Construction method of drilling holes with rotary drilling and air lifting for large diameter and ultra-long rock-embedded piles

Abstract

The present invention relates to a construction method for large-diameter and ultra-long rock-embedded piles using a rotary drill and air-lift reverse slag hole formation, which belongs to the technical field of pile foundation construction. After the reverse circulation drilling rig drills to the rock entry elevation, a rotary drill bit is used to break the rock, and an air-lift reverse circulation method is used when the rotary drill bit is drilling. The drilling process of the reverse circulation drilling rig is divided into three stages. The present invention uses a rotary drill instead of an impact drill to break the rock mass, which greatly improves the drilling efficiency while reducing the risks of pile foundation hole collapse and concrete over-cubicity; the present invention discharges rock slag blocks in the hole in time during drilling, keeps the bottom of the hole clean, reduces repeated crushing of drill cuttings at the bottom of the hole, has high hole cleaning efficiency, and has better pile quality; the mud is recycled between the casing and the mud pool, and is equipped with special filtering facilities, which can effectively prevent the pollution of the water environment by pile foundation construction, and has economic and social benefits.

Description

Technical Field

[0001] The invention relates to the technical field of pile foundation construction, in particular to a roller drilling and air lifting reverse slag hole forming construction method for large-diameter and ultra-long rock-embedded piles. Background Art

[0002] According to the Technical Specifications for Highway Bridge and Culvert Construction (JTG / T F50-2011), the definition of large-diameter piles is: bored cast-in-place piles with a diameter greater than or equal to 2.5m; the definition of super-long piles is: bored cast-in-place piles with a pile length greater than or equal to 90m.

[0003] At present, large-diameter and ultra-long pile drilling mainly adopts construction technologies such as rotary drilling, impact drilling, and rotary drilling. Among them, rotary drilling is divided into positive circulation drilling and reverse circulation drilling. Both positive circulation drilling and reverse circulation drilling protect the hole wall and remove slag through the circulation of mud. They are the same in drilling and hole-forming technology, and the applicable strata are basically the same. The difference is the circulation method of mud. Since the positive circulation drilling rig relies on the natural circulation of mud to remove slag, the circulation capacity and slag removal capacity are relatively weak. For large-diameter and ultra-long pile construction, only a part of the drilling slag can be discharged, and the drilling slag with larger particles cannot be discharged. There is a lot of drilling slag remaining in the hole, which affects the drilling speed and causes greater wear on the drilling tools. The mud circulation method of the reverse circulation drilling rig is just the opposite. It uses a mud pump to transport mud from the hole mouth (outside the drill pipe) into the hole, and then uses compressed air or a mud pump to draw it out from the middle of the drill pipe. Therefore, the circulation capacity and slag discharge capacity are relatively strong. Not only is the slag discharge relatively clean, but also the drill cuttings with relatively large particles can be discharged. Therefore, it is more suitable for drilling holes in soft strata for large-diameter and ultra-long piles.

[0004] In recent years, both domestic and international researchers have been exploring new technologies and techniques for large-diameter hard rock drilling. Although some conclusions with practical significance have been summarized, there is a lack of unified and systematic understanding of the construction technology and construction method characteristics of large-diameter and ultra-long rock-embedded piles in water.

[0005] For the construction of the main pier pile foundation of a super-large bridge with high requirements for navigation and environmental protection, the efficiency of using traditional impact drilling is extremely low, and it is difficult to control the thickness of the sediment to meet the design requirements. In addition, the combination of reverse circulation drilling and impact drilling has high requirements for various indicators such as mud density, which is easy to cause hole collapse and concrete over-cubic. Therefore, when the pile is long, the hole diameter is large, and the sediment index is strict, the traditional method cannot meet the construction requirements. Summary of the invention

[0006] The invention aims to provide a large-diameter and ultra-long rock-embedded pile roller drilling and air-lift reverse slag hole-forming construction method, which can make up for the shortcomings of traditional hole-forming methods.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The large-diameter and ultra-long rock-embedded pile roller drilling and air-lift reverse slag hole-forming construction method uses a roller drill bit to break up the rock after the reverse circulation drilling rig drills to the rock entry elevation, and the roller drill bit uses an air-lift reverse circulation method when drilling.

[0009] Furthermore, the reverse circulation drilling process is divided into the following three stages:

[0010] Drilling stage in casing: From 2.0m above the bottom of the casing, reverse circulation pressurized water drilling is used, and the hourly footage is controlled at 2m to 4m. Clean water is added in the hole, and the mixed mud is returned to the casing after treatment;

[0011] Drilling stage of soft formation below casing: when drilling to 1-2m near the bottom of steel casing, replace the mechanical drill bit, and start the reverse circulation idling of the drill bit during drilling, start the mud circulation system, and replace the mud in the hole; when the mud index in the hole meets the requirements, reverse circulation decompression drilling of mud wall is carried out, and slow drilling is carried out near the bottom of casing to form a stable hole wall, and the footage per hour is controlled at about 0.3m-0.8m. After the drill bit is out of one end of casing, normal drilling is resumed;

[0012] Rock drilling stage: When the reverse circulation drilling rig drills into the hard rock layer, stop drilling and confirm the rock entry elevation of the pile foundation.

[0013] Preferably, during the drilling stage of the soft formation below the casing, normal drilling is resumed after the drill bit is 5m to 6m out of the casing.

[0014] Furthermore, the mud circulation system includes a connected steel sedimentation tank and a steel mud tank, which are supported on the water by a support frame. New mud is prepared in the steel mud tank and pumped into the borehole through a mud pump. The mud carrying drilling slag discharged from the hole is pumped into the steel sedimentation tank for sedimentation and then enters the steel mud tank for recycling.

[0015] Preferably, a scraper drill bit with a diameter of φ2.5m is used for drilling in the casing drilling stage.

[0016] Further preferably, during the drilling stage in the soft formation below the casing, the normal drilling footage is 1 m to 3.5 m per hour.

[0017] Furthermore, during the drilling process of the reverse circulation drilling rig, slurry is added into the hole to maintain the water head height in the hole so that the mud surface in the hole is more than 3.0m above the water surface.

[0018] Furthermore, after confirming the rock penetration depth, the reverse circulation rotary drill rig is used to lift the drill, replace the cone drill bit and install the air lift slag removal equipment, which includes an air compressor, an air duct and a slag filter device;

[0019] When the roller drill bit is drilling and rotating on the rock at the same time, compressed air is supplied into the air duct through the air compressor, so that the drilling hole forms an air lift reverse circulation. The three-phase flow of mud, air and sediment in the hole runs upward along the drill pipe, is discharged from the hole mouth and enters the filter device. The filtered mud re-enters the hole for recycling.

[0020] Furthermore, after drilling to the designed elevation, the hole is cleaned and the slurry is replaced. When cleaning the hole, the drill bit is lifted 30cm to 50cm from the bottom of the hole, the drill bit is slowly rotated, high-quality mud is added, and reverse circulation is performed to clean the hole. At the same time, the water head in the hole is maintained to prevent hole collapse.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention adopts a rotary drill instead of an impact drill to break the rock mass, which greatly improves the drilling efficiency and reduces the risk of pile foundation collapse and concrete over-cubicity;

[0023] 2. The present invention can timely discharge the rock slag in the hole while drilling, keep the bottom of the hole clean, reduce the repeated crushing of the drill cuttings at the bottom of the hole, improve the hole cleaning efficiency and improve the pile quality;

[0024] 3. The mud is recycled between the casing and the mud pool and is equipped with special filtering facilities, which can effectively prevent the pollution of the water environment caused by pile foundation construction, and has economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a flow chart of the present invention;

[0026] Figure 2 It is the sequence diagram of pile foundation drilling;

[0027] Figure 3 It is a structural schematic diagram of the mud circulation system in the present invention;

[0028] Figure 4 It is a schematic diagram of the longitudinal section of the steel mud tank and sedimentation tank platform;

[0029] Figure 5 It is a cross-sectional schematic diagram of the steel mud tank and sedimentation tank platform;

[0030] Figure 6 It is a three-dimensional diagram of a steel plate box (reinforcement channel steel is not shown);

[0031] Figure 7 A schematic diagram of one side of a steel plate box;

[0032] Figure 8 It is a schematic diagram of the principle of gas lift slag removal. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings.

[0034] like Figure 1 As shown, the invention discloses a large-diameter ultra-long rock-embedded pile roller drilling air-lift reverse slag hole-forming construction method. After the drilling rig drills to the rock entry elevation, the roller drill bit is used to break the rock, and the roller drill bit uses the air-lift reverse circulation method for drilling. This hole-forming method can timely discharge the rock slag blocks in the hole while drilling, keep the bottom of the hole clean, and reduce repeated breaking, which can greatly improve the drilling efficiency.

[0035] This embodiment takes the main pier pile foundation construction of the Dongli River Extra-Large Bridge in the Chenghai section of Shanbei Avenue in Shantou City as an example to introduce the construction method of the present invention in detail.

[0036] The navigation level of Dongli River is the inland waterway of Class III, so this embodiment sets up a water drilling platform and completes the mud circulation operation on the platform to meet the high requirements for navigation and environmental protection. The diameter of the main pier pile foundation of this bridge is 2.5m, and it is inserted into the rock at a depth of about 120m. The design requires that the bottom of the pile is embedded in the medium-weathered rock by no less than 2.5 times the pile diameter, and the thickness of the sediment is no more than 5cm. Under the requirement of nearly 6.25m into the rock, the efficiency of using traditional impact drilling is extremely low, and it is difficult to control the thickness of the sediment to meet the design requirements. In addition, the combination of reverse circulation drilling and impact drilling has high requirements on various indicators such as mud specific gravity, which is easy to cause hole collapse and concrete over-cubic.

[0037] Therefore, the drilling construction of the present invention adopts the construction technology of reverse circulation rotary drilling rig and cone drill air lift reverse slag drilling, which mainly includes mud wall protection, drilling hole and hole cleaning.

[0038] (1) Drilling sequence

[0039] like Figure 2 As shown, pile foundation construction requires skipping holes to reduce the impact of the subsequent pile foundation construction on the previous pile foundation concrete before it reaches the design strength.

[0040] (2) Drilling rig selection

[0041] The main pier of Dongli River Bridge has 36 bored piles in total, with a depth of about 130 meters from the top of the casing to the bottom of the hole, which requires high torque and drill rod quality for the drilling rig. Six vehicle-mounted Xinfeng 351 reverse circulation drilling rigs with advanced technical performance and strong lifting capacity are selected to drill soft formations. Each drilling rig is equipped with a roller drill bit for rock drilling. The performance indicators of Xinfeng 351 reverse circulation drilling rig are shown in Table 1.

[0042] Table 1 Drilling rig performance index table

[0043]

[0044]

[0045] The working principle of Xinfeng 351 reverse circulation rotary drilling rig is as follows: mud is injected between the drill pipe and the borehole, and the drill pipe jets air to cut the soil. Since the pipe diameter is much smaller than the hole, the mud and the cut soil debris are quickly discharged from the drill pipe to the ground, and after being treated in the mud sedimentation tank, it can be recycled.

[0046] (3) Mud preparation and performance indicators

[0047] The wall protection mud is very important in drilling, especially for large diameter deep holes, where the mud layer and sand layer have poor slurry making performance, and mud control is particularly important. The present invention selects non-dispersible, low solid phase, high viscosity PHP mud.

[0048] In order to ensure the smooth construction of bored piles, before the formal drilling, calcium-based bentonite from different origins and different proportions of water, bentonite, caustic soda, PHP, etc. are selected for trial mixing and verification again, and the mud ratio with the best mud indicators is selected. The mud is prepared in the platform mud preparation area.

[0049] Before drilling construction, first use a mud mixer to stir the bentonite mud in the mud preparation area, and then use a mud pump to pump it into the steel casing. When the mud performance indicators in the steel casing meet the construction requirements, the hole is opened for drilling.

[0050] The performance index requirements of the mud at each construction stage in the present invention are detailed in Table 2.

[0051] Table 2 Mud performance index list

[0052]

[0053] (4) Mud circulation system

[0054] In order to prevent the pollution of the environment caused by the pile foundation construction on water, the present invention is specially equipped with a mud pool and a sedimentation pool of a water-shaped tempered steel structure.

[0055] like Figure 3 , 4 As shown in Figure 5, the mud circulation system of the present invention comprises a steel mud pool 8, a steel sedimentation pool 9 and a connecting pipe. The steel sedimentation pool 9 is connected to the steel mud pool 8. The steel mud pool 8 and the steel sedimentation pool 9 are supported on the water by a support frame 10. A plurality of pile foundation steel casings 6 are connected in series through a connecting pipe 14. The steel mud pool 8 is connected to one of the pile foundation steel casings 6 through a slurry outlet pipe 13.

[0056] The support frame 10 includes multiple basic steel pipes 101, a main cross beam 102, a main longitudinal beam 103 and a bridge deck 104. The main cross beam 102 is erected on the basic steel pipe 101. The bottom of the main longitudinal beam 103 is fixedly connected to the main cross beam 102. The top of the main longitudinal beam 103 is connected to the bridge deck 104. The steel mud pool 8 and the steel sedimentation tank 9 are installed on the bridge deck 104.

[0057] There are three main cross beams 102, and each main cross beam 102 is connected to two basic steel pipes 101. A diagonal brace 105 and a parallel joint 106 are arranged between the two basic steel pipes 101 connected to the same main cross beam 102.

[0058] In this embodiment, the length of the steel mud pool 8 and the steel sedimentation pool 9 are both 6m, the width is 4m, and the height is 3m. The bridge deck 104 is a 12cm thick shaped plate, the main longitudinal beam 103 is a 1021 type Bailey plate, and the main longitudinal beams 103 are connected by a connecting beam, and the connecting beam is a No. 8 channel steel.

[0059] The main crossbeam 102 is a 45a double-jointed I-beam, the foundation steel pipe 101 is a round steel pipe with a diameter of 630mm and a wall thickness of 10mm, and the diagonal brace 105 and the parallel link 106 are both 20a channel steel.

[0060] like Figure 6 As shown, a vertical partition 111 is provided in a steel plate box 11 to separate the steel plate box into two compartments, one compartment is used as a steel mud pool 8, and the other compartment is used as a steel sedimentation tank 9, and the box opening of the steel plate box 11 faces upward. Figure 7 As shown, the box opening and bottom of the steel plate box 11 are reinforced with No. 8 channel steel 12, and the scissor back ribs are made of No. 8 channel steel 12 around. An overflow port 112 is set at the top of the vertical partition 111 to connect the two compartments. The steel plate box 11 is 1 cm thick, and the overflow port 112 is a rectangular notch of 50 cm*50 cm.

[0061] When in use, the newly made mud is prepared in the steel mud pool 8 and delivered to the pile foundation steel casing 6 through the mud pump through the mud outlet pipe 13. After drilling, the drilling rig pumps the mud with drilling debris to the steel sedimentation tank 9 for sedimentation and then overflows into the steel mud pool 8, and then delivers it to the pile foundation steel casing 6 through the mud pump through the mud outlet pipe 5, and flows into each borehole through the connecting pipe between the pile foundation steel casing 6. During the drilling process, a special excavator is configured to clean the drilling debris in the mud casing in time, and the drilling debris is transported to the waste dump by the slag truck.

[0062] (5) Positioning and debugging of reverse circulation drilling rig

[0063] Before the drilling rig is put into place, all preparations for drilling should be thoroughly checked and the rig should be put into place only after confirmation that everything is correct.

[0064] The base and top of the drilling rig should be stable after installation to ensure that there is no displacement during drilling. The drilling rig should be kept in good working condition, the electrical part should have no safety hazards, and the motor housing should be grounded.

[0065] The drilling rig is in place and the base is leveled. Carefully measure and check whether the center of the drill bit and the center of the casing are on the same plumb line, and whether the deviation from the center of the hole is within the allowable range of the specification. After confirmation, finally check again whether the verticality of the drill pipe meets the requirements, whether the connection between the drill pipe and the drill bit is firm, whether the operation is good, whether the drill bit diameter is the same as the designed pile diameter, check the length of the drilling tool, and test various indicators of the mud. When everything is ready, you can start drilling.

[0066] During the drilling process, the horizontality of the pile foundation base is checked once a day. If the diagonal height difference of the drilling rig base is found to be greater than 10mm, the rig will be stopped and the drill will be started to level the base in time.

[0067] (6) Reverse circulation drilling rig drilling

[0068] ① The drilling process is divided into three stages: drilling inside the casing, drilling in the soft strata below the casing, and drilling in the rock strata.

[0069] Drilling stage inside the casing: From 2.0m above the bottom of the casing, use a φ2.5m diameter scraper drill bit to reversely circulate and pressurize clean water for drilling. The penetration rate is controlled at around 2 to 4m per hour. Clean water is added to the hole, and the mixed mud is precipitated in the sedimentation tank before flowing back into the casing. The drilling slag is transported to the waste dump.

[0070] Drilling stage of soft formation below casing: when drilling to about 1-2m close to the bottom of steel casing, replace the mechanical drill bit with diameter of φ2.5m, and reverse circulate and idle when drilling, start the mud circulation system, replace the mud in the hole, and when the mud index in the hole meets the requirements, reverse circulation and decompression drilling with high-quality mud wall protection are carried out, and slow drilling is carried out near the bottom of casing to form a stable hole wall, and the footage per hour is controlled at about 0.3-0.8m.

[0071] Normal drilling is resumed after the drill bit has exited the casing for 5m to 6m. According to the characteristics of different formations, the wall protection mud index and drilling speed are adjusted in time during the drilling process, with an advance of 1m to 3.5m per hour, and high-quality mud is added to the hole.

[0072] The corresponding drilling process parameters are adopted according to the geological conditions of the formation, as shown in Table 3 for details.

[0073] Table 3 Drilling parameters for different formations

[0074] Strata Drilling pressure (KN) Speed ​​(r / min) Drilling speed (m / h) Drilling in casing ≤4.0 Fine sand layer (dense) 100～150 10～15 1.5～2.0 Silt, silty clay layer 100～120 10～15 1～2 Medium coarse sand layer (dense) 150～300 5～10 2.0～3.0 Casing bottom stratum ＜100 5～10 0.3～0.8

[0075] ②Precautions for drilling

[0076] a. During the drilling process, pay attention to adding slurry into the hole at any time to maintain the water head height in the hole. The mud surface in the hole should be more than 3.0m above the river water surface at any time.

[0077] b. The drilling tools should be raised and lowered smoothly, especially when the drill bit is at the bottom of the casing. Careful operation must be taken to prevent the drill bit from hooking the casing and colliding with the steel casing to disturb the borehole wall.

[0078] c. When extending the drill pipe, stop drilling first, lift the drill tool 20-30cm away from the bottom of the hole, maintain mud circulation for more than 10 minutes to remove the sediment at the bottom of the hole and drain the drilling debris in the pipeline, then stop the pump to extend the drill pipe. The drill pipe connecting bolts should be tightened firmly, and the sealing ring should be carefully checked to prevent water and air leakage from the drill pipe joint, which will prevent the reverse circulation from working normally.

[0079] d. The drilling process should be carried out continuously without long-term stops, and the drilling cycle should be shortened as much as possible.

[0080] (7) Confirmation of rock penetration elevation and rock penetration depth

[0081] When the reverse circulation drilling rig reaches the hard rock layer and cannot drill further, the rock penetration elevation of the pile foundation is confirmed and the specific rock penetration depth is given.

[0082] (8) Replace the roller drill bit and install the gas lift equipment

[0083] After confirming the rock penetration depth on site, the reverse circulation drilling rig will lift the drill, replace the cone drill bit, and install the gas lift equipment. Figure 8 As shown, the air lift slag removal equipment includes an air compressor 1, an air duct 4 and a slag filtering device 5.

[0084] The working platform 2 is installed at the opening of the pile foundation hole 7, the inlet end of the conduit 3 extends into the bottom of the pile foundation hole 7, the outlet of the conduit 3 leads to the filter device 5, the air outlet of the air duct 4 extends to the inlet end of the conduit 3, and the air inlet of the air duct 4 is connected to the air compressor 1.

[0085] The outlet of the residue filter device 5 is connected to the mud circulation system. Preferably, the air duct 4 is coaxial with the conduit 3, and a residue receiving basket is selected as the residue filter device 5.

[0086] Selection and installation of gas lift equipment:

[0087] like Figure 8 As shown, the depth from the bottom of the air duct 4 to the top surface of the mud in the hole is h1, the height difference from the top surface of the mud in the hole to the top surface of the mud in the drill pipe is h2, and the three-phase flow density in the drill pipe is ρ n , the density of the liquid outside the drill pipe is ρ ω , then the pressure difference between the internal and external liquid columns acting on the liquid surface at the bottom of the air duct is:

[0088] αP=ρ ω*h1-ρ n (h1+h2)=(ρ ω -ρ n )*h1-ρ n *h2 (1)

[0089] It is this pressure difference that drives the three-phase flow above the bottom of the air duct 4 in the drill pipe to rise along the drill pipe and overcome various resistances in the circulation process to form a reverse circulation. Considering the pressure loss of the air supply pipeline, the air pressure in the present invention is calculated according to formula (2):

[0090] P=ρ n *h1 / 102+P s (2)

[0091] In formula (2), P s is the gas pipeline pressure loss, take 0.05~0.1MPa.

[0092] From formula (1), we can know that the mud density outside the pipe is ω When h1 and h2 are relatively stable, the density ρ of the three-phase flow is reduced. n (Achieved by increasing the compressed air volume) will increase the pressure difference driving the gas lift reverse circulation, so the air flow and pressure sent to the hole are important parameters affecting the gas lift slag removal ability. The larger h1 is, the smaller h2h2 is, the greater the pressure difference is. Therefore, when there is a lack of slurry in the hole, reverse circulation cannot be formed. The mud surface in the hole should be kept at a suitable height to increase h1h1 and reduce h2h2; ρ ω ρw is the three-phase flow density. When the proportion of the solid phase in the hole is large, reverse circulation cannot be formed. ω When ρw is relatively small, increase ρ ω ρw and ρ n The difference of ρn can improve the slag removal efficiency.

[0093] It can be seen from formula (2) that the selection of air compressor should be determined by P, which is mainly affected by h1h1 and ρ n ρn control. When the hole is deep and the mud density is high, the required pressure is high. Therefore, the air compressor model should be determined based on the actual pile length of the project; minimize P as much as possible. s , you should regularly check whether the air duct is leaking and whether the joints are tight to minimize pressure loss.

[0094] (9) When the roller drill is drilling, turn on the gas lift equipment to form a gas lift reverse circulation in the hole.

[0095] The working principle of roller drill bit drilling: the drill rig applies a sufficiently large axial pressure and rotary torque to the drill bit through the drill pipe. When the roller drill bit rotates, each roller rolls around its own axis, and the rolling direction is opposite to the rotation direction of the drill bit. The roller teeth roll on the rock during the pressurized rolling process; because the roller teeth contact the rock alternately with single teeth and double teeth, the axis of the roller is high when the single tooth touches the ground, and the axis is low when the double teeth touch the ground, and this is repeated, so that the rock is subjected to periodic impact; and because of the over-top, axis withdrawal, movement of the roller and the complex cone shape of the roller, the roller also slides to a certain extent when working at the bottom of the hole, which produces a cutting effect on the rock. Therefore, the crushing of rock by the roller drill bit is actually a composite effect of impact, rolling and cutting.

[0096] The calculation method of relevant parameters of roller drill bit drilling is as follows:

[0097] Axis pressure

[0098] The reasonable axial pressure can be calculated according to formula (3):

[0099] P=(0.06~0.07)f D (3)

[0100] In formula (3), f is the rock strength coefficient, and D is the drill bit diameter.

[0101] If the teeth of the cone are blunt, increase the axial pressure; if there are cracks or blocks in the rock, reduce the axial pressure appropriately to reduce the vibration of the drilling rig.

[0102] b. Drilling tool torque

[0103] The torque M (N·m) of the drilling tool is calculated according to formula (4):

[0104] M=29.6kDP 1.5 (4)

[0105] In formula (4), k is the rock characteristic coefficient; D is the diameter of the drill bit, mm; P is the axial pressure, kN.

[0106] c. Drilling speed

[0107] The drilling speed of the roller drill bit is estimated according to formula (5):

[0108]

[0109] In formula (5), P is the axial pressure, kN; n is the rotation speed of the drilling tool, r / min; D is the diameter of the drill bit, mm; and f is the hardness coefficient of the ore.

[0110] Working principle of gas lift equipment: Figure 3 , 8As shown, the air compressor delivers compressed air into the air duct, and the air is discharged from the bottom of the air duct to form a gas-liquid mixture with the mud. The sediment at the bottom of the hole is suspended under the impact of the ejected gas. Due to the density difference between the liquid inside and outside the pipe, the three-phase flow of mud, air and sediment in the hole runs upward along the drill pipe, is discharged from the hole mouth, and enters the slag receiving basket. The sediment in the mud is filtered out, and the filtered mud flows into the steel sedimentation tank 9 for sedimentation and then overflows into the steel mud tank 8, and then re-enters the hole through the mud pump through the slurry outlet pipe 13, and the cycle is repeated until the thickness of the sediment at the bottom of the hole meets the specification requirements.

[0111] The reverse circulation system uses gas as the motive medium and liquid as the lifting carrier medium to carry solid particles upward to finally complete the three-phase mixed movement of gas, liquid and solid, so as to achieve the purpose of rapid hole formation and removal of sediment and cuttings in the borehole.

[0112] (10) After the hole reaches the predetermined drilling depth, measure the hole depth and sediment thickness to confirm the final hole elevation. The sediment thickness is equal to the difference between the drilling depth and the hole depth before grouting.

[0113] During the drilling process, the drill slag samples from each stratum should be collected. When the reverse circulation rotary drill is drilling, a slag sample (2.5-3m) should be taken each time the drill rod is changed; after entering the rock, the slag sample should be extracted every 0.5m of drilling, and the slag sample should be picked up from the slag outlet and rinsed with clean water. The amount extracted each time is 100g and numbered and saved.

[0114] (11) One-time hole cleaning

[0115] After the hole is completed, clean the hole in time. When cleaning the hole, lift the drill bit about 30cm to 50cm from the bottom of the hole, slowly rotate the drill bit, add high-quality mud, and perform reverse circulation to clean the hole. At the same time, maintain the water head in the hole to prevent the hole from collapsing. When the thickness of the sediment at the bottom of the hole meets the design requirements after testing, and the mud index in the hole meets the requirements after cleaning the hole (the cycle time is controlled within 2 to 4 hours, and the cycle meets more than 2 cycles), stop the drill in time, remove the drill rig, and inspect the hole. Use a fully automatic ultrasonic hole detector to detect the hole diameter and verticality. After the hole inspection is qualified, pile construction should be carried out as soon as possible.

[0116] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, technicians familiar with the field may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. The large-diameter and ultra-long rock-embedded pile rotary drilling and air-lift reverse slag hole forming construction method is characterized by: After the reverse circulation drill reaches the rock entry elevation, the reverse circulation rotary drill lifts the drill, replaces the cone drill bit to break the rock, and installs the air lift slag removal equipment. The cone drill bit uses the air lift reverse circulation method for drilling; The air lift slag removal equipment includes an air compressor, an air duct and a slag filter device. The working platform is installed at the hole mouth of the pile foundation hole. The inlet end of the conduit extends into the bottom of the pile foundation hole. The outlet of the conduit leads to the slag filter device. The outlet of the slag filter device is connected to the mud circulation system. The air outlet of the air duct extends to the inlet end of the conduit. The air inlet of the air duct is connected to the air compressor. The mud circulation system includes a steel sedimentation tank and a steel mud pool that are connected. The steel sedimentation tank and the steel mud pool are supported on the water by a support frame. New mud is prepared in the steel mud pool and pumped into the borehole by a mud pump. The mud carrying drilling slag discharged from the hole is pumped to the steel sedimentation tank for sedimentation and then enters the steel mud pool for recycling. When the roller drill bit is drilling and rotating on the rock at the same time, the compressed air is supplied to the air pipe through the air compressor, so that the drilling hole forms an air lift reverse circulation. The three-phase flow of mud, air and sediment in the hole moves upward along the drill pipe, is discharged from the hole and enters the filter device. The filtered mud re-enters the hole for recycling. The reverse circulation drilling process is divided into the following three stages: Drilling stage in casing: From 2.0m above the bottom of the casing, reverse circulation pressurized clean water drilling is carried out using a φ2.5m scraper drill bit, and the hourly footage is controlled at 2m to 4m. Clean water is added to the hole, and the mixed mud is returned to the casing after treatment; Drilling stage of soft formation below casing: when drilling to 1-2m near the bottom of steel casing, replace the mechanical drill bit, reverse circulate and idle when drilling, start the mud circulation system, and replace the mud in the hole; when the mud index in the hole meets the requirements, reverse circulation and decompression drilling are carried out with mud wall protection, and slow drilling is carried out near the bottom of casing, with the footage controlled at 0.3m-0.8m per hour, and normal drilling is resumed after the drill bit is out of one end of casing; Rock drilling stage: When the reverse circulation drilling rig drills into the hard rock layer, stop drilling and confirm the rock entry elevation of the pile foundation; During the drilling stage of the soft stratum below the casing, the normal drilling is resumed after the drill bit is 5 to 6 meters out of the casing.

2. The large-diameter and ultra-long rock-socketed pile rotary drilling and air-lift reverse slag hole forming construction method according to claim 1 is characterized by: During the drilling stage in the soft strata below the casing, the normal drilling speed is 1m to 3.5m per hour.

3. The large-diameter and ultra-long rock-socketed pile rotary drilling and air-lift reverse slag hole forming construction method according to claim 1 is characterized by: During the drilling process of the reverse circulation drilling rig, slurry is added to the hole to maintain the water head height in the hole so that the mud surface in the hole is more than 3.0m above the water surface.

4. The large-diameter and ultra-long rock-socketed pile rotary drilling and air-lift reverse slag hole forming construction method according to claim 1 is characterized by: When drilling to the designed elevation, clean the hole and replace the slurry. When cleaning the hole, lift the drill bit 30cm to 50cm away from the bottom of the hole, rotate the drill bit, add high-quality mud, and perform reverse circulation hole cleaning.

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