| The development and utilization of global nuclear energy not only brings great convenience to human beings,but also brings huge security risks to the living environment of human beings with a large amount of high-level radioactive waste."deep geological disposal"is one of the most promising means of safe disposal of high-level radioactive waste at present.Beishan pre-selection zone in gansu province is one of the five geological disposal pre-selection zones in China.With the selection of key areas in the pre-selection zone and the selection of candidate sites,some key hydrogeological problems need to be solved urgently.Xinchang area is a key area of disposal reservoir in beishan pre-selected area in gansu province.The main part of its surrounding rock is granite with low porosity,good densification and low water cut.However,the existence of complex geological structural planes in granitic rocks makes the interconnected joints and fissures in the surrounding rock constitute the dominant path for nuclides accompanying groundwater migration in high-level radioactive waste.This paper focuses on the development and distribution of structural planes in granite and the seepage characteristics of fluids in fractured rock mass.50 groups of measuring points were arranged in the 4km2 area around the BS32,BS36 and BS39 boreholes in the middle of the Xinchang area to conduct structural plane surveys.Using the equal-area erythroscopic projection method combined with Dips software,it was determined that there are 4 sets of superior joints in the middle of the Xinchang area:279°?79°,98°?76°,227°?79°and 36°?76°.Using the circular window method,the average track lengths of 4 sets of dominant joints were obtained:500.1764mm,520.6401mm,394.8174mm and 407.5427mm;the joint surface density values:6.15333m-2,7.94875m-2,3.67241m-2 and 4.73334m-2.The statistical characteristics of the joints of the dominant group obtained above were statistically analyzed and the distribution of each parameter was analyzed with a probability density function.It was found that its tendency and inclination were normally distributed,and the length of the trace was lognormally distributed.The Monte-Carlo method is used to generate an array that conforms to the probability distribution of inclination,inclination,and trace length,and a three-dimensional network model program for the structural plane is written and visualized.Before analyzing the permeability characteristics of the bored rock mass,the BS32,BS36and BS39 boreholes were divided into quantitative homogeneous regions with correlation coefficient and structural area density as indicators,and finally the BS32 borehole was divided into[20m90m],[150m220m],[270m380m],[410m470m]and[500m600m]five sections;BS36 drill hole is divided into[20m90m],[150m220m],[270m380m],[410m470m]and[500m600m]five sections;BS39 drill hole is divided into[140m205m],[240m350m],[350m400m],[400m450m],[450m470m]and[470m550m]six intervals.On this basis,the geometric characteristics of fractures?presence,gap width,trace length?are statistically analyzed for each section of the borehole,and the permeability and main direction of the fractured rock mass with different depths of the borehole are obtained according to the permeability tensor theory.The overall comprehensive permeability coefficient of the borehole is in the order of 10-13-10-8.Compared with the results of on-site hydraulic tests,the results show that as the borehole depth increases,the comprehensive permeability coefficients of BS32,BS36 and BS39 boreholes decrease gradually,which is in line with the general law of seepage in fractured rock masses. |
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