Global concern about the environmental impacts of waste disposal and stringent implementation of environmental laws lead to numerous research on recycled materials. Increased awareness about the inherent engineering values of waste materials, lack of landfill sites and strong demand for construction materials have encouraged research on composite materials, which are either fully or partly made of recycled materials. This trend is particularly strong in transportation and geotechnical projects, where huge quantities of raw materials are normally consumed. Owing to the low mass-to-volume ratio, disposal of Expanded Polystyrene (EPS) is a major problem. In addition, EPS recycling methods are expensive, labour intensive and energy demanding. Hence, this thesis is focused on the development of a new soil composite made by mixing recycled EPS with expansive clays. Given the high cost of damage to various buildings, structures and pavements caused by the unpredictable ground movements associated with expansive soils, it has been considered prudent to try and develop a new method of soil modification using recycled EPS beads as a swell-shrink modifier and desiccation crack controller. The innovative application of recycled EPS as a soil modifier will minimise the quantity of waste EPS destined to the landfill considerably. An extensive experimental investigation has been carried out using laboratory reconstituted expansive soils - to represent varied plasticity indices - consisting of fine sand and sodium bentonite. Three soils notated as SB16, SB24 and SB32 representing 16%, 24% and 32% of bentonite contents respectively were tested with four EPS contents of 0.0%, 0.3%, 0.6% and 0.9%. The tests performed include compaction, free swell, swell pressure, shrinkage, desiccation, shear strength and hydraulic conductivity. All the tests have been performed at the respective maximum dry unit weight and optimum moisture content of the mixes. It has been observed that by mixing of recycled EPS beads with the reconstituted soil, a lightweight geomaterial is produced with improved engineering properties in terms of dry unit weight, swelling, shrinkage and desiccation. The EPS addition depends on the moulding moisture content of the soil. With increasing moisture content, additional EPS can be added. Also, there is a reduction in dry unit weight with the addition of EPS. Furthermore, the reduction of swell-shrink potential and desiccation cracking in soils, for example, is related to the partial replacement of soil particles as well as the elasticity of the EPS beads. There is a reduction in shear strength with the addition of EPS to soils. However, mixing of chemical stabilisers along with EPS can enhance the strength in addition to improved overall properties.

This thesis compares foundation methods for buildings on low-strength, limited-depth soil. The study focuses on soil replacement and piling, specifically concrete and steel piles. The studyaims to answer the key questions about the possibility to use short piles on limited depth, cost-efficiency, and environmental impact of these methods. Geotechnical and structural calculations are used to assess the loads on the piles and evaluate their strength. WIN-statik Frame Analysis helps analyze deformations, moments, and stresses. The foundation transfers vertical loads to three piles, generating horizontal loads at the pile tops. However, the challenge lies in short piles in clay, which experience low earth pressure and may rotate due to bad stabilization. The analysis reveals that concrete piles are unable to transfer loads to solid rock effectively. Without fixed anchorage points, they are prone to rotation due to insufficient stiffness and lateral earth pressure. In contrast, steel piles are preferred because they can be drilled into the rock, providing fixed anchorage at the clay-rock transition and enabling them to withstand loads transferred through the foundation. Soil replacement is considered as an alternative method but proves economically expensive, approximately three times more than piling with steel piles. From an environmental standpoint, piling contributes only slightly more carbon dioxide emissions, about 0.4 tons, compared to soil replacement. Considering the significant cost advantage and minor environmental impact difference between soil replacement and piling, piling with steel piles is recommended as the optimal foundation method. Concrete piles are dismissed due to their instability. This choice ensures stability, cost-efficiency, and reduced environmental impact for buildings on low-strength, shallow-depth soil.

Railway tracks experience elevated rail deflections when the supporting soil is soft and/or the train speed is greater than approximately 50% of the wave propagation velocity in the track-soil system (i.e. the critical velocity). Such vibrations are undesirable, so soil replacement or soil improvement of the natural soil (or alternatively mini-piles or lime-cement treatment) is often used to increase track-ground stiffness prior to line construction. Although areas of existing soft subgrade might be easily identified on a potential new rail route, it is challenging to determine the type and depth of ground remediation required. Therefore, major cost savings can be made by optimising ground replacement/improvement strategies. This paper presents a numerical railway model, designed for the dynamic analysis of track-ground vibrations induced by high speed rail lines. The model simulates the ground using a thin-layer finite element formulation capable of calculating 3D stresses and strains within the soil during train vehicle passage. The railroad track is modelled using a multi-layered formulation which permits wave propagation in the longitudinal direction, and is coupled with the soil model in the frequency-wavenumber domain. The model is validated using a combination of experimental railway field data, published numerical data and a commercial finite element package. It is shown to predict track and ground behaviour accurately for a range of train speeds. The railway simulation model is computationally efficient and able to quickly assess dynamic, multi-layered soil response in the presence of ballast and slab track structures. Therefore it is well-suited to analysing the effect of different soil replacement strategies on dynamic track behaviour, which is particularly important when close to critical speed. To show this, three soil-embankment examples are used to compare the effect of different combinations of stiffness improvement (stiffness magnitude and remediation depths up to 5 m) on track behaviour. It is found that improvement strategies must be carefully chosen depending upon the track type and existing subgrade layering configuration. Under certain circumstances, soil improvement can have a negligible effect, or possibly even result in elevated track vibration, which may increase long-term settlement. However, large benefits are possible, and if detailed analysis is performed, it is possible to minimise soil improvement depth with respect to construction cost.