Study On Fatigue Mechanical Properties Of Sandstone After Dry And Wet Circulation

With the rapid development of China's economy,the construction of many large water conservancy infrastructure has completed,large reservoirs and dams have played a huge role in flood control,power generation,shipping and water supply,and also caused many engineering problems.In the construction and use of large water conservancy projects,affected by the periodic load environment,the dry and wet cycle problems caused by rising water are increasingly significant.The fatigue damage of rocks caused by repeated beating of waves on the waterfront is increasingly prominent,and there are not a few earthquakes caused by large reservoirs and dams.Therefore,it is of great significance to study the rock damage test under the cycle load.The main research results of this paper are as follows:(1)The processed standard sandstone test blocks shall undergo dry and wet cycles with 0,8,16 and 24 cycles respectively.The quality after dry and wet cycle was recorded to analyze the change of water absorption rate after dry and wet.Through statistical analysis,the quality after drying decreases with the number of dry and wet cycles;the sandstone quality increases with the number of dry and wet cycles.In the early stage of dry and wet cycle,the sandstone mass changes are the largest,and with the number of dry and wet cycles,the amount of sandstone mass changes gradually slows down.The water absorption rate of sandstone samples increases with the number of dry and wet cycles,and it gradually decreases with the number of dry and wet cycles,and finally tends to be stable.(2)Explore the change law of the uniaxial mechanical characteristics of sandstone along with the number of dry and wet cycles.The test results show that the uniaxial compressive strength of sandstone shows the decrease with the number of dry and wet cycles.The uniaxial compressive strength of sandstone samples is 112.16MPa,after 8 dry and wet cycle,the uniaxial compressive strength of sandstone samples drops to 16 and 2468.55MPa,dry and wet cycles,and the uniaxial compressive strength is the 91.89MPa,peak strength in the early dry and wet cycle.The change law of peak strain and elastic modulus of sandstone samples are the same as that of peak stress,which shows a trend with the increase of the number of dry and wet cycle,changing greatly in the early stage of dry and wet cycle,and the small change amount of late dry and wet cycle.It is shown that after the dry wet cycle,the sandstone suffered the most damage in the early dry wet cycle.(3)Study the impact of upper limit stress and stress amplitude of cycle addition and unloading on rock fatigue life.The test data show that the upper limit stress of cycle addition and unloading has the greatest damage to rock fatigue life.When the upper limit stress ratio is set to 0.8,the number of sandstone is 894 times,increasing the upper and lower stress ratio to 0.85,262 times and the upper limit stress ratio to 0.9,only 9 times of sandstone samples,among many factors,the influence of the upper limit stress factor is the greatest.The fatigue life of the stress amplitude of sandstone will gradually decrease.When the stress amplitude ratio is 0.3,the sandstone fatigue life is 34 times.When the stress amplitude ratio of sandstone cycle and unloading is reduced to 0.4 by 44.12%and the amplitude stress ratio is 0.5 and 0.6 respectively,the fatigue life of sandstone is decreased by 36.84%and 25%.It can be found that when the impact of amplitude stress on rock fatigue life,the earliest damage to sandstone life.With the improvement of amplitude stress,the sandstone fatigue life gradually decreases,but its reduction amplitude gradually decreases.Figure[56]table[19]reference[62]...