垂直荷載樁筏基礎之溫克基礎分析方法

Practical Winkler Analysis Method for Piled Rafts Subjected to Vertical Loading

林易劭(Yi-Shao Lin)

指導教授 ： 邱俊翔

國立臺灣大學/工學院/土木工程學系/碩士(2023年)

https://doi.org/10.6342/NTU202300606

摘要

樁筏基礎結合樁基礎和筏基礎的特色，其中樁和筏均會提供承載力，但由於樁和筏的互制效應，使得樁筏基礎中的樁和筏部件行為與單純樁基和筏基的行為不同。樁筏間的互制效應主要有三個影響：樁筏基礎中筏基部件的承載壓力會因為樁的影響而降低、筏基底部土壤受到載重產生額外應力影響樁身的摩擦力，以及樁因群樁效應使得其行為與單樁不同。
本研究基於有限元素分析發展垂直荷載樁筏基礎的溫克基礎分析方法。研究首先利用有限元素分析模擬樁筏基礎之垂直荷載試驗以及土壤三軸試驗，率定分析模型的參數，以建立樁筏基礎的有限元素分析模型，接著利用此模型進行參數分析取得建立溫克分析所需的筏基應力修正係數，並比較幾個群樁效應修正法在樁筏基礎中的適用性，以及考量筏基造成土壤中應力增量改變所導致的樁身摩擦力增加，以建立垂直荷載樁筏基礎的溫克基礎分析方法，最後利用有限元素模型驗證所發展分析方法的適用性。
本研究提出的溫克分析方法中，需要先取得單樁與筏基的力—位移關係，接著利用筏基應力修正係數將筏基的力—位移關係修正為樁筏中筏基部件的力—位移關係，再透過筏基部件的力—位移關係計算在不同位移下各自對土壤造成多少額外的應力增量，以計算因為筏基引致的樁身摩擦力，並與單樁的力—位移關係相加取得修正後樁的力—位移關係，最後利用群樁效應修正法修正樁的力—位移關係得到樁筏中樁部件的力—位移關係，再與筏基部件的力位移關係一起進行樁筏分析。經過一系列三維有限元素驗證分析結果顯示，此修正方法可以掌握筏基受到樁影響後承載壓力降低的現象，並反映出筏基引致的樁身摩擦力增加與群樁效應對樁行為的影響。

關鍵字

樁筏基礎 ； 垂直載重 ； 樁筏互制效應 ； 溫克基礎模式

並列摘要

A piled raft foundation is a combination of a raft foundation and piles, in which both raft and pile components in the piled raft carry parts of the applied load. Due to the interaction between pile and raft components, the behaviors of pile and raft components in a piled raft are different from the single pile and raft. This interaction has three main effects: the reduction in the bearing pressure of the raft component due to piles, the pile shaft friction increase due to the confinement of the raft, and the group pile effect.
This study attempts to develop a Winkler analysis method for piled rafts subjected to vertical loading based on finite element analyses. Piled raft load tests and triaxial tests in the literature are simulated to calibrate the parameters for the finite element model, by which the Winkler analysis method is developed.
The proposed Winkler analysis method has five steps. The first step is to obtain the load-settlement relationships for both the single pile and the raft. The second step is to calculate the load-settlement of the raft component in the piled raft from the raft using the stress modification factors. The third step is to consider the increase in pile shaft friction due to the additional confining stress raft provided. The fourth step is to apply group pile modification factors to modify the load-settlement relationship of the pile to obtain those of the pile components in the piled raft. The final step is to apply the modified load-settlement relationships for raft and pile components in the piled-raft Winkler analysis. A series of finite element verification analyses show that the proposed method can effectively consider the aforementioned effects of pile-raft interaction.

並列關鍵字

Piled rafts ； Vertical loading ； Pile-raft interaction ； Winkler foundation model

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