現有水文地質調查結果顯示，台灣雲林地區沉陷之部分來自於含水層，而週期性地下水壓的變化對於砂性土壤壓縮行為的影響仍有待釐清，本研究主軸為探討土壤元素於側向束縛時因地下水壓週期性升降引致之壓縮行為，研究以自行研發之自動化三軸設備系統進行三軸Ko反覆壓縮試驗，此系統整合伺服馬達與氣電轉換閥之控制與感測器資料擷取，可進行高自動化與精度之試驗。一般反覆壓縮試驗多以於垂直方向產生軸差應力的方式進行，但地下水壓引致之有效應力變化，應以試體孔隙水壓的升降模擬，此二者其應力路徑不同，因此本研究以維持垂直軸向總應力並控制反水壓升降之反水壓控制法進行數個階段Ko反覆壓縮試驗；研究以乾淨渥太華砂與含雲母細粒料之渥太華試體進行試驗，試驗結果顯示飽和顆粒性土壤因孔隙水壓升降造成之壓縮行為與震陷理論相符，且反覆壓縮之效應不可忽略。

Hydrogeological investigations in Yun-Lin area, Taiwan reveals that significant portions of ground subsidence occurred in aquifer layers, which are made of mainly granular soils. To identify the mechanism of subsidence in this area, the compressibility of granular soils due to periodic variations of hydrostatic pressure still need to be clarified. A triaxial Ko controlled consolidation system integrating electro-pneumatic transducers (E/P transducers), a direct drive servo motor and a data acquisition system was developed to,perform highly accurate and automatic Ko consolidation tests on remold specimen of Ottawa sand mixed with Mica fines. To simulate the field stress conditions due to periodical variation of hydrostatic pressure, a controlled back pressure method, which periodically varied the back pressure under a constant vertical total stress and zero lateral strain, was adopted. The testing results reveal that the the compressibility of saturated granular soils due to the periodical variation sof hydrostatic pressure is significant and the behaviors agree with the shakedown theory.

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