Raj V. Siddharthan

Validation of a Pavement Response Model Using Full-scale Field Tests

This paper provides details on a field verification program undertaken to validate the applicability of a finite-layer mechanistic model that has been selected to perform pavement response calculations. The proposed pavement response model is more realistic since it can handle moving traffic loading conditions, and it takes into consideration important factors such as vehicle speed and the non-uniform stress distributions (normal and shear) at the tire-pavement interface. Typically in pavement studies, the strain responses are required only at a few selected locations and for such problems the proposed approach is ideally suited. The applicability of the finite-layer approach and the ensuing computer program 3D-Moving Load Analysis (3D-MOVE) has been verified using two well-documented full-scale field tests (Penn State University test track and Minnesota road tests). As many as thirty eight measured strain responses were compared with those computed by 3D-MOVE and the comparison is very good. The computed impact of vehicle speed on the tensile strain at the bottom of the AC layer is consistent with those measured in both the field tests. Many mechanistic pavement response models are deficient since they do not incorporate the influence of vehicle speed and the complex tire-pavement contact stress distribution.

Finite-Layer Approach to Pavement Response Evaluation

The following aspects of the proposed continuum-based finite-layer model are presented: (1) theoretical basis, (2) applicability in evaluating pavement response, and (3) verification of predictive capability. The model incorporates important pavement response factors such as noncircular contact area, complex contact stress distributions (normal and shear), vehicle speed, and viscoelastic material characterization. The proposed model is much more computationally efficient than the moving-load models based on the finite-element method. A verification study, undertaken to validate the predictive capability of the proposed approach and its ensuing computer program, is also presented. The validation study includes (1) verification using results from ELSYM5, a widely used pavement response model, and (2) laboratory verification using two foam rubber models. Very good agreement was observed in both cases. Applicability of the proposed approach has also been demonstrated using realistic pavement loading. The proposed finite-layer approach is therefore an ideal tool for modeling the behavior of asphalt concrete layer and for studying the effects of vehicle speed and complex tire-pavement interface stresses on pavement response.

Expected Signature of Nonlinearity on Regression for Strong Ground-Motion Parameters

This study examines the response of soil profiles with nonlinear properties to several hundred synthetic seismograms, generated to represent rock ground motions from magnitude 6.4 and 7.0 scenario earthquakes. Two shear-wave velocity models (developed to represent Class CD and D sites with water table at 3 m) are tested. The computed ratios of peak ground acceleration (PGA) between the surface of the soil profile and the bedrock decreases with increasing PGA values. The transition from amplification to deamplification occurs at about 0.2–0.3 g. The spectral acceleration (SA) ratios, defined as the ratios of SA between the surface of the soil profile and the input, vary with the natural period of the oscillators. At short periods less than 0.3 sec, the behavior of the SA ratios is similar to the PGA ratios: amplification for lower input SA and deamplification for higher input SA level. At longer periods, the influence of the input SA level on SA ratio decreases, and deamplification is seldom observed. We define the mean trends of these calculations as rock motion modification curves (RMM curves). The use of these curves is as follows: a ground-motion relation on rock is multiplied by the RMM curve for that ground motion to obtain the expected ground-motion relation at the soil surface. This procedure is applied to six sets of empirical ground-motion relations. A majority of the empirical ground-motion relations are consistent with the RMM curves. In the best case, the comparisons indicate that the empirical soil site PGA and SA ground-motion relations are very close to the predicted curves at all epicentral distances. For both PGA and SA, the differences between the empirical and predicted curves are within one standard deviation of the empirical curves. It is quite encouraging that this physical model for soil behavior predicts the average characteristics of the surface motion, given the highly scattered nature of the data set.

Equivalent Loading Frequencies for Dynamic Analysis of Asphalt Pavements

AbstractAn investigation of the existence of predominant frequency, fp (or frequencies), and the ability to predict critical pavement responses in asphalt layers using those predominant frequencies has been presented. The study used an extensive database of computed pavement response histories of four different asphalt pavement structures (thin and thick) at two temperatures (21 and 40°C) subjected to a tandem axle load at three speeds (16, 65, and 97  km/h) using the pavement response analysis program 3D-Move Analysis. The conversion of load duration to frequency and the validity of using one response component (σzz) alone in the estimation of the pulse time (tp) were explored. Instead of focusing on only σzz, attention is given to all pavement response components (stresses and strains). In addition, verification of whether the use of a consistent set of fp value(s) can in fact adequately capture all components of pavement response has also been undertaken. The viscoelastic properties that are representa...

IMPACT OF HEAVY VEHICLES ON LOW-VOLUME ROADS

A recent study sponsored by the South Dakota Department of Transportation evaluated the impact of agricultural equipment on the actual response of low-volume roads. To meet this objective, one gravel pavement section and one blotter pavement section were instrumented in South Dakota and tested under agricultural equipment. Each section was instrumented with pressure cells in the base and subgrade and deflection gauges to measure surface displacement. Field tests were carried out during fall 2000, spring 2001, and summer 2001. Testing in different seasons offered the opportunity to evaluate the impact of heavy equipment on low-volume roads under variable environmental conditions: high and low temperatures and wet and dry conditions. Test vehicles included two Terragators, a grain cart, and a tracked tractor. The field testing program collected the pavement responses under five replicates of each combination of test vehicle and load level and under the 18,000-lb single-axle truck. Data were examined for repeatability, and the average of the most repeatable set of measurements was calculated and used in the analysis. The first part of the research evaluated the relative impact of the different equipment, defined as the ratio of pavement response under each combination of vehicle-load level over the pavement response under the 18,000-lb single-axle truck. Analysis of the pavement response ratios indicated that (a) the tracked tractor is not more damaging than the 18,000-lb single-axle truck, (b) Terragators 8103 and 8144 are more damaging than the 18,000-lb single-axle truck only when they are fully loaded, and (c) the grain cart is more damaging than the 18,000-lb single-axle truck only when it is loaded over the legal load limit. The second part of the research evaluated load equivalency factors for agricultural equipment on gravel and blotter pavements. Analysis of the load equivalency data indicated that an agency can effectively reduce the impact of agricultural equipment on a low-volume road by increasing the thickness of the base layer and keeping the load as close to the legal limit as possible.

SOIL-FOUNDATION-STRUCTURE BEHAVIOR AT THE OAKLAND OUTER HARBOR WHARF

The California Strong Motion Instrumentation Programs Loma Prieta records at Oakland Outer Harbor Wharf maybe used to study the free-field motions, the possible softening of soils surrounding the piles supporting the instrumented wharf, the determination of the motion on the instrumented wharf using free-field motion input and deflection-compatible lateral and vertical pile foundation stiffnesses, and conditions under which a soil-foundation interaction failure or structural failure of the batter piles might have developed.

Robust Deflection Indices from Traffic-Speed Deflectometer Measurements to Predict Critical Pavement Responses for Network-Level Pavement Management System Application

AbstractTraffic-speed deflectometers (TSD) are used in several countries to evaluate the pavement structural condition at the network level. Fatigue and rutting strains are commonly used as pavement critical responses in mechanistic-empirical design procedures to predict pavement structural performance. For successful pavement management system (PMS) application, robust indices that can be readily computed from TSD measurements and best related to the pavement critical responses should be identified. In this study, a comprehensive sensitivity analysis on deflection basin indices and their correlations with fatigue and rutting strains is performed using a range of pavement structures. A commercially available program was used in the first part of the study to compute dynamic deflection basins and evaluate the effects of material properties and vehicle speed on the indices. The indices that best relate to critical responses were identified from the software analyses and subsequently evaluated with a wider r...

Estimation of Stress Conditions for the Flow Number Simple Performance Test

The flow number simple performance test for asphalt mixtures was one of the final three tests selected for further evaluation from the 24 tests initially examined under the NCHRP 9-19 project. Currently, no standard triaxial testing conditions for the magnitude of the deviator and confining stresses have been specified. The objective of this research was to develop recommendations for the selection of the deviator and confining stresses that best simulate the stress conditions encountered in the pavement under traffic loads. Extensive mechanistic analyses of three different asphalt pavement structures subjected to moving traffic loads at various speeds and under braking and nonbraking conditions were conducted with the 3D-Move model. Prediction equations for estimating the anticipated deviator and confining stresses as a function of pavement temperature, vehicle speed, and asphalt mixtures stiffness have been developed. An increase of 40% was observed for the deviator stress when braking conditions were incorporated. A preliminary validation of the recommended magnitudes for the deviator and confining stresses on a field mixture from WesTrack showed consistent results between the flow number test results and field performance.

Investigation and Implications of Mechanically Stabilized Earth Wall Corrosion in Nevada

The Nevada Department of Transportation has more than 150 mechanically stabilized earth (MSE) walls at 39 locations. Wall reinforcement corrosion was found by accident during construction projects at two of these locations. The resulting investigations of these walls produced direct measurements of metal losses and electrochemical properties of the MSE-reinforced fill. One MSE wall was replaced with a cast-in-place concrete tie-back wall at great expense. A statistical analysis addresses the variability in measured corrosion and electrochemical data to predict corrosion behavior. The original MSE-reinforced fill approval electrochemical test results are significantly different from those measured in postconstruction investigations. A correlation has been developed between two distinctly different soil resistivity test methods: the Nevada T235B and AASHTO T-288 methods. Overprediction made by the Nevada T235B method has proven detrimental to the service lives of MSE walls. The internal stability analyses (using AASHTO 2007 load and resistance factor design specifications) of two remaining MSE walls at an intersection were also performed by using metal loss models developed from the statistical analysis. The findings of the study were subsequently extrapolated to other Nevada MSE walls. Through review of the reinforced fill approval data, suspect Nevada MSE walls have been identified relative to estimated reinforced fill aggressiveness.

Dynamic analyses of traffic speed deflection devices

Abstract Two traffic speed deflection devices (TSDDs) that measure surface deflections at posted traffic speeds (up to 80–96 kph) were evaluated through a recent Federal Highway Administration project that included field trials at the MnROAD facility. Four geophones were embedded near the pavement surface to measure surface deflections during field trials at each of three MnROAD cells. In addition, the MnROAD facility counted with numerous other sensors such as strain gauges to measure pavement responses and thermocouple trees to collect pavement temperature at various depths. For the implementation of TSDDs in any network-level pavement management system, it is important to utilise a proper analytical model that can accommodate moving load and viscoelastic properties of pavement layers in the simulation of TSDD measurements. The 3D-Move software was chosen for this purpose. The viscoelastic properties used for the asphalt concrete (AC) layer include dynamic modulus and damping coefficient as a function of frequency relevant to the temperature at the time of the MnROAD field trials. The field trials and available data represented realistic field case scenarios to validate once more 3D-Move specifically for TSDD measurements. The proposed dynamic analytical model provided a good match with a variety of independent pavement responses that included surface deflection bowls (measured using embedded geophone sensors) as well as horizontal strains at the bottom of the AC layers (measured using MnROAD sensors).