Table 2. Models currently available in NELAPAV (from Yang 1988).
Model
no.
Name
Specification
Mr = constant
0
Linear
Mr = k1θk2
1
Bulk stress
k2 + k3 (k1 - σd ) σd < k1
Mr =
2
Deviator stress
k2 + k4 (σd - k1) σd ≥ k1
Mr = k1( J2 τoct )k2
3
Second stress invariant
Mr = k1τoctk2
4
Octahedral shear stress
Mr = k1σ vk2
5
Vertical stress
Mr = k1σ1k2
6
Major principal stress
Mr = k1( J12 + J1p )k2 (1 + τoct )k3 kck4
2
7
First stress invariant
0
octahedral shear stress
and anisotropic
consolidation ratio
Notes:
θ
=
bulk stress
k1, k2, k3, k4
=
constants
σd
=
deviator stress
σv
=
vertical stress
σ1
=
major principal stress
J10
=
first stress invariant due to overburden only
J1p
=
first stress invariant due to overburden and load
kc
=
anisotropic consolidation ratio
developed by the Corps of Engineers (U.S. Army
third simulation series, the anticipated traffic was
1990), which is based on the horizontal stress at
revised to 3,300,000 ESALs during 5 years, ap-
the base of the PCC.
plied at a rate of 1808 ESALs per day.
The program assumes that all applications will
CUMDAM includes several damage models
pass over the location being modeled. That is, the
previously developed for determining Ni (Table
damage is not reduced according to a pass-to-
3). Of the damage models for flexible pavements,
coverage algorithm to simulate the lateral wander
four are based on horizontal strain at the bottom
of the axle within the travel lane. It is recognized
of the asphalt layer, and relate to damage effects
that some of the equations are being applied out-
that result in fatigue pavement cracking. These
side the original assumptions used in their devel-
models were developed by the Asphalt Institute
opment; however, they are representative of cu-
(1982), Witczak (1972), the Corps of Engineers
mulative damage models currently available and
(U.S. Army 1988), and Coetzee and Connor
are used for the initial analysis until more appro-
(1990). Three other damage models for flexible
priate equations can be determined.
pavements are based on the vertical strain at the
top of the subgrade, and these relate to subgrade
rutting damage in the pavement. They were devel-
MATERIAL TESTING
oped by the Asphalt Institute (1982), the Federal
Aviation Administration (Bush 1980), and the
CRREL conducted various laboratory tests on
Corps of Engineers (U.S. Army 1987). For rigid
base and subgrade materials from Mn/ROAD, with
pavements, CUMDAM uses the damage model
8
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