Study on the Strength Characteristics and the Mix Proportion Design Method of Similar Materials of Transparent Cemented Soil in Tunnel Surrounding Rock
The visualization physical modeling test plays an increasingly significant role in mechanical mechanism and deformation characteristics of tunnel engineering, and the surrounding rock similar material meeting the transparency and similarity theory is key to ensure the great agreement between the testing results and practical engineering. This paper summarizes the strength property of prepared transparent cemented soil with similar material based on statistical analysis of orthogonal test data, so as to explore the quantitative design method representing the mix proportion of similar material of tunnel surrounding rock. The experiment utilized molten quartz sand, nano-silica, and N-dodecane mixed with 15# white oil as raw materials, designing a 2-factor, 3-level orthogonal test to measure unit weight, internal friction angle, and cohesion. Using the concatenation method, multiple nonlinear regression equations were fitted to describe the relationships between unit weight, internal friction angle, cohesion, and both the particle size of quartz sand and the cement-stone ratio (the mass ratio of nano-silica to quartz sand). The joint solution of these regression equations was then employed to determine the optimal quartz sand particle size, cement-stone ratio, and geometric similarity constant. The test results indicate that: 1) the ranges for unit weight, internal friction angle, and cohesion of the transparent cemented soil are 16.13~12.53 kN/m3, 27.07°~14.82°, and 31~2.3 kPa, respectively, with shear stress-shear displacement curves displaying both post-peak platform and post-peak drop characteristics;2) T-tests and F-tests reveal that the independent variables in the fitted nonlinear regression equations significantly influence the dependent variables, and the equations are authentic and reliable; 3) Combining the regression equations for specific gravity and internal friction angle, the optimal particle size and cement-stone ratio of quartz sand are calculated, which are then substituted into the cohesion regression equation to finalize the cohesion calculation. This study establishes a novel quantitative design method for determining similar material mix ratios and geometric similarity constants, providing a theoretical foundation and data reference for designing visual physical model tests in tunnel engineering.