Utilization of tunnel spoils as a lightweight filling material for the voids behind tunnel excavation contour

Tunnel spoils has put great pressure on the environment protection, geological risk control and construction cost because of the increasing tunnel construction in China. This paper aims to investigate the possibility of reusing the spoils from tunnel as a lightweight filling material for the voids behind tunnel excavation contour. Laboratory tests were carried out with an orthogonal table L16 (44) by varying the water-cement ratio from 0.8 to 1.8, the tunnel spoils content from 40% to 100%, the sodium dodecyl benzene sulfonate content from 1% to 7%, and the sodium meta-aluminate content from 0.5% to 1.5%. The tests results show that optimum formulation of light-weight filling material for the voids behind tunnel excavation contour is suggested to be water-cement ratio of 1.2 and corresponding weight percentages of tunnel spoil content (80%), sodium dodecyl benzene sulfonate (5%), and sodium meta-aluminate (1%). The optimum formulation exhibited the good performance in pumping, short gel time, high stability (2 h bleeding rate was 0%), minimal shrinkage (bulk shrinkage was 0.7%) and light weight of hardened material (the dry density was 1.19 g/cm(3)). Furthermore, a detailed microanalysis illustrated the micro-characteristics of the lightweight backfill materials. Finally, a guiding framework was proposed for recycling the discharged tunnel spoils as the lightweight backfill material. These findings suggested that dis-charged tunnel spoils can be suitably used as a lightweight backfill material for filling the voids behind exca-vation contour in tunnel construction, and such light filling material not only can fulfill the engineering requirements but also turns out cost effective and eco-friendly.

Automated summary

The increasing tunnel construction in China has posed significant challenges to environmental protection, geological risk control, and construction costs due to the handling of tunnel spoils. This study investigates the possibility of reusing tunnel spoils as lightweight filling material for filling the voids behind tunnel excavation contour. Laboratory tests were conducted to determine the optimal formulation, and a guiding framework for recycling tunnel spoils as lightweight backfill material was proposed. These findings indicate that tunnel spoils can be effectively reused, satisfying engineering requirements while being cost-effective and environmentally friendly.