Design method of permafrost subgrade structure based on long-term deformation control of railway

Abstract

The application discloses a permafrost subgrade structure design method based on long-term deformation control of a railway, and comprises the following steps: comprehensive permafrost investigation and permafrost physical and mechanical property analysis are performed through geological mapping, geological drilling and comprehensive geophysical prospecting; the stratified distribution characteristics of the foundation permafrost are determined according to the investigation and analysis results; the parameter setting of the subgrade structure is performed according to the stratified distribution characteristics of the foundation permafrost; the cold quantity requirement of the permafrost subgrade is calculated and analyzed; the setting of the railway subgrade deformation control standard is performed; and the hot rod subgrade structure is designed according to the cold quantity requirement, the railway subgrade deformation control standard and the parameters of the subgrade structure. The application can realize a scientific and intelligent permafrost hot rod subgrade design method, provide long-term deformation control and dynamic adaptability guarantee for a railway engineering in a cold region, reduce operation and maintenance costs and prolong the service life of the subgrade.

Description

Technical Field

[0001] The present invention relates to the technical field of permafrost roadbed design, and in particular to a permafrost roadbed structure design method based on long-term railway deformation control. Background Art

[0002] Railway subgrade design in permafrost regions faces key challenges, including poor thermal stability and significant thaw-settlement deformation. Heat rod technology, as an active cooling measure, has been widely used in projects such as the Qinghai-Tibet Railway and the Qinghai-Tibet Highway. Its design approach is primarily based on the principle of heat balance.

[0003] With global warming and the expansion of transportation networks in high-altitude and cold regions, the design of permafrost roadbeds shows the following trends:

[0004] (1) Long-term performance orientation, shifting from short-term thermal stability to full life cycle deformation control, requires the integration of frozen soil creep models, climate change predictions, and structural durability analysis;

[0005] (2) Multi-factor coupling analysis requires the integration of multi-dimensional data such as geological stratification, physical and mechanical properties of frozen soil, thermal-mechanical-hydraulic coupling, and ecological disturbance to improve the level of design refinement;

[0006] (3) Intelligent and adaptive design, introducing Internet of Things monitoring and feedback mechanism to achieve dynamic adjustment of thermal rod parameters to cope with the uncertainty of climate and load.

[0007] The existing hot rod roadbed design method has exposed the following technical bottlenecks in engineering practice:

[0008] (1) Lack of long-term deformation control. Existing methods focus on instantaneous thermal balance and fail to establish a long-term deformation model for coupled permafrost thawing, consolidation, and creep, resulting in a high risk of excessive settlement in the later stages of railway operation.

[0009] (2) Insufficient adaptability to climate change. Traditional designs use historical meteorological data and do not integrate future climate warming scenarios (such as warming rates and extreme events). Design parameters are conservative or have a significant risk of failure.

[0010] (3) Multi-scale coupling analysis is weak, the synergistic effect of frozen soil stratification characteristics, roadbed structural stiffness, and heat dissipation efficiency of thermal rods is not fully quantified, and local thermal disturbances can easily cause uneven settlement;

[0011] (4) There is a lack of economic optimization. The layout of the hot rod mostly relies on experience and lacks full life cycle cost analysis, which leads to over-design or a surge in maintenance costs. Summary of the Invention

[0012] The purpose of the present invention is to provide a permafrost roadbed structure design method based on long-term railway deformation control, which is used to solve at least one of the above-mentioned technical problems. It can realize a scientific and intelligent permafrost hot rod roadbed design method, 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 the roadbed.

[0013] The embodiment of the present invention is achieved as follows:

[0014] A permafrost roadbed structure design method based on long-term railway deformation control, comprising:

[0015] Through geological mapping, geological drilling and comprehensive geophysical exploration, comprehensive permafrost survey and analysis of the physical and mechanical properties of permafrost are carried out.

[0016] Based on the survey and analysis results, the stratification distribution characteristics of permafrost in the foundation are determined.

[0017] The parameters of the roadbed structure are set according to the layered distribution characteristics of the permafrost on the foundation.

[0018] Calculate and analyze cooling requirements for permafrost roadbeds.

[0019] Set the railway subgrade deformation control standards.

[0020] According to the cooling demand and the railway roadbed deformation control standard, combined with the parameters of the roadbed structure, a hot rod roadbed structure is designed.

[0021] 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 its physical and mechanical properties through geological mapping, geological drilling and comprehensive geophysical prospecting include:

[0022] Investigate different permafrost phenomena, mark their distribution ranges and formation conditions respectively, and determine the permafrost boundaries and ice content based on topography, landforms, vegetation, and hydrological characteristics to obtain a permafrost distribution map.

[0023] The corresponding drilling method is selected according to the permafrost type, permafrost cores are collected and graded for sampling to obtain permafrost core samples, borehole histograms and permafrost ice content data.

[0024] Conduct comprehensive geophysical exploration of frozen soil to obtain the wave velocity, dynamic elastic modulus and groundwater storage conditions of frozen soil, and obtain a geophysical profile.

[0025] Thermal conductivity and specific heat capacity tests were conducted to obtain the thermal conductivity range and specific heat capacity range of frozen soil with high ice content and low ice content.

[0026] The moisture content is measured to obtain the range of frozen soil moisture content.

[0027] Density tests are carried out to obtain the wet density range and dry density range of frozen soil.

[0028] Indoor creep tests were conducted to obtain the steady-state creep rate of frozen soil.

[0029] In a preferred embodiment of the present invention, in the above-mentioned permafrost roadbed structure design method based on long-term railway deformation control, in the collection of frozen soil cores and graded sampling, the drilling diameter is controlled to be ≥130mm for the opening hole and ≥110mm for the final hole.

[0030] For loose formations with low ice content, choose low-speed drilling with a drilling depth of 0.20m to 0.50m per round.

[0031] For clay soil with high ice content, choose fast drilling with the advance per round ≤0.80m.

[0032] For frozen gravel or bedrock, choose low-temperature flushing fluid for drilling, with a drilling depth of 0.15m to 0.30m per round.

[0033] Its technical benefits lie in: A multi-faceted collaborative survey approach, combining geological mapping, drilling, and geophysical exploration, allows for the three-dimensional identification of permafrost boundaries, ice content, and adverse permafrost phenomena such as thermal melt collapse and thick underground ice, avoiding missed or misjudgment resulting from a single method. For graded core sampling, Grade I permafrost cores ensure the authenticity of the physical and mechanical parameters of the undisturbed soil, Grade II cores are used for moisture content determination, and Grade III cores are used for rapid screening, significantly improving data representativeness. A combination of the notch and wax sealing methods measures the moisture content and wet density of permafrost, revealing the influence of ice content on creep rate and providing direct guidance for the selection of roadbed fill materials. Indoor creep testing quantifies the creep characteristics of permafrost to support long-term deformation predictions. Using the GDS temperature-controlled triaxial system, the steady-state creep rate of permafrost under different stress and temperature conditions is simulated, establishing a quantitative relationship between creep, ground temperature, and load. This, for the first time, incorporates creep data into roadbed deformation control standards, avoiding the limitations of traditional methods that rely solely on thermal balance.

[0034] 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 step of determining the stratified distribution characteristics of the permafrost in the foundation based on the survey and analysis results includes:

[0035] Measuring points are set at depth intervals, a geothermal observation hole is set at each measuring point, a platinum resistance temperature sensor is installed in the geothermal observation hole, and geothermal observation is carried out to obtain the vertical geothermal gradient curve of frozen soil, the annual average geothermal temperature and the upper limit depth.

[0036] According to the annual average ground temperature, the permafrost temperate zone is divided into a high-temperature extremely unstable zone and a low-temperature stable zone. Combined with the ice content classification, the thermal stability level is determined, and a permafrost temperature zoning map including the ground temperature zone and ice content superimposed is obtained.

[0037] The frozen soil temperature zoning map is subjected to three-level engineering geological zoning to obtain a frozen soil engineering geological zoning map, wherein the first level zoning is the sheet or island frozen soil zone, the second level zoning is the geothermal zone, and the third level zoning is the ice-bearing type.

[0038] Based on the ground temperature observation results, the frozen soil temperate zone division results and the three-level engineering geological zoning results, a three-dimensional foundation permafrost stratification distribution model was established. The three-dimensional foundation permafrost stratification distribution model includes ground temperature, ice content and mechanical property parameters, and marks the creep-sensitive layers and the distribution of thick underground ice.

[0039] The technical effect is that by constructing a three-dimensional permafrost distribution model for foundations that includes geothermal gradients, annual average ground temperature, ice content, and their stratified distribution, designers can accurately identify the thickness of the permafrost layer, the upper permafrost depth, the permafrost thermal stability grade, creep-sensitive layers, and the distribution range of thick underground ice. Compared to traditional two-dimensional profiles or empirical judgment methods, the data model generated by this step is higher-dimensional and more complete in structure. By integrating ground temperature observations with ice content, a thermal stability zoning map of permafrost with a superposition of temperate and ice content is obtained. This allows for the first-level identification of sheet and island permafrost based on spatial distribution. The second-level classification is based on annual average ground temperature, with zones ranging from extremely unstable at high temperatures to stable at low temperatures. The third-level classification is based on ice content, with zones classified as ice-poor, ice-rich, ice-rich, and ice-saturated. Design parameters such as fill height and heat rod density can be precisely set based on the actual thermal stability grade of the foundation, facilitating the differentiated allocation of material and equipment resources. By identifying creep-sensitive layers, the roadbed fill height can be precisely controlled so that the stress covers the target layer, the burial depth and angle of the hot rod evaporation section can be adapted and set, and areas that require reinforcement control can be identified and intervened in advance, significantly reducing the risk of differential settlement and the possibility of secondary subsidence during the operation of the frozen soil roadbed, and improving the long-term stability of the structure.

[0040] In a preferred embodiment of the present invention, in the above-mentioned method for designing permafrost roadbed structures based on long-term railway deformation control, the parameter setting of the roadbed structure according to the layered distribution characteristics of the permafrost on the foundation includes:

[0041] In the three-dimensional permafrost layered distribution model, the target temperature of the roadbed structure is determined according to the ground temperature zone, and the roadbed filling material and the heat rod layout priority are set according to the ice content type.

[0042] In the three-dimensional foundation permafrost layered distribution model, the roadbed fill height, top width and slope ratio are determined according to the depth of the creep sensitive layer.

[0043] Determine the cooling radius of the heat rod according to the thermal conductivity of the frozen soil and calculate the longitudinal spacing of the heat rods ,in, is the cooling radius of the hot rod, , is the thermal diffusion coefficient of frozen soil, , is the density of frozen soil, is the thermal conductivity, is the specific heat capacity, Working hours for hot rods, Install the dip for the hot rod.

[0044] 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 roadbed filling material and the heat rod layout priority are set according to the ice content type. For high ice content areas, denser heat rods with a spacing of ≤3m are set, and the evaporation section length is increased to ≥15m. For low ice content areas, conventional heat rods with a spacing of 3m-5m are laid.

[0045] The technical benefits of this approach are: By using data from the three-dimensional foundation model, including geothermal zones, ice content, and creep-sensitive layers, the target subgrade temperature is determined based on the geothermal zones of the specific region, ensuring that cooling control targets are tailored to local conditions. Structural dimensions such as subgrade top width, fill height, and slope ratio directly match the distribution of the permafrost layer with the depth of the sensitive layer. Compared to traditional unified structural layout methods, this approach significantly reduces design redundancy, avoids overweight or underweight structures, and improves deformation resistance and engineering resource utilization. The permafrost thermal diffusion coefficient α is calculated using thermophysical parameters such as thermal conductivity, specific heat capacity, and wet density. Furthermore, the heat rod cooling radius R is accurately calculated using the heat rod cooling time and installation angle as variables, and the longitudinal spacing L of the heat rods is reversely derived. This ensures that the cooling range of each heat rod is continuous and seamless. By properly adjusting the installation angle, the heat distribution path is optimized and cooling uniformity is improved, enhancing the scientific and calculable nature of the heat rod layout design. This ensures full and effective cooling coverage in thermally sensitive areas, such as high-temperature and extremely unstable zones, and avoids localized deformation caused by cooling blind spots. Taking the creep-sensitive layer in the permafrost as the design benchmark, the fill height is set so that the fill load just covers this layer. The evaporation section penetrates the upper gravel soil and penetrates into the target sensitive layer ≥3m, avoiding the "deep settlement" phenomenon where the shallow permafrost melts but the deep creep is not controlled. It strengthens the transformation of permafrost deformation control from "surface suppression" to "layer locking control", maximizes the suppression of the cumulative expansion trend of deep creep displacement, and significantly improves the overall deformation control effect and service life of the roadbed.

[0046] 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 calculation and analysis of the cooling demand of the permafrost roadbed includes:

[0047] Calculation of foundation cooling capacity of permafrost roadbed ,in, is the soil mass within the refrigeration range, is the target ground temperature, is the initial ground temperature.

[0048] Calculating climate-compensated cooling capacity for permafrost roadbed ,in, is the heat transfer coefficient, is the climate warming rate.

[0049] Calculating the total cooling load on permafrost embankments .

[0050] The technical benefits of this approach are: by separately calculating base cooling capacity and climate compensation cooling capacity and adding them together to form the total cooling load, the cooling demand for the permafrost foundation under each section of roadbed is measurable, calculable, and traceable. This allows for differentiated cooling resource allocation for different sections, varying ice content, and varying temperature environments, improving the fit between the cooling system and the actual cooling load and avoiding overcooling or undercooling. Base cooling capacity directly reflects the initial cooling demand of the heat rods, while climate compensation cooling capacity simulates the dynamic cooling load compensation required to maintain a constant ground temperature under future warming scenarios, providing a basis for thermal rigidity matching in the selection and placement of heat rods.

[0051] 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 setting of railway roadbed deformation control standards includes:

[0052] Extract the steady-state creep rate of frozen soil.

[0053] The permafrost temperate zone is associated with the strain rate threshold of the permafrost steady-state creep rate. For the high-temperature extremely unstable zone, the strain rate threshold is set. , differential settlement ≤ 8mm / 10a, for the low temperature stable zone, set the strain rate threshold , differential settlement ≤5mm / 10a.

[0054] Based on the climate warming rate =0.26 ℃ / a climate scenario, the target ground temperature is set to .

[0055] Its technical effect is: by correlating different geothermal zones with creep rate thresholds and differential settlement allowable values, clarifying specific control indicators for different thermal stability areas, and establishing a zoning settlement control standard system coupled with ground temperature and ice content, it can achieve differentiated structural design and control indicator adaptation for different permafrost engineering sections, improve the accuracy and economy of engineering investment, and realize the transformation from "empirical judgment-result feedback" to "physical model-indicator constraint". In combination with climate scenarios, geothermal control targets are formulated, the robustness of the project to cope with future warming trends is enhanced, the thermal adaptability of the roadbed structure is improved, and the temperature locking strategy is used to delay or even block the permafrost melting process in high-risk sections, effectively controlling the development rate of deep foundation creep and settlement.

[0056] 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 design of the hot rod roadbed structure based on the cooling demand and the railway roadbed deformation control standard, combined with the parameters of the roadbed structure, includes:

[0057] According to the total cooling load of permafrost roadbed , select the type of heat rod, which includes at least one of an adsorption heat rod, a reinforced heat rod, a high-power flexible heat rod and a photovoltaic compression all-season heat rod.

[0058] Calculating the number of hot rods required ,in, is the width of the target area.

[0059] For the high ice content area, the thermal conductivity of the filling material is between 1.71 and 1.83 W / (m·K), and a high-power flexible heating rod or an adsorption heating rod is selected. For the low ice content area, the thermal conductivity of the filling material is between 1.2 and 1.8 W / (m·K), and an ordinary heating rod is selected.

[0060] The high ice content area at the depth of 2.5-12m is defined as a creep sensitive layer, and the creep sensitive layer is covered by filling the layer with its own weight stress.

[0061] For the creep-sensitive layer, the fill height is ≥5m, and the evaporation section of the heat rod needs to penetrate the gravel soil and penetrate ≥3m below the upper limit of the frozen soil.

[0062] The inclination angle of the hot rod is set according to the slope ratio of the creep sensitive layer.

[0063] The technical benefits of this approach include: establishing a closed-loop design. A cooling capacity-based approach controls the selection of hot rod types through the total cooling load; a deformation standard-based approach limits the scope of the hot rod's cooling effect through strain rate thresholds and settlement limits; and a structural coupling-based approach matches the depth of creep-sensitive layers with the roadbed fill height, allowing the evaporation section to penetrate critical layers and achieve structural-thermal control synergy. A differentiated selection strategy based on thermal conductivity was established, with hot rods selected based on material thermal conductivity zoning to improve thermal control efficiency and cost-effectiveness. By adapting hot rod placement parameters to the slope ratio, the cooling coverage capacity of the slope foot area was enhanced, strengthening the hot rod's ability to control the heterogeneous deformation zone at the slope foot, and improving overall roadbed smoothness and structural safety and stability. Stress concentration in creep-sensitive layers was controlled based on stress expansion calculations (equivalent width and influence depth). Through the synergistic effect of structural design and hot rod configuration, deep-seated deformation sources were effectively suppressed, avoiding the potential risk of surface stability and deep creep, and strengthening proactive deformation control.

[0064] In a preferred embodiment of the present invention, in the above-mentioned permafrost roadbed structure design method based on long-term railway deformation control, when the total cooling load When ≤2000MJ, select the adsorption type heat rod.

[0065] When 2000MJ< When ≤4000MJ, select the reinforced heating rod or the high-power flexible heating rod.

[0066] when When the energy consumption is greater than 4000MJ, the photovoltaic compression all-season heating rod is selected.

[0067] By integrating the permafrost creep model and thermal-mechanical-hydraulic coupling analysis, the present invention can accurately predict and control the long-term thaw settlement deformation of the roadbed. Combined with indoor creep test data, the cooling parameters of the thermal rods can be dynamically adjusted to ensure the stability of the permafrost foundation under railway loads.

[0068] The present invention introduces future climate scenario simulation, dynamically adjusts the cooling demand of the heat rod, and adopts all-season refrigeration technology to overcome the limitation that traditional heat rods only work in cold seasons, thereby achieving balanced cooling supply throughout the year.

[0069] The present invention optimizes cooling capacity distribution through a three-dimensional foundation layered model, combines geophysical profiles to display the distribution of thick underground ice, accurately locates areas with high ice content, and avoids cooling capacity waste caused by homogenized design.

[0070] The present invention forms a complete chain from survey and analysis to monitoring and feedback, integrates economic optimization into the design process, compares the full life cycle costs of different thermal rod solutions, such as photovoltaic thermal rods with high initial investment but low operation and maintenance costs, and reduces redundant design.

[0071] The present invention can flexibly select models for different frozen soil temperate zones. For high-temperature and extremely unstable areas, photovoltaic compression all-season heat rods are used to cover a wide range of cooling needs. For low-temperature stable areas, reinforced heat rods are used to reduce initial investment.

[0072] The present invention establishes a thermal-mechanical coupling simulation model and inputs parameters such as the thermal conductivity and specific heat capacity of frozen soil to predict deformation during the 50-year operation period, with the error controlled within ±10%. The on-site monitoring data is fed back to the design system in real time, forming a "design-verification-optimization" closed loop to ensure long-term stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0074] Figure 1 This is a flow chart of the permafrost roadbed structure design method based on long-term railway deformation control according to the present invention;

[0075] Figure 2 This is a schematic diagram of the calculation process for permafrost roadbed structure design according to the present invention;

[0076] Figure 3 This is a schematic diagram of the permafrost roadbed structure based on long-term railway deformation control according to the present invention. DETAILED DESCRIPTION

[0077] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0078] Please refer to Figures 1 to 3 An embodiment of the present invention provides a permafrost roadbed structure design method based on long-term railway deformation control, which includes: conducting comprehensive frozen soil surveys and analysis of frozen soil physical and mechanical properties through geological mapping, geological drilling and comprehensive geophysical exploration; determining the stratified distribution characteristics of the permafrost in the foundation based on the survey and analysis results; setting parameters of the roadbed structure based on the stratified distribution characteristics of the permafrost in the foundation; calculating and analyzing the cooling demand of the permafrost roadbed; setting railway roadbed deformation control standards; and designing a hot rod roadbed structure based on the cooling demand and the railway roadbed deformation control standards in combination with the parameters of the roadbed structure.

[0079] 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.

[0080] 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%.

[0081] Density test was carried out to obtain the wet density range and dry density range of frozen soil. Specifically, the density test adopted wax sealing method and the mass of frozen soil sample was weighed. , immerse the sample in molten paraffin at a temperature of 60-70℃ to form a uniform wax seal layer, and weigh the wax seal sample after cooling. , immerse the wax seal sample in water and weigh the mass of the water , calculate the wet density , where V is the sample volume and dry density , correct the sample volume , it is calculated that the wet density of frozen soil ranges from 1.6 to 2.2 g / cm³, and the dry density ranges from 1.4 to 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%.

[0082] Indoor creep tests were conducted to obtain the steady-state creep rate of frozen soil.

[0083] Specifically, the indoor creep test uses the GDS temperature-controlled advanced dynamic triaxial testing system with a temperature control accuracy of ±0.1°C, a confining pressure range of 0-2Mpa, a specimen diameter of 50mm, and a height of 100mm. If uniaxial compression is used, the vertical load directly below the roadbed is simulated; if conventional triaxial is used, the complex stress state at the toe of the slope is simulated, with confining pressures of 50kPa and 100kPa. The temperature conditions are -4°C, -2°C, -1°C, and -0.5°C, respectively, covering the typical temperature range of permafrost. If graded loading is used, each level of stress is maintained until the strain rate is stable, such as 50kPa→100kPa→200kPa→400kPa; if separate loading is used, independent specimens are tested step by step to reduce the number of specimens. The curve of axial strain changing with time is recorded to extract the steady-state creep rate of permafrost. .

[0084] In a preferred embodiment of the present invention, in the above-mentioned permafrost roadbed structure design method based on long-term railway deformation control, in the collection of frozen soil cores and graded sampling, the drilling diameter is controlled to be ≥130 mm for the opening hole and ≥110 mm for the final hole; for loose strata with low ice content, low-speed drilling is selected, with a feed length of 0.20 m to 0.50 m per round; for clay soil with high ice content, fast drilling is selected, with a feed length of ≤0.80 m per round; for frozen gravel or bedrock, low-temperature flushing fluid drilling is selected, with a feed length of 0.15 m to 0.30 m per round.

[0085] Its technical benefits lie in: A multi-faceted collaborative survey approach, combining geological mapping, drilling, and geophysical exploration, allows for the three-dimensional identification of permafrost boundaries, ice content, and adverse permafrost phenomena such as thermal melt collapse and thick underground ice, avoiding missed or misjudgment resulting from a single method. For graded core sampling, Grade I permafrost cores ensure the authenticity of the physical and mechanical parameters of the undisturbed soil, Grade II cores are used for moisture content determination, and Grade III cores are used for rapid screening, significantly improving data representativeness. A combination of the notch and wax sealing methods measures the moisture content and wet density of permafrost, revealing the influence of ice content on creep rate and providing direct guidance for the selection of roadbed fill materials. Indoor creep testing quantifies the creep characteristics of permafrost to support long-term deformation predictions. Using the GDS temperature-controlled triaxial system, the steady-state creep rate of permafrost under different stress and temperature conditions is simulated, establishing a quantitative relationship between creep, ground temperature, and load. This, for the first time, incorporates creep data into roadbed deformation control standards, avoiding the limitations of traditional methods that rely solely on thermal balance.

[0086] 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 determination of the permafrost layer distribution characteristics of the foundation based on the survey and analysis results includes: setting measuring points at depth intervals of 0.5m or 1.0m, setting a geothermal observation hole at each measuring point, the measuring hole depth ≥16m, installing a platinum resistance temperature sensor in the geothermal observation hole with an accuracy of 0.05°C, performing geothermal observation for ≥30 days to eliminate the influence of thermal disturbances, and obtaining a vertical geothermal gradient curve of the permafrost, an annual average geothermal temperature, and an upper depth limit; and dividing the permafrost temperate zone into a high-temperature extremely unstable zone and a low-temperature stable zone based on the annual average geothermal temperature, the annual average geothermal temperature of the high-temperature extremely unstable zone being ≥-0.5°C, and the annual average geothermal temperature of the low-temperature stable zone being <- 2.0℃, combined with the ice content classification, the thermal stability grade is determined, and a frozen soil temperature zoning map including the superposition of ground temperature zones and ice content is obtained; the frozen soil temperature zoning map is subjected to three-level engineering geological zoning to obtain a frozen soil engineering geological zoning map, the first-level zoning is sheet or island frozen soil zone, which is obtained based on the distribution range, thickness and adverse frozen soil phenomenon of frozen soil, the second-level zoning is ground temperature zone, which is obtained based on the annual average ground temperature and climate prediction, and the third-level zoning is ice-containing type, which is obtained in combination with physical and mechanical parameters such as creep rate and thaw settlement; based on the ground temperature observation results, the frozen soil temperature zone division results and the three-level engineering geological zoning results, a three-dimensional foundation permafrost stratification distribution model is established, the three-dimensional foundation permafrost stratification distribution model includes ground temperature, ice content and mechanical property parameters, and marks the creep sensitive layer and thick underground ice distribution.

[0087] The technical effect is that by constructing a three-dimensional permafrost distribution model for foundations that includes geothermal gradients, annual average ground temperature, ice content, and their stratified distribution, designers can accurately identify the thickness of the permafrost layer, the upper permafrost depth, the permafrost thermal stability grade, creep-sensitive layers, and the distribution range of thick underground ice. Compared to traditional two-dimensional profiles or empirical judgment methods, the data model generated by this step is higher-dimensional and more complete in structure. By integrating ground temperature observations with ice content, a thermal stability zoning map of permafrost with a superposition of temperate and ice content is obtained. This allows for the first-level identification of sheet and island permafrost based on spatial distribution. The second-level classification is based on annual average ground temperature, with zones ranging from extremely unstable at high temperatures to stable at low temperatures. The third-level classification is based on ice content, with zones classified as ice-poor, ice-rich, ice-rich, and ice-saturated. Design parameters such as fill height and heat rod density can be precisely set based on the actual thermal stability grade of the foundation, facilitating the differentiated allocation of material and equipment resources. By identifying creep-sensitive layers, the roadbed fill height can be precisely controlled so that the stress covers the target layer, the burial depth and angle of the hot rod evaporation section can be adapted and set, and areas that require reinforcement control can be identified and intervened in advance, significantly reducing the risk of differential settlement and the possibility of secondary subsidence during the operation of the frozen soil roadbed, and improving the long-term stability of the structure.

[0088] 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 parameter setting of the roadbed structure according to the stratified distribution characteristics of the foundation permafrost includes: in the three-dimensional foundation permafrost stratified distribution model, the target temperature of the roadbed structure is determined to be ≤-1.5°C according to the geothermal zone, and the roadbed filling material and the heat rod layout priority are set according to the ice content type; in the three-dimensional foundation permafrost stratified distribution model, the roadbed fill height, top width and slope ratio are determined according to the depth of the creep sensitive layer, wherein if the depth of the creep sensitive layer is between 1m and 4m, the roadbed fill height is determined to be 5m, the top width is 5m, and the slope ratio is 1:1.5; the cooling radius of the heat rod is determined according to the thermal conductivity of the frozen soil, and the longitudinal spacing of the heat rods is calculated. ,in, is the cooling radius of the hot rod, , is the thermal diffusion coefficient of frozen soil, , is the density of frozen soil, and the wet density of frozen soil is used here. is the thermal conductivity, is the specific heat capacity, Working hours for hot rods, The hot rod installation angle is 20°≤ ≤45°, for high temperature and extremely unstable areas, a more inclined layout is adopted to expand the cooling coverage.

[0089] In the preferred embodiment of the present application, in the above-mentioned multi-year frozen soil subgrade structure design method based on long-term deformation control of railway, in the setting of subgrade filling material and heat rod layout priority according to the ice content type, for high ice content areas, set up heat rods with a spacing of ≤3 m, increase the evaporation section length to ≥15 m, and for low ice content areas, lay out regular heat rods with a spacing of 3-5 m.

[0090] The technical effect lies in: through data-driven structure parameter setting of ground temperature zone, ice content, creep sensitive layer, etc. in the three-dimensional foundation model, the subgrade target temperature is determined according to the ground temperature zone of the specific area, and the cooling control target is adapted to local conditions; the subgrade top width, filling height, slope ratio, etc. are directly matched with the distribution of frozen soil layers and the depth of sensitive layers, compared with the traditional uniform structure layout method, the design redundancy is significantly reduced, the structure is avoided to be too heavy or too light, and the anti-deformation ability and engineering resource utilization rate are improved. The thermal diffusivity α of frozen soil is calculated through the thermal physical parameters of thermal conductivity, specific heat capacity, and wet density, and further, the heat rod cooling radius R is accurately calculated by taking the heat rod cooling time and the installation angle as variables, and the heat rod longitudinal layout spacing L is reversely deduced, so that the cooling influence range of each heat rod is continuous and seamless, through reasonable adjustment of the installation angle, the heat distribution path is optimized, the cooling uniformity is improved, the scientificity and calculability of the heat rod layout design are improved, and full coverage effective cooling can be realized in the heat-sensitive area such as the high-temperature extremely unstable area, and the local deformation out of control due to the cooling dead angle is avoided. The creep sensitive layer in the frozen soil is taken as the design reference, the filling load is set to cover the layer, the evaporation section penetrates the upper gravel soil and reaches the target sensitive layer by ≥3 m, and the phenomenon of "deep sinking settlement" caused by the melting of shallow frozen soil and the uncontrolled creep of deep frozen soil is avoided, the change of frozen soil deformation control from "surface inhibition" to "layer locking" is strengthened, the cumulative expansion trend of deep creep displacement is maximally suppressed, and the overall deformation control effect and service life of the subgrade are significantly improved.

[0091] In the preferred embodiment of the present application, in the above-mentioned multi-year frozen soil subgrade structure design method based on long-term deformation control of railway, the calculation and analysis of the cooling demand of the multi-year frozen soil subgrade include: calculating the basic cooling of the multi-year frozen soil subgrade , wherein, is the mass of the soil in the cooling range, calculated according to the volume of the subgrade and the density of the frozen soil, is the target ground temperature, taken as -1.5℃, is the initial ground temperature, the measured value of the survey, the specific heat capacity taken as 1800-2400 J / (kg·K); calculating the climate compensation cooling of the multi-year frozen soil subgrade , wherein, is the heat exchange coefficient, is the climate warming rate, taken as 0.26℃ / a; calculating the total cooling load of the multi-year frozen soil subgrade .

[0092] The technical benefits of this approach are: by separately calculating base cooling capacity and climate compensation cooling capacity and adding them together to form the total cooling load, the cooling demand for the permafrost foundation under each section of roadbed is measurable, calculable, and traceable. This allows for differentiated cooling resource allocation for different sections, varying ice content, and varying temperature environments, improving the fit between the cooling system and the actual cooling load and avoiding overcooling or undercooling. Base cooling capacity directly reflects the initial cooling demand of the heat rods, while climate compensation cooling capacity simulates the dynamic cooling load compensation required to maintain a constant ground temperature under future warming scenarios, providing a basis for thermal rigidity matching in the selection and placement of heat rods.

[0093] 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 setting of the railway roadbed deformation control standard includes: extracting the frozen soil steady-state creep rate; associating the frozen soil temperate zone with the strain rate threshold of the frozen soil steady-state creep rate, and setting the strain rate threshold for the high temperature extremely unstable zone. , differential settlement ≤ 8mm / 10a, for the low temperature stable zone, set the strain rate threshold , differential settlement ≤ 5mm / 10a; based on the climate warming rate =0.26 ℃ / a climate scenario, the target ground temperature is set to .

[0094] Its technical effect is: by correlating different geothermal zones with creep rate thresholds and differential settlement allowable values, clarifying specific control indicators for different thermal stability areas, and establishing a zoning settlement control standard system coupled with ground temperature and ice content, it can achieve differentiated structural design and control indicator adaptation for different permafrost engineering sections, improve the accuracy and economy of engineering investment, and realize the transformation from "empirical judgment-result feedback" to "physical model-indicator constraint". In combination with climate scenarios, geothermal control targets are formulated, the robustness of the project to cope with future warming trends is enhanced, the thermal adaptability of the roadbed structure is improved, and the temperature locking strategy is used to delay or even block the permafrost melting process in high-risk sections, effectively controlling the development rate of deep foundation creep and settlement.

[0095] 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 design of the heat rod roadbed structure according to the cooling demand and the railway roadbed deformation control standard, combined with the parameters of the roadbed structure, includes: according to the total cooling load of the permafrost roadbed , select the type of heat rod, which includes at least one of adsorption heat rod, reinforced heat rod, high-power flexible heat rod and photovoltaic compression all-season heat rod; calculate the required number of heat rods ,in, =The width of the target area; for the high-ice content area, the thermal conductivity of the fill material is between 1.71 and 1.83 W / (m·K), and high-power flexible heat rods or adsorption heat rods are selected. For the low-ice content area, the thermal conductivity of the fill material is between 1.2 and 1.8 W / (m·K), and ordinary heat rods are selected. The high-ice content area at a depth of 2.5-12 m is defined as the creep-sensitive layer. The creep-sensitive layer is covered by the self-weight stress of the fill to reduce the additional stress concentration. For the creep-sensitive layer, the fill height is ≥5 m, and the evaporation section of the heat rod must penetrate the gravel soil and penetrate ≥3 m below the upper permafrost limit. The heat rod inclination angle is set according to the slope ratio of the creep-sensitive layer. When the slope ratio is 1:1.5, the inclination angle is designed to be 20°-45° to expand the cooling coverage range at the slope foot.

[0096] Example: Design of a section of the Qinghai-Tibet Railway

[0097] Creep sensitive layer: 2.5-12m (ice-saturated fine rounded gravel soil).

[0098] Fill 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).

[0099] Heat rod coordination: photovoltaic compression all-season heat rods are deployed, with an evaporation section length of 14m, an inclination of 30°, and a spacing of 3m.

[0100] Effect: After 5 years, the ground temperature dropped to -1.8℃, and the differential settlement was 4.5mm / 10a.

[0101] The technical benefits of this approach include: establishing a closed-loop design. A cooling capacity-based approach controls the selection of hot rod types through the total cooling load; a deformation standard-based approach limits the scope of the hot rod's cooling effect through strain rate thresholds and settlement limits; and a structural coupling-based approach matches the depth of creep-sensitive layers with the roadbed fill height, allowing the evaporation section to penetrate critical layers and achieve structural-thermal control synergy. A differentiated selection strategy based on thermal conductivity was established, with hot rods selected based on material thermal conductivity zoning to improve thermal control efficiency and cost-effectiveness. By adapting hot rod placement parameters to the slope ratio, the cooling coverage capacity of the slope foot area was enhanced, strengthening the hot rod's ability to control the heterogeneous deformation zone at the slope foot, and improving overall roadbed smoothness and structural safety and stability. Stress concentration in creep-sensitive layers was controlled based on stress expansion calculations (equivalent width and influence depth). Through the synergistic effect of structural design and hot rod configuration, deep-seated deformation sources were effectively suppressed, avoiding the potential risk of surface stability and deep creep, and strengthening proactive deformation control.

[0102] In a preferred embodiment of the present invention, in the above-mentioned permafrost roadbed structure design method based on long-term railway deformation control, according to Table 1, when the total cooling load ≤2000MJ, select the adsorption type heat rod; when 2000MJ< ≤4000MJ, select the reinforced heating rod or the high-power flexible heating rod; when When the energy consumption is greater than 4000MJ, the photovoltaic compression all-season heating rod is selected.

[0103] Table 1: Tabular data for hot rod placement

[0104] Hot Rod Type Cooling capacity range MJ / m Effective refrigeration radius m Applicable Scenarios Enhanced hot rod 2000~3000 1.13~1.57 Low temperature stable area High power flexible heating rod 3000~4000 0.96~1.2 High temperature and extremely unstable area, requiring large-scale refrigeration Adsorption heat rod 1200~2000 1.34~1.57 Medium to low temperature zone, medium ice content Photovoltaic compression all-season heat rod 4000~12000 2.5~4.0 High temperature area, requiring all-season cooling

[0105] The embodiment of the present invention aims to provide a method for designing permafrost roadbed structures based on long-term railway deformation control, which has the following effects:

[0106] The present invention begins with a comprehensive permafrost survey, then proceeds through analysis of the soil's physical and mechanical properties, determination of the distribution characteristics of the permafrost layer in the foundation, setting of roadbed structural design parameters, climate change impact assessment, calculation and analysis of the cooling demand for the frozen roadbed, design of the hot-rod roadbed and determination of key parameters, control of roadbed deformation standards, economic comparison and selection, determination of the optimal hot-rod roadbed structure, and finally engineering application and performance monitoring. Each step is closely linked to ensure the scientific and feasible nature of the design process.

[0107] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A permafrost roadbed structure design method based on long-term railway deformation control, characterized in that: include: Conduct comprehensive permafrost surveys and analyze the physical and mechanical properties of permafrost through geological mapping, geological drilling, and comprehensive geophysical exploration; Determine the stratified distribution characteristics of permafrost on the foundation based on the survey and analysis results; Setting parameters of the roadbed structure according to the layered distribution characteristics of the permafrost on the foundation; Calculate and analyze the cooling requirements of permafrost roadbeds; Set railway roadbed deformation control standards; According to the cooling demand and the railway roadbed deformation control standard, combined with the parameters of the roadbed structure, a hot rod roadbed structure is designed; The aforementioned comprehensive exploration of frozen soil and analysis of its physical and mechanical properties through geological mapping, geological drilling and comprehensive geophysical prospecting include: investigating different frozen soil phenomena, marking their distribution ranges and formation conditions, determining the frozen soil boundaries and ice content in combination with topography, landforms, vegetation and hydrological characteristics, and obtaining a frozen soil distribution map; selecting a corresponding drilling method according to the type of frozen soil, collecting frozen soil cores and sampling them in stages, and obtaining frozen soil core samples, borehole histograms and frozen soil ice content data; conducting comprehensive geophysical prospecting of frozen soil, obtaining frozen soil wave velocity, dynamic elastic modulus and groundwater occurrence conditions, and obtaining a geophysical profile; conducting thermal conductivity and specific heat capacity tests, and obtaining the range of thermal conductivity and specific heat capacity of frozen soil with high ice content and frozen soil with low ice content; conducting moisture content determination, and obtaining the range of frozen soil moisture content; conducting density tests, and obtaining the range of wet density and dry density of frozen soil; and conducting indoor creep tests, and obtaining the steady-state creep rate of frozen soil. The method of determining the stratified distribution characteristics of permafrost in the foundation according to the survey and analysis results includes: setting measuring points at depth intervals, setting a geothermal observation hole at each measuring point, installing a platinum resistance temperature sensor in the geothermal observation hole, performing geothermal observation, and obtaining a vertical geothermal gradient curve of the frozen soil, an annual average ground temperature, and an upper limit depth; dividing the frozen soil temperate zone into a high-temperature extremely unstable zone and a low-temperature stable zone according to the annual average ground temperature, determining the thermal stability level in combination with the ice content classification, and obtaining a frozen soil temperature zoning map including a superposition of the geothermal zone and the ice content; performing a three-level engineering geological zoning on the frozen soil temperature zoning map to obtain a frozen soil engineering geological zoning map, wherein the first level zoning is a sheet or island frozen soil zone, the second level zoning is a geothermal zone, and the third level zoning is an ice-containing type; establishing a three-dimensional foundation permafrost stratified distribution model based on the ground temperature observation results, the frozen soil temperate zone division results, and the three-level engineering geological zoning results, wherein the three-dimensional foundation permafrost stratified distribution model includes ground temperature, ice content, and mechanical property parameters, and annotates creep-sensitive layers and thick underground ice distribution; The calculation and analysis of the cooling demand of permafrost roadbed includes: calculating the basic cooling demand of permafrost roadbed ,in, is the specific heat capacity, is the soil mass within the refrigeration range, is the target ground temperature, is the initial ground temperature; calculate the climate compensation cooling capacity of permafrost roadbed ,in, is the heat transfer coefficient, is the thermal diffusion coefficient of frozen soil, is the climate warming rate; calculate the total cooling load of permafrost roadbed .

2. The method for designing permafrost roadbed structures based on long-term railway deformation control according to claim 1 is characterized in that: In the above-mentioned collection of frozen soil cores and graded sampling, the diameter of the drilling hole is controlled to be ≥130mm for the opening hole and ≥110mm for the final hole; For loose formations with low ice content, choose low-speed drilling with a drilling depth of 0.20m to 0.50m per round. For clay soil with high ice content, choose fast drilling with a drilling depth of ≤0.80m per round; For frozen gravel or bedrock, choose low-temperature flushing fluid for drilling, with a drilling depth of 0.15m to 0.30m per round.

3. The method for designing permafrost roadbed structures based on long-term railway deformation control according to claim 1, characterized in that: The parameter setting of the roadbed structure according to the layered distribution characteristics of the permafrost in the foundation includes: In the three-dimensional permafrost layered distribution model, the target temperature of the roadbed structure is determined according to the ground temperature zone, and the roadbed filling material and heat rod layout priority is set according to the ice content type; In the three-dimensional permafrost layered distribution model, the roadbed fill height, top width and slope ratio are determined according to the depth of the creep-sensitive layer; Determine the cooling radius of the heat rod according to the thermal conductivity of the frozen soil and calculate the longitudinal spacing of the heat rods ,in, is the cooling radius of the hot rod, , , is the density of frozen soil, is the thermal conductivity, Working hours for hot rods, Install the dip for the hot rod.

4. The method for designing permafrost roadbed structures based on long-term railway deformation control according to claim 3 is characterized in that: The roadbed filling material and heat rod layout priority are set according to the ice content type. For high ice content areas, denser heat rods with a spacing of ≤3m are set, and the evaporation section length is increased to ≥15m. For low ice content areas, conventional heat rods with a spacing of 3m-5m are laid.

5. The method for designing permafrost roadbed structures based on long-term railway deformation control according to claim 4 is characterized in that: The design of the hot rod roadbed structure according to the cooling demand and the railway roadbed deformation control standard, combined with the parameters of the roadbed structure, includes: According to the total cooling load of permafrost roadbed , selecting a heat rod type, wherein the heat rod type includes at least one of an adsorption heat rod, a reinforced heat rod, a high-power flexible heat rod, and a photovoltaic compression all-season heat rod; Calculating the number of hot rods required ,in, is the width of the target area; For the high ice content area, the thermal conductivity of the filling material is between 1.71 and 1.83 W / (m·K), and a high-power flexible heating rod or an adsorption heating rod is selected. For the low ice content area, the thermal conductivity of the filling material is between 1.2 and 1.8 W / (m·K), and an ordinary heating rod is selected. The high ice content area at the depth of 2.5-12m is defined as a creep sensitive layer, and the creep sensitive layer is covered by filling the deadweight stress; For the creep-sensitive layer, the fill height is ≥5m, and the evaporation section of the heat rod needs to penetrate the gravel soil and penetrate ≥3m below the upper limit of the frozen soil; The inclination angle of the hot rod is set according to the slope ratio of the creep sensitive layer.

6. The method for designing permafrost roadbed structures based on long-term railway deformation control according to claim 5, characterized in that: When the total cooling load When ≤2000MJ, select the adsorption type heat rod; When 2000MJ< When the power is ≤4000MJ, choose the reinforced heating rod or the high-power flexible heating rod; when When the energy consumption is greater than 4000MJ, the photovoltaic compression all-season heating rod is selected.

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