Pumped storage power station shallow covering layer tunnel entry construction method
By constructing intercepting ditches and setting up seepage-proof hardening zones under shallow overburden geological conditions, combined with guide walls and composite support systems, and using core soil as a construction platform, the problems of high cost, low efficiency, and safety risks in tunnel entry construction were solved, achieving efficient and safe construction results.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA GEZHOUBA GROUP NO 5 ENG
- Filing Date
- 2026-03-10
- Publication Date
- 2026-06-16
AI Technical Summary
Under shallow overburden geological conditions, tunnel construction faces challenges such as high costs, low efficiency, significant difficulties, and prominent safety risks. In particular, the poor stability of the overburden soil and the significant impact of rainwater infiltration lead to low construction safety and efficiency.
By constructing a water interception ditch on the tunnel roof, setting up a seepage-proof hardening zone, adopting a guide wall excavation and composite support system, combining advanced small guide pipes and anti-gravity retaining walls, and using the core soil as a construction platform, layered excavation and timely support are carried out to ensure construction safety and efficiency.
It has enabled efficient and safe tunnel construction under shallow overburden geological conditions, reduced project investment costs, improved construction efficiency, reduced safety risks, and ensured the stability and safety of the construction process.
Smart Images
Figure CN122215769A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of engineering construction technology, specifically relating to a method for tunnel entry construction in shallow overburden layers of pumped storage power stations. Background Technology
[0002] In the construction of pumped storage power stations, tunnel entry is a crucial link connecting the construction site outside the tunnel with the construction area inside, directly affecting the construction progress and quality of the entire power station project. However, under shallow overburden geological conditions, tunnel entry faces numerous challenges due to the poor stability and low bearing capacity of the overburden soil, as well as its susceptibility to external factors such as rainwater infiltration.
[0003] Existing methods for constructing tunnels with shallow overburden have significant shortcomings: First, high investment costs: Traditional construction requires the investment of a large amount of steel, scaffolding and other equipment and materials to build temporary construction platforms to ensure operational safety. At the same time, in order to deal with the risk of slope collapse, support measures are often over-strengthened, resulting in a significant increase in costs. Second, the excavation efficiency is low: the excavation method is not targeted enough, and the characteristics of shallow overburden and soft rock are not fully combined. Furthermore, the support and excavation processes are not well connected, and work stoppages and rework are often caused by geological instability, which delays the construction progress. Third, the construction is difficult: the shallow overburden slope is prone to collapse and slippage during the excavation process, and the sidewall of the foundation pit is at high risk of deformation after excavation, which brings great inconvenience to the construction operation. Fourth, significant safety risks: Inadequate waterproofing measures allow rainwater to easily penetrate the cover layer, exacerbating geological instability. The insufficient reliability of the slope and tunnel support system can easily lead to safety accidents such as slope collapse and tunnel collapse, threatening the lives of construction workers and the safety of project property. Summary of the Invention
[0004] To address the aforementioned issues, this invention provides a method for constructing shallow overburden tunnels in pumped storage power stations. This method resolves the technical challenges of high investment costs, low excavation efficiency, significant construction difficulties, and prominent safety risks in existing shallow overburden tunnel construction. By optimizing the construction process and support system, it achieves a balance between safety, efficiency, and economy in the construction of shallow overburden tunnels with high sidewalls.
[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for tunnel entry construction in a shallow overburden layer of a pumped storage power station includes the following steps: S1: Construct a drainage ditch at the top of the tunnel and set up an anti-seepage hardening strip to prevent rainwater from seeping into the shallow cover layer and eroding the slope during the rainy season construction. S2: Carry out the clearing of exposed earth and rock at the tunnel entrance and the excavation and support of the slope; S3: Retain the core soil for guide wall excavation, excavating space for the guide wall foundation and the installation of arch frame and guide wall steel reinforcement formwork; S4: After the guide wall is poured, the foundation of the guide wall is backfilled, and the core soil is used as a construction platform for the construction of the advanced large pipe shed. At the same time, anti-gravity retaining walls are built on both sides of the opening to prevent the slope from collapsing. S5: Excavation of the tunnel overburden and soft rock sections is carried out using excavators, hydraulic breakers, and manual prying. S6: The tunnel entrance section is supported by steel supports, advanced small guide pipes, and sprayed concrete with wire mesh. S7: After the tunnel shotcrete construction is completed, excavation continues below the bottom design line. I-beams are used to connect the arch frame from the bottom and the invert arch concrete is poured.
[0006] In S1, the intercepting ditch is excavated 3.0-5.0m outside the excavation edge line on the top side of the tunnel entrance. The intercepting ditch is constructed according to the designed slope ratio and cross-sectional dimensions. The end of the intercepting ditch is smoothly connected to the site drainage system. The seepage-proof hardening zone is a concrete layer poured after the steel mesh is laid.
[0007] In S2, based on the tunnel design axis and the tunnel entrance plan, a total station was used to measure and mark the tunnel entrance excavation outline, construction site boundary line and slope control line. Simultaneously carry out tunnel slope excavation construction, and promptly trim the slope surface after excavation to ensure that the slope flatness is consistent with the design slope ratio; The slope protection adopts a composite support system of hollow grouting anchor rods, steel mesh, and shotcrete. At the same time, permeable pipes are installed in the slope protection system at the designed intervals, and the pipes are wrapped with non-woven fabric to form an anti-clogging filter structure.
[0008] In S3, a small excavator is used in conjunction with manual labor to excavate the guide wall. During the excavation, the core soil in the middle of the foundation pit is retained. The plane dimension of the core soil is not less than the width of the guide wall foundation. Operating space is reserved on both sides of the guide wall, and the vertical height is consistent with the design height of the guide wall. The stability of the foundation pit sidewall and core soil is monitored in real time during the excavation. If any abnormality is found, temporary steel support or shotcrete sealing is immediately used. After the foundation pit is excavated to the design elevation, the bottom surface of the foundation trench should be cleaned and leveled in a timely manner, and loose soil and loose rocks should be removed to ensure that the load-bearing surface of the guide wall foundation is dense and flat, so as to meet the conditions for subsequent concrete pouring.
[0009] In S4, the guide wall is constructed using a layered excavation process to precisely control the excavation range and simultaneously reserve the working space required for the guide wall foundation, arch frame installation, and steel reinforcement formwork support. After the concrete pouring is completed and the concrete strength meets the design requirements, the guide wall foundation is backfilled. The advanced large pipe shed is constructed using the reserved core soil as a temporary construction platform, without the need for additional scaffolding.
[0010] In S5, excavation is stopped and timely support is provided every 0.75m.
[0011] In S6, the tunnel entrance section uses advanced small guide pipes for advanced support, and the advanced small guide pipes are grouting small guide pipes. Steel supports are installed as the core load-bearing structure of the initial support, and hollow anchor rods are used as locking anchor rods for the steel supports. After laying a steel mesh on the outer layer of the steel support, spray concrete to seal the bedrock surface.
[0012] The hollow small guide pipes used in the anchor bolts not only ensure the stability of the steel support, but also act as drainage pipes to drain seepage water from the rock mass.
[0013] In S7, after the tunnel excavation is completed for 30-50m, the bottom slab invert arch is excavated. After each steel arch frame is excavated, the lower part of the steel arch frame is immediately connected with I-beams. Then, the invert arch concrete is poured. The invert arch concrete pouring is carried out continuously and is vibrated to ensure compaction.
[0014] Drainage ditches were installed at the top of the tunnel slope, and the slope was hardened with sprayed concrete to prevent rainwater infiltration and erosion.
[0015] The main beneficial effects of this invention are as follows: 1. In the construction of the guide wall, the present invention utilizes the reserved core soil as a temporary construction platform, eliminating the need for additional scaffolding and reducing the equipment, materials and labor input required for scaffolding erection; at the same time, by optimizing the construction process, the various processes are closely connected, avoiding unnecessary construction links and material waste, and effectively reducing the total investment cost of the project.
[0016] 2. A layered excavation and timely support construction mode is adopted to avoid work stoppages and rework caused by geological instability. In view of the characteristics of the overburden and soft rock sections of the tunnel, a combination of excavators, hydraulic breakers and manual prying is selected to adapt to the excavation needs under different geological conditions, which speeds up the excavation and improves the overall construction efficiency.
[0017] 3. Effectively reduce construction difficulty: By constructing intercepting ditches and anti-seepage hardening strips on the tunnel top, the problems of rainwater infiltration and erosion are solved; the use of composite slope support system and anti-gravity retaining wall effectively controls the risk of slope collapse and landslide; the use of hollow small pipes as anchor bolts effectively solves the problem of tunnel seepage; the design of the support system for the tunnel entrance section and the tunnel body ensures the stability of the tunnel excavation, reducing the construction difficulty under shallow overburden geological conditions in multiple dimensions.
[0018] 4. Comprehensive safety risk mitigation: Real-time monitoring of the stability of the pit sidewalls and core soil during the excavation of the guide wall, and timely handling of potential safety hazards; support is carried out after each certain distance of excavation; the comprehensive support system ensures the stability of the slopes, openings and tunnel bodies, comprehensively protects the lives of construction personnel and the safety of project property, and significantly reduces safety risks. Attached Figure Description
[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.
[0020] Figure 1 This is a schematic diagram of the construction structure of the present invention; Figure 2 This is a side sectional view of the construction structure of the present invention; Figure 3 This is a side view of the construction structure of the present invention.
[0021] In the diagram: 1. Retaining wall; 2. Guide wall; 3. Pipe shed; 4. Core soil; 5. Inverted arch concrete; 6. Pre-construction small guide pipe; 7. Tunnel top intercepting ditch; 8. Steel support; 9. Steel arch frame. Detailed Implementation
[0022] In this embodiment, the area at the outlet of the pumped storage power station is a shallow overburden geological layer with a thickness of 5-8m. It is mainly composed of a mixture of humus and gravel, which has poor stability. In addition, the area experiences concentrated rainfall during the rainy season, which has a significant impact on construction safety. The tunnel is designed to be 5.5m wide, and the entrance section has a high sidewall structure. Reliable construction methods are required to ensure the safety of construction work inside the tunnel.
[0023] like Figures 1-3 As shown, a method for tunnel entry construction in a shallow overburden layer of a pumped storage power station includes the following steps: S1: Construct a drainage ditch 7 on the top of the tunnel and set up an anti-seepage hardening strip to prevent rainwater from seeping into the shallow cover layer and eroding the slope during the rainy season construction. S2: Carry out the clearing of exposed earth and rock at the tunnel entrance and the excavation and support of the slope; S3: Retain the core soil 4 and excavate the guide wall 2 to create space for the foundation of the guide wall 2, as well as the installation of the arch frame and the steel reinforcement formwork of the guide wall 2. S4: After the guide wall 2 is poured, the foundation of the guide wall 2 is backfilled, and the core soil 4 is used as a construction platform for the construction of the advanced large pipe shed 3. At the same time, anti-gravity retaining walls 1 are built on both sides of the opening to prevent the slope from collapsing. S5: Excavation of the tunnel overburden and soft rock sections is carried out using excavators, hydraulic breakers, and manual prying. S6: The tunnel entrance section is supported by steel supports (8), advanced small guide pipes (6), and sprayed concrete with wire mesh. S7: After the tunnel shotcrete construction is completed, continue excavation below the bottom design line, connect the arch frame from the bottom with I-beams and pour the inverted arch concrete 5.
[0024] In S1, a water interception ditch is excavated 4.0m outside the excavation edge line on the top side of the tunnel entrance, with a design slope ratio of 1:1.5, a cross-sectional size of 0.8m wide and 0.6m deep. The end of the water interception ditch is connected to the existing drainage ditch in the site with a concrete pipe to ensure smooth drainage of water. A φ6@200×200 steel mesh is laid between the excavation line and the intercepting ditch, and then C25 concrete is poured to form a hardened layer with a thickness of 180mm, forming an anti-seepage hardened zone.
[0025] In S2, based on the tunnel design axis and the tunnel entrance plan, a total station was used to lay out the tunnel entrance excavation outline with a radius of 3.25m, the construction site boundary line, and the slope control line with a slope ratio of 1:1.2. A PC200 hydraulic excavator was selected for layered excavation, with each layer being 2 meters thick. During the excavation process, a level instrument was used to monitor the excavation depth in real time to avoid over-excavation or under-excavation.
[0026] After the slope excavation is completed, the slope surface is trimmed to ensure that the error does not exceed 50mm; The slope support system uses φ36 hollow grouting anchors, 3.5m long, spaced 1.5m×1.5m, φ8@200×200 steel mesh, and C25 shotcrete with a thickness of 120mm. The process involves drilling holes, inserting the anchors, and grouting them at a pressure controlled between 0.5-1.0MPa. Next, the steel mesh is installed and welded to the anchors. Finally, a wet shotcrete machine is used to ensure uniform and dense concrete coverage. At the same time, φ50 permeable pipes are installed at 2.5m intervals, and the permeable pipes are covered with 200g / ㎡ non-woven fabric. The bottom of the permeable pipes extends into the intercepting ditch to realize drainage inside the slope.
[0027] In S3, a small excavator is used in conjunction with manual labor to excavate the guide wall 2. During the excavation, the core soil 4 in the middle of the foundation pit is retained. The planar dimensions of the core soil 4 are not less than the foundation width of the guide wall 2. Operating space is reserved on both sides of the guide wall 2, and the vertical height is consistent with the design height of the guide wall 2. The stability of the foundation pit sidewall and core soil 4 is monitored in real time during the excavation. If any abnormality is found, temporary steel support or shotcrete sealing is immediately used. The guide wall 2 is designed to be 8.8m high and 6.5m wide. A PC60 mini excavator was used in conjunction with manual excavation. During the excavation, a total station was used to monitor the displacement of the pit sidewalls. When a minor crack was found in one sidewall, the excavation was stopped immediately. I18 steel was used for temporary support with a spacing of 1.0m between the steel sections. Excavation continued after the crack stabilized. After the pit was excavated to the design elevation, the loose soil and loose rocks at the bottom of the trench were manually cleared to ensure that the flatness error of the bottom of the trench did not exceed 20mm.
[0028] After the foundation pit is excavated to the design elevation, the bottom surface of the foundation trench should be cleaned and leveled in a timely manner, and loose soil and loose rocks should be removed to ensure that the bearing surface of the guide wall 2 foundation is dense and flat, so as to meet the conditions for subsequent concrete pouring.
[0029] In S4, the guide wall 2 is constructed using a layered excavation process to precisely control the excavation range and simultaneously reserve the working space required for the foundation, arch frame installation, and steel reinforcement formwork support of the guide wall 2. The guide wall 2 is constructed using C30 reinforced concrete with a steel reinforcement protective layer thickness of 50mm. During the pouring process, a vibrator is used to vibrate in layers with a layer thickness of 300mm to ensure the compactness of the concrete. After 7 days of concrete curing, the foundation of guide wall 2 was backfilled with graded sand and gravel with a compaction degree of ≥95%. Core soil 4 was used as a construction platform. A geological drilling rig was used to drill holes with a diameter of 120mm. φ108 advanced pipe shed 3 was constructed at a spacing of 0.4m, with a pipe shed length of 36m. Cement grout was used for grouting inside the pipe with a water-cement ratio of 1:1 and a grouting pressure of 1.0-1.5MPa.
[0030] In S5, anti-gravity retaining walls 1 are constructed at the bottom of the slopes on both sides of the tunnel entrance. Retaining walls 1 are made of C30 concrete, with a height of 5m, a top width of 5m, and a bottom width of 2.8m. The walls are equipped with φ50 drainage holes spaced 2.0m x 2.0m apart, and the drainage holes are covered with non-woven fabric to prevent soil loss.
[0031] A PC200 excavator was used in conjunction with a hydraulic breaker to excavate the overburden and soft rock sections of the tunnel body, while loose rock blocks on the excavation surface were manually pried and cleared. Excavation is stopped after every 0.75m of excavation, and timely support is provided. Once no abnormalities are confirmed, the support process begins, achieving a seamless connection between excavation and support.
[0032] In S6, the tunnel entrance section uses advanced small guide pipe 6 for advanced support. The advanced small guide pipe 6 is a φ42 grouting small guide pipe with a length of 5.0m, a spacing of 0.3m, and an external insertion angle of 10°-15°. The grouting uses cement-water glass double liquid grout with a volume ratio of 1:1 and a grouting pressure of 0.8-1.2MPa. I20b steel supports 8 are installed as the core load-bearing structure of the initial support. The steel supports 8 are spaced 0.75m apart. The gap between the steel supports 8 and the surrounding rock is filled with C25 shotcrete. Hollow anchor rods are used as locking anchor rods for the steel supports 8. The anchor rods are 4.0m long and 8 locking anchor rods are set for each steel support 8. After laying a φ6@200×200 steel mesh on the outer layer of the steel support 8, spray concrete was used to seal the bedrock surface with a thickness of 150mm.
[0033] In S7, after the tunnel excavation is completed for 40m, the bottom slab invert is excavated, with an excavation depth of 0.5m. Every 0.75m of excavation corresponds to the distance of one steel arch frame 9. Immediately after excavation, I18 I-beams are used to connect the lower part of the steel arch frame 9. The I-beams are welded to the steel arch frame 9 for fixation. Subsequently, the invert arch reinforcement was tied, with main reinforcement φ18@200 and distribution reinforcement φ12@200. After the formwork was installed, C25 invert arch concrete 5 was poured. The invert arch concrete 5 was poured continuously and vibrated to ensure compaction. The concrete was transported by tanker truck and vibrated with a vibrator. After curing for 14 days, it reached the design strength.
[0034] Drainage ditches were installed at the top of the tunnel slope, and the slope was hardened with sprayed concrete to prevent rainwater infiltration and erosion.
[0035] The above embodiments are merely preferred technical solutions of the present invention and should not be considered as limitations on the present invention. The embodiments and features described in these embodiments can be arbitrarily combined without conflict. The scope of protection of the present invention should be limited to the technical solutions described in the claims, including equivalent substitutions of the technical features described in the claims. That is, equivalent substitutions and improvements within this scope are also within the scope of protection of the present invention.
Claims
1. A method for tunnel entry construction in shallow overburden layers of a pumped storage power station, characterized in that... Includes the following steps: S1: Construct a water interception ditch on the top of the tunnel (7) and set up an anti-seepage hardening belt to prevent rainwater from seeping into the shallow cover layer and rainwater from scouring the slope during construction. S2: Carry out the clearing of exposed earth and rock at the tunnel entrance and the excavation and support of the slope; S3: Retain the core soil (4) and excavate the guide wall (2) to excavate the foundation of the guide wall (2) and the space for the installation of the arch frame, guide wall (2) steel reinforcement formwork; S4: After the guide wall (2) is poured, the foundation of the guide wall (2) is backfilled, and the core soil (4) is used as a construction platform to carry out the construction of the advanced large pipe shed (3). At the same time, anti-gravity retaining walls (1) are built on both sides of the opening to prevent the slope from collapsing. S5: Excavation of the tunnel overburden and soft rock sections is carried out using excavators, hydraulic breakers, and manual prying. S6: The tunnel entrance section is supported by steel supports (8), advanced small guide pipes (6), and wire mesh spraying. S7: After the tunnel shotcrete construction is completed, continue excavation below the bottom design line, connect the arch frame from the bottom with I-beams and pour the invert arch concrete (5).
2. The method for tunnel entry into a shallow overburden layer of a pumped storage power station according to claim 1, characterized in that: In S1, the intercepting ditch is excavated 3.0-5.0m outside the excavation edge line on the top side of the tunnel entrance. The intercepting ditch is constructed according to the designed slope ratio and cross-sectional dimensions. The end of the intercepting ditch is smoothly connected to the site drainage system. The seepage-proof hardening zone is a concrete layer poured after the steel mesh is laid.
3. The method for tunnel entry into a shallow overburden layer of a pumped storage power station according to claim 1, characterized in that: In S2, based on the tunnel design axis and the tunnel entrance plan, a total station was used to measure and mark the tunnel entrance excavation outline, construction site boundary line and slope control line. Simultaneously carry out tunnel slope excavation construction, and promptly trim the slope surface after excavation to ensure that the slope flatness is consistent with the design slope ratio; The slope protection adopts a composite support system of hollow grouting anchor rods, steel mesh, and shotcrete. At the same time, permeable pipes are installed in the slope protection system at the designed intervals, and the pipes are wrapped with non-woven fabric to form an anti-clogging filter structure.
4. The method for tunnel entry into a shallow overburden layer of a pumped storage power station according to claim 1, characterized in that: In S3, a small excavator is used in conjunction with manual labor to excavate the guide wall (2). During the excavation process, the core soil (4) in the middle of the foundation pit is retained. The planar dimensions of the core soil (4) are not less than the foundation width of the guide wall (2). Operating space is reserved on both sides of the guide wall (2). The vertical height is consistent with the design height of the guide wall (2). During the excavation process, the stability of the foundation pit sidewall and the core soil (4) is monitored in real time. If any abnormality is found, temporary steel support or shotcrete sealing is immediately used. After the foundation pit is excavated to the design elevation, the bottom surface of the foundation trench is cleaned and leveled in a timely manner, and loose soil and loose rocks are removed to ensure that the bearing surface of the guide wall (2) foundation is dense and flat, so as to meet the conditions for subsequent concrete pouring.
5. The method for tunnel entry construction in a shallow overburden layer of a pumped storage power station according to claim 1, characterized in that: In S4, the guide wall (2) is constructed using a layered excavation process to precisely control the excavation range and simultaneously reserve the working space required for the foundation, arch frame installation and steel reinforcement formwork support of the guide wall (2). After the concrete is poured and the concrete strength meets the design requirements, the guide wall (2) foundation is backfilled. The advanced large pipe shed (3) uses the reserved core soil (4) as a temporary construction platform for construction, without the need for additional scaffolding.
6. The method for tunnel entry into a shallow overburden layer of a pumped storage power station according to claim 1, characterized in that: In S5, excavation is stopped and timely support is provided every 0.75m.
7. The method for tunnel entry construction in a shallow overburden layer of a pumped storage power station according to claim 1, characterized in that: In S6, the tunnel entrance section is supported by advance small guide pipe (6), which is a grouting small guide pipe; Install steel supports (8) as the core load-bearing structure of the initial support. The steel supports (8) use hollow anchor rods as locking anchor rods. After laying a steel mesh on the outer layer of the steel support (8), spray concrete to seal the bedrock surface.
8. The method for tunnel entry into a shallow overburden layer of a pumped storage power station according to claim 7, characterized in that: The hollow small guide pipe used in the anchor bolts not only ensures the stability of the steel support (8), but also acts as a drainage pipe to drain the seepage water in the rock mass.
9. The method for tunnel entry into a shallow overburden layer of a pumped storage power station according to claim 1, characterized in that: In S7, after the tunnel excavation is completed for 30-50m, the bottom slab invert arch is excavated. After each steel arch frame (9) is excavated, the lower part of the steel arch frame (9) is immediately connected with I-beams. Then, the invert arch concrete (5) is poured. The invert arch concrete (5) is poured continuously and vibrated to ensure compaction.
10. The method for tunnel entry construction in a shallow overburden layer of a pumped storage power station according to claim 1, characterized in that: Drainage ditches were installed at the top of the tunnel slope, and the slope was hardened with sprayed concrete to prevent rainwater infiltration and erosion.