To determine the durability of concrete in the actual temperature and humidity of the tunnel environment, this study investigates the mechanical properties, permeability of chloride ion, relative dynamic elastic modulus, and mass loss ratio of concrete specimens cured in the temperature which varied from normal, 40, 60, 75, and 90°C, and the humidity was kept at 90% continuously. Experimental results reveal that the hot temperature curing environment may benefit early stage strength development but reduce the long-term strength. It is proved that 60°C is a critical point. At above 60°C, the strength of the concrete material and its resistance to chloride ion permeability showed a decreasing trend; however, in the appropriate temperature range, the frost resistance properties of the concrete are improved with increasing temperature.

Urea can solve the problem of concrete cracking due to temperature stress. However, its effect is affected by temperature. The influencing mechanism of temperature on urea-doped cement pastes is still unclear. This paper explores the effect of different temperatures on the hydration kinetics of urea-doped cement pastes. The isothermal calorimeter (TAM Air) was used to test hydration at three constant temperatures (20 °C, 40 °C, and 60 °C). The effects of the urea admixture and temperature on the hydration process and hydration kinetics parameters were investigated. The hydration mechanism was analyzed, and the changes in macroscopic mechanical compressive strength and porosity were tested. The results show that, as the urea content (UC) increases, the rate of hydration gradually decreases, and the increase in temperature promotes the inhibitory effect of urea. At 60 °C, UC of 8% can be reduced by 23.5% compared with the pure cement (PC) group’s hydration rate. As the temperature increases from 20 °C to 60 °C, the Krstulovic–Dabic model changes from the NG-I-D process to the NG-D process. The effect of urea on the compressive strength of the cement is mainly shown in the early stage, and its effect on later strength is not obvious. In addition, urea will increase its early porosity. The porosity will gradually decrease in the later stage. The results of the study clarify the effect of temperature on urea-doped cement pastes. The optimal content of urea in cement is about 8%, which will provide theoretical guidance for solving the cracking problem of large-volume concrete due to temperature stress.

It is very important to clarify the optimization method of the rock-like material ratio for accurately characterizing mechanical properties similar to the original rock. In order to explore the optimal ratio of rock-like materials in gneissic granite, the water–paste ratio, iron powder content and coarse sand content were selected as the influencing factors of the ratio. An orthogonal test design and sensitivity analysis of variance were used to obtain the significant influencing factors of the ratio factors on seven macroscopic mechanical parameters, including compressive strength σ_c, tensile strength σ_t, shear strength τ_f, elastic modulus E, Poisson’s ratio ν, internal friction angle φ and cohesion c. A multivariate linear regression equation was constructed to obtain the quantitative relationship between the significant ratio factors and the macroscopic mechanical parameters. Finally, a rock-like material ratio optimization program based on genetic algorithm inversion was written. The results show that the water–paste ratio had extremely significant effects on σ_c, σ_t, τ_f, E, ν and c. The iron powder content had a highly significant effect on σ_c, σ_t, τ_f and c, and it had a significant effect on ν and φ. Coarse sand content had a significant effect on σ_c, E and c. The multiple linear regression model has good reliability after testing, which can provide theoretical support for predicting the macroscopic mechanical parameters of rock-like materials to a certain extent. After testing, the ratio optimization program works well. When the water–paste ratio is 0.5325, the iron powder content is 3.975% and the coarse sand content is 15.967%, it is the optimal ratio of rock-like materials.

The hydrological cycle is altered by climate change and human activities, amplifying extreme precipitation and heightening the flood risk regionally and globally. It is imperative to explore the future possible alterations in flood risk at the regional scale. Focusing on the Hanjiang river basin (HRB), this study develops a framework for establishing a scientific assessment of spatio-temporal dynamics of future flood risks under multiple future scenarios. In this framework, a GCMs statistical downscaling method based on machine learning is used to project future precipitation, the PLUS model is used to project future land use, the digitwining watershed model (DWM) is used to project future runoff, and the entropy weight method is used to calculate risk. Six extreme precipitation indices are calculated to project the spatio-temporal patterns of future precipitation extremes in the HRB. The results of this study show that the intensity (Rx1day, Rx5day, PRCPTOT, SDII), frequency (R20m), and duration (CWD) of future precipitation extremes will be consistently increasing over the HRB during the 21st century. The high values of extreme precipitation indices in the HRB are primarily located in the southeast and southwest. The future annual average runoff in the upper HRB during the near-term (2023–2042) and mid-term (2043–2062) is projected to decrease in comparison to the baseline period (1995–2014), with the exception of that during the mid-term under the SSP5-8.5 scenario. The high flood risk center in the future will be distributed in the southwestern region of the upper HRB. The proportions of areas with high and medium–high flood risk in the upper HRB will increase significantly. Under the SSP5-8.5 scenario, the area percentage with high flood risk during the future mid-term will reach 24.02%. The findings of this study will facilitate local governments in formulating effective strategic plans for future flood control management.