A panel block caving system operates at a depth of 1,295 m. Dimensions of the panels are 46 m by 92 m ft in plan. The undercut is 6.4 m high. Initial bulking porosity at the start of the cave, which forms rubble, is 0.25. Solid ground specific gravity is 2.60; caved ground has a specific gravity of 1.73; the angle of friction between muck and rock is 23◦, and the angle of internal friction of the muck is 33◦. The ratio of horizontal to vertical stress in the caved ground is estimated to be 0.32.

(a) Estimate the cave height possible before the swell must be drawn in order to maintain caving.

(b) What values of vertical, horizontal, and shear stresses are realized at the undercut level when the cave height reaches 183 m?

(c) What bulking porosity is indicated when the cave just reaches the surface after drawing the necessary swell?