Table 4 (below) lists soil characteristics and their approximate k values. It is suggested that k not exceed 200 lb/in.³ (54 MPa/m), and values of 150-175 lb/in.³ (40-48 MPa/m) are generally suitable for design purposes. Either type of material offers good support values as defined in terms of the Westergaard modulus of subgrade reaction (k). Unless precautions are taken as described in “Clays and Highly Expansive Soils” (see below), the permeable sub-base can be either 1-inch (25 mm) maximum-size aggregate, or a natural subgrade soil that is predominantly sandy with moderate amounts of silt, clay, and poorly-graded soil.
The design of a pervious pavement base should normally provide a 6-to-12-inch (150-300 mm) layer of permeable sub-base. Regardless of the procedure used, guidelines for roadbed (subgrade) soil properties, pervious concrete materials characteristics, and traffic loads should be considered. Pervious concrete pavements can be designed using either a standard pavement procedure (AASHTO, WinPAS, PCAPAV, ACI 325.9R, or ACI 330R) or using structural numbers derived from a flexible pavement design procedure. Laboratory research in these areas has only recently begun. Projects with good to excellent performance over service lives of 20 to 30 years provide a great deal of empirical evidence related to material properties, acceptable subgrades, and construction procedures. Although these characteristics differ from conventional concretes, they are predictable and measurable. Pervious concrete is a unique material that has a matrix and behavior characteristics unlike conventional portland cement concrete or other pavement materials. Procedures described provide a rational basis for analysis of known data and offer methods to determine the structural thickness of pervious concrete pavements.
This section provides guidelines for the structural design of pervious concrete pavements. Pervious Pavement Design Structural Design Considerations Design | Hydrological | Structural
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