Due to its advantages of fast construction speed, high quality of hole forming, small environmental pollution, flexible and convenient operation, high safety performance and strong applicability, the machine has become the primary hole forming equipment for Bored Pile Construction in engineering field. Rotary bored pile is widely used in railway, highway bridge, municipal construction, high-rise buildings and other foundation projects. The rotary drilling rig was introduced in the United States before World War II, and developed in Europe after World War II. In the early 1980s, China began to introduce its core technology from Japan and the United States and digest and absorb it. It is mainly suitable for the construction of sandy soil, cohesive soil, silty soil and other soil layers, and is widely used in the construction of cast-in-place pile, continuous wall, foundation reinforcement and other foundation construction. Rotary drilling bored pile is mainly divided into dry rotary excavation method and wet rotary excavation method with static slurry wall protection. Based on many years of site construction management experience, the paper briefly discusses the problems existing and should be paid attention to in the construction of wet rotary excavation method with static slurry wall protection.
1、 Construction technology of Rotary Pile
Construction technology: pile foundation positioning → steel casing embedding → mud making → drilling machine in place → soil drilling → slag removal → reinforcement cage fabrication and installation → pipe penetration → underwater concrete pouring → casing pulling out.
1. Pile foundation positioning. According to the coordinate points given by the construction, the axis coordinate control point is led to the fixed position which is not affected by the construction. The axis detail orientation is determined by the total station or theodolite. The pile center and original ground elevation of each pile are determined according to the plane size of pile foundation construction, and the reinforcement (length of 25cm-30cm) is embedded, and lime marking line is sprinkled; Inform Party A's on-site personnel, supervision personnel and relevant engineering and technical personnel to recheck the pile position and original ground elevation.
2. Embed steel casing. The pile casing shall be positioned according to the center orientation of the original pile position, and the control positioning point shall be led out without affecting the pile casing embedding. The pile casing shall be buried correctly, and the length of embedding shall be determined according to the site soil conditions, and shall be buried deeply and firmly as far as possible, and the surrounding soil shall be tamped in layers. The upper edge of the pile casing shall be higher than the ground (about 10cm), and the center of the pile casing mouth shall coincide with the setting out center of the pile foundation as much as possible, with an error of less than 5cm. The coordinates of the pile foundation and the original ground elevation shall be rechecked here.
3. Mud production. According to the specific conditions of the construction site, the slurry pit is set up, and the natural slurry making method is selected to make the slurry according to the specific conditions of the construction soil. Prepare to transport the mud, and the slurry pipeline shall not have cracks to prevent mud leakage from polluting the construction site. The diversion pipeline is used together to lead the mud from the pile hole of the rotary excavator into the mud pit, and the mud is reused to prevent the mud from flowing around the construction site.
4. Rig in place. Move the drilling rig to align the drill bit with the pile position, determine that the pile position error is less than 1.5cm, and adjust the straightness of drill pipe to ensure the straightness of hole forming.
5. Drilling step soil. According to the soil condition of the specific soil layer, the rotary excavator determines the drilling speed of the drilling machine, ensures the quality of the hole forming and prevents various accidents in the construction.
6. Slag removal. When the drilling meets the planning requirements (pile length, rock socketed depth, rigid angle, etc.), the drilling rig stops construction, informs the relevant personnel to carry out pile hole inspection and prepare to put the reinforcement cage device in place. After the inspection is qualified, the reinforcement cage device will be arranged before the pile hole finishing, and the reinforcement cage will be installed immediately after the pile hole finishing, and then the concrete will be poured.
7. Fabrication and installation of reinforcement cage. The length and reinforcement specification of reinforcement cage shall be processed according to the planning requirements of planning drawings, and the welding and binding of reinforcement shall meet the requirements of construction specifications. When placing the reinforcement cage with crane, it should be aligned with the hole position, install according to the planned depth, fix the orientation in time, and take measures to ensure the thickness of the protective layer of the reinforcement.
8. Catheterization. Before using the conduit, try to connect it to ensure that there is no water leakage, air leakage and deformation of the pipe, so as to prevent the occurrence of water and slurry leakage accidents in the process of concrete pouring, which will affect the quality of concrete pouring. The connection length of the conduit shall not be slightly greater than the depth of the borehole to ensure that the distance between the bottom of the conduit and the bottom of the hole is less than 0.5m during the initial concrete pouring. The connection of conduit should be carried out immediately after the reinforcement installation to prevent the soil falling from the pile hole wall, increase the amount of sediment in the pile hole and affect the quality of the pile body.
9. Underwater concrete pouring.