正梯度冲击下冻结红砂岩力学性能及损伤效应研究

A study on mechanical properties and damage effect of frozen red sandstone under positive gradient impact

随着冻结法立井建设在西部矿区富水地层的大规模运用,研究冻结壁在爆破、机械破岩等不同强度冲击荷载下的力学特性及损伤效应,对解决冻结壁开裂渗水及失稳透水问题具有重要意义。因此,该文章以甘肃省五举煤矿冻结凿井穿越的白垩系富水软岩为研究对象,分析不同冻结温度(25℃,-5℃,-10℃,-15℃和-20℃)红砂岩在正梯度冲击下(即冲击荷载逐渐加强)的动力学特性,同时采用核磁共振(nuclear magnetic resonance,NMR)技术对冲击过程中红砂岩孔隙数量、面积及孔隙度的变化进行检测,分析冻结红砂岩在正梯度冲击作用下的损伤演化规律。结果表明:相较于低、中速率冲击,在高速率冲击时,冻结红砂岩应变率随冻结温度的下降变化明显,温度效应显著;不同冻结温度红砂岩的峰值应力和弹性模量增幅随冲击荷载的升高而增加;峰值应变在-5℃时达到最大值,在-10℃~-20℃随冻结温度的降低其增长趋势逐渐放缓;由T谱曲线及谱面积可知,在正梯度冲击作用下,温度由25℃下降到-10℃,小孔隙孔径先减小后增大,数量先增加后降低,中、大孔隙孔径及数量则相反,谱面积先降低后升高,由-15℃下降到-20℃,小孔隙数量增加、孔径减小,中、大孔隙数量和孔径均呈小幅稳定增长,谱面积呈小幅增长;采用孔隙度的变化定义岩石损伤度,发现在正梯度冲击作用下,-10℃红砂岩的损伤趋势和损伤度最大,在-5℃~-10℃内出现损伤薄弱区。

With the large-scale application of frozen shaft construction in water rich strata in western mining area,it is of great significance to study the mechanical properties and damage effects of frozen walls under different strength impact loads such as blasting and mechanical rock breaking.The Cretaceous water rich soft rock crossed by frozen sinking in Wuju coal mine in Gansu province was taken as the research object.The dynamic characteristics of red sandstone with different frozen temperatures(i.e.,25℃,-5℃,-10℃,-15℃and-20℃)under positive gradient impact(The impact load is gradually strengthened)were analyzed.At the same time,the changes of pore number,area and porosity of red sandstone during impact were detected by nuclear magnetic resonance(NMR)technology,and the damage evolution law of frozen red sandstone under positive gradient impact was analyzed.The results show that the strain rate of frozen red sandstone changes obviously with the decrease of frozen temperature and the temperature effect is significant compared with low and medium velocity impact.The stress and elastic modulus of red sandstone at different frozen temperatures increase with the increase of impact load.The strain reaches the maximum at-5℃,and the growth trend slows down with the decrease of frozen temperature between-10℃and-20℃.According to the Tspectrum curve and spectrum area,under the positive gradient impact,the temperature decreases from 25℃to-10℃,the pore size of small pores first decreases and then increases,and the number first increases and then decreases,while the pore size and number of medium and large pores are on the contrary,the spectral area first decreases and then increases,and decreases from-15℃to-20℃,the number of small pores increases and the pore size decreases,and the number and pore size of medium and large pores increase slightly and stably.The change of porosity is used to define the rock damage degree.It is found that under the positive gradient impact,the damage trend and damage degree of-10℃red sandstone are the largest,and there are weak damage areas in the range of-5℃--10℃.