## 1 Introduction
[9] assessed the rock quality in excavated tunnels by combining practical experience with numerical analysis and analyzed the stability of the tunnels before and after excavation. [PERSON] et al. [10] established a new model of fuzzy comprehensive judgment of the risk level of existing tunnels based on the cloud model and applied it to the evaluation of the risk level of tunnels of the Guangzhou-Shenzhen-Hong Kong Express Railway, verifying the feasibility of the new model by comparing the results with those of the traditional method as well as the inspection data of the actual project. [PERSON] et al. [11] proposed a small-clearance tunnel construction risk assessment model based on an entropy weight-normal cloud model for small-clearance tunnels traversing rockpile bodies and demonstrated the feasibility and unique advantages of applying the model in the quantitative assessment of small-clearance tunnel construction risk by taking an actual tunnel project as an example. [PERSON] et al. [12] took Yunnan Xishanying Tunnel as an example and established a combined weight calculation method based on the entropy weight and hierarchical analysis methods, constructing an evaluation model for the quality of tunnel peripheral rock by using gray correlation analysis, which accurately evaluates the stability of the tunnel peripheral rock, reducing the risk in the excavation process. [PERSON] et al. [13] constructed an evaluation model based on EW-AHP and uncertainty measurement theory to evaluate the tunnel gas risk based on the Yudu No. 2 Tunnel Project of Xingquan Railway. [PERSON] et al. [14] constructed an evaluation model based on combined empowerment and unconfirmed measurements to evaluate the rockburst hazard of deep-buried tunnels in complex mountainous areas, taking the Sangzhuling Tunnel in the Sichuan-Tibet transportation corridor as an example. At present, the research on tunnel condition mainly focuses on railroad and highway tunnels, while relatively few studies have been conducted on hydraulic tunnels, which remain in a water environment for extended periods; the research mainly focuses on construction quality control and safety risks in tunnels but ignores the evaluation of the construction quality grade. Additionally, the research methods cannot comprehensively take into account the actual situation of the project, making it difficult to solve the randomness and ambiguity of the quality of tunnel construction in a better way. Compared with highway tunnels, the concrete structure of hydraulic tunnels remains in a complex water environment for extended periods, which makes it susceptible to erosive ions, acidic substances, carbonization, penetration pressure and other factors, resulting in a series of quality problems. The construction period of concrete structures in hydraulic tunnels is long, the construction environment is complex, and there are many influencing factors. The construction quality requirements are high, not only to meet the strength requirements, but also according to its specific operating environment to achieve erosion resistance, crack resistance, seepage resistance, impact wear resistance and other design requirements. The quality of construction affects compactness, strength, water seepage, cracking, corrosion of reinforcing steel and other conditions of the concrete structure in hydraulic tunnels. Therefore, there is an urgent need for a set of scientific and reasonable construction quality evaluation index systems and an evaluation model for the construction of concrete structures in hydraulic tunnels, which can effectively assess construction quality conditions, guide actual project construction, and ensure the quality and durability of construction. In summary, this paper proposes a set of new methods for evaluating the construction quality level of concrete structures in hydraulic tunnels.