The findings of an extensive literature survey on the structural response of unbound aggregates are discussed in two companion papers. In this paper, a state of the art is presented on resilient stress-strain characteristics of such materials, as well as different modeling techniques. The resilient response of aggregates is affected by several factors with varying degrees of importance. These are presented, and different views on the impact of each individual factor are discussed. Research efforts in the past have resulted in different math- ematical models for predicting the resilient response of aggregates under repeated traffic-type loading. The models found in the literature are listed, and their advantages and shortcomings are reviewed. The permanent strain characteristics of unbound aggregates are considered in a separate companion paper.

State of the art .i : r esilient response of unbound aggregates

Application of soil mechanics principles to the design of pavement foundations, the design of complete pavements and to their structural evaluation'in-service' has lagged some way behind knowledge accumulated through research. Present design methods are generally empirical and often based on use of the California Bearing Ratio test, which was abandoned in California some fifty years ago. The soil mechanics problem is one of understanding how soils and granular materials respond to repeated loading and applying this knowledge to pavement design with the aid of appropriate theoretical analysis and an understanding of failure mechanisms. Non-linear stress-strain characteristics are a particular feature of the problem and have to be catered for in design and evaluation. Various ‘tools’ are available to assist the pavement engineer. These include theoretical analysis, laboratory testing apparatus, field testing and full-scale trials with appropriate instrumentation. The resilient and permanent strain response ...

Soil mechanics in pavement engineering

This report evaluates test procedures for measuring the fatigue response of asphalt paving mixtures, and summarizes current knowledge of the factors that influence fatigue response. Available test methods are classified, and criteria used to evaluate each method for its potential use as a laboratory standard are discussed. The 3 most promising methods are considered to be simple flexure, diametral fatigue, and tests based on fracture mechanics principles. Factors affecting fatigue repsonse include specimen fabrication, mode of laoding, mixture variables, and loading and environmental variables. Mode of loading, typically either controlled-stress or controlled-strain for laboratory testing, is one of the primary factors affecting fatigue response. Air void content and temperature, both affecting mixture stiffness, may have more significant influence on fatigue repsonse than any other variable. Many mixture, load, and environmental factors also influence fatigue respose and must be considered both in the development of test protocols and in the determination of asphalt and mixture properties that are essential for fatigue-resistant pavements.

Summary report on fatigue response of asphalt mixtures

Mechanistic pavement design procedures based on elastic layer theory require the specification of elastic moduli for each material in the pavement section. Repeated load tests yielding a resilient modulus are frequently used to characterize the soil subgrade. Due to difficulties associated with cyclic testing, approximate methods are often used for design estimates of resilient modulus. These approximations are often based only on shear strength measures and do not account for the dependence on the magnitude of cyclic deviator stress. A procedure is described to relate the soil-index properties and the moduli obtained from unconfined compression tests, to resilient modulus. Two statistical models are described and demonstrated for 11 soils from throughout the state of Tennessee. One model provides an estimation of the breakpoint resilient modulus, or the modulus at a deviator stress of 6 psi (41 kPa). The second model provides a general nonlinear relationship for the modulus of fine-grained soils as a function of deviator stress. Both models are demonstrated for a range of soils and are shown to provide a good characterization of the response for the soils investigated. Similar relationships can be developed for other subgrade soils, and may prove useful to agencies that use deterministic pavement design procedures, but lack the capability for high-production repeated-load testing.

Estimation of subgrade resilient modulus from standard tests

The Austroads publication Guide to Pavement Technology, Part 2: Pavement Structural Design is intended to assist those required to plan and design new pavements. It was originally produced in 1987 as a result of review of the NAASRA Interim Guide to Pavement Thickness Design (1979). In 1992, the Austroads Pavement Design Guide was revised to include an updated procedure for the design of rigid pavements and also relevant portions of Chapter 6 (Pavement Materials) and Chapter 7 (Design Traffic). An essential element in the use of the Guide is a thorough understanding of the origins of the design procedures, their scope and limitations. Accordingly, this report contains the following five technical reports detailing the technical basis of: 1. Chapter 1: 1992 Guide procedures for the design of flexible pavements; 2. Chapter 2: 1992 Guide procedures for design of rigid pavements; 3. Chapter 3: Guide to Pavement Technology Part 2 Design of flexible pavements; 4. Chapter 4: Guide to Pavement Technology Part 2 Design of rigid pavements; 5. Chapter 5: Guide to Pavement Technology Part 2: Development of design charts for lightly trafficked roads

Technical basis of Austroads Guide to Pavement Technology: part 2: pavement structural design

THE PURPOSE IS TO DEFINE BETTER THOSE PROPERTIES OF GRANULAR BASE MATERIALS THAT CONTRIBUTE TO THE RESILIENT RESPONSE OF PAVEMENT STRUCTURES. A STUDY IS INCLUDED OF THE INFLUENCE OF AGGREGATE DENSITY, AGGREGATE GRADATION (PERCENT PASSING NO. 200 SIEVE), AND DEGREE OF SATURATION ON THE RESILIENT RESPONSE OF TWO AGGREGATES REPRESENTATIVE OF THOSE USED IN THE CONSTRUCTION OF ASPHALT CONCRETE PAVEMENTS. TESTS CARRIED OUT IN TRIAXIAL COMPRESSION, CONSISTED OF APPLYING REPEATED AXIAL STRESSES WITH REALISTIC STRESS HISTORIES AT A FIXED FREQUENCY AND AT A LOAD DURATION REPRESENTATIVE OF THAT EXPECTED IN THE FIELD. FOR BOTH GRANULAR MATERIALS, THE RESILIENT MODULUS INCREASED CONSIDERABLY WITH AN INCREASE IN CONFINING PRESSURE AND ONLY SLIGHTLY WITH AN INCREASE IN AXIAL STRESS. POISSON'S RATIO INCREASED WITH A DECREASE IN CONFINING PRESSURE AND AN INCREASE IN REPEATED STRESS. THE RESILIENT MODULUS AND POISSON'S RATIO WERE ALSO AFFECTED TO LESSER DEGREES BY DENSITY, PERCENT PASSING THE NO. 200 SIEVE, AND DEGREE OF SATURATION. AN ANALYSIS OF A CONVENTIONAL ASPHALT CONCRETE PAVEMENT OVER A SANDY CLAY SUBGRADE INDICATED THAT REASONABLE CHANGES IN THE MODULUS OR POISSON'S RATIO OF THE GRANULAR BASE LAYER CAN RESULT IN CONSIDERABLE CHANGES IN THE RESPONSE OF THE PAVEMENT STRUCTURE TO LOAD. /AUTHOR/

C L Monismith

Papers

Factors influencing the resilient response of granular materials