• General requirements

1. In areas without groundwater or with a small amount of groundwater and relatively dense soil layers or weathered rock layers, or where mechanical drilling is not feasible or extremely difficult, and where hydrogeological conditions permit, manual bored piles can be used for construction. Manual bored pile construction shall not be adopted when the pile diameter or minimum side width is less than 1200mm.

2. It is not advisable to use manual excavation construction in karst areas and goaf areas.

3. When the air pollutants in the hole exceed the third-level concentration limit stipulated in the current Environmental Air Quality Standard (GB3095) and there is no reliable ventilation guarantee, manual excavation shall not be adopted.

4. Artificial excavation shall not be used in areas rich in groundwater, weak soil layers and areas accessible to rock and soil and mechanical drilling equipment that release harmful gases.

5. Before the construction of manual bored piles, a special construction plan for manual bored piles shall be prepared, safety protection and emergency measures shall be implemented, experts shall be organized to demonstrate and approval procedures shall be fulfilled when the excavation depth of manual bored piles is greater than or equal to 16 meters, and safety technical instructions shall be given to operators and process control shall be strengthened.

6. Manhole bored piles should be selected according to the engineering geology and hydrogeological conditions, and the hole wall support mode should be selected according to local conditions.

7. The opening shall be equipped with a lock opening no less than 300mm above the ground, and the surrounding 60cm area of the lock opening shall be hardened, and a temporary drainage ditch shall be set up to prevent debris and surface water from flowing into the hole.

8. When excavating holes, adjacent piles shall not be excavated at the same time, and it is advisable to alternate and jump excavation.

9. For pile holes supported by concrete retaining walls, the wall must be constructed section by section as it is excavated. The height of each segment of the retaining wall must follow the construction technical plan; it is strictly prohibited to perform risky operations without proper support. The space between the outer side of the retaining wall and the hole wall should be filled solidly. If the filling is not dense or there are voids, measures should be taken to address the issue.

10. The diameter of the pile hole shall comply with the design provisions, and the support of the hole wall shall not occupy the size of the pile diameter. During the excavation process, the size, plane position and vertical axis inclination of the pile hole shall be checked frequently, and any deviation shall be corrected at any time.

11. The abandoned soil excavated should be transferred in time, and the abandoned soil and other debris shall not be piled up within the working range around the hole opening.

• Construction technology of manually excavated piles

1. Wall protection construction shall comply with the following provisions:

1.1 The thickness of the retaining wall and the strength grade of concrete shall meet the requirements of the scheme or design. When the design does not specify, the strength grade of the concrete retaining wall shall be implemented as follows:

① When the pile diameter is less than or equal to 1.5m, it should not be less than C25.

② When the pile diameter is greater than 1.5m, it should not be less than C30.

1.2 The protective wall formwork is generally removed 24 hours after the concrete pouring is completed and the concrete strength is greater than 2.5 MPa.

1.3 Pay attention to the hole wall at any time during construction, and deal with problems in time if any is found.

• Blasting construction shall comply with the following regulations:
  • Toxic gas detection must be conducted before homework.
  • When the depth of the hole is greater than 10m, mechanical forced ventilation measures must be taken.
  • When a pile hole encounters a rock layer and requires blasting operations, a special design plan should be prepared, and shallow hole loosening blasting method should be adopted. The relevant provisions of the current national standard "Blasting Safety Regulations" should be followed, and the amount of explosives should be strictly controlled and support should be strengthened near the blast hole. Finally, within 30cm, a draft should be used to excavate to the bottom of the hole.When the depth of the hole is greater than 5m, detonating cords or electric detonators must be used for detonation, and it is strictly prohibited to expose the explosive package.
  • Electric detonators must be used for blasting and blasting, and it is strictly prohibited to expose the explosive package.For soft rock boreholes, their depth should not exceed 0.8m, and for hard rock boreholes, it should not exceed 0.5m. The number, location, and oblique insertion direction of boreholes should be determined according to the direction of the rock section, with a central group centered around the center and oblique insertion and excavation edges around the edges.

2.5 After several rounds of blasting, the data of borehole layout direction and dosage shall be summarized to determine the best blasting scheme. After blasting in the hole, smoke shall be discharged immediately, and personnel can go down to the hole for construction only after checking that there is no harmful gas in the hole.

2.6 Waterproof LED lights should be installed in the pile hole, and the voltage should be safe voltage. The cable should be waterproof insulated cable, and leakage protector should be set. 

• Slag removal and transportation

3.1 The spoil removal of manually excavated piles should be carried out by the hoisting process of a winch with anti-impact top and limit device, and the manual hand-operated derrick spoil removal hoisting process is prohibited. The bearing capacity, stability and anti-overturning ability of the lifting system should be checked in advance.

3.2 Protective measures such as crescent plates should be installed inside the hole.

3.3 Waste soil should be transported in a timely manner, and no waste soil or other debris should be piled up within the operating range around the borehole.

4. Final hole inspection

After the hole reaches the designed elevation, it should be checked whether the geological conditions at the pile bottom meet the design requirements. If confirmed to be correct, the spoil should then be removed to complete the final hole. During the final hole cleaning, all loose debris and other materials at the bottom of the hole should be thoroughly cleared. When the geological conditions at the bottom of the hole do not match the design, further investigation into the geological situation below the hole should be conducted, and treatment should be carried out according to the design requirements.

5. Reinforcement cage processing and positioning

5.1 The steel frame is made in the processing yard by segment. Measures should be taken to prevent deformation during the process of making, transporting and placing the steel frame.

5.2 Before placing the steel reinforcement skeleton, it is necessary to check the situation inside the hole again to ensure that there is no collapse or sediment inside the hole.The placement should be aligned with the hole position, held firmly, slowly, and straight, avoiding collision with the hole wall. It is strictly prohibited to use pier cages or twist cages.

6. Pouring concrete

6.1 The concrete for the pile body is required to be poured in one go.In case of special reasons such as power outages, if construction joints must be left, an appropriate amount of short steel bars can be inserted around the concrete surface.Before pouring new concrete, the joint surface must be cleaned thoroughly and there must be no accumulated water or isolation materials.

6.2 When there is no accumulated water in the hole, the pouring of concrete can be carried out dry construction according to the relevant provisions of section 3.3 of this specification. When there is accumulated water in the hole that cannot be completely drained, it is advisable to follow the requirements for underwater concrete pouring.

• Quality control requirements

1. During the hole digging process, the hole position, hole diameter, hole shape, inclination and wall protection quality should be tested.

2. Geological records should be kept during excavation to verify whether they match the designed geological data.

3. When the hole is completed, the bottom of the hole should be treated to make it flat and free from loose slag. When the geological situation is complicated, the geological situation below the bottom of the hole should be probed to see whether it meets the design requirements.