Predicting required time for stabilising Norwegian quick clays by potassium chloride

Abstract

Salt wells filled with potassium chloride (KCl) were installed in a highly sensitive, low-salinity, glaciomarine quick clay at Dragvoll, Trondheim, Norway, to investigate the improvement in geotechnical properties and the required time to stabilise the clay volume sufficiently to inhibit retrogressive landslide development. Improving the remoulded shear strength (c ur) beyond 1 kPa reduces the risk for successive back-scarp failures. When more than 20% of the cations in the pore water consist of potassium (K+), magnesium (Mg2+) and calcium (Ca2+) ions, c ur is improved beyond 1 kPa. Optimisation of the well grid is necessary prior to installation to ensure that c ur > 1 kPa within 2–3 years. PHREEQC simulations predicted a diameter of stabilised clay of minimum 1·5 m within 3·3 years after installation, which fits reasonably with observed pore-water compositions and improved geotechnical properties in situ. Salt wells may be used as landslide mitigation, preventing backward successive, retrogressive development, and PHREEQC can be used to give a rough estimate of the required time to stabilise the quick-clay volume around the wells.