長基樁靜動態載重試驗詮釋方法之研究

基樁靜動態試驗（Statnamic test）是國外近期發展出之基樁承載力試驗方法，其具有快速、經濟與機動等特性。目前常用於詮釋靜動態載重試驗的方法有單質點模型詮釋法、分段卸載點法與單向度應力波傳法。然而現有之詮釋方法套用於長樁非線性土壤之靜動態載重試驗分析，其詮釋結果之土壤反力與位移關係曲線後段不甚理想。本研究首先針對廣泛應用於短樁之單質點模型詮釋方法及應用於長樁之分段卸載點法作研究與探討，探討其於三種常見土壤彈簧模式(線彈性、完全彈塑性與非線性)下之優缺點與適用性，同時提出改進之單質點詮釋方法。研究中針對此一部份提出初始阻尼法，其利用試驗開始之初始段估算阻尼係數，進而推估土壤反力。由研究成果顯示，初始阻尼法可以有效將土壤參數推估而得，且可以更廣泛的應用於各種土壤模式。爾後檢核現行之單向度應力波傳詮釋方法，並整理其優缺點，最後提出分段信號比對法。分段信號比對法是以單向度應力波傳理論為基礎，利用分段來增加比對條件及限制條件，並利用影響網格之概念與有限差分之計算，推導分段底端之軸力反應函數，爾後逐段以推導所得之分段底端軸力反應函數與試驗紀錄作信號比對及識別土壤參數，最後則是利用識別之t-z曲線預測基樁受靜力作用時之反應。由兩數值案例之驗證顯示，分段信號比對法能考慮樁體內波傳效應之影響，同時適用於非線性土壤之分析。最後本研究取四個實際案例作為驗證分段信號比對法之可行性研究，研究成果顯示，以分段信號比對法所識別之非線性t-z曲線擬基樁受靜態力作用之反應，模擬結果與基樁靜態載重試驗結果之樁頭荷載位移曲線趨勢與大小皆相符，由此可知分段信號比對法之有效性及適用性。

關鍵字

基樁靜動態載重試驗；系統識別；分段信號比對法

並列摘要

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.

並列關鍵字

Statnamic pile test ； system identification ； segmental signal matching method

參考文獻

19. Lin, S. S., Yeh, S.C., Juang, C.H., and Chang, Y. H., “Statnamic tests for six long rock socketed shafts,” Foundations and Ground Improvement, ASCE, GSP No. 113, pp.524-538 (2001b).

20. Lin, S.S., Yeh, S.C., Juang, C.H. and Chang, Y.H., “Capacity evaluation of statnamic tested long piles,” Soil Dynamics and Earthquake Engineering, Vol. 24, pp. 829-838 (2004).

21. Lin, S.S., Yeh, S.C., Juang, C.H. and Chang, Y.H., “Structural damping concept for interpretation of statnamic pile oad test results,” GeoSupport, ASCE, (2004).

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長基樁靜動態載重試驗詮釋方法之研究

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