Load Reduction Rate Research Articles

Sponge City and Water Environment Planning and Construction in Jibu District in Changde City

Urban waterlogging and urban water environment problems in Changde city caused by extreme weather have seriously hindered the sustainable development of cities. A sponge city not only involves the inheritance and development of foreign technology but also a new method for its use. The background of sponge city construction based on green infrastructures in China was introduced in this study. As one of the first pilot construction cities based on the sponge concept, Changde city possesses natural geographical advantages. The current urban situation, rainfall type and water environment in the sponge construction area were analyzed and the causes of urban waterlogging and deterioration of urban inland river water quality are presented. Based on the urban water environment and ecological status, the specific strategic objectives of the sponge city transformation are given. Meanwhile, the overall technical route and the concrete realization path of each index, such as the water environmental system, water ecological system and security system, are also presented. The annual net flow total control rate and the runoff pollution reduction reached 77.56% and 45.18%, respectively. The total runoff and peak flow were also reduced by 35.08% and 26.82%, respectively. Meanwhile, the peak flow of runoff pollution concentration was reduced by 31.99%. The pollutant load reduction rate of non-point source pollution in the area reached more than 45%. The project not only alleviated the problems of urban waterlogging and black and odorous water bodies but also ensured the sustainable development of the urban water environment.

An adaptive surrogate model approach for random vibration analysis of the train–bridge system

To improve the efficiency of random vibration analysis of the train–bridge system, a new approach is proposed based on the adaptive sampling (AS) surrogate model in this paper. First, an initial sample set and a candidate sample set are generated by the method based on Generalized F (GF)-discrepancy. Second, a theoretical model is used to calculate the maximum dynamic response of the train–bridge system corresponding to the initial sample set, and a surrogate model based on Gaussian process regression (GPR) is constructed. Third, the learning function is used to identify new samples in the candidate sample set to optimize the current surrogate model until it meets satisfactory prediction accuracy. Finally, the maximum dynamic response of each sample in the representative sample set is predicted by the final surrogate model, and then the statistical properties of the dynamic response of the train–bridge system are analyzed. To verify the effectiveness of the proposed method, the distribution of training sample points and prediction accuracy of the AS surrogate model and the one-stage sampling (OS) surrogate model are compared and analyzed, taking the prediction of the maximum wheel load reduction rate (WLRR) of a train on the bridge as an example. On this basis, the prediction accuracy of the AS and OS surrogate models for the random characteristics of the train on the bridge is evaluated. The results show that the proposed method can significantly improve the prediction accuracy of the surrogate model without increasing the number of training samples.

Effect of frost heave deformation of bridge foundation on operation safety of high-speed railway

The frost heave deformation of the bridge foundation in seasonal frozen soil regions threatens the safe operation of high-speed trains. The first high-speed railway in extremely cold zones, the Harbin-Dalian Line, is used as the background in this study, and finite element analysis (FEA) is used to investigate the impact of freezing temperature and moisture content on the frost heave force and deformation of the bridge foundation. Furthermore, the dynamic response of the train crossing the frost heave deformation region of the bridge foundation is analyzed based on finite element (FE) and multi-body dynamics co-simulation. Conclusively, the frost heave threshold of the bridge foundation is proposed in accordance with the limit of the train’s dynamic response indicators. The results indicate that the normal frost heave stress at the bottom section of the cap is distributed in a “W” shape along the lateral direction of the cap. The magnitude of the stress at the edges of the cap and the inner hole of the pile foundation is relatively large. the frost heave deformation is negatively and positively linked with the fluctuations of temperature and moisture content, respectively. The train's vertical acceleration grows gradually as the pier's upward deformation increases, while there is no discernible relationship between the train’s lateral acceleration and the pier’s upward deformation. Additionally, variations in the train speed and the pier’s upward deformation are positively correlated with the derailment coefficient and wheel load reduction rate. To enable the high-speed railway’s operation safety, it is proposed that the deformation threshold of frost heave be 14.4 mm.

Study on Impact Load and Head Cap Load Reduction Performance of Vehicle Entering Water at High Speed

Aiming at the problem of high-speed entry of vehicles with a diameter of 200 mm, a numerical model of high-speed entry of vehicles is established based on the arbitrary Lagrange–Euler (ALE) algorithm, and the numerical simulation of high-speed entry of flat-nosed and round-nosed vehicles is carried out. On this basis, the experimental research on the entry of vehicle with buffer caps is carried out. The following conclusions are obtained through simulation. The peak value of the axial load of the vehicle raises with the increase of the inlet velocity and angle, while the stable value only raises with the increase of the inlet velocity. The impact load on the round-nosed vehicle is obviously smaller than that on the flat-nosed vehicle when the water entry angle is greater than 80°. The peak value of axial load can be reduced by 22% when entering water vertically at 100 m/s. The following conclusions are obtained through experiments. The buffer head cap has a significant load reduction effect. It shows compaction, cracks and breakage under the impact of water. These processes can absorb part of the impact energy, reduce the peak value of axial load and increase the pulse width. The load reduction rate grows from 4.7% to 18.5% when the length of the buffer head cap is increased from 200 mm to 300 mm while the water inlet speed is the same. The damage level of the head cap increases sharply, and the load reduction rate raises when the water entry speed is increased while the length of the buffer head cap is the same.

Study on the threshold for superposed deformation of simply supported bridge creep and track slab upwarp in high-speed railway

Based on long-term inspection data about track geometric irregularity of 32 m-span simply supported girder bridge in China Railway High-Speed for nearly 10 years, it is found that there is continuous periodic track longitudinal level (TLL) with different wavelengths, thereinto, simply supported girder bridges creep and ballastless track slab upwarp are the primary reasons. Moreover, there are two types of variation trends for bridge creep of 32 m simply-supported bridges with ballastless track, that is, stable type and increasing type, and the maximum [Formula: see text] (the peak-to-peak value of track longitudinal level) is 7.1 mm for track longitudinal level caused by bridge creep, and the maximum [Formula: see text] caused by upwarp deformation of ballastless track slab is 3.2 mm. Hence, this paper investigated the effects on running performance and structure service performance of random track irregularity and additional track irregularity caused by bridge creep, track slab upwarp deformation or superposition of both, a three-dimensional finite element model of vehicle-track-bridge for dynamic simulation calculation was established, the threshold values for bridge creep and track slab deformation under 350 km/h were proposed based on running performance and structure service performance. Finally, research results show that bridge creep influences on the ride comfort significantly, but running safety barely. Due to the short wavelength of TLL, the track slab upwarp deformation affects both the ride comfort and running safety heavily. The car bodies are more sensitive to bridge creep and produce mainly low-frequency vibration, but the rate of wheel load reduction is more sensitive to the track deformation and shows the high-frequency vibration. For 32 m simply supported bridges without track slab deformation, the [Formula: see text] caused by bridge creep should be limited to 7 mm, and 9 mm in difficult situations. When the [Formula: see text] caused by bridge creep is small (less than 5 mm), the [Formula: see text] caused by track slab upwarp deformation must be less than 4 mm. When both deformations exist simultaneously, the [Formula: see text] caused by superposition deformations of both should not exceed 10 mm, with track slab upwarp deformation not exceeding 4 mm. In the presence of both structural deficiencies, it is suggested that the track slab deformation must be eliminated when it is difficult to eliminate the bridge creep.

Impact of co-contamination by PAHs and heavy metals on micro-ecosystem in bioretention systems with soil, sand, and water treatment residuals

Rainfall runoff contained toxic pollutants such as polycyclic aromatic hydrocarbons (PAHs) and heavy metals. Bioretention systems can effectively remove PAHs and heavy metals from runoff. When PAHs and heavy metals accumulated in the media of bioretention systems, co-contamination occurred. To reveal the response processes of co-contamination in the media micro-ecosystem, bioretention systems were constructed and simulated rainfall tests were carried out to reveal the media micro-ecosystem evolution in the bioretention system under the co-contamination of PAHs and heavy metals. The simulated rainfall tests showed that the bioretention systems with different media had good purification effects with load reduction rates >90% (PAHs) and >40% (heavy metals). The microbial α-diversities in different media decreased by 6.67%–32.27%, and 9.21%–18.69% after the tests. The most dominant species of microorganisms in the media were Proteobacteria (all relative abundances >62%). As a typical PAHs-heavy metal degrading bacteria, the relative abundances of Pseudomonas increased significantly after the tests (both >9%). The co-contamination of PAHs and heavy metals inhibited all enzyme activities. The long-term operation of the bioretention system gradually increased the level of co-contamination in the media, and the stability of the media micro-ecosystem gradually deteriorated. The results of this paper can provide a theoretical basis and technical support for maintaining the operational efficiency of the bioretention system with modified-media and avoiding the risk of potential contamination.

Analysis of Thermal Pollution Reduction Efficiency of Bioretention in Stormwater Runoff under Different Rainfall Conditions

The thermal pollution of stormwater runoff is an important factor in the degradation of the urban water environment. Bioretention is an effective way to control the thermal pollution of stormwater runoff. To understand the influence of different rainfall conditions on the reduction of thermal pollution load of rainwater runoff from bioretention facilities and the correlation between the parameters, an experimental study was carried out by using the Beijing P&C rainfall pattern to change the rainfall parameters. By proposing innovative evaluation index parameters and analysis methods, the correlation between different parameters was quantified. The results showed that the heat pollution load reduction rate (HR) had a strong negative correlation with rainfall inflow volume (IV), rainfall duration (RD), and the service area ratio of bioretention facilities (CAR), and the correlation coefficients were −0.95, −0.73, and −0.73, respectively. HR was weakly correlated with rainfall return period (RP), rainfall temperature (RT), and air temperature (At) during the experiment, and the correlation coefficients were −0.29, 0.20, and 0.20, respectively. The delay between the peak value of heat output from the bioretention and the peak value of heat input from rainfall was about 10 min. Through the research on the change of rainwater heat entering and exiting the facility, we can master some rules of heat reduction in bioretention facilities, which will provide a reference for subsequent research on the difference between the internal heat change and bioretention temperature change.

An Improved Optimal Routing Strategy on Scale-Free Networks

Traffic dynamics have drawn more and more attention from physical and engineering field recently. In this brief, we focus on the traffic capacity that can be measured by the critical point of phase transition from free flow to congestion, and propose a routing strategy by constructing a cost function based on the ratio of degree to closeness centrality to improve the transportation efficiency of scale-free network. The maximum node betweenness, average path length and traffic load are investigated with simulations. Moreover, load reduction rate, load mean, and load variance are introduced to analyse the traffic distribution. Remarkable improvement of traffic capacity and more even load distribution can be achieved with our strategy, which is much better than the efficient routing (ER) strategy.

A New Derailment Detection Method of Rail Vehicles

Aiming at the problem of train derailment detection, researchers at domestic and abroad mainly focus on the derailment coefficient and wheel load reduction rate, but the derailment coefficient and wheel load reduction rate can’t accurately reflect the status of rail vehicle derailment in time. In this paper, a new derailment detection method of rail vehicles is designed based on the lateral acceleration and roll angle as the key characteristic physical quantities of wheelset derailment. Firstly, the virtual simulation method is used to grasp the characteristics of the key physical quantities. Then, the appropriate scheme of derailment detection system is proposed to measure the key characteristic physical quantities and judge whether the rail vehicle is derailed. Finally, the simulation data is used to prove the effectiveness of the detection method, which can lay the foundation for the practical engineering application.

Investigating the influences of concave depths on stormwater runoff and pollution retention of urban grasslands.

In this study, scale-based runoff plots of concave grasslands were designed and simulated rainfall experiments were conducted to investigate their retention effectiveness for runoff volume and pollutant loads, and to analyze the influences of concave depths on runoff and pollution retention of grasslands. Results showed that mean time to runoff of concave grasslands was 88.5 minutes, which was 5.3 times than that of flat grassland. Average peak flow rate of concave grasslands was reduced by 36.2% compared with flat grassland. Concaved grasslands averagely retained 58.2% of stormwater runoff. Deeper concave depths significantly increased runoff detention and retention performance of grasslands. Total suspended solids (TSS) load reduction rates of concave grasslands were ranged from 50.8% to 97.3%. Total nitrogen (TN) load reduction rate was 49.8% for concave depth of 10 cm. Total phosphorus (TP) load reduction rates were 45.0% and 93.9% for grasslands with 5 cm and 10 cm concave depths, respectively. Pollution load reduction rates of TSS, TN and TP enhanced along with the increase in concave depths. The estimated minimum area ratios of upslope impervious surface to grasslands of 5 cm and 10 cm concave depths were approximately 1:1 under 20 mm rainfall events, and 38:1 under 5 mm rainfalls, respectively.

Simulation of dynamic performance and wheel-rail wear of railway wagon under deviation of cargo gravity center

A multibody dynamic model of railway wagon is established by Simpack software, and the derailment coefficient, wheel load reduction rate, impact angle and wear index of freight car are calculated under different gravity center offsets and different curve conditions. The simulation results show that the lateral and longitudinal offsets of cargo gravity center have a great influence on the derailment coefficient, wheel unloading rate, impact angle and wear index of the vehicle. The larger the offset of the cargo gravity center is, the worse the operation performance of the wagon is, the more serious the wheel-rail wear is, and the shorter the transport life of the wagon is. The smaller the radius of the curve is, the greater the impact is.

Characteristics of rail deformation caused by tunnel floor heave and corresponding running risk of high-speed train

• A four-year-long observation of uneven rail deformation is performed in two HSR tunnels. • The predominant wavelength and amplitude of rail deformation in tunnel are 3–30 m and 2–10 mm, respectively. • The heave transfer within track structure exhibits more significantly on wavelength than on amplitude. • Speed raising has strong effects on the magnitude and location of wheel-rail contact force. • The risk of derailment and passenger comfort is more sensitive to short- and long-wavelength floor heave, respectively. Floor heave is a huge threat to the safe operation of high-speed trains in tunnels. However, rare research recognizes the characteristics of the rail irregularity caused by tunnel floor heave and the corresponding running risk of high-speed trains. In this paper, uneven rail profiles observed within four years in two HSR tunnels are used to investigate the temporal variation and spatial distribution of tunnel floor heave. The predominant wavelength and amplitude of the heave profile are determined. Hypothetic floor heave profiles with a wide range of wavelength and amplitude are used as the input in the simulation of the dynamic response of a VRT (vehicle-rail-track) system. Based on the simulation, the transfer laws for the wavelength and amplitude of heave within the track structure are revealed. The wheel-rail contact force, the wheel load reduction rate, and the sperling factor under various floor heave profiles are calculated. The floor heave profile that may lead to a high risk of derailment and low passenger comfort is presented for two train speeds. The research reveals that the predominant range of the wavelength for the rail heave in the tunnel is from 3 m to 30 m, and that of the amplitude is 2 mm to 10 mm. The heave transfer law within the track structure is strongly affected by both the wavelength and amplitude of the floor heave profile. The deformation of the rail varies more significantly on wavelength than on amplitude. Speed raising strongly influences the wheel-rail contact force, the wheel load reduction rate, and the sperling factor. The passenger comfort is more sensitive to longer-wavelength floor heave, whereas the risk of the derailment is more sensitive to shorter-wavelength floor heave.

Application and evaluation of phase change materials for improving photovoltaic power generation efficiency and roof overheating reduction

With the development of countries, concerns about global warming have increased. Many countries are taking steps to implement green building-related policies to reduce carbon dioxide emissions; however, these policies are generally applied to new buildings. Therefore, this study focused on the applicability of phase change materials (PCMs) and the optimal application method for educational buildings that have a long service period and are difficult to dismantle among existing buildings. The best application is focused on reducing the building energy demand. phase change materials were applied to address concerns regarding surface temperatures of the building. The passive element, phase change material integrated brick, was applied to the roof, while the active element was a phase change material packed into the back of photovoltaic (PV) panels. Five scenarios were considered in assessing these technologies. photovoltaic installation on the roof surface was assumed for all scenarios, except scenario 1. In scenario 3, the phase change material was applied to the back of the photovoltaic panel, and in scenario 4, a brick layer impregnated with the phase change material was added to the roof surface. In scenario 5, the technologies of scenarios 3 and 4 were applied in combination. As a result of the analysis across the five scenarios, a maximum annual cooling load reduction of 14 521.6 kWh was derived. The overall heating demand increased, with the maximum annual heating demand increasing by 7134.2 kWh. Electrical energy was produced by installing photovoltaic panels, and energy savings were achieved; the highest overall load reduction rate was 22.55%. The calculated shortest payback period was seven years, which is reasonable. Based on cost and energy aspects, scenario 4 is considered the optimal retrofit plan. These results suggest that significant cost and energy savings can be achieved through building renovation with phase change materials.

A vertical coupling dynamic analysis method and engineering application of vehicle–track–substructure based on forced vibration

PurposeThis study aims to propose a vertical coupling dynamic analysis method of vehicle–track–substructure based on forced vibration and use this method to analyze the influence on the dynamic response of track and vehicle caused by local fastener failure.Design/methodology/approachThe track and substructure are decomposed into the rail subsystem and substructure subsystem, in which the rail subsystem is composed of two layers of nodes corresponding to the upper rail and the lower fastener. The rail is treated as a continuous beam with elastic discrete point supports, and spring-damping elements are used to simulate the constraints between rail and fastener. Forced displacement and forced velocity are used to deal with the effect of the substructure on the rail system, while the external load is used to deal with the reverse effect. The fastener failure is simulated with the methods that cancel the forced vibration transmission, namely take no account of the substructure–rail interaction at that position.FindingsThe dynamic characteristics of the infrastructure with local diseases can be accurately calculated by using the proposed method. Local fastener failure will slightly affect the vibration of substructure and carbody, but it will significantly intensify the vibration response between wheel and rail. The maximum vertical displacement and the maximum vertical vibration acceleration of rail is 2.94 times and 2.97 times the normal value, respectively, under the train speed of 350 km·h−1. At the same time, the maximum wheel–rail force and wheel load reduction rate increase by 22.0 and 50.2%, respectively, from the normal value.Originality/valueThis method can better reveal the local vibration conditions of the rail and easily simulate the influence of various defects on the dynamic response of the coupling system.

Administrative responsibility and land-sea synergistic regulating indicators for nutrient pollution: Linking terrigenous emission to water quality target in Laizhou Bay, China

Globally, many bays have been subjected to water quality (WQ) deterioration, due to excessive discharge of terrigenous total nitrogen (TN). In China, several projects have been implemented to control TN loads; however, due to the lack of linkage between a bay’s polluted segments and its basin’s jurisdictions, the WQ improvement efficiency usually is lower than expected. In this study, we focus on the basin of Laizhou Bay (LZB), China. A series of differentiated TN reduction indicators for 13 cities in the basin of LZB were developed on the base of the total maximum allocated loads (TMALs), which meets the WQ standard of LZB. Four land-sea synchronous investigations were conducted to discern seasonally polluted segments of LZB in 2017. The seriously nitrogen-polluted segments located at southwest and southeast of LZB and the largest area accounted for about 70% of LZB. Due to the heterogeneity of the terrigenous TN load and TMALs of the 13 jurisdictions in the basin, the responsibility apportionment rate for the nitrogen-polluted segments showed a spatial disparity, the city of Weifang with the highest value of 32%, followed by Zibo (28%), Ji’nan (20%), and the other 10 cities (19%). Accordingly, the TN load reduction rate among the 13 jurisdictions varied from 1% to 99%, with an average of 62%. The average values for reduction rate of TN generation, increase rate of TN removal by wastewater treatment, increase rate of TN retention in soil matrix, and TN attenuation in riverway were 44% (21%-69%), 53% (0–88%), 31% (0–61%), and 63% (15–84%), respectively. The three-dimensional seawater quality model simulation results showed that the “precise reduction indicator scheme” was six years earlier than the “equal percent reduction indicator scheme” in each jurisdiction to achieve the WQ standard. Seven cities need to cut emissions more than the current rate. The precise indicators throughout the land-based pollutant entire migration pathway will help implement the TN reduction plan more efficiently.

Running Safety Assessment of a Train Traversing a Long-Span Bridge Under Sudden Changes in Wind Loads Owing to Damaged Wind Barriers

In the event of partial damage to the wind barriers installed on a bridge, the wind loads of a train will change abruptly as they enter and exit the damaged area, resulting in the deterioration of the train running safety. This study aimed to assess the running safety of a CRH2 high-speed train traversing a four-tower cable-stayed bridge with damaged wind barriers. Formulas were deduced for the static and dynamic wind loads on the bridge and train and their combined effect. The aerodynamic coefficients of the train and bridge were obtained through wind tunnel tests of a train–bridge sectional model, and a model of the wind–train–track–bridge coupled system was established using multi-body dynamics and the finite element method. The effects of the length of the damaged area and average wind speed on the train running safety were investigated based on the proposed model. The results reveal that the car body lateral displacements and accelerations reach their maximum amplitudes when the vehicles enter and leave the damaged area, respectively. The amplitude of the car body lateral displacement increases as the length of the damaged area increases, until it reaches 72[Formula: see text]m. The wheel load reduction rates (WLRRs) and derailment coefficients (DCs) of the vehicles increase owing to the damage of the wind barriers; however, the percentage increases for each vehicle are considerably different. The train can safely traverse the damaged area of wind barriers at a designed speed of 180[Formula: see text]km/h when the average wind speed is lower than 10[Formula: see text]m/s. When the average wind speed reaches 20[Formula: see text]m/s, the train can still safely cross the damaged area if the length of the damaged area is less than 12[Formula: see text]m.

Impact of nutrient removal on microbial community in bioretention facilities with different underlying types/built times at field scale

As the bioretention facilities have been extensively built in the construction of “Sponge City” in China, urban non-point source pollutants could be effectively controlled. The influences on microbial community in three bioretention facilities with different underlying types/built times at field scale were studied. The results showed that nutrient loads in road runoff were 1.1–3 times higher than of roof. Compared with the other two rain gardens, the bioretention tank (BT) was relatively stable and showed >90% nutrient load reduction rates. The nutrients brought by the stormwater runoff changed the original habitat in the soil. Nutrient removal led to the deterioration of the living environment of microorganisms, and then the number of microorganisms and diversity changed. Ten dominant bacteria species were found in the facilities, and Proteobacteria were the most dominant bacteria phyla, with the relative abundances all >30%. Suspended solids were found to be the most important factor and had a high correlation to the most dominant microorganisms. With the increased operation period, the microorganism species tended to be concentrated on Proteobacteria, resulting in decreases of other functional microorganisms. The bioretention facility with the road underlying had the lowest microbial diversity, and the built time was the factor that had the greatest impact on microbial diversity. Based on these results, the future design and construction of bioretention facilities should consider the risk after nutrients entered the bioretention facility and the changes in microbial diversity.

Dynamic Characteristics of Metro Vehicle under Thermal Deformation of Long-Span Cable-Stayed Bridge

In order to study the influence of thermal deformation of long-span cable- stayed bridge (LSCSB) on the dynamic characteristics of metro vehicle on the bridge, based on the theory of vehicle-track coupled dynamics, the rigid-flexible coupled dynamic model of metro vehicle-track-LSCSB system is established by using finite element method and multi-rigid-body dynamics. Adopting this model, the deformation of LSCSB subject to temperature is analyzed, then the comprehensive effect of track random irregularity and rail deformation caused by temperature load is considered to study the dynamic characteristics of metro vehicle running through the bridge, and finally the influences of temperature increment and running speed on concerned dynamic indices of vehicle are studied. The results show that the LSCSB deforms obviously subject to temperature load, and the overall performance is that the cooling is arched, and the heating is bent, and the shape variable changes almost linearly with the temperature load. According to the parameters studied in this paper, the rail deformation caused by temperature load increases the wheel-rail vertical force, derailment coefficient and wheel load reduction rate by 1.5%, 3.1% and 5% respectively. The vertical acceleration of the vehicle body decreases by 2.4% under the cooling condition, while increases by 3.7% under the heating condition. The dynamic response of the bridge changes under temperature load. The maximum vertical and horizontal displacement in the middle of the main beam span are 6.24 mm and 2.19 mm respectively, and the maximum vertical and horizontal acceleration are 1.29 cm/s2 and 2.54cm/s2 respectively. The derailment coefficient and vertical acceleration of vehicle body are more affected by temperature load, and the wheel load reduction rate and wheel-rail vertical force are more affected by speed. The conclusion of this paper provides a reference for subsequent scholars to study the influence of thermal deformation on the dynamic response of vehicles on LSCSB.

Evaluation of ammonia and nitrate distribution and reduction within stormwater green infrastructure with different woody plants under multiple influencing factors

The impact of stormwater green infrastructures (GIs) with different woody plants on nitrogen (N) distribution is still poorly understood. Laboratory experiments were conducted for GIs without or with Sophora japonica and Malus baccata to investigate the distribution of NH3–N and NO3–N. The test data was utilized to calibrate and validate the HYDRUS-2D. The validated model was subsequently used to analyze the distribution of NH3–N and NO3–N within the different GIs under three different rainfall conditions: inflow/runoff pollutant concentration, rainfall recurrence interval (runoff amount of a rainfall event), and number of dry days (during which no rainwater infiltrates into the soil). The average NH3–N and NO3–N concentrations in the upper soil (0–30 cm) of the GIs were about 4.8 and 2.4 times those of the lower layer (30–60 cm). Compared to the control (Vc), the average NH3–N concentrations in soil with Sophora japonica (Vs) and Malus baccata (Vm) decreased by 15.8% and 35.1% while those of NO3–N decreased by 15.5% and 27.2%, respectively. Degrees of influence by the three factors on the average soil NH3–N and NO3–N concentrations were inflow concentration > number of dry days > recurrence interval. The number of dry days was the smallest influence factor for the overflow N load while the inflow concentration was the most significant influence factor for the outflow, bio-utilization, and soil nitrogen loads. Compared to the control, outflow (groundwater recharge) loads of NO3–N from the Vs and Vm increased by 14.0–16.6% and 3.7–6.8%, respectively under different conditions. The overflow (runoff) loads from Vs and Vm decreased by 16.8–36.3% and 6.6%–8.4%, respectively. A multiple regression equation was used to establish a quantitative coupling relationship between N pollutant load reduction rates and influence factors (R2 ≥ 0.83). This relationship can be used to estimate the runoff treatment effectiveness of green infrastructure on target pollutants.

Train Derailment Process Analysis on Heavy Haul Railway Bridge under Ship Impact

In order to research train derailment law under ship impact, the spatial vibration calculation model of a freight train-track-bridge (FTTB) system is used to establish the vibration model of the FTTB system under ship impact. Meanwhile, the calculation method of a train derailment process under ship impact is proposed based on the random analysis method of train derailment energy. Further, the train derailment process on a bridge under ship impact is calculated, and the variation law of the FTTB system spatial vibration response under different impact loads and speeds is analyzed. The results show that the ship impact load has a great influence on wheel lift value. When the impact load is greater than 15 MN, the wheel derails more easily. With the increase of impact load, the derailment coefficient, wheel load reduction rate, and lateral relative displacement of bogie and rail, the lateral displacement of the bridge increases significantly, but the limits of them make it difficult to determine whether the wheel has derailed. The lateral relative displacement of the bogie and rail considering the safety factor is calculated at the moment of derailment, which is taken as the early warning threshold of train derailment. The above conclusions can provide a reference for controlling train safety under ship impact.