What are Post Hole Diggers?

Artificial digging piles, engineering terms, digging soil by manpower, and reinforced concrete piles poured on site. Artificial digging piles are generally thicker in diameter and the thinnest are more than 800 mm in diameter. They can support structural bodies with fewer floors and higher pressure, and are widely used. A cap is set on the pile, and the cap beams are used to tie and connect them, so that the force of each pile is evenly distributed to support the entire building. Manually digging cast-in-situ pile refers to a pile formed by artificially excavating a hole in a pile, and then placing a steel cage and pouring concrete. ^[1]

Manually excavated piles are easy to construct, fast, and do not require large mechanical equipment. Excavated piles are more earthquake-resistant than wooden piles and concrete driven piles, and the cost is more than punch cone punching, impact cone punching, impact drill punching, Rotary drilling rig drilling and sinking foundation savings. It is widely used in highways and civil buildings. However, the digging pile has poor operating conditions, harsh environment, high labor intensity, and safety and quality are particularly important. When pumping water from a precipitation well in the site, when it is really necessary to take a small-scale pumping due to the construction, attention should be paid to the surrounding strata and buildings. If abnormal conditions are found, the relevant unit should be notified in time to deal with it. ^[1]

The pile foundation construction shall be taken in accordance with the current relevant codes and regulations and in combination with the actual conditions of the project.

1. The pile retaining wall is made of C25 concrete, and the reinforcement is made of HPB300;

2. The first section is about one meter deep, and the concrete protective tube is poured. When the next section is constructed, each section is used as a construction cycle (that is, the concrete protective wall is poured after each section is dug);

3. In order to facilitate drainage in the well organization, a drainage hole (the same diameter as the outer diameter of the water pipe) is reserved in the retaining wall of the pervious layer section to facilitate the drainage of the pipe and block it before pouring the concrete. To ensure the verticality of the pile, it is required The center position and verticality of the core pile shall be checked once every three sections of the retaining wall are poured;

4. In addition to digging the ditch around the surface of the pier, the water outside the hole should be properly drained away from the pile hole. When pouring pile foundation concrete, if there is only a small amount of water seepage through several pile holes, measures should be taken at the same time to prevent the concentration of water in one hole to increase the difficulty. If the amount of porous water seepage is large, which affects the quality of pouring, concentrated pumping should be carried out in one hole to reduce the water level of other holes. This hole is finally filled with concrete under water;

5. If the confined water of the diving layer with large gushing water is encountered when digging the hole, the cement layer can be used to seal the diving layer with the pebble ring.

6. After the excavation reaches the design level, the bottom of the hole should be treated. It must be level and free of loose layers such as loose slag, sludge and sediment;

7. The unexplained places shall be constructed strictly in accordance with the current national regulations.

1. The top wall is protected by round steel with a diameter of 20mm, and 2 ~ 4 lifting ears are added, and the steel wire rope is fixed on the ground stake.

2. Enclose the vertical reinforcement of the retaining wall and allow the reinforcement to protrude more than 20cm, connect it with the vertical reinforcement of the next retaining wall and the stirrup, and then cast it. If necessary, a hole with a diameter of about 200mm can be reserved in the middle retaining wall of the excavation pile. However, the geology of the site should be relatively hard soil, and then the retaining wall and the soil around the retaining wall should be anchored together. Bamboo stakes are fine. This way the retaining wall will not break off.

3. Drill holes in the formed retaining wall to the weak layer of sand and soil, fill the grouting material into the pores of the soil in the form of filling, infiltration and compaction to consolidate the soil around the retaining wall and protect the surrounding sand and sand. Collapse, which increases friction around the pile. Pressure grouting materials can be selected from fly ash, early-strength cement concrete, and lime-clay mixture.

(1) Before pouring the concrete, check whether the geology and hole diameter of the hole bottom meet the design requirements, clean the hole bottom, and drain the water as much as possible.

(2) In order to reduce the accumulation of groundwater, when any digging pile is sealed to the bottom, the stagnant water in the adjacent holes must be pumped out at the same time. In order to reduce the impact of water accumulation in adjacent holes on working holes.

(3)

Site management personnel should carefully explain the geological conditions and groundwater conditions at the digging piles to the construction personnel, and propose possible problems and emergency treatment measures. It is necessary to have adequate mental preparation and adequate materials and machinery for emergency measures. Security measures should be formulated and checked and implemented frequently.

No more than 2 people can work under the hole. Wear safety helmets, raincoats, rain pants, and long rain boots when operating. Operators under the hole and personnel above the hole must have a contact signal. Don't place hammers, hoes, stones, and iron rods on the ground to hurt people. Every 1h of work, underground personnel and ground personnel exchange.

Underground personnel should pay attention to observation

Groundwater is the most common problem in deep foundation construction, and it brings many difficulties to the construction of artificial digging piles. The water in the aquifer destroys its equilibrium state during excavation, so that the surrounding static water fills the pile hole, which affects the normal construction of the artificial digging pile. If it encounters the dynamic hydraulic pressure soil layer construction, it will not only excavate Difficult, the concrete retaining wall is difficult to be formed and even crushed by water pressure, quality problems of the pile body and even construction safety problems occur. If you encounter fine sand and silt soil layers, under the action of pressure water, quicksand and well leakage will easily occur. During construction, the safety of the construction personnel shall be ensured, and the presence of toxic gases and hypoxia shall be detected in a timely manner, and effective measures shall be taken. ^[1]

Acceptance information of foundation piles and caps

1. When the design elevation of the pile top is similar to the construction site elevation, the acceptance of the pile foundation project shall be accepted after the completion of the pile formation. When the design elevation of the pile top is lower than the construction site elevation, the acceptance shall be performed after excavation to the design elevation.

2. The acceptance of foundation piles shall include the following information:

1) Engineering geological survey report, pile foundation construction drawing, review summary of drawings, design change and notice of material substitution, etc.

2) Changes in the approved construction organization design, construction plan, and implementation.

3) Line drawing for pile position measurement, including the project visa check line for pile position.

4) Piling quality inspection report. (Small strain)

5) Single pile bearing capacity test report. (Static load test, core pulling, etc.)

6) Completion plan of the foundation pile and the elevation of the pile top when the foundation pit is dug to the design elevation.

3 The following information shall be included in the acceptance of the capping project:

1) Construction and inspection records of steel and concrete for the platform;

2) Record of the anchorage between the pile head and the cap, the distance between the side pile and the edge of the cap, and the protective layer of the cap of the cap;

3) Cap thickness, length and width records and appearance description.

Piling quality inspection

1. The pile quality inspection of the cast-in-place pile mainly includes the quality inspection of the three processes of hole formation and clearing, the production and placement of steel cages, concrete mixing and pouring.

1) Concrete mixing should be checked for the quality and measurement of raw materials, the mix ratio of concrete, slump, and the strength level of concrete;

2) The production of steel cages should check the specifications of the steel bars, welding rod specifications, varieties, weld joint specifications, weld length, weld appearance and quality, and manufacturing deviations of main and stirrups.

3) Before pouring the concrete, carefully check the center position, hole depth, hole diameter, verticality, hole bottom sediment thickness, and actual position of the reinforcement cage in accordance with the relevant construction quality requirements, and fill in the corresponding quality Inspection records.

4 For pile foundation projects with complex geological conditions or low reliability of pile quality, the pile quality inspection shall be carried out. The detection method can adopt reliable dynamic measurement method. For large diameter piles, core drilling, ultrasonic detection method of embedded pipes, and the number of tests can be determined by design according to specific conditions.

5. The pile position deviation should be checked according to different pile types according to (relevant) regulations.

Single pile bearing capacity test

In order to ensure that the standard value of the actual vertical pile's ultimate bearing capacity meets the design requirements, a single pile static load test or a reliable dynamic test should be performed according to the importance of the project, geological conditions, design requirements, and construction conditions.

Construction of manual digging pile

1. Before opening the hole, the pile position should be positioned and staked out accurately. A gantry pile is positioned outside the pile position. The wall template must be installed with the pile center point to correct the template position, and a special person is responsible.

2. The first section well wall protection shall meet the following requirements:

1) The deviation between the well circle centerline and the design axis shall not be greater than 20;

2) The top surface of the well circle should be 150-200 higher than the site, and the wall thickness should be 100-150 higher than the thickness of the well wall below.

3 The following requirements shall be observed in the construction of well wall protection:

1) The thickness of the retaining wall, the tie bar reinforcement, the reinforcement, and the strength of the concrete shall meet the design requirements;

2) The overlap length of the upper and lower sections of the retaining wall shall not be less than 50;

3) Each section of retaining wall shall be continuously constructed on the same day;

4) The retaining wall concrete must be dense, and the accelerator should be used according to the water seepage of the soil layer;

5) The removal of the retaining wall formwork should be performed after 24h;

6) When there is honeycomb or water leakage in the retaining wall, it should be reinforced in time to prevent accidents;

7) The range of any diameter of well circle on the same horizontal plane shall not be greater than 50.

4 In the case of local or thick silt with a thickness of not more than 1.5m and the possibility of sand and soil inrush, the construction of the retaining wall should be handled as follows:

1) The height of each section of the retaining wall can be reduced to 300-500, and the concrete can be excavated, inspected, and poured;

2) Use steel protective cylinder or effective precipitation measures.

5. When digging to the design elevation, no water should accumulate at the bottom of the hole. After the hole is finished, the mud on the retaining wall and the bottom of the hole should be cleaned up, and then the water should be checked for acceptance.

6. When pouring the concrete of the pile body, the concrete must pass through the chute; when the height exceeds 3m, a string tube should be used. The height of the end of the string tube from the bottom of the hole should not be greater than 2m, and the concrete should be compacted with an insert vibrator.

7. When the infiltration is too large (when affecting the quality of concrete pouring), effective measures should be taken to ensure the quality of concrete pouring.

Construction preparation

1. The construction of cast-in-situ piles should have the following information:

1) Engineering geological data and necessary hydrogeological data of the building site;

2) Construction drawings of pile foundation projects (including all pile foundations in the same unit project) and review minutes of drawings;

3) Survey data of underground pipelines (pipes, cables), underground structures, dangerous buildings, precision instrument workshops, etc. in the construction site and adjacent areas;

4) Technical performance data of main construction machinery and its supporting equipment;

5) Construction organization design or construction plan of pile foundation project;

6) Quality inspection report of raw materials such as cement, sand, stone, steel bars and their products;

7) Reference materials for load and construction process test.

2. The design of the construction organization shall, in accordance with the characteristics of the project, formulate corresponding quality management measures in a targeted manner, mainly including the following:

1) Construction plan, indicating pile position, number, construction sequence, location of hydropower lines and temporary facilities;

2) Determine the relevant data of the hole forming machinery, supporting equipment and reasonable construction technology;

3) Construction operation plan and labor organization plan;

4) mechanical equipment, spare parts (equipment), tools (including quality inspection tools), material supply plan;

5) In the construction of pile foundations, safety, labor protection, fire protection, rain protection, typhoon protection, blasting operations, cultural relics and environmental protection shall be implemented in accordance with relevant regulations;

6) Technical measures to ensure project quality, production safety and seasonal (winter, rainy) construction.

3 Piling machinery must be qualified and unqualified machinery must not be used.

4 Before the construction, a review of the drawings shall be organized, and the review minutes together with the construction drawings shall be used as the construction basis and included in the project archives.

5. Temporary facilities for pile foundation construction, such as water supply, power supply, roads, drainage, temporary houses, etc., must be prepared before construction starts, and the construction site should be leveled to ensure the normal operation of the construction machinery.

6. The control points and level base points of the foundation pile axis shall be set at places not affected by construction. Before the start of construction, it should be properly protected after the review, and it should be re-tested frequently during the construction ^[1] .