樁基礎於排水土層之樁底承載力分析模式研究

Analysis Model of Tip Capacity for Pile Foundations in Drained Soils

吳浩瑋(Hao-Wei Wu)

指導教授 ： 陳逸駿

中原大學/工學院/土木工程研究所/碩士(2011年)

https://doi.org/10.6840/cycu201100813

摘要

由國內外排水土層之樁載重試驗資料，包含場鑄樁於砂土層、場鑄樁於卵礫石層及植入PC樁於砂土層，透過樁軸向詮釋法詮釋樁底實際底承力與承載力理論公式比較，發現在排水土層分析時，理論公式所計算之結果於場鑄樁和植入PC樁皆高於樁底實際承載力約10倍。因此，本研究之目的藉由修正其中之參數以使理論預測值能與實際量測值一致。
　　首先加入設計深度之觀念，並透過分析理論承載公式中的各項係數之變異性與標準偏差，對變異性和標準偏差較大的覆土壓力因子(Nq)及土壤勁度修正係數(ζqr)進行修正分析。藉由實際樁載重詮釋法之上限值(Chin法)、中等值(L2法)及下限值(L1法)，由回饋分析所新建立之係數以能達到最佳之統計結果。
　　修正後之Nq及ζqr仍維持其原本與摩擦角之關係，即Nq因子隨著摩擦角遞增、而ζqr係數則隨摩擦角遞減。透過修正後之Nq及ζqr，可使修正後的理論承載公式與樁底實際承載力一致，且其判定係數(r2)可達0.70~0.94。本研究所建立之場鑄樁及植入PC樁於排水土層之修正承載力公式運用於工程案例，可增加理論承載力之精確度。

關鍵字

理論底承力 ； 設計深度 ； 植入PC樁 ； 場鑄樁 ； 排水土層 ； 詮釋法

並列摘要

This study evaluates the tip bearing capacity of pile foundations based on numerous pile load test data. The evaluation includes drilled shafts in drained soils and gravelly soils, as well as pre-bored PC piles in drained soils. Since the predicted tip capacity using the traditional bearing capacity equation shows ten times, on average, higher than the measured tip capacity, the related analysis coefficients of bearing capacity are modified using the measured results.
First, the concept of the desired design depth is considered. Then, the more variable analysis coefficients are used for the modification of analysis equation. According to the analyses of all coefficients, the overburden bearing capacity factor (Nq) and the bearing capacity modifier (ζqr) present the highest coefficient of variation and standard deviation. These coefficients are modified from the back-calculation analysis of the interpreted capacities of load test. The high, middle, and low interpreted capacities by Chin, L2 and, L1 methods, respectively, are used for the back calculation analysis.
The modified bearing capacity coefficients still hold their typical relation to friction angle in which Nq factor increases with increasing friction angle while ζqr coefficient decreases. Based on the analysis results, the bearing capacity equation using the modified coefficients can better evaluate the pile capacity and has more accurate and reliable results, with the determination coefficient (r2) ranging from 0.70~0.94. It can be reliably applied in engineering practice.

並列關鍵字

bearing capacity equation ； desired design depth ； pre-bored PC piles ； drilled shafts ； drained soils ； interpretation criteria

參考文獻

27.朱祖宏，「場鑄樁於卵礫石層之軸向及側向載重詮釋法及承載力評估」，碩士論文，私立中原大學土木工程研究所，桃園中壢，2009。

28.陳俊宏，「預鑽孔植入PC樁於排水土層之受壓載重行為評估」，碩士論文，私立中原大學土木工程研究所，桃園中壢，2010。

26.張馨文，「場鑄樁樁身摩擦力及拉拔詮釋法之評估」，碩士論文，私立中原大學土木工程研究所，桃園中壢，2007。

25.方顗忠，「場鑄樁樁底承載力及壓載詮釋法之評估」，碩士論文，私立中原大學土木工程研究所，桃園中壢，2007。

1. Chen, YJ, Chang, HW and Kulhawy, FH, “Evaluation of uplift interpretation criteria for drilled shaft capacity”, J. of Geotech. & Geoenvironmental Eng., ASCE, Vol. 134, No. 10, 1459-1468, 2008.