Classification for tunnel surrounding rock based on multiple geological methods and extension model

Rock mass classification is an essential basis for evaluating the stability of surrounding rock in tunnels and for determining reasonable construction methods and supporting parameters. The classification of surrounding rock mass in tunnels has a scale effect and advance demand. The grade of surrounding rock needs to be predicted in advance for different tunnel scales, so as to allow reaction time for support design optimization. Due to the concealment and uncertainty of parameter acquisition, the preliminary classification of surrounding rock in the tunnel exploration is quite different from the actual surrounding rock grade. This paper proposes a fine classification of surrounding rock in tunnel construction. Multiple geological methods such as geological mapping, ground-penetrating radar, tunnel seismic prediction, deepened blast holes, and advanced horizontal drilling are used to obtain the engineering geological response parameters and information relating to the surrounding rock in front of tunnel faces. Based on the sample database of surrounding rock in excavated sections, the influencing factors are analyzed and weighed. Finally, a prediction model for classifying the surrounding rock mass in unexcavated tunnel sections is established using extension theory and validated using actual engineering. Through the correction of the surrounding rock mass grades, the support optimization of the corresponding unexcavated tunnel sections has been completed, and the stability of the tunnel construction has been maintained. This study effectively improves the accuracy and engineering practicality of surrounding rock mass classification for tunnels and provides practical guidance for tunnel construction optimization.