反復扭轉剪力夯實造成之砂土密度增加

Abstract

本論文以實驗方法探討反復扭轉剪力夯實造成之沉陷量及相對密度的變化。 本研究使用自行設計建造之交通大學反復扭轉剪力夯實儀。扭力板手被安裝在夯 實儀上，用來施加反復扭矩和反復剪應力在土層表面。本研究以氣乾之渥太華砂 為回填土，試體整層填土高度為0.6 m。回填土初始相對密度為34.5 %，試體採 用直徑為0.3 m 的鋼質圓盤施加垂直正向應力9.24 kPa。施加反復剪應力的扭剪轉角為+5°，反復扭剪作用次數包含1、2、5、10、20、30 及40 次。本研究採用雷射測距儀來量測土體表面沉陷量，密度控制盒埋置於試體內部以量測各點土壤相對密度。實驗結果顯示，靜態垂直載重在深度150 mm (圓盤半徑)以內有效的造成土壤密度增加，在深度150 mm 以下區域造成的土壤密度增加量不明顯。在前2次反復扭轉剪力作用後，土壤表面沉陷量增加明顯。在反復扭轉剪力作用20 次後，土壤的顆粒重新排列趨於緊密，後續扭轉造成之沉陷量會趨緩。在20 次反復扭轉剪力作用後，深度150 mm 以內土壤的相對密度增加至大於70 %，反復扭剪方法改良的有效深度僅限於土層深度 150 mm 以內。土壤的相對密度會隨著反復扭剪次數的增加而增大，在反復扭剪20 次以後，夯實的效果會趨緩。對4 層各0.15 m 厚的土層表面分別進行反復扭轉剪力夯實20 次後，各土層內的土壤的相對密度值都被成功的增加至大於70 %.

This paper presents experimental data on the settlement and relative density change of a cohesionless soil due to cyclic torsional shearing compaction. A new cyclic torsional shearing compactor was designed and constructed at National Chiao Tung University. Torque wrenches were attached to the compactor to apply the cyclic torque and cyclic shearing to the soil surface. Air-dry Ottawa sand was used as fill material. The thickness of the soil to be compacted was 0.6 m. The initial relative density of the backfill was 34.5 %. The static vertical normal stress of 9.24 kPa was applied on the soil surface with a 0.3 m-diameter circular steel disc. Then cyclic shearing was applied with rotation angles of plus and minus 5 degrees, and the number of cycles of 1, 2, 5, 10, 20, 30 and 40. Surface settlement of the fill was measured with a laser distance meter. Soil density cups were buried in the cohesionless specimen to monitor the relative density of soil. Test results showed that the density increase due to the static vertical load was obvious in the top 150 mm (radius of the circular loading disc) of the fill. Below the depth of 150 mm, the density increase due to the static surface loading was less obvious. In the first 2 cycles of cyclic torque application, surface settlement increased significantly. However, after 20 cycles, soil particles were rearranged and reached a densely-packed condition, little surface settlement was observed. After 20 cycles, the relative density of soil located 150 mm below the surface was successfally increased to a value greater than 70 %. The cyclic torsional shear soil improvement was effective for the top 150 mm (disc radius) of soil. The relative density of soil increased with increasing number of cycles of torsional shearing. After the first 20 cycles of shearing, the compaction effect became less significant. For the compaction on four 0.15 m-thick lifts, the relative density achieved in each lift was greater than the required value of 70 %.