Abstract: Shield slurry is a mixture of mud and slag generated from tunnel excavation. It is difficult to be directly utilized due to its high fines content, high fluidity, and low strength. The study introduces a novel approach involving initial granulating followed by compaction of the slurry utilizing phosphogypsum-based cementitious materials to address difficulties associated with the continuous solidification construction of slurry with high-water-content. The research investigates the particle size distribution of the granulated slurry and its strength characteristics post-compaction. Findings reveal that granulation significantly increases particle size of the slurry significantly increased, with substantial portion of fine particles (<0.075 mm) being transformed into “sand-sized particles” (0.075-2 mm). This transformation enhances inter-particle friction, thereby improving both the shear and compressive strengths of the granulated slurry. The phosphogypsum-based cementitious materials content, granulation duration, and curing age collectively influence the physical and mechanical properties of the granulated slurry in a synergistic manner. The optimal conditions for achieving a harmonious balance between granulation and compaction-solidification are as the phosphogypsum-based cementitious material content of 20% 20%, a granulation duration of 14 days, and a curing age of 28 days, resulting in a compressive strength of 5.62 MPa. Meanwhile, some samples after the compressive strength test were taken to conduct mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) tests, revealing the strength formation mechanism of slurry granulated into sand and solidified into blocks. Finally, the cost per unit strength and carbon sequestration rate associated with the utilization of phosphogypsum-based cementitious materials for granulating and solidifying slurry were calculated, and their economic and environmental advantages were assessed. The results show that the continuous implementation method of “granulation-compaction-solidification” is reliable and cost-controllable, offering technical support for the resource utilization of shield slurry.

Key words: shield slurry, granulation, compaction, phosphogypsum