Modeling and application of while drilling identification of sandification grade in sandy dolomite tunnels

Accurate identification of sandification grades is crucial fordisaster prevention and control in sandy dolomite tunnels. However，the existing sandification grade classification methods cannot be effectively combined with advanced geological prediction，which weakens the role of advanced horizontal drilling results in disaster prevention and control to a certain extent. Based on the analysis of disaster cases，the rock breaking of bit numerical simulation under six typical working conditions was conducted by the ABAQUS. The drilling results of the corresponding rock strata were analyzed from two aspects of drilling displacement and real-time drilling speed，and the field drilling test was carried out. The frequency distribution characteristics of the drilling speed of the surrounding rock with different sandification grades were analyzed. Furthermore，a prediction model of sandification grade based on drilling speed was constructed and verified. The results show that：(1) The drilling speed of sandy dolomite increases with the increase of sandification grade，and it is reasonable and feasible to use drilling speed as a prediction index of dolomite sandification grade. (2) Based on the statistical analysis of 434 groups of actual advanced horizontal drilling speed，the likelihood of drilling speed in the range of 2.33–5 mm/s in weak sandy dolomite is 92.47%，the possibility of drilling speed in the range of 3.33–6.67 mm/s in severe sandy dolomite is 87.18%，and the possibility of drilling speed in the range of 4.17–9.17 mm/s in complete sandy dolomite is 90.74%，all of which show normal distribution. (3) The prediction model of sandification grade is applied to the Water Diversion Project in Central Yunnan，and the identification results are consistent with the actual sandification grade. The research results directly promote the application of advanced horizontal drilling results to the prediction and identification of sandification grade and guide the disaster prevention and control of sandy dolomite tunnels.