Requirements of Efficient Deep Soil Mixing Treatment in Clayey Soils: A Field-based Assessment of Water Pre-drilling and Auger Free Blade Effects

Achieving a uniform/high-strength deep soil mixed (DSM) column and avoiding sticking cohesive soils to blades (i.e., entrained mixing/rotation phenomenon) requires multi-disciplinary involvement, including drilling tools configuration and mix designs. A series of 80 cm diameter DSM columns was executed in high cohesive clays using various drilling auger formations containing different numbers of free blades, and with/without water predrilling phases. Data interpretation was combined with full-depth coring and rig sensor records. The outcomes highlighted that adding free blades to the auger in a proper formation (dimensions/placement/shape/stiffness) resulted in uniform columns and facilitated the drilling by reducing the drilling pressure by about 40% while all the parameters were the same. The required water discharge in the predrilling phase was formulated to aim for a water content (about 46%) beyond the liquid limit of clayey deposits (21-44%); a decisive technique to facilitate drilling in stiff cohesive soils. A 100% increase in the strength and a 50% enhancement in uniformity indexes in the executed columns of this project were achieved only through a tuned free-blade auger (number/configuration) and an optimal amount of added water. Besides, simultaneously implementing the predrilling phase and free blades to maximize drilling quality was inevitable due to their intertwined functions. Moreover, a new practical equation has also been proposed to consider the effect of free blades on the BRN within cohesive soil layers.