CIVIL ENGINEERING SYSTEMS ANALYSIS by LUIS AMADOR-JIMENEZ

Author:LUIS AMADOR-JIMENEZ
Language: eng
Format: epub
Publisher: CRC Press

5.2.1 Worked Example for Pavement Deterioration

This section describes a worked example that estimates pavement deterioration in the form of international roughness index (IRI). This index measures the total amount of vertical variation of a dumping system of a vehicle rolling through a road. The smoother the ride, the less vertical oscillations the system will experience. Vertical variations are measured from rest, and they all accumulate whether the tire moves up or down; it is like using the absolute value of the deviations.

The response for this example is an indication of the condition of the pavement, and a brand new pavement should be equivalent to a surface that has zero imperfections; hence, the ride should be very smooth and the value of IRI should be close to zero. As time passes, the layers underneath the pavement suffer from the effects of the weather and lose strength; this leads to loss of support which translates into deformations of the surface.

Thicker pavements are commonly associated to higher strength, however this must be contrasted to the number of heavy trucks using the pavement every year and environmental factors: the water in the subgrade soil could freeze and heave and certain types of soils swell with the presence of water.

The previous paragraph provides us with a description of factors (elements) that contribute to explain the selected response. Now, we need to move through the steps of the estimation. The first step is to identify the elements that play a role, and this signifies the need to have one measurable indicator per element. So here is our list of elements: truck traffic, subgrade soil and pavement layer strength and weather (water). As it turns out, we could estimate the number of equivalent single axles (ESALs) of a given weight (80 kN or 18,000 lb) per year from traffic counts.

There is an expression called structural number developed by the American Association of State, Highway and Transport Officials that combines the thickness and quality of materials of the pavement into one that provides an indication of how strong the pavement is. Finally, there is an expression called Thornthwaite Moisture Index which reflects the weather of a given region by estimating its degree of water arriving to the soil. Table 5.1 shows the process of identification of factors and response we are trying to model.

The next step is to identify the nature of the relationship between the factors and the response. First, we need to think of the response moving in one particular direction, which is typically chosen as the undesired direction; in this case, an increase in deterioration is also an increase in IRI (Table 5.1).

Next, we identify the movement on each variable that produces an incremental effect on the response. For the first factor, an increase in the number of trucks will damage the pavement and so it will deteriorate more. So we could identify a direct response.

For us, a direct response signifies that an increase on the factor returns an increase on the response. For the

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.