Construction method for low-clearance rotary excavating cone drill pile foundation in hard rock area adjacent to existing line

Abstract

The invention discloses a construction method for a low-clearance rotary excavating roller cone drill pile foundation in a hard rock area adjacent to an existing line, and relates to the technical field of road construction, which comprises the following steps of: 1, burying a full pile casing at a pile position, and pressing the pile casing to a designed elevation section by section by adopting a rotary excavating drill static pressure method; 2, the rotary drilling rig breaks the hard rock stratum in the pile casing in a static pressure and impact combined mode for drilling; and 3, after the rotary drilling rig drills to the designed depth, hole cleaning is conducted, a reinforcement cage and a guide pipe are placed, and concrete is poured to form a pile foundation. The pile casing is driven by the power head of the rotary drilling rig to sink, and the pile foundation follows up all the pile casing, so that construction hidden dangers such as hole collapse, sand gushing and hole wall collapse can be restrained precisely from the source, the problems such as stratum disturbance and surrounding soil settlement deformation caused by hole wall instability in traditional construction are avoided, indirect interference of construction on operation safety of an existing line is reduced, and the construction efficiency is improved. And a reliable risk prevention and control solution is provided for complex geological pile foundation construction adjacent to the existing line.

Description

Technical Field

[0001] This invention relates to the field of road construction technology, and in particular to a low-clearance rotary drilling pile foundation construction method in hard rock areas adjacent to existing railway lines. Background Technology

[0002] With the development of urban rail transit networks, the number of pile foundation constructions near existing railways and subway lines is increasing. Traditional construction methods typically employ impact drills and rotary drills. However, in hard rock (uniaxial compressive strength > 30MPa), these methods are slow and the drill bits wear out quickly, requiring frequent shutdowns for replacement. This not only extends the construction period but also increases costs. Furthermore, the construction process generates significant vibration and noise, which can easily lead to roadbed settlement and track deformation on existing lines, potentially causing operational safety accidents. Additionally, drilling in hard rock formations is prone to borehole collapse and sand inrush. Traditional mud slurry wall protection methods are insufficient to prevent these phenomena, resulting in significant disturbance to the surrounding soil and thus considerable interference with existing lines in the construction area, impacting construction quality. Therefore, to solve the above problems, we propose a low-clearance rotary drilling pile foundation construction method for hard rock areas adjacent to existing railway lines. Summary of the Invention

[0003] The purpose of this invention is to provide a low-headroom rotary drilling pile foundation construction method for hard rock areas adjacent to existing railway lines, in order to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a low-clearance rotary drilling rig pile foundation construction method in hard rock areas adjacent to existing railway lines, comprising the following steps: Step 1: Install a full casing at the pile location and use a rotary drilling static pressure method to press the casing section by section into the design elevation; Step 2: Inside the casing, the rotary drilling rig uses a combination of static pressure and impact to break up hard rock formations and drill. Step 3: After drilling to the designed depth with the rotary drilling rig, clean the hole, place the reinforcing cage and guide pipe, and pour concrete to form the pile foundation.

[0005] Preferably, in step 1, the installation of the full casing specifically involves: Step 1.1: Level the construction site and determine and mark the locations where drilling is required; Step 1.2: Use steel plates to make short sections of the casing, and extend multiple short sections of the casing into a single-end casing by double-sided full welding; Step 1.3: The first casing section is installed at the drilled location using the pit-burying method. Subsequent casing sections are installed using the rotary drilling static pressure method until the casing reaches the design elevation.

[0006] Preferably, in step 1.2, the casing is made by rolling a steel plate into a cylindrical shape on a plate rolling machine. The difference between the inner diameter of the casing and the pile diameter is greater than or equal to 20cm. The top surface of the casing is 1-2m above the groundwater level and 0.3-0.5m above the ground surface to meet the height requirements of the mud surface inside the casing.

[0007] Preferably, in step 1.3, the double-method installation of the casing specifically includes: Pit excavation and burial method: Excavate a pit at the pile location with a diameter 30-50cm larger than the outer diameter of the casing. Bury the first section of the casing in the pit. After the casing is buried, guide the center of the pile location back through four control piles so that the center of the casing coincides with the center of the pile location. Mark the position of the direction line of the control piles on the casing with a conspicuous color. Rotary drilling static pressure method: First, use a rotary drilling rig to drill a hole inside the casing. Stop drilling when the hole is 0.5m below the casing. Fix the static pressure plate of the rotary drilling rig to the lifting lug at the top of the casing. Then, use the rotary drilling rig to apply static pressure to the casing, causing the casing to sink. Repeat this process until the casing reaches the design elevation.

[0008] Preferably, in step 2, the drilling by the rotary drilling rig specifically includes: Step 2.1: Position and fix the rotary drilling rig at the pile location, and adjust the center position and verticality of the drill rod on the rotary drilling rig; Step 2.2: The rotary drilling rig first uses a cylindrical drill bit to lower the cylindrical drill bit into the hole to the predetermined depth, then rotates and pressurizes it to squeeze the soil that is swirled into the drill barrel until the drill barrel is full. Then the cylindrical drill bit is reversed to seal the bottom of the drill bit and withdraw it from the hole. The waste soil in the barrel is cleaned up and then it is re-entered into the hole to drill. This process is repeated until the hard rock layer is reached. Step 2.3: When drilling into the hard rock layer, the drill bit is withdrawn from the borehole, and the cylindrical drill bit on the rotary drilling rig is replaced with a roller cone drill bit. Then, drilling is carried out in sequence according to the rock layer top surface breakthrough stage, normal drilling stage and rock layer interface transition stage until the borehole depth reaches the design depth.

[0009] Preferably, in step 2.1, the adjustment of the drill rod center and verticality on the rotary drilling rig specifically involves: Move the rotary drilling rig to an empty position, adjust its upper outriggers to make the rig level, and ensure that the deviation between the center of the drill rod and the center of the casing is ≤5mm. Lower the drill bit to a position 10-20cm above the top of the casing, then adjust the drill rod angle to ensure that the verticality deviation of the drill rod is ≤1%.

[0010] Preferably, in step 2.3, the drilling process of the rotary drilling rig using a roller cone drill bit to break through the top surface of the rock strata specifically includes: Lower the roller cone drill bit to the top of the rock formation, apply low axial pressure and start the drill rod to rotate slowly, so that the roller cone drill bit can rotate in a rolling manner, and the cutting teeth can act on the rock formation in a point contact manner until the cutting teeth on the roller cone drill bit are fully embedded in the rock formation. Then, gradually increase the axial pressure to the preset value and maintain a stable speed to carry out the breaking drilling operation. The low axial pressure on the roller cone bit is 60%-70% of the preset axial pressure value. When the drill rod rotates slowly, the rotation speed is 5-8 r / min. When the torque of the roller cone bit steadily rises to 80% of the preset value, it indicates that the cutting teeth are fully embedded in the rock formation.

[0011] Preferably, in step 2.3, the drilling process of the rotary drilling rig using a roller cone drill bit during the normal drilling phase specifically includes: The drill bit is controlled to maintain a low speed, high torque, and stable pressure mode for drilling. The drill bit is stopped once a single drilling operation is controlled according to the drilling distance or whether the rock cuttings volume has reached the preset value. The drill rod is then lifted to clean up the rock cuttings. After each lifting of the drill rod, the borehole depth is measured using a measuring rope, the drilling speed is recorded, and the water level in the borehole is observed to understand the drilling situation. The criteria for stopping drilling and cleaning a roller cone drill bit are as follows: the drill bit must be stopped when the single drilling distance is 30-50cm or when the rock debris in the drill bucket reaches 70%-80% of its volume.

[0012] Preferably, in step 2.3, the drilling process of the rotary drilling rig using a roller cone drill bit in the transition stage of the rock strata interface specifically includes: When the roller cone bit drills to the interface between the rock layer and the soft soil layer or the rock layer with different hardness, reduce the speed of the roller cone bit to 50%-60% of the original speed, reduce the axial pressure to 65%-75% of the original pressure, and continue to drill slowly for 20-30cm to determine the interface position. Adjust the drilling parameters of the roller cone bit according to the hardness of the rock layer. When the torque of the roller cone bit increases suddenly and the rotation speed decreases during drilling, the axial pressure applied to the drill rod is adjusted to be applied intermittently, with each axial pressure lasting for 5-10 seconds. The rotation speed of the roller cone bit is then reduced to a slow speed until the boulder is completely broken.

[0013] Preferably, in step 3, the hole cleaning operation is performed twice, with the first hole cleaning performed after drilling is completed and the second hole cleaning performed after the steel cage and guide pipe are installed. After hole cleaning, the mud specific gravity is ≤1.10 and the sediment thickness is ≤50mm. When placing the steel cage, positioning bars are used to control the thickness of the protective layer. The top elevation deviation of the steel cage is controlled within ±50mm, and the center deviation is ≤20mm. When pouring concrete, the tremie pipe method is used, and the tremie pipe is buried at a depth of 2-6m. The pouring process is continuous, and the over-pour height at the top of the pile is ≥0.8m.

[0014] The technical effects and advantages of this invention are as follows: The construction method provided by this invention enables the rotary drilling rig to precisely control the verticality and drilling depth of the drill rod, ensuring that the drill bit performs drilling operations according to the designed pile position and hole diameter. The power head of the rotary drilling rig drives the casing to sink, and the entire casing of the pile foundation follows. This can precisely curb construction hazards such as hole collapse, sand inrush, and hole wall collapse from the root, and completely avoid problems such as ground disturbance and surrounding soil settlement and deformation caused by hole wall instability in traditional construction. This ensures the quality of pile foundation hole formation and construction efficiency, and can also minimize the indirect interference of construction on the operational safety of existing lines. It achieves safe coordination between the advancement of pile foundation engineering and the normal operation of existing lines, and provides a reliable risk prevention and control solution for pile foundation construction in complex geological conditions adjacent to existing lines.

[0015] In the construction method provided by this invention, a rotary drilling rig, in conjunction with a roller cone drill bit, uses the axial pressure and rotational torque applied by the drilling rig to make the roller cone roll at the bottom of the hole. The alloy cutting teeth on the roller cone act on the rock surface in a point contact manner, crushing the rock under high unit axial pressure. At the same time, the change in the height of the cone center during the rotation of the roller cone generates an impact load, which further enhances the rock crushing effect. This rock breaking method that combines static pressure and impact can efficiently break hard rock strata. Attached Figure Description

[0016] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention, but do not constitute a limitation thereof. In the drawings: Fig. 1 This is a flowchart of the method of the present invention.

[0017] Fig. 2 This is a flowchart of the construction process of the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] This invention provides, for example Figs. 1-2 The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines, as shown, includes the following steps: Step 1: Install a full casing at the pile location, and use a rotary drilling rig with static pressure to press the casing section by section into place until it reaches the design elevation; specifically including: Step 1.1: Level the construction site and determine and mark the locations where drilling is required; Step 1.2: Use steel plates to make short casing sections, with a steel plate thickness of 16mm being optimal. Multiple casing sections are joined together using double-sided full welding to form a single-end casing. The casing is made by rolling steel plates into a cylindrical shape on a plate rolling machine. The difference between the inner diameter of the casing and the pile diameter is greater than or equal to 20cm. The top surface of the casing is 1-2m above the groundwater level and 0.3-0.5m above the ground surface to meet the mud level requirements inside the casing. Using a full casing follow-up method for pile foundations can precisely curb construction hazards such as borehole collapse, sand inrush, and borehole wall collapse from the root, completely avoiding problems such as ground disturbance and surrounding soil settlement and deformation caused by borehole wall instability in traditional construction. This ensures the quality of pile foundation drilling and construction efficiency, and minimizes indirect interference with the operational safety of existing lines. It achieves safe coordination between pile foundation engineering progress and the normal operation of existing lines, providing a reliable risk control solution for complex geological pile foundation construction near existing lines.

[0020] Step 1.3: The first section of the casing is installed at the drilled location using the pit-burying method. Subsequent casings are installed using the rotary drilling static pressure method until the casing reaches the design elevation. The pit-burying method involves excavating a pit at the pile location with a diameter 30-50cm larger than the outer diameter of the casing. The first section of the casing is then buried in the pit. After installation, the center of the pile is guided back using four control piles to ensure the casing center coincides with the pile center. The direction lines of the control piles are clearly marked on the casing. The rotary drilling static pressure method involves drilling a hole inside the casing using a rotary drill until it reaches 0.5m below the casing. The rotary drilling static pressure plate is then fixed to the lifting lug at the top of the casing. The rotary drilling static pressure is then applied to the casing to lower it. This process is repeated until the casing reaches the design elevation. During the casing placement process, the center position and verticality of the casing are strictly controlled. The center position deviation must not exceed 3cm, and the verticality deviation must not exceed 1%. A total station and a level are used to monitor and adjust the center position and verticality of the casing in real time to ensure accurate placement of the casing. During the static pressure casing installation process, the pressing speed and pressure must be carefully controlled. The pressing speed should be uniform, avoiding being too fast or too slow. The pressure should be determined based on the geological conditions of the construction site and the specifications of the casing, and must not exceed the casing's bearing capacity to prevent deformation or damage. Simultaneously, the casing's settlement and the stability of the borehole wall should be closely monitored. If any abnormalities are found, static pressure work should be stopped immediately, the cause analyzed, and appropriate measures taken. After the casing installation is completed, a comprehensive inspection of the installation quality is required. Inspection items include the casing's center position, verticality, installation depth, top elevation, and the compaction degree of the surrounding backfill. After passing the inspection, a casing installation quality inspection record form should be filled out and submitted to the supervising engineer for acceptance. Only after the supervising engineer's acceptance can the next step of construction proceed. During drilling, the drilling rig precisely controls the verticality of the drill rod and the drilling depth to ensure that the drill bit operates according to the designed pile position and hole diameter. The rotary drilling rig's power head drives the casing to sink, resulting in less compression and vibration of the surrounding strata. Compared to traditional mud-wall systems, which may cause ground deformation due to mud loss, full casing better controls ground displacement in the construction area, reduces the impact on existing railway subgrades, tracks, and other structures, and further ensures the operational safety of existing lines.

[0021] Step 2: Inside the casing, the rotary drilling rig uses a combination of static pressure and impact to break up hard rock formations and drill; specifically including: Step 2.1: Position and fix the rotary drilling rig at the pile location, and adjust the center position and verticality of the drill rod on the rotary drilling rig. The specific operation is as follows: First, move the rotary drilling rig to the empty position, adjust its upper outriggers to make the drilling rig level, and ensure that the deviation between the center of the drill rod and the center of the casing is ≤5mm. Then, lower the drill bit to a position 10-20cm above the top surface of the casing, and then adjust the angle of the drill rod to ensure that the verticality deviation of the drill rod is ≤1%. Step 2.2: The rotary drilling rig first uses a cylindrical drill bit to lower the cylindrical drill bit into the hole to the predetermined depth, then rotates and pressurizes it to squeeze the soil that is swirled into the drill barrel until the drill barrel is full. Then the cylindrical drill bit is reversed to seal the bottom of the drill bit and withdraw it from the hole. After cleaning the waste soil in the barrel, it re-enters the hole to continue drilling. This process is repeated until the hard rock layer is reached. Generally, when the uniaxial compressive strength of the rock is greater than 30 MPa, it indicates that the hard rock layer has been reached. Step 2.3: When drilling reaches the hard rock layer, the drill bit is withdrawn from the borehole, and the cylindrical drill bit on the rotary drilling rig is replaced with a roller cone drill bit. Then, drilling is carried out sequentially according to the rock layer top surface breakthrough stage, the normal drilling stage, and the rock layer interface transition stage until the borehole depth reaches the designed depth. When the roller cone drill bit of the rotary drilling rig is working, the axial pressure and rotational torque applied by the drilling rig cause the roller cone to roll at the bottom of the hole. The cutting teeth (i.e., alloy inserts) on the roller cone act on the rock surface in a point contact manner, crushing the rock under high unit axial pressure. At the same time, the impact load generated by the change in the height of the cone center during the rotation of the roller cone further enhances the rock crushing effect. This rock breaking method that combines static pressure and impact can efficiently break hard rock formations. The rock formation top surface breakthrough stage refers to lowering the roller cone drill bit to the top surface of the rock formation, applying low axial pressure, and starting the drill rod to rotate slowly. The low axial pressure on the roller cone drill bit is 60%-70% of the preset axial pressure value. When the drill rod rotates slowly, the rotation speed is 5-8 r / min, so that the roller cone drill bit operates in a rolling manner, and the cutting teeth act on the rock surface in a point contact manner until the cutting teeth on the roller cone drill bit are completely embedded in the rock formation. The judgment standard is that when the torque of the roller cone drill bit stably rises to 80% of the preset value, it means that the cutting teeth are completely embedded in the rock formation. Finally, the axial pressure is gradually increased to the preset value and a stable rotation speed is maintained to carry out the breaking drilling operation. The normal drilling phase refers to drilling in a mode where the roller cone drill bit is controlled to maintain low speed, high torque, and stable pressure. The single-time stopping of the roller cone drill bit is controlled based on whether the drilling distance or the volume of cuttings reaches a preset value, and the drill rod is lifted to clear the cuttings. After each lifting of the drill rod, the borehole depth is measured using a measuring rope, the drilling speed is recorded, and the water level in the borehole is observed to understand the drilling situation. If mud is used for wall protection, mud needs to be added up to 20cm below the top surface of the casing to maintain stable pressure in the borehole. In a specific embodiment, the determination of stopping the roller cone drill bit for cuttings clearing is when the single drilling distance of the roller cone drill bit is 30-50cm or when the cuttings in the drill bucket reach 70%-80% of the drill bucket's volume. Whether the cuttings volume in the drill bucket is sufficient can be judged by the lifting resistance of the drill rod or by observing the amount of cuttings discharged from the borehole. When lifting the drill rod, the lifting speed should be ≤0.5m / min to avoid negative pressure causing borehole wall collapse. The rock strata interface transition stage refers to the situation where the roller cone bit reaches the interface between the rock strata and the soft soil layer or the rock strata of different hardness. When drilling to this position, the actual phenomenon is a sudden drop or increase in torque. Immediately reduce the roller cone bit speed to 50%-60% of the original speed and reduce the axial pressure to 65%-75% of the original pressure. Then continue drilling slowly for 20-30cm. After determining the interface position, adjust the drilling parameters of the roller cone bit according to the rock hardness. It should be noted that when the roller cone bit experiences a sudden increase in torque and a decrease in speed during drilling, it indicates that an isolated boulder has been encountered. The corresponding adjustment strategy is to adjust the axial pressure applied to the drill rod from continuous to intermittent, with each axial pressure maintenance time being 5-10s. Reduce the speed of the roller cone bit to a slow state until the isolated boulder is completely broken. After breaking, clean the slag. Do not force pressure during this process, as it may easily cause the drill rod to bend or the drill bit to be damaged. The roller cone drill bit revolves around the drill string and rotates on its own axis around the tooth center at the bottom of the hole, operating in a rolling manner. This results in low operating resistance and the ability to withstand high drilling pressure. Furthermore, when the roller cone drill bit contacts the rock at the bottom of the hole, the small contact area between the alloy insert teeth and the rock makes it easier to obtain a high unit axial pressure. Combined with the impact load generated when the roller cone rotates, this greatly improves the rock breaking effect. Compared with traditional drilling rigs, the drilling efficiency in hard rock formations is significantly improved, and the construction period can be effectively shortened.

[0022] The low vibration and low noise characteristics of rotary drilling rigs effectively reduce disturbance to existing railway line foundations, mitigating risks such as foundation settlement and track deformation. Simultaneously, low noise minimizes environmental impact, avoiding economic compensation and project delays due to noise complaints. Using rotary drilling rigs effectively avoids these economic losses caused by interference with existing railway line operations, ensuring normal operation, stable transportation revenue, and maintaining a positive image for construction companies, demonstrating its indirect economic benefits in multiple ways.

[0023] After completing the final drilling in step 2, the geological conditions must be verified. This involves comparing the drill cuttings with the geological columnar section to confirm whether the geological conditions meet the design requirements. If there are discrepancies with the survey and design data, the supervising engineer and on-site design representative must be notified immediately for confirmation and handling. If the design requirements are met, the hole depth, diameter, and hole type must be checked immediately. Hole diameter, hole wall thickness, and verticality are tested using a borehole measuring instrument. After confirming that the design and acceptance standards are met, the hole is submitted to the supervising engineer for acceptance. Once the supervising engineer approves the hole, it must be cleaned immediately.

[0024] Step 3: After drilling to the designed depth using a rotary drilling rig, clean the borehole, install the reinforcing cage and tremie pipe, and pour concrete to form the pile foundation. The borehole cleaning operation is designed to be carried out twice. The first cleaning is carried out after drilling is completed, and the second cleaning is carried out after the reinforcing cage and tremie pipe are installed. During the cleaning process, the mud specific gravity after cleaning is ≤1.10, and the sediment thickness is ≤50mm. During the installation of the reinforcing cage, positioning bars are used to control the thickness of the protective layer. The top elevation deviation of the reinforcing cage is controlled within ±50mm, and the center deviation is ≤20mm. At the same time, the tremie pipe method is used when pouring concrete. The tremie pipe burial depth is controlled between 2-6m. The pouring process is continuous, and the over-pour height at the pile top is ≥0.8m. In step 3 of this embodiment, the traditional construction method is mainly used to complete the subsequent pile foundation work. The main steps include hole cleaning, side hole work, installation of steel cage, installation of guide pipe, secondary hole cleaning, concrete pouring, pile head chiseling, and final pile foundation testing. In the two hole cleaning operations, it is necessary to check the mud specific gravity and sediment thickness.

[0025] In addition, in this embodiment, the overall height and dimensions of the rotary drilling rig can be optimized by improving the equipment, reducing the equipment height, and allowing the mast angle on the equipment to be adjusted, so that the equipment can operate flexibly in the clearance space and meet the usage requirements of pile foundation construction in low clearance areas; thereby, by optimizing the overall height and dimensions of the equipment, the safe and efficient operation of the equipment in low clearance areas can be ensured.

[0026] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines, characterized in that... Includes the following steps: Step 1: Install a full casing at the pile location and use a rotary drilling static pressure method to press the casing section by section into the design elevation; Step 2: Inside the casing, the rotary drilling rig uses a combination of static pressure and impact to break up hard rock formations and drill. Step 3: After drilling to the designed depth with the rotary drilling rig, clean the hole, place the reinforcing cage and guide pipe, and pour concrete to form the pile foundation.

2. The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines as described in claim 1, characterized in that, In step 1, the installation of the full casing specifically involves: Step 1.1: Level the construction site and determine and mark the locations where drilling is required; Step 1.2: Use steel plates to make short sections of the casing, and extend multiple short sections of the casing into a single-end casing by double-sided full welding; Step 1.3: The first casing section is installed at the drilled location using the pit-burying method. Subsequent casing sections are installed using the rotary drilling static pressure method until the casing reaches the design elevation.

3. The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines as described in claim 2, characterized in that, In step 1.2, the casing is made by rolling steel plates into a cylindrical shape on a plate rolling machine. The difference between the inner diameter of the casing and the pile diameter is greater than or equal to 20cm. The top surface of the casing is 1-2m above the groundwater level and 0.3-0.5m above the ground surface to meet the height requirements of the mud surface inside the casing.

4. The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines as described in claim 2, characterized in that, In step 1.3, the double-method installation of the casing specifically includes: Pit excavation and burial method: Excavate a pit at the pile location with a diameter 30-50cm larger than the outer diameter of the casing. Bury the first section of the casing in the pit. After the casing is buried, guide the center of the pile location back through four control piles so that the center of the casing coincides with the center of the pile location. Mark the position of the direction line of the control piles on the casing with a conspicuous color. Rotary drilling static pressure method: First, use a rotary drilling rig to drill a hole inside the casing. Stop drilling when the hole is 0.5m below the casing. Fix the static pressure plate of the rotary drilling rig to the lifting lug at the top of the casing. Then, use the rotary drilling rig to apply static pressure to the casing, causing the casing to sink. Repeat this process until the casing reaches the design elevation.

5. The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines as described in claim 1, characterized in that... In step 2, the drilling of the rotary drilling rig specifically includes: Step 2.1: Position and fix the rotary drilling rig at the pile location, and adjust the center position and verticality of the drill rod on the rotary drilling rig; Step 2.2: The rotary drilling rig first uses a cylindrical drill bit to lower the cylindrical drill bit into the hole to the predetermined depth, then rotates and pressurizes it to squeeze the soil that is swirled into the drill barrel until the drill barrel is full. Then the cylindrical drill bit is reversed to seal the bottom of the drill bit and withdraw it from the hole. The waste soil in the barrel is cleaned up and then it is re-entered into the hole to drill. This process is repeated until the hard rock layer is reached. Step 2.3: When drilling into the hard rock layer, the drill bit is withdrawn from the borehole, and the cylindrical drill bit on the rotary drilling rig is replaced with a roller cone drill bit. Then, drilling is carried out in sequence according to the rock layer top surface breakthrough stage, normal drilling stage and rock layer interface transition stage until the borehole depth reaches the design depth.

6. The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines as described in claim 5, is characterized in that... In step 2.1, the adjustment of the drill rod center and verticality on the rotary drilling rig specifically involves: Move the rotary drilling rig to an empty position, adjust its upper outriggers to make the rig level, and ensure that the deviation between the center of the drill rod and the center of the casing is ≤5mm. Lower the drill bit to a position 10-20cm above the top of the casing, then adjust the drill rod angle to ensure that the verticality deviation of the drill rod is ≤1%.

7. The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines as described in claim 5, is characterized in that... In step 2.3, the drilling process of the rotary drilling rig using a roller cone drill bit to break through the top surface of the rock strata specifically includes: Lower the roller cone drill bit to the top of the rock formation, apply low axial pressure and start the drill rod to rotate slowly, so that the roller cone drill bit can rotate in a rolling manner, and the cutting teeth can act on the rock formation in a point contact manner until the cutting teeth on the roller cone drill bit are fully embedded in the rock formation. Then, gradually increase the axial pressure to the preset value and maintain a stable speed to carry out the breaking drilling operation. The low axial pressure on the roller cone bit is 60%-70% of the preset axial pressure value. When the drill rod rotates slowly, the rotation speed is 5-8 r / min. When the torque of the roller cone bit steadily rises to 80% of the preset value, it indicates that the cutting teeth are fully embedded in the rock formation.

8. The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines as described in claim 5, characterized in that, In step 2.3, the drilling process of the rotary drilling rig using a roller cone drill bit during the normal drilling phase is specifically as follows: The drill bit is controlled to maintain a low speed, high torque, and stable pressure mode for drilling. The drill bit is stopped once a single drilling operation is controlled according to the drilling distance or whether the rock cuttings volume has reached the preset value. The drill rod is then lifted to clean up the rock cuttings. After each lifting of the drill rod, the borehole depth is measured using a measuring rope, the drilling speed is recorded, and the water level in the borehole is observed to understand the drilling situation. The criteria for stopping drilling and cleaning a roller cone drill bit are as follows: the drill bit must be stopped when the single drilling distance is 30-50cm or when the rock debris in the drill bucket reaches 70%-80% of its volume.

9. The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines as described in claim 5, characterized in that, In step 2.3, the drilling process of the rotary drilling rig using a roller cone drill bit in the transition stage of the rock strata interface is specifically as follows: When the roller cone bit drills to the interface between the rock layer and the soft soil layer or the rock layer with different hardness, reduce the speed of the roller cone bit to 50%-60% of the original speed, reduce the axial pressure to 65%-75% of the original pressure, and continue to drill slowly for 20-30cm to determine the interface position. Adjust the drilling parameters of the roller cone bit according to the hardness of the rock layer. When the torque of the roller cone bit increases suddenly and the rotation speed decreases during drilling, the axial pressure applied to the drill rod is adjusted to be applied intermittently, with each axial pressure lasting for 5-10 seconds. The rotation speed of the roller cone bit is then reduced to a slow speed until the boulder is completely broken.

10. The construction method for low-clearance rotary drilling rig pile foundations in hard rock areas adjacent to existing railway lines according to claim 1, characterized in that, In step 3, the hole cleaning operation is performed twice. The first hole cleaning is performed after drilling is completed, and the second hole cleaning is performed after the steel cage and guide pipe are installed. After hole cleaning, the mud specific gravity is ≤1.10 and the sediment thickness is ≤50mm. When placing the steel cage, positioning bars are used to control the thickness of the protective layer. The top elevation deviation of the steel cage is controlled within ±50mm, and the center deviation is ≤20mm. When pouring concrete, the tremie pipe method is used, and the tremie pipe is buried at a depth of 2-6m. The pouring process is continuous, and the over-pour height at the top of the pile is ≥0.8m.

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