Study On The Load Capacity Test Method Of Extra-long Pile In The Middle And Lower Reaches Of The Yellow River

With rapid development of transport, the extra-long pile is being more and more applied in construction of highways and bridges. Based on the considerations of economic and security, it is very important and necessary to study bearing properties of pile and determine the bearing capacity and integrity accurately.Traditional load test is the most directly and reliable method for determining the bearing capacity of piles. Because the method needs special reaction system, it will take more money and require high condition for test field, so it cannot be done randomly and widely and cannot be done under hard conditions. By contrast, self-balanced method has its advantage on technology and economy. It has been applied in Beijing, Jiangsu, Henan, Gansu and other regions, But because of the difference of loading way and load transfer mechanism, its transferred result has some deflection with traditional load test.This paper first analyzes the basic principles of traditional load test and self-balanced load test, and then compare the two methods of capacity test, summarized the characteristics and differences between their respective.This issue relies on the Huanghe bi-purposed bridge, uses the traditional static load test and self-balance pile load test to test pile at the same time. Through the analysis of experimental results from four aspects, Q-S curve, lateral friction resistance of pile, resistance at the end of pile, and vertical ultimate bearing capacity, We can see because of the limitations of self-balance pile load test, the results not only have big differences with the traditional method, and even the vertical ultimate bearing capacity by the same self-balance method is also very different. Therefore, the result of self-balancing test should be used with caution in middle and lower reaches of Yellow River.Finally, this paper presents a finite element numerical model to determine the 'self-balance point' method of location, and verifies the reliability of the method according to the measured data. This method has guiding significance to the project for middle and lower reaches of Yellow River. And it can be applied to other areas.