Experimental Study On The Influence Of Different Initial Damages On The Mechanical Properties Of Soft Rock

With the development of deeper coal mining,more complicated geo-stress could pose challenges to mining operations.The excavation process of the roadway would inevitably cause unloading and stress concentration in the surrounding rock area,which would cause different damage to different areas of the surrounding rock and eventually made the changes in mechanic properties of the surrounding rock.This could bring great difficulty to the prediction of stability of surrounding rock.Generally the changes of the macro-mechanical properties of soft rocks as typical porous media materials were caused by changes in micro-structure.According to this,the yellow fine-grained sandstone from the mining area in central region of Shandong Province was selected as the research object.To prepare soft rock with different initial damage,the soft rock was artificially pre-damaged with 40% to 80% of its compressive strength.To investigate the mechanical properties of soft rock damaged by different initial stresses,a series of microscopic observation tests and macroscopic mechanics tests was carried out,numerical simulation of soft rock after different initial damage effects was conducted based on discrete element algorithm.In addition,the mechanical properties of soft rock after different initial stress damage were explored by combining the research method of macro and microscopic analysis and statistics.The research work and results of this paper can be drawn as follows:1)The XRD diffraction and energy spectrum analysis tests were performed on the soft rocks with different initial damages,and the composition of the soft rocks after different initial damages was obtained.The morphological shapes of the soft rocks after different initial damages were studied by SEM observation.2)CT scanning was performed on the soft rock samples after different initial damage effects,and three-dimensional reconstruction was carried out on the soft rock samples based on CT scanning.The effects of different initial damages on the spatial distribution of the microstructure of soft rock samples were qualitatively characterized.The effects of different initial damages on the microstructure parameters of soft rock samples were quantitatively analyzed.3)Uniaxial and tri-axial(1MPa,3MPa and 5MPa)compression tests were carried out on the soft rock samples with different initial damage.The compressive strength andelasticity of soft rocks under different initial damages were studied in combination with micro-structure parameters.The effects of modulus and peak strain were explained from a micro-level perspective.4)Uniaxial and tri-axial(3MPa)creep tests were performed on soft rock samples with different initial damage effects.The effects of different initial damages on creep characteristics of soft rocks were studied.5)The numerical simulation of uniaxial compression failure of soft rock samples was carried out by using the test data and conclusion based on discrete element algorithm.The internal unit displacements and force chains of the soft rock specimens during the compression failure process were analyzed,and different initial damages were studied.The crack evolution in the uniaxial compression failure of soft rock samples with different initial damage was investigated.