Abstract
Based on the results of experimental studies concerning the filtration coefficient, the Darcianity of the observed flows for eight cohesive soils at four hydraulic gradients was analyzed. It is observed that linear dependence of flow velocity on hydraulic gradient is an approximation only, and it is the worse the more cohesive a given soil is. Despite this, Darcy’s law can be a correct approximation of the empirical relationship between hydraulic gradient and the flow velocity, also in very cohesive soils. A statistical analysis was carried out to identify correlation between soil properties and permeability coefficient. For each soil, 109 parameters were analyzed, among others applying mercury intrusion porosimetry, scanning electron microscopy, dynamic image analysis, and laser diffraction. Ultimately, three single-variable models best fitted to the experimental data were found, using the plasticity index IP as the independent variable, the average pore diameter DP, and the convexity of silt fraction particles. All model parameters are statistically significant at p < 0.05. Comparison with reference multi-variable models showed that the best fit for experimental data is observed by the model with the plasticity index, while the results suggest low usability of single-variable models with structural parameters.
Highlights
Increasing interest in cohesive soils and clay minerals has been observed in recent years on the part of environmental engineering
The tests of eight soils conducted using the triaxial testing apparatus allowed obtaining the values of permeability coefficients at four different hydraulic gradient values
Four common metrics were used in the validation process for measuring the differences between permeability coefficient values predicted by the proposed models and the values observed: Mean Absolute Error (MAE), Mean Bias Error (MBE), Mean Absolute Percentage Error (MAPE), and Root-Mean-Square Error (RMSE)
Summary
Increasing interest in cohesive soils and clay minerals has been observed in recent years on the part of environmental engineering Soils of this type show a tendency for particles to stick to each other due to intermolecular interactions and, as a result, they usually have low permeability. Negative impact of the filtration forces on soil is observed, for example, in the vicinity of flood banks when water level is high in rivers (most often at the foot of landside slope and drainage facilities), and while making constructional foundation trenches (there is the risk involving the loss of soil stability in riverbed and slopes). An attempt to search for models with the number of soil parameter limited to one has an essential theoretical meaning, allowing for a strict identification of soil properties most responsible for the flow phenomena in clay-water systems
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