總應力與有效應力地動分析法偏差評估之研究-以臺灣垂直陣列為例

Evaluation of Biases in Predictions from Total-stress and Effective-stress Ground Response Modeling Methods by Using Vertical Arrays in Taiwan

陳泊鈞(Bo-Jun Chen)

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(2016年)

https://doi.org/10.6342/NTU201603105

摘要

當地震發生時，地震波傳遞的過程中經過不同土層及岩盤，地震波的性質會隨之改變，如頻率、振幅及傳遞方向等。地盤反應分析法為模擬土壤在地震波傳遞過程中的行為，地動分析法又可概分為頻率域分析法與時間域分析法。頻率域擬線性分析法原理簡單且輸入參數易於選取，在工程上的應用是最為普遍的方法，不過當土壤處於大應變下，擬線性分析法無法準確的模擬土壤的非線性行為。時間域非線性分析法能準確的模擬土壤於大應變下的非線性行為，且與擬線性分析法相較下有較佳的預測能力。非線性分析法中土壤的應力計算又可分別使用總應力法以及有效應力法進行分析，其中有效應力分析法能估計土壤受震時孔隙水壓激發與消散的過程。
本研究是以台灣井下觀測網之垂直陣列進行一維地盤反應分析，其中地表井下觀測網之建立為氣象局近幾年的重點工作項目之一，截至2015年底，約有50個井下陣列以安裝於全台各地。本研究目標為觀察不同理論模型預測結果與地表觀測記錄的比較，評估它們偏差行為，並且建立該些陣列完整的地工模型提供給一維地盤反應分析使用。本研究發現中央氣象局所提供部分測站之剪力波速剖面可能有不精確或不確定性等影響，而利用附近地層資料進而修正剪力波速已提供後續分析使用。輸入弱震的情況下，其擬線性與非線性分析法的地表預測結果相當相似，並且與地表觀測記錄互相比較下，在短週期上預測結果多為低估的情形，而在長週期則有高估的結果。

關鍵字

地盤反應分析 ； 非線性 ； 垂直陣列 ； 有效應力

並列摘要

When earthquake waves propagate through geologic deposits, frequency content and amplitude of the waves would be changed. Ground response analysis can be performed to model the wave propagation process by incorporating detailed site conditions. These analyses can be in either frequency domain or time domain. In engineering practice, equivalent linear frequency analysis is widely used because of its simplicity in parameter selection and code usage. However, equivalent linear analyses may not be able to accurately model the nonlinear behavior of soil, especially when shear strain level is high. Nonlinear time domain analyses can accurately represent the soil nonlinear behavior and thus have the potential to better predict the ground response (compared to equivalent-linear analysis). Also, nonlinear time domain analyses can allow the soil stress to be evaluated in terms of total stress or effective stress. In addition, pore water pressure generation and dissipation can be evaluated through effective stress ground response analyses.
The construction of surface-downhole monitoring network is one of the important tasks for strong motion monitoring by the Central Weather Bureau in recent years. Almost fifty vertical arrays have been installed in Taiwan until Year 2015. The objective of this research is to evaluate the performance of different ground response analysis methods by utilizing the ground motion data recorded at selected vertical arrays. To facilitate this evaluation, geotechnical models were first developed and the downhole records were used as the input motions for equivalent-linear frequency-domain and nonlinear time domain analyses. It is found that some of the shear wave profiles provided by the Central Weather Bureau may contain errors. Improved predictions can be obtained when the profiles are modified according to nearby site data. In addition, predicted surface response from different analysis methods are generally similar as most input motions are weak motions. By comparing the predicted and recorded surface response spectra, there is under-prediction at short periods while over-prediction can be observed at long periods.

並列關鍵字

ground response analysis ； nonlinear ； vertical array ； effective stress

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