Abstract: Onsite recycled utilization of muck generated from EBP shield tunneling can resolve many challenges, such as mucking transportation and treatment, high cost and synchronous grouting materials, and nonrenewable resources. Herein, a case study is conducted on a shield tunnel section of the extension line of Ningbo metro line 4 in China bored by a EBP shield in composited strata. First, the material mix proportions are determined based on laboratory tests and onsite engineering practice, and the muck generated from shield tunneling is mixed with cement and soil hardener to prepare synchronous grouting material meeting performance requirements. Then, to further meet the requirements of industrial promotion and application, relevant process technology research and equipment development are carried out in combination with the composite strata conditions of the project, and a two-step slurry preparation process route of "slurry preparation using muck + finished slurry preparation" is proposed. This technology has been successfully promoted and applied in multiple engineering projects. Practical application results show that: (1) For the muck from EPB shield tunneling in composite strata with a soil content of ≥25%, after adding cement and soil hardener, the synchronous grouting material meeting requirements can be prepared. Its 7-day compressive strength is≥0.15 MPa, 28-day compressive strength is≥1.00 MPa, and bleeding rate is ≤1%, whose performance is better than that of conventional thick slurry. (2)The optimized slurry preparation process and equipment exhibit a slurry preparation efficiency of more than 12 m³/h, which can adapt to EPB shield tunneling in composite strata and meet the grouting supply demand of conventional double-track tunnels. (3) The application of this technology can directly reduce the onsite muck transportation by more than 10% and lower the construction cost of shield tunnels by approximately 800 000 CNY per kilometer.

Key words: shield tunneling muck, on-site resource recycling, composite strata, EPB shield, recycled synchronous grouting slurry