Imad Basheer

Selection of Methodology for Neural Network Modeling of Constitutive Hystereses Behavior of Soils

Classic constitutive modeling of geomaterials based on the elasticity and plasticity theories suffers from limitations pertaining to formulation complexity, idealization of behavior, and excessive empirical parameters. This article capitalizes on the modeling capabilities of neural networks as substitutes for the classic approaches. The neural network-based modeling overcomes the difficulties encountered in understanding the underlying microscopic processes governing the materials behavior by redirecting the efforts into learning the cause-effect relations from behavioral examples. Several methodologies are presented and cross-compared for effectiveness in approximating a theoretical hysteresis model resembling stress-strain behavior. The most effective methodology was used in modeling the constitutive behavior of an experimentally tested soil and produced models that simulated the real behavior of the soil with high accuracy. Although these models are empirical, they are retrainable and thus, unlike classic constitutive modeling techniques, can be revised and generalized easily when new data become available.

CalME, a Mechanistic-Empirical Program to Analyze and Design Flexible Pavement Rehabilitation

A computer program known as CalME has been developed for analysis and design of new flexible pavements and rehabilitation of existing pavements. The paper describes the overlay design procedure and the calibration of the models for reflection cracking and permanent deformation through heavy vehicle simulator (HVS) tests. To simplify the input process, the program includes databases for traffic loading, climatic conditions, and standard materials. A companion program was developed for backcalculation of layer moduli, and the results may be automatically imported into the CalME database. The program incorporates the existing, empirical California Department of Transportation design methods as well as an incremental–recursive analysis procedure based on the mechanistic–empirical method. The effects of different pavement preservation and rehabilitation strategies on pavement damage may be studied with several options for triggering timing of placement. The influence of within-project variability on the propagation of damage can be evaluated using Monte Carlo simulation. The program also permits importation of the results of HVS or track tests into the database and simulation of the experiments on the computer. This feature is useful for the calibration of the mechanistic–empirical models but may also be used for in-depth interpretation of accelerated pavement testing results. An HVS experiment that was used for calibration of the reflection cracking and the permanent deformation models is described.

Mechanistic-Empirical and Life-Cycle Cost Analysis for Optimizing Flexible Pavement Maintenance and Rehabilitation

In this study, an attempt was made to evaluate and select an optimal Maintenance and Rehabilitation (MR Maintenance; Rehabilitation; Life cycles; Costs. Author keywords: Mechanistic; Empirical; Perpetual; Pavement; Maintenance & rehabilitation; Preservation; Life cycle cost.

CalBack: Enhancing Caltrans Mechanistic-Empirical Pavement Design Process with New Back-Calculation Software

In 1996, California Department of Transportation (Caltrans) initiated an extensive project to develop mechanistic-empirical (ME) pavement design and analysis tools, which will help state design engineers incorporate the impact of new products and technologies, increased traffic volumes and axle loading, and variable climatic conditions. As part of the development of new ME design procedures, Caltrans is developing a suite of dedicated software. CalME is a ME design program for flexible pavements that parallels the NCHRP 1-37A (MEPDG) and is calibrated for California conditions. CalBack is a sophisticated back-calculation program that contains specific features pertinent to California and is designed to work standalone, or in concert with CalME. CalBack is a unique and important addition to the existing knowledge base in that it possesses multiple data input/output methods, several new analytical modeling methods, and numerous user performance options. This paper describes the successful development and implementation of CalBack in three ways: (1) why and how Caltrans developed CalBack; (2) how CalBack functions; and (3) representative studies that show how well the software performs. Application of CalBack in several California projects, including the case studies presented in this paper, has shown that back-calculated moduli for different layers in the flexible and rigid pavement systems agreed reasonably well with laboratory measured values. Furthermore, the importance of avoiding temperature gradients when evaluating portland cement concrete pavements with the falling weight deflectometer is also well captured by CalBack.