A discrete analytical procedure for predicting soil failure patterns and reactions of bent leg ploughs

Abstract

Many proven analytical models have already been developed to predict the forces acting on soil working blades. These models can possibly be applied to submerged blades, if the blade's soil failure boundaries are defined properly. But, if the submerged blade is like that of the bent leg plough, by virtue of its longitudinal and lateral angles of orientation, it generates a complex three dimensionally unsymmetrical failure wedge, which cannot be modeled as a single full wedge. Hence, a procedure was developed to analytically predict the soil reactions of such a submerged blade, particularly that of the bent leg plough. The tool's soil failure wedge was discretized into finite number of longitudinal sections and then an already proven soil–tool model was applied to each section. The forces contributed by each, in the plane parallel to the direction of travel, were then summed up to obtain the total tool forces. The correctness of this procedure was verified by predicting the soil reactions of a simple raked surface tool, and by comparing results with those of a full wedge analysis. The bent leg tool's failure wedge and forces acting on it were then logically assumed and the above procedure implemented through suitably developed computer routines. Soil reactions and failure fronts of bent leg tools with different tool configurations were predicted and compared with actual values obtained from an earlier study. While the procedure predicted the draft forces accurately, it overpredicted the vertical forces. Overpredictions are caused by the fact that the measured draft versus vertical force ratio of the bent leg plough is inherently larger than that proposed by the earth moving equation. Nevertheless, this procedure can be used to calculate the energy demand of surface or submerged blades that have three dimensionally unsymmetrical failure wedges, by way of predicting their draft forces. It can cater to any type of orientation of the blade in the soil, since the failure wedge caused is discretized into longitudinal sections. It is also capable of predicting the failure front of such complex tool blades. The implementation of the procedure is simple and easy on a computer and the design of soil working tools causing complex failure fronts can be effected without conducting expensive experimental trials.