Original Title: Causes of Sediment of Rotary Drilling Pile and Hole Cleaning Treatment! Introduction Rotary drilling rig has high automation level and strong adaptability. However, due to the differences in mechanical property of different drilling rigs, personnel operation level and on-site technical management ability, especially the influence of site stratum conditions, and the industry has not yet compiled relevant construction technical specifications for rotary bored piles, and has not formed a systematic research on construction methods, a large number of quality problems of rotary bored piles in the construction process have also arisen. Thick sediment at the bottom of pile is one of the common quality problems. Excessive or too thick sediment at the bottom of the pile will have a serious impact on the quality of the pile foundation, which is mainly reflected in the following aspects: too thick sediment will seriously restrict the bearing capacity of the pile end and increase the settlement and displacement of the piles, which will cause huge hidden dangers to the overall structural safety of the superstructure. In view of the above problems, the current pile foundation code puts forward clear requirements for the thickness of sediment at the bottom of bored piles. In the Technical Code for Building Pile Foundations (JGJ94-2008), it is stipulated that the sediment thickness of end-bearing piles is ≤ 50mm, and the sediment thickness of friction piles is ≤ 100mm. Many local industry codes have also issued clear regulations to restrict this. However, in the actual construction, due to the lack of training for the operators of rotary drilling rig and the lax grasp of the construction process by the on-site technical management personnel, especially the influence of complex strata, the problem of excessive sediment at the bottom of piles is still serious. Therefore, how to prevent the generation of pile hole sediment in the construction process of rotary drilling pile, reasonably select the secondary hole cleaning process of pile hole, and ensure that the sediment at the bottom of the hole meets the design and specification requirements, has become an objective evaluation and application prospect of the rotary drilling rig in the industry. Based on the construction situation of rotary drilling cast-in-place pile in Shenzhen area, this paper analyzes the causes of sediment at the bottom of rotary drilling pile hole, puts forward several effective secondary hole cleaning methods, discusses the characteristics of different hole cleaning methods, and puts forward the comprehensive optimization selection method. 01 Cause Analysis and Control Measures of Sediment at the Bottom of Rotary Excavation Pile The sediment at the bottom of the rotary drilling cast-in-place pile may be produced in the drilling and hole forming, reinforcement cage placing, concrete pouring and other links of the rotary drilling rig construction. The analysis shows that the reasons for the sediment can be roughly divided into the following categories: 1.1 Collapse of pile hole wall 1.1.1 Cause analysis The filling layer of the pile hole orifice is unstable and collapses into the hole; the specific gravity of the mud is too low and the suspension capacity is poor; the drilling tool is lifted too fast, resulting in upward suction in the hole; the mud level in the hole drops when the drilling tool is lifted, and the mud in the hole is not replenished in time; the drilling tool scratches the hole wall when it is lifted and lowered; the reinforcement cage scratches the hole wall when it is lowered; concrete is not poured in time after the completion of the hole, and the. 1.1.2 Control measures: steel casing shall be placed at the orifice to protect the orifice, and the length of the casing shall be properly lengthened according to the formation conditions; the specific gravity of the mud shall be increased to improve the viscosity of the mud and reduce the sedimentation at the bottom of the hole; the footage of each round of rotary drilling shall be controlled, and it is strictly prohibited to lift the drill when the drilling cylinder is full, so as to avoid sucking the site; before the drilling tool raises the orifice, the mud in the hole shall be replenished in time to maintain the; When lifting and lowering the drilling tool, keep it centered and slowly lift and lower it to prevent scraping; lower the reinforcement cage to keep it centered and vertical; pour the pile body concrete in time after finishing the hole to reduce the auxiliary operation time. Expand the full text 1.2 Mud Sedimentation 1.2.1 Cause analysis The performance parameters of the mud are not qualified, and the wall protection effect is not good; the waiting time before pouring is too long, and the mud precipitates; the sand content of the mud is high. 1.2.2 Control measures Prepare the mud with appropriate parameters, and timely detect and adjust the mud performance; shorten the waiting time for pouring to avoid mud sedimentation; set up a mud sedimentation tank or a mud separator to separate the sediment in the mud and adjust the mud performance. 1.3 Drilling residues 1.3.1 Cause analysis The bottom of the drilling tool is deformed or worn too much, and the muck leaks to form sediment; the bottom of the drilling tool is limited by the structure itself, such as the height and spacing of the drill teeth, which cause too much muck to form sediment. 1.3.2 Control measures Appropriate drilling tools shall be selected, and the drilling bottom structure shall be checked frequently; the clearance between the rotary bottom and the fixed bottom shall be reduced; the diameter protection strip shall be repaired and welded in time, and the side teeth with serious wear shall be replaced; the arrangement angle and spacing of the drilling teeth shall be adjusted reasonably; the number of slag removal shall be increased to reduce the residue at the pile bottom. 1.4 Hole cleaning process 1.4.1 Cause analysis Hole collapse is caused by suction during hole cleaning; the mud performance is not up to standard during hole cleaning, and the sediment cannot be carried out of the hole bottom; the selection of hole cleaning process is unreasonable, and the sediment cannot be removed completely. 1.4.2 Control measures Control the suction force of the pump during hole cleaning to reduce the impact on the hole wall; change the slurry during hole cleaning and adjust the slurry performance index; select the appropriate secondary hole cleaning process according to the drilling conditions. Secondary hole cleaning technology of rotary drilling cast-in-place pilot Appropriate measures shall be taken to avoid sediment during rotary drilling construction. After the placement of reinforcement cage and pouring conduit, appropriate secondary hole cleaning process shall be selected for sediment treatment for pile holes with too thick sediment. Secondary hole cleaning is a key process to remove the sediment at the bottom of the hole by using the pouring conduit after the completion of rotary excavation, reinforcement cage and pouring conduit. The reasonable selection of secondary cleaning technology for pile hole is very important to remove the sediment at the bottom of the hole and ensure the quality of the pile body. At present, the secondary hole cleaning technology of rotary digging pile in the industry can be divided into the following three categories according to the mud circulation mode: mud positive circulation hole cleaning, reverse circulation hole cleaning and drilling tool without mud circulation hole cleaning. 02 Mud positive circulation hole cleaning 2.1.1 Process principle Mud positive circulation hole cleaning process is a commonly used hole cleaning method, in which the mud pumped by the mud pump is connected with the pouring conduit at the orifice through the rubber hose, and the mud is sent to the bottom of the hole; the mud sent to the bottom of the hole is suspended and carries the sediment at the bottom, and then returns to the ground through the annular space between the pouring conduit and the hole wall, flows into the circulation ditch and sedimentation tank, and then enters the mud tank for recycling. See Fig. 1 for the principle of positive circulation secondary hole cleaning process. Fig. 1 Schematic diagram of positive circulation secondary hole cleaning principle 2.1.2 Precautions for hole cleaning Attention shall be paid to the following items during the operation of mud positive circulation slag removal: (1) Select the appropriate mud pump. If the mud flow is too large, the hole wall will be scoured and the hole will collapse easily. If the mud flow is small, the sediment will rise slowly, the slag removal effect will be poor and the time will be long. In the actual construction, the flow and lift are taken as the basis for selecting the mud pump, and the 3PN mud pump with the power between 12 and 30 KW can be prepared according to the diameter of the pile hole. (2) Reduce the number of pipeline joints, avoid drastic changes in pipeline diameter and running direction, and reduce the on-way resistance and local resistance consumption in the mud circulation system. (3) In the process of mud circulation, the mud circulation system contains more coarse particles or rock debris, which will be brought into the hole repeatedly, affecting the hole cleaning effect. The waste residue in the sedimentation tank and mud tank shall be cleaned regularly. The mud circulation ditch can be enlarged or lengthened, and special personnel shall be assigned to dredge the slag in the ditch. (4) In the process of cleaning the hole, the guide pipe shall be lifted up and down and moved left and right according to the slag removal effect to speed up the disturbance of the sediment at the bottom of the hole, so as to achieve the effect of rapid slag removal. 2.2 Mud cyclone positive circulation hole cleaning 2.2.1 Process principle In order to reduce the large content of coarse particles in the mud in the secondary hole cleaning process of the positive circulation, improve the performance index of the mud, shorten the hole cleaning time and improve the hole cleaning effect, a mud cyclone is introduced to assist in hole cleaning in the mud positive circulation hole cleaning system, that is, a mud cyclone is connected in series on the ground on a rubber hose for pumping the mud into the bottom of the hole by a mud pump,dth drilling hammer, and the coarse particles in the slurry are discharged before the slurry is pumped into the bottom of the hole. The effective separation of slurry and slag in advance ensures that high-quality slurry enters the bottom of the hole, reduces the repeated introduction of rock slag, effectively improves the slag-carrying capacity of the slurry, greatly shortens the hole cleaning time, improves the work efficiency and ensures the hole cleaning effect. See Fig. 2 for the plane layout of the secondary hole cleaning process of the mud cyclone. Fig. 2 Schematic diagram of secondary hole cleaning of cyclone 2.2.2 Precautions for hole cleaning Slurry cyclone positive circulation secondary hole cleaning relies on the cyclone device to effectively separate the slurry, which is easy to operate and has good separation effect. It is an upgraded process of ordinary slurry positive circulation hole cleaning system and a utility model patent technology owned by our company. At the same time, it has been appraised as the municipal construction method of Shenzhen engineering construction in 2011 and the provincial construction method of Guangdong engineering construction. It is practical and effective. And provides a new reliable choice for secondary hole cleaning. Attention shall be paid to the following during the secondary hole cleaning of the positive circulation of the mud cyclone: (1) Assign a special person to take charge of the working state of the cyclone and observe whether the slag outlet is blocked; if large foreign matters such as block stones, oyster shells and cement blocks are sucked into the inlet of the cyclone, the slurry inlet speed will be reduced, which shall be removed in time. (2) If the content of solid coarse particles in the slurry at the inlet of the cyclone is too high, or the valve at the underflow port is adjusted too small, the cyclone will be overloaded and the underflow port will be blocked. The bottom valve can be adjusted to keep the bottom slag discharge smooth. (3) Set special slag discharge tank at the slag outlet of the cyclone, and clean and discharge the slag in time. (4) The selection of cyclone shall be matched with the mud pump capacity. 2.3 Pump suction reverse circulation secondary hole cleaning 2.3.1 Process principle In order to ensure that the hole cleaning meets the design and specification requirements, the common practice for large and deep piles is to adopt the mud pump suction reverse circulation process. Pump suction reverse circulation secondary hole cleaning is to use the suction effect of the sand pump to create a negative pressure state in the inner cavity of the filling conduit. Under the action of atmospheric pressure, the mud in the annular space between the filling conduit and the hole wall flows to the bottom of the hole, is sucked into the inner cavity of the filling conduit, and then rises to the ground mud circulation system. After sedimentation treatment in the mud sedimentation tank, it flows into the hole from the mud tank and the mud circulation ditch. See Figure 3 for the working principle of pump suction reverse circulation secondary hole cleaning. Fig. 3 Schematic Diagram of Working Principle of Pump Suction Reverse Circulation Secondary Hole Cleaning 2.3.2 Precautions for hole cleaning Secondary hole cleaning by pump suction reverse circulation has the characteristics of strong suction capacity, short hole cleaning time and clean hole bottom, but attention shall be paid to the following during hole cleaning: (1) 6 BS reverse circulation sand pump is required to be added during hole cleaning. The pipeline layout of the overall circulation system is complex, the reverse circulation site operation is highly professional, and the formation of vacuum degree is difficult. (2) As the flow of the pump suction reverse circulation sand pump can reach 180m3/H, the suction capacity is super strong, and the negative pressure formed has a certain impact on the stability of the hole wall. For the pile hole with deep silt and thick sand layer, the reverse circulation flow shall be controlled. (3) When cleaning the hole,Tapered Rock Bit, pay attention to keep the water head height of the mud surface in the casing, and keep the balance between the amount of mud flowing back into the hole and the amount of suction. The consumption of pump suction reverse circulation mud is large, so it is necessary to control the performance and parameters of the mud and do a good job in the treatment of waste slurry and waste residue. 2.4 Air-lift reverse circulation treatment method 2.4.1 Process principle Air-lift reverse circulation hole cleaning is to insert a galvanized pipe with a length of about 2/3 hole depth into the conduit to send high-pressure air into the 2/3 hole depth of the conduit and mix it with the mud in the conduit. After inflation, a low-pressure area is generated in the conduit. The pressure difference between the inside and outside of the continuously inflated conduit increases continuously. When a certain pressure difference is reached, the balance is broken, and the mud is forced to spray back from the conduit under high pressure. At the same time, the rock slag at the bottom of the hole is carried by the high-speed mud and ejected back out of the orifice from the conduit. The principle of gas lift reverse circulation is shown in Figure 4 below. Fig. 4 Principle of gas lift reverse circulation 2.4.2 Precautions for hole cleaning The gas lift reverse circulation secondary hole cleaning process has the advantages of large pressure difference, fast flow rate and strong slag carrying capacity. During the operation of the slag removal process, in addition to reducing the resistance, moving the conduit, separating the mud and sand in the slurry, attention should also be paid to: (1) The configuration of air-lift reverse circulation equipment is relatively complex, so it must be debugged and optimized before the actual work, especially for the selection of air compressor, setting the appropriate length of air inlet pipe directly affects the efficiency of circulating slag removal. (2) Gas lift reverse circulation will cause negative pressure at the bottom of the pile hole, and hole collapse must be prevented when it is used in unstable strata. (3) In the process of reverse circulation operation, the water head height of the mud level in the casing shall be kept all the time, and the balance between the amount of mud flowing back into the hole and the amount of suction shall be kept consistent to prevent hole collapse. 2.5 "Submersible pump + mud purifier" secondary hole cleaning system 2.5.1 Process principle In order to solve the problems of poor secondary hole cleaning effect, complex mud circulation and large mud discharge of large-diameter and ultra-deep piles, our company has developed a "submersible pump + mud purifier" secondary hole cleaning system, that is, the submersible pump is connected with the perfusion conduit, when the submersible pump starts, it directly pumps the sediment at the bottom of the hole to form mud reverse circulation; The submersible electric pump is connected with the mud purification device with a rubber hose. The pumped mud enters the mud purification system to realize the separation of slurry and slag. The slag is directly discharged and loaded for transportation. The mud flows into the orifice through the outlet of the mud purifier again to maintain the height of the mud level in the hole, maintain the stability of the hole wall, and recycle to achieve the purpose of hole cleaning. See Fig. 5 and Fig. 6 for the working principle of the secondary hole cleaning system of "submersible pump + mud purifier". Fig. 5 Schematic Diagram of Secondary Hole Cleaning System of "Submersible Pump + Mud Purifier" Fig. 6 Site Layout of Secondary Hole Cleaning of "Submersible Pump + Mud Purifier" 2.5.2 Precautions for hole cleaning (1) The selection of mud purification device model shall be based on the submersible pump model, processing capacity, etc. When the submersible pump flow is not more than 100 m3/H, ZX-100 can be selected; When the flow of submersible electric pump is greater than or equal to 100 m3/H, ZX-200 can be selected to achieve the balance between flow and processing capacity and meet the requirements of mud purification capacity. (2) Orifice submersible electric pump is an important machine and equipment in the process of secondary hole cleaning. The submersible electric pump is respectively connected with the filling conduit and the mud purification device to form the mud reverse circulation secondary hole cleaning process. In order to ensure the sealing of the submersible pump, the submersible pump is generally sunk below the mud level to prevent air leakage. (3) After the hole cleaning system is installed, special inspection shall be carried out, including: the height of the filling conduit from the bottom of the hole, the tightness of each interface, the stability of the mud purification device, the safety of various electrical appliances, etc. The secondary hole cleaning shall be carried out if the inspection meets the requirements. (4) In the process of hole cleaning, closely monitor the height of the mud level at the orifice, and keep the amount of mud pumped and discharged by the submersible pump basically consistent with the amount of backflow mud, so as to ensure the water head height of the mud in the hole and keep the hole wall stable. 2.6 Hole cleaning with rotary drilling bucket (hole cleaning without mud circulation) 2.6.1 Process principle Rotary drilling bucket hole cleaning refers to a hole cleaning method in which a special slag fishing drilling bucket is used to remove the sediment in the hole. In the process of drilling and before pouring concrete, it is not necessary to use slurry positive circulation or reverse circulation to clean the hole. In this hole cleaning method, the rotary drilling bucket is mainly used to fish out the sediment at the bottom of the hole, and at the same time, the mud is used to protect the stability of the hole wall and suspend the sediment, so that the coarse particles or drilling slag in the mud in the hole are in a suspended state for a long time. After the installation of the reinforcement cage and the pouring conduit, there is little or no sediment at the bottom of the hole. 2.6.2 Practice of rotary drilling bucket for hole cleaning without mud circulation (1) Project overview: The pile foundation of Guoxin Financial Building in Futian Central District of Shenzhen has a diameter of φ1800, φ2000, φ2200 and φ2600mm, mining dth bit ,fastest dth hammer, a pile hole depth of 38 ~ 41mm, a pile bottom bearing stratum of 2m into moderately weathered granite or 0.5m into slightly weathered granite, and a compressive strength of 75 MPa for slightly weathered granite. (2) Pile foundation construction and hole cleaning measures: Sany Heavy Industry SR420II rotary drilling rig is selected for pile foundation construction, 3m pile casing is buried at the orifice, and chemical slurry is prepared from sodium hydroxide powder, sodium hydroxide and CMC. Taking the hole with a pile diameter of 2,600 mm as an example, the upper fill, silty clay, residual soil and strongly weathered rock stratum (about 38 m deep) shall be drilled in two stages according to the diameter of 2,200 mm and 2,600 mm by the rotary drilling bucket. Since the rotary drilling is carried out with static mud without circulation, the drilling speed is fast (about 6 hours), and the mud wave on the hole wall is thin, At this stage, the mud shall be controlled at a specific gravity of 1.08 ~ 1.20 and a viscosity of 18 ~ 20 S. The lower moderately weathered and slightly weathered rock strata are hard and deeply penetrated into the rock. The rotary drilling of hard rock adopts stepped reaming, that is, the cutter drill barrel with a diameter of φ 800 mm is used to drill to the designed final hole depth, and the rock core is directly taken out; After the final hole depth is determined, the rotary drilling bucket or drill barrel with diameters of φ1300mm, φ1500mm, φ1800mm, φ2000mm, φ 2200mm, φ 2400mm and φ2600mm shall be used to ream the hole from top to bottom. After the drilling of each stage of hole is completed, the dredger bucket shall be used to clean the hole. The rock strata are reamed and dredged by stages, so that the construction time of drilling hard rocks in each stage of hole is shortened, the resistance of hard rock drilling is reduced, and the rock drilling efficiency is improved. In order to reduce the heat energy of the friction between the drill bit pick and the hard rock, the mud is controlled to have a low specific gravity and medium viscosity during drilling in the rock formation, with a specific gravity of 1.05 ~ 1.15 and a viscosity of 18 ~ 22 S. After finishing the hole and before placing the reinforcement cage and pouring the guide pipe, use sodium hydroxide to adjust the performance of the mud at the bottom of the hole, so that the mud with small specific gravity (specific gravity 1.05 ~ 1.10) and large viscosity (viscosity 22 ~ 25s) can be formed within about 10 m above the bottom of the hole, so that the mud at the bottom is in a flocculent state and the coarse particles in the mud are in a suspended state. Ensure that the sediment at the bottom of the hole meets the design requirements after the reinforcement cage and pouring conduit are placed. (3) Rotary drilling and pile-forming effect: for the rotary drilling pile of Guoxin Mansion, the pile with a diameter of 2,600 mm, a depth of 41 m, and a depth of 3 m into the moderately (slightly) weathered granite shall be cleaned without slurry circulation, and the pile formation shall be completed every 2.0 ~ 2.5 days; for the piles with a diameter of 2,000mm and below, 2 ~ 3 piles can be completed every day. 2.6.3 Precautions for rotary drilling bucket without mud circulation slag removal (1) Protect the orifice and hole wall. When the rotary drilling bucket is used to remove the slag, the pile casing at the orifice shall be fully buried, and the water head height of the mud level in the pile casing shall be maintained to prevent the collapse of the orifice and the collapse of the hole wall during drilling. Due to the large pile diameter, the mud level in the pile casing will drop by about 1.2m before the rotary drilling bucket is lifted from the orifice. At this time, it is necessary to supplement the mud in time to maintain the liquid level in the pile casing. (2) The structure of the dredge bucket is reasonable. After drilling to the depth of the designed bearing stratum of the pile hole, use the pick bailing bucket to idle for several circles without pressurization, so as to make the pile bottom as flat as possible and facilitate slag removal; when drilling in the rock stratum, the slag removal guide plate should be as short as possible or flat-bottomed as possible, so that the slag soil at the bottom of the hole can enter the cylinder; the smaller the height of the slag removal guide plate is, the better the effect of slag removal is. The bottom structure of the slag removal drilling bucket must be modified according to the shape of the pick bucket bottom to minimize the height of the guide plate and the center cone. (3) Mud management is the key. The rotary drilling rig shall be equipped with a special mud team, and a special person shall be assigned to be responsible for the modulation and management of mud. (4) The control of mud performance is the key in the slag cleaning process of the rotary drilling bucket. In order to realize the hole cleaning without mud circulation, it is necessary to scientifically and reasonably control the allocation of mud and dynamically use the mud. For example, if the drilling time of the upper soil layer is short, the specific gravity of the mud should be increased appropriately to maintain the stability of the hole wall; if the drilling resistance of the rock stratum is large and the drilling time is relatively long, the specific gravity of the mud can be reduced appropriately; After the rotary drilling bucket is dredged after the hole is finished, due to the need to place the reinforcement cage and pour the conduit, the mud is prepared into low specific gravity and high viscosity at this time, so that the mud at the bottom section forms flocculent and consistency, which improves the suspension capacity of the mud and prevents the solid particles in the mud from sinking to the bottom of the hole. (5) After the drilling tool is cleaned, the auxiliary operation time shall be shortened, and the concrete of the pile body shall be poured into the cage immediately to minimize the amount of sediment at the bottom of the hole. 03 Comparison and analysis of secondary hole cleaning technology for rotary drilling pile bottom sediment The characteristics of the slag removal method are compared and analyzed from four aspects of application scope, equipment configuration, slag removal efficiency and mud consumption: 3.1 Scope of application (1) Normal circulation slag removal: including cyclone normal circulation slag removal, which is suitable for pile holes with small diameter and depth, and is convenient for mud to carry sediment back upward. Generally, the pile diameter is 1.5m and below, and the depth is within 40m. Otherwise, it is necessary to configure a super-power mud circulating pump for implementation. (2) Reverse circulation slag removal: including pump suction reverse circulation, submersible pump + mud purifier reverse circulation hole cleaning, and air-lift reverse circulation slag removal. It is applicable to large-diameter piles with a pile diameter of more than 1.5m. In order to provide sufficient pressure difference for circulation, it is generally required that the pile hole depth is more than 10m, the pump suction reverse circulation pile depth can reach about 80m, and the air-lift reverse circulation hole depth can exceed 100m. (3) Slag removal of drilling tools adopts slag-fishing drilling tools and mud hole cleaning, which is suitable for all rotary drilling processes, especially for long casing, full casing drilling and mud circulation which is easy to cause hole collapse. To sum up, the application range of positive circulation slag removal is small, the application range of reverse circulation slag removal is large, and the application range for drilling tool slag removal is the widest. 3.2 Equipment configuration (1) Positive circulation slag removal: the required equipment includes mud pump, conduit, etc.; (2) Cyclone positive circulation slag removal: the required equipment includes mud cyclone, mud pump, conduit, etc.; (3) Pump suction reverse circulation slag removal: the required equipment is sand and gravel pump and conduit; (4) Equipment required for gas lift reverse circulation slag removal: air compressor, mud pump, conduit, air inlet pipe, joint, etc.; (5) Submersible electric pump + mud purifier reverse circulation hole cleaning: Dth electric pump, mud purifier, conduit, etc.; (6) Drilling tool slag removal: configure the slag removal drill bit suitable for the pile diameter. In the above six slag removal methods, the reverse circulation system requires the most equipment, the system structure is more complex, and the operation has certain technical difficulties, such as the control of reverse circulation vacuum degree. In addition, the drilling tool does not need too much external equipment for slag removal, but because the price of the rotary drilling bucket for slag removal is close to that of the ordinary rotary drilling tool, the price of the large-diameter drilling tool for slag removal is more expensive, and different diameters of drilling buckets are needed when the diameters are different, the initial investment is more, which is a disadvantage compared with the mud circulation slag removal. 3.3 Slag removal efficiency Among the above positive circulation, reverse circulation and drilling tool slag-cleaning methods without mud circulation, the drilling tool has the highest slag-cleaning efficiency, which can meet the injection requirements after 3 to 5 times of lifting and discharging; the gas lift or pump suction reverse circulation takes the second place, which takes 2 to 4 hours to clean the slag, while the positive circulation has the lowest efficiency, which takes 4 to 6 hours. However, the actual slag removal time is closely related to equipment configuration, engineering geological characteristics, mud quality and other factors, so it is difficult to generalize. 3.4 Mud consumption Among the above six hole cleaning processes, the reverse circulation mud consumption is the largest, the positive circulation is the second, and the drilling tool slag cleaning is the smallest. 04 Optimization and selection of slag removal technology for rotary drilling pile The key to ensure the quality of pile hole is to optimize the selection of rotary drilling pile slag removal and secondary hole cleaning process. We believe that the following points should be grasped: (1) There are many methods for slag removal of rotary drilling piles. We advocate that there is no best method, only suitable method. Each process method must be suitable for equipment, personnel, stratum and environment. If it can be handled simply, it will not be complicated to operate, so as to achieve the purpose of hole cleaning. (2) For small-diameter piles and shallow piles, due to small pile hole section and small hole cleaning depth, the secondary hole cleaning with positive circulation of mud can better meet the requirements. (3) For large-diameter piles and ultra-deep piles, it is slow and ineffective to use slurry positive circulation for hole cleaning. At this time, it is necessary to use slurry reverse circulation for hole cleaning. In the reverse circulation hole cleaning process, the pump suction or gas lift circulation process is reasonably selected according to the hole diameter and depth. (4) In the process of secondary hole cleaning, the use of mud purification device (such as cyclone, black cyclone series) can quickly separate the solid coarse particles in the mud, reduce the sand content of mud, improve the performance of mud, accelerate the separation of slurry and slag, improve the speed of hole cleaning, ensure the quality of hole cleaning and reduce the amount of mud discharge, which can get twice the result with half the effort. (5) The drilling tool has no slurry to clean the slag circularly, which is a new method of hole cleaning worth advocating in the construction of rotary drilling pile. Its biggest characteristic is that after the reinforcement cage is placed in the drilling hole and the conduit is poured, the bottom of the hole can be kept less or no sediment, and there is no need for secondary hole cleaning. It has good slag cleaning effect and less auxiliary equipment, which greatly improves the efficiency of pile formation. The high efficiency of the rotary excavator is brought into full play. This slag removal technology has been used in a number of rotary pile foundation construction sites such as Guoxin Financial Building, Alibaba Building, Aliyun Building and Life Building, and has achieved satisfactory results, which should be vigorously promoted. (6) There are a large number of rotary pile construction teams in Shenzhen, and the number of individuals is large. The performance, management level and operation ability of pile drivers are quite different. They are often hastily started, lack of training, and lack of mastery of rotary pile construction technology and operation skills, especially the mastery of drilling mud performance. It is often difficult to achieve the desired results. Therefore, in the specific operation of secondary hole cleaning, the hole cleaning process should be adjusted according to the actual situation. In particular,dth drill bits, if the drilling tool without mud circulation cleaning process is adopted, its practical application has a high technical content. If the sediment at the bottom of the hole cannot meet the design requirements after placing the reinforcement cage and pouring the guide pipe and before pouring the concrete, the mud positive circulation or reverse circulation must be used for secondary hole cleaning. Return to Sohu to see more Responsible Editor:. wt-dthtools.com