Heavy weights dropped from a height for the purpose of consolidating soil (referred to originally as heavy tamping but now known as dynamic consolidation) have been used for some time, with a trend toward increasing weights and drop heights (e.g. the largest known rig has a lifting capacity of 200t and a drop height of 25m). Laboratory tests have indicated that dynamic loading gives a more pronounced depth effect than static loading concentrated on a base area of equal size as that of the falling weight. However, equations prediction depth from drop height and mass of the weight were found to be too optimistic for very fine- or coarse-grained subsoil, e.g. clay or rockfill, although they are accurate for silt, sand or gravel. Dynamic consolidation works by causing a decrease in void and an increase in porewater pressure (decrease in effective stress) eventually leading to liquefaction and hence to a nullifiction of the shear strength. Between applications, when the excess, pore-water pressure dissipates, the shear strength increases to values above those existing before the previous phase of compaction, i.e. each application will cause a successive but gradually decreasing improvement of the soil, finally reaching a point of diminishing return where further compaction is no longer viable. In any compaction procedure, the following factors should be taken into account: weight mass, drop height, energy input, spacing and pattern of compaction points, number and order of applications or "passes"; and estimated settlement due to compaction, i.e. required volume of extra fill necessary establish the final correct ground level (after each pass, the compaction craters have to be filled.) These may vary within parts of the area to be compacted and at different phases of the procedure. In order to ascertain when compaction can be terminated, several methods are suggested in lieu of expensive full-scale loading tests, most notably, dynamic loading tests and measuring the deceleration of the falling weight itself.

  • Availability:
  • Corporate Authors:

    Foundation Publications Limited

    7 Ongar Road
    Brentwood CM15 9AU, Essex,   England 
  • Authors:
    • HANSBO, S
  • Publication Date: 1978-7

Media Info

  • Features: Figures; Photos; References;
  • Pagination: p. 27
  • Serial:
    • Volume: 11
    • Issue Number: 5
    • ISSN: 0017-4653

Subject/Index Terms

Filing Info

  • Accession Number: 00184596
  • Record Type: Publication
  • Source Agency: Ground Engineering
  • Files: TRIS
  • Created Date: Feb 3 1979 12:00AM