Experimental Study On Dynamic Mechanical Properties Of Saturated Limestone After Freeze-thaw Cycles

In the cold region,the rock mass is affected by water and freeze-thaw cycle due to the change of seasons and the large temperature difference between day and night.Underground engineering in cold area is not only subject to mechanical disturbance,but also includes impact caused by drilling blasting.In this regard,the study of static mechanical properties of rock has no practical significance for the study of cold area engineering,but the study of rock damage patterns and wave energy changes in the process of propagation is of great significance for cold area engineering.Similarly,since the tensile strength of rock is far less than the compressive strength,brittle tensile failure is easy to occur in the case of impact disturbance.Therefore,it is equally important to explore the dynamic tensile mechanical properties of rock samples under saturated water and freeze-thaw environment as well as the change of crushing mechanism and energy for the construction and containment of rock mass engineering in cold areas.This paper takes the limestone of the roadway of Bagongshan Coal Mine of Huainan Mining Group in Anhui Province as the research object.The mass,volume,density,longitudinal wave velocity and other basic physical indexes of limestone at room temperature and after freeze-thaw cycles are tested,and the change rules of basic physical indexes of limestone at room temperature and after freeze-thaw cycles are compared and analyzed.The dynamic compression and tensile characteristics of limestone specimens with different freeze-thaw cycles were studied by using SHPB test equipment.The main research contents are as follows:1.After different freeze-thaw cycles(0,10,20,30,40,50,60,70,80,90,100 cycles),the changes of the mass,density,volume,porosity of the open type and the longitudinal wave velocity of the samples were studied.It was found that the average saturated mass increase rate and density of the rock samples showed a continuous increase.The average volume change rate and longitudinal wave velocity kept decreasing,while the porosity of open type increased first and then decreased.2.Using the RMT-150-b rock mechanics test system for limestone specimens under normal temperature static uniaxial compression test,the static stress-strain curves,and detailed analysis of the characteristics,the change of the stress-strain curve and the dynamic load cases full stress-strain curve were analyzed,found that the dynamic load cases small strain range,The failure mode of rock samples changes from brittleness to elasticity,and the plastic yield stage is obvious.3.The impact compression tests at eight loading rates were carried out using SHPB test equipment.Analyses the number of freeze-thaw cycle effect on the damage evolution characteristics of limestone physical properties,and analyzed the limestone specimens after freeze-thaw cycle effect of dynamic compression mechanics characteristic and the law of energy dissipation,found that with the increase of strain rate,a quadratic functional dynamic elastic modulus increases,and the sample dynamic peak intensity with the increase of impact velocity increase three functional.It is found that the average strain rate and dynamic compressive strength of rock samples increase with the increase of absorbed energy.4.Dynamic tensile tests under different cyclic gradients and the same impact velocity were carried out using SHPB test equipment.The dynamic tensile mechanical properties and energy dissipation law of saturated limestone specimens were discussed,and the effects of loading rate on dynamic tensile strength,failure mode and dissipated energy density of freeze-thaw saturated limestone were analyzed.It is found that both the dynamic peak strength and loading rate of saturated limestone decrease with the increase of the number of freeze-thaw cycles,while the dynamic tensile strength is positively correlated with the loading rate.The dissipated energy density increases with the increase of loading rate,and the dynamic tensile strength also increases with the increase of dissipated energy density.5.Using high speed camera to observe the normal temperature(25?)were analyzed and after different freeze-thaw cycles in SHPB experiment limestone whole process from distortion to damage and analyzes its deformation and failure characteristics,found that the failure mode as the change of loading rate can be roughly divided into two kinds,one kind is sample from the center position along the loading diameter direction throughout a main cracks,The other is that the parallelogram is formed in the central region of the rock specimen under the action of shear and tensile cracks.6.Limestone SHPB test pieces after the freeze-thaw cycle effect screening test,obtained the limestone specimens under different impact pressure average particle diameter,broken blocks of fractal dimension,the quantitative analysis of the characteristics of limestone impact,found that with the increase of impact pressure,average particle size of fractured rock blocks of the declining trend,and the changing rule of the fractal dimension of continues to increase.Figure[53]table[18]reference[88]...