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analysis. Other techniques include non-intrusive surface geophysics (e.g. seismic refraction/reflection,
steady-state surface wave, spectral analysis of surface wave) and borehole geophysics (e.g. cross-hole,
down-hole, up-hole, supension PS logging). These tests provide the compression wave velocity (V p )
and/or shear wave velocity (V s ) that are needed to derive the dynamic moduli. Data collected by the
non-intrusive surface geophysics methods are difficult to interpret without experienced users. The cost
of the borehole geophysics methods is very high, because the holes are drilled, cased, and grouted, then
cured for several days before the tests are performed (Figure 1).
The seismic piezocone test (SCPTu) is a hybrid field method that combines the virtues of the cone
penetration test (CPT) with downhole geophysics (Campanella, et al., 1986). Five separate readings are
obtained in the same sounding: cone tip stress (qi), sleeve friction (f s ), penetration porewater pressure
(Ub), dissipation-time recordings (tso), and shear wave velocity (V s ), providing site-specific information
on the geostratigraphy, dynamic soil properties, and ground liquefaction susceptibility (Figure 2).
Compared with the SPT and the geophysics methods mentioned before, the SCPTu is more costeffective,
its procedure is simpler and more standardized, and its continuous record of soil properties
with depth enables a better look at soil variability.
bownhole Testing
Horizontal Plank
Seismic Piezocone
Tests (SCPTu)
; Shear Wave Velocity K-^2!S
[ V,. = AR/A-t
Figure 1. Conventional Downhole
Geophysics Test Using Cased Borehole
Figure 2. Soil Property Evaluation from
Seismic Piezocone Test Results
SEISMIC PIEZOCONE TEST
The SCPTu system used by the authors includes 5-, 10-, and 15-tonne Hogentogler penetrometers, field
computer, and anchored hydraulic rig. Each penetrometer consists of a 60° angled-apex cone at the
front end, two load cells, a transducer, an inclinometer, and one geophone. The front load cell directly
measures the force over the tip area to give the cone tip resistance, q c . A second load cell records the
axial force over the cylindrical sleeve area to provide the sleeve friction, f s . A saturated porous element
is used to measure the porewater pressure. The pressures m and U2 are measured either at the midface
of the tip or at the cone shoulder, respectively. An inclinometer is used to monitor the vertical angle, i,
as a warning signal that the rods might buckle or shear during hard pushing. The geophone is
incorporated at the back end of the penetrometer to provide a direct measure of the arrival times from a
downhole shear wave.