Construction method for protecting entrance of shallow-buried unsymmetrical-pressure tunnel penetrating through accumulation body

Abstract

The invention discloses a construction method for protecting a shallow-buried unsymmetrical pressure tunnel portal penetrating through an accumulation body. Comprising the steps that slide-resistant piles are constructed on the open cut tunnel backing side, open cut tunnel bias pressure ear walls are constructed on the free side, miniature steel pipe piles are constructed on ear wall foundations, slide-resistant piles are constructed on the concealed tunnel backing side, slide-resistant piles are constructed on the concealed tunnel free side, back pressure backfilling is conducted on the concealed tunnel shallow buried side, advanced grouting reinforcement supporting is conducted, a single-side-wall pilot tunnel construction method is adopted, monitoring and measuring are conducted, and the like. The slide-resistant piles are constructed on the side, close to the mountain, of the open cut tunnel, the excavation height of the side slope and the front slope is reduced, and the relative stable state of the mountain is maintained with less disturbance of accumulation bodies; the protection structure is stable in structure and good in stress performance, under the combined protection effect of the slide-resistant piles, the bias pressure lug walls, the miniature steel pipe piles and the hidden hole advance supports, safety, reliability and economical efficiency of hole entering construction of the shallow-buried bias pressure tunnel penetrating through the accumulation body are guaranteed, large digging and large filling of a hole opening are avoided, and the construction efficiency is improved. The tunnel design follows the basic principle of safety, durability, economy, energy conservation and environmental protection.

Description

Technical Field

[0001] The invention relates to a construction method for protecting a shallow buried biased tunnel opening through an accumulation body, and belongs to the technical field of tunnel construction. Background Art

[0002] The overall stability of a shallow bias tunnel passing through an accumulation body is poor, which may cause landslide damage on the outward-inclined structural surface or soil sliding along the rock-soil interface. Therefore, it is necessary to study the entry measures for a shallow bias tunnel passing through an accumulation body to ensure the safety of tunnel entry. Summary of the invention

[0003] The purpose of the present invention is to provide a construction method for protecting the entrance of a shallowly buried biased tunnel through an accumulation body. The protection structure can reduce the disturbance to the accumulation body, avoid large-scale excavation, reduce construction risks, and reduce damage to the ecological environment and landscape of the mountain.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body, which includes constructing a ditches 5m outside the excavation line before excavating the entrance, clearing dangerous rocks or rolling stones on the top of the entrance slope and setting up a passive protection net, constructing anti-sliding piles on the mountain side of the open tunnel, constructing biased ear walls on the air side, constructing crown beams and micro steel pipe piles on the base of the ear walls, constructing pre-reinforced anti-sliding piles on the mountain side of the dark tunnel section, constructing retaining plates after constructing anti-sliding piles on the air side, using cement stabilized soil for counter-pressure backfilling of the thinner covering soil on the tunnel top, constructing an advanced large pipe shed at the junction of the open and dark tunnels, After the pipe shed is constructed, the open hole structure is cast in time, and C15 concrete, crushed stone soil, clay watertight layer and cultivated soil are backfilled in turn. Then the dark hole is constructed, and the advanced small pipe support is applied. The single side wall pilot pit method is used for construction. The deep buried side pilot pit is constructed first. At the same time, the surface subsidence measurement, the vault subsidence in the hole, the surrounding convergence and other monitoring measurements and the deformation monitoring of the slope of the accumulation body and the anti-sliding piles outside the hole are carried out. The monitoring measurement results are analyzed and fed back in time to optimize the support parameters and adjust the construction plan to ensure the project quality and construction safety. It includes the following steps:

[0006] S1. Survey and lay out the lines. According to the terrain, before excavating the tunnel, a drainage ditch on the top of the tunnel shall be constructed 5m outside the excavation line and completed before the rainy season.

[0007] S2. Before the construction of anti-slide piles, clear away the dangerous rocks or rolling stones on the slope above the tunnel entrance and set up a passive protection net;

[0008] S3, excavate the construction access road and level the anti-slip pile foundation construction site;

[0009] S4. Spray anchor protection on the top slope of the anti-sliding pile;

[0010] S5. Construct anti-sliding piles on the mountain side, excavate one section and support the other section, and use manual digging and segmented skipping for pile foundation pit excavation;

[0011] S6. Construct anti-sliding piles on the airside, excavate one section and support the other section, and use manual digging and segmented skipping for pile foundation pit excavation;

[0012] S7. After the anti-slide piles on the air side are constructed, retaining plates are constructed, and then cement stabilized soil is used for backfilling at the thinner covering area on the left side of the tunnel top;

[0013] S8. Excavate the back slope of the open tunnel and carry out spray anchor protection, excavate from top to bottom, and support as you dig;

[0014] S9. First construct the crown beam and micro steel pipe piles under the open hole bias pressure ear wall foundation, and then construct the open hole bias pressure ear wall;

[0015] S10. Construct the guide wall. One side of the guide wall foundation is placed on the biased ear wall, and the other side of the arch foot is filled with C15 concrete;

[0016] S11. Build a large pipe shed ahead of time and carry out grouting construction;

[0017] S12, the open hole foundation is replaced and reinforced by grouting, and then the open hole structure is constructed;

[0018] S13, backfill C15 concrete on both sides of the open hole side wall, and backfill gravel soil, clay waterproof layer and cultivated soil in the arch part;

[0019] S14. After the cave top is backfilled with cultivated soil, grass planting and greening construction is carried out on the cave top;

[0020] S15: After the open hole structure is completed, the dark hole structure will be constructed.

[0021] Preferably, the construction steps of the dark hole structure are as follows:

[0022] Step 1: The blind tunnel structure at the entrance section is constructed using the single side wall pilot pit method, first constructing the deep buried side pilot pit, and then constructing the shallow buried side pilot pit;

[0023] Step 2: Surface subsidence monitoring sections are set up outside the tunnel. The horizontal spacing of the surface subsidence measuring points is 4m, and the measurement range is larger than the influence range of tunnel excavation. Horizontal convergence and arch subsidence monitoring and measurement sections are set up inside the tunnel, with one section every 10m, 7 points in each section, 1 point on the arch, and 6 points on the side wall and temporary support;

[0024] Step 3: Measure and lay out, and install the initial I-beam of the blind hole section;

[0025] Step 4: Concealed excavation construction, advance support in the tunnel, set up advance small conduits for the dark tunnel section at the position of the initial steel arch frame of the dark tunnel section, and perform grouting reinforcement; grouting small conduit support parameters: Φ42×4mm advance small conduit, length L=4.0m, circumferential spacing 0.4m, longitudinal spacing 2.4m, external insertion angle 5°~12°, set within 120° of the tunnel arch, grouting uses 425 silicate cement slurry, water-cement ratio 1:1, grouting pressure 0.5~1.0MPa;

[0026] Step 5: Excavate each section in turn according to the single-side wall pilot method and construct the initial support lining of the blind tunnel section. The advance of each cycle shall not exceed the spacing of one steel frame, and the left and right pilot pits shall be staggered by 3 to 5 meters.

[0027] Step 6: Remove temporary supports and pour the invert lining and backfill concrete of the dark tunnel section;

[0028] Step 7: Apply secondary lining to the blind hole section.

[0029] Preferably, the temporary slope on the mountain side of the open tunnel section is supported by anti-slide piles. The size of the anti-slide piles is 2.0×3.0m, the pile spacing is 3 to 7m, the centerline of the anti-slide piles is 7 to 9m away from the centerline of the tunnel, and two 6φs15.2 prestressed anchor cables are installed 1 to 2m and 3 to 4m away from the top of the pile. The length of the anchor cables is 30.0m.

[0030] Preferably, spray anchor protection is carried out on the top slope of the anti-sliding pile, and the protection parameters are: Φ42×4mm grouting small pipe length L=4m, spacing 120×120cm, plum blossom shape arrangement, 10cm thick C25 sprayed concrete, hanging Φ6 steel mesh 20×20cm; grouting uses 425 silicate cement slurry, water-cement ratio 1:(0.8~1), grouting pressure 0.5~1.0MPa.

[0031] Preferably, micro steel pipe piles are constructed under the open hole bias ear wall foundation. The micro steel pipe piles are Φ108×6mm steel flower tubes with a length of L=10m, a spacing of 75×75cm, a plum blossom shape arrangement, and the pile tops are connected with crown beams.

[0032] Preferably, anti-slide piles are arranged on the mountain side of the blind tunnel section parallel to the tunnel axis, the center of the anti-slide pile is 10 to 15 m away from the tunnel centerline, the pile spacing is 4 to 8 m, the pile length is 25 to 32 m, the anti-slide pile size is 1.5×2.0 m, and C30 reinforced concrete is used.

[0033] Preferably, anti-slide piles are installed on the air-facing side of the blind tunnel section parallel to the tunnel axis. The center of the anti-slide pile is 12 to 15 m away from the tunnel centerline, the pile spacing is 3 to 7 m, the pile length is 20 m, the anti-slide pile size is 1.5×2.0 m, and C30 reinforced concrete is used. After the anti-slide piles are constructed, retaining walls are constructed, and cement-stabilized soil is used for backfilling. The backfill slope is not steeper than 1:1.5.

[0034] Preferably, the advance support of the tunnel portal section adopts a Φ108×6mm advance large pipe shed + Φ42×4mm advance grouting small pipe combined support, and the Φ108×6mm steel pipe (constituting the advance large pipe shed) and the Φ42×4mm grouting small pipe are arranged at intervals;

[0035] Among them, the length of the Φ108×6mm advanced large pipe shed is L=42m, the annular spacing is 0.2~0.7m, a steel cage is set in the steel pipe, the main reinforcement of the steel cage is 4 C25 steel bars, and the grouting adopts 425 silicate cement slurry with a water-cement ratio of 1:(0.8-1.2) and a grouting pressure of 2.0~2.5MPa. After the grouting is completed, the pipe is filled with M20 cement mortar;

[0036] The length of the Φ42×4mm advance small duct is L=4.0m, the circumferential spacing is 0.2~0.5m, the longitudinal spacing is 1.5~2m, and the grouting uses No. 425 silicate cement slurry with a water-cement ratio of 1:(0.8-1.2) and a grouting pressure of 0.5~1.0MPa.

[0037] Preferably, the base of the blind cave section is located in a gravel soil layer, and grouting reinforcement is carried out using a 5m long Φ42×4mm grouting small pipe. The spacing between the grouting small pipes is 120×120cm, and they are arranged in a plum blossom shape. The grouting uses No. 425 silicate cement slurry with a water-cement ratio of 1:(0.8-1.2) and a grouting pressure of 0.5 to 1.0 MPa.

[0038] Preferably, the blind tunnel section is constructed using the single-side wall pilot pit method, and on-site monitoring and measurement are carried out inside and outside the tunnel at a frequency required by the specifications to ensure safety of construction inside the tunnel.

[0039] The beneficial effects of the present invention are:

[0040] The protective structure and construction method are suitable for the construction of tunnel portal sections that pass through accumulation strata and have shallow buried and biased terrain. The manpower, equipment, and materials invested are those required for conventional tunnel construction, and there is no need to increase new equipment and resource investment, so the construction cost is low. The tunnel portal protection structure has a stable type, a simple structure, and good force performance. Through the combined action of anti-slip piles on both sides of the tunnel, biased ear walls and micro-steel pipe piles at their base, it can withstand the uneven load of biased terrain and provide bearing capacity for the tunnel. It can also provide dark excavation protection for shallow buried and biased tunnels that pass through accumulation bodies. The protective structure and construction method greatly improve the safety, reliability and economy of tunnel construction, avoid large-scale excavation, and protect the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a plan layout diagram of the present invention;

[0042] Figure 2 This is the cross-section of the Myeongdong section;

[0043] Figure 3 This is the cross-section of the dark cave section;

[0044] Figure 4 This is the longitudinal section drawing of the tunnel section;

[0045] Figure 5 This is the design drawing of the advance support of the tunnel entrance section.

[0046] In the figure: 1- tunnel top intercepting ditch, 2- open tunnel section anti-sliding piles on the mountain side, 3- anchor cable, 4- dark tunnel section anti-sliding piles on the mountain side, 5- dark tunnel section anti-sliding piles on the air side, 6- retaining board, 7- passive protection net, 8- guide wall, 9- anti-sliding pile top slope, 10- open tunnel side back slope, 11- cement stabilized soil, 12- biased ear wall, 13- crown beam, 14- micro steel pipe pile, 15- grouting steel flower pipe, 16 -Open tunnel structure, 17-blind tunnel structure, 18-base replacement, 19-C15 concrete, 20-gravel soil, 21-clay waterproof layer, 22-cultivated soil, 23-advanced large pipe shed, 101-advanced small pipe of blind tunnel section, 102-initial support I-beam of blind tunnel section, 103-initial support lining of blind tunnel section, 104-inverted arch lining and inverted arch backfill concrete of blind tunnel section, 105-secondary lining of blind tunnel section. DETAILED DESCRIPTION

[0047] The present application provides a construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body, comprising the construction of anti-slip piles on the mountain side of the open tunnel, the construction of biased ear walls on the air side of the open tunnel, the construction of micro-steel pipe piles on the ear wall foundation, the construction of anti-slip piles on the mountain side of the dark tunnel, the construction of anti-slip piles on the air side of the dark tunnel, the backfilling of the shallow buried side of the dark tunnel, advance grouting reinforcement support, single side wall pilot pit method, monitoring and measurement, etc.; by constructing anti-slip piles on the mountain side of the open tunnel, the excavation height of the side slope is reduced, so that the accumulation body is disturbed less and the mountain is maintained in a relatively stable state; the entrance protection of the shallow-buried biased tunnel through the accumulation body provided by the present application has a stable structure and good stress performance. Under the combined protection of anti-slip piles, biased ear walls, micro-steel pipe piles and advance support of the dark tunnel, the safety, reliability and economy of the entry construction of the shallow-buried biased tunnel through the accumulation body are ensured, and large excavation and filling of the entrance are avoided. The tunnel design follows the basic principles of "safety, durability, economy, energy saving and environmental protection".

[0048] For details, see Figure 1 to Figure 5 As shown in the figure, the construction method of the tunnel entrance protection of the shallow buried bias pressure tunnel through the accumulation body includes the following steps:

[0049] S1: Survey and lay out the lines. According to the terrain, a drainage ditch 1 is constructed on the top of the cave 5m outside the excavation line before excavation of the cave entrance, and it should be completed before the rainy season.

[0050] S2: Before the construction of anti-slide piles, the slope above the tunnel entrance shall be cleared of dangerous rocks or rolling stones, and a 4m high passive protection net shall be set up7;

[0051] S3: Excavate the construction access road and level the anti-slip pile foundation construction site;

[0052] S4: spray anchor protection is performed on the top slope 9 of the anti-sliding pile. The protection parameters are: Φ42×4mm grouting small pipe, L=4m, spacing 120×120cm, plum blossom arrangement, 10cm thick C25 sprayed concrete, hanging Φ6 steel mesh 20×20cm; grouting uses 425 silicate cement slurry, water-cement ratio 1:1, grouting pressure 0.5~1.0MPa;

[0053] S5: Excavate 2 anti-sliding piles on the mountain side of the open tunnel section and 4 anti-sliding piles on the mountain side of the blind tunnel section, excavate one section of the wall support and one section of the foundation pit, and use manual digging and segmented skipping construction for the pile foundation pit; when the anti-sliding pile 2 on the mountain side of the open tunnel section reaches 100% of the design strength, anchor cables 3 are installed at 1.5m and 3.5m from the top of the pile, using 30m long 6φ s 15.2mm prestressed anchor cable;

[0054] S6: dig 5 anti-sliding piles on the air side of the blind tunnel section, dig one section of retaining wall and support one section, and use manual digging and segmented skipping construction for the pile foundation pit;

[0055] S7: After the anti-sliding piles are constructed on the air side of the blind tunnel section, a 0.4m thick retaining wall 6 is constructed between the piles, and then cement stabilized soil 11 is used to backfill the thinner covered soil on the left side of the tunnel top. The backfill slope is not steeper than 1:1.5;

[0056] S8: Excavate the back slope 10 at the side of the open tunnel and carry out spray anchor protection. The protection parameters are: Φ42×4mm grouting small pipe, L=3m, spacing 120×120cm, plum blossom arrangement, 10cm thick C25 sprayed concrete, hanging Φ6 steel mesh 20×20cm; grouting uses 425 silicate cement slurry, water-cement ratio 1:1, grouting pressure 0.5~1.0MPa;

[0057] S9: Micro steel pipe piles 14 are constructed at the base of the open hole bias ear wall. The micro steel pipe piles 14 are made of Φ108×6mm steel tubes, L=10m, the pile spacing is 75×75cm, and they are arranged in a plum blossom shape. The tops of the piles are connected by crown beams 13, and then the open hole bias ear wall 12 is constructed, using C30 plain concrete;

[0058] S10: Construct the guide wall 8 at the junction of light and dark areas, and use C30 concrete for pouring. Set 4 I18 I-beams in the guide wall 8, and embed Φ127×4.5mm guide steel pipes according to the designed drilling positions. One side of the guide wall foundation is placed on the bias ear wall, and the arch foot on the other side is filled with C15 concrete.

[0059] S11: construct the advanced large pipe shed 23, using Φ108×6mm steel flower pipe, inserting a steel cage into the steel pipe, with 4 C25 steel bars as the main reinforcement of the steel cage, and performing grouting construction. The grouting uses 425 silicate cement slurry, the water-cement ratio of the cement slurry is 1:1, and the grouting pressure is 2.0-2.5MPa. After the grouting is completed, the pipe is filled with M20 cement mortar;

[0060] S12: C15 concrete is used to replace the base 18 within 1.0m of the open hole base, and Φ42×4mm grouting steel tubes 15 are used for grouting reinforcement. The length of the steel tubes is L=5.0m, the spacing is 120×120cm, and they are arranged in a plum blossom shape. Then the open hole structure 16 is constructed, and C35 reinforced concrete is used for the open hole;

[0061] S13: C15 concrete 19 is used to backfill the two sides of the open hole side wall, and the backfill height is 7m; the arch top is backfilled with crushed stone 20, clay waterproof layer 21, and cultivated soil 22 in sequence;

[0062] S14: After the cave top is backfilled with cultivated soil, grass and greening construction is carried out on the cave top;

[0063] S15: After the construction of the open hole structure 16 is completed, the dark hole structure 17 is constructed.

[0064] The construction steps of the dark hole structure are as follows:

[0065] S1: The blind tunnel structure of the tunnel entrance section is constructed using the single side wall pilot pit method, first constructing the deep buried side pilot pit and then the shallow buried side pilot pit.

[0066] S2: Surface subsidence monitoring sections are arranged outside the tunnel, with the horizontal spacing of surface subsidence measuring points being 4m, and the measurement range being larger than the influence range of tunnel excavation; horizontal convergence and arch subsidence monitoring and measurement sections are arranged inside the tunnel, with one section every 10m, 7 points in each section, 1 point on the arch, and a total of 6 points on the side walls and temporary supports;

[0067] S3: Measure and lay out, and install the initial I-beam 102 of the blind hole section;

[0068] S4: Concealed excavation, advanced support in the tunnel, set up an advanced small conduit 101 for the dark tunnel section at the position of the initial support steel arch frame 102 of the dark tunnel section, and perform grouting reinforcement; grouting small conduit 101 support parameters: Φ42×4mm advanced small conduit, length L=4.0m, circumferential spacing 0.4m, longitudinal spacing 2.4m, external insertion angle 5°~12°, set within 120° of the tunnel arch, grouting uses 425 silicate cement slurry, water-cement ratio 1:1, grouting pressure 0.5~1.0MPa;

[0069] S5: Excavate each section in turn according to the single-side wall pilot method and construct the initial support lining 103 of the blind tunnel section. The advance of each cycle shall not exceed the spacing of one steel frame, and the left and right pilot pits shall be staggered by 3 to 5 meters.

[0070] S6: Remove temporary supports and pour the invert lining and invert backfill concrete 104 of the blind tunnel section;

[0071] S7: construct secondary lining 105 of the blind tunnel section.

[0072] In the above construction methods, any parts not fully explained are all within the scope of conventional tunnel construction and existing construction methods, and will not be elaborated here.

[0073] The above is only a preferred implementation of the patent of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the patent of the present invention. These improvements and modifications should also be regarded as the scope of protection of the patent of the present invention.

Claims

1. A construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body, characterized in that: The steps include: S1. Measure and lay out the lines, and construct the drainage ditch on the top of the cave outside the excavation line of the cave entrance; S2. Clean the slope above the cave entrance and set up a passive protection net; S3, excavate the construction access road and level the anti-slip pile foundation construction site; S4. Spray anchor protection on the top slope of the anti-sliding pile; S5. Install anti-slide piles on the mountain side, excavate one section of the wall and support another section; S6. Install anti-sliding piles on the airside, excavate one section and support the other section; S7. Build retaining walls and then use cement stabilized soil to backfill the thinner areas on the top of the tunnel; S8. Excavate the back slope of the open tunnel and carry out spray anchor protection, excavate from top to bottom, and support as you dig; S9. First construct the crown beam and micro steel pipe piles under the open hole bias pressure ear wall foundation, and then construct the open hole bias pressure ear wall; S10. Construct a guide wall, with one side of the guide wall foundation placed on the biased ear wall and the other side of the arch foot filled with concrete; S11. Build a large pipe shed ahead of time and carry out grouting construction; S12, the open hole foundation is replaced and reinforced by grouting, and then the open hole structure is constructed; S13. Backfill concrete on both sides of the open hole side wall, and backfill gravel soil, clay waterproof layer and cultivated soil in the arch part in sequence; S14. After the cave top is backfilled with cultivated soil, grass planting and greening construction is carried out on the cave top; S15: After the open hole structure is completed, the dark hole structure will be constructed.

2. The construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body according to claim 1 is characterized in that: The construction steps of the dark hole structure are as follows: Step 1: The blind tunnel structure at the entrance section is constructed using the single side wall pilot pit method, first constructing the deep buried side pilot pit, and then constructing the shallow buried side pilot pit; Step 2: Set up a surface subsidence monitoring section outside the tunnel; set up a horizontal convergence and arch subsidence monitoring measurement section inside the tunnel; Step 3: Measure and lay out, and install the initial I-beam of the blind hole section; Step 4: Concrete excavation, advanced support in the tunnel, installation of small advanced conduits for the dark tunnel section at the initial steel arch support position, and grouting reinforcement; Step 5: Excavate each section in turn according to the single-side wall pilot tunnel method and construct the initial support lining of the blind tunnel section; Step 6: Remove temporary supports and pour the invert lining and backfill concrete of the dark tunnel section; Step 7: Apply secondary lining to the blind hole section.

3. The construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body according to claim 1 is characterized in that: The temporary slope on the mountain side of the Mingdong section is supported by anti-slide piles with a pile spacing of 3 to 7m. The centerline of the anti-slide pile is 7 to 9m away from the centerline of the tunnel. Two prestressed anchor cables are installed 1 to 2m and 3 to 4m away from the top of the pile.

4. The construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body according to claim 1 is characterized in that: The top slope of the anti-sliding pile is protected by sprayed anchor, and the protection parameters are: small grouting pipe, plum blossom shape arrangement, sprayed concrete, hanging steel mesh; grouting uses silicate cement slurry, water-cement ratio 1: (0.8 ~ 1.2), grouting pressure 0.5 ~ 1.0MPa.

5. The construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body according to claim 1 is characterized in that: Micro steel pipe piles are constructed under the open hole biased ear wall foundation. The micro steel pipe piles use steel flower tubes, arranged in a plum blossom shape, and the pile tops are connected with crown beams.

6. The construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body according to claim 1 is characterized in that: Anti-slip piles are installed on the mountain side of the blind tunnel section parallel to the tunnel axis. The center of the anti-slip pile is 10 to 15 meters away from the tunnel centerline, the pile spacing is 4 to 8 meters, and reinforced concrete is used.

7. The construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body according to claim 1 is characterized in that: Anti-sliding piles are set up on the air side of the blind tunnel section parallel to the tunnel axis. The center of the anti-sliding pile is 12 to 15 meters away from the tunnel centerline, and the pile spacing is 3 to 7 meters. Reinforced concrete is used. After the anti-slide piles are constructed, retaining walls are constructed and cement-stabilized soil is used for backfilling. The backfill slope is not steeper than 1:1.

5.

8. The construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body according to claim 1 is characterized in that: The advance support of the tunnel portal section adopts the combined support of advance large pipe shed and advance grouting small pipe, and the advance large pipe shed and advance grouting small pipe are arranged at intervals; Among them, the circumferential spacing of the advanced large pipe shed is 0.2 to 0.7m. A steel cage is arranged inside the steel pipe of the advanced large pipe shed. The grouting adopts silicate cement slurry with a water-cement ratio of 1:(0.8 to 1.2) and a grouting pressure of 2.0 to 2.5MPa. After the grouting is completed, the steel pipe body constituting the advanced large pipe shed is filled with cement mortar; The circumferential spacing of the advance small ducts is 0.2 to 0.5 m, and the longitudinal spacing is 1.5 to 2 m. The grouting uses silicate cement slurry with a water-cement ratio of 1:(0.8 to 1.2) and a grouting pressure of 0.5 to 1.0 MPa.

9. The construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body according to claim 1, characterized in that: The base of the blind cave section is located in the gravel soil layer and is reinforced by grouting using small grouting tubes arranged in a plum blossom shape. The grouting uses silicate cement slurry with a water-cement ratio of 1:(0.8~1.2) and a grouting pressure of 0.5~1.0MPa.

10. The construction method for protecting the entrance of a shallow-buried biased tunnel through an accumulation body according to claim 1, characterized in that: The blind tunnel section was constructed using the single side wall pilot tunnel method.

Images