Fibre Reinforcement Of CSM Walls To Enhance Strength, Crack Resistance And Seepage Cut-off

Cutter soil mix (CSM) walls are created by mixing soils while in situ with cement and bentonite slurry to produce a soil mix with modest tensile and compressive strengths. CSM walls may be stabilised using internal steel beams and ground anchors. Presented here are results of a CSM wall field trial in which polypropylene fibres were added to a soil mix. One objective of the trial was to explore whether or not fibres have the potential to increase wall resistance to bending and reduce the quantity of steel needed to provide stability. Another objective was to explore whether or not the fibres provide a reduced tendency for crack formation and thus the potential for enhanced seepage cut-off. The trial involved mixing fibres into a 4 m deep single CSM wall panel using a conventional mixing procedure employed by Wagstaff Piling. 24 hours after placement a 20 tonne excavator was used to remove the wall panel. Samples were collected and tested 28 days and 2 years later to assess unconfined compressive strengths, indirect tensile strengths and flexural tensile strengths. The fibre orientation distribution in the soil fibre mix was also assessed. The testing confirmed that the mixing technique resulted in a uniform orientation distribution of fibres and significantly improved strength characteristics. The testing also showed that the fibres made the CSM wall mix very ductile and prevented brittle failure. Adding fibres to the CSM material enabled larger bending deformations to be tolerated before major cracking and failure occurred. Also presented is a hypothetical design of a fibre reinforced CSM wall to show that steel quantity can be reduced while maintaining stability and crack prevention, leading to significant cost reductions.