LIQUEFACTION AND CYCLIC MOBILITY OF SATURATED SANDS-DISCUSSION

Comments are made on statements regarding liquefaction and cyclic mobility, and assumptions made with regard to the use of a constant conversion factor are examined. It is suggested that the term liquefaction as commonly used is the extreme case of cyclic mobility and not a different phenomenon. Although a laboratory study may not represent the effect of an earthquake vary realistically, nevertheless the observed increase of pore pressure in undrained conditions appears to be the same phenomenon as that which occurs in some soil deposits during an earthquake. This buildup of pore pressure reduces effective normal stress, leaves effective shearing stress unchanged, and the effective stress state of the soil is moved closer to the failure envelope. Soils that are particularly liable to this increase or pore pressure may fail under shearing stresses (static plus earthquake where these are additive), which exist in the natural state. Failure may occur in deposits which are denser than critical, and post-failure behavior may be that of the critical state. Foundations built on soils which show cyclic mobility need to be designed to lower induced shearing stress levels in order to have the same factor of safety in earthquake conditions as those built on firmer soils. An attempt to apply the authors plot evaluating liquefaction potential is detailed by a second discusser, who also examines the use of constant conversion factor of 0.7 for all magnitudes, and the calculation of shear stresses based on a rigid body assumption. The use of a magnitude-dependent shear stress conversion factor R, and the use of a stress reduction factor are also described.

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  • Accession Number: 00134655
  • Record Type: Publication
  • Report/Paper Numbers: ASCE #11388
  • Files: TRIS
  • Created Date: Jun 23 1976 12:00AM