| In recent years,there has been an increasing demand for mineral resources,with shallow resources being relatively scarce and the trend towards deeper resource extraction being inevitable.On the one hand,the concrete of the well wall will be subjected to high pressure water for a long time when it passes through the water-rich bedrock section,in addition,the concrete will produce internal pores and micro-cracks and other defects during the casting and maintenance stage,which will provide an important channel for infiltration.On the other hand,it may suffer from stress waves caused by blasting loads and may also be subjected to dynamic loads such as stress waves or seismic waves caused by blasting loads.Therefore,in this thesis,in order to simulate the actual service environment of concrete materials in the bedrock section with high pressure water subjected to complex dynamics such as ground pressure and mining disturbance,different levels of water pressure(1,5 and 10 MPa)were applied to concrete specimens,and the time of water pressure(1,7 and 14d)and impact air pressure(0.4,0.45,0.5 and 0.55 MPa)were used as influencing factors.The dynamic mechanical properties of concrete materials were investigated,while the T2 spectra,pore size distribution and microscopic morphological changes of the specimens were tested after water pressure application with the help of nuclear magnetic resonance technique and scanning electron microscopy,which have the characteristics of non-damaging and high efficiency.The main findings are as follows:(1)According to the SHPB test,it can be seen that under the same water pressure,with the increase of impact pressure,the peak stress of concrete specimens increased,while the peak strain decreased.Under the same impact pressure,with the increase of applied water pressure,the overall peak stress decreases,while the peak strain increases gradually.(2)Through the calculation of energy conservation formula,it is found that the input total energy and dissipation energy curves increase with the increase of strain in the whole process.The elastic strain energy curve shows an upward trend with the increase of strain before the specimen reaches the peak stress,and reaches the maximum at the peak point.When the specimen is damaged,the elastic strain energy curve decreases with the increase of strain.With the increase of impact pressure and water pressure,the fractal dimension of fracture of concrete samples shows an upward trend.(3)According to the NMR test,there are three peaks in the T2 spectrum distribution curve of the specimen after water pressure,and the peak value of P1 is far greater than that of P2 and P3,indicating that the pore distribution in concrete is mainly small pores.The integral of T2 spectrum distribution curve shows that the total area of T2 curve increases with the increase of water pressure.The extension of water pressure action time promotes the development of medium and small pores to large pores and micro cracks,and the number of large pores increases.At the same time,the fractal dimension of pore volume is calculated,and the microscopic characteristics of pores are characterized.Through SEM images,it is found that the internal structure of concrete under the action of external water pressure increases pores,micro cracks appear in the interface transition zone,and the bonding between mortar and aggregate is weakened.Figure[36]Table[13]Reference[92]... |
PDF Full Text Request