Predicting fractures in glacially related fine-grained materials and a synthetic soil of bentonite and sand using soil texture

Scientists and engineers from many disciplines have been studying the formation of fractures in fine-grained natural geologic materials and fill. Naturally occurring fractures in the fine-grained materials can create preferential flow paths, which can allow water to infiltrate quickly, resulting in recharge to underlying aquifers but also allowing contaminants to pass through to aquifers, potentially threatening ground water drinking water sources. They can also create zones of weakness that allow piping in dams and slip zones in fill materials. Glacially related fine-grained materials are widely distributed across the northern hemisphere, including the U.S. states of Minnesota, Wisconsin, Michigan, Iowa, Illinois, Indiana, and Ohio; Canada; and much of Northern Europe. It has been difficult to predict the presence of these fractures. The objective of this research was to analyze soil textures of fractured soils and determine boundary conditions for predicting the likelihood of fractures in similar materials, graphically representing the predictive model on the USDA soil texture ternary diagram. An extensive Midwestern U.S. data set (275 data points) including Ohio, Iowa, Michigan, and Wisconsin soil samples was studied. The texture data of those glacially related fine-grained materials containing fractures indicate that those with < 79% sand and > 6.5% clay can be predicted to support fractures. An auxiliary experiment using bentonite suggests that this predictive model may be applicable beyond the clay mineralogies common to the U.S. Midwest. This is a promising method of predicting which soil textures are most likely to form fractures, and can be a useful field tool for engineering geologists, soil scientists, and other environmental professionals. It is immediately applicable to the U.S. Midwestern sites, and with additional analyses using other soils, could be used more widely across glaciated North America and Northern Europe.