壁樁受靜態側向力作用之行為與承載機制研究

Study on Lateral Load Behaviors and Bearing Mechanism of Barrette Piles

黃達瑋(Da-wei Huang)

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(2020年)

https://doi.org/10.6846/TKU.2020.00207

摘要

本研究以壁樁受靜態側向力之行為與承載力詮釋為研究主題，研究係以三維有限元素分析軟體Midas GTS NX為主，所考慮的混凝土壁樁模型其截面長度為2.8m、寬度為1.2m，壁樁長度可分為20m和50m。黏土與砂土之土壤採莫爾庫倫破壞模式，混凝土壁樁為線彈性，觀察黏土層和砂土層壁樁在長側受力（橫向受力）與短側受力（縱向受力）的力學行為差異。研究發現:1.隨著土壤強度越低，壁樁的位移量與彎矩會越大。2. 短的壁樁撓曲變形小，但內力將分布於全部樁身。3. 長樁在長側受力之最大位移和短樁長側受力最大位移相似，撓曲變形的反曲現象特別明顯，樁身內力影響深度約為0.4倍樁長；若在短側受力，內力影響深度將達0.6倍樁長。
此外，本研究並建議壁樁樁身正規化變形曲線的回歸方程式，以及壁樁長樁和短樁條件，可涵蓋不同土壤強度對其定義影響，研究發現: 4. 黏土層壁樁在長側受力時，L/R>5即可視為長樁；在短側受力時，L/R<3為剛性樁，L/R>7為長樁。若為砂土層壁樁，則無論在長側或短側受力時，L/R<2可視為剛性樁，L/R>6即可視為長樁。
為了解工程界常用的張有齡公式和LPILE分析應用於壁樁可行性，本研究亦將壁樁視為等效圓樁，以淺層土壤P-y曲線的最大地盤反力係數k進行分析，並和Midas結果比較。結果顯示: 5. LPILE分析過於保守，僅在部分砂土層長側受力狀態和砂土層短側受力時和Midas分析結果相似。6. 張氏法僅能滿足壁樁在長側(橫向)受力的設計所需；作用力在短側下，使用張氏法將會低估樁身彎矩。另研究也以不同詮釋法解讀壁樁的力位移曲線圖，7. 研究發現: 一般詮釋法較難估計壁樁側向承載力，雙曲線法或許適合判讀壁樁側向承載力，但其載重需遠超過一般試驗荷重。

關鍵字

壁樁 ； 有限元素分析 ； LPILE ； P-Y曲線 ； 側向力 ； 張有齡公式

並列摘要

This study is on barrette behaviors under lateral loads. Three dimensional FEM analysis using program Midas GTS NX was conducted on a 2.8m×1.2m barrette model embedded in clays and sands. 20m and 50m barrettes were studied with loads acting on the longitudinal and transverse directions of the barrette respectively. LPILE analysis and the solutions associated with the Chang’s formulas were also conducted to make the comparisons. Four interpretation methods were adopted to check the lateral capacity of the barrette. The conclusions are summarized as follows, 1. The barrette displacements and bending moments will become larger as the soils get softer. 2. Shorter barrette bends less but will have internal stresses along the whole structure. 3. Longer barrette with load at the transverse direction will have moments and shears existing in the upper region of the barrette (0.4 times its length). If it was loaded at the longitudinal direction, then it became more rigid and the internal stress affected more regions of the barrette (0.6 times its length). The modulus of subgrade reaction of the barrette k was found much larger when the barrette is subjected to the loads in the longitudinal direction. Polynomial functions of the normalized deflections of the barrette were suggested regardless of the soil stiffness, however they must be calibrated if the load magnitude was changed. 4. The definitions of long barrette and short barrette were studied by checking the deflection ratio of u/R, v/R or u/T, v/T along the barrette shaft. The criteria were made. 5. LPILE was found to provide significant overestimations of the displacements and internal stresses of the barrette in clays. 6. Chang’s formulas were found applicable when barrette was subjected to load in transverse direction, for barrette with load in longitudinal direction, the formula will underestimate the bending moments. 7. The interpretation methods will encounter difficulty to estimate the lateral capacity of barrette because the resistance of the barrette is really significant compared to ordinary piles. The hypoblic method perhaps is applicable in this case.

並列關鍵字

Barrette ； FEM analysis ； LPILE ； P-y curve ； Lateral load ； Chang’s formula

參考文獻

參考文獻

1. Abbas, J.M., Chik, Z.H. and Taha, M.R. (2008) "Single pile simulation and analysis subjected to lateral load", Electronic Journal of Geotechnical Engineering , 13E.

2. Bahloul , D. and Moussai, B. (2016) "Three-dimensional analysis of laterally loaded barrette foundation using Plaxis 3D" Tanda Kardinal Pemeriksaan Eksternal Jenasah Diduga Tenggelam Dari Data Bagian Ilmu Kedokt. Forensik Rsup Sanglah Bali Tahun 2012–2014. 2015, 4, 29–42. Available online: http://www.eventscribe.com/2016/CECAR7/assets/pdf/326516.pdf (accessed on 28 March 2019).

3. Broms, B.B. (1964) "Lateral resistance of piles in cohesionless soils" Journal of the Soil Mechanics and Foundations Division, ASCE, 90(3), pp. 123-156

4. Chang, Y.L. (1937) “Discussion on lateral pile-loading tests by Feagin,” Trans., ASCE.