Tunnel portal cover arch supporting structure

Abstract

The utility model discloses a tunnel portal cover arch supporting structure which comprises a cover arch installed on a tunnel portal section, the two ends of the cover arch are located on cast-in-place concrete piles, the cast-in-place concrete piles are vertically arranged in a side slope of the tunnel portal section, a plurality of main reinforcements are arranged in the cast-in-place concrete piles in the axial direction, and the main reinforcements are arranged in the tunnel portal section. And the main reinforcement extends out of the cast-in-place concrete pile and extends into the cover arch to be connected with the cover arch. According to the utility model, not only is the installation stability of the cover arch ensured, but also the excavation depth of the annular groove of the cover arch is reduced, so that the excavation height of a tunnel portal section side slope and an upward slope is reduced, the excavation and support engineering amount of the portal section is reduced, and meanwhile, the arrangement of the cast-in-place concrete piles also provides certain support for a slope toe.

Description

Technical Field

[0001] This utility model relates to tunnel engineering, specifically to a tunnel entrance arch support structure. Background Technology

[0002] In underground engineering, tunnel construction environments are complex. The portal section, a crucial link and key process in tunnel construction, typically traverses severely weathered and unstable mountain overburden layers. Due to the influence of geological structure and weathering, slope instability and collapse are common. To ensure the safety and stability of the portal section, pre-support measures such as pipe roofs are usually implemented before entering the tunnel. The arch support, a vital structure located at the starting point of the pipe roof, serves a fixing or supporting function. Its construction sequence includes: clearing the portal section → excavating the annular trench for the arch support → constructing the arch support foundation → installing the inner arch frame → positioning and fixing the orifice pipes → installing the formwork → pouring the arch support concrete → curing and formwork removal. Only after the arch support concrete reaches a certain strength can it provide the necessary support for the construction of the portal section.

[0003] However, in actual engineering projects, tunnel portal sections are often constrained by objective factors, such as poor geological conditions and the need to cross existing highways and railways. In such cases, if conventional construction methods are followed, placing the arch support on stable bedrock would inevitably result in a large amount of excavation and support work on the portal slopes. Inadequate protection could lead to slope instability and collapse. Furthermore, the existing highways and railways above the portal may restrict the excavation of the slopes. Therefore, it is necessary to design a tunnel portal arch support structure to address these problems. Utility Model Content

[0004] The technical problem to be solved by this utility model is that, for some tunnel entrances where it is not suitable to directly install the arch on the bedrock, this utility model provides a tunnel entrance arch support structure that can not only achieve stable installation of the arch but also reduce the amount of excavation and support work on the slope of the tunnel entrance.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A tunnel portal arch support structure includes an arch installed at the tunnel portal section. The structure is characterized in that: both ends of the arch rest 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 multiple main reinforcement bars are arranged axially inside the concrete cast-in-place piles. The main reinforcement bars extend out of the concrete cast-in-place piles and extend into the arch to connect with the arch.

[0007] This invention places the arch on a concrete pile, with the lower part of the concrete pile extending into the bedrock of the tunnel entrance slope. This avoids the traditional method of placing the arch on the bedrock, ensuring the stability of the arch installation, reducing the excavation depth of the arch annular groove, and thus reducing the excavation height of the tunnel entrance slope, reducing the amount of excavation and support work at the entrance. At the same time, the concrete pile provides some support for the slope toe.

[0008] Preferably, the inner cavity of the arch is provided with several guide pipes along the tunnel axis. The guide pipes are mainly used to fix and control the steel perforated pipes. Before the pipe roof construction, the arch is constructed first, and the guide pipes are fixed inside the arch. When installing the guide pipes, allowance should be made for the upper platform and the elevation angle of the steel perforated pipes should be controlled to ensure the correct orientation of the pipe orifices. The steel perforated pipes are arranged in a ring and form a shell structure around the tunnel arch contour, effectively supporting the surrounding rock above. In addition, the steel perforated pipes can be used for grouting; the grout is injected into the fissures of the surrounding rock through the pipe wall holes, consolidating the rock mass and enhancing its bearing capacity.

[0009] Preferably, the inner side of the guide tube is provided with several segmented and spliced ​​I-beams along the circumferential direction, and the adjacent I-beams are connected by longitudinal connecting bars. The outer side of the guide tube is provided with several longitudinal reinforcing bars along the tunnel axis and several circumferential reinforcing bars along the tunnel circumferential direction. The intersections of the longitudinal reinforcing bars and the circumferential reinforcing bars are tied together.

[0010] Preferably, the arch is a cast-in-place concrete structure with a concrete strength grade of C25 and a concrete mix design of grade 2.

[0011] Preferably, the concrete pile is a reinforced concrete structure with a steel reinforcement cage inside.

[0012] Preferably, the concrete pile is a cast-in-place concrete structure with a concrete strength grade of C30 and a concrete mix design of grade 2.

[0013] Preferably, the reinforcing cage includes several vertically arranged main reinforcing bars distributed in a ring, spiral reinforcing bars sleeved around the main reinforcing bars, and stirrups distributed within the ring formed by the main reinforcing bars. The main reinforcing bars and spiral reinforcing bars are welded together, and the spiral reinforcing bars and stirrups are welded together. Because the spiral reinforcing bars are circular and have a small diameter, making them easily deformable, the stirrups are distributed within the ring formed by the spiral reinforcing bars and main reinforcing bars to support the spiral reinforcing bars, thus making the reinforcing cage structure more stable.

[0014] Preferably, the bottom of the main reinforcing bars of the steel cage is bent inward to facilitate the cutting of the steel cage.

[0015] Preferably, positioning bars are evenly arranged around the perimeter of the reinforcing cage, and the positioning bars are welded integrally with the main reinforcing bars. The positioning bars facilitate the positioning of the reinforcing cage within the pile hole.

[0016] Preferably, a plurality of reinforcing ribs are arranged axially on the reinforcing cage, and the reinforcing ribs are welded to the main reinforcing bars. The addition of reinforcing ribs can improve the strength and stability of the reinforcing cage.

[0017] Compared with the prior art, the beneficial effects of this utility model are:

[0018] 1) This utility model places the arch on a concrete pile, and the lower part of the concrete pile extends into the bedrock of the tunnel entrance slope, thus avoiding the traditional method of placing the arch on the bedrock. This not only ensures the stability of the arch installation, but also reduces the excavation depth of the arch annular groove, thereby reducing the excavation height of the tunnel entrance slope. At the same time, the concrete pile provides certain support for the slope toe.

[0019] 2) This utility model overcomes the problem that the tunnel portal section needs to be equipped with a sleeve arch, but there are limiting factors that do not meet the conditions for side slope excavation. It reduces the amount of excavation and support work in the portal section, and the construction technology is simple and reliable, with certain economic benefits. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a plan view of the arch-shaped and concrete-filled pile of this utility model.

[0022] Figure 2 It is an elevation view of the arch and the concrete cast-in-place pile.

[0023] Figure 3 It is a set of longitudinal section diagrams of the arch.

[0024] Figure 4 This is a diagram showing the distribution of reinforcing steel bars inside the arch.

[0025] Figure 5 This is a front view of the steel reinforcement distribution inside a cast-in-place concrete pile.

[0026] Figure 6 This is a top view of the steel reinforcement distribution in a cast-in-place concrete pile.

[0027] Figure 7 This is a diagram showing the state of the tunnel entrance section before construction.

[0028] In the diagram: 1-Concrete pile, 2-Arch, 3-Tunnel entrance section, 4-Guide pipe, 5-Steel pipe, 6-I-beam, 7-Reinforcing bar, 8-Main reinforcement, 9-Helical reinforcement, 10-Positioning reinforcement, 11-Strengthening reinforcement, 12-Stirrup, 13-Sonic logging pipe. Detailed Implementation

[0029] The present invention will be further described below with reference to specific preferred embodiments, but this does not limit the scope of protection of the present invention.

[0030] In the description of this utility model, it should be noted that the terms "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings and are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0032] Please see Figure 1 - Figure 6 An embodiment of the tunnel entrance arch support structure of this utility model includes an arch 2 installed on the tunnel entrance section 3. The two ends of the arch 2 are located on concrete piles 1, and the lower part of the concrete piles 1 extends into the bedrock of the slope of the tunnel entrance section 3.

[0033] In this embodiment, the arch 2 is a cast-in-place concrete structure with a concrete strength grade of C25 and a two-stage concrete mix. Several guide pipes 4 are installed inside the arch 2 along the tunnel axis, and steel perforated pipes 5 are arranged inside the guide pipes 4. On the inner side of the arch 2, i.e., the inner side of the guide pipes 4, several segmented and spliced ​​I-beams 6 are installed along the tunnel circumferential direction. Adjacent I-beams 6 are connected by longitudinal connecting bars (not shown in the figure). On the outer side of the guide pipes 4 inside the arch 2, several longitudinal reinforcing bars are installed along the tunnel axis, and several circumferential reinforcing bars are installed along the tunnel circumferential direction. The intersections of the longitudinal and circumferential reinforcing bars are tied together with lead wire (here, the longitudinal and circumferential reinforcing bars are uniformly represented by the designation 7).

[0034] In this embodiment, the concrete pile 1 is a cast-in-place concrete structure with a concrete strength grade of C30 and a two-stage concrete mix. A reinforcing cage is installed inside the concrete pile 1. The reinforcing cage includes several vertically arranged main bars 8, spiral bars 9 sleeved around the main bars 8, and stirrups 12 arranged in an equilateral triangle inside each main bar 8. The main bars 8 are spliced ​​from multiple steel bars using mechanical joints. Each main bar 8 is arranged in a ring and welded to the spiral bars 9. The stirrups 12 are welded to the spiral bars 9 to support them. The upper part of each main bar 8 extends out of the concrete pile 1 and into the arch 2, where it is fixedly connected. Positioning bars 10 are evenly arranged around the reinforcing cage and welded to the main bars 8. Reinforcing bars 11 are arranged axially every two meters along the reinforcing cage and welded to the main bars 8.

[0035] To facilitate the cutting of the steel cage, the main reinforcement bars 8 at the bottom of the steel cage are bent inward.

[0036] The construction method for the tunnel portal arch support structure as described above includes the following steps:

[0037] Step 1: Clear the topsoil and unstable rocks at the tunnel entrance, excavate the arch-shaped groove, and excavate downwards at the end of the arch-shaped groove to the top elevation of the concrete pile 1.

[0038] Step 2: Pile location layout, determine the location of concrete cast-in-place pile 1, construct the drilling rig platform, install the casing, and position the drilling rig;

[0039] Step 3: Set up a mud pit at the pile hole location. At the beginning of drilling, perform empty drilling first to strengthen the wall protection and hole consolidation effect at the hole opening. After the mud in the hole reaches the design requirements, start drilling.

[0040] Step 4: When the borehole reaches the predetermined depth, the drill bit can be raised by 0.3m to 0.5m, and the hole can be cleaned by changing the slurry. After the hole is cleaned, a comprehensive inspection of the hole formation quality and the thickness of the sediment layer should be carried out.

[0041] Step 5: Weld the reinforcing cage at the borehole opening and slowly lower it into the borehole for fixation;

[0042] Step 6: Pour concrete into the hole and then pull out the casing;

[0043] Step 7: After the concrete pile 1 reaches a certain strength, install and fix the I-beam 6 inside the arch 2 in the annular groove of the arch, and weld the I-beam 6 together into a whole using longitudinal connecting bars, locate the position of the guide pipe 4 and complete its welding reinforcement.

[0044] Step 8: Construct the inner and outer formwork and end plates of arch 2, pour concrete for arch 2, and complete the drilling and grouting construction of the advanced pipe roof.

[0045] Application examples

[0046] 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 highway and railway tunnels, except that highway and railway tunnels carry cars and trains, while long rubber tunnels carry conveyor belts for transporting goods). Long rubber tunnel No. 1 is responsible for transporting materials from the Dawantou Wharf to the downstream warehousing and transfer center. Long rubber tunnel No. 2 is responsible for transporting materials from the original Taiping storage yard to the Xiangjiaba long rubber transport line transfer point 7 tunnel to the downstream warehousing and transfer center. Long rubber tunnel No. 2 runs independently for 1.2km before merging with long rubber tunnel No. 1 and sharing the tunnel until the tunnel exit.

[0047] Based on the site selection and overall technological layout of the Dawantou Wharf, the entrance to the No. 1 Changjiao Tunnel—located on the bank of the Xiangjiaba Reservoir on the Jinsha River—is situated in a low mountain valley topography characterized by tectonic erosion and denudation. The entrance section is a sloping section with well-developed steep slopes and cliffs, with elevations ranging from 380m to 787m. The Shuisui Class II Highway passes through the slope at an elevation of 440m. The tunnel entrance below the highway is located on a small ridge with a natural slope angle of 45° to 60°, exhibiting a significant gradient and localized minor landslides. The upper part of the highway is a steep slope with natural slope angles exceeding 75°, and the cliffs are nearly vertical, with some areas exhibiting reverse slopes. The mountain is imposing and majestic, resembling a sheer cliff. The bedrock of the steep cliffs and embankments is well exposed, but due to joint fissures and weathering, unstable rock masses are developed. Visible evidence of rockfalls has damaged the highway guardrails, resulting in severe damage. Only areas near the highway are protected with active protective netting, shotcrete, and cable anchors. In some sections, the highway was formed by backfilling the roadbed with retaining walls. The current slope environment at the tunnel entrance section consists of exposed bedrock, with a surface layer of strongly weathered mudstone and a middle to lower layer of moderately weathered mudstone, interspersed with small amounts of sandstone and sandy mudstone. Affected by faulting and weathering, the surface rock mass is fractured to relatively fractured, exhibiting a layered to fragmented structure. Small landslides are well-developed in the shallow surface layer, and the slope in the landslide area is unstable. The overall slope is stable, but the strongly weathered layer is highly susceptible to circular arc sliding failure. The surrounding rock is soft rock with well-developed joints and fissures. The rock mass is relatively fractured to fragmented. Within the fault-affected area, the rock mass exhibits a fragmented to loose structure, while outside the affected area, it has a layered structure, classifying it as Class V surrounding rock, with an affected depth greater than 40m.

[0048] Before construction at the tunnel entrance, vegetation and loose rocks outside the excavation line should be cleared. During construction, temporary monitoring should be strengthened, attention should be paid to the rock conditions of the upper slope, and hazard sources should be investigated and cleared. Safety precautions and management for slope construction should be strengthened. Depending on the disturbance caused by construction at the entrance, shotcrete and anchor support or combined with slope system support should be used to reinforce the upper slope.

[0049] First, construct four concrete piles (1.0m in diameter and 14.0m in length) at both ends of the arch 2. (Please refer to...) Figure 1 The centerline spacing of the piles along the tunnel axis is 3.6m, the concrete strength grade of the pile body is C30, and the concrete mix is ​​grade II. Figure 5 , Figure 6 As shown, the reinforcing cage contains five types of reinforcing bars: ① Main bars 8 are 20C28 in size and are connected in sections using mechanical joints. The main bars 8 are arranged in a ring, with their upper ends inserted 0.95m into the arch 2; ② Reinforcing bars 11 are C22@2000 in size and are installed every 2.0m along the axial direction of the reinforcing cage inside. The lap joints are double-sided welded and spot-welded to the main bars 8; ③ Spiral bars 9 are A10@100 in size and are distributed around the main bars 8, welded to them as a single unit; ④ Stirrups 12... The specifications are C22@2000, and they are distributed in an equilateral triangle on the inner side of the ring formed by the main reinforcement 8 to support the spiral reinforcement 9 and make the steel cage structure stable; ⑤ Four positioning reinforcements 10 are arranged in each section, evenly distributed around the reinforcing reinforcement 11, and welded together with 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; Each pile is equipped with three sonic logging tubes 13, which are steel pipes with an outer diameter of 50mm and a wall thickness of 1.2mm. They are tied to the stirrups 12 and distributed in an equilateral triangle. The sonic logging tubes 13 need to protrude 30cm from the top of the pile for ultrasonic testing of the pile.

[0050] After the concrete pile 1 reaches a certain strength, the arch 2 will be constructed. The arch 2 is 0.8m thick and 2.0m long along the tunnel axis. The concrete strength grade is C25, and the concrete mix is ​​grade II. Four I18 H-beams 6 are installed inside the arch 2, spaced 0.6m apart. They are securely welded to the H-beams 6 using longitudinal connecting bars C22@1000. Each H-beam 6 is divided into 5 sections. A φ140×4.5mm guide pipe 4 is fixed inside the arch 2. When installing the guide pipe 4, allowance should be made for the upper platform and the elevation angle of the steel pipe should be controlled to ensure the correct borehole orientation. The pipe shed is constructed using φ108×4.5mm hot-rolled seamless steel perforated pipes (5 sections). The sections of the steel perforated pipes are 3.0m and 6.0m long, with a circumferential spacing of 0.4m and an elevation angle of 1°–3°. Construction tolerances include: the front end of the pipe shed should not exceed 0.2m; the number of joints within the same longitudinal cross-section should not exceed 50%; and joints of adjacent steel perforated pipes must be staggered by at least 1.0m. The total length of the pipe shed is tentatively set at 30.0m based on geological conditions, and construction will be controlled according to the crossing of the Shui-Sui Class II highway above. The pipe shed will be constructed using the drilling method. During drilling, the drill rod axis must be strictly controlled, the scaffolding must be reliably erected, and the drilling rig must be firmly fixed. During drilling, a slant gauge should be used to measure the drilling deviation; if the deviation exceeds the design requirements, it should be corrected promptly. The pipe roof uses threaded connections, with each thread being 15cm long. To stagger the steel pipe joints, the first section of pipe at odd-numbered holes is 3.0m long, the first section at even-numbered holes is 6.0m long, and subsequent sections are all 6.0m long. Grouting of the pipe roof is designed according to the soil and rock mass within a limited area surrounding the pipe roof, with a grout diffusion radius of not less than 0.7δ (δ being the center-to-center distance between two adjacent steel pipes). Grouting is performed in sections; the pipe roof construction is carried out in sections with intervals. Odd-numbered holes are drilled first, and even-numbered holes are constructed after grouting is completed, to check the grouting effect at the odd-numbered holes. The grouting pressure and water-cement ratio should be determined comprehensively through testing based on the rock fracture condition and grout diffusion. After the pipe roof grouting is completed and reaches 75% of the design strength, excavation is carried out under the support of the pipe roof. Immediately after excavation, shotcrete is applied, anchor bolts are installed, wire mesh is hung, steel arches are erected, and then shotcrete is applied to the design thickness.

[0051] The above description is merely a specific embodiment of this utility model, but the protection scope of this utility model is not limited thereto. Any person skilled in the art can make many possible variations and modifications to the technical solution of this utility model, or modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of this utility model. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this utility model without departing from the content of the technical solution of this utility model should fall within the protection scope of the technical solution of this utility model.

Claims

1. A tunnel portal arch support structure, comprising an arch installed at the tunnel portal section, characterized in that: The two ends of the arch are resting on concrete piles. The lower part of the concrete piles extends into the bedrock of the tunnel entrance slope. Multiple main reinforcement bars are arranged axially inside the concrete piles. The main reinforcement bars extend out of the concrete piles and into the arch to connect with the arch.

2. The tunnel entrance arch support structure according to claim 1, characterized in that, The interior of the arch is equipped with several guide pipes along the tunnel axis.

3. The tunnel entrance arch support structure according to claim 2, characterized in that, The inner side of the guide tube is provided with several segmented and spliced ​​I-beams along the circumferential direction. Adjacent I-beams are connected by longitudinal connecting bars. The outer side of the guide tube is provided with several longitudinal reinforcing bars along the tunnel axis and several circumferential reinforcing bars along the tunnel circumferential direction. The intersections of the longitudinal reinforcing bars and the circumferential reinforcing bars are tied together.

4. The tunnel entrance arch support structure according to claim 1, characterized in that, The arch is a cast-in-place concrete structure with a concrete strength grade of C25 and a two-stage concrete mix design.

5. The tunnel entrance arch support structure according to claim 1, characterized in that, The concrete pile is a reinforced concrete structure with a steel reinforcement cage inside.

6. The tunnel entrance arch support structure according to claim 5, characterized in that, The concrete pile is a cast-in-place concrete structure with a concrete strength grade of C30 and a concrete mix design of grade 2.

7. The tunnel entrance arch support structure according to claim 5, characterized in that, The steel cage includes several vertically arranged main bars distributed in a ring, spiral bars sleeved around the main bars, and stirrups distributed within the ring formed by the main bars. The main bars and the spiral bars are welded together, and the spiral bars and the stirrups are welded together.

8. The tunnel entrance arch support structure according to claim 7, characterized in that, The main reinforcement bars of the steel cage are bent inward at the bottom.

9. The tunnel entrance arch support structure according to claim 7, characterized in that, Positioning bars are evenly arranged around the perimeter of the steel cage, and the positioning bars are welded to the main bars as a whole.

10. The tunnel entrance arch support structure according to claim 7, characterized in that, The steel cage is provided with several reinforcing bars along the axial direction, and the reinforcing bars are welded to the main reinforcing bars.

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