The Influence Of Impact Velocity And Water Content On The Dynamic Response Characteristics Of Red Sandstone

Underground rock engineering is generally troubled by groundwater.The difference in water content will cause variation in the mechanical properties of the rock,which leading to changes in the dynamic response characteristics of the rock mass under dynamic loads during the drilling and blasting excavation process.Using split Hopkinson pressure bar to carry out impact tests on red sandstones with different water content at different impact velocity.The stress-strain curve,average strain rate and energy distribution ratio of red sandstone are obtained for that investigate the effect of impact velocity on dynamic strength and deformation characteristics,strain rate effects,damage conditions and energy dissipation characteristics of red sandstones with different water content.The main research contents and conclusions are as follows:(1)When the impact velocity is 8m/s,10m/s and 12m/s,the maximum dynamic strain first increases then tends to remain unchanged with the increase of water content,but when the impact velocity is 15m/s,the maximum dynamic strain first increases then decreases with the increase of water content.The relationship between the maximum dynamic strain and the moisture content is a quadratic function.The increase of impact velocity leads to a larger variation range of maximum dynamic strain with water content.(2)The average strain rate of red sandstone increases slightly with the increase of water content,which conforms to the exponential function relationship;the increase of impact velocity enhances the sensitivity of red sandstone strain rate to water content change.The strain rate of red sandstone linear increases with the increase of the impact velocity.The relationship between the average strain rate and impact velocity of red sandstone conforms to the first order function.At higher water content,the average strain rate is more significant with the increase of impact velocity.(3)With the increase of water content,the dynamic peak stress of red sandstone gradually decreases,and the rate of decline gradually slows down,which conforms to the exponential function relationship.The increase of impact velocity leads to a larger range of dynamic peak stress variation with water content.When the moisture content causes the average strain rate to increase,the dynamic peak stress decreases,but this trend does not indicate the rate dependence.When the impact velocity causes the average strain rate to increase,the dynamic peak stress increases,which have a positive correlation and conforms to the trend of a power function,but as the water content increases,this positive correlation weakens.(4)The fragmentation degree of red sandstone increases with the increase of impact velocity.When the impact velocity is 15m/s,the fractal dimension of red sandstone fragments increases first and then tends to remain unchanged with the increase of water content,which are 2.12,2.49,2.59,2.66,2.72,2.72,respectively.(5)With the increase of water content,the energy reflection coefficient increase;the energy transmission coefficient decreases but the rate of decrease gradually becomes slower;the energy dissipation coefficient first increases then tends to remain unchanged at an impact velocity of 8m/s,but it first increases and then decreases with the increase of water content at impact velocities of 10m/s,12m/s and 15m/s.The energy transmission coefficient and the moisture content conform to the exponential function relationship;the energy dissipation coefficient and the moisture content conform to the quadratic function relationship.With the increase of impact velocity,the variation range of energy transmission coefficient and dissipation coefficient with water content is larger,and the water content is smaller when the energy dissipation coefficient reaches the peak value.