未飽和崩積土之動靜態力學行為探討

Abstract

本論文採用包括新竹湖口台地、瑞芳金瓜石等地的崩積土，藉由不壓密不 排水三軸壓縮試驗以及等向性三軸壓密試驗來探討不排水動態荷重與土壤 飽和度對於崩積土之力學行為的影響。其中，動態荷重的型式乃頻率為1 Hz、振幅強度為六分之一之靜態不排水三軸剪力強度之規則式正弦波。在 施加如此之動態荷重20個週期之後，試體將繼續接受靜態不排水之三軸加 壓，以與原始靜態不排水強度作一比較。 試驗結果顯示：(1)試體之 不排水三軸剪力強度隨飽和度的增加而降低，直至飽和度為80%以上時， 此強度降低的趨勢將逐漸緩和。(2)飽和度影響不排水三軸試驗之摩擦角 甚鉅，當土壤完全飽和時，摩擦角將接近零度。同時新竹湖口崩積土之摩 擦角與凝聚力小於瑞芳金瓜石者。(3)動態荷重會使土壤之不排水摩擦角 與凝聚力減小。(4)動態作用後之強度折減率Fred與動態作用所激發之正 規化超額孔隙水壓有如下雙對數對應關係： 新竹湖口 瑞芳金瓜石M 0.1415 0.0742N -0.127 -0.098此結果若配合現地之水壓監測則可做為地 震後土壤強度的預測模式。(5)飽和度對於土壤壓縮特性影響極大，飽和 度由60%增加至完全飽和時，其體積壓縮係數可增加至二倍以上。 The research is aimed to investigate the effect of undrained dynamic cyclic loading and degree of saturation on the mechanical behavior of colluvial deposit, such as Hu-Ko and Chin-Qua-Shih soil, by conducting experiments of UU triaxial tests and isotropic triaxial consolidation tests. The mode of theundrained cyclic loading is regular sine wave with the frequency of 1 Hz, and the peak amplitude of the wave is 1/6 the peak strength of static undrained triaxial test under the same condition. After being carried out the undrained cyclic loading, the static undrained triaxial test will be applied to the specimen for comparison to the strength of originally static undrained test. The results show that: (1)The undrained triaxial shear strength decreases with increasing degree of saturation. Above 80% degree of saturation, the strength reduction trend becomes gentle. (2)The degree of saturation influences the friction angle of UU condition. When the soil reaches 100% saturation, the friction angle will be close to zero. (3)Dynamic cyclic loading decreases the peak shear strength, friction angle and cohesion of the soil. (4)The shear strength reduction after dynamic cyclic loading (Fred) bear a log-log relationship with the normalized excess pore water prassure excited by dynamic cyclic loading shown as follows： . The relation can be used as a prediction model of in-situ soil strength after earthquake. (5)Degree of saturation influences the soil compression index enormously beyond the extend of double.