不飽和土壤變形參數之研究

Abstract

地下水位以上的不飽和土壤相關工程問題主要包括有效應力變化所導致的地層沉陷以及邊坡穩定。在沉陷方面，若地層屬砂性土壤含量居多的話，則有效應力增減所反應的土壤體積變化量並非太大；反之，當地層為具有一定厚度的黏性土壤時，往往地表的沉陷行為會出乎工程師意料，使得地表建物將持續受到地層下陷的困擾。 本研究之目的主要在於探討不飽和黏質土壤孔隙壓力參數之變化。本研究之試驗乃利用改良式單向度壓密滲透儀與壓力容器來進行不飽和土壤體積變形試驗及相關保持曲線實驗，觀察體積變化以推求孔隙壓力參數，最後並利用土壤—水保持曲線試驗結果來建立孔隙壓力參數隨結構張力變化之線性方程式。 實驗結果顯示：黏質土壤孔隙壓力參數會隨飽和度下降而成非線性減小，分析中也發現孔隙壓力參數的變化與正規化土壤—水保持曲線有近似的趨勢，藉由這層關係推導出孔隙壓力參數隨對數化結構張力變化之線性方程式。

The engineering problems related to unsaturated soils are land subsidence resulting from change of effective stress and slope stability. For sandy soil,change of volumn resulted from change of effective stress is not significant. The objective of this research is to study the pore pressure factor of unsaturated clayey soils. The pore pressure factor varies with the degree of saturation. Deformation tests and soil-water characteristic tests of unsaturated soils were performed by using specially designed consolidometer simulate the behavior of field suction. The experimental results indicate that pore pressure factor of clayey soil will decrease nonlinearly with degree of saturation . The results also show that pore pressure factor is closely related to soil-water characteristic curve . Equation for pore pressure factor and matric suction is developed.