Strength Characteristics and Micromechanisms of Mucky Soil Co-Stabilized with Geopolymer and Gold Tailings Sand

A carbide-slag-activated slag-fly ash geopolymer (CSF) and waste gold tailings sand were used to co-stabilize mucky soil, aiming to promote the valorization of multiple industrial solid wastes and provide a low-carbon treatment approach for mucky soil in river and lake regions. Unconfined compression, direct shear, water stability, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS), and heavy metal leaching tests were conducted to investigate the effects of CSF and gold tailings sand contents on the mechanical properties, water stability, microstructure, and environmental safety of the stabilized soil. The results showed that the unconfined compressive strength (UCS) and shear strength increased with increasing CSF content, whereas the strength gain became marginal when the CSF content exceeded 15%. With the CSF content fixed at 15%, both the strength and water stability initially increased and then decreased as the gold tailings sand content increased. The CSF15-G30 specimen exhibited favorable overall performance, with 7 d and 28 d UCS values of 0.65 and 1.53 MPa, respectively, representing increases of 25.0% and 12.5% relative to CSF15. Its cohesion and internal friction angle reached 88.21 kPa and 47.13°, corresponding to increases of 44.5% and 8.1%, respectively. The water stability coefficients at 7 d and 28 d were 76.9% and 87.6%, respectively. SEM-EDS observations indicated that the cementitious products generated by CSF, together with the filling and skeletal effects of gold tailings sand, enhanced interparticle bonding and matrix densification. Although the concentrations of leached heavy metals increased with increasing gold tailings sand content, all measured values remained below the relevant leaching-toxicity limits. These results demonstrate that an appropriate amount of gold tailings sand can effectively improve the mechanical properties and water stability of CSF-stabilized mucky soil while maintaining satisfactory environmental compatibility.