动态加载率对巷道内裂纹扩展速度及动态起裂韧度的影响

在巷道的钻爆法掘进过程中,巷道围岩周围将诱发较多的径向裂隙。为了研究不同冲击载荷作用下巷道内裂纹扩展速度及起裂韧度的变化规律,采用落锤冲击试验机对裂纹巷道模型试件进行冲击加载,模型试件选用青砂岩制作;试验中,采用裂纹扩展计进行裂纹扩展速度及起裂时间的测定,对不同冲击高度下裂纹扩展速度及起裂时间进行分析;随后采用ABAQUS有限元程序结合试验-数值法计算巷道模型试样在不同动态加载率作用下的动态起裂韧度,并对起裂韧度的变化规律进行统计分析。得出如下结论:①巷道内预制裂纹的扩展速度随着动态加载高度的增加而增大,随后逐渐趋于稳定,实测裂纹扩展速度略小于0.38倍砂岩纵波波速;②巷道内预制裂纹的起裂时间,随着动态加载率的增加呈缓慢下降的趋势,降低幅度范围约为50μs;③随着动态加载率的增加,巷道内裂纹的动态起裂韧度逐渐增大,上升趋势也逐渐加大。

Effect of dynamic loading rate on crack propagation velocity and dynamic fracture toughness in tunnels

In the process of tunnel blasting excavation,blasting activities may induce radial cracks in the surrounding rock of tunnels.In order to investigate the propagation velocity and dynamic initiation toughness of cracks in a tunnel under different impact loads,impact experiments by using green sandstone tunnel models with a mode I crack were carried out by the middle-low speed drop weight impact test system.In the tests,the crack propagation velocity and crack initiation time were measured by crack propagation gauges(CPGs),and the measuring results were analyzed.The dynamic stress intensity factors were calculated by using ABAQUS code,and the dynamic initiation toughness under different dynamic loading rates was obtained by using an experimental-numerical method,and the property of initiation toughness was analyzed.The studying results show that:①Crack propagation velocities increase with dynamic loading rates,and as loading rate is larger than a certain value,it gradually tends to be a constant value.Crack propagation velocity is slightly less than 0.38 times of the P-wave velocity of sandstone.②Crack initiation time decreases slowly with the dynamic loading rates,and the range of reduction is about 50μs.③As the dynamic loading rate increases,the dynamic initiation toughness increases gradually.