Experimental and applied research on similar materials to granular mixtures for solid-liquid coupling model test of an underwater tunnel

To study the response characteristics of seepage and stress fields induced by underwater shield tunnelling in granular mixtures, similar materials suitable for similar simulation experiments were developed based on the solid-liquid coupling similarity theory. Firstly, twenty-five groups of proportioning schemes were established for preparing the specimens using the orthogonal test method, and the aggregates content, fines content, cementaggregate ratio and coarse-to-fine aggregate ratio were taken as controlling factors. Results show that the content of aggregates and fines are the two critical controlling factors that influence the bulk density; the cementaggregate ratio is the most significant factor deciding cohesion; and all the factors exert certain controlling effects on the internal friction angle and permeability coefficient. Furthermore, the regulative effects of silicone oil (SO), liquid paraffin (LP), industrial glycerin (IG) and petrolatum jelly (PJ) on the hydro-mechanical properties of similar materials were quantitatively analyzed. After normalizing the effects of different regulators, the goodness-of-fit between the additive amounts of regulators and increase rate of similar materials' parameters is greater than 0.97, and similar materials have a moderate range of parameters, steady performance, convenient preparation and affordable cost. Finally, the newly-developed similar materials were successfully applied to the excavation seepage model test in the Bahe Tunnel of Xi'an Metro Line 9. The evolution laws of osmotic pressure, surrounding rock stress and internal force of lining were obtained, which facilities to reveal the mechanism of water and sand gushing as well as liner deterioration under the actions of groundwater seepage and excavation disturbance. The material can effectively simulate the granular mixtures, which provides the scientific basis for better selection and configuration of solid-liquid coupling materials.