Principles of Soil-Vehicle Mechanics

The object of soil-vehicle mechanics is defined and existing theories briefly described. Experiments have shown that these theories work quite well for frictionless clay soils and for lightly loaded vehicles in firm soils where sinkage is small. For other soft soils performance cannot be predicted and the theory does not agree with experimental evidence. It is proposed that an improved and unified theory can be based on equations developed using the methods of soil mechanics, making appropriate allowance for the effect of compressibility. A resulting new pressure sinkage equation is shown to give better agreement with experiment. The complexities of the soil stress pattern imposed by vehicles are described and it is shown that these cannot be neglected. The effect of superimposing horizontal and vertical loads is to cause slip sinkage and experimental measurements show this to be important in sand but not in clay. An analysis is made which explains why this is so and gives insight into the physical nature of the phenomenon. The aims of current research are described and illustrated with results from recent measurements of wheel performance.