The project is located in Qingyuan City, Guangdong Province, invested by Guoneng Qingyuan Power Generation Co., Ltd., and our company was responsible for the pile foundation construction of the project.
The project site area is located in the east bank of Beijiang River, the terrain is generally high in the east and low in the west, the cover layer in the depression is mainly alluvial clay and residual powder clay, the cover layer in the slope section is mainly slope residual powder clay, the underlying bedrock is mainly slightly weathered limestone. The adverse geological influence of the plant site is mainly the strong development of caves and earth caves, so the existence of cave development in the limestone of the plant site is considered. The pile foundation adopts reinforced concrete bored pile, and the design requires that there is no weak interlayer, fracture zone and cave distribution within 3 times the thickness of pile diameter and not less than 5m below the pile end, and there is no free surface of rock mass within the stress diffusion at the pile bottom.
According to the geological conditions of the project and the construction experience in similar projects, the hole is drilled by rotary drilling technology, and the rotary drilling rig is equipped with two kinds of drill rods, including friction rod and machine locking rod, as well as a variety of drill bits.
The project started on April 10, 2021 and the pile construction was completed on January 27, 2022. During the construction period, more than 200 construction personnel and 10 high-power rotary drilling rigs and related matching mechanical equipment were invested in the project. Overcoming many unfavorable factors such as rainy season, high temperature and complicated geological conditions, a total of 1,857 bored piles were completed and about 31,000m³ of caves were treated.
This project construction ensures that the project fully meets the design and specification requirements, and the allowable deviation project qualification rate is over 98%. The quality inspection and evaluation of each sub-project shows that the construction is qualified. The quality standard of the project meets the national specification and design requirements, and the passing rate is 100%.
In order to test the pile bearing capacity, a total of 62 piles were tested by static load test and 55 piles were tested by high strain test, the proportion of pile bearing capacity test was 6.3%, the test results showed that the vertical bearing capacity of all tested piles met the design requirements. The pile integrity test used the low strain test of 1,857 piles, the test ratio is 100%, and the coring test of 204 piles, the test ratio is 11%. According to the test results, the proportion of Class I piles is 98%.
This project summarized a lot of experience about the construction process of using rotary drilling in karst area and in the treatment of cavern (earth cavern) during the construction, which can provide reference for the subsequent construction of similar projects. At the same time, during the construction process, the project department strictly abides by the laws, regulations and rules on civilized construction issued by the state and the owner, and does a good job in civilized construction and environmental protection to meet the requirements of the state, local government and the owner on civilized construction and environment, and the site is cleaned up as required after the construction is completed. During the construction process, the safety and civilized construction management, quality management and construction progress control have been praised by the owner and supervision department.
