Pier foundation hole leading method construction

(1) The diameter of the pilot hole should not exceed 0.9 times of the diameter of the pipe pile, and measures to prevent collapse of the hole should be taken. The depth of the pilot hole should not exceed 12m;

(2) It is advisable to use long spiral drilling machine to lead the hole. Long spiral drilling machine can drill through strong weathered granite layer, high strength hard interlayer or solitary stone, and the vertical deviation should not be greater than 0.5%;

(3) When the borehole needs to pass through the hard interlayer, the diameter of the borehole can be taken as D-20mm of the pile diameter; when the borehole enters the high number of strikes and deep weathered rock layer, the same diameter borehole can be used;

(4) The pilot hole should be 1m into the bearing layer to reduce the soil extrusion effect, and the diameter of the pilot hole can be taken as D-50mm;

(5) For the "cautious use of site" of pipe piles with relatively inclined bearing stratum, thin non-soft soil layer and obvious soil extrusion effect, the construction measures of hole drilling method should be determined according to the site type, pile driving method and pile tip form.

Note: Pre-drilled holes (pilot holes) are commonly used in pipe pile construction to penetrate hard interlayers and isolated rocks, reduce soil displacement effects, and increase pile penetration depth. Based on engineering experience and site conditions, the pilot hole diameter should be determined according to soil properties, pile diameter, and pile density. Generally, pilot holes can be 10cm or 5cm smaller than the main pipe pile diameter, with equal-diameter pilot holes being optional when necessary. Pilot holes should not exceed 12m in depth, as excessive depth complicates vertical alignment control and makes misalignment correction difficult, potentially causing pile breakage. When drilling into high-strength weathered rock layers with deep penetration, even larger pilot holes (D-20mm) may result in "hanging foot piles" where sinking fails to reach the bottom. Equal-diameter pilot holes should be used when necessary. For water accumulation in pilot holes, open-type pile heads are recommended; using sealed-type pile heads may lead to similar issues as hanging foot piles.

Preliminary prestressed pipe pile foundation floating pile, pile delivery, and re-drive (press)

(1) When static load test is carried out with 2~2.2 times single bearing capacity characteristic value R, the settlement can be controlled within 15~25mm;

(2) The uplift of the pile is less than 10mm, which has little influence on the single bearing capacity and settlement (15~25mm), so it can be not re-driven (pressed);

(3) When the pile floating amount is 10~20mm, it has little influence on the bearing capacity of a single pile but the settlement may be too large, it is advisable to re-drive (press);

(4) The floating amount of the pile>20mm may have a great impact on the bearing capacity and settlement of the single pile, and all parties on site should jointly study measures; 

(5) When the range where floating piles may be generated needs to be re-bored (pressed), the pile length should not be greater than 1m;

(6) When the shallow soil belongs to the weak soil layer, the static pressure recompaction should be used with caution; when the pile head has been cut off, the hammer compaction should be used with caution;

(7) Pile driving depth without need for re-driving (pressing) range: Hammer type should not be greater than 2m, if the power loss is not obvious during construction, it can be controlled to be less than 3m; static pressure type should not be greater than 6m.