Sustainable soil stabilization for unsealed roads subjected to operational loads

<p>Unsealed road infrastructure are an important asset providing the necessary connections between regional and metropolitan areas of a country. However, these roads when constructed on expansive soils are affected by severe moisture fluctuations in addition to the exposure of recurring traffic loads that result in excessive maintenance. During their service life, road pavements are partially saturated, resulting indistinct volume and strength changes with changes in saturation. Since recently, soil stabilization using traditional calcium-based treatments have been commonly recognized as an effective solution for pavement degradation, despite its associated environmental concerns. Therefore, the shift towards green, sustainable and cost effective road construction has led engineers to reconsider the use current traditional chemical based stabilizers in favour of environmentally friendly cements and novel non-traditional stabilizers. The current study evaluates the durability and efficiency of such alternatives for unsealed road pavements incorporating realistic soil and traffic conditions to facilitate economic and safe design.</p> <p>In this study, the response of sustainably stabilized unsealed road pavements under operational loads (traffic loads and moisture impact) was investigated using a comprehensive laboratory testing programme. The mechanical behaviour of stabilized subgrade soil was evaluated under practical moisture conditions and characterized using a number of  microstructural and pore-structural techniques. The hydraulic behaviour was also investigated for state variation and stabilizer influence on the soil water characteristic curve (SWCC). The results from the experimental programme were systematically analysed and discussed to devise the stabilization mechanism and optimal dosage of sustainable additives for expansive soil. Experimental tests further evaluated the durability and hydraulic characteristics of stabilized soils by assessing its performance under the effect of moisture impacts. The application of sustainable stabilization to subgrade soils has been evaluated through a verified modelling approach.</p> <p>The behaviour of stabilized unsealed road pavements in unsaturated conditions was then simulated using 3-dimensional (3-D) finite element (FE) method using calibrated constitutive soil models. The models were first validated for volume change and cyclic loading using reported field data and experimental results conducted in the current study. A parametric study was performed using 3-D FE analysis to simulate and assess the effectiveness of the novel stabilization methodology for constructing unsealed road pavements. A series of 3-D FE analyses were used to develop an analytical model for predicting rutting performance of unsealed roads constructed on stabilized subgrades considering soil saturation effects. Results from the FE analysis revealed importance of considering realistic soil conditions in pavement design. The proposed expression shows a strong correlation between predicted and observed rutting of stabilized expansive subgrades subjected to moisture and loading cycles.</p> <p>The thesis offers a sustainable replacement to traditional calcium-based additives for durable road pavements. The findings of this study unveiled the stabilization mechanism of sustainable additives in expansive soil, presenting as a viable alternative to traditional stabilization approaches. The sustainable stabilization of expansive soils proves to be effective in improving and maintaining soil strength. The application to unsealed roads was found to highlight the need to capture the hydraulic response of stabilized subgrade soils in order to realistically predict strength and volume changes due to operational loads. The results and findings from this study have been published in a number of international journals.</p>