台湾浊水溪冲积扇地下水位变化及地面沉降对高铁之影响

Influence of high-speed-railway engineering works on groundwater drawdown and land subsidence on the Choushui River alluvial plain, Taiwan

浊水溪冲积扇是台湾水资源最为丰富但也是地面沉降最严重地区。近年来该区域的地面沉降因有可能威胁高铁行车安全而备受关注。本文整合历年累积的地下水位及地面沉降等相关监测数据,验证了地下水位变化与含水层补给之机制,探讨了地下水周期性波降条件下土层压缩特性以及高铁路堤与桩基础工程结构的沉降行为。认为对于设置桩基础的线型高架结构而言,区域性地下水位波降不致增加桥墩间的差异沉降,但桩基础若承受邻近局部的额外载重,则可能伴随地下水位波降产生持续性的差异沉降,其长期效应将对线型交通结构物的平整度及安全性造成负面影响。

The Choushui River alluvial plain （Taiwan） is a nch source of water resources. However, it suffers from a severe land subsidence problem due to unbalanced land development and excess exploitation of groundwater. In recent years, this issue has received considerable attention because land subsidence has threatened the safety of the high-speed rail network in the region. This study integrates and analyzes various data recorded over the last 10 years, and confirms the source of recharge to the 2nd aquifer and compression from the contraction of the aquifer system. It also discusses the features of soil compression and settlement behavior of geotechnical structures, including ground, embankments, and piles, caused by fluctuations in seasonal groundwater drawdown. Monitoring data indicates that the region between the ground surface and a depth of 220 m is moving in-phase with the fluctuations in groundwater level, which may affect pile capacity due to negative pile friction. An additional minor consequence, the angular displacement between piers, was noticed on a viaduct structure built on this wide, flat, agncultural alluvial plain. However, if and when the pile structures take on additional loading from the adjacent fill work, the combined effects of this extra loading and groundwater fluctuations will induce increased pile settlement. The long-term angular displacement between piers will therefore be accentuated, and lead to negative impacts on structure safety.