Method for forming hole of super-long cast-in-place pile in same hole of complex stratum

Abstract

The application discloses a complex stratum same pouring pile hole super-long pouring pile hole forming construction method, which comprises the following steps: S1, a pouring pile-stratum three-dimensional model for intuitively displaying the stratum type condition of each pouring pile in the vertical direction is established by using a three-dimensional modeling software; S2, different drilling equipment is selected and processed according to different stratum types, including a steel casing, a guide frame device, a three-wing drill bit assembly and a roller cutter drill bit assembly; S3, the processed steel casing is inserted and driven; and S4, the drilling equipment is used to perform super-long pouring pile hole drilling construction in the complex stratum of the same pouring pile hole. The method can effectively solve the technical problems of the quality accidents, such as the large deviation of the inclination of the super-long pouring pile, the paste drilling, the pipe sticking and the pipe burying of the drill bit, the reduction of the pouring pile drilling efficiency, the shortening of the pouring pile length and the reduction of the bearing capacity of the pouring pile body caused by the artificial misjudgment of the solitary stone or the solitary stone group as the bedrock.

Description

Technical Field

[0001] This invention relates to the field of bridge pile foundation construction technology, and in particular, to a method for constructing ultra-long cast-in-place piles in the same bored pile hole in complex strata. Background Technology

[0002] Cast-in-place piles are a common type of pile foundation. The inclination of a cast-in-place pile refers to its vertical deviation, which is crucial to the stability of the building structure. Current national standards and specifications stipulate that the inclination deviation of drilled cast-in-place piles must not exceed 1% of the pile length and must be ≤500mm. Excessive inclination deviation can lead to instability in the entire building structure, thus affecting the building's service life and safety.

[0003] For the 30 cast-in-place piles of the main piers of a single-tower cable-stayed bridge in the Guangdong Delta Plain, a bridge project located in a strong earthquake zone with a seismic fortification intensity of 8 degrees (0.20g), affected by strong typhoons from June to October, with high-strength and strongly developed isolated boulders or boulder clusters at a depth exceeding 110m, alternating layers of silty clay and permeable gravel, and strongly weathered granite bedrock, a river-marine alluvial facies strata, drilling was carried out to a depth exceeding 135m. The rate of encountering isolated boulders or boulder clusters during drilling reached 41%. Traditional methods for drilling cast-in-place piles include percussion drilling, percussion-grab drilling, forward and reverse circulation drilling, and rotary drilling. Percussion drilling has good terrain adaptability and can meet various geological conditions such as pebbles, gravel, boulders, and bedrock. It can handle drilling construction of isolated boulders or groups of isolated boulders with a burial depth of more than 110m. However, according to local policy regulations, the construction of bridge pier pile foundations near water sources and river embankments is prohibited from using construction techniques with high vibration such as impact and hammering. Therefore, the drilling construction of the bridge pier cast-in-place piles is more difficult.

[0004] To withstand strong seismic forces, the single-tower cable-stayed bridge is equipped with a 25m permanent steel casing that works in conjunction with the cast-in-place concrete piles to resist earthquakes. Given the complex environment and local policy restrictions, including the presence of alluvial strata, strongly developed boulders or boulder clusters, alternating layers of silty clay and permeable gravel, and the need for a permanent steel casing in the seismic design, the traditional drilling methods for cast-in-place piles exceeding 135m depth were simply insufficient to meet the requirements for drilling.

[0005] During the drilling of cast-in-place piles exceeding 135m in depth, the presence of hidden boulders or boulder clusters in alternating layers of silty clay and permeable gravel often causes significant deviations in the pile's inclination, exceeding the limits specified in current national standards and specifications, thus rendering the piles unqualified. During drilling, drill bit jamming occurs when encountering clay layers, and drill bit getting stuck or buried when encountering hidden boulders or boulder clusters, both leading to low drilling efficiency. Furthermore, hidden boulders or boulder clusters also significantly impact the drilling process, easily leading to misjudgments where boulders or boulder clusters are mistaken for bedrock, resulting in artificially shortened pile lengths and severely affecting the pile's bearing capacity. Summary of the Invention

[0006] This invention provides a method for constructing ultra-long cast-in-place piles in the same borehole in complex strata, in order to solve technical problems such as large deviations in the inclination of ultra-long cast-in-place piles, drill bit jamming, stuck drill bits and burying drill bits, which reduce the drilling efficiency of cast-in-place piles, and human error in misjudging boulders or groups of boulders as bedrock, which shortens the length of cast-in-place piles and reduces the bearing capacity of the pile body.

[0007] The technical solution adopted in this invention is as follows:

[0008] A method for constructing ultra-long cast-in-place piles in the same borehole in complex strata includes the following steps: S1: Based on the "Engineering Geological Survey Report," a three-dimensional model of the cast-in-place pile-stratum is established using three-dimensional modeling software to visually display the stratum types encountered by each cast-in-place pile in the vertical direction; S2: Different drilling equipment is selected and manufactured according to different stratum types, including steel casing, guide frame device, three-wing drill bit assembly for drilling in soft strata and preventing drill jamming, and roller cone drill bit assembly for grinding drilling in hard strata and preventing drill jamming and burying; S3: The manufactured steel casing is driven; S4: Drilling of ultra-long cast-in-place piles in complex strata within the same borehole is carried out using drilling equipment.

[0009] Further, step S2 specifically includes the following steps: S201: selection of vibratory hammer and verification of excitation force; S202: processing and transportation of steel casing; S203: selection of drilling rig; S204: fabrication of guide frame device; S205: processing and fabrication of three-wing drill bit assembly for soft formations; S206: processing and fabrication of roller cone hob drill bit assembly for hard formations.

[0010] Furthermore, the three-wing drill bit assembly includes: a first drill bit connecting device for connecting to the drill pipe guide of the drilling rig; a first guide wheel device for increasing the weight of the three-wing drill bit assembly and controlling the diameter and verticality of the grouting pile hole; a first counterweight device for increasing the weight of the three-wing drill bit assembly; a three-wing drill bit device for drilling the formation; and a first mud guide for sucking out the slag generated during drilling from the pile hole. The first drill bit connecting device, the first guide wheel device, the first counterweight device, and the three-wing drill bit device are arranged sequentially along the axial direction and are detachably fixed. The first mud guide is sequentially threaded through and connected to the first drill bit connecting device, the first guide wheel device, the first counterweight device, and the three-wing drill bit device along the axial direction, and the top end of the first mud guide is also connected to the drill pipe guide, while its opposite bottom end extends out of the bottom end of the three-wing support in the three-wing drill bit device.

[0011] Furthermore, the three-wing drill bit assembly includes a three-wing support for installation, a first top flange fixed to the top of the three-wing support, a flange connector for connection and fastening, and a guide drill bit for drilling. The three-wing support is fixedly fitted onto the outer circle of the first mud guide tube and is detachably fixed to the bottom end of the first counterweight device through the first top flange and flange connector at its top. The three-wing support is hollowed out to allow mud to pass through, and it is also provided with cutting teeth for cutting and drilling. The guide drill bit is located at the bottom end of the three-wing support and is fixedly fitted onto the outer circle of the first mud guide tube, with the bottom end of the first mud guide tube extending into the guide drill bit.

[0012] Furthermore, the roller cone cutter assembly includes: a second drill bit connecting device for connecting to the drill pipe guide of the drilling rig; a second guide wheel device for increasing the weight of the roller cone cutter assembly and controlling the diameter and verticality of the grouting pile hole; a second counterweight device for increasing the weight of the roller cone cutter assembly; a roller cone cutter device for grinding and drilling; and a second mud guide for sucking out the slurry generated during drilling from the pile hole. The second drill bit connecting device, the second guide wheel device, the second counterweight device, and the roller cone cutter device are arranged sequentially along the axial direction and are detachably fixed. The second mud guide is sequentially threaded through and connected to the second drill bit connecting device, the second guide wheel device, the second counterweight device, and the roller cone cutter device along the axial direction, and the top end of the second mud guide is also connected to the drill pipe guide, while its opposite bottom end extends out of the roller cone cutter device.

[0013] Furthermore, the roller cone hobbing drill bit assembly includes a solid sixth annular cylinder fixedly mounted on the outer circumference of the second mud guide tube, a second top flange fixed to the top of the sixth annular cylinder, a flange connector for connection and fastening, multiple protruding cylinders, and a cutter head for grinding and drilling; the sixth annular cylinder is detachably fixed to the bottom end of the second counterweight device through the second top flange and flange connector at its top; the multiple protruding cylinders are sequentially and spaced apart on the outer circumference of the sixth annular cylinder; the cutter head is fixed to the bottom end of the sixth annular cylinder and the multiple protruding cylinders.

[0014] Further, step S3 specifically includes the following steps: S301: embed a temporary circular steel pipe with its top end higher than the ground at the core of the cast-in-place pile; S302: carry out the pilot hole construction for the cast-in-place pile inside the temporary circular steel pipe; S303: fix and install a guide frame device on the ground close to the temporary circular steel pipe, and make the guide frame device coaxial with the temporary circular steel pipe and fix it; S304: drive the steel casing.

[0015] Further, step S4 specifically includes the following steps: S401: mud preparation; S402: drilling construction of pile holes in soft strata within the same pile hole; S403: drilling construction of pile holes in hard strata within the same pile hole.

[0016] Furthermore, during step S402: when drilling the pile holes through plain fill, silty clay, and soft clay strata, a high-speed rotation of a three-wing drill bit assembly and a mud reverse circulation drilling method are adopted; during the drilling process, based on the drill cuttings sample discharged by air-lift reverse circulation and the drilling depth, a three-dimensional modeling software is used to draw a three-dimensional diagram of the drill cuttings sample-drilling depth; the drawn three-dimensional diagram of the drill cuttings sample-drilling depth is compared with the three-dimensional model of the pile-strata to conduct dynamic control and analysis of the pile hole drilling.

[0017] Furthermore, during step S403: when drilling the pile holes through fine sand, medium sand, gravel, boulders or groups of boulders, or hard granite strata, a decompression, low-speed rotation, and mud reverse circulation drilling method using roller cone cutter bit assembly is adopted; during drilling, based on the drill cuttings sample discharged by air-lift reverse circulation and the drilling depth, a three-dimensional modeling software is used to draw a three-dimensional diagram of drill cuttings sample-drilling depth; the drawn three-dimensional diagram of drill cuttings sample-drilling depth is compared with the three-dimensional model of the pile-stratum to conduct dynamic control analysis of the pile hole drilling.

[0018] The present invention has the following beneficial effects:

[0019] In the construction method of ultra-long cast-in-place piles in the same grouting pile hole in complex strata of the present invention, (1) according to the "Engineering Geological Survey Report", the Rhinoceros three-dimensional modeling software is used to establish a three-dimensional model of cast-in-place pile-stratum for intuitive display of the stratum type encountered by each cast-in-place pile in the vertical direction; (2) the planar position of the steel casing is controlled when the steel casing is driven by the guide frame device, coordinate fitting center, total station online technology, and the verification method of dual control of the plumb bob and the total station; the verticality of the steel casing is controlled by two theodolites in two mutually perpendicular directions to realize the inclination control of the cast-in-place pile in the steel casing section, thereby controlling the drilling inclination of the ultra-long cast-in-place pile; (3) when drilling the pile hole of cast-in-place piles through soft strata such as plain fill, silty clay, and silty clay, a three-wing drill is used. High-speed rotation of head assembly and reverse circulation drilling method of mud; When drilling the pile hole of cast-in-place pile through hard strata such as fine sand, medium sand, gravel, boulders or boulder groups, granite, etc., the decompression, low-speed rotation and reverse circulation drilling method of the processed roller cone cutter bit assembly is adopted; (4) During the drilling of cast-in-place pile, the drill cuttings sample and drilling depth are extracted by air lift reverse circulation, and the drill cuttings sample-drilling depth three-dimensional diagram is drawn using Rhinoceros three-dimensional modeling software. The dynamic control analysis of the drilling of cast-in-place pile is carried out again with the three-dimensional model of cast-in-place pile-stratum to quickly determine whether the drilling of cast-in-place pile should continue or stop, avoiding drill bit jamming, drill bit stuck and drill bit buried, avoiding human misjudgment of boulders or boulder groups as bedrock, artificially shortening the length of cast-in-place pile, and reducing the quality accident of the bearing capacity of the cast-in-place pile. The present invention provides a method for constructing ultra-long cast-in-place piles in the same borehole in complex strata. This method can effectively solve technical problems such as large deviations in the inclination of ultra-long cast-in-place piles, drill bit jamming, stuck drill bits, and buried drill bits reducing drilling efficiency, and the artificial shortening of pile length due to misjudging boulders or boulder groups as bedrock, thus reducing the bearing capacity of the pile body. Moreover, this construction method is simple to operate and easy to use widely.

[0020] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0021] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 This is a schematic diagram of a three-dimensional model of a cast-in-place pile-stratum according to a preferred embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of the main structure of the guide frame device according to a preferred embodiment of the present invention;

[0024] Figure 3 yes Figure 2 Top view of the guide frame device;

[0025] Figure 4 This is a schematic diagram of the spatial structure of the three-wing drill bit assembly according to a preferred embodiment of the present invention;

[0026] Figure 5 yes Figure 4 A schematic diagram of the sectional front view structure;

[0027] Figure 6 yes Figure 4 A schematic diagram of the main structure of a three-wing drill bit assembly;

[0028] Figure 7 This is a schematic diagram of the spatial structure of a roller cone hob drill bit assembly according to a preferred embodiment of the present invention;

[0029] Figure 8 yes Figure 7 A schematic diagram of the sectional front view structure;

[0030] Figure 9 yes Figure 7 Schematic diagram of the spatial structure of a medium-diameter roller cutter bit assembly;

[0031] Figure 10 This is a schematic diagram of the drilling section of a cast-in-place pile in a soft stratum within the same pile hole.

[0032] Figure 11 This is a schematic diagram of the drilling section of a cast-in-place pile in a hard stratum within the same pile hole.

[0033] Legend:

[0034] 1. Cast-in-place pile; 3. Isolated boulder or group of isolated boulders; 4. Steel casing; 5. Guide frame device; 6. Drilling rig; 601. Drill pipe guide; 7. Three-wing drill bit assembly; 702. First mud guide; 703. First drill bit connection device; 7031. First top flange; 7032. First bottom flange; 7033. First reinforcing support rib; 7034. First reinforcing connecting steel bar; 704. First guide wheel device; 7043. First annular column Body; 7044, First guide ring; 7045, First reinforcing ring frame; 7046, Second reinforcing support rib; 705, First counterweight device; 7053, Second ring cylinder; 7054, Second reinforcing ring frame; 7055, Third reinforcing support rib; 706, Three-wing drill bit assembly; 7062, Three-wing support; 7063, Gauge retaining ring; 7064, Cutting teeth; 7065, First slag suction nozzle; 7066, Guide drill bit; 8, Teeth 802. Second mud guide; 803. Second drill bit connecting device; 8031. Second top flange; 8032. Second bottom flange; 8033. Fourth reinforcing support rib; 8034. Second reinforcing connecting steel bar; 804. Second guide wheel device; 8043. Third annular cylinder; 8044. Second guide ring; 8045. Third reinforcing annular frame; 8046. Fifth reinforcing support rib; 805. Second counterweight device; 8053, fourth circular cylinder; 8054, fourth reinforcing circular frame; 8055, sixth reinforcing support rib; 806, roller cone cutter bit device; 8062, fifth circular cylinder; 8063, fifth reinforcing circular frame; 8064, protrusion cylinder; 8065, rectangular protrusion; 8066, cutter head; 80661, cutter bracket; 80662, toothed cutter; 80663, outer disc; 8067, second slag suction port. Detailed Implementation

[0035] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered below.

[0036] Reference Figure 1-11 A preferred embodiment of the present invention provides a method for constructing ultra-long cast-in-place piles in the same borehole in complex strata, comprising the following steps:

[0037] S1: Based on the "Engineering Geological Survey Report", a three-dimensional model of the cast-in-place pile-stratum is established using three-dimensional modeling software to visually display the stratum type encountered by each cast-in-place pile in the vertical direction;

[0038] S2: Select and process different drilling equipment according to different formation types, including steel casing 4, guide frame device 5, three-wing drill bit assembly for drilling soft formations and preventing drill jamming 7, and roller cone hob drill bit assembly for grinding drilling in hard formations and preventing drill jamming and drill burial 8.

[0039] S3: Drive the steel casing 4 that has been processed and manufactured into place;

[0040] S4: Use drilling equipment to drill long cast-in-place pile holes in complex strata within the same cast-in-place pile hole.

[0041] In the construction method of ultra-long cast-in-place piles in the same grouting pile hole in complex strata of the present invention, (1) according to the "Engineering Geological Survey Report", the Rhinoceros three-dimensional modeling software is used to establish a three-dimensional model of the cast-in-place pile-stratum for intuitive display of the stratum type encountered by each cast-in-place pile 1 in the vertical direction; (2) the guide frame device 5, coordinate fitting center, total station online technology, and the verification method of dual control of the plumb bob and the total station are used to control the planar position of the steel casing 4 when driving the steel casing 4; the verticality of the steel casing 4 is controlled by two theodolites in two mutually perpendicular directions to realize the inclination control of the cast-in-place pile in the steel casing section, thereby controlling the drilling inclination of the ultra-long cast-in-place pile; (3) when drilling the cast-in-place pile hole through soft strata such as plain fill, silty clay, and silty clay, the three-dimensional model of the cast-in-place pile is constructed by processing and manufacturing three-dimensional modeling software. High-speed rotation and mud reverse circulation drilling method of wing drill bit assembly 7; When drilling the pile hole of cast-in-place pile through hard strata such as fine sand, medium sand, gravel, boulders or boulder groups 3, granite, etc., the decompression, low-speed rotation and mud reverse circulation drilling method of the processed roller cone cutter assembly 8 is adopted; (4) During the drilling of cast-in-place pile, the drill cuttings sample and drilling depth sucked out by air lift reverse circulation are used to draw a three-dimensional diagram of drill cuttings sample-drilling depth using Rhinoceros three-dimensional modeling software, and then the dynamic control analysis of the drilling of cast-in-place pile is carried out again with the three-dimensional model of cast-in-place pile-stratum to quickly determine whether the drilling of cast-in-place pile should continue or stop, avoiding drill bit jamming, stuck drill and buried drill, avoiding human misjudgment of boulders or boulder groups as bedrock, artificially shortening the length of cast-in-place pile, reducing the quality accident of the bearing capacity of cast-in-place pile. The present invention provides a method for constructing ultra-long cast-in-place piles in the same borehole in complex strata. This method can effectively solve technical problems such as large deviations in the inclination of ultra-long cast-in-place piles, drill bit jamming, stuck drill bits, and buried drill bits reducing drilling efficiency, and human error in misjudging boulders or boulder groups as bedrock, leading to shortened pile length and reduced pile bearing capacity. Furthermore, this construction method is simple to operate and easy to use widely.

[0042] Optionally, when performing step S1, such as Figure 1As shown in the Engineering Geological Survey Report, the 30 piles of the No. 7 pier of the cable-stayed bridge, each 128m long and φ2200mm in diameter, pass through complex strata from top to bottom, including plain fill, silty clay, fine sand, medium sand, gravel, boulders or groups of boulders, and Yanshanian granite. Before drilling the first pile hole, based on the geological distribution of the 30 piles at the No. 7 pier of the cable-stayed bridge as revealed in the "Engineering Geological Survey Report", a three-dimensional model of the pile-clay + sand and gravel + isolated rock or isolated rock group 3 + granite stratum was established using Rhinoceros three-dimensional modeling software (hereinafter referred to as "pile-stratum three-dimensional model"). This model simulates the three-dimensional diagram of the 30 piles in the vertical direction of the clay + sand and gravel + isolated rock or isolated rock group 3 + granite stratum, intuitively showing the specific hidden location of the isolated rock or isolated rock group 3 in the stratum, providing a reliable construction basis for the drilling of the first pile hole. Compared with the borehole geological columnar section in the "Engineering Geological Survey Report", the 3D model of cast-in-place piles and strata can rotate 360° to show the specific hidden location of the isolated rock or group of isolated rocks 3 in the strata from all angles; it can show the overall strata distribution in the area of ​​the 30 cast-in-place piles 1 of Pier 7 and the specific hidden location of the isolated rock or group of isolated rocks 3 in the strata; it has the advantages of being intuitive, accurate and scientific.

[0043] Step S2 specifically includes the following steps: Since the 30 cast-in-place piles (1) of pier #7 of the main bridge of this cable-stayed bridge are all 128m long, they are considered ultra-long cast-in-place piles (1). Based on the "Technical Specifications for Highway Bridge and Culvert Construction," construction experience, and the complex geological distribution of this project, drilling equipment must be rationally configured to ensure smooth drilling through various geological formations. The drilling equipment includes a vibratory hammer, a steel casing (4), a guide frame device (5), a drilling rig (6), a three-wing drill bit assembly (7), and a roller cone cutter bit assembly (8). The vibratory hammer's main function is to generate excitation force to drive the steel casing 4 into the ground. The main functions of the steel casing 4 are: firstly, to form a steel casing concrete-cast pile with the cast-in-place pile 1, sharing the load and resisting strong earthquake forces; secondly, to provide a protective coating on the outer wall of the steel casing 4, preventing groundwater corrosion of the permanent steel casing and extending its service life, while also isolating it from groundwater corrosion of the reinforcing steel in the cast-in-place pile 1 concrete structure; and thirdly, to guide the drilling rig 6 vertically downwards during the drilling of the cast-in-place pile 1, promptly correcting the drilling inclination to ensure the inclination of the cast-in-place pile 1 within the permanent steel casing section. The guide frame device 5's main function is to utilize the steel casing installed within it... The hydraulic jacks and limit wheels for positioning, correction, and adjustment of the casing 4 control the verticality and planar position of the steel casing 4; the drilling rig 6 adopts the ZJD4000 / 350C fully hydraulic drilling rig to improve the drilling speed and drilling depth of the pile hole 1; the three-wing drill bit assembly 7, due to its large drill bit space, can prevent the drill bit from getting stuck when drilling in soft strata such as plain fill, silty clay, and silty clay, thus improving the drilling efficiency of the pile hole 1; the roller cone cutter drill bit assembly 8, due to its hard drill bit, can break rocks and remove debris, thus preventing the drill bit from getting stuck and buried when drilling in hard strata such as fine sand, medium sand, gravel, boulders or boulder groups 3, and granite, thus improving the drilling efficiency of the pile hole 1.

[0044] S201: Selection of vibratory hammer and verification of excitation force; specifically, it includes the following steps:

[0045] (1) Selection of vibratory hammer: The vibratory hammer is selected according to its excitation force P and the dynamic friction resistance R of the soil around the pile hole of the cast-in-place pile 1 to the steel casing 4 when the steel casing 4 is driven. The vibratory hammer adopted is DZJ150 vibratory hammer with excitation force of 1140kN and hammer weight of 8700kg.

[0046] Excitation force: P>R=∑L K ×U×f k -G

[0047] In the formula: L K - The depth of steel casing 4 in different strata;

[0048] U-Steel casing 4 Perimeter length;

[0049] f k - Frictional resistance of different formations after liquefaction;

[0050] G-Steel casing 4 and the weight of the vibratory hammer.

[0051] (2) Vibration force calculation: Based on the drilling parameters of the QSZK27 borehole of the 30 cast-in-place piles 1 of the No. 7 pier of the cable-stayed bridge, it can be obtained that: after the pilot hole of the cast-in-place pile 1 is 9m deep, the dynamic friction resistance generated by the soil is 148.9t, while the weight of a single steel casing 4 with a length of 25m and an inner diameter of Φ2.5m is about 30.42t. Actual vibration force during driving: Vibratory hammer vibration force + vibratory hammer weight + steel casing 4 weight is 153.1t (i.e., 8.7 + 114 + 30.42 = 153.12t), which is greater than the dynamic friction resistance of the soil of 148.9t.

[0052] S202: Fabrication and transportation of steel casing 4; steel casing 4 is constructed by welding permanent steel casing segments with a length of 25m and wall thickness of 0.018m and 0.028m, and replacement steel casing segments with a length of 7m and wall thickness of 0.018m. The end of the 0.028m wall thickness segment of the permanent steel casing is the cutting edge of steel casing 4, and the end of the replacement steel casing segment is the top of steel casing 4; the length of the replacement steel casing segment is 7m of the empty pile portion at the top of cast-in-place pile 1 (depth from the top of cast-in-place pile 1 to the original ground surface). Specifically, it includes the following steps:

[0053] (1) Steel casing material and structure: The permanent steel casing is welded from two sections of steel pipe with diameters of φ2.5×0.018×22.6m and φ2.5×0.028×2.4m, and the replacement section of the steel casing is made of steel pipe with diameters of φ2.5×0.018×7.0m.

[0054] ① Steel casing material: Made of Q345C stainless steel plate with a thickness of 0.018m, processed into two-section circular hollow steel pipes with dimensions of φ2.5×0.018×22.6m and φ2.5×0.018×7.0m; and made of Q345C stainless steel plate with a thickness of 0.028m, processed into one-section circular hollow steel pipe with dimensions of φ2.5×0.028×2.4m.

[0055] ② Permanent steel casing construction: One end of a φ2.5×0.018×22.6m circular hollow steel pipe is butt-welded to one end of a φ2.5×0.028×2.4m circular hollow steel pipe to form a 25m long permanent steel casing. On the inner circumference of the permanent steel casing, two shear rings spaced 0.4m apart are welded from the top of the casing to the bottom cutting edge within a 0-1m range; four shear rings spaced 1m apart are welded from the top of the casing to the bottom cutting edge within a 1-5m range; and nine shear rings spaced 2m apart are welded from the top of the casing to the bottom cutting edge within a 5-25m range. Each shear ring is made of Q345C stainless steel plate, consisting of two semi-circular segments, each 50mm wide and 25mm thick. During welding, the two semi-circular segments are joined and welded together with a 200mm gap to form a single ring. The shear rings are then welded perpendicularly to the steel casing 4 along its longitudinal centerline. The shear rings enhance the rigidity of the permanent steel casing, preventing deformation; they also strengthen the bond between the concrete of the cast-in-place pile 1 and the permanent steel casing, forming a steel casing concrete cast-in-place pile that shares the load and resists strong earthquake forces. The four segments of the steel casing are butt-welded using a single-sided V-groove full-section fusion welding method. After welding, the inner walls of the two circular hollow steel pipe segments are aligned and flat, while the outer walls are convex.

[0056] The benefits of using steel casing: Permanent steel casing with shear rings enhances the bond between the cast-in-place pile concrete and the permanent steel casing, forming a steel casing concrete cast-in-place pile that works together to resist strong earthquake forces. The replacement steel casing serves two purposes: first, vibratory hammers stimulate the replacement steel casing, causing the lower end of the permanent steel casing to vibrate and continue driving until it reaches the designed elevation of the permanent steel casing bottom; second, it facilitates pile positioning, drilling guidance, borehole opening protection, and pile top elevation control during drilling; prevents stones from falling into the borehole; isolates surface water from the borehole, preventing surface water from flowing into the borehole during drilling, maintaining the mud level (pressure) inside the borehole, and preventing borehole wall collapse.

[0057] (2) Steel casing protective coating: The steel casing is coated with a protective coating using sandblasting and rust removal process, with copper ore sand as an auxiliary material. The surface treatment reaches Sa2.5 standard and has a certain roughness. The coating is applied within 4 hours after sandblasting to ensure the adhesion between the paint and the steel surface. On the outer wall of the 25m permanent steel casing, a high-performance composite ordinary double-layer fusion bonded epoxy powder coating is used, wherein: the inner layer thickness is >300μm, the surface layer thickness is >350μm, and the total coating thickness is >650μm. The inner layer is a corrosion-resistant coating, and the surface layer is a scratch-resistant and wear-resistant coating. The coating is tested and qualified before it can be used.

[0058] (3) Transportation and Protection of Steel Casings: Steel casings 4 are transported to the site using flatbed trucks. Nylon slings are used for gentle lifting and transport to prevent impact deformation and mechanical damage. During loading, to prevent excessive bending of long steel casings 4 that could damage the outer coating, each coated finished steel casing 4 is fitted with an isolation gasket. The size and position of the gaskets are designed to protect the coating from damage during stacking. Steel casings 4 are φ2.5m circular hollow steel pipes with a large diameter. To ensure that steel casings 4 do not deform during handling and transportation, a cross brace is installed 1.0m from the top and bottom openings of each casing, and another cross brace is installed every 10.0m along the inner side. Steel casings 4 are transported using flatbed trucks. To ensure the stability of steel casings 4 during transportation, an arc-shaped base is installed on the truck and secured with steel wire ropes. A designated person is responsible for directing the transport to the platform and clearing any obstacles beforehand.

[0059] (4) Steel casing lifting equipment: Since the weight of a single 25m permanent steel casing is about 30.42t, a crawler crane with a lifting capacity of 150t is used as the lifting equipment during the installation.

[0060] (5) Steel casing insertion equipment: The steel casing insertion equipment adopts DZJ150 vibratory hammer for vibration insertion.

[0061] S203: Selection of Drilling Rig 6; Since the main bridge pier #7 of this cable-stayed bridge has 30 cast-in-place piles, with one pile length of 128m plus a 7.0m length of the empty pile portion at the top of the first pile (depth from the top of the cast-in-place pile to the original ground level), the total drilling depth is 135m. Based on the "Technical Specifications for Highway Bridge and Culvert Construction," construction experience, and the complex geological distribution of this project, to ensure smooth drilling through various geological formations, drilling rig 6 adopts a ZJD4000 / 350C fully hydraulic drilling rig. Its technical parameters are: total weight 56t, maximum borehole diameter φ4.0m, maximum borehole depth 160m, maximum lifting force 220t, guide frame inclination angle 25°, power head inclination angle 55°, drill rod guide pipe 601 specification φ377×24×3000mm, slag removal method air lift reverse circulation, and maximum rock-embedded strength up to 200MPa.

[0062] S204: Fabrication of guide frame device 5; such as Figure 2-3 As shown, the guide frame device 5 is made of I20 I-beams and [16 channel steel, forming a square column double-layer guide frame. Both the top and bottom are square, with each side of the square frame being 150mm larger than the outer diameter of the temporary circular steel pipe. The guide frame device 5 uses a double-layer guide with a 3.0m gap between the two layers, both employing adjustable guide structures. Inside the guide frame device 5 are hydraulic jacks and limit wheels for positioning, correcting, and adjusting the steel casing 4, to control the installation plane position and verticality of the steel casing 4.

[0063] S205: Fabrication of a three-wing drill bit assembly for soft formations;

[0064] Reference Figure 4-6 The three-wing drill bit assembly 7 includes: a first drill bit connecting device 703 for connecting to the drill rod guide 601 of the drilling rig; a first guide wheel device 704 for increasing the weight of the three-wing drill bit assembly and controlling the diameter and verticality of the pile hole; a first counterweight device 705 for increasing the weight of the three-wing drill bit assembly; a three-wing drill bit device 706 for drilling into the formation; and a first mud guide 702 for suctioning and discharging slurry generated during drilling out of the pile hole; the first drill bit connecting device 703. The first guide wheel device 704, the first counterweight device 705, and the three-wing drill bit device 706 are arranged sequentially along the axial direction and are detachably fixed; the first mud guide tube 702 is sequentially connected to the first drill bit connecting device 703, the first guide wheel device 704, the first counterweight device 705, and the three-wing drill bit device 706 along the axial direction, and the top end of the first mud guide tube 702 is also connected to the drill pipe guide tube 601, and its opposite bottom end extends out of the bottom end of the three-wing bracket 7062 in the three-wing drill bit device 706.

[0065] The three-wing drill bit assembly 7 of the present invention, due to the arrangement of the first drill bit connecting device 703, the first guide wheel device 704, and the first counterweight device 705, helps to increase the overall weight of the three-wing drill bit assembly 7, thereby increasing the stability and cutting ability of the three-wing drill bit device 706 at the bottom of the three-wing drill bit assembly 7, and thus reducing the risk of drilling. At the same time, due to the arrangement of the first guide wheel device 704 and the gauge ring 7063 of the three-wing drill bit device 706, it is also beneficial to control the diameter and verticality of the pile hole 1 during the drilling of the pile hole 1. On the other hand, the length of the mud guide 702 is set and lengthened in the three-wing drill bit device 706. Compared with the existing three-wing or four-wing drill bits, the cutting space at the front of the three-wing drill bit device 706 is increased, and the capacity of drill cuttings at the bottom of the pile hole of the cast-in-place pile 1 is increased. The hollow three-wing support 7062 is set in the three-wing drill bit device 706, which helps to increase the drill bit space and reduce the contact area between drill cuttings and the three-wing support 7062. This solves the technical problem of drill bit "blurring" when drilling in soft strata such as plain fill, silty clay, and silty clay, shortens the drilling time, and improves the drilling efficiency of cast-in-place piles.

[0066] Optionally, such as Figure 5As shown, the first drill bit connection device 703 includes a first top flange 7031 and a first bottom flange 7032, which are arranged opposite each other and respectively fixedly fitted onto the outer circumference of the first mud guide 702; a flange connector for connection and fastening; and multiple first reinforcing support ribs 7033. The first top flange 7031 is used to detachably fix to the flange at the bottom end of the drill pipe guide 601 through the flange connector, and the first bottom flange 7032 is used to detachably fix to the first guide wheel device 704 through the flange connector. Multiple first reinforcing support ribs 7033 are arranged circumferentially and spaced between the first top flange 7031 and the first bottom flange 7032, and each first reinforcing support rib 7033 is welded and fixed to the first top flange 7031, the first bottom flange 7032, and the outer wall of the first mud guide 702.

[0067] In this optional embodiment, the first mud conduit 702 is a hollow conduit, located at the center of the first top flange 7031 and the first bottom flange 7032, and arranged at a 90° angle to the first top flange 7031 and the first bottom flange 7032; preferably, as Figure 5 As shown, the outer diameter of the first top flange 7031 is smaller than the outer diameter of the first bottom flange 7032. The outer diameter of the first top flange 7031 is the same as and connected to the outer diameter of the bottom flange of the drill pipe guide 601. The outer diameter of the first bottom flange 7032 is the same as and connected to the outer diameter of the top flange of the first guide wheel device 704. The connecting parts between the two flanges are high-strength large hexagonal head bolts, large hexagonal nuts, gaskets, and washers for steel structures. In this optional scheme, such as... Figure 4-5 As shown, the first reinforcing support rib 7033 is made of Q345C stainless steel plate with a thickness of 18mm and is processed into a "triangular" rib. It mainly serves to strengthen the connection between the first mud guide 702 and the first top flange 7031 and the first bottom flange 7032. The effect of setting the first reinforcing support rib 7033 is: to facilitate the smooth flow of mud from the top of the pile hole to the bottom of the pile hole; to reduce the upward lifting resistance of the three-wing drill bit assembly 7 when it is lifted upward; to facilitate the connection between the drill pipe guide 601 and the three-wing drill bit assembly 7; and to strengthen the connection between the first top flange 7031 and the first mud guide 702, and between the first bottom flange 7032 and the first mud guide 702, so as to prevent the first mud guide 702, the first top flange 7031 and the first bottom flange 7032 from being loosely welded, which could lead to separation and detachment, causing drilling safety accidents.

[0068] Preferably, such as Figure 4 and 5As shown, after the first drill bit connecting device 703 and the first guide wheel device 704 are connected by a flange, multiple first reinforcing connecting steel bars 7034 are evenly distributed along the outer circumference of the flange connection. Each first reinforcing connecting steel bar 7034 is made of Q345C stainless steel plate with a thickness of 50mm, and is processed into a rectangular steel bar with a length of 150mm and a width of 80mm. It is welded to the outer circumference of the adjacent flange between the first drill bit connecting device 703 and the first guide wheel device 704. The first reinforcing connecting steel bars 7034 are set to prevent the bolts and nuts between adjacent flanges from loosening, which would cause the first drill bit connecting device 703 and the first guide wheel device 704 to separate and fall off, resulting in a drilling safety accident. During the drilling of the cast-in-place pile, it prevents the connection between adjacent flanges from contacting and rubbing with the drill cuttings in the pile hole, thus preventing wear on the flange.

[0069] Optionally, such as Figure 4 and 5 As shown, the first guide wheel device 704 includes a solid first annular cylinder 7043 fixedly mounted on the outer circumference of the first mud conduit 702, a first top flange and a first bottom flange fixed at the upper and lower ends of the first annular cylinder 7043, a flange connector for fastening, a first guide ring 7044 fitted on the outer circumference of the first annular cylinder 7043, and multiple support plates for connecting and supporting. The first annular cylinder 7043 is detachably fixed to the bottom end of the corresponding first drill bit connecting device 703 and the top end of the first counterweight device 705 via the first top flange and the first bottom flange and the flange connector at both ends. The multiple support plates are arranged sequentially at intervals along the circumference of the first annular cylinder 7043, and their inner and outer sides are fixedly connected to the outer wall surface of the first annular cylinder 7043 and the inner wall surface of the first guide ring 7044, respectively. The axial length of the first guide ring 7044 is less than the length of the first annular cylinder 7043, and the two ends of the first guide ring 7044 are not aligned with the corresponding two ends of the first annular cylinder 7043. The first guide wheel device 704 is designed to increase the overall weight of the three-wing drill bit assembly, enhance the stability and cutting capability of the three-wing drill bit device 706 at the bottom of the three-wing drill bit assembly 7, and reduce drilling risks. It also helps control the diameter and verticality of the pile hole 1, prevents the lifting of the three-wing drill bit assembly 7 from getting stuck at the pre-embedded permanent steel casing cutting edge, and ensures smooth entry and exit of the three-wing drill bit assembly 7 from the permanent steel casing. In this optional scheme, the connection and setting method of the first top flange and the first bottom flange of the first guide wheel device 704 are the same as those of the first top flange 7031 and the first bottom flange 7032 in the first drill bit connecting device 703.

[0070] In this optional design, the first guide ring 7044 is made of Q345C stainless steel plate with a thickness of 50mm, forming a circular hollow steel pipe with an outer diameter of 2100mm and a height of 800mm. The intersection of the outer surface and the two end faces of the first guide ring 7044 is cut off into triangles and ground smooth to form upper and lower bevels. This helps prevent operators from being injured by the intersection of the first guide ring 7044's edges. The upper bevel of the first guide ring 7044 also facilitates the smooth flow of mud from the top of the pile hole to the bottom of the pile hole; it also reduces the resistance when the three-wing drill bit assembly 7 is lifted upwards. The lower bevel of the first guide ring 7044 facilitates the smooth upward overflow of mud from the pile hole when the three-wing drill bit assembly 7 is lowered downwards, reducing the resistance when the three-wing drill bit assembly 7 is lowered downwards.

[0071] Furthermore, four rectangular support plates are evenly distributed on the outer circumference of the first annular cylinder 7043, which are welded to the first guide ring 7044 to form a whole. The support plates are made of 50mm thick Q345C stainless steel plate. After welding, a cavity is left between the first guide ring 7044 and the first annular cylinder 7043, and the first guide ring 7044 is suspended on the outside of the rectangular support plates. This facilitates the overflow of drill cuttings from the bottom of the pile hole, speeds up the drilling of the drill bit, and improves the drilling efficiency of the pile. It also facilitates the smooth flow of mud from the top of the pile hole to the bottom of the pile hole. Furthermore, it reduces the upward lifting resistance or downward lowering resistance of the three-wing drill bit assembly 7 when it is raised or lowered.

[0072] Preferably, such as Figure 4 and 5 As shown, the first guide wheel device 704 also includes a first reinforcing ring frame 7045 for enhancing the connection strength between the first annular cylinder 7043 and the first top flange at the top. The first reinforcing ring frame 7045 includes: a steel ring fixedly fitted onto the outer circumference of the upper end of the first annular cylinder 7043, and multiple steel bars that provide connection and support. The multiple steel bars are arranged sequentially at intervals along the circumference of the first annular cylinder 7043, and the upper and lower ends of each steel bar are fixed to the first top flange and the steel ring, respectively, while their inner ends are welded to the outer wall surface of the first annular cylinder 7043. In the design, a connecting screw hole is provided on the first top flange 7041 between two adjacent steel bars. The installation of the first reinforcing ring frame 7045 can effectively prevent the first annular cylinder 7043 from separating and falling off due to weak welding between it and the first top flange, thus preventing drilling safety accidents.

[0073] Preferably, such as Figure 4 and 5As shown, the first guide wheel device 704 also includes multiple second reinforcing support ribs 7046 for strengthening the connection between the first annular cylinder 7043 and the first bottom flange. The multiple second reinforcing support ribs 7046 are arranged sequentially at intervals along the circumference of the first annular cylinder 7043, and each second reinforcing support rib 7046 is welded and fixed to the outer surface of the first annular cylinder 7043 and the first bottom flange, respectively. In this preferred embodiment, the second reinforcing support ribs 7046 are made of Q345C stainless steel plate with a thickness of 18mm and are processed into "triangular" ribs. Their main function is to strengthen the support between the first annular cylinder 7043 and the first bottom flange, preventing the first annular cylinder 7043 from separating and falling off due to weak welding, thus avoiding drilling safety accidents.

[0074] Preferably, such as Figure 4 and 5 As shown, after the first guide wheel device 704 and the first counterweight device 705 are connected by flanges, multiple first reinforcing connecting steel bars 7034 are evenly distributed along the outer circumference of the flange connection. Each first reinforcing connecting steel bar 7034 is made of Q345C stainless steel plate with a thickness of 50mm, and is processed into a rectangular steel bar with a length of 150mm and a width of 80mm. It is welded to the outer circumference of the adjacent flanges between the first guide wheel device 704 and the first counterweight device 705. The first reinforcing connecting steel bars 7034 are set to prevent the bolts and nuts between adjacent flanges from loosening, which would cause the first guide wheel device 704 and the first counterweight device 705 to separate and fall off, causing a drilling safety accident; during the drilling of the cast-in-place pile 1, they prevent the connection of adjacent flanges from contacting and rubbing with the drill cuttings in the pile hole of the cast-in-place pile 1, thus preventing wear on the flanges.

[0075] Optionally, such as Figure 4 and 5As shown, the first counterweight device 705 includes a solid second annular cylinder 7053 fixedly mounted on the outer circumference of the first mud conduit 702, a first top flange and a first bottom flange fixed at the upper and lower ends of the second annular cylinder 7053, and a flange connector for connecting and fastening. The second annular cylinder 7053 is detachably fixed to the bottom end of the corresponding first guide wheel device 704 and the top end of the three-wing drill bit device 706 through the first top flange and the first bottom flange at both ends and the flange connector, respectively. The first counterweight device 705 further includes a second reinforcing ring frame 7054 for enhancing the connection strength between the second annular column 7053 and the first top flange at the top. The second reinforcing ring frame 7054 includes: a steel ring fixedly fitted onto the outer circumference of the upper end of the second annular column 7053, and multiple steel bars that provide connecting support. The multiple steel bars are arranged sequentially at intervals along the circumference of the second annular column 7053, and the upper and lower ends of each steel bar are respectively fixed to the first top flange and the steel ring, and their inner ends are welded to the outer wall surface of the second annular column 7053. The first counterweight device 705 also includes multiple third reinforcing support ribs 7055 for enhancing the connection strength between the second annular column 7053 and the first bottom flange at the bottom. The multiple third reinforcing support ribs 7055 are arranged sequentially at intervals along the circumference of the second annular column 7053, and each third reinforcing support rib 7055 is welded to the outer surface of the second annular column 7053 and the first bottom flange. In this optional embodiment, the connection and arrangement of the first top flange and the first bottom flange of the first counterweight device 705 are the same as those of the first top flange 7031 and the first bottom flange 7032 in the first drill bit connection device 703. The first counterweight device 705 also includes a second reinforcing ring frame 7054 and a third reinforcing support rib 7055, and the structure and arrangement of the second reinforcing ring frame 7054 and the third reinforcing support rib 7055 are the same as those of the first reinforcing ring frame 7045 and the second reinforcing support rib 7046 in the first guide wheel device 704. The arrangement of the first counterweight device 705 helps to increase the weight of the three-wing drill bit assembly 7, increase the stability and cutting ability of the three-wing drill bit device 706, and reduce the risk of drilling.

[0076] Preferably, such as Figure 4 and 5As shown, after the first counterweight device 705 and the three-wing drill bit device 706 are connected by flanges, multiple first reinforcing connecting steel bars 7034 are evenly distributed along the outer circumference of the flange connection. Each first reinforcing connecting steel bar 7034 is made of Q345C stainless steel plate with a thickness of 50mm, and is processed into a rectangular steel bar with a length of 150mm and a width of 80mm. It is welded to the outer circumference of the adjacent flanges between the first counterweight device 705 and the three-wing drill bit device 706. The first reinforcing connecting steel bars 7034 are set to prevent the bolts and nuts between adjacent flanges from loosening, which would cause the first counterweight device 705 and the three-wing drill bit device 706 to separate and fall off, causing a drilling safety accident. During the drilling of the cast-in-place pile 1, it prevents the connection of adjacent flanges from contacting and rubbing with the drill cuttings in the pile hole of the cast-in-place pile 1, thus preventing wear on the flanges.

[0077] Optionally, such as Figure 5 and Figure 6 As shown, the three-wing drill bit assembly 706 includes a three-wing support 7062 for mounting and support, a first top flange fixed to the top of the three-wing support 7062, a flange connector for connection and fastening, a guide drill bit 7066 for drilling, and a gauge ring 7063 for controlling the diameter and verticality of the pile hole. The three-wing support 7062 is fixedly fitted onto the outer circumference of the first mud conduit 702, and is detachably fixed to the bottom end of the first counterweight device 705 through the first top flange and flange connector at its top. The three-wing support 7062 is hollowed out to allow mud to pass through, and is also provided with cutting teeth 7064 for cutting and drilling. The guide drill bit 7066 is located at the bottom end of the three-wing support 7062 and is fixedly fitted onto the outer circumference of the first mud conduit 702, with the bottom end of the first mud conduit 702 extending into the guide drill bit 7066. In this optional scheme, the hollow three-wing support 7062 is designed to increase the drill bit space, reduce the contact area between drill cuttings and the three-wing support 7062, prevent drill bit jamming when drilling in soft strata such as plain fill, silty clay, and silty clay, and improve the drilling efficiency of the cast-in-place pile 1.

[0078] In this optional solution, such as Figure 5 and 6As shown, the three-wing support 7062 includes three wing plates and a hollow annular retaining ring 7063. The three wing plates are evenly spaced along the circumference of the first mud conduit 702, and the inner ends of each wing plate are welded and fixed to the outer wall of the first mud conduit 702. A first top flange is simultaneously fixed to the top of the three wing plates. Each wing plate also has cutting teeth 7064 arranged sequentially and extending downwards along the inclined edge. The retaining ring 7063 is fixedly fitted onto the outer ends of the three wing plates, and the outer circumference of the retaining ring 7063 also has cutting teeth 7064 arranged sequentially and extending downwards along the circumference. In this optional embodiment, the retaining ring 7063 is made of Q345C stainless steel plate with a thickness of 50mm, processed into a circular hollow steel pipe with an outer diameter of 2200mm. The retaining ring 7063 is welded to the first mud conduit 702 and the first top flange to form a whole through the three wing plates. During welding, the root end of the cutting tooth 7064 is connected to the retaining ring 7063 by manual arc welding. The cutting tooth 7064 on the retaining ring 7063 prevents the retaining ring 7063 from contacting and rubbing against the drill cuttings inside the pile hole, thus preventing wear on the retaining ring 7063. The horizontal rotation of the retaining ring 7063 drives the cutting tooth 7064 to horizontally cut the soil layer on the pile hole wall of the pile hole, effectively controlling the diameter and verticality of the pile hole, ensuring that the diameter and verticality of the pile hole meet the design and standard specifications.

[0079] In this optional scheme, a cuttings overflow outlet is formed between the first top flange and the gauge ring 7063. The cuttings overflow outlet reduces the contact area between the three-wing drill bit device 706 and the cuttings, which is beneficial to the drilling of the three-wing drill bit device 706. It solves the problem of drill bit sticking when drilling in soft strata such as plain fill, silty clay, and silty clay, shortens the drilling time, and improves the drilling efficiency of cast-in-place piles. It also facilitates the smooth flow of mud from the top of the cast-in-place pile hole to the bottom of the hole. Furthermore, it reduces the upward lifting resistance or downward lowering resistance of the three-wing drill bit assembly 7 when it is raised or lowered. In this optional scheme, the cutting teeth 7064 on the retaining ring 7063 prevent the retaining ring 7063 from contacting and rubbing against the drill cuttings inside the pile hole of the cast-in-place pile 1, thus preventing wear and tear on the retaining ring 7063. By rotating the retaining ring 7063 horizontally, the cutting teeth 7064 drive the cutting teeth 7064 to cut the soil layer of the pile hole wall of the cast-in-place pile 1 horizontally, effectively controlling the diameter and verticality of the pile hole of the cast-in-place pile 1, so that the diameter and verticality of the pile hole of the cast-in-place pile 1 meet the design and standard specifications.

[0080] In this optional solution, such as Figure 5 and 6 As shown, the guide drill bit 7066 includes a guide drill bit 7066 mounting plate fixed on the outer circle of the bottom end of the first mud conduit 702. The lower end of the guide drill bit 7066 mounting plate is provided with two inclined extending mounting edges, and each mounting edge is provided with cutting teeth 7064 that are arranged sequentially at intervals along the mounting edge and extend downward.

[0081] Furthermore, such as Figure 6 As shown, the top of the mounting plate of the guide drill bit 7066 is provided with a recessed mounting groove. The mounting plate also has a first slag suction port 7065 that vertically penetrates the plate surface, and the first slag suction port 7065 communicates with the mounting groove. The bottom end of the first mud guide tube 702 is vertically inserted into the mounting groove and communicates with the first slag suction port 7065. In this optional scheme, the first slag suction port 7065 is semi-elliptical. The semi-elliptical shape of the first slag suction port 7065 helps to increase its size, thereby increasing the amount of slag suctioned from the bottom of the pile hole 1. This allows the slag from the bottom of the pile hole 1 to be promptly suctioned out of the pile hole through the first mud guide tube 702, preventing clay drill cuttings from encasing the guide drill bit 7066 and causing drill bit jamming.

[0082] S206: Machining of roller cone hob drill bit assembly for hard strata.

[0083] Reference Figure 7-8 The roller cone hob drill bit assembly 8 includes: a second drill bit connection device 803 for connecting to the drill rod guide 601 of the drilling rig; a second guide wheel device 804 for increasing the weight of the roller cone hob drill bit assembly and controlling the diameter and verticality of the grouting pile hole; a second counterweight device 805 for increasing the weight of the roller cone hob drill bit assembly; a roller cone hob drill bit device 806 for grinding drilling; and a second mud guide 802 for sucking out the slurry generated during drilling from the pile hole. The connecting device 803, the second guide wheel device 804, the second counterweight device 805, and the roller cone cutter bit device 806 are arranged sequentially along the axial direction and are detachably fixed; the second mud guide tube 802 is sequentially connected to the second drill bit connecting device 803, the second guide wheel device 804, the second counterweight device 805, and the roller cone cutter bit device 806 along the axial direction, and the top end of the second mud guide tube 802 is also connected to the drill rod guide tube 601, and its opposite bottom end extends out of the roller cone cutter bit device 806.

[0084] The roller cone hob drill bit assembly 8 of the present invention, due to the arrangement of the second drill bit connecting device 803, the second guide wheel device 804, and the second counterweight device 805, is beneficial to increasing the overall weight of the roller cone hob drill bit assembly 8, increasing the stability and cutting ability of the roller cone hob drill bit device 806 at the bottom of the roller cone hob drill bit assembly 8, effectively breaking rocks and removing debris, preventing the drill bit from getting stuck or buried when drilling in hard strata such as fine sand, medium sand, gravel, boulders or groups of boulders, and granite, thereby improving the drilling efficiency of the cast-in-place pile 1. At the same time, due to the arrangement of the second guide wheel device 804 and the rectangular protrusion 8065 of the roller cone hob drill bit device 806, it is beneficial to control the diameter and verticality of the cast-in-place pile 1 hole during the drilling process, thereby improving the hole formation quality of the cast-in-place pile 1. On the other hand, the roller cone cutter assembly 8 of the present invention includes a second drill bit connecting device 803, a second guide wheel device 804, a second counterweight device 805 and a roller cone cutter device 806 arranged and fixedly connected in sequence along the axial direction, and a second mud conduit 802 is arranged and connected to the four in sequence along the axial direction, so as to remove the mud generated during the drilling process from the pile hole in a timely manner and improve the drilling efficiency of the cast-in-place pile 1.

[0085] Optionally, such as Figure 8 As shown, the second drill bit connection device 803 includes a second top flange 8031 ​​and a second bottom flange 8032, which are arranged opposite each other and respectively fixedly fitted onto the outer circumference of the second mud guide 802, a flange connector for connection and fastening, and multiple fourth reinforcing support ribs 8033. The second top flange 8031 ​​is used to detachably fix to the flange at the bottom end of the drill pipe guide 601 through the flange connector, and the second bottom flange 8032 is used to detachably fix to the second guide wheel device 804 through the flange connector. Multiple fourth reinforcing support ribs 8033 are arranged circumferentially between the second top flange 8031 ​​and the second bottom flange 8032, and each fourth reinforcing support rib 8033 is welded and fixed to the second top flange 8031, the second bottom flange 8032, and the outer wall of the second mud guide 802.

[0086] In this optional embodiment, the second mud conduit 802 is a hollow conduit, located at the center of the second top flange 8031 ​​and the second bottom flange 8032, and arranged at a 90° angle to them; preferably, as... Figure 8As shown, the outer diameter of the second top flange 8031 ​​is smaller than the outer diameter of the second bottom flange 8032. The outer diameter of the second top flange 8031 ​​is the same as and connected to the outer diameter of the bottom flange of the drill pipe guide 601. The outer diameter of the second bottom flange 8032 is the same as and connected to the outer diameter of the top flange of the second guide wheel device 804. The connecting parts between the two flanges are high-strength steel structure bolts, large hexagonal nuts, gaskets, and washers. In this optional scheme, if... Figure 7-8 As shown, the fourth reinforcing support rib 8033 is made of Q345C stainless steel plate with a thickness of 18mm and is processed into a "triangular" rib. It mainly serves to strengthen the second mud guide 802 and the second top flange 8031 ​​and the second bottom flange 8032. The effect of the fourth reinforcing support rib 8033 is: to facilitate the smooth flow of mud from the top of the pile hole to the bottom of the pile hole; to reduce the upward lifting resistance of the roller cone cutter assembly 8 when it is lifted upward; to facilitate the connection between the drill pipe guide 601 and the roller cone cutter assembly 8; and to strengthen the connection between the second top flange 8031 ​​and the second mud guide 802, and between the second bottom flange 8032 and the second mud guide 802, to prevent the second mud guide 802, the second top flange 8031 ​​and the second bottom flange 8032 from being loosely welded, which could lead to separation and fall off, causing drilling safety accidents.

[0087] Preferably, such as Figure 7 and 8 As shown, after the second drill bit connecting device 803 and the second guide wheel device 804 are connected by a flange, multiple second reinforcing connecting steel bars 8034 are evenly distributed along the outer circumference of the flange connection. Each second reinforcing connecting steel bar 8034 is made of Q345C stainless steel plate with a thickness of 50mm, and is processed into a rectangular steel bar with a length of 150mm and a width of 80mm. It is welded to the outer circumference of the adjacent flange between the second drill bit connecting device 803 and the second guide wheel device 804. The setting of the second reinforcing connecting steel bars 8034 prevents the bolts and nuts between adjacent flanges from loosening, which could lead to the separation and detachment of the second drill bit connecting device 803 and the second guide wheel device 804, causing a drilling safety accident. During the drilling of the cast-in-place pile 1, it also prevents the connection of adjacent flanges from contacting and rubbing with the drill cuttings in the pile hole of the cast-in-place pile 1, thus preventing wear on the flanges.

[0088] Optionally, such as Figure 7 and 8As shown, the second guide wheel device 804 includes a solid third annular cylinder 8043 fixedly mounted on the outer circumference of the second mud guide tube 802, a second top flange and a second bottom flange fixed at the upper and lower ends of the third annular cylinder 8043, a flange connector for fastening, a second guide ring 8044 fitted on the outer circumference of the third annular cylinder 8043, and multiple support plates for connecting and supporting. The third annular cylinder 8043 is detachably fixed to the bottom end of the corresponding second drill bit connecting device 803 and the top end of the second counterweight device 805 via the second top flange and the second bottom flange and the flange connector at both ends. Multiple support plates are arranged sequentially at intervals along the circumference of the third annular cylinder 8043, and their inner and outer sides are fixedly connected to the outer wall surface of the third annular cylinder 8043 and the inner wall surface of the second guide ring 8044, respectively. The axial length of the second guide ring 8044 is less than the length of the third annular cylinder 8043, and the two ends of the second guide ring 8044 are not aligned with the corresponding two ends of the third annular cylinder 8043. The second guide wheel device 804 is designed to increase the overall weight of the roller cone cutter assembly 8, enhance the stability and cutting ability of the bottom roller cone cutter device 806, and reduce drilling risks. It also helps control the diameter and verticality of the pile hole 1, prevents the roller cone cutter assembly 8 from getting stuck at the pre-embedded permanent steel casing cutting edge, and ensures smooth entry and exit of the roller cone cutter assembly 8 from the permanent steel casing. In this optional scheme, the connection and arrangement of the second top flange and the second bottom flange of the second guide wheel device 804 are the same as those of the second top flange 8031 ​​and the second bottom flange 8032 in the second drill bit connection device 803.

[0089] In this optional design, the second guide ring 8044 is made of Q345C stainless steel plate with a thickness of 50mm, forming a circular hollow steel pipe with an outer diameter of 2100mm and a height of 800mm. The intersection of the outer surface and the two end faces of the second guide ring 8044 is trimmed into triangles and ground smooth to form upper and lower bevels. This helps prevent operators from being injured by the intersection of the second guide ring 8044's edges. The upper bevel of the second guide ring 8044 also facilitates the smooth flow of mud from the top of the bored pile 1 hole to the bottom; it also reduces the resistance when the roller cone drill bit assembly 8 is lifted upwards. The lower bevel of the second guide ring 8044 allows the mud in the bored pile 1 hole to overflow smoothly when the roller cone drill bit assembly 8 is lowered downwards, reducing the resistance when the roller cone drill bit assembly 8 is lowered downwards.

[0090] Furthermore, four rectangular support plates are evenly distributed on the outer circumference of the third annular cylinder 8043, which are welded to the second guide ring 8044 to form a whole. The support plates are made of 50mm thick Q345C stainless steel plate. After welding, a cavity is left between the second guide ring 8044 and the third annular cylinder 8043, and the second guide ring 8044 is suspended on the outside of the rectangular support plates. This facilitates the overflow of drill cuttings from the bottom of the pile hole 1, speeds up the drilling of the drill bit, and improves the drilling efficiency of the pile 1. It also facilitates the smooth flow of mud from the top of the pile hole 1 to the bottom of the pile hole 1. Furthermore, it reduces the upward lifting resistance or downward lowering resistance of the roller cone drill bit assembly 8 when it is raised or lowered.

[0091] Preferably, such as Figure 7 and 8 As shown, the second guide wheel device 804 also includes a third reinforcing ring frame 8045 for strengthening the connection between the third annular column 8043 and the second top flange at the top. The third reinforcing ring frame 8045 includes: a steel ring fixedly fitted onto the outer circumference of the upper end of the third annular column 8043, and multiple steel bars that provide connection and support. The multiple steel bars are arranged sequentially and at intervals along the circumference of the third annular column 8043, and the upper and lower ends of each steel bar are fixed to the second top flange and the steel ring, respectively, while their inner ends are welded to the outer wall surface of the third annular column 8043. In the design, one connecting screw hole is provided on the second top flange between two adjacent steel bars. The setting of the third reinforcing ring frame 8045 can effectively prevent the third annular column 8043 from separating and falling off due to weak welding between the second top flange, thus preventing drilling safety accidents.

[0092] Preferably, such as Figure 7 and 8 As shown, the second guide wheel device 804 also includes multiple fifth reinforcing support ribs 8046 for strengthening the connection between the third annular column 8043 and the second bottom flange. The multiple fifth reinforcing support ribs 8046 are arranged sequentially at intervals along the circumference of the third annular column 8043, and each fifth reinforcing support rib 8046 is welded and fixed to the outer surface of the third annular column 8043 and the second bottom flange, respectively. In this preferred embodiment, the fifth reinforcing support ribs 8046 are made of Q345C stainless steel plate with a thickness of 18mm and are processed into "triangular" ribs. Their main function is to strengthen the support between the third annular column 8043 and the second bottom flange, preventing the third annular column 8043 from separating and falling off due to weak welding, thus avoiding drilling safety accidents.

[0093] Preferably, such as Figure 7 and 8As shown, after the second guide wheel device 804 and the second counterweight device 805 are connected by flanges, multiple second reinforcing connecting steel bars 8034 are evenly distributed along the outer circumference of the flange connection. Each second reinforcing connecting steel bar 8034 is made of Q345C stainless steel plate with a thickness of 50mm, and is processed into a rectangular steel bar with a length of 150mm and a width of 80mm. It is welded to the outer circumference of the adjacent flanges between the second guide wheel device 804 and the second counterweight device 805. The setting of the second reinforcing connecting steel bars 8034 prevents the bolts and nuts between adjacent flanges from loosening, which would cause the second guide wheel device 804 and the second counterweight device 805 to separate and fall off, resulting in a drilling safety accident; during the drilling of the cast-in-place pile 1, it prevents the connection of adjacent flanges from contacting and rubbing with the drill cuttings in the pile hole of the cast-in-place pile 1, thus preventing wear on the flanges.

[0094] Optionally, such as Figure 7 and 8As shown, the second counterweight device 805 includes a solid fourth annular column 8053 fixedly mounted on the outer circumference of the second mud conduit 802, a second top flange and a second bottom flange fixed at both ends of the fourth annular column 8053, and flange connectors for connecting and fastening. The fourth annular column 8053 is detachably fixed to the bottom end of the corresponding second guide wheel device 804 and the top end of the roller cone hob bit device 806 via the second top flange and the second bottom flange and flange connectors at both ends. The second counterweight device 805 further includes a fourth reinforcing ring frame 8054 for enhancing the connection strength between the fourth ring column 8053 and the second top flange at the top. The fourth reinforcing ring frame 8054 includes: a steel ring fixedly fitted on the outer circle of the upper end of the fourth ring column 8053, and multiple steel bars that provide connecting support. The multiple steel bars are arranged sequentially and spaced apart along the circumference of the fourth ring column 8053, and the upper and lower ends of each steel bar are respectively fixed to the second top flange and the steel ring, and their inner ends are welded and fixed to the outer wall surface of the fourth ring column 8053. The second counterweight device 805 also includes multiple sixth reinforcing support ribs 8055 for enhancing the connection strength between the fourth ring column 8053 and the second bottom flange at the bottom end. The multiple sixth reinforcing support ribs 8055 are arranged sequentially and spaced apart along the circumference of the fourth ring column 8053, and each sixth reinforcing support rib 8055 is welded and fixed to the outer surface of the fourth ring column 8053 and the second bottom flange. In this optional embodiment, the connection and arrangement of the second top flange and the second bottom flange of the second counterweight device 805 are the same as those of the second top flange 8031 ​​and the second bottom flange 8032 in the second drill bit connection device 803. The second counterweight device 805 also includes a fourth reinforcing ring frame 8054 and a sixth reinforcing support rib 8055, and the structure and arrangement of the fourth reinforcing ring frame 8054 and the sixth reinforcing support rib 8055 are the same as those of the third reinforcing ring frame 8045 and the fifth reinforcing support rib 8046 in the second guide wheel device 804. The arrangement of the second counterweight device 805 helps to increase the weight of the roller cone hob drill bit assembly 8, increase the stability and cutting ability of the roller cone hob drill bit device 806, and reduce the risk of drilling.

[0095] Preferably, such as Figure 7 and 8As shown, after the second counterweight device 805 and the roller cone cutter bit device 806 are connected by a flange, multiple second reinforcing connecting steel bars 8034 are evenly distributed along the outer circumference of the flange connection. Each second reinforcing connecting steel bar 8034 is made of Q345C stainless steel plate with a thickness of 50mm, and is processed into a rectangular steel bar with a length of 150mm and a width of 80mm. It is welded to the outer circumference of the adjacent flange between the second counterweight device 805 and the roller cone cutter bit device 806. The setting of the second reinforcing connecting steel bars 8034 prevents the bolts and nuts between adjacent flanges from loosening, which would cause the second counterweight device 805 and the roller cone cutter bit device 806 to separate and fall off, causing a drilling safety accident; during the drilling of the cast-in-place pile 1, it prevents the connection of adjacent flanges from contacting and rubbing with the drill cuttings in the pile hole of the cast-in-place pile 1, thus preventing wear on the flange.

[0096] Optionally, such as Figure 8 and Figure 9 As shown, the roller cone hobbing drill bit assembly 806 includes a solid fifth annular cylinder 8062 fixedly mounted on the outer circumference of the second mud guide tube, a second top flange fixed to the top of the fifth annular cylinder 8062, a flange connector for fastening, multiple protruding cylinders 8064, a cutter head 8066 for grinding drilling, and rectangular protrusions 8065 for controlling the diameter and verticality of the pile hole 1. The fifth annular cylinder 8062 is detachably fixed to the bottom of the second counterweight device 805 via the second top flange and flange connector at its top. The multiple protruding cylinders 8064 are sequentially and spaced apart along the circumference of the fifth annular cylinder 8062 on its outer circumference. The cutter head 8066 is fixed to the bottom of the fifth annular cylinder 8062 and the multiple protruding cylinders 8064.

[0097] Preferably, such as Figure 8 and Figure 9 As shown, a steel ring of Q345C material, 100mm thick and 60mm wide, is welded to the outer circumference of the fifth circular column 8062, located 200mm from the bottom surface of the second top flange. Twenty-two steel bars of Q345C material, 170mm long, 100mm thick and 50mm wide, are vertically welded between the steel ring and the second top flange. Each steel bar is welded at both ends to the steel ring and the bottom surface of the second top flange, and its inner end is welded to the outer wall of the fifth circular column 8062. A fifth reinforcing circular frame 8063 is installed to prevent the fifth circular column 8062 from separating and falling off due to weak welding between it and the second top flange, thus avoiding drilling safety accidents.

[0098] Furthermore, such as Figure 8 and Figure 9As shown, a "triangle" is cut out within 300mm of the bottom surface of the fifth reinforcing ring 8063 on the outer side of the protrusion cylinder 8064 and ground flat to form a bevel, dividing the outer side of the protrusion cylinder 8064 into an upper bevel and a lower straight side; the inner and outer sides of each protrusion cylinder 8064 are arc-shaped along the width direction of the protrusion cylinder 8064, thus forming a "pentagonal" arc-shaped protrusion cylinder 8064. After welding, vertical "concave" grooves with a certain spacing are left between adjacent protrusion cylinders 8064, which facilitates the flow of mud in the pile hole of the first pile into the bottom of the pile hole along the "concave" grooves.

[0099] Furthermore, such as Figure 9 As shown, on the outer arc-shaped surface of each protrusion cylinder 8064, a rectangular protrusion 8065 is welded vertically upwards and downwards to the corresponding locations of the protrusion cylinder 8064, with the length of the rectangular protrusion 8065 aligned with the vertical direction of the protrusion cylinder 8064. The rectangular protrusions 8065 prevent contact and friction between the protrusion cylinder 8064 of the roller cone cutter bit device 806 and the drill cuttings inside the pile hole during drilling of the cast-in-place pile 1, thus preventing wear on the protrusion cylinder 8064. Furthermore, the horizontal rotation of the roller cone cutter bit device 806 drives the rectangular protrusions 8065 to horizontally cut the soil around the pile hole wall of the cast-in-place pile 1, effectively controlling the diameter and verticality of the pile hole and ensuring that these dimensions meet design and standard specifications.

[0100] In this optional solution, such as Figure 9 As shown, the cutter head 8066 includes an outer disk 80663 extending in a ring shape along the outer periphery of the fifth annular cylinder 8062 and the outer periphery of multiple protruding cylinders 8064; a hob support 80661 sequentially fixed circumferentially to the bottom ends of each protruding cylinder 8064 and sequentially fixed circumferentially at intervals to the bottom end and center of the fifth annular cylinder 8062; and a toothed hob 80662 rotatably mounted on each hob support 80661. The hob support 80661 at the bottom end of each protruding cylinder 8064 and the toothed hob 80662 mounted on the hob support 80661 constitute an annular outer ring hob, and the outer ring hob portion extends radially out of the outer disk 80663. The hob support 80661 at the bottom end of the fifth annular cylinder 8062 and the toothed hob 80662 mounted on the hob support 80661 constitute an annular middle ring hob. The hob support 80661 at the bottom center of the fifth annular cylinder 8062 and the toothed hob 80662 mounted on the hob support 80661 constitute the central hob. Further, the toothed hob 80662 includes a hob shaft and a hob cylinder. The two ends of the hob shaft are fixedly connected to the hob support 80661 by bolts. The hob cylinder, which rolls around the hob shaft, is sleeved in the middle of the hob shaft. Multiple pointed grinding heads are embedded on the outer surface of the hob cylinder, and the multiple grinding heads are evenly spaced on the hob cylinder.

[0101] Preferably, such as Figure 8 and Figure 9 As shown, the outer end circular cross-section of each toothed hob 80662 on the outer ring hob, middle ring hob, and center hob is larger than the inner end circular cross-section, forming a frustum-shaped cone. The inner end of each toothed hob 80662 extends upward towards the center, and the centerline of each toothed hob 80662 forms an angle of 20° to 50° with the bottom end face of the corresponding fifth ring cylinder 8062 and the protrusion cylinder 8064. The outer end of each toothed hob 80662 is arranged towards the outer disk 80663. The outer end of each toothed hob 80662 on the outer ring hob extends radially out of the outer disk 80663. Because the outer ends of the toothed hobs 80662 on the outer ring hob extend radially outward from the outer disk 80663, it is beneficial for the roller cone hob drill bit device 806 to cut circular pile holes with a diameter 40-100mm larger than the diameter of the pile hole of the cast-in-place pile 1, ensuring that the diameter of the pile hole of the cast-in-place pile 1 is greater than or equal to the design diameter requirement; it also reduces the adhesion of drill cuttings to the drill bit inside the pile hole of the cast-in-place pile 1. During operation, the rotation of the drill rod guide 601 of the drilling rig drives the roller cone hob drill bit device 806, so that the moving trajectory of the toothed hobs 80662 forms a hob grinding trajectory ring, and the moving trajectory of the roller cone hob drill bit device 806 forms a roller cone grinding trajectory ring. Multiple hob grinding trajectory rings and multiple roller cone grinding trajectory rings completely cover the bottom end face of the fifth circular cylinder 8062 and the protrusion cylinder 8064, so as to cut boulders or groups of boulders and granite.

[0102] Preferably, such as Figure 8 and Figure 9 As shown, the bottom end of the fifth annular cylinder 8062 is flush with the bottom end of the multi-protrusion cylinder 8064. The bottom end face of the toothed hob 80662 is lower than the bottom end face of the outer disk 80663. The bottom end face of the outer disk 80663 is lower than the bottom end face of the second mud conduit, and the bottom end face of the second mud conduit is lower than the bottom end faces of the protrusion cylinder 8064 and the fifth annular cylinder 8062. In actual design, the bottom end face of the second mud guide pipe 802, i.e. the second slag suction port 8067, is 50-100mm higher than the bottom end face of the outer plate 80663. This facilitates the timely suction of the drill cuttings from the bottom of the cast-in-place pile 1 hole by the second slag suction port 8067 through the second mud guide pipe 802. The bottom end face of the outer plate 80663 is 50-100mm higher than the bottom end face of the toothed cutter 80662. This helps prevent the outer plate 80663 from contacting and rubbing against the bottom of the cast-in-place pile 1 hole with the toothed cutter 80662 when cutting boulders, boulder groups, and granite. This prevents wear on the outer plate 80663 and hinders the collection and containment of drill cuttings from the cast-in-place pile 1 hole.

[0103] Step S3 specifically includes the following steps:

[0104] S301: A temporary circular steel pipe with its top end above the ground is embedded at the core location of pile 1. Specifically, technicians use a total station to determine the core location of pile 1. An XR360 rotary drilling rig is used to drill a hole with a diameter equal to the outer diameter of the temporary circular steel pipe. After drilling 3m deeper to embed the temporary circular steel pipe, the core location of pile 1 must be measured and verified, and the center of the temporary circular steel pipe must be adjusted to ensure it is aligned vertically with the core of pile 1. A DZJ150 vibratory hammer is used with an excitation force of 1140kN to drive the remaining temporary circular steel pipes into the ground, ensuring the top end of the temporary circular steel pipe is 300mm above the ground and on a horizontal plane. A 50mm thick, 200mm high foam layer is wrapped around the outer wall of the temporary circular steel pipe to isolate it from the ground concrete, facilitating easy extraction. C20 concrete is used to harden the ground around the foam layer to facilitate the installation of the guide frame device 5. The temporary circular steel pipe is made of Q345C stainless steel plate with a thickness of 0.020m, and is a circular hollow steel pipe with a diameter of φ2.8×0.020×6.0m. The temporary circular steel pipe is set up to facilitate the installation of the permanent steel casing and the replacement steel casing, as well as the verification of its horizontal position and verticality.

[0105] S302: The pilot hole construction for the cast-in-place pile is carried out inside the temporary circular steel pipe. Specifically, before installing the guide frame device 5, technicians must use a total station to re-lay out and determine the position of the core of the cast-in-place pile 1. After precise adjustment, on the ground surface at the bottom of the temporary circular steel pipe where the pilot hole has been drilled for 3m, an XR360 rotary drilling rig is used to drill a circular hole with a diameter equal to the outer diameter of the steel casing 4, and then drill for another 6m to the designed elevation of the top of the cast-in-place pile 1. This allows the steel casing 4 to be directly inserted into the pile hole for initial installation. The pilot hole for the cast-in-place pile 1 serves three purposes: first, it facilitates the direct insertion of the 25m long steel casing 4 into the pile hole for initial installation without vibration; second, it reduces the vibration workload of the steel casing 4 and avoids deviations in the verticality of the steel casing 4 due to uneven vibration force; and third, it facilitates the connection and installation of the three-wing drill bit assembly 7 and the drilling rig 6 inside the pile hole of the cast-in-place pile 1.

[0106] S303: The guide frame device 5 is fixedly installed on the ground close to the temporary circular steel pipe, and the guide frame device 5 is coaxial with and fixed to the temporary circular steel pipe; specifically, such as... Figure 2-3 As shown, the guide frame device 5 is fixedly installed on the hardened ground close to the outside of the temporary circular steel pipe. During installation, the verticality of the guide frame device 5 is adjusted by using a plumb bob, a spirit level, and heightening blocks. When the verticality of the guide frame device 5 is controlled to ≤1%, the bottom square frame of the guide frame device 5 is welded and fixed to the outer wall of the temporary circular steel pipe to prevent the guide frame device 5 from moving back and forth or left and right.

[0107] S304: Steel casing 4 driving construction; Steel casing 4 is constructed by welding a 25m long permanent steel casing and a 7m long replacement steel casing section. A DZJ150 vibratory hammer is used to vibrate and drive the permanent steel casing and the replacement steel casing section. Specifically, it includes the following steps:

[0108] (1) Permanent steel casing installation includes the following steps:

[0109] ① Installation of permanent steel casing: After the guide frame device 5 is installed, a 150t crawler crane and wire rope are used to hoist the permanent steel casing and place it inside the guide frame device 5, so that the 28mm thick wall of the permanent steel casing is facing down, passes through the top guide frame and the bottom guide frame, and extends into the pilot hole of the cast-in-place pile 1 to contact the bottom stratum of the pilot hole, thus completing the initial installation of the permanent steel casing.

[0110] ② Verification of the planar position and verticality of the permanent steel casing: The planar position and verticality of the permanent steel casing are verified. The verification method is as follows: First, the coordinates of the three monitoring points on the permanent steel casing are measured using the total station in prism-free mode, and the center of the fitted circle is determined by connecting the total station to the total station. This allows for the rapid calculation of the distance from the monitoring points to the center of pile 1, thus accurately determining the planar position of the permanent steel casing. Second, using the distance between the inner edge of the temporary circular steel pipe and the outer edge of the permanent steel casing as the control standard, the centerline of the permanent steel casing is aligned with the centerline of pile 1 by using a dual control method of a plumb bob and a total station, as well as adjusting the top and bottom guide wheels of the guide frame device 5. Finally, the verticality of the permanent steel casing is adjusted by using a total station for monitoring and by means of the crawler crane's boom, lifting boom, and lowering boom.

[0111] ③ Installation and Quality Control: After the planar position and verticality of the permanent steel casing meet the requirements, clamp the top wall of the permanent steel casing with the DZJ150 vibratory hammer clamp, remove the hoisting wire rope from the permanent steel casing, and drive the permanent steel casing stably into the formation with an excitation force of 1140kN. During the installation of the permanent steel casing, two theodolites are used to control the verticality of the installation in two mutually perpendicular directions, and a total station is used to check its planar position. The verticality of the permanent steel casing installation is controlled to ≤1%.

[0112] ④ When the permanent steel casing is driven to a height of 1.2m above the ground, the replacement steel casing section is butt-welded to the top end of the permanent steel casing.

[0113] (2) The installation of the steel casing for the replacement section includes the following steps:

[0114] ① Butt welding of the replacement steel casing: The connecting steel plates are made of Q345C stainless steel plate with a thickness of 20mm, and are processed into trapezoidal steel plates with a top edge width of 75mm, a bottom edge width of 150mm, a height of 60mm, and a thickness of 20mm. Eight trapezoidal steel plates are evenly distributed on the outer circumference of the top side wall of the permanent steel casing. The top edge of the trapezoidal steel plates is welded to the outer side wall of the top port of the permanent steel casing, and the bottom edge of the trapezoidal steel plates is welded to the outer side wall of the bottom port of the replacement steel casing. After welding, the trapezoidal steel plates are shaped "wider at the top and narrower at the bottom" in the vertical direction of the steel casing, which can quickly locate the position of the replacement steel casing and facilitates the butt welding between the permanent steel casing and the replacement steel casing.

[0115] When welding the permanent steel casing to the replacement steel casing, two temporary fixing points are welded after the ends of the two steel casing sections are aligned. The verticality of the replacement steel casing is controlled by adjusting the position of the crawler crane hook. When the vertical center lines of the two steel casing sections overlap, the bottom edge of the trapezoidal steel plate is welded to the outer wall of the bottom end of the replacement steel casing, and the gap between the top end of the permanent steel casing and the bottom end of the replacement steel casing is welded full and tight. If the gap between the top end of the permanent steel casing and the bottom end of the replacement steel casing is uneven due to the deviation of the vertical center lines of the two steel casing sections, the gap is filled by welding with reinforcing bars to fill the wider gap. The permanent steel casing and the replacement steel casing are welded together using eight trapezoidal steel plates with side strips, which facilitates the cutting and removal of the replacement steel casing during the construction of the pier No. 7 of the main bridge of the cable-stayed bridge.

[0116] ② Elevation control of the replacement section steel casing: After the replacement section steel casing is installed, the top surface of the replacement section steel casing should be 300mm above the ground and on a horizontal plane.

[0117] ③ Installation and Quality Control: After the permanent steel casing and the replacement steel casing are butt-welded, a DZJ150 vibratory hammer with an excitation force of 1140kN is used to steadily drive the remaining permanent steel casing and the replacement steel casing into the stratum until the bottom of the permanent steel casing reaches the designed elevation. This ensures the top surface of the permanent steel casing is at -2.3m and anchored 200mm into the abutment of pier #7 of the cable-stayed bridge. During the installation of the replacement steel casing, two theodolites are used in two mutually perpendicular directions to control the verticality of the installation, and a total station is used to check its planar position. The verticality of the replacement steel casing is controlled to ≤1%.

[0118] ④ Temporary circular steel pipe removal: After the permanent steel casing and the replacement steel casing are driven in, remove the temporary circular steel pipe. Harden the ground around the outside of the replacement steel casing with C20 concrete to facilitate the installation of drilling rig 6.

[0119] Optionally, since the drilling depth of the 30 cast-in-place piles at Pier 7 of the cable-stayed bridge reaches 135m, it passes through complex strata from top to bottom, including plain fill, silty clay, fine sand, medium sand, gravel, boulders or groups of boulders, and Yanshanian granite. Based on the above drilling depth and strata conditions, drilling rig 6 adopts a ZJD4000 / 350C fully hydraulic drilling rig; the mud used is characterized by low relative density, low viscosity, low sand content, low water loss, low leakage, thin and tough mud cake, strong stability, good wall-fixing effect, good fluidity, low drill bit rotation resistance, high drilling efficiency, high recycling rate, and strong suspension and cuttings carrying capacity. This effectively solves the technical problems of easy pile wall collapse, slow drilling speed, large mud leakage, and low mud recycling rate during the drilling of the 1st pile hole of the cast-in-place pile exceeding 100 meters in depth. Step S4 specifically includes the following steps:

[0120] S401: Mud preparation, specifically including the following steps:

[0121] S4011: Types of Mud and Their Preparation

[0122] (1) Drilling mud type: Bentonite mud was used for drilling the first pile hole. The bentonite mud consisted of mixing water, sodium-based bentonite, sodium carbonate, nano-calcium carbonate, gypsum, sodium carboxymethyl cellulose, potassium polyacrylate, and polyacrylamide. Depending on the geological conditions of the first pile hole, the mud was selected based on a relative density of 1.071–1.072 g / cm³ for plain fill, silty clay, and soft silty clay strata. 3 Clay drilling mud with a viscosity of 18.8–19.2 Pa·s, a sand content of 0.3%, a colloid content of 99%, a water loss rate of 18.82–19.29 mL / 30 min, a mud cake thickness of 0.88–0.91 mm / 30 min, and a pH of 8.85–8.95 can suspend more small-particle, low-density clay drill cuttings, which is beneficial for carrying and removing clay drill cuttings, increasing the lateral pressure of the mud on the pile borehole wall, stabilizing the pile borehole wall, and ensuring smooth drilling. It is suitable for fine sand, medium sand, gravel, boulders or boulder groups, and hard granite strata with a relative density of 1.086–1.089 g / cm³. 3 The mud with a viscosity of 20.8–21.5 Pa·s, a sand content of 0.5–0.6%, a colloid content of 99%, a water loss rate of 17.98–18.28 mL / 30 min, a mud cake thickness of 1.05–1.09 mm / 30 min, and a pH of 9.03–9.06, which contains sand and gravel layers, can suspend more large-particle, relatively dense sand and gravel drill cuttings. This is beneficial for carrying and discharging sand and gravel drill cuttings, increasing the mud's lateral pressure on the pile borehole wall, stabilizing the borehole wall, and ensuring smooth drilling.

[0123] (2) Mud preparation and transportation: Since the 30 cast-in-place piles 1 of the No. 7 pier of the cable-stayed bridge are close to the river embankment of the city, in order to prevent mud pollution of the river, the mud must be prepared in a mud pool near the No. 7 pier cast-in-place pile 1 of the main bridge using a mud mixer. The mud in the mud pool is circulated by a mud pump. After the mud is prepared, the mud is pumped to the hole of the cast-in-place pile 1 to be drilled.

[0124] (3) Mud Quality Requirements: The prepared mud shall be tested according to the determination methods for various performance indicators of mud in Appendix K of the "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T3650-2020), including relative density, viscosity, sand content, colloid content, water loss rate, and mud cake thickness. The pH value shall be tested using a pH meter. All performance indicators of the mud must meet the requirements for reverse circulation drilling methods and mud performance indicators for easily collapsible strata specified in the "Technical Specification for Construction of Highway Bridges and Culverts" (JTG / T3650-2020).

[0125] S4012: Drilling Mud Control

[0126] For mud quality control during drilling, the main parameters to be measured are specific gravity, viscosity, sand content, pH value, and colloid content. Adjustments should be made promptly if these parameters do not meet requirements. Particularly when transitioning from one geological formation to another, monitoring of mud parameters must be strengthened. When drilling into fine sand, medium sand, or gravelly formations prone to collapse, the specific gravity, viscosity, and colloid content of the mud should be increased to ensure wall thickness and prevent borehole collapse. During drilling, mud quality must be strictly guaranteed according to construction process requirements. Mud-making materials and mix proportions should not be arbitrarily changed; any use of other mud-making materials must be approved beforehand. Two to three days before the termination of drilling in the first pile hole, all parameters must be controlled according to the requirements for borehole cleaning mud. If the requirements are not met, the mud must be replaced to achieve the required cleaning mud parameters. Drill rods must not be removed if the mud in the first pile hole does not meet the predetermined parameters upon termination of drilling. Before drilling the next pile hole, sufficient mud-making materials must be prepared in advance according to the mud mix proportion; drilling is prohibited if mud-making materials are insufficient.

[0127] S4013: Sludge circulation, sludge reverse circulation and discharge

[0128] (1) Mud circulation: During the drilling process, mud prepared in the mud tank is used for replacement while drilling. The principle of mud replacement is as follows: First, the mud containing drill cuttings is sucked out from the drill bit suction port at the bottom of the pile hole 1; then it enters the mud tank slag discharge filter screen to filter out large drill cuttings, and the mud flows into the mud tank for sedimentation. Part of the mud flows back to the mud tank through the return pipe, and part of the mud is transported to the mud purifier through the mud pump to remove sand and purify it before flowing back into the mud tank; finally, the mud is pumped to the pile hole to be drilled in the pile 1 using the mud pump.

[0129] (2) Mud Reverse Circulation: At the bottom of the No. 1 pile hole, circulating mud containing drill cuttings is sucked out through the drill bit suction nozzle and drill pipe guide 601. Mud is then added at the top of the No. 1 pile hole to maintain the mud head pressure inside the pile hole, thereby ensuring the stability of the pile hole wall. Mud reverse circulation reduces the ineffective work of the drill bit repeatedly grinding drill cuttings, and significantly improves the drilling efficiency of the No. 1 pile hole.

[0130] (3) Mud discharge: During the drilling process, the mud level in the pile hole of the cast-in-place pile 1 is adjusted to be 2m higher than the surface water level outside the pile hole by the mud pump to prevent surface water outside the pile hole from seeping into the pile hole and changing the mud properties; During the drilling process, the drill cuttings discharged by the mud circulation are placed in a funnel at the outlet of the mud processor. The drill cuttings enter the funnel, and the funnel is lifted by a crane and poured into the slag box next to the platform and transported to the designated location.

[0131] S402: Drilling construction of cast-in-place piles in soft strata within the same pile hole; during the drilling of pile hole 1, due to the compact and narrow cage structure of the ordinary four-wing drill bit, the cut clay drill cuttings cannot be promptly discharged from pile hole 1 with the drilling mud, thus encasing the drill bit; when cutting plain fill, silty clay, and silty clay layers, if the relative density of the drilling mud is >1.15g / cm³ 3 When the viscosity is greater than 20 Pa·s, the drill bit components are not lubricated, increasing frictional resistance. Friction causes the drill bit components to heat up, promoting the adhesion of clay drill cuttings to the components. Furthermore, due to the slow rotation speed of the drill bit, the clay drill cuttings adhering to its components experience little centrifugal force and cannot be thrown out by centrifugal force. These factors promote and accelerate the development of "drill bit clogging," causing the drilling of the first pile hole of the cast-in-place pile to stop and reducing drilling efficiency.

[0132] During the drilling of pile 1 through strata of plain fill, silty clay, and soft silty clay, reverse circulation drilling with mud was adopted. The mud had a relative density of 1.071–1.072 g / cm³. 3 The clay mud, with a viscosity of 18.8–19.2 Pa·s, a sand content of 0.3%, a colloid content of 99%, a water loss rate of 18.82–19.29 mL / 30 min, a mud cake thickness of 0.88–0.91 mm / 30 min, and a pH of 8.85–8.95, effectively lubricates the drill bit and drill rod, reduces friction between the mud and the three-wing drill bit assembly 7, lowers drilling resistance, reduces drilling accidents in the cast-in-place pile 1 hole, increases the drilling speed of the cast-in-place pile 1 hole, and lowers drilling costs. The mud is poured from the top of the cast-in-place pile 1 into the bottom of the pile, washing away the clay drill cuttings adhering to the drill bit, providing good lubrication to all components of the drill bit, diluting the mud concentration around the drill bit, reducing the viscosity of the mud around the drill bit, and decreasing the adhesion of the clay drill cuttings.

[0133] S403: Drilling of cast-in-place piles within the same hard stratum; when drilling cast-in-place pile 1 through hard strata such as fine sand, medium sand, gravel, boulders or groups of boulders, or granite, reverse circulation drilling with mud is adopted, using mud with a relative density of 1.086~1.089g / cm³. 3 The mud, consisting of sand and gravel layers with a viscosity of 20.8–21.5 Pa·s, a sand content of 0.5–0.6%, a colloid content of 99%, a water loss rate of 17.98–18.28 mL / 30 min, a mud cake thickness of 1.05–1.09 mm / 30 min, and a pH of 9.03–9.06, effectively lubricates the drill bit and drill rod, reduces friction between the mud and the roller cone drill bit assembly 8, lowers drilling resistance, reduces drilling accidents in the cast-in-place pile 1 hole, increases the drilling speed of the cast-in-place pile 1 hole, and lowers drilling costs. The mud is poured from the top of the cast-in-place pile into the bottom of the pile, washing away the sand and gravel drill cuttings adhering to the drill bit, providing good lubrication to all components of the drill bit, diluting the mud concentration around the drill bit, reducing the viscosity of the mud around the drill bit, and decreasing the adhesion of sand and gravel drill cuttings.

[0134] When performing step S402, if Figure 10 As shown:

[0135] (1) When drilling the pile hole of the cast-in-place pile 1 through the plain fill, silty clay and soft clay strata, the three-wing drill bit assembly 7 is used for drilling; specifically, the high-speed rotation and mud reverse circulation drilling method of the three-wing drill bit assembly 7 with a counterweight and an outer diameter of 2.2m is adopted. When the three-wing drill bit assembly 706 rotates at high speed in soft clay strata, the overall weight of the assembly is increased due to the presence of a first drill bit connecting device 703, a first guide wheel device 704, and a first counterweight device 705. This increases the stability and cutting capacity of the three-wing drill bit assembly 706 at its bottom, ensuring that the three-wing drill bit assembly 706 remains vertical. This prevents the three-wing drill bit assembly 706 from tilting during drilling in soft clay strata due to its light weight and unstable center of gravity, which could lead to a significant deviation in the inclination of the cast-in-place pile 1 exceeding the current national standards and specifications, thus rendering it an unqualified pile. Furthermore, the high-speed rotation of the three-wing drill bit assembly 7 increases the centrifugal force on the clay drill cuttings, dislodging some of the clay drill cuttings adhering to the drill bit and preventing "drill bit clogging". Furthermore, the inclusion of the first guide wheel device 704 and the gauge ring 7063 in the three-wing drill bit device 706 facilitates control over the diameter and verticality of the grout pile 1 hole during drilling. The addition and extension of the mud guide tube 702 in the three-wing drill bit device 706 increases the cutting space at the front of the device and the capacity of the drill cuttings at the bottom of the grout pile 1 hole. The inclusion of a hollow three-wing support 7062 in the three-wing drill bit device 706 increases the drill bit space and reduces the contact area between the drill cuttings and the support 7062, thereby solving the technical problem of drill bit "bumping" when drilling in soft strata such as fill, silty clay, and clay, shortening drilling time, and improving the drilling efficiency of the grout pile.

[0136] (2) During the drilling of the cast-in-place pile 1, based on the drill cuttings sample discharged by the air lift reverse circulation and the drilling depth, the Rhinoceros 3D modeling software was used to draw a 3D diagram of the drill cuttings sample and the drilling depth.

[0137] (3) Compare the three-dimensional diagram of the drill cuttings sample-drilling depth with the three-dimensional model of the cast-in-place pile-stratum to conduct dynamic control analysis of the drilling of the cast-in-place pile hole; specifically, analyze whether the stratum of the drilled hole of cast-in-place pile 1 is the same as the stratum in the three-dimensional model of the cast-in-place pile-stratum, and determine whether the stratum revealed in the "Engineering Geological Survey Report" is real and reliable; quickly determine whether the drilling of the cast-in-place pile should continue or stop, and avoid the drill bit from getting stuck. When the three-wing drill bit assembly 7 of the cast-in-place pile 1 approaches a hidden boulder or boulder group 3 during drilling, the operator should be properly instructed to replace the roller cone drill bit assembly 8 in a timely manner. This is to prevent the three-wing drill bit assembly 7 from being worn or damaged by the boulder or boulder group 3 in soft strata; to prevent the three-wing drill bit assembly 7 from stopping drilling or continuing to drill into the soft strata around the pile wall of the cast-in-place pile 1 due to the high hardness or large size of the boulder or boulder group 3, which would cause a large deviation in the inclination of the cast-in-place pile 1 exceeding the current national standards and specifications; and to prevent the three-wing drill bit assembly 7 from stopping drilling when encountering a boulder or boulder group 3, thus misjudging the boulder or boulder group 3 as bedrock, artificially shortening the length of the cast-in-place pile, and seriously affecting the bearing capacity of the pile body of the cast-in-place pile 1.

[0138] When performing step S403, if Figure 11 As shown:

[0139] (1) When drilling the pile hole of the cast-in-place pile 1 through the fine sand, medium sand, gravel, boulders or boulder groups 3, granite hard strata, the roller cone cutter assembly 8 is used for drilling; specifically, the roller cone cutter assembly 8 with a counterweight and an outer diameter of 2.2m is used for decompression, low speed rotation and mud reverse circulation drilling, and the roller cone cutter assembly 8 is frequently lifted to sweep and clean the bottom of the hole. When the roller cone hobbing bit assembly 806 slowly grinds within the strata of boulders or boulder clusters 3, the overall weight of the roller cone hobbing bit assembly 8 is increased due to the inclusion of a second drill bit connecting device 803, a second guide wheel device 804, and a second counterweight device 805. This increases the stability and cutting capacity of the roller cone hobbing bit assembly 806 at its bottom end, ensuring that the roller cone hobbing bit assembly 806 remains vertical. This effectively breaks up rocks and removes debris, preventing damage to the teeth. When drilling into the inclined top surface of the hard boulder 3, the roller cone drill bit device 806, due to its light weight and unstable center of gravity, may drill towards the soft strata inside the pile hole of the cast-in-place pile 1, causing a large deviation in the inclination of the cast-in-place pile 1 that exceeds the current national standards and specifications, thus rendering it an unqualified pile. This also prevents the drill bit from getting stuck when drilling into the gaps between adjacent boulders in the hard boulder group 3, which would prevent timely drill bit retrieval and easily lead to sand and gravel cuttings burying the drill bit, thereby reducing the drilling efficiency of the cast-in-place pile 1. Furthermore, the inclusion of the second guide wheel device 804 and the rectangular protrusion 8065 of the roller cone drill bit device 806 facilitates control of the diameter and verticality of the pile hole during drilling, improving the quality of the formed hole.

[0140] (2) During the drilling of the cast-in-place pile 1, based on the drill cuttings sample discharged by the air lift reverse circulation and the drilling depth, the Rhinoceros 3D modeling software was used to draw a 3D diagram of the drill cuttings sample and the drilling depth.

[0141] (3) The three-dimensional diagram of drill cuttings sample-drilling depth is compared with the three-dimensional model of cast-in-place pile-stratum to dynamically control and analyze the drilling of cast-in-place pile 1. Specifically, it is analyzed whether the stratum of cast-in-place pile 1 is the same as the stratum in the three-dimensional model of cast-in-place pile-stratum, and whether the stratum revealed in the "Engineering Geological Survey Report" is real and reliable. It is also used to quickly determine whether the drilling of the cast-in-place pile should continue or stop, so as to avoid the drill bit getting stuck or buried. This prevents the roller cone cutter bit device 806 from stopping drilling when it encounters a boulder or boulder group 3 and misjudging the boulder or boulder group 3 as bedrock, thus artificially shortening the length of the cast-in-place pile and seriously affecting the bearing capacity of the cast-in-place pile 1.

[0142] Optionally, the above describes a method for constructing ultra-long cast-in-place piles within the same bored pile hole in complex geological formations for bridge engineering. In addition to the construction fields described in the above embodiments, it can also be applied to the construction of support pile foundations for building foundations, urban rail transit systems, and underground utility tunnels.

[0143] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for constructing ultra-long cast-in-place piles within the same bored pile hole in complex strata, characterized in that, Includes the following steps: S1: Based on the "Engineering Geological Survey Report", a three-dimensional model of the cast-in-place pile-stratum was established using three-dimensional modeling software to visually display the stratum type of each cast-in-place pile (1) in the vertical direction. S2: Select and process different drilling equipment according to different strata types, including steel casing (4), guide frame device (5), three-wing drill bit assembly (7) for drilling soft strata and preventing drill jamming, and roller cone cutter bit assembly (8) for grinding drilling in hard strata and preventing drill jamming and drill burial. S3: Drive the steel casing (4) that has been processed and manufactured into place; S4: Drilling of ultra-long cast-in-place piles in complex geological formations within the same cast-in-place pile hole using drilling equipment, specifically including the following steps: S401: Mud preparation; S402: Drilling construction of cast-in-place pile holes in soft strata within the same cast-in-place pile hole; When drilling cast-in-place pile holes through soft strata such as plain fill, silty clay, and silty clay, a three-wing drill bit assembly (7) with high-speed rotation and mud reverse circulation drilling method is adopted; During the drilling process, based on the drill cuttings sample and drilling depth discharged by air-lift reverse circulation, a three-dimensional modeling software is used to draw a three-dimensional diagram of drill cuttings sample-drilling depth; The three-dimensional diagram of drill cuttings sample-drilling depth is compared with the three-dimensional model of cast-in-place pile-strata to dynamically control and analyze the drilling of cast-in-place pile holes; S403: Drilling construction of cast-in-place pile holes in hard strata within the same cast-in-place pile hole; When drilling cast-in-place pile holes through fine sand, medium sand, gravel, boulders or groups of boulders (3), or granite hard strata, the decompression, low-speed rotation and mud reverse circulation drilling method of roller cone cutter assembly (8) is adopted; During the drilling process, based on the drill cuttings sample and drilling depth discharged by air lift reverse circulation, a three-dimensional modeling software is used to draw a three-dimensional diagram of drill cuttings sample-drilling depth; The three-dimensional diagram of drill cuttings sample-drilling depth is compared with the three-dimensional model of cast-in-place pile-strata to conduct dynamic control analysis of the drilling of cast-in-place pile holes.

2. The method for constructing ultra-long cast-in-place piles in the same bored pile hole in complex strata according to claim 1, characterized in that, Step S2 specifically includes the following steps: S201: Selection of vibratory hammer and verification of excitation force; S202: Steel casing (4) processing, manufacturing and transportation; S203: Drilling rig (6) selection; S204: Fabrication of guide frame device (5); S205: Fabrication of a three-wing drill bit assembly for soft strata (7); S206: Machining of roller hob drill bit assembly for hard strata (8).

3. The method for constructing ultra-long cast-in-place piles in the same bored pile hole in complex strata according to claim 2, characterized in that, The three-wing drill bit assembly (7) includes: a first drill bit connection device (703) for connecting to the drill rod guide (601) of the drilling rig; a first guide wheel device (704) for increasing the weight of the three-wing drill bit assembly and controlling the diameter and verticality of the pile hole; a first counterweight device (705) for increasing the weight of the three-wing drill bit assembly; a three-wing drill bit device (706) for drilling the formation; and a first mud guide (702) for sucking out the slag generated during drilling from the pile hole. The first drill bit connecting device (703), the first guide wheel device (704), the first counterweight device (705), and the three-wing drill bit device (706) are arranged sequentially along the axial direction and can be detachably fixed. The first mud guide tube (702) is sequentially connected to the first drill bit connecting device (703), the first guide wheel device (704), the first counterweight device (705) and the three-wing drill bit device (706) along the axial direction. The top end of the first mud guide tube (702) is also connected to the drill pipe guide tube (601), and its opposite bottom end extends out of the bottom end of the three-wing support (7062) in the three-wing drill bit device (706).

4. The method for constructing ultra-long cast-in-place piles in the same bored pile hole in complex strata according to claim 3, characterized in that, The three-wing drill bit assembly (706) includes a three-wing support (7062) for installation support, a first top flange fixed to the top of the three-wing support (7062), a flange connector for connection and fastening, and a guide drill bit (7066) for drilling. The three-wing support (7062) is fixedly mounted on the outer circle of the first mud conduit (702), and is detachably fixed to the bottom of the first counterweight device (705) through the first top flange and flange connector at its top. The three-wing support (7062) is hollowed out to allow mud to pass through, and is also provided with cutting teeth (7064) for cutting and drilling. The directional drill bit (7066) is located at the bottom of the three-wing support (7062) and is fixedly fitted on the outer circle of the first mud conduit (702). The bottom end of the first mud conduit (702) extends into the directional drill bit (7066).

5. The method for constructing ultra-long cast-in-place piles in the same bored pile hole in complex strata according to claim 2, characterized in that, The roller cone cutter assembly (8) includes: a second drill bit connection device (803) for connecting to the drill rod guide (601) of the drilling rig; a second guide wheel device (804) for increasing the weight of the roller cone cutter assembly and controlling the diameter and verticality of the grouting pile hole; a second counterweight device (805) for increasing the weight of the roller cone cutter assembly; a roller cone cutter device (806) for grinding drilling; and a second mud guide (802) for sucking out the slag generated during drilling from the pile hole. The second drill bit connecting device (803), the second guide wheel device (804), the second counterweight device (805), and the roller cone cutter bit device (806) are arranged sequentially along the axial direction and can be detachably fixed. The second mud guide tube (802) is sequentially connected to the second drill bit connecting device (803), the second guide wheel device (804), the second counterweight device (805), and the roller cone cutter bit device (806) along the axial direction. The top end of the second mud guide tube (802) is also connected to the drill pipe guide tube (601), and its opposite bottom end extends out of the roller cone cutter bit device (806).

6. The method for constructing ultra-long cast-in-place piles in the same bored pile hole in complex strata according to claim 5, characterized in that, The roller cone hob drill bit assembly (806) includes a fifth annular cylinder (8062) that is solidly set and fixedly fitted on the outer circle of the second mud guide, a second top flange fixed to the top of the fifth annular cylinder (8062), a flange connector for connecting and fastening, a multi-bulb cylinder (8064), and a cutter head (8066) for grinding and drilling. The fifth annular cylinder (8062) is detachably fixed to the bottom end of the second counterweight device via the second top flange and flange connector at its top; Multiple protruding cylinders (8064) are sequentially and spaced apart on the outer circle of the sixth annular cylinder (8062) along the circumference of the fifth annular cylinder (8062); The cutter head (8066) is fixed to the bottom of the fifth annular cylinder (8062) and the multi-protrusion cylinder (8064).

7. The method for constructing ultra-long cast-in-place piles in the same bored pile hole in complex strata according to claim 1, characterized in that, Step S3 specifically includes the following steps: S301: A temporary circular steel pipe with its top end higher than the ground is buried at the core of the cast-in-place pile; S302: Construction of pilot hole for cast-in-place piles inside a temporary circular steel pipe; S303: Fix the guide frame device (5) on the ground close to the temporary circular steel pipe, and make the guide frame device (5) coaxial with the temporary circular steel pipe and fix it; S304: Steel casing (4) driving construction.

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