Study On The Application Of Reflection Wave Method For Pile Testing

As an important part of high-speed railway project, bridge pile foundation, especially long and big pile foundation has been widely used in high-speed railway bridges. In order to ensure good quality of piles, it has become more important to carry out quality testing for piles as many as possible (100% as specified in Railway Specifications) by using a simple and fast pile dynamic testing method. With the flourishing development of pile foundation projects, related pile foundation dynamic testing techniques are also progressing greatly. The low-strain reflection wave method is an economical, practicable and effective method, which is widely used for pile integrity testing and plays more and more important role in the field of pile foundation testing.This paper first analyzes and introduces the development,status quo and theoretical basis of pile dynamic testing and reflection wave method. Based on the bridge pile testing in the Qinghuangdao-Shenyang Passenger Dedicated Railway Line, this paper focuses on the working procedures of pile integrity testing by reflection wave method as well as data analyzing methods. Then it discusses and studies several issues that may occur during low-strain dynamic testing, in particular, wave velocity, blind zone in shallow part, tested pile length and integrity classification of pile body. Through analyzing the factors that may have effect on the quality of low strain pile testing, this paper proposes the solutions and indicates important notices during pile testing.Though it has been gradually accepted and actively promoted by the Engineering Field, the low-strain reflection wave method still has its limitations and a lot of problems have not been solved yet. The highlighted problems include: unable to quantitatively analyze the defect degree of pile body, a certain error in estimating pile length caused by wave velocity and too many man-created factors in integrity classifications. Especially, when determining the defect degree and types, technicians often fail to find out or misdiagnose the defects due to their various skill levels.In China, standards have not been unified for quantitative analysis on pile body integrity and consequent type and classification of pile integrity. Based on the practical experiences from the Qinghuangdao-Shenyang Passenger Dedicated Railway Line, this paper proposes"4-grade"classification standard for pile body integrity and provides some reference curves. But it must be pointed out that the pile body integrity is a comprehensive qualitative index not a strict quantitative index.Through studying and discussing the issues of the low-strain reflection wave method, the reliability and accuracy of pile testing quality of the low strain reflection wave method have been improved in practice.