Tunnel Two-way Exit Construction Method under the Condition of Steep Accumulated Slope

Abstract

The invention discloses a construction method for the two-way exit of a tunnel under the condition of a steep accumulation slope. A single-side wall section and a double-side wall section are planned on one side of the tunnel body close to the exit. The single-side wall section and the double-side wall section are divided into a plurality of pilot tunnel blocks by setting a support wall and a temporary inverted arch. The pilot tunnel blocks are gradually driven through in sequence by a two-way driving method, and bolts and mesh are installed on the inner side wall of the tunnel body corresponding to the pilot tunnel blocks, and shotcrete is used to seal and reinforce the inner side wall of the tunnel body. This application is suitable for the exit construction of large-sized tunnel openings under the condition of a steep accumulation slope. The single-side wall section is changed to the double-side wall section, and after driving through the upper left pilot tunnel block to exit, the tunnel is driven into from the outside of the double-side wall section to complete the penetration. At the same time, this application also fully considers the force system conversion involved in the conversion of the pilot tunnel in the single-side wall section to the double-side wall section, minimizes the workload of the double-side wall as much as possible, and improves the construction efficiency.

Description

Technical Field

[0001] The present invention relates to the field of tunnel construction, and particularly to a construction method for double-way tunnel exit under the condition of a steep accumulation slope. Background Art

[0002] Tunnel exit is the most complex working condition and the highest safety risk link in tunnel construction. Excessive cyclic footage or improper control of explosive charge is extremely likely to cause collapse. For the conventional tunnel exit construction method, before the tunnel exit, it is necessary to complete the construction of the catchment ditch at the top of the exit end, the excavation and protection of the side slope and the inverted arch, the drilling and grouting of the pipe shed, and the advanced support, and it needs to be completed at least 1 month in advance before the tunnel exit. This construction method has a large amount of work. Especially for the grade-V surrounding rock with limestone as the main component at the tunnel entrance and the steeply inclined bedding with a dip angle of 43° - 48°, due to the lack of sufficient site for the construction of the catchment ditch, side slope and inverted arch excavation, etc., a large amount of slope cutting is required, and the excavation disturbance destroys the topography and landform, which is easy to cause the sliding and collapse of the surrounding rock and landslides and other disasters. The construction difficulty is large, the safety risk is high, and there are certain irrationalities in terms of progress and economy.

[0003] Especially when the tunnel exit is located on a steep loose accumulation slope and belongs to a shallow-buried and bias-pressure tunnel, the safety risk of tunnel exit construction is high. When the tunnel is short, it can be selected to drive unidirectionally from the end with better entrance conditions to the other end. When the tunnel is long, a transverse tunnel or an inclined shaft can be considered to enter the main tunnel and then drive in the reverse direction to the entrance with poor conditions. However, both of the above methods face the problem of tunnel exit construction. Since the cover depth of the entrance section is often shallow and the surrounding rock is broken, the tunnel exit is likely to cause the overall instability and sliding of the slope. In addition, accidents such as cave-ins inside and outside the tunnel are likely to occur during the tunnel exit construction. And the treatment of cave-ins is difficult, increasing investment and delaying the construction period, which will bring huge losses to the tunnel construction. Summary of the Invention

[0004] In view of the above problems, the present invention aims to provide a construction method for double-way tunnel exit under the condition of a steep accumulation slope.

[0005] To achieve the technical purpose, the solution of the present invention is: a construction method for double-way tunnel exit under the condition of a steep accumulation slope, and the specific steps are as follows:

[0006] S1. Block planning: Plan a single-side wall section and a double-side wall section on the side of the tunnel body close to the exit, and divide the single-side wall section and the double-side wall section into a plurality of pilot tunnel blocks by setting support walls and temporary inverted arches;

[0007] S2. Double-way tunneling: Adopt the double-way tunneling method to gradually drive through the pilot tunnel blocks in sequence, install bolts and mesh on the inner side wall of the tunnel body in the corresponding pilot tunnel blocks, and spray concrete to seal and reinforce the inner side wall of the tunnel body. At the same time, during the tunneling process, quickly support the excavated area in the pilot tunnel blocks;

[0008] S3. Demolition: After all the driving of the conduction blocks is completed and the inner side walls of the corresponding tunnel cavities are all closed and reinforced, the support wall and the temporary invert are demolished.

[0009] Preferably, in step S1, the support wall includes a first support wall, a second support wall, and a third support wall, and the temporary invert includes a first temporary invert, a second temporary invert, a third temporary invert, a fourth temporary invert, a fifth temporary invert, and a sixth temporary invert.

[0010] Among them, the single-side wall section is divided into four pilot tunnel blocks by the first support wall, the first temporary invert, and the second temporary invert. The pilot tunnel blocks in the single-side wall section include an inner upper left area 1, an inner lower left area 3, an inner upper right area 2, and an inner lower right area 9.

[0011] Among them, the double-side wall section is divided into seven pilot tunnel blocks by the second support wall, the third support wall, the third temporary invert, the fourth temporary invert, the fifth temporary invert, and the sixth temporary invert. The pilot tunnel blocks in the double-side wall section include an outer upper left area 1, an outer lower left area 3, an outer middle upper area 6, an outer middle area 7, an outer middle lower area 8, an outer upper right area 4, and an outer lower right area 5.

[0012] Among them, the outer upper left area 1 corresponds to the inner upper left area 1 in terms of both size and position, and the outer lower left area 3 corresponds to the inner lower left area 3 in terms of both size and position.

[0013] Preferably, the more specific construction process in step S2 is as follows:

[0014] S21. Drive from the inner upper left area 1 along the first temporary invert to the junction of the single-side wall section and the double-side wall section, and during the driving process, close and reinforce the inner side wall of the tunnel cavity in the inner upper left area 1.

[0015] S22. Drive forward from the inside to the outside and carry out support. Drive from the outer upper left area 1 in the double-side wall section along the third temporary invert to complete the connection between the inner upper left area 1 and the outer upper left area 1, and during the driving process, close and reinforce the inner side wall of the tunnel cavity in the outer upper left area 1. At the same time, drive from the inner upper right area 2 along the second temporary invert to the edge of the double-side wall section, and during the driving process, close and reinforce the inner side wall of the tunnel cavity in the inner upper right area 2.

[0016] S23. Drive backward from the outside to the inside and quickly carry out support. Drive from the outer lower left area 3 to the junction of the single-side wall section and the double-side wall section to complete the connection between the outer lower left area 3 and the inner lower left area 3, and during the driving process, close and reinforce the inner side wall of the tunnel cavity in the outer lower left area 3.

[0017] Excavate from the outer upper right fourth zone inward to the designated position in the middle of the double side wall section, with the excavation depth greater than the initial excavation distance S1; then excavate from the outer lower right fifth zone inward to the designated position in the middle of the double side wall section, with the excavation depth less than the initial excavation distance S1; finally, excavate from the outer middle upper sixth zone inward to the designated position in the middle of the double side wall section, with the excavation depth less than the initial excavation distance S1;

[0018] S24, continue to excavate in the reverse direction from outside to inside and quickly support, excavate from the outer right upper fourth zone inward to the junction of the single side wall section and the double side wall section; then excavate from the outer right lower fifth zone inward to the junction of the single side wall section and the double side wall section; then excavate from the outer middle upper sixth zone inward to the designated position in the middle, and the excavation depth is greater than the secondary excavation distance S2; finally, excavate from the outer middle seventh zone and the outer middle lower eighth zone inward to the designated position in the middle of the double side wall section, and the excavation depth is greater than the secondary excavation distance S2. At this time, the length of the initial support closed loop at the exit end of the tunnel body reaches the first preset value L1;

[0019] S25, continue to excavate in the reverse direction from outside to inside and quickly support, excavate inward from the outer middle upper sixth zone to the junction of the single side wall section and the double side wall section; continue to excavate inward for at least 5m in the outer middle seventh zone and the outer middle lower eighth zone, at which time the length of the initial support closed loop at the exit end of the tunnel body reaches the second preset value L2, and the upper step of the middle guide tunnel is connected;

[0020] S26, continue to excavate in the reverse direction from outside to inside and quickly support, continue to excavate inward from the outer middle seventh zone and the outer middle lower eighth zone to the junction of the single side wall section and the double side wall section, and complete the initial support ring of the double side wall section at the exit end of the tunnel body;

[0021] S27, forward, excavate from inside to outside and quickly support, excavate from the inner right lower ninth area to the junction of the single side wall section and the double side wall section, complete the initial support and closure of the entire tunnel body into a ring, and the entire tunnel body is completed.

[0022] Preferably, the area of the tunnel is greater than 200m 2 The inner wall of the tunnel body is sealed with φ22 anchor rods, φ8@20*20cm mesh, and sprayed with concrete with a thickness of more than 10cm.

[0023] Preferably, the length of the double side wall section is greater than or equal to 12 m, and the length of the single side wall section is greater than or equal to 15 m;

[0024] The first preset value L1 is greater than or equal to 5 m, and the second preset value L2 is greater than or equal to 11 m.

[0025] Preferably, the initial excavation distance S1 is greater than 5 m and less than 15 m; the secondary excavation distance S1 is greater than 5 m.

[0026] Advantages of the present invention: This application is suitable for the construction of the exit of a large - sized tunnel opening under the conditions of a steep accumulation body slope. It adopts the method of converting from a single - side - wall section to a double - side - wall section. First, the upper - left pilot tunnel block is excavated and exited, and then the tunnel is penetrated by reverse driving from the outer double - side - wall section. At the same time, this application also fully considers the conversion of the stress system involved in the conversion of the pilot tunnel from a single - side - wall section to a double - side - wall section. Considering the through - hole construction period and safety requirements, while ensuring safety, the workload of the double - side - wall should be minimized as much as possible to improve construction efficiency. At the same time, during the reverse driving process at the tunnel opening, the full - face driving distance should be minimized as much as possible. After each full - face reverse driving for a certain distance, rapid support is carried out. The tunnel opening is first closed into a ring and then construction is carried out towards the inside of the tunnel, which can make full use of the self - stabilizing ability of the unexcavated soil mass to ensure the balanced force and safety and stability of the tunnel opening. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a cross - sectional view of the single - side - wall section of the present invention as seen from the inside outwards;

[0028] Figure 2 It is a cross - sectional view of the double - side - wall section of the present invention as seen from the inside outwards;

[0029] Figure 3 It is a top - view cross - sectional view and cross - sectional view during the excavation process of step S21 of the present invention;

[0030] Figure 4 It is a top - view cross - sectional view and cross - sectional view during the excavation process of step S22 of the present invention;

[0031] Figure 5 It is a top - view cross - sectional view and cross - sectional view during the excavation process of step S23 of the present invention;

[0032] Figure 6 It is a top - view cross - sectional view and cross - sectional view during the excavation process of step S24 of the present invention;

[0033] Figure 7 It is a top - view cross - sectional view and cross - sectional view during the excavation process of step S25 of the present invention;

[0034] Figure 8 It is a top - view cross - sectional view and cross - sectional view during the excavation process of step S26 of the present invention;

[0035] Figure 9 It is a top - view cross - sectional view and cross - sectional view during the excavation process of step S27 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] The following combines the attached Figures 1-9 drawings and specific embodiments to further elaborate on the present invention in detail.

[0037] The specific embodiment of the present invention is a construction method for the two - way exit of a tunnel under the conditions of a steep accumulation body slope. The specific steps are as follows:

[0038] S1. Block planning: On the side of the tunnel body 1 near the exit, a single-sidewall section 2 and a double-sidewall section 3 are planned. The single-sidewall section and the double-sidewall section are divided into a plurality of pilot tunnel blocks by setting support walls and temporary inverted arches. The support walls include a first support wall 4, a second support wall 5, and a third support wall 6. The temporary inverted arches include a first temporary inverted arch 7, a second temporary inverted arch 8, a third temporary inverted arch 9, a fourth temporary inverted arch 10, a fifth temporary inverted arch 11, and a sixth temporary inverted arch 12;

[0039] Such as Figure 1 The cross-sectional view is the cross-section at the single-sidewall section when looking from inside the tunnel to the outside of the tunnel entrance; Figure 2 The cross-sectional view is the cross-section at the double-sidewall section when looking from inside the tunnel to the outside of the tunnel entrance ( Figures 3-9 The cross-sectional views are also all when looking from inside the tunnel to the outside of the tunnel entrance). Among them, the single-sidewall section 2 is divided into four pilot tunnel blocks by the first support wall 4, the first temporary inverted arch 7, and the second temporary inverted arch 8. The pilot tunnel blocks of the single-sidewall section include an inner upper left area 1A, an inner upper left area 3A, an inner upper right area 2A, and an inner lower right area 9A;

[0040] Among them, the double-sidewall section is divided into seven pilot tunnel blocks by the second support wall 5, the third support wall 6, the third temporary inverted arch 9, the fourth temporary inverted arch 10, the fifth temporary inverted arch 11, and the sixth temporary inverted arch 12. The pilot tunnel blocks of the double-sidewall section include an outer upper left area 1B, an outer lower left area 3B, an outer middle upper area 6B, an outer middle area 7B, an outer middle lower area 8B, an outer upper right area 4B, and an outer lower right area 5B;

[0041] Among them, the outer upper left area 1B corresponds to the inner upper left area 1A in both size and position. Among them, the outer lower left area 3B corresponds to the inner upper left area 3A in both size and position. The edge of the first support wall 4 is adjacent to the second support wall 5 (it can be straight and coincident, or the end of the first support wall gradually bends and then connects to the second support wall);

[0042] S2. Two-way tunneling: Adopt the two-way tunneling method to gradually and sequentially drive through the pilot tunnel blocks, and install bolts and mesh on the inner sidewalls of the tunnel body 1 in the corresponding pilot tunnel blocks, and spray concrete to seal and reinforce the inner sidewalls of the tunnel body. The specific construction process of two-way tunneling in step S2 is as follows:

[0043] S21. Drive from the inner upper left area 1A along the first temporary inverted arch 7 to the junction of the single-sidewall section 2 and the double-sidewall section 3. During the driving process, seal and reinforce the inner sidewall of the tunnel body 1 in the inner upper left area 1A;

[0044] S22. Drive forward from the inside to the outside in the positive direction and carry out support. Drive forward from the outer upper left area 1B of the double-side drift section 3 along the third temporary inverted arch 9 to complete the penetration between the inner upper left area 1A and the outer upper left area 1B. During the driving process, seal and reinforce the inner sidewall of the tunnel body 1 in the outer upper left area; at the same time, drive forward from the inner upper right area 2 along the second temporary inverted arch 8 to the edge of the double-side drift section 3. During the driving process, seal and reinforce the inner sidewall of the tunnel body 1 in the inner upper right area 2.

[0045] S23. Drive forward from the outside to the inside in the reverse direction and carry out rapid support. Drive forward from the outer lower left area 3B to the junction of the single-side drift section 2 and the double-side drift section 3 to complete the penetration between the outer lower left area 3B and the inner lower left area 3A. During the driving process, seal and reinforce the inner sidewall of the tunnel body 1 in the outer lower left area 3B.

[0046] Drive forward from the outer upper right area 4B to a specified position inside the middle of the double-side drift section 3. The driving depth is greater than the initial driving distance S1; then drive forward from the outer lower right area 5B to a specified position outside the middle of the double-side drift section 3. The driving depth is less than the initial driving distance S1; finally, drive forward from the outer middle upper area 6B to a specified position outside the middle of the double-side drift section 3. The driving depth is less than the initial driving distance S1.

[0047] S24. Continue to drive forward from the outside to the inside in the reverse direction and carry out rapid support. Drive forward from the outer upper right area 4B to the junction of the single-side drift section 2 and the double-side drift section 3; then drive forward from the outer lower right area 5B to the junction of the single-side drift section 2 and the double-side drift section 3; then drive forward from the outer middle upper area 6B to a specified position inside the middle. The driving depth is greater than the secondary driving distance S2; finally, drive forward from the outer middle area 7B and the outer middle lower area 8B to a specified position outside the middle of the double-side drift section 3 respectively. The driving depth is greater than the secondary driving distance S2. At this time, the length of the initial support closed loop at the outlet end of the tunnel body 1 reaches the first preset value L1.

[0048] S25. Continue to drive forward from the outside to the inside in the reverse direction and carry out rapid support. Drive forward from the outer middle upper area 6B to the junction of the single-side drift section 2 and the double-side drift section 3; the outer middle area 7B and the outer middle lower area 8B continue to drive forward at least 5m. At this time, the length of the initial support closed loop at the outlet end of the tunnel body 1 reaches the second preset value L2, and the upper bench of the pilot tunnel is penetrated.

[0049] S26. Continue to drive forward from the outside to the inside in the reverse direction and carry out rapid support. Drive forward from the outer middle area 7B and the outer middle lower area 8B to the junction of the single-side drift section 2 and the double-side drift section 3 to complete the initial support closed loop of the double-side full section at the outlet end of the tunnel body 1.

[0050] S27. Forward, tunneling from the inside out and quickly supporting, tunneling from the inner right-lower ninth area 9B to the junction of the single-sidewall section 2 and the double-sidewall section 3, completing the initial support closure of the entire tunnel body 1 into a ring, and the entire tunnel body 1 is completely penetrated.

[0051] S3. Demolition. When the tunneling of all the conductive blocks is completed and the inner sidewalls of the corresponding tunnel body 1 are all completed and reinforced, the support wall and the temporary inverted arch are demolished.

[0052] The method of this application is suitable for the area of the tunnel body greater than 200 m 2 ; among which, the inner sidewall of the tunnel body uses φ22 anchor bolts, φ8@20*20 cm wire mesh is hung, and concrete with a thickness of more than 10 cm is sprayed for closure.

[0053] The length of the double-sidewall section is greater than or equal to 12 m, and the single-sidewall section is greater than or equal to 15 m;

[0054] The first preset value L1 is greater than or equal to 5 m, and the second preset value L2 is greater than or equal to 11 m.

[0055] The initial tunneling distance S1 is greater than 5 m and less than 15 m; the secondary tunneling distance S1 is greater than 5 m.

[0056] Embodiment 1

[0057] This method is selected for testing in a certain tunnel, where the starting and ending pile mileage is K61+873~K62+527. The double-sidewall section and single-sidewall section pilot tunnel method are used for construction, and the maximum excavation section reaches 254.54 ㎡. This tunnel passes through a hilly landform area, with a relative ground height difference of about 66.4 m, a total tunnel length of 654 m, including a 63 m long open cut tunnel and a 591 m long buried tunnel. The rock joints and fissures of the tunnel body are developed, the rock mass is extremely broken, with low strength, easy to soften when encountering water. The exit end is located on a landslide loose accumulation body with a height of about 70 m and a width of about 120 m. There is a relatively serious shallow buried and eccentric pressure phenomenon at the tunnel entrance section, and there are 3 small collapse bodies at the toe of the slope.

[0058] Before construction, surface steel flower pipe reinforcement is combined with the setting of a micro-pile group and a cable anchor crown beam to form a portal frame system to solve the landslide thrust in the direction along the tunnel line, perpendicular to the tunnel axis, and at an angle of 48° obliquely intersecting with the main landslide direction of the mountain body, ensuring the safety of the tunnel excavation and support system.

[0059] Due to the too large excavation area of the single pilot tunnel and high safety risks, for the rock stratum of the exit accumulation body, it is planned to change from single-sidewall to double-sidewall. First, the upper bench is advanced out of the tunnel and then backfilled. Since the conversion from single-sidewall pilot tunnel to double-sidewall involves the conversion of the stress system and the redistribution of the surrounding rock, considering the through-tunnel construction period and safety requirements, it is necessary to minimize the double-sidewall workload while ensuring safety.

[0060] Moreover, since the surrounding rock is prone to deformation during the out-of-tunnel stage, improper construction sequence can easily lead to safety accidents such as roof fall and face collapse. Therefore, two-way tunneling is adopted for the construction during the out-of-tunnel stage. The forward direction means excavation from the inlet end to the outlet end, and the reverse direction is excavation from the outlet end to the inlet end.

[0061] A construction method for out-of-tunnel is as follows:

[0062] Step 1: The left and right pilot tunnels at the inlet end of the tunnel body are advanced synchronously. The upper bench of Area 1A in the upper left inner section is excavated to K62+490, and a temporary inverted arch is set. The lower bench of Area 3A in the upper left inner section is advanced to K62+470. The upper bench of Area 2A in the upper right inner section is advanced to K62+465. The top-down cross-sectional view and the double-sidewall section view after excavation are as Figure 3 shown.

[0063] Step 2: The upper bench of Area 2A in the upper right inner section at the inlet end mutates from K62+490 to the double-sidewall section. φ22 rock bolts are used, and a φ8@20*20cm wire mesh is hung, and 10 cm of shotcrete is sprayed to seal the inner sidewall of the tunnel body. At the same time, Area 1B in the upper left outer section and Area 1A in the upper left inner section are first connected. The upper bench of Area 2A in the upper right inner section is advanced to K62+490, and the lower bench of Area 9A in the lower right inner section is advanced to K62+480. Quick support is carried out after excavation. The top-down cross-sectional view and the double-sidewall section view and the single-sidewall section view after excavation are as Figure 4 shown (in order to clearly see the construction changes, the top-down cross-sectional view and the section view of the tunnel body are shown in a single block diagram, which can better understand the construction process).

[0064] Step 3: Stop the face at the inlet end. At the outlet end, the lower bench of Area 3B in the lower left outer section is excavated to K62+502 (in the reverse direction, excavating from the outside to the inside) according to the double-sidewall section pilot tunnel size, and the initial support of the left pilot tunnel is closed into a ring. The upper bench of Area 4B in the upper right outer section is excavated to K62+507 (in the reverse direction, excavating from the outside to the inside), the lower bench of Area 5B in the lower right outer section is excavated to K62+512 (in the reverse direction, excavating from the outside to the inside), and the upper bench of Area 6B in the middle upper outer section is excavated to K62+517 (in the reverse direction, excavating from the outside to the inside). Quick support is carried out after excavation. The top-down cross-sectional view and the double-sidewall section view after excavation are as Figure 5 shown.

[0065] Step 4: Stop the entry face, excavate the upper step of 4B in the outer right upper fourth zone at the exit to K62+490 (reverse, excavate from outside to inside), connect the upper step of the right pilot tunnel, follow up the lower step of 5B in the outer right lower fifth zone to K62+490 (reverse, excavate from outside to inside), excavate the upper step of 6B in the outer middle upper sixth zone to K62+502 (reverse, excavate from outside to inside), follow up the lower step of 7B in the outer middle seventh zone and 8B in the outer middle lower eighth zone to K62+512 (reverse, excavate from outside to inside), close the initial support at the exit to form a ring of 10m, and carry out rapid support after excavation. The top view and the cross-section of the double side wall section after excavation are shown as follows: Figure 6 shown.

[0066] Step 5: Stop the tunnel face at the entrance, excavate the upper step of the outer middle upper sixth zone 6B to K62+490 (reverse, excavate from outside to inside), and follow up with the lower steps of the outer middle seventh zone 7B and the outer middle lower eighth zone 8B to K62+507 (reverse, excavate from outside to inside). The initial support at the exit is closed into a ring of 15m, the upper step of the middle guide tunnel is connected, and rapid support is carried out after excavation. The top view and the double side wall section section after excavation are shown as follows: Figure 7 shown.

[0067] Step 6: Stop the construction of the upper and lower steps at the entrance, and follow up the lower steps of the middle and outer middle seventh zone 7B and the outer middle and lower eighth zone 8B at the exit to K62+490 (reverse direction, excavation from outside to inside) to complete the initial support of the full section of the double side walls at the exit to form a ring. After excavation, carry out rapid support. The top view cross-section diagram after excavation and the single side wall section cross-section diagram are shown as follows Figure 8 shown.

[0068] Step 7: Stop the construction of the exit face, and construct the remaining steps from K62+480 to K62+490 from the inner right lower ninth area 9A at the entrance (forward, excavating from the inside to the outside), complete the initial support and closure of the entire tunnel into a ring, and the entire tunnel is connected. After excavation, rapid support is carried out. The top view and single side wall section section after excavation are shown as follows: Figure 9 shown.

[0069] Among them, the inner left upper zone 1A, the inner right upper zone 2A, and the inner right lower zone 9A are forward excavation construction, the inner left upper zone 3A, the outer left upper zone 1B, the outer left lower zone 3B, the outer middle upper zone 6B, the outer middle zone 7B, the outer middle lower zone 8B, the outer right upper zone 4B, and the outer right lower zone 5B are reverse excavation construction. At the same time, the corresponding areas of the outer middle upper zone 6B, the outer middle zone 7B, the outer middle lower zone 8B, the outer right upper zone 4B, and the outer right lower zone 5B are not all-through construction at one time. Each time the excavation advances a certain distance, the construction sequence is carried out from small to large numbers.

[0070] The principle is as follows: When the tunnel section is large (greater than 200m 2) and the exit position is in a shallow-buried and eccentrically loaded steep loose accumulation body. Due to the poor stress-bearing capacity of the surrounding rock, the conventional single-sidewall exit method is adopted at the entrance of the tunnel body. The widths of the left and right pilot tunnels are both large, and the construction safety risk is high, which is extremely likely to cause safety accidents such as roof collapse and face collapse. Therefore, the single-sidewall section is mutated into a double-sidewall section at the entrance of the tunnel body. Among them, the specific range of the pilot tunnel block set in the double-sidewall section is determined according to the coverage range of the loose accumulation body at the entrance.

[0071] For example, the double-sidewall pilot tunnel construction method is adopted in CN114607389A "Improved Double-Sidewall Pilot Tunnel Construction Method for Urban Ultra-Large Cross-Section Shallow-Buried Stations". However, the double-sidewall construction only adopts the unidirectional forward-drilling method, and the risk is greater at the position closer to the entrance. If the construction support is not timely, there is a risk of collapse; moreover, this double-sidewall construction method will also greatly reduce the construction speed. Therefore, the present application adopts a two-way excavation and exit method. First, a small pilot tunnel is formed by the inner upper left area 1A and the outer upper left area 1B to penetrate outward for forward excavation and exit, minimizing the disturbance of the loose accumulation body at the entrance of the tunnel body to the greatest extent; at the same time, the full-face advance distance is reduced during the reverse excavation and tunneling process at the entrance of the tunnel body (the initial excavation distance and the secondary excavation distance are set). After each full-face reverse excavation and advance a certain distance at the entrance position, rapid support is carried out on the specified pilot tunnel block. After the entrance position is first closed into a ring, construction is carried out towards the inside of the tunnel, which can make full use of the self-stabilizing ability of the unexcavated soil body to ensure the balanced force and safety and stability at the entrance, and improve the construction efficiency. The two-way exit construction method of the present application can significantly reduce the disturbance to the steep loose accumulation body, make full use of the self-stabilizing ability of the loose accumulation body, reduce the pre-reinforcement measures for the steep loose accumulation body at the entrance, realize "fast excavation, fast support, and early closure" at the entrance, ensure the safety of the tunnel exit, reduce the construction risk, and have significant economic and social value. The construction method of the present application makes full use of the relatively stable characteristics of the surrounding rock on the inner side of the tunnel body. Adopting a single-sidewall on the inner side can ensure construction safety, and the construction efficiency of the single-sidewall is higher than that of the double-sidewall. Then, a combination of single-sidewall and double-sidewall construction is adopted to ensure stability while improving the construction efficiency.

[0072] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any minor modifications, equivalent replacements, and improvements made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the technical solution of the present invention.

Claims

1. A construction method for the two-way exit of a tunnel under the condition of a steep accumulation slope, characterized in that: The specific steps are as follows: S1. Block planning: Plan a single-sidewall section and a double-sidewall section on the side of the tunnel body close to the exit. Divide the single-sidewall section and the double-sidewall section into a plurality of pilot tunnel blocks by setting support walls and temporary inverted arches; S2. Two-way tunneling: Adopt the two-way tunneling method to gradually penetrate the pilot tunnel blocks in sequence, and install bolts and mesh on the inner sidewalls of the tunnel body in the corresponding pilot tunnel blocks, and spray concrete to seal and reinforce the inner sidewalls of the tunnel body. At the same time, quickly support the excavated area in the pilot tunnel blocks during the tunneling process; S3. Demolition: When all the pilot tunnel blocks are excavated and the inner sidewalls of the corresponding tunnel body are all sealed and reinforced, remove the support walls and temporary inverted arches; In step S1, the support walls include a first support wall, a second support wall and a third support wall, and the temporary inverted arches include a first temporary inverted arch, a second temporary inverted arch, a third temporary inverted arch, a fourth temporary inverted arch, a fifth temporary inverted arch and a sixth temporary inverted arch; Among them, the single-sidewall section is divided into four pilot tunnel blocks by the first support wall, the first temporary inverted arch and the second temporary inverted arch. The pilot tunnel blocks in the single-sidewall section include an inner upper left area 1, an inner lower left area 3, an inner upper right area 2, and an inner lower right area 9; Among them, the double-sidewall section is divided into seven pilot tunnel blocks by the second support wall, the third support wall, the third temporary inverted arch, the fourth temporary inverted arch, the fifth temporary inverted arch and the sixth temporary inverted arch. The pilot tunnel blocks in the double-sidewall section include an outer upper left area 1, an outer lower left area 3, an outer middle upper area 6, an outer middle area 7, an outer middle lower area 8, an outer upper right area 4, and an outer lower right area 5; Among them, the outer upper left area 1 corresponds to the inner upper left area 1 in terms of size and position, and the outer lower left area 3 corresponds to the inner lower left area 3 in terms of size and position; The more specific construction process in step S2 is as follows: S21. Tunnel from the inner upper left area 1 along the first temporary inverted arch to the junction of the single-sidewall section and the double-sidewall section, and seal and reinforce the inner sidewall of the tunnel body in the inner upper left area 1 during the tunneling process; S22. Tunnel forward from the inside to the outside and carry out support. Tunnel from the outer upper left area 1 in the double-sidewall section along the third temporary inverted arch to complete the penetration of the inner upper left area 1 and the outer upper left area 1, and seal and reinforce the inner sidewall of the tunnel body in the outer upper left area 1 during the tunneling process; At the same time, tunnel from the inner upper right area 2 along the second temporary inverted arch to the edge of the double-sidewall section, and seal and reinforce the inner sidewall of the tunnel body in the inner upper right area 2 during the tunneling process; S23. Tunnel backward from the outside to the inside and quickly support. Tunnel from the outer lower left area 3 to the junction of the single-sidewall section and the double-sidewall section to complete the penetration of the outer lower left area 3 and the inner lower left area 3, and seal and reinforce the inner sidewall of the tunnel body in the outer lower left area 3 during the tunneling process; Tunnel from the outer upper right area 4 to a specified position inside the middle of the double-sidewall section, and the tunneling depth is greater than the initial tunneling distance S1; then tunnel from the outer lower right area 5 to a specified position outside the middle of the double-sidewall section, and the tunneling depth is less than the initial tunneling distance S1; finally tunnel from the outer middle upper area 6 to a specified position outside the middle of the double-sidewall section, and the tunneling depth is less than the initial tunneling distance S1; S24, continue to excavate in the reverse direction from the outside to the inside and quickly support, excavate from the outer right upper fourth area inward to the junction of the single side wall section and the double side wall section; then excavate from the outer right lower fifth area inward to the junction of the single side wall section and the double side wall section; then excavate from the outer middle upper sixth area inward to the designated position in the middle, and the excavation depth is greater than the secondary excavation distance S2; finally, excavate from the outer middle seventh area and the outer middle lower eighth area inward to the designated position in the middle of the double side wall section, and the excavation depth is greater than the secondary excavation distance S2, and at the same time, quickly support the area in the excavated pilot tunnel block, at this time, the length of the initial support closed loop at the exit end of the tunnel body reaches the first preset value L1; S25, continue to excavate in the reverse direction from outside to inside and quickly support, excavate inward from the outer middle upper sixth zone to the junction of the single side wall section and the double side wall section; continue to excavate inward for at least 5m in the outer middle seventh zone and the outer middle lower eighth zone, at which time the length of the initial support closed loop at the exit end of the tunnel body reaches the second preset value L2, and the upper step of the middle guide tunnel is connected; S26, continue to excavate in the reverse direction from outside to inside and quickly support, continue to excavate inward from the outer middle seventh zone and the outer middle lower eighth zone to the junction of the single side wall section and the double side wall section, and complete the initial support ring of the double side wall section at the exit end of the tunnel body; S27, forward, excavate from inside to outside and quickly support, excavate from the inner right lower ninth area to the junction of the single side wall section and the double side wall section, complete the initial support and closure of the entire tunnel body into a ring, and the entire tunnel body is completed.

2. The construction method for two-way tunnel exit under the condition of steep accumulation slope according to claim 1, characterized in that: The area of the tunnel body is greater than 200 m 2 ; The inner sidewall of the tunnel body is closed with φ22 anchor bolts, φ8@20*20 cm mesh sheets are hung, and concrete with a thickness of more than 10 cm is sprayed.

3. The construction method for the two-way exit of a tunnel under the conditions of a steep accumulation slope according to claim 1, characterized in that: The length of the double side wall section is greater than or equal to 12m, and the length of the single side wall section is greater than or equal to 15m; The first preset value L1 is greater than or equal to 5 m, and the second preset value L2 is greater than or equal to 11 m.

4. The construction method for two-way tunnel exit under the condition of steep accumulation slope according to claim 1, characterized in that: The initial excavation distance S1 is greater than 5m and less than 15m; the secondary excavation distance S1 is greater than 5m.

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