Research Of High Strain Curve Fitting Method In PHC Pipe Testing

Currently, pile foundation is increasingly applied in engineering. Since the pile foundations are concealed engineering projects, the design, calculation, construction, testing and other aspects of pile foundation are often more complex than the upper building structure. Therefore, the quality inspection of pile foundation becomes an important part of engineering quality control. The single static load method is daily unable to meet the needs of diagnosis in the pile construction quality. That’s why the high-strain method is numerously used in detecting the quality of pile foundation. Based on the previous studies, this paper attempted to make a further study in the damping coefficient of high-strain CSAE method and the parameters of high-strain curve fitting method by means of high-strain tests. The accuracy of high-strain CSAE method and high strain curve fitting method was verified through destructive static load tests. Besides, the range of CASE damping coefficient under two kinds of strata was proposed. The main results and conclusions are as follows:(1) The one-dimensional wave equation and its solution of rod were summarized. Situations such as the infinite rod, finite rod, impedance changing interface, friction resistance rods were classified and discussed, which provided a rigorous theoretical basis for the research in high-strain method of pile foundations.(2) Three kinds of calculation analysis methods including SMITH method, CASE method and curve fitting method were studied. Besides, the basic principles and technical means of these three methods were summarized. So was the pile-soil model.(3) The measured curves of 9 piles in site were obtained through high-strain tests and the bearing capacity of single pile was calculated by means of fitting the measured curves. By separately changing the related parameters of the curve fitting method model and calculating, the influences and laws of a certain parameter on the calculation curve were obtained.(4) For the high strain CASE method, the optimal value of CASE damping coefficient under different stratum was obtained through the contrast between the static and dynamic tests of PHC pipe pile.(5) For the high-strain curve fitting method, it is relatively more accurate through contrast between static and dynamic tests of PHC pipe piles. The tests proved that high strain dynamic testing method can effectively complement and even partially replace the traditional static load test.