# New Perspectives on Excavation Disturbance Zones: Main Driving Forces
## 3 Influence of Humidity Factor
### Analysis of Simulation Results
#### 3.2.2 Load Condition  
Figures 7 and 8 present the evolution processes of humidity, elastic modulus, and damage during humidity diffusion with and without the waterproofing layer within 150 days after the tunnel excavation under loading, respectively. After tunnel excavation, the surrounding rock was exposed to external high-humidity conditions, which caused the humidity level on the surface of the surrounding rock to exceed that in the interior of the surrounding rock. Over time, the moisture gradually migrated into the interior of the surrounding rock, thus resulting in the deterioration of the mechanical properties and the corresponding additional deformation of the surrounding rock, which in turn caused damage and led to the formation of the EDZ. As can be seen from Figures 7 and 8, the weakened zones of the mechanical properties of the surrounding rock and failure zone increased continuously with an increase in the humidity diffusion range. However, there were several differences in their development processes. The weakened zone of mechanical properties of the surrounding rock evenly expanded around the tunnel wall. The failure zone was initially mainly distributed in the corner and sidewall of the tunnel and then gradually extended to the interior of the surrounding rock and tunnel floor. Figure 7: Distributions of the relative humidity (**a1–a3**) (unit: 100%), elastic modulus degradation (**b1–b3**) (unit: MPa), and damage (**c1–c3**) (unit: J) during the diffusion of humidity without waterproofing. A comparison of the results in Figures 7 and 8 suggests that timely waterproofing measures can significantly reduce the migration velocity and amount of moisture migrating into the interior of the surrounding rock after tunnel excavation, thereby significantly reducing the scope and degree of the weakened zone in terms of the mechanical properties of the surrounding rock. Simultaneously, the damage area and damage extent of the surrounding rock can be significantly reduced due to the reduction in the humidity stress, which is conducive to maintaining the stability of the tunnel. A comparison of Figures 6 and 7 reveals that the depth of the EDZ is larger, and the surrounding rock damage is critical under the action of load. This is mainly because the load aggravates the damage of the weakened rock mass, and the generated cracks cause local stress concentration, which promotes the further expansion of cracks. Conversely, the development of cracks provides a migration path for moisture, which contributes to the further diffusion of moisture in the surrounding rock. Therefore, humidity diffusion and damage are interaction processes, which lead to the humidity-stress-damage coupling process. If the initial strength of the surrounding rock is low and waterproofing measures are not taken, the tunnel is particularly prone to collapse under the effects of both the load and humidity weakening action. Figure 8: Distributions of the relative humidity (**a1–a3**) (unit: 100%), elastic modulus degradation (**b1–b3**) (unit: MPa), and damage (**c1–c3**) (unit: J) during the diffusion of humidity with waterproofing. The circle in the figure represents acoustic emission, and its size indicates how much energy is released. Figure 9 presents a comparison of the displacements of parts A, B, and C with and without the waterproofing layer within 150 days after tunnel excavation. In a tunnel with a high-humidity environment, the diffusion of humidity results in a large time-dependent deformation of the surrounding rock. The presence of humidity weakened the structure of the rock mass, which significantly influenced the stability of the tunnel. The roof, sidewall, and floor of the tunnel were significantly deformed. However, the influence of humidity on different parts of the tunnel varied, among which the sidewall deformation of the tunnel was the largest (560.39 mm), followed by that of the floor (210.25 mm), and the smallest was that of the roof (164.35 mm).