Development of models for the interpretation of the dynamic cone penetrometer data Me ´lanie Boutet a1 , Guy Dore ´ b *, Jean-Pascal Bilodeau b2 and Pascal Pierre b3 a Roche Lte ´e Groupe-Conseil, Que ´bec, Canada G1W 4Y4; b Department of Civil Engineering, Laval University, Que ´bec, Canada G1V 0A6 (Received 10 September 2008; final version received 20 April 2010) This study deals essentially with the development of models that describe the relations between the strength properties of soils (undrained shear strength obtained with a vane tester) on one hand, and the resilient properties (back-calculated modulus obtained with deflection tests) on the other hand, and the penetration index values obtained with the dynamic cone penetrometer. Laboratory tests were performed on five coarse-grained reconstituted soils. Also, field tests were performed on 10 fine-grained soils and on each of the four subgrade soils of the Laval University Experimental Test Road Site. The results obtained in the laboratory and in the field were compared and analysed in order to develop the relations between the strength and the resilience for different types of soils. Using a statistical analysis with three different sophistication levels, reliable correlations that include explanatory variables were developed. Keywords: mathematical correlations; penetration index; modulus; strength; resilience; geotechnical properties 1. Introduction The dynamic cone penetrometer (DCP) is a very useful tool for pavements structural evaluation or for pavement design studies. Indeed, the DCP is often used in pavement engineering for the evaluation of the characteristics (thickness and properties) of each layer of the pavement structure. The DCP is widely used in many countries for its simplicity, portability, low cost and capacity to obtain data allowing the rapid determination of in situ mechanical properties. This bearing capacity tool and test method are also standardised (ASTM 2003). In fact, when combined with correlations, the DCP allows the determination of basic characteristics of the pavement layers without having to perform long and expensive destructive tests. In the literature, there are correlations that establish relationships between the dynamic cone penetration index (DCPI) and some parameters such as the California bearing ratio (CBR) and the elastic, resilient and back-calculated modulus commonly used in pavement design. Although CBR tests are less used nowadays, the correlation that relates directly the DCPI values to modulus is valid only for a limited range of conditions. This is an important fact, as the American Association State Highway and Transportation Officials (AASHTO 1993) suggests using the resilient modulus of soils for pavement design. Moreover, only few relationships found in the literature consider soil character- istics such as Atterberg limits, water content and density. Because there are gaps in the understanding of the relationship between the strength (plastic or viscoelastic domain) and the resilience (elastic domain) of soils, the elaboration of complete models representative of soils typically found in the province of Quebec (Canada) is fundamental to ensure a good exploitation of the data obtained with the DCP. Table 1 presents a summary of the main correlations found in the literature between the DCPI and the elastic, resilient and back-calculated modulus. 2. Objective The main objective of this study is to develop models that relate the strength properties of soils (undrained shear strength obtained with a vane tester) on one hand, the resilient properties (back-calculated modulus obtained with deflection tests) on the other hand, and the penetration index values. More specifically, the objective is to define the relationship between the strength and the resilience for different kinds of soils and to see if it is possible to make groupings. The relationships should include parameters that take into account soil characteristics. 3. Experimental programme 3.1 Tests methodology and parameters considered in models development The experimental programme was developed based on previous work and, among others, on a study conducted by Lambert et al. (2006) on the assessment of coarse granular pavement foundation materials. It is divided into two main parts. The first one consists in laboratory testing of five coarse-grained reconstituted soils and the second one, in field testing of 10 fine-grained soils and the four subgrade soils of the Laval University Experimental Test Road Site ISSN 1029-8436 print/ISSN 1477-268X online q 2011 Taylor & Francis DOI: 10.1080/10298436.2010.488727 http://www.informaworld.com *Corresponding author. Email: guy.dore@gci.ulaval.ca International Journal of Pavement Engineering Vol. 12, No. 3, June 2011, 201–214