Non-destructive testing to monitor the strength increase of electrokinetically treated soil

Abstract

Electrokinetics in geotechnical engineering is used to increase the shear strength of soft soils and the load carrying capacity of piles embedded in these soils. This is achieved by decreasing the water content of the soil by electrokinetics, and often by inducing cementation. Practical issues such as determining the treatment effectiveness along with determining the appropriate treatment duration have limited its use in the field. In this study, a steel pile foundation model was inserted in clayey soil that was treated with electrokinetics with bender elements embedded in the soil to monitor the shear wave velocity in the soil during the treatment. Changes in the shear-wave velocity were used as an indicator of changes in the structure and shear strength of the soil throughout treatment. After the shear wave velocity ceased to increase, the gain in the strength of the soil by the treatment was considered to plateau and the treatment was terminated. Two weeks after treatment, the pile models were loaded. Shear vane tests were carried out to accurately define the zones of soil stiffened and the extent of the changes. To better comprehend the mechanisms which contributed to soil stiffening, by x-ray diffraction, x-ray energy dispersive spectrometry, Atterberg limits and pH tests were performed. It was found in this study that by using bender elements to monitor the changes in the shear-wave velocity, the treatment time and total power consumed were reduced by more than 40 percent and 34 percent, respectively while achieving a similar reduction in water content and increase in shear strength to a test with seven days of treatment. The load carrying capacity after the treatment increased by 300 percent compared to the control.