Analysis of viscoelastic deformation behavior of shallow-buried decomposed-rock tunnel after preliminary support

In order to analyze the viscoelastic effect of shallow-buried decomposed-rock tunnel surrounding rock deformation with time after preliminary support, the analytic solutions of equivalent elastic modulus and equivalent coefficient of confining pressure were derived adopting inverse back analysis methods firstly. Secondly, taking the concrete engineering practice of shallow-buried and blind excavated decomposed-rock tunnel for example, which belongs to the shore segment of Xiang'an subsea tunnel engineering in Xiamen, Fujian Province, and the representative sections and collecting their surrounding rock measured displacement data after preliminary support are selected, the regularity of the ratio of equivalent coefficient of confining pressure to equivalent elastic modulus varying with time after surrounding rock preliminary support of this type tunnel was derived by the analytic means of mathematic statistics; and the representative sections and collecting their surrounding rock measured displacement data after preliminary support are selected. Finally, the viscoelastic model of surrounding rock deformation after preliminary support is established; and its viscoelastic effect of deformation with time was researched. The research results show that in the first place, the ratio of equivalent coefficient of confining pressure to equivalent elastic modulus increases in monomolecular growth model without external action such as rainfall after shallow-buried decomposed-rock tunnel surrounding rock preliminary support; and it will finally be stabilized. Namely, the viscoelastic effect of surrounding rock deformation varying with time agrees with this regularity also; and the surrounding rock deformation varies in the inverse ratio of equivalent coefficient of confining pressure. In addition, in the tunnel segment of surrounding rock with higher stiffness and weak groundwater moving, the deformation of surrounding rock may converge more rapidly after its preliminary support.