Method for controlling temperature shrinkage cracks in filling high-speed railway subgrade with aeolian sand improved soil

Abstract

This invention relates to the field of engineering technology, and in particular to a method for controlling thermal shrinkage cracks in high-speed railway subgrades filled with aeolian sand-modified soil. The method includes the following steps: obtaining the optimal mix ratio of subgrade filling materials with aeolian sand as the primary material based on historical temperature data of the subgrade construction section; preparing aeolian sand-modified soil for subgrade filling based on the optimal mix ratio; filling the subgrade construction section in layers using the aeolian sand-modified soil, and reserving expansion joints at longitudinal intervals along the subgrade construction section during the filling process; and installing a monitoring system in the expansion joints, implementing thermal shrinkage crack prevention measures based on temperature, humidity, and displacement data collected by the monitoring system. This invention effectively optimizes the material mix ratio of the aeolian sand-modified soil by collecting temperature data from the subgrade construction section and enhances the structural integrity through the filling method. Simultaneously, it combines an intelligent temperature monitoring system to monitor subgrade temperature changes in real time, providing timely warnings and preventing the occurrence of thermal shrinkage cracks.

Description

Technical Field

[0001] This invention relates to the field of engineering technology, and in particular to a method for controlling thermal shrinkage cracks in high-speed railway subgrades filled with aeolian sand-modified soil. Background Technology

[0002] Aeolian sand refers to fine-grained, loose sediments deposited on the land surface by wind transport. It is characterized by uniform grain size, poor cementation, high internal friction angle but low tensile strength, high porosity, and good permeability. In engineering applications, aeolian sand in its natural state exhibits insufficient bearing capacity, poor deformation control, and weak resistance to freeze-thaw cycles, making it difficult to meet the stringent strength, stiffness, and durability requirements of high-speed railway subgrades.

[0003] To improve its physical and mechanical properties, cement and other binding materials are usually added to aeolian sand in a certain proportion. The mixture is then dry-mixed or wet-mixed, layered, compacted, and cured under cover to prepare cement-modified aeolian sand (hereinafter referred to as "aeolian sand-modified soil"). Aeolian sand-modified soil exhibits significantly improved compressive and shear strength under static and dynamic loads, as well as a marked increase in elastic and rigid moduli. Furthermore, the dry density and air content can be precisely controlled by adjusting the cement content and moisture content, achieving reduced freeze-thaw cycle loss and controllable settlement deformation for roadbed filling performance.

[0004] However, in inland seasonally frozen regions, with large diurnal temperature variations and extreme low temperatures in winter, roadbed materials improved with aeolian sand will undergo thermal shrinkage due to temperature drops—that is, the material volume shrinks linearly or volutely as the temperature decreases. When the surface or interlayer of the aeolian sand-improved soil is subjected to structural constraints, compaction, or rolling, the thermal shrinkage strain cannot be fully released, easily leading to thermal shrinkage cracks in the weakest areas of tensile strength. Once thermal shrinkage cracks form, surface cracks become channels for moisture infiltration, promoting more severe freeze-thaw damage and the accumulation of microscopic damage, resulting in uneven settlement, lateral displacement, and a decrease in overall structural strength of the roadbed. Summary of the Invention

[0005] This invention provides a method for controlling thermal shrinkage cracks in high-speed railway subgrades constructed with aeolian sand-modified soil, comprising the following steps: Based on historical temperature data of the roadbed construction section, the optimal mix ratio of roadbed filling material with aeolian sand as the primary material is obtained, and aeolian sand-modified soil for roadbed filling is prepared according to the optimal mix ratio of the roadbed filling material. The roadbed construction section is constructed by filling the improved aeolian sand soil in layers, and expansion joints are reserved at longitudinal intervals along the roadbed construction section during the filling process. The projection of the expansion joint on the longitudinal section of the roadbed construction section is trapezoidal. A monitoring system is installed in the expansion joint, and temperature, humidity and displacement data collected by the monitoring system are used to implement thermal shrinkage crack protection measures.

[0006] In some examples, the method for controlling thermal shrinkage cracks in high-speed railway subgrades filled with aeolian sand-improved soil provided by the present invention, wherein obtaining the optimal mix ratio of subgrade filling materials with aeolian sand as the first material based on historical temperature data of the subgrade construction section includes the following steps: Based on the historical temperature data of the roadbed construction section, the temperature conditions of the roadbed construction section are obtained, and based on the temperature conditions, the initial mix ratio range and performance test conditions of the roadbed filling material are set. Based on the initial mix ratio range, several mix ratio combination schemes are constructed, and based on each mix ratio combination scheme, corresponding roadbed filling materials are prepared in the laboratory. Based on the aforementioned performance test conditions, the performance of roadbed filling materials under different mix proportion combinations was tested in the laboratory, and based on the performance test results, at least two mix proportion combinations were pre-selected. Based on at least two pre-selected mix proportion combinations, on-site verification is conducted in the roadbed construction section. Based on the consistency between the performance test results under on-site verification and the performance test results under laboratory conditions, an optimal mix proportion combination is selected from the at least two pre-selected mix proportion combinations.

[0007] In some examples, the method for controlling thermal shrinkage cracks in high-speed railway subgrades filled with aeolian sand provided by the present invention includes aeolian sand, cementitious admixtures, and water as the subgrade filling material.

[0008] In some examples, the method for controlling thermal shrinkage cracks in high-speed railway subgrades using aeolian sand-improved soil provided by the present invention includes silt and silicate cement as the cementing admixture.

[0009] In some examples, the temperature shrinkage crack control method for high-speed railway subgrade filled with aeolian sand-improved soil provided by the present invention includes extreme minimum temperature, extreme maximum temperature, annual maximum temperature difference, and annual freeze-thaw cycles. The performance test includes temperature shrinkage coefficient test and freeze-thaw cycle test. The temperature range of the temperature shrinkage coefficient test is a gradient from the extreme minimum temperature to the extreme maximum temperature, with the annual maximum temperature difference uniformly distributed within 24 hours. The number of freeze-thaw cycles in the freeze-thaw cycle test is the annual freeze-thaw cycle number.

[0010] In some examples, in the method for controlling thermal shrinkage cracks in high-speed railway subgrades using aeolian sand-improved soil provided by the present invention, during the process of layered filling of the subgrade construction section, the thickness of each sub-filling layer ranges from 20cm to 30cm, and the compaction degree of each sub-filling layer is not less than 95%.

[0011] In some examples, in the method for controlling thermal shrinkage cracks in high-speed railway subgrades filled with aeolian sand-improved soil provided by the present invention, the expansion joints are arranged at longitudinal intervals of 15m to 20m along the subgrade construction section, and the depth of the trapezoidal groove of the expansion joint is at least 1 / 3 of the thickness of the filling layer.

[0012] In some examples, in the method for controlling thermal shrinkage cracks in high-speed railway subgrades filled with aeolian sand-modified soil provided by the present invention, geogrids are installed in at least one sub-fill layer during the process of layered filling of the subgrade construction section.

[0013] In some examples, in the method for controlling thermal shrinkage cracks in high-speed railway subgrades filled with aeolian sand provided by the present invention, the geogrid is made of polypropylene fiber.

[0014] In some examples, the method for controlling thermal shrinkage cracks in high-speed railway subgrades filled with aeolian sand-improved soil provided by the present invention includes the following steps: deploying a monitoring system in the expansion joint and implementing thermal shrinkage crack protection measures based on temperature, humidity, and displacement data collected by the monitoring system. For each expansion joint, an expansion joint monitoring unit is set up. The monitoring unit includes a first temperature sensor, a second temperature sensor, a humidity sensor, and a displacement sensor. The risk status of each subgrade construction section is assessed by using temperature data, humidity data, and displacement data. Protective measures are implemented based on the risk status of each sub-subgrade construction section.

[0015] The method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-improved soil proposed in this invention has benefits including, but not limited to, the following: Based on the analysis and experimental verification of historical temperature data, this invention selects the optimal mix design to ensure the material has good adaptability in low temperature and freeze-thaw environments. At the same time, by layered compaction, setting up geogrids, and using an intelligent sensing system to monitor temperature and deformation, the overall stability of the roadbed structure is achieved. Furthermore, by combining different maintenance processes for normal and low temperature environments, it helps to reduce the probability of cracks, enhance the crack resistance of the roadbed, and thus improve the long-term safety and durability of high-speed rail operation. Attached Figure Description

[0016] Figure 1 The flowchart of a method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-modified soil is shown in one example of the present invention. Figure 2 This invention illustrates a process for obtaining the optimal mix proportion of roadbed filling materials using aeolian sand as the first material in one example; and Figure 3An example of the present invention illustrates the longitudinal spacing of expansion joints along the roadbed construction section. Detailed Implementation

[0017] In the following description, specific details such as particular systems, structures, and techniques are set forth for illustrative purposes rather than limiting, in order to provide a thorough understanding of the examples in this application. Those skilled in the art will understand that this application can also be implemented in other examples without these specific details.

[0018] In the description of this application, detailed descriptions of well-known systems, apparatuses, circuits, and methods have been omitted to avoid unnecessary detail from obscuring the description. Furthermore, it should be noted that terms such as "first" and "second" are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0019] To address the thermal shrinkage problem in roadbeds constructed with aeolian sand-improved soil, this invention provides a method for controlling thermal shrinkage cracks in high-speed railway roadbeds constructed with aeolian sand-improved soil.

[0020] In one example of the present invention, the method for controlling thermal shrinkage cracks in high-speed railway subgrades filled with aeolian sand-improved soil specifically includes, as follows: Figure 1 The steps shown are as follows: S01. Based on historical temperature data of the roadbed construction section, obtain the optimal mix ratio of roadbed filling material with aeolian sand as the first material, and prepare aeolian sand improved soil for roadbed filling according to the optimal mix ratio of the roadbed filling material.

[0021] Furthermore, the roadbed construction section mentioned in this example refers to a continuous section within a high-speed railway line where improved soil is needed to fill the surface aeolian sand in layers, and structural reinforcement and monitoring are carried out simultaneously. Typically, the roadbed construction section extends from a predetermined starting point to an ending point, and its specific length can be determined based on the project scale, generally ranging from tens to hundreds of meters.

[0022] In other examples, the roadbed construction section can also be other infrastructure projects such as municipal roads, airport runways, and industrial plant site foundations. That is, any road area with loose sand / soil that needs to be improved by adding cementing agents and controlled for thermal shrinkage cracks can be regarded as the roadbed construction section described in this invention.

[0023] In this invention, the first material refers to the aggregate component with the largest mass or volume proportion in the entire roadbed filling material, such as aeolian sand in this example. Its particle size distribution, moisture content, mineral composition and other characteristics determine the subsequent ratio range of cementitious agent and functional admixture.

[0024] In other embodiments, the first material may also be different natural or recycled aggregates such as river pebble powder, silty clay, sand-mixed crushed stone, and recycled concrete aggregate.

[0025] In this example, step S01, which involves obtaining the optimal mix ratio of roadbed filling material using aeolian sand as the primary material based on historical temperature data of the roadbed construction section, includes, for example: Figure 2 The steps shown are as follows: S011. Based on the historical temperature data of the roadbed construction section, obtain the temperature conditions of the roadbed construction section, and based on the temperature conditions, set the initial mix ratio range and performance test conditions of the roadbed filling material.

[0026] In some specific embodiments, the historical temperature data mentioned in step S011 may refer to the historical temperature records of the local meteorological bureau in recent years (such as the last 5 years).

[0027] In some other embodiments, the historical temperature data mentioned in step S011 can also be obtained through a sensor network deployed in the roadbed construction section.

[0028] It is understood that the temperature conditions described in this example are characterized by engineering indicators derived from statistical analysis of historical temperature data of the roadbed construction section.

[0029] In some specific embodiments, the temperature conditions are characterized by the extreme minimum temperature (i.e., the lowest daily minimum temperature in historical temperature data), the extreme maximum temperature (i.e., the highest daily maximum temperature in historical temperature data), the annual maximum diurnal temperature range (i.e., the annual maximum value of the highest and lowest temperature differences on the same day in historical temperature data), and the annual number of freeze-thaw cycles (i.e., the annual cumulative number of times the temperature crosses the 0°C closed loop in historical temperature data).

[0030] In other embodiments, temperature conditions can also be characterized by other engineering indicators, such as annual average temperature (i.e., the arithmetic mean of all daily average temperatures in a year), number of days with low temperatures (i.e., the number of days in a year where the daily average temperature is continuously below 0°C), number of days with high temperatures (i.e., the number of days in a year where the daily maximum temperature exceeds 35°C), daily temperature difference frequency (i.e., the number of days in a year where the daily maximum and minimum temperature difference exceeds a set threshold, such as 15°C), number of 0°C cross-cycles (the number of times in a year when the temperature crosses 0°C from positive to negative or from negative to positive), and annual cumulative freezing equivalent (the sum of the daily average temperature difference below 0°C multiplied by the number of days).

[0031] By combining the above-mentioned multiple indicators, this invention can depict the thermal environment of the construction section from macro to micro and from daily to extreme dimensions, thereby providing more refined data support for material ratio determination (such as the amount of expansion agent and crack prevention agent), heat preservation / heating strategy design, construction period selection and post-maintenance monitoring.

[0032] Typically, the roadbed filling material system includes water, main aggregate material (i.e., the first material in this invention, such as aeolian sand in this example), and cementitious admixture material (used to improve the bonding force and overall strength between the main aggregate materials, such as silicate cement, fly ash, slag powder, etc.).

[0033] In some specific embodiments, in order to improve the performance of the material in one or more performance indicators (such as crack resistance, frost resistance, deformation compatibility or early strength), the roadbed filling material system also includes functional modified materials, such as micro-expansion agents (used to inhibit thermal shrinkage cracks), crack-resistant agents (enhancing tensile toughness), antifreeze agents (improving freeze-thaw durability), water-reducing agents (improving workability and density), and other modified admixtures.

[0034] It should be noted that functional modified materials can be flexibly configured according to ambient temperature, filling structure requirements and engineering performance objectives to construct a roadbed filling material system with high adaptability, strong stability and excellent durability.

[0035] In this example, the roadbed filling material with aeolian sand as the primary material also includes water and cementitious admixtures; furthermore, the cementitious admixtures are selected from silt and silicate cement; specifically, the silt is the silt in the roadbed construction section, and the silicate cement is P.042.5D retarded silicate cement with an initial setting time of 243 min and a final setting time of 389 min.

[0036] This example uses aeolian sand as the main aggregate, which has a uniform particle size distribution but poor natural cementing properties. The cementing admixtures are silt and silicate cement. The silt is used to optimize the gradation, fill the gaps between aeolian sand particles, and improve the frictional bonding performance between particles. After hydration, the silicate cement forms a strong cementing skeleton, which significantly improves the compressive strength, shear strength, and freeze-thaw durability of the improved soil. The amount of water added is strictly controlled according to the optimal moisture content determined by the compaction test to ensure good plasticity and density of the improved soil during mixing, spreading, compaction, and curing, thereby ensuring the structural stability of the high-speed railway subgrade and the control of thermal shrinkage cracks.

[0037] In this example, based on the extreme minimum temperature, extreme maximum temperature, annual maximum temperature difference, and annual number of freeze-thaw cycles of the roadbed construction section, the aeolian sand:silt ratio range of 6:4 to 8:2 and the cement content range of 5%-9% were pre-set; and the temperature range and temperature gradient for the temperature shrinkage coefficient test were set based on the temperature conditions, and the number of freeze-thaw cycles for the freeze-thaw cycle test were set.

[0038] Specifically, the temperature range for the temperature shrinkage coefficient test is a gradient from the extreme minimum temperature to the extreme maximum temperature, with the annual maximum temperature difference evenly distributed within 24 hours, and the number of freeze-thaw cycles for the freeze-thaw cycle test is the annual freeze-thaw cycle number.

[0039] S012. Based on the initial mix proportion range, construct several mix proportion combination schemes, and based on each mix proportion combination scheme, prepare corresponding roadbed filling materials in the laboratory.

[0040] Furthermore, based on the initial mix ratio range, this example pre-sets the aeolian sand:silk ratio range to three levels: 6:4, 7:3, and 8:2, and the cement content range to five levels: 5%, 6%, 7%, 8%, and 9%, and uses a total of 15 candidate mix ratios through full factor combination.

[0041] The mixing ratio range set in this example is based on actual environmental data, which can cover the crack resistance requirements under severe cold conditions and meet the strength development requirements of cement in high temperature environments.

[0042] S013. Based on the performance test conditions, test the performance of roadbed filling materials under different mix proportion combinations in the laboratory, and pre-select at least two mix proportion combinations based on the performance test results.

[0043] Secondly, for the above candidate mix proportions, a series of tests were conducted in the laboratory under the following performance testing conditions: 1. Temperature shrinkage coefficient test: Place the mix proportion sample in a temperature control chamber, and use the annual maximum temperature difference (e.g., from 10℃ to -30℃, ΔT=40℃) as the temperature measurement range. Cool at a constant rate of 5℃ / h, and hold at 5℃ for 4h every 5℃, and complete 10 cycles continuously. Record the volume change in real time through a laser displacement sensor and calculate the temperature shrinkage coefficient. 2. Freeze-thaw cycle test: According to the "Code for Geotechnical Testing of Railway Engineering TB10102-2023", specimens cured for 7 days, 14 days and 28 days were subjected to 10 and 20 freeze-thaw cycles respectively in the range of -25℃ to 25℃. After the cycle, unconfined compressive strength and direct shear strength tests were carried out to evaluate the freeze-thaw durability of different mix proportions. 3. Mechanical strength test: Standard compaction was performed on the specimens of each mix proportion to prepare cylindrical specimens with a diameter of 100 mm and a height of 100 mm. After curing for 7 days and 28 days, the unconfined compressive strength index was measured respectively. 4. Based on the thermal shrinkage coefficient ≤ 8 × 10⁻⁶ 6 Based on screening criteria such as / ℃, freeze-thaw strength loss rate ≤15%, 7-day unconfined compressive strength ≥1.2MPa, and 28-day unconfined compressive strength ≥2.5MPa, at least two sets of mix proportion combinations are pre-selected.

[0044] The above test conditions were designed to take into full account the characteristics of large diurnal temperature differences and frequent freeze-thaw cycles in inland seasonally frozen areas, providing reliable support for the effective control of thermal shrinkage cracks in high-speed railway subgrades.

[0045] S014. Based on at least two pre-selected mix proportion combinations, conduct on-site verification in the roadbed construction section, and select an optimal mix proportion combination from the at least two pre-selected mix proportion combinations based on the consistency between the performance test results under on-site verification and the performance test results under laboratory conditions.

[0046] Furthermore, in this example, control test sections were set up in the construction area, and two to three pre-selected mix proportion combinations were used for layered filling, compaction and standard curing. In each test section, field samples were taken according to the same laboratory steps, and temperature shrinkage coefficient test, unconfined compressive strength test and freeze-thaw cycle test were carried out on them respectively.

[0047] By comparing the performance consistency between field samples and laboratory samples (difference in thermal shrinkage coefficient ≤10%, unconfined compressive strength error between 7-day and 28-day soil samples ≤±0.2MPa, and freeze-thaw strength loss rate change ≤5%), and combining indicators such as field crack width <0.3mm and settlement deformation ≤±5mm, the optimal material ratio scheme of this invention was finally selected from the pre-selected mix proportions, which has the best engineering performance and a high degree of matching between laboratory and field performance.

[0048] S02. Using the aeolian sand-improved soil, the roadbed construction section is filled in layers, and expansion joints are reserved at longitudinal intervals along the roadbed construction section during the filling process. The projection of the expansion joint on the longitudinal section of the roadbed construction section is trapezoidal.

[0049] Specifically, during the roadbed filling process, the aeolian sand-improved soil is evenly spread with a loose layer thickness of 20cm to 30cm per layer, and a rolling procedure of one static compaction, four vibratory compaction, and one static compaction finishing is adopted. The rolling speed is controlled within 4km / h to ensure that the compaction degree of each layer is not less than 95%.

[0050] This example demonstrates how layered compaction can effectively reduce soil porosity, eliminate internal loose voids, and avoid uneven settlement and stress concentration caused by excessively thick fill in one go. This reduces the accumulation of internal stress caused by temperature changes and helps improve the overall stability of the roadbed.

[0051] Furthermore, along the longitudinal direction of the roadbed ( Figure 3 (As indicated by the middle arrow, in the opposite direction) An expansion joint is reserved every 15m to 20m. The projection of the expansion joint on the longitudinal section is trapezoidal, and the depth of its groove is not less than 1 / 3 of the thickness of the same layer of fill. It should be noted that the top and bottom widths of the trapezoidal expansion joint can be adjusted appropriately according to drainage and construction requirements.

[0052] This example demonstrates how setting trapezoidal expansion joints at fixed intervals provides a stress release channel for the roadbed during temperature rises and falls. This effectively disperses and guides thermal shrinkage stress, prevents large-area continuous shrinkage from causing cracks, and significantly improves the crack resistance of the roadbed.

[0053] Furthermore, a polypropylene fiber geogrid is laid in at least one layer of improved soil, with one layer laid horizontally every 0.6m, and the density increased to one layer every 0.3m in the expansion joint area; the longitudinal overlap length of the geogrid is not less than 0.3m, and the overlap parts of the upper and lower layers are staggered by not less than 3m.

[0054] In this example, the geogrid and the improved soil together form a continuous stress network, which enhances the interlayer bonding and lateral restraint, inhibits the initiation and propagation of microcracks, and improves the tensile toughness and deformation resistance of the subgrade, thereby further ensuring the long-term stability of the subgrade under temperature loads.

[0055] S03. Install a monitoring system in the expansion joint, and implement thermal shrinkage crack protection measures based on the temperature data, humidity data and displacement data collected by the monitoring system.

[0056] Understandably, step S03 involves burying temperature, humidity, and displacement sensors in the expansion joint groove to directly capture key physical quantities during the initiation and expansion of thermal shrinkage cracks, thereby achieving refined monitoring of the roadbed condition.

[0057] In this example, step S03, which involves installing a monitoring system in the expansion joint, specifically includes the following steps: S031. For each expansion joint, an expansion joint monitoring unit is set up, the monitoring unit including a first temperature sensor, a second temperature sensor, a humidity sensor and a displacement sensor.

[0058] In this example, the first temperature sensor is installed in the shallow buried layer of the expansion joint groove wall near the ground surface, with a burial depth of 5cm to 10cm, to monitor the surface temperature of the roadbed in real time and reflect the dynamic changes of rapid temperature rise and fall of the ground surface.

[0059] In this example, the second temperature sensor is installed in the deep buried layer below the expansion joint groove wall, with a burial depth of 15cm to 25cm, to monitor shallow temperature changes and reflect the conduction and hysteresis effects of temperature changes inside the soil.

[0060] Furthermore, the first temperature sensor and the second temperature sensor provided in this example form a vertical correspondence to each other, and are used to obtain the temperature gradient and average temperature change.

[0061] In this example, the humidity sensor is installed in the improved soil near the bottom of the expansion joint groove at a depth of 8cm to 12cm. It is used to monitor the changes in the moisture content or saturation of the roadbed filling material to reflect the influence of soil moisture conditions on thermal shrinkage cracks during drying shrinkage or freeze-thaw processes.

[0062] In this example, a displacement sensor is installed between the two side walls of the expansion joint to monitor changes in the opening width or displacement of the expansion joint. Specifically, the displacement sensor can be a mechanical joint width gauge, with its fixed end anchored to one side wall of the expansion joint and its movable end spanning the other side wall, displaying changes in joint width via a pointer and scale.

[0063] In other embodiments, the displacement sensor may also be a resistance strain gauge, with its measuring rod fixed at both ends to the side walls of the expansion joint, so as to realize the automated acquisition of the joint displacement.

[0064] Furthermore, the wires of the first temperature sensor, the second temperature sensor, and the humidity sensor are all run through a waterproof protective pipe and led to the acquisition box at the edge of the expansion joint.

[0065] Furthermore, the acquisition box is equipped with a low-power data acquisition module and a power module, which are used to uniformly receive and store data from various sensors, and can transmit the data to a remote monitoring platform via a wireless communication module as needed.

[0066] In this example, step S03, which involves implementing thermal shrinkage crack protection measures based on temperature, humidity, and displacement data collected by the monitoring system, specifically includes the following steps: S032. Assess the risk status of each sub-subgrade construction section using temperature, humidity, and displacement data.

[0067] It should be noted that the sub-subgrade construction section mentioned in this example is a partial sub-subgrade construction section. Under normal circumstances, any sub-subgrade construction section corresponds to two adjacent expansion joints, that is, one expansion joint is located at one end of the sub-subgrade construction section, and the other expansion joint is located at the other end of the sub-subgrade construction section.

[0068] Furthermore, the risk status of any subgrade construction section is obtained through the following assessment method: S0321. Based on the temperature data, humidity data and displacement data collected by the first expansion joint monitoring unit of the subgrade construction section, generate the first local index.

[0069] Specifically, the first local index includes a first temperature gradient, which is obtained through the following calculation model: ,in, The first temperature gradient represents the temperature difference distribution from shallow to deep layers at the first expansion joint at one end of a subgrade construction section. Indicates the depth of the pre-embedded part The measured temperature of the first temperature sensor at time t. Indicates the depth of the pre-embedded part The measured temperature of the second temperature sensor at time t. , This indicates the embedding depth of the first temperature sensor, typically 5cm to 10cm. The pre-embedded depth for the second temperature sensor is typically 15cm to 25cm.

[0070] Furthermore, the first local index also includes a first average temperature, which is obtained through the following calculation model: , The first average temperature represents the change in the average shallow and deep temperatures of the first expansion joint at one end of a subgrade construction section relative to the reference temperature. Indicates the depth of the pre-embedded part The measured temperature of the first temperature sensor at time t. Indicates the depth of the pre-embedded part The measured temperature of the second temperature sensor at time t. The reference temperature is usually taken from the initial temperature during construction or the multi-year average temperature of the area.

[0071] Furthermore, the first local index also includes a first humidity index, which is obtained through the following calculation model: ,in, The primary humidity index indicates the saturation of the improved soil near the bottom of the first expansion joint trench at one end of a subgrade construction section. This represents the measured volumetric moisture content at time t, corresponding to the first expansion joint at one end of a subgrade construction section. This represents the void ratio of the soil, which can be determined through laboratory tests.

[0072] Furthermore, the first local index also includes a first displacement index, which is obtained through the following calculation model: ,in, The first displacement index represents the change in the width of the first expansion joint at one end of a subgrade construction section relative to its initial state. This represents the measured joint width at time t, corresponding to the displacement sensor at one end of a subgrade construction section. This indicates the reference measured joint width at the initial monitoring moment of the displacement sensor corresponding to the first expansion joint at one end of a subgrade construction section.

[0073] S0322. Based on the temperature data, humidity data, and displacement data collected by the second expansion joint monitoring unit of the subgrade construction section, a second local index is generated.

[0074] In this example, step S0322 generates a second local index based on the temperature data, humidity data, and displacement data collected by the second expansion joint monitoring unit of the subgrade construction section.

[0075] Specifically, the second local index corresponds to the first local index and also includes the second temperature gradient, the second average temperature, the second humidity index, and the second displacement index. Its calculation method is the same as that of the first local index described in step S0321, except that the input data comes from the second expansion joint monitoring unit at the other end of the subgrade construction section.

[0076] Furthermore, the second temperature gradient is calculated from the measured temperature difference and burial depth difference between the shallow and deep buried temperature sensors of the second expansion joint; the second average temperature is calculated from the average of the measured temperatures of the shallow and deep buried temperature sensors of the second expansion joint relative to the reference temperature; the second humidity index is obtained by converting the measured volumetric water content of the humidity sensor installed at the bottom of the second expansion joint groove with the soil void ratio; and the second displacement index is calculated from the measured joint width of the second expansion joint displacement sensor relative to the initial reference width.

[0077] It should be noted that the calculation models and parameter definitions of the above-mentioned indicators correspond to the first local indicator in step S0321, and will not be repeated here.

[0078] S0323. Using the first local index and the second local index, assess the risk status of the subgrade construction section.

[0079] Furthermore, the risk status of any sub-subgrade construction section is determined by a comprehensive index generated based on the first local index and the second local index, combined with evaluation rules.

[0080] In this example, the comprehensive index includes the thermostatic stress safety index, which is obtained through the following calculation model: ,in, The thermostatic stress safety index, with a value ranging from 0 to 1 (excluding endpoint values), is used to correspond to the relationship between the thermostatic stress that may occur in the subgrade of a subgrade construction section under the current temperature and humidity conditions and the tensile strength of the material itself. The index represents the soil's resistance to tensile cracking in aeolian sand-improved soil. The equivalent modulus of aeolian sand-improved soil. This represents the coefficient of linear expansion of aeolian sand-improved soil. This indicates the degree to which the roadbed in the subgrade construction section is constrained by adjacent soil or structure in the longitudinal direction. This indicates the degree of bending restriction of the subgrade in the subgrade construction section under the action of a temperature gradient. This indicates the thickness of a single layer of subgrade fill in the subgrade construction section. The sensitivity coefficient for volume shrinkage caused by a decrease in the moisture content of aeolian sand-improved soil. This indicates the initial saturation of aeolian sand-improved soil. and These are the first and second average temperatures, respectively. and The first and second temperature gradients are respectively. and These are the first and second humidity indicators, respectively.

[0081] Furthermore, the comprehensive index also includes a comprehensive displacement index, which is obtained in the following manner: ,in, The comprehensive displacement index is the larger value among the displacement data of the expansion joints at both ends. and These are the first and second displacement indices, respectively.

[0082] S033. Based on the risk status of each sub-subgrade construction section, implement protective measures.

[0083] In this example, the specific evaluation rules are as follows: when the thermal stress safety index is lower than the safety index threshold and the comprehensive displacement index is less than the displacement threshold, it is determined to be a safe state; when the thermal stress safety index exceeds the safety index threshold or the comprehensive displacement index exceeds the displacement threshold, it is determined to be a warning state.

[0084] Furthermore, the safety index threshold is a control parameter determined based on the tensile strength of the improved soil, typically set between 0.7 and 0.9; the displacement threshold is a control parameter determined based on the geometric opening of the crack, typically set between 0.2 and 0.5 mm. These thresholds can be adjusted and optimized by combining indoor test results, field monitoring data, and relevant engineering specifications.

[0085] In these examples, when a warning is triggered, corresponding protective measures can be automatically or manually activated, including: locally covering the crack with an insulating membrane, adding geogrids, or injecting expandable joint repair material; supplementing watering and covering with shade cloth during high-temperature periods, or thickening the plastic film and turning on heating devices during low-temperature periods; simultaneously, adjusting the compaction rhythm and maintenance frequency to ensure timely suppression and repair of cracks. The orderly implementation of the above protective measures can effectively block the crack propagation channel and ensure the integrity and durability of the roadbed structure.

[0086] In this example, based on the thermal shrinkage problem that occurs in the roadbed filling process of aeolian sand-improved soil, a three-layer progressive strategy is provided, from climate-adaptive materials to structural constraints, and then to intelligent monitoring and maintenance. This strategy achieves thermal shrinkage crack control from micro to macro and from passive to active, which can not only effectively suppress crack generation, but also ensure the strength, continuity and durability of aeolian sand-improved high-speed railway subgrade from the perspective of the entire life cycle, including overall structure and operation and maintenance.

[0087] In the examples above, the descriptions of each example have their own emphasis. For parts that are not described or recorded in detail in a certain example, please refer to the relevant descriptions in other examples.

[0088] It should be noted that the above examples can be freely combined as needed. The above are merely preferred embodiments of the present invention; it should be observed that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for controlling thermal shrinkage cracks in high-speed railway subgrades constructed with aeolian sand-modified soil, characterized in that, Includes the following steps: S01. Based on historical temperature data of the roadbed construction section, obtain the optimal mix ratio of roadbed filling material with aeolian sand as the first material, and prepare aeolian sand improved soil for roadbed filling according to the optimal mix ratio of the roadbed filling material. S02. Using the aeolian sand-improved soil, the roadbed construction section is filled in layers, and expansion joints are reserved at longitudinal intervals along the roadbed construction section during the filling process. The projection of the expansion joint on the longitudinal section of the roadbed construction section is trapezoidal. S03. Install a monitoring system in the expansion joint, and implement thermal shrinkage crack protection measures based on the temperature data, humidity data and displacement data collected by the monitoring system. S03 includes the following steps: For each expansion joint, an expansion joint monitoring unit is set up. The monitoring unit includes a first temperature sensor, a second temperature sensor, a humidity sensor, and a displacement sensor. The risk status of each subgrade construction section is assessed using temperature, humidity, and displacement data. The risk status of any given subgrade construction section is obtained through the following assessment method: S0321. Based on the temperature data, humidity data, and displacement data collected by the monitoring unit of the first expansion joint in the subgrade construction section, a first local index is generated; the first local index includes a first temperature gradient, a first average temperature, a first humidity index, and a first displacement index; wherein, the first temperature gradient represents the temperature difference distribution from shallow to deep layers of the first expansion joint at one end of the subgrade construction section; the first average temperature represents the change in the average temperature of the shallow and deep layers of the first expansion joint at one end of the subgrade construction section relative to the reference temperature; the first humidity index represents the saturation of the improved soil near the bottom of the first expansion joint trench at one end of the subgrade construction section; and the first displacement index represents the change in the width of the first expansion joint opening at one end of the subgrade construction section relative to the initial state. S0322. Based on the temperature data, humidity data and displacement data collected by the second expansion joint monitoring unit of the subgrade construction section, a second local index is generated. The second local index corresponds to the first local index and also includes the second temperature gradient, the second average temperature, the second humidity index and the second displacement index. S0323. Using the first local index and the second local index, assess the risk status of the subgrade construction section; The risk status of any sub-subgrade construction section is determined by a comprehensive index generated based on the first local index and the second local index, combined with the evaluation rules. The comprehensive indicators include the thermostatic stress safety index and the comprehensive displacement index, which is obtained through the following method: ,in, The comprehensive displacement index is the larger value among the displacement data of the expansion joints at both ends. and These are the first and second displacement indices, respectively; Based on the risk status of each sub-subgrade construction section, protective measures are implemented; if the temperature and shrinkage stress safety index is lower than the safety index threshold and the comprehensive displacement index is less than the displacement threshold, it is determined to be a safe state; if the temperature and shrinkage stress safety index exceeds the safety index threshold or the comprehensive displacement index exceeds the displacement threshold, it is determined to be a warning state.

2. The method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-improved soil according to claim 1, characterized in that, The process of obtaining the optimal mix ratio of roadbed filling material with aeolian sand as the primary material based on historical temperature data of the roadbed construction section includes the following steps: Based on the historical temperature data of the roadbed construction section, the temperature conditions of the roadbed construction section are obtained, and based on the temperature conditions, the initial mix ratio range and performance test conditions of the roadbed filling material are set. Based on the initial mix ratio range, several mix ratio combination schemes are constructed, and based on each mix ratio combination scheme, corresponding roadbed filling materials are prepared in the laboratory. Based on the aforementioned performance test conditions, the performance of roadbed filling materials under different mix proportion combinations was tested in the laboratory, and based on the performance test results, at least two mix proportion combinations were pre-selected. Based on at least two pre-selected mix proportion combinations, on-site verification is conducted in the roadbed construction section. Based on the consistency between the performance test results under on-site verification and the performance test results under laboratory conditions, an optimal mix proportion combination is selected from the at least two pre-selected mix proportion combinations.

3. The method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-improved soil according to claim 2, characterized in that, The roadbed filling materials include aeolian sand, cementitious admixtures, and water.

4. The method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-improved soil according to claim 3, characterized in that, The cementing admixture includes silt and silicate cement.

5. The method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-improved soil according to claim 2, characterized in that: The temperature conditions include extreme minimum temperature, extreme maximum temperature, annual maximum temperature difference, and annual freeze-thaw cycles; the performance tests include temperature shrinkage coefficient test and freeze-thaw cycle test. The temperature range for the temperature shrinkage coefficient test is a gradient from the extreme minimum temperature to the extreme maximum temperature, with the annual maximum temperature difference evenly distributed within 24 hours. The number of freeze-thaw cycles for the freeze-thaw cycle test is the annual freeze-thaw cycle.

6. The method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-improved soil according to claim 1, characterized in that, During the process of layered filling of the roadbed construction section, the thickness of each sub-fill layer ranges from 20cm to 30cm, and the compaction degree of each sub-fill layer is not less than 95%.

7. The method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-improved soil according to claim 1, characterized in that, The expansion joints are laid out at longitudinal intervals of 15m to 20m along the roadbed construction section, and the depth of the trapezoidal groove of the expansion joint is at least 1 / 3 of the thickness of the filling layer.

8. The method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-improved soil according to claim 1, characterized in that, During the process of layered filling of the roadbed construction section, geogrids are installed in at least one sub-fill layer.

9. The method for controlling thermal shrinkage cracks in high-speed railway subgrade filled with aeolian sand-improved soil according to claim 8, characterized in that, The geogrid is made of polypropylene fiber.

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