Determination of Translational Landslide Slip Surface Depth Using Balanced Cross Sections

摘要

An apparently little-recognized but powerfultechnique for determining slip surface depth of translationallandslides is the use of balanced cross-sections. Conceptually, themethod is simple and the necessary parameters can be determinedwithout subsurface exploration. To determine the depth of the slipsurface for a given landslide, a longitudinal cross-section throughthe approximate center of the slide is drawn. From the crosssection, the area of the depression (zone of depletion) formed atthe head of the slide above the listric part of the slipsurface is determined. The displacement along the planar(translational) part of the slide is also determined, either by directfield measurement or by some indirect method. Finally, the depthof the slip surface is determined by dividing the area of thedepression by the displacement. Determining the slip surfacedisplacement is likely to be the most uncertain aspect of themethod. In some cases, the displacement can be determined directlyby measurement of offset features such as roads, fences, or surfacedrains. However, in many, if not most cases, the displacement mustbe determined by indirect methods such as using displacementsfound along the scarp(s) off the landslide. In using scarps, the styleof internal deformation of the slide mass is important. Styles ofdeformation include penetrative shear strain and/or the slippagealong discrete shear planes. Based on the displacement determinedfrom the scarp(s), a reasonable calculation of the slip surface depthcan be made.