High-speed Railway Foundation Research Articles

Synergistic stabilization of red-bedded mudstone with microbial-geopolymer: An experimental study

To enhance the stabilization effect of microorganisms and metakaolin on red-bedded mudstone filler, an innovative approach was introduced by implementing a synergistic stabilization technology combining microorganisms and geopolymers. The performance of the proposed approach was evaluated using physical, mechanical, and microstructural properties. Under the synergistic stabilization effect of microbial-geopolymer, the presence of cementitious materials increased by 60.80 percent, and longitudinal velocity increased by 6.63 %. furthermore, the surface porosity decreased by 20.52–23.49 %, the unconfined compressive strength increased by 250.00 % (i.e., 1.26 MPa), and the level of disintegration improved from Garde I (strong) to Grade Ⅳ (no disintegration). The synergistic effect of microorganisms and geopolymer ultimately formed a composite cementing structure of calcium carbonate, hydration products, and polymers, effectively enhancing the density and bonding strength between soil particles. The findings of this paper can guide the stabilization of red-bedded mudstone filler in high-speed railway foundation construction.

Experimental Study on the Ratio of Similar Materials of Micro-swelling Mudstone for High-Speed Railway Foundation

Experimental Study on the Ratio of Similar Materials of Micro-swelling Mudstone for High-Speed Railway Foundation

Lateral deformation of high-speed railway foundation induced by adjacent embankment construction in soft soils: Numerical and field study

The excessive displacement of an existing high-speed railway foundation due to the adjacent construction of a railway composite foundation significantly threatens the railway operation safety. In the typical soft soil region of Southeast China, a series of in-situ tests are carried out in this paper to investigate the layered settlement of newly constructed embankment and lateral displacement of an existing high-speed railway foundation induced by the new embankment. A two-dimensional (2D) finite element (FE) model is built to investigate the displacement of stratums and the modified Cam-clay (MCC) model is adopted to pursue the mechanical properties of the silt. Combining the genetic algorithm (GA), a back analysis framework was developed to determine the optimized input parameters of MCC model for silt layer. The results indicate that the displacement of the existing high-speed railway foundation induced by the adjacent construction of a railway embankment decreases with depth and horizontal distance from the newly constructed embankment toe. A hysteresis phenomenon is found in the foundation settlement data during the loading procedure of the embankment. Moreover, the optimized parameters for silt layer (i.e., λ = 0.361, M = 0.828, e0 = 1.347 and k = 0.826 × 10-8m/s) have the potential for the engineer application in the soft soil region.

Intelligent adaptive control method for key parameters of vibration rolling during high-speed railway subgrade compaction

To improve the intelligent construction of high-speed railway foundations using continuous subgrade compaction control techniques, a large amount of measured data was accumulated through rolling tests at four sites along the Tianjin Beichen Station high-speed railway foundation. An intelligent adaptive control program for key technical parameters of vibration rolling was then proposed using a long short-term memory neural network. The accuracy of the proposed method was verified, the corresponding calculation process presented, and case validation carried out. The results show that between the measured and predicted values of the compaction quality control index, the average absolute value percentage error (APE) was limited to within 10% with a minimum of 4%, and the mean APE was limited to within 5.5% with a minimum of 3.397%; and the root mean square error was limited to within 2.5 with a minimum of 1.135. These results demonstrate that the proposed model was successfully trained to store the non-linear function describing the relationship between the data in the system and that its learning effect was reasonable, meeting the accuracy requirements of the project. The proposed method can fulfil the requirements for real-time precise intelligent compaction by determining the key parameters of the vibratory roller. It can thereby realize modular management and precise pressure compensation to ensure the efficiency and quality of high-speed railway subgrade fill compaction by vibratory rolling.

Study on the Influence of Soil Engineering Geological Characteristics at Key Tectonic Sites on High-Speed Railway Foundation—A Case of the Beijing–Zhangjiakou High-Speed Railway (Huailai Section)

The soil engineering geological characteristics and hidden fault creep activity are the main geological factors affecting the stability of the Beijing–Zhangjiakou high-speed railway foundation. In order to reveal the deep formation structure and physical and mechanical properties of the soil under the Beijing–Zhangjiakou high-speed railway foundation and explore the influence of soil settlement under the static load and dynamic load of high-speed railways, according to the deep-hole engineering geological drilling and soil test, this paper reveals the soil structure and physical and mechanical properties within a 500 m buried depth of the Huailai section of the Beijing–Zhangjiakou high-speed railway. Based on the drilling data, we constructed a 3D geological structure model across fault segments to study the influence mechanism of the dynamic load of trains on differential ground settlement. The results show that the basic physical and mechanical parameters of all kinds of soil have little change with the increase of buried depth, and the ratio of secondary consolidation index Cs to compression index Cc is 0.0036–0.0516. Under the dynamic load of a high-speed train, the vertical displacement of soil gradually decreases with the increase of depth, which mainly affects the soil within a 50 m depth. Within the influence range, the vertical displacement at a certain point is negatively correlated with the speed of a high-speed railway and the horizontal distance from the railway line and the fault. The research results are expected to provide scientific support for the safe operation of the Beijing–Zhangjiakou high-speed railway.

Experimental Study on the Dynamic Characteristics of a New Long-Short Pile Composite Foundation under Long-Term Train Load

Long-short pile composite foundation (PC-LSPCF) composed of part-screw pile and cement-soil compaction pile is a new railway foundation treatment method, which has been widely used in high-speed railway construction projects in China. To explore the dynamic characteristics and deformation characteristics of railway PC-LSPCF under long-term train loads, the dynamic characteristics of long piles, short piles, and soil between piles under long-term train loads are tested by an indoor dynamic model test. The dynamic amplification of pile and soil under dynamic load and the temporal and spatial distribution of peak response are analyzed, and the stress and deformation development mechanism of PC-LSPCF under cyclic loading of large-cycle trains is revealed. The results show that the neutral point of the long pile is at 1/2 of the pile length and that of the short pile is at 3/8 of the pile length. The part-screw pile has a certain absorption effect on vibration energy. The deformation of a long-short pile composite foundation under long-term train loads can be divided into three stages: extreme growth, transition, and stability. The train speed is negatively correlated with the cumulative settlement of the long-short pile composite foundation. The higher the train speed, the smaller the cumulative settlement, and the smaller the number of cycles of the N-S curve entering the gentle period. As the number of train cyclic loads increases, the load-sharing relationship of the long pile-short pile-soil system will be redistributed. The research results have important reference significance for the optimization design of high-speed railway foundation treatment.

Long-term responses of high-speed railway subjected to extreme precipitation events

Serious track settlement of high-speed railways can be induced as the groundwater table in a normal geologic environment is uplifted or partial embankment is submerged following extensive rainfall. However, the settlement development of ballastless track as well as the internal mechanisms underlying this process remains unclear, which becomes more urgent with the frequent occurrence of extreme weather events. In this study, a full-scale model test on the widespread high-speed railway foundation was therefore conducted under sequentially elevated water tables, coupled with millions of axle loads at train speeds of 108 km/h, 216 km/h, and 360 km/h. The results obtained indicate that overall settlement converged on 4.1 mm under a normal water table, even subjected to a long-term train load at 360 km/h. Indeed, given submerged subsoil conditions, this value increased by 5.0 mm due to temporary increases in pore pressure in subsoil and stabilized at 9.8 mm after drainage route formation. These results suggest plastic shakedown behavior. As the subgrade was submerged, pore pressure in the subsoil as well as overall foundation settlement increased continuously under 108 km/h and 216 km/h, presenting plastic creep responses. Abrupt increases in pore pressure were induced under 360 km/h, resulting in rapid development of overall settlement up to 70.0 mm. This implied that foundations stepped into incremental collapse states. A settlement prediction approach that considers water table rises is therefore proposed; a critical water table of 0.973 m beneath the subsoil surface is therefore necessary for safe operations at speeds lower than 360 km/h. As a typical high-speed railway foundation, the obtained results will be useful references for water table warning under similar geologic conditions.

Influence of Foundation Deformation and Vehicle Parameters on the Vertical Safety of High-Speed Trains

This paper analyzes the influence of foundation deformation and the variation coefficient of vehicle parameters on the reliability of a vehicle vertical safety. Based on the theory of stochastic analysis of nonlinear vehicle–track coupled systems, combining the generalized probability density evolution theory, this paper takes the reduction rate of wheel load as the measurement index, considering the combined effects of stochasticity of track irregularity, stochasticity of vehicle parameters and foundation deformation, and studies the reliability of vehicle vertical safety under different working conditions. The results showed that (1) compared with the up-arch deformation, the settlement deformation has a greater impact on the operation safety; (2) with the increase of the variation coefficient of the vehicle parameters, the reliability of the vehicle vertical safety gradually decreases, so it should be combined with vehicle maintenance when setting the settlement limits; (3) when the vehicle operation speed is lower than 375 km/h, the stochasticity of the vehicle parameters has a more significant impact on the vehicle vertical safety, while when the speed is higher than 375 km/h, the foundation deformation amplitude has a more significant influence; (4) when the running speed is higher than 350 km/h, there may be a better set of vehicle parameters to ensure driving safety. It can be seen that in the determination of the high-speed railway foundation deformation limit value, the influence of deformation direction, vehicle parameters stochasticity, and operation speed should be considered.

Research on Cumulative Deformation Characteristics of Subgrade Filling under Cyclic Train Loading

The smoothness of high-speed railway is extremely strict. As an important part of the high-speed railway foundation, the subgrade structure has strict deformation requirements. It is necessary to ensure that the subgrade structure does not have plastic cumulative deformation under the long-term cyclic load of the train, which is the most critical geodynamic problem in high-speed railway subgrade. This paper studied the cumulative deformation characteristics of subgrade filling under cyclic train loading through the cyclic triaxial test, three types of accumulative plastic deformation trends, and the value of critical volume shear strain was discussed, which would provide the theoretical support for the dynamic design of high-speed railway.

Influence of building topography around high-speed railway foundation on wind environment and thermal comfort

The influence of the surrounding building topography of the Datong-Xi?an high-speed railway foundation on the wind environment and the thermal comfort is studied, especially the outdoor wind environment and indoor air-flow organization of the surrounding buildings are analyzed numerically, and the building terrain and the indoor temperature and the wind?s speed distribution are systematically evaluated. The results show that the surrounding terrain of the roadbed has a significant effect on the wind environment of the site, affecting the natural ventilation in summer and wind-proof and energy-saving in winter. The terrain surrounding of the building in summer reduces the wind speed by 30.5%, and it increases in winter by 31.6%; the wind speed in the indoor personnel activity area of the building around the roadbed is less than 0.35 m/s, leading to a comfortable body feeling.

Size Effect Analysis of Scale Test Model for High-speed Railway Foundation under Dynamic Loading Condition

Size Effect Analysis of Scale Test Model for High-speed Railway Foundation under Dynamic Loading Condition

Research on Settlement and Deformation Control of Newly-built High-speed Railway and Existing Line Foundation under Different Overlap and Filling Types

Subgrade filling of high-speed railway will cause additional settlement and deformation of existing lines.In this paper,using the finite element analysis platform (Taxis 2D) and considering the settlement of the existing line itself, This paper analyzes the impact of the new and old subgrade lap type and the layer filled this lesson of the new subgrade on the implementation of the existing subgrade. The results illustrate the following points:(1) Compared with different overlapping surface types, different filling those points have a greater impact on the settlement of the existing line; (2) The height of the steps is 0.6m and the width is 1.0m.In the subsequent layered filling construction process, each level The loading capacity of 30cm is more reasonable, which can effectively control the influence of the existing line on the additional settlement of the existing railway. The research results can provide a reference for the optimization of similar roadbed width construction.

The study of frost heave mechanism of high-speed railway foundation by field-monitored data and indoor verification experiment

Due to the rigid deformation limit of high-speed railways, the anti-frost heave design has become a critical concern in seasonally frozen regions. In this study, the authors explained the frost heave mitigation techniques adopted for the high-speed railway between Harbin and Dalian in northeast China and then presented the thermal, deformation, and water content data monitored on the Gongzhuling test site. According to these data, the authors proposed the possible frost heave mechanisms of the high-speed railway foundation. The foundation is composed of well-graded gravel with cement and A/B group fill, which are treated as non-frost-susceptible materials in general. Based on the monitored data, the authors found that the surface layer (0–0.5 m) contributed most to the total frost heave and this might be caused by local water accumulation inside the foundation (0.6–1.2 m). In order to demonstrate the frost heave ability of these “non-frost-susceptible” materials, the authors conducted an indoor frost heave test with a mixture of gravel and 3% Kaolinite clay. Through this experiment, it was demonstrated that, with sufficient water supply, gravel with a limited amount of fine material can produce significant frost heave. Accordingly, we can conclude that the accumulated water inside high-speed railway foundation causes the frost heave deformation. Therefore, the treatment of the water accumulation within the fills needs to be considered for frost heave elimination or prevention.

The thermal regime evaluation of high-speed railway foundation by mixed hybrid FEM

The construction of high-speed railways in permafrost and seasonally frozen regions will disturb the local heat balance and affect the original thermal regime significantly. The accurate evaluation of thermal regime is the critical step of frost heave and thawing settlement predictions. In order to evaluate the thermal regime precisely, we adopt a modified Finite Element Method which is called as Mixed Hybrid FEM (MHF) in this study. MHF allows simultaneous computation of side temperature, element temperature, and heat flux. Since freezing rate can affect the accuracy of frost heave prediction, therefore direct element temperature obtained by MHF is highly significant for improving the accuracy of frost heave evaluation. In the thermal analysis, we consider the phase change of water and the latent heat influence by equivalent heat capacity method. To demonstrate the applicability of MHF in the application of thermal regime simulation, we compare the numerical simulation results obtained by MHF with field monitoring data from high-speed railway foundation. The real field monitoring data from high-speed railway foundation demonstrate that, under sine-curved air temperature changes, MHF shows a good accuracy for the thermal regime evaluation in high-speed railway foundation. Also, through the numerical simulation results of MHF, we compare the freezing depth in the first and second year to verify the influence of the construction to the thermal regime of natural ground. Through this study, we demonstrate that MHF could be applied for the thermal analysis of high-speed railway foundation successfully. The construction of high-speed railway increases the freezing depth in the first year. Moreover, we recommend adopting the MHF in the thermal analysis of frost heave and thawing settlement evaluation model due to its promising advantages.

New Analytic Method for Subgrade Settlement Calculation of the New Cement Fly-ash Grave Pile-slab Structure

At present, reducing subgrade settlement of soft soil foundation is a key problem in high-speed railway construction. Pile-slab structure is a widely-utilized form of foundation structure to reduce the subgrade settlement in China. In order to save the engineering cost for high-speed railway construction in developing countries, the author developed a pile-slab structure and named it as the new CFG pile-slab structure. This work analyzed the settlement controlling effect of new CFG pile-slab structure and summarized two calculation methods on its subgrade settlement which are further formulated into an analytic method. Three methods were used to calculate the subgrade settlement of CFG pile-slab structure for a soft soil foundation in Chinese Shanghai-chengdu high-speed railway. The research showed that: (1)The settlement controlling effect of CFG pile-slab structure can satisfy the requirement of high-speed railway construction. (2) The new analytic method is proved to be more accurate and can reflect the mechanism of load transferring．Furthermore，the new analytic method can provide theoretical guidances for engineering designs and constructions of the CFG pile-slab structure．

Numerical simulation of high-speed railway foundation improved by PVD-DCM method and compared with field measurements

A PVD-DCM method combined with prefabricated vertical drains (PVDs) and deep cement mixing (DCM) piles is presented in this paper based on the field case of Beijing–Shanghai high-speed railway in China. The field performance of soft soil foundation improved by this method is comprehensively analysed, and shows that the PVD-DCM method takes full advantages of PVDs and DCM piles, in which the DCM piles increase the bearing capacity and reduce the total settlement of the soft foundation, while PVDs accelerate the consolidation of the soil by shortening the drainage paths. A plane strain numerical simulation on the field case is then conducted, which is converted by a three-dimensional (3D) problem with equivalent properties and dimensions. The numerical simulation is found to be an effective method to predict the true behaviour of the foundation improved by the PVD-DCM method, such as the load transfer and settlement, with reasonable accuracy. The PVD-DCM method is finally assessed both by PVD method and DCM method in terms of the settlement, implying that the PVD-DCM method can provide an effectiveness of foundation improvement and create a more economical solution.

First application of cast-in-place concrete large-diameter pipe (PCC) pile-reinforced railway foundation: a field study

Cast-in-place concrete large-diameter pipe (PCC) piles have been widely used in highway construction for foundation reinforcement, where soft ground was encountered, due to their fast on-site construction and high capacity, hence economics. This paper reports the performance of their first application in high-speed railway foundation reinforcement on soft soil ground. To satisfy the strict settlement requirement for railway design, PCC piles with large diameters (D = 1 m), thick pile wall thicknesses (t = 0.15 m), and close spacing (s = 2.5 m) were constructed. The foundation performance has been monitored by measuring in situ foundation settlement, excess pore pressure in soil, lateral displacement of soil, and tension in the geogrid during and after embankment construction. The measurements of this project have been compared with that of a previous project when PCC piles were used. It is found that the PCC pile arrangement in this project has performed as predicted and fulfilled the strict settlement requirement set by the Chinese design guidelines.

Deterioration of dynamic mechanical property of concrete with mineral admixtures under fatigue loading

The dynamic mechanical property of concrete is one of the key parameters, which greatly influences durability of infrastructures subjected to continuous heavy loading, such as girder and track slab of high-speed railway foundation structure. This paper reports serials of experiments designed to investigate the deterioration of dynamic mechanical properties of different concretes under fatigue loading condition. Four parameters including relative dynamic elastic modulus (RDEM), relative dynamic shear modulus (RDSM), relative compressive strength (RCS) and water absorption (WA) of concrete were evaluated to assess the dynamic properties and microstructures of concretes. Results show that the fatigue stress levels and fatigue cycle durations significantly influence the dynamic mechanical properties of concrete including dynamic elastic modulus and dynamic shear modulus. Addition of proper mineral admixture can improve the dynamic mechanical characteristics of concrete and increase its resistance against the fatigue loading effect. Keeping the amount of mineral admixture in concrete constant, its dynamic mechanical property with fly ash is lower than that with fly ash and silica fume. The water absorption in concrete, which is an indirect parameter reflecting capillary porosity, increases evidently after bearing fatigue-loading. There is a close correlation between the deterioration of dynamic mechanical property and the increasing of water absorption of concrete. This indicates that the damage of microstructure of concrete subjected to fatigue loading is the indispensable reason for the decay of its dynamic mechanical performance.

Experimental investigation on dynamic mechanical characteristics and microstructure of steam-cured concrete

Steam-cured concrete is widely used to manufacture prefabricated units of high-speed railway foundation structure such as girder and track slab. The dynamic mechanical property of steam-cured concrete is one of the key properties affecting service performance of high-speed railway foundation structure. In the present paper, serial macro/micro-experiments were carried out to investigate the dynamic elastic modulus, shear modulus, damping ratio, and microstructure of steam-cured concrete. The relationships between compositions, curing regime, microstructure, and dynamic properties of steam-cured concrete as well as the corresponding mechanisms were discussed. The results indicate that steam-cured concrete in early age has a larger dynamic elastic modulus and shear modulus as well as a smaller damping ratio compared with standard-cured concrete. On the contrary, at a later age a slightly smaller dynamic elastic modulus and a larger damping ratio of steam-cured concrete are observed. Addition of mineral admixture results in a bit lower dynamic elastic modulus and damping ratio of concrete than that of the control specimen without mineral admixtures. The achievements can provide some fundamental suggestions for materials parameters selection during structural design of steam-cured concrete precast element.

Calculating method based on deformation time effect on thickness of compressible stratum in high-speed railway foundation

Calculating method based on deformation time effect on thickness of compressible stratum in high-speed railway foundation