(1. School of Civil Engineering，Wuhan University，Wuhan，Hubei 430072，China；2. The Key Laboratory of Safety for
Geotechnical and Structural Engineering of Hubei Province，Wuhan university，Wuhan，Hubei 430072，China；3. State Key Laboratory of Water Resources and Hydropower Engineering Science，Wuhan University，Wuhan，Hubei 430072，China；4. Zhejiang Jiaogongluqiao Construction Co.，Ltd.，Hangzhou，Zhejiang 315101，China)
Abstract：The surrounding rock mass of underground engineering generally contains a large amount of irregular and multi-scale cracks or fissures，making the seepage problem extremely complicated. Therefore，it is of great practical significance to study the seepage characteristics and flow distribution of fractured rock mass for the maintenance of engineering safety and the utilization of deep resources. In this paper，the online analysis and imaging system of NMR rock seepage process was used to carry out seepage tests on sandstone samples with different fracture characteristics，and the parameters such as Volumetric moisture content，T2 spectrum and permeability coefficient in the seepage process were analyzed. The results showed that the permeability of fractured samples was related to the angle and quantity of fractures，and the fracture initiation and propagation were affected by the increase of permeability pressure，the permeability coefficient of the samples showed a trend of slow growth and stabilization. The permeability coefficient decreased with the increase of confining pressure，and the sensitivity of the change of permeability coefficient decreased when the confining pressure exceeded 10MPa. The results of the T2 spectrum showed that the fluid diffuses through the micro pores and then accumulated in the main fractures，gradually forming a complete seepage channel. The formula for calculating the permeability coefficient derived from cubic law can well reflect the test results，and it provides a more safe and reliable method for calculating the permeability coefficient of fractured rock mass under low confining pressure in practical engineering. Finally，nuclear magnetic resonance imaging(MRI) was carried out for the seepage process to intuitively obtain the law of fluid distribution inside the fractured sample，which can accurately describe the flow state of fluid in the fractured rock sample and provide meaningful guidance for the seepage problem of fractured rock mass in practical engineering.
