3.5 A steel pipe with 200 mm outer diameter and 10 mm wall thickness is buried in the ground, and is to be lifted out. The ground pressure varies linearly from the surface to the bottom, and so the frictional resistance to sliding varies as well. Say the frictional shear stress varies from 0 at the top to 40 kPa at 12 m. Determine the tensile stress in the pipe when the lifting force is just enough to overcome the frictional resistance. 3.6 A steel pipe with 200 mm outer diameter and 10 mm wall thickness is buried in the ground, and is to be lifted out. The ground pressure varies linearly from the surface to the bottom, and so the frictional resistance to sliding varies as well. Say the frictional shear stress varies from 0 at the top to 40 kPa at 12 m. Assuming the bottom does not move, how much does the upper end of the pipe displace when the upward force lifting the pipe is just enough to overcome the frictional resistance? 200 mm 12 m Tmax Probs. 3.5-6