Long-term Service Performance Research Articles

Viscoelastic creep model and parameter inversion of bond interface in steel plate reinforced tunnel lining

The interface filler material (epoxy resin) used for reinforcing tunnel linings with steel plates exhibits time-dependent mechanical properties, commonly referred as creep behavior. The creep behavior of the filler material will significantly influence the long-term service performance of the reinforced tunnel, especially considering the design service life scale of 100 years. This paper presents an experimental test and mathematical modelling to illustrate the creep mechanical behavior of bond interfaces within shield tunnels reinforced with steel plates. It was observed that in the initial moments of stress application, the bond interface demonstrates an instantaneous response through elastic strain and on-set of creep deformation stage at maximum stress value. Three stages can be characterized in the creep deformation process: the decay creep stage, the steady-state creep stage and the accelerated creep stage. In the accelerated creep stage, the bond interface rapidly deteriorated after experiencing 90 % of the ultimate shear stress for 186 hours or 90 % of the ultimate tensile stress for 96 hours. Based on the fractional-order calculus theory and drawing inspiration from the modeling principles of classical component combination models, a constitutive equation that accurately characterizes the creep mechanical behavior of the bond interface between steel plates and concrete linings was formulated. The model parameters are inversely computed using the principle of least squares and the accuracy of this model is validated through a comparison with the results of the creep tests.

Cumulative frost heave and hydrothermal process of the high-speed railway subgrade under extreme climate conditions in northwest China

The mechanisms underlying the long-term deformation response and hydrothermal processes of high-speed railway subgrades in high altitude, seasonally frozen regions remain poorly understood, especially under extreme weather conditions. This study, based on an eight-year continuous field monitoring of the Lanzhou-Xinjiang High-Speed Railway (LXHR), presents several novel findings. From 2015 to 2022, air temperature, ground surface temperature, and subgrade surface temperature consistently increased, while the average annual rainfall showed a decreasing trend. During this period, sporadic heavy rainfall events occurred, and the climate demonstrated anomalous fluctuations. Such occasional heavy rainfall can cause a rise in the groundwater table, leading to an increase in frost heave within the subgrade. Given the same climatic conditions, embankments display a greater frozen depth compared to road cuts, but experience relatively less frost heave. Frost heave deformation within the subgrade comprises two components: residual deformation and inherent frost heave deformation. Residual deformation primarily contributes to the annual cumulative increase in frost heave, a process succinctly described as the transportation and deposition of fine particles (less than 2 mm in diameter) in coarse fillers by water, in close proximity to the frozen edge, ranging from 0.8 m to 1.2 m of the subgrade. In summary, the results of this study serve as a reminder for engineering designers and researchers to give more attention influence of residual deformation and the current climate change, in consideration of the stability and long-term service performance of subgrade under extreme weather conditions in the future.

Interplay between high-temperature creep deformation behavior and nanoscale precipitate evolution in a newly designed Fe–Ni-based superalloy

In an endeavor to achieve the critical goals of carbon neutrality, an explorative study was conducted to scrutinize the precipitate evolution and high-temperature creep behavior of an innovative and cost-effective Fe–Ni-based superalloy that was meticulously engineered for the next-generation ultra-supercritical (USC) power plants. The creep experiments conducted at temperatures and stresses of 650 °C/280 MPa (17,179 h), 675 °C/250 MPa (10,271 h), and 700 °C/250 MPa (2378 h), coupled with proficient data fitting were employed to accurately assess the long-term service performance of the superalloy under real-world operational environments. Though it can withstand theoretically an intense stress of 130 MPa at 700 °C for approximately 30 years as calculated by the Larson-Miller equation, its performance was not without a degree of perceived vulnerability. This was primarily traced to the conspicuous coarsening behavior of the precipitate-free zones (PFZs)/discontinuous coarsening zones (DCZs) formed in the grain boundaries (GBs) on a longer time scale. It had a significant diminishing impact on the overall strength of the GBs, resulting in a recorded creep life that was considerably shorter than initially projected. Moreover, a synergistic mechanism between PFZs/DCZs with TiC carbides was advanced to interpret the intergranular fracturing dynamic, which was postulated due to the evidence gathered from electron backscatter diffraction (EBSD), highlighting that the banded distribution of TiC carbides circumambient to GBs engendered considerable stress aggregation. Conversely, the plentiful supply of coincidence site lattice (CSL) boundaries disrupted the continuous network structure of random high-angle grain boundaries (HAGBs), thereby creating an effective barricade against the proliferation of cracks. These empirical findings paved the way for the proposition of an enhanced blueprint and the industrial utilization of such.

An optimised grinding target profile considering long-term service performance: A case study of no. 18 high-speed turnout

The design of rail grinding profiles for turnout has always been a significant subject of research. This paper proposes a rail grinding target profile design method that can improve the serviceability of turnout. Firstly, the high-speed turnout rail profile was parameterised by non-uniform rational B-spline (NURBS), with the amount of key section control point grinding used as a design variable. Secondly, considering the evolution mechanism of turnout dynamics performance and rail wear, a turnout long-term service performance prediction model is established based on deep feedforward network (DFN), with relevant evaluation indexes as the objective function. Non-dominated sorting genetic algorithm-Ⅱ (NSGA-Ⅱ) is used to solve this multi-objective optimisation problem. Finally, a comparative analysis of the performance of the turnout profile before and after optimisation is conducted. The computed outcomes demonstrate that after the turnout is ground, all the dynamic performance indicators have substantially improved in the short term. Additionally, the maximum wear on the straight switch rail has been reduced by 31.2 % and the position of the occurrence has shifted backward, which has improved the stressing of the weak rail elements to some extent. In long-term service conditions, the optimised turnout profile sustains a higher level of riding quality compared to the measured profile. Optimisation of the profile can effectively decelerate the rail wear rate and aid in prolonging the service life of the turnout.

Use of condition-based valuation approach to evaluate the maintenance decision of pavement assets: a case study of Yunnan Province in China

Pavements are critical components of highway assets, but accurately estimating their value can be challenging due to the lack of connection between valuation and long-term service performance degradation. To address this issue, the replacement cost and condition-based valuation methods were introduced using the Yunnan province highway in China as an example, which divided pavement into four performance states based on service stages. The rationality of maintenance decisions and the impact of preventive maintenance investment on life cycle assessments were also considered. The results indicate that there are issues of irrational allocation of maintenance funds of the highway in Yunnan province, and a higher proportion of preventive maintenance investment is required. Moreover, it is recommended to balance the maintenance funds for bridge and tunnel engineering in the following year, focusing on bridge engineering with a rapid decline in the newness rate. The implementation of preventive maintenance has a positive correlation with the replacement cost and newness rate of the road sections. Through comparison, it was found that the road surface renewal rate in 2019 was lower than that in 2018, and some highway management departments in certain regions need to adjust their preventive maintenance strategies. Overall, the condition-based pavement asset valuation method comprehensively considers each stage of pavement operation and can serve as an effective tool for evaluating pavement asset depreciation. This research finding can promote the sustainable development of road infrastructure.

Pollutant transport behavior through polymer cutoff wall: Laboratory test and analytical model investigation

Polymer cutoff wall has emerged as a new and promising technology for anti-seepage and anti-pollution in geotechnical engineering. With notable advantages such as rapid sealing, high efficiency, and environmental friendliness, this technology has garnered significant attention. This study presents a systematic investigation into the transport characteristics of pollutants in polymer materials, with a specific focus on the transport mechanisms through polymer cutoff wall. The research investigates various factors that influence the pollutant transport characteristics in polymer materials. The objective is to analyze the pollutant transport behavior and obtain the transport parameters. Moreover, the study develops and solves a one-dimensional transport model incorporating partition-diffusion-partition mechanisms, aiming to determines the long-term service performance of polymer wall. These findings contribute to a better understanding of pollutant transport through polymer walls, which is crucial for the future advancement and utilization of this technology.

Preparation of superhydrophobic shape memory composites with uniform wettability and morphing performance

Superhydrophobic shape memory surfaces have attracted much attention in recent years, as they can intelligently control surface wettability. However, less research has focused on the development of superhydrophobic shape memory materials that can maintain uniform wettability in any morphing shape. It is common in nature that species such as lotus leaves and kingfisher show good superhydrophobicity in any movement under/on water. Based on this inspiration, this work presents a novel superhydrophobic shape memory composite (SSMC) by coupling superhydrophobic coatings and shape memory epoxy composites. The SSMC exhibits excellent water repellency and self-cleaning performance regardless of how it is bent. In addition, its good shape memory effect and variable stiffness characteristics enable it to be potentially used as deployable marine structures and morphing skin of aquatic unmanned aerial vehicles. On the other hand, the SSMC also offers good anti-icing properties and mechanical/chemical robustness that enhance long-term service performance all year round. This research provides a fresh idea for the design of new smart superhydrophobic materials and expands applications in the field of marine and aviation facilities.

Development of rail technology for high speed railway in China

PurposeThe purpose of this paper is to summarize the status and characteristics of rail technology of high-speed railway in China, and point out the development direction of rail technology of high-speed railway.Design/methodology/approachThis study reviews the evolution of high-speed rail standards in China, comparing their chemical composition, mechanical attributes and geometric specifications with EN standards. It delves into the status of rail production technology, shifts in key performance indicators and the quality characteristics of rails. The analysis further examines the interplay between wheels and rails, the implementation of grinding technology and the techniques for inspecting rail service conditions. It encapsulates the salient features of rail operation and maintenance within the high-speed railway ecosystem. The paper concludes with an insightful prognosis of high-speed railway technology development in China.FindingsThe rail standards of high-speed railway in China are scientific and advanced, highly operational and in line with international standards. The quality and performance of rail in China have reached the world’s advanced level. The 60N profile guarantees the operation quality of wheel–rail interaction effectively. The rail grinding technology system scientifically guarantees the long-term good service performance of the rail. The rail service state detection technology is scientific and efficient. The rail technology will take “more intelligent” and “higher speed” as the development direction to meet the future needs of high-speed railway in China.Originality/valueThe development direction of rail technology for high-speed railway in China is defined, which will promote the continuous innovation and breakthrough of rail technology.

An approach for quantifying the calcium leaching effect on service performance of concrete cutoff wall of embankment dams

Calcium leaching is one of the essential diseases of concrete impermeable structures; therefore, an effective numerical approach to quantifying the effect of calcium leaching on concrete impermeable structures is critical for evaluating the long-term service performance of the structure. To this end, a seepage and dissolution coupling model for simulating the degradation of hydraulic concrete properties is proposed in this paper by introducing performance parameter evolutionary models based on saturated–unsaturated seepage and calcium dissolution and migration theories. The model is developed in COMSOL with a staggered solution scheme, and a detailed numerical implementation method is presented. The effectiveness of the proposed method is examined by laboratory calcium leaching tests. On this basis, the model was applied to evaluate the effect of calcium leaching on the service performance of a concrete cutoff wall (CCW) of an embankment dam in Shaanxi Province, China. The results demonstrate that the proposed method can effectively reproduce the calcium leaching process of concrete, and the variation of leaching depth based on model simulations is highly consistent with the experimental results. Calcium leaching primarily occurs at the CCW’s upstream waterfront surface, bypass seepage area and the partition of adjacent soil layers where the permeability varies greatly. Under seepage dissolution, the amount of leached calcium, average porosity, diffusion coefficient and hydraulic conductivity of the CCW increased exponentially with service duration, and solid-phase calcium leaching was the underlying cause of structural performance degradation. The length of the seepage path in the CCW decreases as the service duration increases, and the hydraulic gradient within it gradually increases. Based on the allowable hydraulic gradient of CCW, the safe service life of the CCW considering the calcium leaching effect was determined to be approximately 52a.

Effects of complex environment on soil thermal regime alteration under crushed-rock embankment structures in the permafrost region on the Roof of the World

The thermal stability of permafrost under complex environment (climate scenarios, permafrost types and regional air temperatures) directly affects the long-term service performance of highway or railway. This study uses a large amount of valuable soil temperature monitoring and simulation data to examine the stability of typical crushed-rock embankments (CREs) along Qinghai-Tibet Railway, which is located in the permafrost region on the Roof of the World. Firstly, a novel numerical model for CREs considering a complex heat transfer environment is established and verified. Then, alteration characteristics of recent-term thermal regime of permafrost across time and space under three CREs are revealed based on a decade of field monitoring data. Finally, long-term thermal regime of permafrost under three CREs under complex environment is analyzed by numerical simulation. Results include: 1) Soil temperature near the ground surface under the three CREs shows a decreasing trend, whereas the overall temperature around the deep permafrost increases over time under a recent climate warming. 2) The warming rate of permafrost under CREs rises with the acceleration of climate scenarios and regional air temperature and the decrease of regional ground temperatures. 3) U-shaped crushed-rock embankment is the most suitable CRE for managing complex environment, especially when the mean annual ground temperature is 0 ∼ − 1 °C or climate scenarios are RCP 2.6 and RCP 4.5. 4) Transition from low-temperature permafrost to warm permafrost is a warning signal of permafrost degradation under climate warming. 5) With an increase of permafrost degradation rate (the thawing and warming rates of permafrost), embankment stability becomes worse. These findings will not only serve as a scientific basis for the embankment damage prevention of the Qinghai-Tibet Railway, but also provide important technical supports for the successful building of infrastructure in permafrost regions under complex environment.

Shrinkage prediction model of high strength lightweight aggregate concrete based on relative humidity

Concrete shrinkage affects the overall stability and long-term service performance of the structures. Lightweight aggregates (LWAs) with a porous structure are an ideal internal curing material to mitigate concrete shrinkage. Nevertheless, the low elastic modulus of LWAs has a negative impact on concrete shrinkage. In order to clarify the influences of LWAs in the high strength lightweight aggregate concrete (HSLC) on its shrinkage performance, the compressive strength, internal relative humidity (IRH), elastic modulus, and autogenous shrinkage (AS) of HSLC were analyzed experimentally in this study. The correlation of these parameters was investigated. As indicated by the results, compressive strength and elastic modulus were negatively related to the content of LWAs. The 28-day AS and IRH of HSLC and the critical moment of IRH increased by 3.9%, 20.2% and 36 h, respectively, when the content of LWAs increased from 0% to 100%. A linear relationship between AS and compressive strength and an exponential relationship between AS and IRH were established. Additionally, a shrinkage prediction model considering IRH of concrete and water absorption by LWAs was proposed for HSLC.

Dynamics of offshore wind turbine and its seabed foundation under combined wind-wave loading

Over the past two decades, a great number of offshore wind turbines (OWTs) have been built in offshore areas worldwide to harvest clean wind energy resources. The dynamic response and stability of OWTs under environmental loads, e.g., wind and wave, is a key technical problem that engineers are most concerned about. In this study, a wave-structure-foundation integrated numerical model OlaFlow–ABAQUS, which was independently developed through the secondary development, is used to study the dynamics characteristics of a thin-walled steel monopile offshore wind turbine and its seabed foundation under extreme wave and wind loads that would occur in typhoon weather. The wave-induced load imposed on the cylindrical tower of the OWT is determined by solving the VARANS (Volume Average Reynolds Average Navier-Stokes) hydrodynamic equation, the wind load on the turbine blades is estimated by applying the pulsating wind theory, and the mechanical behavior of seabed foundation soil is described by the ideal elastoplastic Mohr-Coulomb model. The computational results show that the OWT and its seabed foundation have a strong dynamic response under the combined action of extreme wind and wave, and there is intensive interaction between them. There is a transient liquefaction zone in the seabed foundation, and the maximum liquefaction depth, in this case, is approximately 2 m. Residual horizontal displacement with a magnitude of approximately 0.4 m occurs at the top of the cylindrical tower of the OWT, resulting in the overall tilting of the OWT. The maximum inclination angle of the cylindrical tower is approximately 0.51°. This angle of inclination may cause significant bending moment and stress concentration in some mechanical components such as the drive shafts and gearboxes that connect to the turbine blades. It reduces the service life of the OWT significantly and also is detrimental to the long-term service performance of the OWT.

Study on the coupling thermal effect of thermokarst lake and high sunny slope on permafrost embankment

Sunny-shady slope and thermokarst lake are widely distributed along the Qinghai-Tibet highway (QTH), and their thermal influence on permafrost embankment can induce serious engineering diseases and affect its long-term service performance. This study aims to reveal the coupling thermal impact mechanism of roadside thermokarst lake and high sunny-slope on permafrost embankment. Firstly, an in-situ ground temperature monitoring site at K2952 + 300 section of QTH has been built and temperature distribution characteristic of observed embankment are investigated. Then, three numerical models are established and spatial–temporal characteristics of asymmetric temperature filed of permafrost embankment have also been analysed and compared. The results show that: (1) Permafrost artificial upper limit of observed embankment has a large fluctuation with the synergy of high sunny slope and thermokarst lake, and severe unilateral thermal erosion leads to the aggravation of subgrade disease despite heat pipes treatment has been adopted. (2) Thermalkarst lake has a certain degree of lateral thermal influence on permafrost embankment, while the magnitude of its thermal impact is related to the distance from embankment. (3) Significant endothermic effect of 5.3 m height sunny slope accelerates the melting depth of embankment underlying permafrost, and triggers off asymmetry morphology of permafrost temperature field. (4) Under the action of ipsilateral thermokarst lake and high sunny slope, the maximum melting depth and thawing plate deviation of embankment underlying permafrost can be exacerbated simultaneously, and the lateral thermal erosion caused by these two factors becomes more intensive as the thermokarst lake gradually approaches the roadbed.

Numerical investigation of seepage dissolution evolution of the bottom expansion cutoff wall in deep overburden

The bifurcation defect at the bottom of the cutoff wall in the deep overburden leads to a sharp increase in the local seepage gradient of the adjacent overburden at the bottom of the cutoff wall, which affects the evolution process of seepage dissolution of the cutoff wall. This study presents a novel type of bottom expansion cutoff wall to alleviate the problem that the seepage gradient of adjacent strata at the bottom of the cutoff wall far exceeds its allowed value. Considering the effects of the pore, aggregate, and convection on the calcium ion diffusion coefficient of concrete, we propose a coupling analytical model of seepage dissolution for two cutoff wall schemes, including the bifurcation defect schemes and bottom expansion schemes, to investigate the evolution of calcium ion concentration, porosity, and seepage characteristics, and to reveal the influence mechanism of the bottom bifurcation defect and bottom expansion of the cutoff wall on the seepage dissolution of the cutoff wall in deep overburden. The results indicate that subjected to the bottom bifurcation defect, the calcium ion concentration of the cutoff wall decreases faster, and the porosity increases faster with the increase of service life compared to the conventional cutoff wall when subjected to the bottom bifurcation defect. With a bifurcation height of 24 m at the bottom of the wall, the service life of the cutoff wall is reduced by 6.64%. In contrast, the novel type of bottom expansion cutoff wall is used to reveal that the concrete porosity increases slowly with the increase of the expansion radius over the same service life. The seepage gradient of the adjacent overburden at the bottom of the cutoff wall is significantly reduced. The service life of the cutoff wall is extended by 47.33% due to its 5 m bottom expansion radius. This study can provide a theoretical basis for the evolution of long-term service performance of the cutoff wall of an earth-rock dam on deep overburden.

Mechanical properties and heavy metal leaching behaviors of municipal solid waste incineration bottom ash as road embankment fillings

With the development of economy and urbanization, the natural gravels and sands for new road construction materials encountered severe shortage issues in recent decades. In the meantime, the municipal Solid Waste Incineration bottom ash (MSWIBA) is regarded as a feasible alternative of mined nature aggregates due to its similar mineralogical, physical and chemical characteristics. However, the uncertainties of long-term service performance and potential environmental pollution risk of MSWIBA prevent its widespread applications in road constructions. For these reasons, this paper investigates the resilient modulus and permanent deformation properties by the repeated load triaxial test at different moisture contents, and examines the long-term environment influence using leaching tests on the samples after subjecting to 5 freeze-thaw cycles and samples after one year weathering. Besides, the existing resilient modulus and permanent deformation prediction models of unbounded granular materials are evaluated for their applicability on MSWIBA. The test results indicate that the MSWIBA shows obvious stress-dependence and moisture-dependence in resilient modulus and permanent deformation behaviors. Moreover, the existing resilient modulus and permanent deformation prediction models with stress and moisture dependence are feasible for MSWIBA as well. Additionally, heavy metal leaching concentrations obtained from column test can meet the standard of surface water quality class V in China. This work is expected to benefit the design work and provide the insight of performance of MSWIBA as road embankment material, and promote its further widespread application in road construction.

An experimental study on microanalytical characterizations and service performances of landfill modified municipal sludge liner materials in contact with leachate

This study aimed to evaluate the long-term service performance of modified municipal dewatered sludge as a landfill liner barrier. Industrial calcium-containing solid waste was used as a modified material for sludge. The shear strength parameters (cohesion c, friction angle φ), compressive strength, and hydraulic conductivity of the modified sludge were studied using direct shear, uniaxial compression, and penetration tests. The leaching toxicity, hydration products, and microscopic morphology of the modified sludge were determined using atomic emission spectroscopy, X-ray diffraction, scanning electron microscopy, and energy dispersion spectroscopy. The corrosion mechanisms of the landfill leachate and acid-base chemical solution on the modified sludge liner barrier were revealed. Under the long-term corrosive environment of the landfill leachate and acid-base chemical solution, the shear strength parameters, i.e., cohesion (c) and friction angle (φ) had values in the ranges of 0.51 − 3.79 MPa and 6.52 − 37.58° of the modified sludge, respectively. The uniaxial compressive strength reached 2.70 − 22.92 MPa, and the permeability coefficient ranged from 0.12 × 10−8 to 3.97 × 10−8 cm/s. After long-term corrosion by landfill leachate and an acid-base chemical solution, the modified sludge liner barrier still had significant bearing capacity and water-blocking properties. Under leachate corrosion, sulfate corrosion (such as ettringite and thaumasite formation) occurred, the modified sludge and some structures were damaged. Under an acidic chemical corrosion solution, alkaline substances, such as calcium hydroxide with hydrogen ions, underwent solvent-out crystallization and chemical dissolution reactions, which caused the decomposition of hydrated gel products such as C–S–H inside the specimen. Under alkaline chemical solution corrosion, the active components in the modified sludge underwent a hydration reaction to form ettringite, C–S–H, etc.

Influence of construction technology on the retroreflective performance of two-component traffic marking

The construction technology of traffic marking has a significant influence on its retroreflective performance. To study the effect of different construction processes on the service performance of traffic markings, two-component spraying paint and two different glass beads were chosen to produce traffic markings that were prepared by single-layer or double-layer spraying, as well as once and twice surface spraying of glass beads. The effects of glass bead coating, spraying times of glass beads and paints on the surface morphology and retroreflective performance of traffic markings were investigated, as well as the variation of the retroreflective coefficient (RC) at the early and middle stages. The results indicated that double-layer spraying was more effective than single spraying. The coated glass beads would decrease the initial RC of the markings, but improved their long-term service performance. The TP-21C has the finest overall retroreflective performance and the lower construction complexity.

Experimental Investigation of Interface Characteristics between Geogrid and Coarse-Grained Soil in a Seasonally Frozen Area

In seasonally frozen soil regions, the influence of temperature change on reinforced-soil engineering cannot be ignored. In particular, the mechanical properties of the reinforced-soil interface have an important impact on the overall stability and long-term service performance of reinforced soil engineering. To explore the interface characteristics and reinforcement mechanism between geogrids and coarse-grained soil under negative temperatures, this paper takes the typical coarse-grained soil in Xinjiang as the material and carries out a direct shear test of the reinforcement–soil interface under different normal stresses, water contents and temperatures. The curve characteristics of the shear displacement-shear stress, the change trend of the peak shear stress and the formation mechanism between the geogrid and coarse-grained soil interface under freezing and nonfreezing conditions are thoroughly analyzed. The formation mechanism of the dilatancy characteristics of the reinforced-soil interface is explained by combining the Mohr-Coulomb strength criterion and apparent friction coefficient. It is concluded that the trend of the shear displacement-shear stress curve between the geogrid and coarse-grained soil interface under the nonfreezing state and freezing state is basically the same. In a state of low normal stress, the curve has no obvious peak, which is closer to the ideal elastic-plastic double linear model. In a state of high normal stress, the curves have more obvious peaks, and the curve type is closer to the elastic-strain softening type. In the nonfreezing state, the shear strength of the reinforcement–soil interface has a great correlation with the water content, which is different in the freezing state. The main sources of the difference are the cementation of pore ice in the soil skeleton in the frozen state, the improvement of the strength of the soil particles themselves, and the further interlocking effect of the geogrid on the soil. In comparison with the reinforced coarse-grained soil under the nonfrozen state, the shear strength under the frozen state is significantly improved. In comparison with coarse-grained soil reinforced by geogrids in the nonfreezing state (0 °C), the shear strength of the frozen state (−5 °C) is significantly improved. Under normal stresses of 40 kPa, 60 kPa, and 80 kPa, when the water content is 2%, the corresponding peak shear stress increases by 19.39%, 21.71% and 11.34%, respectively. When the water content is 4.5%, the corresponding peak shear stress decreases by 29.98%, 16.17%, and 13.83%. When the water content is 7%, the corresponding peak shear stress decreases by 50.85%, 18.64%, and 21.96%. The apparent friction coefficient between the geogrid coarse-grained soil interface in the nonfrozen state and frozen state decreases with increasing normal stress. With the decrease in temperature, the dilatancy phenomenon of the reinforced soil composite is more obvious. The research results can provide a reference for the construction of reinforced engineering in seasonal frozen soil areas.

Study on the Causes of Highway Pavement Cracks in Desert Environment

According to relevant statistics, more than 90% of domestic high-grade asphalt pavement is semi-rigid base pavement, and semi-rigid base cracking is a congenital stubborn disease and common. In Tengger Desert section of Wuma expressway, the temperature difference is large, and the cracking of temperature shrinkage and dry shrinkage is difficult to avoid, resulting in the decline of pavement structure strength. Once the semi-rigid base is cracked, the asphalt pavement is equivalent to a flexible structure; the residual fatigue strength is greatly reduced; the long-term service performance of pavement structure can not be guaranteed; the durability is poor, the damage layer is deep; the repair is difficult and the cycle is long; maintenance costs are relatively high. This paper analyzes the causes of pavement cracks in the harsh environment in the hinterland of Tengger Desert, and studies its mechanism and treatment scheme.

Experimental Research on the Load Transfer Mechanism of Tie Plates for 400 km/h High-Speed Turnouts

Based on the research and development demand of the 400 km/h high-speed turnout, a new type of elastic iron tie plate based on stiffness optimization is proposed. The new elastic iron tie plate is expected to reduce the stiffness unevenness and effectively solve the problems in the use of existing elastic iron tie plates. However, the new plate uses rubber bosses instead of rubber washers. There are certain differences in the force transmission mechanism from the original tie plate because of the change in structure of the new tie plate. In this paper, a series of experiments are designed to quantitatively compare and analyze the overall stiffness characteristics of different tie-plate structures and the differences in bolt force transmission and distribution laws. The main conclusions are as follows. The laws of vertical load transfer and distribution in the new tie plate are remarkably different from those for the original tie plate because of the differences in their structures. Under the rated bolt torque, the force transferred to the upper surface of the tie plate through the rubber boss in the new tie plate is less than that in the original tie-plate structure by 5.18 kN in the assembled state. Further, the new structure also has lower tie plate precompression; hence, the influence on the stiffness characteristics of the tie plate is less than that in the original structure. However, the steel sleeve deflection in the new tie plate is greater than that in the original tie plate; that is, a larger proportion of the bolt preload force is borne by the steel sleeve, thus making the vulcanized rubber under the steel sleeve more vulnerable to shear damage. If put into actual use, the tie plate bolt torque will be somewhat different from the rated torque; because of the difference in the torques coupled with the different vertical load transfer mechanisms between the new and the original tie-plate structures, the precompression and the proportion of the bolt preload force borne by the steel sleeves of the two tie plates will also show different degrees of deviation corresponding to different deviations of the tie plate bolt torque. Therefore, the new tie plate structure needs to be further optimized to make the transfer mechanism of preload force of bolt as consistent with the original tie plate as possible. In addition, the vibration and deformation characteristics and long-term service performance of the new type of plate under the condition of vehicle passing will be studied through a small-scale field trial and systematic dynamic tests.