Abstract: Shield tunneling produces a significant volume of excavated soil, leading to environmental pollution and elevated transportation and disposal costs. To address this issue, a case study is conducted on a section of the Nanjing metro line 6. A technical method is proposed to utilize the silty clay generated by shield tunneling for grouting behind lining. The performance of the grout, incorporating various water-cement ratios and mixing proportions of hardeners A and B, is evaluated through laboratory testing, non-linear regression analysis using statistical package for the social sciences (SPSS), and multi-objective optimization to identify the optimal mix for both performance and economic efficiency. The main findings are as follows: (1) TW-G is suitable for high-clay-content grout. Hardener A exhibits retarding and water-reducing effects, while Hardener B enhances coagulation and early strength. (2) Multi-objective optimization results indicate optimal performance at a water-cement ratio of 0.75, with 0.86% hardener A and 12.95% hardener B. The grout with a water-cement ratio of 0.84, 3.66% hardener A, and 2.91% hardener B achieves the greatest economic benefit. (3) Field application demonstrates that, compared to conventional single-component hard grout, the grout mixed with shield muck yields superior performance. After application, surface settlement is limited to within 12 mm, segment uplift is controlled within 25 mm, and mucking is reduced by over 10%, resulting in a 35% cost reduction.

Key words: shield tunnel, shield muck, grouting behind lining, muck recycling, grout mixing proportion