不同节理间距条件下岩体双孔爆破动焦散试验研究

Dynamic caustics test of rock mass under different joint spacing conditions with two-hole blasting

采用爆炸加载数字激光动态焦散线测试系统(DLDC),研究双孔同时起爆条件下3条平行预制裂纹的扩展行为及裂纹尖端应力强度因子的变化规律,分析预制裂纹间距对其扩展及断裂破坏的影响规律。研究结果表明:双孔同时起爆条件下,炮孔近端预制裂纹尖端应力强度因子均呈先增大后减小的趋势,表明爆炸荷载作用分为两个阶段:加载阶段和卸载阶段,其中卸载阶段裂纹尖端应力强度因子逐渐减小,但扩展速度较大,在爆炸过程中占主导地位;中间裂纹扩展效果明显的试样中,其尖端应力强度因子从峰值6.52×10~5N/mm^3/2逐渐减小,并且两组试样的中间预制裂纹尖端扩展方向不同,表明中间预制裂纹扩展属于卸载扩展,爆炸应力波对中间预制裂纹尖端扩展主要起导向作用,爆生气体在中间预制裂纹尖端扩展过程中占主导作用;中间预制裂纹尖端扩展效果受与其贯通的两条次生裂纹的垂直距离影响,距离越小,中间预制裂纹尖端扩展越充分。

The dynamic behavior of two notched boreholes in PMMA material with three prefabricated cracks under blasting load was studied by a new digital laser experimental system of dynamic caustics and the influence of crack prefabricated position on crack propagation and fracture failure was analyzed. The experimental results show that the stress intensity factor of the proximal prefabricated crack of the borehole increases first and then decreases after the two boreholes detonate at the same time.The explosion load is divided into two stages： loading stage and unloading stage.In the unloading stage,the stress intensity factor of crack tip decreases gradually,but the expansion speed is larger,this stage is dominant during the explosion.The stress intensity factor of the intermediate prefabricated crack which extension effect is obvious is gradually reduced from the peak of 6.52×10^5 N/mm^3/2.In the intermediate prefabricated crack tip of the two sets of samples,the extension direction of the crack tip is different,indicating that the intermediate prefabricated crack extension belongs to the unloading extension.The explosion stress wave determines the direction of the intermediate prefabricated crack tip,and the detonation gas plays a leading role in the process of intermediate prefabricated crack.The extension effect of the intermediate prefabricated crack is affected by the vertical distance of the two secondary cracks passed through the intermediate prefabricated crack,the smaller the distance,the more fully the intermediate prefabricated crack tip expands.