THE PERFORMANCE OF PUSH-IN SPADE CELLS INSTALLED IN STIFF CLAY

In the design of geotechnical structures, increasing use is being made of advanced numerical methods that require realistic data on the in situ stress conditions in the ground. The assessment of vertical effective stress is relatively straightforward from a knowledge of the bulk unit weight of the soil layers and the variation of porewater pressure with depth, but the measurement of in situ lateral stress is more difficult. The use of spade cells at the site investigation stage to determine lateral stresses has not been generally adopted because of uncertainties as to their performance in soil. This Technical Note attempts to provide a suitable calibration of cells installed in stiff clays. In this study, a unique opportunity was available to install spade cells in London clay horizontally from the shaft for the Heathrow Express trial tunnel and calibrate the instruments against known overburden stresses. Cells were installed at different depths from boreholes drilled to 15 m from the shaft to ensure that vertical stresses were outside the influence zone of the shaft, and therefore at overburden values. Great care was taken during installation to maintain the active surfaces of the cells in a truly horizontal orientation. The overburden pressure at each spade cell location was then determined using the bulk density obtained from high-quality soil samples taken from an additional vertical borehole in the vicinity of the spade cells. (A)

  • Availability:
  • Corporate Authors:

    Thomas Telford Limited

    London,   United Kingdom 
  • Authors:
    • RYLEY, M D
    • CARDER, D R
  • Publication Date: 1995-9

Language

  • English

Media Info

  • Features: References;
  • Pagination: p. 533-9
  • Serial:
    • GEOTECHNIQUE
    • Volume: 45
    • Issue Number: 3
    • Publisher: Thomas Telford Limited
    • ISSN: 0016-8505

Subject/Index Terms

Filing Info

  • Accession Number: 00715880
  • Record Type: Publication
  • Source Agency: Transport Research Laboratory
  • Files: ITRD
  • Created Date: Jan 31 1996 12:00AM