THE PROBLEM OF ELECTRIC SOUNDING - METHOD OF CALCULATION - ANISOTROPY AND ELECTRIC EQUIVALENCE OF SOILS - LIMIT OF THE METHOD - BIBLIOGRAPHIC STUDY

IN SPITE OF THE DIFFICULTY OF INTERPRETING DIRECT CURRENT ELECTRIC SOUNDINGS, THE ENGINEER CAN, IN CASES WHERE THE SOIL STRUCTURE CAN BE LIKENED TO A TERRAIN OF 2 OR 3 HORIZONTAL LAYERS, MAKE USE OF GRAPHS TO DETERMINE QUANTITATIVE RESULTS FROM MEASUREMENTS TAKEN ON THE TERRAIN. BUT SINCE SOIL IS RARELY ENCOUNTERED IN THIS SCHEMATIC FORM, THE PRESENT BIBLIOGRAPHIC STUDY IS AIMED AT ASSEMBLING CERTAIN FACTORS WHICH WILL PERMIT AN APPROXIMATE SOLUTION OF ANY PROBLEM INVOLVING HORIZONTAL LAYERS. THE MANNER OF CONSTRUCTING CURVES OF ELECTRIC SOUNDINGS, FROM HYPOTHESES ON THE RESISTIVITY AND THICKNESS OF LAYERS, IS DESCRIBED. THE VALIDITY OF THE HYPOTHESES MADE IS SHOWN BY COMPARING THE CONSTRUCTED CURVE WITH THAT OBTAINED ON THE TERRAIN. THE RATHER LONG CALCULATION PROCEDURE /FLATHE METHOD/ PROHIBITS THE ESTABLISHMENT OF MANY CURVES. THE RESULTS ADVANCED WILL THUS BE SOMETIMES INEXACT, BUT THEY WILL PERMIT AN ASSESSMENT OF THE HORIZONTAL AND VERTICAL VARIATIONS OF SOIL CONDITIONS. IN MOST CASES AN ASSEMBLY BY LAYERS CAN BE REGARDED AS A SINGLE LAYER, LIKENING THE SOIL TO A SINGLE THREE OR TWO-LAYER STRUCTURE. THIS NOTION OF THE ELECTRIC EQUIVALENCE OF LAYERS IS DERIVED FROM THE CONCEPT OF MICROANISOTROPY. THE PHENOMENA OF ELECTRIC MICROANISOTROPY ARE LESS IMPORTANT THAN IN OTHER FIELDS OF SOIL SCIENCE, BUT THEY ARE NO LESS REAL. AN ISOTROPIC LAYER OF CONDUCTIBILITY CAN BE SUBSTITUTED FOR AN ANISOTROPIC LAYER OF CONDUCTIBILITY. SIMILARLY AN ASSEMBLY OF ISOTROPIC LAYERS CREATES A MACROANISOTROPY OF SUCH OF THESE LAYERS AS CAN BE AFFECTED BY VERTICAL RESISTIVITY OR CONDUCTIBILITY. WE THEN CONSIDER, AS IN MICROANISOTROPY, A SINGLE EQUIVALENT ISOTROPIC LAYER HAVING AN AVERAGE RESISTIVITY WHICH IS CALCULATED, AND A THICKNESS THAT IS NOT THE SUM OF THE THICKNESSES OF THE REPLACED LAYERS. IT CAN THUS BE UNDERSTOOD WHY CERTAIN LAYERS CANNOT BE DETECTED BY ELECTRIC SOUNDING. THE INTRODUCTION OF DAR ZARROUK PARAMETERS AND CURVES, ALLIED TO SURVEYING AND REASONABLE HYPOTHESES, WOULD SOLVE THE PROBLEM AS TO WHETHER LAYERS WERE SUFFICIENTLY DIFFERENT OR SUFFICIENTLY THICK TO BE DETECTED. IT IS POSSIBLE TO ESTABLISH BEFOREHAND THE APPROXIMATE LIMITS OF THE METHOD OF ELECTRIC SOUNDING. IF MORE THAN THREE LAYERS CAN BE DETECTED INDIVIDUALLY, THE GEOPHYSICIST WILL HAVE NO ALTERNATIVE BUT TO APPLY THE FLATHE METHOD TO THE SOUNDING CURVE.

  • Supplemental Notes:
    • Vol 1, 37 PP, 25 FIG, 6 TAB, 16 REF
  • Corporate Authors:

    Laboratoire Central des Ponts et Chausees (LCPC)

    Boulevard Lefebvre 58
    Paris Cedex 15,   France  F-75732
  • Authors:
    • Bertrand, Y
  • Publication Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 00228708
  • Record Type: Publication
  • Source Agency: Road Research Laboratory /UK
  • Files: TRIS
  • Created Date: Aug 15 2004 2:09AM