One-dimensional consolidation in unsaturated soils under an external time-varying loading

• Main Authors: Jhe-WeiLee, 李哲瑋
• Other Authors: Wei-Cheng Lo
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/95896580649318666993

博士 === 國立成功大學 === 水利及海洋工程學系 === 103 === Soil consolidation plays an important role in practical applications related to the field of engineering as well as in disaster prevention. In particular, subsidence is a common problem in coastal regions and in the alluvial fans in Taiwan. Drought-induced soil consolidation has also become a problem. As consolidation proceeds, the excess pore fluid pressure decreases, and the effective stress increases, reducing pore spaces and consolidating the soil grains. Time-varying loading, a common phenomenon in practical geotechnical engineering problems, is significant during the process of soil consolidation. Analytical solutions for quantifying soil consolidation can provide useful information to engineers and policymakers. This study applies a set of coupled partial differential equations of momentum balance for two-phase fluid flows in a deformable porous medium developed by Lo et al. (2002) and linear stress-strain relations (Lo et al., 2005) to formulate a poroelasticity theory of consolidation. Closed-form analytical solutions describing the excess pore air and water pressure and the total settlement in response to an external loading under three types of boundary drainage conditions are formulated by employing the Laplace transform. To establish the initial conditions, Biot’s assumption (1941) that water is not allowed to escape when the loading is instantly applied on a porous medium is used. The effects of water content, soil texture, and the dimensionless frequency on one-dimensional consolidation in unsaturated soils are then determined. The results show that the dissipation of excess pore water pressure is significantly sensitive to soil texture, which is almost completed in very short elapsed time in sand, followed by loamy sand, sandy loam, loam, sandy clay loam, silt loam, clay loam, sandy clay, silty clay loam, silt clay, and clay at water saturation equal to 0.9. This trend is consistent with the coefficient of consolidation for water. Irrespective of the elapsed time, the excess pore water pressure always dissipates faster under full-permeable boundaries than under a semi-permeable boundary. For a given soil texture, the dissipation rate of excess pore water pressure is higher in wetter soil. In the early stage of consolidation, the initial pore water pressure is affected by the loading efficiency for water, which is strongly controlled by the initial water saturation. For soil consolidation under time-varying loading, the amplitude of excess pore water pressure is not only controlled by the initial water saturation but also by the dimensionless frequency. The transient response decays immediately and produces an increase in the rate of change of water pressure immediately after the application of the time-varying loading. In reference to the time-dependent total settlement, it is found that it has a positive relationship with the inverse of the soil bulk modulus.