Precautions for the Super Cell installation and lowering with CFA cage
2022-05-16
The construction process of CFA pile (bored and grouted pile) is as follows. There are several precautions for the super cell installation and lowering with CFA cage.
A) In addition to meeting the design and relevant acceptance specifications for the rebar cage production, each section of the coiled rebar and the telltale rod that transmits the displacement must be firmly connected to the main rebar by solid welding. The bottom part of the rebar cage with length of 300-1000mm should be made into a cone shape as below picture by firm and reliable welding (It should have some distance between the cone part and the Super Cell to avoid the impact of excessive force when the cone part inserts into the concrete), and there should be a reinforced structure to ensure that the vibration force is effectively transmitted to the cage toe.
B) Lift the Rebar Cage
When lifting the rebar cage installed with the Super Cell, the Super Cell should be prevented from being bent, and must be lifted by two hooks (for example: use a 50T crane to hoist the vibrator, the vibration tube and the rebar cage as a whole, align the pile hole, and insert vertically from the center).
C) Lower the Rebar Cage
① Modify the CFA drill rig to reduce the time difference between grouting and lowering the cage. Start inserting the rebar cage within three minutes after the superfluid concrete is grouted. By reducing the time difference, it can reduce the difficulty of inserting the rebar cage.
② After the CFA rig completes the drilling and grouting, clean up the surface soil in time, and immediately carry out rebar cage insertion construction. Insert the steel pipe for vibration (it is necessary to ensure that the steel pipe is 2 meters longer than the total length of the rebar cage) into the rebar cage at the ground level (and must pass through the center hole of the Super Cell), and firmly connect the top of the rebar cage with the vibration device.
③ Because the rebar cage is long, during the process of lowering and inserting the cage, the verticality of both cage sides should be observed through plumb lines. If the verticality deviation gets big, the rig operator should stop the operation, and the installation operator should align the rebar cage with the pile position, then continue.
④During the rebar cage lowering process, it is necessary to bind the telltale tubes and the hoses to the main rebars. The telltale tube is tied by wire every 0.5m, and the hose is tied every 1 meter. When the telltale wire is used and arranged outside the rebar cage, it is necessary to add 4pcs of main rebars on the outside of the rebar cage to guide and tie the telltale wire up to the ground, to ensure the verticality and effective protection of the telltale wire.
⑤ If the length of the rebar cage is long, in order to avoid the difficulty in cage transportation and penetration of vibration pipe, the rebar cage should be made in several sections, and the weld them together after vibration steel pipe is installed.
⑥ When lower the rebar cage, the cage must be pressed in by its self-weight first, vibrating hammer will be only used when the self-weight doesn’t work, to avoid the cage deviation caused by the vibrating hammer. The insertion speed should be controlled at 1.2~1.5m/min.
⑦ After inserting the steel cage to the designed position, switch off the power of the vibrating hammer, and take off the steel wire rope. Use the CFA rig to lift the vibrating steel pipe and hammer out of the pile. During the lifting process, the extraction speed should be slowed down at the position of the Super Cell. It is recommended that during the lifting out process, the vibrating hammer is turned on once every 3m height to ensure the compactness of the concrete and soil.
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