Analysis And Application Research On High Stain Dynamic Testing Method For The Bearing Capacity Of Pile

Pile foundation engineering is concealed engineering, the quality of it is directly related to the safety of the entire structure. Whether the ultimate bearing capacity of single pile meets the design requirements is one of main problems in quality test of pile foundation engineering. At present, static load testing method and high stain dynamic testing method are the main methods of testing the ultimate bearing capacity of single pile. High stain dynamic testing method gets the value of the ultimate bearing capacity of single pile by solving the wave equation. It use dynamic impact load to replace static stability load, which makes resistance of soil around pile give a full play. The method has got extensive application all over the word because of its Incomparable merit such as short time-consuming, low cost, high efficiency and so on. Though the method tends to be mature today, it is imperfect. There are certain theory significance and practical value in further analysis and research on the method.First, this paper proceeds from the basic theory of high stain dynamic testing method, summarizes the basic theory of high stain dynamic testing method, that is one-dimensional wave theory. The total soil resistance formula of CASE method is re-derived, the CASE method and its improved method are analyzed. CASE damping coefficient is a empirical coefficient which need to be selected artificially, so it has a certain degree of subjectivity. Wrong results may be produced if CASE damping coefficient is selected improperly. This paper analyses the selection of CASE damping coefficient, puts forward an assistant method; of CASE method to test the rationality of the value of CASE damping coefficient in a practical engineering. By testing, the assistant method has a certain application value, but it has limitation for its specific application condition.Second, the paper analyses and studies the measured curve fitting method. The models of pile and soil are explained. The setting of pile-soil model is the most important link in CAPWAPC program, so it is directly related to the success of fitting and the rationality of bearing capacity value, as well as the reliability of other results. All coefficients need to be entered, and the rationality of the pile-soil model needs to be repeatedly checked and debugged by analyst. The paper analyses and discusses the questions of parameter setting in measured curve fitting method, points. out the shortages of measured curve fitting method, corrects some existing problems, adds some calculation models such as residual stress, pile-toe gap, softening of the pile- toe soil . All of above makes the method more perfect. Then the improved measured curve fitting method is applied to practical engineering. By refitting and the contrast test, more accurate results are given. The contrast test results errors could be controlled in 10%, which states the improved program can meet the test requirements of some engineering well.In the end, the paper analyses the error sources of the high stain dynamic testing method and puts forward some methods which can reduce error. The errors of the high stain dynamic testing method are concerned by people all the time. It's very meaningful for the development of the high stain dynamic testing method to study the he error sources of it and improved it purposefully.