Mountainous region existing tunnel portal extension section structure and systematic construction method thereof

Abstract

The application discloses a mountainous area existing tunnel portal extension section structure and a systematic construction method thereof, and belongs to the technical field of tunnel engineering. The structure is a reinforced concrete open tunnel structure extending outward from an original tunnel portal, and forms a "pile-pier-lining" collaborative stress system. The structure comprises a deep anchoring system, an inclined anchor pile group being arranged at an unstable slope or a key foundation position on a mountain side; a gravity type bearing pier, a reinforced concrete gravity pier being arranged at a key point on the bottom of the extension section, and being used as a vertical main bearing and anti-sliding component of the open tunnel structure; and an open tunnel lining body, an arch-shaped lining being poured by using reinforced concrete and being used as a direct protection and bearing structure, and a "non-woven fabric+EVA waterproof board" composite waterproof layer being laid on the outside of the whole section. The application realizes integrated and long-acting treatment of geological disasters of a high and steep slope of a tunnel portal, significantly improves the stability and operation safety of the portal area, and is suitable for treatment of geological disasters of different scales and different geological conditions of the mountainous area existing tunnel portal.

Description

Technical Field

[0001] This invention belongs to the field of tunnel engineering disaster prevention and mitigation and slope protection technology. Specifically, it relates to a structural extension section system and its integrated construction method for the treatment of geological disasters on steep slopes at the entrance of existing tunnels in mountainous areas. It is applicable to the comprehensive treatment of geological disasters such as slope instability, rockfall, and water seepage at the entrance of existing tunnels in mountainous highways and railways. Background Technology

[0002] In mountain tunnel engineering, existing tunnel entrances are often threatened with operational safety by geological hazards such as steep slope instability, rock weathering, groundwater erosion, and rockfalls. Traditional remediation methods are mostly decentralized. ① In terms of slope protection: commonly used methods include wire mesh spraying and anchoring, retaining walls or anti-slide piles; these measures are mostly applied to the slope surface or toe, failing to form an integral load-bearing system with the tunnel entrance structure, and have limited reinforcement of the deep slope. ② Regarding the reinforcement of the opening: local lining reinforcement or the addition of arches are often used; however, the structural extension length is insufficient, making it difficult to effectively share the mountain's bias pressure, and the joint between the old and new structures is prone to becoming a weak point in waterproofing. ③ In terms of waterproofing and drainage: drainage ditches are often set up separately or local grouting is performed, without forming an integrated waterproofing and drainage system with the support structure. The long-term effect is easily affected by siltation or structural deformation.

[0003] Existing technologies suffer from problems such as fragmented treatment measures, poor structural coordination, and insufficient durability. In particular, for tunnels that are still in operation, construction safety risks are high and traffic disruptions are significant. There is a lack of a comprehensive, low-interference treatment solution that integrates structural extension, deep reinforcement, and systemic waterproofing and drainage. Summary of the Invention

[0004] This invention aims to provide a structure for the extension of an existing tunnel portal that integrates "structural extension, active deep support, integrated drainage and buffer protection" and its systematic construction method. This will solve the problems of poor structural coordination, large construction interference, unsystematic treatment, and insufficient long-term reliability of traditional treatment methods, and achieve integrated and long-term treatment of geological hazards on steep slopes at tunnel portals, significantly improving the stability and operational safety of the portal area.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A structure for extending the entrance of an existing tunnel in mountainous areas is a reinforced concrete open-cut tunnel structure extending outward from the original tunnel entrance, forming a "pile-pier-lining" collaborative load-bearing system; including: Deep anchoring system: On unstable slopes or key foundation locations on the mountainside, inclined anchor pile groups are installed; Gravity-type load-bearing piers: Reinforced concrete gravity piers are set at key points at the bottom of the extended section to serve as the main vertical load-bearing and anti-slip components of the open-cut tunnel structure; The tunnel lining body: The arched lining is made of reinforced concrete as the direct protection and load-bearing structure, and the outer side is covered with a composite waterproof layer of "non-woven fabric + EVA waterproof board".

[0006] In some embodiments, in a deep anchoring system, the anchor piles are made of high-strength steel bars that are inserted into the stable rock mass at a certain angle and formed into a composite anchor body through pressure grouting.

[0007] In some embodiments, the foundation of the gravity bearing pier is situated on a calculated stable foundation.

[0008] In some embodiments, it also includes a buffer backfill system: forming a multi-level buffer and drainage barrier in the vaulted ceiling of the tunnel.

[0009] In some embodiments, the multi-level buffer and drainage barrier consists of a gravel drainage layer, a clay waterproofing layer, a soil-rock buffer layer, and a concrete protective layer that are sequentially backfilled on the arch of the tunnel.

[0010] In some embodiments, the method further includes: cutting a groove at the center of the end of the lining of the existing opening (the connection point between the old and new structures) and pre-embedding a steel-edged rubber waterstop.

[0011] In some embodiments, the system further includes: a post-installed anchor rod in the groove at the end of the lining; the post-installed anchor rod is connected to the newly added lining reinforcement to achieve a reliable transition in terms of both load-bearing capacity and waterproofing.

[0012] In some embodiments, the system also includes an integrated drainage system: flexible permeable pipes or perforated corrugated pipes are laid circumferentially behind the lining, and drainage pipes are installed longitudinally to direct water to the tunnel's existing drainage system.

[0013] In some embodiments, the method further includes slope toe and foundation protection: the slope toe of the outer side of the extension section is reinforced with slope protection, and small retaining walls are installed if necessary to prevent rainwater from eroding the foundation.

[0014] In some embodiments, the "non-woven fabric + EVA waterproof membrane" composite waterproof layer includes: Back-adhesive waterstop: It is installed close to the outside of the EVA waterproof membrane to form the first seal on the outside of the joint; EVA waterproof membrane and non-woven fabric: continuously laid across construction joints, and connected to the back-adhesive waterstop at the joints by hot-melt welding to form a whole.

[0015] A systematic construction method for the extension section structure of an existing tunnel portal in mountainous areas includes the following steps: S1. Survey and Dynamic Design Stage: Dynamically adjust the extension length and anchor pile layout parameters according to the actual situation; S2. Sectional and sequential excavation and temporary support: Excavation is carried out in layers and sections using a combination of mechanical and manual methods, with timely support. S3. Anchor pile construction: Drill holes according to the designed hole positions and angles, clean the holes, install the steel reinforcement bundles and perform pressure grouting; S4. Foundation treatment and gravity pier construction: Clean the foundation and construct the gravity pier foundation and pier body after it is qualified; S5. Construction of the main structure of the tunnel; S6. Construction of drainage and waterproofing system; S7. Buffer layer backfilling and greening; S8. Traffic organization during construction: Develop a special traffic management plan to minimize interference with tunnel operation.

[0016] Compared with the prior art, the present invention provides a structure for the extension section of the entrance of an existing tunnel in a mountainous area and its systematic construction method, which has the following beneficial effects.

[0017] This invention enables integrated and long-term management of geological hazards on steep slopes at tunnel entrances, significantly improving the stability and operational safety of the tunnel entrance area.

[0018] The system of this invention provides long-lasting treatment: through the integrated structure of "pile-pier-lining-buffer", it achieves coordinated reinforcement and protection of deep, shallow and opening slopes, significantly improving overall stability and providing lasting treatment results.

[0019] This invention minimizes construction safety disruptions: it employs dynamic design and information-based construction, enabling timely responses to geological changes; and its refined traffic organization scheme minimizes the impact of construction on tunnel operation.

[0020] This invention ensures reliable quality control: it clarifies the quality control standards and testing methods for key processes such as non-destructive testing of anchor piles, airtightness testing of waterproof layers, and connection between new and old structures, thus guaranteeing project quality.

[0021] This invention has a wide range of applications: the system and method can flexibly adjust parameters and are applicable to the management of geological disasters at the entrances of existing tunnels in mountainous areas of different scales and geological conditions, and have high value for promotion and application.

[0022] Other advantages, objectives and features of the invention will be set forth in part in the description which follows; and in part will be apparent to those skilled in the art upon examination of the following description; or may be learned from practice of the invention. Attached Figure Description

[0023] Figure 1 This is an intentional longitudinal section of the import.

[0024] Figure 2 This is a schematic diagram of the construction joint.

[0025] Figure 3 for Figure 1 Detailed view of point A in the middle.

[0026] Figure 4 This is a diagram of the excavation and support for the open-cut tunnel entrance.

[0027] Figure 5 for Figure 4 Detailed view of point C.

[0028] Figure 6 This is a cross-sectional view of the open-cut tunnel entrance.

[0029] Figure 7 This is a detailed drawing of the anchorage at the outer end of the anchor pile. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0031] Reference Figure 1-7 A structure for extending the entrance of an existing tunnel in mountainous areas forms a multi-layered collaborative protection system from the outside to the inside and from the deep to the shallow. The extension section is a reinforced concrete open-cut structure extending outward from the original tunnel entrance, and its core is to form a collaborative force-bearing system of "piles-piers-lining".

[0032] Mainly includes: 1) Deep Anchoring System: An inclined anchor pile group is installed on unstable slopes or key foundation locations on the mountainside. The anchor piles use high-strength steel bar bundles (e.g., 3Φ25) inserted into the stable rock mass at a certain angle (e.g., 60°) to a certain depth (e.g., ≥6m). A composite anchor body is formed through pressure grouting (e.g., M30 cement mortar, final pressure ≥0.2MPa). 2) Gravity bearing piers: Reinforced concrete gravity piers are set at key points at the bottom of the extension section. Their foundations must be located on a stable foundation that has been verified (bearing capacity ≥800kPa) to serve as the main vertical load-bearing and anti-slip components of the open-cut tunnel structure. 3) Open-cut tunnel lining body: Before the construction of the open-cut tunnel lining, a groove about 15cm deep is cut in the center of the existing tunnel lining, and a steel-edged rubber waterstop is pre-embedded; an arched lining made of reinforced concrete (such as C25) is used as the direct protection and load-bearing structure; a composite waterproof layer of "non-woven fabric + EVA waterproof board" is laid on the entire outer section. 4) Buffer backfill system: The arch of the tunnel is backfilled in sequence with a crushed stone drainage layer, a clay waterproof layer, a soil-rock buffer layer and a concrete protective layer to form a multi-level buffer and drainage barrier.

[0033] Among these, attention should be paid to key nodes and integrated systems.

[0034] ① Connection node between old and new structure: Grooves are cut at the end of the existing opening lining, steel-edged rubber waterstops are pre-embedded, and the new lining steel bars are connected by post-installed anchor rods to achieve a reliable transition in terms of both load-bearing capacity and waterproofing.

[0035] ② Integrated drainage system: Flexible permeable pipes or perforated corrugated pipes are laid circumferentially behind the lining, and drainage pipes are installed longitudinally to direct water to the tunnel's existing drainage system. The overlaps of the waterproof membrane are hot-melt welded and airtightness is tested.

[0036] ③ Slope toe and foundation protection: The slope toe of the outer side of the extended section is reinforced and protected. If necessary, a small retaining wall is set up to prevent rainwater from eroding the foundation.

[0037] It is important to note that geophysical non-destructive testing should be used to randomly check the length of the anchor piles and the grout saturation.

[0038] The main construction steps of the tunnel include: ① excavating the soil and rock mass on both sides of the road curb to the foundation depth; ② constructing anchor piles (3Φ25, L=900cm, @200x200cm) at the outer foundation, with the main reinforcement extending 35 times the diameter of the steel bar into the foundation (see...). Figure 7 ); ③ Construct the main structure of the tunnel and implement waterproofing and drainage measures; ④ Backfill the tunnel roof with soil and rock as a buffer layer; ⑤ Construct drainage ditches and maintenance passages inside the tunnel.

[0039] A systematic construction method for the extension section of an existing tunnel portal in mountainous areas is proposed, following the principles of "dynamic design, information-based construction, and low-interference operation"; the specific steps are as follows.

[0040] S1. Exploration and Dynamic Design Stage: Conduct a detailed investigation of the slope geology and existing structural conditions, and dynamically adjust the extension length and anchor pile layout parameters according to the actual situation (such as the geology revealed during excavation).

[0041] S2. Segmented and sequential excavation and temporary support: Excavation is carried out in layers and sections using a combination of mechanical and manual methods. Temporary support (such as shotcrete) is applied in a timely manner after each layer is excavated, and slope deformation is monitored in real time.

[0042] S3. Anchor pile construction: Drill holes according to the designed hole positions and angles, clean the holes, install the steel reinforcement bundles and pressure grout; use geophysical non-destructive testing (such as sonic method) to conduct random checks on the pile length and grout saturation (the proportion shall not be less than 3%-5%).

[0043] S4. Foundation treatment and gravity pier construction: Clean the foundation to the design requirements, and construct the gravity pier foundation and pier body after the excavation site passes inspection.

[0044] S5. Construction of the main structure of the tunnel: tying reinforcing bars and erecting formwork. Key procedures: slotting at the original opening, installing waterstops and connecting the old and new reinforcing bars; pouring concrete in layers, vibrating thoroughly, and curing to the specified strength.

[0045] S6. Construction of waterproofing and drainage system: Lay non-woven fabric and EVA waterproof board, install ring and longitudinal drainage pipes, and seal all joints.

[0046] The construction joint adopts a composite structure combining "external application + central embedding" double waterproofing with steel reinforcement connection: ① External waterproof layer Back-adhesive waterstop: It is installed close to the outside of the EVA waterproof membrane, with a specification of 300mm×4mm, and is made of rubber or plastic. It is used to form the first seal on the outside of the joint. EVA waterproof membrane and non-woven fabric: continuously laid across construction joints, and connected to the back-adhesive waterstop at the joints by hot-melt welding to form a whole.

[0047] ②Inner seam waterproofing strip Steel-edged rubber waterstop: Pre-embedded in concrete, located in the middle of the construction joint section, with a specification of 300mm×6mm; steel strips on both sides reinforce the anchorage, and the rubber body provides elastic sealing.

[0048] ③ Concrete interface treatment The surface of the first-poured concrete should be roughened to expose fresh aggregate, and moistened but without standing water before pouring. The subsequent-poured concrete should be of the same strength grade (e.g., C25), and a micro-expansion agent can be added to reduce shrinkage.

[0049] ④ Reinforcing bar connection The main reinforcement bars of the lining on both sides of the construction joint are connected by reserved joints or mechanical connections (such as welding) to ensure continuous stress; positioning components such as steel bar clips are set to ensure that the steel edge waterstop is accurately positioned and does not shift.

[0050] ⑤ External protective layer After backfilling to the junction of soil and rock, a 7cm thick C20 fine stone concrete protective layer is constructed to prevent the backfill soil and rock from damaging the waterproof layer.

[0051] S7) Buffer layer backfilling and greening: Backfill various materials in layers according to the design sequence, compact with small machinery, and finally restore the top greening.

[0052] S8) Traffic organization during construction period: Develop a special traffic management plan and adopt measures such as setting up warning signs, arranging traffic assistants, and allowing single-lane traffic in different time periods to minimize interference with tunnel operation.

[0053] Taking a geological disaster remediation project along a certain dedicated highway as an example, the original tunnel entrance slope was at risk of cracking and spalling; the method of this invention is adopted: ① Design: Extend the tunnel by 15 meters and install 18 anchor piles (3Φ25, 60° downward angle) with a length of 9 meters. The gravity pier foundation is required to have a bearing capacity of ≥800kPa. ② Construction: Construction shall proceed according to the steps outlined above. All anchor piles passed acoustic testing after grouting; no leakage was observed at the joints between the old and new structures after a water pressure test; during construction, single-lane traffic management was implemented to maintain tunnel capacity at over 85%. ③Results: After the project was completed, it withstood the test of a rainy season. The slope remained stable, and there was no water seepage or falling rocks at the opening. Monitoring data showed that the structural deformation was within the allowable range, and the safety hazards were completely eliminated.

[0054] The following should be noted: ① The location and spacing of the anchor piles can be adjusted appropriately according to the actual site conditions; ② The grouting material is cement mortar with a cement-sand ratio of 0.5~1 and a water-cement ratio of 0.38~0.54, and the grouting end pressure is 0.2MPa; ③ The cement mortar must be fully filled and compacted. Geophysical non-destructive testing is required to check the length of the anchor piles and the mortar saturation. The sampling rate shall not be less than 3% to 5% of the total number of anchor piles. ④ The orifice is sealed with asphalt-impregnated hemp fiber and cement mortar, with a minimum sealing length of 0.6m. When sealing the orifice, a 1.0~1.5m long Φ25 steel pipe is buried as a return grout pipe during grouting. ⑤ The length of the anchor pile is 9m, and the anchor pile must penetrate into the relatively intact rock mass for no less than 6m; ⑥ The borehole inclination of the anchor pile should be maintained at a 60° downward angle to the horizontal, and the deviation of the bottom of the hole should not exceed 3%; ⑦ When the grouting volume is large, measures such as injecting thick grout or intermittent grouting should be adopted to solve the problem.

[0055] This invention achieves integrated and long-term management of geological hazards on steep slopes at tunnel entrances, significantly improving the stability and operational safety of the tunnel entrance area; compared with existing technologies, it has at least the following significant effects: The treatment system has a long-lasting effect: Through the integrated structure of "pile-pier-lining-buffer", it achieves coordinated reinforcement and protection of deep, shallow and opening slopes, significantly improves overall stability and has a lasting effect. Minimal disruption to construction safety: The use of dynamic design and information-based construction enables timely responses to geological changes; the refined traffic organization plan minimizes the impact of construction on tunnel operation. Reliable quality control: The quality control standards and testing methods for key processes such as non-destructive testing of anchor piles, airtightness testing of waterproof layer, and connection between new and old structures have been clearly defined to ensure project quality; Wide applicability: The system and method allow for flexible parameter adjustment and are applicable to geological disaster management at the entrances of existing tunnels in mountainous areas of different scales and geological conditions, making it highly valuable for promotion and application.

[0056] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0057] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0058] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A structure for extending the entrance of an existing tunnel in a mountainous area, characterized in that, The structure is a reinforced concrete open-cut tunnel extending outward from the original tunnel entrance, forming a "pile-pier-lining" collaborative load-bearing system; including: Deep anchoring system: On unstable slopes or key foundation locations on the mountainside, inclined anchor pile groups are installed; Gravity-type load-bearing piers: Reinforced concrete gravity piers are set at key points at the bottom of the extended section to serve as the main vertical load-bearing and anti-slip components of the open-cut tunnel structure; The tunnel lining body: The arched lining is made of reinforced concrete as the direct protection and load-bearing structure, and the outer side is covered with a composite waterproof layer of "non-woven fabric + EVA waterproof board".

2. The structure of the extension section of the existing tunnel entrance in mountainous areas according to claim 1, characterized in that, In deep anchoring systems, anchor piles are made of high-strength steel bars that are inserted into stable rock mass at a certain angle and then pressure grouting is used to form a composite anchor body.

3. The structure of the extension section of the existing tunnel entrance in mountainous areas according to claim 1, characterized in that, The foundation of the gravity-bearing pier rests on a stable foundation that has been verified.

4. The structure of the extension section of the existing tunnel entrance in mountainous areas according to claim 1, characterized in that, It also includes a buffer backfill system: forming a multi-level buffer and drainage barrier in the arch of the tunnel.

5. The structure for extending the entrance of an existing tunnel in a mountainous area according to claim 4, characterized in that, The multi-level buffer and drainage barrier consists of a gravel drainage layer, a clay waterproofing layer, a soil-rock buffer layer, and a concrete protective layer, which are backfilled sequentially on the arch of the tunnel.

6. The structure for extending the entrance of an existing tunnel in a mountainous area according to claim 1, characterized in that, Also includes: A groove is cut at the center of the end of the existing opening lining, and a steel-edged rubber waterstop is pre-embedded.

7. The structure for extending the entrance of an existing tunnel in a mountainous area according to claim 6, characterized in that, Also includes: Post-installed anchor rods are installed in the grooves at the ends of the lining; the post-installed anchor rods are connected to the newly added lining reinforcement to achieve a reliable transition in terms of both load-bearing capacity and waterproofing.

8. The structure for extending the entrance of an existing tunnel in a mountainous area according to claim 1, characterized in that, It also includes an integrated drainage system: flexible permeable pipes or perforated corrugated pipes are laid circumferentially behind the lining, and drainage pipes are installed longitudinally to guide water to the tunnel's existing drainage system.

9. The structure of the extension section of the existing tunnel entrance in mountainous areas according to claim 1, characterized in that, The composite waterproof layer of "non-woven fabric + EVA waterproof board" includes: Back-adhesive waterstop: It is installed close to the outside of the EVA waterproof membrane to form the first seal on the outside of the joint; EVA waterproof membrane and non-woven fabric: continuously laid across construction joints, and connected to the back-adhesive waterstop at the joints by hot-melt welding to form a whole.

10. The systematic construction method for the extension section structure of the portal of an existing tunnel in a mountainous area as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Survey and Dynamic Design Stage: Dynamically adjust the extension length and anchor pile layout parameters according to the actual situation; S2. Sequential excavation and temporary support: Excavation is carried out in layers and sections using a combination of mechanical and manual methods, with timely support. S3. Anchor pile construction: Drill holes according to the designed hole positions and angles, clean the holes, install the steel reinforcement bundles and perform pressure grouting; S4. Foundation treatment and gravity pier construction: Clean the foundation and construct the gravity pier foundation and pier body after it is qualified; S5. Construction of the main structure of the tunnel; S6. Construction of drainage and waterproofing system; S7. Buffer layer backfilling and greening; S8. Traffic organization during construction: Develop a special traffic management plan to minimize interference with tunnel operation.

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