A circular ore pass 13 ft (4 m) in diameter has a muck cushion that extends 9 ft (9 m) above the bottom of the ore pass. The ore pass is vertical and extends 150 ft from level to level. The muck has a specific weight of 105 pcf (16.6kN/m3), is considered cohesion less with an angle of internal friction of 38◦, and has a coefficient of friction against rock of 0.57. The ratio of horizontal to vertical normal stress in the ore pass is estimated at 0.33. Three tons of ore are dumped into the ore pass. Analysis of the ore fall indicates that on impact, the muck decelerates at 4g. Thus, the impact force on the muck cushion top is four times the muck weight. Consider this force to be a static surcharge, then determine the associated increase in vertical stress (psf, kPa) at the bottom of the muck cushion.