顆粒性土壤受反覆載重與永久變形之關係

Abstract

雲林縣位於台灣中西部，濁水溪沖積扇，且水資源匱乏，因為長期超抽地下水導致地層下陷。為了解其地層下陷的機制，交通大學研究團隊於2012年在雲林縣虎尾鎮光復國小設置100m深的光纖監測井，觀測地層下陷(上浮)與孔隙水壓間的關係。24小時連續讀數紀錄顯示在30至40m深度間孔隙水壓在上午與傍晚有規律性之上下起伏，懷疑此一現象與附近相對應深度水井間歇性抽水行為相關。為確認此一孔隙水壓所造成土層內有效應力重複性起伏是否導致周圍顆粒性土壤累積而永久性應變，利用傍壓儀做反覆加壓減壓試驗，觀察反覆性側向應力、側向應變累積關係。論文敘述敘述本研究之背景，傍壓試驗儀器之修改與現地試驗結果。

Yunlin County is located in Central Western Taiwan, within the alluvial fan of Tsuo Shue river, where surface water resources are limited. Excessive ground water pumping in this region has caused ground subsidence. In order to evaluate the mechanisms of ground subsidence, the research team of National Chiao Tung University installed a 100m deep observation well at Guan Fu elementary school in Hu Wei Township of Yunlin County. Relationships between pore water pressure and ground subsidence (heaving) were observed using this monitoring system. 24 hour continuous readings showed that the pore water pressure fluctuated repeatedly in the morning and evening at depths between 30 and 40m. It was suspected that this fluctuation of pore water pressure was related to the on-and-off type of ground water pumping from wells nearby. To verify if this repeated effective stress variations induced by pore water pressure fluctuation was responsible for the accumulation of permanent strains, a series of pressuremeter tests (PMT) were performed. Relationships between the PMT repeated loading-unloading and the radial strain accumulation were evaluated. The thesis describes the background of this research, modifications of the PMT device and available test results.