集集大地震後水井水位變化模擬及分析

本研究利用簡化的黏彈性模式，描述含水層中粗顆粒礫石沈積物與細顆粒砂石沈積物交界面處至拘限含水層尖滅端，於地震力作用下液相之動力行為。假設拘限含水層中砂石沈積物所在研究區域於震動時爲液相可壓密且孔隙介質不排水狀況下，將液相及固相耦合的波動方程式分離，僅考慮液相控制方程式，推導出解析解，同時套配921集集大地震中於濁水溪沖積扇中所觀測到之水井水位變化資料，獲致良好的結果。本研究亦參照地質井取樣調查所描繪的水文地質剖面圖，描述921集集大地震中發生土壤液化地區，與含水層中粗顆粒礫石沈積物與細顆粒砂石沈積物交界面處位置關係，據觀察紀錄顯示，地震所引起之水井水位變化最大處皆位於含水層中礫石與砂石交界面處，而導致該區域靠近扇頂部分於地震後數日陸續發生土壤液化之現象，顯示於大地震中評估土壤液化潛能，除現有工程評估方法外，還需考慮工程所在水文地質環境之影響。

關鍵字

集集大地震；水井水位變化；黏彈性力學；孔隙介質；土壤液化

並列摘要

The simplified visco-elastic model is adopted to describe the earthquake induced dynamic behavior of the liquid phase from the interface between the gravels and the sands to the pin-off in the confined aquifer. We assume the porous media is undrained and the liquid phase is compressible in the sanded confined aquifer during the vibration, and then decouple the momentum equation of the liquid phase to find the analytical solution. The presented model is derived to match the captured data of the high dense network of hydrologic monitoring wells after the Chi-chi earthquake and does fairly well. Consulting the hydrogeological profiles identified from the drilled cores, the highest well water level changes are located at the interface between the gravels and the sands in the confined aquifer and induce the liquefaction at the upstream area in the next few days. The field observation emphasizes the importance of the hydrogeological influences in evaluating the liquefaction potential.

並列關鍵字

The Chi-Chi earthquake ； Well water level changes ； Visco-elasticity ； Porous media ； Liquefaction

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