Experimen on mechanical properties of various graded collapse column fills

In order to study the mechanical properties of collapse column fill under different consolidation pressures and grain compositions. Base on similar simulated rock-soil mass sample under different states of geotechinal consolidation test preparing, we investigated the mechanical characteristics and microstructure evolution mechanism of collapse column filling by conducting the triaxial loading test, mercury intrusion porosimetry and scanning electron microscopy in different states of rock-soil mass. The results show that the rock-soil mass has obvious shaping characteristics and the stress-strain curve can be divided into four stages: pore compaction stage, stable deformation stage, deformation failure stage and creep-like stage. The compressive strength of rock-soil mass increases first and then decreases with Talbol index n. Besides, the triaxial compressive strength and Talbol index of rock-soil mass were fitted with the quadratic polynomial, with higher degree of fitting, and the Talbol index corresponding to the optimal compressive strength is 0.71, 0.65 and 0.64 respectively. Generally, the compressive strength increases linearly with the increase of consolidation pressure, while the growth rate decreases with the increase of consolidation pressure and Talbol index. According to the results of mercury intrusion porosimetry and scanning electron microscopy, it is indicated that the change of consolidation pressure and Talbol index changes the contact state between particles, which in turn affects the compressive strength of rock-soil mass specimens. With the increase of Talbol index, the interaction between particles in rock-soil mass is enhanced, the proportion of initial external load increases, the skeleton structure effect is more significant, and the compressive strength mainly comes from the contact stress concentration of rock-soil mass particles. To sum up, the mechanical test and microstructure characteristics study of rock-soil mass provide a reference for the effect of particle gradation from the macro-scale and micro-scale.