Laboratory investigation on salt migration and its effect on the geotechnical strength parameters in quick clay mini-block samples from Dragvoll

Abstract

Investigations of the effect of salt diffusion as ground improvement of quick clay is importantto provide a clear understanding of the method, to be able validate the potential of commercialuse. Previous extensive investigations by laboratory work has been carried out. Laboratory in-vestigations of salt migration lead to extended storage time for the clay samples, as diffusion inclays is considered a slow process.TheobjectiveoftheworkistoanalyzetheeffectofKCldiffusioninrelationtopotentialweather-ing and storage effects. The effect is analyzed in the laboratory with regards to both geotchnicalproperties, variations in pH and salinity. A literature study of previous findings related to saltmigration and storage effects on both geotechnical properties and geochemistry, is also consid-ered.A series of mini block samples are submerged in cells containing deaired, ionized water anddeaired, KCl solution. The samples are stored in the cell in a time period from 42 to 102 days.The samples are investigated in the laboratory to provide results relating to undisturbed andremoulded strength parameters, compressibility and general geotechnical properties. pH andsalinity is also recorded. The findings are compared to a detailed depth profile of referenceparameters,fromapreviousinvestigationdoneonminiblocksamplesfromthesameborehole.Testsarealsocarriedoutinsectionsthroughoutthewaterandsalttreatedclays,tomapchangeswith regard to the time dependent diffusion and weathering.Theresultsindicatedageneralincreaseinpeakundrainedshearstrengthforthesamplesstoredin KCl solution, approximately 50% of the observed general increase is also observed in the claystored in water. A minor increase of plasticity limit is seen in both the water and salt treatedsamples. The comparison between sections for each sample show no clear deviations betweenthe sections. Further, results from the salt migrated samples confirm the findings from previousinvestigations.The samples are to some extent effected by weathering, in particular the peak undrained shearstrength resulting from triaxial tests. However, the geotechnical properties observed after saltmigration are changed to such an extent that the clay show a completely different behavior. Thesame distinct change is not observed in the clays only exposed to potential weathering.The comparability between the samples are however, considered to be relatively low due to in-homogeneity in the soil profile and varying storage time prior to testing and cell installation.Loss of samples during sampling also lead to occasional large distance in depth, between thecompared results.