Date of Graduation


Document Type


Degree Name

Bachelor of Science in Civil Engineering

Degree Level



Civil Engineering


Hall, Kevin D


Dennis, Norman D

Second Reader

Elliott, Robert P.


In designing new pavements, engineers rely on many different measures to characterize the average traffic, climate and soil conditions of the region. Of those, soil conditions are the most elusive, but are also the most crucial for designing a pavement of proper thickness and stiffness. This problem is compounded when the design is for an overlay instead of a new pavement. For overlay designs, engineers require a quantitative characterization of the strength of the existing pavement as well as the underlying soil. Especially for new Mechanistic-Empirical design procedures, direct measures and/or estimates of pavement stiffness are essential inputs. A variety of methods exist for measuring the appropriate strength properties for soil, concrete and asphalt. The most traditional method - regardless of the material - is to retrieve a sample of the material from the field and use laboratory tests to determine the strength of the material, which is then considered representative for other materials near the location from which the sample was taken. The problem with this approach is that, in the field, construction materials experience a confining pressure from the other materials that surround them; even when carefully removed, the strength properties measured in the laboratory are not truly representative of the strength of the materials in the field. Nondestructive testing (NDT) refers to a collection of methods that are used to estimate material properties without removing or otherwise damaging the material. Generally, NDT is faster, cheaper and less intrusive to the traveling public. Two NDT methods, the falling weight deflectometer (FWD) and the spectral analysis of surface waves (SASW), have both become popular for their ability to estimate in-situ (in-place) stiffness properties of pavement materials. Each method measures a different local response (i.e. deflection or wave propagation) caused by a specific load. The measurement of the local response is then used to "backcalculate" the strength property that is desired. The appropriate backcalculation technique is different for each test, and for each test the appropriate technique varies according to the type of material on which the test is being performed and for which stiffness is sought. This study proposes to assess the validity of several backcalculation procedures associated with these two NDT methods and to compare their relative appropriateness in backcalculating pavement stiffness.