Thus, it is imperative to evaluate values obtained from the different procedures and ascertain the influence of procedural choice on the design thickness of pavement layers. A successful implementation of the MEPGD requires a comprehensive database for local subgrade soils and its assessment to determine desired input parameters.
#Aashto material classification how to
This difference causes engineers significant confusion about how to appropriately input the resilient modulus in the MEPDG software. However, the difference between the resilient moduli obtained from these two methods is considerably large due to the fact that these tests are conducted under different conditions. It is known that a laboratory resilient modus test and a falling weight deflectometer (FWD) test are usually used to obtain the resilient modulus of subgrade. These agencies have found their databases to be very useful tools for improving pavement designs and analyses using the MEPDG. Several departments of transportation (DOTs) have already created or are in the process of creating databases for local soils. Level 3, the lowest reliability level, uses default values based on soil classifications. The required design data inputs for level 2 could be selected from an agency database, derived from a limited testing program, or estimated through correlations. values are estimated from correlations with the soil index and other properties such as CBR or layer coefficient. The level 2 design uses correlations to determine soil properties and gives intermediate reliability. Level 1 requires material constants (, , and ) from actual testing data. Moisture and temperature variations within the pavement structure are calculated internally using the Enhanced Integrated Climatic Model (EICM). The Mechanistic-Empirical Design Guide (MEPDG) requires the resilient modulus of unbound and cohesive soil materials to characterize layers for their structural design. One of the inputs of these procedures is the effective value of the resilient modulus of the roadbed soil, which is a function of seasonal changes, soil type, moisture content, and testing method. In the past, the Indiana Department of Transportation’s (INDOT’s) flexible and rigid pavement design process followed the procedures outlined in the 1993 American Association of State Highway and Transportation Officials (AASHTO) Guide for Design of Pavement Structures (Design Guide). Therefore the determination of the resilient modulus of pavement materials is of vital importance for any mechanistically based design/analysis procedure for pavements. Resilient modulus ( ) is an important mechanical property widely used for the analysis and design of pavements. Correlations between the laboratory resilient modulus and the FWD modulus were developed and are discussed in this paper. A comparison was made of the resilient moduli obtained from the laboratory resilient modulus tests with those from the FWD tests. Furthermore, FWD tests were conducted on several Indiana highways in different seasons, and laboratory resilient modulus tests were performed on the subgrade soils that were collected from the falling weight deflectometer (FWD) test sites. The reasonably good correlations of material constants along with with routine soil properties were established.
Stress-based regression models were evaluated using a statistical tool (analysis of variance (ANOVA)) and Z-test, and pertinent material constants (, and ) were determined for different soil types. Based on each group, this study develops statistical analysis and evaluation datasets to validate these models. The data were categorized in accordance with the AASHTO soil classifications and divided into several groups. In order to implement MEPDG hierarchical inputs for unbound and subgrade soil, a database containing subgrade, index properties, standard proctor, and laboratory for 140 undisturbed roadbed soil samples from six different districts in Indiana was created.
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