Evaluation of the compactness of subbase and base geomaterials by using stiffness

Stiffness of soil that is defined as ratio of load to deflection depends on some physical properties such as compactness and water content. The purpose of this research study is to use stiffness for estimating compactness of granular geomaterials that are used as subbase and base courses of roads. In this research study, the stiffness of soil samples was determined according ASTM D6758-08 test method by using electro-mechanical device. The dry density of the compacted soil was determined by sand-cone method in the field. More than 80 laboratory and in situ tests were performed. The obtained stiffness data was used to establish a relationship between stiffness, compaction ratio and water content. The results showed that there is a strong relationship between the stiffness, compaction ratio and water content. Also, the result of validation showed that there is good correlation between in situ and laboratory tests results.