條形振動夯實造成砂土密度及土壓力變化

Abstract

本論文以實驗方法探討條形振動夯實造成砂土密度和土壓力的變化。本研究以氣乾之渥太華砂為回填土，回填土高1.5公尺。回填土初始相對密度(Dr)為34%。為了在實驗室模擬雙向平面應變的情況，本研究採用塑膠膜潤滑層來降低砂土和填砂槽側牆間的摩擦力。本研究進行一連串相關的實驗，來探察振動夯實對砂土所產生的影響。這些影響包括夯實後土壤表面的沉陷、相對密度的變化和夯實前後的垂直和側向殘餘土壓力。根據實驗結果，本研究獲得以下幾項結論： 1.對於疏鬆砂土，土體內的垂直土壓力和水平土壓力可分別以σv=γz 和Jaky公式來進行合理的估算。 2.隨著夯實機夯實趟數的增加，條形夯實區之地表沉陷量隨之增大。地表沉陷量和夯實趟數之間的關係可以用雙曲線的模式來模擬。 3.砂土的相對密度變化等高線範圍，會隨著夯實趟數增加而擴大。 4.垂直土壓力變化量的等高線近似於同心圓的形狀，而殘餘垂直土壓力Δσv會由圓心區域向外逐漸減少。土體內最大Δσv值會隨著夯實趟數增加而增大。 5.在夯實機夯實1和2趟後，殘餘水平土壓力Δσh的等高線會形成兩個較高的應力區，水平土壓力變化量會由中心區域逐漸減少。然而在夯實機夯實4和8趟後，殘餘水平土壓力的等高線則近似於一個同心圓的形狀。夯實影響的區域 (Δσh = 0.2 kN/m2 應力等高線) 深度會隨著夯實能量增加而增大。 6.在夯實一趟後，土壤所受夯實影響的機制可以用基礎下方土壤之局部剪力破壞的情況來解釋。然而，當夯實趟數增加到8趟後，被夯實土壤之機制可用方形鋼樁以振動打樁機貫入砂質地盤的情況來模擬。

This paper studies the variation of soil density and earth pressure due to the strip compaction with a vibratory compactor. In this study, dry Ottawa sand was used as backfill material, and the height of backfill was 1.5 m. The initial relative density of the backfill (Dr) was 34 %. To simulate a 2-way plane strain condition in the laboratory, the friction between the soil and sidewalls of the soil bin was reduced as much as possible. Experiments were conducted to investigate the effects of soil densification with a vibratory compactor. The surface settlement and change of relative density were measured after compaction. The vertical and horizontal stresses in the soil mass were measured before and after compaction. Based on the test results, the following conclusions can be drawn. 1. For loose sand, the vertical and horizontal earth pressure in the soil mass could be properly estimated with the equation σv=γz and Jaky’s equation, respectively. 2. The surface settlement increased with the increasing number of passes of the compactor. The relationship between the surface settlement and the number of passes of the compactor could be modeled by the hyperbolic model. 3. After compaction, the range of contours of relative density (Dr = 36 %) would become larger with increasing number of passes. 4. The contours of Δσv were analogous to concentric circles, and the Δσv would decrease gradually from the central region. The vertical stress increment Δσv increased with increasing number of passages of the compactor. 5. The contours of Δσh formed two circles of high stresses and Δσh decreased gradually from the center region after the first and the second passes of compactor. The contours of Δσh were analogous to concentric circles after 4 and 8 passes of the compactor. The depth of the compaction-induced zone increased with increasing compaction energy input. 6. Based on the test results, the mechanism of soils after the first pass of the compactor could be explained by local shear failure. However, the mechanism of soils after 8 passes of the compactor could be simulated by a steel square pile driven in sand with a vibratory hammer.