Method for calculating optimal length of multi-type thermal insulation structure of tunnel in cold region based on subsection differentiation adjustment

Abstract

The invention discloses a cold region tunnel multi-type thermal insulation structure optimal length calculation method based on segmented differentiation adjustment, and the method comprises the steps: obtaining a tunnel temperature distribution rule through cold region tunnel temperature monitoring and field investigation; constructing a temperature parameter distribution function along the radial depth and the longitudinal distance according to a tunnel heat preservation distribution rule; according to engineering constraint conditions, determining an optimal thermal insulation structure type and an initial thickness value of a corresponding thermal insulation structure; based on the optimal thermal insulation structure type and the initial thickness value, a thermal insulation effect correction coefficient of the thermal insulation structure is obtained; based on the thermal insulation effect correction coefficient of the thermal insulation structure, the temperature parameter distribution function and the initial thickness value, obtaining an initial length value of the thermal insulation structure; partitioning and segmenting the tunnel length based on the initial length value; selecting an adaptive longitudinal distribution form of the thermal insulation structure according to a segmentation result; and optimizing the initial thickness value and the adaptive longitudinal distribution form of the thermal insulation structure according to a partition and segmentation logic principle to obtain the optimal length value of the thermal insulation structure.

Description

Technical Field

[0001] This invention belongs to the field of thermal insulation technology for underground engineering in cold regions, and particularly relates to a method for calculating the optimal length of multi-type thermal insulation structures for tunnels in cold regions based on segmented differential adjustment. Background Technology

[0002] As core hubs of transportation networks in high-latitude, high-altitude regions, cold-region tunnels constantly face severe challenges in their construction and operation due to extreme low temperatures and freeze-thaw cycles. The freezing damage problem in cold-region tunnels is essentially the result of the coupled effects of temperature, stress, and seepage fields. Under extreme low-temperature conditions, the repeated freezing, expansion, thawing, and contraction of moisture in the tunnel's surrounding rock and lining easily leads to defects such as lining cracking, concrete spalling, frost heave deformation, and water seepage freezing. These defects not only cause a sharp decline in tunnel structural durability and a shortened service life but also directly threaten traffic safety and significantly increase operation and maintenance costs.

[0003] Thermal insulation structures are an effective and economical engineering measure for preventing frost damage in tunnels in cold regions. The rationality of their length directly determines the effectiveness of frost prevention and the economic benefits of the project. If the insulation length is insufficient, the freezing depth of the surrounding rock at the tunnel entrance will significantly exceed the design expectations, leading to repeated frost damage such as frost heave cracking, water seepage, and freezing. If the length is redundant, it will cause waste of insulation materials and construction time, resulting in additional investment. However, there is currently no unified calculation method system in the field of calculating the length of thermal insulation structures for tunnels in cold regions. Existing technical approaches mainly include taking values ​​from empirical tables, empirical analysis of meteorological parameters, and the Kurokawa Kiyonori formula. Some empirical methods rely heavily on simplified formulas, using only the average annual temperature or freezing depth of the tunnel area as core parameters for estimation. They fail to fully consider the dual effects of interannual freeze-thaw cycles and diurnal freeze-thaw cycles at the tunnel entrance, and neglect the complex coupled heat transfer effects between the insulation structure, surrounding rock, and airflow within the tunnel. While some numerical simulation methods possess high computational accuracy, they suffer from limitations such as cumbersome procedures, high parameter sensitivity, and stringent requirements for professional technical capabilities, making them unsuitable for rapid design and decision-making needs on engineering sites. Furthermore, existing methods do not systematically incorporate the differences in thermal conductivity of different insulation structure types, leading to significant deviations between calculation results and actual engineering conditions. This results in a common technical pain point: "disconnect between design values ​​and on-site measurements."

[0004] As tunnel construction in cold regions extends to deeper and colder areas, the demand for precise insulation structure design becomes increasingly urgent. There is a pressing need to establish a method for calculating the length of insulation structures that balances scientific rigor, convenience, and applicability. This method would overcome the limitations of traditional empirical and coarse-grained approaches, as well as the high barriers to entry and low efficiency of numerical methods, providing reliable technical support for frost damage prevention and control in cold-region tunnels. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a method for calculating the optimal length of various types of thermal insulation structures in cold-region tunnels based on segmented differential adjustment. This method overcomes the limitations of traditional empirical and coarse-grained methods, as well as the high barriers to entry and low efficiency of numerical methods.

[0006] To achieve the above objectives, this invention provides a method for calculating the optimal length of various types of thermal insulation structures for tunnels in cold regions based on segmented differential adjustment, including: The temperature distribution patterns in tunnels in cold regions were obtained through temperature monitoring and field investigation. Based on the aforementioned tunnel insulation distribution pattern, a temperature parameter distribution function along radial depth and longitudinal distance is constructed; Based on the engineering constraints, determine the optimal insulation structure type and the corresponding initial thickness value of the insulation structure; Based on the optimal insulation structure type and initial thickness value, obtain the thermal insulation effect correction coefficient of the insulation structure; Based on the thermal insulation effect correction coefficient of the thermal insulation structure, the temperature parameter distribution function, and the initial thickness value, the initial length value of the thermal insulation structure is obtained; Based on the initial length value, the tunnel length is divided into sections and segments; Based on the segmentation results, select a suitable longitudinal distribution pattern for the thermal insulation structure; Based on the principle of segmentation and partitioning, the initial thickness value and the longitudinal distribution of the suitable insulation structure are iteratively optimized to obtain the optimal length value of the insulation structure.

[0007] Optionally, constructing the temperature parameter distribution function along the radial depth and longitudinal distance includes: Based on the annual and daily temperature variation data at the tunnel entrance, the annual average temperature, annual temperature amplitude, and daily temperature amplitude are extracted. Based on the radial distribution patterns of the annual average temperature, annual temperature amplitude, and daily temperature amplitude, the radial temperature distribution function is obtained. Based on the longitudinal distribution patterns of the annual average temperature, annual temperature amplitude, and daily temperature amplitude, the longitudinal temperature distribution function is obtained.

[0008] Optionally, the radial depth temperature distribution function includes: radial daily temperature amplitude distribution function, radial annual temperature amplitude distribution function, and radial annual average temperature distribution function; The radial diurnal temperature amplitude distribution function for: ; The radial annual temperature amplitude distribution function for: ; The radial annual average temperature distribution function for: ; in, The radial depth of the tunnel. This is the attenuation coefficient of the daily temperature amplitude with radial depth. Distance from the tunnel entrance Daily temperature amplitude, The longitudinal distance from the tunnel entrance end, Distance from the tunnel entrance Annual temperature amplitude, The volumetric heat capacity of the tunnel. The thermal conductivity of the tunnel. The freeze-thaw cycle of the tunnel. Distance from the tunnel entrance The average annual temperature, The annual average temperature increases linearly with radial depth.

[0009] Optionally, the temperature distribution function of the longitudinal distance includes: the longitudinal daily temperature amplitude distribution function at the tunnel entrance, the longitudinal annual temperature amplitude distribution function, and the longitudinal annual average temperature distribution function; The longitudinal daily temperature amplitude distribution function is: ; The longitudinal annual temperature amplitude distribution function is: ; The longitudinal annual average temperature distribution function is: ; in, and These are the parameters used to calculate the daily temperature amplitude as a function of the tunnel's longitudinal distance. and For the opening end and distance The daily temperature amplitude at the surface, and These are the parameters used to calculate the annual temperature amplitude as a function of the tunnel's longitudinal distance. and For the opening end and distance Annual surface temperature amplitude and The parameters for calculating the annual average temperature as a function of the tunnel's longitudinal distance are:

[0010] Optionally, based on engineering constraints, determining the optimal insulation structure type and the corresponding initial thickness value of the insulation structure includes: From four main categories and eleven subcategories of insulation structures, including single-layer insulation structures, double-layer insulation structures, composite single-layer insulation structures, and composite double-layer insulation structures, the optimal insulation structure type is selected based on engineering constraints. These engineering constraints include: climate characteristics of the tunnel site area, temperature variation patterns, freezing depth, engineering hydrogeological conditions, thermophysical properties of the surrounding rock, insulation material performance, engineering cost, and construction technology. The thickness parameters of the insulation structure are calculated based on the optimal insulation structure type and the corresponding calculation formula to obtain the initial thickness value.

[0011] Optionally, the longitudinal distribution of the insulation structure includes: uniform distribution of the insulation structure, progressive distribution of the insulation structure, stepped distribution of the insulation structure, and combined distribution of the insulation structure. The uniform distribution of the thermal insulation structure includes: continuous uniform distribution and discontinuous uniform distribution; The progressive distribution of the thermal insulation structure includes: linear progressive distribution and curved progressive distribution; The stepped distribution of the thermal insulation structure includes: a stepped segmented distribution with four influence zones, a stepped continuous distribution with three influence zones, a stepped segmented distribution with three influence zones, and a stepped continuous distribution with two influence zones. The combined distribution of the thermal insulation structure includes: a two-influence zone stepped-linear progressive distribution, a two-influence zone stepped-curved progressive distribution, a three-influence zone stepped-linear progressive distribution, and a three-influence zone stepped-curved progressive distribution.

[0012] Optionally, based on the principle of segmentation and partitioning, the initial thickness value and the adapted longitudinal distribution of the insulation structure are iteratively optimized to obtain the optimal length value of the insulation structure, including: Based on the principle of segmentation and partitioning, the tunnel is divided into different impact zones, and the initial thickness value of each impact zone is adjusted accordingly. Based on the adjusted insulation structure thickness value, the correction coefficient of each section is recalculated, the initial length is updated, and a suitable longitudinal distribution form of the insulation structure is reselected. Through multiple rounds of iterative calculations until the preset conditions are met, the optimal length value of the insulation structure is obtained.

[0013] Compared with the prior art, the present invention has the following advantages and technical effects: 1. Improve the precision of frost damage prevention and control, and ensure structural safety. This invention can accurately calculate the reasonable length of the insulation structure based on the specific geographical location of the tunnel, the thermophysical properties of the surrounding rock, and the performance of the insulation material. This effectively avoids lining cracks, frost heave, and other defects caused by insufficient length, controls the freezing depth of the surrounding rock within the design allowable range, improves the durability and safety of the tunnel structure, and reduces the incidence of frost damage in tunnels in cold regions.

[0014] 2. Optimize project investment and improve economic efficiency. This invention avoids material and construction waste caused by excessive insulation through precise calculations, while reducing the cost of later frost damage repair, extending the service life of the tunnel, and achieving the engineering goals of precise design, optimized cost, and lightweight operation and maintenance.

[0015] 3. Simplified design process and improved practicality. This invention eliminates the complex numerical simulation process, providing clear calculation logic and an operable formula system. Engineering technicians can complete the calculations without professional numerical analysis skills, significantly shortening the design cycle. It is especially suitable for on-site investigation and rapid design of tunnels in cold regions, providing a convenient technical tool for tunnel engineering in remote areas. Attached Figure Description

[0016] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a radial temperature distribution characteristic diagram of a cold-region tunnel according to an embodiment of the present invention; Figure 2 This is a longitudinal temperature distribution feature diagram of a cold-region tunnel according to an embodiment of the present invention; Figure 3 This is a flowchart of the method for calculating the optimal length of multiple types of thermal insulation structures for cold-region tunnels based on segmented differential adjustment, according to an embodiment of the present invention. Figure 4 This is a flowchart of the iterative calculation of the optimal length of multi-type thermal insulation structures for cold-region tunnels based on segmented differential adjustment, according to an embodiment of the present invention. Figure 5 These are schematic diagrams of the longitudinal distribution of thermal insulation structures for tunnels in cold regions. Figure (a) shows a continuous uniform distribution, Figure (b) shows a discontinuous uniform distribution, Figure (c) shows a linear progressive distribution, Figure (d) shows a curved progressive distribution, Figure (e) shows a stepped segmented distribution of four influence zones, Figure (f) shows a stepped continuous distribution of three influence zones, Figure (g) shows a stepped segmented distribution of three influence zones, Figure (h) shows a stepped continuous distribution of two influence zones, Figure (i) shows a stepped-linear progressive distribution of two influence zones, Figure (j) shows a stepped-curved progressive distribution of two influence zones, Figure (k) shows a stepped-linear progressive distribution of three influence zones, and Figure (l) shows a stepped-curved progressive distribution of three influence zones. Figure 6 This is a schematic diagram of the radial temperature distribution characteristics of a highway tunnel according to an embodiment of the present invention, wherein (a) is a schematic diagram of the radial distribution law of annual temperature amplitude, (b) is a schematic diagram of the radial distribution law of the average daily temperature amplitude of the coldest month, and (c) is a schematic diagram of the radial distribution law of annual average temperature. Figure 7This is a schematic diagram of the longitudinal temperature distribution characteristics of a highway tunnel according to an embodiment of the present invention, wherein (a) is a schematic diagram of the longitudinal distribution law of annual temperature amplitude, (b) is a schematic diagram of the longitudinal distribution law of the average daily temperature amplitude of the coldest month, and (c) is a schematic diagram of the longitudinal distribution law of annual average temperature. Figure 8 The thermal insulation structure and the correction coefficient for wind speed inside the tunnel in this embodiment of the invention. The influence law of thermal conductivity, where (a) is the effect of thermal conductivity of insulation structure on thermal conductivity. Schematic diagram of the effect of insulation structure thickness on the thermal insulation structure thickness. (b) shows the effect of insulation structure thickness on the thermal .... The diagram illustrates the impact of different insulation structure settings on the thermal insulation effect. (c) shows the effect of different insulation structure settings on the thermal insulation effect on the thermal insulation effect of different insulation structure settings ... The diagram illustrates the effect of wind speed on the wind speed. (d) shows the effect of wind speed on the wind speed. Schematic diagram of the impact; Figure 9 This is a schematic diagram of the thickness of a highway tunnel insulation structure according to an embodiment of the present invention; Figure 10 This is a schematic diagram illustrating the variation of frost heave force with freezing depth in a tunnel according to an embodiment of the present invention. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0018] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0019] This embodiment proposes a method for calculating the optimal length of various types of thermal insulation structures in cold-region tunnels based on segmented differentiated adjustments, such as... Figure 3-4 As shown, the specific steps include: The temperature distribution patterns in tunnels in cold regions were obtained through temperature monitoring and field investigation. Based on the aforementioned tunnel insulation distribution pattern, a temperature parameter distribution function along radial depth and longitudinal distance is constructed; Based on the engineering constraints, determine the optimal insulation structure type and the corresponding initial thickness value of the insulation structure; Based on the optimal insulation structure type and initial thickness value, obtain the thermal insulation effect correction coefficient of the insulation structure; Based on the thermal insulation effect correction coefficient of the thermal insulation structure, the temperature parameter distribution function, and the initial thickness value, the initial length value of the thermal insulation structure is obtained; Based on the initial length value, the tunnel length is divided into sections and segments; Based on the segmentation results, select a suitable longitudinal distribution pattern for the thermal insulation structure; Based on the principle of segmentation and partitioning, the initial thickness value and the longitudinal distribution of the suitable insulation structure are iteratively optimized to obtain the optimal length value of the insulation structure.

[0020] Specifically, (1) Temperature characteristics of the tunnel foundation: Based on the radial temperature distribution function and combined with field monitoring data, the key temperature parameters corresponding to the annual freeze-thaw cycle and daily freeze-thaw alternation are extracted to clarify the radial distribution law of annual average temperature, annual temperature amplitude and daily temperature amplitude; at the same time, based on the longitudinal temperature distribution characteristic formula and monitoring results, the longitudinal distribution law of the above three types of temperature parameters is calculated.

[0021] (2) Selection of thermal insulation structure schemes: Taking into account multiple constraints such as the characteristics of cold climate, the thermophysical properties of surrounding rock, the freezing depth of tunnels, the performance parameters of insulation materials, the budget of engineering costs and the feasibility of construction technology, for insulation structures of 4 major categories and 11 subcategories, the optimal insulation structure scheme is determined by combining the corresponding insulation structure thickness calculation formulas and through comprehensive technical and economic comparison, and the preliminary value of insulation structure thickness is obtained by solving simultaneously.

[0022] (3) Heat transfer (heat convection) and material parameters: Based on the specific insulation structure scheme determined above, different calculation formulas are used to solve for physical parameters such as thermal conductivity, volumetric heat capacity, and convective heat transfer coefficient of the lining concrete of the cold region tunnel; at the same time, a correction coefficient calculation formula matching the insulation structure is selected, and the corresponding correction coefficient is obtained by combining the combination of heat convection and heat conduction under the actual working conditions of the project.

[0023] (4) Preliminary length calculation and iterative optimization: Substituting the correction coefficients and the aforementioned parameters into the insulation structure length calculation formula, the initial length of the insulation structure is initially calculated. Based on the calculated initial length, and within a preset range, a suitable longitudinal arrangement of the insulation structure is selected according to actual engineering needs. Then, based on the principles of zoning, economic rationality, and functional matching, the insulation structure thickness for different sections of the cold-region tunnel is optimized, forming a differentiated insulation system for each zone. Since adjusting the insulation structure thickness directly affects the distribution of its reasonable length, the length needs to be recalculated after any change in thickness parameters. Multiple rounds of iterative optimization are used to dynamically adjust the insulation structure thickness for each zone, ultimately achieving the dual optimal goals of insulation and control effectiveness and project cost. If, after multiple iterations, the insulation structure thickness and length parameters still cannot meet the insulation requirements of the cold-region tunnel, the process must return to the insulation structure selection stage for re-comparison. Then, the parameter solution and iterative optimization are repeated according to the complete calculation process described above until the optimal combination of insulation structure thickness and length parameters is determined.

[0024] Furthermore, constructing the temperature parameter distribution functions along the radial depth and longitudinal distance includes: Based on the annual and daily temperature variation data at the tunnel entrance, the annual average temperature, annual temperature amplitude, and daily temperature amplitude are extracted. Based on the radial distribution patterns of the annual average temperature, annual temperature amplitude, and daily temperature amplitude, the radial temperature distribution function is obtained. Based on the longitudinal distribution patterns of the annual average temperature, annual temperature amplitude, and daily temperature amplitude, the longitudinal temperature distribution function is obtained.

[0025] Specifically, influenced by both long-term (annual freeze-thaw) and short-term (daily freeze-thaw) freeze-thaw cycles in the tunnel site area, the temperatures of the atmosphere, insulation structure, lining structure, and surrounding rock within the cold region tunnel all exhibit periodic variations within a year and a day. Taking the Type I1 insulation structure as an example, under the influence of the air temperature in the tunnel site area, the temperature variations of the corresponding insulation structure, lining, and surrounding rock over time are as follows: Figure 1 As shown.

[0026] according to Figure 1 at any time temperature It can be expressed as a function of annual average temperature, annual temperature amplitude and daily temperature amplitude, annual period and daily period, annual phase and daily phase, 0 m and The formulas for calculating the temperature at point m are as follows: At 0 m: (1); At point m: (2); In the formula, , They are time Tunnel surface temperature and depth Temperature at that location; , These are the annual average surface temperature and depth of the tunnel, respectively. The average annual temperature at that location; This represents the annual temperature amplitude of the tunnel surface. This represents the daily temperature amplitude of the tunnel surface. It has an annual cycle, consisting of 365 days (8760 hours). Daily cycle, 1 day (24 hours); , These are the initial phase angles (in radians) for the annual and daily cycles, respectively, used to adjust the starting position of the temperature wave; For time (units consistent with the period, usually days or hours); , These are the annual damping depth and the daily damping depth, respectively. , , ,in It is thermal conductivity. It's density. Specific heat capacity is an inherent property of the medium that determines the rate at which heat is transferred within it. (365 days) far greater than (1 day), so the annual damping depth Much greater than the daily damping depth (generally ).

[0027] Based on meteorological analytical formulas, considering the annual average temperature at different depths in tunnels in cold regions Annual temperature amplitude Daily temperature amplitude radially along the tunnel When freezing does not occur at point m, the tunnel lining temperature meets the following condition: (3); In the formula, For depth The lowest temperature at that location, if Let the thickness of the insulation structure be denoted as , and Equation (3) be the minimum temperature at which the secondary lining will not freeze. Take the thickness of the secondary lining as , and Equation (3) is the lowest temperature at which the initial support (or the outer side of the waterproof membrane) does not freeze. Take the initial support thickness as , and Equation (3) is the minimum temperature at which the surrounding rock does not freeze; For depth The average annual temperature at that location; For depth Annual temperature amplitude at the location; For depth The daily temperature amplitude at that location.

[0028] The base temperature is the temperature at 0 m inside the tunnel in the cold region. The temperature at point m is the target temperature, and a mapping relationship between the two is established; combining the above formulas (1) and (2), for example, taking the non-freezing of the surrounding rock as the control condition, the radial temperature distribution characteristics of the tunnel in the cold region are as follows: Longitudinal distance from the tunnel entrance Annual temperature amplitude at the location With depth The change can be represented as: (4); In the formula, This refers to the longitudinal distance from the tunnel entrance. Distance from the entrance Annual temperature fluctuation at the tunnel surface; The volumetric heat capacity of the surrounding rock; The thermal conductivity of the surrounding rock is denoted as . For the freeze-thaw cycle of the tunnel, here .

[0029] thermal conductivity of surrounding rock Represented as: (5); The volumetric heat capacity of the surrounding rock is expressed as: (6); In the formula, , and denoted as , respectively, the weight heat capacity of the surrounding rock skeleton particles, water, and ice.

[0030] Distance from the tunnel entrance The daily temperature amplitude at a given location varies with radial depth as follows: (7); In the formula, This is the attenuation coefficient of the daily temperature amplitude with radial depth, and its value is related to the specific date, resulting in... The temperature fluctuates frequently. In practical applications, it is generally determined by combining the date with actual measurement fitting or numerical simulation. Alternatively, the monthly average value of the daily temperature amplitude can be calculated on a monthly cycle to simplify the value. The specific value needs to be determined based on the actual working conditions on site. Distance from the entrance The daily temperature amplitude of the tunnel surface at that location.

[0031] depth The mapping relationship between the annual average temperature at a certain location and the annual average temperature at 0 m needs to be obtained through engineering analogy, numerical simulation, or field measurement. If it is not possible to obtain this relationship due to limitations, the distance from the tunnel entrance end... The annual average temperature at a location can also be estimated using the following formula: (8); In the formula, Distance from the entrance The average annual surface temperature of the tunnel at that location; The value represents the linear growth rate of annual average temperature with radial depth, ranging from 0.06 to 1.80.

[0032] Furthermore, the longitudinal temperature distribution characteristics include: longitudinal daily temperature amplitude characteristics, longitudinal annual temperature amplitude characteristics, and longitudinal annual average temperature characteristics at the tunnel entrance. Specifically, along the tunnel's longitudinal direction, the entrance end is most strongly affected by both the interannual freeze-thaw cycle and the diurnal freeze-thaw cycle, resulting in significant periodic fluctuations in the longitudinal temperature within the tunnel on both annual and daily timescales: the temperature range at the entrance end is large, gradually decreasing towards the middle section of the tunnel, and the longitudinal temperature distribution is mostly asymmetrical. Therefore, this embodiment focuses on the temperature at one end of the tunnel entrance section (with traffic and ventilation directions aligned), and its longitudinal temperature distribution characteristics are shown in Figure 2.

[0033] in accordance with Figure 2 Longitudinal temperature distribution characteristics, and the attenuation relationship between daily and annual temperature amplitudes at the tunnel entrance along the tunnel's longitudinal direction: (9); (10); In the formula, and The parameters for calculating the daily temperature amplitude as a function of the tunnel's longitudinal distance are generally obtained through field measurements, numerical simulations, or engineering experience. and For the opening end and distance The daily temperature amplitude of the tunnel surface at that location; and The annual temperature amplitude is a parameter for calculating the longitudinal distance of the tunnel, and is generally obtained through field measurements, numerical simulations, or engineering experience. and For the opening end and distance The annual temperature amplitude of the tunnel surface at that location.

[0034] Annual average temperature generally changes exponentially with increasing longitudinal distance: (11); In the formula, and The parameters for calculating the annual average temperature as a function of the tunnel's longitudinal distance are:

[0035] Based on the above calculation model, for Type I1 insulation structures, taking the prevention of surrounding rock freezing as the control criterion, the optimal length of the insulation structure is determined. The calculation is as follows: (12); Furthermore, based on engineering constraints, the optimal insulation structure type and the corresponding initial thickness value of the insulation structure are determined, including: From four main categories and eleven subcategories of insulation structures, including single-layer insulation structures, double-layer insulation structures, composite single-layer insulation structures, and composite double-layer insulation structures, the optimal insulation structure type is selected based on engineering constraints. These engineering constraints include: climate characteristics of the tunnel site area, temperature variation patterns, freezing depth, engineering hydrogeological conditions, thermophysical properties of the surrounding rock, insulation material performance, engineering cost, and construction technology. Based on the optimal insulation structure type, select the corresponding insulation structure thickness calculation equation, solve for the insulation structure thickness parameters, and obtain the initial thickness value of the insulation structure.

[0036] Specifically, the equation for calculating the thickness of the thermal insulation structure is as follows: The equation for calculating the thickness of the I1 (wall-mounted) thermal insulation structure is: (13); The equation for calculating the thickness of the I2 (mezzanine) insulation structure is: (14); The equation for calculating the thickness of the Ⅰ3 (separate from the wall) thermal insulation structure is: (15); The equation for calculating the thickness of the Ⅱ1 (wall-mounted + sandwich) insulation structure is: (16); The equation for calculating the thickness of the Ⅱ2 (wall-separated + sandwich) insulation structure is: (17); The equation for calculating the thickness of CⅠ1 (wall-attached + wall-separated) thermal insulation structure is: (18); The equation for calculating the thickness of CⅠ2 (separate from wall + attached to wall) thermal insulation structure is as follows: (19); The equation for calculating the thickness of CⅠ3 (wall-attached + wall-separated + wall-attached) thermal insulation structure is as follows: (20); The equation for calculating the thickness of CⅡ1 (wall-mounted + wall-separated + sandwich) insulation structure is as follows: (twenty one); The equation for calculating the thickness of CⅡ2 (separate wall + attached wall + sandwich layer) insulation structure is: (twenty two); The equation for calculating the thickness of CⅡ3 (wall-mounted + wall-separated + wall-mounted + sandwich) thermal insulation structure is: (twenty three); In the above formula, and The thickness and thermal conductivity of the secondary lining; and The thickness and thermal conductivity of the initial support; and are the thermal conductivity coefficients of the insulation structure and the air layer in a wall-mounted insulation structure, respectively; and These represent the thicknesses of the insulation structure and the air layer in a wall-mounted insulation structure, respectively. and The thermal conductivity and thickness of the wall-mounted insulation structure; and The thermal conductivity of the first and second layers of insulation material in the wall-mounted insulation structure; and The thicknesses of the first and second layers of insulation material in the wall-mounted insulation structure, respectively; and The thermal conductivity and thickness of the wall-mounted sandwich insulation structure; , , , and The convective heat transfer coefficients of the thermal insulation structure surfaces are I1(Ⅱ1), I3(Ⅱ2), CⅠ1(CⅡ1), CⅠ2(CⅡ2), and CⅠ3(CⅡ3), respectively. The convective heat transfer coefficient of the lining concrete surface; This is the equivalent inner diameter of the tunnel secondary lining; This refers to the tunnel freezing depth. Specifically, the eleven subcategories are shown in Table 1: Table 1 More specifically, the thermal insulation effect of tunnel insulation structures in cold regions is corrected.

[0037] The above-mentioned insulation structure is set with a length of The calculations are based on the temperature field distribution characteristics of the tunnel after lining. With the insulation structure installed, the heat flow rate of convective heat exchange between the air and surrounding rock inside the tunnel decreases due to increased thermal resistance. This means that the amount of heat absorbed by the cold air blowing into the tunnel from the surrounding rock decreases during its flow, implying that the cold air needs to travel a longer distance to achieve the same heat exchange with the surrounding rock as when no insulation structure is installed. Therefore, the original calculated length needs to be adjusted after installing the insulation structure. Make corrections, with a correction factor of 1. Actual set length for: (twenty four); After the insulation structure is installed, the heat exchange characteristics between the airflow and the insulation structure inside the tunnel change. In addition, the insulation structure itself has a low thermal conductivity. Therefore, the correction coefficient needs to take into account both heat convection and heat conduction under the action of the insulation structure.

[0038] convective heat transfer coefficient of the insulation structure surface The calculation formula is: (25); In the formula: The roughness of the secondary lining concrete surface; The surface roughness of the insulation structure; For roughness correction index, during turbulent flow During transition flow laminar flow ; For the thickness of the insulation structure; The correction index is geometric and needs to be determined based on the actual working conditions on site. If on-site data cannot be obtained, it should be taken as -0.2 based on engineering experience. The temperature of the lining concrete wall; To differentiate the wall surface temperature of the insulation structure; The air temperature inside the tunnel; The correction index for the temperature gradient needs to be determined based on the actual working conditions on site. If on-site data is unavailable, it should be taken as 0.12 based on engineering experience.

[0039] The convective heat transfer coefficient of the lining concrete needs to be obtained through on-site measurement or numerical simulation. If conditions are limited, it can also be estimated using the following calculation formula: (26); In the formula, The average wind speed inside the tunnel is calculated based on the statistical analysis of the measured wind speed inside the tunnel throughout the year. When designing the insulation structure of a new tunnel, the design wind speed for a one-way highway tunnel should not exceed 10.0 m / s, and in special cases should not exceed 12.0 m / s; the design wind speed for a two-way highway tunnel should not exceed 8.0 m / s.

[0040] Based on the different structural forms of thermal insulation structures for tunnels in cold regions, and considering the coupled effects of various insulation structures on longitudinal heat transfer during heat conduction and convection, the correction coefficients for different insulation structures must be specifically calibrated and quantified using field measurements, laboratory tests, or numerical simulations. This ensures that the correction coefficients accurately reflect the actual heat transfer mechanism, providing reliable parameter support for predicting the temperature field of tunnels in cold regions and optimizing the design of thermal insulation structures. If measured data is unavailable due to limitations, estimations can be made using the following formulas: (1) Correction coefficient for type I1 thermal insulation structure The calculation formula is: (27); (2) Correction coefficient for type I2 thermal insulation structure The calculation formula is: (28); (3) Correction coefficient for type I3 ​​thermal insulation structure The calculation formula is: (29); (4) Correction coefficient for Type II1 thermal insulation structure The calculation formula is: (30); (5) Correction coefficient for type II2 thermal insulation structure The calculation formula is: (31); (6) Correction coefficient for CⅠ1 type thermal insulation structure The calculation formula is: (32); (7) Correction coefficient for CⅠ2 type thermal insulation structure The calculation formula is: (33); (8) Correction coefficient for CⅠ3 type thermal insulation structure The calculation formula is: (34); (9) Correction coefficient for CⅡ1 type thermal insulation structure The calculation formula is: (35); (10) Correction coefficient for CⅡ2 type thermal insulation structure The calculation formula is: (36); (11) Correction coefficient for CⅡ3 type thermal insulation structure The calculation formula is: (37); In the above formula, , , , and The surface roughness of the thermal insulation structure are I1(Ⅱ1), I3(Ⅱ2), CⅠ1(CⅡ1), CⅠ2(CⅡ2), and CⅠ3(CⅡ3), respectively. The annual temperature amplitude of the air inside the tunnel; This represents the annual temperature amplitude at a constant temperature point in the surrounding rock. For the period, it can be taken as or .

[0041] Based on the initial length of the insulation structure calculated above, within the preset range, according to the tunnel influence zoning (the tunnel influence zoning can be combined with the actual conditions of the specific project, comprehensively considering the distribution characteristics and variation law of tunnel temperature along the longitudinal distance and radial depth, flexibly adopting two, three or four categories from strong influence zone, medium influence zone, weak influence zone and no influence zone for combination), a suitable longitudinal arrangement of the insulation structure is selected. The selection of the longitudinal arrangement of the tunnel insulation structure should be combined with the actual needs of the project, following the basic principles of zoning and segmentation, economic rationality, and functional matching. Based on this, the present invention innovatively proposes 4 major categories and 12 subcategories of longitudinal distribution forms. For details of the specific distribution forms, please refer to... Figure 5 (a)-(l), based on the differences in design logic and applicable scenarios, can be summarized as follows: The first type is characterized by a uniformly distributed thermal insulation structure. Continuous uniform distribution Discontinuous uniform distribution ; The second type is characterized by a gradually distributed thermal insulation structure. Linear asymptotic distribution The curve gradually distributes ; The third type is a stepped distribution of thermal insulation structure. The four affected areas are distributed in a stepped manner. The three impact zones are distributed in a stepped, continuous pattern. The three impact zones are distributed in a stepped manner. The two affected areas are distributed in a stepped, continuous pattern. ; The fourth category is the combined distribution of thermal insulation structures. Based on the four-level zoning of tunnel disturbance (strong influence zone, influence zone, weak influence zone, and no influence zone), the longitudinal distribution of tunnel insulation structures can be divided into a two-influence zone stepped-linear progressive distribution. The two affected areas are gradually distributed in a step-curve pattern. The three-influence zone is distributed in a stepped-linear asymptotic manner. The three-zone step-curve gradual distribution .

[0042] In detail, taking the longitudinal zoning threshold of a high-latitude tunnel in Inner Mongolia Autonomous Region as an example, the zoning and segmentation of tunnel length will be explained: When the tunnel is severely frozen, with a large freezing depth (≥3.5 m), low freezing temperature (minimum temperature ≤-25℃, average temperature of the coldest month ≤-10℃, annual average temperature ≤-0.5℃), and a long duration of negative temperature (≥120 days), the longitudinal influence zone of the insulation structure is divided into a strong influence zone. When the tunnel is moderately frozen, with a large freezing depth (2.0–3.5 m), low freezing temperature (-25℃ < minimum air temperature ≤ -15℃, -5℃ ≤ average air temperature of the coldest month < -10℃, -0.5℃ < average annual air temperature ≤ 0.7℃), and the negative temperature lasts for a long time (90–120 days), the longitudinal influence zone of the insulation structure is divided into the influence zone. When the tunnel is weakly frozen, with a shallow freezing depth (0.5–2.0 m), a high freezing temperature (-15℃ < minimum air temperature ≤ -8℃, -3℃ ≤ average temperature of the coldest month < -5℃, 0.7 < annual average temperature ≤ 1.5℃), and a short duration of negative temperature (45–90 days), the longitudinal influence zone of the insulation structure is divided into a weak influence zone. When the tunnel is extremely weakly frozen or does not freeze, the freezing depth is very shallow (<0.5 m), the freezing temperature is high (minimum temperature > -8℃, average temperature of the coldest month > -3℃, annual average temperature > 1.5℃), and the duration of negative temperature is very short (<45 days), and no insulation structure is installed, the longitudinal influence zone of the insulation structure is divided into an unaffected zone.

[0043] Furthermore, based on the principle of segmentation and partitioning, the initial thickness value and the adapted longitudinal distribution of the insulation structure are iteratively optimized to obtain the optimal length value of the insulation structure, including: Based on the principle of segmentation and partitioning, the tunnel is divided into different impact zones, and the initial thickness value of each impact zone is adjusted accordingly. Based on the adjusted insulation structure thickness value, the correction coefficient of each section is recalculated, the initial length is updated, and a suitable longitudinal distribution form of the insulation structure is reselected. Through multiple rounds of iterative calculations until the preset conditions are met, the optimal length value of the insulation structure is obtained.

[0044] To verify the accuracy and effectiveness of the above formula for correcting the length of the insulation structure, a case study and effect analysis were conducted using a highway tunnel as an example.

[0045] 1. Project overview of a certain tunnel: A highway tunnel is located in a high-latitude, frigid region. Due to the combined effects of extreme low temperatures, interannual freeze-thaw cycles, and deep seasonal permafrost, the surrounding rock has historically frozen to a depth far exceeding design expectations, leading to a series of typical cold-region tunnel frost damage problems. These include circumferential, longitudinal, and diagonal cracking in the lining structure, spalling of the concrete surface, frost heave deformation in some sections, and increased water leakage in the lining due to freeze-thaw cycles. This not only seriously affects the stability and durability of the tunnel structure but also significantly restricts traffic safety and operational efficiency, becoming a typical technical challenge in the construction and operation of cold-region tunnel projects.

[0046] 2. Parameter settings for a tunnel insulation structure: Based on field measurement data from a tunnel (15 monitoring sections covering the shallow buried section at the tunnel entrance, the middle section of the tunnel, and the deep buried section, with the monitoring period encompassing a complete annual freeze-thaw cycle and typical diurnal alternation processes), and according to the statistical analysis results of the measured data, the radial and longitudinal temperature distribution patterns of the tunnel are as follows: (1) Radial temperature distribution pattern in a highway tunnel: The entrance section of a highway tunnel is located in a high-latitude, frigid region. Due to the combined effects of interannual freeze-thaw cycles and diurnal freeze-thaw cycles, the temperature fluctuations inside the tunnel have a significantly stronger impact on the temperature field of the surrounding rock and lining than in the middle section of the tunnel. Based on field measurement data of the tunnel, the distribution patterns of its annual temperature amplitude, daily temperature amplitude, and annual average temperature along the radial direction of the tunnel (from the inner surface of the lining to the deep part of the surrounding rock) are as follows: Figure 6 As shown in (a)-(c).

[0047] The daily temperature amplitude with radial depth can be expressed as: (38); The annual temperature amplitude with radial depth is expressed as: (39); The annual average temperature with radial depth is expressed as follows: (40); (2) The longitudinal temperature distribution pattern of a highway tunnel: The entrance and exit ends of a highway tunnel are significantly affected by topography, ventilation conditions, and the external environment, resulting in significant differences in temperature variations. The distribution patterns of annual temperature amplitude, daily temperature amplitude, and annual average temperature along the tunnel's longitudinal direction at both ends are shown below. Figure 5 As shown in (a)-(c).

[0048] according to Figure 7(a)-(c), the corresponding calculation formula is: Import segment: (41); (42); (43); Exit section: (44); (45); (46); In the formula, This refers to the total length of the tunnel. This represents the annual atmospheric temperature amplitude at the tunnel exit section. The annual atmospheric temperature amplitude at the tunnel entrance; The annual atmospheric temperature amplitude at the tunnel exit end; This refers to the daily atmospheric temperature amplitude at the tunnel entrance section. This represents the daily atmospheric temperature amplitude at the tunnel exit section. This represents the daily atmospheric temperature amplitude at the tunnel entrance. This represents the daily atmospheric temperature amplitude at the tunnel exit end. The annual average atmospheric temperature at the tunnel entrance section; This represents the annual average atmospheric temperature at the tunnel exit section.

[0049] 3. Calculation of the length of a tunnel insulation structure: To effectively reduce the corrosive effect of high-frequency daily freeze-thaw cycles and large-temperature-difference seasonal freeze-thaw cycles on the lining concrete, and to reduce the risk of lining cracking and spalling caused by freeze-thaw cycles, a highway tunnel adopted a thermal protection scheme in which Fulikai insulation boards were laid on the outside of the secondary lining. This type of insulation board has the core advantages of excellent thermal insulation and frost resistance, light weight (easy to construct and install), high fire resistance and strong corrosion resistance, and can be adapted to the humid and low-temperature service environment of the tunnel for a long time. Combining the I1 type insulation structure of this invention, the insulation structure thickness calculation formula shown in Equation (13) is used to solve for the preliminary thickness of the insulation structure of a certain tunnel; on this basis, the length calculation correction formula matching the insulation structure is selected and determined (see Equation 27). Then, based on Equation (12) as the basic model, the thermal physical parameters such as thermal conductivity and specific heat capacity of the insulation material are combined with the radial and longitudinal temperature distribution characteristics of the tunnel revealed above, and the quantitative solution is carried out in accordance with the aforementioned calculation process, and the reasonable setting lengths of the insulation structure of the inlet and outlet sections of a certain highway tunnel are 32240 m and 7540 m, respectively. Since the sum of the calculated lengths of the two sections exceeds the actual total length of the tunnel, it indicates that a full-line insulation solution is required. The calculation results are in high agreement with the field measurement data, further verifying the reliability of this method. Field measurement results show that the surrounding rock along the entire length of the highway tunnel exhibits freezing phenomena, confirming the necessity and rationality of installing insulation structures along the entire length.

[0050] For insulation structures with different thermal conductivity, laying thickness, and installation methods, The pattern of change is as follows Figure 8 As shown in (a)-(d), the thermal conductivity of the insulation structure and the thickness of the insulation layer affect the thermal conductivity of the insulation structure and the thickness of the insulation layer. The impact is quite significant. The lower the thermal conductivity, the thicker the layer needs to be. The larger the size, the longer the insulation structure is needed to achieve the same effect. The insulation structure design method affects... The order of impact is: outer side of the secondary lining (Type I1 insulation structure) > double-layer insulation structure (Type II1 insulation structure) > between the primary support and the secondary lining (Type I2 insulation structure). Furthermore, the wind speed inside the highway tunnel is relatively low. The change is small with increasing wind speed, see Figure 6 (d) Calculate using average wind speed It can meet the requirements for setting the length of the insulation structure.

[0051] 4. Optimization of longitudinal thickness of thermal insulation structure: Based on measured temperature field data of the tunnel and adhering to the requirements for frost damage prevention, the reasonable thickness of the insulation structure in different sections was determined through synergistic optimization of data analysis and theoretical calculations. Specific optimization results and parameter correspondences are detailed below. Figure 9To ensure effective frost damage prevention while optimizing construction costs, the project adopted a tiered, differentiated design approach for the insulation structure. Based on the degree of impact of cold airflow on different longitudinal sections of the tunnel, the tunnel was divided into three insulation level zones, each with a corresponding insulation structure of different thicknesses: the strong impact zone at the entrance and exit sections had insulation structure thicknesses of 80mm (entrance side) and 50mm (exit side); the impact zone at the entrance and exit sections had insulation structure thicknesses of 65mm (entrance side) and 45mm (exit side); and the weak impact zone (middle section of the tunnel) uniformly used a 40mm thick insulation structure.

[0052] The long-term protection of thermal insulation structures depends on their complete service condition. To avoid localized damage leading to insulation performance failure, a regular inspection mechanism needs to be established during the operation and maintenance phase. When water leakage occurs in a localized area of ​​the tunnel or physical damage occurs to the thermal insulation structure, the damaged area, the leakage point, and the surrounding area with obvious water stains should be replaced in a timely manner to ensure that the thermal insulation structure always maintains a continuous and complete protective state, thereby continuously playing its role in preventing frost damage.

[0053] 4. Evaluation of thermal insulation effect: In a highway tunnel engineering project, a significant linear negative correlation was observed between the freezing depth of the surrounding rock and the frost heave force; that is, the frost heave force decreased linearly with decreasing freezing depth. Taking Class IV surrounding rock as an example, for every 1 m decrease in freezing depth, the resulting frost heave force decreased by 0.16 MPa (see...). Figure 10 This principle fully demonstrates that reducing the freezing depth of the surrounding rock through technical means is an economical and effective way to reduce the frost heave force of tunnel structures and prevent frost damage.

[0054] Based on the above mechanism, installing thermal insulation structures in key sections at the tunnel entrance can significantly weaken the convective heat transfer effect between the surrounding rock and the airflow inside the tunnel by enhancing radial thermal resistance. Simultaneously, it reduces the thermal conductivity of the insulation structure, lining, and surrounding rock, thereby reducing heat loss from the surrounding rock during cold seasons and effectively inhibiting the development and extension of freezing depth. After maintenance and long-term operational monitoring of a highway tunnel, no serious frost damage problems such as lining cracking, frost heave, or water seepage and icing were observed. The overall operating condition remained stable and good, further confirming the technical feasibility and engineering effectiveness of reducing freezing depth through the installation of thermal insulation structures to prevent frost damage.

[0055] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for calculating the optimal length of various types of thermal insulation structures in cold-region tunnels based on segmented differentiated adjustment, characterized in that, include: The temperature distribution patterns in tunnels in cold regions were obtained through temperature monitoring and field investigation. Based on the tunnel temperature distribution pattern, a temperature parameter distribution function along radial depth and longitudinal distance is constructed; Based on the engineering constraints, determine the optimal insulation structure type and the corresponding initial thickness value of the insulation structure; Based on the optimal insulation structure type and initial thickness value, obtain the thermal insulation effect correction coefficient of the insulation structure; Based on the thermal insulation effect correction coefficient of the thermal insulation structure, the temperature parameter distribution function and the initial thickness value, the initial length value of the thermal insulation structure is obtained; Based on the initial length value, the tunnel length is divided into sections and segments; Based on the segmentation results, select a suitable longitudinal distribution pattern for the thermal insulation structure; Based on the principle of segmentation and partitioning, the initial thickness value and the longitudinal distribution of the suitable insulation structure are iteratively optimized to obtain the optimal length value of the insulation structure.

2. The method for calculating the optimal length of multi-type thermal insulation structures for cold-region tunnels based on segmented differential adjustment according to claim 1, characterized in that, Constructing the temperature parameter distribution function along the radial depth and longitudinal distance includes: Based on the annual and daily temperature variation data at the tunnel entrance, the annual average temperature, annual temperature amplitude, and daily temperature amplitude are extracted. Based on the radial distribution patterns of the annual average temperature, annual temperature amplitude, and daily temperature amplitude, the radial temperature distribution function is obtained. Based on the longitudinal distribution patterns of the annual average temperature, annual temperature amplitude, and daily temperature amplitude, the longitudinal temperature distribution function is obtained.

3. The method for calculating the optimal length of multi-type thermal insulation structures for cold-region tunnels based on segmented differential adjustment according to claim 2, characterized in that, The radial depth temperature distribution function includes: radial daily temperature amplitude distribution function, radial annual temperature amplitude distribution function, and radial annual average temperature distribution function; The radial diurnal temperature amplitude distribution function for: ; The radial annual temperature amplitude distribution function for: ; The radial annual average temperature distribution function for: ; in, The radial depth of the tunnel. This represents the attenuation coefficient of the daily temperature amplitude with radial depth. Distance from the tunnel entrance Daily temperature amplitude, The longitudinal distance from the tunnel entrance end, Distance from the tunnel entrance Annual temperature amplitude, The volumetric heat capacity of the tunnel. The thermal conductivity of the tunnel. The freeze-thaw cycle of the tunnel. Distance from the tunnel entrance The average annual temperature, The annual average temperature increases linearly with radial depth.

4. The method for calculating the optimal length of multi-type thermal insulation structures for cold-region tunnels based on segmented differential adjustment according to claim 3, characterized in that, The temperature distribution function of the longitudinal distance includes: the longitudinal daily temperature amplitude distribution function at the tunnel entrance, the longitudinal annual temperature amplitude distribution function, and the longitudinal annual average temperature distribution function; The longitudinal daily temperature amplitude distribution function is: ; The longitudinal annual temperature amplitude distribution function is: ; The longitudinal annual average temperature distribution function is: ; in, and These are the parameters used to calculate the daily temperature amplitude as a function of the tunnel's longitudinal distance. and For the opening end and distance The daily temperature amplitude at the surface, and These are the parameters used to calculate the annual temperature amplitude as a function of the tunnel's longitudinal distance. and For the opening end and distance Annual surface temperature amplitude and The parameters for calculating the annual average temperature as a function of the tunnel's longitudinal distance are:

5. The method for calculating the optimal length of multi-type thermal insulation structures for cold-region tunnels based on segmented differential adjustment according to claim 1, characterized in that, Based on engineering constraints, the optimal insulation structure type and the corresponding initial thickness value of the insulation structure are determined as follows: From four main categories and eleven subcategories of insulation structures, including single-layer insulation structures, double-layer insulation structures, composite single-layer insulation structures, and composite double-layer insulation structures, the optimal insulation structure type is selected based on engineering constraints. These engineering constraints include: climate characteristics of the tunnel site area, temperature variation patterns, freezing depth, engineering hydrogeological conditions, thermophysical properties of the surrounding rock, insulation material performance, engineering cost, and construction technology. The thickness parameters of the insulation structure are calculated based on the optimal insulation structure type and the corresponding calculation formula to obtain the initial thickness value.

6. The method for calculating the optimal length of multi-type thermal insulation structures for cold-region tunnels based on segmented differential adjustment according to claim 5, characterized in that, The longitudinal distribution of the thermal insulation structure includes: uniform distribution of thermal insulation structure, progressive distribution of thermal insulation structure, stepped distribution of thermal insulation structure, and combined distribution of thermal insulation structure. The uniform distribution of the thermal insulation structure includes: continuous uniform distribution and discontinuous uniform distribution; The progressive distribution of the thermal insulation structure includes: linear progressive distribution and curved progressive distribution; The stepped distribution of the thermal insulation structure includes: a stepped segmented distribution with four influence zones, a stepped continuous distribution with three influence zones, a stepped segmented distribution with three influence zones, and a stepped continuous distribution with two influence zones. The combined distribution of the thermal insulation structure includes: a two-influence zone stepped-linear progressive distribution, a two-influence zone stepped-curved progressive distribution, a three-influence zone stepped-linear progressive distribution, and a three-influence zone stepped-curved progressive distribution.

7. The method for calculating the optimal length of multi-type thermal insulation structures for cold-region tunnels based on segmented differential adjustment according to claim 6, characterized in that, Based on the principle of segmentation and partitioning, the initial thickness value and the appropriate longitudinal distribution of the insulation structure are iteratively optimized to obtain the optimal length value of the insulation structure, including: Based on the principle of segmentation and partitioning, the tunnel is divided into different impact zones, and the initial thickness value of each impact zone is adjusted accordingly. Based on the adjusted insulation structure thickness value, the correction coefficient of each section is recalculated, the initial length is updated, and a suitable longitudinal distribution form of the insulation structure is reselected. Through multiple rounds of iterative calculations until the preset conditions are met, the optimal length value of the insulation structure is obtained.

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