Construction method of cast-in-situ bored pile penetrating through super-thick riprap layer

Abstract

The invention discloses a construction method for a cast-in-situ bored pile penetrating through an ultra-thick riprap layer. The construction method comprises the steps that S1, a drilling platform is designed and built; s2, the full-slewing drilling machine is in place; s3, the perpendicularity of the tool type pile casing is calibrated, and the full-slewing drilling machine is started to drive the tool type pile casing to rotate and sink; s4, an inner pile casing is put down into the tool type pile casing; s5, an annular gap between the tool type pile casing and the inner pile casing is filled with a self-compacting material, and the crawler crane removes the tool type pile casing section by section and removes the full-slewing drilling machine; s6, the steps S3-S5 are repeated until the inner pile casing in the construction area is completely sunk; and S7, percussion drill hole forming, reinforcement cage lowering, secondary hole cleaning and pouring are conducted. According to the method, the technical breakthrough of the problems of large pile casing in-time follow-up difficulty, slurry leakage, hole collapse and the like in super-thick riprap layer construction is achieved, and the method has good practicability for special construction scenes close to existing wharf revetments and caisson foundation beds and the geological conditions of super-thick riprap layers with different thicknesses and particle sizes.

Description

Technical Field

[0001] This invention relates to the field of bored pile construction methods. More specifically, this invention relates to a method for constructing bored piles through ultra-thick riprap layers. Background Technology

[0002] With the leapfrog development of my country's transportation industry and port construction, the construction of the coastline has gradually become more complete. More and more new construction and expansion are being carried out near existing wharves. When constructing new piers, approach bridges and other structures near existing caisson wharves, bored pile foundations are often used. Bored pile foundations are usually drilled through the rock riprap layer using percussion drilling. In the rock riprap layer area, steel casings are used to protect the hole opening to prevent damage.

[0003] The conventional construction process for cast-in-place piles has many defects due to the influence of the construction environment (near existing wharves and coastlines) and the characteristics of the process. In areas near existing caisson wharves, it is difficult to lower the casing on the sloping bank. The seabed geology may have been disturbed, and landslides are prone to occur during the impact drilling process. At the same time, the casing needs to be pre-drilled before being lowered, and abnormal situations such as grout leakage and hole collapse often occur because the casing cannot be lowered in real time. In addition, it is difficult to ensure the accuracy and verticality of the casing by extending and lowering it multiple times. Summary of the Invention

[0004] The main objective of this invention is to propose an economical and efficient method for constructing cast-in-place piles through ultra-thick riprap layers in areas close to existing wharf revetments and caisson foundation beds. This method is characterized by simple installation, safety and reliability, and wide applicability. It can effectively solve the problems of grout leakage and hole collapse caused by the inability of the casing to keep up with the piles when they penetrate ultra-thick riprap layers, thereby further improving construction efficiency.

[0005] A preferred embodiment of the present invention provides a method for constructing bored piles through ultra-thick riprap layers, comprising the following construction steps: S1. Design and build a drilling platform. The bottom of the steel pipe pile foundation of the drilling platform adopts an anchor pile structure that extends into the riprap layer slope. The drilling platform only reserves holes at the preset drilled pile positions for subsequent tool-type casing placement and drilling operations. S2. The crawler crane set on the drilling platform lifts the full-rotation drilling rig to the designed pile position. The full-rotation drilling rig is equipped with a tool-type casing. The tool-type casing is a steel tubular structure composed of multiple segments spliced ​​together. Adjacent segments are connected by socket joints and fixed with high-strength bolts. The lower end of the bottom segment is equipped with an alloy serrated cutter head. S3. Calibrate the verticality of the tool-type casing, start the full-rotation drilling rig to drive the tool-type casing to rotate and sink, and the tool-type casing rotates to cut the ultra-thick rock-filled layer until the tool-type casing penetrates the ultra-thick rock-filled layer. S4. Lower the inner casing into the tool-type casing; S5. Use self-compacting material to fill the annular gap between the tool-type casing and the inner casing, and use a crawler crane to remove the tool-type casing section by section and remove the full-rotation drilling rig. S6. Move the full-rotation drilling rig to the next pile position and repeat steps S3 to S5 until all the inner casing in the construction area is sunk. S7. The crawler crane lifts the impact drill to the designed pile position. The impact drill continues to drill along the initial duct inside the inner casing, extending and enlarging the hole to the designed pile bottom. The process is carried out in sequence: first hole cleaning, lowering the steel cage, second hole cleaning, and underwater pile casting using the tremie method.

[0006] Preferably, in step S3, every 2 meters of drilling or when drilling becomes difficult and stops, the crawler crane lifts an independently installed grab bucket, which extends into the tool-type casing to grab the rock fragments generated during cutting. This step is repeated until the tool-type casing penetrates the ultra-thick rock layer.

[0007] Preferably, in S3, if drilling becomes difficult, the tool-type casing can be rotated in the opposite direction to lift it by 10-20cm, and then the rotation and sinking can be started again. Drilling is stopped every 2m of drilling or when repeated forward and reverse rotations still result in drilling difficulties.

[0008] Preferably, the diameter of the grab bucket is 5-25cm from the inner diameter of the tool-type casing. The grab bucket stops grabbing 20-30cm above the bottom of the tool-type casing to prevent the hole from collapsing due to excessive grabbing.

[0009] Preferably, in S5, for every 2 meters of filling, the full-rotation drilling rig rotates in the opposite direction to lift the tool-type casing by 2 meters, and the operation is repeated until the tool-type casing leaves the revetment and is then removed in one go.

[0010] Preferably, S4 specifically includes the following steps; The first inner casing section is hoisted to a position directly above the tool-type casing. Using the inner wall of the tool-type casing as a guide, the first inner casing section is vertically lowered into the tool-type casing along its axis. The length of the first inner casing section is the same as that of the tool-type casing. Subsequent inner casing sections are hoisted one by one to the top of the lowered inner casing using a crawler crane. The previous and subsequent inner casing sections are welded together and extended. A vibratory hammer is used to assist in the sinking process, ensuring that the bottom of the inner casing reaches the design requirement position or 2m below the impermeable layer.

[0011] Preferably, the drilling platform consists of a steel pipe pile foundation, a double-I-shaped main crossbeam, Bailey longitudinal beams, and a composite steel panel.

[0012] Preferably, the thickness of the tool-type casing is 3 to 5 cm, the inner diameter is the diameter of the cast-in-place pile plus 30 to 40 cm, and the length is not less than the top elevation of the drilling platform minus the lowest elevation of the bottom of the riprap layer plus 2 meters.

[0013] Preferably, the diameter of the inner casing is the diameter of the cast-in-place pile plus 10 to 20 centimeters, and the fixed length of each subsequent section of the inner casing is 9 meters or 12 meters.

[0014] The present invention has at least the following beneficial effects: This invention proposes a method for constructing bored piles through ultra-thick riprap layers. Through a full-span drilling platform design, a relay drilling process using a full-rotation drilling rig and an impact drilling rig, and a double-casing construction process with tool-type casings penetrating ultra-thick riprap layers, it achieves a technological breakthrough in addressing challenges such as the difficulty of timely casing follow-up, grout leakage, and borehole collapse during construction in ultra-thick riprap layers. It is highly practical for special construction scenarios near existing wharf revetments and caisson foundations, as well as for geological conditions of ultra-thick riprap layers with varying thicknesses and particle sizes. Compared to mainstream processes such as double-casing and full-rotation full-casing techniques, it is simpler, safer, and more efficient, offering advantages such as convenient installation, wide applicability, and good economic benefits. In terms of construction efficiency, the relay of equipment and modular cyclical processes reduce interference from overlapping operations, improving the overall construction pace. Economically, the tool-type casings are reusable, and the platform uses standardized components, reducing material and labor costs. Regarding safety and engineering protection, the anchor pile structure enhances the stability of the revetment, reduces disturbance to existing wharf facilities, and ensures the safety of the construction process and the structural safety of existing structures.

[0015] (1) Easy to install and convenient to construct: The specifications and models of the drilling platform can be optimized based on existing materials without the need for specially customized materials. The specifications and load-bearing capacity can be adjusted according to the actual site conditions. The equipment hoisting, casing extension and dismantling, drilling rig relocation and other processes are all modular operations. There is no need for complicated special tools, and no need for specific processing, manufacturing or modification of the equipment. Construction is convenient and quick.

[0016] (2) Wide range of applications: The construction process causes little disturbance to existing facilities and strengthens the stability of the revetment through the anchor pile structure. It is particularly suitable for pile foundation construction of near-existing structures such as port and wharf reconstruction and expansion. The thickness and inner diameter of the tool-type casing, the diameter of the grab bucket, etc. can be selected according to the situation, which can meet the construction needs of ultra-thick riprap layers with different environments, thicknesses, and particle sizes.

[0017] (3) Good economic benefits: Tool-type casing can be reused, reducing the consumption of disposable casing materials. High-strength bolt connection can reduce the losses caused by repeated welding and cutting compared with welding connection. The full-span drilling platform only reserves holes at the location of the cast-in-place pile, and the remaining areas use standardized components such as composite steel panels and Bailey longitudinal beams, which reduces the material cost of platform construction. The circular and standardized construction process reduces the complexity of manual operation and reduces the workload and number of construction workers.

[0018] (4) High construction efficiency: The division of labor between full-rotation and impact drilling relay construction is clear and each can give full play to its strengths, avoiding the efficiency loss of a single equipment in different strata. The modular and cyclical organization of the process avoids the mutual interference of equipment cross-operation and improves the overall construction rhythm. The tool-type casing rotates forward and sinks, and rotates backward and dismantles section by section. The use of high-strength bolts to connect greatly improves the overall construction rhythm and hole-forming efficiency.

[0019] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the construction process of the drilling and grouting pile construction method for penetrating ultra-thick riprap layers according to the present invention.

[0021] Figure 2 This is a schematic diagram of the drilling platform of the present invention.

[0022] Figure 3 This is a schematic diagram of the installation of the full-rotation drilling rig of the present invention.

[0023] Figure 4 This is a schematic diagram showing the connection between the bottom segment of the tool-type sleeve and the cutter head in this invention.

[0024] Figure 5 This is a schematic diagram of the installation and rotation of the tool-type casing of the present invention.

[0025] Figure 6 This is a schematic diagram of the reverse rotation of the tool-type protective sleeve of the present invention for removal. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0027] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious modifications will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0028] Those skilled in the art should understand that, in the disclosure of this invention, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0029] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0030] like Figure 1-6 As shown, a preferred embodiment of the present invention provides a method for constructing bored piles through ultra-thick riprap layers, comprising the following construction steps: S1. Design and build drilling platform 1. The bottom of the steel pipe pile foundation of drilling platform 1 adopts anchor pile structure to extend into the riprap layer slope. The drilling platform only reserves holes at the preset drilled pile positions for subsequent tool-type casing and drilling operations. Drilling platform 1 is a temporary structure providing the working foundation for bored pile construction, used to support construction equipment, personnel, and construction loads; the steel pipe pile foundation is the core load-bearing component of the drilling platform. The drilling platform is a full-span drilling platform, composed of a steel pipe pile foundation, double-I-shaped main crossbeams, Bailey longitudinal beams, and composite steel panels. The bottom of the steel pipe pile foundation adopts an anchor pile structure, extending into the riprap slope 2 at the designed angle to ensure the stability of the steel pipe pile foundation and enhance the platform's anti-slip and anti-pull-out structural form. During the construction of the drilling platform, steel pipe piles are first driven into the preset positions using a pile driver, then the double-I-shaped main crossbeams are installed. The main crossbeams are fixedly connected to the pile caps at the top of the steel pipe piles using high-strength bolts. Bailey longitudinal beams are then laid on the main crossbeams, and finally, composite steel panels are laid on the Bailey longitudinal beams. During the design phase, only hole positions were reserved at the locations of the bored piles to facilitate the drilling rig's positioning and drilling. The key calculations focused on the lowering of the tool-type casing during the rotary drilling rig's rotation and the raising of the tool-type casing during the reverse rotation of the rotary drilling rig.

[0031] S2. The crawler crane 3 set on the drilling platform lifts the full-rotation drilling rig 4 to the designed pile position. The full-rotation drilling rig 4 is equipped with a tool-type casing 5. The tool-type casing 5 is a steel tubular structure composed of multiple segments. Adjacent segments are connected by socket joints and fixed with high-strength bolts. The lower end of the bottom segment is equipped with an alloy sawtooth cutter head.

[0032] S3. Calibrate the verticality of the tool-type casing 5, start the full-rotation drilling rig to drive the tool-type casing 5 to rotate and sink, and the tool-type casing 5 rotates to cut the ultra-thick rock-filled layer until the tool-type casing penetrates the ultra-thick rock-filled layer. S4. Lower the inner casing 6 into the tool-type casing 5; S5. Use self-compacting material 7 to fill the annular gap between the tool-type casing and the inner casing. The crawler crane removes the tool-type casing section by section and removes the full-rotation drilling rig. Self-compacting material is a building material that can fill the gap by itself without vibration, such as medium-coarse sand.

[0033] S6. Move the full-rotation drilling rig to the next pile position and repeat steps S3 to S5 until all the inner casing in the construction area is sunk. S7. The crawler crane lifts the impact drill to the designed pile position. The impact drill continues to drill along the initial duct inside the inner casing, extending and enlarging the hole to the designed pile bottom. The process is carried out in sequence: first hole cleaning, lowering the steel cage, second hole cleaning, and underwater pile casting using the tremie method.

[0034] Furthermore, according to an embodiment of the present invention, preferably, in S3, every 2 meters of drilling or when drilling becomes difficult and stops, the crawler crane hoists an independently installed grab bucket, which extends into the tool-type casing to grab the rock fragments generated during cutting, and this step is repeated until the tool-type casing penetrates the ultra-thick rock layer.

[0035] This embodiment effectively removes obstacles inside the tool-type casing by stopping drilling every 2 meters or when drilling becomes difficult and grabbing the riprap fragments. This reduces the casing's sinking resistance, allowing the tool-type casing to smoothly penetrate the ultra-thick riprap layer. It avoids problems such as casing jamming and sinking difficulties caused by the accumulation of riprap fragments, improves construction efficiency, and reduces deformation of the casing caused by uneven stress, ensuring the casing's verticality. This lays a good foundation for subsequent inner casing lowering and impact drilling.

[0036] Furthermore, according to one embodiment of the present invention, preferably, in S3, if drilling becomes difficult, the tool-type casing can be rotated in the reverse direction to lift it by 10-20 cm, and then the rotation and sinking can begin again. Drilling is stopped every 2 m drilled or when repeated forward and reverse rotations still result in difficulty. This embodiment, by rotating in the reverse direction to lift the tool-type casing and then rotating and sinking it again, effectively loosens the rock-filled layer at the bottom and around the casing, solving the problem of drilling difficulties caused by dense rock-filled layers or large rock fragments, reducing the probability of casing jamming, avoiding risks such as casing deformation and drilling rig overload caused by forced drilling, ensuring the continuity and safety of tool-type casing drilling operations, and improving the efficiency of crossing ultra-thick rock-filled layers.

[0037] Furthermore, according to one embodiment of the present invention, preferably, the diameter of the grab bucket is 5-25 cm of the inner diameter of the tool-type casing. The grab bucket stops grabbing 20-30 cm above the bottom of the tool-type casing to prevent excessive grabbing and hole collapse. In this embodiment, the diameter of the grab bucket is selected as 1.3 meters to ensure that the grab bucket can smoothly extend into the tool-type casing while maintaining a reasonable gap with the inner wall of the casing to avoid collision with the inner wall of the casing and to effectively grab the rubble. When the grab bucket descends to 20-30 cm above the bottom of the tool-type casing, it stops descending. In this embodiment, the stopping position is selected as 25 cm above the bottom of the tool-type casing. At this time, the opening and closing mechanism of the grab bucket is operated to grab the rubble. During the grabbing process, the grab bucket is prevented from excessively descending and touching the bottom of the tool-type casing or the bottom of the hole.

[0038] After the grab is completed, slowly lift the grab bucket to unload the rubble into the designated area. After each grab operation, check whether the bucket body is intact and whether the bucket teeth are worn or deformed. Repair or replace them in time to ensure the normal operation of subsequent grab operations.

[0039] Furthermore, according to an embodiment of the present invention, preferably, in S5, for every 2 meters of filling, the full-rotation drilling rig rotates in the opposite direction to lift the tool-type casing by 2 meters, and the operation is repeated until the tool-type casing leaves the revetment and is then removed in one go.

[0040] In this embodiment, a cyclical operation of rotating and lifting the tool-type casing 2 meters in the opposite direction every 2 meters of filling height ensures that the self-compacting material evenly and densely fills the annular gap, effectively fixing the inner casing and preventing displacement or deformation of the inner casing due to incomplete filling of the gap. Once the tool-type casing is removed from the revetment, it is pulled out in one go, reducing disturbance to the revetment and surrounding riprap layer during removal, ensuring the stability of the revetment structure, improving the efficiency of casing removal, and allowing for reuse of the tool-type casing after removal, thus reducing construction costs.

[0041] Furthermore, according to an embodiment of the present invention, preferably, S4 specifically includes the following steps: hoisting the first inner casing section to directly above the tool-type casing, using the inner sidewall of the tool-type casing as a guide reference for positioning, so that the first inner casing section is vertically lowered into the tool-type casing along its axial direction, the length of the first inner casing section being consistent with the length of the tool-type casing, and subsequent inner casing sections being hoisted one by one to the top of the lowered inner casing section by a crawler crane, and welding the previous inner casing section and the next inner casing section together, and using a vibratory hammer to assist in vibration and sinking, and ensuring that the bottom of the inner casing is lowered to the design required position or 2m below the impermeable layer.

[0042] By lowering the first section of the inner casing using the inner wall of the tool-type casing as a guide reference, the initial verticality of the inner casing was ensured. Subsequent sections of the inner casing were then welded together and vibratory hammers were used to assist in sinking, allowing the inner casing to smoothly sink to the designed position or 2 meters below the impermeable layer. This effectively enhanced the stability of the borehole wall and prevented borehole collapse. The welding extension method ensured the integrity and sealing of the inner casing, while the vibratory hammer-assisted sinking improved the sinking efficiency, meeting the construction requirements.

[0043] Furthermore, according to one embodiment of the present invention, preferably, the tool-type casing has a thickness of 3 to 5 cm, an inner diameter equal to the diameter of the cast-in-place pile plus 30 to 40 cm, and a length not less than the top elevation of the drilling platform minus the lowest elevation of the bottom of the riprap layer plus 2 meters. The tool-type casing needs to be compatible with the cast-in-place pile, and its thickness, inner diameter, and length are reasonably determined according to the geological conditions, so that the tool-type casing can adapt to the geological conditions of ultra-thick riprap layers, possess sufficient strength and rigidity, effectively cut the riprap layer during the rotational sinking process, and at the same time provide sufficient space for the grab bucket operation and the lowering of the inner casing.

[0044] Furthermore, according to one embodiment of the present invention, preferably, the diameter of the inner casing is the diameter of the cast-in-place pile plus 10 to 20 centimeters, and the subsequent fixed length of a single section of the inner casing is 9 meters or 12 meters. Determining the inner casing diameter by adding 10 to 20 centimeters to the cast-in-place pile diameter ensures a reasonable gap between the inner casing and the borehole wall, providing sufficient space for concrete pouring, while avoiding material waste and increased construction difficulty caused by excessive gaps. Using a fixed length of 9 meters or 12 meters adapts to the lifting capacity and transportation conditions of the construction equipment, reduces the number of times the inner casing needs to be extended, improves construction efficiency, and ensures the integrity and stability of the inner casing. The manufacturing precision and anti-corrosion treatment of the inner casing meet construction requirements, ensuring the construction quality and safety of the bored cast-in-place pile.

[0045] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A construction method of a cast-in-place pile by drilling through an ultra-thick riprap layer, characterized in that, The construction steps include the following: S1. Design and build a drilling platform. The bottom of the steel pipe pile foundation of the drilling platform adopts an anchor pile structure that extends into the riprap layer slope. The drilling platform only reserves holes at the preset drilled pile positions for subsequent tool-type casing placement and drilling operations. S2. The crawler crane set on the drilling platform lifts the full-rotation drilling rig to the designed pile position. The full-rotation drilling rig is equipped with a tool-type casing. The tool-type casing is a steel tubular structure composed of multiple segments spliced ​​together. Adjacent segments are connected by socket joints and fixed with high-strength bolts. The lower end of the bottom segment is equipped with an alloy serrated cutter head. S3. Calibrate the verticality of the tool-type casing, start the full-rotation drilling rig to drive the tool-type casing to rotate and sink, and the tool-type casing rotates to cut the ultra-thick rock-filled layer until the tool-type casing penetrates the ultra-thick rock-filled layer. S4. Lower the inner casing into the tool-type casing; S5. Use self-compacting material to fill the annular gap between the tool-type casing and the inner casing, and use a crawler crane to remove the tool-type casing section by section and remove the full-rotation drilling rig. S6. Move the full-rotation drilling rig to the next pile position and repeat steps S3 to S5 until all the inner casing in the construction area is sunk. S7. The crawler crane lifts the impact drill to the designed pile position. The impact drill continues to drill along the initial duct inside the inner casing, extending and enlarging the hole to the designed pile bottom. The process is carried out in sequence: first hole cleaning, lowering the steel cage, second hole cleaning, and underwater pile casting using the tremie method.

2. The construction method of a cast-in-place pile penetrating through an ultra-thick riprap layer according to claim 1, characterized in that, In S3, every 2 meters of drilling or when drilling becomes difficult, the crawler crane lifts the independently installed grab bucket, which extends into the tool-type casing to grab the rock fragments generated during cutting. This step is repeated until the tool-type casing penetrates the ultra-thick rock layer.

3. The method for constructing bored piles through ultra-thick riprap layers according to claim 1, characterized in that, In S3, if drilling becomes difficult, the tool-type casing can be rotated in the opposite direction to lift it by 10-20cm, and then the rotation and sinking can be started again. Drilling should be stopped every 2m of drilling or if drilling becomes difficult after repeated forward and reverse rotations.

4. The method for constructing bored piles through ultra-thick riprap layers according to claim 2, characterized in that, The diameter of the grab bucket is 5-25cm from the inner diameter of the tool-type casing. The grab bucket should stop grabbing 20-30cm above the bottom of the tool-type casing to prevent the hole from collapsing due to excessive grabbing.

5. The method for constructing bored piles through ultra-thick riprap layers according to claim 1, characterized in that, In S5, for every 2 meters of filling, the full-rotation drilling rig rotates in the opposite direction to lift the tool-type casing by 2 meters. This process is repeated until the tool-type casing leaves the revetment and is then removed in one go.

6. The method for constructing bored piles through ultra-thick riprap layers according to claim 1, characterized in that, S4 specifically includes the following steps; The first inner casing section is hoisted to a position directly above the tool-type casing. Using the inner wall of the tool-type casing as a guide, the first inner casing section is vertically lowered into the tool-type casing along its axis. The length of the first inner casing section is the same as that of the tool-type casing. Subsequent inner casing sections are hoisted one by one to the top of the lowered inner casing using a crawler crane. The previous and subsequent inner casing sections are welded together and extended. A vibratory hammer is used to assist in the sinking process, ensuring that the bottom of the inner casing reaches the design requirement position or 2m below the impermeable layer.

7. The method for constructing bored piles through ultra-thick riprap layers according to claim 1, characterized in that, The drilling platform consists of a steel pipe pile foundation, a double-I-shaped main crossbeam, Bailey longitudinal beams, and a composite steel panel.

8. The method for constructing bored piles through ultra-thick riprap layers according to claim 1, characterized in that, The thickness of the tool-type casing is 3 to 5 centimeters, the inner diameter is the diameter of the cast-in-place pile plus 30 to 40 centimeters, and the length is not less than the top elevation of the drilling platform minus the lowest elevation of the bottom of the riprap layer plus 2 meters.

9. The method for constructing bored piles through ultra-thick riprap layers according to claim 1, characterized in that, The diameter of the inner casing is the diameter of the cast-in-place pile plus 10 to 20 centimeters, and the fixed length of each subsequent section of the inner casing is 9 meters or 12 meters.

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