Evaluation of Sandwich Layer System of Flexible Pavements in Virginia

About the report:

The use of a weak sandwich layer in a four-layer system is common in the construction of flexible pavements, but the use of a sandwich layer in a three-layer system is in the experimental stage in Virginia. Theoretical and field studies have been carried out to determine how sandwiched layers affect the design and performance of pavement systems. It has been determined that a flexible sandwiched layer can be economically used in a four-layer system by providing an optimum thickness of the sandwiched material. The optimum thickness as determined in this investigation is the minimum thickness that will: (1) act as a cushion to prevent cracking in the soil cement subbase from reflecting to the surface, and (2) permit compliance with the density specifications. For crushed stone this thickness is 4". Use of this thickness should increase pavement life .and reduce construction costs. It has also been shown that the four-layer system pavements can be evaluated through elastic layered theory. A three-layer sandwich system of economical design and based on traffic requirements is recommended for low traffic volumes. In this case it has been determined that the optimum thickness is that which will (1) prevent reflection cracking through the untreated aggregate from the 6-inch soil cement layer, and (2) satisfy the density specification. These requirements can be met with a 3" to 4" layer of crushed stone with a prime and double seal. The evaluation of the four-and three-layer systems has shown that the strains and the resulting pavement life can be predicted from dynaflect deflections.

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