【Haichuan Civil Engineering Issues】Take a look, what is this for? Do you know the particularities of this job?

Could it be manual pile hole digging: lol

Someone is working in the manhole. From a safety perspective, supervision is necessary.

Manual dug piles are easy to construct, fast to build, and do not require large mechanical equipment. They possess greater seismic resistance compared to wooden piles and concrete driven piles, and their cost is lower than that of drilling using impact hammers, rotary drills, or caisson foundations. Thus, it is widely used in highways and civil buildings. However, shaft sinking pile work involves poor working conditions, a harsh environment, and high labor intensity, making safety and quality particularly important. 1. Technical measures during construction: Before starting construction, it is necessary to carefully analyze the geological drilling data related to the pile drilling site. In the event of thick layers of sandy soil, quicksand, or silt, reinforcement measures must be determined first before proceeding with the actual work. Appropriate solutions should be adopted for the problems commonly encountered during construction. (1) Collapse of mud and sediment on the hole wall: When drilling into sandy soil, silt, or quicksand, it is easy for the mud and sediment surrounding the retaining wall to collapse. If the groundwater inflow is not high and the collapse is not severe, retaining walls can be used for support; simultaneously, 25 mm diameter round steel bars can be employed for reinforcement, or steel plate sleeves can be used to drill holes and pour concrete lining. (2) When drilling, thick layers of quicksand or silt are encountered, especially when there is a large amount of groundwater; as a result of the massive collapse of sediment around the retaining wall, the concrete retaining wall ends up suspended with no support, which leads to cracks and eventually to its rupture and detachment. Many construction firms were forced to use caisson foundations instead, which increased the cost.

(2) When drilling, thick layers of quicksand or silt are encountered, especially when there is a large amount of groundwater; as a result of the massive collapse of sediment around the retaining wall, the concrete retaining wall ends up suspended with no support, which leads to cracks and eventually to its rupture and detachment. Many construction firms were forced to use caisson foundations instead, which increased the cost. In such cases, reinforcement measures should be taken during construction: (2.1) For the top retaining wall, use round steel bars with a diameter of 20 cm and add 2 to 4 lifting lugs, which are then fixed to wooden piles in the ground using steel wire ropes. (2,2) Encrypt the vertical rebar of the retaining wall, allowing the rebar to extend more than 20 cm outward so as to connect with the vertical rebar and stirrups of the next section of the retaining wall, and then pour concrete to give it shape. If necessary, holes with a diameter of around 200 mm can be prepared in the middle section of the retaining wall of the bored pile; however, the soil in that area should be relatively hard. The retaining walls should then be secured to the soil surrounding them, and concrete piles or bamboo/wooden piles can be used for this purpose. In this way, the retaining wall will not break or fall off. (2, 3) Drilling is carried out in the formed retaining wall to reach the weak layers of sand, and grouting material is injected into the pores of the soil through filling, infiltration, and compaction. This process consolidates the soil surrounding the retaining wall and prevents the sediment around it from collapsing, thereby increasing the friction force around the pile. Pressure grouting materials can include fly ash, early-strength cement concrete, lime-clay mixtures, etc.

(3) Backfill concrete: 3. Before pouring the concrete, it is necessary to check whether the geology at the bottom of the hole and its diameter meet the design requirements; the bottom of the hole should be cleaned thoroughly, and any accumulated water should be drained as much as possible. 3. To reduce the accumulation of groundwater, when sealing the bottom of any bored pile, the water accumulated in adjacent holes must also be pumped out simultaneously. To reduce the impact of water accumulation in adjacent holes on the working hole. 3. When the depth of the hole is over 6 meters, care must also be taken to prevent concrete segregation. Generally, the mixed concrete is placed in a sturdy canvas bag with a capacity of around 1–2 m3, and the bag is tied shut with ropes. When the concrete is delivered to the bottom of the hole, the ties can be untied to release the concrete at the bottom of the hole. Continuous operation allows the bottom of the hole to be quickly sealed, thereby blocking most or even all of the groundwater there. 3, 4: If there is a large amount of groundwater and the drill holes are deep, as soon as the water pump is started, the water level at the bottom of the hole reaches or exceeds 20 cm. Using the methods mentioned above to seal the bottom of the hole will result in too high a water content in the concrete. After removing the debris from the bottom of the hole, allow the water level to rise again; once the water level in the hole becomes relatively stable, insert a conduit into the bottom of the hole and feed mixed early-strength concrete into it. The amount of concrete used should be at least 30 cm above the bottom lining of the hole. Then, slowly withdraw the conduit. Due to the water pressure, the concrete used for sealing the bottom becomes quite dense. After the concrete has set, proceed with pumping out the water. Since the concrete used for sealing the bottom already extends above the bottom lining, there is no more groundwater seeping in. Once all the water has been pumped out, deal with any remaining water. Remove and take out the loose parts of the surface concrete (the cement paste in this part of the concrete will escape into the water), then proceed to the next step.