Effect of Steel Fibres on the Behaviour of a Chemically Stabilised Soil-Paper

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The study examined how steel-fibre content affects the compressive and tensile behaviour of chemically stabilised soft soil. Soil from Baixo Mondego, Portugal, was treated with 375 kg/m³ of a cement–blast-furnace-slag binder and reinforced with crimped steel fibres at 0, 25, 50, 100 or 150 kg/m³. After 28 days of curing, specimens were tested in unconfined compression (UCS) and direct tension (DTS).<br /><br />Fibre effects depended on the test and its failure mechanism. In UCS tests, adding fibres reduced compressive strength, with the greatest reduction at 25–50 kg/m³. However, fibres made the post-peak response less brittle and increased residual strength. In DTS tests, fibres improved tensile strength, which peaked at 50–100 kg/m³. Despite this improvement, tensile failure remained abrupt: the fibres could not sustain the load transferred from the soil matrix after failure, due to breakage or insufficient anchorage. Stiffness also varied nonlinearly, generally decreasing at low fibre content, recovering slightly around 50 kg/m³, and then declining at higher contents.<br /><br />The tensile-to-compressive strength ratio reached a maximum of about 0.26 at 50 kg/m³ of fibres. The authors propose a ratio of 0.2 as a conservative design value for fibre-reinforced stabilised soil. Further research is recommended to verify these findings and better characterise tensile behaviour.

Keywords

steel fibres

soft soil stabilization

compressive strength

tensile strength

unconfined compression

direct tension

cement blast furnace slag

residual strength

fibre reinforcement

Baixo Mondego soil