- 學位論文
夯實土壤直接張力試驗之初探
Direct Tension Tests on Compacted Sand-Clay Mixture
摘要
大地工程之設計與分析往往忽略土壤之張力強度，但根據許多案例指出，土壤之張力強度具有相當的重要性，尤其是應用在預測土壩的裂縫行為、機場跑道或公路的鋪面設計以及邊坡穩定分析中的張力裂縫。在室內試驗中，量測岩石與土壤材料的張力強度通常分為直接法以及間接法。常見的間接法有巴西圓盤試驗、劈裂試驗、無圍壓貫入試驗及雙貫入棒試驗，上述間接法求得張力強度的試驗都有完整的試驗程序及理論基礎，且比較適合岩石材料，但直接量測土壤之張力強度欠缺一個具有完整性及理論基礎的試驗來求得及驗證。土壤之張力強度相當低，因此在直接施加拉力於試體時有一定的困難性，施加直接拉力的方法對於試驗量測結果也有一定程度的影響。 本研究以近期開發的直接拉力儀器量測夯實複合低塑性土壤的張力強度，透過儀器的分裂盒裝置及固定速率馬達施加拉力，以達到直接量測土壤張力強度的效果。首先，探討是否分裂盒的移動速率會影響土壤之張力強度，再透過影像後處理技術(PIV)了解楔型塊形狀對於試體裂縫發展的行為有何影響進而選定最適當的楔型塊形狀。最後量測不同尺寸之土壤張力強度，探討在直接土壤張力試驗的試驗結果與尺寸的相依性。經由實驗結果及分析結果發現，儀器分裂盒裝置的移動速率對於土壤的張力強度沒有太大的影響。在梯形、長方形及三角形楔型塊的PIV分析中發現，三角形楔型塊是比較適合直接張力試驗，而三角形的角度對於實驗結果影響相當小。在土壤張力強度中，確實存在著試體的尺寸效應，土壤之張力強度會隨著試體尺寸增大而下降，但當試體的斷面積達到相當大的值之後，張力強度會趨向定值。因此，當試體的斷面積大到某個程度後，試體之尺寸效應對於土壤直接張力試驗影響相當小。
並列摘要
The common laboratory tests for determining the tensile strength of soils can be categorized into direct and indirect methods. For direct methods, there are no standard testing apparatus and procedures to measure the tensile strength of soils. For direct tension tests, major affecting factors on tensile strength include the size of specimen, tensile pulling rate and the shape of apparatus mold. A recent development of a direct tension apparatus and tensile strength testing on compacted soil are presented in this thesis. Firstly, the influence of the tensile pulling rate on tensile strength of soil was studied. Secondly, the behavior of crack propagation due to the shape of the direct tension mold was discussed. Three types of wedges were used in tests, including triangular, trapezoid-shaped and rectangular wedges. Using the particle image velocimetry (PIV) technique, the crack propagation along with the developed tensile stress was captured. The suitability of the wedges was then evaluated. In addition, tests measuring tensile strength of soils with different specimen depths and cross sectional areas were conducted. These affecting factors in the developed direct tension apparatus and measurement of tensile strength were discussed. From the results of the direct tension tests, the displacement rate of the split box might had little influence on the tensile force versus displacement curve and crack propagation. Furthermore, the peak tensile force was not influenced by the tensile pulling rate. From the results of the PIV analyses, it is concluded that triangular wedges are suitable for direct tension experiments. Most importantly, tensile strength was found size dependent from the direct tension tests, where the cross sectional area could influence the tensile strength of compacted soil mixture. It is concluded that the tensile strength leads to a constant value when the area ratio exceeded a great value.