Browsing by Subject "Backcalculation"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Delineation of the Stiff Layer from FWD Measurements(Minnesota Department of Transportation, 2001-10) Guzina, Bojan; Cao, DongweiThe Falling Weight Deflectometer (FWD) is a widely used non-destructive test device for estimating the pavement stiffness properties. However, the conventional elastostatic interpretation of FWD measurements is generally associated with a number of inconsistencies. The purpose of this project is to develop a reliable and effective dynamic backcalculation method capable of estimating the location and properties of the permanent or seasonal stiff layer (as well as other pavement stiffness properties) from FWD measurements. The backcalculation method is implemented in the form of a user-friendly software that allows unedited deflection time histories from the FWD test to be used as an input to the back-analysis. The backcalculation scheme developed in this study is based on the Artificial Neural Network (ANN) approach and employs a three-dimensional multilayer viscoelastic dynamic model as a predictive tool.Item Development Of A Comprehensive Backcalculation Procedure For Rigid Pavement Design Parameters Using Slab-Edge Deflection Basins(2016-06) Paitich, SamuelBackcalculation of structural parameters for rigid pavements is commonly conducted with falling weight deflectometer (FWD) deflection basins measured at the center of slabs. Although a number of established techniques exist to backcalculate pavement parameters for the slab-center location, a reliable technique to backcalculate such parameters at the neighboring slab-edge location does not exist. The slab-edge location is critical to the design and management of rigid, concrete pavements because high stress levels and early signs of degradation originate at the slab edge. An edge backcalculation procedure accounting for the load transfer efficiency (LTE) of inter-slab joints is developed in this study. The proposed procedure is based on finite element modeling and dimensional analysis. Testing and validation of the edge backcalculation procedure is performed using FWD basins measured at the slab-edge location of in-situ pavements, along with measured LTEs, via the Long Term Pavement Performance (LTPP) program. Some prospective applications of the new procedure, in conjunction with the LTPP database, are presented. It is shown that the new edge backcalculation procedure is robust and satisfactory, particularly for pavements in good structural condition.Item Initial Characterization of Subgrade Soils and Granular Base Materials at the Minnesota Road Research Project(Minnesota Department of Transportation, 1995-12) Newcomb, David E.; Chadbourn, Bruce A.; Van Deusen, David A.; Burnham, Thomas R.This research was conducted on the behavior of materials at the Minnesota Road Research Project (Mn/ROAD), the construction of which was completed in 1994. Falling-Weight Deflectometer (FWD) tests were conducted on the test sections at all stages of pavement construction (pre-base, post-base, and post pavement). Deflection values were highly variable due to variability in surface condition, soil moisture content, density, and stressdependent effects. In general, backcalculated subgrade moduli tended to increase with increasing FWD sensor offset (decreasing stress). Post-base and post-pavement testing also indicated an apparent increase in subgrade modulus relative to pre-base values. Moduli values were also determined for granular base results. These results were compared to Dynamic Cone Penetrometer (DCP) penetration index values as well as to resilient moduli values from tests conducted on subgrade and granular base materials in the lab. The backcalculated subgrade soil modulus values compared well with the laboratory resilient modulus values, but no correlation was seen between backcalculated moduli and penetration index values. The results of this testing will provide a baseline for future analysis of the test sections at Mn/ROAD.Item 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.