## 4 Examples of Engineering Applications
### Reasons Affecting Construction Quality  
The construction process of concrete structures in hydraulic tunnels is complex, and there are numerous uncertainty factors affecting construction quality, which can be basically summarized as five aspects: personnel, materials, machinery, methods and environment according to quality management theory. Therefore, according to the actual situation of the project and the existing literature, this paper adopts the fishbone diagram method [26] to carry out a hierarchical analysis of the aspects of people, materials, machines, methods and environment to summarize the reasons affecting construction quality.  
1. In the process of construction measurement, due to the unskilled surveyors and the unfavorable influence of the environmental factors, such as heavy rain, gales, high temperatures, etc., there will be quality problems, such as horizontal penetration errors, vertical penetration errors and marking the wrong direction of digging.
2. In the process of tunnel excavation, due to unskilled tunneling operators and the low level of construction site management and monitoring, there will be quality problems, such as uneven excavation surfaces, groundwater seepage caused by excavation, and tunnel over-excavation and under-excavation.
3. In the process of support construction, the low business level of the constructor and poor inspection and management causes problems such as collapsed holes, deviation of the position and direction of anchor holes, low stability of steel arches, insufficient thickness of sprayed concrete and lagging of the sprayed concrete construction surface.
4. In the process of anti-drainage construction, the performance and laying of water-proof materials are not qualified due to non-timely testing; improper treatment of construction joints and deformation joints due to insufficient construction technology levels; and the drainage system is unreasonable due to the lack of scientific planning.
5. In the process of secondary lining concrete construction, the performance of concrete materials and mixing ratios does not meet the design requirements due to the lack of timely testing, insufficient maintenance of concrete, low strength of concrete demolding and inadequate concrete pouring and vibration due to the low level of  
Figure 1: Construction quality evaluation process of concrete structures in hydraulic tunnels based on CWM-UM modeling.  
construction management and poor construction environment, along with other quality problems. In addition, the quality of secondary lining concrete construction will also be affected by factors such as non-standardized concrete pouring, failure to clean the surface of the formwork in time, insufficient reinforcement of the formwork and incomplete assembly.
6. In the process of tunnel grouting, due to unskilled construction personnel, it is impossible to strictly control key parameters such as hole diameter, hole position, verticality, etc., resulting in irrational disposal of the drilled holes; due to the lack of advance hydrogeological and engineering geological exploration, it is not possible to effectively predict the ambient temperature of the construction area, which results in the grouting temperature being too high or too low; and irregularities in the grouting test result in too high or too low a grouting pressure being selected.  
In summary, the fishbone diagram of the quality problems of concrete structure construction of hydraulic tunnels is shown in Figure 2.