Theory and technology of real-time temperature field monitoring of vertical shaft frozen wall under high-velocity groundwater conditions

Abstract

Abstract This study aims to address the problems arising from frozen wall closing in prolonged time under high-velocity groundwater in artificial ground freezing. Based on the development and closure law of frozen wall in strata with seepage, an analytical formula of transient temperature rising in frozen soil is derived, and a deterministic relationship between the geometric dimensions of the frozen wall is revealed. Then a longitudinal temperature measurement analysis theory is established. To accurately locate the weak points of the frozen wall and groundwater flow direction in case of groundwater disturbance, the gray correlation analysis is used to uncover the correlation between the weak freezing pipes. These relationships and correlations constitute a systemic framework for monitoring the temperature field during ground freezing under the condition of fast groundwater flow. Finally, the theory is applied to analyze the frozen wall closure of an air shaft in the Dongpang Mine, China. The results show that the smallest radius of the frozen soil column is produced around No. 9 and 20 freezing pipes according the proposed longitudinal temperature theory. Using No. 9 and 20 holes as the parent factors and the analyses based on the gray correlation theory, No. 7 through 10 and 18 through 22 frozen holes with higher correlation coefficients are determined as the weak positions within the frozen wall, and the predicted weak positions were confirmed during the shaft excavation. The proposed theory and method are shown to be effective in identifying frozen wall weak points and preventing accidents related to frozen wall closure under high-velocity groundwater conditions.