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Concrete pavement systems have great capacity to provide long service lives; however, if the subbase layer is improperly designed or mismanaged, service life would be diminished significantly since the subbase layer performs many important roles in a concrete pavement system. The erosion of material beneath a concrete slab is an important performance-related factor that if applied to the selection of base materials can enhance the overall design process for concrete pavement systems. However, erosion of the subbase has not been included explicitly in analysis and design procedures since there is not a well accepted laboratory test and related erosion model suitable for design. Previous erosion test methods and erosion models are evaluated in terms of their utility to characterize subbase materials for erosion resistance. With this information, a new test configuration was devised that uses a Hamburg wheel-tracking device for evaluating erodibility with respect to the degree of stabilization and base type. Test devices, procedures, and results are explained and summarized for application in mechanistic design processes. A proposed erosion model is calibrated by comparing erosion to lab test results and LTPP field performance data. Subbase design guidelines are provided with a decision flowchart and a design assistant spread sheet for the economical and sustainable design of concrete pavement subbase layers by considering many design factors that affect the performance of the subbase.

The construction of road works in the world has always been a challenge for engineering, especially in areas where the conditions and types of soil are not adequate for the execution of this type of projects. The present investigation has as main objective to determine the influence that has the rice husk ash (RHA) to stabilize the subgrade layer of a pavement, composed of a low resistance clayey soil. RHA is a waste and pollutant material for the environment; therefore that its use can be considered as an economic and ecological alternative. Thus, several tests were carried out where it proved the value of CBR increased from 4.30% to 20.70%, by adding a 20% RHA dosage, achieving its optimum value to be considered a very good subgrade. In this way, it is possible to affirm that the addition of RHA improves the geotechnical properties of the soil.

Compacted soils are frequently used as subgrade for pavements as well as commercial and residential buildings. The stiffness and shear strength properties of compacted soils, which are collectively denoted as Ω in this thesis, fluctuate with moisture content changes that result from the influence of environmental factors such as the evaporation and infiltration. For example, mechanistic pavement design methods require the information of resilient modulus (MR), which is the soil stiffness behavior under cyclic traffic loading, and its variation with respect to the soil moisture content determined from laboratory tests or estimation methods. Significant advances have been made during the last five decades to understand and model the variation of the Ω with respect to soil moisture content and soil suction (s) based on the principles of mechanics of unsaturated soils. There are a variety of models presently available in the literature relating the Ω to the s using different approaches. There are however uncertainties extending these models for predicting Ω - s relationships when they are used for a larger soil suction range. In addition, the good performance of these models are only valid for certain soil types for which they were developed and calibrated. Studies presented in this thesis are directed towards developing a unified methodology for modelling the relationship between the Ω and the s using limited while easy-to-obtain information. However, more emphasis has been focused on the MR - s relationships of pavement subgrade soils considering the need for the application of the mechanistic pavement design methods in Canada. The following studies have been conducted: (i) State-of-the-art review on existing equations in the literature for the MR - s relationships is summarized. A comparison study is followed to discuss the strengths and limitations of these equations; (ii) A unified methodology for modelling the Ω - s relationships is proposed. Experimental data on 25 different soils are used to verify the proposed unified methodology. The investigations are applied on small strain shear modulus, elastic modulus, and peak and critical shear strength. Good predictions are achieved for all of the investigated soils; (iii) Performance of the proposed methodology is examined for the MR - s relationships using experimental data of 11 subgrade soils. Reasonably good predictions are achieved for all of the subgrade soils; (iv) Extensive experimental investigations are conducted on the MR - s relationships for several subgrade soils collected from various regions in Canada. Experimental results suggest non-linear variation in the MR with respect to s, moisture content and the external stress. The measured results are modelled using the proposed methodology with adequate success; (v) Additional experimental investigations are performed to determine the variation of the elastic modulus (E) and unconfined compression strength (qu) with the s and the gravimetric moisture content (w) for several Canadian subgrade soils. An approach, which is developed extending the proposed unified methodology, is used to normalize the measured MR - w, E - w and qu - w relationships. It is shown that the normalized MR - w, E - w and qu - w relationships exhibit remarkable similarity and can be well described using the proposed approach. Such similarity in the normalized Ω - moisture content relationships are also corroborated using the experimental data on several other soils reported in the literature. The proposed unified methodology alleviates the need for the determination of the Ω - s relationships which requires elaborate testing equipment that needs the supervision of trained personnel and is also time-consuming and expensive. In addition, experimental programs in this thesis provide detailed experimental data on the MR, E, qu, and soil-water characteristic curves of Canadian subgrade soils. These data will be helpful for the better understanding of the hydro-mechanical behavior of the Canadian subgrade soils and for the implementation of the mechanistic pavement design method in Canada. The simple tools presented in this thesis are promising and encouraging for implementing the mechanics of unsaturated soils into conventional geotechnical engineering practice.

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<p> The behaviour of asphaltic concrete, granular base and subbase materials, and subgrade soils in repeated dynamic loading is best represented by their resilient moduli in rational flexible pavement designs. The recoverable, or resilient, strains in pavement structures due to repetitions of moving traffic loads can be predicted through the use of appropriate material parameters in analytical or numerical models of pavement response. It appears that the repeated-load triaxial test offers the most promising means of applying simulated field loading conditions to representative samples of flexible pavement components. This testing of laboratory or field prepared samples provides a good estimate of the material 1 s overall dynamic behaviour and the desired resilient modulus and Poisson's ratio for design analyses. The purpose of this research was to simulate field loading conditions for a range of typical Southern Ontario granular base and subbase materials by means of repeated-load, variable and constant confining pressure, triaxial tests using laboratory research equipment readily adaptable to regular design use. The pavement materials were characterized in a condition corresponding to optimum density and moisture content with repeated loadings representative of field stress conditions of 0.1 second pulse duration at a frequency of 20 cycles per minute. In addition to determining the resilient modulus and Poisson 1 s ratio for four basic conditions -unsaturated drained, unsaturated undrained, partially saturated drained, partially saturated undrained -the results were examined for significant trends. The characterization of typical base, subbase and subgrade materials for Southern Ontario, coupled with previous work on asphaltic concrete, allows the use of representative moduli for all flexible pavement components in Ontario pavement design systems such as OPAC. </p> / Thesis / Master of Engineering (ME)