Construction method for cast-in-situ bored pile in inclined stratum area

Abstract

The invention relates to the technical field of pile foundation engineering, and discloses a construction method of a cast-in-situ bored pile in an inclined stratum area, which comprises the following steps of: firstly, arranging an outer-layer pile casing to an inclined rock-soil interface; then, rapid-hardening chemical grout is injected into an irregular gap formed between the bottom of the outer-layer pile casing and the inclined rock surface in a pressing mode through a preset grouting pipe; after plugging is completed, the outer-layer pile casing continues to be lowered, and a bottom opening of the outer-layer pile casing is embedded into a stable rock stratum below the outer-layer pile casing; then, an inner-layer pile casing is arranged on the lower portion in the outer-layer pile casing, and a double-layer pile casing supporting system is formed; and finally, pile hole forming, pile body structure construction and subsequent detection are carried out under the protection of the system. Through the combination of the double-layer pile casing and chemical slurry plugging, the influence of adverse geology outside the hole is effectively isolated, stable conditions are provided for hole forming operation, the problem of construction on an inclined rock surface is successfully solved, the hole forming quality is remarkably improved, and the integrity and safety of a pile foundation are guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of pile foundation engineering, in particular to a method for constructing bored cast-in-place piles in an inclined stratum area. Background Art

[0002] Bored piles are a high-bearing, widely applicable form of pile foundation, widely used in the foundation engineering of bridges, high-rise buildings, and various large structures. The typical construction process involves precise layout, followed by drilling to the designed elevation using a drilling rig. A rebar cage is then placed in the hole and concrete is poured. During the drilling process, a steel casing is often installed at the hole mouth as a temporary support structure to prevent collapse of the soft soil near the surface and to establish a stable working environment.

[0003] The effectiveness of conventional construction methods relies heavily on relatively homogeneous or horizontally distributed ground conditions. When engineering practices encounter more complex geological structures, such as areas where a sloped hard rock-soil interface exists beneath a soft soil layer, the limitations of traditional casing follow-up processes become apparent.

[0004] Under these specific geological conditions, when the steel casing is lowered to the inclined interface, one side of its bottom will first contact the hard rock surface and be blocked, preventing further penetration, while the other side remains in the overlying soft soil layer, leaving room for further sinking. This uneven resistance prevents the casing from being placed flat and densely on the rock surface, and an irregular gap inevitably forms between its bottom and the inclined rock surface.

[0005] The existence of this gap will cause a series of subsequent construction problems. It forms a leakage channel for groundwater and saturated soft soil outside the hole to invade the hole. Continuous leakage makes it difficult to maintain a stable mud liquid level in the hole, which is used to balance the lateral pressure, reducing the protective effect on the hole wall, and may cause the already formed hole wall below to become unstable. At the same time, soil particles carried by the groundwater flow enter the pile hole through this gap, gradually hollowing out the soil around the bottom of the casing, and then causing large-scale collapse of the weak stratum above, a phenomenon known as "hole collapse." Such accidents not only make hole cleaning operations difficult and extend the construction period, but also seriously affect the pouring quality of the pile concrete, thereby compromising the integrity and bearing capacity of the pile foundation. Summary of the Invention

[0006] The purpose of the present invention is to provide a bored cast-in-place pile construction method in an inclined stratum area, which solves the problem that when bored cast-in-place piles are constructed in a complex stratum where some areas are silty clay and some areas are inclined rock, the conventional rotary drilling process is prone to collapse in the silty clay layer, and when a steel casing is used to follow up to the inclined rock-soil interface, one side of the casing contacts the hard rock layer while the other side is still in the soft soil, resulting in the casing being unable to continue to be effectively lowered, thereby forming a leakage channel between the bottom of the casing and the inclined rock surface; this not only makes the mud wall protection ineffective and makes it difficult to prevent the hole wall from collapsing, but may also cause problems such as water gushing and slurry leakage, seriously affecting the quality of the pile and the safety of construction.

[0007] In order to solve the above technical problems, the present invention provides a method for constructing bored piles in an inclined stratum area, the method comprising: The outer casing is provided below to the inclined rock-soil interface; When the bottom of the outer casing cannot be sealed due to the inclination of the rock-soil interface, chemical slurry is injected into the gap formed between the bottom of the outer casing and the rock-soil interface to seal it; An inner casing is provided below the outer casing; A hole is drilled in the inner casing to form a pile hole, and subsequent pile foundation construction is completed.

[0008] The technical principle of this invention is to first establish a preliminary support structure using an outer casing. To address the specific problem of gaps caused by the tilted rock surface, where one side of the casing is suspended or in poor contact, a chemical slurry is used to actively and precisely inject pressure to seal these gaps. This chemical slurry has rapid solidification properties, forming a water-stopping curtain with specific strength and impermeability within the irregular gaps, thereby blocking the exchange channels between water and soil inside and outside the hole, stabilizing the casing bottom structure, and creating an isolated and stable working environment for subsequent construction. On this basis, an inner casing is then applied as a precise pile body forming mold, achieving high-quality pile formation in complex strata.

[0009] In an optional embodiment, after the chemical slurry is injected for sealing, the outer casing is further advanced until its bottom enters the stable rock layer below the rock-soil interface.

[0010] In an optional embodiment, the step of lowering the outer casing includes: using a casing driver of a rotary drilling rig to lower the outer casing section by section, and the bottom opening of the first section of the outer casing is tooth-shaped.

[0011] In an optional embodiment, the outer casing is a temporary casing, and the inner casing is a permanent casing.

[0012] In an optional embodiment, the step of completing the subsequent pile foundation construction includes: after pouring concrete in the pile hole to form the pile body, removing the outer casing.

[0013] In an optional embodiment, the diameter of the outer casing is larger than the diameter of the inner casing, and the diameter of the inner casing is larger than the designed pile diameter.

[0014] In an optional embodiment, the step of drilling a hole in the inner casing is specifically performed by using a rotary drilling rig supplemented by a mud wall protection process.

[0015] In an optional embodiment, completing the subsequent pile foundation construction includes lowering a steel cage into the pile hole and performing underwater concrete pouring using a conduit method.

[0016] In an optional embodiment, an acoustic detection tube is provided on the steel cage for performing non-destructive testing on the formed pile body.

[0017] In summary, the present invention includes at least one of the following beneficial technical effects: 1. This invention directly and effectively addresses leakage and instability issues at the bottom of the casing on inclined rock surfaces by lowering the outer casing to the inclined rock-soil interface and actively injecting a chemical slurry to seal the gaps between the bottom and the rock-soil interface. The chemical slurry forms a water-stopping curtain that prevents mud loss from the hole and the influx of water and soil from outside the hole, fundamentally avoiding the risk of hole collapse caused by poor casing sealing and ensuring pile hole stability.

[0018] 2. This invention utilizes a double-layer casing structure. After the outer casing is stabilized through a chemical slurrying process, an inner casing is installed underneath. This structure provides a reliable external environment for precise centering and verticality correction of the inner casing, ensuring accurate installation. The inner casing, acting as a permanent casing, provides a regular, smooth pile formwork for subsequent concrete pouring, improving the geometric accuracy and structural quality of the resulting pile.

[0019] 3. This invention uses an outer casing with a serrated bottom section in the first section, which is lowered section by section using the rotary drill's built-in casing driver. This enhances the casing's ability to penetrate soil and soft rock, while reducing lowering resistance. This method integrates drilling and casing follow-up operations into the same device, optimizing the construction process, reducing the need for coordination of auxiliary equipment, and improving the efficiency of casing follow-up in complex and hard formations. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a flow chart of the method of the present invention; Figure 2 This is a schematic diagram of drilling according to the present invention; Figure 3 Schematic diagram of the first section and the second section of the steel casing of the present invention; Figure 4 This is a schematic diagram of the installation and lowering of the second section of steel casing and the cyclic installation of the remaining pipe sections of the present invention. DETAILED DESCRIPTION

[0021] The following is combined with Figure 1 -Attached Figure 4 , the present invention is described in further detail.

[0022] Refer to the attached Figure 1 , Figure 1 The present invention provides a method for constructing bored piles in an inclined stratum area, which may include the following steps: S100: Execute construction preparation and benchmark setting, including technical and site preparation, and precise measurement and stakeout of pile positions. S200: Construct a double-layer casing system and perform key sealing, including lowering the outer casing to the inclined rock-soil interface, chemically slurry-sealing the gap between the casing bottom and the rock surface, and installing the inner casing within it. S300: Execute pile hole forming, including drilling to the designed elevation under the guidance of the inner casing, and completing the final hole inspection and hole cleaning operations; S400: Execute the pile structure construction, including placing the steel cage in the pile hole and pouring underwater concrete using the conduit method; S500: Perform finishing and inspection, including removing the outer casing and conducting quality inspection on the formed pile foundation.

[0023] The core of the complete construction process of this embodiment lies in establishing a double-layer casing system consisting of an outer casing and an inner casing through step S200. For the specific working condition of the inclined rock-soil interface, when the outer casing cannot be sealed due to the inclined rock surface, chemical slurry is actively injected into the gap at its bottom. After the slurry solidifies, it forms a reliable water-stop curtain. This structure not only solves the problems of bottom obstruction, bottom leakage, and resulting hole wall instability encountered by conventional casing follow-up in this stratum, but also provides a stable and reliable prerequisite for the precise installation of the inner casing and the smooth drilling of the subsequent pile hole.

[0024] During the drilling process in step S300, a mud wall protection process is used. The performance of the mud is crucial to maintaining the stability of the hole wall. The technical parameters of the mud are controlled and calculated in the following ways: Relative density of mud ρ m Calculated by the following formula: Where G is the weight of the mud sample; V m is the volume of the mud sample taken. During construction, the mud density meter is used for on-site measurement, and ρ m Controlled within the range of 1.05 to 1.30 g / cm3.

[0025] The viscosity T of the mud is measured using a standard Marsh funnel meter. Its value is the time required for a certain amount of mud to completely flow out of the funnel, in seconds (s). Depending on the type of silty clay or rock formation, the viscosity T is controlled within the range of 16 to 22 seconds.

[0026] Sand content of mud X s Calculated by the following formula: Where V s V is the volume of sand contained in the mud sample measured by the mud sand content meter; m is the original volume of the mud sample used for measurement. During drilling, the sand content X s Not more than 4%.

[0027] Through precise control of the above-mentioned mud parameters and the support effect of the double-layer casing system, the continuous stability of the pile hole wall can be ensured throughout the drilling and subsequent construction process.

[0028] In step S100, construction preparation and benchmark setting are performed. This step provides the technology, site and accurate position benchmark for all subsequent drilling, casing installation and pile casting processes.

[0029] First, technical and site preparations are carried out. Before construction, the design drawings are reviewed to verify the planar position, elevation, geometric dimensions, and spatial relationship of the pile foundation to adjacent structures. All incoming raw materials, including steel for the reinforcement cage, cement and aggregate for concrete, and slurry materials for chemical slurrying, are sampled and inspected. Only qualified materials can be put into use.

[0030] Afterward, the construction site is prepared. Debris and obstacles are cleared, and the site is leveled and compacted layer by layer using rollers or compaction equipment until the site's bearing capacity meets the requirements of heavy machinery such as rotary drilling rigs, crawler cranes, and concrete trucks. For the construction of overwater pile foundations, the island construction method is used. By filling the water with earth and stone, a working platform above the designed water level is constructed in the water, providing a working surface for land-based construction equipment.

[0031] After site preparation is complete, precise surveying and setting out are performed. Using a total station or other surveying instrument, the center coordinates of the pile positions on the design drawings are accurately projected onto the construction site and marked with wooden stakes or steel chisels. Around the marked center points of the pile positions, the outer casing outline is sprinkled with lime powder to serve as a visual reference for installation.

[0032] To ensure positional accuracy throughout the construction process, after the pile center point is staked out, four control piles are placed at specific distances from the pile center, along a cross-shaped axis perpendicular to the pile center. These control piles serve as a fixed measurement reference, used in the subsequent S200 step for initial positioning of the casing and for checking and correcting its verticality and center position during the lowering process, ensuring that its planar position error and vertical tilt meet design specifications.

[0033] Please refer to the attached Figure 2 -Attached Figure 4 In step S200, a double-layer casing system is constructed and key plugging is performed. This step is the core of this embodiment and aims to provide a prerequisite for subsequent pile hole formation by constructing an isolated and stable support system.

[0034] This step begins with the installation of the outer casing. In this example, the outer casing serves as a temporary casing. It is rolled from Q235 steel plate with a wall thickness of 10 mm. The inner diameter of the outer casing is selected to be larger than the diameter of the inner casing to be installed later. For example, for a pile with a designed diameter of 2.0 m, a steel casing with an inner diameter of 2.4 m can be selected as the outer casing.

[0035] To enhance its ability to cut into the soil, the bottom of the first section of the outer casing is processed into a tooth-like structure. This tooth-like structure cuts the soil and soft rock when the casing is pressed down and rotated. The length of the first section of the casing is set to 4m. When initially lowered, drill to a depth of 3m, then stop drilling and start installing the first section of the outer casing. Please refer to the attached Figure 2 .

[0036] Please refer to the attached Figure 3, use a crawler crane to vertically lift the outer casing of the first section of the toothed bottom, and align it precisely within the outline drawn in step S100. After the first section of casing is in place, hoist the second section of casing so that the connecting flange or bolt hole at its end is precisely aligned with the top of the first section of casing, and fasten it with high-strength bolts. Subsequently, move the casing driver on the rotary drilling rig to the top of the connected casing, and fasten the driver to the top of the casing with anchor bolts. Start the casing driver, and spin the outer casing downward by applying torque and axial pressure. This process is cyclical, connecting and lowering each section until the outer casing reaches the predetermined formation interface. During the entire lowering process, the set control piles are continuously used to review and correct the verticality of the casing.

[0037] When the outer casing reaches the inclined rock-soil interface, it stops lowering. Due to the inclined rock surface, one side of the casing's serrated bottom contacts the hard rock layer and cannot cut further, while the other side remains in the soft stratum such as silty clay. As a result, an irregular gap is formed between the bottom of the casing and the inclined rock surface, which constitutes a leakage channel.

[0038] At this point, chemical slurry sealing is performed. A chemical slurry is injected into the gap through a grouting pipe pre-installed on the outer wall of the casing. The chemical slurry used in this embodiment is a quick-setting cement-water glass slurry. After the slurry is injected into the gap, it rapidly undergoes a chemical reaction and solidifies, forming a water-stop curtain with specific strength and anti-seepage properties between the bottom of the casing and the irregular inclined rock surface. This water-stop curtain can completely fill the gap, thereby blocking the leakage channel and reinforcing the weak soil around the bottom of the casing.

[0039] After confirming that the chemical slurry has solidified and there is no leakage at the bottom of the casing, continue to use the casing driver to lower the outer casing through the rock-soil transition zone until the serrated bottom of the casing is completely inserted into the medium-weathered rock layer below and reaches an embedded depth of 2m. At this point, the outer temporary casing is installed and its top is not less than 30cm above the ground. Figure 4 The content shown.

[0040] Finally, an inner casing is installed within the stabilized outer casing. In this embodiment, the inner casing serves as a permanent casing, and its diameter is selected to be larger than the designed pile diameter. For example, for a designed pile diameter of 2.0 m, a steel casing with an inner diameter of 2.2 m is selected. The inner casing is hoisted and inserted into the outer casing. Its center position and verticality are then accurately verified and corrected using control piles. Once all indicators meet design requirements, it is securely fixed to the borehole.

[0041] In step S300, pile hole forming is performed. This step is carried out under the protection of the constructed double-layer casing system, aiming to form a final pile hole that meets the design requirements.

[0042] This step begins with rotary drilling within the already-placed inner permanent casing. A rotary drilling rig is used, and a drill bucket is selected based on the characteristics of the stratum. When drilling into upper soil and soft rock formations, a cylindrical drill bucket with a dump port is used. When drilling into the lower, harder rock formations, a rock drill bucket with carbide picks is used.

[0043] During the entire drilling process, the mud wall protection technology is used simultaneously. A mud pool, a sedimentation tank and a circulation tank are set up near the hole mouth to form a complete mud circulation system. The mud is injected into the hole by pumping or gravity from the mud pool. The mud liquid level in the hole is always maintained at a height of not less than 2m above the groundwater level. Its hydrostatic pressure balances the lateral soil pressure and water pressure of the hole wall to maintain the stability of the hole wall. The mud carrying drill cuttings is discharged from the hole to the sedimentation tank, where the drill cuttings are precipitated and separated. The purified mud is returned to the mud pool for recycling. During this process, the relative density, viscosity and sand content of the mud are continuously monitored and adjusted to keep its performance indicators within the preset parameter range described in step S100.

[0044] Drilling continues until the bottom of the hole reaches the designed depth. At this point, drilling is stopped and a final hole inspection is performed. Hole depth is measured using a weight attached to a measuring line, hole diameter is measured using a caliper, and verticality of the hole is measured using an inclinometer to confirm that all geometric parameters of the hole meet the design specifications. For example, in this embodiment, the bottom of the hole sediment thickness is required to be no more than 200 mm during the initial measurement.

[0045] After the final hole inspection is qualified, the secondary hole cleaning operation is carried out immediately. This step is to completely remove the loose slag and sediment at the bottom of the hole to provide a clean bearing surface for subsequent concrete pouring. Use a high-power sludge suction machine or air lift reverse circulation method to clean the hole. Lower the suction pipe of the sludge suction machine or the reverse circulation conduit to a position close to the bottom of the hole, and start the equipment to suck out the sediment, drill cuttings and mud with a high sand content at the bottom of the hole. The hole cleaning operation continues until the thickness of the sediment at the bottom of the hole is less than 50mm, and the various performance indicators of the mud in the hole are basically consistent with the indicators of the new mud in the circulating mud pool. After the secondary hole cleaning is completed, the pile hole forming step is completed, and then the subsequent pile body structure construction is carried out.

[0046] In step S400, the pile body structure is constructed. This step completes the construction of the pile body structure in the formed and stable pile hole.

[0047] This step begins with the fabrication and placement of the steel cage. The cage is fabricated at the construction site's rebar processing yard according to the design drawings. Due to the deep depth of the pile foundation, the cage is designed to be manufactured in sections, with the length of each section determined by the crawler crane's lifting capacity and transportation conditions. Concrete pads are welded evenly along the circumference of the main reinforcement of the cage to ensure a concrete protective layer of the specified thickness is formed between the cage and the hole wall after the cage is lowered. At the same time, the sonic detection tubes are tied or welded to the main reinforcement along the inside of the cage. Their quantity and layout follow the design requirements. The bottom of the sonic detection tubes must be sealed, the top must be covered, and the joints must be sealed.

[0048] The rebar cage is placed using a crawler crane. First, the first cage section is hoisted and slowly lowered vertically into the hole. The second cage section is then hoisted, aligned with the top of the lowered first cage section. The main bars of the two cage sections are connected using single- or double-sided welding to ensure the connection strength meets the design requirements. This process is repeated until the last cage section is lowered to the designed elevation. The top of the cage is securely suspended from the hole opening using a tool-type suspension member to prevent it from shifting or floating during the subsequent concrete pour.

[0049] After the steel cage is in place, underwater concrete pouring is carried out. This embodiment utilizes the conduit method for construction. The conduit is constructed from multiple sections of steel pipe connected together with sealing rings. Its total length is sufficient to extend from the hole opening to the bottom, and its inner diameter is typically between 200mm and 300mm. The assembled conduit is lowered into the hole, with its bottom end 300mm to 500mm from the bottom.

[0050] Install a funnel on the top of the conduit and pour the first batch of concrete to form a bottom seal. The first batch of concrete pouring volume V initial The following requirements must be met: Where D p is the actual diameter of the pile hole; h e The initial burial depth of the conduit must be at least 1.0m. The initial concrete, under its own weight, forces the slurry and water out of the conduit, forming a concrete pile at the bottom of the hole into which the lower end of the conduit is buried, effectively isolating the subsequently poured concrete from the slurry in the hole.

[0051] After the first batch of concrete is poured, subsequent concrete pours begin immediately and continuously. During the pouring process, the guide tube is raised synchronously with the rising concrete level in the hole. A measuring rope or hammer is used to continuously detect the position of the concrete surface and the bottom of the guide tube, ensuring that the bottom of the guide tube is always buried in the poured concrete. The burial depth is controlled within a range of 2 to 6 meters. Concrete pouring continues until the top surface elevation exceeds the designed pile top elevation by 0.5 to 1.0 meters. This ensures the quality of the concrete at the pile head and concentrates the floating slurry layer within this reserved height for subsequent removal.

[0052] In step S500, finishing and inspection are performed. This step is performed after the pile body concrete pouring is completed and reaches a specific strength. It aims to complete all construction processes of the single pile and evaluate its final quality.

[0053] This step begins with the removal of the outer temporary casing. The timing of this removal operation is precisely controlled, typically occurring after the pile concrete has been poured and has reached initial setting but before final setting. This timing window ensures that the newly poured concrete has sufficient self-stabilization to prevent collapse due to casing removal, while also preventing excessive concrete strength from causing excessive adhesion to the casing, which could complicate removal or damage the pile.

[0054] Casing removal is performed using a crawler crane in conjunction with a vibratory hammer or a rotary drilling rig's casing driver. The vibratory hammer or casing driver is fixed to the top of the outer casing and activated to apply high-frequency vibration or reverse torque to reduce friction between the casing and the surrounding soil and solidified chemical slurry. Simultaneously, the crawler crane applies a continuous upward lifting force to smoothly and vertically remove the outer casing.

[0055] After the pile concrete reaches at least 70% of its design strength, the pile head is broken. This process removes the concrete above the pile top elevation, which contains slurry and impurities, exposing the dense, intact concrete at the design elevation. A hydraulic pile breaker is used. The breaker's modules are assembled and positioned over the area of ​​the pile head to be broken. The hydraulic system is activated, and multiple hydraulic cylinders simultaneously press inward, causing the concrete at the pile head to fracture horizontally. Breaking down the concrete layer by layer continues until the pile top reaches the design elevation.

[0056] Finally, nondestructive testing of the pile integrity is performed. This embodiment employs the ultrasonic transmission method, utilizing the acoustic detection tubes pre-buried with the reinforcement cage in step S400. Prior to testing, all acoustic detection tubes are filled with clean water. A pair of ultrasonic probes (one transmitting probe, one receiving probe) are lowered to the bottom of two adjacent acoustic detection tubes.

[0057] The ultrasonic detector is activated, and the transmitting and receiving probes are raised synchronously at the same speed. During this process, the transmitting probe continuously emits high-frequency ultrasonic pulses, which pass through the concrete between the two acoustic detection tubes and are picked up by the receiving probe. The detector automatically records and analyzes parameters such as the acoustic duration, amplitude, and frequency of the ultrasonic waves, generating a profile of the pile integrity. By analyzing the changes in the propagation velocity of the sound waves in the concrete and the attenuation of the amplitude, it is possible to accurately determine whether the pile body has defects such as necking, segregation, mud inclusions, and voids, thereby objectively evaluating the overall quality of the pile foundation.

[0058] Example 1: This embodiment is intended to illustrate the complete process of constructing a bored pile with a designed pile diameter of 2.0 m and a pile length of 50.0 m using the method of the present invention under specific geological conditions.

[0059] The geological conditions of the pile foundation are as follows: 0m to 20m below the surface is a silty clay layer; 20m to 22m is an inclined alternating layer of strongly weathered granite and silty clay, with the rock-soil interface inclined at an angle of 15 degrees; below 22m is moderately weathered granite, which serves as the bearing layer at the pile end.

[0060] First, during the construction preparation stage, a total station was used to accurately stake out the pile positions, and four independent steel control piles were set 5.0m at both ends of the cross axis of the pile center.

[0061] Next, the construction of the double-layer casing system began. Q235 steel plates were used to construct the temporary outer casing, with an inner diameter of 2.4m and a wall thickness of 12mm. A 4.0m-long section of casing was serrated at its base, serving as the first section. A rotary drilling rig was initially used to drill to a depth of 3.0m, followed by the installation of the first outer casing using a crawler crane. Subsequently, casings of the same specifications were connected section by section, and using a casing driver compatible with the rotary drilling rig, they were lowered by spinning to a depth of 20.0m, reaching the inclined rock-soil interface.

[0062] At this point, a quick-setting chemical slurry, made from a mixture of cement and water glass in a volume ratio of 1:0.5, is injected into the pre-set grouting pipeline on the outer wall of the casing. The injection pressure is controlled at 0.5-1.0 MPa. After the slurry solidifies to form a water-stop curtain, the outer casing is lowered until its bottom is 2.0 m deep into the moderately weathered granite layer below, resulting in a casing bottom elevation of -24.0 m.

[0063] Inside the outer casing, a Q235 steel permanent casing with an inner diameter of 2.2m and a wall thickness of 12mm is installed. Its lowering length is 25.0m to ensure that its bottom is stably seated in the moderately weathered rock layer.

[0064] Next, the pile hole forming stage begins. Under the protection of the inner casing, a rotary drilling rig is used for drilling. The drill bit is a 2.15m diameter alloy head barrel drill bucket. During the drilling process, mud is used to protect the wall, and the relative density of the mud is controlled at 1.15g / cm 3 , with a viscosity of 18s and a sand content of no more than 2%. After drilling to the designed depth of 50.0m, a final hole inspection was conducted. Subsequently, a secondary hole cleaning process was performed using an air lift reverse circulation process until the bottom hole sediment thickness was measured to be less than 50mm.

[0065] Next, the pile structure construction phase begins. A segmented steel cage (outer diameter 1.8m) constructed with HRB400-grade, 32mm diameter main reinforcement is hoisted into the hole, with the intersegments connected by double-sided welding. Four 50mm diameter steel acoustic detection pipes are pre-fixed to the cage. After the cage is placed and secured, C35 underwater concrete is poured using the conduit method, with a controlled slump of 180-220mm. During the pouring process, the 250mm diameter conduit is buried at a depth of 2.0m to 6.0m, until the top surface of the concrete exceeds the designed pile top elevation by 0.8m.

[0066] Finally, the finishing and inspection phase began. Four hours after the pile concrete had been poured and reached its initial setting state, the outer temporary casing was removed using a vibratory hammer and crawler crane. Once the concrete reached 75% of its design strength, a hydraulic pile breaker was used to remove the excess concrete from the pile head. Finally, the acoustic testing tube was filled with clean water, and the pile integrity was tested using an ultrasonic detector. The results showed the pile was continuous, dense, and free of defects.

[0067] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for constructing bored piles in an inclined stratum area, characterized in that: The steps include: Step A: Lower the outer casing to the inclined rock-soil interface; Step B: When the bottom of the outer casing cannot be sealed due to the inclination of the rock-soil interface, injecting chemical slurry into the gap formed between the bottom of the outer casing and the rock-soil interface to seal it; Step C: installing an inner casing inside the outer casing; Step D: drilling a hole in the inner casing to form a pile hole, completing subsequent pile foundation construction.

2. A bored pile construction method in an inclined stratum area according to claim 1, characterized in that: The step of lowering the outer casing in step A includes: using the casing driver of the rotary drilling rig to lower the outer casing section by section, and the bottom opening of the first section of the outer casing is tooth-shaped.

3. The method for constructing bored piles in an inclined stratum area according to claim 1, characterized in that: After step B, the outer casing is further advanced until its bottom enters the stable rock layer below the rock-soil interface.

4. The method for constructing bored piles in an inclined stratum area according to claim 1, characterized in that: The outer casing is a temporary casing, and the inner casing is a permanent casing.

5. The method for constructing bored piles in an inclined stratum area according to claim 1, characterized in that: The step D comprises: Drilling a hole in the inner casing to form a pile hole; placing a steel cage in the pile hole and pouring concrete to form a pile body; After the pile body concrete reaches a predetermined strength, the outer casing is removed.

6. The method for constructing bored piles in an inclined stratum area according to claim 1, characterized in that: The diameter of the outer casing is greater than the diameter of the inner casing, and the diameter of the inner casing is greater than the designed pile diameter.

7. The method for constructing bored piles in an inclined stratum area according to claim 1, characterized in that: The step of drilling a hole in the inner casing in step D is specifically performed by using a rotary drilling rig supplemented by a mud wall protection process.

8. The method for constructing bored piles in an inclined stratum area according to claim 1, characterized in that: The subsequent pile foundation construction in step D includes lowering a steel cage into the pile hole and performing underwater concrete pouring using a conduit method.

9. A method for constructing bored piles in an inclined stratum area according to claim 8, characterized in that: The steel cage is provided with an acoustic detection tube for performing non-destructive testing on the formed pile body.

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