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The reversible mechanical behavior of unbound granular layers (UGLs) is commonly characterized by a stress-state dependent resilient modulus. This paper investigated the dependency of in situ resilient modulus upon a change in temperature above freezing conditions, i.e., the thermal sensitivity of UGLs in pavement systems excluding frost action. Such sensitivity is usually ignored in design and analysis because, on a material level, resilient modulus parameters are temperature independent. A model was developed to analyze this dependency by considering the stress-state changes that arise when UGLs are suppressed from thermally expanding or contracting. The formulation was incremental, based on linear thermoelasticity equations, and required as input readily available information; it assumed that changing temperature conditions are exogenous to the model and that no external loads are applied. A transcendental equation was subsequently derived, from which the sought sensitivity of UGLs could be resolved and quantified. Based on a parametric investigation of the model, covering a wide range of representative parameters, it is concluded that UGLs exhibit non-negligible thermal sensitivity. The extent of the calculated sensitivity coincides with field observations based on deflection testing, and also with seasonal factors that are traditionally applied to adjust field-measured moduli. Ultimately, the study shows that resilient modulus of UGLs is governed by an initial stress-state that is associated with a certain reference temperature level, and also by the temperature change compared to the reference.

Soils originating from weathering processes present considerable heterogeneity in their composition, which can make it difficult to analyse their behaviour in a systematic way. For the granitic saprolites discussed in this paper, based on a trend between soil density and weathering degree, there appears to be two different domains of behaviour, a granular domain and a clay matrix one, according to the degree of weathering reached. Recognition of these domains can reduce the apparent scatter of data for the engineering behaviour of weathered soils. A number of one-dimensional compression tests are presented for saprolitic soils from Hong Kong having different weathering degrees. In addition, isotropic and one-dimensional compression tests from the literature on other saprolites from Hong Kong and around the world were reanalysed and used to identify possible trends in the mechanisms of compression for these two domains. From practical considerations, the trends considered were between compressibility and common engineering grading descriptors. An attempt was also made to provide the physical explanations behind the behaviour observed, and the particle breakage was investigated in detail, both from a quantitative and qualitative point of view. It was found that the values of relative breakage (Hardin in ASCE J Geotech Geoenviron Eng 111(10):1177–1192, 1985), for a same stress level, might be very similar for soils having different compressibility values and different initial gradings. When studying particle breakage in further detail, it can be observed that it is linked to the amount of large particles and their characteristics. The maximum particle size, rather than the amount of fines in a mixture, may be a better predictor for differences in compressibility and breakage.