Evaluation of in-situ relationships between variable soil moisture and soil strength using a plot-scale experimental design

Off-road vehicle trafficability depends on mechanical soil properties and terrain characteristics that reflect the soil forming environment. Empirical laboratory data show how soil moisture influences soil strength; however, such relationships are mostly devoid of in-situ soil conditions. This study presents results from field experiments conducted at four research sites in the western and midwestern United States to examine the effects of increased soil moisture on in-situ soil strength. Plot-scale grids were used to apply water to the soil surface at regular 24-hour intervals. Soil samples were collected at three depth intervals prior to each of five water application/infiltration periods to compare field-based soil moisture with soil strength measurements. Systematic increases in saturation levels were observed that correspond with reduction of compressive strength, cohesive strength, and penetration resistance. These results exhibit regional differences in the responses of dynamic soil properties that can be explained using soil taxonomic information and differences in the state factors of soil development. Our results provide an expanded dataset to improve the development of relationships between soil type and soil strength to impact next generation mobility models, and enable remote evaluation of vehicle trafficability under soil moisture conditions based on knowledge of regional geomorphic and pedogenetic characteristics. (C) 2022 ISTVS. Published by Elsevier Ltd. All rights reserved.