Observations of soil cutting with blades

Abstract The failure phenomena associated with blade action in soil have been observed with two-dimensional glass box apparatus for different blade configurations and different soil types. The three soils used were (1) a medium-dense, dry Ottawa sand, (2) a silty clay, and (3) a plastic clay. The situation examined were (1) a vertical blade in all soils, (2) a blade inclined 45 deg to the rear in silty clay and plastic clay, (3) an L-shaped blade with horizontal cutting edge in all soils, and (4) a blade inclined 20 deg forward in sand. A series of photographs were taken to show the soil deformations and mode of failure in each case. In sand the failure patterns generally resemble those prescribed by ‘passive earth pressure’ theories, but the failure surfaces did not intersect the soil surface at the angle of 45 - o/2 deg indicated in the theories. After each failure occurred addition blade movement was required before the next one formed. The inclination of these successive failure surfaces decreased due to build up to overburden with blade movement. The soil particle adjacent to the blade remained stationary, the slippage occurring in the soil. In silty clay and plastic clay, passive shear failure occurred for the vertical blade and a tensile failure or splitting due to the uplift for the inclined blade. The passive shear failure sursfaces were approximately plane and slippage of the soil occurred along the blade. The failures were discontinuous and the inclination changed as for the sand. The L -shaped blade initiated a tensile crack and then a shear failure through the rupture zone after the vertical part of the blade came into contact with the soil.