A case history describing the use of blast densification by the Washington State Department of Transportation to densify a 40-m-deep, loose debris flow is presented. Debris flow from the 1980 eruption of Mount St. Helens would pose a high risk for liquefaction and ground settlement should a seismic event occur. A single-span bridge was to be constructed on the debris flow. It was determined that the only practical means of supporting the structure were spread footings founded on the debris flow, once improved by ground densification. Blast densification was chosen over more common means to improve the ground; it was considered the most cost-effective and feasible method of construction through boulder-laden debris flow. First, a test section was constructed to verify the blast design and to confirm its feasibility given the unusual geologic deposit. The goal was to improve the relative density of the deposit, as measured by standard penetration testing (SPT) and Becker penetration testing. Additionally, the site was instrumented to measure ground response. Instrumentation included surface and subsurface settlement devices, inclinometers, piezometers, ground-vibration instruments, and geophysical surveys. Blast densification successfully increased the SPT values of the deposit from an average N sub 1(60) = 8 to N sub 1(60) = 20 above 15 m, to N sub 1(60) = 19 below 15 m.


  • English

Media Info

  • Features: Figures; References;
  • Pagination: p. 102-109
  • Monograph Title: Design and construction of auger cast piles, and other foundation issues
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00672562
  • Record Type: Publication
  • ISBN: 0309060532
  • Files: TRIS, TRB
  • Created Date: Jan 13 1995 12:00AM