Prediction of the forces of blade penetration and build-up heap in front of the blade during bulldozer operation

Several of the existing models of soil-blade interaction are based on very basic relations known from soil mechanics. The best-known model, developed by McKyes (1989), is used to calculate the vertical and horizontal forces applied on the blade during quasistatic bulldozer operation. McKeys's approach does not consider the effect of the build-up heap in front of the blade on the forces applied on the blade. In addition, the McKyes approach assumes a constant sinkage of the blade, and consequently the penetration force is not taken into the account, either. The literature includes no models based on classic soil mechanics theories that predict the process of blade penetration into soil and the build-up heap in front of the blade. The forces that are created by the penetration and the heap are very significant and cannot be ignored. The goal of the present research is to develop models to predict the effect of the penetration and the build-up heap in front of the blade on the forces applied to the blade, by using classic soil mechanics theories. The model of the build-up heap in front of the blade is based on the following assumptions: (1) The soil accumulates in a heap; the maximum height of the heap is equal to the height of the blade. (2) When the height of the heap is less than the height of the blade, the shape of the heap is triangular and the natural angle of repose is the vertex; when the height of the heap is equal to the height of the blade, the shape of the heap is trapezoid. (3) All the soil that is cut during the blade operation is accumulated in the heap until the maximum capacity of the blade is reached. Any additional soil is channeled out of the heap. (4) Estimation of the swelling of the soil due to tilling operations is based on empirical tables. (5) The cohesion of the soil in the heap is negligible. (6) The heap weight applies a uniform pressure on the ground surface above the failure zone. For heaps comprised of relatively small amounts of soil, it is reasonable to assume a triangular. When the heap contains significant amounts of soil, its shape depends upon the natural angle of repose. When the natural angle of repose is relatively small, the shape of the heap can be approximated using a triangle. When the natural angle of repose is relatively large, the shape of the heap can be approximated using a trapezoid. The assumption that the heap fills in a triangular shape until it reaches the height of the blade may be reasonable for the calculation of force, regardless of the value of the angle of repose. Beyond this point, the trapezoid shape cannot properly represent the case of a small natural angle of repose. However, in this case, the amount of the soil in the heap will be very large, which will at any rate prevent the bulldozer operation. In practice, the soil particles in a heap of dry soil behave like cohesionless material. In reality, the heap weight applies a non-uniform pressure on the ground surface above the failure zone. In the calculation, the average pressure is taken as uniform pressure. The model of penetration force is developed using bearing capacity theory. The models were verified in a soil bin laboratory using a scale blade connected to a controlled system by two-directional force sensors. Dragging and penetration tests were performed. The model assumption of the heap shape was verified by the experimental results.