夯實機振動頻率對砂土地盤沉陷量 及密度改變之影響

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沉陷及密度的改變。本研究使用自行設計及建造之變頻式振動夯實機進行實驗，變頻範圍可從10至75 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，填入土層高度為1.2 m之疏鬆砂土。填土之初始相對密度約為35 %。本研究採用雷射測距儀來量測土體表面的沉陷量，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。根據實驗結果，本研究獲得以下幾項結論。砂土試體經過夯實機第一次通過造成最大量的沉陷，夯實機第三和第四次通過造成的沉陷量則相對小許多，土壤密度會隨著夯實機通過次數增加而增加。夯實機施加之反復正應力會隨著偏心馬達振動頻率的提高而成平方增加，因此當施加一較高的振動頻率，砂土試體之尖峰相對密對將會明顯提升。在夯實頻率60至75 Hz之間出現極限的相對密度(112至123%)在此狀況下，砂土顆粒很難再排列得更緊密。土體表面沉陷量及有效夯實深度也隨著振動頻率提高而增加。藉由控制夯實頻率而增加反復正應力，可以成功增進振動夯實的地盤改良效果。

This paper presents experimental data on the surface settlement and the change of relative density in a cohesionless soil mass due to vibratory compaction at different vibration frequencies. A variable-frequency compactor with frequency range 10 ~ 75 Hz 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 about 35 %. The vibratory compaction was applied on the surface of a 1.2 m-thick lift. 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 with depth. Based on the test results, the following conclusions were drawn. The fill subsided significantly after the first pass of the tamper, the extra surface settlement due to the third and fourth pass was much less. The relative density of the soil due to vibratory compaction increased with increasing number of compactor passes. Under the application of a higher frequency, and thus a cyclic normal stress, the relative density of soil increased. The peak relative density of the fill increased with increasing compaction frequency. Vibration frequency of 60 to 75 Hz, an ultimate peak relative density (Dr = 112 ~ 123%) was achieved, it would be difficult to pack the soil particles any closer. The surface settlement and the effective compaction depth increased with increasing compaction frequency. It was obvious that controlling the compaction frequency is an effective measure to improve the compaction effects.