Evolution Of Mechanical Properties And Damage Mechanism Of Cemented Paste Backfill Under Seepage

The cemented paste backfill,as a kind of artificial porous medium,is not only affected by in-situ stress,gravity stress and other stress fields,but also by seepage of groundwater,which leads to the deterioration of its mechanical properties and the reduction of its bearing capacity,leading to the collapse of the stope.Under the first safety situation,conservative design should be adopted The mechanical index of paste backfill will lead to the excessive amount of cementitious materials.In order to prevent the occurrence of accidents and reduce the cost of filling,this paper takes the cemented paste backfill under different osmotic water pressure as the research object,carries out uniaxial compression test on the cemented paste backfill on the microcomputer controlled electronic universal test system,studies the axial stress-strain curve of the cemented paste backfill under different osmotic water pressure,and analyzes the peak stress,peak strain and elasticity of the cemented paste backfill The change rule of mechanical parameters such as modulus with osmotic pressure.At the same time,nuclear magnetic resonance(NMR)technology,scanning electron microscope(SEM)and other advanced detection methods were used to explore the evolution and damage law of the cemented paste backfill microstructure under different osmotic pressure.Finally,with the help of Weibull random distribution statistical theory,the damage constitutive model of cemented paste backfill under different osmotic pressure is established,and the influence of random distribution parameters on the model is analyzed.The main research contents and results are as follows:(1)The uniaxial compression test of the cemented paste backfill under seepage shows that the peak strength and peak strain show different trends with the change of seepage water pressure.When the osmotic pressure increases from 0MPa to 0.8MPa,the peak strength decreases from 6.41MPa to 5.07MPa,and the peak strain increases from 1.19%to 1.35%.Compared with the natural state(osmotic pressure is 0MPa),the change rate of peak strength ranges from 10.28%to 20.9%,and the change rate of peak strain ranges from 7.8%to 13.45%.The relationship between deformation parameters and osmotic pressure is a linear function,and decreases with the increase of osmotic pressure.When the osmotic pressure increases from0MPa to 0.8MPa,the elastic modulus of the cemented paste backfill increases from7.67×10~2MPa to 5.94×10~2MPa,secant modulus from 5.86×10~2MPa to 4.79×10~2MPa Compared with the natural state(osmotic pressure is 0MPa),the change rate of elastic modulus ranges from 8.87%to 22.56%,and the change rate of secant modulus ranges from 8.02%to 18.26%.(2)It is found that when the osmotic pressure is low,the surface of the cemented paste backfill is mostly Y-shaped crack,and the failure mode is single shear failure.When the osmotic pressure is high,there is a main crack on the surface of the cemented paste backfill,and there are many secondary cracks around it.The failure mode is mostly tensile failure,and local shear failure,The destruction forms are complex.The fractal theory is used to quantitatively describe the crack morphology.It is concluded that the fractal dimension of surface crack increases with the increase of osmotic pressure.When the osmotic pressure increases from 0MPa to 0.8MPa,the fractal dimension changes from 1.1 to 1.17.It shows that osmotic pressure can promote the damage of the cemented paste backfill.(3)The results show that there are three peaks in the T2 spectrum curve of the cemented paste backfill before and after the action of osmotic pressure.After the action of osmotic pressure,the T2 spectrum area of each sample increases significantly,that is,the porosity increases,and the small pore spectrum peak area accounts for 90%of the total peak area.The results show that there are a lot of holes and cracks in the paste backfill under different resolutions.The fractal theory is used to analyze the internal structure of the cemented paste backfill under different osmotic pressure.It is found that the fractal dimension changes from1.83 to 1.95 when the osmotic pressure increases from 0MPa to 0.8MPa.It shows that the higher the osmotic pressure is,the higher the disorder degree is,which matches with the increase of fractal dimension of surface cracks under different osmotic pressures.(4)Based on the theory of Weibull random statistical distribution,the damage model of the cemented paste backfill is established,and the mathematical expression is derived.The model curve is highly consistent with the experimental curve.The different values of parameters m and F0 are discussed.It is found that the geometric shape of stress-strain curve of the cemented paste backfill does not change significantly when the parameters are different,which mainly affects the post peak deformation of the cemented paste backfill The effect is not significant in the compaction stage and elastic deformation stage.