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 drill bits, 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.  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,mining drill bit, 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