Numerical and experimental analyses for rubber-sand particle mixtures applied in high-filled cut-and-cover tunnels

With the rapid development of the automobile industry and transportation, the disposal of scrap tires has become an internationally recognized economic and environmental problem. Fortunately, high-filled cut-and-cover tunnels (first construction and then layered backfill) provide ideal solutions for waste treatment and resource reuse as mixtures of scrap tire rubber particles and sand are used as lightweight fill material (LFM) in high-fill cut-and-cover tunnels (HFCCT). Because the backfill above the cut-and-cover tunnel (CCT) requires a large quantity of material, an appropriate ratio of scrap tire rubber particles and sand should be selected as the LFM mixture. If LFM of different thicknesses is buried above the CCT, it will inevitably bring varying degrees of influence on the earth pressure around the CCT, leading to structural deformation and soil settlement above the CCT. In this paper, a method of combining numerical simulation and model test is presented to help analyze the macroscopic and micromechanical properties of LFM through the stress–strain change and the contact force chain distribution. In the model test, certain factors influencing the earth pressure, the structural deformation, and the soil settlement mentioned above are considered, including the fill height and the embedding depth of the LFM. The results show that when the rubber fraction by volume (RF) is between 30% and 45%, the deformation and load-bearing capacity of the LFM are the most stable. Moreover, a suitable rubber fraction by volume (RF = 40%) and backfill height (between 0.63 ∼ 0.83 times the height of the CCT) can eliminate the stress concentration at the top center of the CCT.