Abstract:

With the increasing emphasis on mine safety exploitation and the environment protection，filling mining method has been widely applied in many underground mines around the world.The damage and strength criterion of backfill is the most basic research content of filling mining and the research on the damage and strength of backfill is the most basic research content of backfill material.Thus，it is of great significance to the underground engineering to determine the mechanical properties and damage characteristics of backfill materials.In oder to reveal the damage mechanism of backfill material under uniaxial loading，firstly，the five successive stages of the stress-strain curves of backfill material under uniaxial loading were analyzed，such as initial compaction stage（OA），elastic deformation stage（AB），strain hardening stage（BC），strain softening stage （CD） and residual strength stage（DE），then taking the damage variable as the internal variable that affecting the mechanical properties of backfill materials，and the classical damage constitutive model of backfill material under uniaxial loading was derived based on the statistical damage theory，maximum-tensile strain yield criterion and strain equivalent hypothesis.Due to the backfill material contains a large number of micro defects such as micro pores and micro cracks，and there is a compaction process of the backfill specimen in the initial loading stage，a compaction hardening coefficient was proposed and introduced to the classical damage constitutive model and the modified damage constitutive model was established，which makes up the defects that the classical damage constitutive model cannot explain the compaction process of backfill in initial compression stage.The modified damage constitutive model was used to fit a variety of experimental data and was compared with the fitted results of the classical damage constitutive model.The results show that the modified damage constitutive model can not only simulate the compaction process of the backfill specimen in the initial loading process，but also be consistent with the stress-strain experimental data，and the fitting results are much better than those of the classical damage constitutive model，which fully indicates the feasibility of the modified damage constitutive model.The influence of the change of fitting parameters on the shape of the fitting curves was also studied and the control variable method was used to change one of the parameters to study the change trend of the shape of the fitting curves.The results of this study show that three different types of fitting parameters have different effects on the shape of the fitting curves.

Key words: filling body, uniaxial loading, damage variables, damage constitutive model, initial loading stage, compaction coefficient, damage evolution