Empirical design method

Often, empirical design methods are recommended only for preliminary studies. Realistically, designers frequently need also to apply the procedures to final designs because of lack of further information. 

The design traffic is expressed as cumulative equivalent standard loads (ESAL) over the design period. To convert daily traffic to ESAT, two different approaches related to the equivalency factors are considered. The first approach is applied to the empirical design method, for flexible pavements with only a thin asphalt layer (25 to 40 mm), and the second approach is applied to the mechanistic design method, for flexible pavements with asphalt, unbound or FfBM layers. 

The theoretical bases concerning mass transfer operations have been available in chemical engineering texts for many years and will not be developed further in this book. Rather, this book provides procedures for designing packed columns based on practical experiences acquired over 40 years that have produced satisfactory column performance. In many commercial situations, the application of rigorous theory is difficult because of the lack of sufficient data on physical or chemical properties. In addition, information on the desired operation may be available only from very small or laboratory-size columns with the resultant problems of scale-up. The empirical design methods presented in this book, in many cases, have been developed as a result of modifications to increase the capacity or efficiency of previously operating columns. These same methods also have been used to design new columns in similar services. 

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