Axle Load Research Articles

DYNAMIC FINITE ELEMENT SIMULATION OF WHEEL–RAIL CONTACT RESPONSE FOR THE CURVED TRACK CASE

The wheel–rail interaction will be intensified on account of the complexity of the wheel–rail contact geometry on a curved track. It also may become more complicated and/or have significant difference as the train speed increases, since the dynamic effects cannot be ignored then. In this study, based on explicit Finite Element (FE) software LS-DYNA 971, a Three-Dimensional (3D) elastic-plastic FE model was built to simulate the dynamic wheel–rail contact behaviour of curve negotiating, where the superelevation and roll angle as well as the strain rate effect were considered. The evolution of contact patch and pressure, wheel–rail contact force, the stress/strain state and the acceleration of the axle were employed to examine the wheel–rail transient dynamic response. Furthermore, the influences of axle load, curve radius and strain rate effect were also discussed. It is found that the maximum vertical contact force, contact pressure, stress and strain on the curved track increase with the decreasing curve radius, and they increase with the increasing axle load except for lateral contact force. The wheel–rail dynamic responses on the curved track are significantly enhanced compared to the straight track. Moreover, the strain rate effect can enhance von-Mises stress and contact pressure, suppress the plastic deformation of the rail and wheel, but it has little effect on the vertical and lateral contact forces and stable acceleration of axle. The Rate-Sensitive Factors (RSF) of the wheel and rail on the curved track are weaker than those on the straight track. These findings will be very helpful to study the competitive relationship between the rolling contact fatigue and wear, as well as the crack initiation and propagation problem.

A roller-bearing-based triboelectric nanosensor for freight train synergistic maintenance in smart transportation

Rail freight is a vital part of global economic development. The hunting instability of freight trains seriously affects safety. The lack of electrical pipelines between freight trains makes the energy of onboard monitoring equipment an urgent problem to be solved. In this paper, an energy self-consistent system (ESCS) based on a roller-bearing-based triboelectric nanosensor is proposed to detect the running status of freight trains while providing electric energy. The proposed ESCS consists of two modules: a roller-bearing-based triboelectric nanosensor (RB-TENS) module and a detection module. The RB-TENS module innovatively combines the advantages of low damping and wear resistance of roller bearings. Moreover, it incorporates energy harvesting and running status sensing for freight trains. While converting the train’s vibrational kinetic energy into electrical energy and storing it, the electrical signal containing the characteristics of the train’s running status is collected. The detection module includes a pre-processing module and a deep learning model based on LSTM. The characteristic electrical signal collected by RB-TENS is enhanced and extracted by the pre-processing module to generate training and testing sets. Using data set training and testing deep learning model, the freight train running status was recognized. On this basis, a dynamic model is established to study the effects of different axle loads, speeds, and pre-processing parameters on the vibration response, electrical performance, and deep learning model of the ESCS. Experiments show that the peak output power and energy density of RB-TENS reach 1.9 μW and 72 mW/m3. The results of the testing set show that the detection accuracy of ESCS reaches 96.6%, indicating that it can effectively detect the hunting instability of freight trains. This ESCS enables TENS to present a breakthrough in smart transportation and practical applications of the zero-energy Internet of Things.

Influences of bus traffic loading on asphalt concrete rutting

ABSTRACT Permanent deformation is the primary failure mode for the asphalt concrete (AC) pavement in urban environment. It is mainly caused by a combination of heavy traffic load, low vehicle speed and channelised traffic. A rut prediction model would therefore be a valuable tool for planning maintenance scheduling and selecting an appropriate asphalt material. This study uses the PEDRO (Permanent deformation in asphalt concrete layers for roads) model to evaluate the rutting performance of flexible pavements in dedicated bus lanes and intersections in urban areas. For this purpose, three road sections along a bus lane in Malmö, Sweden, were selected. To achieve this, AC cores from the road sections were tested using a Shear Box Tester to characterise the asphalt mixtures. Traffic data such as axle load, tyre configuration, speed, and lateral wander distribution of vehicles, and climate data were measured for the selected sections. Field measurements were carried out to assess the structural conditions of the pavements and to measure transverse profiles. This study introduced a procedure for the evaluation and local calibration of the PEDRO rutting model. The results revealed that the prediction of the transverse profiles are generally in good agreement with the rut measurements.

Rutting Prediction of Hot Mix Asphalt Mixtures Modified by Nano silica and Subjected to Aging Process

High-volume traffic with ultra-heavy axle loads combined with extremely hot weather conditions increases the propagation of rutting in flexible pavement road networks. Several studies suggested using nanomaterials in asphalt modification to delay the deterioration of asphalt pavement. The current work aims to improve the resistance of hot mix asphalt (HMA) to rutting by incorporating Nano Silica (NS) in specific concentrations. NS was blended into asphalt mixtures in concentrations of 2, 4, and 6% by weight of the binder. The behavior of asphalt mixtures subjected to aging was investigated at different stages (short-term and long-term aging). The performance characteristics of the asphalt mixtures were evaluated using the Marshall stability, flow, and wheel tracking tests. Field Emission Scanning Electron Microscopy (FESEM) was utilized to understand the microstructure changes of modified asphalt and estimate the dispersion of NS within the asphalt. The results revealed that using NS–asphalt mixtures as a surface layer in paving construction improved pavement performance by increasing stability, volumetric characteristics, and rutting resistance before and after aging. The FESEM images showed adequate dispersion of NS particles in the mixture. Results indicated that adding 4% of NS to asphalt mixtures effectively enhanced the pavement’s performance and rutting resistance. Doi: 10.28991/CEJ-SP2023-09-01 Full Text: PDF

Influence of Type of Sleeper–Ballast Interface on the Shear Behaviour of Railway Ballast: An Experimental and Numerical Study

The shear resistance at the sleeper–ballast interface of a ballasted track is an important contributor in maintaining track stability under faster and heavier axle loads where the ballast undergoes significant lateral sliding. Different types of sleeper–ballast interfaces based on the type of sleeper arrangements, such as concrete sleepers, timber sleepers, and under sleeper pads (USPs) attached to the concrete sleepers influence the lateral stability of railway tracks. Therefore, in this study the shear and degradation behaviour of ballast at concrete–ballast, timber–ballast, and USP–ballast interfaces were examined in the laboratory using large-scale direct shear tests under 60 kPa normal stress. The use of waste materials in the construction of civil infrastructure is gaining a lot of interest in the engineering community. Therefore, in addition to commercial USPs manufactured using raw materials, recycled USPs manufactured from granulates of end-of-life rubber tyres were also tested in this study. The discrete element modelling (DEM) approach was used to predict the shear behaviour of ballast at 30, 90, 120, 150, and 180 kPa normal stresses. The bonded particle model (BPM) was adopted in the DEM to simulate the effects of particle breakage during shearing. The results exhibited that both commercial and recycled USPs significantly improve the shear resistance at the sleeper–ballast interface while reducing particle degradation compared to concrete and timber sleeper interfaces.

Field and laboratory investigations on the effective contact surface between sleeper and ballast particles in railway tracks

Ballast is a porous layer that reduces the effective contact surface between sleeper and ballast. Also, the sleeper does not have a smooth bottom surface, which causes a reduction of the contact surface between the sleeper and ballast particles. At field experiments, by installing sensitive papers under the sleepers of a track, the cyclic load was imposed by passing trains, and after passing a certain amount of loads, the sensitive pressure paper was removed, and the contact surface was measured while in the laboratory investigation, the ballast box test was used to achieve a similar goal. The values obtained for the contact surface showed that the 200 kN axle load contact area is about 4.9% for concrete sleepers and about 8.1% for wooden sleepers, and this value increases with increasing axle load and load cycle. The average contact area for ballast type 1 was 4.6%, for ballast type 4 was 5.5%, and for the sample of ballast from the field test site was 5.3%. Two types of soft and stiff under sleeper pads (USP) were used. The results showed that the effective contact area between sleeper and ballast was 21.6% and 15.9% for soft and stiff USP, respectively.

The hidden cost of road maintenance due to the increased weight of battery and hydrogen trucks and buses—a perspective

Decarbonisation of transport emissions is essential to meet climate targets. For road transport, currently available technologies are battery electric vehicles and hydrogen fuel cell electric vehicles. Battery vehicles are more established than hydrogen; both could deliver the emissions reduction required. However, battery vehicles are considerably heavier than equivalent hydrogen vehicles, which are in turn slightly heavier than internal combustion engine (ICE) vehicles; a heavier vehicle will have a bigger impact on road wear and associated costs. Here we carry out a desk-based analysis, developed in 2021–2022, examining the impact and cost of the increased weight of zero emissions vehicles on road wear in an entire national vehicle fleet. The novelty is in the first quantified application of the long-understood relationship between axle load and road wear to the problem of the additional weight of zero emissions vehicles. This leads to an approximate quantification of additional costs of road maintenance as the vehicle fleet transitions to zero emissions vehicles. We examine these in four scenarios: all battery vehicles; all hydrogen vehicles; a combination; current ICE vehicles for comparison. We find 20–40% additional road wear associated with battery vehicles compared to ICE vehicles; hydrogen leads to a 6% increase. This is overwhelmingly caused by large vehicles – buses, heavy goods vehicles. Smaller vehicles make a negligible contribution. Governmental bodies liable for road maintenance may wish to set weight limits on roads, require additional axles on heavier vehicles, or construct new roads to a higher standard, to decrease road wear.Graphical abstractBEV large vehicles create a significantly greater increase in road wear than HFCEV, both compared to ICE

Ultimate capacity of large-span soil-steel structures

The ultimate limit states provided by current design codes and standards were based on full-scale field and laboratory tests performed on soil-steel structures (SSS) of spans less than 10.0 m. Recently, the spans of SSS have increased up to 32.4 m with the tendency to exceed this record. The ultimate capacity of SSS utilizing the deepest corrugation profile, i.e., 237 mm depth and 500 mm pitch, has not been yet investigated under earth and truck loading. The current study evaluates the ultimate capacity of the world’s largest-span SSS with 32.4 m span and 9.57 m rise, using three-dimensional (3D) nonlinear finite element simulation. The investigation covered both the maximum backfill height and ultimate truck loading conditions. The 3D finite element modelling technique under ultimate loading was validated by full-scale test measurements of 10.0 m span soil-steel structure subjected to tandem axle loading. The critical straining actions obtained from the steel structure at ultimate condition was used to evaluate the ultimate limit states provided by the Canadian Highway Bridge Design Code (CHBDC, 2019) and AASHTO (AASHTO LRFD, 2019). The results revealed that the ultimate capacity of the SSS was reached without conforming to all ultimate bounds provided by the current design codes. Finally, a limit state function was proposed to account for the structure instability that may occur to the steel structure under ultimate loading condition. The proposed function successfully predicted failure in the steel structure under all cases considered in the current analysis before failure occurred in the numerical results.

Conventional and Asphaltic Underlayment Track Performance Subjected to Argo Jati Passenger Trains

Abstract This study performed the 2-dimensional modeling of Indonesia’s conventional track and the asphaltic underlayment track according to four different cyclic loading conditions by varying the train speeds and bogie load of Indonesia’s Argo Jati passenger trains set. Three different mechanical responses were considered, i.e., horizontal strains, vertical stress, and deformation, to investigate and compare the performance of Indonesia’s conventional track and the asphaltic underlayment track and to seek the possibility of Indonesia’s passenger trains to travel with higher speed and heavier axle load in the future. The numerical simulation results conclude that the asphaltic underlayment track capable of serving Argo Jati passenger trains set with the medium speed, 240 km/h, or 100 % higher than the existing operating speed. In addition, the application of a 20 cm asphalt layer below ballast will allow each passenger coach to carry the maximum payload up to 30 tons, or 50 % higher than the existing maximum payload. Furthermore, asphaltic underlayment track utilization in Indonesia’s railway systems could be beneficial for the optimization of the life cycle cost of the rail track since it could reduce the structure’s height, minimize the maintenance needs, and decrease track deterioration especially the mud pumping and deformation.

Kinematic analysis of the axle box unit operation

The axle load acts on the box unit and has shock-pulse nature when the car is moving, that can lead to a mutual change in the surface positions of the roller ends with the edges of the bearing races. The ways are proposed to optimize the internal geometry of the radial and end contact elements of the roller bearing of the axle box unit. It is proposed to eliminate the occurrence of possible conditions that lead to the movement of bearing rollers into the thrust and locking of bearing rollers by increasing the minimum limit in the axle clearance of the axle box.

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.

Experimental study on vibration characteristics of the floating slab with under-slab polyurethane mats considering fatigue loading effect

Under-slab polyurethane mats (USPM) are commonly recommended as a reliable vibration-damping measure in metro traffic. Since the design speed and axle load of the urban rail transit lines are different from those of the ordinary speed lines, the vibration characteristics of polyurethane mat floating slab track (PMFST) during long-term service need to be studied furtherly. This study investigated the vibration characteristics and transmission law of PMFST during the fatigue process and compared it with ordinary track (OT), which is the same as PMFST but without the under-slab mat using full-scale indoor laboratory models. The results show that: 1). Under-sleeper subsystem (including track slab, USPM, and foundation) experienced hardening during the fatigue process. The static and dynamic stiffness change rates after 5 million cycles were 6.4% and 10.8%; The overall change rates of static and dynamic stiffness after 10 million cycles were 8.7% and 12.8%. 2). The time-domain analysis showed that PMFST could significantly reduce the vibration duration and ground acceleration; Fatigue loading accelerated the degradation of the USPM, reducing the capacity of dissipating energy. 3). The slab-ground subsystem was the main attenuation section for PMFST, which could significantly reduce the energy transfer ratio. Compared with OT, PMFST performed better in dissipating the vibration energy along the longitudinal direction; However, fatigue loading would aggravate the vibration level. Overall, the vibration levels of PMFST (0 million, 5 million, and 10 million) can be reduced by 14.4 dB, 13.5 dB, and 10.9 dB, respectively.

Experimental Investigation of the Fracture Properties for Crumb Rubber Modified (CRM) Asphalt Mixtures

Cracks that develop daily and seasonally due to the environmental or mechanical effects caused by axle loads, propagate over time and become an important type of distress in asphalt layers. This type of distress can significantly increase the maintenance and rehabilitation costs of pavements. The use of rubber powder or fine granules in certain proportions to the bitumen content can extend the life of the pavements and reduce the environmental problems caused by waste tire disposal. In this study, the fracture behavior of normal and rubber-modified asphalt mixtures was investigated in accordance with AASHTO TP105 by adding waste tire granules at the ratio of 20% by weight of bitumen to hot mix asphalt. It has been determined that when the waste tire powders are added to the hot mix asphalt by replacing 20% of the bitumen weight, coatings with 37% more elastic ability could be made on sustainable pavements. Waste tire powder-mixes performed 118% higher in maximum load and 97% higher in fracture toughness compared to control-mixes. It has been shown that low temperature performance could be improved when waste tire powder-added bitumen processed by dry method is mixed to hot mix asphalt up to 20%.

Prediction Method of Heavy Load Wheel/Rail Wear Mechanical Properties Based on GA-BP Hybrid Algorithm

Due to its large axle load and high-density operation mode, heavy haul transportation has greatly improved the cargo transportation capacity, and is receiving unprecedented attention from all countries in the world. Since the development of heavy haul freight transport in China, wheel rail wear has been paid much attention, especially the use of heavy axle load locomotives on upgraded heavy haul lines, which makes reducing wheel rail wear and damage become a technical problem to be solved urgently. Considering that there are too many mechanical parameters involved in the prediction of heavy load wheel rail wear mechanical properties, the prediction accuracy is reduced. Therefore, this paper proposes a method based on GA-BP hybrid algorithm to predict the mechanical properties of heavy load wheel/rail wear. Hertz contact theory is used to simplify the wheel rail contact relationship, and the wheel rail contact model is established. According to the wheel/rail contact model, the expressions of heavy load wheel/rail in the case of vertical, horizontal, direction and gauge irregularity are analyzed, and based on this, a mechanical model of heavy load wheel/rail wear is established. In order to solve the problems of slow convergence speed and easy to fall into local optimum of BP neural network in the prediction of heavy load wheel/rail wear mechanical properties, the global convergence of genetic algorithm is used to optimize the BP network. According to the obtained mechanical parameters of heavy load wheel/rail wear, the mechanical parameters are input into the optimized model, and the relevant prediction results are output. So far, the research on the prediction method of heavy load wheel/rail wear mechanical properties based on GA-BP hybrid algorithm has been realized. The experiment is designed from three aspects of wear degree, hardness and tensile strength, and compared with the measured value, reference [4] method, reference [5] method and reference [6] method to verify the effectiveness of the proposed method. The experimental results show that the predicted results of wear degree, hardness and tensile strength by this method are closer to the measured results. It is proved that the proposed method has higher prediction accuracy and better practical application effect.

Multifactorial Analysis of the Axle Load of Truck Sets during the Transport of Sawmill By-Products

The aim of the study was to investigate the actual axle loads of vehicles used for the transport of sawmill by-products, resulting from the total weight of the transport set (GVW) at different times of the year and depending on the type of sets and transported assortment. Sawmill by-product loads were divided into groups: wood chips, sawdust, slabs and recycled wood. The research was carried out at the recipient of the sawmill by-products as well as at the producer. The GVW was determined on the basis of weighing the entire set on a stationary scale at the premises of the companies. The load on the individual axles of high tonnage truck units was measured using Model DINI ARGEO WWSD portable truck scales with a 3590M309 weighing terminal. Almost 230 transports were analyzed. It was shown that the average GVW is 39.25 t for transport sets with a load of 22.44 t of sawmill by-products with the usage of the semi-trailer capacity of 0.85. For all transport sets, the average load on the individual axles range from 6.72 t (axle 5 in a six-axle truck and trailer-TT) to 10.29 t for axle 2 in a truck and semi-trailer (TST), where the highest occurs on axle 2 of the truck (drive axle). The influence of the type of transport set (TST or TT) and the type of the assortments on the axle load is shown, and the existing correlations are at the level of 0.604–0.669 for axles 3–5 in the TST set. The static axle loads of the transport sets for the sawmill by-products and the distribution of the total weight of the set among the axles are different from those for roundwood transport.

Analysis of performance of asphalt pavements in Qatar using mechanistic-empirical approaches

Qatar roads are experiencing heavy traffic loads due to the rapid increase in the country’s population and construction projects over the past two decades. Considering the demand for high-performing, sustainable, and cost-efficient pavements, emphasis has been placed on using different asphalt modifiers and recycled materials in pavement layers. These modifiers/recycled materials change asphalt mixture properties, and consequently, influence pavement performance. The main objective of this study is to evaluate the performance of pavement sections that incorporate various types of asphalt mixtures and are subjected to traffic levels that range from 5 to 200 million equivalent single axle loads (ESALs). The analysis of pavement performance was conducted via three methods: Australian pavement design method implemented in Circly software, perpetual pavement design using PerRoad software, and a simplified mechanistic-empirical pavement design method (MEPD) that utilizes performance models used in AASHTOWare. The outcome of these analyses was the selection of suitable combinations of asphalt mixtures as well as the optimization of pavement layer thicknesses for different traffic loads. The results highlighted that the use of a high-stiffness mixture incorporating modified asphalt (PG 82E-10) in the wearing course should be used with caution in high traffic load sections (≥100 million ESALs). These stiff layers could be susceptible to cracking when the underneath asphalt layers have much less stiffness (50–70% less stiffness). However, in the medium traffic level (10–50 million ESALs) sections, pavement performance improved by using a stiff mix incorporating a PG 82E-10 binder in the wearing course layer. In addition, the use of crumb rubber (CR) modified asphalt reduced the material cost of a pavement section relative to the use of polymer-modified binder. The results show that it is desirable to use French EME (Enrobés à Module Elevé) mix in the base course layer for heavy traffic roads as this mix help to reduce pavement layer thicknesses and overall material cost. The outcomes of the analysis showed that the rutting thresholds commonly used in MEPD method are too restrictive (low thresholds) for heavy-duty pavements in Qatar hot climate. It is recommended to increase the rutting thresholds for such pavements.

Fatigue performance of basalt fibre-reinforced polymer bar-reinforced sea sand concrete slabs

Combining both Fibre-reinforced polymer (FRP) and sea sand concrete (SSC), the new composite structure of FRP bar-reinforced SSC can not only solve the issue related to reinforcement corrosion but also alleviate the problem of river sand shortage. Here, four-point bending tests were performed to investigate the fatigue performance of basalt FRP (BFRP) bar-reinforced SSC slabs. Results revealed that fatigue life decreased significantly with the increasing load levels. The average reduction of fatigue life was about 28% when the load levels increased by 0.05. The main fatigue failure mode of BFRP bar-reinforced SSC slabs was the BFRP bar rupture, which occurred at the mid-span or loading point. The load levels had no evident effect on the attenuation rate of bending rigidity. The critical value for the fatigue deflection growth rate could be set at 35%. An equation for the mid-span deflection at upper loads was established. Herein, considering the growth rate of fatigue deflection, insights to detect the deflection of BFRP bar-reinforced SCC slabs were presented. Meanwhile, based on the S–N curve, Miner rule, and axle load frequency spectrum, a fatigue life prediction method was proposed.

A Practical Design Guide for Unbonded Jointed Plain Concrete Roads over Deteriorated HMA Roads: Realistic Traffic Loading

This study aimed to determine the material properties and the thickness of the layers of an unbonded jointed plain concrete pavement design over a deteriorated flexible pavement that lost its service capability. Maximum principal stresses occurring under the concrete pavement should not exceed the modulus of rupture of the concrete. Three-dimensional finite element analyses using ANSYS (Release 18.1 SAS IP, Inc.) software were carried out with the Taguchi method. The most reliable solution for the pavement design was investigated with whole configuration axle loading that reflects the realistic traffic situation. The stress values under the concrete slab due to the positive temperature gradient neglected in the American Association of State Highway and Transportation Officials (AASHTO) method were also investigated. The concrete slabs are exposed to these stresses for longer than the axle loads. Temperature distributions throughout the thickness of the concrete slab were calculated with the bilinear formulas suggested in the study. Axle loadings were applied on both the pavement edge and corner to reflect the most critical loading condition in the pavement design. The critical axle type was found to be 1.2. It was observed that a 0.15 m concrete thickness was appropriate for the concrete class, joint spacing and hot mix asphalt (HMA) elasticity modulus levels used for the 1.22, 1.122, and 1.2 + 111 axle types, but it was not appropriate for the 1.2 axle types. The slab thicknesses calculated with the AASHTO method, and the finite element method were found to be close to each other. It was determined that the concrete thickness significantly affected the maximum principal stress, with a performance statistic (S/N) value of 1692 for the 1.2 axle type. This was followed by the modulus of elasticity of the concrete with an S/N value of 0.356, the modulus of elasticity of the existing flexible pavement with an S/N value of 0.244, and the concrete joint spacing with an S/N value of 0.105. A practical design guide was recommended to extend the service life of a highly deteriorated flexible pavement with the construction of unbonded jointed plain concrete.

Effect of rail axle load on geosynthetic reinforced back-to-back mechanically stabilized earth walls: Experimental and numerical studies

Back-to-back Mechanically Stabilized Earth (BBMSE) walls are generally used in approach embankments of flyovers and bridges. The complex geometry of two interactive MSE walls in a single structure makes it a special case for the study. This paper presents the performance evaluation of unconnected, connected and overlapped geogrid reinforced back-to-back mechanically stabilized earth walls supporting the railway tracks at bridge approaches. Scaled model tests were conducted to study the behaviour of BBMSE walls. Overburden (OB) waste generated from coal mining was used as the sustainable backfill. 3D Finite Element analysis was carried out to validate the model test. A parametric study was also carried out on varying W/H ratio, overlapping length, connected and unconnected geogrid reinforcement, geogrid stiffness and spacing. Train bogie load with its eight-point load was used as a loading condition. Lateral, vertical deformations of walls, geogrid strain, maximum tensile force developed in the geogrid for all the cases were investigated and discussed in detail. Geogrid arrangements were found to be critical in reducing the wall displacement. The overlapping length of the geogrid resulted in lesser deformation with the deformation reduction of 58 % compared to the connected geogrid.

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.