Pore Pressure Response to Sedimentation, Erosion and Sea Level Change and their Influence on Submarine Slope Stability

(AGU)

Lincoln F. Pratson (1) and Ulisses T. Mello (2)

(1) Lamont-Doherty Earth Observatory, Palisades, NY 10964
(2) IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598

Abstract

For saturated submarine slopes, excess pore pressures induce a seepage force that decreases the frictional resistance of the slope to failure while also potentially enhancing the downslope shear stress due to gravity. Delinger and Iverson (1992) and Orange and Breen (1992) have examined the influence of seepage forces on the stability of submarine slopes assuming a 2-D, infinite slope and steady-state fluid flow. Here, we also assume a 2-D infinite slope, but examine pore pressures and seepage forces resulting from transient pore fluid flow in response to sedimentation, erosion and sea level change. Initial results indicate that for sedimentation rates in which accumulation occurs faster than dewatering during compaction, pore pressures increase while the effective stress on the slope sediments (i.e., the total stress minus the pore pressure) decreases, promoting frictional slope failure, and in the limiting case liquefaction. The model predicts that rapid erosion fosters the opposite response, reducing the pore pressure and increasing the effective stress, thereby lowering the possibility frictional slope failure and liquefaction on an infinite slope. Changes in sea level, on the other hand, have no effect on slope stability, regardless of rate of sea level fall/rise or the hydraulic conductivity of the slope sediments. This is because while changing water depth does cause a corresponding change in pore pressure, the effective stress on the slope sediments remains unchanged.