Deep soil mixing (DSM) is a well-established in-situ technique in which stabilized columns are created by specialized equipment by mixing the binder and the soil to a required depth. Conventionally cement and lime or a combination of both are used as binder materials for DSM column preparation. The present study investigates 100% replacement of conventional binders with low-calcium fly ash (FA) to stabilize high plastic clay. To enhance the reactivity of fly ash, liquid alkali-activator (LAA), a combination of sodium silicate and sodium hydroxide, was proposed in different proportions. The influence of LAA was investigated by varying the LAA/FA from 1 to 1.5. For this study, a laboratory-scale fully functional DSM set-up was developed to replicate the field DSM technique in the laboratory. The DSM columns were installed in a compacted high plastic clay in cylindrical chambers and cured for seven days in a controlled humidity chamber. The performance of the stabilized columns was accessed through a series of experiments including, unconfined compressive strength (UCS) tests, scanning electron microscopic (SEM) images, and X-ray diffraction (XRD) analysis. The test results were compared with the standard tests conducted under controlled test conditions. The UCS of the in-situ DSM columns is about 60% of the traditional static compacted UCS specimens with LAA/FA = 1.25 and 1.5. The SEM images show that the layer structure of clay soil changes to a dense crystalline structure for fly ash stabilized specimens. The XRD analysis also confirms the increase in crystalline peaks with the binder proportion.