Four kinds of construction techniques for bored pile with rotary drilling rig

Rotary drilling rig is a kind of Construction Machinery suitable for hole-forming operation in building foundation engineering. It is widely used in municipal construction, highway bridge, high-rise building and other ground foundation construction projects. With different drilling tools, it is suitable for dry (short spiral), wet (rotary bucket) and rock formation (core drill) hole-forming operation. Rotary drilling rig has large installed power, large output torque, large axial pressure, and flexibility, High construction efficiency and multi-function.
The rotary drilling rig is suitable for the soil geological conditions in most areas of China, and has a wide range of applications. It can basically meet the needs of bridge construction, high-rise building foundation and other projects. At present, the rotary drilling rig has been widely used in various bored pile projects. It is of great significance to discuss the construction technology of the rotary drilling rig technically.

Dry pore-forming process

1. Dry pore-forming characteristics
1. Because the geology is solid and dense, drilling can be done directly without other auxiliary hole-forming materials or equipment. Dry hole forming process is the simplest process in rotary excavation construction, which is characterized by simple process and low construction cost.
2. The dry hole forming process is aimed at hard plastic and solid geology, with or without groundwater, but preferably without groundwater. Before adopting the dry hole forming process, the rock, soil and groundwater conditions must be mastered, and the premise is that the hole will not collapse.
2. Advantages and disadvantages of dry drilling
1. Disadvantages of dry hole forming: Although there is no need to worry about hole collapse, due to the loss of lubrication, softening, cooling and buffering of water and mud, the drilling resistance of some formations is increased, especially for dense dry soil and coarse sand layer, which is difficult to pour slag, exacerbating the loss of drill teeth and vibration of drill pipe.
2. Advantages of dry hole forming: in addition to simple process and low construction cost, under specific geological conditions, due to the softening of mudstone with water, mud lubrication, slip, tooth plugging and lake bottom phenomenon are formed. Dry hole forming can eliminate the above phenomena and improve the shear crushing efficiency.

Mud static pressure process

1. Mud static pressure
The mud pressure supports the hole wall to prevent construction quality problems and accidents such as hole shrinkage, hole collapse and buried drilling.
2. Three indicators of mud
1. Mud pressure
2. Mud retaining wall
3. Sand content
Three sets of mud: mud hydrometer, mud viscometer and sand content tester.

Casing process

1. Casing
1. Role of pile casing: protect the safety of pile hole, equipment and personnel. The length of the casing is determined according to the geotechnical and groundwater conditions. Generally, the length of the casing is between 2M and 4M, and the diameter of the casing is usually greater than the pile diameter of 200MM;
2. Lower casing method: reamer, drill bucket, special tooling, vibration hammer;
3. Control requirements: verticality and center deviation of buried pile casing.
2. Casing
The casing driver, pipe kneader or full rotary drill, as well as the vibration hammer buries the casing, and the rotary drill bucket follows the pipe in the casing. The casing technology can replace the static pressure technology of mud wall protection, and is applicable to occluded piles, inclined piles, unstable strata and outdoor construction, limited resources (no water and electricity), urban environmental protection construction, etc.

Concrete wall-making process

The concrete wall-building process of rotary drilling rig is not a normal rotary drilling process. This passive safety process lags behind the mud static pressure and the active safety of the casing process, and has certain operational risks.
1. Concrete walling
Generally, in the construction of plateau, mountainous area, backfill and karst cave, due to the lack of groundwater or lack of groundwater, or the lack of water resources, when the dry hole forming process is adopted, the hole will be deviated and partially collapsed, and the C15 concrete will be backfilled into the hole, and the abnormal parts in the hole will be backfilled. After the concrete reaches the initial setting strength, the pick barrel will be used for core drilling.
Backfilling concrete into the deviated hole can repair the deviated hole. Backfilling concrete into the local hole collapse position can produce a wall protection layer locally; The hollow karst cave shall be backfilled with concrete, filled with karst cave and drilled for guidance to prevent jamming and deviation.
2. Concrete wall building application
1. Karst cave geology
2. Deviator hole
3. Local hole collapse
3. Precautions for concrete wall construction
1. Lag: the concrete retaining wall has certain advantages when dealing with karst caves and deviated holes, but when dealing with local hole collapse, due to the lag problem, if the drill bucket collapses at the bottom of the hole, it is likely to lead to burying the hole, and similar accidents have occurred in actual construction. Therefore, when adopting concrete retaining wall, it is necessary to fully prepare for prevention, fully understand the geological and hole conditions, and take this process when absolutely sure.
2. Cost: due to the massive use of concrete, when signing the contract, the project department of Party A shall bear the cost of backfilling concrete and pouring excess volume.
3. Construction efficiency: it takes time to reach the initial setting state when concrete retaining wall is used, which results in discontinuous construction of single hole and reduces the construction efficiency.