Laboratory assessment of pavement foundation materials
The main aim of this research was to improve laboratory test methods for describing pavement foundation materials so that analytical design based on appropriate mechanical parameters of materials could be performed in practice. The study started by assessing the relevance of currently available methods to describe materials in pavement foundations and reviewing factors influencing the responses of these materials to repeated loading. Two simplified repeated load triaxial apparatuses of different sizes have been developed and their capabilities in characterizing materials in sub-base and sub grade layers have been examined. The large one is for specimens of size 280 mm diameter and 560 mm high and is suitable for full scale Department of Transport Type 1 sub-base granular materials. The small one is for cohesive soil specimens, either recompacted or undisturbed, with a diameter of 103 mm and height of 206 mm. Both apparatuses are equipped with simple loading mechanisms, user-friendly computer data acquisition systems and high precision on-sample, but easy to fix, instrumentation to monitor axial and radial displacements. A complete testing method necessitated the provision of the associated testing techniques. The whole test, including aggregate and soil preparation and testing, was designed to be conducted by one person. Development of the test procedures is detailed. Evaluation of the simplified repeated load apparatuses and the testing techniques involved testing 13 aggregate specimens and more than 26 soil specimens. Furthermore, comprehensive preliminary tests have been performed on the tested materials to provide background information which enabled results from the simplified repeated load triaxial apparatuses to be assessed in detail. For unbound granular materials, the tests included a series of particle examinations and shear box testing. For soils, besides classification tests, the soil suctions and the permanent deformation development under wheel loading were examined. To check the reliability of the two simplified facilities, tests were also carried out on pre-existing sophisticated repeated load triaxial apparatuses. Comparison of aggregate test results has enabled further understanding of the effects on resilient strain, permanent deformation and compressive strength of grading, density, shape, surface profile, surface friction and material type to be gained. Effects from waveform and frequency of load pulses were also discussed. For-soils, sufficient test results not only allowed different materials to be compared but also permitted models to describe resilient strain behaviour and permanent deformation development to be developed.