Fracture controlling of vertical shaft lining using grouting into neighboring soil deposits: A case study

Vertical shaft lining (VSL), which usually performs as a place for shaft sets to bolt into and a smooth surface to minimize resistance to airflow for ventilation, is one of the important approaches to gain access to underground coal seam. Extensive fracturing phenomenon of VSL were uniquely observed in Southeastern China due to the rapid increase of negative skin friction (NSF) from continuous settlement of thick soil deposits. Compaction grouting into these soil deposits was utilized to reduce the existing strain in fractured VSL, thus controlling the fracture development. And the efficacy of grouting was quantitatively interpreted via the strain variation in VSL and VSL rise comprehensively. The results showed that the strain as well as the elevation of VSL presents perfect increasing, decreasing, and then increasing characteristics correspondent to the grouting, grouting intermission, and re-grouting respectively. Further, the maximum released strain εmaxre induced from grouting accounts for over 50% of the accumulated strain εbgac, with the maximum VSL rise making up over 25% of the VSL settlement. These significant observations identify that the method of using grouting to stabilize and strengthen fractured VSL works well under such special strata. The capability and reliability of this method make it attractive in controlling of fractured VSL constructed in thick alluvium deposit.