Freezing techniques in the deep shaft construction of Chensilou Coal Mine

Chensilou Coal Mine is located, in Henan Province, bordering on Lianghuai coal field and has productivity of 2.4 mt∕a. Its main and auxiliary shafts were constructed by using freezing technique and the freezing depth is the most in China at present. The coal measure strata in Chensilou was formed in littoral environment and its geological structure is similar to the one in Lianghuai coal field. There are four water-bearing strata in the thick overburden with abundent water. In case that the freezing pipes break, a mine flooding will probably ensue. The rest of the overburden is clayey soil. It takes more than a half of the overburden in upper part and about 70% of it is under the depth of 220m, with seven clay beds of thickness from 15 m to 26m. According to our tests, most of this clayey soil is of high or mid liquid limit. The water content decreases as the depth increases. The clayey soil, especially the aluminous and calcareous one, is of good expansiblity, low freezing strength and clear creep property. The results of frozen soil tests by Beijing Institute of Shaft Sinking are listed in Table 1 ∙