REPORT ON THE ACTIVITY OF THE NORWEGIAN GEOTECHNICAL INSTITUTE FROM 1ST JANUARY 1972 TO 31ST DECEMBER 1973

BERETNING OVER NORGES GEOTEKNISKE INSTITUTTS VIRKSOMHET FRA 1. JANUARY 1972 TIL 31. DESEMBER 1973

A test fill 20 m wide and 60 m long has been laid on a very soft clay with a plasticity index of about 30. The thickness of the dry crust varies from 0.8 to 1.5 meters. Just below the dry crust the undrained shear strength, determined be in situ vane test, is about 1.1 t/sq m. The natural water content is about 60 percent. The factor of safety for the fill, according to the undrained stability analysis, based on the in situ vane strength, is 1.25. By observing how the deformations develop with time, one hopes to check and to develop further the methods used today for calculating factor of safety and deformations for approximately undrained conditions. The following observations and preliminary interpretations have been made: (1) Two and a half months after the fill had been laid out, the settlement was 27 cm under the center of the fill at the original ground surface. The horizontal displacement below the edge of the fill at a depth of 2 m was 5 cm. Ten months later the corresponding figures were 40 and 10 cm. The deformations, both horizontal and vertical, decrease rapidly with depth. At a depth of about 9 m, there is practically no deformation. The excess pore pressure was at a maximum at a depth of 6 to 8 meters. At this depth the excess pore pressure was about 70 percent of the additional pressure on the original ground surface. At depths of from 6 to 12 meters the pore pressure showed a slight tendency to increase during the first months after the filling. (2) Preliminary calculations with a finite element program, based on undrained compression and extension triaxial tests, gave an approximately correct settlement under the center of the fill at the end of filling. However, the distribution of the settlements with depth deviated greatly from those observed. The calculated horizontal deformations were much larger than the observed ones. The following factors are believed to be important for the difference between observed and calculated deformations: sampling disturbance, drainage neglection in the computations, and assuming the vertical stress below the fill to be evenly distributed. (3) Apart from the uppermost 4 meters of the clay layer, observed pore pressures and pore pressures calculated using the finite element program agree well. The increase in minor principal stress due to the filling was measured using the hydraulic fracturing method. The measured values agree fairly well with those calculated with the finite element program. /Author/

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    Norwegian Geotechnical Institute

    P.O. Box 40 Tasen
    Oslo 8,   Norway 
  • Publication Date: 1974

Language

  • Norwegian

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  • Accession Number: 00096111
  • Record Type: Publication
  • Files: TRIS
  • Created Date: Jun 10 1975 12:00AM