Study On Damage Characteristics Of Coal Pillar Dam Body Of Groundwater Reservoir Under Dynamic And Static Load

The proposed idea of water storage in the mined-out area has effectively alleviated the contradiction between coal mining and water resource protection in the arid and water-deficient western mining area.Coal pillar dam is an important part of underground water reservoir.The static load and dynamic load disturbance caused by mining will have some impact on it.Once the coal pillar dam is damaged,it will affect the safe operation of the entire reservoir system.Therefore,studying the mechanical damage characteristics of water-containing coal samples under static load and dynamic load has important engineering guidance significance for studying the stability of coal pillar dam under the influence of mining.In this paper,through the combination of laboratory tests and numerical calculations,the mechanical damage,structural damage law of coal samples under the influence of water content and loading rate and the behavior of coal pillar dam under the influence of mining are studied from the perspective of static load and dynamic load.First,through XRD and water immersion tests,the composition characteristics of coal samples and the evolution law of water content with water immersion time are obtained: kaolinite in clay minerals enhances the water absorption and plastic characteristics of coal samples;the process of coal sample immersion includes rapid,slow and saturated In the three stages of water absorption,with the increase of the immersion time,the water absorption rate of the coal sample gradually slows down.Then,through uniaxial compression and acoustic emission tests,the mechanical damage,structural damage laws and acoustic emission characteristics of coal samples under different water content and loading rates were obtained: the compressive strength and elastic modulus were negative linear,respectively,with the increase of water content.The negative index decreases,and the increase in water content causes the coal sample to gradually change from tensile failure to shear failure,and the acoustic emission count and energy change to low frequency and low amplitude distribution,and the acoustic emission event decreases.As the loading rate increases,the compressive strength and elastic modulus increase first and then decrease,and there is a critical loading rate.At high loading rates,coal samples are violently damaged,and cone-shaped failure characteristics are more likely to form.Acoustic emission count and energy direction The distribution of low frequency and high amplitude changes,and the number of acoustic emission events decreases.Acoustic emission localization responded well and verified the influence of water content and loading rate on coal sample damage and destruction characteristics.Through the SHPB test,the mechanical damage,crack propagation and structural damage laws of coal samples under different water content and strain rates were obtained: with the increase of impact velocity,the coal sample strain rate increased exponentially,and the higher the water content,the strain rate affected the impact velocity The more sensitive.The dynamic compressive strength and elastic modulus of coal samples increase exponentially and logarithmically as the strain rate increases.As the water content increases,the dynamic compressive strength of the coal sample decreases and the dynamic elastic modulus increases,showing different mechanical characteristics from the static load process.The increase of water content makes the crack initiation and propagation of coal samples change from flat cracks to staggered cracks,and the coal sample failure time is shortened and the degree of breakage is higher.The water content and strain rate are positively correlated with the damage degree of coal sample damage.Finally,based on the test results,the damage characteristics of the coal pillar dam body under the action of different advancing speed and mining dynamic load of the adjacent working face are studied by numerical calculation.It is found that the water effect and mining disturbance have significant influence on the stress change and damage damage of the coal pillar dam body.