In order to study the influence of different water content and salt content on the water-salt migration mechanism of Ili salinized loess. The water-salt migration test of saline loess under the action of the freeze-thaw cycle was carried out, and the temperature, moisture, and salt fields and their cohesion change rules were analyzed. The study shows that under the action of freezing and thawing, the temperature field, moisture field and salt field of saline loess show cyclic changes. With the increase of the number of freezing and thawing cycles, the water content of the soil column as a whole is increased, showing a pattern of high water content at the two ends and low water content in the middle. The change of salts in the soil layer under freezing and thawing is consistent with the overall change of moisture, and the salts in each soil layer show a homogeneous distribution before the unfreezing and thawing. Under the effect of temperature potential, the water carries the salts to migrate upward, resulting in higher salinity in the middle and upper part of the soil column. The increase of water content and salinity has a promoting effect on the migration of water and salts. In addition, the increase in water content will have a lubricating effect between the soil particles, resulting in the cohesion of the sample with low water content being greater than that of the sample with high water content. With the increase of salt content, the agglomerates formed by the salt crystals wrapped around the soil particles play the role of skeleton, which makes the cohesion of the specimen with high salt content larger than that of the specimen with low salt content, the value of internal friction angle of salinized loess after freeze-thawing shows a wave distribution.

In order to study the effect of freeze-thaw on the strength of low-liquid limit salinized silt, after the freeze-thaw cycle test of salted silt with different initial moisture content, non-consolidating and non-drainage (UU) shear and scanning electron microscopy (SEM) tests were carried out to reveal the deterioration mechanism of the strength of low-liquid limit salinized silt from macro-micro perspectives. The test results show that the change of moisture content does not cause the stress-strain curve morphology of low-liquid limit salinized silt to change when it is not freeze-thawed, and all of them are softening. Under the action of freeze-thaw, the curve shape of the specimen will not change when the moisture content is less than 14%, showing a softening type, and the stress-strain curve shape of the specimen with high moisture content will change to hardening. By analyzing the relationship between freeze-thaw and moisture content and failure intensity, it is found that the failure intensity of low-liquid limit salted silt decays linearly with the increase of moisture content, and the failure intensity decays exponentially with the increase of freeze-thaw cycles, and the attenuation rate and amplitude of the failure intensity are the largest in the first three freeze-thaw processes, and then tend to be stable. With the increase of confining pressure, the stress-strain curve of the specimen will transition from softening type to hardening type. In terms of microstructure, freeze-thaw will change the contact form between soil particles, resulting in the development of pores and fissures, and the variation law of microstructure and deterioration of macroscopic mechanical indicators in the freeze-thaw process are consistent. Combined with the soil damage mechanics, a low-liquid limit salinized silt cohesion damage deterioration model under freeze-thaw action was constructed, and the deterioration degree during the freeze-thaw process conformed to the hyperbolic relationship, and the final deterioration degree A_c had an exponential relationship with the moisture content, and the deterioration rate was B_c linear relationship with the moisture content.

The service environment in which the lining structure of tunnels in high cold regions was usually harsh and susceptible to the coupling effects of various extreme factors, leading to different forms of cracks in the lining concrete and posing significant safety hazards to the entire tunnel structure. Therefore, monitoring and predicting the cracking behavior of tunnel lining structures in high cold regions has important engineering significance, so, a multi-factor coupling prediction model for tunnel lining strain in cold regions based on deep learning is proposed. Firstly, a CNN-Bilstm-Transformer (CBLT) multi-factor coupling prediction model was developed based on the LSTM model, using a high cold region tunnel of Xinjiang as a supporting project. Then, based on a large amount of on-site monitoring data, CBLT was trained and tested to explore the influence of different input features on the model’s predictive performance, and the predictive performance between CBLT and different models was compared and analyzed. The research results indicate that: With the improvement of input features, the predictive performance of CBLT gradually improves; the average RMSE, MAE and MAPE on the test set were only 2.61 με, 2.22 με and 1.24%, R² can reach 0.815; the predictive performance of CBLT is better than RNN, LSTM, CNN-Bilstm and Bilstm-Transformer. The application of CBLT in predicting lining cracking behavior in practical engineering could achieve high accuracy. The research results can provide scientific guidance for the analysis of cracking behavior of tunnel lining in high cold regions and the prevention of frost damage.

In order to investigate the evolution law of microscopic pore structure and macroscopic damage characteristics of weathered carbonaceous slate under freeze-thaw cycles, nuclear magnetic resonance testing was conducted on carbonaceous slate with different degrees of weathering in the surrounding rock of tunnels under construction in the Karakoram Mountains of the Qinghai Tibet Plateau after different freeze-thaw cycles. The evolution law of pore structure of freeze-thaw slate was quantitatively analyzed. Research shows that: (1) The saturated mass and volume of weathered slate show a trend of slowly increasing and then rapidly decreasing. After the occurrence of macroscopic damage, its damage propagation speed accelerates. Compared to strongly weathered slate, moderately weathered slate with dense and high strength needs to undergo more frequent freeze-thaw cycles to undergo macroscopic damage; (2) The nuclear magnetic resonance T₂ spectrum of weathered slate mainly presents two peaks, with a discontinuous third peak representing extremely large pores. Under the freeze-thaw cycle, the pore size gradually expands, the pores increase, the connectivity between medium and large pore sizes is enhanced, and the proportion of large pore sizes significantly increases; (3) Research has found that the porosity of slate will reach a critical value when subjected to freeze-thaw damage. The critical values of freeze-thaw damage porosity for moderately weathered slate and strongly weathered slate are 15.36% and 17.16%, respectively. When the pore structure expands and the local porosity increases close to the critical value, local macroscopic damage of rock block detachment occurs. The mechanism of slate freeze-thaw damage is analyzed from the perspective of critical porosity. The research results have strong reference value for the antifreeze design and construction of rock mass engineering with different degrees of weathering in cold regions.