The in situ deformability of rock masses is determined by relating the applied load to the radial displacements of points on the borehole wall that are outside of the loaded surfaces. The external displacaement method includes the steps in which: a) radial displacement sensors are installed to measure the change in length of a diameter of a borehole; b) unidirectional self-equilibrating pair of forces perpendicular to the direction of radial displacement measurements is applied on opposite sectors of the borehole wall; and c) using elastic theory, the in-situ deformability of the rock mass can be related with the applied loads and measured radial displacements. The displacements outside the loaded surfaces are comparatively smaller in magnitude than displacements inside the loaded surfaces. These displacements, however, are sufficiently large and can be measured precisely by commercially available linear displacement sensors. Loads are applied by conventional borehole jack. Existing methods for measuring the in situ deformability of rock masses yield unreliable results due to the complex boundary stresses, small and varying contact areas, and the existence of fractures. It was shown that in the external displacement method, the effect of boundary pressure distribution and contact area are negligible. Also, since the displacements measured in the external displacement method were due to materials that are deeper inside the rock mass, borehole fractures have less influence on the calculated deformation modulus. The external displacement method may be used by itself or combined in the same device with the nx borehole jack method and the modified Goodman jack method. For the covering abstract of the symposium see TRIS 452576. (Author/TRRL)

Media Info

  • Features: Figures; References;
  • Pagination: p. 778-789

Subject/Index Terms

Filing Info

  • Accession Number: 00452604
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD, TRIS
  • Created Date: Jul 31 1986 12:00AM