震動夯實造成之土壤應力及密度變化(III)

Abstract

本研究計畫探討震動夯實造成砂土內垂直應力、水平應力及密度之變化。本研究將 運用國立交通大學之剛性土槽試驗設備，以氣乾渥太華砂為回填土進行實驗研究，本研 究採用電動平板夯實機在試驗室夯實土壤。本研究將許多個土壤密度盒及土壓力計埋置 於土體內之不同深度、不同位置，量測土體內各點因夯實造成的密度及土壓力改變。 本研究計畫分三年進行，第一年探討疏鬆砂土經過地表「單點震動夯實」對土體的 影響，本研究發現: (1)在鬆砂表面點夯實7 秒及123 秒後，隨著夯實時間的增加，Dr = 36% 相對密度等高線會往深處發展。(2)非凝聚性土壤表面受點夯實的受力情況，可以方形鋼 樁承受振動式打樁機打擊貫入土體的模式加以模擬。 本研究第二年探討「條型震動夯實」對土體的影響。本研究發現: (1)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。(2)在夯實機夯實1和2趟後，殘餘水平 土壓力的等高線會形成兩個較高的應力區，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。 本研究第三年將探討「全面震動夯實」對土體內部密度及應力之影響。本研究全面 夯實疏鬆砂土。依據埋入回填土中的密度盒及土壓力計數據，探討：(1) 土壤受到動態 夯實作用，所造成之應力路徑；及(2)土壤受到振動夯實過程的行為機制(mechanism)。 為模擬現地平滑鼓式振動壓路機的夯實效果，本研究第三年將採用第一年經費所研發的 實驗室振動平滑鋼輪夯實機進行土壤夯實，依據實驗結果比較平板式與鋼輪式振動夯實 機施工對土壤應力及密度影響之差異。

This study investigates the change of vertical and horizontal stresses in a soil mass due to vibratory compaction. In this study, the non-yielding model soil-bin of the National Chiao Tung University is used for experiments. Air-dry Ottawa silica sand is used as the fill material. A flat-plate vibratory compactor is used to compact the loose fill. The dry sand is placed into the soil bin with the air-pluviation method to form a loose specimen. Before compaction, soil-density cups and soil pressure transducers are buried in the soil mass at different elevations and locations to measure the variation of soil density and earth pressure due to vibratory compaction. A three-year research project is proposed. In the first year, the effects due to the compaction at a point on the surface of a loose fill are investigated. It is found that (1) after 7 and 123 seconds of point compaction, with the increase of time, the Dr = 36% relative density contour moves to a deeper location. (2) The stress condition in a soil mass due to the point compaction of a square-plate compactor can be simulated with the penetration of a square steel pile into the a soil mass. In the second year of this study, vibratory compaction is applied to a strip area on the surface of the fill. It is found that: (1) the surface settlement and the number of passes of the compactor can be modeled with the hyperbolic model. (2) After 1 or 2 passes of the compactor, the residual horizontal earth pressure is concentrated at two high stress areas under the compaction plate. The induced stresses in the soil mass can be explained with the local shear failure behavior under a shallow footing. In the third year of this project, vibratory compaction is applied on the entire surface area of the loose fill. Based on the test data obtained from the density cups and soil pressure transducers, the stress paths and mechanism of soil under dynamic compaction is discussed. A laboratory smooth-drum vibratory compactor is developed in the second year of this project. In the third year, experiments are conducted to compare the effects of compaction with the plate-type and the smooth-drum-type vibratory compactors.