Dynamic Mechanical Properties Of Open-Pit Slope Rock In Cold Region Under Different Natural Conditions

In recent years,many large-scale geotechnical engineering projects have been carried out in the cold regions of China.At present,the research conditions of freezing-thawing rock are concentrated in normal temperature and static state,and the dynamic mechanical properties of rock with different water content and temperature are seldom studied.In this paper,with the help of SHPB experimental system with low temperature control system,dynamic tensile and compression mechanics experiments were carried out on rock samples under three states of normal temperature and dry,normal temperature and sufficient water and low temperature freezing,in order to explore the influence of temperature and water content on dynamic mechanical properties of rock,and analyze the mesoscopic changes and energy dissipation law of freezing-thawing rock.The details are as follows:（1）The microstructure of rock such as pore size distribution,porosity and T₂ spectrum changes during freezing and thawing were studied by using nuclear magnetic resonance system.The quantitative law of freezing-thawing cycle number,density,wave velocity,porosity and other macro and micro basic physical parameters is obtained.The pore changes in rock samples are not single and continuous,but dynamic.The porosity,wave velocity and density ofФ50×25mm rock sample with smaller size are more affected by freezing and thawing.（2）The dynamic compressive mechanical properties of rock samples are obviously degraded by freezing and thawing cycles.In the early freezing-thawing stage,the dynamic compression stress-strain curve has no obvious compaction stage,and the compaction stage of the curve appears in the late freezing-thawing stage.The decreasing rate of the curve after the peak changes with the increase of impact pressure,and the peak strain has no obvious change rule.Freezing-thawing effect also deteriorates tensile mechanical properties.There are fewer compaction stages on dynamic tensile stress-strain curve,and there are no obvious laws on peak strain and brittleness.（3）The effect of freezing and thawing on dynamic strength deterioration of rock samples is mainly reflected in the early and middle period of freezing and thawing cycle.Under the condition of low temperature,the compressive strength of rock matrix is increased due to thermal expansion and cold contraction.The sensitivity of dynamic strength to strain rate decreases due to freezing and thawing cycles.Freezing and thawing cycles change the strain rate dependence and deformation resistance of rock samples in different states.The freezing-thawing cycle and saturation interaction weaken each other,and the strength of rock samples converging after freezing-thawing in different states.（4）In different states,incident energy and absorbed energy decrease with freezing-thawing,and the influence range of freezing-thawing cycle on incident energy is smaller than that on absorbed energy.Under the same strain rate,the energy of frozen rock samples is most affected by freezing and thawing.For the five freezing-thawing cycles,incident energy and absorbed energy increase with the increase of strain rate.The freezing-thawing cycles have little influence on incident energy as they do on absorbed energy,and the freezing-thawing cycles change the sensitivity of incident energy to strain rate...