Mixing and compaction of fibre- and lime-modified cohesive soil

Fibre reinforcement is a versatile method of increasing the shear strength of soils for earthwork applications. However, research to date has encountered a number of problems when utilising cohesive host soils. The aim of this study was to develop a suitable site-applicable method of mixing fibre into cohesive host soils. Intermediate plasticity clay reinforced with monofilament polypropylene fibres was used in the laboratory investigations. In order to mix the fibres successfully, the initial moisture content of the host soil was increased prior to the introduction of fibres. By introducing quicklime, excess moisture was removed through the hydration process, and a portion of free water was effectively held within aggregations of flocculated clay particles, thereby having little influence on the dynamic boundaries. Fibrous inclusions within the clay clods resisted compactive effort, forming an interlocked structure. As a result, the optimum moisture content increased and the maximum dry density decreased. This trend was heavily dependent on the interfacial shear resistance along the fibre boundary, which consequently decreased as the water content increased or the compactive effort was increased. Results from strength tests confirmed that both peak and post-peak shear strength increased, creating a more ductile material capable of maintaining shear strength at high levels of strain.