本研究主要目的為探討改良砂土之水中抗分散特性與改良成效之影響。試驗方式以西螺砂為主要回填材料，並以自由沉降模式模擬改良土之現地水中回填，經取樣後，進行一系列之無圍壓縮試驗與動力三軸試驗。為減少改良砂土於水中回填時所產生之水泥與砂土分離現象，故於改良砂土中添加聚丙烯醯胺或羧甲基纖維素鈉作為抗分散劑，並探討抗分散劑添加率、水泥配比及養治時間對改良土剪力強度與動態性質之影響。 試驗結果顯示，改良砂土之無圍壓縮強度會隨水泥配比之加大而增強。然無圍壓縮強度之變化則因抗分散劑添加率及種類之不同而有所變化。當以羧甲基纖維素鈉為抗分散劑時，改良砂土之無圍壓縮強度隨抗分散劑添加率之增加而持續遞增；而於抗分散劑採用聚丙烯醯胺者，其無圍壓縮強度則隨抗分散劑添加率之增加呈現先遞增而後遞減之趨勢。再者，經由動力三軸試驗結果得知，以羧甲基纖維素鈉為抗分散劑且添加率為3.5 g/kg，水泥配比8 %，養治時間為28天時之試驗條件下，改良砂土之液化阻抗即可獲得大幅改善。因此，添加水泥及抗分散劑確有助於砂土剪力強度之提升與動態特性之改善。 The purpose of this study is focused on the prevention of separation and the improving effects of cement treated sand in water. The Shiluo sand was adopted as the main backfilling material. The water sedimentation method was used to prepare specimens for simulating the actual reclamation in water. A series of unconfined compression tests and cyclic triaxial tests was carried out. In order to avoid the separation of cement and sand particles from treated sand during the process of backfilling in water, two kinds of coagulants (Sodium carboxy methyl cellulose and polyacrylamide) were added into the cement treated sand respectively. The effects of coagulant content, cement content and curing time for treated sand were discussed in this study. The experimental results showed that the unconfined compression strength of treated sand increased as the cement content increased. The variation of unconfined compression strength would be affected by the coagulant type and coagulant content. When the Sodium carboxy methyl cellulose was used as the coagulant, the unconfined compression strength increased as the coagulant content increased; while the coagulant was changed to polyacrylamide, the values of unconfined compression strength increased initially and then decreased as the coagulant content increased continuously. Furthermore, the cyclic resistance of cement treated sand for curing time of 28 days would be increased significantly due to adding the Sodium carboxy methyl cellulose of 3.5 g/kg and cement content of 8 %. Therefore, the coagulant and cement both can improve the dynamic properties of treated sands effectively.
