Abstract: To address the low utilization efficiency of shield spoil in current tunneling projects, a novel approach is proposed based on a shield tunnel project of Wuxi Metro, in which the retrieved shield spoil is used to replace all of the bentonite and a portion of river sand for the preparation of synchronous grouting slurry. A two-stage component substitution test was conducted, and single-factor analysis was employed to investigate the influence of shield spoil under different substitution schemes on the performance of synchronous grouting materials, thereby verifying the practical feasibility of preparing synchronous grouting slurry using shield spoil. Moreover, an optimized mix proportion meeting engineering requirements was recommended. The results indicate that when only bentonite is completely substituted, the cohesive filling effect of shield spoil enhances the compressive strength progressively, demonstrating its potential for partially replacing sand. It is feasible to replace all bentonite and part of the sand using shield spoil for synchronous grouting in practical applications. The recommended mix proportion is: water-to-binder ratio of 0.96, binder-to-sand ratio of 0.83, powder-to-ash ratio of 2.2, and a mass ratio of shield spoil to water of 0.60. Under this proportion, 42.8% material cost can be saved, and the resource utilization of 1 ton of shield spoil contributes a carbon reduction benefit of 277.66 kg CO2e.