A panel block caving system operates at a depth of 4,250 ft (1,417 m) as shown in the sketch. Dimensions of the panels are 150 ft by 300 ft (45.7 ?? 91.4 m) in plan. The initial undercut is 21 ft (6.4 m) high. Initial bulking porosity at the start of the cave, which forms rubble, is 0.37. Estimate the cave height possible before the swell must be drawn in order to maintaincaving.

Surface - 4,250 ft