THRUST ANGLE

The thrust angle is the direction the center of gravity of the slide mass moves when displacement first occurs. For a planar slip surface parallel to the slope (an infinite slope), this angle is the slope angle. For simple planar block sliding, the thrust angle is the inclination of the basal shear surface. For circular rotational movement, Newmark (1965) showed that the thrust angle is the angle between the vertical and a line segment connecting the center of gravity of the slide mass and the center of the slip circle. For irregular shear surfaces, the thrust angle can be approximated visually, by estimating an "equivalent" circular surface, or by averaging the inclinations of line segments approximating the surface.