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Beyond Engineering

Is shield tunneling spoil a waste? A novel solution says no.

Shenzhen Metro Line 14 features an overall distance of 50.34 km, connecting Futian District with Pingshan District. A group of 49 TBMs have been employed for the tunneling work, adopting earth pressure balance shield method. The process of shield tunneling produces massive shield spoil containing sand, stone, gravel, clay, water, shield additives, etc. Due to its high moisture and weak mechanical properties, shield spoil has commonly been regarded as waste. Traditionally, shield spoil is shipped by special purpose vehicles to designated sites for dumping. However, dumping usually

requires a large area of land, and this is unsustainable for an over-crowded city. To address the mentioned issues, a sustainable, efficient and low-carbon solution for the disposal of shield spoil has been developed during the construction of Shenzhen Metro Line 14. It features an intelligent, modular and compact kit used on-site for deriving valuable composing materials (recycled coarse aggregate, fine aggregate, clayey residue and recycled water) from shield spoil. This particular solution, including the application of the kit, has been widely adopted in metro tunneling projects across Shenzhen. In total, an accumulative volume of nearly 11,600,000 m3 shield spoil has been treated through this solution across the city, reducing half of the dumping volume of shield spoil.