Construction process
Generally, the rotary drilling rig is used to form holes for drilled piles, together with a mud mixer and pump, as well as cage processing equipment and lifting equipment. In order to prevent the two adjacent piles from being too close to each other or the interval time is too short, which may cause the collapse of the holes, the construction is carried out by skipping holes in batches, and the adjacent holes should not be constructed consecutively, and the interval between the two adjacent piles is ≥24h.
Drilled piles construction process: Pile position defense line, manual digging exploration → burying the shroud → drilling rig in place → drilling → love holes → holes checking → drilling rig shifting → cage making and installing → lower conduit → preparation for concretization → dismantling and filling → concrete filling → concrete filling → the work is done by rotary driller, and the concrete filling equipment and hoisting equipment. Work→concrete filling→dismantling and pulling out the protective tube→backfilling the hole.
Preparation work before construction
After entering the site, debris should be removed in time. Due to the complexity of underground pipelines in Beijing, it is necessary to carry out manual excavation first, determine the pile position without pipelines, set the centerline according to the design drawings of the relevant requirements of the drilled pile position, as well as the pile position P. Measurement of the line using a total station, determine the position of the pile, and then do the corresponding marking and protection.
3.3 Burying the shroud
When burying the shield, its center axis should be right at the center of the pile, maintain its verticality, and backfill the surrounding area with clay in layers to prevent the displacement and fall of the shield caused by mud loss. If the soil layer at the bottom of the shield is not clayey, it should be dug deeper or replaced, and then the shield should be put in place.
Installation of drilling rig
The drilling rig should be installed under the guidance of technical experts and should be carefully leveled to prevent tilting and shifting after it is installed in the designated position.
Mud preparation
Due to the fast speed of the rotary drilling rig, once the wall construction is not handled well, it is easy to collapse the hole P, so attention should be paid to the quality of wall mud requirements. The mud used to open the hole is made of high-quality bentonite, and the specific gravity, viscosity, sand content and colloid rate should be measured frequently during the construction.
Construction control
Drilling rig in the construction of the early need for slow running, in order to grasp the various factors affecting the formation, and then determine a variety of drilling parameters. Because of the use of mud wall protection, need to give it enough time to protect the wall, so the drilling should not be too fast, and keep the mud surface higher than the top of the barrel 40cm. lifting the drill, need to make up the slurry to the hole in a timely manner, in order to maintain the height of the slurry.
Hole inspection and hole cleaning
When the drilling reaches the specified depth, lower the conduit in time to clear the hole. Through the mill type ”, slag fishing method, can be a slag fishing or multiple slag fishing. According to various geometric size testing requirements, qualified and then under the steel cage conduit, and mud pump to clear the hole again. Review the thickness of the sediment at the bottom of the hole, if more than required, before pouring concrete, the bottom of the hole for a few minutes of high-pressure water jet or blowing, so that the sediment floats immediately after the pouring of underwater concrete.
Reinforcement cage production, security
The reinforcement cage is processed uniformly through the processing yard, and the main bars are connected by welding. In order to ensure that the center of the cage and the drill hole coincide with each other, and to ensure the thickness of the protective layer, along the longitudinal and circumferential direction, every certain distance to set the protective pads. When the cage is lowered, the center of the pile is marked on the sheath to ensure that the center is the same as the center of the pile. The reinforcement cage should be fixed with a hanging bar to avoid floating when pouring concrete.
Underwater concrete filling construction
The concrete filling usually chooses to lift the conduit method, the conduit down to the bottom of the hole from 0.5m, and the diameter of the conduit is 30cm, every 1~2m for the subsection. The bottom section is 4m long, and flange bolts will be connected to each section, before filling the pipe needs to be checked, after passing the inspection can be used.
The bottom funnel should be installed on the conduit, use the homemade concrete ball to form a waterproof plug between the two, and seal the bottom by dialing the ball method. When lifting the conduit, keep it smooth, and forbid to raise the conduit to the concrete surface, when pouring the conduit buried depth in 2~6 m. While pouring and pulling, strictly control the calculation of the last pouring concrete quantity, make the top elevation higher than the design elevation 0.5~0.8 m, and ensure the quality of the pile top concrete.
Rotary drilling rigs are widely used in subway construction, which can improve the construction quality and efficiency. With the continuous development of construction technology, rotary drilling rigs have more mature construction technology and some of the original defects have been effectively solved, which enhances the economic efficiency of the construction enterprises and has a better development prospect.
For more details on specific adjustments and maintenance practices, consult another article or contact a qualified technician.
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