To decrease track derailment of tracked fire trucks in forested areas, a fish-bellied swing arm torsion bar suspension system is proposed in this research. Derived from a tracked forest fire engine, this study converts the shaft tube swing arm of the original vehicle to a fish-bellied swing arm, improving the semi-rigid shaft tube suspension to a torsion bar suspension. Static and kinematic simulation analysis of the improved virtual sample vehicle is carried out, and the stress and dynamic characteristics before and after the improvement are analyzed. The simulation force cloud diagram of the improved swing arm and the motion simulation curve of the supporting wheel is obtained. The results show that the design of the fish-bellied swing arm can effectively reduce the bending moment caused by force acting on the swing arm, and that the design of the torsion bar spring suspension can reduce vertical displacement of the supporting wheel by 58.53%, and reduces horizontal displacement by 46.58% under the same impact force. According to the design of the virtual sample to build a prototype vehicle, a comparative test is carried out to determine an optimized virtual sample vehicle. The results show that the trend of the test curve is essentially consistent with that of the simulation curve.

Forest vehicle operation causes different degrees of compaction damage to the soil, which is related to the pressure-bearing characteristics of the soil. However, scholars have not profoundly investigated the pressure-bearing factors of forest soil. In this paper, disturbed brown coniferous forest soil was collected layer by layer, dried, screened, and conducted indoor pressing-plate tests with different pressing-plate shapes and diameters (side lengths) . A kind of pressure subsidence curve of hard soil, which is different from farmland soil and homogeneous remolded soil, is obtained and drawn as the P-Z pressure subsidence curve. The results show that in the process of pressure subsidence, the forest soil gradually changed from loose to compact. Furthermore, the change of pressure-bearing subsidence of layered soil from this forest region was characterized first by the rapid increase of soil subsidence with the increase of pressure. Then, the subsidence speed became slower with the increase of pressure; finally, subsidence speed was much less affected by the increase. According to the pressure-bearing subsidence curve of forest soil, a new subsidence model is put forward in this paper. The new model has a good prediction effect on the subsidence curve of forest soil. This paper aims to provide a theoretical basis for studying soil pressure-bearing characteristics and the development of vehicles in high-passing forest areas.