Construction method of prefabricated cable shaft and shaft structure

Abstract

The application belongs to the technical field of underground engineering, and discloses a construction method of a prefabricated cable shaft and a shaft structure. In view of the problem that the existing shaft construction is prone to damage to the adjacent existing subway facilities in deep and soft strata, the construction method comprises the following steps: using a rotary digging tool to form a hole and simultaneously following up to sink a construction casing; hoisting the prefabricated shaft structure with a closed bottom into the casing and injecting water to resist floating; installing an embedded guide isolation component at the cable entry and exit reserved hole of the side wall of the structure main body, simultaneously removing the casing in sections while grouting, and continuing to remove the next section after the filling material reaches the strength; after the shaft is completely constructed and it is confirmed that there is no obvious water seepage, the hole is cleaned and the cable is laid. The application fundamentally avoids unloading rebound of the open cut method and soil squeezing effect of the caisson method, overcomes the deep water anti-floating problem, guarantees the smoothness of the cable passage, realizes the unity of extremely low stratum disturbance and extremely high construction efficiency, and effectively protects the safety of the existing underground facilities.

Description

Technical Field

[0001] This invention relates to the fields of underground engineering and urban rail transit technology, specifically to a construction method and shaft structure for a prefabricated cable shaft. Background Technology

[0002] During the construction and operation of urban rail transit networks, existing subway tunnels often experience partial breaks in sections due to the construction of new lines and hub renovations, resulting in cable severance. Such cable severance directly causes the failure of the corresponding section's power and communication systems, seriously affecting the orderly operation of the urban transportation system and the safety and smooth travel of citizens. It is urgent to connect the cables at both ends by combining ground cables with vertical shafts.

[0003] In specific scenarios involving deep, soft strata (such as silty sand and muddy soil layers with a thickness exceeding 17m and exhibiting high compressibility and low rheological strength) and the need to protect existing underground facilities (such as operating subway tunnels directly beneath or adjacent to the site), shaft construction faces significant risks. Current technologies primarily employ open-cut or caisson methods. (1) The open-cut method of excavating and unloading the foundation pit is very likely to cause the soil at the bottom of the pit to rebound, which directly causes the tunnel below or adjacent to rise, resulting in the cracking of the segments and the opening of the joints; and the construction period of the open-cut construction of ultra-deep vertical shafts in soft soil areas is as long as 1 to 2 years and the cost is high. (2) The soil squeezing effect generated during the sinking of the caisson method will create additional lateral pressure on the tunnel segments, leading to segment damage; at the same time, the soil plugging effect will cause the soil at the bottom of the caisson to rise and be transmitted in the opposite direction to the bottom of the tunnel, causing upward deformation, and the quality of underwater sealing is difficult to control.

[0004] In summary, existing shaft construction techniques, when dealing with deep and soft strata, are prone to causing severe and uncontrollable structural disturbances to surrounding existing underground facilities. Furthermore, they suffer from significant drawbacks such as long construction periods, high costs, and difficulties in ensuring the quality of the sealing layer. Therefore, there is an urgent need in this field to develop a new shaft construction scheme that balances geological adaptability, construction efficiency, and minimal disturbance to existing facilities. Summary of the Invention

[0005] To address the significant shortcomings of existing shaft construction technologies in terms of adaptability to deep, soft strata and protection of existing underground facilities, this invention proposes a construction method and structure for prefabricated cable shafts. This method achieves rapid construction while controlling deformation of surrounding existing tunnels within a safe range, balancing construction safety and operational reliability. The specific technical solution is as follows: A construction method for a prefabricated cable shaft includes the following steps: S1. Use rotary drilling equipment to perform vertical shaft drilling operations, and simultaneously sink the construction casing during the drilling operation. The sinking depth of the construction casing is consistent with the current drilling depth until the design elevation of the vertical shaft is reached. S2. The prefabricated shaft structure is hoisted into the construction casing as a whole, and water is injected into the internal cavity of the shaft structure to counteract buoyancy during the sinking process; wherein, the shaft structure includes a main body with an open top and a bottom sealed by a steel plate, and a cable support pre-installed inside the main body of the structure, and the side wall of the main body of the structure is provided with reserved holes for cable entry and exit; S3. After the shaft structure is lowered to the design elevation and the planar position and verticality of the shaft structure are adjusted, temporary supports are used for fixation. S4. Install embedded guide isolation components at the cable entry and exit reserved holes on the side wall of the main structure to form a physical isolation area between the cable entry and exit reserved holes and the inner wall of the construction casing; then, fill the annular gap between the outer wall of the main structure and the inner wall of the construction casing in layers and compact it with vibration; during the filling of the filling material, remove the construction casing in sections simultaneously, and after each section of the filling material reaches the preset strength, continue to remove the next section of the construction casing upwards; S5. After the construction casing is completely removed and the filling material reaches the preset strength requirement, the temporary support is removed, and the surface voids generated after the construction casing is removed are backfilled and compacted. After the overall construction of the shaft project is completed and it is confirmed by inspection that there is no obvious water seepage in the entire shaft, the cable can be laid. The reserved holes for cable entry and exit are cleaned, and the cable is inserted into the shaft through the reserved holes and fixed and sealed in layers along the cable support.

[0006] In a preferred implementation, the use of rotary drilling rigs for vertical shaft drilling specifically includes: The center of the drill rod of the rotary drilling machine is aligned with the center of the hole-forming operation, with the deviation controlled within 10mm; the deviation of the hole diameter is controlled within ±50mm; and the deviation of the sinking depth is controlled between +100mm and -50mm.

[0007] In a preferred implementation, adjusting the planar position and verticality of the shaft structure specifically includes: A total station is used to monitor in real time the deviation of the actual center of the shaft structure from the design center in terms of planar position and verticality. The deviation of the planar position from the design center is controlled within ±20mm, and the deviation of the verticality is controlled ≤1‰.

[0008] In a preferred embodiment, the filling material is cement mortar, and the pouring height of each layer in the layered pouring is ≤500mm; and the preset strength requirement is to reach more than 75% of the design strength of the filling material; the backfilling and compaction treatment adopts graded sand and gravel layered backfilling and compaction, and controls the backfill density to ≥95%.

[0009] In a preferred implementation, removing the construction casing specifically includes: A vibratory hammer fixed to the top of the construction casing is used to separate the construction casing from the surrounding soil, and then it is lifted upwards by a lifting device.

[0010] A prefabricated cable shaft structure, applied in any of the above-described construction methods, the shaft structure comprising: The main body of the structure is cylindrical, and a sealing steel plate is fixed at the bottom of the main body to form a U-shaped cavity with an open top. The side wall of the main body of the structure is provided with reserved holes for cable entry and exit. Multiple sets of cable brackets are arranged at intervals along the vertical direction and are symmetrically fixed to both sides of the inner wall of the main structure. A ladder is fixedly connected to the inner wall of the main structure in a vertical direction, and the ladder is located beside the multiple sets of cable supports; A waterproof sealing ring is fixedly installed at the cable entry and exit reserved hole on the side wall of the main structure, and the outer side of the waterproof sealing ring is provided with an embedded guide isolation component for isolating the filling material during injection. A bottom concrete slab is poured at the bottom of the U-shaped cavity above the sealing steel plate.

[0011] In a preferred embodiment, the main body of the structure is made of Q355 steel, and the thickness of the main body of the structure is 30mm to 50mm; and the thickness of the waterproof sealing ring is ≥10mm.

[0012] In a preferred implementation, the multiple cable brackets are angle steel or I-beam structures, and the two sides of the multiple cable brackets are fully welded to the inner wall of the main structure.

[0013] In a preferred implementation, the shaft structure further includes: Multiple rest platforms are fixedly and vertically spaced on the inner wall of the main structure above the multiple sets of cable supports; The rest platform is a semi-circular steel plate structure, the vertical distance between two adjacent rest platforms is 6m, and the thickness of the semi-circular steel plate structure is ≥10mm.

[0014] In a preferred embodiment, the main structure, the multiple cable supports, the ladder, the multiple rest platforms, and the waterproof sealing ring are all components that are welded and formed in the factory during the prefabrication stage.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention adopts a process of rotary drilling rig drilling and simultaneous construction of casing, and innovatively adopts a non-continuous construction logic of "synchronous segmented removal and real-time replacement under pressure". By removing the casing in segments during the grouting process and waiting for the filling material to reach the preset strength, the hardened filling material provides lateral support in real time, ensuring the pressure balance of the borehole wall in the soft strata. This fundamentally avoids the risk of borehole wall instability or collapse caused by the casing being removed too quickly at once, effectively avoiding the unloading rebound of the traditional open excavation method and the soil squeezing effect of the caisson method, and controlling the construction disturbance at an extremely low level.

[0016] (2) By prefabricating the shaft structure in the factory and then hoisting it as a whole, the present invention directly eliminates the complicated procedures such as on-site foundation pit support, large-volume concrete pouring and long curing. At the same time, during the hoisting and sinking process, water is cleverly injected into the U-shaped internal cavity for counterweight. The dynamic water gravity effectively counteracts the huge Archimedes buoyancy generated in the deep water-rich soft soil layer, ensuring that the shaft can sink into place quickly and accurately, and greatly reducing the overall construction period from the traditional several months or even several years.

[0017] (3) The present invention introduces an embedded guide isolation component at the reserved hole, which on the one hand eliminates the risk of the isolation component being damaged by collision with the external construction casing or temporary support during the deep well hoisting process; on the other hand, it realizes the physical occupation of the hole space during the grouting stage, which not only protects the hole from being blocked by mortar, but also avoids irreversible damage to the waterproof sealing ring sealing structure caused by the need for secondary drilling due to the hole being blocked in the later stage, thus ensuring the long-term water-free operation of the vertical shaft in complex hydrological environment. Attached Figure Description

[0018] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0019] Figure 1 A cross-sectional view of a vertical shaft provided in an embodiment of the present invention; Figure 2 A plan view (AA section) of the vertical shaft structure provided for an embodiment of the present invention; Figure 3 A cross-sectional view of a rest platform provided in an embodiment of the present invention; Figure 4 A cross-sectional view (BB cross-section) of the reserved hole in the sidewall of the vertical shaft provided for an embodiment of the present invention. Figure 5A vertical shaft construction monitoring data table provided for embodiments of the present invention.

[0020] In the diagram: 1. Main structure; 2. Cable support; 3. Ladder; 4. Rest platform; 5. Waterproof sealing ring; 6. Bottom concrete slab; 7. Construction casing; 8. Filling material. Detailed Implementation

[0021] The present invention will be further described below through specific embodiments, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or improvements based on the basic idea of ​​the present invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the protection scope of the present invention.

[0022] like Figures 1 to 4 As shown, this embodiment of the invention provides a prefabricated cable shaft structure, which can be widely used in the restoration and connection project of existing subway tunnel cables after they have been cut in urban rail transit. It is particularly suitable for harsh construction scenarios with deep and weak strata (such as widely distributed deep fine sand and silty soil layers) and where it is necessary to protect existing underground facilities at close range.

[0023] The prefabricated cable shaft structure of this invention mainly includes: a cylindrical structural body 1, with a sealing steel plate fixed at the bottom of the structural body 1, thus forming a U-shaped cavity with an open top together with the side wall; and reserved holes for cable entry and exit are provided on the side wall of the structural body 1. To resist the huge water and soil pressure outside the shaft, the structural body 1 is made of Q355 steel, with an inner diameter designed to be between 1.5m and 2m, and the thickness of the structural body 1 is preferably between 30mm and 50mm. Meanwhile, to resist the water pressure at the bottom of the shaft, a bottom concrete slab 6 is poured at the bottom of the U-shaped cavity above the sealing steel plate. This bottom concrete slab 6 is a concrete and steel reinforcement structure, and its specific thickness and reinforcement need to be calculated and determined according to the actual bottom water pressure of the project.

[0024] Within the internal cavity of the main structure 1, multiple sets of cable supports 2 are arranged vertically at intervals. These cable supports 2 are symmetrically and fixedly connected to both sides of the inner wall of the main structure 1, used for the classified laying and support of various types of cables. The cable supports 2 can be constructed using angle steel or I-beams, and their sides are fully welded to the inner wall of the main structure 1 to ensure load-bearing strength. To facilitate subsequent maintenance and cable installation, ladders 3 are fixedly connected vertically to the inner wall of the main structure 1, and the ladders 3 are arranged beside the cable supports 2.

[0025] Furthermore, to ensure the safety and physical recovery of workers inside the deep shaft, multiple rest platforms 4 are fixedly installed vertically at intervals on the inner wall of the main structure 1 above the multiple sets of cable supports 2. Each rest platform 4 is a semi-circular steel plate structure with a thickness of not less than 10mm, and the vertical distance between adjacent rest platforms 4 is set to 6m. Waterproof sealing rings 5, with a thickness of not less than 10mm, are fixedly installed at the cable entry and exit pre-reserved holes on the side wall of the main structure 1. These rings are used for waterproof sealing of cables and conduits entering and exiting the shaft, and the outer side of the waterproof sealing rings 5 ​​is equipped with embedded guide isolation components to isolate the filling material during injection. Notably, the main structure 1, multiple sets of cable supports 2, ladders 3, multiple rest platforms 4, and waterproof sealing rings 5 ​​are all prefabricated components welded together in the factory, thereby minimizing on-site construction work.

[0026] Based on the aforementioned prefabricated cable shaft structure, this embodiment of the invention also provides a construction method for prefabricated cable shafts. In actual construction: First, a rotary drilling rig is used for vertical shaft drilling. After the rig is in place, the verticality of the drill rod must be strictly adjusted to ensure that the center of the drill rod is aligned with the center of the drilling operation, with a deviation controlled within 10mm. During the layered drilling operation, the casing 7 is simultaneously lowered, ensuring that the lowering depth of the casing 7 remains consistent with the current drilling depth until the designed elevation of the shaft is reached. At this stage, borehole probes and other equipment are used for inspection, controlling the deviation of the borehole diameter within ±50mm and the deviation of the lowering depth between +100mm and -50mm to ensure borehole quality and borehole wall stability.

[0027] After the borehole is drilled, the prefabricated shaft structure, including the main structure 1 and the cable support 2 pre-installed within it, is hoisted into the construction casing 7. Because the bottom of the shaft structure is sealed by a steel plate and is large in volume, it will experience significant buoyancy when sinking in water-rich strata. Therefore, during the hoisting and sinking process, water is simultaneously injected into the internal cavity of the shaft structure as a counterweight. The weight of the water counteracts the buoyancy, allowing the shaft structure to sink smoothly. After the shaft structure sinks to the design elevation, a total station is used to monitor the actual center of the shaft structure relative to the design center in real time, as well as its verticality. Fine-tuning with a crane ensures precise positioning of the components, controlling the deviation of the plane position relative to the design center to within ±20mm and the verticality deviation to no more than 1‰. After adjustment, temporary supports made of materials such as steel sections are used to fix the shaft structure and prevent it from shifting.

[0028] After the fixing is completed, since there are reserved holes for cable entry and exit on the side wall of the main structure 1, direct grouting would seal the holes. Therefore, an embedded guide isolation component needs to be installed at the reserved holes for cable entry and exit on the side wall of the main structure 1 to form a physical isolation area between the reserved holes for cable entry and exit and the inner wall of the construction casing 7. In this embodiment, the embedded guide isolation component is mainly used to physically occupy the hole space during the grouting stage to ensure the smooth passage of cables later. Considering the differences in different construction environments and operational levels, in order to avoid the potential risk of collision between the isolation component and the temporary support or construction casing 7 during deep well hoisting, as a preferred embodiment, the outer end face of the embedded guide isolation component can be designed not to protrude from the outer wall of the main structure 1. Although secondary drilling (such as re-drilling an 89mm inlet / outlet within a 100mm hole) is often used as a remedial method in actual engineering, this design can further improve the fault tolerance of the hoisting operation, ensure the smooth sinking and positioning of the prefabricated components, and effectively protect the edge integrity of the waterproof sealing ring 5, avoiding damage to the sealing performance caused by component damage or forced secondary drilling later. Subsequently, debris and accumulated water in the gap are cleaned, and filling material 8 is poured in layers into the annular gap between the outer wall of the main structure 1 and the inner wall of the construction casing 7. The filling material 8 is preferably cement mortar selected according to the stratum, and the pouring height of each layer is controlled within 500mm, and it is compacted with a vibrator to prevent quality defects such as voids and honeycombs.

[0029] During the layered injection of the filling material 8, the construction casing 7 is simultaneously removed in sections. Specifically, during removal, the vibratory hammer fixed to the top of the construction casing 7 is turned on to fully separate the construction casing 7 from the surrounding soil, and then it is lifted out in sections by lifting equipment.

[0030] Based on the site geological conditions and the performance of the filling material, the preferred removal distance for each segment of the construction casing 7 is 5 meters. In actual operation, after one segment of the construction casing 7 is removed, the removal operation must be temporarily stopped until the filling material 8 of that segment reaches the preset strength requirement (e.g., 75% of the design strength). Then, its hardened lateral support force is used to stabilize the borehole wall in real time, preventing instability or collapse of the borehole wall due to the rapid removal of the casing in weak strata. The next segment is then removed. After the construction casing 7 is completely removed and all the filling material 8 has reached the preset strength requirement, the temporary support is removed, and the surface voids are promptly backfilled with graded sand and gravel in layers and compacted. The backfill density is strictly controlled to be no less than 95% to effectively prevent ground subsidence. This "segmented strengthening" replacement process effectively prevents borehole wall instability in weak strata.

[0031] After the entire shaft project is completed and on-site inspection confirms that there are no obvious signs of water seepage inside the shaft and that it is in a dry and stable operating environment, formal cable laying operations can begin. Workers will clean the guide and isolation components and debris from the cable entry and exit holes inside and on the side walls of the shaft to ensure unobstructed passage. Then, the cables will be introduced into the shaft from the ground, laid in layers along the prefabricated cable support 2 and reliably fixed. Horizontal cables will pass through the pre-drilled holes into the shaft and reliably connect with the vertical cables. After the cables are laid, the waterproof sealing ring 5 will be sealed to prevent groundwater from seeping into the shaft along the passage. Finally, cable performance testing will be completed to ensure that the laying quality meets the usage requirements.

[0032] like Figure 5 As shown in the monitoring data table, when using the prefabricated structure and construction method of this invention for shaft construction near an existing subway tunnel, the cumulative maximum horizontal displacement was only -1.86mm. All monitoring indicators were far below the warning values, and the deformation was precisely controlled at an extremely low level, effectively reducing the safety risks of construction in deep, soft strata. Simultaneously, the process of rotary drilling combined with prefabricated component hoisting significantly simplified the time-consuming on-site pouring and curing procedures, effectively reducing the overall construction period from several months required by the traditional open-cut method to 7-14 days. This achieved intensive management of the construction cycle and significantly improved the project's economic benefits.

[0033] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A construction method for a prefabricated cable shaft, characterized in that, Includes the following steps: S1. Use rotary drilling equipment to perform vertical shaft drilling operations, and simultaneously sink the construction casing during the drilling operation. The sinking depth of the construction casing is consistent with the current drilling depth until the design elevation of the vertical shaft is reached. S2. The prefabricated shaft structure is hoisted into the construction casing as a whole, and water is injected into the internal cavity of the shaft structure to counteract buoyancy during the sinking process; wherein, the shaft structure includes a main body with an open top and a bottom sealed by a steel plate, and a cable support pre-installed inside the main body of the structure, and the side wall of the main body of the structure is provided with reserved holes for cable entry and exit; S3. After the shaft structure is lowered to the design elevation and the planar position and verticality of the shaft structure are adjusted, temporary supports are used for fixation. S4. Install embedded guide isolation components at the cable entry and exit reserved holes on the side wall of the main structure to form a physical isolation area between the cable entry and exit reserved holes and the inner wall of the construction casing; then, fill the annular gap between the outer wall of the main structure and the inner wall of the construction casing in layers and compact it with vibration; during the filling of the filling material, remove the construction casing in sections simultaneously, and after each section of the filling material reaches the preset strength, continue to remove the next section of the construction casing upwards; S5. After the construction casing is completely removed and the filling material reaches the preset strength requirement, the temporary support is removed, and the surface voids generated after the construction casing is removed are backfilled and compacted. After the overall construction of the shaft project is completed and it is confirmed by inspection that there is no obvious water seepage in the entire shaft, the cable can be laid. The reserved holes for cable entry and exit are cleaned, and the cable is inserted into the shaft through the reserved holes and fixed and sealed in layers along the cable support.

2. The construction method for prefabricated cable shafts according to claim 1, characterized in that, The use of rotary drilling rigs for vertical shaft drilling specifically includes: The center of the drill rod of the rotary drilling machine is aligned with the center of the hole-forming operation, with the deviation controlled within 10mm; the deviation of the hole diameter is controlled within ±50mm; and the deviation of the sinking depth is controlled between +100mm and -50mm.

3. The construction method for prefabricated cable shafts according to claim 1, characterized in that, The adjustment of the planar position and verticality of the shaft structure specifically includes: A total station is used to monitor in real time the deviation of the actual center of the shaft structure from the design center in terms of planar position and verticality. The deviation of the planar position from the design center is controlled within ±20mm, and the deviation of the verticality is controlled ≤1‰.

4. The construction method for prefabricated cable shafts according to claim 1, characterized in that, The filling material is cement mortar, and the pouring height of each layer in the layered pouring is ≤500mm; and the preset strength requirement is to reach more than 75% of the design strength of the filling material; the backfilling and compaction treatment adopts graded sand and gravel for layered backfilling and compaction, and controls the backfill density to ≥95%.

5. The construction method for prefabricated cable shafts according to claim 1, characterized in that, The synchronous, segmented removal of the construction casing specifically includes: A vibratory hammer fixed to the top of the construction casing is used to separate the construction casing from the surrounding soil, and then it is lifted upwards by a lifting device.

6. A prefabricated cable shaft structure, applied in the construction method according to any one of claims 1-5, characterized in that, The shaft structure includes: The main body of the structure is cylindrical, and a sealing steel plate is fixed at the bottom of the main body to form a U-shaped cavity with an open top. The side wall of the main body of the structure is provided with reserved holes for cable entry and exit. Multiple sets of cable brackets are arranged at intervals along the vertical direction and are symmetrically fixed to both sides of the inner wall of the main structure. A ladder is fixedly connected to the inner wall of the main structure in a vertical direction, and the ladder is located beside the multiple sets of cable supports; A waterproof sealing ring is fixedly installed at the cable entry and exit reserved hole on the side wall of the main structure, and the outer side of the waterproof sealing ring is provided with an embedded guide isolation component for isolating the filling material during injection. A bottom concrete slab is poured at the bottom of the U-shaped cavity above the sealing steel plate.

7. The prefabricated cable shaft structure according to claim 6, characterized in that, The main structure is made of Q355 steel, and the thickness of the main structure is 30mm to 50mm; and the thickness of the waterproof sealing ring is ≥10mm.

8. The prefabricated cable shaft structure according to claim 6, characterized in that, The multiple cable brackets are angle steel or I-beam structures, and the two sides of the multiple cable brackets are fully welded to the inner wall of the main structure.

9. The prefabricated cable shaft structure according to claim 6, characterized in that, The shaft structure also includes: Multiple rest platforms are fixedly and vertically spaced on the inner wall of the main structure above the multiple sets of cable supports; The rest platform is a semi-circular steel plate structure, the vertical distance between two adjacent rest platforms is 6m, and the thickness of the semi-circular steel plate structure is ≥10mm.

10. The prefabricated cable shaft structure according to claim 9, characterized in that, The main structure, the multiple cable supports, the ladder, the multiple rest platforms, and the waterproof sealing ring are all components that are welded and formed in the factory during the prefabrication stage.

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