Closed construction framework and prefabricated mold device for multilayer karst geological pile foundation

Abstract

The utility model discloses a kind of closed construction framework and prefabricated mould device for multilayer karst geology pile foundation, comprising: pile hole structure;Tool steel casing, positioning setting in the pile hole structure;Prefabricated closed ring assembly is provided with several groups of prefabricated closed ring;Several groups of prefabricated closed ring are all located inside the pile hole structure, and several groups of prefabricated closed ring are based on the tool steel casing and sequentially adjustable long type joint connection setting.Solved the technical problem that permanent steel casing follows and fills in when carrying out pile foundation construction in the prior art for the karst cave deeper and the geological of multiple karst caves in string-bead type layered distribution.

Description

Technical Field

[0001] This utility model relates to the field of bridge pile foundation engineering technology, and more specifically, to a closed construction structure and prefabrication mold device for multi-level karst geological pile foundations. Background Technology

[0002] With the continuous and rapid development of the transportation industry, bridges, as a key component of transportation routes, are becoming increasingly important, and the construction technology of bridge pile foundations is gradually becoming more and more perfect and is being widely used.

[0003] Currently, when construction is carried out near existing operational railway lines, it is generally necessary to minimize disruption to the normal operation of the existing railway. Traditional impact drilling is strictly prohibited due to its strong impact and vibration characteristics, which can easily cause adverse effects on the existing railway subgrade and track structure. Rotary drilling, on the other hand, has become the preferred construction method in this situation due to its high efficiency and low disturbance.

[0004] Meanwhile, due to complex geological conditions, different regions encounter different geological situations, with karst caves having a particularly significant impact on pile foundation construction. When facing shallow karst caves, construction typically employs a method of backfilling with a mixture of rubble and loess before drilling. This method can, to some extent, fill the cave space and create relatively stable geological conditions for drilling operations. However, when karst caves are deeper than the ground level or when multiple caves are distributed in a beaded, layered manner, backfilling alone is insufficient to meet the filling requirements.

[0005] Conventional construction methods typically involve using permanent steel casings to follow up with the filling. However, this approach has revealed numerous problems in practice. For instance, the lowering and welding of the steel casings is time-consuming, severely hindering construction efficiency; welding operations are inefficient and of questionable quality, affecting not only the connection strength of the steel casings but also posing a potential threat to the overall stability of the pile foundation; furthermore, precise verticality control during the extension of the steel casings further impacts the load-bearing capacity of the pile foundation; additionally, the use of steel casings in conventional geological sections between karst caves results in unnecessary material waste, significantly increasing construction costs and negatively impacting construction efficiency and economic benefits. Therefore, there is an urgent need to design a closed-loop structure and its prefabricated mold device specifically for pile foundation construction in karst cave geology. Utility Model Content

[0006] Therefore, this utility model provides a closed construction structure and prefabricated mold device for multi-layer karst geological pile foundations, in order to solve the above-mentioned technical problems in the prior art when carrying out pile foundation construction in karst cavities that are deep and have multiple cavities distributed in a beaded layered manner, using permanent steel casings for follow-up filling.

[0007] To achieve the above objectives, this utility model provides the following technical solution:

[0008] A closed construction framework for multi-level karst geological pile foundations includes:

[0009] Pile hole structure;

[0010] A tool steel casing is positioned within the pile hole structure;

[0011] The prefabricated closed-loop assembly is provided with several sets of prefabricated closed loops;

[0012] Several sets of prefabricated closed rings are located inside the pile hole structure, and the several sets of prefabricated closed rings are connected in an adjustable manner based on the tool steel casing.

[0013] Based on the above technical solution, the present invention is further described as follows:

[0014] As a further embodiment of this utility model,

[0015] The pile hole structure includes a vertically extending pile hole body and an outwardly expanding limiting shoulder correspondingly disposed on the inner side wall of the top of the pile hole body.

[0016] The tool steel casing includes a steel casing body;

[0017] The lower part of the steel casing body is embedded in the pile hole body, and the bottom of the steel casing body is placed on the limiting shoulder, while the upper part of the steel casing body extends to the outside of the pile hole body.

[0018] As a further aspect of this utility model, it also includes:

[0019] Extended steel bar hook;

[0020] The prefabricated closed rings include at least one set of middle prefabricated closed rings and at least one set of bottom prefabricated closed rings. The at least one set of middle prefabricated closed rings and at least one set of bottom prefabricated closed rings are connected in sequence via the extended steel bar hook or directly in an adjustable length connection based on the tool steel casing.

[0021] As a further embodiment of this utility model,

[0022] The outer diameter of the central closed ring body is smaller than the inner diameter of the steel casing body;

[0023] The outer diameter of the bottom closed ring body is smaller than the inner diameter of the steel casing body.

[0024] As a further embodiment of this utility model,

[0025] The tool steel casing also includes at least four sets of hoisting reinforcing bars;

[0026] At least four sets of the hoisting reinforcing bars are vertically extended and fixedly connected to the bottom of the main body of the steel casing;

[0027] The prefabricated central closed ring includes a central closed ring body and at least four sets of central steel bar hooks fixedly connected to the central closed ring body;

[0028] At least four sets of the central steel bar hooks are provided with hooks at both ends, and the hooks at both ends of each set of the central steel bar hooks extend one-to-one to the outer sides of both ends of the central closed ring body. The top hooks of the at least four sets of the central steel bar hooks are detachably and fixedly connected to the at least four sets of the lifting steel bars.

[0029] As a further embodiment of this utility model,

[0030] The top hook of the middle steel bar hook is fixed to the lifting steel bar by an adjustable height weld.

[0031] As a further embodiment of this utility model,

[0032] The prefabricated bottom closed ring includes a bottom closed ring body and at least four sets of bottom steel bar hooks fixedly connected to the bottom closed ring body;

[0033] At least four sets of bottom steel bar hooks are provided with hooks at their top ends, and the hooks at the top ends of each set of bottom steel bar hooks extend to the outer side of the top end of the bottom closed ring body;

[0034] The top hook of the extended rebar hook and the bottom hook of the middle rebar hook are detachably and fixedly connected. The bottom hook of the extended rebar hook and the top hook of the middle rebar hook or the top hook of the bottom rebar hook are detachably and fixedly connected. The top hook of the bottom rebar hook and the bottom hook of the extended rebar hook or the bottom hook of the middle rebar hook are detachably and fixedly connected.

[0035] A prefabrication mold apparatus for preparing the aforementioned prefabricated closed ring, the prefabrication mold apparatus comprising:

[0036] The inner mold is a circular steel tube, which serves as the inner mold for forming the pre-made closed ring;

[0037] The bottom support steel plate platform can be directionally slidably fitted onto the inner mold circular steel tube, and the outer edge of the bottom support steel plate platform is higher than its inner edge relative to the outer edge of the inner mold circular steel tube.

[0038] A sheet metal outer ring template is correspondingly set on the outer side of the inner mold round steel tube body, and one end of the sheet metal outer ring template is detachably and correspondingly limited to the inner side of the outer edge of the bottom support steel plate platform. The other end of the sheet metal outer ring template is flush with the end of the inner mold round steel tube body away from the bottom support steel plate platform, so as to serve as the forming outer mold of the prefabricated closed ring.

[0039] The U-shaped limiting buckle is positioned at both ends of the inner mold round steel tube away from the bottom support steel plate platform and at the other end of the outer iron ring template.

[0040] As a further embodiment of this utility model,

[0041] The bottom support steel plate platform is evenly provided with at least four sets of longitudinally extending reinforcing bar reserved holes along its circumference; at least four sets of pre-embedded reinforcing bars are respectively extended through the at least four sets of pre-embedded reinforcing bars, and the ends of the at least four sets of pre-embedded reinforcing bars away from the bottom support steel plate platform extend beyond the inner mold circular steel pipe.

[0042] As a further aspect of this utility model, it also includes:

[0043] A flexible steel mesh is wrapped around the outer side of at least four sets of pre-embedded steel bars, and the flexible steel mesh is fixedly tied to the at least four sets of pre-embedded steel bars by binding wire.

[0044] This utility model has the following beneficial effects:

[0045] This architecture replaces permanent steel casings with prefabricated closed rings, which can effectively combine the specific development parameters of the karst caves to perform targeted alignment, extension and sealing of the caves, effectively reducing material waste in non-karst cave sections. At the same time, the use of prefabricated mold devices allows the prefabrication process of the closed rings to be carried out without taking up construction time. The closed rings can be prefabricated independently and flexibly according to the specific conditions of different pile foundations, which significantly improves the functional adaptability of the architecture. Attached Figure Description

[0046] To more clearly illustrate the embodiments of this utility model or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The structures, proportions, sizes, etc., drawn in this specification are only used to complement the content disclosed in the specification, so that those skilled in the art can understand and read them. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and purposes that this utility model can produce, should still fall within the scope of the technical content disclosed in this utility model.

[0047] Figure 1This is a schematic diagram of the overall structure of the closed construction framework for multi-level karst geological pile foundations provided in an embodiment of the present invention.

[0048] Figure 2 This is one of the side sectional structural schematic diagrams of a prefabricated mold device for prefabricating a closed ring in a closed construction framework for multi-level karst geological pile foundations provided in this utility model embodiment.

[0049] Figure 3 The prefabrication mold device for prefabricating a closed ring in the closed construction framework for multi-level karst geological pile foundations provided in this embodiment of the utility model corresponds to... Figure 2 A schematic diagram of the isometric structure in the state.

[0050] Figure 4 This is the second side sectional view of the prefabricated mold device for prefabricating a closed ring in the closed construction framework for multi-level karst geological pile foundations provided in this embodiment of the present invention.

[0051] Figure 5 The prefabrication mold device for prefabricating a closed ring in the closed construction framework for multi-level karst geological pile foundations provided in this embodiment of the utility model corresponds to... Figure 4 A schematic diagram of the isometric structure in the state.

[0052] The attached diagram lists the components represented by each number as follows:

[0053] Pile hole structure 1: Pile hole body 11, limiting shoulder 12;

[0054] Tool steel casing 2: Steel casing body 21, hoisting steel bars 22;

[0055] Central prefabricated closed ring 3: central closed ring body 31, central steel bar hook 32;

[0056] Extended steel bar hook 4;

[0057] Bottom prefabricated closed ring 5: Bottom closed ring body 51, bottom steel bar hook 52;

[0058] 6. Inner mold circular steel tube body;

[0059] 7. Base support steel plate platform: 71. Reinforcing bar reserved hole; 72. Embedded steel bar; 73. Flexible steel mesh; 74. Binding steel wire;

[0060] 8. Sheet metal outer ring template; 9. U-shaped limit buckle;

[0061] Cave a. Detailed Implementation

[0062] The following specific embodiments illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0063] The terms "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity of description and are not intended to limit the scope of implementation of this utility model. Any changes or adjustments to their relative relationships, without substantially altering the technical content, shall also be considered within the scope of implementation of this utility model.

[0064] like Figures 1 to 5 As shown, this utility model embodiment provides a closed construction framework and prefabricated mold device for multi-level karst geological pile foundations. The closed construction framework includes a pile hole structure 1, a tool steel casing 2, a central prefabricated closed ring 3, an extended steel bar hook 4, and a bottom prefabricated closed ring 5. The prefabricated mold device includes an inner mold circular steel pipe 6, a bottom support steel plate platform 7, a sheet metal outer ring template 8, and a U-shaped limiting buckle 9. This allows the prefabricated closed ring to replace the permanent steel casing, effectively combining the specific development parameters of karst cave a to perform targeted alignment, extension, and sealing of karst cave a, effectively reducing material waste in non-karst cave sections. Simultaneously, the prefabricated mold device allows the prefabrication of the closed ring to be carried out without interrupting the construction period, enabling independent and flexible prefabrication of the closed ring according to the specific conditions of different pile foundations. This significantly improves the construction efficiency of the closed construction framework and enhances the functional adaptability of the framework and device. Specific settings are as follows:

[0065] Please refer to Figure 1 The pile hole structure 1 includes a vertically extending pile hole body 11 and an outwardly expanding limiting shoulder 12 correspondingly disposed on the inner side wall of the top of the pile hole body 11.

[0066] The tool steel casing 2 includes a steel casing body 21 and lifting reinforcing bars 22; wherein, the lower part of the steel casing body 21 is embedded in the pile hole body 11, and the bottom of the steel casing body 21 is stably placed on the limiting shoulder 12, and the upper part of the steel casing body 21 extends to the outside of the pile hole body 11 to prevent the pile hole from collapsing; at least four sets of lifting reinforcing bars 22 are provided, and at least four sets of lifting reinforcing bars 22 are respectively vertically extended and fixed at the bottom position of the steel casing body 21.

[0067] The prefabricated central closed ring 3 includes a central closed ring body 31 and at least four sets of central steel bar hooks 32 fixedly connected to the central closed ring body 31. The outer diameter of the central closed ring body 31 is smaller than the inner diameter of the steel casing body 21, so that the central closed ring body 31 can pass through the steel casing body 21 to reach the interior of the pile hole body 11. Both ends of the at least four sets of central steel bar hooks 32 are provided with hooks, and the hooks at both ends of each set of central steel bar hooks 32 extend one-to-one to the outer sides of both ends of the central closed ring body 31. The top hooks of the at least four sets of central steel bar hooks 32 are detachably and fixedly connected one-to-one with the at least four sets of lifting steel bars 22.

[0068] As a preferred embodiment, the top hook of the middle steel bar hook 32 is welded and fixed to the lifting steel bar 22 with an adjustable height, so as to effectively and flexibly adapt to the height position of the karst cave a through the middle prefabricated closed ring 3, thereby improving the overall functional applicability.

[0069] The prefabricated bottom sealing ring 5 includes a bottom sealing ring body 51 and at least four sets of bottom reinforcing bar hooks 52 fixedly connected to the bottom sealing ring body 51; the outer diameter of the bottom sealing ring body 51 is smaller than the inner diameter of the steel casing body 21, so that the bottom sealing ring body 51 can pass through the steel casing body 21 to reach the interior of the pile hole body 11; the top end of the at least four sets of bottom reinforcing bar hooks 52 is provided with hooks, and the hooks at the top end of each set of bottom reinforcing bar hooks 52 extend to the outer side of the top end of the bottom sealing ring body 51.

[0070] Both ends of the extended steel bar hook 4 are equipped with hooks, and the top hook of the extended steel bar hook 4 is detachably and fixedly connected to the bottom hook of the middle steel bar hook 32. The bottom hook of the extended steel bar hook 4 is detachably and fixedly connected to the top hook of the middle steel bar hook 32 or the top hook of the bottom steel bar hook 52. The top hook of the bottom steel bar hook 52 is detachably and fixedly connected to the bottom hook of the extended steel bar hook 4 or the bottom hook of the middle steel bar hook 32. This is to enable the extended steel bar hook 4 to further connect to the middle prefabricated closed ring 3 or the bottom prefabricated closed ring 5 to complete the targeted alignment, extension and sealing of the multi-level depth karst cave a, reducing material waste in non-karst cave sections and improving practicality.

[0071] The application process of the closed construction framework for multi-level karst geological pile foundations described above includes the following steps:

[0072] S101: Accurately lay out the design pile foundation location to determine the design and construction pile positions;

[0073] S102: Corresponds to the drilling and detection hole position of the designed and constructed pile location;

[0074] The specific process is as follows: Based on the center position of the designed construction pile, a tool steel casing 2 is pre-set on the same axis, and vertical holes are drilled corresponding to the outer side and center position of the designed construction pile to form at least four sets of outer detection holes and one set of center detection holes. The diameter of the circle formed by connecting the at least four sets of outer detection holes is greater than the diameter of the pre-set tool steel casing position.

[0075] S103: Obtain the specific location and development depth parameters of cave a based on the detection borehole locations;

[0076] The specific process is as follows: use an in-hole imaging detector to probe each hole location, and determine the specific location and development depth parameters of cave a based on the displayed images and depth information;

[0077] S104: 2 steel casings for installation tools;

[0078] The specific process is as follows: a tool steel casing 2 is buried at the preset location, and the height of the tool steel casing 2 exposed above the ground is not less than 50cm. The tool steel casing 2 serves as a protective guide foundation for subsequent drilling and construction.

[0079] S105: Rotary drilling is performed based on the designed construction pile location to form the main body 11 of the construction pile hole;

[0080] S106: Based on the determined specific location and development depth parameters of the karst cave a, the karst caves are sequentially aligned from bottom to top and prefabricated closed rings are lowered, based on the main body 11 of the construction pile hole and the tool steel casing 2.

[0081] The specific process is as follows: the bottom prefabricated closed ring 5 is lowered to correspond to the main body of the construction pile hole, and the four sets of bottom steel bar hooks 52 of the bottom prefabricated closed ring 5 are welded to the tool steel casing to establish temporary fixation;

[0082] Then, the middle prefabricated closed ring 3 is lifted, and the four sets of middle steel bar hooks 32 of the middle prefabricated closed ring 3 and the four sets of bottom steel bar hooks 52 of the bottom prefabricated closed ring 5 are bent according to the determined specific location and development depth parameters of the karst cave, so as to obtain steel bar hooks of the appropriate length and connect the two sections of the prefabricated closed ring accordingly, thereby cutting off the temporary fixation between the bottom prefabricated closed ring 5 and the tool steel casing 2;

[0083] Continue lowering the middle prefabricated closed ring 3 and the bottom prefabricated closed ring 5, and weld the four sets of middle steel bar hooks 32 of the middle prefabricated closed ring to the tool steel casing 2 respectively. Then continue to lift the next section of the middle prefabricated closed ring 3, and connect the middle steel bar hooks 32 between the next section of the middle prefabricated closed ring 3 and the previous section of the middle prefabricated closed ring 3. Continue this process until all the prefabricated closed rings are lowered into place. Retain the temporary fixation between the last section of the middle prefabricated closed ring 3 and the tool steel casing 2, so that all the prefabricated closed rings are firmly connected to the tool steel casing 2, and the targeted sealing of the distributed karst cave is completed.

[0084] More specifically, based on the determined specific location and development depth parameters of the karst cave, a prefabricated sealing ring of a specific length that can completely seal the karst cave is pre-selected. When connecting the prefabricated sealing ring with a steel bar hook, the bending position of the steel bar hook is determined according to the standard that the prefabricated sealing ring can accurately align with the corresponding karst cave. And / or, at least one extended steel bar hook 4 of a preset length is added between the steel bar hooks of two adjacent prefabricated sealing rings to accurately seal all distributed karst caves with determined specific locations and development depths.

[0085] S107: Continue to lower the reinforcing cage corresponding to the tool steel casing and the prefabricated closed ring connected in series;

[0086] S108: After the steel cage is lowered into place, a guide pipe extending to the bottom of the pile hole is installed to perform the pumping and cleaning operation. After the cleaning operation is completed, concrete is poured into the corresponding steel cage to complete the entire pile foundation construction process.

[0087] Please refer to Figures 2 to 5 The inner mold circular steel pipe 6 is set as a circular steel pipe with an inner diameter not less than the outer diameter of the karst pile foundation reinforcement cage, and is used as the forming inner mold of the prefabricated closed ring through the inner mold circular steel pipe 6.

[0088] The bottom support steel plate platform 7 is configured as an annular platform fitted around the outer side of the inner mold circular steel tube 6. The longitudinal section of the annular bottom support steel plate platform 7 is L-shaped at any position, that is, the height of the outer edge of the annular bottom support steel plate platform 7 is greater than that of its inner edge, thereby forming a bottom support limiting platform.

[0089] The bottom support steel plate platform 7 is evenly provided with at least four sets of longitudinally extending reinforcing bar reserved holes 71 along its circumference; at least four sets of pre-embedded reinforcing bars 72 are respectively extended through the at least four sets of pre-embedded reinforcing bars 71, and the ends of the at least four sets of pre-embedded reinforcing bars 72 away from the bottom support steel plate platform 7 extend beyond the inner mold circular steel tube 6, so as to form a prefabricated closed ring reinforcing bar hook by bending the pre-embedded reinforcing bars 72.

[0090] At least four sets of pre-embedded reinforcing bars 72 are wrapped with flexible reinforcing mesh 73 on their outer sides. The flexible reinforcing mesh 73 is tied and fixed to the at least four sets of pre-embedded reinforcing bars 72 by binding wires 74, so as to significantly improve the anchoring performance for subsequent concrete pouring.

[0091] The outer ring template 8 is configured as an annular cylindrical structure, and one end of the outer ring template 8 is separable and abuts against the inner side of the annular bottom support steel plate platform 7. The other end of the outer ring template 8 is flush with the end of the inner mold circular steel tube 6 away from the bottom support steel plate platform 7. At least four sets of U-shaped limiting buckles 9 are provided, and at least four sets of U-shaped limiting buckles 9 are evenly limited and fastened between the end of the inner mold circular steel tube 6 away from the bottom support steel plate platform 7 and the other end of the outer ring template 8, so as to form an end limiting effect through the U-shaped limiting buckles 9, effectively preventing the outer ring template 8 from expanding and running out of the formwork due to subsequent concrete pouring.

[0092] As a preferred embodiment, the outer side of the inner mold round steel tube 6, the inner end face of the bottom support steel plate platform 7, the inner side of the sheet metal outer ring template 8, and the inner end face of the U-shaped limiting buckle 9 are all coated with a release agent layer and / or an oil layer to facilitate the demolding of the closed ring.

[0093] As another preferred embodiment, a number of pads are provided between the inner side of the outer ring template 8 and the flexible steel mesh 73 to further improve the positional stability of the outer ring template 8.

[0094] As another preferred embodiment, the inner mold circular steel tube 6 and the bottom support steel plate platform 7 are slidably assembled together, and the other end of the outer iron ring template 8 is always flush with the end position of the inner mold circular steel tube 6, so as to adapt to the preparation of prefabricated closed rings of different lengths.

[0095] Although the present invention has been described in detail above with general descriptions and specific embodiments, some modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A closed construction framework for multi-level karst geological pile foundations, characterized in that, include: Pile hole structure; A tool steel casing is positioned within the pile hole structure; The prefabricated closed-loop assembly is provided with several sets of prefabricated closed loops; Several sets of prefabricated closed rings are located inside the pile hole structure, and the several sets of prefabricated closed rings are connected in an adjustable manner based on the tool steel casing.

2. The closed construction framework for multi-level karst geological pile foundations according to claim 1, characterized in that, The pile hole structure includes a vertically extending pile hole body and an outwardly expanding limiting shoulder correspondingly disposed on the inner side wall of the top of the pile hole body. The tool steel casing includes a steel casing body; The lower part of the steel casing body is embedded in the pile hole body, and the bottom of the steel casing body is placed on the limiting shoulder, while the upper part of the steel casing body extends to the outside of the pile hole body.

3. The closed construction framework for multi-level karst geological pile foundations according to claim 2, characterized in that, Also includes: Extended steel bar hook; The prefabricated closed rings include at least one set of middle prefabricated closed rings and at least one set of bottom prefabricated closed rings. The at least one set of middle prefabricated closed rings and at least one set of bottom prefabricated closed rings are connected in sequence via the extended steel bar hook or directly in an adjustable length connection based on the tool steel casing.

4. The closed construction framework for multi-level karst geological pile foundations according to claim 3, characterized in that, The central prefabricated closed ring includes a central closed ring body, the outer diameter of which is smaller than the inner diameter of the steel casing body; The prefabricated bottom sealing ring includes a bottom sealing ring body, the outer diameter of which is smaller than the inner diameter of the steel casing body.

5. The closed construction framework for multi-level karst geological pile foundations according to claim 3, characterized in that, The tool steel casing also includes at least four sets of hoisting reinforcing bars; At least four sets of the hoisting reinforcing bars are vertically extended and fixedly connected to the bottom of the main body of the steel casing; The prefabricated central closed ring includes a central closed ring body and at least four sets of central steel bar hooks fixedly connected to the central closed ring body; At least four sets of the central steel bar hooks are provided with hooks at both ends, and the hooks at both ends of each set of the central steel bar hooks extend one-to-one to the outer sides of both ends of the central closed ring body. The top hooks of the at least four sets of the central steel bar hooks are detachably and fixedly connected to the at least four sets of the lifting steel bars.

6. The closed construction framework for multi-level karst geological pile foundations according to claim 5, characterized in that, The top hook of the middle steel bar hook is fixed to the lifting steel bar by an adjustable height weld.

7. The closed construction framework for multi-level karst geological pile foundations according to claim 6, characterized in that, The prefabricated bottom closed ring includes a bottom closed ring body and at least four sets of bottom steel bar hooks fixedly connected to the bottom closed ring body; At least four sets of bottom steel bar hooks are provided with hooks at their top ends, and the hooks at the top ends of each set of bottom steel bar hooks extend to the outer side of the top end of the bottom closed ring body; The top hook of the extended rebar hook and the bottom hook of the middle rebar hook are detachably and fixedly connected. The bottom hook of the extended rebar hook and the top hook of the middle rebar hook or the top hook of the bottom rebar hook are detachably and fixedly connected. The top hook of the bottom rebar hook and the bottom hook of the extended rebar hook or the bottom hook of the middle rebar hook are detachably and fixedly connected.

8. A prefabrication mold device for preparing a closed construction structure for multi-level karst geological pile foundations as described in any one of claims 1-7, characterized in that, The precast mold device for multi-level karst geological pile foundations includes: The inner mold is a circular steel tube, which serves as the inner mold for forming the pre-made closed ring; The bottom support steel plate platform can be directionally slidably fitted onto the inner mold circular steel tube, and the outer edge of the bottom support steel plate platform is higher than its inner edge relative to the outer edge of the inner mold circular steel tube. A sheet metal outer ring template is correspondingly set on the outer side of the inner mold round steel tube body, and one end of the sheet metal outer ring template is detachably and correspondingly limited to the inner side of the outer edge of the bottom support steel plate platform. The other end of the sheet metal outer ring template is flush with the end of the inner mold round steel tube body away from the bottom support steel plate platform, so as to serve as the forming outer mold of the prefabricated closed ring. The U-shaped limiting buckle is positioned at both ends of the inner mold round steel tube away from the bottom support steel plate platform and at the other end of the outer iron ring template.

9. The precast mold device for multi-level karst geological pile foundations according to claim 8, characterized in that, The bottom support steel plate platform is evenly provided with at least four sets of longitudinally extending reinforcing bar reserved holes along its circumference; at least four sets of pre-embedded reinforcing bars are respectively extended through the at least four sets of pre-embedded reinforcing bars, and the ends of the at least four sets of pre-embedded reinforcing bars away from the bottom support steel plate platform extend beyond the inner mold circular steel pipe.

10. The precast mold device for multi-layer karst geological pile foundations according to claim 9, characterized in that, Also includes: A flexible steel mesh is wrapped around the outer side of at least four sets of pre-embedded steel bars, and the flexible steel mesh is fixedly tied to the at least four sets of pre-embedded steel bars by binding wire.

Images