垂直力作用下樁筏基礎的基樁彈性阻抗折減影響分析

Stiffness reduction of piles due to pile-to-pile interactions for piled raft foundation under vertical load

洪名和(Ming-He Hung)

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.2020.00393

摘要

本研究以WEAPR-S程式為分析基礎，模擬樁筏基礎在垂直均布載重下的變形量，該分析係藉二維筏基變形差分式和一維基樁變形差分式而建立。本研究另以改良之Lysmer類比模式模擬筏基底部土壤彈簧，同時使用極限強度模式模擬基樁等效彈簧勁度，並考慮群樁互制影響，完成WEAPR-S2程式之開發，其可求解線彈性樁筏基礎受力行為，具簡易分析特性。程式分析結果並與三維有限元素法Midas-GTS NX分析結果進行比較，以了解軟弱黏土地盤之樁筏沉陷量分布、應力分布、差異沉陷量、基樁折減係數、基樁受力分配情況，和相關參數影響。
研究成果顯示：1.採用改良Lysmer土壤彈簧搭配極限強度之基樁土壤彈簧，並引用群樁互制公式，可改善原WEAPR-S分析，使樁筏基礎的沉陷量與有限元素法分析結果相似。2.大型樁筏基礎的筏基下方土壤對基礎行為影響趨於明顯，基礎的沉陷以中心處最大，而受力亦以中心部位基樁較大，該受力現象與剛性基礎迴異。3.柔性樁筏基礎之基樁配置數量明顯影響基樁行為，基樁數量越多時，基樁的受力和其等效彈簧勁度愈均勻，其互制影響不明顯；但基樁數量減少時，角隅樁所受勁度之影響較其餘基樁明顯。4.研究發現：剛性樁筏基礎之基樁荷重比例將遠大於柔性基礎之基樁，其沉陷量亦將較柔性基礎低許多，故柔性樁筏中筏基下方土壤的承載力相對重要，若將剛性樁基礎之群樁設計概念套用於柔性樁筏基礎時，設計將過於保守。5.WEAPR-S2分析雖能大致掌握樁筏基礎受力行為，但仍會低估基樁的最大內力，使用時仍須謹慎。

關鍵字

樁筏基礎 ； 差異沉陷 ； 群樁互制 ； 基樁受力分配 ； 等效樁彈簧勁度 ； 折減影響

並列摘要

This study, the WEAPR-S program is used as the analysis framework to simulate the deformation of the piled raft foundation under vertical uniform load. The analysis is based on two-dimensional deformations of the raft and one-dimensional deformations of the piles. In this study, a modified Lysmer analog model was used to simulate the soil spring at the bottom of the raft foundation. At the same time, the ultimate strength model was used to simulate the equivalent pile stiffness, and the pile-to-pile interactions were considered to complete the development of the WEAPR-S2 program. Validation of the proposed program was conducted with the 3D FEM analysis using Midas-GTS NX program. To understand the distribution of the piled raft foundation settlement, stress distribution, differential settlements, reduction effect, and load distribution, the effects of the structural and soil parameters in design were discussed for the applicability of such analysis.
The study reveals that: 1. The use of modified Lysmer soil springs combined with ultimate strength soil springs around the piles, and pile-to-pile interactions formula, can improve the original WEAPR-S analysis, so that the settlement of the pile raft foundation can be analyzed with the finite element method, the results are similar. 2. The soil under the raft foundation of the large pile-raft foundation is having obvious influence on the behavior of the foundation. The settlement of the foundation is the largest at the center, and the stress is also larger at the center. The stress distribution is different from the rigid foundation 3. The number of piles on the flexible pile raft foundation obviously affects the behavior of the foundation piles. The greater the number of piles, the more uniform the force of the pile and the equivalent pile stiffness it will be, and the resulting reduction effect is trivial. When the number of piles decreases, the pile-to-pile interaction influence on the stiffness of the corner pile is more obvious than rest of the piles. 4. The study reveals that the load carried by the piles of the rigid piled raft foundation will be much greater than the piles of a flexible piled raft foundation, and its settlement will be much smaller than that exerted at the flexible foundation. Therefore, the bearing capacity of the soil under the raft foundation in a flexible piled raft is relatively important. When the design concept of grouped piles with rigid pile cap is applied to flexible piled raft foundation, the design will be over conservative. 5. Although the WEAPR-S2 analysis can roughly grasp the piled raft foundation load-deformation behavior, it will underestimate the maximum internal stresses of the piles, and care must be taken when using it.

並列關鍵字

piled raft foundation ； differential settlements ； pile-to-pile interactions ； pile load distribution ； equivalent pile stiffness ； reduction effect

參考文獻

參考文獻

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