The evaluation on shock absorption performance of buffer layer around the cross section of tunnel lining

Abstract

The buffer layer around the cross section of lining structure would be the most simple and effective shock absorption measure, which can cut off the transferring paths of adverse effects from surrounding rock to lining structures. Meanwhile, it can reduce the seismic action intensity and minimize the extra pressure from surrounding rock by changing seismic acting patterns. This paper presents outcomes by investigating the interaction between lining structure and surrounding rock during excitation as well as deriving influencing parameters with regard to shock absorption performances of buffer layer. Afterwards, series numerical calculations are systematically carried out with attention given to the seismic-induced deformation responses of rock-layer-lining system. Finally, an elaborated evaluation method for assessing shock absorption performance of buffer layer with an evaluation expression is proposed, which is validated by series shaking table model tests and numerical simulations. This evaluation expression would be able to guide the selection and construction of buffer layer according to the geological conditions and construction circumstances by changing geometric and material parameters. The evaluation result would have uniqueness once all the parameters are confirmed. From this expression and its derivation process, the following findings can be drawn: (1) The cross section of tunnel has the identical particular deformation pattern in each constructing phase during excitation regardless of the existence of lining structure and buffer layer, that is, the two orthogonal diagonal diameters of cross section alternatively expand and contract. (2) The geometric and material parameters simultaneously determine the shock absorption performances of buffer layer, which grows in direct proportion to geometric variables but decreases in inversely proportion to material variables. (3) When the ratio of lining inside radius to buried depth is equal to 0.2 (i.e. r0/H = 0.2), the buried depth of tunnel engineering should be the ideal position for adopting buffer layer. Meanwhile, when the ratio of buffer layer thickness to lining inside radius is equal to 0.2 (i.e. tb/r0 = 0.2), it can be confirmed the optimal thickness of buffer layer. (4) The evaluation expression of shock absorption performance is independent of seismic waveforms but involved in the excitation intensities and the destruction states of lining structure.