Railway Subgrade Research Articles

Study on Railway Subgrade Settlement induced by an Ultra-Large-Diameter Shield Tunnel Crossing under Railway Subgrade

This paper presents a study on the influence of the construction of an ultralarge-diameter shield tunnel undercrossing the existing high-speed railway using the empirical method, numerical analysis method, and geotechnical centrifuge model experiment based on the Wuhan Lianghu Highway Tunnel project. The comparison of the results obtained from the three methods shows first, that the results obtained from the centrifuge model experiment and numerical simulation match well with the results obtained from the empirical method for the worst-case scenario and the most likely scenario, which are consistent with the unfavorable geological and construction conditions modeled in the centrifuge test and the possible geological and construction conditions modeled in numerical simulation. Second, both the results obtained from the numerical method and the centrifuge model experiment show that the asymmetry of the settlement of railway subgrade was induced by a shield tunnel, while the asymmetry of railway subgrade settlement curve is gradually weakening with tunneling. Third, the maximum settlement of the railway subgrade could vary between 20 mm (in the most likely scenario) and 65 mm (in the worst scenario). Both the results from the centrifuge test and the numerical simulation show that the allowed value of maximum differential settlement along the railway subgrade (5 mm/10 m) would be exceeded when the tunnel excavation passes the first track at 10 m. It indicates that some mitigation measures should be taken for controlling the influence of the construction of a shield tunnel, especially when the shield tunnel machine is about underneath the pass railway subgrade. It is suggested that the shield machine should underpass the railway subgrade during the skylight period of railway operation.

Coupled DEM-FEM methods for analyzing contact stress between railway ballast and subgrade considering real particle shape characteristic

To investigate the stress concentration at the interface between crushed ballast and soil subgrade, this study developed a coupling program of discrete element method (DEM) and finite element method (FEM) using OOFEM and YADE software. Based on the penalty function method, an interface element was introduced for the DEM-FEM coupling simulation. Moreover, an adaptive volume coupling algorithm was proposed to address the unrestricted behavior of the particles across the interface elements. Therefore, the change in the interface contact stress distribution was analyzed in the process of ballast particles penetrating the subgrade soil. Based on the statistical analysis of the ballast shape scanning results, a morphology reconstruction method was adopted to restore the real irregular shapes of the ballasts. Consequently, a DEM-FEM coupling model of a ballasted railway was established and validated through laboratory test results. The meso-scale mechanism revealed the discontinuous characteristics of the contact stress caused by the ballast aggregates. In addition, the adaptive volume coupling algorithm in the case of ballast penetrating subgrade soil was preliminarily proven to be reasonable. This study provides a more accurate approach for calculating the interface stress between ballast and subgrade, which can support a further refined analysis of ballast railway subgrade deterioration.

Математическое моделирование процесса промерзания грунтов земляного полотна железных дорог в условиях холодного климата

Purpose: Mathematical model for studying the process of soil freezing given moisture migration is developed. Numerical modeling of temperature mode of railway subgrade at non-stationary pro-cess in cold climate conditions is performed. Methods: Numerical implementation of the model is performed by mathematical module processing in COMSOL Multiphysics program, which’s based on partial differential equations (PDE), with finite element method. The model reliability is con-firmed by the comparison with previous experimental data and the results of simulation by other authors. Results: Calculation results on the developed model basis show the best correlation with experimental data in comparison with the results for other models. Calculation example and calcu-lation results for subgrade temperature mode in freezing-thawing fifth cycle are presented. The analysis of soil freezing depth change and soil temperature fluctuation change by depth by fifth year are carried out. Practical significance: The developed mathematical model makes it possible to predict soil freezing depth, taking into account moisture migration, including freezing and thawing depth changes caused by climate warming. The developed model can be used both, to study the mechanism of subgrade temperature mode distribution at freezing and thawing, and to improve subgrade construction for to protect it from soil frost heaving.

Evaluation of cement stabilised residual soil on macro- and micro-scale for road construction

Lateritic soil is a kind of residual soil widespread in tropical countries. This soil usually possesses acceptable engineering properties to be laid under the construction projects. However, it needs treatment for transportation infrastructure such as railway and road subgrade and embankment, particularly when it is in fine-grained form. Thus, cement, one of the very common stabiliser agents in soil stabilisation, was selected to study its influence on lateritic soil at macro- and micro-levels. In order to achieve this goal, UCS, durability, FESEM and EDX tests were conducted. The results obtained indicate that the UCS increase occurs with an increase in cement content and curing time. It was also found that the shear modulus increases with cement content and curing time. The durability test results disclosed that 3% cement is not enough for soil stabilisation when used for projects in the areas subjected to cyclic wetting-drying cycles. The durability test results revealed that the UCS decreased for specimens treated with 6% cement, while on the other hand, the UCS increased for samples treated with 9% and 12% cement. The FESEM results revealed that the soil micro-structure changed with the addition of cement and curing time. The EDX results presented the chemical elements change upon adding cement and increasing curing time. Overall, it was found that cement-stabilised residual soil can be used for road construction. However, the cement percentage needed to stabilise residual soil differs depending on the standards.

A Study on the Train-Induced Vibration Responses of Heavy Haul Railway Subgrade in Seasonally Frozen Regions Using Field Experiments

The dynamic response resulting from heavy haul train leads to the deterioration of the railway subgrade, especially those built in seasonally frozen regions. In this work, a typical heavy haul railway section in a seasonally frozen region is monitored on-site. The time domain and the frequency domain analysis of the subgrade vertical vibration acceleration, dynamic speed, and displacement during the non-frozen period and the frozen period are investigated. The results show that the vibration response of the subgrade is affected by various factors, including the train type, locomotive, traveling speed, train formation, heavy load, and the prevalent season. Further, it is observed that the maximum and average vertical acceleration of the subgrade, the vibration speed, and the dynamic displacement increase during the frozen period. However, the main frequency of the natural vibration remains significantly higher than that before freezing. Moreover, the frozen soil has a significant amplification effect both on the acceleration and the attenuation rate. Similarly, the subgrade’s vibration mode has a low frequency and high amplitude during the freezing period, and the dynamic response characteristics become increasingly apparent as the axle load increases.

Field evaluation of the three-dimensional dynamic stress state of the subgrade induced by the heavy-haul train load

The three-dimensional stress state of subgrade soil elements plays a crucial role in railway subgrade design and service life evaluation, especially in heavy-haul railways. To solve the complex problem of the field test of three-dimensional stress state in subgrade induced by train vehicles, a novel regular dodecahedron soil pressure sensor (RDSPS) was developed and applied to field tests, which can measure dynamic stress components, including normal stress and shear stress in ×,y and z directions. Then the field test of total stress components of subgrade was carried out on the Datong-Qinhuangdao heavy-haul railway. The dynamic stress, including three normal stresses and three shear stresses, was determined at seven points in the subgrade for trains with 25 t axle load at different speeds (45, 55, and 60 km/h). The result indicates that the distributions of dynamic stresses of railway subgrade show periodic fluctuation subjected to moving train load, and each bogie can be regarded as a loading point for the field test section. Meanwhile, the stress path of soil elements in the subgrade changes continuously during the passage of a heavy-haul train, and the maximum principal stress angle changes between -π/2 and π/2. The normal stress in the × and y directions decreases first slowly and then rapidly with the depth of subgrade, while the attenuation law of normal stress in the z-direction with the depth of subgrade is just the opposite. Due to the stress superposition effect, the normal stress in the y-direction of the measuring points below the track centerline is greater than that at other measuring points. A calculation model of vertical normal stress was proposed based on the measured data. The empirical model for the attenuation coefficient of normal stress in the ×, y, and z directions was established to predict the stress attenuation coefficient more accurately. In this paper, the total stress components of the railway subgrade were measured for the first time during the passage of the train, which can provide helpful guidance for a better understanding of the dynamic response of the subgrade.

Low-temperature cracking resistance of asphalt concretes for railway substructure exposed to repeated freeze-thaw cycles

The waterproofing substructure under high-speed railway track is of importance to avoid the infiltration of surface water and maintain the bearing capacity of railway subgrade. In this study, the low-temperature cracking resistance of composite polymerized asphalt concretes for high-speed railway waterproofing layer (shortened to railway asphalt concretes) was investigated when exposed to freeze-thaw cycles. Although the measured maximum load, fracture energy and fracture toughness indicated a certain degree of low-temperature performance deterioration after repetitive freeze-thaw cycles, railway asphalt concretes showed excellent moisture susceptibility in this regard. In addition, the railway asphalt concretes prepared with binder B and gradation AC-10 were generally superior to their counterparts in this respect. On the other hand, the image processing of specimens' fracture surfaces indicated that the cracking of railway asphalt concretes at low temperatures could be mainly attributed to the binder cohesion failure. Besides, the contribution rate of aggregate-binder adhesion failure to the overall cracking gradually exceeded that of aggregate fracture with the increased freeze-thaw cycles. Finally, a statistically significant correlation between the fracture energy and interfacial adhesion failure was found. This implied that the deterioration of low-temperature cracking resistance could be primarily contributed to the reduced aggregate-binder adhesion strength during freeze-thaw cycles.

Field Measurements and Numerical Simulation of Snowdrift on Railway Subgrade

Abstract Snowdrift is a major natural hazard, endangering basic installation and human life in cold regions. Drifting snow can cause snow grains to accumulate on the road, blocking transportation, reducing visibility, and even leading to fatal traffic accidents. Field measurements and numerical simulations of roadbed snow characteristics were carried out along the railway in snowy weather to study the effect of snowdrift on railway subgrade. The influence of a typical roadbed structure is considered, and the basic model of a typical subgrade structure under the action of snowdrift is proposed. Snow particles that accumulate on the embankment present a U-shaped distribution along the inflow direction. Within the increase of embankment height, wind velocity on the roadbed surface is accelerated, and snow cover is reduced, thus mitigating the snow drift disaster of the embankment. Snow covers at embankment heights of 1 and 2 m are considerably greater than those at 3 and 5 m, and identical with those at roadbed heights of 3 and 5 m. Along the inflow direction, the snow cover on the cutting presents an M-shaped distribution. As cutting depth is reduced, wind velocity inside the cutting is decelerated, and snow cover is increased, which aggravates the snow drift disaster of the cutting. The snow depths of roadbed parts at 1-, 2-, and 3-m depths of the cutting are nearly the same, and that at a 5-m depth of the cutting is relatively small but still larger than that on the embankment. Numerically simulating the snow-driving wind via computational fluid dynamics, which can consider the motion characteristics of snow particles and their influence on flow field, is feasible. Simulation results agree with the measured results. Thus, this research provides a path for the further prediction of snow cover pattern.

Semianalytical Model of Unloading-Induced Pore-Water Pressure and Consequent Consolidation Settlement of Surcharge Preloading Railway Subgrade

Surcharge preloading is a suitable foundation treatment for high-speed railways in soft soil regions. As a temporary preload on the foundation, the surcharge load must be removed before track construction. In this process, rebound deformation of the foundation and variation in the pore-water pressure have been widely observed. These phenomena significantly influence the further evolution process of foundation consolidation. Although Biot’s consolidation theory is suitable for unloading-induced soil consolidation, the conventional Laplace transform method for solving Biot’s equations entails a time-consuming procedure and cannot reflect the time-dependent characteristics of the preloading and unloading process. To address these issues, a time difference method is proposed in this work. The ordinary differential equation in the transformation domain is obtained using the backward two-step difference method, and a physical analytical solution of the plane strain problem of overloaded subgrade is obtained via the Fourier inverse transform method. The proposed solution is validated through a comparison with existing literature data and actual engineering practices. Finally, based on this calculation method, the influence of the surcharge preloading amount, loading time, and soil properties on pore-water pressure dissipation and distribution after surcharge preloading removal is investigated.

Analysis of vibration mitigation for CFG pile-supported subgrade of high-speed railway

Ground vibrations due to a train moving on the pile-supported subgrade are investigated using a 2.5-dimensional finite element model (2.5D FEM). The equivalent pile wall approach is used to model the piles and soils. Two types of subgrades, with or without cement fly-ash gravel (CFG) piles, are analyzed to evaluate the performance of CFG pile-supported subgrade in mitigating ground vibration. The effects of area replacement ratio aR and pile-soil stiffness ratio Sps on vibration mitigation performance are studied. Results show that the CFG pile-supported subgrade exhibits positive performance in vibration mitigation, and this performance gets better away from the track than near it. The improved subgrade could elevate the critical speed, and the resonance-like amplification of ground vibration as the train runs at the critical speed for the unimproved subgrade is completely excluded. Increasing either the aR or Sps can enhance the vibration mitigation performance. However, there are the critical values of aR = 8.70% and Sps = 138.89, beyond which the vibration reduction performance would no longer be improved.

Field measurement and outdoor wind tunnel test of snow-drifting: Snow distribution characteristics of railway subgrade and deposition mechanism

The snow deposits caused by snow-drifting are closely associated with railway cutting forms, which affect wind distribution and snow particle motion. Neither indoor wind tunnel tests using simulated material, nor tests which involve moving snow into a low-temperature wind tunnel, can reproduce the real properties and states of snow particles. This paper introduced a set of mobile low-speed direct current wind tunnel equipment, and outdoor wind tunnel tests were carried out to study the snow-drifting effect of railway cutting during snowfall.By adjusting the wind tunnel to simulate the natural flow field, and compared with the field monitoring results to verify the rationality of the wind tunnel design and the accuracy of results. According to the actual snowfall conditions, snow-drifting was tested under different forms of railway cutting and different inflow conditions, and the real-time kinematic photogrammetry was used to establish three-dimensional models for snow depth analysis. Finally, the mechanism of snow deposition was explained from the dynamic equilibrium shift of snow-drifting movement.

Numerical simulation on flow field, wind erosion and sand sedimentation patterns over railway subgrades

Numerical simulation on flow field, wind erosion and sand sedimentation patterns over railway subgrades

Dynamic Response Characteristics of Railway Subgrade Using a Newly-Developed Prestressed Reinforcement Structure: Case Study of a Model Test.

Poor subgrade conditions usually induce various subgrade diseases in railways, leading to some adverse influences. An innovative technology that involves installing a prestressed reinforcement structure (PRS) that consists of steel bars and lateral pressure plates (LPP) for subgrade was introduced to improve its stress field and provide compulsive lateral deformation constraints for slope. In this study, an investigation into the dynamic acceleration responses of railway subgrade strengthened according to different PRS schemes was presented using a 1:5 scale model test, aiming to explore the effects of the axle load, the reinforcement pressure, and the loading cycles on the acceleration characteristics of the subgrade. The experimental results showed that (1) after pretension of the steel bar, prestress loss occurred due to the soil creep behavior and group anchor effect, so a moderate amount of over-tension in practices would be necessary; (2) a distinctive periodical behavior of subgrade subjected to the cyclic loads was observed, the horizontal accelerations were generally less than the vertical accelerations at the same measurement heights, and the vibration energy attenuated gradually from the shoulder to the toe along the slope; (3) in the short-term tests, the peak accelerations at all measurement points had a linear correlation with the axle load, and oppositely, it showed an approximately linear decrease with the increasing reinforcement pressure; And (4) in the long-term tests, to simulate the heavy haul wagon with a 35 t axle load, the variation in the effective acceleration with loading cycles under reinforcement pressure 100 kPa initially exhibited a decrease and subsequently tended to be stable, which is apparently less than that without reinforcement pressure. Consequently, it was demonstrated that the PRS itself and increasing reinforcement pressure can effectively mitigate the subgrade vibration, and provide an appropriate alternative to improve the dynamic performance of railway subgrade under the moving train loads.

Performance evaluation of composite polymerized asphalt materials for waterproofing layer in high-speed railway system

The asphalt concrete waterproofing layer can effectively prevent the infiltration of surface water into the railway subgrade and preserve the ride safety in the prolonged design life of high-speed railway. To improve the durability of waterproofing layer, composite polymerized asphalt materials were developed in this study using Styrene-Butadiene-Styrene (SBS) and High-Viscosity Reagent (HVR) with several dosages. The air void contents of three composite polymerized asphalt concrete mixtures with the optimal binder content were below 3% and the permeability coefficient was 0, indicating the satisfactory waterproofing performance. The high-temperature deformation resistance of composite polymerized asphalt materials was sufficient to avoid bleeding diseases. Although the HVR negatively affected stress-releasing properties of binders at low temperatures, the cracking resistance of composite polymerized asphalt concrete mixtures was found to be improved. Moreover, the addition of HVR as composite modifiers could improve the adhesion strength of binders and the moisture damage resistance of mixtures under freeze–thaw cycles. Additionally, the added HVR also exhibited remarkable aging resistance with the increased dosage. Under the repeated train loading, the permanent deformation of composite polymerized asphalt concretes during the design service life was proved to be far lower than the technical criteria.

The modelling of railway subgrade strengthening foundation on weak soils

Abstract As a consequence of increased axle loads and speeds of trains on modernised railway lines, there may occur problems with bearing capacity and stability of the subgrade in some sections of the railway network. This is the situation we are dealing with right now on the Polish State Railways network. Therefore, as a case study, a fragment of an existing railway embankment based on a weak foundation was chosen for the analysis of train–track–subgrade interaction. A two-stage train–track–subgrade model has been developed. The model consists of the upper part (train–track) and the lower part (subgrade-foundation). The first part is modelled as a self-contained system of differential equations which are solved by means of finite difference method and yield the stress levels on the subgrade. These stresses are treated as a load for the lower system modelled using FEM. The model has been validated using experimental data from literature, authors’ measurements, and railway staff measurements of the track geometry. Several cases of strengthening methods were calculated and compared with measurements on the railway section under consideration. Good agreement between the prediction and the measurement was found. The novelty of the model is including the heterogeneity of the subgrade, the strengthening methods, and very deep layers of its foundation as well as adding the influence of vibration on the weakening of soils. It was found that this influence is noticeable and should be included in the prediction of railway subgrade behaviour

Frost resistance and mechanical degradation characteristics of cement-stabilized macadam under the long-term freezing–thawing cycles

• Three different cement contents and removal of two different fine particle sizes of cement-stabilized macadam (CSM) were tested. • The mechanical strength characteristics were degraded by long-term freezing−thawing cycles. • The removal size of larger fine particles had adverse effects on the strength and degradation rate of CSM. • The increase in the cement content led to an increase in the frost resistance and strain energy density of CSM. • The initial elastic modulus determined using unconfined compressive strength tests could be applied to characterize the stiffness of CSM for high-speed railway lines. The high-speed railway subgrade in seasonal frozen soil regions should be able to resist long-term freezing and thawing cycles. In consideration of cement-stabilized macadam (CSM) as the subgrade surface material needs to have resistant to freeze–thaw strength deterioration. This study aimed to evaluate the mechanical degradation characteristics of CSM under the long-term freezing-thawing cycles by the unconfined compressive strength tests. Three different cement contents (3 %, 5 %, and 7 %) and removal of two different fine particle sizes (0.1 and 0.25 mm) of CSM were studied and analyzed. The number of freezing–thawing cycles was set to 0, 1, 3, 5, 7, 10, 15, 20, 30, 40, and 50, respectively. Based on the unified calculation model of strength deterioration, evaluation index of frost resistance, and analysis of strain energy density failure, C 5 P 0.1 could be used in seasonal frozen soil regions. If the subgrade bed had requirements for permeability, fine particles with larger sizes could be removed. The results indicated that, first, the strength of fine particles with larger size removal was smaller and the strength deterioration was faster under the same cement content. Second, when the cement content was higher, CSM showed better resistance to freezing–thawing strength degradation. Further, when the cement content increased, the increase in the amplitude of strain energy density varied significantly; the increasing effect was the best when the cement content increased from 3 % to 5 %. Finally, the initial elastic modulus of the Duncan-Chang hyperbolic model was used to characterize the stiffness of CSM in the high-speed railway subgrade bed. This study revealed the mechanical degradation characteristics of CSM under the long-term freezing–thawing cycles with different cement contents and removal sizes of fine particles. The findings were useful for understanding the mechanical behavior of CSM under the long-term freezing–thawing cycles.

Intellectualization of monitoring and regulation of the technological processes implementation in railway construction

The article presents abstract theorems and practical options for monitoring and regulating the technological process implementation of building a railway track object using artificial intelligence methods and tools. Railway construction as a complex dynamic system requires certain resources for its maintenance. Under these conditions, effective control over the construction work technology is of decisive importance. This can be achieved by improving the existing engineering and technical support system for railway construction through the introduction of an engineering and intellectual support subsystem for technological processes for railway facilities construction. One of the tasks of the subsystem is the effective use of automation tools with artificial intelligence elements. The deviations occurrence from planned requirements during construction work, due to the stochastic nature of railway construction, leads to violations of technology, an increase in labor costs, prime cost, an increase in duration, and as a result, a deterioration in the operational railway facility characteristics. To avoid such a development of events, a prompt review of the adopted technological solutions is necessary. To this end, within the scope of the methodology formation for engineering and intellectual support of railway construction technological processes, a system for monitoring and regulating work production has been developed. Intellectualization of monitoring the technological process implementation consists of the use of an expert system at the evaluation stage, built on a probabilistic inference model. The main purpose of the system is to process the monitoring results of the work progress during the railway track facility construction. The data obtained at the evaluation stage serve as the basis for predicting the implementation of the technological process. The essence of the forecast is based on the solution of general methodological issues of applying Markov processes. The regulation of the process implementation is based on the monitoring results. Adjusting the technological process to changing conditions of work provides flexibility in railway track facilities construction. This is achieved through rapid decision-making using the capabilities of an artificial neural network and subsequent adjustment of the work progress. Based on the theoretical study results, the article presents the practical aspects of monitoring and regulating the production of works in railway construction using intelligent technologies by the example of the construction of a flooded embankment section of a railway subgrade. The results presented in the article were obtained in the course of dissertation research carried out by the author.

Investigation of asphalt concrete used as the ballastless track substructure in long-span railway bridges

The application of asphalt concrete is common in railways. However, the asphalt concrete substructure (ACS) is mainly used above the subgrade of general railway. The studies on the asphalt concrete used as the ballastless track substructure in long-span railway bridges (LSRB) still remained to be explored. The purpose of this research is to clarify mechanical responses of the ballastless track ACS in LSRB, and determine its structure and material design method. Firstly, the numerical model of LSRB ballastless track model with the ACS was established. Then, the mechanical responses of ACS under the train load were obtained. Besides, the effects of temperature changes and substructure thickness on the mechanical responses were also discussed. Next, the recommended substructure thickness and material design indicators were given based on the simulation results and environment requirements. Lastly, a type of designed asphalt concrete was taken as a case study, and its material performance was evaluated based on the proposed design indicators. Results show that the temperature has a great effect on its mechanical response. Its thickness was recommended as 300 mm. The designed asphalt concrete can meet the proposed technical requirements. The findings in this paper could provide a reference to the design of the ballastless track ACS in LSRB.

The influence of geotextile on the characteristics of railway subgrade mud pumping under cyclic loading

The mud pumping beneath railways is both widespread and harmful and seriously affects the stability of railroad tracks and their operational safety. This paper presents a series of mud pumping tests, and analyses the influence of geotextile on the characteristics of saturated subgrade mud pumping. Our results show that the addition of geotextile between subgrade and gravel layers can significantly reduce accumulated axial strain by 40% to 76%, reduce residual excess pore water pressure by 33% to 92%, and reduce soil moisture content at the interface between the subgrade and gravel layers. However, we find that geotextile has no significant effect on soil dynamic stress. This suggests that the geotextile can act as a separator between the subgrade and gravel layers thus significantly reducing the thickness of an interlayer. Additionally, geotextile can also act as a filter and reduce the displacement caused by the migration of fine particles. In general, placing geotextile between the subgrade and gravel layers can mitigate railway subgrade mud pumping under cyclic loading, but with an increase in cyclic loading amplitude, the mitigating effectiveness of geotextile on mud pumping gradually weakens.

Laboratory Experiments and Numerical Simulation Study of Composite-Material-Modified Loess Improving High-Speed Railway Subgrade.

Construction of high-speed railway subgrade on loess soils in the Loess Plateau is risky because such soil is susceptible to differential settlements. Various soil-improvement methods have been used to enhance the mechanical properties of loess. Lime-ash soil and cement-lime soil are the most commonly used methods in the improvement of loess subgrade, while few studies have been found on loess subgrade improvement by using composite material consisting of traditional materials and new materials. A series of direct shear tests and unconfined compressive tests were conducted on the loess specimen with the addition of three kinds of composite materials: traditional material cement, new material polypropylene fiber and SCA-2 soil curing agent. The numerical simulation was conducted on loess subgrade in an actual engineering practice. The experimental results show that cement, polypropylene fiber and SCA-2 soil curing agent can effectively improve the shear strength and compressive strength of loess, and the influence degree is cement > fiber > curing agent. Additionally, based on the relative strength characteristics of the improved loess, an optimal improvement scheme for the composite-material-modified loess was obtained: 16% cement content + 0.5% fiber content + 4% curing agent content. The numerical simulation results revealed that the compressive strength index of the improved loess has a significant impact on the subgrade settlement, and the optimal improvement scheme obtained from comprehensive analysis can effectively improve the settlement of high-speed railway subgrade under vibration load.