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Abstract

A natural illitic, chloritic, silty clay having an undisturbed shear strength of 20 kPa was stabilized using Al(OH)2.5C10.5 (denoted OH-A1) alone or together with KCl or K2SO4. Results of field tests on three-year-old in situ stabilized clay columns and the surrounding undisturbed clay were compared with earlier field and laboratory tests. The clay columns were stabilized by remolding the soil by more or less complete mixing of the chemicals with an auger of 0.5-m diameter. After three years the shear strengths measured on 1-m-long sections of the columns had increased to 40 kPa. On 8-cm high, homogeneous, mixed samples from the same column, the shear strength was as much as 230 kPa. In the clay surrounding the columns, the undisturbed shear strength increased gradually from about 20 kPa in the quick clay to about 40 kPa within a few centimeters from the columns, and the remolded shear strength increased from 0.1 to 12 kPa. As a result, the sensitivity decreased from 200 to 8. The improvement in the geotechnical properties in the soil surrounding the columns was apparently caused by increased acidity and increased salt content in the pore water. The salt in the pore water originated by the diffusion of H+, K+, Ca2+, Cl, and SO42− from columns and by subsequent ion-exchange reactions with the clays releasing Na+, K+, Mg2+, and Ca2+. Because of this ion diffusion, the surrounding clay completely changed its geotechnical behavior. The total stabilized cross section of each column increased from the original 0.2 m2 to more than 4 m2 after three years.

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