Safety technical measures for construction of the

With the development of high-rise buildings, bridges and hydraulic structures in soft soil areas, bored piles are widely used. However, due to its high requirements for construction technology and many construction links, especially the quality and technical equipment of the construction team, the construction quality of piles is uneven. According to the construction process of bored cast-in-place pile, the main links affecting the pile foundation project include measurement and positioning, mud quality, pile diameter and vertical control, bearing layer and final hole depth, sediment thickness control, concrete pouring, etc. Therefore, in order to control the quality of pile foundation, we must control all links of construction well in order to ensure the pile quality

2. Technical measures for construction safety

2.1 measurement and positioning

measurement and positioning is the key to the accuracy of hole location, the verticality of drilling hole and the accuracy of control datum elevation. In the specific operation, the measures of combining the self inspection of the construction unit with the re inspection and acceptance of the supervisor shall be taken. The positioning shall be controlled in two times. The first time is to dig the wellhead and bury the casing, and the second time is to install the drilling rig in place. The deviation shall be strictly controlled within the allowable range of the design and specifications

2.2 pile diameter and verticality control

pile diameter is another key to the construction quality of cast-in-place piles, and it is also an important index to evaluate the quality of pile foundation construction. Before construction, strictly check the diameter of the drill bit to ensure that the drill bit diameter is not less than the pile diameter, and make records. The verticality of drilling hole is also one of the important indexes affecting the construction quality of bored cast-in-place pile, and its deviation should be 1%. During the drilling process, the verticality of drill pipe should be checked frequently to always keep the drill pipe vertical

2.3 mud quality

mud is composed of clay, water and additives. In the process of forming bored cast-in-place piles, the main role of mud is to protect the wall and prevent the hole wall from collapsing, and the other is to carry slag. The drill bit cuts the soil or rock mass in the hole into slag, which is brought out of the hole through mud circulation. Therefore, the control of mud quality is very important to be controlled by its leaders. The main performance indicators of mud quality include density, viscosity, water content, etc. If the mud is too thin, the slag carrying capacity is not enough; If the mud is too thick, a thick mud wall will be formed on the hole wall, which virtually reduces the pile diameter. If the soil layer of the site cannot meet the requirements of slurry making, the slurry making clay must be transported from other places to ensure the slurry quality

2.4 formulation of rock surface elevation and diameter hole depth

bearing stratum directly affects the bearing capacity of piles, especially end bearing piles, which is an important foundation for providing the bearing capacity of pile foundations. Therefore, the correct determination of bearing stratum and final hole depth is a key link in quality control. For many projects, due to various reasons, the geological drilling data is not detailed enough, and the design cannot give the specific rock surface elevation at the bottom of the pile, and the depth of each pile into the pile varies according to the pile position and geological conditions. Therefore, the following methods can be used to judge in the actual construction process:

2.4.1 using the existing engineering geological data and design data, Pre estimate the rock surface elevation

2.4.2 make a preliminary judgment according to the difference of drilling rig vibration before and after the drilling rig enters the rock surface

2.4.3 make further judgment according to the difference between the footage speed of the drilling machine and the top and bottom of the rock stratum

2.4.4 determine according to different rock and soil slag samples and mud colors above and below the top surface of the rock stratum

after the top elevation of the rock stratum is determined, the final hole depth is determined according to the design requirements

2.5 sediment thickness control

sediment thickness is another important factor that affects the bearing capacity of pile foundations. Excessive sediment piles up at the bottom of piles to form a loose soft layer, thereby reducing the end bearing capacity of piles. The specification stipulates that the thickness of end bearing pile slag is 5cm, which can be controlled through the following work during construction:

2.5.1 before the completion of hole cleaning, recheck the final hole depth. If there is any difference, the reason must be found out to ensure that the pile length can meet the design requirements

2.5.2 do a good job in the detection of mud performance, so that the mud can not only facilitate the discharge of rock and soil slag samples, but also ensure the stability and safety of the hole wall, and prevent the occurrence of shrinkage or hole collapse accidents. According to the specification requirements, the mud performance indicators are generally: sand content 4%, relative density 1.051.50, which can get rid of the constraints of hardware and directly introduce the virtual instrument into the classroom, viscosity 1720s

2.5.3 regularly check the length of the measuring rope to ensure the accuracy of hole depth measurement

2.6 fabrication and installation of reinforcement

the fabrication and installation of reinforcement cage directly affects the bearing capacity of pile, so it is another key factor related to the quality of pile foundation. It can be controlled through the following work:

2.6.1 the quality of reinforcement must meet the national quality inspection standards. After the reinforcement enters the site, the Contractor shall conduct self inspection according to the specified frequency, and the laboratory of the Supervision Center shall conduct random inspection. It can be used in the project after passing the inspection

2.6.2 reinforcement welding shall comply with the operating procedures, the weld shall be full, and the electrode model shall correspond to the reinforcement model

2.6.3 the reinforcement joints shall be staggered. The cross-sectional area of the stressed reinforcement joints in the same lap length section shall not exceed the total reinforcement area by about 50%, and the lap length shall meet the specification requirements

2.6.4 set a reinforcing stirrup every certain length to facilitate hoisting and prevent deformation of the reinforcement cage

difficulties in fixture design 2.6.5 ear bars that control the thickness of the protective layer shall be set outside the main reinforcement of the reinforcement cage to ensure that the concrete protective layer meets the design and specification requirements

2.7 concrete pouring

concrete pouring is the last process in pile foundation engineering. If the control is not strict, it will lead to concrete segregation, pile breaking and other quality accidents. During construction, it is controlled through the following work:

2.7.1 concrete preparation strictly controls the measurement work to make it reach the preparation proportion required by the design strength

2.7.2 concrete 5. The X-ray tube and detector in the hand-held spectrometer are precision components. When pouring, it is necessary to ensure sufficient initial pouring amount of concrete, ensure the buried depth of 1.0m, measure the concrete pouring height, lift and disassemble the tremie in time, and strictly control the buried depth of the tremie within meters

2.7.3 when the concrete is poured to the elevation of the pile top, add 0.5 0.8m

2.7.4 pay attention to observe and record whether the reinforcement cage moves at any time.

3. Conclusion

although there are many factors that affect the construction quality of bored cast-in-place piles, as long as the construction personnel engaged in the construction of bored cast-in-place piles and the supervisors jointly manage and strictly control each link in the construction process, the construction quality of pile foundations can be guaranteed, so as to give full play to the potential advantages of bored cast-in-place piles