摘要 動力夯實係以夯錘夯擊地表,夯擊地表面時產生之衝擊能量藉由應力波)傳遞至地盤中,促使在應力區內之土壤顆粒重新排列且趨於緊密,進而改善土層之工程性質、降低砂土液化之機率。 隨著電腦軟硬體科技不斷之提升,運用數值方法分析工程問題越來越受到重視。本研究以數值方法模擬動力夯實,並與前人之研究結果相互比較,旨在探討夯擊引致之土壤振動及錘底形狀對改良效果之影響。 模擬分析結果顯示,使用錐尖角90度夯錘引起之地盤表面振動較平底夯錘小,此表示傳入地盤之夯擊能量應較高,故對土壤改良效益應較佳。就所模擬之一次夯擊地盤而言,錐尖角90度夯錘夯擊產生之應力其影響範圍較平底夯錘大;夯擊後地盤淺層之側向應力均較鉛直方向應力大。就產生之陷坑體積而言,不同之錘底型式造成陷坑之大小約略相同。為避免應力波之作用重疊,相鄰夯擊點應有較大之間距,模擬結果顯示夯擊點間距36 cm(約4.5倍夯錘直徑)較18 cm(約2.3倍夯錘直徑)佳。比較數值模擬與現地試驗之最大振動加速度量测值,夯擊中心點水平距離10 m處均約為1 g,差異不大。
Abstract A pounder impacting ground surface causes stress waves that make sand particles rearrange and improve density to modify engineering properties and decrease liquefaction probability. This study uses numerical method to simulate the dynamic compaction. The objectives include discussing ground vibration caused by dynamic compaction and comparing the efficiency of modification with different types of pounder base. The results of analysis indicate that the modification by conical-bottom pounder with 90o apex angle is better than flat bottom pounder. For the simulation of impact once, the influence range of stress caused by the conical-bottom pounder is wider than the flat bottom pounder. After impact, the value of Ko is greater than 1 in shallow soil layer. The results show that the volume of crater is almost the same, irrespective of the type of pounder. The spacing of impaction point with 36 cm get better modification than 18 cm. Comparing the simulation value with the measured field value, the maximum amplitude of accelerations at ground surface 10 m from the impact point are both about 1 g.