Estimation of Subgrade Modulus Using Falling Weight Deflectometer

A direct and simple method (YONAPAVE) for evaluating the structural needs of flexible pavements is presented. It is based on interpretation of measured falling-weight deflectometer (FWD) deflection basins using mechanistic and practical approaches. YONAPAVE estimates the effective structural number (SN) and the equivalent subgrade modulus independently of the pavement or layer thicknesses. Thus, there is no need to perform boreholes, which are expensive, time-consuming, and disruptive to traffic. Knowledge of the effective SN and the subgrade modulus together with an estimate of the traffic demand allows the determination of the overlay required to accommodate future needs. YONAPAVE’s simple equations can be solved using a pocket calculator, making it suitable for rapid estimates in the field. The simplicity of the method, and its independence from major computer programs, make YONAPAVE suitable for estimating the structural needs of a road network using FWD data collected on a routine or periodic basis along network roads. YONAPAVE can be used with increased experience and confidence as the basis for nondestructive testing structural evaluation and overlay design at the project level.

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A practical approach to falling-weight deflectometer (FWD) data reduction

Canadian Geotechnical Journal ◽

10.1139/t04-098 ◽

2005 ◽

Vol 42 (2) ◽

pp. 641-645 ◽

Cited By ~ 3

Author(s):

Dieter Stolle ◽

Peijun Guo

Keyword(s):

Mechanical Properties ◽

Shear Modulus ◽

Falling Weight Deflectometer ◽

Layer System ◽

Surface Loading ◽

Back Calculation ◽

Pavement Response ◽

Subgrade Modulus ◽

Falling Weight

The authors present a simplified methodology for preprocessing falling-weight deflectometer (FWD) data, which identify a pseudo-static pavement response to surface loading. This allows one to employ static analysis to back-calculate the mechanical properties of the pavementsubgrade system. It is shown that the subgrade modulus can be identified, independent of the details of the pavement structure itself, at least for a two-layer system. The quality of the effective shear modulus is sensitive to the value of Poisson's ratio selected.Key words: pavementsubgrade system, subgrade modulus, back-calculation, FWD.

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Interpretation of pavement deflection measurement data using an elastodynamic stochastic approach

Canadian Journal of Civil Engineering ◽

10.1139/l97-074 ◽

1998 ◽

Vol 25 (1) ◽

pp. 151-160 ◽

Cited By ~ 2

Author(s):

Mehdi Parvini ◽

Dieter FE Stolle

Keyword(s):

Finite Element ◽

Measurement Data ◽

Stochastic Approach ◽

Falling Weight Deflectometer ◽

Stochastic Finite Element ◽

Element Approach ◽

Subgrade Modulus ◽

Low Sensitivity ◽

Falling Weight ◽

Surface Deflections

Pavement deflection measurements, together with backcalculation procedures, are widely used to estimate the layer moduli of pavement-subgrade systems. Sensitivity analysis of a sample problem indicates that conclusions drawn from static analyses with regards to deflection sensitivity to variation in layer moduli may apply when characterizing uncertainty associated with the interpretation of the falling weight deflectometer (FWD) data. The uncertainty associated with the values of the backcalculated parameters from deflection data is investigated in this paper using an elastodynamic, stochastic finite element approach. The results of the simulations indicate that, in order to properly estimate surface layer moduli, loading frequencies higher than that of excitation by typical FWD loading are required. The low sensitivity of deflection uncertainty to random variations in surface modulus, when compared with that associated with subgrade modulus, is demonstrated to contribute to high variations in backcalculated surface modulus from measured surface deflections. Although focus is placed on uncertainties in elastic modulus and deflection, the methodology presented in the paper can be used to quantify uncertainties associated with other layer properties and pavement responses.Key words: stochastic, finite element, pavement deflection, elastodynamic, backcalculation, layer moduli, falling weight deflectometer test.

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Comparison of Simplified Elastostatic and Elastodynamic Models for Falling Weight Deflectometer Data Interpretation

Transportation Research Record Journal of the Transportation Research Board ◽

10.1177/0361198196154000110 ◽

1996 ◽

Vol 1540 (1) ◽

pp. 72-76

Author(s):

Dieter F. E. Stolle

Keyword(s):

Structural Integrity ◽

Data Interpretation ◽

Falling Weight Deflectometer ◽

System Parameters ◽

Dynamic Impedance ◽

In Situ Conditions ◽

Subgrade Modulus ◽

Falling Weight

The characterization of pavements and subgrades by interpreting falling weight deflectometer data is discussed. Two backcalculation strategies—one based on an approximate elastostatic model and the other on dynamic impedance for a two-layered pavement subgrade system—are presented and applied to data collected along experimental pavement sections. Both strategies characterize the structural integrity of a pavement by equivalent asphalt thickness and the stiffness of the subgrade by effective subgrade modulus. It is indicated that, although both procedures predict similar trends, the values of the system parameters differ, particularly the equivalent asphalt thickness. The net pavement-subgrade stiffness predicted using dynamic impedance was found to be consistently higher than that obtained with the elastostatic model for the data studied. The capability of dynamic impedance to identify variations of in situ conditions along a section of roadway is also demonstrated.

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