| Summary: | 碩士 === 國立中央大學 === 土木工程研究所 === 91 === 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.
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