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The test is conducted by advancing an instrumented electronic probe with a hydraulic pushing system
at constant rate of 20 mm/s. The penetration data are logged continuously by computer giving
unparalleled details on the soil layering profiles, while downhole geophysics are taken at 1-m intervals
during the successive addition of rods. The 6-tonne truck utilizes twin-screw earth anchors installed to
depths of 2 m for increased reaction. With lightweight rigs, soundings of 30 m can be achieved in 3
hours time. Using larger 25-tonne vehicles, penetration depths of up to 90 m are possible.
The tip resistance (q c ) is a point stress related to bearing capacity and soil strength. The measured q c
must be corrected for porewater pressure effects on unequal tip areas (Lunne, et. al., 1997), especially
in clays and silts, and this corrected value is termed q T . The uo position element is required for this
correctio. The tip resistance (q-r), sleeve friction (f s ), and porewater pressures (ui or 112) are used to
characterize the subsurface layering, soil behavioral type, and strength properties. Porewater dissipation
(tso) can be conducted to measure permeability (k) and coefficient of consolidation (c h ).
Shear waves are generated by striking a horizontal steel plank at the ground surface. A downhole
geophone is oriented parallel to the plank to detect the horizontally-polarized shear waves. From the
measured wave train at each depth, a pseudo-interval shear wave velocity (V s ) is determined. The
velocity is the difference in travel distance between any two successive events divided by the
difference in travel times (Campanella et al., 1986). The seismic data are useful for subsequent site
amplification studies, as well as the evaluation of soil resistance to liquefaction susceptibility.
DYNAMIC SOIL PROPERTIES
During the cyclic loading by earthquakes, soils exhibit nonlinear and hysteretic stress-strain behavior.
The secant shear modulus G decreases with the shear strain level j c , but with a less rapid decay than
that in the condition of mono tonic loading (Figure 3). At very low strain levels (less than 10") the
small-strain shear modulus (G ma x - GO) is operational and the soil behaves as an elastic medium. As the
strain goes beyond 10" 5 , the soil response becomes nonlinear, and at large strains (larger than 10" 3 ), the
soils experience permanent plastic deformation and eventually reach an unstable condition at peak
strength. Since ground motions during earthquakes may involve both small and large strains, the whole
curve of shear modulus reduction is desirable for engineering computation and analysis.
The magnitude of the snear strain for plane waves can be given by the expression j c = u/V s , where u
is the peak particle velocity (Stokoe, et al., 1978). It is found that the shear strain caused by shear
waves generated during the SCPTu travels through the soil mass below the elastic strain level. The
Gmax can therefore be obtained from the following equation:
Where p T is the total mass density p r = j r /g and g = 9.8m/V . Mayne (2001) compiled data of unit
weight y sat and V s from saturated geomaterials (Figure 4) to define the following trend:
(2)
where y sat is in kN/m 3 , V s in m/s, and z in meters.