Experimental investigation of factors affecting the characterisation of soil strength properties using a Bevameter in-situ plate sinkage and shear test apparatus

The Bekker-Wong soil-wheel interaction model has been widely adopted in the terramechanics field. This model requires the soil to be characterised using a Bevameter, which entails performing in situ plate sinkage and shear stress tests. Bevameter soil characterisation is not a standardised test procedure, and the test setup may influence the identified soil model parameters. This study investigates the influence of the following five factors for partially saturated sandy soil: I) soil preparation method on pressure-sinkage, II) soil preparation method on shear stress, III) torsional vs. translational shear mechanism, IV) shear contact area, and V) the influence of shear velocity. The results indicate that the influence of soil preparation on pressure-sinkage response is substantial, exhibiting an order-of-magnitude difference. The influence of soil preparation on shear tests is notable, but less significant. The shear mechanism, shear contact area and shear velocity exhibited a maximum absolute shear stress difference of 18%, 20% and 10%, respectively. Moreover, depending on the test setup configuration and data processing decisions, the estimated internal soil friction angles ranged from 16.5 to 37.5° for the same soil. The findings are expected to have significant implications for the prediction of vehicle drawbar pull using the Bekker-Wong model.