Vibrocone Penetrometer for Evaluating Liquefaction Potential
GRAs: James Schneider, and Tom Casey
USGS Technical Report
USGS Non-technical Summary
Results of Vibrocone Soundings in Charleston, SC
Seismic Zone
Joint Research Project between Georgia Tech (PI: P.W. Mayne) &
Virginia Tech (PI: J.K. Mitchell with T. Brandon); Funded by U.S. Geological Survey (John Sims) and National
Science Foundation (Dr. Cliff Astill). A special vibratory piezocone is under development
for use in detecting liquefiable zones in highly seismic active areas.
Following some pioneering efforts by the Public Works Research Institute
(Japan), UBC (Canada), and ISMES (Italy), a new class of vibrocone is being studied in
laboratory chamber tests and field trials. Previous vibrocone devices were flawed because
they either used horizontal centrifugal excitation (causing gaps between the soil &
penetrometer and shoulder porewater measurements, or else applied dynamic forces at the
top of the rods.
The USGS/NSF model will utilize verticallyapplied dynamic forces and
simultaneous measurements of penetration porewater pressures at midface and shoulder
filter positions. Midface porewater measurements provide data on the contractive nature of
the liquefiable zone, whilst the shoulder element permits the correction of tip
resistances. A pneumatically-controlled solenoid and timer are being used to provide
impulse forces. A triple-element piezocone has been provided by Fugro Geosciences for the measurements of tip, sleeve, and
multiple porewater pressures.
Figure 1. Prototype Vibrator and Triple Element
Piezocone
Figure 2. Vibratory Unit Connected to a 10 cm2 Piezocone (Pictured with Nitrogen Tank with Two Stage Regulator, Control Panel, and Oscilloscope)
January 27, 1998