1. Piling equipment shall comply with the following provisions:

1.1 Based on site conditions, project characteristics, pre-construction pile-sinking process tests, pipe pile cross-sectional dimensions and strength, characteristic value of bearing capacity, soil properties of the bearing stratum and penetration depth, refer to Appendix D of the Technical Specification for Hammer-Driven Prestressed Concrete Pipe Pile Engineering DBJ/T 15-22-2021 and follow the principle of "pile-hammer matching, heavy hammer with low blow" for comprehensive consideration before selection.

Appendix D

1.2 The pile frame and base must have sufficient strength, stiffness and stability, and shall match the pile hammer.

1.3 Hydraulic hammers or diesel hammers should be selected for piling; free-fall hammers should not be used;

1.4 For diesel hammers, tubular diesel hammers should be selected.

1.5 The construction site shall be equipped with auxiliary equipment and measuring instruments according to work requirements.

2. The arrangement of pile caps and cushion layers shall comply with the following provisions:

2.1 The pile cap shall have the required strength, stiffness and driving resistance;

2.2 The sleeve of the pile cap shall match the diameter of the pipe pile being driven. The sleeve at the lower part of the pile cap for fitting the pile head shall be made cylindrical, and the center of the cylinder shall coincide with the center of the hammer cushion. The depth of the cylinder body should be 350mm~400mm, and the inner diameter should be 20mm~30mm larger than the outer diameter of the pipe pile. It is strictly prohibited to use transitional steel sleeves or to drive small-diameter pipe piles with large pile caps;

2.3 During piling, an elastic pile cushion shall be placed between the bottom surface of the pile cap sleeve and the pile head. The pile cushion may be made of materials such as cardboard, coir rope, plywood, and steel strand, and its thickness shall be uniform. After compression, the thickness of the pile cushion shall be 120mm~150mm, and it shall be frequently inspected during piling and replaced or replenished in a timely manner;

2.4 A hammer cushion shall be placed at the upper part of the pile cap where it directly contacts the pile hammer. The hammer cushion shall be made of straight-grained hardwood, steel wire rope, and high-molecular polymers, etc., with a thickness of 150mm~220mm, and shall be inspected, corrected or replaced before piling.

3. The pile follower and its cushion arrangement shall comply with the following provisions:

3.1 The body of the pile follower should be made cylindrical and shall have sufficient strength, stiffness and driving resistance. The upper and lower end surfaces shall be flat and perpendicular to the central axis of the pile follower. The length of the pile follower shall meet the requirements of the follow-driving depth, and the bending degree of the body shall not exceed 1/1000;

3.2 A sleeve shall be provided at the lower end of the pile follower, with a sleeve depth of 300mm~350mm and an inner diameter 20mm~30mm larger than the outer diameter of the pipe pile;

3.3 It is prohibited to use plug-pin type pile followers with only a small cylinder provided in the middle of the lower end surface; it is also prohibited to use cylindrical pile followers without any limiting device on the lower end surface;

3.4 During pile following operations, cushioning such as hard cardboard or waste plywood shall be placed inside the sleeve of the pile follower, and the thickness of the cushion after being compacted by hammer blows should not be less than 60mm.

4. Pile sinking construction shall comply with the following provisions:

4.1 After the first section of pipe pile is lifted into position and inserted into the ground, the pile position and verticality deviation of the pile body shall be carefully checked. The pile position deviation shall not exceed 20mm. The verticality deviation shall not exceed 0.5%;

4.2 When the pipe pile encounters a thick silt layer or soft backfill soil after being sunk into the surface soil, the diesel hammer shall be operated in a non-ignition idle hammer manner. The hydraulic hammer shall be operated with a drop height of 200mm~300mm;

4.3 During the driving of pipe piles, heavy hammers with low blows should be used, and the centerlines of the pile hammer, pile cap and pile body shall be kept on the same straight line, and the verticality of the pile body shall be checked at all times. When the verticality deviation of the pile body exceeds 0.8%, the cause shall be identified and corrective measures taken; after pile sinking, it is strictly prohibited to correct deviation by moving the pile frame;

4.4 When driving pipe piles in deep clay, silty clay layers, or sandy soil, pile sinking, pile splicing and pile following should be carried out continuously to minimize intermediate rest time, and pile splicing near the design depth should be avoided as much as possible;

4.5 The elevation positions of pile joints should be appropriately staggered, and the number of piles at the same joint elevation should not exceed 50% of the total number of piles;

4.6 For pipe piles with a diameter not less than 700mm, or when the inner hole of the pipe pile is filled with water or silt during construction, an exhaust (water) hole shall be provided at the pile top;

4.7 When pile sinking difficulties occur during the driving of pipe piles in deep clay, silty clay layers, or sandy soil, reliable pile sinking measures should be selected based on trial piling experience, site conditions, construction equipment, etc. When using a hydraulic hammer for construction, the stroke of the heavy hammer shall be controlled, and the stroke should not exceed 1m. When necessary, reliable auxiliary measures such as pre-boring, high-pressure water jetting or other methods should be adopted to assist pile sinking, and pipe piles inserted into cement-soil or the implant method may also be used for pile sinking;

4.8 During the sinking of inclined piles, the pile frame shall be kept consistent with the design inclination of the pile.

5. The specifications and structure of pipe pile tips should comply with the provisions of Appendix E of the Technical Specification for Hammer-Driven Prestressed Concrete Pipe Pile EngineeringDBJ/T 15-22-2021The welding machine, welding electrodes, current, process, quality and other requirements adopted for welding shall comply with the provisions of the industry standard Code for Welding of Steel Structures GB50661.

6. Pile sinking shall be suspended when any of the following special circumstances occurs. Construction may continue only after research and handling with design, supervision and other relevant personnel:

6.1 Sudden change in pile penetration resistance;

6.2 Large discrepancy between the pile penetration depth and the design requirements;

6.3 The actual pile sinking situation obviously does not conform to the soil layer properties in the geological report;

6.4 Spalling or crushing of the pile head concrete, or cracks or crushing of the pile body concrete;

6.5 Sudden inclination of the pile body;

6.6 Obvious ground heave, upward floating or excessive displacement of adjacent piles;

6.7 Abnormal sounds during pile sinking;

6.8 Pile pressing not reaching the required position, or the total number of hammer blows exceeding the specified value.

7. Pile following shall comply with the following provisions:

7.1 When there is a relatively thick silt layer below the ground surface, the pile following depth should not exceed 2m. When re-driving is planned, the pile following depth should not exceed 1m;

7.2 When the pile top is driven close to the ground and pile following is required, the verticality of the pile shall be measured and the pile head quality checked, and pile following shall be carried out immediately after passing inspection;

7.3 The final penetration of pile following shall be corrected by reference to the final penetration of piles under the same conditions without pile following;

7.4 When there is no silt layer below the ground surface, the buried depth elevation of the top surface of the bearing stratum at the pile end is basically consistent, and the thickness of the bearing stratum is not less than 4m, or there is a relatively thick fully weathered rock layer, hard plastic to hard clay layer, or medium dense to dense sandy soil layer above the bearing stratum, the pile following depth may be appropriately increased, but should not exceed 6m.

8. When the bearing stratum at the pile end is a weathered rock (soil) layer that softens upon contact with water, an integrated pile tip should be used. If the design requires bottom-sealing concrete construction inside the pipe pile hole, the bottom-sealing concrete construction shall comply with the following provisions:

8.1 The pile tip shall be of the closed type, and the weld seam during pile tip welding shall be continuous and full without water seepage;

8.2 After the first section of pipe pile is driven into the soil (rock) layer, C20 fine stone concrete with a height of 1.5~2.0m should be immediately poured manually into the bottom of the pipe pile inner hole, or after the hammer is stopped and the inner wall of the pipe pile is checked by lighting or in-hole camera to be basically intact, bottom-sealing concrete should be poured immediately.