| 摘要: | 本研究以雲林麥寮濁水溪粉質砂土為試驗材料，探討在不同反覆剪應力作用下改良土及未改良土之動態性質，以深入了解改良之效果。本次論文之實驗重點乃以相對密度為45%之粉質砂土，配以1%及2%的水泥配比來製作改良土試體，經7天、14天、28天養治後，使用動力三軸儀進行試驗，試驗結果顯示。 (1)、本研究所進行之濕搗法靜態三軸不排水軸向壓縮試驗之應力－應變曲線及孔隙水壓曲線，試驗之有效圍壓由98kPa~294 kPa。軸向壓縮應變量在2.1%左右時，試體之軸差應力即達尖峰強度值，一旦過此尖峰值後，軸差應力開始下降至一固定之殘餘值。當應變量到達12%左右時，試體即達到所謂的穩定狀態，此時試體之剪應力及體積達到一定值（軸差應力及孔隙水壓已呈現定值）。因此，本研究對於穩定狀態點之決定，以試驗前最後一筆資料為其對應之穩定狀態點。 (2)、改良砂土試體之孔隙水壓激發情形大致相同，不會因齡期之不同而所差異，在施加反覆軸差應力時，當試體受壓時，孔隙水壓激發情形往正值遞增，而試體解壓時，孔隙水壓激發情形往負值遞增，最後，試體即開裂破壞產生較大之負值。此一現象與一般未改良砂土試體之孔隙水壓激發情形，逐漸累積往正的方向遞增情形有明顯地不同。 (3)、改良砂土試體的液化阻抗隨改良砂土試體之養護齡期越長，其液化阻抗越高，齡期28天比齡期7天約增加36%，齡期14天比齡期7天約增加13%。本試驗之改良砂土試體養護齡期為7、14及28天，其液化阻抗約為未改良砂土試體之4.4~6.4倍之間。 This research focused on dynamic characteristics of treated and untreated sand which is taken from Choshui Meliao, to study the effect of cement improvement. Cement treated sand specimens with relative density of 45﹪and cement mixing rate of 1% or 2% were used in the tests. After various curing period classified as 7, 14 or 28 days, the cyclic loading tests were carried out by using dynamic triaxial apparatus. First, static triaxial tests were carried out to realize the basic properties of sand. From the experimental results, it is revealed that the peak deviator stress is reached when the axial strain of specimen is about 2.1% under various efficient confined pressures from 98kPa to 294kPa. As we can observe from the stress-strain curve and pore water pressure-curve that are obtained by moist tamping method and undrained triaxial axial compression test, the deviator stress begins to decrease and reaches to a residual stress after the peak point. The test result also shows that the shear stress and volume of the specimens reach to the unchangeable value when the value of strain is about 12%. Therefore, in this study, the determination of stability point is obtained from the last value before test. Second, the course of the excess pore water pressure increased in the treated sand specimens is similar with various curing period, and the excess pore water pressure increases to the direction of positive value when the specimens are compressed under cyclic deviator stress;on the other hand, the excess pore water pressure increases to the direction of negative value when the specimens are decompressed under cyclic deviator stress; Finally the specimens are destroyed in final stage. Meanwhile, the excess pore water pressures become larger negative value. Above mentioned, the untreated sand differs from the treated sand in which the excess pore water pressure increases gradually to the direction of negative value. Last, with increasing curing period of the sand specimens, the liquefaction resistance of treated soil increase. The results are observed as followed: the liquefaction resistance in 28 days is 36% higher than that in 7 days; the liquefaction resistance in 14 days is 13% higher than in 7 days. On the whole, the liquefaction resistance of treated soil is 4.4~4.6 times higher than that of untreated soil increase when the curing period are classified into three broad categories-7, 14, and 28 days. |
