本研究的試驗土樣取自於湖山水庫借土區共三種土樣，即殼層土壤SM、ML 與心層土壤CL。採用單位體積能量法之概念，利用特製夯模製作標準夯實能量下之重模試體，並以改良的飽和方法使夯實試體達飽和。由於土石壩是分區滾壓夯實構築而成，壩體內部的靜態應力除了水平與垂直應力外，尚包含初始剪應力。因此，夯實土壤的動態強度與變形特性除需考慮等向壓密狀態，尚須考慮非等向壓密狀態，本研究控制有效圍壓1kg/cm2，施作等向壓密與非等向壓密應力比(Kc= )Kc=1.5和Kc=2.0狀態下三種夯實土樣之動力三軸試驗，以瞭解夯實土壤在不同壓密應力比下之動態強度、孔隙水壓變化與變形之特性。 試驗結果顯示，初始剪應力比愈大的夯實土壤，其動態強度愈強，激發的超額孔隙水壓愈低，且土壤到達破壞時所需之反覆應力比愈大。與貓羅溪砂性土壤的動態試驗結果相比，可知夯實土壤的動態強度遠高於貓羅溪砂性土壤，其超額孔隙水壓隨動態荷載的作用週數增加而趨於穩定，在等向壓密狀況下的超額孔隙水壓比至多達0.8，非等向壓密的水壓比約為0.5~0.7，不會像一般砂性土壤發生液化破壞之現象。從有效應力路徑可觀察出夯實土壤在反覆受剪的過程中，有顯著的剪脹性，動態變形量也會隨作用週數趨於穩定，可合理地推測夯實土壤在震後僅會發生有限的變形。並將試驗結果再整理成不同壓密應力比下反覆剪應力比與殘餘剪應變之關係及再壓密體積應變與剪應變關係曲線，可用於估算土石壩受震所產生之永久變形與沉陷，供工程界參考。 The cyclic strength of compacted soil is very different from ordinary sandy soil. In order to study the dynamic strength of compacted soil, this paper performed a series of dynamic triaxial tests on three kinds of compacted soils, SM, ML and CL for constructing an earth dam. This paper proposed a vacuum method for improving the saturation of compacted soils. Test results showed that both methods make the Skempton’s coefficient B of all specimens greater than 0.95. Compacted soils of the earth dam have different initial shear stress conditions which range from Kc=1.5 to Kc=2.0. Based on the test results, the higher initial shear stress ratio, the larger the dynamic strength and the less the pore water pressure. Dynamic strength of compacted soil is stronger than ordinary medium dense sand. Compacted soils have no liquefaction potential due to their shear dilation behavior and only sustain limited cyclic strain.
