以實驗方法探討靜態及反復載重對砂土夯實之影響

Abstract

本研究以實驗方法探討以平板式振動夯實機於不同靜態及反復載重下對乾砂填土造成之相對密度分佈及表面沉陷之改變。本研究使用自行設計與建造之振動式可調質量平板夯實機。夯實實驗於長、寬、高皆為1.5公尺之填土表面進行，以氣乾渥太華砂作為填土材料，填土之初始相對密度為24  1.8 %。夯實實驗施加之地表靜態應力分別為1.9、4.9及9.1 kN/m2，反復夯實應力分別為10.1、20.3及30.2 kN/m2。本研究採用雷射測距儀量測土體表面的沉陷量，利用埋置於試體內部的密度盒量測土體內各點土壤密度。實驗結果顯示，夯實機施加之靜態及反復應力可以有效提升填土之密度，土層內砂土最大相對密度隨著靜態及反復應力之增加而上升。填土之有效夯實深度亦隨靜態及反復應力之增加而增加。於反復夯實應力為30.2 kN/m2的這一組實驗中，實驗測得之有效夯實深度為0.21至0.32公尺，符合美國海軍設計手冊所列以平板式振動機夯實粗顆粒土壤夯實土厚度0.2至0.25公尺之建議。土體表面沉陷量隨施加之靜態地表加載應力增加而輕微增加、隨反復夯實應力增加而明顯增加。

This thesis presented experimental data on the relative density distribution with depth due to compaction with different static and cyclic stresses. A variable-mass vibratory plate compactor was designed and constructed. Compaction tests were conducted on the surface of a 1.5 m  1.5 m  1.5 m soil specimen with different static and cyclic stresses. Air-dry Ottawa sand was used as fill material. The relative density of the uncompacted fill was about 24  1.8 %. Surface settlement of the fill was measured with a laser distance meter. Before testing, soil density cups were buried in the cohesionless specimen to investigate the distribution of relative density with depth. The static normal stresses applied were 1.9, 4.9 and 9.1 kN/m2, and the cyclic normal stresses applied were 10.1, 20.3 and 30.2 kN/m2. Based on the experimental results, it was found that the magnitude of applied static and cyclic normal stresses effectively increased the soil density in the fill. The peak relative density increased with both increasing static and cyclic stresses. The effective compaction depth increased with both the static and cyclic stresses. For tests with a constant cyclic stress 30.2 kN/m2, the effective depth of compaction varied from 0.21 to 0.32 m. These values were in good agreement with the lift thickness of 0.20 to 0.25 m for coarse-grained soil compacted by a vibratory baseplate compactor, as suggested by US Navy design manual DM 7-2. Measured surface settlement slightly increased with increasing static normal stress, and significantly increased with increasing cyclic normal stress