反復扭轉剪力夯實造成之砂土密度及體積變化

Abstract

摘要 本論文以實驗方法探討反復扭轉剪力夯實造成砂質填土土體內相對密度的改變及沉陷量。本研究使用自行設計建造直徑為0.45 m之剪力盤之反復扭剪夯實儀，在土層表面施加靜態垂直應力與反復剪應力。本研究以氣乾之渥太華砂為填土，填入整層高度為1.5 m或5層高度0.3 m之疏鬆砂土。填土初始相對密度為36 %。本研究採用雷射測距儀來量測土體表面沉陷量，採用密度控制盒埋置於試體內部以量測各點土壤相對密度。根據實驗結果，本研究可獲得以下幾項結論。在最初5次的反復扭轉夯實次數 (N = 5)，表面沉陷量明顯地增加。進行反復扭轉剪力夯實20次後 (N = 20)，土壤顆粒排列趨於緊密，土體達到主要地表沉陷量，後續扭剪造成之地表沉陷量趨緩。對5層厚度各0.3 m的土體分別進行反復扭轉剪力夯實後20次後，各層之平均體積應變量為9.77 %、10.53 %、10.37 %、10.05 % 與10.32 %，顯示反復扭轉剪力夯實對各土層造成之體積變化是相對地均勻。而整層的相對密度值都被成功的增加到大於70 %。對5層土層施作分層夯實，改良土體平均相對密度值為76.3 %，標準差為6.2 %。證明此反復扭轉剪力夯實方法成功的將整層土層改良。

Abstract This paper presents experimental data on the change of volume and relative density in a cohesionless soil mass due to static vertical load and cyclic torsional shearing compaction. A cyclic torsional shearing compactor was with a 0.45 m-diameter circular shearing disc was designed and constructed at National Chiao Tung University. Air-dry Ottawa sand was used as fill material. The initial relative density of the fill was 36 %. The static vertical load and cyclic torsional shearing were applied on the surface of a 1.5 m-thick lift, and then on another specimen with five 0.3 m-thick lifts, with the rotation angles be +5°. Surface settlement of the fill was measured with a laser distance meter. Soil density cups were buried in the cohesionless specimen to monitor the distribution of relative density of with depth soil. Based on the test results, the following conclusions were drawn. In the first 5 cycles of cyclic torsional shearing application, the surface settlement increased significantly. However, after 20 cycles, the major part of settlement was accomplished, soil particle were sheared and reached a densely-packed condition. As a result, it was difficult to increase the surface settlement any further with more cyclic shear application. For shearing compaction on five 0.3 m-thick lifts, after 20 cycles of torsional shearing with the torsional angle of =±5˚, the average volumetric strain for the lift 1, 2, 3, 4, and 5 was 9.77, 10.53, 10.37, 10.05 and 10.32 %, respectively. It was clear that the cyclic torsional shearing compaction in each lift was relatively uniform. Most of the relative density measured in compacted fill were greater than 70 %. The entire soil body was successfully compacted with cyclic torsional shearing compaction. For five compacted lifts, the mean relative density was 76.3 % with a standard deviation of 6.2 %. It was obvious that the entire soil body was successfully compacted with this ground improvement technique.