Interpretation Method for Statnamic Test on Long Piles

• Main Authors: Wei-Kuang, Chang, 張為光
• Other Authors: Cheng-Hsing, Chen
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/48369999767305637053

博士 === 臺灣大學 === 土木工程學研究所 === 95 === Recently, Statnamic (STN) test is one of the prevailing methods applied for the loading test of a pile. The loading generated by the STN test has longer duration than an impact test, however, the response of pile during a test still includes the dynamic effects. In order to deduce the static resistance from the result of a STN test, many interpretation methods had been developed, based on the lumped mass model or the stress wave model. This study is to investigate the applicability of all available methods, and further to develop an improved method to be used for interpreting the result of a STN test on long piles. For short piles, the interpretation methods currently used are based on the lumped mass model in general. At first, the applicability of all lumped-mass methods is investigated for the conditions with soil springs in the form of linear, elasto-plastic and nonlinear conditions, respectively. Then, an improved method named the Initial Damping Method is developed in this study. It utilizes the responses at the beginning stage of a test to estimate the equivalent damping coefficient of the soil-pile system. Based on that, the static resistance of soils in a STN test can be deduced. Numerical examples show that it is satisfactory for short piles with various soil conditions. For a STN test on longer piles, the stress wave model is more proper to simulate the effect of wave propagation in the pile. The available interpretation methods are still not applicable to identify the nonlinear response of surrounding soils. This study is to develop an innovatory system identification method to be suitable for a STN test on long piles. The Segmental Signal Matching method is developed to identify the nonlinear soil response around each segment of the pile during the loading process of a STN test. This method is based on the wave equation, discretized by the finite-difference scheme, to formulate the independent influence area and its explicit expression for each node displacement. It therefore can be used to directly calculate the associated soil parameters during the loading process of a STN test. By using this method, the nonlinear t-z curve for soils corresponding to each segment of the pile can then be established. Finally, a numerical example and four in-situ pile tests are selected to verify the effectiveness and applicability of the developed method of analysis.