土壤液化所引致之地盤永久位移，是諸多地震災害中最常見也最 具破壞性之地變型態。以九二一集集大地震為例，台中港碼頭區、貓 羅溪堤防、南投縣霧峰鄉旱溪河岸太子城堡社區及彰化縣員林鎮等地 區皆因土壤液化所引致的地盤位移而產生嚴重的破壞。因此針對此高 危險性之破壞形態，實有必要加以深入研究。 Newmark (1965)滑塊模式為工程實務上最常用的地盤變位分析 方法，其中假設滑動土體為剛性體，此剛性體在一平面上滑動。於地 震作用過程中，當地震所產生之加速度超過土體之降伏加速度時，使 得土體慣性力大於滑動阻抗力，因而產生下坡方向之地盤永久位移， 其大小可由塊體對破壞面之相對加速度經兩次積分後求得。 在應用Newmark滑塊模式時，有一項非常重要的參數必須確定， 此參數即是不排水剪力強度(Su)。本研究於液化場址取得液化土樣， 並採溼搗法製作重模土體以進行三軸壓密不排水剪力強度試驗(CIU test)，待獲得Su 後，即可求得降伏加速度，再利用相對運動之觀念， 進一步得到地盤之側向流動永久位移。 針對九二一集集大震，台灣發生液化地區進行現地取樣，經由一 系列室內試驗瞭解液化土壤之基本性質與強度特性，藉由Newmark 滑塊理論推估永久位移量，與現地量測之位移值作一比較，結果顯示 Newmark 滑塊理論之適用性良好，唯須注意現地地形之量測所造成 之誤差。上述研究之成果可進一步建立台灣本土之土壤液化所引致地 盤永久位移之資料，爾後供作防災、救災之參考。 Liquefaction induced permanent horizontal displacement is one of the most destructive ground failures during strong earthquake. During Chi-Chi earthquake, severe damage as caused by permanent horizontal displacement induced by soil liquefaction in many areas. Therefore, it becomes very important to predict the permanent displacement with a degree of reasonable accuracy to provide a reference for hazard prevention. This study documented and mapped the case histories of lateral spreading occurred during Chi-Chi earthquake. The liquefied soils were remolded and tested to obtain the steady-state strength by the triaxial undrained test. Relationships between normalized steady-state strength and relative density Dr or normalized standard penetration value (N1)60 were established for four kinds of liquefied soils. Newmark’s rigid block sliding model is used to estimate the permanent horizontal displacement with the steady-state strength parameter obtained from laboratory . It was found that the estimated displacements are in acceptable agreement with those measured in the field after earthquake.
