垂直循環荷載下樁筏基礎於黏土層之變形行為與動態特性

The deformation behavior and dynamic characteristics of piled raft foundation in clay subjected to vertically cyclic load

楊敏昀(Min-Yun Yang)

指導教授 ： 葛宇甯

國立臺灣大學/工學院/土木工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202000070

摘要

樁筏基礎 (piled raft foundation) 為目前國內大地工程所探討的重要議題之一，其設計原理為結合筏式基礎與樁基礎來達到抑制軟弱地盤沉陷量過大之問題，並減少差異沉陷。樁筏基礎設計具有經濟與環保之功能，適用於大樓與離岸風機等基礎，然而當基礎受到動態力時，若動態力之頻率與系統的自然頻率相符時，會產生大量沉陷，無法達到原本之抑制沉陷量過大之成效。
本研究主要探討樁筏基礎在不同組成律模式的情況下改變不同參數的變形行為與動態特性。使用有限元素套裝軟體PLAXIS 3D分析並在筏基上設置參考點，並針對參考點之沉陷量與系統之自然頻率做探討。
為觀察在不同組成律模式與不同參數下變形行為與動態特性之變化，將使用線彈性模式 (Linear Elastic) 與非線彈性之莫爾庫倫模式 (Mohr-Coulomb model) 與修正劍橋黏土模式 (Modified Cam-Clay)，並調整土壤之剪力波速與柏松比以及樁筏基礎之樁長跟樁心距以及筏基厚度作為觀察重點。
研究結果發現，在土壤參數部份，雖然剪力波速與柏松比皆為設計與施工的重要參數，但影響樁筏基礎沉陷量與自然頻率的主要控制參數為剪力波速；而在樁筏基礎結構的部份，因樁筏基礎並無上方結構物，故樁筏基礎結構改變並不影響系統之自然頻率。

關鍵字

樁筏基礎 ； 自然頻率 ； PLAXIS ； 差異沉陷

並列摘要

Piled raft foundation plays an important role in geotechnical engineering, which can be used as the foundation of superstructures and offshore wind turbines. In order to reduce the large settlement on the soft soil and the differential settlement, the piled raft foundation combines the raft foundation and pile foundation. The raft in pile foundation design can lead to a considerable economy without compromising the safety or performance of the foundation. However, when the foundation is subjected to seismic loading and the frequency of the seismic loading is close or identical with the natural frequency of the system, the piled raft foundation will have excessive settlement.
In this study, the main concern is the effect on deformations and dynamic characteristic with different constitutive laws and different parameters. Using the finite element software PLAXIS 3D, a series of analyses were carried out. A set of reference points on the raft foundation were selected, where the settlement and natural frequency at these locations were discussed.
In order to observe the deformation and dynamic characteristic of piled raft foundation, the constitutive laws will use Linear Elastic model, Mohr-Coulomb model and Modified Cam-Clay model. Also, changing the shear wave velocity, Poisson’s ratio, pile length, S/d and raft thickness as the variables.
According to the result, both shear wave velocity and Poisson’s ratio are the important parameters while design and construction phase, the main control parameter of settlement and natural frequency is shear wave velocity. In addition, because there is no structure on the piled raft foundation, changing the structure of piled raft foundation has no significant effect on natural frequency.

並列關鍵字

piled raft foundation ； natural frequency ； PLAXIS ； differential settlement

參考文獻

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