Application of Dynamic Stiffness Method in Evaluating Status of Existing Bridge Pile Foundation

Currently there is a growing demand for quality inspection of existing bridge pile foundation. Due to requirements of normal operation and various restricted conditions, those common testing methods used for new bridge foundation piles (i.e. static load testing, high-strain gauge method, low-strain gauge method, ultrasonic method and core-drilling method, etc.) are difficult to be implemented and also the testing results are not sufficient enough to comprehensively evaluate the status of foundation piles. The mechanical impedance method with transient excited force (also called dynamic stiffness method) is proposed to collect the pile-soil response signal under the action of excited force via a sensor mounted on top of the piles and the curve between admittance and frequency is drawn to derive the capacity resistance of foundation piles. A large quantity of theoretical research and practice has shown that such a method could provide acceptable engineering accuracy for foundation pile evaluation. Existing foundation pile in a highway section is tested with the dynamic stiffness method and the results are verified with core-drilling and low-strain gauge methods. It has shown that in normal operation, the dynamic stiffness method could perform nondestructive testing for foundation pile in use so as to evaluate the capacity resistance and reference could be made for testing and evaluation of similar pile foundation.

References
1. Technical Code for Testing of Building Foundation Piles (JGJ 106-2003), Beijing, China Building Industry Publishing House, 2003 (in Chinese). 2. Specification for Low Strain Dynamic Testing of Piles, Beijing, China Building Industry Publishing House, 1995 (in Chinese). 3. Xu Hui and Jiao Yusen. “Low-strain Transient Admittance State Regulation Factor Method for Detecting Capacity Resistance of Foundation Pile,” Evaluation Report of the Science & Technology Department, MOR, 1996 (in Chinese). 4. Yang Jianxun. “Primary Study on Determination of Dynamic Stiffness and Capacity Resistance by Transient Excited Force,” China Railway Science, 1994 (in Chinese). 5. Ying Huaiqiao. “Vibration Test and Analysis,” China Railway Science, 1987 (in Chinese). 6. Chen Changju, et al. “Analysis on Vertical Vibration by Mechanical Admittance Method,” Journal of Hu’nan University, 1985(in Chinese). 7. Ewins, D.J. Measurement and Application of Mechanical Mobilitity Data. Solartron Instrumentation Group. 1983.
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