How deep is the bored pile? What problems should be paid attention to when piling? How to deal with it?

Bored piles are usually non-compacted piles, and some are partially compacted piles. The types of bored piles can be divided into: a. According to the pile diameter, they can be divided into the following types: small piles are mostly used for foundation reinforcement and composite pile foundation (such as root piles) because of their small pile diameter and simple construction machinery, construction site and construction method. There are many pile-forming methods and construction techniques for middle piles, which are widely used in industrial and civil buildings and are the most widely used pile types at present. The diameter of large pile is large, the pile end can not be expanded, and the bearing capacity of single pile is high. It has developed rapidly in the past 20 years, and is mostly used in heavy buildings, structures, ports and docks, highways, railways, bridges and culverts and other projects. B bored piles can be divided into: dry bored piles; The bored pile adopts mud wall protection method; Wall protection method of bored pile. Characteristics of bored piles Bored piles have the following technical characteristics: a. There is basically no noise, no vibration, no ground heave or lateral displacement during construction, which has little harm to the environment and surrounding buildings; B. Large-diameter bored piles have large diameter and large buried depth; C. For the soil layer penetrated by the pile, in-situ test can be conducted in the air to detect the properties of the soil layer; D. Bored cast-in-place pile with enlarged bottom can give full play to the bearing capacity of pile tip; E. It is often designed as one column and one pile, and there is no pile cap, which simplifies the form of foundation structure; F bored piles usually have large pile spacing and small pile group effect; G. Partial "squeezed branch" bored piles can effectively reduce the diameter and length of piles, improve the bearing capacity of piles and reduce settlement; H. It can pass through various soil layers and be embedded in bedrock, and other pile types are difficult; First, the construction equipment is simple and light, and it can pile under the condition of low clearance; J. During the construction of bored pile, there are many factors that affect the quality of pile, and the quality is not stable enough. Sometimes, the phenomena such as shrinkage and local mud inclusion in the pile body occur, and the exertion of pile side resistance and pile end resistance will change with the change of technology, which is greatly affected by construction operation; K. Due to the high bearing capacity of bored pile, it is generally difficult to determine its ultimate load by conventional static load test, and the stress, deformation and failure mechanism of pile under various technological conditions have not been fully grasped. The design theory needs to be further improved. Bored pile construction method Bored pile construction can be divided into mud wall protection method and full pipe construction method because of the different strata of retaining wall selected. 1) The construction method of mud wall protection can adopt impact drill, impact drill and rotary drilling. The process of this construction method is as follows: leveling the site → mud preparation → burying the casing → laying the working platform → installing the positioning drill → drilling → cleaning the hole to check the quality of the hole → lowering the reinforcing cage → pouring underwater concrete → pulling out the casing → checking the quality. Construction sequence (1) Construction preparation includes: selection of drilling rig, drilling tools, site layout, etc. Drilling rig is the main equipment for bored pile construction, which can be selected according to geological conditions and the use conditions of various drilling rigs. (2) Installation and positioning of drilling machine If the foundation for installing the drilling machine is unstable, adverse effects such as inclination of drilling machine, inclination of pile and eccentricity of pile will easily occur during construction, so it is required to install the foundation firmly. For the soft and sloping foundation, bulldozers can be used to level it and steel plates or sleepers can be used to reinforce it. In order to prevent the pile location from being inaccurate, it is very important to determine the center position and install the drilling rig correctly. For a drilling rig with a derrick, firstly, the drill pipe is roughly positioned by using the power of the drilling rig and the nearby ground cage, and then the frame is jacked up for precise positioning, so that the clamping holes of the lifting pulley, the drill bit or the fixed drill pipe are in a vertical line with the center of the casing to ensure the verticality of the drilling rig. The deviation of drilling rig position is not more than 2cm. After aligning the pile position, level the beam of the drilling rig with sleepers, and pull the cable wind rope at the top of the tower symmetrical with the axis of the drilling rig. (3) The key to the success of buried pipe drilling is to prevent the hole wall from collapsing. When the hole is deep, the soil on the hole wall below the groundwater level will collapse into the hole under the action of hydrostatic pressure, and even sand flow will occur. If we can maintain the high head of the groundwater level in the borehole and increase the hydrostatic pressure in the borehole, we can protect the borehole wall and prevent the borehole from collapsing. In addition to this function, the casing also has the functions of isolating surface water, protecting orifice ground, fixing pile hole position and guiding drill bit. There are three kinds of materials for lining: wood, steel and reinforced concrete. Casing should be durable and impervious, and its inner diameter should be larger than the diameter of the borehole (about 20cm for rotary drilling rig, 40cm for down-the-hole drilling rig, impact or grab cone), and each section is about 2~3m in length. Steel lining is usually used. (4) Preparation of Mud Drilling mud consists of water, clay (bentonite) and additives. It has the functions of suspending drilling slag, cooling the drill bit and lubricating drilling tools, increasing hydrostatic pressure, forming mud skin on the hole wall, isolating seepage inside and outside the hole and preventing hole collapse. The mud consistency of modulated drilling mud and circulating purified mud should be determined according to drilling methods and formation conditions, and the mud consistency should be flexibly mastered according to formation changes or operation requirements. The mud is too thin, the slag discharge ability is small, and the wall protection effect is poor; Too thick mud will weaken the impact of the drill bit and reduce the drilling speed. (5) Drilling is a key process, and the construction must be carried out in strict accordance with the operation requirements to ensure the quality of hole formation. First of all, we should pay attention to the quality of opening, so we must aim at the center line and verticality and press the liners. During construction, pay attention to continuously adding mud and pump slag (impact use), and check whether the hole is deviated at any time. When impact or grab drilling rig is used for construction, the nearby soil layer will be affected by vibration, thus affecting the stability of adjacent holes. Therefore, the borehole should be cleaned in time, the reinforcing cage should be lowered, and underwater concrete should be poured. The drilling sequence should also be planned in advance to ensure that the construction of the next pile hole will not affect the last pile hole, and the moving distance of the drilling rig will not be too far to interfere with each other. (6) The depth, diameter, position and hole shape of hole cleaning drilling are directly related to the number of equipment and the curvature of pile body. Therefore, in addition to close observation and supervision when drilling, after drilling reaches the design depth, the hole depth, hole position, hole shape and aperture should also be checked. When the final hole inspection completely meets the design requirements, the bottom of the hole should be cleaned immediately.