貫入複合土層中鑽掘樁軸向承載力評估模式之探討

Investigation on Analysis Models for Axial Capacity of Drilled Shafts in Multiple Strata

田淳華(Chunn-Hua Tian)

指導教授 ： 陳皆儒

國立暨南國際大學/科技學院/土木工程學系/碩士(2013年)

https://doi.org/10.6837/NCNU.2013.00298

摘要

鑽掘樁為大型構造物常用的深基礎，其軸向承載行為於過去數十年間已被廣泛的研究，並有許多學者提出各種類型的分析計算公式。在世界各地經常遭遇到的土層構造為複合地層，然而既有分析計算公式多是由探討基樁在單一土層的研究所得，其對一般性土層的適用性為何，尚待實質檢討。本研究藉由蒐集所得世界各地在複合土層鑽掘樁之試樁資料庫，探討樁受軸向壓載時－既有分析設計模型所計算出的承載力是否合理。進行檢討之分析模型包括：(1) 美國聯邦公路管理局法(FHWA(2010) method)，(2) 內政部營建署─建築物基礎構造設計規範(TBFDS (2001) method)。本研究針對樁身摩擦阻抗及樁底承載力分別探討，其預測結果均具離散性及高估現象。評估樁身阻抗時，單一土層之結果均較在複合土層之結果好，而各類土層含量比例的多寡對樁身阻抗預測之結果，初步並未發現有明顯之影響效應。本研究進一步並分析樁身阻抗及樁底承載力各分析公式之模型偏差係數，在複合土層中的鑽掘樁之軸向承載力預估，在考量偏差係數後可得較合理且一致的結果。

關鍵字

鑽掘樁 ； 詮釋法 ； 軸向承載力 ； 樁身阻抗 ； 樁底承載力

並列摘要

Drilled shafts have been the preferred foundation system for infrastructure and buildings. Significant advances in drilled shaft research have been made over the past few decades, where many scholars have suggested analysis models. Most past models were developed based on data of drilled shafts in a predominate type of geomaterial, such as clay, sand, gravel, or rock. Ground profile with multiple layers is often encountered in several metropolises around the world. It is warranted to assess the applicability of existing models on shafts in a ground profile with multiple layears. In this study, a database of load test case histories for drilled shafts in multiple strata is compiled. Two commonly used analysis models that can considere all types of geomaterials along the depth of drilled shafts are evalauated critically, namely (1) approaches given by the drilled shafts design guidelines by the Federal Highway Administration (FHWA(2010) method) and (2) design recommendations given by the Taiwan Buildings Foundation Design Specification (TBFSD (2001) method). Tip and side ressitances were first evaluated separately. On average, both models overpredict the side and tip resistances with significant scatter. For side resistance, prediction is better for shafts in a single soil (sand or clay) profile than that in a mixed profile. The model bias or model factor was computed and analyzed for each analysis equation. For the compression capacity, a consistent evaluation can be resulted with consideration of these model factors.

並列關鍵字

drilled shafts ； load test ； axial compression ； side resistance ； tip resistance

參考文獻

1. Brown, D. A., Turner, J. P., Castelli, R. J. (2010). ” Drilled Shafts: Construction Procedures and LRFD Design Methods”, FHWA-NHA-10-016, U.S. Department of Transportation Federal Highway Administration, New York.

2. Chen, J. R. (2004). “Axial Behavior of Drilled Shafts in Gravelly Soils”, Ph. D. Dissertation, Vol. I & II, Cornell University, Ithaca, NY.

3. Chin, FK (1970). “Estimation of the Ultimate Load of Piles not Carried to Failure,” Proceedings, 2nd Southeast Asian Conference on Soil Engineering, Singapore, 81-90.

4. Chang, N.Y., Hien Nghiem (2008). ” Drilled Shaft Axial Capacity-Effects Due to Anomalies”, FHWA-CFL/TD-08-008, U.S. Department of Transportation Federal Highway Administration, Denver.

5. Chen, J. R. and Kulhawy, F. H. (2010). “Axial Load-Displacement Behavior of Augered Cast-In-Place Piles and Pressure-Injected Footings”, Geo Florida 2010: Advances in Analysis, Modeling & Design (GSP 199), Ed. D. O. Fratta, A.