Experimental Research On Mechanical Properties Of Tuff Under Different Cycle Conditions

As the temperature difference between the four seasons and day and night increases,the degree to which the rock and soil are affected by the freeze-thaw cycle and the dry-wet cycle in the natural environment will gradually increase.Finally,the rock and soil will be affected by the freeze-thaw cycle and the dry-wet cycle.The physical and mechanical properties also have obvious deterioration.Therefore,this paper takes the tuff in Ningbo,Zhejiang as the research object,carries out the freezethaw cycle,dry-wet cycle and dry-wet-freeze-thaw cycle test research,and compares and analyzes the changes of the physical and mechanical parameters of the tuff under different cycle conditions.The main research conclusions are as follows:First of all,for the experimental study of the cycle time,the freeze-thaw cycle time is divided into the freezing process time and the melting process time.The freezing process time is further divided into the initial freezing stage,the water-ice phase transition stage and the deep freezing stage,and the melting process is also divided into the initial melting stage.In the same way,the cycle time of the ice-water phase transition phase and the deep melting phase is also divided into corresponding phases.The time required for the complete freeze-thaw cycle,the time required for the freezing process,and the time required for the thawing process all satisfy the increase in the number of freeze-thaw cycles,but the rate of increase gradually decreases.Except for the water-ice phase transition phase and the ice-water phase transition phase,the time required for the other phases is similar to the time required for the freeze-thaw cycle.Secondly,according to the experimental study on the change law of physical properties,as the number of freeze-thaw cycles increases,a small amount of debris falls off the edges and corners of the rock sample,and the quality gradually decreases with the increase of the number of freeze-thaw cycles,but the overall quality changes.If it is smaller,the decrease value of the wave velocity will gradually increase,but the increase rate will gradually decrease.After the sample undergoes different wet and dry cycles,the surface of the sample does not change significantly,and the quality and wave speed of the sample only change slightly in the later stage.After the sample undergoes different times of dry-wet-freeze-thaw cycles,the degree of particle shedding of the sample is slightly greater than the degree of particle shedding under the freeze-thaw cycle.The overall mass loss rate of the sample is relatively low,but the loss rate is greater than the mass loss rate after the sample undergoes a freeze-thaw cycle.The more times the sample undergoes wet and dry cycles,the influence of freeze-thaw cycles on the wave speed of the sample gradually increases.Finally,according to the experimental study on the change law of mechanical properties,after the freeze-thaw cycle test,the peak compressive strength of the sample is continuously reduced,but its strength reduction rate,strain and frost resistance coefficient are gradually reduced,and the degree of reduction is gradually reduced.The failure of the rock sample is no longer destroyed according to several failure planes.The main failure plane gradually changes from the initial inclined plane to the vertical plane,and finally there is no obvious failure plane.In the dry-wet cycle group,as the number of dry-wet cycles increases,the decrease in the peak compressive strength of the sample is smaller than that under the freeze-thaw cycle sample,and with the increase in the dry-wet cycle With the increase of the number of times,the fine particles of the tuff sample gradually increase,but under any number of wet and dry cycles,the fragments of the sample after uniaxial compression failure will have a certain failure surface failure.In the dry-wet-freeze-thaw cycle group,with the increase of the number of freeze-thaw cycles,the influence of the dry-wet cycle on the compressive strength of the different groups of samples gradually decreases,and the change law of the freezethaw coefficient is also similar.When the number of freeze-thaw cycles gradually increased,the particle size after uniaxial compression failure is relatively small,and the fine particles accounted for more.