage can reduce uncertainty and risks in the construction process and improve construction efficiency and quality.

[0105] As a preferred example, the first pre-reinforced pile assembly 110 extends downward to a depth of 0.3h below the tunnel arch bottom. s1 , where h s1 is the height from the top of the first pre-reinforced pile assembly 110 to the bottom of the tunnel arch, in meters; the depth of the second pre-reinforced pile assembly 120 extending downward to below the bottom of the tunnel arch is 0.3h s2 , where h s2 is the height from the top of the second pre-reinforced pile assembly 120 to the tunnel arch bottom, unit: m.

[0106] Specifically, by extending the first pre-reinforced pile assembly 110 and the second pre-reinforced pile assembly 120 downward to a certain depth below the tunnel arch bottom (0.3h s1 and 0.3h s2 ), can effectively enhance the overall stability of the tunnel structure and effectively improve the bearing capacity of the piles, thereby ensuring the safety and stability of the tunnel during construction and operation.

[0107] Furthermore, a plurality of first steel pipes 260 arranged at intervals along the annular direction of the first arch section 220 are inserted into the first arch section 220, and a plurality of second steel pipes 270 arranged at intervals along the annular direction of the second arch section 240 are inserted into the second arch section 240, and both the first steel pipes 260 and the second steel pipes 270 extend along the extension direction of the tunnel. In the actual construction process, the first steel pipes 260 and the second steel pipes 270 are inserted as an advance long pipe shed for advance support to improve the safety of tunnel excavation.

[0108] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the protection scope of the present invention.

Claims

1. A construction method for a large-span multi-arch tunnel entrance structure at a pass section, characterized in that: The following steps are involved: S1, constructing a first pre-reinforced pile assembly located outside the left tunnel and a second pre-reinforced pile assembly located outside the right tunnel; wherein the bottoms of the first pre-reinforced pile assembly and the second pre-reinforced pile assembly both extend downward below the tunnel arch bottom, and the tops of the first pre-reinforced pile assembly and the second pre-reinforced pile assembly both extend upward to the ground surface; S2, excavating a temporary slope to construct a middle guide tunnel, and then excavating a middle guide tunnel extending in the extension direction of the tunnel, and after the middle guide tunnel is penetrated, constructing a middle partition wall extending in the extension direction of the tunnel in the middle guide tunnel; S3, backfilling soil and rocks to the bottom height of the protective arch, and constructing the protective arch located above the left tunnel and the right tunnel; wherein the protective arch is connected between the first pre-reinforced pile assembly and the second pre-reinforced pile assembly; S4, constructing an open tunnel section and an end wall type tunnel portal, and then backfilling the top of the arch to the designed height, and then synchronously constructing the left tunnel and the right tunnel to the dark tunnel section.

2. The construction method of the entrance structure of a large-span multi-arch tunnel in a pass section according to claim 1 is characterized in that: The step S4 of synchronously constructing the left tunnel and the right tunnel to the dark tunnel section specifically includes the following steps: S41: excavate the upper step rock and soil of the left tunnel and the right tunnel simultaneously, and then carry out the initial support corresponding to the upper step; the excavation advance of the upper step rock and soil per cycle is set to 0.5~1m; S42, excavate the middle step rock and soil of the left tunnel and the right tunnel simultaneously, and then carry out the initial support corresponding to the middle step; the excavation advance of the middle step rock and soil is 1m per cycle, and the longitudinal distance between the excavation face of the upper step rock and soil and the excavation face of the middle step rock and soil is 5m; S43, excavate the lower step rock and soil of the left tunnel and the right tunnel simultaneously, and then carry out the initial support corresponding to the lower step; the advance of each cycle of the lower step rock and soil is 1m, and the longitudinal distance between the excavation face of the middle step rock and soil and the excavation face of the lower step rock and soil is 3~5m; S44, remove the temporary support of the middle guide tunnel located in the left tunnel and the temporary support located in the right tunnel; S45, excavating the invert area and constructing the invert lining; wherein the longitudinal distance between the invert excavation face and the excavation face of the lower step rock mass is 6-9m; S46, pouring of secondary lining in the arch wall area; S47, loop steps S41 to S46 until the construction reaches the dark tunnel section.

3. The construction method of the entrance structure of a large-span multi-arch tunnel in a pass section according to claim 1 is characterized in that: The guard arch includes a first connecting section, a first arch section, a second connecting section, a second arch section and a third connecting section which are connected in sequence along the transverse direction of the tunnel, wherein the first connecting section is connected to the first pre-reinforced pile assembly, the shape of the first arch section matches the shape of the left hole of the tunnel and is located at the top of the left hole of the tunnel, the second connecting section is overlapped on the top of the middle partition wall, the shape of the second arch section matches the shape of the right hole of the tunnel and is located at the top of the right hole of the tunnel, and the third connecting section is connected to the second pre-reinforced pile assembly.

4. The construction method of the entrance structure of a large-span multi-arch tunnel in a pass section according to claim 3 is characterized in that: The longitudinal section design dimensions of the arch guard are obtained through the following design steps: S31, treating the first pre-reinforced pile assembly, the second pre-reinforced pile assembly and the guard arch as equivalent to a rigid structure; S32, obtaining a first potential sliding surface of a first slope corresponding to the first pre-reinforced pile assembly and a second potential sliding surface of a second slope corresponding to the second pre-reinforced pile assembly, and calculating a residual sliding force P1 of the first slope according to the first potential sliding surface, and calculating a residual sliding force P2 of the second slope according to the second potential sliding surface; S33, calculating the equivalent horizontal load f1 per linear meter of the pile body of the first pre-reinforced pile assembly above the first potential sliding surface subjected to the residual sliding force P1, and the equivalent horizontal load f2 per linear meter of the pile body of the second pre-reinforced pile assembly above the second potential sliding surface subjected to the residual sliding force P2; S34, based on collapse arch theory using formula q h =Q / L to obtain the vertical surrounding rock pressure q per meter of the arch h ; Wherein, Q is the deadweight of the soil covering the arch per linear meter, and L is the current transverse design dimension of the horizontal projection of the arch; S35, obtain the vertical surrounding rock pressure q per meter at the top of the middle partition wall z ; S36, obtain the horizontal surrounding rock pressure q per meter at the top of the middle partition wall e ; S37, based on the equivalent horizontal load per linear meter f1, equivalent horizontal load per linear meter f2, vertical surrounding rock pressure per linear meter of the arch q h , vertical surrounding rock pressure per linear meter q z , horizontal surrounding rock pressure per meter at the top q e , using the finite element method to calculate the internal force of the rigid structure; wherein the internal force includes an axial force N and a bending moment M; S38, perform structural safety verification according to the axial force N, bending moment M, the current design dimension b of the guard arch along the longitudinal direction of the tunnel, and the current design thickness h of the guard arch, and determine whether the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch meet the structural safety requirements; if so, use the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch as the longitudinal section design dimensions of the guard arch.

5. The construction method of the entrance structure of a large-span multi-arch tunnel in a pass section according to claim 4 is characterized in that: The step S38 performs structural safety calculation according to the axial force N, the bending moment M, the current design size b of the guard arch along the longitudinal direction of the tunnel, and the current design thickness h of the guard arch, and determines whether the current design size b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch meet the structural safety requirements. Specifically, the steps include: Use the load-bearing capacity calculation formula KNe≤R w bx(h o -x / 2)+R g A g '(h o -a') to check the bearing capacity of the rigid structure and determine whether the bearing capacity of the rigid structure meets the design requirements; where the safety factor K=2.0, e=M / N, e is the distance from the center of gravity of the steel bar to the point of action of the axial force, R w is the ultimate compressive strength of concrete, x is the height of the concrete compression zone, h o is the effective height of the section, R g is the standard value of tensile or compressive strength of steel bars, A g ' is the cross-sectional area of ​​the steel bar in the compression zone, a' is the distance from the center of gravity of the steel bar to the nearest edge of the cross section; When the bearing capacity of the rigid structure meets the design requirements, it is determined that the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch meet the structural safety requirements.

6. The construction method of the entrance structure of a large-span multi-arch tunnel in a pass section according to claim 5 is characterized in that: Also includes the steps: When the bearing capacity of the rigid structure does not meet the design requirements, it is determined that the current design dimension b of the guard arch along the longitudinal direction of the tunnel and the current design thickness h of the guard arch do not meet the structural safety requirements, and the current design dimension b of the guard arch along the longitudinal direction of the tunnel or the current design thickness h of the guard arch are readjusted until the bearing capacity of the rigid structure meets the design requirements.

7. The construction method of the entrance structure of a large-span multi-arch tunnel in a pass section according to claim 4 is characterized in that: The step S35 specifically includes the following steps: Using the formula q z =2W / L z Get the vertical surrounding rock pressure per meter at the top of the middle partition wall q z ; Where W is the weight of the soil covering the triangular area between the arch and the middle partition wall, L z It is the horizontal projection dimension from the top of the first arched segment to the top of the second arched segment.

8. The construction method of the entrance structure of a large-span multi-arch tunnel in a pass section according to claim 4 is characterized in that: The step S36 specifically includes the following steps: Using the formula q e =λq h Get the horizontal surrounding rock pressure q per meter at the top of the middle partition wall e ; Where λ is the lateral static earth pressure coefficient.

9. The construction method of the entrance structure of a large-span multi-arch tunnel in a pass section according to claim 4, characterized in that: The first pre-reinforced pile assembly extends downward to a depth of 0.3h below the tunnel arch bottom. s1 , where h s1 is the height from the top of the first pre-reinforced pile assembly to the bottom of the tunnel arch; the depth of the second pre-reinforced pile assembly extending downward to below the bottom of the tunnel arch is 0.3h s2 , where h s2 It is the height from the top of the second pre-reinforced pile assembly to the bottom of the tunnel arch.

10. The construction method of the entrance structure of a large-span multi-arch tunnel in a pass section according to claim 3, characterized in that: A plurality of first steel pipes arranged at intervals in the circumferential direction of the first arch segment are inserted into the first arch segment, and a plurality of second steel pipes arranged at intervals in the circumferential direction of the second arch segment are inserted into the second arch segment. Both the first steel pipes and the second steel pipes extend in the extension direction of the tunnel.

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