Modeling of Mn/ROAD Test Sections with the CRREL Mechanistic Pavement Design Procedure

Modeling of Mn/ROAD Test Sections

with the CRREL Mechanistic

Pavement Design Procedure

SUSAN R. BIGL AND RICHARD L. BERG

Availability of data from the Mn/ROAD facil-

INTRODUCTION

ity will allow us to verify and refine various as-

This is one of four reports related to the full-

pects of the model.

scale pavement test facility, Mn/ROAD, con-

structed by the Minnesota Department of Trans-

portation (Mn/DOT) adjacent to Interstate 94 in

COMPUTER MODELS

Otsego, Wright County. One report describes the

results of laboratory tests conducted to determine

The mechanistic design procedure consists of

the physical and freeze-thaw related characteris-

the four programs FROST, TRANSFORM,

tics of the on-site subgrade and two of the pave-

NELAPAV, and CUMDAM (Fig. 1). FROST pre-

ment system materials used in the test sections

dicts the amount of frost heave and thaw settle-

(Bigl and Berg 1996a). Another report discusses

ment of the pavement structure and conditions

resilient modulus tests conducted on the above

throughout the depth of the structure (tempera-

materials (Berg et al. 1996). This report provides

ture, water content, pore water pressure, ice con-

an initial description of the computer programs

tent, density) at a given time increment. TRANS-

used in a mechanistic pavement design procedure

FORM uses the output from FROST as input and

under development by CRREL, and then describes

divides the pavement structure into "layers" based

a computer modeling effort that utilizes the re-

on moisture or temperature conditions. Each layer

sults of the material testing program in the proce-

is then assigned a resilient modulus, Poisson's

dure to predict the performance of some Mn/

ratio and density value. NELAPAV, a nonlinear

ROAD test sections. The final report of the series

layered elastic program, calculates stresses, strains

summarizes information in the first three reports

and deflections at specified locations within a pave-

(Bigl and Berg 1996b).

ment profile when a load is applied to the surface.

The mechanistic pavement design procedure is

CUMDAM calculates the incremental and cumu-

being developed for use in seasonal frost areas

lative damage the pavement undergoes using sev-

and considers seasonal variations in pavement

eral available damage models. The behavior is

strength such as:

normally modeled for a one-year period, with out-

1. Large increases in base and subgrade strengths

put on a daily basis. By assuming that the results

when frozen.

from a single year will be repeated annually, the

2. Loss of base and subgrade strengths during

number of applications to failure is estimated.

the spring when thawing and excess water

FROST

weakens the layers.

FROST is a one-dimensional coupled heat flow

3. Loss of asphaltic concrete strength during

and moisture flow model that computes frost heave

the summer months when asphalt moduli

and thaw settlement of a pavement or soil profile

decrease with higher temperatures.