In order to study the uniaxial compression mechanical characteristics of limestone under high temperature treatment, the physical characteristics test, uniaxial compression test, SEM electron microscope scanning and XRD diffraction analysis were carried out on limestone treated at room temperature (25 ℃) and high temperature (100 ℃, 200 ℃, 300 ℃, 400 ℃, 500 ℃ and 600 ℃). Based on the micro-fracture law of rock, the mechanical characteristics of limestone under uniaxial compression were analyzed. The results show that with the increase of treatment temperature, the apparent color of limestone changes from gray to reddish brown, and the volume growth rate and mass loss rate increase nonlinearly. High temperature treatment makes limestone micro-texture stratification, fracture development, pore dissolution, and the fluctuation and sharp angle characteristics of compression fracture surface are significant. High temperature catalyzes the pyrolysis and chemical reaction of limestone mineral components, and there is a significant linear correlation between the comprehensive hardness coefficient and the firmness coefficient of rock. It is revealed that the threshold temperature of thermal damage of limestone is 200 ℃, and the peak strength and elastic modulus reach the peak at this temperature.

The strata in urban backfill areas mostly exist in the form of loose soil-rock mixture, with high structural porosity, low strength, and poor engineering performance. They are sensitive to dynamic loads such as tunnel construction disturbance and subway train operation. The hysteretic curve can reflect the deformation, stiffness and energy dissipation of soil under dynamic load. It is of great significance to study the hysteretic curve of soil-rock mixture for the construction and operation safety of subway in backfill area. Using KTLDYN servo-controlled dynamic triaxial test system, the cyclic load test on soil-rock mixture samples in backfill area was carried out by means of cyclic loading. The effects of stone content (P), water content (ω), consolidation stress ratio (k_c) and loading frequency (f) on the morphological characteristics (including adjacent center spacing (d), long axis slope (k), enclosing area (S) and degree of non-closure (ε_p)) and backbone curves of hysteretic curves are investigated. The results show that the typical hysteretic curves of soil-rock mixture are in long fusiform shape on the whole, with pointed lobes at both ends. With the increase in vibration level, d, S and ε_p increase nonlinearly, while k decreases logarithmically. For the same vibration level, d and ε_p decrease with the increases of P, k_c and f, and first decrease and then increase with the increase of ω. k increases with the increases of P, k_c and f, and increases first and then decreases with the increase of ω. S is positively correlated with P, increasing first and then decreasing with the increase of ω, and decreasing with the increases of k_c and f. The dynamic stress and slope of backbone curve increase with the increases of P, k_c and f when the dynamic stress variation is the same, and they first increase and then decrease with the increase of ω.