4.1 Drum-type diesel hammer impact pile driving method
(1) The method of “heavy hammer and low strike” should be adopted for piling.
(2) The pile frame generally adopts a 3-point support crawler pile driver.
(3) The elevation of the pile top of the steel pipe pile in the piling sequence is often buried below the natural ground according to the design. During construction, it can be adopted: @ excavate the soil to the design elevation of the pile top before piling; ② The pile top is driven to the natural ground, and then the pipe is cut To the design elevation of the pile top, then excavate the soil; ③ After the pile is sent to the design elevation of the pile top, the soil is excavated;
When the soil is weak, it is difficult to dig the soil first and then piling; or when the pile is relatively long, the hammering energy is large when the pile feeding method is used, and the predetermined depth may not be driven; or when the engineering geology is complex and the bearing layer elevation fluctuates, Method 2 can be used. For short piles or when the piling resistance is small, the piles can be sent to the pile top elevation, and the pile delivery depth is generally controlled at 5-7m (the eighth method). When precipitation measures are available and the soil quality at the design elevation of the pile top is good, the first method can be used.
According to the flow method, the piling sequence is considered, and in principle, it is carried out according to “first group piles and then single piles”, “deep first and then shallow”, “large and then small”, and “deviation from environmental protection objects”.
(4) Penetration of the middle layer Generally speaking, the situation of opening 11 steel pipe piles to penetrate the hard middle layer is as follows: the gravel layer with a CN value of 50 or more is often impossible to penetrate when the thickness is 5m. ②The viscous layer with N value above 30, when the thickness is 2~3m, generally cannot penetrate; if the N value is less than 30, it may penetrate between 5~-6m. 3 For the sand layer, it is easy to penetrate when the particle size is the same, and it is difficult to penetrate when the particle gradation is good. When the lower layer of the middle layer is weak, it is easy to penetrate even if the middle layer is slightly hard. When the depth of the middle layer is up to 20m, it is easy to penetrate, but when the depth is 25~30m, it cannot penetrate. 6 When it cannot be penetrated, the middle excavation method or the pre-drilling method can be used, and the penetration becomes easy. ⑦ When the middle layer is used as the bearing layer at the pile end, the consolidation settlement of the lower layer should be considered. In the above cases, there are some differences depending on the diameter of the pile and the size of the hammer. Compared with the open pile of the same diameter, the ability of the closed pile to penetrate the middle layer is reduced by 1/4~1/2 with the same pile hammer.
(5) After connecting the pile, the lower section of the pile sinks to the point where the top of the pile is 0.5~0.8m away from the ground, and then the strike is suspended. Check whether the top of the lower section of the pile is deformed. If there is any damage, it can be repaired with a jack, etc. Oil stains and other attachments that are harmful to welding. If the upper section pile is deformed, it needs to be repaired and then erected. On-site joint welding needs to be cooled for 1 minute before piling operation. (6) When the pile-feeding shaft is used for pile driving, there should be no discontinuous surface between the pile feeding shaft and the pile top, otherwise the pile top will move laterally during driving, and the transmission of the shock wave will be unstable, which often causes the penetration of the pile. Enter impossible.
(7) The reference standard for stopping hammering of piles, as shown in Table 3.