BREAKOUT RESISTANCE OF OBJECTS EMBEDDED IN OCEAN BOTTOM

Soil resistance to withdrawal is found to be greatly affected by failure patterns. For relatively shallow anchors in undisturbed dense and stiff soils general shear along a convex, torical slip surface is observed. For remolded, compressible and semiliquid soils this pattern degenerates into a cylindrical surface. For deeply embedded objects punching shear failure is observed. In semiliquid soils this is accompanied by flow of soil into the vacuum created by withdrawal of the object. Theoretical analysis considering soil to be rigid-plastic near the surface and elastic-plastic at greater depth appears to give reasonable estimates in soft and loose soils; it underestimates the breakout resistance in stiff and dense soils. The least understood components of breakout force are those attributed to soil suction and adhesion between the object and surrounding soil. It appears that the problem of soil suction can be handled as a problem of pore-pressure difference on two sides of the pulled object.