Predicting tire performance on soft, fine-grained soils is required for many off-road explorations in the military, mining, agricultural, and earth-moving sectors. However, the mobility in deformable material is extremely challenging, especially in the presence of water. Although there is a significant amount of research on terrains such as sands, there is a lack of research on fine-grained soils. This research is part of a bigger project that presents a novel approach to improve the mobility of off-road vehicles on wet deformable soils. The approach integrates experimental data from small-scale soil testing, large-scale soil-tire interaction testing, and advanced physics-based numerical simulation techniques. In particular, this thesis attempts to characterize the clay-tire interface by conducting large-scale direct shear tests. In addition to clay-tire contact friction, the properties and strength parameters of the soft clay are determined by conducting various index properties and advanced tests. The testing program accounts for different stresses, loading conditions, and boundary conditions, decided taking into account real field conditions. The results from all these experiments will be used to calibrate and validate the material constitutive models required for the development of a mobility predictive numerical model. Overall, this study contributes to the development of more advanced and accurate terramechanics models that involve deformable terrains like soft clays. / Master of Science / The prediction of Vehicle mobility on soft, fine-grained soils is challenging due to the impact of soil behavior on mobility, which is not taken into account by traditional vehicle simulation software. However, as off-road exploration and resource extraction become increasingly important, particularly in military, agricultural, and earth-moving sectors, the study of vehicle mobility on deformable soils is inevitable. The difficulty in predicting tire performance on soft, fine-grained soils is due to the lack of proper experimental data and numerical modeling techniques that accurately characterize the interaction between soil and vehicle tires, known as "terramechanics." The study forms a constituent part of a broader project, which aims to integrate the experimental research data from small-scale soil testing, large-scale soil-tire interaction testing, and advanced physics-based numerical simulation techniques. The main contribution of this study is to investigate soil-tire interaction to determine the contact friction between the soil and tire by conducting large-scale direct shear tests. It also involves conducting basic index properties tests and advanced shear strength and compression tests. The results from all these tests contribute to developing more accurate soil-tire interaction models in terramechanics. Given the scarcity of research on large deformable terrains like soft clays, this study can make a significant contribution towards developing more advanced and accurate terramechanics models that involve deformable terrain, which can be useful in various applications.