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In order to cope with the frost damage problems that occur in cold-region tunnels, the engineers have proposed the measure of setting up a heated air curtain at the tunnel entrance. In this paper, a three-dimensional transient heat transfer numerical model was first established to calculate the temperature distribution of the tunnel under the natural wind, which has a good agreement with field test data. The insulation effects of the heated air curtain were demonstrated, and effects of five factors, namely, temperature (Tn) and speed (Sn) of the natural wind, speed (S), temperature (T), and angle (A) of the jet airflow of the air curtain, were discussed. Then, an orthogonal test sensitivity analysis was conducted on the operating parameters (T, S, and A). Finally, effects of the air curtain were predicted by neural networks. The results show that the use of air curtains can effectively shorten the length of the negative temperature section of the tunnel structure. Low temperatures and large speed of the natural wind will weaken the effects of the air curtain. In the two cases, the operating parameters of the air curtain require adjustment according to demand. Increasing S and T can effectively enhance insulation effects. And the optimal A is between − 15° (toward inside the tunnel) and 0°. The sensitivities of the influences of the three operating parameters on the insulation effects are ranked as T (2.142), S (1.832), and A (0.77). The prediction results of the neural network indicate that using Tn, Sn, T, S, and A to predict the length of the negative temperature section (Lv) and temperature of the tunnel vault surface (Tv) is feasible and efficient. This research can provide a reference for the application of air curtains as anti-freeze measures in cold-region tunnels. [ABSTRACT FROM AUTHOR]

Abstract To solve the problem of freezing damage in cold-region tunnels, this study proposed a rubber airbag interlayered composite lining system, and tested its performance of buffering, pressure adjustment, waterproofing, and heat preservation by simulating a low-temperature environment in an artificial freezing chamber. The experiment results show that the frost-heaving force exerted on the lining can always be lower than 1.69 kPa by constantly adjusting the airbag pressure, and the maximum frost-heaving force can reach 28.25 kPa without the airbag. In addition, the airbag also has good waterproof performance. Finally, the airbag can significantly improve the temperature field of the surrounding rock and reduce the freezing depth (6.75 cm

To solve the problem of freezing damage in cold-region tunnels, this study proposed a rubber airbag interlayered composite lining system, and tested its performance of buffering, pressure adjustment, waterproofing, and heat preservation by simulating a low-temperature environment in an artificial freezing chamber. The experiment results show that the frost-heaving force exerted on the lining can always be lower than 1.69 kPa by constantly adjusting the airbag pressure, and the maximum frost-heaving force can reach 28.25 kPa without the airbag. In addition, the airbag also has good waterproof performance. Finally, the airbag can significantly improve the temperature field of the surrounding rock and reduce the freezing depth (6.75 cm < 17.25 cm). The insulation effect of the airbag is positively correlated with its thickness and negatively correlated with the thermal conductivity of the filling gas. The insulation effect of CO2 is better than that of air. The rubber airbag interlayered composite lining system provides a new scheme for freezing damage control in cold-region tunnels. [ABSTRACT FROM AUTHOR]

The damage caused by the frost heaving pressure on the surrounding rocks and lining structure of cold-region tunnels is always common, which can seriously threaten the safety and stability for cold-region tunnels. Although many achievements of frost heave pressure model have been obtained, two factors have been often ignored, which are in-situ stress and freeze-thaw cycles. Therefore, the calculation mechanical model of cold-region tunnels is established and the expression of frost heaving pressure considering frost heaving effect and in-situ stress is derived based on the elastic theory. The relationship between the elastic modulus of surrounding rocks and the number of freeze-thaw cycles was fitted by experimental data and the calculation formula of frost heaving rate of rocks considering their porosity change caused by freeze-thaw cycles is derived. Based on that, the calculation method of frost heaving pressure considering in-situ stress and freeze-thaw cycles is proposed. The example analysis results show that frost heaving ratio and frost heaving pressure gradually increase with freeze-thaw cycles, which are eventually subjected to a steady value. Simultaneously, the frost heaving pressure acting on lining increases with in-situ stress for tunnels in cold regions and some effective insulation measures should be applied to prevent frost damage. [ABSTRACT FROM AUTHOR]

High-speed railway tunnels in the cold region, whose numbers are increasing, are widely exposed to the threat of frost damage caused by extremely negative temperatures. The operation of high-speed trains has made this problem even more pronounced. But there are fewer studies focusing on the dynamic changes in temperature during train operation. In this paper, the air thermodynamic behavior of trains passing through a tunnel and its consequences were investigated with the help of the CFD method. In numerical simulations, conditions of different natural airflows, different train speeds, different blockage ratios, as well as two trains intersecting in the tunnel were involved. The following valuable results were obtained. In cold environments, train-induced pressure wave effects will affect the air thermodynamic behavior, but the overall trend in air temperature is mainly influenced by the heat transfer between cold and warm air. The high-speed train will lead to massive cold air being carried into the tunnel and some warm air inside being pushed out. Heat transfer between cold and warm air will cause a significant decrease in tunnel air temperature. This air thermodynamic behavior is particularly prominent in the case of large blockage ratios. When there are same-direction natural airflows, they will be coupled with train-induced airflows, causing a greater decrease in tunnel air temperature. In contrast, opposite-direction natural airflows can reduce the negative effects of the train. Taking the case of opposite-direction natural airflow velocity of 5 m/s as an example, the temperature changes of the three cross-sections are only 16.7 %, 14.8 %, and 42.1 % of those in the case of no natural airflow. Whatever the direction of natural airflows, coupling effects between them and train-induced airflows will be more significant as the natural airflow speed increases. Greater train speed means more cold air entering the tunnel and stronger heat transfer between cold and warm air, causing a more significant temperature decrease. When two trains intersect through the tunnel, airflows caused by them will be coupled. As a result, only a little air enters the tunnel from the entrance and exit, and the heat transfer between air with different temperatures is weak. In this case, the air temperature doesn't decrease but slightly increases as the air is compressed. [ABSTRACT FROM AUTHOR]

Solar seasonal thermal storage heating (SSTSH) system is a new type of energy-efficient and environment-friendly anti-freezing technology in cold-region tunnels. The purpose of this study is to investigate the energy performance of an SSTSH system operated in different modes by using field experimental tests and numerical simulation. The experimental system is installed in Tianshan Shengli Tunnel of Xinjiang, China. Three operation modes including single heat storage, single heat extraction, and combined operation mode are investigated under different flow rates and inlet temperatures. The thermal performance, system operational efficiency and borehole wall temperature are analyzed and compared under various modes. The experimental results indicate that for the single heat storage operation mode, the thermal storage performance can be improved by enhancing the flow rate and inlet temperature. However, when ensuring the thermal storage amounts, a lower flow rate or inlet temperature should be employed to improve system efficiency. For single heat extraction operation mode, the heat extraction performance is effectively improved by lowering the inlet temperature, while the coefficient of performance (COP) is decreased. It is advisable to maintain a higher inlet temperature to improve operational efficiency of heat extraction. For the combined operation mode, the simulation shows the heat extraction performance of the SSTSH system can be greatly improved by the increasing the heat storage inlet temperature. When the heat storage inlet temperature increases by 5 °C, the growth rate of the average heat extraction amount is 2.45 W/m during the combined operation mode. The seasonal heat stored raises the surrounding rock temperature to a higher level, which is beneficial for increasing the COP of the heat pump, and effectively addresses the thermal imbalance in cold regions. The combined operation mode of the SSTSH system is recommended for the tunnel heating in cold regions. [Display omitted] • A novel sustainable system is proposed in cold-region tunnels to address frost damage issue. • The energy performance of the SSTSH (Solar seasonal thermal storage heating) system is investigated. • For single heat extraction mode, lowering inlet temperature rises the thermal performance. • For the combined mode, a higher heat storage inlet temperature improves the thermal performance. • The seasonal heat stored raises the rock temperature and the system efficiency. [ABSTRACT FROM AUTHOR]

In order to solve frost damage problems in cold-region tunnels, a new sustainable energy based freeze proof method for tunnel drainage system is proposed. The method is applied to Tianshan Shengli Tunnel, China as a case study to show the concept and details of tunnel drainage system ground heat exchangers (GHEs) including calculation of active heating length and maximum heating load, design of heat extraction in cross tunnel, the segmented design method. Long-term performance of tunnel drainage system GHEs is also fully discussed. Multi-field simulations are performed to achieve corresponding thermal responses of the tunnel drainage system GHEs. Results show that anti-freezing measures provide an initial heating length 900 m of the drainage system at the entrance of Tianshan Shengli Tunnel during full life cycle. When the tunnel drainage system GHEs are employed, the heating length can be reduced to 600 m. Maximum total heating load of the tunnel drainage system in heating period is 84.40 kW. The calculation method of segmented heating load is suggested for precise prevention and control of frost damage in cold-region tunnels, owing to varying tunnel air temperature with the distance from the tunnel entrance. The use of boiler heating in winter will enhance the compensation between operation and recovery period and provides good long-term performance. This study provides a potential reference for antifreeze design of cold-region tunnels utilizing geothermal energy.

There is an increasing trend of tunnel infrastructure construction in cold regions due to the advance of a western development strategy. To reduce the frost damage sustained by a tunnel, it is important to consider the mechanical properties of frost heave in the surrounding rock by analyzing the anisotropic frost heave of a cold-region tunnel. This paper elaborates on the behavior of anisotropic frost heave in the rock surrounding a cold-region tunnel, and the coefficient of displacement relief is adopted to indirectly quantify the influence of the tunnel construction process. The analytical elasto-plastic solutions of the stress and deformation in the surrounding rock are derived with Drucker-Prager criteria (hereinafter referred to as the D-P criteria) by modifying the constitutive equation for the frozen surrounding rock. Finally, an example is given to obtain the influence law of the distribution of stress and deformation in the surrounding rock. The results indicate that the plastic radius and frost force calculated by considering isotropic frost heave are greater than those obtained by considering anisotropic frost heave. The influence of the related parameters also analyzed. Some useful insights are provided for future numerical simulations and the design and construction of cold-region tunnels. [ABSTRACT FROM AUTHOR]

Precise evaluation of the frost heaving force and surrounding rock plastic zone is an important basis of the prevention of freezing damage in cold-region tunnels. The temperature gradient along the radial direction of cold-region tunnels surrounding rock results in the dual non-uniform frost heaving of surrounding rock, namely, the gradual change of frost heave ratio along the radial direction and the unequal frost heaving deformation in the circumferential and radial directions. A new elastoplastic solution of tunnel frost heaving force considering double non-uniform frost heave and intermediate principal stress was derived based on the elastoplastic mechanics theory, thick-cylinder theory, and unified strength theory to better guide the frost resistance design of tunnels in cold regions. The rationality and advantages of the unified plastic solution of tunnel frost heaving force were verified by model tests and engineering examples. Results showed that the theoretical calculation value of frost heaving force was in good agreement with the measured value. When the gradual change in the frost heave ratio of surrounding rock in the radial direction was ignored, the frost heaving force and radius of the surrounding rock plastic zone were large and conservative. The solution in this paper can accurately evaluate the tunnel frost heaving force and surrounding rock plastic zone. Finally, this paper studies the influences of intermediate principal stress coefficient, the frost heaving coefficient of unit temperature of frozen surrounding rock, non-uniform frost heaving coefficient in different directions, and maximum freezing depth on the evolutionary law of frost heaving force and plastic zone of cold-region tunnels are studied. • A dual non-uniform frost heaving model of cold region tunnels is proposed. • Use temperature gradient to describe the non-uniform frost heave of the surrounding rock. • An elasto-plastic solution for frost heave force based on dual non-uniform frost heave is derived. • Theoretical solutions, model test results and engineering tunnel cases were compared. [ABSTRACT FROM AUTHOR]

In recent years, the construction of cold-region tunnels has increased in western China. However, the studies of the analytical elasto-plastic solution for the stress and deformation of surrounding rock in cold-region tunnels are limited. To solve this engineering problem and propose new theoretical insights for analysis and design, the elasto-plastic calculation model for surrounding rock in cold-region tunnels is established in this paper. In this model, the entire surrounding rock is divided into four zones, namely, the unfrozen elastic zone, the frozen elastic zone, the frozen plastic zone and the support zone. The frozen surrounding rock is assumed to conform to the ideal elasto-plastic model and the Mohr–Coulomb yield criterion. The stress and deformation fields in each zone are solved according to continuity conditions. A case is introduced to obtain the distribution of stress and strain in the surrounding rock of cold-region tunnels. The reason that the circumferential stress is less than the radial stress in the unfrozen zone is explained and the range of that is also addressed. Moreover, the location in which no displacement is generated is determined in the freezing circle. The produced high stress is mainly influenced by the linear frost strain. The results of stress field and strain field are verified by the existing elastic solution. At last, parameter analysis is performed to obtain the influence of the related parameters on plastic radius and the surrounding rock stresses at the inner and outer edges of the freezing circle. The results can guide for numerical simulations and field engineering practice. [ABSTRACT FROM AUTHOR]

Frost damage frequently occurs in cold-region tunnels due to temperature changes, posing risks to the structural stability and traffic safety. Therefore, temperature variations and its distribution in tunnels are crucial factors that have to be considered. Temperature measurements were conducted in the Xing'anling tunnel in northeast China from 2016 to 2019 to investigate the spatiotemporal characteristics of the temperature field. An equation to determine frost depth based on the Stephen's method was established to evaluate the influence of different factors on frost depth. The sensitivity of frost depth to different influencing factors was investigated using system stability analysis. The results showed that mean annual temperature inside the Xing'anling tunnel has gradually increased from 2016 to 2019 due to global warming. Freezing front was characterized by three stages based on the freezing rate, i.e., the fast freezing stage, transitional freezing stage, and stable freezing stages. The maximum frost depth ranged from 1.5 to 5.1 m without an insulating layer covering the lining, and a lag of about 2 months was observed with air temperature. Along the length of the entire tunnel, four stages of frost depth were observed, namely, fluctuations and a decrease, a steady decrease, fluctuations and an increase, and a steady increase. Frost depth exhibited an asymmetrical distribution to the length of the entire tunnel. Temperature parameters had the largest influence on frost depth, followed by water parameters and thermal parameter. Density parameters had relatively little influence on frost depth. • Temperature field measurements in a long highway tunnel were conducted for a long term in cold regions. • Distribution characteristics of the tunnel temperature along depth and length were revealed. • Characterized stages of freezing front over time on the basis of freezing rate were classified. • Influencing factors on frost depth were analyzed to determine its change laws and sensitivities in cold-region tunnels. [ABSTRACT FROM AUTHOR]

Frost heave in cold-region tunnels is caused by complex water-ice phase changes with coupled heat and moisture transfer, which will lead to frost damage and thus threatens the structural stability and traffic safety. To describe the frost heave force, a new model is established for the coupled heat and moisture transfer in the freezing surrounding rock, which consider the major influence factors of the three primary frozen theories for cold-region tunnels simultaneously. An analytical solution for the coupled multifactor is proposed, in which the calculated parameters could be classified into three categories: 1) the frost heave ratios(α fr , α mr , α i); 2) the geometric parameters(R , T mr , T i); and 3) the confinement strength(K r , K fr , K mr , K l , K i). All parameters are studied, in which frost depth is deduced by comprehensively considering the ice content, thermal coefficient and freezing index, and a new method based on a difference value method for the equivalent elasticity coefficient of the lining or ice is also proposed. Furthermore, the method is validated in the Daban Mountain tunnel, and the results have indicated that the proposed analytical solution can accurately reflect frost heave force. • A model for frost heave force was established from the coupled heat and moisture transfer in cold-region tunnels. • Parameters to frost heave force were studied in detail to determine the distribution range or the calculation method. • Frost depth was deduced by comprehensively considering the ice content, thermal coefficient and freezing index. • A method based on a difference value method for the equivalent elasticity coefficient of the lining or ice was proposed. [ABSTRACT FROM AUTHOR]

Studying tunnel temperature fields could prevent frost damage. However, few studies have revealed the distribution laws of freeze-thaw cycles in cold-region tunnels. In this study, the distribution laws of freeze-thaw cycles in a tunnel were carried out, and the concrete deterioration induced by freeze-thaw cycling was explored. First, in situ monitoring equipment was used to collect the temperature in the longitudinal direction of the tunnels. A one-dimensional heat transfer model was used to analyze the temperature distribution in the circumferential direction of the tunnels, where a function was proposed to describe both the annual and diurnal temperature fluctuations. After that, the distribution laws of freeze-thaw cycles inside a tunnel were investigated. Specifically, in the tunnel longitudinal direction, the number of freeze-thaw cycles decreased from the entrance to the middle and then increased while approaching the exit, thereby exhibiting a V-shaped distribution. In the circumferential direction, the intrados lining nearly always exhibited freeze-thaw cycles. The number of freeze-thaw cycles and the temperature amplitude decreased rapidly with increasing depth. Furthermore, a series of unsaturated concrete experiments were performed to explore the concrete deterioration under different numbers of freeze-thaw cycles. The results showed that after being subjected to 100 freeze-thaw cycles, the concrete specimens displayed visible damage, whereas the concrete compressive strength was not affected. These findings can enrich the research of freeze-thaw cycles for cold-region tunnels and are significant for guiding tunnel maintenance. • Freeze-thaw cycles are an important characteristic of temperature fluctuations in cold-region tunnels. • In longitudinal direction, freeze-thaw cycles decrease in the middle and increases at the exit. • In circumferential direction, freeze-thaw cycles and the temperature amplitude decrease with depth. • After 100 freeze-thaw cycles, unsaturated concrete shows damage while the strength does not decrease. [ABSTRACT FROM AUTHOR]