UCS and CBR behaviour of Perth sandy soil reinforced with waste tyre fibres and cement

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Bazazorde, Seyed M. A.
CBR; cement; compaction; waste tyre fibres; sandy soils; UCS; Civil and Environmental Engineering
thesis / dissertation description
Weak and unsuitable soil conditions have always caused problems for civil engineers during the construction of structures. To avoid problems in a cost-effective manner, proper and reliable solutions need to be developed. Fibre reinforcement and cement stabilisation are the most efficient and common methods in geotechnical engineering applications when engineers have problematic soil conditions. These methods can be used in different applications, such as pavement layers, retaining walls and slopes.Over the past three decades, many studies have been done to investigate the effects of adding synthetic and natural fibres to soil as the reinforcing material alone or with cement. The present work focuses on investigating the characteristics of local Perth sandy soil after inclusion of waste tyre fibres and cement. These wastes can be utilised in ground improvement projects in large quantities and could provide a cost-effective and environmentally friendly strategy that avoids tyre disposal problems.Fibres for reinforcement applications in soils are available in different types in terms of materials and their geometrical configurations. Using waste materials, which are present nowadays in large quantities and in different forms, such as used tyres and carpets, as reinforcing materials can be environmentally and economically beneficial. In the past, waste tyres have been used in some geotechnical applications, such as highway construction, retaining wall backfill and drainage layers for roads, but the efforts seem to be insufficient. Although much research has been conducted on cement stabilisation, but on fibre reinforcement, and their combination, no comprehensive research has been done to investigate the UCS and CBR behaviour of sandy soils mixed with cement and tyre fibres, especially on the sandy soils available in Perth and its surrounding areas.A series of laboratory tests including compaction, unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were conducted to investigate the effects of adding tyre fibre and cement on the engineering behaviour of Perth sandy soil. The contents were varied from 0 to 5% of dried soil by weight for cement and 1% of dried soil by weight for tyre fibres. The cemented specimens were cured in for 3, 7, 14, and 28 days.This study aims at investigating the effect of different parameters, including cement content, tyre fibre content, curing time and confining pressure on the CBR behaviour of Perth sandy soils. Feasible, ecologically friendly, and economically reasonable solutions, both theoretically and practically, are studied in this research so that geotechnical/civil engineers can effectively use them in the construction projects.The compaction test results indicate that the maximum dry unit weight generally increases by adding cement and decreases by tyre fibres inclusion, while adding cement and tyre fibre results in a lower optimum water content.For the fibre-reinforced and unreinforced materials, the compressive strength increases with an increase in the cement content. Adding 1% of tyre fibres to mixtures increases the UCS of the soil approximately by 10-70%. The results also show that as the curing time increases, the UCS increases, and the effect of curing is more pronounced for higher stabiliser contents.