SHALLOW SLIDES DUE TO 1971 SAN FERNANDO EARTHQUAKE

The San Fernando Earthquake of 1971 resulted in over 1,000 identified hillside slope failures. Of the several modes of slope failure which have been observed in San Fernando and in other seismically active areas of the world, shallow slides are by far the most common. This paper deals exclusively with shallow slope failure. Twenty-one slides were mapped in the general vicinity of Lopez Canyon. Soil samples were taken and tested, and analyses were made. The slides were chosen in the San Fernando region in an attempt to define common characteristics and mechanisms attributed to this type of failure. Field evidence indicates that many of the slides occur within the residual soil mantle overlying parent rocks or older colluvial slopes. Laboratory study suggests that the soils are predominately silty sands or clayey sands, regardless of the lithologic associations of the slides. Considering the shallow depth of the slides, the shear stress-stain relationships under low normal load appear to be significant in choosing strength parameters for analyzing slope stability. Because of the low ratio of depth to length of the slides and their planar mode of failure, a one-dimensional mathematical model with an equivalent inertia term is used to account for the accumulative shaking effect causing failure. The model assumes as elastic soil layer bonded to a rigid plastic base. As all the cases studied failed during the 1971 earthquake, back calculations from surveyed and tested conditions are used to check the validity and applicability of the theoretical model for evaluating seismically-induced, shallow slope failures. Although more research is needed to further understand the frequently occurring but largely neglected problem of seismically-induced, shallow hillside failures, the article concludes that the simple one-dimensional approach shows promise for estimating slide stability. The method of analysis and field data discussed herein could serve as national guides for planning structure set-back or transportation and utility corridors in seismically active foothill regions. /Author/

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: p. 1076-96

Subject/Index Terms

Filing Info

  • Accession Number: 00179798
  • Record Type: Publication
  • Report/Paper Numbers: Proceeding
  • Files: TRIS
  • Created Date: Oct 12 1978 12:00AM