LABORATORY SCALE EVALUATION OF THE FEASIBILITY OF USING GUANIDINIUM SALTS AS A MEANS OF INSITU SOIL STRENGTHENING FOR WEAK CLAYS

Deep-seated, slow moving landslides are widespread throughout the prairie provinces of Canada, especially in Saskatchewan and eastern Alberta. These landslides are characterized by a thick deposit of glacial drift underlain by poorly lithified cretaceous shale (Bearpaw, Lea Park formations). Multiple thin layers of extremely weak, smectite rich, clayey soils are often found within the upper portions of these cretaceous shale formations. The interfaces of these smectitic clay lenses typically produce a pronounced shear plane, turning the overlying soils into a large slump block. Landslides of this nature can span several hundred meters in length, which provides a threat to infrastructure such as roads, bridges, and pipelines.\n\nDue to the depth of these shear zones, and the scale of these types of creeping failures, remediation via traditional geotechnical engineering solutions is either not feasible or extremely costly to pursue. The lack of available solutions for this common problem has prompted research that stems from a multi-disciplinary approach. The current research is intended to evaluate the feasibility of modifying the porewater chemistry of these smectitic shear zones by using guanidinium chloride to propagate mineralogical alteration through ion exchange, as a means of insitu soil strengthening.\n\nThis study was limited to laboratory scale testing. The specific objectives for this research were to: i.) characterise the mechanism by which guanidinium salts can alter the mineralogical and macroscopically observable properties of natural expansive clay soils; and, ii.) assess fundamental questions pertaining to the full-scale implementation of the proposed insitu strengthening technique.\n\nA local prairie soil, Regina Clay, was used for the majority of testing procedures, as it is readily available and is representative of the types of soils associated with the problem that this research aimed to address. The results from a series of batch-style geotechnical and mineralogical testing procedures contributed to a clearer understanding of the mechanisms associated with this treatment, the required strengths of saline solution for treatment, quantified the effects of treatment, and the permanence of the effects associated with this treatment.\n\nTreating expansive soils with concentrations of 0.1 molar guanidinium chloride saline solutions were found to cause permanent alterations to the smectite mineral’s basal spacing and soil fabric, increase the permeability by half an order of magnitude, and increase the residual shear strength by up to 100%, all without reducing the oedometric stiffness.\nAs the present study is limited to laboratory-scale trials, a full-scale test site is recommended to further validate the effects found in this research. However, despite the limitations of this work, the potential for insitu soil strengthening via guanidinium salts appears to be significant.

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