夯實機振動頻率對砂土密度之影響

Abstract

本論文以實驗方法探討夯實機以不同頻率振動造成砂質填土之密度改變。本研究使用自行設計、建造之變頻式平板振動夯實機進行實驗，變頻範圍可從10至100 Hz，在土層表面施加振動夯實。本研究以氣乾之渥太華砂為填土，填入高度為1.5 公尺之疏鬆砂土層。填土之初始相對密度約為33.3 %。本研究採用埋置於試體內部的密度控制盒量測土體內各點土壤密度。本實驗改變夯實機頻率為45, 58, 64, 74, 83, 89 和 100 Hz，並控制其反覆振動正應力為30 kN/m2。根據實驗結果，本研究獲得以下幾項結論。在土層深度0.3公尺內，即夯實機底部的平板寬度，土壤的相對密度明顯的增加，深度0.3公尺以下之土壤密度增量會隨著深度增加而減少。夯實過後量測到的砂土最大相對密度介於114至119%，與夯實頻率沒有明顯的關係。在砂土表層深度0.3公尺內，平均相對密度增量介於60.9 至 70 %，平均相對密度增量與夯實頻率沒有明顯的關係。有效夯實深度介於0.43至0.54公尺，相較於美國海軍DM-7設計手冊提出有效夯實深度約為0.15公尺至0.3公尺，本實驗的有效夯實深度大於其建議值。實驗結果顯示，有效夯實深度和夯實頻率沒有明顯的關係。

This paper presents experimental data on the change of relative density in a cohesionless fill due to vibratory compaction at different vibration frequencies. A variable-frequency plate compactor with a frequency range of 10 ~ 100 Hz was constructed at National Chiao Tung University. Air-dry Ottawa sand was used as fill material. The initial relative density of the uncompacted fill was about 33.3 %. The vibratory compaction was applied on the surface of a 1.5m-thick lift. Soil density molds were buried in the cohesionless specimen to measure the distribution of relative density with depth. The cyclic normal stress applied on the surface of the fill was 30 kN/m2, and the compaction frequencies of 45, 58, 64, 74, 83, 89 and 100 Hz were used. Based on the test results, the following conclusions were drawn. Within the depth of 0.3 m, which was the width of the compaction plate, the density increase was most significant. The density increase effect was reduced with increasing depth. The measured peak relative densities varied from 114 to 119 %. The peak relative density of the fill was not significantly influenced by the compaction frequency. In the top 0.3 m of fill, the average relative density increment varied from 60.9 to 70 %. The relative density increment values slightly increased with increasing compaction frequency. It may be concluded that the average relative density increment was not influenced by different frequencies compaction. The effective compaction depths varied from 0.43 to 0.54 m, which was much deeper than the maximum permissible lift thickness 0.15 ~ 0.3 m suggested by NAVFAC DM-7.2 (1982).The effective compaction depth was not significantly influenced by the compaction frequency.