Efficiency Evaluation of Deep Soil Mixing Method in Stiff Clayey Soils: A Comprehensive Field Study

The quality of deep soil mixing (DSM) columns in fine-grained soils remains challenging and needs to be addressed unequivocally to solve the existing practical problems. Breakthroughs can be achieved through field investigations; hence in the present study, the results of a field study on 16 DSM elements with various mix designs in cohesive clayey soils are presented. The rig data, continuous full-depth coring, and unconfined compressive strength (UCS) tests were used to evaluate the strength and uniformity of DSM columns. The results shed light on the fact that the occurrence of entrained mixing phenomena, an issue in which cohesive soils stick the blades, could be estimated using rig data, which might be solved by implementing a water predrilling phase. Furthermore, by following the fluctuations in the pull-down, rotary, and hoist pressures of the drilling rig data, the uniformity of DSM elements could be assessed indirectly. Based on the finding, it is noticeable that a conspicuous discrepancy has been observed between the Federal Highway Administration (FHWA) equation for predicting the UCS of DSM columns and the captured results. Furthermore, the correlations between elastic modulus and UCS of DSM elements were about the half of values by FHWA.