CrawlerRigIn the process of drilling into the hole, according to the formation, hole depth changes, reasonable selection of drilling parameters and bit, timely modulation of mud, to ensure the quality of the hole. When entering the sand layer and pebble layer, the footage speed should be appropriately slowed down, the consistency of the mud should be improved, and the footage of each drilling return should be reduced to ensure the stability of the hole wall. During drilling construction, the front shovel shall be used to remove the drilling slag in time to ensure the site is clean and tidy, which is conducive to the next construction. After the drilling reaches the required hole depth and the drilling is stopped, pay attention to maintain the slurry surface elevation of the mud in the hole to ensure the stability of the hole wall.
 1. Mud preparation
The mud pit (including sedimentation tank for slurry return and mud reserve tank) set on site is generally 1. 5~2. 0 times of the borehole volume, and it should have better anti-seepage ability. A muck area is set beside the sedimentation tank, and the sediment is cleaned by backhoe and placed in the muck area to ensure the itinerant space and storage space of mud. There are two kinds of equipment for mud preparation, one is mud mixer and the other is hydraulic mixer. When using clay powder to make slurry, it is best to use a hydraulic mixer; when using bentonite to make slurry, use a mud mixer. Regeneration treatment of mud for wall protection: gravity sedimentation slag removal method is adopted in construction, I .e. the method of using the relative density difference between mud and soil slag to precipitate soil slag to remove soil slag. The recovery mud pit is set up on site to be used as the recovery wall protection mud. After the mud is purified by precipitation, it is transported to the slurry storage tank and further treated in the slurry storage tank (adding appropriate amount of soda ash and CMC to improve the mud performance) and reused after passing the test.
 2. Buried casing
After the pile foundation is positioned, four control piles are placed by the cross nails according to the pile positioning points, and the steel casing is buried based on the four control piles. In order to protect the orifice from collapse and form the water head and positioning guide in the hole, the burial of the casing is the key in the rotary excavation operation. The pile casing is made of 10mm thick steel plate. The inner diameter of the pile casing is 20cm and the height is 2.0m. Two overflow holes are opened on the upper part. When the pile casing is buried, it is completed by manual and mechanical cooperation. The top of the pile casing is mainly pressed into the soil by drilling rig rotary bucket. The top of the pile casing shall be 20cm higher than the ground and kept horizontal. The buried depth is 1.8 m. The deviation between the pile casing center and pile casing center shall not be more than 50mm. The casing shall be buried vertically and the inclination rate shall be less than 1.5%.

 3. Drilling positioning
The drilling rig can only be in place on the basis that the pile position is checked correctly, the casing is buried in line with the requirements, and the casing and floor elevation have been measured. The positioning of the pile crane shall be accurate, horizontal, vertical and stable, and the center line of the drilling rig guide rod, the center line of the swivel plate and the center line of the casing shall be kept in the same straight line. After the rotary drilling rig is in place, its verticality shall be adjusted by the automatic control system. When the drilling rig is placed and positioned, the base shall be flat, the tower shall be vertical, the center of the rotary table (drill bit) shall be aligned with the center of the cross line of the casing, and the drilling shall be carried out after the stable liquid is injected.
 4. Drilling into the hole
Before hole formation, check the diameter of the drill bit, the wear of the drill bit, and replace the drill bit in time if the wear exceeds the standard during construction; correctly select the shape, specification and angle of the cutting teeth at the bottom of the drill bucket according to the soil layer condition; calculate the pile bottom elevation according to the pile casing elevation, pile top design elevation and pile length, so as to control it during drilling.
 5. Hole-forming
The construction shall be carried out according to the parameters determined in the test pile construction, and a full-time recorder shall be set up to record various parameters of the hole-forming process, such as adding drill pipe, drilling depth, geological features, mechanical equipment damage, obstacles, etc. Records must be careful, timely, accurate and clear. During the drilling process, the footage speed shall be controlled according to geological conditions: when drilling from hard formation to soft formation, the drilling speed can be appropriately accelerated; when soft formation becomes hard formation, slow down and advance slowly; in formation easy to shrink diameter, the number of hole sweeping shall be appropriately increased to prevent shrinkage; for hard plastic layer, fast speed drilling shall be adopted to improve drilling efficiency; for sand layer, slow speed drilling shall be adopted and mud weight and viscosity shall be appropriately increased. When the drilling rig is in place, it must be kept flat, stable and not inclined. In order to accurately control the depth of the hole, a wire measuring rope of 100 meters after checking shall be provided, and an automatic depth recorder shall be observed for observation and recording during construction.
 6. Hole bottom sedimentation control
The cutting and lifting mechanism of rotary drilling bucket is completely different from the cutting and lifting form of positive and reverse circulation hole formation in common rotary drilling. The former is to cut the undisturbed soil at the bottom of the hole into strips through the drilling bucket and load it into the drilling bucket for lifting and unearthed, while the latter is to break the undisturbed soil at the bottom of the hole through the drill bit and unearthed by the mud circulation belt. The bottom surface of the former is slow, the disturbance to the soil caused by drilling to the design elevation is very small, and there is no polysilting funnel. Therefore, the management of stable liquid should be strengthened, the solid content should be controlled, the viscosity should be increased, the rapid precipitation should be prevented, and the rotary digging amount of the two drilling buckets before the final hole should be controlled. After the hole-forming depth meets the design requirements, the drilling rig shall be displaced and the final hole acceptance shall be carried out as soon as possible. From the stop of hole cleaning to the start of concrete pouring, it should be controlled within 1.5-3h, generally not more than 4h, otherwise the hole should be cleaned again. The construction method of rotary bored pile has the advantages of reliable construction quality, fast hole-forming speed, high hole-forming rate, strong adaptability, greatly shortening the construction period, less waste slurry, low noise and low pollution, protecting the environment, overcoming the shortcomings of more silt at the bottom of the hole, low pile side friction resistance and poor mud management during mechanical hole-forming, and greatly improving the construction quality. Although the first input cost is large, the economic and technical indicators such as hole-forming cost consumption are lower than other methods of hole-forming cost, is an ideal construction process, compared with other processes, comprehensive consideration is to reduce the cost.