Failure Criteria Evaluation and Shear Strength of Granular Base Course for Thin Flexible Pavement

Abstract

This study aims to report theoretically the possible approach of confinement evaluation of unbound granular base course using the finite element method and the permanent deformation evaluation of crushed rock under repeated cyclic loading triaxial tests performed at different stress levels in order to implement current pavement material test algorithm. Road rutting is the main cause of damage in flexible pavements which the most explanation is crushed rock still not obviously understanding about plastic deformation under service load. The permanent deformation that accumulates under the repeated loading can normally describe and define the types of responses. Theoretical approach of the unbound granular materials (UGMs) permanent deformation used to describe the behaviour of tested materials subject to repeated loading triaxial (RLT) tests by macro-mechanical observations of the UGMs response. The plastic limit is able to use predict the accumulated plastic deformation in the UGMs layer of road pavement or whether deterioration will be unacceptable. Tested material will determine the limit of working stress level and the plastic deformation should be considered in this behaviour. As is well known, triaxial and California bearing ratio (CBR) test are used to simulate the real condition of pavement materials under traffic loads by using static confinement and actuator loads. However static confining conditions in pavement structure occur only when no vehicle travels.As the effects of traffic loads and material attributes are generated when vehicles travel, horizontal stress and confinement behaviours of pavement structure were determined. CBR sample of crushed rock base was modelled using finite element in order to study the confining pressure behaviour of such material subjected to applied stress. During the load application procedure, a single wheel with a standard pressure of 750 kPa was selected to compare with the analysed strength of crushed rock base (CRB) based on laboratory test results. The results showed that horizontal stress of base course layer consists of overburdened soil and passive force from applied stress. When vehicle travels pass observed point, horizontal pressures of base course layer increase from overburdened weight and complete with passive force effect depend on applied stress and its internal friction. Seemingly, the conventional triaxial test results with finite element back calculation are able to describe the confining behaviour of unbound granular base course. In this study, triaxial tests and the confinement evaluation using finite element approach on an unbound granular base course were introduced to explain and define its limited use in order to implement the current performance test of unbound granular base course material.