本研究探討土體受超載後之壓密行為，包含殘餘沉陷量的比較及 次壓縮之變化情形，而排水帶對促進土體壓密沉陷之影響亦將在此作 一研究。最後，由室內試驗之結果將與大型土槽之沉陷量監測結果作 一驗証比較，以瞭解室內試驗值與接近現地情況之量測值間的差異。 試驗結果顯示，超載移除後能抑制土體次壓縮的產生，且超載越 大或超載作用時間越長，越能抑制次壓縮以減少土體的殘餘沉陷量。 一般而言，土體在次壓縮階段的變形與對數時間為線性的關係，因此 次壓縮指數Ca為一常數，並用以計算土體次壓縮沉陷量，但試驗中俟 超載移除後土體之次壓縮指數Ca不再為一常數，其值將隨時間而有增 加之趨勢，因此，對超載移除後之沉陷量的概算工作，可利用次壓縮 沉陷曲線中一另行定義的次壓縮指數C²a進行之。若另於試驗土體內 打設排水帶以促進壓密時，則對其沉陷行為有何影響亦為本研究探討 於大型土槽的超載試驗部分，將土槽劃分為打設排水帶區與無排 水帶區等兩區，以比較排水帶加速土層壓密之效能，而經歷約450 天 的沉陷量監測後，開始將屬於超載的0.5 公尺高之回填砂移除，剩餘 之1 公尺高的回填砂則視為作用於土層上之結構荷重，並將繼續對土 層受此結構荷重下之沉陷量作監測工作，以觀察超載移除後土層次壓 縮之變化情形，而綜合各項試驗結果顯示，室內試驗值與大型土槽的 ABSTRACT The research investigated the consolidation behavior of soft clay after subjected to a surcharge load, included the comparison of residual settlements and the secondary compression. Besides, the plastic board drain accelerate the consolidation of clay were also investigated here. Finally, the results of laboratory experiments were compared with the settlement monitoring results of indoor pit test. The test reveals that as the magnitude of simulated surcharge stress increases, the time interval following removal of the surcharge load during which little secondary compression occurs also increases, and when secondary compression reappears, the coefficient of secondary compression Cα decreases. For most practical purposes a constant Cα with time can be used to compute secondary compression settlements. Postsurcharge secondary compression index, Cα¢, always increases with time. A secant postsurcharge secondary compression index, Cα², is therefore introduced for a simple computation of secondary compression settlements. In the indoor pit test, the pit were divided into two zones, with or without installing plastic board drain, which compared the consolidation behavior accelerated by plastic board drain on soft clay. After 450 days settlement monitoring work, removed the 0.5m of surcharge fills and left the 1m of fills which were considered as the permanent load. Then, the settlement monitoring work were continued, and no apparent settlement occurred. The test results indicated that the values between laboratory experimental results and the indoor pit test results made few differences.
