If the excavation width a in Problem 8.2 is 105 ft (32 m), the initial height of the circular region is 14 ft (4.3 m); the arch extends 35 ft (10.7 m) above the floor. What bulking porosity is indicated if the cave just reaches the surface from a seam depth (surface to seam top) of 1,150 ft (350m)?

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н 2a