Permanent and temporary combined enclosure structure suitable for high slope excavation and construction method

Abstract

The invention relates to the technical field of civil engineering construction, in particular to a permanent and temporary combined enclosure structure suitable for high slope excavation and a construction method. The building envelope comprises a first anti-slide pile, a second anti-slide pile and a support pile, the first anti-slide pile and the second anti-slide pile are arranged on the side close to the side slope, the support pile is arranged on the side not close to the side slope, the second anti-slide pile is located between the first anti-slide pile and the support pile, and the pile top elevation of the first anti-slide pile, the pile top elevation of the second anti-slide pile and the pile top elevation of the support pile are sequentially reduced. A connecting beam is transversely arranged between the pile top of the second anti-slide pile and the pile body of the first anti-slide pile, and a plurality of layers of transverse supporting structures are arranged in the foundation pit between the second anti-slide pile and the supporting pile. The permanent retaining structure of the side slope and the temporary enclosure structure of the subway station foundation pit are combined to form an integral structure, the safety and stability of the side slope and the foundation pit are ensured, meanwhile, coordination and unification with natural landscapes are achieved, and the ecological environment is protected.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering construction, and in particular to a permanent and temporary combined retaining structure suitable for high slope excavation and a construction method. Background Art

[0002] With the rapid development of urbanization, urban rail transit has become an integral part of modern urban transportation, and its construction is particularly crucial. However, rail transit construction in complex geological environments faces numerous challenges. For example, some subway station projects located adjacent to natural mountain slopes can create high slopes ranging from 0 to 30 meters. Using a traditional slope reduction and anchor lattice beam support solution (with a slope ratio of 1:1.50) would require large-scale mountain excavation, leading to the following prominent issues: Severe ecological damage: Large-scale excavation directly destroys the original mountain landscape and natural landscape, leading to a decrease in vegetation cover, increased soil erosion, and a threat to the regional ecosystem balance. The dust, noise, and waste generated by mountain excavation have long-term negative impacts on the lives of surrounding residents and the urban environment.

[0003] Significant engineering safety hazards: During excavation, high slopes are prone to geological hazards such as landslides and collapses due to soil stress release. This is especially true during the rainy season when groundwater levels rise, significantly increasing the risk of slope stability. Traditional support structures (such as anchored lattice beams) can become unstable over long periods of service due to material aging and anchor failure, threatening the safety of stations and pedestrians.

[0004] Inefficient and inefficient construction: Large-scale excavation requires significant investment in machinery, manpower, and time, resulting in a long construction period and susceptible to weather and geological conditions. Temporary support structures (such as retaining systems for slope excavation) cannot be integrated with permanent structures, resulting in wasted resources and increased project costs.

[0005] Therefore, how to reduce earth excavation volume, lower ecological impact, and achieve an organic combination of temporary support structures and permanent projects while ensuring the safety and stability of high slopes and foundation pits has become a technical problem that needs to be solved urgently. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this paper proposes a combined permanent and temporary retaining structure and construction method suitable for high-slope excavations. This structure combines the permanent retaining structure for the slope with the temporary retaining structure for the subway station foundation pit to form an integrated structure, ensuring the safety and stability of both the slope and the pit while also achieving harmony with the natural landscape and protecting the ecological environment.

[0007] In order to solve the above technical problems, the present invention is implemented through the following technical solutions: A permanent and temporary combined retaining structure suitable for high slope excavation includes a first anti-slip pile and a second anti-slip pile arranged on one side of the adjacent slope, and a supporting pile arranged on the side not of the adjacent slope, the second anti-slip pile is located between the first anti-slip pile and the supporting pile, and the pile top elevations of the first anti-slip pile, the second anti-slip pile and the supporting pile decrease in sequence; a connecting beam is transversely arranged between the pile top of the second anti-slip pile and the pile body of the first anti-slip pile, and a multi-layer transverse support structure is arranged in the foundation pit between the second anti-slip pile and the supporting pile.

[0008] Preferably, a first pile crown beam is provided on the top of the first anti-slip pile, a first retaining plate is provided on the side of the first anti-slip pile facing away from the slope, and a drainage hole is provided on the first retaining plate; a first prestressed anchor rod anchored in the slope is provided on the first anti-slip pile, and the outer end of the first prestressed anchor rod is fixedly connected to the first anchor rod waist beam provided on the first retaining plate.

[0009] Preferably, a second pile crown beam is provided on the top of the second anti-slip pile, a second retaining plate is provided on the side of the second anti-slip pile facing away from the slope, and a drainage hole is provided on the second retaining plate; a second prestressed anchor rod anchored in the slope is provided on the second anti-slip pile, and the outer end of the second prestressed anchor rod is fixedly connected to the second anchor rod waist beam provided on the second retaining plate.

[0010] Preferably, a first jet grouting pile is provided inside the second anti-slip pile in an area adjacent to the foundation pit, and the bottom elevation of the first jet grouting pile needs to be lower than the bottom elevation of the foundation pit.

[0011] Preferably, a third pile crown beam is provided on the top of the supporting pile, and a second jet grouting pile is provided inside the supporting pile in an area adjacent to the foundation pit, and the bottom elevation of the second jet grouting pile needs to be lower than the bottom elevation of the foundation pit.

[0012] Preferably, the lateral support structure includes a first inner support, a second inner support and a third inner support, one end of the first inner support is fixed to the third pile crown beam at the top of the supporting pile, and the other end is fixed to the concrete waist beam on the side wall of the second anti-slip pile; the second inner support and the third inner support are both located below the first inner support, one end of the second inner support and the third inner support are both against the steel purlin on the inner wall of the second anti-slip pile, and the other end are both against the inner wall of the supporting pile.

[0013] Preferably, the first inner support is a M-shaped reinforced concrete structure to enhance the rigidity of the support and more effectively control the deformation of the foundation pit.

[0014] Preferably, the second inner support and the third inner support both include multiple intermediate sections and fixed ends and movable ends provided at both ends of the intermediate sections, the movable ends abut against the steel purlins, and the fixed ends abut against the inner walls of the support piles.

[0015] A construction method for a permanent and temporary combined retaining structure suitable for high slope excavation, the construction method comprising: Step 1: Relocate existing pipelines within the station area, complete the first site leveling to elevation 1, construct the first anti-slide pile, the first pile crown beam, the first retaining wall, the first prestressed anchor rod, the first anchor rod waist beam, and excavate to the platform section to complete the first-level pile-sheet retaining wall protection; Step 2: Complete the second site leveling to elevation 2, construct the second anti-slide pile, the first jet grouting pile, the second pile top beam, the second retaining plate, the second prestressed anchor rod, the second anchor rod waist beam, and set a connecting beam between the first anti-slide pile and the second anti-slide pile; Step 3: Complete the third leveling to elevation 3, construct the support piles on the side not facing the slope, the second jet grouting piles, and the dewatering well in the pit; Step 4: Excavate the foundation pit to the bottom elevation of the third pile top beam, and construct the third pile top beam and the first internal support; Step 5: After the third pile crown beam and the first internal support reach the designed strength, excavate the foundation pit from top to bottom. According to the principle of excavation and support, complete the construction of steel purlins, the second internal support, and the third internal support, and excavate to the bottom of the foundation pit; Step 6: Prepare the bottom of the foundation pit, construct the cushion layer, ground it, lay the waterproof layer, construct the bottom plate and bottom beam, and reserve construction joints on the side walls; Step 7: After the bottom plate reaches the designed strength, remove the third inner support and cast part of the side wall. Continue to lay the waterproof layer upwards, cast the side wall structure, and construct the columns, middle longitudinal beams and middle plate. Step 8: After the middle plate reaches the designed strength, remove the second support, continue to lay the waterproof layer upwards, and construct the remaining columns, side walls, top longitudinal beams and top plate of the station hall; Step 9: After the roof structure strength reaches the design strength, remove the first support, lay the roof waterproof layer, construct the anti-floating pressure beam, backfill the soil, restore the road surface, and construct the internal structure of each floor of the station.

[0016] The present invention combines the permanent retaining structure of the high slope with the temporary retaining structure of the foundation pit to form an overall structure with reasonable stress, which has significant advantages in terms of safety, environmental protection, economy and construction efficiency. The following are the specific beneficial effects: (1) The present invention reduces the amount of excavation and does not require the traditional 1:1.50 large slope reduction. It significantly reduces the amount of earth excavation and saves land resources. It is particularly suitable for high slope areas with dense surrounding buildings and restricted terrain (such as the 0-30m high slope scene on the west side of the subway station). It also saves project costs. Through the permanent and temporary combined design, it reduces the independent setting of temporary support structures, reduces the amount of materials such as steel and concrete, simplifies the construction process, and thus reduces the overall project cost. The first anti-slip pile and the second anti-slip pile, the crown beam, the retaining plate and the prestressed anchor rod serve as permanent support structures and directly participate in the long-term stability of the slope. The support piles serve as temporary retaining structures for the foundation pit during the construction phase (sharing the soil pressure with the internal support). After the main structure is completed, they are converted into part of the permanent support system to avoid repeated construction. The jet grouting piles in the anti-slip piles serve as a temporary water-stop curtain (to prevent water seepage in the foundation pit) and are combined with the permanent anti-slip piles to form a deep reinforcement system to improve the long-term stability of the slope.

[0017] (2) The present invention designs a graded support system. By setting up the first anti-slip pile (first-level support) and the second anti-slip pile (second-level support), combined with prestressed anchor rods and retaining plates, the high slope soil pressure is graded and transferred to the deep stable stratum, reducing the stress risk of a single pile and adapting to the differences in geological conditions at different heights of the slope. In terms of spatial synergy, the first and second anti-slip piles are horizontally connected by a connecting beam to form a rigid frame double-row pile system, which improves the overall anti-overturning and anti-slip capabilities and enhances the overall stability; three transverse support structures (M-shaped reinforced concrete support + steel support) are set between the second anti-slip pile and the support pile, forming a three-dimensional force system with the anti-slip pile, crown beam, and waist beam, effectively controlling the deformation of the foundation pit. In terms of water-stopping and reinforcement functions, the first rotary jet pile is set inside the second anti-slip pile and the second rotary jet pile is set inside the support pile to form a water-stop curtain, cut off the groundwater infiltration path, and at the same time reinforce the pit bottom soil, prevent uplift and sand flow, and improve the stability of the base.

[0018] (3) The present invention improves construction efficiency and safety. It implements dynamic construction in stages, combines layered excavation of the foundation pit, and simultaneously completes the construction of anti-slip piles and support structures, achieving "support as you dig" and shortening the construction period. The steel support adopts a multi-section intermediate section + fixed end / movable end detachable design, which is convenient for rapid assembly, disassembly and reuse. It reduces construction risks, avoids large-scale excavation and exposes slopes, and reduces the risk of collapse. The support structure is prestressed in stages, and deformation is monitored in real time to ensure a safe and controllable construction process.

[0019] (4) This invention minimizes environmental impact, does not require large-scale destruction of the mountain, preserves the original landform, and reduces interference with the natural landscape and ecosystem, in line with the concept of green construction. The integrated landscape design, after construction completion, will form a three-dimensional street corner green space by covering the retaining wall with climbing green plants and composite planting greening the roof and surrounding areas, and restore the terraced landscape ecology, achieving a harmonious unity between the support structure and the natural landscape. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the longitudinal cross-section structure of the permanent and temporary combined retaining structure of the present invention suitable for high slope excavation.

[0021] Figure 2 It is a schematic diagram of the planar layout structure of the first inner support of the present invention.

[0022] Figure 3 It is a schematic diagram of the planar layout structure of the second inner support or the third inner support of the present invention.

[0023] Figure 4 It is a schematic diagram of the support node structure of the second inner support or the third inner support of the present invention.

[0024] Numbers in the figure: 1-first anti-sliding pile, 101-first pile top beam, 102-first retaining plate, 103-first prestressed anchor, 104-first anchor waist beam, 2-second anti-sliding pile, 201-second pile top beam, 202-second retaining plate, 203-second prestressed anchor, 204-second anchor waist beam, 205-first rotary jet grouting pile, 3-support pile, 301-third pile top beam, 302-second rotary jet grouting pile, 4-connecting beam, 5-lateral support structure, 501-first inner support, 502-second inner support, 503-third inner support, 504-middle section, 505-fixed end, 506-movable end, 6-steel purlin, 7-concrete waist beam, 8-existing mountain ground line, 9-slope. DETAILED DESCRIPTION

[0025] To help those skilled in the art better understand the technical solutions of the present invention, the preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the drawings are for illustrative purposes only and are not to be construed as limiting this patent. To better illustrate this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are for illustrative purposes only and are not to be construed as limiting this patent.

[0026] The construction area of a subway station foundation pit is surrounded by buildings and a mountain to the west of the station, forming a high slope of 0-30m. If this high slope is addressed using a 1:1.50 slope reduction combined with anchor lattice beam protection, large-scale excavation and a huge amount of earthwork would be required. This would inevitably damage the mountain and affect the natural environment, disrupting the natural landscape, hindering the harmonious development of man and nature, and having long-term negative impacts on regional ecological security and sustainable development. Therefore, to reduce earthwork excavation and damage to the mountain, a two-stage pile-sheet retaining wall is used for the slope protection of this subway station. The first stage of the pile-sheet retaining wall utilizes a first anti-slide pile + a first prestressed anchor + a first retaining board. The second stage of the pile-sheet retaining wall utilizes a second anti-slide pile + a second prestressed anchor + a second retaining board. This retaining wall is located in the same vertical plane as the temporary retaining structure of the subway station foundation pit. Considering the requirements of support safety and efficient and convenient construction, a combined construction of the two is considered. The temporary retaining structure of the subway station foundation pit adopts a pile-supported support structure (support piles + three internal supports), thus forming a permanent and temporary combined retaining structure system.

[0027] In this permanent and temporary retaining structure system, the temporary retaining structure of the subway station foundation pit can be destroyed after the main structure is completed and during subsequent use, without compromising the safety and stability of the slope's second-level pile-sheet retaining wall. Therefore, after the main structure is completed, the second anti-slip piles in the slope's second-level pile-sheet retaining wall will be supported at the top elevation of the subway station's roof. Backfill above the roof should be promptly filled to a depth sufficient to accommodate the embedded depth of the second anti-slip piles in the slope support structure.

[0028] Based on this, Figure 1-Figure 4 As shown, an embodiment of the present invention provides a permanent and temporary combined retaining structure suitable for high slope excavation, including a first anti-slip pile 1 and a second anti-slip pile 2 arranged on one side of the adjacent slope 9, and a supporting pile 3 arranged on the side of the non-adjacent slope 9, the second anti-slip pile 2 is located between the first anti-slip pile 1 and the second anti-slip pile 2, and the pile top elevations of the first anti-slip pile 1, the second anti-slip pile 2 and the supporting pile 3 decrease in sequence; a connecting beam 4 is transversely arranged between the pile top of the second anti-slip pile 2 and the pile body of the first anti-slip pile 1, and a multi-layer transverse support structure 5 is arranged in the foundation pit between the second anti-slip pile 2 and the supporting pile 3.

[0029] In this embodiment, a first pile crown beam 101 is provided on the top of the first anti-slip pile 1, a first retaining plate 102 is provided on the side of the first anti-slip pile 1 facing away from the slope 9, and a drainage hole is provided on the first retaining plate 102; a first prestressed anchor rod 103 anchored in the slope 9 is provided on the first anti-slip pile 1, and the outer end of the first prestressed anchor rod 103 is fixedly connected to the first anchor rod waist beam 104 provided on the first retaining plate 102.

[0030] In this embodiment, a second pile crown beam 201 is provided on the top of the second anti-slip pile 2, a second retaining plate 202 is provided on the side of the second anti-slip pile 2 facing away from the slope 9, and a drainage hole is provided on the second retaining plate 202; a second prestressed anchor rod 203 anchored in the slope 9 is provided on the second anti-slip pile 2, and the outer end of the second prestressed anchor rod 203 is fixedly connected to the second anchor rod waist beam 204 provided on the second retaining plate 202.

[0031] The above scheme uses graded support to optimize force distribution. The high slope 9 (0-30 m) faces significant soil pressure and potential sliding risk, making a single-stage anti-slide pile insufficient to effectively bear the entire load. By implementing two stages of anti-slide piles (the first stage consists of the first anti-slide pile 1, prestressed anchors, and retaining wall, and the second stage consists of the second anti-slide pile 2, prestressed anchors, and retaining wall), the soil pressure can be transferred to the deeper, stable strata in a graded manner, reducing the stress and deformation risk of a single pile. Graded support can adapt to the varying geological conditions (such as slope stability and geotechnical parameters) at different elevations of slope 9, improving the adaptability of the support structure. Overall stability is enhanced: The two-stage anti-slide piles form a spatial synergy with the coupling beam 4, which laterally connects the first and second anti-slide piles 2, forming a rigid frame structure. This significantly improves the overall resistance to overturning and sliding, enhancing the overall stability of the high slope. The coupling beam 4 constrains the lateral displacement of the anti-slide piles, preventing pile instability due to local soil deformation. Reduced excavation: The traditional slope-cutting and anchor lattice beam solution requires extensive excavation (a 1:1.50 slope). The combination of two-stage anti-slide piles and a temporary retaining structure (support piles 3 + internal supports) reduces the footprint of the temporary support structure, avoids excessive damage to the natural mountain landscape, and complies with environmental protection requirements. Phased construction improves efficiency: The first and second anti-slide piles 2 and coupling beams 4 are completed in phases during construction. Support measures can be dynamically adjusted based on the progress of the foundation pit excavation, shortening the construction period and reducing construction risks.

[0032] The earth pressure on the high slope 9 gradually increases with height, while the soil pressure distribution at the bottom of the foundation pit is complex after excavation. By designing the top elevations of the first anti-slope pile 1, the second anti-slope pile 2, and the support pile 3 to decrease in sequence (from the side adjacent to the slope 9 to the side not adjacent to the slope 9), the earth pressure on the high slope 9 is transferred in stages to the deeper, stable strata, preventing the failure of single-stage anti-slope piles due to excessive load. This step-by-step reduction in pile top elevation matches the layered excavation depth of the foundation pit, allowing the anti-slide piles to gradually exert their support function at different excavation stages, reducing deformation and uneven settlement of the entire structure.

[0033] In this embodiment, a first rotary jet pile 205 is arranged inside the second anti-slip pile 2 in an area adjacent to the foundation pit. The bottom elevation of the first rotary jet pile 205 needs to be lower than the bottom elevation of the foundation pit, and the bottom elevation of the second anti-slip pile 2 needs to be lower than the bottom elevation of the support pile 3. The embedding depth of the anti-slip pile on the mountain side is increased to ensure the safety of high slope projects.

[0034] In this embodiment, a third pile crown beam 301 is provided on the top of the support pile 3, and a second jet grouting pile 302 is provided inside the support pile 3 in an area adjacent to the foundation pit. The bottom elevation of the second jet grouting pile 302 needs to be lower than the bottom elevation of the foundation pit.

[0035] The core functions of the jet grouting piles in the above scheme are: (1) It has the function of a water-stop curtain, cutting off the groundwater infiltration path. The jet grouting piles and the anti-slip piles form a combined curtain, forming a continuous consolidation body through high-pressure jet grouting, effectively blocking the hydraulic connection between the groundwater inside and outside the foundation pit, preventing the pit bottom soil from rising or sand flow, and ensuring the dryness of the foundation pit and construction safety. Enhance the anti-seepage performance. The diameter (600mm) and spacing (1200mm) of the jet grouting piles are designed to cover the gaps between the anti-slip piles to form an overall water-stop barrier, which is especially suitable for water-rich strata or sandy soil layers. (2) It has the function of soil reinforcement and improves soil strength. The jet grouting piles mix with the in-situ soil by spraying cement slurry to form a high-strength jet grouting consolidation body (similar to artificial piles), which can improve the physical and mechanical properties of the pit bottom and surrounding soil and reduce the impact of soil deformation on the support structure. The bearing area of the pile end is expanded, and the bottom of the jet grouting pile is lower than the bottom of the foundation pit (for example, the bottom of the jet grouting pile of the second anti-slip pile 2 is 3m lower than the bottom of the foundation pit), which is equivalent to extending the embedding depth of the anti-slip pile, increasing the pile end resistance and enhancing the overall stability.

[0036] The design logic of the pile bottom elevation difference is as follows: (1) The bottom of the second anti-slip pile 2 is lower than the supporting pile 3 to adapt to the force difference between the slope 9 and the foundation pit. The second anti-slip pile 2 is located on the side adjacent to the slope 9 and needs to bear higher soil pressure and potential sliding force. The deeper pile bottom can enhance its embedded stability and prevent the slope 9 soil from sliding and causing the anti-slip pile to fail. The supporting pile 3 is located on the side not adjacent to the slope 9. The geological conditions are relatively stable and the pile bottom can be appropriately shallowed to save construction costs. Coordinate deformation and settlement. The stepped design of the pile bottom elevation (the second anti-slip pile 2 is deeper) can balance the settlement difference of the piles on both sides and avoid structural cracking or tilting caused by uneven settlement. (2) The bottom of the jet grouting pile is lower than the bottom of the foundation pit to prevent the soil at the bottom of the pit from rising. After the foundation pit is excavated, the soil at the bottom of the pit may rebound or rise due to unloading. The jet grouting pile penetrates the bottom of the foundation pit to a certain depth (such as 3m), which can restrain the deformation of the soil at the bottom of the pit and maintain the stability of the base. To suppress groundwater seepage damage, the jet grouting piles penetrate deep into the impermeable layer (such as clay layer or rock layer) to form a water-proof curtain, avoiding the risk of pressurized water bursts or pipe bursts at the bottom of the pit.

[0037] In this embodiment, the transverse support structure 5 includes a first internal support 501, a second internal support 502 and a third internal support 503. One end of the first internal support 501 is fixed to the third pile crown beam 301 at the top of the supporting pile 3, and the other end is fixed to the concrete waist beam 7 on the side wall of the second anti-slip pile 2; the second internal support 502 and the third internal support 503 are both located below the first internal support 501, and one end of the second internal support 502 and the third internal support 503 are both against the steel purlin 6 on the inner wall of the second anti-slip pile 2, and the other end are both against the inner wall of the supporting pile 3.

[0038] In the above scheme, the support structure is divided into three layers, which are constructed layer by layer from top to bottom, which perfectly matches the construction process of "layered excavation and support as excavation" of the foundation pit. The first internal support 501: is constructed immediately after excavation reaches the crown beam elevation of the support pile 3, quickly closing the top of the foundation pit to prevent the instability of the slope 9 soil. The second and third internal supports 503: as the foundation pit is excavated downward layer by layer, prestressing is gradually applied to ensure that the deformation of the soil after each layer of excavation is controllable. The three internal supports, anti-slip piles, connecting beams 4, and crown beams together form a three-dimensional spatial structure, reducing construction risks. The layered support avoids the risk of collapse caused by excessive exposure of the foundation pit area, especially in soft strata or high groundwater levels, and can effectively control the deformation of the foundation pit.

[0039] In this embodiment, the first inner support 501 is a M-shaped reinforced concrete structure.

[0040] The M-shaped reinforced concrete support provides uniform load distribution in all directions, making it particularly suitable for the complex load-bearing environment on the side of high slope 9 (adjacent slope 9). Its rigid structure effectively resists soil pressure, groundwater pressure, and potential slip forces. Working in synergy with the crown and middle beams, the rigid connection between the crown beam of the support pile 3 and the concrete middle beam 7 of the second anti-slip pile 2 forms a coordinated "crown beam-support-middle beam" system, distributing soil pressure to deeper, stable strata.

[0041] In this embodiment, the second inner support 502 and the third inner support 503 both include multiple intermediate sections 504 and fixed ends 505 and movable ends 506 arranged at both ends of the intermediate sections 504. The movable end 506 abuts against the steel purlin 6, and the fixed end 505 abuts against the inner wall of the support pile 3. The multiple intermediate sections 504 are connected by flange bolts, which is convenient for quick assembly and disassembly and is suitable for scenarios that require repeated use. The fixed end 505 is connected to the intermediate section 504 by welding or flange bolts. During the construction of the support pile 3, a steel plate with anchor bars can be pre-embedded, and the steel support fixed end 505 is fixed thereto by welding or high-strength bolts. The movable end 506 is connected to the intermediate section 504 by an adjustable device, which is usually a hinged structure with a flange or a telescopic structure with a built-in jack. The movable end 506 needs to be designed to be detachable so that it is convenient to lock the position with a steel wedge after prestressing is applied.

[0042] The first anti-slide pile, the second anti-slide pile and the support pile are all bored cast-in-place piles. Their main technical parameters are as follows: The pile diameter and length should be determined according to the geological conditions, slope height, and foundation pit excavation depth. The bored piles of this subway station have a diameter of 1000mm / 1200mm and a spacing of 1200mm / 2000mm. (2) Mud preparation Use a dedicated mud mixer to ensure that the mud is evenly mixed. Bentonite with stable quality and excellent performance should be selected. The mud density is generally controlled between 1.05-1.25, and is adjusted according to the geological conditions and construction requirements. The sand content should be less than 4% to reduce wear on the drill bit and damage to the hole wall. The pH value of the mud is generally controlled between 8-10 to maintain the stability of the mud. (3) Select a suitable drilling rig based on the geological conditions, pile diameter, and hole depth. During the drilling process, use equipment such as inclinometers to monitor the verticality of the borehole in real time and make timely adjustments to ensure that the verticality deviation of the borehole generally does not exceed 1%. (4) High-quality mud should be used for wall protection. The mud injection rate should match the drilling speed to ensure that the mud can fill the borehole in time and form an effective wall protection layer. (4) After drilling, the final hole inspection phase is carried out to check the hole position, hole diameter, hole depth, hole shape, etc. to ensure that there are no errors and pass the inspection before cleaning the hole. (5) The hole diameter should meet the design requirements, and the deviation should be controlled within ±50mm. The hole depth should reach the design elevation to ensure that the pile end enters the bearing layer.

[0043] The technical parameters of the first and second rotary jet grouting piles are as follows: The jet grouting piles and anti-slip piles form a combined curtain to stop water and enhance the anti-seepage performance of the support structure. One jet grouting pile is used for each pile. The jet grouting piles are 3m deep into the foundation pit, with a diameter of 600mm and a spacing of 1200mm. (2) The jet grouting piles use a cement slurry with a water-cement ratio of 0.8-1.0. 32.5R composite silicate cement is used for slurry preparation. In order to maintain the shape of the jet grouting body, an appropriate amount of accelerator is added. (3) The high-pressure pump pressure is 25-30MPa, the nozzle diameter is 2.00-2.80mm, the drill pipe rotation speed is 15-25r / min, the drill pipe lifting speed is 10-15cm / min, the slurry material and mix ratio are 0.8-1.0, and the cement dosage is 150kg / m.

[0044] The technical parameters of the first and second prestressed anchor rods are as follows: (1) Anti-sliding piles are set up at the slope support position with three prestressed anchor rods, one at a time. The anchor rods are made of 6 bundles of low-relaxation high-strength steel strands with a nominal diameter of 15.2mm, with a length of 24m-27m and an anchoring length of 11m. The anchor head is set with a reinforced concrete waist beam. (2) The grouting material is pure cement slurry with a water-cement ratio of 0.5-0.6 mixed with 42.5R composite silicate cement. (3) During the first grouting, a grouting pump is used to transport the slurry to the bottom of the hole through the grouting pipe, and then return it to the hole mouth from the bottom of the hole. When the slurry overflows from the hole mouth, the grouting can be stopped. After 4 hours, a high-pressure grouting pump is used for the second grouting. (4) When the anchor body strength is greater than 75% of the design strength, tensioning is carried out. Prestress is applied in stages according to the design requirements. After each stage of tensioning, the pressure is stabilized for a period of time and the elongation value is recorded. (5) After tensioning to the design value, the anchor is locked and the prestress loss is checked to ensure that it is within the allowable range. (6) The second prestressed anchor rod 203 should be set away from the first anti-slip pile 1 to avoid damaging the first anti-slip pile 1 during construction.

[0045] The technical parameters of the first, second and third internal supports are as follows: (1) Internal supports are set at the temporary retaining structure of the subway station foundation pit, with a total of three internal supports. (2) The first internal support is a reinforced concrete cross brace, cast with C30 concrete, with a cross-sectional size of 700×1000mm, a horizontal spacing of 9m, and is set at an elevation of 43.65m. A 1000×1000mm concrete waist beam is set at the support end. (3) The second and third internal supports are both steel supports. The steel supports are made of round tubes with a diameter of 800mm and a wall thickness of 16mm, Q355B grade steel, with a horizontal spacing of 3m, and are set at elevations of 36.6m and 31.65m respectively. The steel enclosure is constructed with two I56c composite steel sections, and the gap between the steel enclosure and the pile is filled with C30 fine stone concrete to maintain the integrity and stability of the structure.

[0046] The embodiment of the present invention further provides a construction method of a permanent and temporary combined retaining structure suitable for high slope excavation, the construction method comprising: Step 1: Relocate the existing pipelines within the station area, complete the first site leveling to elevation 1, construct the first anti-slip pile, the first pile crown beam, the first retaining wall, the first prestressed anchor rod, the first anchor rod waist beam, and excavate to the platform section to complete the first level of pile-plate retaining wall protection.

[0047] Step 2: Complete the second site leveling to elevation 2, construct the second anti-slip pile, the first rotary jet pile, the second pile top beam, the second retaining plate, the second prestressed anchor rod, the second anchor rod waist beam, and set a connecting beam between the first anti-slip pile and the second anti-slip pile.

[0048] The position and angle of the anchor rods are determined according to the design drawings. The prepared anchor rods are slowly inserted into the drilled holes to avoid damaging the first anti-slip pile. The anchor rods are then tensioned in stages. After tensioning is completed, the anchor rods are locked with anchors to maintain the prestress. If the construction schedule permits, the prestressed anchor rods can be constructed after all anti-slip piles are completed. This way, the anti-slip pile construction will not be interfered with by the anchor rod construction, and the construction efficiency is high. During the anchor rod construction, the anti-slip piles have formed a stable support, facilitating the positioning and tensioning of the anchor rods. If the construction schedule is tight, anti-slip piles and prestressed anchor rods can also be constructed alternately. First, a portion of the anti-slip piles are constructed (e.g., one for every few piles). After the strength of the constructed anti-slip piles reaches the required level, anchor rod construction is carried out in the corresponding area. The anti-slip pile and anchor rod construction are then carried out alternately until all are completed.

[0049] Step 3: Complete the third site leveling to elevation 3, construct the support piles on the side not adjacent to the slope, the second rotary jet grouting piles, and the dewatering well in the pit.

[0050] Step 4: Excavate the foundation pit to the bottom elevation of the third pile top beam, and construct the third pile top beam and the first internal support.

[0051] Step 5: After the crown beam of the third pile and the first internal support reach the designed strength, excavate the foundation pit from top to bottom. According to the principle of supporting while digging, complete the construction of steel purlins, the second internal support, and the third internal support, and excavate to the bottom of the foundation pit.

[0052] During excavation, proper drainage of the foundation pit is crucial. This dewatering process should continue throughout the structural construction process. After the top slab is covered with soil, the dewatering wells are sealed, micro-expansive concrete is poured, and steel plates are welded to seal the holes. Steel supports are fabricated off-site, with specialists completing their measurements and layout during this time to ensure efficient construction. The steel supports are constructed from Ø800 welded steel pipe with a wall thickness of 16mm. The longitudinal welds are double-sided, V-grooved. The pipes are factory-fabricated in sections. After ensuring the quality of each section, they are assembled on-site. First, the steel purlin supports are installed. A gantry crane is then used to hoist the pipe supports into position. The flexible ends are extended to support the steel purlins. Under the guidance of a specialist, two 100t jacks are operated jointly to lower them onto the flexible ends. The oil pipeline connections are then connected. The construction is inspected and, if correct, prestressing is applied. During installation, the axes of the waist beam, end cap, and jack must be aligned. To ensure straightness, the flange bolts on the cross brace should be tightened diagonally and in equal intervals. When the longitudinal waist beam is in place, it should be placed slowly on the steel support without any impact. The jack itself must be equipped with a pressure gauge and calibrated in a laboratory before use. Both jacks must be prestressed simultaneously, and the prestressing should be applied in stages. Once the design value is reached, the steel wedges must be tightened before the jacks can be removed. During construction, ensure that the over-excavation depth for each support does not exceed 0.5 meters.

[0053] Step 6: Treat the bottom of the foundation pit, construct the cushion layer, grounding, lay the waterproof layer, construct the bottom plate and bottom beam, and reserve construction joints on the side walls.

[0054] Step 7: After the base plate reaches the designed strength, remove the third inner support and cast part of the side wall, continue to lay the waterproof layer upwards, cast the side wall structure, and construct the columns, middle longitudinal beams and middle plate.

[0055] Step 8: After the middle plate reaches the designed strength, remove the second support, continue to lay the waterproof layer upwards, and construct the remaining columns, side walls, top longitudinal beams and top plate of the station hall.

[0056] Step 9: After the roof structure strength reaches the design strength, remove the first support, lay the roof waterproof layer, construct the anti-floating pressure beam, backfill the soil, restore the road surface, and construct the internal structure of each floor of the station.

[0057] A composite planting system of trees, shrubs, and herbs is employed on the station roof and flat plazas to improve land utilization and enhance the landscape's greening effect, creating a three-dimensional street corner park. Two vertical retaining walls are decorated with climbing plants, creating an overall green landscape that harmonizes with the natural landscape.

[0058] The above is only a preferred embodiment of the present invention, but the present invention is not limited to the above specific embodiment. Those skilled in the art may make several modifications, supplements or use similar methods instead without departing from the principles of the present invention, and these should also be considered as the scope of protection of the present invention.

Claims

1. A permanent and temporary combined retaining structure suitable for high slope excavation, characterized by: The invention comprises a first anti-slip pile (1) and a second anti-slip pile (2) arranged on a side adjacent to a side slope (9), and a support pile (3) arranged on a side not adjacent to the side slope (9), wherein the second anti-slip pile (2) is located between the first anti-slip pile (1) and the second anti-slip pile (2), and the pile top elevations of the first anti-slip pile (1), the second anti-slip pile (2) and the support pile (3) decrease in sequence; a connecting beam (4) is transversely arranged between the pile top of the second anti-slip pile (2) and the pile body of the first anti-slip pile (1), and a multi-layer transverse support structure (5) is arranged in the foundation pit between the second anti-slip pile (2) and the support pile (3).

2. The permanent and temporary combined retaining structure suitable for high slope excavation according to claim 1 is characterized in that: A first pile crown beam (101) is provided on the top of the first anti-sliding pile (1); a first retaining plate (102) is provided on the side of the first anti-sliding pile (1) facing away from the slope (9); a drainage hole is provided on the first retaining plate (102); a first prestressed anchor rod (103) anchored in the slope (9) is provided on the first anti-sliding pile (1); an outer end of the first prestressed anchor rod (103) is fixedly connected to a first anchor rod waist beam (104) provided on the first retaining plate (102).

3. The permanent and temporary combined retaining structure suitable for high slope excavation according to claim 1 is characterized in that: A second pile crown beam (201) is provided on the top of the second anti-slip pile (2); a second retaining plate (202) is provided on the side of the second anti-slip pile (2) facing away from the slope (9); a drainage hole is provided on the second retaining plate (202); a second prestressed anchor rod (203) anchored in the slope (9) is provided on the second anti-slip pile (2); an outer end of the second prestressed anchor rod (203) is fixedly connected to a second anchor rod waist beam (204) provided on the second retaining plate (202).

4. The permanent and temporary combined retaining structure suitable for high slope excavation according to claim 1 is characterized in that: A first jet grouting pile (205) is arranged inside the second anti-slip pile (2) in an area adjacent to the foundation pit, and the bottom elevation of the first jet grouting pile (205) needs to be lower than the bottom elevation of the foundation pit.

5. The permanent and temporary combined retaining structure suitable for high slope excavation according to claim 1 is characterized in that: A third pile crown beam (301) is provided on the top of the support pile (3), and a second jet grouting pile (302) is provided inside the support pile (3) in an area adjacent to the foundation pit. The bottom elevation of the second jet grouting pile (302) must be lower than the bottom elevation of the foundation pit.

6. The permanent and temporary combined retaining structure suitable for high slope excavation according to claim 1 is characterized in that: The transverse support structure (5) comprises a first inner support (501), a second inner support (502) and a third inner support (503), wherein one end of the first inner support (501) is fixed to the third pile crown beam (301) at the top of the support pile (3), and the other end is fixed to the concrete waist beam (7) on the side wall of the second anti-slip pile (2); the second inner support (502) and the third inner support (503) are both located below the first inner support (501), and one end of the second inner support (502) and the third inner support (503) are both against the steel purlin (6) on the inner wall of the second anti-slip pile (2), and the other end are both against the inner wall of the support pile (3).

7. The permanent and temporary combined retaining structure suitable for high slope excavation according to claim 6 is characterized in that: The first inner support (501) is a M-shaped reinforced concrete structure.

8. The permanent and temporary combined retaining structure suitable for high slope excavation according to claim 6 is characterized in that: The second inner support (502) and the third inner support (503) both include multiple intermediate sections (504) and fixed ends (505) and movable ends (506) arranged at both ends of the intermediate sections (504), the movable ends (506) abutting against the steel purlin (6), and the fixed ends (505) abutting against the inner wall of the support pile (3).

9. A construction method for a permanent and temporary combined retaining structure suitable for high slope excavation according to any one of claims 1 to 8, characterized in that: The construction method comprises: Step 1: relocate the existing pipelines within the station area, complete the first site leveling to elevation 1, construct the first anti-slide pile (1), the first pile top beam (101), the first retaining plate (102), the first prestressed anchor rod (103), the first anchor rod waist beam (104), and excavate to the platform section to complete the first-level pile-plate retaining wall protection; Step 2: Complete the second site leveling to the second elevation, construct the second anti-slide pile (2), the first jet-jet pile (205), the second pile top beam (201), the second retaining plate (202), the second prestressed anchor rod (203), the second anchor rod waist beam (204), and set a connecting beam (4) between the first anti-slide pile (1) and the second anti-slide pile (2); Step 3: Complete the third leveling to elevation 3, construct the support piles (3) on the side not facing the slope (9), the second jet grouting piles (302), and the dewatering well in the pit; Step 4: excavate the foundation pit to the bottom elevation of the third pile top beam (301), and construct the third pile top beam (301) and the first inner support (501); Step 5: After the third pile crown beam (301) and the first inner support (501) reach the design strength, the foundation pit is excavated from top to bottom. According to the principle of excavation and support, the construction of the steel purlin (6), the second inner support (502), and the third inner support (503) is completed, and the excavation is carried out to the bottom of the foundation pit; Step 6: Prepare the bottom of the foundation pit, construct the cushion layer, ground it, lay the waterproof layer, construct the bottom plate and bottom beam, and reserve construction joints on the side walls; Step 7: After the bottom plate reaches the designed strength, remove the third inner support (503) and cast part of the side wall, continue to lay the waterproof layer upwards, cast the side wall structure, and construct the columns, middle longitudinal beams and middle plate; Step 8: After the middle plate reaches the designed strength, remove the second support, continue to lay the waterproof layer upwards, and construct the remaining columns, side walls, top longitudinal beams and top plate of the station hall; Step 9: After the roof structure strength reaches the design strength, remove the first support, lay the roof waterproof layer, construct the anti-floating pressure beam, backfill the soil, restore the road surface, and construct the internal structure of each floor of the station.

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