Design method for construction platform of tunnel entrance and exit in high and steep canyon area

Abstract

The invention relates to the technical field of engineering construction, in particular to a high and steep canyon area tunnel entrance and exit construction platform design method, and aims to solve the problems of large excavation investment, serious environmental damage, inconvenient traffic and the like in the prior art. Concrete slag blocking walls flush with a tunnel bottom plate are filled at mountain feet on the two sides of the river valley, and the concrete slag blocking walls serve as supporting structures to arrange traffic bridges to achieve traffic communication of the two banks; permanent slope excavation or high slope excavation of a tunnel portal is avoided by adopting a protective arch strong entry scheme; waste slag is contained in the space behind the slag blocking wall, and outward transportation of the waste slag is reduced; a sufficient working face is provided through the backfilling platform and the traffic bridge. The scheme also covers specific construction processes, monitoring measures and ecological restoration strategies, so that the construction safety is ensured, the investment cost is reduced, and meanwhile, the influence on the environment is reduced to the greatest extent. The scheme is successfully applied to water diversion engineering in Yunnan, and it is proved that the method has remarkable technical advantages and practical application value and is suitable for tunnel construction projects similar to complex terrains.

Description

Technical Field

[0001] The present invention belongs to the field of engineering construction, and relates to an optimization design of a tunnel engineering construction plan, in particular to a design method of an entrance and exit construction platform for a tunnel in a high and steep canyon area. Background Art

[0002] Tunnel construction in steep canyon areas presents numerous challenges in hydropower and water conservancy projects. Currently, tunnel entrances and exits in such areas typically utilize a single-sided excavation platform, created by cutting the slope. However, existing construction methods have the following drawbacks: First, the investment required for excavation, waste disposal, and support is high; second, large-scale excavation severely damages mountain vegetation, compromising the environmental friendliness of the project; and third, due to the isolation of the deep canyon, connecting adjacent tunnel faces is difficult, requiring separate construction roads and increasing transportation investment. Summary of the Invention

[0003] The present invention aims to address the problems of high slopes, narrow construction platforms, and lack of connectivity between the two banks during tunnel construction in steep canyon areas. To achieve this, the present invention proposes a method for designing construction platforms for tunnel entrances and exits in steep canyon areas. The specific steps are as follows: At the foot of the mountains on both sides of the valley, slag retaining walls, with their tops flush with the tunnel floor, were constructed. These walls are constructed of concrete, with a thickness of at least 1.5 meters. Cross-sectional dimensions were determined based on geological conditions and stress analysis to ensure sufficient stability and load-bearing capacity. The walls were constructed using concrete that met strength and durability requirements, with appropriate admixtures added to improve impermeability and crack resistance. During foundation treatment, weak foundations were replaced with fill or pile foundations were implemented to ensure the foundation's bearing capacity met design requirements.

[0004] Using two slag retaining walls as support structures, a traffic bridge was constructed to facilitate access between the two working faces. The traffic bridge utilizes either a simply supported beam or continuous beam structure, with the bridge type determined based on the actual terrain and span requirements. The design load for the traffic bridge is Highway Class II or no less than the maximum load standard for construction vehicles and equipment, ensuring safe passage during construction.

[0005] Both the front and rear tunnel faces utilize a reinforced arch construction scheme to ensure entry without permanent excavation. The arch is constructed of reinforced concrete, with an arch ring thickness of at least 1.2 meters. The arch axis configuration is determined based on geological conditions and stresses, such as a semicircular arch or a three-center arch. During arch construction, appropriate anchor rods or cables are installed, with a length of at least 5 meters and spacing no greater than 1.5 meters. This strengthens the connection between the arch and the surrounding rock mass, ensuring safety and stability during tunnel entry.

[0006] The slag retaining wall is used to accommodate some of the excavated slag from tunnel construction, reducing the amount of long-distance slag disposal work. A dedicated slag storage area is set up behind the slag retaining wall to properly stack and manage the slag to prevent landslides and debris flows.

[0007] The backfill platform and access bridge provide a working surface, solving the problem of a narrow tunnel construction surface in steep canyons. The backfill platform is constructed in layers, with each layer no thicker than 30 cm and fully compacted to ensure the platform's flatness and load-bearing capacity meet construction requirements.

[0008] Furthermore, the substructure abutments of the traffic bridge utilize counterweight retaining walls. Φ25 mortar anchors are installed at the retaining wall foundation and back of the wall. The anchors are 6m long, 1.5m apart, and have an exposed anchor length of 80cm. The construction process is as follows: surveying and setting out → excavation of the foundation trench → anchor installation → concrete pouring permit → concrete pouring of the retaining wall base → erection of scaffolding and formwork → reporting to the supervising engineer → concrete pouring of the retaining wall body → backfilling of the back of the wall.

[0009] During construction, the Ditianpo Tunnel exit was excavated from upstream to downstream using a single working face. The tunnel was penetrated by rock plug blasting, and the entrance was sealed with reinforced concrete. An exposed arch was extended to ensure construction safety. Furthermore, utilizing the already completed Ditianpo Tunnel for transportation, small machinery and manual labor were used to construct piers and retaining walls on both sides of the river. A steel frame bridge was constructed on the piers to provide access to the Dapozi Tunnel entrance. The backfill behind the retaining wall served as a site for the layout of construction equipment such as air compressors.

[0010] The Ditianpo Tunnel excavation has a cross-section of 4.0m x 4.9m, suitable for a 50t crane and a 2m³ excavator. The elevation from the Ditianpo Tunnel exit to the riverbed is approximately 20m, allowing small machinery to be maneuvered to the riverbed for construction. Earthwork was excavated using a 2m³ excavator and a breaker, loaded with a 6m³ bucket, and transported to the Ditianpo Tunnel exit platform by a 20t truck crane. The excavated rock was then loaded onto a dump truck and transported to the waste dump. The rock foundation piles were drilled using down-the-hole drilling and concrete poured using the duct exhaust method. The concrete for the piers and retaining walls was transported to the Ditianpo Tunnel exit using 3m³ concrete tankers, assembled with steel formwork, and then chute-loaded into a silo. The concrete was then vibrated with a 2.2kW handheld vibrator. The backfill behind the wall was filled with excavated material from the tunnel and the pier foundations. The excavated material was transported from the waste dump by a 5t dump truck and placed in layers. A frog-type rammer was used for compaction.

[0011] During the hoisting of the steel bridge, due to limited space at the Ditianpo Tunnel exit, the steel bridge had to be transported backwards from the Ditianpo Tunnel to the exit. A 50t crane was used for the hoisting, and guardrails were installed on both sides of the steel bridge to ensure safety during the hoisting process. After the construction platform and traffic bridge were completed, excavation and support were carried out at the entrance of the Dapozi Tunnel. A "zero excavation" approach was used whenever possible to avoid the formation of steep slopes. The entrance was locked and an exposed arch was extended to ensure construction safety.

[0012] Throughout the construction process, a detailed monitoring plan and safety measures were developed. Monitoring included slope deformation, surface subsidence, and groundwater level monitoring. Advanced monitoring instruments and equipment, such as total stations, levels, and inclinometers, were used to regularly monitor the construction area. Construction plans were adjusted promptly based on monitoring data to ensure construction safety. A geological disaster early warning mechanism was established to provide early warning of potential collapses, landslides, and other disasters, allowing effective preventive measures to be implemented. Furthermore, comprehensive safety and protection facilities, such as guardrails, safety nets, and warning signs, were installed to ensure the safety of construction workers.

[0013] During the construction process, we prioritize ecological protection and restoration. We protect vegetation within the construction area to avoid unnecessary damage. For areas affected by construction, we develop detailed ecological restoration plans, including measures such as vegetation restoration, soil improvement, and water and soil conservation, to minimize the impact of construction on the ecological environment. We also strengthen the treatment of wastewater, waste gas, and waste residue generated during construction, employing environmentally friendly construction equipment and processes to reduce environmental pollution.

[0014] Compared with the prior art, the present invention has the following beneficial effects: It solves the problems of high slope excavation, narrow construction platform and lack of traffic connection between the two banks during tunnel construction in steep canyon areas, and reduces the investment in excavation, waste disposal and support.

[0015] It reduces the damage to mountain vegetation and is more environmentally friendly.

[0016] The construction traffic organization has been optimized and the transportation investment has been reduced.

[0017] Reasonable monitoring and safety measures ensure the safety and stability of the construction process.

[0018] We focus on ecological restoration and environmental protection, and achieve coordinated development of engineering construction and the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 This is a schematic diagram of on-site construction provided by the present invention. DETAILED DESCRIPTION

[0021] like Figure 1As shown, the present invention is described in detail by taking the tunnel connected to the Hongbaijikan Aqueduct of the Red River section of the Dianzhong Water Diversion Project as an example. A steep cliff is formed at the bottom of the Ditianpo Tunnel outlet in this area. The terrain above it has a slope of 40 to 45 degrees and a slope height of 275m. The limestone is strongly dissolved and weathered, and a strong unloading zone is developed. The natural slope has poor local stability and the excavated slope is unstable. The terrain slope of the entrance section of the Dapozi Tunnel is 15 to 20 degrees, with a slope height of 65m. It is a forward slope that leans outward from the mountain, with a dip angle greater than the slope angle. The natural slope is basically stable, and the excavated slope has poor local stability. The maximum excavation height of the Ditianpo Tunnel outlet slope is about 40m, and the earthwork excavation volume is 1,256m³; the maximum excavation height of the Dapozi Tunnel entrance slope is about 56m, and the earthwork excavation volume is 2,527m³. 1000kN-grade anchor cables are used for strong support. The exit of the Ditianpo Tunnel is located on a steep mountain, making it difficult to construct a construction road. Therefore, a branch tunnel was constructed approximately 1 km upstream for access. A construction access road was constructed on the side of the Dapozi Tunnel entrance.

[0022] The specific implementation is as follows: At the foot of the mountains on both sides of the valley, slag retaining walls were cast, with their tops flush with the tunnel floor. The walls are constructed of concrete, 1.8 meters thick, and their cross-sectional dimensions determined based on geological conditions and stress analysis. C30 concrete was selected for the walls, with appropriate admixtures added to improve their impermeability and crack resistance. During foundation treatment, weak foundations were replaced with fill to ensure the foundation's bearing capacity met design requirements.

[0023] With two slag retaining walls as the supporting structure, a traffic bridge was arranged to facilitate traffic between the two working faces. The traffic bridge adopts a simply supported beam structure with a span of 24 meters and a design load of Highway-II to ensure safe passage during the construction period.

[0024] Both the front and rear tunnel faces employed a reinforced arch construction scheme for tunnel entry, eliminating the need for permanent excavation. The arch is constructed of reinforced concrete, with a 1.2-meter-thick arch ring and a semicircular arch axis. During arch construction, Φ25 mortar anchors were installed, each 5 meters long and spaced 1.2 meters apart, to strengthen the connection between the arch and the surrounding rock mass, ensuring safety and stability during tunnel entry.

[0025] A special waste slag storage area is set up behind the slag retaining wall to properly stack and manage the waste slag to prevent disasters such as waste slag landslides and mud-rock flows.

[0026] The backfill platform is constructed in layers, with each layer being 20 cm thick, and is fully compacted to ensure that the flatness and bearing capacity of the platform meet construction requirements.

[0027] The substructure abutments of the traffic bridge utilize counterweight retaining walls. Φ25 mortar anchors are installed at the retaining wall foundation and back of the wall. Anchor length L = 6m, spacing 1.5m, and exposed anchor length 80cm. The construction process is as follows: surveying and setting out → foundation trench excavation → anchor bolting → concrete pouring permit → concrete pouring at the retaining wall base → scaffolding and formwork erection → report to the supervising engineer → concrete pouring at the retaining wall body → backfilling. During construction, high-precision surveying instruments were used for setting out to ensure accurate positioning and dimensions of the retaining wall. During foundation trench excavation, the surrounding geological conditions were closely monitored to prevent safety hazards such as collapse. During anchor bolting construction, drilling and grouting were carried out in strict accordance with design requirements to ensure effective anchoring. During concrete pouring, high-quality concrete materials and advanced pouring techniques were used to ensure concrete density and strength. During backfilling, the back of the wall was compacted layer by layer to ensure the density and stability of the soil behind the wall.

[0028] The Ditianpo Tunnel exit was excavated using a single working face from upstream to downstream. The tunnel was penetrated by rock plug blasting, with the entrance sealed with reinforced concrete and an extended exposed arch for construction safety. The existing Ditianpo Tunnel served as transportation, with small machinery and manual labor employed to construct piers and retaining walls along the riverbank. A steel frame bridge was constructed on the piers to provide access to the Dapozi Tunnel entrance. The backfill behind the retaining wall provided space for the layout of construction equipment such as air compressors. The Ditianpo Tunnel excavation section measures 4.0m x 4.9m, accommodating a 50t crane and a 2m³ excavator. The elevation from the Ditianpo Tunnel exit to the riverbed is approximately 20m, allowing small machinery to be maneuvered to the riverbed by crane for construction. Earthwork was excavated using a 2m³ excavator and a breaker, loaded with a 6m³ bucket, and transported by a 20t truck crane to the Ditianpo Tunnel exit platform for loading onto a dump truck and transported to the waste dump. The rock foundation piles were drilled using down-the-hole drilling, and concrete was poured using the duct exhaust method. The concrete for the piers and retaining walls was transported to the Ditianpo Tunnel exit using 3m³ concrete tankers, assembled into steel formwork, and then chute-fed into a silo. The concrete was then vibrated with a 2.2kW handheld vibrator. The backfill behind the wall was filled with excavated material from the tunnel and the pier foundations. 5t dump trucks transported the excavated material from the waste dump, layered, and compacted with a frog-type rammer. During the installation of the steel bridge, due to limited space at the Ditianpo Tunnel exit, the steel bridge had to be transported backwards from the Ditianpo Tunnel to the exit. A 50t crane was used for the hoisting, and guardrails were installed on both sides of the steel bridge to ensure safety during the hoisting process. After the construction platform and traffic bridge were completed, excavation and support were carried out for the Dapozi Tunnel entrance. The tunnel entrance was entered using a "zero-excavation" method whenever possible to avoid the formation of steep slopes. The tunnel entrance was sealed and an exposed arch was extended to ensure construction safety.

[0029] Throughout the construction process, operations were strictly carried out in accordance with monitoring plans and safety measures. Slope deformation, surface subsidence, and groundwater levels were regularly monitored, and construction plans were adjusted promptly based on monitoring data. A geological disaster early warning mechanism was established to provide early warnings for potential collapses, landslides, and other disasters, allowing effective preventive measures to be taken. Comprehensive safety and protection facilities, such as guardrails, safety nets, and warning signs, were installed to ensure the safety of construction workers. At the same time, emphasis was placed on ecological protection and restoration, with vegetation within the construction area protected and detailed ecological restoration plans developed to minimize the impact of construction on the ecological environment. Treatment of wastewater, waste gas, and waste residue generated during construction was strengthened, and environmentally friendly construction equipment and processes were employed to reduce environmental pollution.

[0030] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be covered by the scope of protection of the present invention.

Claims

1. A method for designing a construction platform for tunnel entrances and exits in steep canyon areas, characterized in that: The following steps are involved: At the foot of the mountains on both sides of the valley, slag retaining walls with top elevations flush with the tunnel floor will be cast. The walls will be constructed of concrete with a thickness of no less than 1.5 meters. The cross-sectional dimensions will be determined based on geological conditions and stress analysis to ensure sufficient stability and bearing capacity. The wall material will be concrete that meets strength and durability requirements, with appropriate admixtures added to improve its impermeability and crack resistance. During foundation treatment, weak foundations will be replaced with fill or pile foundations to ensure the bearing capacity of the foundation meets the design requirements. Using two slag retaining walls as the supporting structure, a traffic bridge is arranged to facilitate traffic between the two working faces. The traffic bridge adopts a simply supported beam bridge or a continuous beam bridge structure, and the bridge type is determined according to the actual terrain and span requirements. The design load of the traffic bridge adopts the highway-II level or no less than the maximum load standard of construction vehicles and equipment to ensure safe passage of the bridge during construction. Both the front and rear tunnel faces adopt a construction scheme of strong tunnel entry with arch protection, which eliminates the need for permanent excavation of slopes or reduces the slope height. The arch protection adopts a reinforced concrete structure with an arch ring thickness of not less than 1.2 meters. The arch axis form is determined according to geological conditions and stress conditions, such as semi-circular arch or three-center arch. During the construction of the arch protection, an appropriate number of anchor rods or anchor cables are installed, with a length of not less than 5 meters and a spacing of not more than 1.5 meters, to enhance the connection strength between the arch protection and the surrounding rock mass and ensure the safety and stability of tunnel entry construction. The slag retaining wall is used to accommodate some of the excavated slag from tunnel construction, reducing the amount of long-distance slag disposal work. A special slag storage area is set up behind the slag retaining wall to properly stack and manage the slag to prevent disasters such as slag landslides and mud-rock flows. The backfill platform and traffic bridge provide a working surface to solve the problem of narrow tunnel construction working surface in steep canyons. The backfill platform adopts a layered filling method, with each layer thickness not exceeding 30 cm and fully compacted to ensure that the platform's flatness and bearing capacity meet construction requirements; With two slag retaining walls as the supporting structure, a traffic bridge is arranged to realize traffic between the two working faces. The abutment of the traffic bridge substructure is a counterweight retaining wall. The retaining wall foundation and back are equipped with Φ25 mortar anchor rods with a length of L=6m, a spacing of 1.5m, and an exposed anchor length of 80cm anchored into the retaining wall. The exit of the Ditianpo Tunnel was excavated from upstream to downstream using a single working face. The exit was penetrated by rock plug blasting. The entrance was sealed with reinforced concrete, and an exposed arch was extended to ensure construction safety. Utilizing the already completed Ditianpo Tunnel as transportation, small machinery and manual labor will be used to construct piers and retaining walls on both sides of the river. A steel frame bridge will be laid on the piers as transportation for the entrance construction of the Dapozi Tunnel. The backfill behind the retaining wall will serve as a site for the layout of construction equipment such as air compressors. The excavation section of the Ditianpo Tunnel is 4.0m×4.9m, which can accommodate a 50t crane and a 2m³ excavator. The elevation from the Ditianpo Tunnel exit to the riverbed is approximately 20m, allowing small machinery to be moved to the riverbed for construction by crane. The earthwork is excavated using a 2m³ excavator and a breaker, loaded with a 6m³ bucket, and transported by a 20t truck crane to the exit platform of the Ditianpo Tunnel, loaded onto a dump truck and transported to the waste dump; The rock foundation piles were drilled using down-the-hole drilling and concrete poured using the duct exhaust method. The pier and retaining wall concrete was transported to the exit of the Ditianpo tunnel using 3m³ concrete tankers, assembled with steel formwork, chute-loaded into the warehouse, and vibrated with a 2.2KW handheld vibrator. The backfill behind the wall is made of slag from the hole and the excavated material from the pier foundation. The slag is transported from the waste dump by a 5t dump truck and filled in layers. The tamping is done by a frog-type rammer. The steel bridge was hoisted from the Ditianpo Tunnel to the Ditianpo Tunnel exit using the reverse method. A 50t crane was used for hoisting, and guardrails were installed on both sides of the steel bridge. After the construction platform and traffic bridge are completed, the entrance of Dapozi Tunnel will be excavated and supported. The "zero excavation" method will be used as much as possible to enter the tunnel to avoid the formation of high and steep slopes. The tunnel entrance will be locked and an open arch will be extended to protect construction safety.

2. The method for designing a construction platform for tunnel entrances and exits in high and steep canyon areas according to claim 1 is characterized in that: The abutment of the lower structure of the traffic bridge is a counterweight retaining wall. The retaining wall foundation and the back of the wall are provided with Φ25 mortar anchor rods with an anchor rod length of L=6m, a spacing of 1.5m, and an exposed anchor length of 80cm anchored in the retaining wall.

3. The method for designing a construction platform for tunnel entrances and exits in high and steep canyon areas according to claim 1 is characterized in that: The exit of the Ditianpo tunnel is excavated from a single working face from upstream to downstream, the exit is penetrated by rock plug blasting, the entrance is locked with reinforced concrete, and a section of open arch is extended to protect construction safety.

4. The method for designing a construction platform for tunnel entrances and exits in high and steep canyon areas according to claim 1 is characterized in that: The completed Ditianpo Tunnel is used as transportation, and small machinery and manual labor are used to construct piers and retaining walls on both sides of the river. A steel frame bridge is laid on the pier as transportation for the construction of the Dapozi Tunnel entrance; the backfill behind the retaining wall can be used as a site for the layout of construction equipment such as air compressors.

5. The method for designing a construction platform for tunnel entrances and exits in high and steep canyon areas according to claim 1 is characterized in that: The excavation section of the Ditianpo Tunnel is 4.0m×4.9m, which can accommodate a 50t crane and a 2m³ excavator. The elevation from the Ditianpo Tunnel exit to the riverbed is about 20m, and small machinery can be moved to the riverbed by a crane for construction.

6. The method for designing a construction platform for tunnel entrances and exits in high and steep canyon areas according to claim 1 is characterized in that: The earth and stone are excavated by 2m³ excavator and breaker, loaded into 6m³ bucket, and transported by 20t truck crane to the exit platform of Ditianpo Tunnel, loaded into dump truck and transported to the waste dump.

7. The method for designing a construction platform for tunnel entrances and exits in high and steep canyon areas according to claim 1 is characterized in that: The rock foundation piles were drilled using down-the-hole drilling and concrete was poured using the duct exhaust method. The pier and retaining wall concrete was transported to the exit of the Ditianpo tunnel using 3m³ concrete tankers, assembled with steel formwork, chute-fed into the warehouse, and vibrated with a 2.2KW handheld vibrator.

8. The method for designing a construction platform for tunnel entrances and exits in high and steep canyon areas according to claim 1 is characterized in that: The backfill behind the wall is made of hole slag and pier foundation excavation materials. 5t dump trucks transport the slag from the waste dump, fill it in layers, and use frog-type rammers for compaction.

9. The method for designing a construction platform for tunnel entrances and exits in high and steep canyon areas according to claim 1 is characterized in that: The steel frame bridge was hoisted by transporting it from the Ditianpo Tunnel to the exit of the Ditianpo Tunnel using the reverse method. A 50t crane was used for hoisting, and guardrails were installed on both sides of the steel frame bridge.

10. The method for designing a construction platform for tunnel entrances and exits in high and steep canyon areas according to claim 1, characterized in that: After the construction platform and traffic bridge are completed, the Dapozi Tunnel entrance will be excavated and supported. "Zero excavation" will be used as much as possible to avoid the formation of steep slopes. The entrance will be locked and an exposed arch will be extended to ensure construction safety. Throughout the construction process, a detailed monitoring plan and safety measures were developed. Monitoring projects included slope deformation monitoring, surface settlement observation, and groundwater level monitoring. Advanced monitoring instruments and equipment, including total stations, levels, and inclinometers, were used to regularly monitor the construction area. Construction plans were adjusted promptly based on monitoring data to ensure construction safety. At the same time, a geological disaster early warning mechanism was established to provide early warnings for possible collapses, landslides, and other disasters, allowing effective preventive measures to be taken. In addition, comprehensive safety protection facilities, including guardrails, safety nets, and warning signs, were installed to ensure the safety of construction workers. During the construction process, we focus on ecological protection and restoration, protect the vegetation in the construction area, and avoid unnecessary damage to it due to construction; for areas affected by construction, we formulate detailed ecological restoration plans including vegetation restoration, soil improvement, soil and water conservation and other measures to reduce the impact of construction on the ecological environment; at the same time, we strengthen the treatment of wastewater, waste gas, waste residue, etc. generated during the construction process, adopt environmentally friendly construction equipment and processes, and reduce pollution to the environment.

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