Development of combined transitional pavement structure for urban tram track-road grade crossings

Abstract

The grade crossings and adjacent pavements of urban trams are generally subjected to complex load conditions and are susceptible to damage. Therefore, in this study, a novel pavement structure between tram tracks and roads constructed using polyurethane (PU) elastic concrete and ultra-high-performance concrete (UHPC), referred to as a track-road transitional pavement (TRTP), is proposed. Subsequently, its performance and feasibility are evaluated using experimental and numerical methods. First, the mechanical properties of the PU elastic concrete are evaluated. The performance of the proposed structure is investigated using a three-dimensional finite element model, where vehicle-induced dynamic and static loads are considered. The results show that PU elastic concrete and the proposed combined TRTP are applicable and functioned as intended. Additionally, the PU elastic concrete achieved sufficient performance. The recommended width of the TRTP is approximately 50 mm. Meanwhile, the application of UHPC under a PU elastic concrete layer significantly reduces vertical deformation. Results of numerical calculations confirmed the high structural performance and feasibility of the proposed TRTP. Finally, material performance standards are recommended to provide guidance for pavement design and the construction of tram-grade crossings in the future.

Graphical abstract

Keywords

urban tram track / grade crossing / combined track-road transitional pavement / polyurethane elastic concrete / finite element method

1 Introduction

The modern tram is an urban transportation mode that features lower construction costs and higher accessibility than metro and light rail transits, thus satisfying the requirements of city traffic while providing good inner-city coverage [1]. Recently, the modern tram has been regarded as a reliable and sustainable alternative to fulfill the increasing demand for public transportation in countries and regions such as America, Europe, and China [1–4]. Urban tramlines have been constructed in more than 15 cities in China, which proved to be effective in alleviating traffic congestion in central areas [5,6].

However, road carriageways near tramway line grade crossings are typically less durable than track beds and road pavements, which significant affects road services and causes bottlenecks in road transportation [7]. Fig.1 shows typical road distresses near the grade crossing, including map cracking, transverse cracking, longitudinal cracking, and surface abrasion. These structural and functional damages near the grade crossings are primarily caused by difficulties in paving and compaction during construction, stiffness differences between the rail and asphalt, and loads induced by trams and other vehicles [8–11]. Furthermore, owing to the intense vibration caused by variations in material stiffness, high passing frequencies, and large heavy-vehicle axle loads, road vehicle loads require more attention than tram loads. Environmental factors, such as water penetration and temperature changes, may exacerbate these issues [12].

Thus, the long-term durability of grade crossings must be improved, which will indirectly improve driving comfort and reduce traffic disruption caused by frequent maintenance and repairs [13]. Despite their importance, minimal effort has been expended to improve the quality of grade crossings via road pavement design. Previous studies primarily focused on tram track-related issues, such as vibration, effects of subgrade settlement, and tram operation countermeasures. Zhao et al. [14] developed a rectified finite element model (FEM) to investigate the vibration and noise responses of a track. Bu and Li [15] conducted a similar study to evaluate the role of filling materials in improving the structural stability of tracks. Guo et al. [16] investigated the effects of differential subgrade settlements on track irregularity and structural stresses. However, their study on tram management is insufficient for guiding material and structural design or for ensuring the desired pavement performance at grade crossings.

Thus, a reliable and durable transitional pavement is required to ensure long-term road performance and driving comfort at track-road grade crossings. Herein, track-road transitional pavement (TRTP) refers to a category of pavement structures that is applied to specific areas of municipal roads at tram grade crossings via elaborate material and structural combination design. Therefore, a novel combined TRTP structure based on polyurethane (PU) elastic concrete ultra-high-performance concrete (UHPC) that is suitable for both new construction and rehabilitation projects is proposed herein. First, the material properties and performance of PU elastic concrete are evaluated via laboratory experiments. Subsequently, the structural design and construction procedures of the proposed combined TRTP are discussed thoroughly. A numerical analysis is performed using an established FEM to investigate the structural performance of the combined TRTP while considering dynamic and static vehicle loads. Subsequently, the performance of PU elastic concrete is evaluated based on the FEM results. The performance standards for PU elastic concrete are summarized herein as a basis for future applications and construction projects.

2 Materials and modeling methods

2.1 Materials and experimental methods

2.1.1 Materials

To accommodate the complex construction situation and loading conditions, materials with sufficient mechanical strength, elasticity, plasticity, impact resistance, adhesion, and workability were selected to construct the TRTP surface layer. PU-based materials satisfy these requirements and are a group of materials with superior physical, chemical, and mechanical properties that have piqued the interest of pavement and civil engineers [17–19]. A PU binder supplied by a local contractor was used as the surface layer of the TRTP owing to its excellent elasticity, deformation properties, and weathering resistance. The PU binder was composed of components A and B at a ratio of 1:0.7. Tab.1 lists the basic properties of the PU binders used.

Fig.2(a) shows the procedure for preparing the PU elastic concrete. First, two components of the PU binder were mixed. Meanwhile, a modified basalt aggregate (measuring 0–5 mm) was preheated at 120 °C for 2 h to allow complete water evaporation and avoid adverse reactions between water and the PU binder. Subsequently, the dehydrated modified aggregates were mixed with a blended PU binder. Notably, the modifiers in the aggregate, such as the defoaming agent, reduced the number of defects in the prepared PU elastic concrete. Finally, the PU elastic concrete was cast in molds for additional testing and evaluation.

2.1.2 Experimental methods

As mentioned previously, four typical types of distress were observed in the TRTP: map cracking, transverse cracking, longitudinal cracking, and surface abrasion. Map cracking is typically regarded as structural failure caused by the insufficient overall strength or bearing capacity of a pavement subjected to a vehicle impact load. Longitudinal and transverse cracking is primarily caused by tensile stress transmission failure due to unsatisfactory pavement material adhesion. In this study, four different tests, as shown in Fig.2(b)–Fig.2(e), were performed to evaluate the feasibility of the prepared PU elastic concrete based on American Society of Testing Materials (ASTM) and Chinese standards; in particular, the compressive strength, impact resistance, tensile strength, interfacial adhesive and shearing strength were evaluated.

1) Compressive strength

The compressive strength test was performed in accordance with ASTM D695 [25]. As shown in Fig.2(d), an increasing load at a loading rate of 5 mm/min was applied to the prepared cubic PU elastic concrete specimens (measuring 100 mm × 100 mm × 100 mm) and then cured from 3 h to 7 d. The compressive strength was calculated by dividing the maximum load by the cross-sectional area of the cubes. The specimens were molded and tested at a temperature of 25 °C (ambient temperature). A compressive load was applied during the tests using a UTM-25 universal testing machine.

2) Impact resistance

Vehicle vibrations adversely affect TRTPs because they cause structural damage. An impact test was performed using a free-falling weight in accordance with ASTM D5628 [26]. The experimental setup is shown in Fig.2(c), which shows the weight released and striking the specimen placed underneath it. Square specimens for the impact were prepared and cured at 25 °C (ambient temperature). Subsequently, the steel ball was lifted to a specified height and released onto the specimen. The tests were performed at three different temperatures, namely, −29, 0, and 70 °C, which represent the lowest, intermediate, and highest temperatures, respectively. Finally, cracking was observed to assess the impact resistance performance of the PU elastic concrete.

3) Tensile strength and recovery rate

A tensile strength test was performed in this study to assess the cracking resistance of the PU elastic concrete based on ASTM D638 [20]. Specimens measuring 100 mm × 100 mm × 20 mm were prepared and cured at 25 °C. Fig.2(d) shows the experimental setup for the tensile strength test. A tensile load was applied at a loading rate of 1 mm/min. Subsequently, the recovery rate was tested at the same temperature (25 °C) and loading rate. The specimens were stretched to an elongation level of approximately 5% and unloaded for 1 h. Finally, the tensile strength and recovery rate were computed using Eqs. (1) and (2), respectively.

(1)TS=\frac{F_{\mathrm{m}}}{W\cdot t},

(2)D=\frac{\mathrm{\Delta }L-\left(L_1-L_0\right)}{\mathrm{\Delta }L}\times 100\mathrm{\%},

where TS is the tensile strength; F_{\mathrm{m}} is the peak tensile load; W and t are the width and thickness of the narrow section of the specimen, respectively; D is the recovery rate; ∆L is the elongated length of the specimen; and L_0 and L_1 are the lengths between the mark lines before and after the test, respectively.

4) Interfacial adhesive and shearing strength

The interfacial adhesive and shearing strength affect the synergy between the PU elastic concrete and the surrounding structures. Hence, the interfacial adhesive and shearing strength were evaluated in accordance with GB/T 16777-2008 [27], as shown in Fig.2(e). In this study, two interfacial materials bonded with PU elastic concrete were considered: UHPC and asphalt concrete. First, the corresponding composite specimens were formed. Subsequently, the interfacial adhesive and shearing strength were evaluated using a UTM-25 universal testing machine at a loading rate of 50 mm/min at 25 °C. The maximum load was recorded at the end of the tests. Subsequently, the failure strength was calculated accordingly.

2.2 Structure modeling

2.2.1 Novel combined transitional pavement structure

Generally, the vertical layers of pavements have different stress conditions and structural functions, which necessitates the appropriate use and selection of materials. The upper layer of the pavement directly supports vehicle loads and serves as an anti-rut, anti-shear, and anti-impact layer. Furthermore, the material used in TRTPs must exhibit a high degree of elasticity. The lower layer primarily supports loads to resist permanent deformations caused by the heavy load of vehicles; hence, it necessitates the use of stiff materials. In this regard, UHPC can be used to construct the lower layer of pavements to resist vertical deformation, whereas elastic concrete can be used in the upper layer to buffer deformation and impact.

Fig.3 shows the detailed structure of the proposed novel combined TRTP. A typical 59R2 grooved rail is embedded in the concrete slab layer. The combined TRTP replaces the original asphalt pavement surrounding the side of the rail with a certain width. Notably, the TRTP investigated in this study features a width of approximately 5–20 cm on both sides of the rail. The primary goal of this replacement is to provide an appropriate and durable transition in terms of stiffness for passing vehicles. Hence, the combined TRTP is designed to comprise two primary structural layers. The upper layer is a PU elastic concrete layer with good elasticity, tensile strength, and weathering resistance that resists cracking, rutting, and abrasion. The bottom layer is constructed using UHPC, which offers sufficient rigidity (elastic modulus and compressive strength exceeding 45 and 120 MPa, respectively) to withstand high compressive stresses and reduce vertical deformation.

2.2.2 Construction procedure

Fig.4 shows an established procedure for constructing the combined TRTP in the rehabilitation project, which was performed at Tram Line 1 in Jiaxing, Zhejiang Province, China. The original road asphalt pavement was removed and replaced with a combined semiflexible TRTP composed of PU elastic concrete and UHPC. The construction procedures were as follows: (1) the asphalt pavement was cut and grooved, and the bottom and sides of the grooves were coated with a PU or an epoxy binder; (2) a quick-setting UHPC was prepared and paved at the bottom of the grooves; (3) the PU binder and PU elastic concrete were prepared on-site shortly after the UHPC was paved; (4) the PU elastic concrete was paved, and the road was immediately opened for traffic. The construction efficiency of the proposed combined TRTP demonstrated the feasibility of its application.

2.2.3 Modeling

The FEM has evolved into an effective tool for assessing structural performance in civil engineering. The mechanical response and application feasibility of the above-mentioned combined TRTP were further evaluated using an established three-dimensional FEM model using the ABAQUS software.

Based on a typical tram track structure in China [16], an FEM model that included the rail, the proposed combined TRTP, a concrete slab (C25 cement concrete), an asphalt pavement (AC-13 and AC-20 dense grade asphalt mixture), and a supporting layer was first created. The combined TRTP was established as a separate component embedded between the asphalt pavement and rail structure. Owing to the structural symmetry, only one-half of the tram track structure was simulated for analysis. The detailed geometry and material parameters of the established FEM are presented in Fig.5(a) and Tab.2. The materials were uniformly modeled as linear elastic materials to reduce the computing cost by reducing the complexity of the structures and the diversity of the materials.

To improve the calculation accuracy and efficiency, the contact mode, interaction, boundary condition, mesh, and load were simplified. In terms of surface interactions, the coupling constraint was adopted to embed the rail, whereas the other components were constrained by “hard contact” and “friction” in the interaction module. In terms of the boundary conditions, all boundaries except those at the bottom region, which was imposed with a fixed constraint, were set with symmetric boundary conditions. Meanwhile, a denser mesh was employed near the loading area, whereas a relatively coarse mesh was used in other areas.

Both dynamic and static vehicle loads were considered in this study. The tram-induced static load was considered as load condition 4, as shown in Fig.5(b). A vertical load of 175 kN and a lateral load of 105 kN were applied to the rail.

In terms of the vehicle-induced static load, the actual tire contact size was simplified to a 600 mm × 200 mm rectangular load area. The tire pressure was modeled as a vertical uniformly distributed load with an axial load of 100 kN, based on JTG D50-2017 [28]. Meanwhile, the vehicle-induced impact and vibration at the track-road grade crossing were considered owing to the uneven road surface. To simulate a realistic situation, the dynamic coefficient K_{\mathrm{d}} was used to represent the superimposed dynamic load [29]. The vertical and lateral static loads were calculated using Eqs. (3) and (4), respectively.

(3)F_{\mathrm{v}}=K_{\mathrm{d}}\cdot F_{\mathrm{s}},

(4)F_{\mathrm{l}}=\alpha \cdot F_{\mathrm{v}},

where F_{\mathrm{v}} and F_{\mathrm{l}} are the vertical and lateral loads, respectively; F_{\mathrm{s}} is the initial 100 kN static load; and \alpha is the coefficient of friction, which is the lateral force to the vertical force. The vertical and lateral loads induced by the vehicle loads were calculated to be 125 and 87.5 kN, respectively. Based on the actual operation of tram cars, the tram induces a vertical load of 175 kN and a lateral load of 105 kN on the rail.

Meanwhile, as shown in Fig.5(b), four different static load conditions, three vehicle load conditions, and one tram load condition were applied to the model. Load conditions 1 and 3 represent the instantaneous entry and exit states of the vehicle, respectively. Load condition 2 is the operating condition, where the vehicle is loaded directly onto the combined TRTP. In load condition 4, the tram is loaded directly onto the rail.

A moving load was used to simulate the load condition as the vehicle passed through the grade crossing for a vehicle-induced dynamic load, as shown in Fig.5(c). In addition to providing a standard finite element analysis, ABAQUS serves as a favorable open secondary development platform owing to the user subroutine interface provided. When the vehicle passed the road-track grade crossing, the movement of vehicles with loads of 100 kN on the wheel track was implemented via Fortran programming using the Dload subroutine. Because of the short length of the TRTP, the action time of the moving loads should be instantaneous. ABAQUS provides a dynamic and explicit analysis step for dynamic load analysis. Compared with an implicit algorithm, an explicit algorithm can use a faster algorithm and requires a shorter time to calculate the mechanical response under rapidly changing loads in a short period. Several explicit steps were established in ABAQUS to implement the application of the moving loads. The governing equation for the applied dynamic load can be expressed as shown in Eqs. (5)–(7) [30].

(5)\mathit{M}\ddot{\mathit{u}}+\mathit{C}\dot{\mathit{u}}+\mathit{K}\mathit{u}=\mathit{P}\left(t\right),

(6)\mathit{M}=\int \mathit{N}\rho \mathit{N}\mathrm{d}\mathit{V},

(7)\mathit{C}=\alpha \mathit{M}+\beta \mathit{K},

where M is the mass matrix; C is the damping matrix; K is the stiffness matrix; \dot{\mathit{u}} and \ddot{\mathit{u}} are the velocity vector and acceleration associated with the nodes, respectively; \mathit{u} is the displacement vector; \mathit{P}\left(t\right) is the external force vector related to the structure dynamic system; \rho is the mass density; N is the form function matrix; V is the unit domain; \alpha is the mass damping coefficient; and \beta is the stiffness damping coefficient.

3 Results and discussion

3.1 Experimental results

Fig.6(a) shows the compressive strength test results of the PU elastic concrete at different curing times of up to 7 d. The compressive strength growth curve of normal PU concrete for road pavements is shown in the same graph for comparison. Initially, the PU elastic concrete exhibited a higher strength growth rate than the normal PU concrete and exhibited an average compressive strength of 6.4 MPa in 3 h. The strength of the PU elastic concrete eventually decreased to below that of normal PU concrete. The higher growth rate and lower final strength indicate the favorable workability of PU elastic concrete in satisfying the requirements of scheduled opening to traffic, as well as its high elasticity for achieving a smooth stiffness transition.

The impact resistance of the PU elastic concrete was evaluated at three different typical temperatures, namely −29, 0, and 70 °C. A typical impact point for a falling ball is shown in Fig.6(b). No cracking was observed at any of the temperatures. The results indicate that the elastic concrete exhibited high impact resistance to withstand vehicle vibration-induced impact under severe high- and low-temperature conditions.

Tensile strength and recovery rate are important indices for assessing the cracking resistance of concrete. Fig.6(c) shows the test results at three different temperatures from −10 to 60 °C. Regardless of the temperature change, the tensile strength and recovery rate of the fabricated PU elastic concrete exceeded 1 MPa and 97%, respectively, thus indicating the high tensile deformation capacity of PU elastic concrete at different temperatures.

Fig.6(d) shows the interfacial adhesive and shearing strength test results of the PU elastic concrete. As mentioned previously, PU elastic concrete is to be used in certain environments to ensure its interfacial bonding with various types of pavement materials. The average adhesive strength between the PU elastic and cement concrete was 2.52 MPa, whereas that between the PU elastic and asphalt concrete was 2.21 MPa (see Fig.6(d)); meanwhile, the corresponding shearing strengths were 3.09 and 2.68 MPa, respectively. The test results were reasonably well compared with the adhesive strength of 0.46 MPa and shearing strength of 2.76 MPa indicated in existing research between normal cement and asphalt concrete [31].

3.2 Numerical evaluation

3.2.1 Effects of structural parameters on simulation results

The preferred width of the combined TRTP and the application feasibility of UHPC as a material for the bottom layer of the proposed structure are discussed in this section. These two aspects significantly affect the stiffness transition of the combined TRTP.

As shown in Fig.7(a), three different widths (50, 100, and 150 mm) were considered. Three types of vehicle-induced static loads and one tram-induced static load were applied. Fig.7(b) shows the maximum principal stress under various static load conditions. The maximum principal stress decreased gradually as the horizontal distance from the rail increased. Furthermore, among the three widths, the 50 mm width resulted in the highest rate of decrease. This might be because vehicles have a limited wheel contact area with transitional pavements. Hence, a smooth stiffness transition is preferred to decrease stress and provide sufficient protection for the connected asphalt pavement. In this study, the width of the combined TRTP was set to approximately 50 mm to ensure its application feasibility, construction efficiency, and low cost.

A comparative study was conducted to determine the application feasibility of UHPC, which exhibits high modulus, durability, and impact resistance. The UHPC layer is vital to the proposed combined TRTP structure. It was designed to provide adequate support to the upper PU elastic concrete layer such that a semi-flexible structure can be achieved. Hence, the maximum vertical deformation of the TRTP with and without UHPC was calculated, as shown in Fig.8. Implementing the UHPC layer may significantly reduce the TRTP deformation under four different static load conditions. The vertical deformation of the TRTP without UHPC indicated significant fluctuations and reached a maximum value of 1.1 mm, whereas the TRTP with UHPC reduced the deformation to only approximately 0.1 mm. This reduction in deformation shows that the UHPC layer satisfies the expectations owing to its high modulus and stiffness.

3.2.2 Static and dynamic evaluation

Using the established FEM, the structural performance of the proposed combined TRTP and the application feasibility of PU elastic concrete were further evaluated.

As mentioned previously, Fig.9(a) shows the relationship between the vertical compressive stress and the distance from the rail center under four different static load conditions. As the distance from the rail center increased, the vertical stress decreased gradually. However, under load condition 2, an abrupt stress change was observed 5–10 cm away from the center, indicating the high requirements for TRTP–rail operations. The maximum vertical stress occurred at the edge of the rail, as confirmed by the stress distribution shown in Fig.9(b). Load condition 2, which represents the condition in which the vehicle was directly loaded onto the combined TRTP, yielded the highest vertical compressive stress of 5.35 MPa. Fig.9(c) shows the transverse stress across the model. Similarly, the rail resisted most of the transverse tensile stress. The maximum tensile stress in the TRTP occurred at a location away from the rail. The maximum tensile stress was 0.70 MPa under load condition 1 (the vehicle entered the area). Additionally, this finding indicates that the material on the outer side of the TRTP is susceptible to tensile failure, as shown in Fig.9(d), with a maximum transversal stress distribution.

The structural performance of the combined TRTP was further evaluated by applying a dynamic moving vehicle load at various speeds ranging from 10 to 60 km/h along the wheel track, as shown in Fig.5(c). The compressive, tensile, and shear stresses in the combined TRTP based on a vehicle speed of 10 km/h are shown in Fig.10(a)–Fig.10(c), respectively. Based on the FEM results, the maximum compressive stress under dynamic loads occurred when the vehicle entered the TRTP, whereas the maximum tensile stress occurred when the vehicle exited it. In addition, as shown in Fig.10(d), the compressive stress decreased as the vehicle accelerated, whereas the tensile and shear stresses remained relatively constant. Under dynamic loads, the maximum tensile, compressive, and shear stresses in the combined TRTP were approximately 4.50, 0.50, and 1.10 MPa, respectively.

Four parameters were selected for finite element analysis. Static and dynamic analyses were performed 24 and 36 times, respectively, as shown in Tab.3. Tab.4 summarizes the maximum stress conditions in the combined TRTP under static and dynamic loads. The maximum compressive, tensile, and shear stresses were calculated to be 5.35, 0.70, and 1.10 MPa, respectively, which were lower than the experimental values for PU elastic concrete, as discussed in Subsection 3.1. Thus, PU elastic concrete with acceptable mechanical properties is applicable to the proposed TRTP combination.

3.3 Material performance standard recommendation

Based on the results of the experimental test as well as the static and dynamic analysis of the FEM, material performance standards are proposed herein to provide a basis for the future design and construction of the combined TRTP structure. Tab.5 presents the final recommendations to ensure high material performance. The materials used in the combined TRTP should be sufficiently strong mechanically to withstand deformation, tensile cracking, adhesion failure, and vehicle impact. However, only a few basic properties were specified in this study. Hence, other time-related factors such as aging and fatigue must be investigated in the future to provide a more comprehensive guidance for the use of the combined TRTP.

4 Conclusions

A novel combined TRTP was proposed herein to ensure the durability and driving comfort of track-road grade crossings as well as mitigate pavement distresses at tram grade crossings. The structural design and construction procedures were discussed comprehensively. The structural performance of the proposed combined TRTP and the feasibility of applying PU elastic concrete and UHPC on the combined TRTP were evaluated experimentally and numerically. Finally, material performance standards were defined based on the results obtained and characterizations. The following conclusions were inferred.

1) In practical applications, PU elastic concrete and the proposed combined TRTP demonstrated high workability and construction efficiency, thus satisfying the requirements of rapid traffic opening.

2) The PU elastic concrete demonstrated adequate compressive strength, impact resistance, tensile deformation capacity, and interfacial adhesive strength under various temperatures.

3) To ensure application feasibility, construction efficiency, and low cost, the width of the combined TRTP should be set to approximately 50 mm. Using UHPC can significantly reduce vertical pavement deformation and facilitate the formation of a semi-flexible structure.

4) The maximum compressive, tensile, and shearing stress values were calculated to be 5.35, 0.70, and 1.10 MPa, respectively. Hence, the values of the mechanical properties of the materials used in the combined TRTP must exceed these values.

5 Recommendations for further research

1) With regard to the performance standards of TRTPs, other time-related factors such as aging and fatigue should be investigated in future studies to provide more comprehensive guidance for pavement design at urban tram grade crossings.

2) The effect of vibration on the surrounding road surface can be modeled, including the tram vibration and vehicle impact, to investigate the deterioration of the pavement around the track.

3) Damping materials for TRTPs can be developed to reduce vibration and protect the pavement structure.

References

[1] VuchicV R. Urban Transit Systems and Technology. 1st ed. New York: Wiley, 2007

[2] Naegeli L, Weidmann U, Nash A. Checklist for successful application of tram–train systems in Europe. Transportation Research Record: Journal of the Transportation Research Board, 2012, 2275(1): 39–48

[3] Nguyen-Phuoc D Q, Currie G, de Gruyter C, Young W. Net impacts of streetcar operations on traffic congestion in Melbourne, Australia. Transportation Research Record: Journal of the Transportation Research Board, 2017, 2648(1): 1–9

[4] Topp H H. Innovations in tram and light rail systems. Proceedings of the Institution of Mechanical Engineers Part F—Journal of Rail and Rapid Transit, 1999, 213(3): 133–141

[5] XuanWBoLXinH. Application of multi-agent simulation in the research of urban space: A case study of the commercial center transfer in Tianjin under the impacts of tram in the early 20th Century. Modern Urban Research, 2015, 4: 105–111 (in Chinese)

[6] Chen C L. Tram development and urban transport integration in Chinese cities: A case study of Suzhou. Economics of Transportation, 2018, 15: 16–31

[7] Sobota A, Żochowska R, Szczepański E, Gołda P. The influence of tram tracks on car vehicle speed and noise emission at four-approach intersections located on multilane arteries in cities. Journal of Vibroengineering, 2018, 20(6): 2453–2468

[8] ReynoldsJPhamDCurrieG. Do trackless trams need stronger roads?––The “weight” of evidence. In: Australasian Transport Research Forum 2021 Proceedings. Risbane: ATRF Inc., 2021

[9] NaI HParkJ Y. Evaluation of bond strength characteristics of tack-coating materials for asphalt pavement application to embedded track system for wireless tram. Journal of the Korean Asphalt Institute, 2020, 10(2): 285–296 (in Korean)

[10] StolarikMPinkaMMohylaM. Dynamic load due to the tram in urban area. In: The 17th International Multidisciplinary Scientific GeoConference SGEM 2017. Sofia: SGEM, 2017, 271–278

[11] Kouroussis G, Pauwels N, Brux P, Conti C, Verlinden O. A numerical analysis of the influence of tram characteristics and rail profile on railway traffic ground-borne noise and vibration in the Brussels Region. Science of the Total Environment, 2014, 482: 452–460

[12] Kisiel P, Mikulski Z, Kwiecień A, Adamus J. The use of polymer flexible joint technology in tramway tracks construction. Logistyka, 2014, 4: 4437–4444

[13] PyrgidisC N. Railway Transportation Systems: Design, Construction and Operation. 2nd ed. Boca Raton: CRC Press, 2021

[14] Zhao Y, Li X, Lv Q, Jiao H, Xiao X, Jin X. Measuring, modelling and optimising an embedded rail track. Applied Acoustics, 2017, 116: 70–81

[15] Bu J, Li J. Numerical analysis of the embedded track structure under mixed traffic load. In: 2018 2nd International Conference on Functional Materials and Chemical Engineering (ICFMCE 2018). Abu Dhabi: MATEC Web of Conferences, 2019, 272: 01042

[16] Guo Y, Zhai W, Sun Y, Pei G, Jiang J. Mechanical characteristics of modern tramcar–embedded track system due to differential subgrade settlement. Australian Journal of Structural Engineering, 2017, 18(3): 178–189

[17] Li X, Li J, Wang J, Yuan J, Jiang F, Yu X, Xiao F. Recent applications and developments of polyurethane materials in pavement engineering. Construction and Building Materials, 2021, 304: 124639

[18] Xiao X, Wang J Y, Cai D G, Lou L W, Xiao F P. A novel application of thermoplastic polyurethane/waste rubber powder blend for waterproof seal layer in high-speed railway. Transportation Geotechnics, 2021, 27: 100503

[19] Xiao X, Cai D G, Lou L W, Shi Y F, Xiao F P. Application of asphalt based materials in railway systems: A review. Construction and Building Materials, 2021, 304: 124630

[20] ASTMD638. Standard Test Method for Tensile Properties of Plastics. West Conshohocken, PA: ASTM, 2014

[21] GB/T531.1-2008. Rubber, Vulcanized or Thermoplastic-Determination of Indentation Hardness—Part 1: Durometer Method (Shore Hardness). Beijing: General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, 2008 (in Chinese)

[22] ASTMD624. Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers. West Conshohocken, PA: ASTM, 2020

[23] JTGE20-2011. Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering. Beijing: Research Institute of Highway Ministry of Transport, 2011 (in Chinese)

[24] GB/T19250-2013. Polyurethane Waterproofing Coating. Beijing: General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, 2013 (in Chinese)

[25] ASTMD695. Standard Test Method for Compressive Properties of Rigid Plastics. West Conshohocken, PA: ASTM, 2010

[26] ASTMD5628. Standard Test Method for Impact Resistance of Flat, Rigid Plastic Specimens by Means of a Falling Dart (Tup or Falling Mass). West Conshohocken, PA: ASTM, 2018

[27] GB/T16777-2008. Test Methods for Building Waterproofing Coatings. Beijing: General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China, 2008 (in Chinese)

[28] JTGD50-2017. Specifications for Design of Highway Asphalt Pavement. Beijing: Research Institute of Highway Ministry of Transport, 2017 (in Chinese)

[29] Aleksandrov A S, Dolgih G V, Kuzin N V. Method of calculating the limiting depth of ruts on the pavement of automobile roads. IOP Conference Series: Materials Science and Engineering, 2020, 753: 052019

[30] BatheK J. Finite Element Procedures in Engineering Analysis. Hoboken, NJ: Prentice Hall, 1982

[31] FuQ HChenX HCaiD GYangJYangG T. Full-section asphalt concrete waterproof sealing structure for high speed railway subgrade. China Railway Science, 2020, 41(2): 24–33 (in Chinese)

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