Rotary drilling rig is a rising star in pile machinery, which has developed rapidly in recent years. In the early market, it was occupied by foreign products with high prices, and users were limited to a few large companies with strength. After 2003, as domestic enterprises saw the superior performance of rotary drilling rigs in the construction of the Qinghai-Tibet Railway, they rushed to produce them, making rotary drilling rigs the most popular pile machinery product in the shortest time. With the significant reduction in prices, the wide application of rotary drilling method in China has been promoted. After nearly ten years of development, the overall performance of domestic rotary drilling rigs has approached or reached the international advanced level. China has now become the world's largest producer and user of rotary drilling rigs.

　　The following is an overview of the construction technology of rotary drilling rigs:
　　I. Construction preparation work.
　　The content includes cofferdam and island building, site leveling, setting out and protecting pile positions, and checking whether the pile positions are accurate. When the rotary drilling rig is in place, the maximum inclination angle with the ground plane shall not exceed 4°, the site ground bearing capacity shall be greater than 250kN/m2, and the drilling rig platform must be compacted. 　　II. Drilling operation procedures.
　　 1. Adjust the drill bit. After the drilling rig is in place, align the drill bit with the center of the pile position, install the reamer blades, and adjust the center and verticality of the drill pipe according to the data provided by the drilling rig instrument. It is required that the center of the drill pipe coincide with the center of the casing when finally positioned. At the same time, slightly lift the drilling tool to ensure that the drill bit ring cutter floats freely in the hole, and then drill.
　　2. Install the casing. When the drilling reaches a certain depth, press in the casing. Selection of casing size: In the static slurry wall protection drilling process of rotary drilling rig, the casing diameter is generally φ + (100～300), and the casing length is determined by the construction geology and the mud used, generally 2～4m high. When the casing length is large, the casing diameter is φ + 100. When there are loose sand layers and sand-gravel layers that require mud to protect the hole wall, the casing diameter is φ + 300. The casing must be not easy to tear, deform, and leak. The requirements for casing embedding: ① The lower foot should be embedded in a stable and non-leakage formation as much as possible; ② The water head height should meet the wall protection requirements; ③ The minimum height above the ground surface is 30cm. According to the site geological conditions, before embedding the casing, protective piles should be set and cross lines should be pulled so that the casing can be reset after embedding to ensure the correctness of the pile position. The deviation of the casing center shall not be greater than 50mm, and the elevation of the upper part of the casing shall be measured at the same time. After the casing is embedded, the surrounding area should be tamped with clay to ensure that there is no water leakage around the casing, so as to avoid hole collapse.
　　3. Mud preparation. Remove the reamer blades, inject mud into the hole as a wall protection stabilizing liquid, and inject polyacrylamide stabilizing liquid if necessary. Mud preparation and circulation are completed by the NE525 mud processor. Two aspects should be noted in mud preparation: The specific gravity of the mud should be controlled between 1.15 and 1.2, and should be adjusted at any time according to different geological conditions. The viscosity should be controlled at 17～20s, and the sand rate should be controlled within 4%. Commonly used mud materials are generally prepared by adding caustic soda, polyacrylamide or cellulose to high-quality bentonite; the second is the speed of mud replenishment. Mud replenishment generally adopts pumping, and its speed is based on ensuring that the liquid level is always above the casing surface. Otherwise, it may cause hole collapse and affect the quality of hole formation.
　　4. Drilling to form a hole. After drilling starts, turn on the hydraulic transmission to pressurize, the drill pipe rotates forward and sinks, cutting the soil to drill, lift the drill pipe to discard the soil out of the hole, and at the same time inject mud into the hole. During the drilling process, the mud water level should be kept higher than the groundwater level to avoid hole collapse. In the drilling process of fine sand layers, the drill bit must be lifted slowly, the drill pipe speed should be reduced to a low gear, and polyacrylamide stabilizing liquid should be used in construction. Through the centrifugal force of the drill bit, the polymer material is condensed on the hole wall, forming a tough adhesive film on the hole wall, so that the mud in the hole will not leak, preventing the hole wall from collapsing, and achieving the effect of stable drilling. When the drilling depth reaches the design requirements, check the hole depth, hole diameter, hole position and hole shape, etc. After confirming that the design requirements are met, immediately fill in the final hole inspection certificate, and after approval by the resident supervision engineer, the preparation work for hole bottom cleaning and underwater concrete pouring can be carried out.
　　5. Hole cleaning operation. Treatment of the hole bottom after drilling is terminated. After drilling is terminated, stay for 20～30 minutes to allow the residue to settle, then replace with a hole cleaning drill bit, lower it slowly, and remove the residue at the bottom of the hole to prevent the drilling slag from floating up and affecting the hole cleaning effect. The thickness of the sediment in the hole is required to be no more than 5cm. Before pouring underwater concrete, use high-pressure water to blow the bottom and turn up the slag to further reduce the thickness of the sediment at the bottom of the pile. After hole cleaning, check the borehole again. The mud performance indicators after hole cleaning: sand content less than 4%, specific gravity 1.05-1.2, viscosity 17-20S. It is not allowed to deepen the hole depth instead of cleaning the hole.
　　6. Accident handling. a. Treatment of hole collapse. If hole collapse occurs during drilling, find out and analyze the cause. After taking measures such as deepening the embedded casing, drilling can continue. A large amount of dry sawdust can also be added to the mud, and the specific gravity of the mud can be increased (controlled between 1.15 and 1.4) to improve the hole wall structure. Each time the drill bit enters the liquid surface, the speed should be very slow. After the drill bit completely enters the slurry, it should be lowered to the bottom of the hole at a uniform speed. The lifting speed each time should be controlled at 0.3～0.5m/s. In case of severe hole collapse, backfill and re-drill.
　　b. Treatment of hole shrinkage. When the borehole has a bent hole or shrinkage, generally the drill bit can be lifted to the deviated hole position for repeated sweeping until the borehole is straight. If severe bending or protruding stones occur, a mixture of small crushed stone or pebbles and clay should be used to backfill the deviated hole position. After the filler settles, drill again to correct the deviation.
　　c. Treatment of buried and stuck drill. Buried drill mainly occurs when the drilling footage is too much at one time and the mud settles too fast in the sand layer; stuck drill mainly occurs when the bottom cover of the drill bit is not closed well, automatically opens during drilling, or when drilling in pebble formations, pebbles fall and cause stuck drill. After buried or stuck drill occurs, a large amount of mud will definitely settle around the drill bit, forming a large lateral resistance. Therefore, the treatment plan should first eliminate the resistance. Forcible treatment is strictly prohibited; otherwise, it may cause more serious accidents such as drill pipe twisting and power head damage. If an accident occurs, ensure that there is enough mud in the hole, maintain the pressure in the hole, stabilize the hole wall and prevent collapse, laying the foundation for accident handling. 　　III. Fabrication and installation of reinforcement cage.
　　After the drilling operation is successfully completed, the installation procedure of the reinforcement cage begins. In order to connect the construction process in time, the reinforcement cage is generally made before the drilling is completed. The rigid skeleton used for the reinforcement cage is processed and manufactured on site. The specific construction method is omitted here.
　　IV. Concrete pouring.
　　After hole cleaning is completed, concrete should be poured as soon as possible, and the interval should not exceed 30 minutes. The commonly used ball-cutting method is used for bottom sealing. The specific construction method is omitted.
　　V. Pile head treatment and pile foundation testing.
　　After the pile foundation reaches 70% of the design strength, pile head treatment can be carried out. According to the requirements of the foundation inspection list and the owner's approval opinions, the pile foundation shall be tested for integrity one by one using dynamic testing, sonic transmission method, and core drilling method. Only after passing the inspection can the next construction process be entered.