本研究以峴港砂為試驗材料，探討在不同水泥配比與養治時間之條件下改良土及未改良土之力學性質，以瞭解水泥對砂土靜態及動態力學性質之改良效果。本研究之實驗重點乃以相對密度為40%之砂土，配以0.3%、0.5%及0.7%的水泥配比製作改良土試體，經7天、14天及28天養治後，進行無圍壓縮試驗、單向度壓密試驗、靜力三軸試驗及動力三軸試驗。 由試驗結果可知，水泥配比愈高，改良土的無圍壓縮強度愈高。改良土的無圍壓縮強度與養治時間之對數約呈線性增加之趨勢，且隨著水泥配比的增加，其△qu /△log tc的斜率愈大。當壓密壓力低於改良預壓力時，改良土水泥配比愈高，其壓縮指數有減少的趨勢，此一現象表示添加水泥的確可使土壤的壓密沉陷減少。 土壤添加水泥後，水泥的膠結作用使得顆粒間獲得大量的凝聚力，但這同時，顆粒間的摩擦力並未隨之等量提高，令抵抗破壞的剪力強度傾向於較大部份由凝聚力承受，亦即凝聚力將因水泥配比提高而大幅增加，摩擦角卻相對地減小。 本研究中，配比為0.5%之改良土試體的液化阻抗在養治時間28天比養治時間7天約增加37%，養治時間14天比養治時間7天約增加16%，而改良土試體養治時間為7、14及28天之液化阻抗約為未改良土試體之1.6~2.4倍。另外，本研究亦探討了改良土之剪力模數、阻尼比與配比間的關係，經試驗後，發現改良土對以上諸特性均有良好之改良效果。 This research focused on mechanical properties of cement treated and untreated sands, and discussed the effects of cement improvement. Cement treated sand specimens with relative density of 40﹪and cement mixing rates of 0.3%, 0.5% and 0.7% were used in the tests. Through various curing periods including 7, 14 and 28 days, unconfined compression tests, consolidation tests, triaxial compression tests and dynamic triaxial tests were performed. From the experimental results, it is observed that the unconfined compression strengths of treated sands increased with the increase of cement mixing rates. The unconfined compression strengths of treated sands are also increased linearly proportional to the logarithm of curing periods. The compression indexes of treated sands decreased with the increase of cement mixing rates under the consolidation pressures lower than the treated preconsolidation pressure. These results show that the consolidation settlements can be reduced through the increase of cement mixing rates. The cohesion of treated sands increased with the increase of cement mixing rates, but the friction angle of sand did not increase as much as that of cohesion under the same condition. These results make the cohesion of treated sands to bear most shear stress until failure. The liquefaction resistance in 28 days is 37% higher than that of 7 days; the liquefaction resistance in 14 days is 16% higher than that of 7 days. On the whole, the liquefaction resistance of treated sands is 1.6~2.4 times higher than that of untreated sands when the curing periods are classified into three procedures including 7, 14, and 28 days. In addition, the relationships of shear modulus, damping ratio and cement mixing rates were investigated.
