were a 2.0% maximum change in Mr from
Table 5. Format of a NELAPAV input file (from Irwin and
Speck 1986).
one iteration to the next and a total of 10
iterations.
Subject
input parameters
NELAPAV allows the use of nonlinear
Header
problem description
(i.e., stress-dependent) modulus values in
Units
input units
the analysis. Modulus values for thawing
and unfrozen fine-grained soils are highly
Load
load, pressure, load radius
nonlinear as illustrated in Figure 5. Table
n
Layered system
4, from Yang (1988), illustrates the vari-
M1 E1 seed ν1 γ1 K0,1 h1 k1,1 k2,1 k3,1 k4,1 t1
ous types of linear and nonlinear models
M2 E2 seed ν2 γ2 K0,2 h2 k1,2 k2,2 k3,2 k4,2 t2
currently available for use in NELAPAV;
.
however, models 2 and 7 are not currently
.
incorporated in the rest of the CRREL
.
design procedure. In the CRREL version
Mn En seed νn γn K0,n hn k1,n k2,n k3, n k4,n tn
of NELAPAV, model 1 has been changed
Tolerance
maximum iterations, tolerance
to the semi-log form:
r1, z1
Calculation points
Mr =k1e(k2θ)
(10)
r2, z2
.
where k1 and k2 are constants and θ is bulk
.
stress. For this study, we utilized models
.
0, 1, 3, and 4, the specifics of which will
rm, zm
be described in a later section.
Notes:
One shortcoming of NELAPAV is that
n = number of layers
it allows only one circular load to be ap-
Supplied for each layer
plied at the surface. This is not a major
M = model number (see Table 4)
problem in this analysis because we are
E seed = seed modulus (lb/in.2)
dealing with roadway pavements rather
ν = Poisson's ratio
than airport pavements, which experience
γ = density (lb/ft3)
much more complex tire configurations.
K0 = lateral earth pressure coefficient
Table 5 is a brief listing of the informa-
h = thickness (in.)
tion included in a NELAPAV input file
k1.. k4 = constants to be used in models (see Table 4)
t = mean temperature (C)
(Irwin and Speck 1986). It may contain
up to 25 layers, with the following values
rm, zm = radius, depth at which to make calculations (in.)
for each: model number (from Table 4),
seed modulus, Poisson's ratio, total den-
During this study, K0, the coefficient of lateral
sity, lateral earth pressure coefficient, thickness,
earth pressure, was assigned to the layers as fol-
and the constants required for the equations from
lows: a value of 1.5 was used for paving materials
Table 4.
and frozen soil; a value of 1.0 was used for all
NELAPAV requires a seed modulus to begin
unfrozen soil layers. We now feel that this system
its predictions of modulus for the various material
is too simplified, and are modifying the section of
layers. The value used for the seed modulus is the
TRANSFORM that assigns K0.
resilient modulus calculated in and passed from
For each layer, NELAPAV expects to receive a
TRANSFORM. The constants required for com-
value for the total density, which is adjusted to a
putations are also passed from TRANSFORM.
The k2 value is a constant assigned on the basis of
buoyed density below the water table. In this study,
material type. The k1 constant varies with the mois-
however, we used dry density instead of total den-
ture/density level of the layer, and is calculated by
sity, and neglected to adjust to a buoyed density
multiplying together all the nonstress terms in the
below the water table. A short sensitivity study,
predictive equation for the material (Table 2).
conducted when these problems were discovered,
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