Construction and Experimental Verification of Sloped Terrain Soil Pressure-Sinkage Model

The construction of a scientific and effective soil pressure-sinkage model under sloped terrain condition has important guiding significance for the investigation of the soil compaction effect. It is also important for the theoretical calculation of driving resistance and design optimization of the undercarriage structure of hillside metal-tracked tractors (HMTs). The classic Bekker’s pressure-sinkage model does not consider the influence of the soil water content, bulk density, slope angle, and other factors; therefore, it cannot be directly used to investigate the relationship between the soil compaction and its sinkage under sloped terrain conditions. To solve this problem, this study first verified that the soil water content and bulk density exert significant effects on the pressure–sinkage relationship under flat terrain condition. Secondly, a pressure-sinkage test was carried out using the quadratic rotation orthogonal combination design method, and the soil water content, density, and slope angle were considered. The pressure-sinkage curves of sloped terrain soils from Yangling and Yangxian in Shaanxi Province, and Huining and Jingning in Gansu Province were obtained. Then the pressure–sinkage parameters (sinkage exponent, cohesive modulus, and frictional modulus) were calculated using the weighted least-squares method. Thirdly, the mathematical relationship between the parameters and the soil water content, bulk density, and slope angle was obtained. Then Bekker’s model was modified to obtain the pressure–sinkage model of sloped terrain. Finally, the control variable method under slope angle of 10°, soil water content of 10%, and bulk density of 2 mg·m −3 were used to validate the model. The results revealed that the root-mean-square error between the calculated pressure value of the model and the measured value of the film pressure sensor was 1.614, 1.601, and 0.822, respectively. In the dynamic operation of a hillside tractor prototype, the calculated pressures between the supporting wheels were close to the measured values. It indicates that the modified soil pressure–sinkage model is more suitable for calculating the force at the bottom of the track between the supporting wheels. It can also provide an important theoretical basis for accurately calculating the pressure–sinkage parameters of sloped terrain soil. Additionally, this approach could provide theoretical and technical support for the rational arrangement of HMT undercarriages to reduce the soil sinkage and driving resistance.