Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Biosystems Engineering

Major Professor

Paul D. Ayers

Committee Members

Donald D. Tyler, Eric C. Drumm, Jeffrey S. Freeman


Rut formation can severely influence soil conditions and vegetation, and reduce vehicle mobility. Vehicle operations can affect rut formation. Ruts formed in straight vehicle paths are different than when the vehicle turns. This research is mainly to investigate the effects of vehicle turning maneuvers on soil rut formation, including field tests, lab tests, and model development.

Field tests were conducted at Yuma Training Center, Fort Riley and Fort Lewis on wheeled and tracked military vehicles. In field tests, rut depth, rut width and rut index were used as the main indicators to quantify a rut. A Vehicle Tracking System was mounted onto each vehicle to utilize the Global Positioning System. The vehicles were operated in spiral patterns to get constantly decreasing turning radius.

The Vehicle Terrain Interaction terrain mechanics model was chosen to modify to predict rut formation during vehicle turning operations on yielding soils. In the modified VTI model, the resultant force on a single wheel is a dynamic variable correlated with the vehicle’s weight, velocity, and turning radius.

In addition, lab tests were conduced on a tire and a track shoe in sand. Lateral forces and lateral displacements were applied under constant normal forces. The tire was pulled laterally and the track shoe was pulled back and forth to represent actual movement during vehicle turning.

Results indicate that (1) rut depth, rut width and rut index increase with the decrease of TR, especially when TR is less than 20 meters; (2) vehicle parameters and soil parameters are statistically significant to affect rut formation; (3) the modified VTI model is able to predict rut formation when turning, with an improved R square of 0.43; (4) in lab tests, the final sinkage caused by the lateral force or displacement is 3 to 5 times the static sinkage; (5) rut depths increase from 65% to 548% of the initial rut depths under the effects of the combination of the multi-pass and turning maneuvers after multiple passes.

This dissertation is a collection of five individual papers. More detailed description of test procedures and conclusions are found in these papers.

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