Bored piles are divided into bored piles and dug piles, which are mainly used in engineering construction.
Piles can be divided into two types according to hole-forming methods: bored piles and dug piles. Digging piles are dug manually, and drilling piles are drilled mechanically, depending on different machines. Then, in the construction of bored piles, the conventional construction technology is as follows:
Construction technology of bored pile;
1, the construction preparation of bored piles shall meet the following requirements:
Before drilling, a firm and watertight orifice casing shall be set. The inner diameter of casing should be about 20 cm larger than the diameter of bit. The top surface of casing shall be 2m higher than the construction water level or underground water level, and meet the requirements for the height of mud surface in the hole, and shall be 0.3m higher than the construction ground in dry land or island buildings. The embedded depth of the gasket shall meet the following requirements:
(1) When burying the liners, clay should be backfilled around the liners and compacted by layers. The liner can be sunk by hammering, pressing and vibration.
(2) When building an island in the river, the pile casing should be buried at a depth of1m; Below the riverbed surface; The buried depth of underwater platform can be determined according to the highest construction water level, flow rate, scouring and geological conditions, and the impervious layer can be driven if necessary.
When the conduit sinks on the underwater platform, there should be a guide device to control the position of the conduit.
③ The deviation between the center of the top surface of the pile casing and the designed pile position is not more than 5cm, and the inclination is not more than 65438 0%.
2, in the sand, broken (egg) stone soil or clay interlayer drilling, appropriate USES bentonite mud wall protection. When drilling in cohesive soil, when the plasticity index is greater than 15 and the scum capacity meets the construction requirements, the undisturbed soil in the hole can be used to make slurry to protect the wall. When drilling a hole with an impact drill, the clay can be processed and put into the hole, and the drill bit can be used for impact pulping.
Drilling construction technology:
1), rig installation and drilling
(1) Before installing the drilling rig, the underframe shall be leveled and kept stable, and no displacement or sinking shall occur. The top of the drilling rig shall be tensioned symmetrically with cable wind rope, and the deviation between the center of drill bit or drill pipe and the center of casing shall not be greater than 5cm.
(2) The hole position of the opening must be accurate, and the initial hole wall should be vertical and round.
(3) When drilling, the water level in the hole should be higher than the bottom of the casing by more than 0.5m or higher than the underground water level1.5 ~ 2.0m.. After the impact drilling stops, water or mud should be added to the hole in time to maintain the head height, mud specific gravity and viscosity in the hole.
(4) When drilling, the speed of lifting and lowering the drill bit should be uniform, and it is not allowed to change speed excessively or suddenly, and it is not allowed to pile up around the drilling hole.
⑤ Drilling operations should be carried out continuously. When stopping drilling for some reason, the drill bit should be lifted out of the hole and the hole should be covered. During drilling, the change of soil layer should be checked and recorded regularly, and checked with the geological profile. After drilling reaches the design depth, check the hole position, aperture, hole depth and hole shape, and fill in the drilling record. Hole position deviation shall not be greater than 5cm.
2), impact drilling
① The weight of the drill bit should consider the adsorption of mud and the weight of wire rope and spreader, so that the total weight does not exceed the lifting capacity of the hoist.
(2) When drilling, small stroke drilling should be adopted, and normal drilling can only be carried out after the drilling depth exceeds the full height of the drill bit plus the normal stroke. In the process of drilling, Qin Ying loosens the rope and puts it in a proper amount, and an empty hammer is not allowed; Frequent slagging makes the drill bit often impact fresh strata. The amount of rope loosening each time is determined by geological conditions, bit form and bit weight.
(3) The steel wire rope for hanging the drill bit must be twisted in the same direction, soft and high quality, without dead bending or broken wires, and the safety factor should not be less than 12. A steering device must be set between the wire rope and the drill bit, and the connection should be firm. During drilling, always check the state and rotation to see if it is normal and flexible. When the main rope and the drill wire rope overlap, the diameters of the two ropes should be the same and the twisting direction must be the same.
(4) There should be a spare drill bit at the drilling site. If it is found that the diameter of the drilling bit wears more than 15mm, it should be replaced and repaired in time. Before replacing a new drill bit, check the hole to the bottom of the hole, and then put in a new drill bit after confirming that the hole is normal.
⑤ In order to prevent the adjacent hole wall from collapsing due to impact vibration or affect the concrete strength of the adjacent hole, the compressive strength of the adjacent hole concrete should reach 2.5Mpa before construction.
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