The project is located in Butuo County, Sichuan Province, invested by the UHV Construction Branch of State Grid Corporation of China, and our company was responsible for the pile foundation construction of the project. The pile foundation is reinforced concrete bored piles and PHC pipe piles. The length of bored piles is from 13.5m to 32m, and the length of PHC pipe piles is from 18m to 32m. The stratum within the pile body is mainly composed of plain fill, clay, gravel, pebbles, etc. TR288FL and SR360R rotary drilling rigs were used for bored piles, and JB62 piling rig was used for PHC pipe piles.
The project started on September 5, 2021, and completed all construction tasks on December 23, 2021, including 724 piles with diameter of 800 mm, 1,988 PHC piles with diameter of 500 mm and 70 PHC piles with diameter of 600 mm.
In this project, it is necessary to cross the ramming replacement fill layer which is about 10 m deep, and it is very easy to collapse when piling in this stratum. When it was hard to drill, the hole collapse problem was solved by using a longer protection casing to cross the fill layer. In order to ensure the successful installation of the protection casing, a rotary drilling rig with a maximum torque of not less than 285 kN·m was selected for the drilling.
During the construction period, the project department ensured the piling quality by reasonably arranging the construction sequence, and making good communication and coordination, scientific scheduling to make full use of the construction site, and ensuring that the safety distance between the construction of pipe piles and bored piles was not less than 30m. The pile foundation testing was conducted by a third-party testing agency, and the proportion of high strain testing was 5%, and the testing results showed that all of them were Class I piles. The proportion of low-strain testing was 20%, and the test results showed that the proportion of the Class I pile of the bored piles was 98.76%, and the proportion of the Class I pile of the pipe piles was 100%. The test results of each test pile are in accordance with the design requirements.
