Tunnel portal cover arch supporting structure and construction method thereof

Abstract

The invention discloses a tunnel portal cover arch supporting structure and a construction method thereof. The cover arch supporting structure comprises a cover arch, the two ends of the cover arch are located on cast-in-place concrete piles, and the cast-in-place concrete piles are vertically arranged in a side slope of a tunnel portal section. During construction, the cover arch annular groove is firstly constructed, and then the concrete cast-in-place piles are constructed at the two ends of the cover arch annular groove. According to the method, the installation stability of the cover arch is guaranteed, the excavation depth of the cover arch annular groove is reduced, then the excavation height of the tunnel portal section side slope and the upward slope is reduced, the excavation supporting engineering amount of the portal section is reduced, and meanwhile certain support is provided for the slope toe through the arrangement of the cast-in-place concrete piles.

Description

Technical Field

[0001] The invention relates to tunnel engineering, and in particular to a tunnel portal sleeve arch support structure and a construction method thereof. Background Art

[0002] In underground engineering, the construction environment of tunnel engineering is complex. The construction of the portal section, as an important link and key process of tunnel construction, usually needs to pass through the mountain cover layer with severe weathering and poor stability. Affected by the structure and weathering degree, it is easy to cause slope instability and collapse. In order to ensure the safety and stability of the portal section, advance support measures such as pipe sheds are usually taken before entering the tunnel. As an important structure set at the starting point of the pipe shed, the sleeve arch plays a fixing or supporting role. Its construction process includes clearing the portal section → excavating the sleeve arch annular groove → sleeve arch foundation construction → sleeve arch inner arch frame installation → hole pipe positioning and fixing → formwork installation → sleeve arch concrete pouring → curing and demolding. After the sleeve arch concrete reaches a certain strength, it can provide necessary support for the construction of the portal section.

[0003] However, in actual engineering, the tunnel portal section is often restricted by some objective factors, such as poor geological conditions at the portal section and the need to cross existing roads and railways. At this time, if the conventional construction plan is followed and the sleeve arch is located on a stable bedrock, it will inevitably cause a large amount of excavation and support work on the back slope of the portal. Improper protection will cause the slope to become unstable and collapse. In addition, due to the restrictions of the existing roads and railways above the portal section, the conditions for excavation of the back slope may not be met. Therefore, it is necessary to design a construction method for the tunnel portal sleeve arch support structure to solve the problems existing in this situation. Summary of the invention

[0004] The technical problem to be solved by the present invention is that, in view of the inconvenience in the installation and construction of tunnel portal sleeves in poor geological conditions, the present invention provides a tunnel portal sleeve support structure and a construction method thereof which can reduce the amount of excavation and support engineering for the back slope at the tunnel portal.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] A tunnel portal sleeve arch support structure includes a sleeve arch installed in a tunnel portal section, and its structural features are:

[0007] A plurality of cast-in-place concrete piles are arranged in the slope of the tunnel entrance section, and the lower part of each cast-in-place concrete pile extends into the bedrock of the slope of the tunnel entrance section. The two ends of the sleeve arch are respectively seated on the corresponding cast-in-place concrete piles. A steel cage is arranged inside the cast-in-place concrete pile, and the steel cage includes a plurality of main bars vertically arranged and distributed in a ring shape, spiral bars sleeved on the outer periphery of the main bars, and stirrups distributed in a ring shape formed by the main bars, and the main bars and the spiral bars are welded into one, and the spiral bars and the stirrups are welded into one.

[0008] The present invention places the sleeve arch on the concrete bored pile, and the lower part of the concrete bored pile extends into the bedrock of the tunnel portal section slope. The steel cage of the concrete bored pile adopts the special structure as mentioned above, thereby avoiding the traditional method of placing the sleeve arch directly on the bedrock. It not only ensures the installation stability of the sleeve arch on the tunnel slope with poor geological conditions, but also reduces the excavation depth of the sleeve arch annular groove, thereby reducing the excavation height of the back slope of the tunnel portal section slope, reducing the excavation support engineering volume of the portal section, and at the same time, the setting of the concrete bored pile provides certain support for the slope foot.

[0009] Preferably, the stirrups are distributed in the shape of an equilateral triangle inside the main reinforcement, and the sonic detection tube is installed inside the stirrups. The stirrups of the present invention are in the shape of an equilateral triangle, which not only improves their installation stability, thereby improving the structural stability of the spiral reinforcement and the steel cage, but also facilitates the installation of the sonic detection tube.

[0010] Preferably, the bottom of the main reinforcement of the steel cage is bent inwards to facilitate the lowering of the steel cage.

[0011] Preferably, positioning bars are evenly arranged around the steel cage, and the positioning bars are welded to the main bars as one body. The arrangement of the positioning bars facilitates the positioning of the steel cage in the pile hole.

[0012] Preferably, a plurality of reinforcing ribs are arranged axially on the steel cage, and the reinforcing ribs are welded to the main ribs. The arrangement of the reinforcing ribs improves the structural strength of the steel cage.

[0013] Preferably, a plurality of guide tubes are arranged inside the sleeve arch along the axial direction of the tunnel, and steel flower tubes for pipe shed are laid inside the guide tubes. The guide tubes are mainly used to fix and control the steel flower tubes. Before the construction of the pipe shed, the sleeve arch is constructed first, and the guide tubes are fixed inside the sleeve arch. When installing the guide tubes, the upper platform should be reserved and the elevation angle of the steel flower tube should be controlled to ensure that the opening direction of the steel flower tube is correct. The steel flower tube is arranged in a ring shape and surrounds the contour of the tunnel top arch to form a shell structure, which can effectively support the surrounding rock above; in addition, the steel flower tube can be used for grouting, and the slurry is pressed into the cracks of the surrounding rock through the holes in the pipe wall to consolidate the rock mass and enhance the bearing capacity of the surrounding rock.

[0014] Preferably, a plurality of I-beams installed in sections are arranged on the inner side of the guide tube along the circumferential direction of the tunnel, and adjacent I-beams are connected by longitudinal connecting ribs. A plurality of longitudinal steel bars are arranged on the outer side of the guide tube along the axial direction of the tunnel, and a plurality of circumferential steel bars are arranged along the circumferential direction of the tunnel, and the intersection points of the longitudinal steel bars and the circumferential steel bars are tied together.

[0015] Based on the same inventive concept, the present invention also provides a construction method of the tunnel portal sleeve arch support structure, which comprises the following steps:

[0016] Step 1: clean the topsoil and dangerous rocks at the tunnel entrance, dig the sleeve arch annular groove, and continue to dig downward at the end of the sleeve arch annular groove to the top elevation of the concrete cast-in-place pile;

[0017] Step 2: Locate the position of the concrete pile, determine the position of the concrete pile, build the drilling platform, bury the casing, and put the drilling rig in place;

[0018] Step 3: Set up a mud pool at the pile hole location. Drill dry first to strengthen the hole protection and hole fixing effect. Drilling will start after the slurry in the pile hole meets the design requirements.

[0019] Step 4: When the drilling hole reaches the predetermined depth, the drill bit is lifted by 0.3m to 0.5m, and the hole is cleaned by the slurry replacement method. After the hole is cleaned, the quality of the pile hole and the thickness of the sedimentation layer are comprehensively inspected;

[0020] Step 5: Slowly lower the steel cage of the concrete pile into the pile hole and fix it;

[0021] Step 6: Pour concrete into the pile hole to form a concrete pile, and then remove the casing;

[0022] Step 7: After the concrete pile reaches a certain strength, the sleeve arch is formed in the sleeve arch annular groove, and the drilling and grouting construction of the advance pipe shed is completed.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The present invention places the sleeve arch on concrete cast-in-place piles, the lower part of the concrete cast-in-place piles extends into the bedrock of the tunnel portal section slope, and a special structure of the steel cage is used in the concrete cast-in-place piles, thereby avoiding the traditional method of placing the sleeve arch on the bedrock, not only ensuring the stability of the sleeve arch installation, but also reducing the excavation depth of the sleeve arch annular groove, thereby reducing the excavation height of the back slope of the tunnel portal section slope, and at the same time, the setting of the concrete cast-in-place piles provides a certain support for the slope foot.

[0025] 2) The present invention overcomes the problem that the tunnel portal section needs to be provided with a casing arch, but there are limiting factors that do not provide conditions for side slope excavation, reduces the amount of excavation and support engineering in the portal section, and the construction technology is simple and reliable, with certain economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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 some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 It is a plan view of the sleeve arch and the concrete cast-in-place pile of the present invention.

[0028] Figure 2 It is an elevation drawing of the arch and concrete piles.

[0029] Figure 3 It is a longitudinal section of the arch.

[0030] Figure 4 It is the steel bar distribution diagram inside the arch.

[0031] Figure 5 It is the main view of the steel bar distribution in the concrete pile.

[0032] Figure 6 It is a top view of the steel bar distribution of cast-in-place concrete piles.

[0033] Figure 7 This is the status diagram of the tunnel portal section before construction.

[0034] In the figure: 1-concrete cast-in-place piles, 2-arch, 3-tunnel portal section, 4-guide pipe, 5-steel flower pipe, 6-I-beam, 7-rebar, 8-main reinforcement, 9-spiral reinforcement, 10-positioning reinforcement, 11-strengthening reinforcement, 12-hoops, 13-sonic detection tube. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with specific preferred embodiments, but the protection scope of the present invention is not limited thereby.

[0036] In the description of the present invention, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0037] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] See also Figure 1 - Figure 6An embodiment of the tunnel portal sleeve arch support structure of the present invention includes a sleeve arch 2 installed on a tunnel portal section 3, both ends of the sleeve arch 2 are seated on concrete cast-in-place piles 1, and the lower part of the concrete cast-in-place piles 1 extends into the bedrock of the slope of the tunnel portal section 3.

[0039] In this embodiment, the sleeve arch 2 is a cast-in-place concrete structure, the concrete strength grade is C25, and the concrete grading is secondary. A plurality of guide tubes 4 are arranged inside the sleeve arch 2 along the axial direction of the tunnel, and steel flower tubes 5 are arranged inside the guide tubes 4. On the inner side of the sleeve arch 2, that is, below the guide tubes 4, a plurality of I-beams 6 installed in sections are arranged along the circumferential direction of the tunnel, and adjacent I-beams 6 are connected by longitudinal connecting bars (not shown in the figure). A plurality of longitudinal steel bars are arranged on the outer side of the sleeve arch 2 along the axial direction of the tunnel, and a plurality of circumferential steel bars are arranged along the circumferential direction of the tunnel, and the intersections of the longitudinal steel bars and the circumferential steel bars are tied together with lead wire (the longitudinal steel bars and the circumferential steel bars are uniformly represented by the reference numeral 7).

[0040] In this embodiment, the concrete pile 1 is a cast-in-place concrete structure, the concrete strength grade is C30, the concrete grading is secondary, and a steel cage is arranged inside the concrete pile 1. The steel cage includes a plurality of vertically arranged main bars 8, spiral bars 9 sleeved on the outer periphery of the main bars 8, and stirrups 12 distributed in a regular triangle on the inner side of each main bar 8. The main bars 8 are spliced ​​by multiple sections of steel bars using a mechanical joint. Each of the main bars 8 is distributed in a ring shape and is welded to the spiral bars 9 as a whole. At the same time, the stirrups 12 are welded to the spiral bars 9 to support the spiral bars 9, and the upper part of the main bars 8 extends out of the concrete pile 1 and extends into the sleeve arch 2 to be fixedly connected to the sleeve arch 2. Positioning bars 10 are evenly arranged around the steel cage, and the positioning bars 10 are welded to the main bars 8 as a whole. Reinforcing bars 11 are arranged every two meters along the axial direction of the steel cage, and the reinforcing bars 11 are welded to the main bars 8.

[0041] To facilitate the cutting of the steel cage, the main reinforcement 8 at the bottom of the steel cage is bent inwards.

[0042] The construction method of the tunnel portal arch support structure as described above comprises the following steps:

[0043] Step 1: clean the topsoil and dangerous rocks at the tunnel entrance, dig the sleeve arch annular groove, and dig downward from the end of the sleeve arch annular groove to the top elevation of the concrete cast-in-place pile 1;

[0044] Step 2: Locate the pile position, determine the position of the concrete pile 1, build the drilling platform, bury the casing, and put the drilling rig in place;

[0045] Step 3: Set up a mud pool at the pile hole location. Drill dry first to strengthen the hole protection and hole fixing effect. Drilling will start after the mud in the hole meets the design requirements.

[0046] Step 4: When the drilling hole reaches the predetermined depth, the drill bit can be lifted by 0.3m to 0.5m, and the hole can be cleaned by the slurry replacement method. After the hole is cleaned, the quality of the pile hole and the thickness of the sedimentation layer are comprehensively checked;

[0047] Step 5: Weld the steel cage at the hole mouth and slowly lower it into the hole to fix it;

[0048] Step 6: Pour concrete into the hole and remove the casing;

[0049] Step 7: After the concrete pile 1 reaches a certain strength, the I-beam 6 in the fixed sleeve arch 2 is installed in the sleeve arch annular groove, and the I-beams 6 are welded and connected into a whole by longitudinal connecting ribs, and the position of the guide tube 4 is located and its welding reinforcement is completed;

[0050] Step 8: construct the inner and outer formworks and the head plate of the arch sleeve 2, pour the concrete of the arch sleeve 2, and complete the drilling and grouting construction of the advanced pipe shed.

[0051] Application Examples

[0052] The first phase of the Shuifu City Urban and Rural Logistics Infrastructure Construction Project is located in Shuifu City, Yunnan Province. The project involves the construction of two long-rubber tunnels (long-rubber tunnels are essentially the same as the highway tunnels and railway tunnels we usually see. The difference is that highway tunnels and railway tunnels can be used for cars and trains, while long-rubber tunnels can be used for belts to transport materials). The 1# long-rubber tunnel is responsible for transporting materials from the Dawantou Wharf to the downstream storage and transshipment center, and the 2# long-rubber tunnel is responsible for transporting materials from the original Taiping yard to the Xiangjiaba long-rubber transportation line at the transfer point 7 tunnel to the downstream storage and transshipment center. The 2# long-rubber tunnel will run alone for 1.2 km before merging with the 1# long-rubber tunnel and sharing the tunnel until the tunnel exit.

[0053] According to the site selection and overall process layout of Dawantou Wharf, the entrance of the 1# Changjiao Tunnel - the entrance of the tunnel on the bank of the Xiangjiaba Reservoir on the Jinsha River is a low mountain valley landform with tectonic erosion and denudation. The entrance section is a slope with steep slopes and cliffs. The mountain elevation is 380m~787m. The Shuisui Class II Highway passes through the slope at an elevation of 440m on the mountainside. The entrance below the highway is located on a small ridge with a natural slope angle of 45°~60°. The slope is large and small landslides are developed in some areas. The upper part of the highway is a steep slope with a natural slope angle of more than 75°. The cliff is almost upright, and there is a reverse slope in some areas. The mountain is majestic and towering, like a cliff. The bedrock of the steep cliffs and steep ridges is well exposed. Due to the cutting of joints and fissures and weathering, dangerous rock masses are developed. It can be seen that the highway guardrails are hit by falling rocks and are severely damaged. Only active protection nets, anchor spraying support and anchor cable support are used in areas close to the highway; the highway is formed by backfilling the roadbed retaining wall in some sections of the highway. The existing environmental slope of the tunnel entrance section is exposed bedrock, with strongly weathered mudstone on the surface and moderately weathered mudstone in the middle and lower parts, intercalated with a small amount of sandstone and sandy mudstone. Affected by faults and weathering, the surface rock mass is broken to relatively broken, with a layered to fragmented structure. Small landslides are developed in the shallow surface layer, and the slope in the landslide area is unstable. The slope is in a stable state as a whole, and the strongly weathered layer is very prone to arc sliding damage. The surrounding rock is soft rock with developed joints and fissures. The rock mass is relatively broken to broken. The rock mass in the fault-affected area is fragmented to scattered, and the rock mass outside the affected area is layered. It belongs to Class V surrounding rock, and the affected depth is greater than 40m.

[0054] Before the construction of the tunnel entrance section, the vegetation and dangerous rocks outside the excavation line should be cleared. During the construction process, temporary monitoring during the construction period should be strengthened, attention should be paid to the rock conditions of the upper slope, and dangerous sources should be checked and cleared. Safety precautions and management of slope construction should be strengthened. According to the disturbance caused by the import construction, sprayed anchor support or combined slope support system should be used to reinforce the upper slope.

[0055] First, the concrete cast-in-place pile 1 is constructed. The pile diameter is 1.0m and the pile length is 14.0m. There are 4 piles in total, which are located at both ends of the sleeve arch 2 (see Figure 1 ), the distance between the centerline of the pile diameter along the tunnel axis is 3.6m, the concrete strength grade of the pile body is C30, and the concrete grading is level 2; Figure 5 , Figure 6As shown, the steel cage is provided with 5 kinds of steel bars, among which ① the specification of the main bars 8 is 20C28, the main bars 8 are spliced ​​and connected in sections by mechanical joints, each main bar 8 is distributed in a ring shape, and the upper end of the main bar 8 is inserted into the sleeve arch 2 by 0.95m; ② the specification of the reinforcing bar 11 is C22@2000, one is arranged every 2.0m along the axial direction of the steel cage, and it is arranged inside the steel cage. The overlapped part of the steel bar is double-sided welded and spot-welded with the main bars 8; ③ the specification of the spiral bars 9 is A10@100, distributed on the periphery of the main bars 8, and welded to the main bars 8 as a whole; ④ the stirrups 12 The specification is C22@2000, distributed in the shape of a regular triangle on the inner side of the ring surrounded by the main reinforcement 8 to support the spiral reinforcement 9, so that the steel cage structure is stable; ⑤ 4 positioning bars 10 are arranged in each section, evenly arranged around the reinforcing bar 11, and welded to the main reinforcement 8. To facilitate the cutting of the steel cage, the main reinforcement 8 at the bottom of the steel cage is bent inward; 3 acoustic detection tubes 13 are installed in each pile, with the specification of 50mm outer diameter steel pipe and 1.2mm wall thickness. They are tied to the stirrups 12 and distributed in the shape of a regular triangle. The acoustic detection tube 13 needs to be exposed 30cm from the top of the pile for ultrasonic detection of the pile.

[0056] After the concrete pile 1 reaches a certain strength, the construction of the arch 2 will be carried out. The thickness of the arch 2 is 0.8m, the length along the tunnel axis is 2.0m, the concrete strength grade is C25, and the concrete grading is level 2. There are 4 I18 I-beams 6 inside the arch 2, with a spacing of 0.6m. The longitudinal connecting bars C22@1000 are used to weld the I-beams 6 firmly. Each I-beam 6 is divided into 5 sections, and the φ140×4.5mm guide tube 4 is fixed in the arch 2. When installing the guide tube 4, the upper platform should be reserved and the steel pipe elevation angle should be controlled to ensure the correct hole direction. The pipe shed is made of φ108×4.5mm hot-rolled seamless steel flower tube 5. The section length of the steel flower tube 5 is 3.0m and 6.0m, the circumferential spacing is 0.4m, and the elevation angle is 1°~3°. The construction error is: the front end of the pipe shed does not exceed 0.2m, the number of joints in the same longitudinal cross section is not more than 50%, and the joints of adjacent steel flower tubes must be staggered by at least 1.0m. The total length of the pipe shed is temporarily set at 30.0m according to geological conditions. During the construction process, it is controlled according to the crossing of the Shuisui Class II Highway above. The pipe shed is constructed by drilling method. The axial direction of the drill rod should be strictly controlled during drilling, the scaffolding should be reliably erected, the drilling rig should be firmly fixed, and the inclination instrument should be used to measure the drilling deviation during drilling. If the deviation exceeds the design requirements, it should be corrected in time. The pipe shed is connected by threaded connection, and the thread length is 15cm. In order to stagger the steel flower pipe joints, the length of the first section of the pipe numbered odd-numbered hole position is 3.0m, and the length of the first section of the pipe numbered even-numbered hole position is 6.0m, and each section thereafter is 6.0m. The grouting of the pipe shed is designed according to the rock and soil body within a limited range around the consolidation pipe shed. The slurry diffusion radius is not less than 0.7δ (δ is the center distance between two adjacent steel flower pipes), and the grouting is segmented; the construction of the pipe shed adopts partitioned interval construction, first drilling holes to construct the pipe shed at odd-numbered holes, and then constructing the pipe shed at even-numbered holes after the grouting is completed, so as to check the grouting effect of the odd-numbered holes. The grouting pressure and water-cement ratio of the pipe shed should be comprehensively determined by testing based on the on-site rock crushing conditions and slurry diffusion. After the grouting of the pipe shed is completed and reaches 75% of the design strength, excavation is carried out under the support of the pipe shed. After excavation, concrete is sprayed immediately, anchors are driven, meshes are hung, steel arch frames are erected, and concrete is sprayed to the design thickness.

[0057] The above is only a specific implementation scheme of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the art can make many possible changes and modifications to the technical scheme of the present invention by using the technical content disclosed above without departing from the scope of the technical scheme of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical scheme of the present invention should fall within the protection scope of the technical scheme of the present invention.

Claims

1. A tunnel portal sleeve arch support structure, comprising a sleeve arch installed in a tunnel portal section, characterized in that: A plurality of cast-in-place concrete piles are arranged in the slope of the tunnel entrance section, and the lower part of each cast-in-place concrete pile extends into the bedrock of the slope of the tunnel entrance section. The two ends of the sleeve arch are respectively seated on the corresponding cast-in-place concrete piles. A steel cage is arranged inside the cast-in-place concrete pile, and the steel cage includes a plurality of main bars vertically arranged and distributed in a ring shape, spiral bars sleeved on the outer periphery of the main bars, and stirrups distributed in a ring shape formed by the main bars, and the main bars and the spiral bars are welded into one, and the spiral bars and the stirrups are welded into one.

2. The tunnel portal arch support structure according to claim 1, characterized in that: The stirrups are distributed on the inner side of the main reinforcement in the shape of an equilateral triangle, and an acoustic detection tube is installed on the inner side of the stirrups.

3. The tunnel portal arch support structure according to claim 1, characterized in that: The bottom of the main reinforcement of the steel cage is bent inwards.

4. The tunnel portal arch support structure according to claim 1, characterized in that: Positioning bars are evenly arranged around the steel cage, and the positioning bars are welded to the main bars as a whole.

5. The tunnel portal arch support structure according to claim 1, characterized in that: A plurality of reinforcing ribs are arranged axially on the steel cage, and the reinforcing ribs are welded and connected to the main ribs.

6. The tunnel portal arch support structure according to claim 1, characterized in that: A plurality of guide pipes are arranged inside the sleeve arch along the axial direction of the tunnel, and steel flower pipes for pipe sheds are laid inside the guide pipes.

7. The tunnel portal arch support structure according to claim 6, characterized in that: The inner side of the guide tube is provided with a plurality of I-beams installed in sections along the circumferential direction of the tunnel, and adjacent I-beams are connected by longitudinal connecting bars. The outer side of the guide tube is provided with a plurality of longitudinal steel bars along the axial direction of the tunnel, and a plurality of circumferential steel bars are provided along the circumferential direction of the tunnel, and the intersection points of the longitudinal steel bars and the circumferential steel bars are tied together.

8. A construction method for a tunnel portal arch support structure according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step 1: clean the topsoil and dangerous rocks at the tunnel entrance, dig the sleeve arch annular groove, and continue to dig downward at the end of the sleeve arch annular groove to the top elevation of the concrete cast-in-place pile; Step 2: Locate the position of the concrete pile, determine the position of the concrete pile, build the drilling platform, bury the casing, and put the drilling rig in place; Step 3: Set up a mud pool at the pile hole location. Drill dry first to strengthen the hole protection and hole fixing effect. Drilling will start after the slurry in the pile hole meets the design requirements. Step 4: When the drilling hole reaches the predetermined depth, the drill bit is lifted by 0.3m to 0.5m, and the hole is cleaned by the slurry replacement method. After the hole is cleaned, the quality of the pile hole and the thickness of the sedimentation layer are comprehensively inspected; Step 5: Slowly lower the steel cage of the concrete pile into the pile hole and fix it; Step 6: Pour concrete into the pile hole to form a concrete pile, and then remove the casing; Step 7: After the concrete pile reaches a certain strength, the sleeve arch is formed in the sleeve arch annular groove, and the drilling and grouting construction of the advance pipe shed is completed.

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