爆破荷载损伤下喷射混凝土孔隙结构及三轴力学性能试验研究

Experimental Study on Pore Structure and Triaxial Mechanical Properties of Shotcrete Damaged by Blasting Load

为探究爆破荷载作用对喷射混凝土孔隙结构及力学性能的影响,利用核磁共振(NMR)检测技术及三轴加载装置对爆破荷载损伤混凝土微观孔隙结构及宏观力学性能开展试验研究,分析不同围压和爆破距离对试件T_(2)谱分布、孔隙结构变化、孔隙率、压缩强度、起裂应力及扩容应力的影响规律。结果表明:①喷射混凝土试件T_(2)谱呈3峰型,且峰1强度远高于峰2、峰3,爆破荷载作用后试件T_(2)谱峰值增大且向右偏移,T_(2)谱分布总面积增大,试件内部孔隙数目增加、直径增大。②未损伤试件孔隙率为1.63%,距离爆源80、140、200、260 mm处试件孔隙度分别为3.78%、3.01%、2.55%、1.89%,爆破荷载作用使得试件孔隙率增大,与爆源间距离的增大使得试件内部孔隙率增幅减小;试件内部微孔、中孔占比均在87.01%以上,爆破荷载作用后损伤试件微孔占比降低,中孔、大孔、裂隙占比均升高。③围压的增大使得试件峰值应力、起裂应力及扩容应力均随之增加,围压增强了试件力学性能。④爆破荷载作用后试件峰值应力、起裂应力及扩容应力均存在不同程度降低,且与爆源间距离越小,试件应力降幅越显著,孔隙度增幅也越大。在锚喷支护及混凝土衬砌过程中要充分考虑到爆破应力波对喷射混凝土力学性能的影响,应提前做好预防措施。

In order to explore the influence of blasting load on the pore structure and mechanical properties of shotcrete nuclear magnetic resonance(NMR)detection technology and triaxial loading device were used to conduct experimental research on the micro pore structure and macro mechanical properties of concrete damaged by blasting load.The effects of different confining pressures and blasting distances on the T_(2)spectrum distribution,pore structure change,porosity,compressive strength,crack initiation stress and dilatancy stress of the specimens were analyzed.The results show that:①the T_(2)spectrum of shotcrete specimens shows a 3-peak shape,and the intensity of peak 1 is much higher than that of peak 2 and peak 3.After blasting loading,the peak value of T_(2)spectrum of specimens increases and shifts to the right,the total area of T_(2)spectrum distribution increases,and the number and diameter of pores inside the specimens increase.②The porosity of the undamaged specimen is 1.63%,and the porosity of the specimens at 80 mm,140 mm,200 mm and 260 mm from the blasting source is 3.78%,3.01%,2.55%and 1.89%,respectively.The blasting load increases the porosity of the specimen,and the increase of the distance from the blasting source decreases the increase of the internal porosity of the specimen.The proportion of micropores and mesopores in the specimens is more than 87.01%.After the blasting load,the proportion of micropores in the damaged specimens decreases,and the proportion of mesopores,macropores and cracks increases.③The increase of confining pressure makes the peak stress,crack initiation stress and dilatancy stress of the specimen increase,and the confining pressure enhances the mechanical properties of the specimen.④After the blasting load,the peak stress,crack initiation stress and dilatancy stress of the specimen are reduced to varying degrees,and the smaller the distance from the explosion source,the more significant the stress reduction of the specimen and the greater the porosity increase.In the process of bolting and shotcrete support and concrete lining,the influence of blasting stress wave on the mechanical properties of shotcrete should be fully considered,and preventive measures should be taken in advance.