Showing papers by "Delwyn G. Fredlund published in 2010"

Measurements of suction versus water content for bentonite-sand mixtures

Abstract: Compacted soils have been widely used as landfill barriers because of favorable characteristics such as low coefficient of permeability and high swelling. Compacted bentonite–sand mixtures are norm...

Secondary Compression of Municipal Solid Wastes and a Compression Model for Predicting Settlement of Municipal Solid Waste Landfills

Abstract: The estimation of the capacity and settlement of landfills is critical to successful site operation and future development of a landfill. This paper reports the results of a study on biodegradation behavior and the compression of municipal solid wastes. An experimental apparatus was developed which had a temperature-control system, a leachate recycling system, a loading system, and a gas and liquid collection system. Experiments were performed both with and without optimal biodegradation for comparative purposes. Test results indicated that settlement resulting from creep was relatively insignificant when the biodegradation process was inhibited. Compression due to decomposition under optimal biodegradation conditions was found to be much larger than compression associated with creep. The biodegradation process was significantly influenced by the operational temperature. A one-dimensional model is proposed for calculating settlement and estimating the capacity of the landfill under relatively optimal biodegradation conditions. The model was developed to accommodate the calculation of settlement in landfills when a multistep filling procedure was used. The calculation method is relatively simple and convenient for design purposes. Simulations of the physical processes showed that enhancing solid waste biodegradation during the filling stage can considerably increase the capacity of the landfill and reduce postclosure settlements.

Moisture Movement Through Cracked Clay Soil Profiles

Abstract: A continuum mechanics approach is used for the formulation of unsaturated hydraulic conductivity functions and the water storage functions for fractured or cracked clay soils in this parametric study. Suggested procedures are based on available research literature related to the behavior of cracked unsaturated porous media. The soil–water characteristic curve, hydraulic conductivity and water storage functions take on the character of bi-modal unsaturated soil property functions. The bimodal character arises out of the independent behavior of the cracks and the intact clay soil. Matric suction changes beneath a slab-on-grade foundation placed on a cracked clay soil profile are modeled for varied surface flux conditions using the proposed unsaturated hydraulic conductivity and water storage functions. The impact of various levels of surface cracking on soil suction distributions is discussed. Suction distribution patterns are dependent on the initial soil surface suction. In particular, the results are dependent upon whether the initial matric suction is less than or greater than the air entry of the cracked clay. There is an extremely wide range of possible conditions that could be modeled but the parametric study results presented in this paper are limited to a series of selected crack widths and densities for an exfiltration case and an infiltration case.

Response parameters for characterization of infiltration

Abstract: Rainwater infiltration is of particular interest with respect to slope stability hazard management. The process of rainfall infiltration into unsaturated soil is complex due to the number of soil parameters involved and the random nature of moisture flux boundary conditions. In this paper, the effect of rainfall intensity on infiltration is investigated through the use of finite element seepage modeling for a 5 m high soil column subjected to various rainfall intensities. The numerical modeling study identified three response parameters that can be used to describe one-dimensional infiltration into an unsaturated soil. The response parameters are the depth of wetting front, the matric suction reduction depth, and the sectional infiltration rate. The practical application of the rainfall response parameters in slope stability analysis is illustrated.

Comparison of Measured and PTF Predictions of SWCCs for Loess Soils in China

Abstract: There are significant advantages in using indirect pedo-transfer functions, (PTFs) for the estimation of unsaturated soil properties. The pedo-transfer functions can be used for the estimation of the soil–water characteristic curve (SWCC) which in turn is used for the estimation of other unsaturated soil properties. The accuracy of the indirect pedo-transfer function method for the estimation of the SWCC depends on the PTF and the equation used to best-fit the particle-size distribution (PSD) data. The objectives of this study are to: (1) evaluate the performance of the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation for best-fitting the particle-size distribution, (PSD) data, and, (2) compare the predictions made by two of the commonly used PTFs; namely, Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) and Fredlund et al. (Can Geotech J 39:1103–1117, 2002), for estimating the SWCC from the PSD. The authors used 258 measured PSDs and SWCC datasets from the Loess Plateau, China, for this study. The dataset consisted of 187 silt–loam soils, 41 loam soils, 11 silt–clay–loam soils, 10 sand–loam soils, 6 silt–clay soils, and 3 loam–sand soils. The SWCC and PSD datasets were measured using a Pressure Plate apparatus and the pipette method, respectively. The comparison between the estimated and measured particle-size distribution curves showed that the Fredlund et al. (Can Geotech J 37:817–827, 2000) equation closely prepresented the PSD for all soils in the Loess Plateau, with a lower root mean square error (RMSE) of 0.869%. The comparison between the estimated and measured water contents at the same suction showed that the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF performed somewhat better than the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) function. The Fredlund et al. method had RMSE value of 0.039 cm3 cm−3 as opposed to 0.046 cm3 cm−3 for the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) method. The Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF produced the closest predictions for sand–loam, loam–sand, and loam soils, with a lower RMSE for gravimetric water content ranging from 0.006 to 0.036 cm3 cm−3. There were consistent over-estimations observed for silt–loam, silt–clay–loam, and slit–clay soils with RMSE values for gravimetric water content ranging from 0.037 to 0.043 cm3 cm−3. The measured and estimated air-entry values were closest when using the Fredlund et al. (Can Geotech J 39:1103–1117, 2002) PTF. The measured and estimated maximum slopes on the SWCC were closest when using the Arya and Paris (Soil Sci Soc Am J 45:1023–1030, 1981) PTF.

Seasonal pattern of matric suctions in highway subgrades

Abstract: The performance of “thin membrane surface” (TMS) highways is largely controlled by the strength of the subgrade soil, which in turn is a function of matric suction. Thermal conductivity matric suct...