Abstract
Targeting the challenging analysis of the temperature field of the artificial freezing shaft sinking projects in Cretaceous strata, this study used the Hongqinghe air shaft freezing project as an example to perform a numerical simulation and measurement analysis of the temperature field of shaft sinking via the artificial freezing method in Cretaceous strata. First, the thermal physical parameters and mechanical properties of frozen Cretaceous rock were measured in the lab. Based on the engineering geological conditions and test parameters, the Hongqinghe air shaft freezing parameters were designed, and the preliminary scheme of the freezing project was obtained, in which a single ring of freezing holes was arranged in Cretaceous strata, the freezing wall had a design thickness of 3.7 m, and the average temperature was -12°C. Next, a numerical model for the temperature field of the freezing project was established to predict and analyze the effective thickness, average temperature, and shaft wall temperature of the frozen wall at different depths of shaft excavation. Finally, a comparison and analysis of field temperatures measured at the inspection holes and shaft walls showed that the numerical simulation results generally agreed with the field measurements. The field measurements showed that at the initial stage of freezing, the cooling rates of fine-, medium- and coarse-grained sandstones were 0.364 °C/d, 0.397 °C/d and 0.440 °C/d, respectively. Informatized construction enabled the air shaft freezing project in the Hongqinghe coal mine to be completed successfully.
Highlights
When an underground coal resource is mined using the shaft method, vertical shafts should be built in strata to transport coal, personnel, material and equipment during coal mine production
This study focuses on the characteristics of the freezing temperature field of Cretaceous strata
The above numerical simulation results of the freezing temperature field show that considering actual conditions, such as the borehole deviation, temperature at the temperature measurement holes, brine temperature and initial stratum temperature, when the excavation formally starts after 60 days of freezing and at a construction speed of 100∼120 m/month, the effective thickness, average temperature and shaft wall temperature of the frozen wall of the Hongqinghe air shaft all meet the construction requirements, indicating the safety and reliability of the frozen wall as well as the validity of the design freezing parameters
Summary
When an underground coal resource is mined using the shaft method, vertical shafts should be built in strata to transport coal, personnel, material and equipment during coal mine production. Based on a theoretical analysis and through extensive field measurement, empirical data such as the expansion rate, closure time and average temperature of the frozen wall in the thick overburden were obtained, and an ice formation formula for the temperature field calculation was established, effectively guiding construction practice This method has been rarely applied to shaft sinking in the Cretaceous strata in northwestern China. The thermal physical parameters, frozen wall expansion rates and temperature field formation pattern as well as field measurement data of the Cretaceous strata at low temperature are scarce, thereby presenting challenges in frozen wall design and construction (Liu et al, 2015; Pimentel et al, 2012) To address this issue, in this paper, using the air shaft freezing project in the Hongqinghe coal mine, Inner Mongolia, China as an example, lab tests, numerical simulation and field measurements were integrated to systematically investigate the temperature field of artificial freezing shaft sinking in Cretaceous strata, providing a technological basis for applying this method to projects in Cretaceous strata
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