Implications of reliability in mechanistic/empirical pavement design applications

Abstract

At present there are many design procedures for both asphalt and concrete pavement structures. The object of any one of these design procedures being to produce a quality riding structure that will satisfy the design engineer and the riding public. A quality riding structure can be achieved if the material characteristics, loading characteristics, and environment are known to the engineer before the design phase commences. The issue at hand is not which of the many design procedures is correct but of design consistency between concrete and asphalt pavements. Unfortunately, there are no design procedures available that properly address the concern of design comparability. Therefore, a methodology must be introduced and is introduced within that addresses this issue. One way to solve the problem is by using mechanistic/empirical models in designing both pavement types and applying the same rules of reliability to both as well. The main characteristic of a mechanistic/empirical design is its capability to yield a functional pavement design for any region, soil condition and environment using the same design criteria. A very important aspect of the design method is the design reliability. A standard definition of reliability that applies to engineering is that; reliability is the probability that an engineered system will perform its required function adequately for a specified period of time under the stated conditions. Reliability is important because of the uncertainty involved with the materials, construction and environment associated with the pavement. Each of the design inputs (i.e. pavement materials) are stochastic in nature and have a probability distribution associated with them. If the selection of a pavement type is to be achieved with equity in mind then the two design procedures must handle design reliability properly and consistently. Since there is uncertainty in any engineering design procedure, the proper measure of reliability must be based in terms of probability. If the structural design process between two pavement types is similar and the design reliability is handled consistently then two alternatives may be compared in terms of their life cycle costs and a judgement may be made as to which is the most suitable structure.