46
Molenaar and Beuving (77) described a methodology in which the FWD
and a dynamic cone penetrometer (DCP) were used to assess stress depen
dent unbound pavement layers and the presence of soft interlayers.
However, the procedure does not provide any direct modulus correlation
but a graphical presentation of FWD surface modulus and DCP profiles.
Geotechnical engineers have, for several years, used various forms
of field tests to assess the engineering properties of soils for con
struction purposes. Recent advances in exploration and interpretation
methods have led to improvements in the determination of important soil
parameters such as strength and deformation moduli. For example, the
following in situ techniques (26,30,50) are suitable for the determina
tion of soil stiffness:
1. Menard Pressuremeter (PMT) and Self-Boring Pressuremeter (SBP)
tests.
2. Cone Penetration Test (CPT), including the mechanical,
electronic, and piezo-cone penetrometers.
3. Marchetti Dilatometer Test (DMT).
4. Plate Loading Tests (PLT), including Screw Plate Tests (SPL).
Some of these tests have the added advantage of providing detailed
information on site stratification, identification, and classification
of soil types. This is of great appeal since the variation of the
subgrade soil properties with depth can be accounted for rather than
assuming an average modulus value as conventionally used in multilayer
analysis.
Unfortunately, the application of the improved techniques to eval
uate or design pavements has been very limited. As evident from the
previous sections, the material characterization part of a rational