Carlos E. Cary

Bio: Carlos E. Cary is an academic researcher from Federal Aviation Administration. The author has contributed to research in topics: Subgrade & Pavement engineering. The author has an hindex of 4, co-authored 15 publications receiving 241 citations. Previous affiliations of Carlos E. Cary include Arizona State University & North Carolina State University.

Resilient modulus for unsaturated unbound materials

Abstract: The suitability of the current resilient modulus test protocol (NCHRP 1-28A) for its application to unsaturated soils was assessed. Modifications to the stress state conditions of the protocol are necessary due to the axis-translation needed during the test when measuring matrix suction. This study presents the modulus of unbound materials resulting from tests performed under unsaturated soil conditions. Two different materials were tested. The base material was tested under drained and undrained boundary conditions, while the subgrade was tested under drained boundary condition. The results allowed for the enhancement of the Universal Model for resilient modulus prediction by incorporating suction as a stress state. This model predicts the resilient response of unbound materials as a function of external stress state and matrix suction levels and therefore, it is independent of moisture variation.

Enhanced Model for Resilient Response of Soils Resulting from Seasonal Changes as Implemented in "Mechanistic–Empirical Pavement Design Guide"

Abstract: The present study deals with the revision of the current model in the Mechanistic-Empirical Pavement Design Guide (MEPDG) used to predict the environmental factor for unfrozen unbound materials (FU), which is used to adjust the resilient response of soils resulting from seasonal changes. A large database with data from the existing literature and studies at Arizona State University was developed to evaluate the model. The results suggest that the environmental factor is underestimated for fine-grained materials with high plasticity under dry (arid) conditions. However, insufficient data were available to enhance the FU models for wetter conditions. Three fundamental factors that may have impacts on the FU values were evaluated in this study: stress state, compaction energy (soil density), and soil type. The stress state was found to have little to no impact on the predictions of FU. But density changes and soil type were found to be important. The potential for soil index properties to be predictive varia...

Pore Water Pressure Response of a Soil Subjected to Traffic Loading under Saturated and Unsaturated Conditions

Abstract: This study presents the results of one of the first attempts to characterize the pore water pressure response of soils subjected to dynamic loading under saturated and unsaturated conditions. The resilient modulus, which captures the soil stiffness under dynamic loading, is a critical parameter for pavement design. It has been recognized that the development of pore water pressure contributes to modulus degradation. Several efforts have been directed to model the effect of air and water pore pressures upon the modulus. However, none of them considered dynamic changes in pressures but rather were based on equilibrium values corresponding to either initial or final conditions. A testing program was conducted to characterize the pore water pressure response of a clayey sand subjected to dynamic loading. Using the results, models capable of predicting the cumulative excess pore pressure under both saturated and unsaturated conditions were proposed. Findings regarding the influence of the controlled va...

Resilient Modulus Testing for Unsaturated Unbound Materials

Abstract: A limited number of equations have been proposed to incorporate moisture variation effects on resilient modulus; however, the models available are in general based on empirical correlations and not on fundamental stress state analysis. The suitability of the current available resilient modulus test protocol for its application on unsaturated soils was assessed. Several modifications in the stress state conditions of the "Harmonized Test Methods for Laboratory Determination of Resilient modulus for Flexible Pavement Design, NCHRP 1-28A" protocol are necessary when measuring matric suction due to the axis-translation needed during the test. This study presents the results of a preliminary exploration into the response of resilient modulus of unbound materials subjected to a full stress state for unsaturated soil conditions. Three different materials were tested, one granular base and two subgrade materials. The granular base material was tested under both, measured (drained conditions) and controlled (undrained conditions) matric suction modes. The two subgrade materials were tested under measured matric suction mode. The results were used to enhance the widely known Universal Model for resilient modulus prediction by incorporating matric suction as a fundamental variable within the stress state for unsaturated soils. This model predicts the resilient response of unbound materials at different stress states and matric suction levels. Thus, a unique set of regression constants independent of moisture variation can be obtained for any material.

Unsaturated Soil Modeling for Airfield Pavement Design

Abstract: This study presents results of one of the first in situ assessment studies on the use of the Mechanistic-Empirical Pavement Design Guide (M-EPDG) methodology applied to the design of airfield pavements. The M-EPDG’s Enhanced Integrated Climatic Model (EICM) introduces unsaturated soil modeling techniques into the prediction of moisture changes in the unbound materials throughout the life of pavements for highway conditions. Field soil moisture content changes measured at several Air Force bases in the U.S. were collected from historic studies and compared to MEPDG predictions. Details and outcomes from this comparative study are presented herein. Despite significant differences in structural dimensions and geometric design, this study showed that the EICM promises to be a suitable predictive methodology to be adapted for airfield pavement conditions and has the potential to become a tool for the incorporation of unsaturated soil modeling for the design of airfield pavements, provided that several enhancements are made to the model applied to highway design. Also, a discussion on possible sources of uncertainty in the predictions of the MEPDG and a series of alternative revisions and enhancements required to incorporate the EICM with current airfield pavement design methodologies are presented.

Resilient modulus for unsaturated unbound materials

Abstract: The suitability of the current resilient modulus test protocol (NCHRP 1-28A) for its application to unsaturated soils was assessed. Modifications to the stress state conditions of the protocol are necessary due to the axis-translation needed during the test when measuring matrix suction. This study presents the modulus of unbound materials resulting from tests performed under unsaturated soil conditions. Two different materials were tested. The base material was tested under drained and undrained boundary conditions, while the subgrade was tested under drained boundary condition. The results allowed for the enhancement of the Universal Model for resilient modulus prediction by incorporating suction as a stress state. This model predicts the resilient response of unbound materials as a function of external stress state and matrix suction levels and therefore, it is independent of moisture variation.

Estimation of Resilient Modulus of Unbound Aggregates Using Performance-Related Base Course Properties

Abstract: This study aims at developing an accurate and efficient methodology to estimate the resilient modulus of unbound aggregates. First, a new resilient modulus model is proposed to incorporate the moisture dependence of the resilient modulus in addition to the stress dependence in existing models. Second, prediction models are developed to conveniently and accurately determine the coefficients in the proposed model. In order to characterize the moisture dependence of unbound aggregates, the degree of saturation and the matric suction parameter are added into the proposed model. The soil-water characteristic curve (SWCC) is used to determine the matric suction value at any given moisture content. The moisture dependence of the model is validated for selected materials with different moisture contents. In order to develop prediction models for the coefficients in the proposed model, laboratory experiments and multiple regression analysis are conducted on 20 different base course materials. The laborator...

Enhanced Model for Resilient Response of Soils Resulting from Seasonal Changes as Implemented in "Mechanistic–Empirical Pavement Design Guide"

Abstract: The present study deals with the revision of the current model in the Mechanistic-Empirical Pavement Design Guide (MEPDG) used to predict the environmental factor for unfrozen unbound materials (FU), which is used to adjust the resilient response of soils resulting from seasonal changes. A large database with data from the existing literature and studies at Arizona State University was developed to evaluate the model. The results suggest that the environmental factor is underestimated for fine-grained materials with high plasticity under dry (arid) conditions. However, insufficient data were available to enhance the FU models for wetter conditions. Three fundamental factors that may have impacts on the FU values were evaluated in this study: stress state, compaction energy (soil density), and soil type. The stress state was found to have little to no impact on the predictions of FU. But density changes and soil type were found to be important. The potential for soil index properties to be predictive varia...

Model for predicting resilient modulus of unsaturated subgrade soil using soil-water characteristic curve

Abstract: Soil suction (ψ) is one of the key factors that influence the resilient modulus (MR) of pavement subgrade soils. There are several models available in the literature for predicting the MR–ψ correla...

State-of-the-Art: Prediction of Resilient Modulus of Unsaturated Subgrade Soils

Abstract: In this paper, equations that were proposed in the literature over the past four decades to estimate or predict the variation of the resilient modulus with respect to soil suction for pavement base-course materials and subgrade soils are summarized into three groups: (1) empirical relationships, (2) constitutive models incorporating the soil suction into applied shearing or confining stresses, and (3) constitutive models extending the independent stress state variable approach. Two equations selected from each of the groups (a total of six equations) are used to predict the resilient modulus–soil suction correlations for three compacted subgrade soils. Strengths and limitations of these widely used equations are discussed based on the comparisons between the measurements and predictions. The key objective of the state-of-the-art research summarized in this paper is for assisting practicing engineers to choose suitable equations for the rational prediction of the resilient modulus taking into accou...