Research On Early Damage Characteristics And Later Mechanical Behavior Of Thin-cemented Cement Layer Specimens

In the deep mine,the original rock has high stress,the surrounding rock of the roadway is broken,and it is very easy for the rock to fall,and the gas and other gases contained in the coal seam are spilled into the roadway.There is a danger at any time.However,the cement layer was affected by the stress of the roadway after the injection,which made the original design unable to achieve the expected results.Therefore,the test piece was made based on the thin sprayed cement layer,and the early damage characteristics and the influence of the mechanical behavior in the later period were studied.In this paper,the RLW-2000 triaxial rheometer was used to conduct an experimental study on early damage and mechanical behavior of indoor cement specimens,analyze the damage mechanism and basic characteristics of early cement specimens,and study the different strengths of early cement specimens on later strength and deformation As well as the influence law of elastic modulus and Poisson’s ratio,the perturbation of damage to creep failure strength,instantaneous strain and creep strain is discussed.The main conclusions are as follows:(1)According to the stress-strain curve of early-age cement specimens,the damage solution equation is determined,and the damage curve is divided into three stages:compaction damage,damage accumulation and damage explosion;the damage cement specimen creep curve is divided into three In this stage,the damage evolution parameters were introduced to improve the Nishihara model,and the creep model of the damaged cement specimen was obtained.(2)As the stress ratio of early-age cement specimens decreases,the average axial strain,transverse strain,and Poisson’s ratio of early-age cement specimens decrease overall,but the elastic modulus shows an increasing trend.The 80% stress ratio of the aged cement specimens is the damage threshold,and the acoustic emission detection method is used to verify that the damage mechanism of the early cement is in compliance.(3)As the early damage of the cement specimen increases,the compressive strength and elastic modulus of the damaged cement specimen increase first and then decrease,while the axial strain,lateral strain and Poisson’s ratio generally increase;at the same time The post-carrying performance of cement specimens before and after the damage threshold of cement specimens respectively shows strength enhancement and strength attenuation;the instability modes of damaged cement specimens can be divided into cumulative penetration instability and initiating divergence instability.(4)As the amount of damage decreases,the creep damage strength of earlydamaged cement specimens shows a trend of rapid increase first and then stability,while the primary damage strain and primary creep strain become a trend of rapid decrease first and then slow decrease;The improved creep model has a high correlation between the theoretical curve and the experimental data curve,and is suitable for characterizing the creep characteristics of damaged cement specimens;the creep instability of damaged cement specimens is divided into two modes: energy storage instability and energy dissipation instability.