| Filling mining method is the preferred mining method to realize green mines,but with the continuous expansion of filling mining depth and scale,the cemented backfill is often in a complex environment of seepage and stress field coupling,and its mechanical properties will be greatly affected.The mechanical properties of backfill body are closely related to its own stability and safety mining.Therefore,it is of important theoretical value and engineering guiding significance for mine safety production to master the mechanical properties of cemented backfill under the action of seepage and stress coupling.Based on this,in this paper,triaxial compression tests were carried out on cemented backfill with different cement-sand ratios under the action of seepage-stress coupling with the help of triaxial creep instrument and scanning electron microscope test equipment,and the mechanical properties and damage and failure evolution law of cemented backfill under the action of seepage-stress coupling were systematically analyzed.The main research contents and conclusions are as follows:（1）Through triaxial compression mechanics experiment,the deviational-axial strain characteristic curve of cemented backfill with different cement-sand ratios under different seepage water pressure was explored,and the influence of seepage water pressure on macro-mechanical parameters of cemented backfill with different cement-sand ratios was studied.It is found that the deviatoric-axial strain curve of cemented backfill passes through six stages.With the seepage water pressure increasing from 0MPa to 0.8MPa,the peak stress,crack initiation stress and dilatation stress all showed a linear decline trend,which decreased by 26.16%-53.29%、31.34%-69.21%and 30.72%-68.95%.Compared with dilatancy stress,the effect of seepage water pressure on initiation stress is more obvious.When the ratio of cement-sand increases,the effect of seepage water pressure on stress characteristic value weakens.With the increase of seepage water pressure,the elastic modulus of cemented backfill decreases by17.23%-32.6%.The seepage water pressure has a weakening effect on the axial peak strain of cemented backfill,and the effect decreases with the increase of cement-sand ratio.（2）Through the analysis of the macro-failure morphology of test specimens,it is found that with the increase of seepage water pressure,the macro-failure crack of cemented backfill body changes from a single"Y"shaped longitudinal crack to an"X"shaped complex crack with secondary crack,and the failure type changes from a single inclined plane shear failure to a tensile failure.By means of scanning electron microscope,the microscopic morphology analysis of the fracture surface of the specimen found that with the increase of seepage water pressure or the decrease of the ratio of lime and sand,the defects such as micro-pores and micro-cracks in the cemented backfill became more obvious.With the increase of seepage water pressure,the fractal dimension of cemented backfill becomes larger,and the increase rate is0.23%-2.91%.The seepage water pressure promotes the internal damage and failure of the cemented backfill,and the improvement of the cement-sand ratio of the cemented backfill can play a certain restraint role.（3）Based on Weibull random distribution statistics theory and effective stress principle,the damage constitutive model of cemented backfill under the coupling effect of seepage and stress was constructed.Parameters m and F0 under different test conditions were obtained by fitting method,and it was found that the theoretical model was in good agreement with the test data. |
