A Study of Unsaturated Consolidated Drained Shear Strength for Weathered Mudstone by Direct Shear Test
| Autor: | Yu-Cheng Chi, 紀有政 |
|---|---|
| Rok vydání: | 2015 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 103 In the dry season, mudstones are just as hard as rocks. In the raining season, however, mudstones absorb excessive water, causing mudstones to swell and disintegrate. As a result, slopes are uncovered. Between underground water and topsoil are unsaturated mudstones. With its matric suction, the unsaturated mudstones stabilize soil firmly in the dry season. However, mudstones lose matric suction in the raining season due to the infiltration of rainwater. As a result, mudstones lose shear strength. With the decreased shear strength, the shallow layer of slope collapses or slides. This study gathered soil samples from a slope nearby the mire volcano in Moon World, Tainliao District, Kaohsiung. Several tests were conducted to identify the basic physical properties of soil samples with emphasis on the characteristics of the weathered mudstone in Tianliao District. Therefore, in-situ moisture content was simulated; remolded specimens were reproduced; the relationship between the matric suction, saturation, and moisture content of weathered mudstone was analyzed using soil water characteristic curve; saturated consolidated drainage direct shear test was conducted using the modified direct shear apparatus developed by National Kaohsiung First University of Science. Five levels of matric suction, namely, 50, 100, 150, 250, and 350kPa, were designated for the unsaturated consolidated drainage direct shear test in which net normal stress was set as 100, 200, and 400kPa, respectively. The test was designed to identify the rise and fall of shear strength due to the changes of moisture content in connection with the varying matric suction of the weathered mudstone in Tianliao District. Gathered from the surface layer of weathered soil, the soil samples were considerably porous with a few soil particles. According to the soil water characteristic curve, the soil has an unsatisfactory water-keeping effect. According to the consolidated drainage test, the sample soil has 43.4kPa of effective cohesion force and 22.6° of inner friction angle. Moreover, the unsaturated consolidated drainage test indicated that the inner friction angles within all levels changed slightly. Using average inner friction angle 23.5° as the shear strength, this study concluded that the matric suction could change the moisture content of the soil samples, causing the soil shear strength to increase as the matric suction increases. Moreover, a non-linear relationship between matric suction and total cohesion force was identified through the test. Based on the non-linear relationship stated above, the angle〖 ϕ〗^b corresponding to the increased matric suction decreased significantly. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|