Dynamic Characteristics Of Cretaceous Water-rich Red Sandstone

Thick Cretaceous soft rock intercalation is widely distributed in western China.The difficulty of soft rock excavation in rich water layer is one of the major engineering problems that limit the mine construction in western China,especially after the dynamic load caused by conventional blasting and large mechanical excavation,the soft rock interlayer is prone to overall instability,and there are huge hidden dangers in the construction process.So that,it is of great theoretical and engineering significance to study the dynamic characteristics of water-rich soft rocks in Cretaceous.Based on a coal mine project in Shaanxi area,taking the Cretaceous red sandstone collected in the field as the research object,the following studies were mainly carried out:(1)The parameters such as density,porosity,uniaxial compressive strength and deformation modulus of red sandstone specimens were obtained by basic mechanical experiments;and the macroscopic water properties of red sandstone were determined by softening test,water resistance test and disintegration test.According to the test results,the Cretaceous red sandstone is sensitive to water,has strong softening property and poor water resistance ability.(2)The meso-structure of rock samples was observed by computer tomography(CT)and scanning electron microscope(SEM)devices.The pore development of the Cretaceous red sandstone is high in detail,and the cementation structure between the rock particles is obvious.A meso-structure model of red sandstone is established based on discrete medium theory,and numerical experiments of uniaxial compression are carried out on PFC2D platform.(3)The impact compression test of dry and saturated red sandstone specimens was carried out by means of 50mm diameter split Hopkinson pressure bar(SHPB)devices.Under impact loading,the tensile failure characteristics of saturated rock under pore water pressure are more obvious,and the dynamic strength and elastic modulus of saturated red sandstone are more sensitive to strain rate.(4)According to the meso-structure characteristics of red sandstone and the dynamic characteristics after saturation,the co-loading mechanism of water-rock is put forward according to the macroscopic mechanical characteristics and meso-integration characteristics of rock,and a model of visco-elastic damage is established based on the mechanism.Finally,the theoretical determination method of model parameters is given,and the reliability of the model is verified by impact compression test.