Showing papers by "Nick Thom published in 2021"

Prediction of resilient modulus with consistency index for fine-grained soils

Abstract: It is crucial to accurately predict the resilient modulus of subgrade soils. The modulus is influenced by a soil’s properties, as characterised by the soil’s moisture index values. Thus, it may be feasible to predict resilient modulus based on the soil index. Consistency index, as one of the common soil indices, incorporates plasticity index and moisture content. Therefore, this study aims to establish its relationship with resilient modulus. By collecting and analysing the previous testing results, it is found that resilient modulus was well correlated and increased with consistency index. Two prediction models, a consistency index model and a modified consistency index model, were also proposed to evaluate the resilient modulus of 15 soils with plasticity indices ranging from 6 to 52 at various moisture contents. Model parameters of the consistency index model were estimated from the plasticity index and exhibited excellent correlation. The modified consistency index model incorporated stress states to predict resilient modulus. The models were validated using selected testing results. Despite some limitations, it proves reasonable as a simple alternative means to determine the resilient modulus of fine-grained soils for foundation design, in place of complex resilient modulus testing.

Stiffening Effect of Fillers Based on Rheology and Micromechanics Models

Abstract: The aggregate in an asphalt mixture is coated with mastic consisting of bitumen (dilute phase) and filler (particulates phase). The interaction of bitumen and filler and packing of filler plays an important role in the properties of mastics. The micromechanics models from composite rheology can be used to predict the stiffening effect of a suspension. In this research, the stiffening effect of fillers was investigated based on the rheology of mastic. The frequency sweep tests in a dynamic shear rheometer at different temperatures were performed within a linear viscoelastic range to construct the master curves. The volume fractions were expressed as compositional volumes of filler in mastic. The particle shape and surface texture are determined through microscopy. We used six micromechanics-based models to predict the stiffening potential of fillers in mastics. The models include Maron–Pierce, Lewis Nielsen, Mooney, Krieger–Dougherty, Chong, Robinson, and Hashin Models. The results show that the same volume content of filler has a different effective volume. The fillers increase the stiffening effect of the composite, especially at high temperatures. The behaviour of fillers with similar effective volume and packing is identical. The filler type affects the stiffening of mastics. Micromechanics modelling results show that most models show an accurate stiffening effect at lower concentrations with the exception of the Chong Model. The Maron–Pierce Model under-estimates the stiffening potential for granite mastic at higher concentrations beyond the 30% filler content fraction. The value of maximum packing fraction (ϕm) and Einstien coefficient (KE) in the Mooney model are significantly different from other models for limestone and granite, respectively. The line of equality graph shows good agreement of measured and predicted stiffness. It is difficult to precisely model the mastic data with any single model due to the presence of complex stiffening effects beyond volume filling.

Using a beam wheel tracker fatigue test to evaluate fatigue performance of asphalt mixtures

Abstract: Fatigue cracking is one of the key distress types, caused by traffic load repetition generating stresses and strains in asphalt layers. In response, polymer modified asphalt (PMA) has been widely u...

Macro- and micro-mechanical investigations on liquefaction behaviour of granular material under bi-directional simple shear

Abstract: This paper presents a comprehensive study of initial- and re-liquefaction behaviour of granular material under bi-directional simple shear by conducting experiments and numerical simulations based on the discrete element method (DEM). In the initial liquefaction stage, various linear and non-linear cyclic loading paths are considered, including cases with and without static shear consolidation (SSC). In the re-liquefaction stage, the linear cyclic loading path along one direction is adopted. It is shown that DEM results are in good agreement with experimental data. The presence of SSC increases liquefaction resistance of granular material, and the reason is related to the initial dense state of granular materials. The re-liquefaction stage features a higher liquefaction resistance than the initial liquefaction stage does. Liquefaction resistance of granular material for various bi-directional simple shear cases is demonstrably related to the characteristics of relative density, amount of principal stress rotation (PSR), coordination number, and initial fabric anisotropy of specimens.