# Bearing Capacity of a Concrete Grouting Pad on the Working Surface of a Highway Tunnel Shaft
## 1 Introduction  
Mountainous terrain is steep, and tunnels have become the main way to break down traffic barriers [1; 2; 3; 4]. To meet the ventilation requirements for construction and operation, constructing deep and large shafts is the optimal choice for extra-long highway tunnels [5; 6]. As shaft sinking depth increases, the problem of water gushing into the fractured surrounding rock during the construction period is highlighted, and the adoption of scientific and rational grouting measures plays an important role in the prevention and control of water damage [7]. To achieve this, it is particularly critical to clarify the bearing capacity of a shaft grouting pad in order to reasonably determine the thickness. Many scholars have focused on the issue of grouting pads in wellbore workings. [PERSON] et al. [8] and [PERSON] et al. [9] have both adopted the elastomechanical method to design the thickness of a high-pressure deep-hole pregrouting pad in the treatment of water inrush in a coal mine shaft of water-enriched geology. [PERSON] and [PERSON] et al. [10; 11] gave empirical formulae for the thickness of a grouting pad for the sudden water flooding project of a verticaliron ore and coal mine shaft, taking into account the stratigraphic-hydrological conditions of the shaft site area. [PERSON] [12] and [PERSON] et al. [13] proposed an empirical formula applicable to the thickness of a grouting pad in a 1\(\%\) sub-shaft aiming at the inrush of water in a Tianxing iron mine. [PERSON] et al. [14] proposed a formula for calculating the thickness of a two-stage underwater cast-in-place grouting pad based on the geological and construction conditions for a mine in the excavation of a sub-shaft cavern in the Nanli Iron Mine. [PERSON] et al. [15] predicted the grouting volume of a gushing shaft using an adaptive fuzzy neural system and multi-regression methods. [PERSON] et al. [16], who analysed the gushing water problem in the construction of a tin mine shaft in Australia, believed that the adoption of reasonable grouting in the construction of a shaft has positive significance for the construction period and construction cost control. [PERSON] [17] established a gushing water hazard risk assessment method for gushing water hazards to determine the potential factors for the occurrence of gushing water in coal mine shafts. [PERSON] et al. [18] analysed the mechanisms of water gushing in a shaft constructed by the freezing method in coal mines in western China, constructed a risk assessment model of water gushing, and proposed the parameters of a grouting pad, which can be used as a reference for the prevention and control of water gushing in a shaft constructed by the anti-freezing method. [PERSON] [19] illustrated the engineering practical experience of successful water plugging by surface pumping grouting with an example from the flooded accident of the abandoned shafts of a coal mine in the former Czechoslovakian area. [PERSON] et al. [20] studied the technology of the simultaneous operation technique of the mechanical shaft boring construction and surface deep-hole grouting for vertical shafts in deep alluvial formations, proposing safety measures that can be implemented. The above research enriches the theory and technology of the prevention and control of water inrush hazards during a shaft construction period and provides a necessary basis for future work. However, there are some limitations and shortcomings. First, most of the research objects pay attention to a coal mine shaft, while there is little literature related to the grouting of the working surface of a highway tunnel shaft, and the shaft diameter is often 1-3 m larger than that of a coal mine shaft. Therefore, the mechanical model of a grouting pad belongs to the problem of plastic mechanics of a thin plate [21], and the calculation formula obtained by combining the plane common point force with experience is unreasonable. Secondly, there is a bias in the understanding of the failure mode of a grouting pad.