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| Investigations on the seepage characteristics of fractured sandstone based on NMR real-time imaging#br# |
| WU Zhijun1，2，3，LU Huai1，2，WENG Lei1，2，LIU Quansheng1，2，3，SHEN Jianqiang4 |
(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) |
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Abstract The surrounding rock mass of underground engineering generally contains a large amount of irregular and multi-scale cracks or fissures，making seepage problems 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 show that the permeability of fractured samples is related to the angle and quantity of fractures，fracture initiation and propagation are affected by the seepage pressure，and the permeability coefficient of the samples presents a trend of slow growth and then stabilization. The permeability coefficient decreases with increasing the confining pressure，while the sensitivity of the permeability coefficient decreases when the confining pressure exceeds 10 MPa. The T2 spectrum indicates that the fluid diffuses through the micro pores and then accumulates in the main fractures，gradually forming a complete seepage channel. The formula for calculating the permeability coefficient derived from the cubic law can well reflect the test results，which provides a more safe and reliable method for calculating the permeability coefficient of fractured rock mass under low confining pressures 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 samples，which can accurately describe the flow state of fluids in the fractured rock samples and provide meaningful guidance for the seepage problems of fractured rock mass in practical engineering.
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2021, Vol. 40 
