壁樁垂直載重試驗數據之模擬分析

Analysis of pile load test data of barrette piles

汪子瑜(Tzu-Yu Wang)

指導教授 ： 張德文

淡江大學/工學院/土木工程學系碩士班/碩士(2018年)

https://doi.org/10.6846/TKU.2018.00497

摘要

壁樁近年來經常被用於建築物基礎，由於其與傳統圓形基樁除斷面形狀不同外，施作方式也有差異，一般常用經驗詮釋法、理論分析法以及數值分析法均以圓樁或方樁為主，其在壁樁的適用性值得檢驗印證。本研究參考台北市大型運動場址壁樁載重試驗數據，以三維有限元素分析程式模擬壁樁在壓力和拉力下的承載行為。土壤採莫爾庫倫破壞模式，混凝土壁樁為線彈性，土樁介面元素則採線彈性完全塑性模式，探討壁樁之t-z曲線，比較壓力與拉力下樁身摩擦力、以及極限承載力/拉拔力等工程特性，同時配合基本靜力公式、經驗詮釋法和APILE分析，了解其適用性。由分析結果顯示，介面元素之附著力、摩擦角及摩擦勁度對於壁樁行為影響甚鉅，樁之力-位移曲線因摩擦勁度固定而較試驗數據更為線性外，餘軸力、摩擦力和t-z曲線趨勢均和試驗相似。拉力樁分析由於現場混凝土樁會不斷產生開裂， t-z曲線並不規律，分析軟體無法進行模擬外，其餘力位移、軸力和摩擦力分布亦大致合理。若現地報告資料充足且可率定材料參數，則採APILE分析所模擬之結果將較有限元素分析更為接近。
承載力分析中，壓力樁案例由於現地數據限制，採用現地數據所詮釋的承載力較採用有限元素法數據所得之承載力為低，採用靜力公式和採介面元素強度以及APILE接近，Davisson法和Van Der Veen法最接近靜力公式計算值。在拉力樁時，Davisson法最接近介面元素強度和APILE結果，採靜力公式所得將偏低，顯示靜力公式折減值過大。本研究另分析樁周摩擦阻抗(t)和SPT-N值以及不排水剪力強度(Su)的關聯性，發現建築物基礎構造設計規範所建議的經驗公式(t=3.3N、單位: kPa)可適用於本研究案例，唯t/Su值較經驗公式值為高，顯示本案例黏土層之壁樁摩擦強度折減量應低於靜力公式，故在設計壁樁時宜注意避免低估其抗拉性。

關鍵字

壁樁 ； 樁載重試驗 ； 有限元素分析 ； APILE ； t-z曲線 ； 承載力

並列摘要

In recent years, many building were constructed using barrette piles. Conventional design methods and load interpretations applicable to ordinary piles need to be examined herein. The load test data of a city stadium site in Taipei were analyzed in this study. Three-dimensional finite element analysis was used to simulate load-displacement of the barrette piles. Axial stresses and frictions of the piles and t-z relationships of the soils were studied. Comparisons were made using APILE analysis and static equations under compressional and tensile load. It was found that the model parameters of interface elements are significant in the simulations. The fixed frictional stiffness of FEM analysis would provide more linearized load-displacement curve. The axial stress, frictions and t-z relations can be similar to the field data. For pull-out loads, t-z relations were found irregular. This is because of the crack occurrences under the tensile loads. The numerical analyses conducted are unable to produce such phenomenon. However other piling behaviors were found agreeable with the field data. If the field load test data was sufficient with good qualities, then APILE analysis can simply simulate the barrette pile behaviors. For the compressional capacities, owing to the limited load-displacement data, the interpretation results from the numerical simulations are larger than the ones read from the field. The ones from the static equations, the interface elements and APILE analysis are about the same. Both Davisson and Van Der Veen methods would provide solutions close to static equations. For pull-out capacities, Davisson method gives similar solutions to the ones from interface elements and APILE. The static equation herein gives the lowest prediction owing to the over-deductions To show the evidence, mobilized frictions along the barrette piles were computed and compared to SPT-N and undrained shear strength of the soils. For clayey soils, frictions of the clays were found greater than what has been suggested commonly. It needs further attentions when estimating the pull-out resistance of barrette piles in Taipei Basin.

並列關鍵字

barrette piles ； pile load test ； FEM analysis ； APILE ； t-z curve ； capacity

參考文獻

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3. ASTM（2007）.“Designation: D1143/D1143M-07: Standard test methods for deep foundations under static axial compressive load”, American Society of Testing and Materials.

4. Bowles, J. E.（1982）.“Foundation Analysis and Design”, 4th Edition,

5. Chattopadhyay, B. C. and Pise, P. J., “Uplift Capacity of Piles in Sand.” Journal of Geotechnical Engineering, ASCE, Vol. 112, NO. 9, pp. 888-904（1986）.