Browsing by Author "Cao, Yuejian"

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    Full waveform analysis of ground penetrating radar measurements.
    (2011-08) Cao, Yuejian
    The purpose of this study is to extend the use of ground penetrating radar methodology towards a more reliable and accurate interpretation of pavement conditions. First, a complete set of 3D layered electromagnetic Green's functions is derived by way of transverse electric and transverse magnetic scalar potentials, featuring a new "direct" formulation for the field forms of the spectral Green's functions. The improper integrals underpinning the computation of the corresponding point-load solutions in the spatial domain are evaluated via the method of asymptotic decomposition, wherein the singular behaviors are entirely extracted and integrated analytically -- so that the remaining residual components can be computed effectively and accurately via adaptive numerical quadrature. It is also found that, in the spectral domain, the decay of the (numerically-integrated) residual field forms is commensurate to that of their potential-form counterparts, which eliminates the perceived gap between the computation of the field forms and respective potential forms of the Green's functions in the spatial domain. The effectiveness and accuracy of the proposed methodology is evaluated via comparison with relevant examples in the literature. Second, utilizing the derived electromagnetic Green's function for a layered system due to a horizontal electric dipole, the GPR scan can be simulated over a wide range of pavement profiles. Examples are provided for GPR simulation on a three-layer pavement system. By virtue of this forward model, the best match of the GPR scan in terms of the full waveform can be recovered within thousands of simulations via a optimization routine, where the in-situ layer parameters associated with the measurement are found to be equal to the simulation inputs. The accuracy of the interpreted layer thickness from the proposed scheme is verified by ground truth, with average error around 2.3% compared to 7.5% average error for the traditional method. In addition, the proposed scheme allows an evaluation of the relevant pavement properties with no prior assumptions or subjective image adjustments, unlike the traditional method.
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    Implementation of Ground Penetrating Radar
    (Local Road Research Board, Minnesota Department of Transportation, 2007-08) Cao, Yuejian; Dai, Shongtao; Labuz, Joseph; Pantelis, John
    The objective of this project was to demonstrate the capabilities and limitations of ground penetrating radar (GPR) for use in local road applications. The effectiveness of a GPR survey is a function of site conditions, the equipment used, and experience of personnel interpreting the results. In addition, not all site conditions are appropriate for GPR applications. GPR is a nondestructive field test that can provide a continuous profile of existing road conditions. GPR utilizes high-speed data collection at speeds up to 50 mph, thus requiring less traffic control and resulting in greater safety. GPR has the potential to be used for a variety of pavement applications, including measuring the thickness of asphalt pavement, base and sub-grade; assisting in the analysis of rutting mechanisms; calculating and verifying material properties; locating subsurface objects; detecting stripping and/or layer separation; detecting subsurface moisture; and determining depth to near-surface bedrock and peat deposits. These applications are discussed in reference to 22 projects completed throughout the State of Minnesota. Three reports were produced. (1) A technical summary report provides an overview of the project. (2) A comprehensive review of GPR applications for use on local roads is also available. (3) The final report describes the results of the GPR surveys.
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    Structural Evaluation of Asphalt Pavements with Full-Depth Reclaimed Base
    (Minnesota Department of Transportation, 2012-12) Tang, Shuling; Cao, Yuejian; Labuz, Joseph F.
    Currently, MnDOT pavement design recommends granular equivalency, GE = 1.0 for non-stabilized full-depth reclamation (FDR) material, which is equivalent to class 5 material. For stabilized full-depth reclamation (SFDR), there was no guideline for GE at the time this project was initiated (2009). Some local engineers believe that GE of FDR material should be greater than 1.0 (Class 5), especially for SFDR. In addition, very little information is available on seasonal effects on FDR base, especially on SFDR base. Because it is known from laboratory studies that SFDR contains less moisture and has higher stiffness (modulus) than aggregate base, it is assumed that SFDR should be less susceptible to springtime thawing. Falling Weight Deflectometer (FWD) tests were performed on seven selected test sections on county roads in Minnesota over a period of three years. During spring thaw of each year, FWD testing was conducted daily during the first week of thawing in an attempt to capture spring thaw weakening of the aggregate base. After the spring thaw period, FWD testing was conducted monthly to study base recovery and stiffness changes through the seasons. GE of SFDR was estimated using a method established by MnDOT using FWD deflections, and the GE of SFDR is about 1.5. The value varies from project to project as construction and material varies from project to project. All the materials tested showed seasonal effects on stiffness. In general, the stiffness is weaker in spring than that in summer and fall.