# Prediction Model for Shield Tunneling Roll Angle and Pitch Angle: A PCA-PSO-LGBM Approach
## 1 Introduction  
As the global population grows, land resources become increasingly precious. The utilization of underground space is a key focus and trend for future sustainable urban development. Extensive use of urban underground space requires the construction of various types of tunnels with minimal disturbance [1], leading to the emergence of the shield tunnelling method. After more than 200 years of development, modern shield machines, such as slurry shields and hard rock shields, have become more diverse to meet the construction needs under different geological conditions. Currently, typical shield tunnelling still relies entirely on drivers and engineers, whose judgments and subsequent operational decisions are based on historical experience and are often delayed [2]. Therefore,research on predicting the advancement state of shield machines can provide decision-making bases for adjusting excavation parameters in advance, thereby largely avoiding the occurrence of major accidents. The complexity of shield machine equipment and the uncertainty of underground geotechnical environments make it difficult for shields to adjust their posture as easily and flexibly as other ground vehicles. Therefore, some scholars have started experiments and posited theory to study the interaction between shields and surrounding strata. [PERSON] et al. [3] studied the influence of different geological conditions on shield tunnelling performance through full-scale laboratory disc-cutting tests. [PERSON] et al. [4] proposed the composition and corresponding calculation methods of the cutterhead torque, which is a very important parameter in machine-rock interaction, by considering various factors such as cutterhead structure and cutting principles. The experiments show that the cutterhead torque changes significantly with geological conditions, and the cutter opening ratio and soil pressure are the two most important factors determining the cutterhead torque. [PERSON] et al. [5] established a total load prediction model that fully reflects the influence of geological, excavation, and structural parameters, providing a reference for load design and parameter control during construction. Based on the theory of machine-rock interaction, some scholars have conducted theoretical analyses of shield posture. [PERSON] et al. [6] proposed a multi-cylinder control system based on a master-slave control strategy, which adjusts the posture of the shield machine under complex geological conditions by controlling the length of each motion chain. [PERSON] et al. [7] derived comprehensive theoretical expressions for the normal force and friction acting on the periphery and cutter face of the shield, established the mechanical balance equation of the shield, and accurately solved the characteristics of shield force and shield posture. Other scholars have studied shield posture through numerical simulation methods. The thrust system is an important parameter affecting shield posture. [PERSON] et al. [8] proposed an equivalent mechanism to model the thrust system in different grouping methods, providing a theoretical basis for further research on thrust performance using parallel mechanism theory. [PERSON] et al. [9] established a two-dimensional discrete element model to study the tunnel mechanics laws and limit range during shield posture adjustment, indicating that increasing the overexcavation rate helps expand the shield posture adjustment range. [PERSON] et al. [10] established a test device for the shield tunnelling unbalanced load model in soil-rock composite strata. Through model tests and numerical simulations, they showed that the interaction between the shield shell and the strata is the main reason for shield posture changes in soil-rock composite strata.