Numerical simulation study on sand gravel layer collapse induced by tunnel lining damage

To solve the problem of ground collapse induced by broken and leaking sand during the construction and operation of tunnel lining, a model library of irregularly shaped sand and gravel and a silo-type water-sand surge model were established based on PFC software. By setting different thickness-to-span ratios, gravel particle contents and particle shapes, the soil-sand transport law and the mechanism of soil arch formation at the leakage were explored. The results showed that the displacement and deformation of the soil body in the sand burst process are inversely proportional to the thickness-to-span ratio, and the skeleton effect of gravel particles becomes more and more obvious with the increase in the thickness-to-span ratio, and the number of calculation steps required to form the soil arch decreases gradually with the increase in the thickness-to-span ratio after it is larger than the critical thickness-to-span ratio. The change of load on the base plate and the coordination number between particles can be used as indicators to reflect the formation of soil arch. The fluctuation of load on the base plate and coordination number indicates that the formation process of force arch is a cyclic process of formation-destruction-reformation-destruction. Coarse particle content and shape together determine whether the soil can form a soil arch effect, the higher the content of gravel particles in the soil, the easier it is to form soil arches at the leakage openings, and when the ratio of the long and short axes of gravel particles l > 2.0, it is easier to form stable force arches.

Automated summary

A study was conducted to investigate the formation of soil arches during soil and sand burst and leakage, using a model library and model. The results showed an inverse relationship between displacement and deformation of the soil body and the thickness-to-span ratio, as well as an increase in the skeleton effect of gravel particles with an increase in the thickness-to-span ratio. The number of calculation steps required for soil arch formation decreased when the thickness-to-span ratio exceeded a critical point. Load fluctuation and coordination number served as indicators of soil arch formation.