The Earthquake Engineering Online Archive

The generation and dissipation of pore water pressures during soil liquefaction

Seed, H. Bolton; Martin, Philippe P.; Lysmer, John

UCB/EERC-75/26, Earthquake Engineering Research Center, University of California, Berkeley, 1975-08, 47 pages (475/S411/1975)

An analytical procedure is presented for evaluating the general characteristics of pore water pressure buildup and subsequent dissipation in sand deposits both during and following a period of earthquake shaking. It is shown that in layers of fine sand, excess hydrostatic pressures may persist for an hour or more after an earthquake. However, evidence of subsurface liquefaction may not appear at the ground surface until several minutes after the shaking has stopped and the critical condition at the ground surface may not develop until 10 to 30 minutes after the earthquake. On the other hand, for coarse sands and gravels with no impedance of drainage due to the presence of sand seams or layers, pore pressures generated by earthquake shaking may dissipate so rapidly that no detrimental buildup of pore pressure or a condition approaching liquefaction can develop. Improving the drainage capability of a sand deposit by the installation of a highly pervious continuous drainage system may thus provide an effective means of stabilizing a potentially unstable deposit. Analyses of the type described also provide the means for assessing whether subsurface liquefaction will have any serious effects on structures supported near the ground surface.

Available online: http://nisee.berkeley.edu/documents/EERC/EERC-75-26.pdf (1 MB)