1. Pile sinking quality control

Pile sinking should be suspended when the following situations occur; analyze the causes and take countermeasures:

(1) During pile sinking, the pile body undergoes significant displacement, sudden settlement or tilting, or there are obstacles underground;

(2) The pile pressing resistance changes drastically, and the pile is difficult to penetrate a hard interlayer with a soft underlying layer;

Pile body squeezed and broken during hammer-driven pile sinking

(3) Abnormal phenomena such as cracks in the pile body and concrete damage at the pile head;

Pile head bursting

Pile body cracks

Pile head buckling

(4) The connectors at the pile joint are uneven or the gap is not tightly filled, or the two pile sections are not on the same straight line, resulting in loosening and cracking at the joint, poor weld quality, and insufficient cooling time; (5) The pile pressing machine sinks, the clamping mechanism slips, the pile pressing machinery operates abnormally, etc.

Pile repair with epoxy resin

2. Soil excavation between piles: Improper excavation methods for soil between piles in pipe pile foundations can easily cause squeezing and displacement due to unbalanced soil pressure on both sides of the pipe pile!

Improper excavation method; silt squeezing causes displacement of pipe piles

Unbalanced soil pressure on both sides of the pipe pile causes squeezing and displacement

2. Technical measures

1. Measures to prevent soil squeezing

To reduce soil compaction and pore water pressure caused by continuous pile sinking and the impact on buildings, and to avoid and mitigate the hazards caused by the above pile pressing, based on past experience, the following measures can be taken:

(1) Speed limit: Strictly control the pile sinking speed, i.e., control the number of piles pressed per unit time (e.g., 1 d), to avoid severe soil squeezing and pore water pressure.

(2) Correctly determine the pile pressing sequence: Optimize the construction process. Generally, soil squeezing is more severe in the advancing direction of pile pressing; therefore, pile sinking should be advanced away from the protected object.

(3) Adopt technical measures such as excavating vibration isolation trenches and drilling stress relief holes filled with sand and gravel.

2. Measures for handling obstacles encountered during pile foundation construction

If obstacles are encountered during construction or if pile driving is relatively deep, single piles are prone to deviation, directly affecting project quality. Therefore, practical and feasible methods must be adopted to handle them so that construction can proceed more smoothly. The specific measures are as follows:

(1) Before construction, set out the pile position axes in advance, conduct targeted probe holes, and promptly notify the owner and supervision unit of the probe hole conditions.

(2) For shallow obstacles, during pile pressing (driving) construction, use a pile follower to probe first and break through the obstacle, and then carry out pile driving construction.

(3) For slightly larger deep obstacles, use an excavator to remove the obstacles before carrying out pile driving construction.

3. Measures for handling difficult pile sinking

When the pressure during pile sinking is too high and the pile cannot be pressed (driven) to the design elevation of the pile top, generally in soil with a silty sand layer, the method of pre-drilling at the original pile position can be adopted to penetrate the sand layer so as to achieve the purpose of pile sinking. The diameter of the pre-drilled hole is generally 350 mm, and the depth is determined according to the depth of the sand layer, leading to the bottom elevation of the sand layer. Pile sinking should be carried out immediately after pre-drilling, minimizing the interval to prevent hole collapse, and achieving drilling and driving in succession. If pile sinking still remains difficult, generally for the last 1-2 piles of a pile group cap, add 2-3 more relief holes.