The influence of organic matter on the shear strength of clays is mainly caused by organic molecules, which disturb the organization of water in the integrated clay/organic system, and by the flexibility of organic compounds and networks. In general, the stress/strain behavior is of the type valid for amorphous bodies in which there are considerable variations in activation energy for flow. This means that organic clays behave as creeping substances with a viscosity which is generally non-linear. In fiber-rich systems weak-link effects cause a reduction in strength resulting from the early breakdown of certain fibers. It is concluded that a proper determination of reliable strength values should be obtained by using creep tests where the shear stresses are applied for very long periods. The influence of organic matter on sensitivity may be two-fold; leaching may convert the humic compounds so that they act as substance, which means that the specific area is small. Organic matter also influences the deformation properties of clays. The high creep rate of soft organic clays may be explained by a largely varying activation energy for flow of organic complexes. In the course of consolidation, local structural brek-down occurs in organic-free clays with concomitant establishment of new bonds. This indicates that consolidation can be regarded as being at least partley governed by creep deformation, which takes place in two stages, the primary, where the number of flow units is successively increased, and the secondary, where the number of flow units tends to be constant. In very organic clays structural break-down is less important and the two creep stages merge into one, which is characterized by a straight-line relationship between compression and log time. In the case of foundations on clay beds, creep is produced in connection with shear as well as compression but the fact that organic soils often show large lateral deformations indicates that shear creep may be dominant in this type of soils.

  • Supplemental Notes:
    • Appears in the synopsis and summaries from National Swedish Building Research reports.
  • Corporate Authors:

    National Swedish Institute for Building Research

    Box 27 163, 102 52
    Stockholm,   Sweden 
  • Authors:
    • Pusch, R
  • Publication Date: 1973

Media Info

  • Features: Photos;
  • Pagination: 2 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00260363
  • Record Type: Publication
  • Report/Paper Numbers: D11:73
  • Contract Numbers: C439
  • Files: TRIS
  • Created Date: Oct 11 1974 12:00AM