Assessment of the Soil Thrust for Off-Road Tracked Vehicles Based on Soil-Track Interaction Theory

Abstract

the failure mode was converted to block failure after a certain transient condition. As soil failure occurred along the weakest failure plane, a transient condition was defined where the soil thrust of the wedge failure plane surpassed that of the block failure surface. Using limit equilibrium analysis, a soil thrust prediction model was newly proposed in terms of the geometry of the track systems and the soil parameters. The applicability of the developed prediction model was then verified through the comparison of the experiment and predicted results, showing good agreement. The results of this thesis can be utilized for the assessment of the performance of off-road tracked vehicles. With the developed model for the soil thrust, the tractive performance of off-road tracked vehicles under silty and clayey soil conditions can be evaluated quantitatively.

The track system, which consists of a wide track plate and protruded grouser, is generally applied for heavy off-road vehicles such as construction vehicles, armored fighting vehicles, and a remotely operated vehicles (ROVs). It cannot sufficiently withstand an engine thrust, however, to drive off the pavement, an unpaved terrain (off-road), restricting the tractive performance. Consequently, a shearing action is induced on the soil-track interface, developing a soil thrust acting as a traction force of an off-road tracked vehicle. This dissertation explores and proposes a new theory for predicting the soil thrust of an off-road tracked vehicle in a quantitative manner. A realistic soil-track system was physically simulated in a 1g gravitational field, and a series of model track experiments was performed on a model track system with silty and clayey soils. To investigate the mechanism of the soil thrust, the shapes of the failure surfaces were observed, and the soil thrust was estimated from the experiment results. Particular attention was given to the development of soil thrust prediction models that could be utilized to assess the performance of off-road tracked vehicles based on the proposed mechanism. To validate the applicability of the 1g similitude law for predicting the behavior of soil-track interaction, the modeling of the model technique was adopted. The verification results showed that the model track experiment, which simulated the soil-track system based on Iais 1g similitude law, could be used to predict the behavior of a soil-track interaction in qualitative and quantitative ways. Subsequently, a series of 1g model track experiments was performed with silty soil, and the mechanism of the soil thrust of silty soil was investigated. Regardless of the relative density of the ground and the imposed vertical stress, it was revealed that a soil block whose shape was identical to that of a model track system was formed and was sheared off along the soil channel (block failure). The experiment results demonstrated that the shearing action on the bottom was a replica of the shearing process in the direct shear test of the soil. Meanwhile, the shear failure patterns on the side were similar to the pattern of the punching shear failure of the loaded footing on the strong soil layer underlying the weak soil deposit. Based on the punching shear theory, a prediction model for the side thrust was newly proposed in terms of the geometry of the track systems and the soil parameters. The applicability of the developed prediction model was verified through the comparison of the measured maximum side thrust values and the predicted values. Lastly, a series of 1g model track experiments was performed with clayey soil, and the mechanism of the soil thrust of clayey soil was investigated. Unlike the soil thrust of silty soil, two different failure modes (block failure and wedge failure) existed. In the development of soil thrust, clayey soil was inclined to make a diagonal failure plane next to the grouser. Wedge failure at a certain inclined angle took place on the weakest plane, and soil thrust was generated along the wedge failure surface. Here, the wedge failure was inevitably accompanied by the uplift of a track system. The high vertical stress suppressed this uplift force, leading to the increase in the length of the soil wedge. Consequently, the soil thrust of wedge failure plane also increased to some extent