Abstract:Aiming at the phenomenon that the wet joints of precast bridge decking are damaged by impact load during service, a functional gradient composite structure design concept was introduced to design a wet joint of functional gradient of precast bridge decks. Taking the relative functional layer thickness and the compressive strength of the UHTC layer as the main variation parameters, the impact resistance of wet joint model specimens was studied by using drop-weight impact test. The results show when the compressive strength is constant, the impact life increases exponentially with the increase of the relative thickness of the functional layer, and the prediction model of the impact toughness of wet joint model specimens about the relative functional layer thickness is established. For the model specimens with the same thickness of UHTC, the impact energy consumption decreases with the increase of the compressive strength of UHTC layer, and the reduction range increases with the increase of the compressive strength of UHTC layer. There is a linear correlation between the initial crack life and the final crack life with different compressive strengths. According to the grey correlation analysis, the degree of influence of the three factors on the fracture life is ranked from strong to weak as follows: initial crack life＞relative functional layer thickness＞compressive strength＞0.5. On the basis of the above, two prediction models of failure impact life, including Model_Ⅰ and Model_Ⅱ，are established. The results show that the prediction accuracy of Model_Ⅰ is high and its applicability is good, while the accuracy and applicability of Model_Ⅱ are poor.

Abstract:Overhanging rock aggregates are the physical basis to trigger large-scale collapse disaster, and it is a major scientific problem in geological disaster monitoring and early warning for overhanging rock aggregates to rupture. This paper established an experimental model to explore exciting vibration of overhanging rock aggregate, and carried out an experiment, which produced about 270 000 pieces of excitation signal data characterized by acceleration. Experiments show that interface integrity between overhanging rock attenuates the transfer efficiency of excitation signal in the aggregates. Meanwhile, main excitation and secondary excitation consist in exciting signal. In the experiment, main excitation appears from 20 ms to 50 ms, and secondary excitation occurs at the 90~100 ms. Especially, dispersivity of secondary excitation is negatively correlated with interface integrity on overhanging rock. The failure of overhanging rock in overhanging rock aggregate is random, however, exciting action is inevitable in aggregate when overhanging rock failure occurs. Model test implies that the main excitation may be the excitation factor of the large-scale and super-large-scale collapse disaster, while the secondary excitation is the pacemaker to trigger avalanche failure of overhanging rock aggregate. The research results provide scientific reference for further study on failure mechanism of overhanging rock aggregate.

Abstract:For the railway in operation period, the high-speed railway subgrade outside its subgrade with the new cantilever retaining wall and other new loads will inevitably produce a certain displacement deformation on the existing subgrade and affect the smoothness of the track. In this paper, based on the construction of the cantilever retaining wall subgrade section of the Nanchang-Jingdezhen-Huangshan railway, combined with the actual conditions, the finite element analysis platform (PLAXIS 3D) is used to establish a three-dimensional numerical analysis model, and the HSS model is adopted to analyze the influence of the new cantilever retaining wall embankment on the adjacent existing lines, and the causes of the disturbance are explained. The actual construction standard value is used to control, and high-pressure jet grouting pile and isolation pile are applied to solve the disturbance caused by the new line to the existing line. Then the control efficiency of various measures is evaluated, and the key control points that need to be focused on for the new embankment of the parallel line are put forward. The calculation results show that the scheme of “8 m high pressure jet grouting pile + 4 m isolation pile” can effectively reduce the deformation of adjacent existing lines. The research results can not only be directly applied to the railway project, but also to the new high-speed railway project in the future, providing construction experience.

Abstract:It is necessary to understand the bending moment distribution law of each surrounding pile, especially under the dynamic load of train, when the surrounding pile-soil arch chord coupling anti-sliding structure (SPSC-AC anti-sliding structure) is used in the control design of creep of high speed railway subgrade. Based on the study of creep mechanism and deformation characteristics of subgrade in a bridge-tunnel transition section of the express railway, a three-dimensional numerical model of subgrade creep protected by SPSC-AC anti-slide structure was established by using Midas/GTS NX,and the non -linear dynamic time course + finite element strength reduction method is adopted to analyse the governing effect of the SPSC-AC anti-slid structure and explore the bending moment characteristics and distribution of the SPSC-AC anti-sliding structure under the dynamic load of different train speeds，and suggesting optimisations.The result shows: Spacing 4d arrangement of main control surrounding piles of the SPSC-AC anti-sliding structure, The distribution of bending moment value of each surrounding pile is roughly in the shape of inverse S; At a certain speed, the variation of the maximum bending moment of each surrounding pile with time is basically the same, showing the shape of "simple harmonic"; With the increase of train speed, the bending moment of surrounding pile in stable stage also increases;At a certain speed, the bending moment of each surrounding pile in the stability stage is No.1 pile ＞ No.3 pile ＞ No.2 pile ＞ No.8 pile ＞ No.4 pile ＞ No.7 pile ＞ No.5 pile＞No.6 pile ; The bending moment distribution ratio of each enclosure pile is 1.00 for No.1 pile, 0.51 for No.3 pile, 0.46 for No.2 pile, 0.46 for No.8 pile, 0.46 for No.4 pile, 0.33 for No.7 pile, 0.31 for No.5 pile and 0.29 for No.6 pile. The research results can provide a basis for the engineering control design of subgrade creep prevention of high-speed railway.

Abstract:In view of the problems of water leakage and structural damage in the tunnel, to find out the location of high water pressure leakage point or imminent leakage, and to quantify the water pressure, the indoor model pressure test of cracked concrete was carried out to simulate the seepage of cracked lining under different water pressure conditions. The temperature distribution of the seepage surface of concrete block was observed by infrared thermal imaging camera to study the correlation between seepage pressure, the size of the crack and temperature. The experimental results are as follows: the seepage volume is proportional to the width of the crack and the water pressure. Under the same crack conditions, the higher the water pressure is, the faster the seepage velocity is. Under the same water pressure conditions, the more the crack develops, the greater the seepage velocity becomes. The seepage area of the non-penetrating crack seepage surface is often larger than the seepage area of the penetrating crack seepage surface. The temperature is usually the lowest at the maximum seepage flow, so the minimum temperature point in the tunnel seepage area can be found by using infrared thermal imaging camera scanning to determine the most suitable punching and pressure relief position.

Abstract:Epoxy resin is a kind of plugging material used in the joints of shield tunnels, which has broad application prospects. The systematic analysis of the influencing factors and change rules of its mechanical properties can provide guidance for the design and construction of the joints of the tunnels, thus improving the waterproof capacity and extending the life of shield tunnels. In this paper, the stress analysis of epoxy resin material is carried out through experiments and numerical simulations, and the influence of related factors on its mechanical state is explored. The conclusion is drawn as follows: ① The bonding strength of epoxy resin: dry adhesion＞ wet surface adhesion＞ complete; in the underwater environment, the bond strength is relatively high under dry and wet surface conditions, and the difference is not much, but the degree of decline is more obvious in the completely underwater environment. ② As the bonding thickness increases, the bonding strength of epoxy resin decreases, the unevenness of the bonding surface stress increases, and it is easy to cause damage at the end. ③ The low modulus epoxy resin material has strong ductility, which can reduce the peak stress and better resist the deformation of the pipe joints. ④ As the displacement of the tube segment increases, the stress on the epoxy resin bonding surface also increases. The opening amount of the tube segment mainly affects the stress value, and the amount of misalignment of the tube segment mainly affects the uniformity of the stress distribution. ⑤ The greater the water pressure is, the greater the stress value of the epoxy resin bonding surface is.

Abstract:Due to the consideration of anti-floating and shield launching safety, the foundation pit of an ultradeep circular shield launching shaft was dewatering outside the pit. However, the surrounding strata settlement was large. The dewatering was stopped and the original groundwater level was restored according to the requirements. In this paper, based on the field monitoring, theoretical and numerical methods were used to study the influence of anti-floating and permeability coefficient of the foundation pit on the retaining structure under high water level. The results show that the foundation pit can rely on the self-weight of retaining structure to resist the buoyancy of groundwater without considering the friction between retaining structure and stratum. Under the same water level, the permeability coefficient of the soil layer at the bottom of the retaining structure is the main factor affecting the uplift of the retaining structure.

Abstract:In order to assess potential risks bridge static test, the equation which adopts the reliability theory that based on probability analysis was deduced to calculate the failure risk of the bridge and the static load test of single beam. The allowable reliability index of the static load test and the risk evaluation method which can be used for the static load test of new bridges, old bridges, elevated bridges and precast beams is proposed, as is illustrated with examples. This method is used to calculate the allowable values of the attenuation coefficient of resistance and the lifting coefficient of basic members, and to define the bridge range that should be evaluated by test. The effects of various influencing factors on the test reliability index were analyzed, and the structural reliability was compared when different test control load value methods were adopted. The results showed that the test reliability index of new bridge was directly proportional to the ratio of dead to live、dead (constructed) to dead (unconstructed). The former was the main factor, and the latter only affected when the ratio of dead to live was not more than 0.5. The decrease of resistance and the increase of vehicle load effect make the test reliability index decrease. When the resistance decreases by 30%, the average decrease of test reliability index is 1.4~2.3, and when the vehicle load effect increases by 50%, the average decrease of test reliability index is 0.7~1.1.

Abstract:Based on the idea of the division of the unit section with unequal length, combined with the attribute characteristics of the infrastructure in the unit section, and taking the track quality index(TQI) as the standard of the division of the unit section, a dynamic division method for unit section considering line state, infrastructure attribute and maintenance capability was proposed. The principle and priority of the division of the unit section were determined. The division of unit section was realized in two stages. The first stage was the division of unequal length and fixed unit section, which could reflect the basic situation of the line infrastructure. In the second stage, the bottom -up algorithm was employed to divide the section with unequal length dynamically, which could reflect the key sections with poor quality of the line infrastructure. By using the proposed method, the division of the unit section of Shanghai-Nanjing intercity railway infrastructure was conducted, and the results show that the method could effectively and variously divide the unit section, and the division results were close to the real state of the line.

Abstract:In order to study the conflict relationship between buses and non -motorized vehicles in linear bus stops and the upstream area, two typical linear bus stops in downtown Fuzhou were selected, and drones were used to obtain the trajectory of buses entering the station and non-motor vehicles and extract the actual location of the bus lane change point. Combining the full-information static non-cooperative game with the cellular automata simulation model, exploring the Nash equilibrium value of the conflicting parties, and improving the cellular automata’s lane changing rules, the paper proposes an improved element based on the full -information static non -cooperative game The cellular automata model was used to simulate the traffic flow operation state when the bus occupied the non-motorized lane and stops. Taking the spatial distribution ratio of lane changing points as the verification index, the verification results show that the error between the simulation value and the actual value is less than 8%. It shows that the improved cellular automata simulation model can better reflect the actual operation of traffic flow. Taking the probability of a short-distance bus lane change as an indicator, the simulation results show that the probability of a short-distance bus lane changing is positively correlated with the traffic volume of non-motor vehicles.

Abstract:In order to alleviate the imbalance between the closed-loop logistics demand growth and the road resources limit, a ground-underground model based on metro network was designed, and a ground-underground closed-loop logistics distribution optimization model was constructed to minimize transportation time cost, time window penalty cost, carbon tax, transshipment cost, vehicle fixed cost and subway station freight operation cost. Based on the semi-initialized and sub-path disturbance strategy, the adaptive genetic algorithm was improved. The implementation effect was evaluated based on the Qinhuai District, Nanjing. The results show that firstly, the improved adaptive genetic algorithm can shorten the calculation time of 49.14%, and the solution is more efficient and stable. Secondly, setting multi-group metro operations, 3 000-piece carriage capacity and 5 min departure interval can effectively reduce the average service time by 4.6% and the total costs by 3.8%, yielding better delivery timeliness and economy. Finally, compared with the traditional logistics mode, the ground-underground closed-loop logistics distribution plan based on the existing metro network can reduce carbon emissions by 57.5%, average delivery time by 8.1% and the distribution model can provide reference for the future development of urban logistics and metro network.

Abstract:In order to ensure that the auxiliary converter of an overseas metro vehicle can meet the noise performance requirements, the statistical energy analysis model of the auxiliary converter is established, and the energy distribution characteristics and noise transmission path of the plate subsystem and the acoustic cavity subsystem are analyzed. The problem of excessive vibration and noise of 1 800 Hz is analyzed for guidance. The results show that the higher noise of test point 2 and test point 5 is related to air transmission, noise transmission and structure radiation noise, and the lower noise of test point 1 is related to the arrangement of sound absorbing materials at the air inlet side. The noise of low-speed half load and high-speed full load conditions is mainly electromagnetic noise of 1 800 Hz, which is twice the switching frequency of IGBT. The vibration spectrum of transformer top panel and air outlet side panel is mainly 1 800 Hz. The vibration and noise can be reduced by pasting damping material and sound-absorbing material at this position. Noise simulation and test can provide guidance for the design and development of metro vehicle auxiliary converter products.

Abstract:The traditional temperature stress detection method is restricted by the detection principle and the efficiency of sensor elements, so it is difficult to monitor the temperature stress of continuously welded rail (CWR) quickly and accurately in real time. Based on the principle of acoustic elasticity, the optimal incident angle of ultrasonic longitudinal wave is calculated by using Snell theorem, and the real-time temperature stress detection of CWR is realized through the neutral temperature point. The hardware and software systems of temperature stress on-line monitoring are built up to practice the theoretical algorithm. The real-time monitoring waveform is sent to the cloud server by mobile network transmission. The peak of the original waveform is taken as the characteristic data, and the interference of residual stress on the temperature stress detection results is removed by calibration experiment. The results show that the critical refracted longitudinal wave can effectively measure the temperature stress of CWR rail. Combined with the established hardware and software system, it provides a new way for the management of key parameters of CWR service performance. It is suggested that the proposed rail temperature stress monitoring scheme be popularized.

Abstract:Stereo matching algorithm plays an important role in binocular vision. Census stereo matching algorithm based on nonparametric transformation has been widely used in recent years, but there are some shortcomings in the process of disparity calculation. In view of the shortcomings of census stereo matching algorithm, there have been many improvements of census stereo matching algorithm. Firstly, the basic principle of disparity calculation based on census stereo matching algorithm is introduced, and the limitation of disparity calculation based on census stereo matching algorithm is analyzed. Then，the improved census stereo matching algorithm is summarized in the form of classification, and the improved census stereo matching algorithms are divided into six categories. Finally, the advantages, disadvantages and core ideas of each kind of improved census stereo matching algorithms are summarized, and six kinds of improved census stereo matching algorithms are compared and analyzed, and the application and development trend of census stereo matching algorithms are summarized.