本研究主要目的為探討抗分散劑對水泥改良土之水中沉降機制與改良效果之影響。為了避免改良土現地進行水中回填時發生水泥與砂土分離現象，故於改良土中添加各種類抗分散劑，並以自由沉降模式模擬改良土之現地水中回填。本研究探討重點以不同抗分散劑添加率0、86、344、600及860 mg/kg並配合1.0%、2.0%、3.0%、4.0%、6.0％及8.0%的水泥配比，改良材料選用波特蘭水泥第I型，養治時間分別為7天、14天、28天與56天，利用回填水槽製作改良土試體，進行無圍壓縮試驗與動力三軸試驗。試驗結果顯示以聚丙烯醯胺為抗分散劑時，改良土之抗分散性最佳，且改良土無圍壓縮強度隨著與抗分散劑添加率之遞增而呈現先升後降之現象，最佳抗分散劑添加率為344 mg/kg。此外，當養治時間為7天時，添加水泥配比8%之改良砂土；養治時間為28天，改良砂土添加水泥配比6%時，液化阻抗可獲得明顯增加，添加水泥及聚丙烯醯胺可有效地改善砂土的動態特性。

The purpose of this study is focused on the sedimentation mechanism and the improved efficiency of cement treated sands with coagulant in water. In order to avoid the separation of cement particles from cement treated sand in the backfilling of free sedimentation mode, the cement treated sands were improved by adding different types of coagulant. In this research, a series of unconfined compression tests and dynamic triaxial tests were carried out for a set of treated sands consisted of different coagulant content (from 0, 86, 344, 600 to 860 mg/kg), different cement contents (1.0%, 2.0%, 3.0%, 4.0%, 6.0% and 8.0%), Portland cement type I and different curing time (by 7, 14, 28, and 56 days). According to the experimental results, the polyacrylamide was the most effective coagulant for reducing the loss of cement. On the other hand, the unconfined compression strength increased initially and then decreased as the dosage increased. The optimum coagulant content is 344 mg/kg. Furthermore, when curing time was 7 days and cement content was 8% or when curing time was 28 days and cement content was 6%, the liquefaction resistance would be significantly increased. The results of this research show that the cement material and polyacrylamide will be contributive to improve the dynamic properties of sands such as shear modulus and cyclic stress ratio .

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