振動夯實造成土壓力及其應力路徑之變化

Abstract

本論文以實驗方法探討振動夯實造成之土壓力及其應力路徑的變化。本研究以氣乾之渥太華砂為回填土，分五層填土並且分層夯實。夯實土層為每層0.3 m，總高度為1.5 m.回填土初始相對密度(Dr)為34.2 %,壓密後的相對密度(Dr)為73.8 %。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的應力變化及其動態應力路徑。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 和Jaky公式來進行合理的估算。 2. 隨著夯實逐漸接近土壓力計，其應力路徑變化越來越明顯；在最靠近擋土牆的地方夯實時，位於土壓力計上方的應力路徑變化是最大的; 隨著覆土深度逐漸升高，因夯實造成之應力變化相當不顯著。 3. 比較各組之應力路徑發現，其大小尺寸是相似的，應力路徑軌跡像是一顆的彗星。而動態應力路徑都介於K0線及Kp線。 4. 相較於Broms在1971提出之加載解載之應力路徑，本實驗量測出的應力路徑軌跡與Broms的應力路徑軌跡有很大的差異。Broms 所提出的應力路徑是在土體上方放置一個很重的且不會振動的壓路機，而本實驗是放置一個重量很輕且具振動力的夯實機。造成差異之原因有可能是因為夯實機不只有垂直方向的出力(Fz)，還有平行牆面的力 ( Fy ) 及與牆表面垂直的力 ( Fx )，這三個方向的出力造成了彗星形狀的應力軌跡。

This paper presents experimental data on the variation of earth pressure and dynamic stress path against a nonyielding retaining wall due to soil filling and vibratory compaction. The instrumented nonyielding wall facility at National Chiao Tung University in Taiwan was used to investigate the effects of vibratory compaction on the change of dynamic stress path. In this study, air-dry Ottawa sand was plated in five lifts and the height of backfill was 1.5 m. The initial relative density Dr of the backfill was 34.2 %, and the compacted relative density Dr of the backfill was 73.8 % . To simulate a plane strain condition in the laboratory, the friction between the soil and sidewalls of the soil bin was reduced with a lubrication layer. The variation of dynamic stress path was measured during compaction with a vibratory compactor. Based on the test results, the following conclusions were drawn. 1. For a loose backfill, the horizontal earth pressure in the soil mass was in good agreement with Jaky’s solutions. The vertical earth pressure in soil was near to the equation □v = □z. 2. As the area of the compaction approached the soil pressure transducer ( SPT ) in x-direction ( perpendicular to the wall face), the dynamic stress path became more obvious when the compactor moved to the lane near the wall. 3. As the area of compaction passed the SPT in y-direction (parallel to the wall surface), the maximum dynamic stress path was obvious when the compactor was right in front of the SPT. 4. For a SPT at a lower elevation, when the area of compaction rose with the elevation of the lift surface, the compaction-induced stress path became less significant. 5. The dynamic stress path of a soil element under vibratory compaction had the shape of a comet. The shape size of the dynamic stress paths obtained at five different lifts was quite similar. The stress paths were bounded by the at-rest K0-line and passive Kp-line. 6. The measured dynamic stress path was quite different from the stress path proposed by Broms (1971). The stress path reported by Broms was induced by a static heavy compactor. The vibratory compactor used in this study vibrated and generated cycle force in three direction: Fx, Fy, and Fz. This was probably the main reason why the dynamic stress path due to vibratory compaction was so different from Broms’finding.