A method for quickly forming a hole of a large-diameter steel pipe stand column in a soft upper and hard lower stratum of a hub station

Abstract

This invention discloses a rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at a hub railway station. The method involves constructing double rows of high-pressure jet grouting piles around the borehole to reinforce it to the rock surface elevation. A steel casing coated with a drag-reducing agent and fitted with a serrated cutting edge at the bottom is then driven down to the rock penetration elevation using a full-rotation drilling rig. Cement grout is injected into the casing gaps to seal any water seepage. A rotary drilling rig equipped with a large-diameter sand-removing bucket is used to remove the soft soil layer, and a clustered down-the-hole hammer is used to guide the borehole through the rock strata. During the borehole enlargement stage, a master-daughter type directional drill bit is used, equipped with alloy cutting teeth, bullet-shaped rotary drilling teeth, and a ring-shaped stabilizer, using the first-stage rock core as a guide channel to control verticality. During the borehole formation stage, an ultrasonic detector is used to perform full-section scanning, collecting borehole wall data and analyzing verticality deviations, and promptly initiating a pre-adjustment correction device. This invention achieves no borehole collapse in soft strata, no interface deviation, high efficiency in hard rock sections, and high-precision borehole quality, meeting the requirements for rapid construction and possessing significant engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of construction technology for underground engineering of urban rail transit, and specifically relates to a method for rapid drilling of large-diameter steel pipe column piles in soft upper and hard lower strata of hub stations. Background Technology

[0002] In the construction of subway stations in the core bustling area of ​​the city using the cut-and-cover reverse construction method, steel pipe columns are the key vertical support system that bears the load of the superstructure, the top slab load and the temporary construction load. Current projects generally encounter composite strata with soft upper soil layer, silty clay, medium and coarse gravelly sand layer, and moderately weathered or slightly weathered hard rock lower layer.

[0003] For example, Chinese invention patent application number CN201410648052.X discloses a method for precise positioning of steel pipe columns in subway stations using the cut-and-cover reverse construction method. The method mainly includes the following steps: (1) positioning measurement of the steel pipe column pile foundation construction; (2) verticality check measurement of the drilling rig rod; (3) installation and positioning measurement of the steel pipe column locator; and (4) steel pipe column installation and positioning. This invention method uses an advanced prism-free electronic total station combined with a high-precision laser plumb line. Through measurement error transmission analysis and by adopting techniques such as the normalization method, it reliably solves the problems of steel pipe column construction positioning and verticality calibration measurement.

[0004] For example, Chinese invention patent application CN202310433367.1 discloses a construction method for steel pipe columns and subway stations in subway stations with soft upper and hard lower strata. By safely connecting the foundation reinforcement cage to the bottom of the steel pipe column and simultaneously lowering the steel pipe column and foundation reinforcement cage as a whole into the borehole, the stability of the bottom foundation of the steel pipe column can be effectively guaranteed after construction. This eliminates the need for separate construction of the bottom foundation of the steel pipe column, thereby reducing the size of the bottom foundation. During borehole drilling, the hole can be divided into a large-diameter upper hole and a small-diameter lower hole, reducing the volume of the borehole in hard rock, thus reducing the construction difficulty of hard rock drilling, improving drilling efficiency, and saving project investment. Furthermore, lowering the steel pipe column and foundation reinforcement cage as a whole into the borehole eliminates the need for installing a mechanical positioning head for the steel pipe column, simplifying the construction process and further improving the construction efficiency of the steel pipe column.

[0005] Existing technologies suffer from several drawbacks: poor borehole wall stability in soft strata, leading to easy borehole collapse and high drilling risks; uneven drill bit stress during drilling at the soft-hard interface, resulting in borehole deviation and skewed holes, and reliance solely on the equipment's own verticality imaging system for correction and early warning, lacking precise detection methods throughout the entire drilling process, making it difficult to guarantee verticality; low drilling efficiency in moderately or slightly weathered hard rock sections, severe drill bit wear, and long construction cycles; and mud-wall drilling leading to a sharp increase in civilized construction costs, with significant environmental pressure from mud disposal. Based on these existing technical problems, this invention provides a rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations. Summary of the Invention

[0006] To address the aforementioned technical problems in existing technologies, this invention provides a rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations. This method utilizes a full-rotation, full-casing rigid wall protection system, secondary reinforcement of the borehole wall through dual-liquid grouting, a combination of graded drill bits and multiple equipment to adapt to different strata, segmented borehole expansion speed control, and ultrasonic testing throughout the entire process. This achieves no borehole collapse in soft strata, no interface deviation, high efficiency in hard rock sections, and high-precision borehole quality, meeting the requirements for rapid construction.

[0007] The present invention adopts the following technical solution:

[0008] This invention provides a method for rapid drilling of large-diameter steel pipe column piles in soft-over-hard strata at a hub station, comprising:

[0009] Step 1: Advanced reinforcement of weak strata. Double rows of high-pressure jet grouting piles are constructed around the designed steel pipe column holes to reinforce the soil around the hole walls in a circumferential manner. The reinforcement depth is up to the rock surface elevation to improve the overall stability of the upper weak strata and the self-stability of the soil.

[0010] Step 2, steel casing pretreatment: The outer surface of the steel casing to be used is derusted and ground, and a water-based transparent drag-reducing agent is evenly applied to reduce the sinking resistance of the steel casing and ensure that the steel casing can be recycled and reused later; at the same time, a serrated wear-resistant blade is installed at the bottom of the lowest part of the steel casing to cut through the string of boulders and completely weathered rock layers in the soft strata, ensuring that the steel casing is evenly pressed down to the rock penetration level;

[0011] Step 3: Pressing down the steel casing and secondary reinforcement of the borehole wall. The steel casing treated in Step 2 is pressed down to the designed reinforcement bottom elevation, i.e. the rock penetration depth elevation, using a full-rotation drilling rig. Then, cement-water glass double liquid grout is injected into the annular gap between the borehole wall and the steel casing using grouting equipment to form a borehole wall reinforcement and double liquid grout filling layer, sealing the seepage channels during the drilling process.

[0012] Step 4: Clearing the soft soil layer and guiding the rock strata for drilling and staged reaming. Using a large-diameter sand-scooping bucket drill bit equipped with a rotary drilling rig, all the soft and uneven soil layers inside the steel casing are scooped out in one go. Then, a cluster-type down-the-hole hammer drill with a diameter of 1500mm is used to guide the drilling of the lower rock strata, achieving rapid and accurate drilling in the hard rock section. Next, staged reaming and verticality control are carried out. A mother-and-child type directional drill bit is used, and the bottom of the drill bit is replaced with an alloy cutting tooth drill bit and bullet-shaped rotary drilling teeth. A ring-shaped stabilizer is added to the side of the drill bit. The first-stage rock core that has been drilled is used as a guide channel for drilling, which effectively restrains the drill bit deviation and ensures the verticality accuracy of the staged reaming stage.

[0013] Step 5: Hole Formation Process Inspection and Deviation Correction. During the construction of the steel pipe column hole, an ultrasonic hole wall detector is used to perform full-section scanning imaging of the formed hole section before each shift, collect hole wall contour data and perform verticality deviation analysis. For any deviation hazards found during the inspection, the drilling equipment guidance and correction system is activated in a timely manner for pre-adjustment and correction, continuously optimizing the verticality of the hole wall, and realizing visual monitoring, advanced deviation analysis and rapid elimination of defects throughout the hole formation process.

[0014] Furthermore, in step 1, the double-row high-pressure jet grouting piles are arranged symmetrically around the borehole, using φ600mm@400 double-row high-pressure jet grouting piles for reinforcement. The water-cement ratio is 1:1.0, the drilling speed is 10cm / min~20cm / min, the lifting speed is 15cm / min~25cm / min, the grouting pressure is 25MPa, the minimum cement content is not less than 25%, the 28-day unconfined compressive strength of the soil is qu≥1.0MPa, the pile body is continuous, and the permeability coefficient after reinforcement is less than 1x10. -7 cm / s, depth to the rock surface line.

[0015] Furthermore, in step 2, the steel casing is an 8mm thick integral steel casing with a water-based transparent drag-reducing agent coating on its outer surface. The serrated wear-resistant cutting edge is welded to the bottom edge of the steel casing, with a cutting angle of 30~35° and a side deviation angle of 6~8°.

[0016] Furthermore, in step 3, the cement-water glass dual-liquid grout injected has a water-cement ratio of 0.5, a water glass Baume degree of 30 to 40 degrees, a cement grout to water glass ratio of 1:1, and an injection pressure of 1 MPa to 3 MPa. After the grouting is completed, subsequent hole drilling operations are carried out.

[0017] Furthermore, in step 4, the input power of the cluster-type down-the-hole hammer drill is 180KW, the rated torque of the drill rod is 40KN*m, and the advance speed of the slightly weathered granite is 2m / h, so as to ensure drilling efficiency in hard rock sections.

[0018] Furthermore, in step 4, the diameter of the main drill bit of the mother-daughter type directional drill bit matches the diameter of the target hole, the diameter of the daughter drill bit matches the diameter of the first-stage core hole, the outer diameter of the loop stabilizer is fitted with the diameter of the already formed hole, and at least two sets of stabilizers are arranged at equal intervals along the drill string axis.

[0019] Furthermore, in step 5, the ultrasonic borehole wall detector is tested at least once before each shift, the testing range covers the entire depth of the formed borehole, the verticality deviation analysis accuracy is not less than 0.1%, and the test results are transmitted in real time to the drilling equipment guide correction system as a basis for pre-adjustment and correction.

[0020] Furthermore, the rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations is applicable to the drilling construction of large-diameter steel pipe column piles in cut-and-cover stations under the condition of soft soil, silty clay, medium-coarse gravelly sand layer in the upper part and medium-slightly weathered hard rock in the lower part.

[0021] Compared with the prior art, the superior effects of the present invention are as follows:

[0022] 1. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations described in this invention uses high-pressure jet grouting piles to reinforce the trench walls in a double row to the rock surface elevation, effectively improving the physical and mechanical properties of the soil, enhancing its self-stability and resistance to lateral deformation, fundamentally suppressing the risk of borehole deviation and collapse caused by abrupt changes in strata, providing stable retaining conditions for steel pipe column drilling, and ensuring the safety and continuity of the entire drilling process;

[0023] 2. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations described in this invention involves coating the outer surface of the steel casing with a water-based transparent drag-reducing agent after rust removal and grinding to reduce sinking resistance and ensure that the casing can be recycled and reused; a serrated wear-resistant cutting edge is added to the bottom to enhance the ability to cut boulders and weathered rock layers, and it is used in conjunction with a full-rotation drilling rig to accurately enter the rock, and the seepage channels are sealed by gap grouting to effectively prevent soil erosion and eliminate the risk of hole collapse;

[0024] 3. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations described in this invention uses a large-diameter sand-dredging bucket to clear the weak and uneven soil layer in one go, avoiding overlapping processes; then, a 1500mm cluster-type down-the-hole hammer drill is used for guiding the drilling. This equipment has high rock grinding efficiency and excellent verticality control accuracy, and can achieve rapid and accurate drilling in hard rock strata, significantly shortening the drilling cycle and ensuring that the drilling quality meets the design requirements.

[0025] 4. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations described in this invention improves the drilling tool in the staged hole reaming stage to a mother-daughter type directional drill bit, with alloy roller cone teeth, alloy cutting teeth and bullet-shaped rotary drilling teeth configured at the bottom, and a ring-shaped stabilizer added to the side. The already drilled rock core is used as a guide channel to effectively restrain the deviation of the drilling tool and ensure the verticality of the hole reaming. At the same time, the hole reaming cost of the rotary drilling rig is significantly reduced compared with other equipment, taking into account both quality and economy.

[0026] 5. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations described in this invention uses an ultrasonic borehole wall detector to perform full-section scanning imaging before each shift, collects borehole wall data and analyzes verticality deviation, so as to achieve quantifiable evaluation of borehole quality; and promptly activates the guide correction system to pre-adjust and correct for potential deviations, forming a closed-loop control of "detection-analysis-correction-verification", which comprehensively improves the accuracy and quality control level of borehole drilling. Attached Figure Description

[0027] Figure 1 This is a flowchart of the rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations according to the present invention.

[0028] Figure 2 This is a schematic diagram of the rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations in this invention, which involves full-rotation downward pressing of the casing to reinforce the rock surface and borehole wall.

[0029] Figure 3 This is a schematic diagram of the cross-section of the hole formed by the cluster-type down-the-hole hammer drill in the rapid hole-forming method for large-diameter steel pipe column piles in soft upper and hard lower strata of hub stations in this invention.

[0030] Figure 4 This is a schematic diagram of the cross-section of the rotary drilling rig in the rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations in this invention.

[0031] Figure 5 This is an enlarged view of the cluster-type down-the-hole hammer drill used in the rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations in this invention.

[0032] Figure 6 This is a front view of the letter-shaped guide drill bit in the rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations according to the present invention;

[0033] Figure 7 This is a top view of the letter-shaped guide drill bit in the rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations according to the present invention.

[0034] Figure 8 This is a schematic diagram of the full-section imaging of the ultrasonic borehole wall detector in the rapid drilling method for large-diameter steel pipe column piles in soft-hard strata above hub stations of the present invention.

[0035] Figure label:

[0036] 1. Full-rotation drilling rig; 2. Hole wall reinforcement and double-liquid grout filling layer; 3. Steel casing; 4. Weathered rock strata; 5. Cluster-type down-the-hole hammer drilling rig; 6. Rotary drilling rig; 7. Ultrasonic hole wall detector; 8. Hole pile foundation; 9. Alloy roller cone teeth; 10. Alloy cutting teeth and bullet-shaped rotary drilling teeth; 11. Bottom impactor of down-the-hole hammer; 12. Slag discharge port of down-the-hole hammer equipment. Detailed Implementation

[0037] To better understand the above-mentioned objectives, features and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0038] Example

[0039] like Figures 1 to 2 As shown, the rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of the hub station includes:

[0040] Before implementing the rapid drilling method for large-diameter steel pipe column piles in soft-hard strata above hub stations according to the present invention, sufficient construction preparation work is required; the construction site should be leveled, surface debris and obstacles should be removed to ensure that the construction machinery can be stably positioned and operated; the pile positions should be laid out according to the design drawings, the center position of the steel pipe column pile hole should be accurately marked using a total station, and cross-shaped guide piles should be set around the pile center point to check the pile position at any time during construction;

[0041] While preparing the site, a detailed investigation of the hydrogeological conditions of the construction area should be conducted to determine parameters such as groundwater level, seepage direction and seepage flow rate, so as to provide a design basis for subsequent grouting construction. After confirming that all preparations meet the requirements, the formal construction phase can begin.

[0042] Step 1: Advanced reinforcement of weak strata. Double rows of high-pressure jet grouting piles are constructed around the designed steel pipe column holes to reinforce the soil around the hole wall in a circumferential manner. The reinforcement depth is up to the rock surface elevation, which is the interface between the upper weak soil layer and the lower medium-weathered rock layer, in order to improve the overall stability of the upper weak strata and the self-stability of the soil.

[0043] Step 2, steel casing 3 pretreatment: the outer surface of the steel casing 3 to be used is derusted and polished, and a water-based transparent drag-reducing agent is evenly applied to reduce the sinking resistance of the steel casing 3, ensuring that the steel casing 3 can be recycled and reused later; at the same time, a serrated wear-resistant cutting edge is installed at the bottom of the lowest part of the steel casing 3 to cut through the string of boulders and completely weathered rock layers in the weak strata, ensuring that the steel casing 3 is evenly pressed down to the rock penetration elevation;

[0044] Step 3: Pressing down the steel casing 3 and secondary reinforcement of the borehole wall. Using a full-rotation drilling rig 1, the steel casing 3 treated in Step 2 is pressed down to the designed reinforcement bottom elevation, i.e. the rock penetration depth elevation. Then, cement-water glass double liquid grout is injected into the annular gap between the borehole wall and the steel casing 3 using grouting equipment to form a borehole wall reinforcement and double liquid grout filling layer 2, sealing the seepage channels during borehole formation.

[0045] After the full-rotation drilling rig 1 is in place, the chassis of the full-rotation drilling rig 1 is leveled to ensure that the rotation center is strictly aligned with the center of the pile position, and the alignment deviation should not exceed 5mm. After the full-rotation drilling rig 1 is in place, before the steel casing 3 is installed, the verticality of the guide frame of the full-rotation drilling rig 1 is repeatedly calibrated in both the X and Y directions using a plumb bob or a high-precision electronic inclinometer to ensure that the verticality deviation of the guide frame of the full-rotation drilling rig 1 is controlled within 1 / 1000. After the verticality calibration is completed, the pre-treated steel casing 3 is hoisted into the clamping mechanism of the full-rotation drilling rig 1.

[0046] Start the full-rotation drilling rig 1, which drives the steel casing 3 to rotate. At the same time, a stable axial downward pressure is applied through the hydraulic system to achieve uniform downward drilling of the steel casing 3. The core advantage of the full-rotation full-casing process is that the steel casing 3 forms rigid support for the borehole wall during the rotation process, preventing the expansion or collapse of the borehole due to unloading in soft strata, thus eliminating the risk of slurry leakage and borehole collapse that exists in the traditional mud wall protection process from the source.

[0047] During the pressing of the steel casing 3, the verticality and sinking speed of the steel casing 3 should be monitored in real time. If any deviation is found, it should be adjusted in time. If the pressing rate is significantly lower than the normal value (e.g., below 60 mm / min), it should be analyzed and determined whether it is caused by boulder resistance or clay adhesion. Boulder resistance can be overcome by increasing the rotation torque or reciprocating rotation. Clay adhesion requires improving the flushing fluid circulation efficiency or replacing the drag-reducing coating. After the steel casing 3 is pressed to the designed reinforcement bottom elevation (i.e., the rock penetration depth elevation), rotation and pressing should be stopped to maintain the stability of the steel casing 3 in the borehole. The designed pressing depth of the steel casing 3 should be at least 50 cm below the hard rock surface to ensure that the bottom of the steel casing 3 is embedded in the hard rock layer, so that the pressure of the upper soft strata is completely borne by the steel casing 3, avoiding seepage in the borehole and lateral pressure from aggravating borehole wall instability.

[0048] After the steel casing 3 is pressed down to the designed depth, the secondary reinforcement grouting process of the borehole wall is immediately carried out. Using special grouting equipment, cement-water glass double liquid grout is injected into the annular gap between the borehole wall and the steel casing 3 through grouting pipes pre-embedded in the wall of the steel casing 3 or grouting pipes inserted along the outer wall of the steel casing 3. This forms a borehole wall reinforcement and double liquid grout filling layer 2, thereby sealing the seepage channels that exist during the borehole formation, avoiding soil and water loss caused by changes in the water level inside the borehole, and fundamentally eliminating the safety hazard of borehole collapse during the borehole formation process.

[0049] Step 4: Clearing the soft soil layer and guiding the rock strata for drilling and staged reaming. Using a large-diameter sand-scooping bucket drill bit equipped with a rotary drilling rig, all the soft and uneven soil layers inside the steel casing 3 are scooped out in one go. Then, a cluster-type down-the-hole hammer drill rig 5 with a diameter of 1500mm is used to guide the drilling of the lower rock strata, achieving rapid and accurate drilling in the hard rock section. Subsequently, staged reaming and verticality control are carried out. A mother-and-child type directional drill bit is used, and the bottom of the drill bit is replaced with an alloy cutting tooth drill bit and bullet-shaped rotary drilling teeth 10. A ring-shaped stabilizer is added to the side of the drill bit. The first-stage rock core that has been drilled is used as the guide channel for drilling, which effectively restrains the deviation of the drill bit and ensures the verticality accuracy of the staged reaming stage.

[0050] Under the rigid protective wall formed by the steel casing 3, the large-diameter sand-dredging bucket drill bit equipped with the rotary drilling rig 6 is used to completely remove all the soft and uneven soil layers remaining inside the steel casing 3 in one go. The diameter of the large-diameter sand-dredging bucket should match the inner diameter of the steel casing 3, with the deviation controlled within the range of -10mm to +20mm. The bucket teeth should be replaced in time after wear. Before lowering the sand-dredging bucket, check whether the bucket body is intact, whether the bucket teeth are complete, and whether the valve opening is flexible. During the retrieval process, the drilling speed should be controlled to prevent the negative pressure from sucking the soil from the borehole wall into the bucket and causing over-diameter. The lifting speed should be controlled between 0.3m / s and 0.5m / s.

[0051] The working principle of the cluster down-the-hole hammer drill 5 is to combine multiple small-diameter pneumatic impactors (sub-hammers) in parallel through a connecting plate into a unified large-diameter impact crushing drilling unit. All sub-hammers are driven by a unified air source to synchronously carry out high-frequency impact crushing. Compared with the traditional rotary drilling rig that relies solely on rotary grinding to break rocks, the cluster down-the-hole hammer drill 5 uses impact crushing as the main method and rotary grinding as a supplement. It can complete rock breaking and hole formation at a faster advance rate in hard rock layers, and is particularly suitable for the demand for large-diameter hard rock holes such as 1500mm.

[0052] After the cluster-type down-the-hole hammer drill 5 completes the directional drilling, it forms the first stage of a smaller diameter directional hole in the hard rock layer. Then it enters the stage of graded hole enlargement to enlarge the hole diameter to the final design diameter. During the hole enlargement process, the drill bit of the rotary drilling rig 6 needs to be replaced with a mother-daughter type directional drill bit.

[0053] The structural features of the mother-daughter type directional drill bit are as follows: Figures 5 to 7As shown, it mainly consists of a concentric inner cylinder (daughter drill bit) and an outer cylinder (mother drill bit). The inner and outer cylinders are connected as a whole by a radial baffle component. The lower end of the inner cylinder extends beyond the lower end of the outer cylinder. The outer diameter of the inner cylinder matches the diameter of the first-stage core borehole. The configured bottom alloy cutting teeth and outer edge auxiliary cutting teeth are used to guide and center the drill bit downwards along the first-stage core guide channel. The alloy cutting teeth and bullet-shaped rotary drilling teeth 10 configured at the bottom of the outer cylinder perform cutting and hole enlargement work. The alloy roller teeth 9, alloy cutting teeth, and bullet-shaped rotary drilling teeth 10 form a multi-tooth, multi-functional composite cutting torque on the outer cylinder / mother drill bit of the mother-daughter type guide drill bit. Figures 3 to 4 As shown, when the drill bit is working in the hole, the inner cylinder slides forward along the bottom of the hole, and the outer cylinder performs rotary drilling and hole enlargement on the rock surface. The ring-shaped stabilizers added on the side are arranged at equal intervals on the outer cylinder wall of the drill bit to form a "point contact" sliding bearing constraint system, which can effectively constrain the lateral displacement that may occur when the drill bit rotates and enlarges the hole, and improve the verticality accuracy of the stage of hole enlargement.

[0054] Step 5, as Figure 8 As shown, the entire process of hole formation is monitored and deviations are corrected. During the construction of the steel pipe column hole, before each shift, an ultrasonic hole wall detector 7 is used to perform full-section scanning imaging of the hole pile 8, collect hole wall contour data and perform verticality deviation analysis. For any deviation hazards found during the detection, the drilling equipment guide correction device is activated in a timely manner for pre-adjustment and correction, continuously optimizing the verticality of the hole wall, and realizing visualized monitoring, advanced deviation analysis and rapid elimination of defects throughout the hole formation process.

[0055] During the construction of steel pipe columns, the main processes include hard rock directional drilling and graded hole enlargement. Before each shift, an ultrasonic borehole wall detector must be used to perform full-section scanning imaging on the drilled pile foundation to collect borehole wall contour data and perform verticality deviation analysis in a timely manner.

[0056] The working principle of the ultrasonic hole wall detector 7 is as follows: the ultrasonic probe is slowly lowered along the center of the hole through the cable. The electromechanical rotation system in the ultrasonic probe enables the ultrasonic sensor to obtain a 360° rotation scan. By utilizing the principle of ultrasonic echo reflection, the distance from the ultrasonic probe to the hole wall at different depths is accurately calculated by measuring the echo amplitude and time difference, and finally a cross-sectional image of the entire hole wall is drawn.

[0057] During the inspection, the ultrasonic probe should first be lowered to the bottom of the hole, with the lifting speed controlled at 5m / min to 10m / min. The ultrasonic probe should scan one cross-section every 10cm to 20cm of lifting. In the actual measurement, the measuring instrument simultaneously records the hole diameter and vertical cross-sectional curves in four directions (such as due north, due east, due south, and due west). By comparing the hole diameter value at each depth with the designed hole diameter, it is possible to accurately determine whether there are any reductions in diameter, expansions in diameter, or collapsed sections. By fitting the hole center offset trajectory at different depths, the verticality deviation of the borehole can be accurately calculated.

[0058] The obtained borehole wall contour data and verticality deviation analysis results are transmitted in real time to the drilling rig's main control computer via wireless or wired data transmission. Once the deviation at any depth exceeds the set alarm threshold (e.g., verticality deviation greater than 1 / 400), the drilling rig's main control computer will automatically trigger an audible and visual alarm and highlight the coordinates of the out-of-tolerance range on the screen. Based on this, on-site technicians use the guiding and correction device on the rotary drilling rig 6 to make data-driven decisions. For example, when the deviation is to the left, the pressure on the right side of the rotary drilling rig 6 is increased, thereby generating a corrective torque to the right and gradually adjusting the drill bit. On the mother-daughter type directional drill bit, the position and clamping degree of the contact point between the ring-shaped stabilizer and the hole wall are adjusted (e.g., by adding a hydraulic fine-tuning structure to the stabilizer) to achieve a slight verticality adjustment without having to start drilling and readjust. After the adjustment is completed, the ultrasonic hole wall detector 7 scans the same section of hole wall data again. Only after verification that the design requirements are met can the next process continue. This "detection-analysis-correction-verification" closed-loop control system realizes the visualization monitoring of the entire hole-forming process, the advanced analysis of deviations, and the rapid elimination of defects, which is significantly different from the traditional detection methods that can only be measured once after hole formation.

[0059] Furthermore, in step 1, the arrangement of the double-row high-pressure jet grouting piles is symmetrical around the borehole, using φ600mm@400 double-row high-pressure jet grouting piles for reinforcement. That is, each row of piles has a diameter of 600mm, the spacing between piles is 400mm, and the row spacing between the two rows of piles is 400mm. This double-row symmetrical arrangement forms a circumferential reinforcement layer with a thickness of 800mm, providing reliable lateral constraint conditions for subsequent full-rotation full-casing drilling, and suppressing the potential borehole deviation and collapse wind caused by sudden changes in strata from the source.

[0060] Ordinary Portland cement with a strength grade of not less than 42.5 is used as the main cementing material. When preparing the grout, the water-cement ratio is 1:1.0. This water-cement ratio was determined after a large number of indoor mix proportion tests and field test spraying verification to ensure that the grout has suitable fluidity and good consolidation performance. If the water-cement ratio is too high, the grout will be too fluid and the consolidation strength will be reduced. If the water-cement ratio is too low, the grout will be too viscous and difficult to spray. The water-cement ratio of 1:1.0 ensures the operability of spraying while making the 28-day unconfined compressive strength of the soil reach more than 1.0 MPa.

[0061] The drilling speed is 10cm / min~20cm / min, the lifting speed is 15cm / min~25cm / min, the grouting pressure is 25MPa, and the equipment should be test-sprayed and debugged before single pile construction. The construction parameters should be fine-tuned according to the site soil conditions. The minimum cement content should not be less than 25% of the mass of the soil to be reinforced. The unconfined compressive strength of the soil at 28 days should be ≥1.0MPa. The pile should be continuous without any breaks, and the permeability coefficient after reinforcement should be less than 1x10. -7 cm / s, depth to the rock surface line, after reinforcement the soil to form a rigid composite body similar to a "stone pillar" shape. The high-pressure jet stream impacts, cuts and forcibly mixes the soil, so that the cement slurry and soil particles are fully mixed, forming a cement-soil pile with a strength much higher than the original soil within the pile body, effectively suppressing the risk of borehole deviation and collapse caused by sudden changes in strata.

[0062] During the construction of high-pressure jet grouting piles, the verticality of the borehole must be strictly controlled to avoid uneven reinforcement layer thickness due to borehole inclination; the grout preparation should be strictly carried out according to the mix ratio, the cement grout should be fully stirred for no less than 2 minutes, and it should be filtered through a sieve to remove lumpy particles; the pressure and flow rate should be kept stable during the grouting process, and the pressure fluctuation should not exceed ±5% of the set pressure; the lifting speed should be uniform and continuous, and it should not be stopped at one position for a long time to avoid local grout accumulation; after the construction of each jet grouting pile is completed, quality inspection should be carried out in a timely manner, and the strength and continuity of the pile can be checked by means of light dynamic penetration test or core sampling test;

[0063] Furthermore, in step 2, the steel casing 3 is an 8mm thick integral steel casing. The diameter of the steel casing 3 is determined according to the design diameter of the steel pipe column, usually 100mm to 150mm larger than the outer diameter of the steel pipe column, so as to leave operating space for the subsequent lowering and positioning of the steel pipe column. The steel casing 3 is manufactured in sections, and the length of each section is determined according to the transportation and hoisting conditions, usually between 4m and 6m. The sections are connected by inner and outer flanges. The flanges are equipped with positioning pins to ensure the docking accuracy. During connection, the tightening torque of the flange bolts is strictly controlled to ensure that the overall straightness deviation after the casing is spliced ​​does not exceed 1 / 1000 of the length of the steel casing 3. The water-based transparent drag-reducing agent coating on the outer surface is of uniform thickness. The serrated wear-resistant cutting edge is welded to the bottom cutting edge position of the steel casing 3, with a cutting angle of 30~35° and a side deviation angle of 6~8°.

[0064] To improve the pressing efficiency of the steel casing 3 and facilitate subsequent recycling, the outer surface of the steel casing 3 is pretreated: first, the outer surface is derusted and polished using a wire brush or sandblasting method to remove surface oxide scale and loose rust, so that its roughness reaches the qualified level; the cleaned surface of the steel casing 3 should be blown clean with compressed air to ensure that there is no oil, rust and dust residue; then, a water-based transparent drag-reducing agent is evenly applied. The drag-reducing agent solution has good Newtonian fluid characteristics and forms a uniformly thick low friction coefficient protective film on the outer surface of the steel casing 3, which significantly reduces the frictional resistance between the steel casing 3 and the soil, thereby reducing the power consumption when the full-rotation drilling rig 1 presses down the casing, and at the same time ensuring that the steel casing 3 can be smoothly pulled out after the hole is formed and can be reused. The coating thickness is controlled between 100μm and 150μm, and the application should be uniform and continuous, without any missed coating or dripping. After the coating is applied, the drag-reducing agent coating should be dried in the natural environment for at least 2 hours before the next operation can be carried out.

[0065] The main component of water-based transparent drag reducer is a polymer aqueous solution. Its molecular chains extend in water to form a three-dimensional network structure. On the one hand, it forms an isolation layer on the metal surface to reduce the coefficient of friction. On the other hand, the molecular network structure can absorb and disperse frictional force, thereby effectively reducing interfacial frictional heating and adhesion. The drag reduction effect increases with the increase of drag reducer concentration. When applying, it should be prepared according to the recommended concentration in the product instructions.

[0066] A serrated wear-resistant cutting edge is welded to the bottom of the lowest part of the steel casing 3. The cutting edge is made of high-strength alloy steel or hard wear-resistant alloy, and its surface hardness is not less than HRC50 after heat treatment. The cutting edge is arranged in an alternating tooth pattern with a tooth height of 30mm to 50mm and a tooth width of 20mm to 25mm. A slag discharge groove is left between adjacent teeth. It can effectively cut and break the string of isolated rocks and weathered rock layers 4 in the soft strata, ensuring that the steel casing 3 can be pressed down at a uniform speed to the predetermined rock penetration elevation. Practice shows that the steel casing 3 with serrated cutting edge has a pressing efficiency that is more than 40% higher than that of ordinary flat casing, and the deviation rate is significantly reduced.

[0067] The serrated wear-resistant cutting edge is welded to the bottom edge of the steel casing 3. The cutting angle should be 30° to 35° and the side deviation angle should be 6° to 8°. The selection of the cutting angle and side deviation angle directly affects the cutting efficiency and verticality control of the steel casing 3: if the cutting angle is too small, the cutting edge will not be able to cut in, and the steel casing 3 will have difficulty entering the harder interlayer; if the cutting angle is too large, the cutting edge will easily break, and the steel casing 3 will easily deflect. The side deviation angle is used to deflect the cutting chips towards the center of the steel casing 3, so that the broken soil is squeezed into the interior of the steel casing 3 during drilling, and the soil is prevented from accumulating on the outer wall of the steel casing 3, which would increase the resistance. The cutting edge should be arranged symmetrically in sections and zones. 16 to 24 cutting edges are evenly distributed along the circumference at the bottom of the steel casing 3 to ensure that the force is balanced during the pressing process and to avoid the steel casing 3 deflecting due to wear or damage of the cutting edge on one side.

[0068] Furthermore, in step 3, the cement-water glass dual-liquid grout injected has a water-cement ratio of 0.5, a water glass Baumé degree of 30 to 40 degrees, a cement grout to water glass ratio of 1:1, and the two grouts are mixed in the same volume. The grouting pressure is 1 MPa to 3 MPa. After the grouting is completed, subsequent hole drilling operations are carried out.

[0069] The grout preparation process is as follows: First, prepare cement grout with a water-cement ratio of 0.5. Mix cement and water evenly in a mixing tank at a speed of not less than 400 r / min for a time of not less than 3 min. After the cement grout is prepared, at the grouting site, the cement grout and the pre-mixed water glass solution are placed in two separate grout tanks and pumped synchronously at a volume ratio of 1:1 using the dual-liquid grouting pump of the grouting equipment. After being fully mixed in the mixer, the mixture is injected into the predetermined hole.

[0070] By grouting through gaps to form a dense water-stop curtain, the two-component grout quickly solidifies in the irregular gaps between the outer wall of the steel casing 3 and the original soil, completely sealing the seepage channels and effectively cutting off the hydraulic connection between the pile hole and the surrounding aquifer. The initial setting time of the grout should be controlled between 30s and 60s to avoid excessive diffusion of the grout and waste, while ensuring the operability of the grouting construction.

[0071] The grouting pipe should be lowered to 0.5m above the bottom of the steel casing 3. Grouting should be carried out in sections from bottom to top, with each section having a grouting height of 2m to 3m. When grouting in sections, the next section can only be grouted after the previous section has been grouted for at least 15 minutes. Grouting should be continuous and not interrupted. During the grouting process, the grouting parameters should be monitored in real time by the pressure gauge and flow meter installed at the outlet of the grouting pump. When the grouting pressure reaches the design final pressure (3MPa) and the grout intake is less than 5L / min, the grouting of that section should be stopped. After the grouting is completed, the grouting pipe should be slowly pulled out and a check device should be installed at the grout outlet to prevent the grout from flowing back. Subsequent hole drilling operations can only be carried out after the grouting is completed.

[0072] Furthermore, in step 4, the input power of the cluster-type down-the-hole hammer drill 5 is 180KW, the rated torque of the drill rod is 40KN*m, and the advance speed of the slightly weathered granite is 2m / h, so as to ensure the drilling efficiency of the hard rock section.

[0073] like Figure 5As shown, the bottom of the cluster-type down-the-hole hammer drill rig 5 is equipped with several down-the-hole hammer bottom impactors 11 and down-the-hole hammer equipment slag discharge ports 12. The impactors apply strong impact force to the rock surface under air pressure. Rock cuttings are transported to the outside of the hole through the down-the-hole hammer equipment slag discharge ports 12 by compressed air or reverse circulation slag discharge. During drilling, the impact energy waveform of the down-the-hole hammer bottom impactor 11 should show a high peak value and narrow pulse to ensure that the rock surface obtains a sufficiently large impact energy per unit area. Field measurement data shows that in slightly weathered granite strata, the drilling speed of the cluster-type down-the-hole hammer drill rig 5 can reach 2m / h, which is about 3 to 5 times higher than the drilling speed of traditional rotary drilling rigs in hard rock.

[0074] Furthermore, in step 4, the main drill bit diameter of the mother-daughter type directional drill bit is matched with the target diameter of the hole enlargement, the daughter drill bit diameter is matched with the diameter of the first-stage core hole, the outer diameter of the ring stabilizer is matched with the diameter of the already formed hole, and at least two sets of stabilizers are arranged at equal intervals along the drill string axis.

[0075] The diameter of the main drill bit (mother drill bit) matches the target diameter of the reaming, the diameter of the daughter drill bit matches the diameter of the first-stage core borehole, and the outer diameter of the loop stabilizer is fitted with a clearance of 2mm to 5mm. At least two sets of stabilizers are arranged at equal intervals along the drill string axis. The axial distance between the two sets of stabilizers is generally 1 / 3 to 1 / 2 of the drill string length. This effectively constrains the lateral deflection of the drill string without increasing resistance or the risk of stuck drill due to excessive stabilizers. During drilling, the rotation speed and feed rate should be reasonably arranged according to the support of the pilot hole: when lowering, a slow positioning speed of 0.5 rpm is usually used initially to prevent impact with the borehole wall; when reaming begins, the rotation speed is increased to 10-15 rpm, while controlling the feed force to not exceed 70% of the drill string's rated load-bearing capacity to avoid overload and breakage of the cutting teeth.

[0076] Furthermore, in step 5, the ultrasonic borehole wall detector 7 is tested at least once before each shift, the testing range covers the entire depth of the formed hole, the verticality deviation analysis accuracy is not less than 0.1%, and the test results are transmitted in real time to the drilling equipment guide correction system as a basis for pre-adjustment correction.

[0077] Furthermore, the rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations is applicable to the drilling construction of large-diameter steel pipe column piles in cut-and-cover stations under composite strata conditions where the upper part is soft soil, silty clay, and medium-coarse gravelly sand, and the lower part is medium-to-slightly weathered hard rock. Such strata are very common in subway construction in coastal and inland cities in my country. The upper Quaternary soil layer has poor self-stability and is prone to collapse, while the lower bedrock has high uniaxial saturated compressive strength, some of which can reach more than 100MPa and has good integrity. Traditional processes cannot simultaneously ensure the wall protection safety of soft strata and the drilling efficiency of hard rock strata. The drilling method of the present invention is mainly applicable to the construction of steel pipe column piles in cut-and-cover stations with a steel pipe column diameter of 1.2m to 1.8m and a drilling depth of 20m to 50m.

[0078] This invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims.

Claims

1. A method for rapid drilling of large-diameter steel pipe column piles in soft-over-hard strata at a hub station, characterized in that, include: Step 1: Advanced reinforcement of weak strata. Double rows of high-pressure jet grouting piles are constructed around the designed steel pipe column holes to reinforce the soil around the hole walls in a circumferential manner. The reinforcement depth is up to the rock surface elevation to improve the overall stability of the upper weak strata and the self-stability of the soil. Step 2, steel casing pretreatment: The outer surface of the steel casing to be used is derusted and ground, and a water-based transparent drag-reducing agent is evenly applied to reduce the sinking resistance of the steel casing and ensure that the steel casing can be recycled and reused. At the same time, a serrated wear-resistant blade is installed at the bottom of the lowest part of the steel casing to cut through the string of boulders and completely weathered rock layers in the soft strata, ensuring that the steel casing is evenly pressed down to the rock penetration level. Step 3: Pressing down the steel casing and secondary reinforcement of the borehole wall. The steel casing treated in Step 2 is pressed down to the designed reinforcement bottom elevation, i.e. the rock penetration depth elevation, using a full-rotation drilling rig. Then, cement-water glass double liquid grout is injected into the annular gap between the borehole wall and the steel casing using grouting equipment to form a borehole wall reinforcement and double liquid grout filling layer, sealing the seepage channels during the drilling process. Step 4: Clearing the soft soil layer and guiding the rock strata for drilling and staged reaming. Using a large-diameter sand-scooping bucket drill bit equipped with a rotary drilling rig, all the soft and uneven soil layers inside the steel casing are scooped out in one go. Then, a cluster-type down-the-hole hammer drill with a diameter of 1500mm is used to guide the drilling of the lower rock strata, achieving rapid and accurate drilling in the hard rock section. Subsequently, staged reaming and verticality control are carried out. A mother-and-child type directional drill bit is used, and the bottom of the drill bit is replaced with an alloy cutting tooth drill bit and bullet-shaped rotary drilling teeth. A ring-shaped stabilizer is added to the side of the drill bit. The first-stage rock core that has been drilled is used as a guide channel for drilling, which effectively restrains the drill bit deviation and ensures the verticality accuracy of the staged reaming stage. Step 5: Hole Formation Process Inspection and Deviation Correction. During the construction of the steel pipe column hole, an ultrasonic hole wall detector is used to perform full-section scanning imaging of the formed hole section before each shift, collect hole wall contour data and perform verticality deviation analysis. For any deviation hazards found during the inspection, the drilling equipment guide correction device is activated in a timely manner for pre-adjustment and correction, continuously optimizing the verticality of the hole wall, and realizing visual monitoring, advanced deviation analysis and rapid elimination of defects throughout the hole formation process.

2. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations according to claim 1, characterized in that, In step 1, the double-row high-pressure jet grouting piles are arranged symmetrically around the borehole, using φ600mm@400 double-row high-pressure jet grouting piles for reinforcement. The water-cement ratio is 1:1.0, the drilling speed is 10cm / min~20cm / min, the lifting speed is 15cm / min~25cm / min, the grouting pressure is 25MPa, the minimum cement content should not be less than 25%, the 28-day unconfined compressive strength of the soil is qu≥1.0MPa, the pile body is continuous, and the permeability coefficient after reinforcement is less than 1x10. -7 cm / s, depth to the rock surface line.

3. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations according to claim 1, characterized in that, In step 2, the steel casing is an 8mm thick integral steel casing with a uniform thickness of water-based transparent drag-reducing agent coating on the outer surface. The serrated wear-resistant cutting edge is welded to the bottom edge of the steel casing with a cutting angle of 30~35° and a side deviation angle of 6~8°.

4. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations according to claim 1, characterized in that, In step 3, the cement-water glass dual-liquid grout injected has a water-cement ratio of 0.5, a water glass Baume degree of 30 to 40 degrees, a cement grout to water glass ratio of 1:1, and an injection pressure of 1 MPa to 3 MPa. After the grouting is completed, subsequent hole drilling operations are carried out.

5. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations according to claim 1, characterized in that, In step 4, the input power of the cluster-type down-the-hole hammer drill is 180KW, the rated torque of the drill rod is 40KN*m, and the advance speed of the slightly weathered granite is 2m / h, so as to ensure the drilling efficiency of the hard rock section.

6. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations according to claim 1, characterized in that, In step 4, the diameter of the main drill bit of the mother-daughter type directional drill bit matches the diameter of the target hole, the diameter of the daughter drill bit matches the diameter of the first-stage core hole, the outer diameter of the loop stabilizer is fitted with the diameter of the already formed hole, and at least two sets of stabilizers are arranged at equal intervals along the drill string axis.

7. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations according to claim 1, characterized in that, In step 5, the ultrasonic borehole wall detector is tested at least once before each shift, the testing range covers the entire depth of the formed hole, the verticality deviation analysis accuracy is not less than 0.1%, and the test results are transmitted in real time to the drilling equipment guide correction device as a basis for pre-adjustment correction.

8. The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata at hub stations according to any one of claims 1 to 7, characterized in that, The rapid drilling method for large-diameter steel pipe column piles in soft-over-hard strata of hub stations is applicable to the drilling construction of large-diameter steel pipe column piles in cap-and-cover reverse construction stations under the condition of soft soil, silty clay, medium-coarse gravelly sand layer above and medium-slightly weathered hard rock below.

Images