Hydraulic response of fibre-reinforced sand subject to seepage

A series of upward seepage tests on unreinforced and reinforced sand specimens was conducted to investigate the influence of soil density and fibre parameters (i.e. fibre contents and lengths) on the piping failure mode, hydraulic conductivity k, and critical hydraulic gradient i_cr of fibre-reinforced soil (FRS). Direct shear tests were also performed to establish the relationships between soil shear strength and i_cr of FRS. A dataset of seepage tests on FRS was compiled from a literature review to assess the overall variation of k and i_cr with fibre content. The test results revealed that k decreases and i_cr increases as the fibre content increases. The fibre is more effective in dense specimens than in loose specimens. The test results also indicate the i_cr of FRS is strongly correlated to its soil shear strength. Finally, two case examples, unreinforced and reinforced embankments subject to flood-induced elevated water level, were analysed numerically. The numerical results demonstrated that the embankment backfilled with FRS possessed the combined merits of soil improvement in both mechanical and hydraulic performance. The use of FRS as backfill can effectively delay the advance of seepage, reduce soil piping potential, and improve system slope stability against seepage.