## 4 Conclusions  
* The fractures found by the test system are consistent with those found by drilling and coring, and the fracture dip angle measured by the test system is also quite consistent with the dip angle manually measured by the compass after drilling and coring. The fractures are basically large dip angle fractures, which is consistent with the conclusion that the dip angles of fractures in this test site are mostly in the range of 30-60\({}^{\circ}\), according to the comprehensive geological survey data. It shows that the slug test system has good reliability and stability in the field test.
* By comparing the calculation results of the field slug test and conventional water pressure test, it is found that the fracture equivalent permeability coefficient gradually decreases with the increase in borehole depth. In addition, the permeability coefficient determined by the slug test in the same test section is basically consistent with the water permeability determined by water pressure test. The permeability of the fractured rock mass in the test site belongs to weak or slightly permeability. The accuracy and applicability of the proposed slug test method for determining the permeability parameters of the fractured rock mass with different dip angles based on the vibration equation of well flow are verified.
* In the case of the same test section, whether pneumatic or water lifting mode, the slug test is conducted, as long as the slug test is conducted under the same excitation mode and the final calculation results are basically consistent, which indicates that the stability of the slug test system is very good and the accidental error is small. The fractured rock mass permeability coefficient tensor in the whole borehole test section at the Huangdao test site is obtained according to the proposed slug test method.
* The research results can be effectively applied to the study of the influence of the permeability of fractured rock mass on underground engineering, and can improve the efficiency and accuracy of the test. In addition, it is necessary to further study the influence of different excitation modes on the slug test results based on the proposed method.  
Conceptualization, Y.Z.; methodology, Y.Z.; validation, Y.W., X.D. and R.R.; formal analysis, Y.Z.; resources, Y.Z.; data curation, Y.Z.; writing--original draft preparation, Y.Z.; writing--review and editing, Y.W., X.D. and R.R.; visualization, H.W. and R.R.; supervision, Y.Z. and J.W.; project administration, Y.Z. and J.W.; funding acquisition, Y.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key Research and Development Program of China, grant number 2019 YFC1510802, the Fundamental Research Funds for the Central Universities, grant number B220205006, and the scientific research project of water conveyance and irrigation project of Xixiayuan water control project in Henan Province, China, grant number XXYSS/GQ-KYXM-02.  
Not applicable.  
The authors would like to thank the School of Earth Sciences and Engineering at Hohai University for partial support of the graduate student on this project.  
The authors declare no conflict of interest.