posted by Ray .
A tunnel of length L = 141 m, height H = 6.9 m high, and width 6.0 m (with a flat roof) is to be constructed at distance d = 60 m beneath the ground. The tunnel roof is to be supported entirely by square steel columns, each with a cross-sectional area of 960 cm^2. The mass of 1.0 cm^3 of the ground material is 2.8 g.
What is the total weight of the ground material the columns must support?