Railway long-term deformation control-based permafrost roadbed structure design method

Abstract

The invention discloses a permafrost roadbed structure design method based on railway long-term deformation control, which comprises the following steps of: carrying out comprehensive investigation and physical and mechanical property analysis on frozen soil through geological plotting, geological drilling and comprehensive geophysical prospecting; according to investigation and analysis results, determining layered distribution characteristics of the permafrost of the foundation; according to the layered distribution characteristics of the permafrost of the foundation, parameters of a roadbed structure are set; calculating and analyzing the cooling capacity demand of the permafrost roadbed; setting a railroad bed deformation control standard; and according to the cooling capacity requirement and the railway roadbed deformation control standard, combining the parameters of the roadbed structure, and designing to obtain the hot rod roadbed structure. The scientific and intelligent permafrost hot rod roadbed design method can be realized, long-term deformation control and dynamic adaptability guarantee is provided for railway engineering in cold regions, the operation and maintenance cost is reduced, and the service life of the roadbed is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of frozen soil subgrade design, and particularly to a design method for a permafrost subgrade structure based on long-term deformation control of railways. Background Art

[0002] The design of railway subgrades in permafrost regions faces core problems such as poor thermal stability of frozen soil and significant thaw settlement deformation. As an active cooling measure, the thermosyphon technology has been widely applied in projects such as the Qinghai-Tibet Railway and the Qinghai-Tibet Highway, and its design method mainly focuses on the principle of heat balance.

[0003] With global warming and the expansion of transportation networks in alpine regions, the design of frozen soil subgrades shows the following trends: (1) Performance-oriented in the long term, shifting from short-term thermal stability to full-life cycle deformation control, which requires integrating permafrost creep models, climate change predictions, and structural durability analysis; (2) Coupled analysis of multiple factors, which requires integrating multi-dimensional data such as geological stratification, physical and mechanical properties of frozen soil, thermo-hydro-mechanical coupling effects, and ecological disturbances to improve the refinement level of design; (3) Intelligent and adaptive design, introducing an Internet of Things monitoring and feedback mechanism to achieve dynamic adjustment of thermosyphon parameters to cope with the uncertainties of climate and loads.

[0004] The existing design methods for thermosyphon subgrades expose the following technical bottlenecks in engineering practice: [[ID=2,2]] (1) Lack of long-term deformation control. The existing methods focus on instantaneous heat balance and do not establish a long-term deformation model that couples permafrost thawing-consolidation-creep, resulting in a high risk of excessive settlement in the later stage of railway operation; (2) Insufficient adaptability to climate change. Traditional designs use historical meteorological data and do not integrate future climate change scenarios (such as warming rates, extreme events), resulting in significant risks of conservative or ineffective design parameters; (3) Weak multi-scale coupled analysis. The synergistic effects of permafrost stratification characteristics, subgrade structure stiffness, and thermosyphon heat dissipation efficiency have not been fully quantified, and local thermal disturbances are likely to cause uneven settlement; (4) Absence of economic optimization. The thermosyphon layout scheme mostly relies on experience and lacks a full-life cycle cost analysis, resulting in over-design or a sharp increase in maintenance costs. Summary of the Invention

[0005] The purpose of the present invention is to provide a design method for a permafrost subgrade structure based on long-term deformation control of railways to solve at least one of the above technical problems. It can achieve a scientific and intelligent design method for permafrost thermosyphon subgrades, provide long-term deformation control and dynamic adaptability guarantee for cold region railway projects, reduce operation and maintenance costs, and extend the service life of subgrades.

[0006] The embodiments of the present invention are implemented as follows: A design method for a permafrost subgrade structure based on long-term railway deformation control, comprising: Through geological mapping, geological drilling, and comprehensive geophysical prospecting, conduct comprehensive permafrost exploration and analysis of permafrost physical and mechanical properties.

[0007] Based on the exploration and analysis results, determine the layered distribution characteristics of permafrost in the foundation.

[0008] Based on the layered distribution characteristics of permafrost in the foundation, set the parameters of the subgrade structure.

[0009] Calculate and analyze the cooling demand of the permafrost subgrade.

[0010] Set the deformation control standards for the railway subgrade.

[0011] Based on the cooling demand and the railway subgrade deformation control standards, and combined with the parameters of the subgrade structure, design and obtain a thermosyphon subgrade structure.

[0012] In a preferred embodiment of the present invention, in the above design method for a permafrost subgrade structure based on long-term railway deformation control, the conducting of comprehensive permafrost exploration and analysis of permafrost physical and mechanical properties through geological mapping, geological drilling, and comprehensive geophysical prospecting includes:

[0013] Investigate different permafrost phenomena, respectively mark the distribution range and formation conditions, and determine the permafrost boundary and ice content in combination with topographic, geomorphic, vegetation, and hydrological characteristics to obtain a permafrost distribution map.

[0014] Select the corresponding drilling method according to the permafrost type, collect permafrost cores and sample them by grade to obtain permafrost core samples, borehole columnar diagrams, and permafrost ice content data.

[0015] Conduct comprehensive permafrost geophysical prospecting to obtain permafrost wave velocity, dynamic elastic modulus, and groundwater occurrence conditions to obtain a geophysical prospecting profile.

[0016] Conduct thermal conductivity and specific heat capacity tests to obtain the permafrost thermal conductivity range and specific heat capacity range for high-ice-content permafrost and low-ice-content permafrost.

[0017] Conduct moisture content determination to obtain the permafrost moisture content range.

[0018] Conduct density tests to obtain the permafrost wet density range and dry density range.

[0019] Conduct indoor creep tests to obtain the steady-state creep rate of permafrost.

[0020] In a preferred embodiment of the present invention, in the above-mentioned design method for a permafrost subgrade structure based on long-term railway deformation control, in the process of collecting permafrost cores and sampling them in grades, the borehole diameter is controlled such that the starting hole diameter is ≥130 mm and the final hole diameter is ≥110 mm.

[0021] For loose strata with low ice content, select low-speed drilling with a round-trip footage of 0.20 m to 0.50 m.

[0022] For cohesive soil with high ice content, select rapid drilling with a round-trip footage of ≤0.80 m.

[0023] For frozen gravel or bedrock, select low-temperature flushing fluid drilling with a round-trip footage of 0.15 m to 0.30 m.

[0024] Its technical effects are as follows: multi-means collaborative exploration, through the combination of geological mapping, drilling and geophysical prospecting, realizes the three-dimensional identification of permafrost boundaries, ice content and adverse permafrost phenomena such as thermokarst slumps and thick-layered ground ice, avoiding misjudgment or false judgment caused by a single method. For core grading and sampling, Grade I permafrost cores ensure the authenticity of the physical and mechanical parameters of undisturbed soil, Grade II cores are used for moisture content determination, and Grade III cores are used for rapid screening, significantly improving the representativeness of data. The combination of the grooving method and the wax-sealing method measures the moisture content and wet density of permafrost, reveals the influence law of ice content on the creep rate, and directly guides the selection of subgrade filling materials. For indoor creep tests, the creep characteristics of permafrost are quantified to support long-term deformation prediction. By using a GDS temperature-controlled triaxial system, the steady-state creep rate of permafrost under different stress and temperature conditions is simulated, and a quantitative relationship between creep, ground temperature and load is established. For the first time, creep data is incorporated into the subgrade deformation control standard, avoiding the limitations of traditional methods that only rely on thermal equilibrium.

[0025] In a preferred embodiment of the present invention, in the above-mentioned design method for a permafrost subgrade structure based on long-term railway deformation control, the determination of the layered distribution characteristics of permafrost in the foundation includes: Set measuring points at depth intervals, set a ground temperature observation hole at each measuring point, install a platinum resistance temperature sensor in the ground temperature observation hole for ground temperature observation, and obtain the vertical ground temperature gradient curve, annual average ground temperature and upper limit depth of permafrost.

[0026] According to the annual average ground temperature, the permafrost zones are divided into a high-temperature extremely unstable zone and a low-temperature stable zone. Combining with the ice content grading, the thermal stability grade is determined to obtain a permafrost ground temperature zoning map including the superposition of permafrost zones and ice content.

[0027] Perform three-level engineering geological zoning on the permafrost ground temperature zoning map to obtain a permafrost engineering geological zoning map. The first-level zoning is the sheet or island permafrost area, the second-level zoning is the permafrost zone, and the third-level zoning is the ice content type.

[0028] Based on the ground temperature observation results, the permafrost zone division results, and the three-level engineering geological zoning results, a three-dimensional layered distribution model of permafrost in the foundation is established. The three-dimensional layered distribution model of permafrost in the foundation includes ground temperature, ice content, and mechanical property parameters, and marks the creep-sensitive layer positions and the distribution of thick-layer underground ice.

[0029] Its technical effects are as follows: By constructing a three-dimensional distribution model of permafrost in the foundation that includes ground temperature gradient, annual average ground temperature, ice content, and its layered distribution, designers can accurately identify the thickness of the frozen soil layer, the depth of the permafrost table, the permafrost thermal stability grade, the creep-sensitive layer positions, and the distribution range of thick-layer underground ice in the foundation. Compared with the traditional two-dimensional sectional view or empirical judgment method, the data model formed in this step has a higher dimension and a more complete data structure. Through the integration of ground temperature observation and ice content, a thermal stability zoning map of the permafrost zone - ice content superposition is obtained, and then the first-level identification of sheet-like and island-like permafrost is carried out according to the spatial distribution, the second-level division is carried out according to the annual average ground temperature from high-temperature extremely unstable to low-temperature stable, and the third-level division is carried out according to the ice content into sections with less ice, more ice, rich ice, saturated ice, etc. Design parameters such as filling height and thermosyphon density can be precisely set according to the actual thermal stability grade zoning of the foundation, which is conducive to the differential allocation of material and equipment resources. Through the identification of the creep-sensitive layer positions, the filling height of the subgrade can be accurately controlled to make the stress cover the target layer positions, the burial depth and angle of the evaporation section of the thermosyphon are adaptively set, and the areas that need to be reinforced and controlled are identified and intervened in advance, significantly reducing the risk of differential settlement and the possibility of secondary settlement during the operation of the permafrost subgrade, and improving the long-term stability of the structure operation.

[0030] In a preferred embodiment of the present invention, in the above-mentioned method for designing the permafrost subgrade structure based on long-term deformation control of railways, the parameter setting of the subgrade structure according to the layered distribution characteristics of permafrost in the foundation includes:

[0031] In the three-dimensional layered distribution model of permafrost in the foundation, the target temperature of the subgrade structure is determined according to the permafrost zone, and the priority of subgrade filling materials and thermosyphon layout is set according to the type of ice content.

[0032] In the three-dimensional layered distribution model of permafrost in the foundation, according to the depth of the creep-sensitive layer positions, the filling height, top width, and slope ratio of the subgrade are determined.

[0033] The refrigeration radius of the thermosyphon is determined according to the thermal conductivity of the frozen soil, and the longitudinal spacing of the thermosyphons is calculated , where is the refrigeration radius of the thermosyphon, , is the thermal diffusivity of the frozen soil, , is the density of the frozen soil, is the thermal conductivity, is the specific heat capacity, is the operating time of the thermal rod is the installation inclination angle of the thermal rod

[0034] In a preferred embodiment of the present invention, in the above-mentioned design method for the permafrost subgrade structure based on long-term railway deformation control, in the setting of the priority of subgrade filling materials and thermal rod layout according to the ice content type, for high-ice-content areas, thermal rods with a spacing ≤ 3 m are set, and the evaporation section length is increased to ≥ 15 m. For low-ice-content areas, conventional thermal rods with a layout spacing of 3 m - 5 m are arranged

[0035] Its technical effects are as follows: By driving the setting of structural parameters with data such as the geothermal zone, ice content, and creep-sensitive layer in the three-dimensional foundation model, the subgrade target temperature is determined according to the geothermal zone of the specific area, ensuring that the cooling control target is adapted to local conditions; the structural dimensions such as the subgrade top width, filling height, and slope ratio are directly matched with the distribution of the frozen soil layer and the depth of the sensitive layer. Compared with the traditional unified structural layout method, it significantly reduces design redundancy, avoids the subgrade being too heavy or too light, and improves the anti-deformation ability and engineering resource utilization rate. Calculate the frozen soil thermal diffusivity α through thermal physical parameters such as thermal conductivity, specific heat capacity, and wet density, and further take the thermal rod cooling time and installation inclination angle as variables to accurately calculate the thermal rod cooling radius R, and inversely deduce the longitudinal layout spacing L of the thermal rod to ensure that the cooling influence range of each thermal rod is continuous and seamless. By reasonably adjusting the installation angle, optimizing the heat distribution path, and improving the temperature reduction uniformity, it improves the scientificity and calculability of the thermal rod layout design, ensuring full coverage and effective cooling in thermally sensitive areas such as extremely unstable high-temperature areas, and avoiding local deformation out of control due to cooling dead zones. Taking the creep-sensitive layer in the frozen soil as the design benchmark, through the setting of the filling height, the filling load just covers this layer, and the evaporation section penetrates the upper gravel soil and reaches ≥ 3 m deep into the target sensitive layer, avoiding the "deep subsidence" phenomenon of shallow frozen soil melting while deep creep is not controlled, strengthening the transformation of frozen soil deformation control from "surface suppression" to "layer locking control", maximizing the suppression of the cumulative expansion trend of deep creep displacement, and significantly improving the overall deformation control effect and service life of the subgrade

[0036] In a preferred embodiment of the present invention, in the above-mentioned design method for the permafrost subgrade structure based on long-term railway deformation control, the calculation and analysis of the cold quantity demand of the permafrost subgrade include

[0037] Calculating the basic cold quantity of the permafrost subgrade , where is the soil mass within the refrigeration range is the target ground temperature is the initial ground temperature

[0038] Calculating the climate compensation cold quantity of the permafrost subgrade , where is the heat transfer coefficient is the climate warming rate.

[0039] Calculate the total cooling load of the permafrost subgrade .

[0040] Its technical effect is as follows: By calculating the basic cooling capacity and climate compensation cooling capacity respectively and superimposing them as the total cooling load, it ensures that the cooling requirements of the permafrost foundation under each section of the subgrade can be measured, calculated, and traced, and the cooling resources can be configured differently for different sections, different ice-containing layers, and different temperature environments, improving the matching degree between the refrigeration system and the actual cooling load, and avoiding over-cooling and under-cooling phenomena. The basic cooling capacity directly reflects the initial cooling requirement of the heat pipe, while the climate compensation cooling capacity simulates the dynamic cooling load compensation requirement to maintain the ground temperature from rising in the future warming scenario, providing a basis for rigid heat matching in the selection and layout of heat pipes.

[0041] In a preferred embodiment of the present invention, in the above-mentioned structural design method of permafrost subgrade based on long-term deformation control of railways, the setting of the deformation control standard for railway subgrade includes:

[0042] Extract the steady-state creep rate of frozen soil.

[0043] Relate the permafrost temperature zone to the strain rate threshold of the steady-state creep rate of frozen soil. For the extremely unstable high-temperature zone, set the strain rate threshold , differential settlement ≤ 8 mm / 10a. For the stable low-temperature zone, set the strain rate threshold , differential settlement ≤ 5 mm / 10a.

[0044] Based on the climate warming rate = 0.26 °C / a climate scenario, set the target ground temperature as .

[0045] Its technical effect is as follows: By correlating different permafrost temperature zones with creep rate thresholds and allowable differential settlement values, the specific control indicators for different thermal stability regions are clarified, and a partition settlement control standard system coupled with ground temperature and ice content is established, which can realize the differential structural design and control index adaptation of different permafrost engineering sections, improve the accuracy and economy of engineering investment, realize the transformation from "empirical judgment - result feedback" to "physical model - index constraint", formulate the ground temperature control target in combination with the climate scenario, enhance the robustness of the project to cope with future warming trends, improve the thermal adaptation ability of the subgrade structure, and delay or even block the frozen soil melting process through the temperature locking strategy in high-risk sections, effectively controlling the development speed of deep foundation creep and settlement.

[0046] In a preferred embodiment of the present invention, in the above-mentioned design method of a permafrost subgrade structure based on long-term railway deformation control, the design of a thermosyphon subgrade structure obtained by combining the cold demand and the railway subgrade deformation control standard with the parameters of the subgrade structure includes:

[0047] Based on the total cold load of the permafrost subgrade , select the type of thermosyphon, and the type of thermosyphon includes at least one of an adsorption thermosyphon, a strengthened thermosyphon, a high-power flexible thermosyphon, and a photovoltaic compression all-season thermosyphon.

[0048] Calculate the required number of thermosyphons , where is the width of the target area.

[0049] For the high ice content area, the thermal conductivity of the filling material is 1.71 - 1.83 W / (m·K), select a high-power flexible thermosyphon or an adsorption thermosyphon; for the low ice content area, the thermal conductivity of the filling material is 1.2 - 1.8 W / (m·K), select an ordinary thermosyphon.

[0050] Define the high ice content area at a formation depth of 2.5 - 12 m as the creep-sensitive layer, and cover the creep-sensitive layer with the self-weight stress of the fill.

[0051] For the creep-sensitive layer, the fill height ≥ 5 m, and the evaporation section of the thermosyphon needs to penetrate the gravelly soil and extend ≥ 3 m below the permafrost table.

[0052] Set the inclination angle of the thermosyphon according to the slope ratio of the creep-sensitive layer.

[0053] Its technical effects are as follows: Establish a design closed-loop. The cold quantity guidance controls the selection of the thermosyphon type through the total cold load, the deformation standard guidance limits the range of the thermosyphon refrigeration effect through the strain rate threshold and the settlement limit value, and the structure coupling guidance makes the evaporation section penetrate the key layer by matching the depth of the foundation creep-sensitive layer with the subgrade fill height, realizing the synergy of structure-thermal control. Establish a differential selection strategy based on thermal conductivity, select the thermosyphon through the partition of the material thermal conductivity, and improve the thermal control efficiency and economy. Through the adaptation design of the thermosyphon layout parameters and the slope ratio, improve the cooling coverage ability of the toe area, strengthen the regulation ability of the thermosyphon on the heterogeneous deformation zone at the toe, and improve the overall subgrade smoothness and structural safety and stability. Control the stress concentration of the creep-sensitive layer based on stress expansion calculation (equivalent width, influence depth), and through the synergistic effect of structural design and thermosyphon configuration, effectively suppress the deep deformation source, avoid the hidden danger mode of surface stability and deep creep, and strengthen the initiative of deformation control.

[0054] In a preferred embodiment of the present invention, in the above-mentioned design method of a permafrost subgrade structure based on long-term railway deformation control, when the total cold load When it is ≤ 2000 MJ, select the adsorption type heat pipe.

[0055] When 2000 MJ < ≤ 4000 MJ, select the enhanced heat pipe or the high-power flexible heat pipe.

[0056] When > 4000 MJ, select the photovoltaic compression type all-season heat pipe.

[0057] By integrating the frozen soil creep model and the thermal-mechanical-hydraulic coupling analysis, the present invention can accurately predict and control the long-term thaw settlement deformation of the subgrade. Combining with the indoor creep test data, the refrigeration parameters of the heat pipe are dynamically adjusted to ensure the stability of the frozen soil foundation under the railway load.

[0058] The present invention solves the limitation that the traditional heat pipe only works in the cold season by introducing future climate scenario simulation, dynamically adjusting the cooling demand of the heat pipe, and adopting the all-season refrigeration technology to achieve the balanced supply of cooling capacity throughout the year.

[0059] The present invention optimizes the cooling capacity distribution through the three-dimensional foundation layered model, combines with the geophysical prospecting profile diagram to show the distribution of thick-layer underground ice, accurately locates the high ice content area, and avoids the waste of cooling capacity caused by homogenized design.

[0060] The present invention forms a complete chain from investigation, analysis to monitoring and feedback, integrates economic optimization into the design process, compares the life cycle costs of different heat pipe schemes, such as the photovoltaic heat pipe has a high initial investment but low operation and maintenance costs, and reduces redundant design.

[0061] The present invention flexibly selects models for different frozen soil temperature zones. For the high-temperature extremely unstable area, the photovoltaic compression type all-season heat pipe is adopted to cover a large range of refrigeration requirements. For the low-temperature stable area, the enhanced heat pipe is used to reduce the initial investment.

[0062] By establishing a thermal-mechanical coupling simulation model and inputting parameters such as the thermal conductivity and specific heat capacity of the frozen soil, the deformation during the 50-year operation period can be predicted, and the error is controlled within ±10%. The on-site monitoring data is real-time fed back to the design system to form a "design-verification-optimization" closed loop to ensure long-term stability. Brief Description of the Drawings

[0063] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present invention, and therefore should not be regarded as a limitation of the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts.

[0064] Figure 1Schematic diagram of the design method process of the permafrost subgrade structure based on long-term deformation control of railways;

[0065] Figure 2 Schematic diagram of the design calculation process of the permafrost subgrade structure of the present invention;

[0066] Figure 3 Schematic diagram of the permafrost subgrade structure based on long-term deformation control of railways of the present invention. Detailed implementation manners

[0067] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated herein can be arranged and designed in various different configurations.

[0068] Please refer to Figures 1 to 3 , the embodiments of the present invention provide a design method for a permafrost subgrade structure based on long-term deformation control of railways, which includes: through geological mapping, geological drilling and comprehensive geophysical prospecting, conducting comprehensive permafrost exploration and analysis of permafrost physical and mechanical properties; determining the layered distribution characteristics of permafrost in the foundation according to the exploration and analysis results; setting parameters of the subgrade structure according to the layered distribution characteristics of permafrost in the foundation; calculating and analyzing the cooling demand of the permafrost subgrade; setting the deformation control standard of the railway subgrade; and designing a thermosyphon subgrade structure according to the cooling demand and the deformation control standard of the railway subgrade, in combination with the parameters of the subgrade structure.

[0069] In a preferred embodiment of the present invention, in the above-mentioned permafrost roadbed structure design method based on long-term railway deformation control, the comprehensive investigation of frozen soil and analysis of the physical and mechanical properties of frozen soil through geological mapping, geological drilling and comprehensive geophysical exploration include: investigating different frozen soil phenomena, marking the distribution range and formation conditions respectively, determining the frozen soil boundary and ice content in combination with the topography, landform, vegetation and hydrological characteristics, and obtaining a frozen soil distribution map, wherein the frozen soil phenomena include at least one of ice cones, frost heave mounds, thick underground ice, thaw mudflows, thermal thaw landslides, thermal thaw lakes and ponds, thermal thaw depressions, frozen soil swamps and frozen soil wetlands; selecting the corresponding drilling method according to the frozen soil type, collecting frozen soil cores and sampling them in stages, and obtaining frozen soil core samples, borehole histograms and frozen soil content. Ice volume data, wherein the collected permafrost cores are sampled in grades, with Grade I permafrost cores kept in a frozen state, Grade II permafrost cores kept in a water content, and Grade III permafrost cores allowed to be disturbed; comprehensive permafrost geophysical exploration is conducted, and for areas with obvious electrical property differences, electrical depth sounding or high-density electrical method is selected; for areas with different elastic wave velocities, seismic exploration or surface wave exploration is selected to obtain permafrost wave velocity, dynamic elastic modulus and groundwater occurrence conditions, and obtain a geophysical profile, wherein the geophysical profile shows the permafrost type, seasonal thawing layer depth and thick underground ice distribution; thermal conductivity and specific heat capacity tests are conducted to obtain the thermal conductivity range and specific heat capacity range of permafrost with high ice content and low ice content; specifically, the thermal conductivity and specific heat capacity tests are conducted using THERMTES The TLS-100 thermal conductivity meter is equipped with a 100mm long probe. Take the original frozen soil sample with a diameter of ≥50mm and a height of ≥100mm. Ensure that the sample surface is flat and there is no gap in contact with the probe. Insert the probe completely vertically into the center of the sample, start the equipment to heat the probe, and record the change curve of the sample temperature over time. The time interval is ≤1 second and continues until the temperature change tends to stabilize, which is about 10-15 minutes. The equipment automatically calculates the thermal conductivity k and specific heat capacity c based on the thermal response data. The final results show that the thermal conductivity of low ice content frozen soil ranges from 1.2-1.8W / (m·K) and the thermal conductivity of high ice content frozen soil ranges from 1.8-2.5 W / (m·K). The specific heat capacity ranges from 1800-2400J / (kg·K), which increases with increasing water content.

[0070] The moisture content is measured to obtain the range of frozen soil moisture content. Specifically, the moisture content is measured by cutting the original frozen soil sample on the wall of the pit or trench to avoid blasting and destroying the ice crystal structure. The wet mass of the sample is quickly weighed. , place the sample in a constant temperature drying oven at 105℃ and dry it to constant weight, and weigh the dry mass , calculate the moisture content , the measurement was carried out twice in parallel, with an allowable error of ≤0.5%. The moisture content of frozen soil was found to be in the range of 15%-60%. For every 10% increase in moisture content, the steady-state creep rate increased by about 30%.

[0071] Perform a density test to obtain the range of wet density and dry density of frozen soil. Specifically, the wax-sealing method is used for the density test, and the mass of the frozen soil specimen is weighed. The specimen is immersed in molten paraffin at a temperature of 60 - 70°C to form a uniform wax-sealing layer, and the mass of the wax-sealed specimen is weighed after cooling. The wax-sealed specimen is immersed in water, and the mass in water is weighed. Calculate the wet density. where V is the volume of the specimen, and the dry density Correct the volume of the specimen. It is calculated that the range of wet density of frozen soil is 1.6 - 2.2 g / cm³, and the range of dry density is 1.4 - 1.8 g / cm³. For every 0.2 g / cm³ increase in density, the thermal diffusivity decreases by about 15%, and the creep rate decreases by 20%.

[0072] Perform an indoor creep test to obtain the steady-state creep rate of frozen soil.

[0073] Specifically, the GDS temperature-controlled advanced dynamic triaxial test system is used for the indoor creep test. The temperature control accuracy is ±0.1°C, the confining pressure range is 0 - 2 Mpa, the specimen diameter is 50 mm, and the height is 100 mm. If uniaxial compression is adopted, the vertical load directly below the subgrade is simulated; if conventional triaxial is adopted, the complex stress state at the toe of the slope is simulated, with confining pressures of 50 kPa and 100 kPa. The temperature conditions are -4°C, -2°C, -1°C, and -0.5°C respectively, covering the typical temperature range of frozen soil. If staged loading is adopted, each stage of stress is maintained until the strain rate is stable, such as 50 kPa → 100 kPa → 200 kPa → 400 kPa; if separate loading is adopted, independent specimens are tested step by step to reduce the number of specimens. Record the curve of axial strain varying with time, and extract the steady-state creep rate of frozen soil. .

[0074] In a preferred embodiment of the present invention, in the above-mentioned design method for a permafrost subgrade structure based on long-term deformation control of railways, in the process of collecting frozen soil cores and sampling them in stages, the drilling diameter is controlled such that the starting hole diameter is ≥130 mm and the final hole diameter is ≥110 mm; for low-ice-content loose strata, low-speed drilling is selected, and the footage per round trip is 0.20 m - 0.50 m; for high-ice-content cohesive soil, high-speed drilling is selected, and the footage per round trip is ≤0.80 m; for frozen gravel or bedrock, low-temperature flushing fluid drilling is selected, and the footage per round trip is 0.15 m - 0.30 m.

[0075] Its technical effects are as follows: Multi-means collaborative exploration combines geological mapping, drilling, and geophysical exploration to achieve three-dimensional identification of permafrost boundaries, ice content, and adverse permafrost phenomena such as thermokarst slides and massive ground ice, avoiding missed or misjudgments caused by a single method. For core grading and sampling, Grade I permafrost cores ensure the authenticity of the physical and mechanical parameters of undisturbed soil, Grade II cores are used for moisture content determination, and Grade III cores are used for rapid screening, significantly improving the representativeness of data. The combination of the grooving method and the wax-sealing method measures the moisture content and wet density of permafrost, reveals the influence law of ice content on the creep rate, and directly guides the selection of subgrade filling materials. For indoor creep tests, the creep characteristics of permafrost are quantified to support long-term deformation prediction. By using a GDS temperature-controlled triaxial system, the steady-state creep rate of permafrost under different stress and temperature conditions is simulated, and a quantitative relationship between creep, ground temperature, and load is established. For the first time, creep data are incorporated into the subgrade deformation control standard, avoiding the limitations of traditional methods that only rely on thermal equilibrium.

[0076] In a preferred embodiment of the present invention, in the above method for designing a subgrade structure of permafrost based on long-term deformation control of railways, the determination of the layered distribution characteristics of permafrost in the foundation includes: setting measurement points at depth intervals, with intervals of 0.5 m or 1.0 m, setting ground temperature observation holes at each measurement point, the depth of the measurement hole being ≥16 m, installing platinum resistance temperature sensors in the ground temperature observation holes, the accuracy of the sensors being 0.05 °C, conducting ground temperature observations for a time ≥30 days to eliminate the influence of thermal disturbance, obtaining the vertical ground temperature gradient curve, annual average ground temperature, and upper limit depth of permafrost; dividing the permafrost zone into a high-temperature extremely unstable zone and a low-temperature stable zone according to the annual average ground temperature, where the annual average ground temperature in the high-temperature extremely unstable zone is ≥ -0.5 °C, and the annual average ground temperature in the low-temperature stable zone is < -2.0 °C, combining the ice content grading to determine the thermal stability grade, and obtaining a permafrost ground temperature zoning map including the superposition of the permafrost zone and ice content; conducting three-level engineering geological zoning on the permafrost ground temperature zoning map to obtain a permafrost engineering geological zoning map. The first-level zoning is the flaky or island permafrost zone, obtained based on the permafrost distribution range, thickness, and adverse permafrost phenomena. The second-level zoning is the permafrost zone, obtained based on the annual average ground temperature and climate prediction. The third-level zoning is the ice content type, obtained by combining physical and mechanical parameters such as creep rate and frost heave. According to the ground temperature observation results, the permafrost zone division results, and the three-level engineering geological zoning results, a three-dimensional layered distribution model of permafrost in the foundation is established. The three-dimensional layered distribution model of permafrost in the foundation includes ground temperature, ice content, and mechanical property parameters, and marks the creep-sensitive layer positions and the distribution of massive ground ice.

[0077] Its technical effects are as follows: By constructing a three-dimensional foundation permafrost distribution model that includes geothermal gradient, annual average ground temperature, ice content, and its layered distribution, designers can accurately identify the thickness of the frozen soil layer, the depth of the permafrost table, the permafrost thermal stability level, the creep-sensitive layer position, and the distribution range of thick-layer subsurface ice in the foundation. Compared with traditional two-dimensional cross-sectional views or empirical judgment methods, the data model formed in this step has a higher dimension and a more complete data structure. Through the integration of ground temperature observation and ice content, a thermal stability zoning map of the frozen ground temperature zone - ice content superposition is obtained, and then the first-level identification of sheet and island permafrost is carried out according to the spatial distribution, the second-level division is carried out according to the annual average ground temperature from high-temperature extremely unstable to low-temperature stable, and the third-level division is carried out according to the ice content into areas with less ice, more ice, rich ice, saturated ice, etc. Design parameters such as filling height and thermosyphon density can be finely set according to the actual thermal stability level zoning of the foundation, which is conducive to the differential allocation of material and equipment resources. Through the identification of the creep-sensitive layer position, the filling height of the subgrade can be accurately controlled to make the stress cover the target layer position, the burial depth and angle of the evaporation section of the thermosyphon can be adaptively set, and the areas that need to be strengthened and controlled can be identified and intervened in advance, significantly reducing the risk of differential settlement and the possibility of secondary settlement during the operation of the permafrost subgrade, and improving the long-term stability of the structure operation.

[0078] In a preferred embodiment of the present invention, in the above-mentioned permafrost subgrade structure design method based on long-term deformation control of railways, the parameter setting of the subgrade structure according to the layered distribution characteristics of the foundation permafrost includes: in the three-dimensional foundation permafrost layered distribution model, according to the ground temperature zone, determine that the target temperature of the subgrade structure is ≤ -1.5 °C, and set the priority of subgrade filling materials and thermosyphon layout according to the ice content type; in the three-dimensional foundation permafrost layered distribution model, according to the depth of the creep-sensitive layer position, determine the filling height, top width, and slope ratio of the subgrade. Among them, if the depth of the creep-sensitive layer position is between 1 m and 4 m, determine the filling height of the subgrade to be 5 m, the top width to be 5 m, and the slope ratio to be 1:1.5; according to the frozen soil thermal conductivity, determine the refrigeration radius of the thermosyphon, and calculate the longitudinal spacing of the thermosyphon , where is the refrigeration radius of the thermosyphon, , is the frozen soil thermal diffusivity, , is the frozen soil density, and here the wet density of the frozen soil is adopted, is the thermal conductivity, is the specific heat capacity, is the working time of the thermosyphon, is the installation inclination angle of the thermosyphon, 20° ≤ ≤ 45°, and for the high-temperature extremely unstable area, a more inclined layout is adopted to expand the refrigeration coverage range.

[0079] In a preferred embodiment of the present invention, in the above-mentioned design method of permafrost subgrade structure based on long-term railway deformation control, in the setting of the priority of subgrade filling materials and thermal piles according to the ice content type, for high-ice-content areas, thermal piles with a spacing ≤ 3 m are set, and the evaporation section length is increased to ≥ 15 m. For low-ice-content areas, conventional thermal piles with a spacing of 3 m - 5 m are arranged.

[0080] Its technical effects are as follows: By setting structural parameters driven by data such as the geothermal zone, ice content, and creep-sensitive layer in the three-dimensional foundation model, the subgrade target temperature is determined according to the geothermal zone of the specific area, ensuring that the cooling control target is adapted to local conditions; the structural dimensions such as the subgrade top width, filling height, and slope ratio directly match the distribution of the frozen soil layer and the depth of the sensitive layer. Compared with the traditional unified structure layout method, it significantly reduces design redundancy, avoids the structure being too heavy or too light, and improves the anti-deformation ability and engineering resource utilization rate. Calculate the thermal diffusivity α of frozen soil through thermal physical parameters such as thermal conductivity, specific heat capacity, and wet density, and further take the thermal pile cooling time and installation inclination as variables to accurately calculate the thermal pile cooling radius R, and inversely deduce the longitudinal layout spacing L of the thermal pile to ensure that the cooling influence range of each thermal pile is continuously seamless. By reasonably adjusting the installation angle, optimizing the heat distribution path, and improving the temperature drop uniformity, the scientificity and calculability of the thermal pile layout design are improved, ensuring full coverage and effective cooling in thermally sensitive areas such as extremely unstable high-temperature areas, and avoiding local deformation out of control caused by cooling dead corners. Taking the creep-sensitive layer in frozen soil as the design benchmark, through the setting of the filling height, the filling load just covers this layer, and the evaporation section penetrates the upper gravel soil and reaches ≥ 3 m deep into the target sensitive layer, avoiding the "deep subsidence" phenomenon of shallow frozen soil melting while deep creep is not controlled, strengthening the transformation of frozen soil deformation control from "surface suppression" to "layer locking control", maximizing the suppression of the cumulative expansion trend of deep creep displacement, and significantly improving the overall deformation control effect and service life of the subgrade.

[0081] In a preferred embodiment of the present invention, in the above-mentioned design method of permafrost subgrade structure based on long-term railway deformation control, the calculation and analysis of the cooling demand of the permafrost subgrade include: calculating the basic cooling of the permafrost subgrade , where is the mass of the soil within the refrigeration range, calculated according to the subgrade volume and the frozen soil density, is the target ground temperature, taking -1.5 °C, is the initial ground temperature, using the measured value from the survey, and the specific heat capacity takes 1800 - 2400 J / (kg·K); calculating the climate compensation cooling of the permafrost subgrade , where is the heat transfer coefficient, is the climate warming rate, with a value of 0.26 °C / a; calculating the total cooling load of the permafrost subgrade .

[0082] Its technical effects are as follows: By separately calculating the basic cooling capacity and the climate compensation cooling capacity and superimposing them as the total cooling load, it is ensured that the refrigeration requirements of the permafrost foundation under each section of the subgrade can be measured, calculated, and traced, and cooling resources can be differentially configured for different sections, different ice-containing layers, and different temperature environments, improving the matching degree between the refrigeration system and the actual cooling load, and avoiding overcooling and undercooling phenomena. The basic cooling capacity directly reflects the initial cooling requirement of the thermosyphon, while the climate compensation cooling capacity simulates the dynamic cooling load compensation requirement to maintain the ground temperature from rising in the future warming scenario, providing a basis for rigid heat matching in the selection and layout of thermosyphons.

[0083] In a preferred embodiment of the present invention, in the above-mentioned design method for the permafrost subgrade structure based on long-term railway deformation control, the setting of the railway subgrade deformation control standard includes: extracting the steady-state creep rate of permafrost; correlating the permafrost temperature zone with the strain rate threshold of the steady-state creep rate of permafrost. For the extremely unstable high-temperature zone, the strain rate threshold , differential settlement ≤ 8 mm / 10a. For the stable low-temperature zone, the strain rate threshold is set, differential settlement ≤ 5 mm / 10a; based on the climate warming rate = 0.26 °C / a climate scenario, the target ground temperature is set to .

[0084] Its technical effects are as follows: By correlating different permafrost temperature zones with the creep rate threshold and the allowable value of differential settlement, the specific control indexes of different thermal stability regions are clarified, and a partition settlement control standard system coupled with ground temperature and ice content is established, which can realize the differential structure design and control index adaptation of different permafrost engineering sections, improve the accuracy and economy of engineering investment, realize the transformation from "empirical judgment - result feedback" to "physical model - index constraint", formulate the ground temperature control target in combination with the climate scenario, enhance the robustness of the project to cope with the future warming trend, improve the thermal adaptation ability of the subgrade structure, and delay or even block the permafrost melting process through the temperature locking strategy in high-risk sections, effectively controlling the development speed of deep foundation creep and settlement.

[0085] In a preferred embodiment of the present invention, in the above-mentioned design method for the permafrost subgrade structure based on long-term railway deformation control, the design of the thermosyphon subgrade structure according to the cooling demand and the railway subgrade deformation control standard, in combination with the parameters of the subgrade structure, includes: according to the total cooling load of the permafrost subgrade, select the type of thermosyphon, and the type of thermosyphon includes at least one of an adsorption thermosyphon, a strengthened thermosyphon, a high-power flexible thermosyphon, and a photovoltaic compression all-season thermosyphon; calculate the required number of thermosyphons , where is the width of the target area; for the high ice content area, the thermal conductivity of its filling material is 1.71~1.83 W / (m·K), and high-power flexible heat pipes or adsorption heat pipes are selected. For the low ice content area, the thermal conductivity of its filling material is 1.2~1.8 W / (m·K), and ordinary heat pipes are selected. The high ice content area at a formation depth of 2.5 - 12m is defined as the creep-sensitive layer. The creep-sensitive layer is covered by the self-weight stress of the fill to reduce the concentration of additional stress. For the creep-sensitive layer, the fill height ≥5m, and the evaporation section of the heat pipe needs to penetrate the gravelly soil and extend ≥3m below the permafrost table. According to the slope ratio of the creep-sensitive layer, the inclination angle of the heat pipe is set. When the slope ratio is 1:1.5, the inclination angle is designed to be 20°~45° to expand the cooling coverage range of the toe of the slope.

[0086] Example: Design of a certain section of the Qinghai-Tibet Railway

[0087] Creep-sensitive layer: 2.5 - 12m (saturated ice-rich fine-rounded gravel soil).

[0088] Fill height design: Initial fill height H = 5m, top width B2 = 8m, slope ratio 1:1.5. Equivalent width Bequivalent = 14m, stress influence depth z ≈ 12.3m (covering the creep layer).

[0089] Cooperation of heat pipes: Install photovoltaic compression all-season heat pipes, evaporation section length 14m, inclination angle 30°, spacing 3m.

[0090] Effect: The ground temperature drops to -1.8°C after 5 years, and the differential settlement is 4.5mm / 10a.

[0091] Its technical effects are as follows: Establish a design closed-loop. The cold quantity guidance controls the selection of heat pipe types through the total cooling load. The deformation standard guidance limits the cooling effect range of the heat pipe through the strain rate threshold and settlement limit. The structural coupling guidance matches the depth of the foundation creep-sensitive layer with the subgrade fill height, enabling the evaporation section to penetrate the key layer and realizing the synergy of structure-thermal control. A differential selection strategy based on thermal conductivity is established, and heat pipes are selected through the partition of material thermal conductivity to improve the thermal control efficiency and economy. Through the adaptation design of the heat pipe layout parameters and slope ratio, the cooling coverage ability of the toe area is improved, the regulation ability of the heat pipe on the heterogeneous deformation zone at the toe is strengthened, and the overall smoothness and structural safety stability of the subgrade are improved. Based on stress expansion calculation (equivalent width, influence depth), the stress concentration of the creep-sensitive layer is controlled. Through the synergistic effect of structural design and heat pipe configuration, the deep deformation source is effectively suppressed, the hidden danger mode of surface stability and deep creep is avoided, and the initiative of deformation control is strengthened.

[0092] In a preferred embodiment of the present invention, in the above-mentioned design method of the permafrost subgrade structure based on long-term deformation control of railways, according to Table 1, when the total cooling load When it is ≤ 2000 MJ, select the adsorption thermal rod; when 2000 MJ < ≤ 4000 MJ, select the enhanced thermal rod or the high-power flexible thermal rod; when > 4000 MJ, select the photovoltaic compression all-season thermal rod.

[0093] Table 1: Tabular data of thermal rod layout

[0094] Thermosyphon type Cooling capacity range MJ / m Effective cooling radius m Applicable scenarios Reinforced thermosyphon 2000~3000 1.13~1.57 Low-temperature stable zone High-power flexible thermosyphon 3000~4000 0.96~1.2 High-temperature extremely unstable zone, large-scale cooling required Adsorption thermosyphon 1200~2000 1.34~1.57 Medium-low temperature zone, medium ice content Photovoltaic compression all-season thermosyphon 4000~12000 2.5~4.0 High-temperature zone, all-season cooling required

[0095] The embodiment of the present invention aims to protect a design method for a permafrost subgrade structure based on long-term deformation control of railways, and has the following effects:

[0096] The present invention starts from the comprehensive investigation of permafrost, through the analysis of the physical and mechanical properties of permafrost, the determination of the layered distribution characteristics of permafrost in the foundation, the setting of subgrade structure design parameters, the assessment of the impact of climate change, the calculation and analysis of the cold quantity demand of the permafrost subgrade, the design of the thermal rod subgrade and the determination of key parameters, the control of the subgrade deformation control standard, the economic comparison, the determination of the optimal thermal rod subgrade structure, and finally the engineering application and effect monitoring. Each step is closely linked to ensure the scientificity and feasibility of the design process.

[0097] It should be understood that the above specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle of the present invention, and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all variations and modification examples falling within the scope and boundary of the appended claims, or equivalent forms of such scope and boundary.

Claims

1. A design method for permafrost subgrade structure based on long-term deformation control of railways, characterized in that Including: Through geological mapping, geological drilling and comprehensive geophysical prospecting, conduct comprehensive permafrost exploration and analysis of permafrost physical and mechanical properties; According to the exploration and analysis results, determine the layered distribution characteristics of foundation permafrost; According to the layered distribution characteristics of the foundation permafrost, set the parameters of the subgrade structure; Calculate and analyze the cooling demand of the permafrost subgrade; Set the deformation control standard of the railway subgrade; According to the cooling demand and the railway subgrade deformation control standard, combined with the parameters of the subgrade structure, design and obtain a thermosyphon subgrade structure.

2. The design method of a permafrost subgrade structure based on long-term railway deformation control according to claim 1, characterized in that The conduct of comprehensive permafrost exploration and analysis of permafrost physical and mechanical properties through geological mapping, geological drilling and comprehensive geophysical prospecting includes: Investigate different permafrost phenomena, respectively mark the distribution range and formation conditions, and determine the permafrost boundary and ice content in combination with topographic, geomorphic, vegetation and hydrological characteristics to obtain a permafrost distribution map; Select the corresponding drilling method according to the permafrost type, collect permafrost cores and sample by grading to obtain permafrost core samples, borehole columnar diagrams and permafrost ice content data; Conduct comprehensive permafrost geophysical prospecting to obtain permafrost wave velocity, dynamic elastic modulus and groundwater occurrence conditions to obtain a geophysical prospecting profile diagram; Conduct tests on thermal conductivity and specific heat capacity to obtain the ranges of permafrost thermal conductivity and specific heat capacity for high-ice-content permafrost and low-ice-content permafrost; Conduct moisture content determination to obtain the range of permafrost moisture content; Conduct density tests to obtain the ranges of wet density and dry density of permafrost; Conduct indoor creep tests to obtain the steady-state creep rate of permafrost.

3. The design method of a permafrost subgrade structure based on long-term railway deformation control according to claim 2, characterized in that, In the collection of permafrost cores and sampling by grading, the borehole diameter is controlled at the starting hole ≥ 130 mm and the ending hole ≥ 110 mm; For low-ice-content loose strata, select low-speed drilling with a round-trip footage of 0.20 m to 0.50 m; For high-ice-content cohesive soil, select high-speed drilling with a round-trip footage ≤ 0.80 m; For frozen crushed stone or bedrock, select low-temperature flushing fluid drilling with a round-trip footage of 0.15 m to 0.30 m.

4. The design method of a permafrost subgrade structure based on long-term railway deformation control according to claim 2, characterized in that, The determination of the layered distribution characteristics of foundation permafrost according to the exploration and analysis results includes: Set measuring points at depth intervals, set ground temperature observation holes at each measuring point, install platinum resistance temperature sensors in the ground temperature observation holes, conduct ground temperature observations to obtain the permafrost vertical ground temperature gradient curve, annual average ground temperature and upper limit depth; Divide the permafrost zone into a high-temperature extremely unstable zone and a low-temperature stable zone according to the annual average ground temperature, and combine the ice content grading to determine the thermal stability grade to obtain a permafrost temperature zoning map with the superposition of permafrost zones and ice content; Conduct three-level engineering geological zoning on the permafrost temperature zoning map to obtain a permafrost engineering geological zoning map. The first-level zoning is the sheet or island permafrost area, the second-level zoning is the permafrost zone, and the third-level zoning is the ice content type; Based on the ground temperature observation results, the permafrost zone division results and the three-level engineering geological zoning results, establish a three-dimensional foundation permafrost layered distribution model. The three-dimensional foundation permafrost layered distribution model includes ground temperature, ice content and mechanical property parameters, and marks the creep-sensitive horizons and the distribution of thick-layer underground ice.

5. The design method of a permafrost subgrade structure based on long-term railway deformation control according to claim 4, characterized in that, The setting of the parameters of the subgrade structure according to the layered distribution characteristics of the foundation permafrost includes: In the three-dimensional foundation permafrost stratified distribution model, determine the target temperature of the subgrade structure according to the geothermal zone, and set the priority of subgrade filling materials and thermosyphon layout according to the ice content type; In the three-dimensional foundation permafrost stratified distribution model, determine the subgrade filling height, top width and slope ratio according to the depth of the creep-sensitive layer; Determine the cooling radius of the heat pipe according to the thermal conductivity of the frozen soil, and calculate the longitudinal spacing of the heat pipes , where is the cooling radius of the heat pipe, , is the thermal diffusivity of the frozen soil, , is the density of the frozen soil, is the thermal conductivity, is the specific heat capacity, is the working time of the heat pipe, is the installation inclination angle of the heat pipe.

6. The design method of permafrost subgrade structure based on long-term railway deformation control according to claim 5, characterized in that, In the setting of the priority of subgrade filling materials and thermosyphon layout according to the ice content type, for the high ice content area, set the thermosyphons with a spacing ≤ 3m and increase the evaporation section length to ≥ 15m. For the low ice content area, lay the conventional thermosyphons with a spacing of 3m - 5m.

7. The design method of a permafrost subgrade structure based on long-term railway deformation control according to claim 6, characterized in that The calculation and analysis of the cooling demand of the permafrost subgrade include: Calculating the basic cooling capacity of permafrost subgrade , where is the soil mass within the refrigeration range, is the target ground temperature, is the initial ground temperature; Calculating the climate compensation cooling capacity of permafrost subgrade , where is the heat transfer coefficient, is the climate warming rate; Calculate the total cold load of permafrost subgrade .

8. The design method of a permafrost subgrade structure based on long-term railway deformation control according to claim 7, characterized in that, The setting of the railway subgrade deformation control standard includes: Extract the steady-state creep rate of the permafrost; Relate the frozen soil temperature zone to the strain rate threshold of the steady-state creep rate of the frozen soil. For the extremely unstable high-temperature zone, set the strain rate threshold , differential settlement ≤ 8 mm / 10a. For the stable low-temperature zone, set the strain rate threshold , differential settlement ≤ 5 mm / 10a; Based on the climate warming rate = 0.26 °C / a climate scenario, set the target ground temperature to .

9. The design method of a permafrost subgrade structure based on long-term railway deformation control according to claim 8, characterized in that, According to the cooling demand and the railway subgrade deformation control standard, combined with the parameters of the subgrade structure, the design of the thermosyphon subgrade structure includes: According to the total cooling load of the permafrost subgrade , select a type of heat pipe, and the type of heat pipe includes at least one of an adsorption heat pipe, a strengthened heat pipe, a high-power flexible heat pipe, and a photovoltaic compression all-season heat pipe; Calculate the number of thermal rods required , where is the width of the target area; For the high ice content area, the thermal conductivity of its filling material is 1.71 - 1.83 W / (m·K), and select high-power flexible thermosyphons or adsorption thermosyphons. For the low ice content area, the thermal conductivity of its filling material is 1.2 - 1.8 W / (m·K), and select ordinary thermosyphons; Define the high ice content area at a formation depth of 2.5 - 12m as the creep-sensitive layer, and cover the creep-sensitive layer with the self-weight stress of the fill; For the creep-sensitive layer, the filling height ≥ 5m, and the evaporation section of the thermosyphon needs to penetrate the gravel soil and extend ≥ 3m below the permafrost table; Set the thermosyphon inclination angle according to the slope ratio of the creep-sensitive layer.

10. The method for designing a permafrost subgrade structure based on long-term railway deformation control according to claim 9, characterized in that When the total cooling load ≤ 2000 MJ, select the adsorption heat pipe; When 2000 MJ < ≤ 4000 MJ, select the enhanced heat pipe or the high-power flexible heat pipe; When > 4000 MJ, select the photovoltaic compression type all-season heat rod.

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