A General Analytical Solution for Axisymmetric Consolidation of Unsaturated Soil with Impeded Drainage Boundaries

The consolidation of soil is one of the most common phenomena in geotechnical engineering. Previous studies for the axisymmetric consolidation of unsaturated soil have usually idealized the boundary conditions as fully drained and absolutely undrained, but the boundaries of unsaturated soil are actually impeded drainage in most practical situations. In this study, we present a general analytical solution for predicting the axisymmetric consolidation behavior of unsaturated soil that incorporates impeded drainage boundary conditions in both the radial and vertical directions simultaneously. The impeded drainage boundary is modeled using the third kind boundary, and it can also realize fully drained and absolutely undrained ones by changing the drainage parameter. A general analytical solution is developed to predict the excess pore-air and pore-water pressures as well as the average degree of consolidation in an unsaturated soil stratum using the common methods of eigenfunction expansion and Laplace transform. The newly developed solution is expressed in the product of the terms of time, depth, and radius, which are derived using Laplace transform, usual Fourier, and Fourier-Bessel series, respectively. The eigenfunctions and eigenvalues are evaluated from the impeded drainage boundaries in both radial and depth dimensions. Then, the correctness of the proposed analytical solution is verified against the existing analytical solution for the case of traditional boundaries and against the finite difference solution for the case of general impeded drainage boundaries, and excellent agreements are obtained. Finally, the axisymmetric consolidation behavior of unsaturated soil involving impeded drainage boundaries is demonstrated and analyzed, and the effects of the drainage parameters are discussed. The results indicate that the larger drainage parameter generally expedites the dissipations of the excess pore pressures and further promotes the soil settling process. As the drainage parameter increases, its influence gradually diminishes and even can be neglected when it is larger than 100. The general analytical solution and findings of this study can help for better understanding the axisymmetric consolidation behavior of the unsaturated soil stratum in the ground improvement project with vertical drains as well as the gas-oil gravity drainage mechanism in the naturally fractured reservoirs.

Agroecological assessment of water-physical properties of irrigated soils of the Trans-Urals in the analysis of the main hydrophysical characteristics

Water-physical properties of soils are a set of soil properties that determine the accumulation, preservation and water transfer in the soil stratum. One of the important indicators of water-physical properties are soil-hydrological constants. These indicators can be used in forecasting yield, calculating the irrigation rate. The determination of soil-hydrological constants is a rather laborious process. In this article, we propose to obtain soil-hydrological constants from the data of the main hydrophysical characteristics. This technique allows to analyze the data and obtain soil-hydrological constants from the data of granulometric composition. The conducted studies have shown that the use of uncontrolled irrigation has led to the transformation of water-physical properties, the content of easily mobile, productive and gravitational moisture has decreased. When modeling the MHC curve, a change in the shape on the graphs can be noted.

ESTIMATION OF KARST SINKHOLE HAZARD — DETERMINISTIC OR STOCHASTIC?

The place of deterministic and probabilistic approaches of estimation of karst-suffusion and karst-landslide hazard is analyzed. It is evident that the field of deterministic calculations in comparison with the landslide capability assessment is turning out to be narrower because of the low availability to study the karst caverns, which are the most important elements in the sinkhole-formation processes. The sinkhole-formation hazard forms as a result of the cooperation of 2 factors in the certain area: the critical size of the zone of possible destruction of the clayly soil stratum (“screen”) over the unfilled karst cavern and the required volume of the receiving cavern or fractured karst collector where the collapsing and decompression material can be carried. At the present day it is impossible to identify in advance the presence of these factors there. In the highly researched areas with fairly simple models of sinkhole-formation processes it is advisable to test and verify the new methods of forecasting the location of the probable karst sinkholes along with the deterministic geomechanical calculations and physical laboratory modeling for sinkhole diameters estimation. In other cases the combination of zoning based on the geological and hydrogeological typing of conditions and mechanisms of sinkhole-formation and probabilistic methods gives the opportunity for more adequate forecasting of the parameters of sinkholes and probable intensity of their formation. It is also stimulates more reasonable appliance of the method of natural (natural and man-made) analogs and helps to use relevant methods for different models of geological massif in deterministic calculations. While the estimation of the sinkhole-formation hazard it is necessary to take into account the presence of the weakened zone along the perimeter of the karst sinkhole and the probable creep of the “screen” soil stratum.