Construction mechanics behavior of double-layer primary support arch cover method

Abstract

The double-layer primary support arch cover method, as a recently flourishing innovative construction technique, is steadily gaining prominence in subterranean engineering projects across various regions in China. Its widespread adoption is particularly notable in the construction of tunnels within soft upper and hard lower geological strata. This article, grounded in practical field observations, conducts a comparative analysis between the primary support arch cover method and the double-layer primary support arch cover method in terms of deformation control. The results underscore the deformation control advantages offered by the double-layer primary support arch cover method.To delve deeper into the construction mechanics of the double-layer primary support arch cover method within soft upper and hard lower geological strata, this study employs indoor model experiments and numerical simulations. It scrutinizes deformation patterns, including surface subsidence, arch crown settlement, and structural stress, during the tunnel excavation process employing the double-layer primary support arch cover method. Additionally, drawing insights from its practical application in the construction of Qingdao Metro Line 2′s Xiaogang Station, this research explores the applicability and construction mechanics of this method.The study reveals that the double-layer primary support arch cover method efficiently harnesses the load-bearing capacity of the underlying hard rock formations, effectively controlling deformations in the surrounding rock within the arch section. This article also highlights the critical importance of the removal of temporary vertical supports to construction safety and elucidates the mechanical behavior transition and operative mechanisms of the second-layer arch during the construction process.