於傾斜地盤場址考慮土壤水平變異性對地盤反應之影響

Effect of Soil Horizontal Variability on Ground Response for Sites Resting on Inclined Bedrock

張惟安(Wei-An Chang)

指導教授 ： 郭安妮

國立臺灣大學/工學院/土木工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201803601

摘要

在大地工程中，均質土壤時常被用來簡化數值模擬上的困難。但是事實上，土壤性質的空間變異性扮演著不可或缺的角色，是必須考慮的因素。另外，不規則的地形也會對地盤反應有劇烈的影響，因此土壤之空間變異性以及模型的幾何形狀都是本研究所著重的要點。
本研究中，模型中土壤的剪力波速會以隨機場理論來模擬。有鑑於土壤性質在垂直方向上可以比較簡單的獲取，在本研究只會考慮土壤的水平變異性。在土壤性質的設定方面，可以透過改變剪力波速不同的分布模式和關聯性長度來得知關於不同的剪力波速組成會對地盤反應有什麼影響。此外，在模型的設置上，透過改變傾斜地盤的傾角來探討地形的不同所帶來的影響。為了統計歸納，每個變數組合會取30組的剪力波速來進行模擬。30組的反應譜會取平均並且計算其標準偏差，用以與其他組合比較。
分析結果顯示，傾斜地盤之傾角比較大的組合於正對傾斜面的場址會使水平方向的反應較其他為小，而在垂直方向的部分，反應則是比較高。另外，擁有比較大關聯性長度的組合，會產生較高的標準偏差。

關鍵字

土壤水平變異性 ； 傾斜地盤 ； 地盤反應 ； 剪力波速 ； 關聯性長度

並列摘要

Soil deposit is often assumed to be homogeneous to simplify the derivations of theoretical solutions for a variety of geotechnical engineering problems. With the advances in computing, modeling of soil deposit with the consideration of spatial variability in soil properties is made possible. However, with limited amount of soil borings available for a subject site, variability in the vertical direction is mainly considered as there may not be enough data to capture the variability in the horizontal direction. In this study, effect of horizontal spatial variability (in terms of shear wave velocity) on site response is investigated. Both sites with horizontal and inclined soil-halfspace interface (bedrock) are considered.
To describe the horizontal spatial variability, random field model is used to describe the distribution of shear wave velocity. Different probability distribution models, scales of fluctuation, and coefficients of variation are considered. Furthermore, different tilt angles of the inclined bedrock are used. To establish the statistics for the predicted ground motions with the consideration of spatial variability, 30 series of shear wave velocity models are generated for each variable setting. The median response spectra and the standard deviations in the predictions for the 30 cases were computed.
The results show that sites with steeper tilt angle of inclined bedrock would have a lower site response in the horizontal direction but a higher response in the vertical direction at the site where the inclined bedrock is facing. Moreover, models with larger scales of fluctuation would have higher standard deviations in the predictions. Choice of probability distribution model does not seem to affect the median and the standard deviation of response spectra.

並列關鍵字

soil horizontal variability ； inclined bedrock ； ground response ； shear wave velocity ； scale of fluctuation

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