A block is formed from the upper half spaces of two joint planes and the lower half spaces of two excavation planes. Block theory analysis demonstrates that the block is removable in the excavation, and we now want to assess its stability. The dip and dip direction values for the two bounding joint planes are as follows: Joint plane Dip 1 40 2 50 Dip Direction 100 220 The block is estimated to weigh 100 metric tons. (a) Assuming the friction angles are 20 on plane 1 and 15 on plane 2, compute the support force required to achieve a limiting equilibrium condition if the bolts are installed 10 below horizontal to the N l0E (azimuth 10). Use a stereographic projection, supplemented by vector calculations. (b) If the friction angle is actually 30 on plane 2, and the bolts are installed as calculated in part (a), what angle of friction on plane 1 would be required to produce a limiting equilibrium condition for the block