CRITICAL ACCELERATION

Also known as yield acceleration, critical acceleration is the base acceleration that must be exceeded for a landslide block to begin moving relative to its base. In other words, critical acceleration is the threshold acceleration required to initiate downslope movement. Accelerations below the critical level will cause no permanent downslope movement of the landslide block; once the critical acceleration is exceeded, the landslide will begin to move downslope. The critical acceleration can be determined by iteratively conducting pseudostatic limit-equilibrium analyses until a ground acceleration is found that yields a factor of safety of 1.0, or it can be estimated using the following equation:

a_c = (FS - 1)g sin

where a_c is the critical acceleration in terms of g, the acceleration of Earth's gravity, FS is the static factor of safety, and is the thrust angle (the angle from the horizontal that the center of mass of the landslide block first moves). For slope-parallel sliding (infinite slope or block sliding on a dip slope) the thrust angle is simply the slope angle.