A method for combined hole forming by full casing rotation and rotary drilling in a riprap stratum

Abstract

The present application relates to complex stratum pile foundation construction technology field, disclose a kind of riprapping stratum full casing rotary and rotary drilling combined hole construction method, comprising the following steps: leveling construction ground;Pile position lofting is carried out, and guiding positioning structure is set;First section casing with grouting passage is installed on full casing rotary drilling machine, grouting passage is used for grouting;Through full casing rotary drilling machine clamping casing, drive casing press into riprapping stratum, while rotary drilling carries out soil taking;Slurry is injected by grouting passage, and riprapping body outside casing is consolidated to form annular consolidated body;The elevation difference between the soil taking surface of rotary drilling and the bottom end of casing is controlled to be within the preset range, and the following protection wall is formed;Lengthen next section casing, and connect adjacent grouting passage;Until casing penetrates riprapping layer and main sand layer and enters lower stable layer.The present application can solve the problems of difficult riprapping stratum hole forming, easy hole collapse, easy grouting leakage and easy drill sticking.

Description

Technical Field

[0001] This invention relates to the field of pile foundation construction technology in complex strata, specifically to a method for hole formation construction using a combination of full-casing rotary drilling and rotary drilling in rock-filled strata. Background Technology

[0002] Rockfill strata are widely found along the coasts of rivers, lakes, and seas, in ports and wharves, in reclaimed land areas, and in areas where old dikes and revetments have been backfilled. These strata are typically composed of a mixture of boulders, pebbles, gravel, sand, clay, and miscellaneous fillers. They are characterized by large differences in particle size, uneven spatial distribution, high porosity, high permeability, and poor stability. Especially in areas near water or affected by tides, the pores in the rockfill layer are often connected to groundwater or external water bodies, which can easily lead to problems such as grout leakage, sand inrush, borehole collapse, borehole wall instability, and boulders falling off during pile foundation drilling.

[0003] Currently, when constructing bored piles, foundation pit retaining piles, or other pile foundations in riprap strata, the commonly used construction methods mainly include rotary drilling, impact drilling, double casing drilling, grouting reinforcement drilling, and full casing drilling.

[0004] Rotary drilling has advantages such as fast construction speed, high drilling efficiency, and strong equipment adaptability, and is widely used in general cohesive soil, sandy soil, and strongly weathered rock strata. However, in riprap strata, due to the large size and irregular distribution of the boulders, the rotary drilling bucket is easily blocked or stuck by the boulders. During the drilling process, problems such as hole collapse, stuck drill, and hole deviation may also occur due to the lack of effective constraint on the borehole wall. Therefore, when using rotary drilling alone, it is difficult to stably penetrate riprap strata with a large thickness, well-developed pores, and large boulders.

[0005] Percussion drilling can break up rocks through repeated impacts and maintain borehole stability with the help of drilling mud, making it suitable for some rocky formations. However, percussion drilling causes significant disturbance, which can easily lead to the rearrangement, slippage, or settlement of surrounding loose boulders. Simultaneously, the porous nature of the boulder layer allows drilling mud to easily leak through the gaps between rocks, causing a drop in the borehole fluid level, failure of the drilling mud wall, and the risk of borehole collapse. Furthermore, percussion drilling has relatively low efficiency, and the workload for drilling mud preparation, circulation, and waste mud treatment is substantial, which is detrimental to improving overall construction efficiency.

[0006] The double-casing process typically uses an outer casing to form an external constraint, and then an inner casing follows the drilling to reduce borehole wall instability and slurry leakage in rock-filled layers. This process can improve casing slippage, borehole wall collapse, and mud leakage to some extent. However, the coaxiality, verticality, and follow-up depth of the inner and outer casings need to be frequently controlled during construction, making the construction organization complex. For deep rock-filled layers or rock-filled sand-filled layers, the casing follow-up resistance is high, and the lengthening, correction, and sinking control are difficult, thus limiting construction efficiency.

[0007] Grouting reinforcement methods can locally consolidate the scattered riprap by injecting cement grout, cement-water glass grout, or other reinforcing grouts into the pores of the riprap layer, thereby improving the overall integrity of the formation and reducing grout leakage channels. Existing grouting casing or pre-grouting processes can form temporary protective walls or consolidation rings to a certain extent, but they usually focus on the static reinforcement of the riprap body and still require subsequent drilling for hole formation. For large-diameter pile holes, if there is a lack of rigid casing to constrain the hole wall in real time, problems such as local hole collapse, diameter reduction, or unstable hole quality may still occur during drilling due to soil disturbance, loosening of rocks, or uneven grout consolidation.

[0008] The full-casing full-rotation drilling method uses a full-casing drilling rig to hold the steel casing and utilizes rotational torque and downward pressure to cut and press the casing into the formation. This method can provide rigid protection for the borehole wall during drilling and has good adaptability to riprap layers, boulder layers, and highly permeable sand layers, effectively reducing the risk of borehole collapse and stuck drill. However, if full-casing construction is used for the entire borehole depth, the equipment investment is large, the casing extension, pressing, and soil extraction cycles are long, and the construction cost is high. Especially after crossing riprap layers and major unstable sand layers, the efficiency advantage of continuing to use full-casing construction in the relatively stable lower formations is not obvious.

[0009] In summary, although existing technologies have addressed the drilling problems in rockfill formations from the perspectives of mud wall protection, casing follow-up, grouting consolidation, and full casing wall protection, the following shortcomings still exist: First, rotary drilling alone lacks effective rigid constraint on the borehole wall of the riprap layer, which easily leads to borehole collapse and drill jamming; second, impact drilling or mud wall construction causes great disturbance and low efficiency, and is prone to slurry leakage in highly permeable riprap layers. Third, simple grouting reinforcement is insufficient to maintain borehole wall stability during drilling disturbances; Fourth, full-casing full-depth construction has good stability, but its efficiency and cost are not ideal. Fifth, existing methods are still insufficient to simultaneously address the needs for borehole wall stability, soil extraction efficiency, grout leakage control, and rapid borehole formation in the underlying stable strata, both in the rock-filled and main sand layers.

[0010] Therefore, there is an urgent need to provide a combined drilling method applicable to riprap layers, riprap-sand layers, and main sand layers, so that it can form a reliable wall protection and consolidation effect in high-risk strata, and improve drilling efficiency in relatively stable lower strata, thereby solving the problems of difficult drilling, easy hole collapse, easy grout leakage, and easy drill bit jamming in riprap strata. Summary of the Invention

[0011] Based on the above description, the present invention provides a method for drilling in rock-filled formations by combining full-casing rotary drilling with rotary drilling to solve the problems of high drilling difficulty, easy hole collapse, easy grout leakage and easy drill jamming in rock-filled formations.

[0012] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for drilling in riprap formations using a combination of full-casing rotary drilling and rotary excavation, comprising the following steps: S1. Level the construction ground. If the riprap layer is exposed, backfill the riprap layer with plain soil and then level it. S2. Lay out the pile positions at the designed pile locations and set up a guide positioning structure to control the center position and verticality of the casing. S3. Install the first casing section with the grouting channel onto the full casing rotary drilling rig. The grouting channel is used to inject grout into the outside of the casing so that the center of the first casing section coincides with the center of the designed pile position. S4. The casing is clamped by the full casing rotary drilling rig, and the casing is driven to be pressed into the rock-filled formation in a rotary manner. S5. During the casing rotation and pressing process, the rotary drilling rig enters the casing to remove soil, and removes the boulders, gravel, sand and sediment inside the casing. S6. Grout is injected into the riprap pores on the outside of the casing through the grouting channel located on the outside of the casing, so that the riprap body on the outside of the casing is solidified to form an annular solidified body. S7. Control the height difference between the rotary drilling soil surface and the bottom of the casing within a preset range so that the casing forms a follow-up protective wall for the rock-filled strata during the drilling process. S8. When the casing is pressed into the predetermined depth or the clamping lower limit of the full casing rotary drilling rig, extend the next section of casing and simultaneously connect the grouting channel between adjacent casings. S9. Repeat S5 to S8 until the casing penetrates the riprap layer and the main sand layer and enters the lower stable layer. S10. The rotary drilling rig continues drilling to the designed bottom elevation of the hole, or enters the designed bearing layer to the preset depth.

[0013] Through the aforementioned technical solutions, a continuous construction process—including ground leveling, pile location layout, guiding positioning, full-casing rotary insertion, soil extraction within the casing using a rotary drill, grouting and consolidation on the outside of the casing, segmented connection, and continued rotary drilling at the bottom—creates a layered and continuously transitioning borehole system between the riprap layer, the main sand layer, and the lower stable layer. The full-casing rotation provides rigid wall protection for the riprap layer, the rotary drill's soil extraction within the casing reduces disturbance to the bare borehole, and grouting on the outside of the casing consolidates the riprap pores. This reduces the risks of borehole collapse, grout leakage, stuck drill bit, and borehole deviation, improving borehole stability and construction efficiency in complex riprap strata.

[0014] Based on the above technical solution, the present invention can be further improved as follows.

[0015] Furthermore, the grouting channel is a grouting pipe vertically fixed on the outside of the casing, the grout outlet of the grouting pipe is located 0.3m to 1.0m above the bottom end of the casing, and the grout inlet of the grouting pipe is located near the top end of the casing. The grouting pipes are evenly arranged in 3 to 8 sections along the circumference of the casing. When two adjacent sleeve sections are extended, the grouting pipes on the adjacent sleeves are connected through joints, hoses, or connecting pipe fittings. The lower sidewall of the casing is provided with an observation hole for observing the slurry return.

[0016] The above technical solution involves vertically installing grouting pipes on the outside of the casing and positioning the grout outlet near the bottom of the casing. This allows the grout to preferentially enter the vicinity of the casing cutting edge and the surrounding rock-filled pores, enabling directional consolidation of areas most prone to grout leakage, sand inrush, and loosening of boulders. Multiple grouting pipes evenly distributed along the circumference facilitate a more uniform annular diffusion range of the grout on the outside of the casing. Simultaneous connection of grouting pipes when adjacent casings are extended ensures a continuous and reliable grouting channel during segmented construction.

[0017] Furthermore, the slurry is one or more of the following: cement slurry, cement-water glass two-component slurry, quick-setting cement slurry, cement mortar, cement-based slurry containing bentonite, or cement-based slurry containing anti-dispersant. The grouting adopts a low-pressure, quantitative, intermittent, segmented grouting method, with a single segment grouting height of 1.0m to 2.0m and a grouting pressure of 0.3MPa to 1.5MPa; When obvious grout leakage or strong water permeability channels are found, the grouting pressure should be increased in stages, but the maximum grouting pressure should not exceed 4MPa. After each section of the casing is grouted, it is left to stand for 0.5 to 4 hours to allow the injected grout and the riprap outside the casing to initially solidify and form a ring-shaped solidified body before continuing the rotary drilling and casing insertion.

[0018] By employing the above technical solutions, cement grout, cement-water glass dual-liquid grout, quick-setting cement grout, cement mortar, and modified cement-based grout can be selected. The grout properties can be adjusted according to the pore size of the riprap layer, the groundwater connectivity, and the degree of grout leakage. Low-pressure, quantitative, intermittent, and segmented grouting can avoid high-pressure disturbance of the loose riprap body and reduce ineffective grout diffusion. After grouting is completed, it is allowed to set statically, allowing the grout and riprap body to form a ring-shaped solidified body, improving the integrity of the strata outside the casing and providing stable external constraints for subsequent soil extraction within the casing and continued casing insertion.

[0019] Furthermore, the height difference between the rotary drilling soil extraction surface and the bottom end of the casing is the vertical distance between the rotary drilling soil extraction surface and the bottom end of the casing, and the height difference is 0 to 3m; In the loose riprap layer where the outer side of the casing has been grouted and consolidated, the elevation difference is controlled to be 2-3m. In the riprap and sand layer where the outer side of the casing has been grouted and consolidated, the elevation difference is controlled to be 1–2.5 m; When the stratum being constructed is a highly permeable sand layer, a sand-flowing layer, or a grout-leaking layer, the bottom end of the casing should be kept flush with the surface of the rotary drilling soil, or the bottom end of the casing should be kept 0.2m to 0.5m below the surface of the rotary drilling soil, to form a casing-advanced wall protection state.

[0020] By using the above technical solutions, the height difference between the rotary drilling rig's soil extraction surface and the bottom of the casing is limited. The control methods are adjusted according to different soil extraction layers, including loose riprap layers, riprap-sand layers, highly permeable sand layers, sand-flowing layers, and grout-leaking layers. This prevents the rotary drilling rig from excessively advancing the soil extraction surface, which could lead to a loss of borehole support. For strata that have already been grouted and consolidated, a certain height difference is allowed to improve soil extraction efficiency. For highly permeable or sand-flowing strata, making the bottom of the casing level with or ahead of the soil extraction surface creates a more reliable rigid seal and follow-up wall protection, reducing the risks of borehole collapse, sand inrush, and grout leakage.

[0021] Furthermore, when the fluid level in the borehole drops, grout leakage, sand inrush, sudden increase in resistance during rotary drilling, casing deviation, or rockfall occurs, rotary drilling should be stopped. Grouting should be supplemented through the grouting channel, or the casing should be driven to continue rotating and pressing in until the bottom of the casing reaches or exceeds the surface of the rotary drilling soil before rotary drilling can be resumed.

[0022] The above technical solutions provide solutions for abnormal conditions such as decreased borehole fluid level, grout leakage, sand inrush, sudden increase in soil extraction resistance, casing deviation, and rockfall. These solutions allow for timely interruption of rotary drilling before the risk of borehole formation escalates. Supplementary grouting or continued casing rotation and pressing ensures the bottom of the casing reaches or exceeds the soil extraction surface, restoring borehole wall support and external consolidation before resuming soil extraction. This reduces the likelihood of stuck drill, borehole instability, localized collapse, and loss of borehole diameter control.

[0023] Furthermore, after penetrating the riprap layer and the main sand layer, the casing continues to enter the lower stable layer for 0.5m to 3.0m to form a lock at the bottom of the casing.

[0024] The above technical solution allows the casing to penetrate the riprap layer and the main sand layer before continuing into the lower stable layer, forming a bottom lock at the bottom of the casing in high-risk formations. This lock can isolate the transmission of adverse disturbances between the upper loose riprap layer, highly permeable sand layer, and the lower stable layer, reducing sand inrush, grout leakage, and borehole wall collapse near the bottom of the casing. This provides stable borehole opening conversion conditions for continued rotary drilling in the lower section and improves borehole verticality and diameter retention.

[0025] Furthermore, in S6, when injecting grout into the riprap pores on the outside of the casing, a staged grouting method of first sealing and then reinforcing is adopted. First, quick-setting grout or cement-water glass dual-liquid grout is injected through the grouting channel to seal the stone burr holes, grout leakage channels and highly permeable channels on the outside of the casing. After the grouting pressure rises and stabilizes, cement grout, cement mortar, cement-based grout containing bentonite, or cement-based grout containing anti-dispersant agent are injected to fill the remaining pores on the outside of the casing and form a continuous annular solidified body. The grouting cessation conditions for each grouting section include any two or more of the following: The grouting pressure reaches the preset pressure and remains stable; The grouting volume in a single section reaches the preset grouting volume; Grouting back occurs at the upper part of the casing, the orifice, the observation hole, or adjacent grouting channels; When the rotary drilling rig continues to extract soil, there will be no more continuous leakage of slurry, sand inrush, or falling rocks. The preset grouting volume is determined based on the outer diameter of the casing, the outer diameter of the designed consolidation ring, the single-section grouting height, the porosity of the riprap layer, and the grout loss coefficient.

[0026] The above technical solution employs a staged grouting method of sealing first and then reinforcing. Quick-setting grout or cement-water glass dual-liquid grout can preferentially seal large pores, grout leakage channels, and highly permeable channels. Subsequent cement-based grout then reinforces and fills the remaining pores, facilitating the formation of a continuous, dense, ring-shaped solidified body. Using grouting pressure, grout volume, grout return phenomena, and grout leakage, sand inrush, and rockfall during continued soil extraction as criteria for stopping grouting allows the grouting termination conditions to better match the site's geological conditions, reducing under-grouting or over-grouting.

[0027] Furthermore, during the construction process of S4 to S9, the casing rotary pressing, soil extraction inside the rotary drilling casing, and grouting outside the casing are controlled in a coordinated manner. The linkage control includes real-time acquisition or segmented recording of casing rotation torque, casing pressing force, casing sinking speed, rotary drilling soil extraction depth, rotary drilling soil extraction resistance, grouting pressure, grouting volume, and changes in the liquid level inside the hole. When the casing rotation torque or pressing force suddenly increases and the soil extraction resistance of the rotary drilling increases simultaneously, it is determined that there are large-diameter boulders or boulder-locking areas at the bottom of the casing or at the soil extraction surface of the rotary drilling. The casing rotation speed is reduced and the casing pressing force is increased, while the soil extraction depth of the rotary drilling is reduced in a single operation. When the liquid level in the hole drops, the grouting pressure is difficult to rise, or the grouting volume increases abnormally, it is determined that there is a grout leakage channel or a strong water permeability channel on the outside of the casing. Rotary drilling is suspended, and grouting is supplemented through the grouting channel. When the casing sinking speed tends to stabilize and the grouting pressure rises steadily, it is determined that the rock-filled body outside the casing has formed a constrained and consolidated state, and then the rotary drilling rig is resumed to extract soil from the casing and rotate the casing to press it in.

[0028] The above technical solution enables coordinated control of casing rotation torque, pressing force, sinking speed, rotary drilling depth, soil removal resistance, grouting pressure, grouting volume, and changes in the fluid level within the borehole. This allows for combined assessment of equipment operating conditions, formation resistance, and grouting effectiveness. When encountering large-diameter boulders or interlocking zones, reducing rotation speed, increasing pressing force, and decreasing single soil removal depth mitigates the risks of jamming and deviation. When encountering grout leakage or highly permeable channels, soil removal is paused and grouting is supplemented, achieving dynamic correction and closed-loop risk control throughout the drilling process.

[0029] Furthermore, in S9, the conditions for determining that the casing has penetrated the riprap layer and the main sand layer and entered the lower stable layer include any three or more of the following: The slag samples extracted by rotary drilling gradually changed from boulders, gravel, and sand to cohesive soil, dense soil layers, strongly weathered rock, or lower stable layer soil and rock. The fluctuation range of casing rotation torque and casing pressing force within the continuous preset advance range is less than the preset threshold. The casing sinking speed tends to stabilize, and there are no more sudden sinking, deviation or abnormal jamming; The liquid level inside the hole did not continue to drop, and the grouting pressure on the outside of the casing was able to be maintained stably. When removing soil from the rotary drilling casing, there will be no more continuous sand inrush, grout leakage, or falling rocks; The depth at which the bottom end of the casing enters the lower stable layer reaches 0.5m to 3.0m; If the above conditions are not met, continue with casing rotation and pressing, internal casing rotary excavation, and external casing grouting and consolidation until the requirements for the bottom locking of the casing are met.

[0030] By comprehensively considering multiple indicators such as changes in slag samples, casing rotation torque, injection force, sinking speed, in-hole liquid level, grouting pressure, sand inrush and grout leakage status, and the depth of casing penetration into the lower stable layer, the formation transition situation can be judged. This avoids relying solely on design geological data or a single drilling depth to determine whether the casing has penetrated the rock-filled layer. This method can more accurately identify the actual boundaries of the rock-filled layer, the main sand layer, and the lower stable layer, ensuring sufficient formation of the casing bottom lock, thereby reducing the risk of bottom instability and subsequent drilling caused by premature casing cessation.

[0031] Furthermore, in S10, as the rotary drilling rig continues to drill to the designed bottom elevation or enters the designed bearing layer to a preset depth, the rotary drilling parameters are adjusted according to the type of the underlying strata. When the lower strata are cohesive soil or dense sand, the rotary drilling rig adopts a layered soil removal method, and the depth of each soil removal is controlled to be 0.5m to 1.5m. When the lower strata are strongly weathered rock layers, fractured rock layers or rock remnants, rotary drilling rigs use low speed and high torque to drill, and remove the debris and sediment at the bottom of the hole by slag removal, bucket changing or bottom cleaning. If, during the drilling process, there are instances of hole wall spalling, increased sediment at the bottom of the hole, a drop in the fluid level in the hole, or abnormal changes in drilling resistance, stop further drilling and pull back the rotary drilling rig to clean the bottom of the hole. If necessary, continue to advance the casing or use the grouting channel for additional sealing. After the hole is completed, the hole depth, hole diameter, verticality, thickness of sediment at the bottom of the hole, stability of the liquid level inside the hole, and the condition of the casing bottom lock are tested. If the test results do not meet the design requirements, the hole cleaning, hole sweeping, soil replenishment, casing follow-up, or additional grouting on the outside of the casing should be carried out again until the hole quality meets the design requirements.

[0032] By adjusting the rotary drilling parameters according to the type of the underlying strata, the drilling process can be matched with the actual geological conditions. Layered soil removal is used in cohesive soil or dense sand layers to control borehole wall disturbance and bottom sediment. Low rotation speed and high torque are used in strongly weathered rock layers, fractured rock layers, or residual rock layers, combined with bottom cleaning measures, to reduce drill bit impact and bottom debris accumulation. After the hole is completed, the hole depth, diameter, verticality, sediment thickness, fluid level stability, and casing bottom lock condition are inspected to improve the reliability of hole acceptance.

[0033] Compared with the prior art, the technical solution of this application has the following beneficial technical effects: 1. This drilling method integrates full casing rotary pressing, soil extraction inside the casing by rotary drilling, and grouting consolidation on the outside of the casing into a continuous construction system, forming a composite drilling mechanism of "rigid inner wall protection, outer ring consolidation, and efficient soil extraction inside the casing". Full casing rotary pressing can overcome the problems of rock blockage and borehole instability in the riprap layer, soil extraction inside the casing by rotary drilling can improve the efficiency of slag removal and reduce the disturbance of the open borehole, and grouting on the outside of the casing can seal the riprap pores, highly permeable channels and grout leakage channels. After the three work together, the risks of borehole collapse, grout leakage, sand inrush, stuck drill, borehole deviation and borehole diameter loss in the riprap layer and the main sand layer can be significantly reduced, and the drilling quality in complex strata can be improved. 2. This drilling method, through segmented pipe connection, synchronous connection of grouting channels, elevation difference control, handling of abnormal working conditions, judgment of stratum transition, and adjustment of subsequent drilling parameters, makes the construction transition between the riprap layer, riprap-sand layer, main sand layer, and lower stable layer more controllable; the pre-set relationship between the bottom end of the casing and the soil extraction surface of the rotary drilling can avoid the rotary drilling from excessively advancing the soil extraction, causing the borehole wall to be exposed; the casing entering the lower stable layer forms a bottom lock, which can provide a stable boundary for subsequent drilling; the final borehole inspection and necessary supplementary cleaning, sweeping, supplementary soil extraction, or supplementary grouting can improve the controllability of borehole depth, diameter, verticality, and bottom quality. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall construction process of the present invention; Figure 2This is a flowchart illustrating the overall construction process of Embodiment 1 of the present invention; Figure 3 This is a flow chart of the casing rotary pressing-in-soil extraction-outside grouting cycle of Embodiment 1 of the present invention; Figure 4 This is a flowchart of the graded grouting process on the outside of the casing in Embodiment 2 of the present invention; Figure 5 This is a flowchart illustrating the height difference control between the rotary drilling soil extraction surface and the bottom of the casing in Embodiment 2 of the present invention. Figure 6 This is a flowchart of the abnormal operating condition linkage control in Embodiment 2 of the present invention; Figure 7 This is a flowchart illustrating the casing penetration determination and casing bottom locking process in Embodiment 2 of the present invention. Figure 8 This is a flowchart of the lower drilling and final hole detection process in Embodiment 2 of the present invention; Figure 9 This is a schematic diagram of the casing and grouting pipe of the present invention.

[0035] Attached reference numerals: 1. Sleeve; 2. Grouting pipe; 3. Observation hole. Detailed Implementation

[0036] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Example

[0038] refer to Figures 1-3 A method for drilling holes in riprap formations using a combination of full-casing rotary drilling and rotary excavation includes the following steps: S1. Level the construction ground. If the riprap layer is exposed, backfill the riprap layer with plain soil and then level it. The thickness of the backfilled plain soil layer shall not be less than 20cm. S2. Lay out the pile positions at the designed pile locations and set up a guide positioning structure to control the center position and verticality of the casing. S3. Install the first casing section with the grouting channel onto the full casing rotary drilling rig. The grouting channel is used to inject grout into the outside of the casing so that the center of the first casing section coincides with the center of the designed pile position. S4. The casing is clamped by the full casing rotary drilling rig, and the casing is driven to be pressed into the rock-filled formation in a rotary manner. S5. During the casing rotation and pressing process, the rotary drilling rig enters the casing to remove soil, and removes the boulders, gravel, sand and sediment inside the casing. S6. Grout is injected into the riprap pores on the outside of the casing through the grouting channel located on the outside of the casing, so that the riprap body on the outside of the casing is solidified to form an annular solidified body. S7. Control the height difference between the rotary drilling soil surface and the bottom of the casing within a preset range so that the casing forms a follow-up protective wall for the rock-filled strata during the drilling process. S8. When the casing is pressed into the predetermined depth or the clamping lower limit of the full casing rotary drilling rig, extend the next section of casing and simultaneously connect the grouting channel between adjacent casings. S9. Repeat S5 to S8 until the casing penetrates the riprap layer and the main sand layer and enters the lower stable layer. S10. The rotary drilling rig continues drilling to the designed bottom elevation of the hole, or enters the designed bearing layer to the preset depth.

[0039] Furthermore, after penetrating the riprap layer and the main sand layer, the casing continues into the lower stable layer for 0.5m to 3.0m to form a lock at the bottom of the casing.

[0040] As a preferred option: Reference Figure 9 The grouting channel is a vertically fixed grouting pipe installed on the outside of the casing. The grout outlet of the grouting pipe is located 0.3m to 1.0m above the bottom of the casing, and the grout inlet of the grouting pipe is located near the top of the casing. There are 3 to 8 grouting pipes evenly arranged along the circumference of the casing. When two adjacent casing sections are extended, the grouting pipes on the adjacent casings are connected through joints, hoses, or connecting fittings. The grouting pipes are stainless steel pipes and are welded to the outside of the casing using a full welding process.

[0041] The lower sidewall of the casing is provided with an observation hole for observing the slurry return. The observation hole is a circular through hole, and a camera can be inserted close to the observation hole to observe the slurry return.

[0042] Preferably, the grout is one or more of the following: cement grout, cement-water glass two-component grout, quick-setting cement grout, cement mortar, cement-based grout containing bentonite, or cement-based grout containing anti-dispersant agent. The grouting adopts a low-pressure, quantitative, intermittent, segmented grouting method, with a single segment grouting height of 1.0m to 2.0m and a grouting pressure of 0.3MPa to 1.5MPa; When obvious grout leakage or strong water permeability channels are found, the grouting pressure should be increased in stages, but the maximum grouting pressure should not exceed 4MPa. After each section of the casing is grouted, it is left to stand for 0.5 to 4 hours to allow the injected grout and the riprap outside the casing to initially solidify and form a ring-shaped solidified body before continuing the rotary drilling and casing insertion.

[0043] Preferably, the height difference between the rotary drilling soil extraction surface and the bottom end of the casing is the vertical distance between the rotary drilling soil extraction surface and the bottom end of the casing, and the height difference is 0 to 3m. In the loose riprap layer where the grouting consolidation on the outside of the casing has been completed, the height difference is controlled at 2 to 3 meters. In the riprap and sand layer where the outer side of the casing has been grouted and consolidated, the elevation difference is controlled to be 1–2.5 m; When the stratum being constructed is a highly permeable sand layer, a sand-flowing layer, or a grout-leaking layer, the bottom end of the casing should be kept flush with the surface of the rotary drilling soil, or the bottom end of the casing should be kept 0.2m to 0.5m below the surface of the rotary drilling soil, to form a casing-advanced wall protection state.

[0044] Furthermore, when the fluid level in the borehole drops, grout leakage, sand inrush, sudden increase in resistance during rotary drilling, casing deviation, or rockfall occurs, rotary drilling should be stopped. Grouting should be supplemented through the grouting channel, or the casing should be driven to continue rotating and pressing in until the bottom of the casing reaches or exceeds the surface of the rotary drilling soil before resuming rotary drilling.

[0045] Preferably, in S6, when injecting grout into the riprap pores on the outside of the casing, a staged grouting method of first sealing and then reinforcing is adopted. First, quick-setting grout or cement-water glass dual-liquid grout is injected through the grouting channel to seal the stone burr holes, grout leakage channels and highly permeable channels on the outside of the casing. After the grouting pressure rises and stabilizes, cement grout, cement mortar, cement-based grout containing bentonite, or cement-based grout containing anti-dispersant agent are injected to fill the remaining pores on the outside of the casing and form a continuous annular solidified body. The grouting cessation conditions for each grouting section include any two or more of the following: ① The grouting pressure reaches the preset pressure and remains stable; ② The grouting volume of a single section reaches the preset grouting volume; ③ Backflow of grout occurs in the upper part of the casing, the borehole, the observation hole, or the adjacent grouting channel; ④ When the rotary drilling rig continues to extract soil, there is no longer continuous leakage of grout, sand inrush, or rockfall. The preset grouting volume is determined based on the outer diameter of the casing, the outer diameter of the designed solidified ring, the grouting height of a single section, the porosity of the riprap layer, and the grout loss coefficient.

[0046] As a preferred option, during the construction process of S4 to S9, the casing rotary pressing, soil extraction inside the rotary drilling casing, and grouting outside the casing are controlled in a coordinated manner. The linkage control includes real-time acquisition or segmented recording of casing rotation torque, casing pressing force, casing sinking speed, rotary drilling soil extraction depth, rotary drilling soil extraction resistance, grouting pressure, grouting volume, and changes in the liquid level in the borehole. When the casing rotation torque or pressing force suddenly increases and the soil extraction resistance of the rotary drilling increases simultaneously, it is determined that there are large-diameter boulders or boulder-locking areas at the bottom of the casing or at the soil extraction surface of the rotary drilling. The casing rotation speed is reduced and the casing pressing force is increased, while the soil extraction depth of the rotary drilling is reduced in a single operation. When the liquid level in the hole drops, the grouting pressure is difficult to rise, or the grouting volume increases abnormally, it is determined that there is a grout leakage channel or a strong water permeability channel on the outside of the casing. Rotary drilling is suspended, and grouting is supplemented through the grouting channel. When the casing sinking speed tends to stabilize and the grouting pressure rises steadily, it is determined that the rock-filled body outside the casing has formed a constrained and consolidated state, and then the rotary drilling rig is resumed to extract soil from the casing and rotate the casing to press it in.

[0047] Preferably, in S9, the conditions for determining that the casing has penetrated the riprap layer and the main sand layer and entered the lower stable layer include any three or more of the following: The slag samples extracted by rotary drilling gradually changed from boulders, gravel, and sand to cohesive soil, dense soil layers, strongly weathered rock, or lower stable layer soil and rock. The fluctuation range of casing rotation torque and casing pressing force within the continuous preset advance range is less than the preset threshold. The casing sinking speed tends to stabilize, and there are no more sudden sinking, deviation or abnormal jamming; The liquid level inside the hole did not continue to drop, and the grouting pressure on the outside of the casing was able to be maintained stably. When removing soil from the rotary drilling casing, there will be no more continuous sand inrush, grout leakage, or falling rocks; The depth at which the bottom end of the casing enters the lower stable layer reaches 0.5m to 3.0m; If the above conditions are not met, continue with casing rotation and pressing, internal casing rotary excavation, and external casing grouting and consolidation until the requirements for the bottom locking of the casing are met.

[0048] Preferably, in S10, as the rotary drilling rig continues to drill to the designed bottom elevation or enters the designed bearing layer to the preset depth, the rotary drilling parameters are adjusted according to the type of the underlying strata. When the lower strata are cohesive soil or dense sand, the rotary drilling rig adopts a layered soil removal method, and the depth of each soil removal is controlled to be 0.5m to 1.5m. When the lower strata are strongly weathered rock layers, fractured rock layers or rock remnants, rotary drilling rigs use low speed and high torque to drill, and remove the debris and sediment at the bottom of the hole by slag removal, bucket changing or bottom cleaning. If, during the drilling process, there are instances of hole wall spalling, increased sediment at the bottom of the hole, a drop in the fluid level in the hole, or abnormal changes in drilling resistance, stop further drilling and pull back the rotary drilling rig to clean the bottom of the hole. If necessary, continue to advance the casing or use the grouting channel for additional sealing. After the hole is completed, the hole depth, hole diameter, verticality, thickness of sediment at the bottom of the hole, stability of the liquid level inside the hole, and the condition of the casing bottom lock are tested. If the test results do not meet the design requirements, the hole cleaning, hole sweeping, soil replenishment, casing follow-up, or additional grouting on the outside of the casing should be carried out again until the hole quality meets the design requirements. Example

[0049] refer to Figures 4-8 A method for constructing boreholes in riprap strata using a combination of full-casing rotary drilling and rotary drilling was developed and applied to the construction of pile holes in a complex, water-adjacent strata. The construction area consists of exposed riprap layers in the upper part, loose riprap layers, riprap-sand layers, and a main sand layer in the middle, and cohesive soil layers, dense sand layers, and locally strongly weathered rock layers in the lower part. The riprap layer is approximately 6m to 16m thick, with boulders ranging from 80mm to 600mm in diameter, and locally exceeding 800mm in diameter. The main sand layer is approximately 2m to 6m thick, and there is some communication between the groundwater and adjacent water bodies. The designed borehole diameter is 1.2m, and the designed borehole depth is 28m. The casing is required to penetrate the riprap layer and the main sand layer before entering the lower stable layer, and then the rotary drilling rig continues drilling to the designed borehole bottom elevation.

[0050] Before construction, the construction area is cleared, removing surface debris, loose soil, and large rocks that may affect equipment positioning. If the riprap layer is exposed at the designed pile location, plain soil is backfilled and leveled on the exposed riprap layer, with a backfill thickness of 0.3m to 0.8m. After compaction in layers, a working surface is formed. Steel plates or crushed stone cushions are laid in the walking area of ​​the full-casing rotary drilling rig and rotary drilling machine to control the local settlement difference in the equipment positioning area within 20mm and the flatness of the construction ground within ±30mm. This ground treatment prevents the full-casing rotary drilling rig from tilting during the initial pressing of the casing, ensuring the foundation for subsequent verticality control of the borehole.

[0051] Subsequently, pile positions are laid out at the designed pile locations; the center of the designed pile position is determined using a total station, and no fewer than four positioning control points are set within a range of 0.5m to 1.5m around the pile position. The center of the designed pile position is verified by using a crosshair. After the pile position is laid out, a guide positioning structure is set up to control the center position and verticality of the casing. The guide positioning structure can be a steel guide frame, a pre-drilled hole in a concrete guide wall, or a steel positioning ring. In this embodiment, a steel guide frame is used, and the diameter of the center hole of the guide frame is 20mm to 50mm larger than the outer diameter of the casing. After the first section of casing is in place, the deviation between the center of the casing and the center of the designed pile position is controlled within 20mm, and the initial verticality deviation of the casing is controlled within 1 / 200.

[0052] The first section of the casing is a steel cylindrical casing with an outer diameter of 1.35m and a single section length of 3m. A grouting channel is provided on the outside of the first section of the casing for grouting to the outside of the casing. In this embodiment, the grouting channel is specifically a grouting pipe vertically fixed on the outside of the casing; six grouting pipes are evenly arranged along the circumference of the casing, or three to eight pipes can be arranged according to the casing diameter, the porosity of the riprap, and the grouting coverage requirements; the grout inlet of each grouting pipe is located near the upper end of the casing and is connected to the grouting pump, pressure gauge, and flow meter through a grouting hose; the grout outlet of each grouting pipe is located 0.5m above the bottom end of the casing, or the grout outlet can be located within the range of 0.3m to 1.0m above the bottom end of the casing; an observation hole for observing the grout return is provided on the lower side wall of the casing, the observation hole is located 0.2m above the bottom end of the casing, and the hole diameter is 20mm to 40mm; an anti-clogging baffle is provided on the outside of the observation hole to reduce the blockage of the observation hole by boulders, sand, or cuttings.

[0053] The first casing section, equipped with a grouting channel, is installed on the full-casing rotary drilling rig, ensuring its center coincides with the designed pile location center. After the full-casing rotary drilling rig clamps the first casing section, it drives the casing to be driven into the rock-filled strata in a rotary manner. During the initial driving stage, a low-speed, high-torque method is used, with the casing rotation speed controlled between 0.5 r / min and 2.0 r / min. The driving force is gradually increased according to the casing's sinking speed and rotational resistance. During the casing's rotary driving process, the casing's verticality, rotational torque, driving force, and sinking speed are monitored in real time. When the casing encounters large-diameter boulders that cause an increase in rotational resistance, the casing rotation speed is first reduced, and then the driving force is gradually increased to allow the casing's cutting edge to shear, squeeze, or disturb and break the boulders, preventing sudden casing deflection or jamming.

[0054] During the casing rotary pressing process, the rotary drilling rig enters the casing to extract soil. The outer diameter of the rotary drilling rig's bucket is smaller than the inner diameter of the casing, and a gap of 50mm to 150mm is reserved between the outer side of the bucket and the inner wall of the casing to prevent the bucket from scraping against the inner wall. The rotary drilling rig removes boulders, gravel, sand, and sediment from inside the casing. For loose riprap layers, the single extraction depth of the rotary drilling rig is controlled at 0.5m to 1.0m; for riprap mixed with sand layers, the single extraction depth is controlled at 0.5m to 1.5m; when encountering concentrated boulders, significantly increased bucket resistance, or a large amount of sediment in the borehole, the single extraction depth is reduced to 0.3m to 0.8m. After each extraction, the condition of the sediment sample is recorded, including the particle size of the boulders, the sand content, the water content, whether sand inrush occurred, and whether there was any abnormal loss of slurry or groundwater. The lowest extraction interface formed after the rotary drilling rig completes one extraction is the rotary drilling extraction surface.

[0055] After the casing is pressed into a grouting section depth, grout is injected into the riprap pores on the outside of the casing through the grouting channel located on the outside of the casing, so that the riprap on the outside of the casing solidifies to form a ring-shaped solidified body. The grouting adopts a low-pressure, quantitative, intermittent, segmented grouting method, with a single-segment grouting height of 1.0m to 2.0m. In this embodiment, the single-segment grouting height is 1.5m. The grouting pressure is usually controlled at 0.3MPa to 1.5MPa. When obvious grout leakage or strong water permeability channels occur, the grouting pressure is increased by a graded pressure increase method, but the maximum grouting pressure does not exceed 4MPa.

[0056] The grout is selected based on the geological conditions, using one or more of the following: cement grout, cement-water glass double-liquid grout, quick-setting cement grout, cement mortar, cement-based grout containing bentonite, or cement-based grout containing anti-dispersant. For ordinary loose riprap layers, cement grout with a water-cement ratio of 0.8:1 to 1.2:1 is used. For borehole sections with significant grout leakage, strong groundwater connectivity, or difficulty in increasing grouting pressure, cement-water glass double-liquid grout or quick-setting cement grout is used for sealing first, followed by reinforcement with cement grout, cement mortar, or cement-based grout containing bentonite. The gel time of cement-water glass double-liquid grout can be controlled between 30s and 180s to meet the sealing requirements of highly permeable channels or large-pore riprap layers. In cement-based grout containing bentonite, the bentonite content can be 3% to 8% of the cement mass. In cement-based grout containing anti-dispersant, the anti-dispersant content is determined based on the groundwater flow rate and grout loss.

[0057] The pre-set grouting volume for a single section is determined by the following formula: ;in, The preset grouting volume for a single section is in m³. The outer diameter of the consolidation ring is specified in meters (m). The outer diameter of the casing is in meters (m). This refers to the grouting height in a single section, expressed in meters (m). The porosity of the rubble layer is taken as 0.25–0.45; The slurry loss coefficient is taken as 1.2 to 2.0. In this embodiment, the outer diameter of the casing... The outer diameter of the consolidation ring is 1.35m. The depth is 1.95m, the single-section grouting height is 1.5m, and the porosity of the riprap layer is... Take 0.35 as the slurry loss coefficient. If we take 1.4, then the preset grouting volume for a single section is approximately 1.1m³ to 1.3m³.

[0058] When injecting grout into the riprap pores on the outside of the casing, a staged grouting method of sealing first and then reinforcing is adopted. First, a quick-setting grout or a cement-water glass dual-liquid grout is injected through the grouting channel to seal the riprap pores, leakage channels, and highly permeable channels on the outside of the casing. After the grouting pressure rises and stabilizes, cement grout, cement mortar, cement-based grout containing bentonite, or cement-based grout containing anti-dispersant agents are injected to fill the remaining pores on the outside of the casing and form a continuous annular solidified body. The grouting cessation conditions for each grouting section include any two or more of the following: the grouting pressure reaches the preset pressure and remains stable, for example, the grouting pressure reaches 0.8MPa~1.5MPa and remains stable for 3min~5min; the grouting volume in a single section reaches the preset grouting volume, for example, the actual grouting volume reaches the calculated grouting volume. The grout level is 0.9 to 1.2 times higher than normal; grout return occurs at the upper part of the casing, the borehole opening, the observation hole, or adjacent grouting channels; continuous grout leakage, sand inrush, or rockfall no longer occur when the rotary drilling rig continues to extract soil. After stopping grouting, inject clean water into the grouting channel to flush it, in order to prevent the grout from solidifying and clogging the grouting pipe.

[0059] After grouting the outer side of each section of the casing is completed, allow it to stand for 0.5 to 4 hours to allow the injected grout and the riprap outside the casing to initially set and form a ring-shaped solidified body before continuing rotary drilling for soil removal inside the casing and casing rotation for pressing in. For quick-setting grouts, the standing time can be 0.5 to 1.0 hour; for cement-water glass two-component grouts, the standing time can be 1 to 2 hours; and for ordinary cement grout or cement mortar, the standing time can be 2 to 4 hours. During the standing period, monitor the stability of the liquid level in the borehole, the drop in grouting pressure, and the grout return around the casing to determine whether the ring-shaped solidified body meets the conditions for continuing construction.

[0060] During the drilling process, the height difference between the rotary drilling surface and the bottom of the casing is controlled within a preset range, so that the casing forms a protective wall against the rockfill strata during drilling. The height difference between the rotary drilling surface and the bottom of the casing is defined by the following formula: ; in, The elevation difference between the soil surface obtained by rotary drilling and the bottom end of the casing, in meters; This refers to the depth of soil extraction by rotary drilling, expressed in meters (m). This represents the depth of the casing bottom, in meters (m); the depth direction is downwards from the ground surface. A positive value indicates that the rotary drilling surface is below the casing bottom; a negative value indicates that the rotary drilling surface is flush with the casing bottom; a negative value indicates that the rotary drilling surface is level with the casing bottom. When the value is negative, it indicates that the bottom of the casing is deeper than the soil surface extracted by rotary drilling, forming a casing-advanced wall protection state.

[0061] In the loose riprap layer where the outer side of the casing has been grouted and consolidated The depth should be controlled to 2m-3m; in the grouted sand layer outside the casing that has been grouted and consolidated. The depth should be controlled between 1m and 2.5m; when the construction stratum is a highly permeable sand layer, a sand-flowing layer, or a grout-leaking layer, the depth should be controlled... or control This means that the bottom of the casing is 0.2m to 0.5m below the surface of the rotary drilling, forming a casing-advanced wall protection state. The depth of the bottom of the casing can be obtained by subtracting the exposed length above the ground from the cumulative length of the casing. The depth of the surface of the rotary drilling can be obtained by the rotary drilling rod scale, depth sensor, or hole depth measuring device.

[0062] If, during construction, the borehole fluid level drops, grout leakage, sand inrush, a sudden increase in rotary drilling resistance, casing deviation, or rockfall occurs, rotary drilling should be stopped. If the abnormality is manifested as a drop in borehole fluid level, difficulty in increasing grouting pressure, or an abnormal increase in grouting volume, it is determined that there is a grout leakage channel or a highly permeable channel on the outside of the casing. Supplementary grouting should be carried out through the grouting channel first. During supplementary grouting, quick-setting grout or cement-water glass dual-liquid grout should be used for sealing first, followed by reinforcement with cement-based grout. If the abnormality is manifested as a sudden increase in rotary drilling resistance, rockfall, or jamming near the bottom of the casing, the casing should be driven to continue rotating and pressing in until the bottom of the casing reaches or exceeds the rotary drilling surface before resuming rotary drilling.

[0063] Linked control is implemented during casing rotation and pressing, soil extraction inside the casing by rotary drilling, and grouting on the outside of the casing. This linked control includes real-time acquisition or segmented recording of casing rotation torque, casing pressing force, casing sinking speed, rotary drilling soil extraction depth, rotary drilling soil extraction resistance, grouting pressure, grouting volume, and changes in the fluid level inside the borehole. When the casing rotation torque or pressing force increases by more than 30% compared to the average value of the previous stable construction section, and the rotary drilling soil extraction resistance increases by more than 30% simultaneously, it is determined that there are large-diameter boulders or boulder-locking zones at the bottom of the casing or the rotary drilling soil extraction surface. The casing rotation speed is reduced, and the casing pressing force is increased, while the single soil extraction depth of the rotary drilling is reduced. When the fluid level inside the borehole drops by more than 0.3m within 10 minutes, or the grouting volume reaches 1.2 times the preset grouting volume but the grouting pressure still cannot rise, it is determined that there is a grout leakage channel or a highly permeable channel on the outside of the casing. Rotary drilling soil extraction is suspended, and supplementary grouting is carried out through the grouting channel. When the casing sinking speed tends to stabilize and the grouting pressure rises steadily, it is determined that the rock-filled body outside the casing has formed a constrained and consolidated state, and then the rotary drilling rig is resumed to extract soil from the casing and rotate the casing to press it in.

[0064] To facilitate quantitative on-site control, a linkage risk assessment coefficient can be set. : ; in, This is the abnormal torque coefficient of the casing rotation. This is the abnormal coefficient of casing infeed force. This represents the abnormal coefficient of soil extraction resistance in rotary drilling. This represents the grouting pressure anomaly coefficient. This refers to the fluid level anomaly coefficient within the orifice; each anomaly coefficient can take values ​​of 0 or 1; it is 0 when the corresponding parameter does not exceed the anomaly threshold, and 1 when the corresponding parameter exceeds the anomaly threshold; when... When this occurs, an early warning system is activated, the soil extraction depth is reduced, and the position of the bottom of the casing is rechecked; when When necessary, rotary drilling should be suspended to remove soil, and casing should be installed, supplementary grouting should be performed, or the bottom of the hole should be cleaned.

[0065] When the casing is driven to the predetermined depth or the clamping lower limit of the full-casing rotary drilling rig, extend the next casing section and simultaneously connect the grouting channels between adjacent casings. Before extending the casing, stop casing driving and rotary drilling for soil removal, hoist the next casing section, and connect it to the lower casing using flanges, welding, or inner and outer sleeves. After the adjacent casings are connected, the grouting pipes on the adjacent casings are connected through joints, hoses, or connecting fittings. After the grouting channels are connected, test them with clean water at a pressure of 0.2MPa to 0.5MPa. After confirming that the grouting channels are connected and there is no obvious leakage, continue construction.

[0066] Repeat the steps of soil extraction inside the rotary drilling casing, grouting consolidation on the outside of the casing, casing rotation and pressing in, and casing extension until the casing penetrates the riprap layer and the main sand layer and enters the lower stable layer. When it is determined that the casing has penetrated the riprap layer and the main sand layer and entered the lower stable layer, it is based not only on the design geological data, but also on a number of on-site indicators during the construction process. The judgment criteria include any three or more of the following: the cuttings sample taken out by rotary drilling gradually changes from boulders, gravel, and sand to cohesive soil, dense soil layer, strongly weathered rock, or lower stable layer soil and rock; the casing rotation torque and casing pressing force fluctuate less than the preset threshold within a continuous preset advance range, for example, the fluctuation range of casing rotation torque is less than 15% and the fluctuation range of casing pressing force is less than 20% within a continuous advance of 1.0m to 2.0m; the casing sinking speed tends to be stable, and there is no longer any sudden sinking, deviation, or abnormal jamming; the fluid level in the borehole does not continue to drop, and the grouting pressure on the outside of the casing can be maintained stably; when the rotary drilling casing is used for soil extraction, there is no longer any continuous sand inrush, grout leakage, or boulders falling; the depth of the bottom end of the casing entering the lower stable layer reaches 0.5m to 3.0m.

[0067] If any three or more of the above conditions are not met, continue with casing rotary pressing, internal rotary drilling for soil removal, and external grouting consolidation until the casing bottom lock-in requirement is met. In this embodiment, after penetrating the riprap layer and the main sand layer, the casing continues to enter the lower stable layer by 1.0m to 1.5m; in other working conditions, the depth of the casing entering the lower stable layer can be controlled to be 0.5m to 3.0m to form the casing bottom lock-in. After the casing bottom lock-in is formed, loose particles, groundwater, and sand in the upper riprap layer and the main sand layer are less likely to flow back into the hole from the bottom of the casing, which is beneficial to maintaining the stability of the hole wall during subsequent drilling. After the casing bottom lock-in is formed, the rotary drilling rig continues to drill to the designed bottom elevation or enter the designed bearing layer to the preset depth. During the continued drilling process, the drilling parameters are adjusted according to the type of the underlying strata. When the underlying strata are cohesive soil or dense sand, the rotary drilling rig adopts a layered soil removal method, with a single soil removal depth controlled at 0.5m to 1.5m. If the borehole wall is stable, the fluid level inside the borehole is stable, and the soil removal resistance changes gradually, the single soil removal depth can be appropriately increased. If borehole wall spalling, a drop in the fluid level inside the borehole, or abnormal drilling resistance occurs, the single soil removal depth is reduced, and the casing bottom lock status is checked. When the underlying strata are strongly weathered rock, fractured rock, or residual rock layers, the rotary drilling rig adopts a low-speed, high-torque drilling method, and removes debris and sediment from the bottom of the borehole by slag removal, bucket changing, or bottom cleaning. The drill bucket can be a core drill, a cutting tooth drill, a sand slag bucket, or a bottom cleaning bucket. During drilling, impact operations should be minimized to avoid disturbing the strata near the bottom of the casing.

[0068] If, during drilling, issues such as hole wall spalling, increased sediment at the bottom of the hole, a drop in the fluid level inside the hole, or abnormal changes in drilling resistance occur, stop further drilling and retrieve the rotary drilling rig for bottom cleaning. If necessary, continue advancing the casing or re-seal the hole through the grouting channel before resuming drilling. After the hole is completed, inspect the hole depth, diameter, verticality, thickness of sediment at the bottom of the hole, stability of the fluid level inside the hole, and the condition of the casing bottom lock. The hole depth should reach the designed bottom elevation or enter the designed bearing layer to the preset depth; the hole diameter should meet the designed hole diameter requirements; the verticality should meet the design or specification requirements; the thickness of sediment at the bottom of the hole should be controlled according to the project type, for example, within 50mm to 100mm; the fluid level inside the hole should not continuously drop; the casing bottom lock should remain stable; if the inspection results do not meet the design requirements, repeat the hole cleaning, sweeping, soil removal, casing advancement, or additional grouting on the outside of the casing until the hole quality meets the design requirements.

[0069] After the above construction steps, continuous and stable pile holes can be formed in the riprap layer, riprap-sand layer, main sand layer and lower stable layer. This construction method achieves rigid inner wall protection by rotating and pressing in the full casing, improves soil removal and slag removal efficiency by removing soil inside the casing by rotary drilling, forms a ring-shaped solidified body by grouting on the outside of the casing to seal the riprap pores and highly permeable channels, and achieves full-process quality control of the hole formation process through elevation difference control, abnormal handling, linkage control, casing extension, casing bottom locking and final hole inspection.

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for drilling in riprap formations using a combination of full-casing rotary drilling and rotary excavation, characterized in that, Includes the following steps: S1. Level the construction ground. If the riprap layer is exposed, backfill the riprap layer with plain soil and then level it. S2. Lay out the pile positions at the designed pile locations and set up a guide positioning structure to control the center position and verticality of the casing. S3. Install the first casing section with the grouting channel onto the full casing rotary drilling rig. The grouting channel is used to inject grout into the outside of the casing so that the center of the first casing section coincides with the center of the designed pile position. S4. The casing is clamped by the full casing rotary drilling rig, and the casing is driven to be pressed into the rock-filled formation in a rotary manner. S5. During the casing rotation and pressing process, the rotary drilling rig enters the casing to remove soil, and removes the boulders, gravel, sand and sediment inside the casing. S6. Grout is injected into the riprap pores on the outside of the casing through the grouting channel located on the outside of the casing, so that the riprap body on the outside of the casing is solidified to form an annular solidified body. S7. Control the height difference between the rotary drilling soil surface and the bottom of the casing within a preset range so that the casing forms a follow-up protective wall for the rock-filled strata during the drilling process. S8. When the casing is pressed into the predetermined depth or the clamping lower limit of the full casing rotary drilling rig, extend the next section of casing and simultaneously connect the grouting channel between adjacent casings. S9. Repeat S5 to S8 until the casing penetrates the riprap layer and the main sand layer and enters the lower stable layer. S10. The rotary drilling rig continues drilling to the designed bottom elevation of the hole, or enters the designed bearing layer to the preset depth.

2. The method for constructing boreholes in riprap formations using a combination of rotary casing and rotary drilling, as described in claim 1, is characterized in that... The grouting channel is a grouting pipe that is vertically fixed on the outside of the casing. The grout outlet of the grouting pipe is located 0.3m to 1.0m above the bottom of the casing, and the grout inlet of the grouting pipe is located near the top of the casing. The grouting pipes are evenly arranged in 3 to 8 sections along the circumference of the casing. When two adjacent sleeve sections are extended, the grouting pipes on the adjacent sleeves are connected through joints, hoses, or connecting pipe fittings. The lower sidewall of the casing is provided with an observation hole for observing the slurry return.

3. The method for constructing boreholes in riprap formations using a combination of rotary casing and rotary drilling, as described in claim 1, is characterized in that... The slurry is one or more of the following: cement slurry, cement-water glass two-component slurry, quick-setting cement slurry, cement mortar, cement-based slurry containing bentonite, or cement-based slurry containing anti-dispersant. The grouting adopts a low-pressure, quantitative, intermittent, segmented grouting method, with a single segment grouting height of 1.0m to 2.0m and a grouting pressure of 0.3MPa to 1.5MPa; When obvious grout leakage or strong water permeability channels are found, the grouting pressure should be increased in stages, but the maximum grouting pressure should not exceed 4MPa. After each section of the casing is grouted, it is left to stand for 0.5 to 4 hours to allow the injected grout and the riprap outside the casing to initially solidify and form a ring-shaped solidified body before continuing the rotary drilling and casing insertion.

4. The method for constructing boreholes in riprap formations using a combination of rotary casing and rotary drilling, as described in claim 1, is characterized in that... The height difference between the rotary drilling soil extraction surface and the bottom end of the casing is the vertical distance between the rotary drilling soil extraction surface and the bottom end of the casing, and the height difference is 0 to 3m. In the loose riprap layer where the outer side of the casing has been grouted and consolidated, the elevation difference is controlled to be 2-3m. In the riprap and sand layer where the outer side of the casing has been grouted and consolidated, the elevation difference is controlled to be 1–2.5 m; When the stratum being constructed is a highly permeable sand layer, a sand-flowing layer, or a grout-leaking layer, the bottom end of the casing should be kept flush with the surface of the rotary drilling soil, or the bottom end of the casing should be kept 0.2m to 0.5m below the surface of the rotary drilling soil, to form a casing-advanced wall protection state.

5. The method for constructing boreholes in riprap formations using a combination of rotary casing and rotary drilling, as described in claim 4, is characterized in that... When the fluid level in the borehole drops, grout leakage, sand inrush, sudden increase in resistance during rotary drilling, casing deviation, or rockfall occurs, stop rotary drilling. First, supplement grouting through the grouting channel, or drive the casing to continue rotating and pressing it in until the bottom of the casing reaches or exceeds the surface of the rotary drilling soil before resuming rotary drilling.

6. The method for constructing boreholes in riprap formations using a combination of rotary casing and rotary drilling, as described in claim 1, is characterized in that... After penetrating the riprap layer and the main sand layer, the casing continues into the lower stable layer for 0.5m to 3.0m to form a lock at the bottom of the casing.

7. The method for constructing boreholes in riprap formations using a combination of rotary casing and rotary drilling, as described in claim 1, is characterized in that... In S6, when injecting grout into the boulders on the outside of the casing, a staged grouting method of first sealing and then reinforcing is adopted. First, quick-setting grout or cement-water glass dual-liquid grout is injected through the grouting channel to seal the stone burr holes, grout leakage channels and highly permeable channels on the outside of the casing. After the grouting pressure rises and stabilizes, cement grout, cement mortar, cement-based grout containing bentonite, or cement-based grout containing anti-dispersant agent are injected to fill the remaining pores on the outside of the casing and form a continuous annular solidified body. The grouting cessation conditions for each grouting section include any two or more of the following: The grouting pressure reaches the preset pressure and remains stable; The grouting volume in a single section reaches the preset grouting volume; Grouting back occurs at the upper part of the casing, the orifice, the observation hole, or adjacent grouting channels; When the rotary drilling rig continues to extract soil, there will be no more continuous leakage of slurry, sand inrush, or falling rocks. The preset grouting volume is determined based on the outer diameter of the casing, the outer diameter of the designed consolidation ring, the single-section grouting height, the porosity of the riprap layer, and the grout loss coefficient.

8. The method for constructing boreholes in riprap formations using a combination of rotary casing and rotary drilling, as described in claim 1, is characterized in that... During the construction process of S4 to S9, the casing rotary pressing, soil extraction inside the rotary drilling casing, and grouting outside the casing are controlled in a coordinated manner. The linkage control includes real-time acquisition or segmented recording of casing rotation torque, casing pressing force, casing sinking speed, rotary drilling soil extraction depth, rotary drilling soil extraction resistance, grouting pressure, grouting volume, and changes in the liquid level inside the hole. When the casing rotation torque or pressing force suddenly increases and the soil extraction resistance of the rotary drilling increases simultaneously, it is determined that there are large-diameter boulders or boulder-locking areas at the bottom of the casing or at the soil extraction surface of the rotary drilling. The casing rotation speed is reduced and the casing pressing force is increased, while the soil extraction depth of the rotary drilling is reduced in a single operation. When the liquid level in the hole drops, the grouting pressure is difficult to rise, or the grouting volume increases abnormally, it is determined that there is a grout leakage channel or a strong water permeability channel on the outside of the casing. Rotary drilling is suspended, and grouting is supplemented through the grouting channel. When the casing sinking speed tends to stabilize and the grouting pressure rises steadily, it is determined that the rock-filled body outside the casing has formed a constrained and consolidated state, and then the rotary drilling rig is resumed to extract soil from the casing and rotate the casing to press it in.

9. A method for constructing boreholes in riprap formations using a combination of rotary casing and rotary drilling, as described in any one of claims 1-8, characterized in that... In S9, the conditions for determining that the casing has penetrated the riprap layer and the main sand layer and entered the lower stable layer include any three or more of the following: The slag samples extracted by rotary drilling gradually changed from boulders, gravel, and sand to cohesive soil, dense soil layers, strongly weathered rock, or lower stable layer soil and rock. The fluctuation range of casing rotation torque and casing pressing force within the continuous preset advance range is less than the preset threshold. The casing sinking speed tends to stabilize, and there are no more sudden sinking, deviation or abnormal jamming; The liquid level inside the hole did not continue to drop, and the grouting pressure on the outside of the casing was able to be maintained stably. When removing soil from the rotary drilling casing, there will be no more continuous sand inrush, grout leakage, or falling rocks; The depth at which the bottom end of the casing enters the lower stable layer reaches 0.5m to 3.0m; If the above conditions are not met, continue with casing rotation and pressing, internal casing rotary excavation, and external casing grouting and consolidation until the requirements for the bottom locking of the casing are met.

10. A method for constructing boreholes in riprap formations using a combination of rotary casing and rotary drilling, as described in any one of claims 1-8, characterized in that... In S10, as the rotary drilling rig continues to drill to the designed bottom elevation or enters the designed bearing layer to a preset depth, the rotary drilling parameters are adjusted according to the type of the underlying strata. When the lower strata are cohesive soil or dense sand, the rotary drilling rig adopts a layered soil removal method, and the depth of each soil removal is controlled to be 0.5m to 1.5m. When the lower strata are strongly weathered rock layers, fractured rock layers or rock remnants, rotary drilling rigs use low speed and high torque to drill, and remove the debris and sediment at the bottom of the hole by slag removal, bucket changing or bottom cleaning. If, during the drilling process, the borehole wall falls off, the sediment at the bottom of the borehole increases, the fluid level in the borehole drops, or the drilling resistance changes abnormally, stop drilling and pull back the rotary drilling rig to clean the bottom of the borehole. If necessary, continue to advance the casing or use the grouting channel to supplement and seal the hole. After the hole is completed, the hole depth, hole diameter, verticality, thickness of sediment at the bottom of the hole, stability of the liquid level inside the hole, and the condition of the casing bottom lock are tested. If the test results do not meet the design requirements, the hole cleaning, hole sweeping, soil replenishment, casing follow-up, or additional grouting on the outside of the casing should be carried out again until the hole quality meets the design requirements.

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