A karst area pile foundation construction system and construction method

Abstract

The present invention provides a karst area pile foundation construction system and construction method, wherein the upper casing of the step-by-step necking and following double casing is positioned and installed on the lower casing; a bag is provided on the outer wall of the step-by-step necking and following double casing corresponding to the position of the karst area; the step-by-step necking and following double casing is sleeved on the inner steel casing; a steel cage for pouring pile foundation is provided in the inner steel casing; a steel cage limiting support is positioned and arranged on the top of the steel cage to achieve the upper limit of the steel cage; a floating closed bag is provided in the pile hole. The present application realizes the positioning and protection of the inner steel casing by setting the step-by-step necking and following double casing, and at the same time realizes the effective limiting of the step-by-step necking and following double casing in the karst area by setting the bag; the floating closed bag is placed in the pile hole, and when pouring concrete, the closed bag floats with the concrete as a monitoring device for concrete pouring, which greatly improves the pile foundation efficiency and pile quality during the pile foundation construction in the karst area.

Description

Technical Field

[0001] The present invention relates to the technical field of pile foundation construction, and in particular to a pile foundation construction system and a construction method in a karst area. Background Art

[0002] In recent years, with the densification and improvement of road networks, the geological conditions encountered during the construction of bridge pile foundations have become increasingly complex and diverse. The pile foundation construction of multi-layer beaded-type larger cave piles in karst areas has always been the focus and difficulty of pile foundation construction in karst areas. The pile foundation construction of caves is unpredictable and dangerous, especially the pile foundation construction of string-like multi-layer caves. Compared with traditional pile foundation construction, more attention should be paid to the bearing capacity of the pile foundation to ensure the overall bearing capacity of the highway or bridge and avoid settlement problems in the later stage.

[0003] Conventional pile foundation construction in karst areas typically involves lowering a steel casing, drilling a pilot hole, and finally pouring concrete to complete the pile. If pressurized water is encountered during pile construction, water inrush can easily occur if no measures are taken at the designated location. Other common problems include grout leakage, deflection, drill bit sticking, and pile breakage. Therefore, there is a need to develop an improved karst pile foundation construction system and method to address these challenges and improve the efficiency and quality of pile construction. Summary of the Invention

[0004] The purpose of the present invention is to provide a karst area pile foundation construction system and construction method, to solve the current technical problem of improving the pile foundation efficiency and pile quality during karst area pile foundation construction.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0006] A karst area pile foundation construction system includes a double casing with gradually shrinking necks and an inner steel casing arranged in a pile hole;

[0007] The step-by-step necking and following double casing comprises an upper casing and a lower casing; the upper casing is positioned and installed on the lower casing;

[0008] The outer side wall of the step-by-step necking and following double casing is provided with a bag corresponding to the position of the karst area; the step-by-step necking and following double casing is sleeved on the inner steel casing;

[0009] The inner steel casing is provided with a steel cage for pouring pile foundation;

[0010] A steel cage limiting support frame and a floating closed bag are also provided; the steel cage limiting support frame is positioned on the top of the steel cage to achieve the upper limit of the steel cage; the floating closed bag is arranged in the pile hole.

[0011] As a further improvement of the present invention, the axial lower end of the upper casing is threadedly connected to the axial upper end of the upper casing, so as to realize an axially detachable fixed connection between the upper casing and the lower casing.

[0012] As a further improvement of the present invention, a pin is further provided on the lower casing; the pin is arranged corresponding to the limiting slot on the upper casing, and the axial rapid positioning of the upper and lower casings is achieved by the penetration of the pin and the limiting slot.

[0013] As a further improvement of the present invention, the limiting slot is a through hole; the through hole is a long waist-shaped hole arranged along the circumferential direction of the upper casing; and a pin is connected with the through hole to achieve rapid axial positioning of the upper and lower casings.

[0014] As a further improvement of the present invention, a bladder bag and an air injection pipe are further positioned on the outer side of the upper casing; the air injection pipe is communicated with the bladder bag.

[0015] As a further improvement of the present invention, the steel cage limiting support frame includes a support rod, a cross rod and a connecting frame; the support rod matches the inner size of the steel cage; the cross rod is arranged inside the support rod, and both ends are respectively connected to the inner side of the support rod; one end of the connecting frame is connected to the cross rod, and the other end extends outward; the outer end of the connecting frame is provided with a downward pointed top, which is used to realize the insertion and positioning of the ground outside the pile hole.

[0016] As a further improvement of the present invention, a rubber buckle is further provided on the circumferential outer side of the support rod, and the rubber buckle can be clamped and limited with the transverse stirrups of the steel cage.

[0017] As a further improvement of the present invention, a device for guiding small holes around the diameter of the pile foundation top plate is also provided; the device for guiding holes comprises a cone top, a fan-shaped steel sheet, a steel wire, a pressure plate, a fixing rod and a pull rope;

[0018] A fixed ring is provided in the top of the cone; the lower end of the sector steel sheet is provided on the top of the cone; one end of the steel wire is positioned and connected to the inner side of the sector steel sheet, and the other end is positioned and connected to the pressure plate; the fixed rod is positioned and provided on the pressure plate; one end of the pull rope passes through the pressure plate and the ring in sequence and is then positioned and connected to the pressure plate;

[0019] The plurality of sector-shaped steel sheets are evenly distributed axially on the cone top, and the pressing plate is arranged on the inner side of the top of the sector-shaped steel sheet, thereby forming an inverted cone-shaped skeleton structure.

[0020] As a further improvement of the present invention, a plurality of the fan-shaped steel sheets are connected to the pressure plate via an umbrella skeleton structure, so that the fan-shaped steel sheets can be expanded and contracted in an umbrella-like shape.

[0021] A pile foundation construction method in a karst area comprises the following steps:

[0022] S1. Construction Preparation: Level the site, remove debris, replace the soft soil on the surface, and compact it. The location of the mud pit, steel bar processing site, and construction access roads should all be reasonably arranged. Special measures should be taken when necessary, and preparations should be made before entering the construction site. Carefully study the geological survey data to determine the thickness of the soft soil layer on the surface of the proposed pile foundation, the location and scope of the karst caves to be crossed, and the possible filling conditions of the karst caves, and make a preliminary assessment of the strata that may collapse.

[0023] S2. Measurement and positioning: Use a total station and a steel ruler to determine the center pile of the hole, and arrange guard piles around the pile. Use cement mortar to reinforce the guard piles and set up obvious signs. Set up a slurry pool and sedimentation tank between each adjacent pier to meet the drilling mud needs.

[0024] S3. Bury the inner steel casing: After determining the location of the inner steel casing, use a crane to lower the inner steel casing, and control the plane position deviation of the inner steel casing within 5cm and the inclination deviation within 1%;

[0025] S4. Follow up double casing installation by necking down section by section: After the inner steel casing is positioned and installed, first hang the lower casing inside the inner steel casing, connect the through-holes on the inner ring plate at the lower end of the upper casing with the pins on the outer ring plate at the upper end of the lower casing, and then rotate the upper casing to tighten it to the lower casing;

[0026] S5. Excavation: In the excavation work at the karst roof, in order to prevent the occurrence of collapse, the hole-guiding device is first used to adjust the hole-guiding taper to perform local small hole excavation, and then the area around the small hole is hammered to form a hole;

[0027] S6. Drilling rig in place: First, the working foundation of the drilling rig is treated with stone slag replacement and compacted before the drilling rig is installed in place. After the percussion drilling rig is installed, the center of the drill bit is accurately aligned with the cross center of the casing. The drill bit is hoisted and slowly lowered into the inner steel casing. The mud pump is started. After a certain amount of mud has been pumped into the hole, the percussion drilling rig is started.

[0028] S7. Mud preparation: excavate a mud pool and a sedimentation tank 5m away from the hole mouth, and connect the casing gap and the mud pool with a mud trench;

[0029] S8. Drilling: Based on the geological histogram, observe and inspect frequently when approaching a karst cave. Determine whether you are approaching a karst formation based on the rock samples collected, the length of the measuring rope, and the sound of the impact on the rock formation. When approaching a karst formation, confirm that the amount of prepared mud is sufficient before drilling through it to avoid a sudden loss of mud after drilling through the cave, which could cause insufficient pressure in the hole and lead to a collapse. When drilling through multiple caves and encountering harder rock formations, control the impact amplitude. If a collapse occurs, backfill the mixture to above the collapse point and re-drill the hole until the designed elevation is reached.

[0030] S9. Finishing and cleaning the hole: After finishing the hole, the quality of the hole is inspected. If it passes the inspection, the first hole cleaning is carried out. The hole is cleaned by changing the slurry. When cleaning the hole, the water head height in the hole must be maintained to prevent the hole from collapsing. The first hole cleaning is carried out before the steel cage is hoisted in.

[0031] S10. Lifting the steel cage and installing the test tube: Immediately after the first hole cleaning is completed, lower the steel cage slowly into the hole. After entering the hole, align the steel cage accurately. At each lifting position, weld a "mouth"-shaped lifting steel bar on the inside of the stiffener. Use the steel cage limit bracket with inner support and outer hoist to limit and fix it to prevent displacement or floating during the pouring process.

[0032] S11. Secondary hole cleaning: After the steel cage is lowered, the guide tube is lowered in time for the second hole cleaning. After the mud index and sediment thickness in the hole meet the requirements, concrete is poured;

[0033] S12. Air injection into the bag: Before filling, conduct a test and use the air injection pipe to inject air into the bag to expand it; and place a floating closed bag in the foundation pit;

[0034] S13. Concrete pouring: During pouring, always keep the concrete conduit buried at a depth of more than 2m to prevent pile breakage. When passing through a cave, the pouring speed should be appropriately slowed down. The pile top pouring elevation should be 0.5m to 0.8m higher than the design elevation. After pouring, observe for about 30 minutes. If there is no change in the concrete surface, slowly pull out the conduit.

[0035] S14. Pile head removal: After the concrete foundation pile is poured and finally set for 3 hours, the excess concrete is manually excavated and the floating sealed bag is removed, and then other parts and equipment are removed to complete the pile foundation construction.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] This application realizes the positioning protection of the inner steel casing by arranging a double casing with gradual necking, and at the same time realizes the effective limitation of the double casing with gradual necking in the karst area by arranging a bag; by placing a floating closed bag in the pile hole, when pouring concrete, the closed bag floats with the concrete as a monitoring device for concrete pouring, which greatly improves the pile foundation efficiency and pile quality during pile foundation construction in karst areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0039] Figure 1 This is the overall schematic diagram of pile foundation drilling in this karst area;

[0040] Figure 2 This is a schematic diagram of the double casing structure with step-by-step necking and follow-up according to the present invention;

[0041] Figure 3 For the present invention Figure 3 Cross-sectional view of the installation state;

[0042] Figure 4 It is a schematic diagram of the upper casing structure of the present invention;

[0043] Figure 5 It is a structural schematic diagram of the hole-guiding device of the present invention;

[0044] Figure 6 A top view of the hole-guiding device of the present invention;

[0045] Figure 7 It is a schematic diagram of the steel cage limiting support structure of the present invention;

[0046] Figure 8 For the present invention Figure 7 Top view;

[0047] Figure 9 This is a flowchart of the pile foundation hole forming and steel casing construction process of the present invention;

[0048] Description of the numbers in the figure:

[0049] 1. Double casing followed by necking section by section; 11. Upper casing; 111. Perforation; 12. Lower casing; 121. Pin; 2. Inner steel casing; 3. Karst area; 4. Bag; 5. Rebar cage; 6. Rebar cage limit support; 61. Support rod; 62. Cross bar; 63. Connecting frame; 631. Spire; 64. Rubber buckle; 7. Floating closed bag; 8. Pile hole; 9. Gas injection pipe; 10. Drilling device; 101. Cone top; 1011. Fixing ring; 102. Fan-shaped steel sheet; 103. Steel wire; 104. Pressure plate; 105. Fixing rod; 106. Pull rope. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0051] Combined with attachment Figures 1 to 9The present invention provides a karst area pile foundation construction system and construction method, which aims to solve the current technical problem of improving the pile foundation efficiency and pile quality during pile foundation construction in karst areas.

[0052] Specifically, a karst area pile foundation construction system includes a double casing 1 and an inner steel casing 2 arranged in a pile hole 8;

[0053] The step-by-step necking double casing 1 comprises an upper casing 11 and a lower casing 12; the upper casing 11 is positioned and installed on the lower casing 12;

[0054] The outer wall of the step-by-step necking and following double casing 1 is provided with a bag 4 corresponding to the position of the karst area 3; the step-by-step necking and following double casing 1 is sleeved on the inner steel casing 2;

[0055] The inner steel casing 2 is provided with a steel cage 5 for pouring pile foundation;

[0056] A steel cage limiting support frame 6 and a floating closed bag 7 are also provided; the steel cage limiting support frame 6 is positioned on the top of the steel cage 5 to achieve the upper limit of the steel cage 5; the floating closed bag 7 is arranged in the pile hole 8.

[0057] The present application realizes the positioning protection of the inner steel casing 2 by setting up a double casing 1 that is necked down section by section, and at the same time realizes the effective limitation of the double casing 1 in the karst area 3 by setting up a bag 4; a floating closed bag 7 is placed in the pile hole 8, and when pouring concrete, the closed bag 4 floats up with the concrete as a monitoring device for concrete pouring, which greatly improves the pile foundation efficiency and pile quality during pile foundation construction in the karst area.

[0058] Furthermore, the axial lower end of the upper casing 11 is threadedly connected to the axial upper end of the upper casing 11 , so as to achieve an axially detachable fixed connection between the upper casing 11 and the lower casing 12 .

[0059] Furthermore, a pin 121 is provided on the lower casing 12 ; the pin 121 is correspondingly arranged with the limiting slot on the upper casing 11 , and the axial rapid positioning of the upper casing 11 and the lower casing 12 is achieved by the penetration of the pin 121 with the limiting slot.

[0060] Specifically, an inner ring plate is provided at the lower end of the upper casing 11; a through hole 111 corresponding to the pin 121 is provided on the inner ring plate; an internal thread structure is provided on the circumferential inner side wall of the inner ring plate;

[0061] An outer ring plate is provided at the upper end of the lower casing 12, and a plurality of pins 121 are provided for circumferential positioning of the outer ring plate; an external thread structure is provided on the circumferential outer side wall of the outer ring plate; thereby realizing a threaded connection between the outer ring plate and the inner ring plate.

[0062] It should be noted that the limiting slot is a through hole 111; the through hole 111 is a long waist-shaped hole arranged along the circumferential direction of the upper casing 11; the pin 121 is connected with the through hole 111 to achieve rapid axial positioning of the upper casing 11 and the lower casing 12, and then the upper casing 11 is rotated to achieve a threaded fastening connection with the lower casing 12. The structure is reasonably set and the operation is convenient and quick.

[0063] Furthermore, a bag 4 and an air injection pipe 9 are positioned on the outer side of the upper casing 11; the air injection pipe 9 is connected to the bag 4, and the gas in the bag 4 is transported by injecting air into the air injection pipe 9, thereby achieving expansion and contact between the bag 4 and the karst area 3, thereby avoiding leakage during concrete pouring.

[0064] Furthermore, the steel cage limiting support frame 6 includes a support rod 61, a cross rod 62 and a connecting frame 63; the support rod 61 matches the inner size of the steel cage 5; the cross rod 62 is arranged in the support rod 61, and both ends are respectively connected to the inner side of the support rod 61; one end of the connecting frame 63 is connected to the cross rod 62, and the other end extends outward; the outer end of the connecting frame 63 is provided with a downward pointed top 631, which is used to realize the insertion and positioning of the ground outside the pile hole 8.

[0065] It should be noted that, by embedding the support rod 61 into the inner side of the steel cage 5 and realizing the positioning setting of the entire steel cage limiting support frame 6 through the outer connecting frame 63, the steel cage 5 is also clamped and limited by the connecting frame 63 and the steel bars of the steel cage 5 from top to bottom.

[0066] Preferably, a rubber buckle 64 is further provided on the circumferential outer side of the support rod 61 , and the rubber buckle 64 can be engaged with the transverse stirrups of the steel cage 5 to limit the position.

[0067] Preferably, the connecting frame 63 is a U-shaped steel bar structure.

[0068] In another embodiment, a device 10 for guiding small holes around the circumference of the pile foundation top plate is further provided; the device 10 comprises a cone top 101, a sector steel sheet 102, a steel wire 103, a pressing plate 104, a fixing rod 105 and a pull rope 106;

[0069] A fixed ring 1011 is provided inside the cone top 101; the lower end of the sector steel sheet 102 is provided on the cone top 101; one end of the steel wire 103 is positioned and connected to the inner side of the sector steel sheet 102, and the other end is positioned and connected to the pressure plate 104; the fixing rod 105 is positioned and connected to the pressure plate 104; one end of the pull rope 106 passes through the pressure plate 104 and the ring in sequence, and is then positioned and connected to the pressure plate 104;

[0070] The plurality of sector-shaped steel sheets 102 are evenly distributed axially on the cone top 101 , and the pressing plate 104 is disposed on the inner side of the top of the sector-shaped steel sheet 102 , thereby forming an inverted cone-shaped skeleton structure.

[0071] It should be noted that when it is necessary to adjust the hole-forming radius of the hole-guiding device 10, taking the expansion of the hole-forming radius as an example, the pull rope 106 is pulled upward. Since the pressure plate 104 is positioned by the fixed rod 105, the cone top 101 moves upward to drive the fan-shaped steel sheet 102 to move upward; since the inner side of the fan-shaped steel sheet 102 is abutted and limited against the pressure plate 104, the annular steel sheet expands radially outward, thereby realizing the opening of the entire conical skeleton plate; similarly, by loosening the pull rope 106 downward, the entire conical skeleton plate can be contracted to achieve the adjustment of the taper. The adjustment is convenient and quick, and the design is ingenious.

[0072] In another embodiment, the side edges of the sector-shaped steel sheets 102 are connected by mild steel sheets.

[0073] Preferably, the plurality of fan-shaped steel sheets 102 are connected to the pressing plate 104 via an umbrella skeleton structure, so that the fan-shaped steel sheets 102 can be expanded and contracted in an umbrella-like shape.

[0074] A pile foundation construction method in a karst area comprises the following steps:

[0075] S1. Construction Preparation: Level the site, remove debris, replace the soft soil on the surface, and compact it. The location of the mud pit, steel processing site, and construction access roads should all be reasonably arranged. Special measures should be taken when necessary. All preparations should be completed before entering the construction site. Carefully study the geological survey data to determine the thickness of the soft soil layer on the surface of the proposed pile foundation, the location and scope of the cave to be crossed, and the possible filling of the cave. Preliminary assessment should be made of the stratum that may collapse.

[0076] S2. Measurement and positioning: Use a total station and a steel ruler to determine the center pile of the hole, and arrange guard piles around the pile. Use cement mortar to reinforce the guard piles and set up obvious signs. Set up a slurry pool and sedimentation tank between each adjacent pier to meet the drilling mud needs.

[0077] S3. Burying the inner steel casing: After determining the location of the inner steel casing 2, lower the inner steel casing 2 using a crane, controlling the plane position deviation of the inner steel casing 2 within 5 cm and the inclination deviation within 1%;

[0078] S4. Follow up double casing installation by necking section by section: After the inner steel casing 2 is positioned and installed, first hang the lower casing 12 inside the inner steel casing 2, connect the through hole 111 on the inner ring plate at the lower end of the upper casing 11 with the pin 121 on the outer ring plate at the upper end of the lower casing 12, and then rotate the upper casing 11 to tighten it to the lower casing 12;

[0079] S5, excavation: In the excavation work at the karst roof, in order to prevent the occurrence of collapse, the hole-guiding device 10 is first used to adjust the hole-guiding taper to perform local small hole excavation, and then the area around the small hole is hammered to form a hole;

[0080] S6. Drilling rig in place: First, the working foundation of the drilling rig is treated with slag replacement and compacted before the drilling rig is installed in place. After the percussion drilling rig is installed, the center of the drill bit is accurately aligned with the cross center of the casing. The drill bit is lifted and slowly lowered into the inner steel casing 2. The mud pump is started. After a certain amount of mud has been pumped into the hole, the percussion drilling rig is started.

[0081] S7. Mud preparation: excavate a mud pool and a sedimentation tank 5m away from the hole mouth, and connect the casing gap and the mud pool with a mud trench;

[0082] S8. Drilling: Based on the geological histogram, observe and inspect frequently when approaching a karst cave. Determine whether you are approaching a karst formation based on the rock samples collected, the length of the measuring rope, and the sound of the impact on the rock formation. When approaching a karst formation, confirm that the amount of prepared mud is sufficient before drilling through it to avoid a sudden loss of mud after drilling through the cave, which could cause insufficient pressure in the hole and lead to a collapse. When drilling through multiple caves and encountering harder rock formations, control the impact amplitude. If a collapse occurs, backfill the mixture to above the collapse point and re-drill the hole until the designed elevation is reached.

[0083] S9. Finishing the hole and cleaning the hole: After finishing the hole, the quality of the hole is inspected. If it passes the inspection, the first hole cleaning is carried out. The hole is cleaned by the slurry replacement method. When cleaning the hole, the water head height in the hole must be maintained to prevent the hole from collapsing. The first hole cleaning is carried out before the steel cage 5 is hoisted in.

[0084] S10, steel cage hoisting and detection tube installation: immediately after the first hole cleaning is completed, the steel cage 5 is lowered and slowly lowered into the hole. After entering the hole, the steel cage 5 is accurately centered. At each lifting position, a "mouth"-shaped hoisting steel bar is welded on the inner side of the stiffener, and the steel cage is fixed in position using the inner support and outer hoist limit bracket 6 to prevent displacement or floating during the pouring process;

[0085] S11, secondary hole cleaning: After the steel cage 5 is lowered, the guide tube is lowered in time for the second hole cleaning. After the mud index and sediment thickness in the hole meet the requirements, concrete is poured;

[0086] S12, air injection of the bag: before filling, a test is conducted and air is injected into the bag 4 using the air injection pipe 9 to expand it; and a floating closed bag 7 is placed in the foundation pit;

[0087] S13. Concrete pouring: During pouring, always keep the concrete conduit buried at a depth of more than 2m to prevent pile breakage. When passing through a cave, the pouring speed should be appropriately slowed down. The pile top pouring elevation should be 0.5m to 0.8m higher than the design elevation. After pouring, observe for about 30 minutes. If there is no change in the concrete surface, slowly pull out the conduit.

[0088] S14, pile head removal: after the concrete foundation pile is poured and finally set for 3 hours, the excess concrete is manually removed and the sealed bag 7 is floated up, and then other components and equipment are removed to complete the construction of the pile foundation.

[0089] It should be noted that some parts not described in detail in the present invention belong to the common knowledge in the art, or can be directly purchased from the market, and those skilled in the art can obtain them without creative work. The specific connection method has extremely wide applications in this art or daily life and will not be described in detail here.

[0090] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0091] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0092] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0093] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0094] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0095] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A pile foundation construction system in a karst area, characterized by: It includes double casings and inner steel casings that are necked down in sections and arranged in the pile hole; The step-by-step necking and following double casing comprises an upper casing and a lower casing; the upper casing is positioned and installed on the lower casing; The outer side wall of the step-by-step necking and following double casing is provided with a bag corresponding to the position of the karst area; the step-by-step necking and following double casing is sleeved on the inner steel casing; The inner steel casing is provided with a steel cage for pouring pile foundation; A steel cage limiting support frame and a floating closed bag are also provided; the steel cage limiting support frame is positioned on the top of the steel cage to achieve the upper limit of the steel cage; the floating closed bag is arranged in the pile hole; The axial lower end of the upper casing is threadedly connected to the axial upper end of the upper casing, so as to realize an axially detachable fixed connection between the upper casing and the lower casing; The lower casing is also provided with a pin; the pin is arranged corresponding to the limiting slot on the upper casing, and the axial rapid positioning of the upper and lower casings is achieved by the penetration of the pin and the limiting slot; The limiting slot is a through hole; the through hole is a long waist-shaped hole set along the circumferential direction of the upper casing; a pin is passed through the through hole to achieve axial rapid positioning of the upper and lower casings; A bladder bag and an air injection pipe are positioned on the outer side of the upper casing; the air injection pipe is connected to the bladder bag; The reinforcement cage limiting support frame includes a support rod, a cross rod and a connecting frame; the support rod matches the inner size of the reinforcement cage; the cross rod is arranged inside the support rod, and its two ends are respectively connected to the inner side of the support rod; one end of the connecting frame is connected to the cross rod, and the other end extends outward; the outer end of the connecting frame is provided with a downward pointed top for achieving insertion and positioning on the ground outside the pile hole; The outer circumferential edge of the support rod is also provided with a rubber buckle, which can be clamped and limited with the transverse stirrups of the steel cage; A device for guiding small holes around the top plate of the pile foundation hole is also provided; the device for guiding small holes comprises a cone top, a fan-shaped steel sheet, a steel wire, a pressure plate, a fixing rod and a pull rope; A fixed ring is provided in the top of the cone; the lower end of the sector steel sheet is provided on the top of the cone; one end of the steel wire is positioned and connected to the inner side of the sector steel sheet, and the other end is positioned and connected to the pressure plate; the fixed rod is positioned and provided on the pressure plate; one end of the pull rope passes through the pressure plate and the ring in sequence and is then positioned and connected to the pressure plate; The plurality of sector-shaped steel sheets are evenly distributed axially on the cone top, and the pressing plate is arranged on the inner side of the top of the sector-shaped steel sheet, thereby forming an inverted cone-shaped skeleton structure.

2. The karst area pile foundation construction system according to claim 1, characterized in that: The plurality of fan-shaped steel sheets are connected to the pressing plate via an umbrella frame structure, so that the fan-shaped steel sheets can be expanded and contracted in an umbrella shape.

3. A karst area pile foundation construction method, based on the karst area pile foundation construction system according to any one of claims 1-2, characterized in that: The following steps are involved: S1. Construction Preparation: Level the site, remove debris, replace the soft soil on the surface, and compact it. The location of the mud pit, steel bar processing site, and construction access roads should all be reasonably arranged. Special measures should be taken when necessary, and preparations should be made before entering the construction site. Carefully study the geological survey data to determine the thickness of the soft soil layer on the surface of the proposed pile foundation, the location and scope of the karst caves to be crossed, and the possible filling conditions of the karst caves, and make a preliminary assessment of the strata that may collapse. S2. Measurement and positioning: Use a total station and a steel ruler to determine the center pile of the hole, and arrange guard piles around the pile. Use cement mortar to reinforce the guard piles and set up obvious signs. Set up a slurry pool and sedimentation tank between each adjacent pier to meet the drilling mud needs. S3. Bury the inner steel casing: After determining the location of the inner steel casing, use a crane to lower the inner steel casing, and control the plane position deviation of the inner steel casing within 5cm and the inclination deviation within 1%; S4. Follow up double casing installation by necking down section by section: After the inner steel casing is positioned and installed, first hang the lower casing inside the inner steel casing, connect the through-holes on the inner ring plate at the lower end of the upper casing with the pins on the outer ring plate at the upper end of the lower casing, and then rotate the upper casing to tighten it to the lower casing; S5. Excavation: In the excavation work at the karst roof, in order to prevent the occurrence of collapse, the hole-guiding device is first used to adjust the hole-guiding taper to perform local small hole excavation, and then the area around the small hole is hammered to form a hole; S6. Drilling rig in place: First, the working foundation of the drilling rig is treated with stone slag replacement and compacted before the drilling rig is installed in place. After the percussion drilling rig is installed, the center of the drill bit is accurately aligned with the cross center of the casing. The drill bit is hoisted and slowly lowered into the inner steel casing. The mud pump is started. After a certain amount of mud has been pumped into the hole, the percussion drilling rig is started. S7. Mud preparation: excavate a mud pool and a sedimentation tank 5m away from the hole mouth, and connect the casing gap and the mud pool with a mud trench; S8. Drilling: Based on the geological histogram, observe and inspect frequently when approaching a karst cave. Determine whether you are approaching a karst formation based on the rock samples collected, the length of the measuring rope, and the sound of the impact on the rock formation. When approaching a karst formation, confirm that the amount of prepared mud is sufficient before drilling through it to avoid a sudden loss of mud after drilling through the cave, which could cause insufficient pressure in the hole and lead to a collapse. When drilling through multiple caves and encountering harder rock formations, control the impact amplitude. If a collapse occurs, backfill the mixture to above the collapse point and re-drill the hole until the designed elevation is reached. S9. Finishing and cleaning the hole: After finishing the hole, the quality of the hole is inspected. If it passes the inspection, the first hole cleaning is carried out. The hole is cleaned by changing the slurry. When cleaning the hole, the water head height in the hole must be maintained to prevent the hole from collapsing. The first hole cleaning is carried out before the steel cage is hoisted in. S10. Lifting the steel cage and installing the test tube: Immediately after the first hole cleaning is completed, lower the steel cage slowly into the hole. After entering the hole, align the steel cage accurately. At each lifting position, weld a "mouth"-shaped lifting steel bar on the inner side of the stiffener. Use the steel cage limit bracket with inner support and outer hoist to limit and fix it to prevent displacement or floating during the pouring process. S11. Secondary hole cleaning: After the steel cage is lowered, the guide tube is lowered in time for the second hole cleaning. After the mud index and sediment thickness in the hole meet the requirements, concrete is poured; S12. Air injection into the bag: Before filling, conduct a test and use the air injection pipe to inject air into the bag to expand it; and place a floating closed bag in the foundation pit; S13. Concrete pouring: During pouring, always keep the concrete conduit buried at a depth of more than 2m to prevent pile breakage. When passing through a cave, the pouring speed should be appropriately slowed down. The pile top pouring elevation should be 0.5m to 0.8m higher than the design elevation. After pouring, observe for about 30 minutes. If there is no change in the concrete surface, slowly pull out the conduit. S14. Pile head removal: After the concrete foundation pile is poured and finally set for 3 hours, the excess concrete is manually excavated and the floating sealed bag is removed, and then other parts and equipment are removed to complete the pile foundation construction.

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