This study investigated relationships between field and laboratory moduli in relation to the pavement thickness design values and how individual foundation layers affect the composite moduli of pavement foundation systems.

Currently, common practice is to determine pavement foundation layer construction quality from unit weight and moisture values, which do not necessarily relate to pavement thickness design input values (e.g. modulus). Moduli, however, provide direct, quantifiable values that describe the physical characteristics of foundation materials and can be related to pavement system performance. Resilient moduli are used in AASHTO 1993 pavement design manual and the current MEPDG.

Laboratory prepared specimens were studied to compare the effects of different conditions found in situ (e.g., moisture and dry unit weight variances). To simulate layered condition in the field, a method was developed to prepare and test layered composite samples. Previous laboratory tests have focused on single layer moduli, whereas in situ tests encompass several layers of pavement foundation systems. Composite samples better simulated the layering effects found in situ. In situ test results were also compared to composite sample laboratory test results to evaluate the relationships between the test methods.

Key results from this investigation demonstrated that 1) composite behavior differs significantly from single sample behavior (i.e., weak lower layers significantly affect the composite moduli); 2) laboratory composite resilient moduli can be estimated from single material resilient moduli; 3) undrained shear strength properties were significantly correlated to laboratory resilient moduli; and 4) laboratory, in situ, and design moduli are poorly related (i.e., between measured laboratory and empirically calculated resilient moduli, as well as between measured elastic and resilient moduli).