Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter
5 INTERPRETATION OF SOIL PROPERTIES
Porewater Pressure Parameter, B q =
-
-
(5.2)
chart using q t , FR, and
B q is presented in Fig. 5. .3, indicating twelve classification regions.
Figure 5.3 Chart for Soil Behavioral Classification by
CPT (Robertson, Et Al., 1986)
5.3
5.3.1
DENSITY
Unit Weight
The calculations of overburden stresses within a soil mass require evaluations of the
unit weight or
mass density of the various strata. Unit weight is defined as soil weight per unit volume (units of
kN/m 3 ) and denoted by the symbol . Soil mass density is measured as
mass per volume (in either
g/cc or kg/m 3 ) and denoted by . In common
use, the terms "unit weight" and "density" are used
interchangeably. Their interrelationship is:
γ = ρ.g
(5.3)
where g = gravitational constantt = 9.8 m/sec 2 . A reference value for fresh water is adopted,
whereby ρ w = 1 g/cc, and the corresponding
γ w = 9.8 kN/ /m 3 . In the laboratory, soil unit weight is
measured on tube samples of natural soils and depends upon the specific gravity of solids (Gs),
water content (w n ), and void ratio (e o ), as well as the degreee of saturation (S). These parameters are
interrelated by the soil identity:
Gs w n = S e o
(5.4)
where S = 1 (100%) for saturated soil (generally assumed for soil layers lying below the
groundwater table) and S = 0 (assumed for granular soils above the water table).
March 2009
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