Mechanical response analysis of tunnel overhead small conduit-arch-anchor support system in loose enclosed rock section

Abstract

[Objective] In order to investigate the mechanical response law of the overreach small conduit-arch anchor support system in the construction of fractured perimeter rock section, Tongzi Tunnel was taken as the engineering background, and constructs the synergistic mechanical model of “overreach small conduit-steel arch-anchor”[Methods] Based on the theory of structural mechanics, combining Simpson's numerical integration method with the principle of virtual work, the load transfer path is analyzed step by step, and the parameters are dynamically calibrated by using the actual tunnel measurement data. [Results] The result show that the model can accurately predict the transfer loads(shear force, bending moment, axial force), arch foot displacement and arch settlement under different excavation steps, and the error is less than 9% compared with the on-site monitoring data, which verifies the reliability of the model; the overtopping small conduit grouting improves the stability of the surrounding rock significantly, and its anchors share about 6% of the surrounding rock load, and the reduction in the spacing of the steel arch frame can inhibit the settlement effectively, but it needs to take into account the economy. The spacing of steel arch can effectively inhibit the settlement, but need to take into account the economy, it is recommended that the spacing of Ⅳ perimeter rock section take 80 cm. [Conclusion] The three-dimensional cooperative mechanical model proposed in this study realizes for the first time the load analysis of the whole path of the overrun support system from the grouting anchor solid to the locking foot anchor, which provides a reference basis of both theoretical rigor and engineering practicability for the design of the dynamic support of overrun small catheters.

Keywords

tunnel excavation / overhead small conduit / arch anchor / excavation step spacing / mechanical transfer / settlement prediction / influence factor / fractured perimeter