In-site monitoring and analysis of shaft lining’s additional strain in failure and formation grouting

More than 100 shaft linings fractured in coal mines of Eastern China region in the past three decades. It is believed that the axial additional force induces the cracking. Based on automatic-monitoring data about over ten shaft linings in recent more than six years, typical evolution curve of shaft lining's additional strain was obtained. Especially, the shaft lining’s additional strain in failure and during formation grouting period was obtained, which points out the curve characters before fracture, in failure, after fracture, in process of formation grouting, in grouting rest and after grouting. Through the comparison analysis of the data it has found that the shaft lining will fracture at strain accumulated to a certain degree when the formation consolidates. The shaft lining’s fracture makes the strain weak, and the formation grouting makes the shaft lining’s strain to the full extent. The in-site monitoring data has indicated that the exiting additional force induces the fracture of shaft lining and also showed that the formation grouting in the surrounding soil can make the shaft lining safer. The strain characters and the results are useful for the shaft lining’s fracture forecast.