Abstract:【Objective】In order to study the influence of mechanical properties of soil-rock mixture on the stability of tunnel excavation when tunnel passes through fault fracture zone.【Method】In this paper, discrete element software PFC 3D are used to construct a fine model of cohesive soil-rock mixture, and the mesoscopic parameter calibration is carried out in combination with the results of large-scale triaxial compression tests to carry out systematic research, and the macro-mechanical properties of non-cohesive soil-rock mixture are compared with those studied by existing scholars, so as to analyze the influence of different factors on the macro-mechanical properties of soil-rock mixture.【Result】With the increase of volumetric block proportion, the relationship between the block and the soil matrix gradually changes to the block-soil skeleton structure, and the shear strength increases rapidly; When the block orientation angle is between 0° and 90°, the shear strength of the soil-rock mixture decreases first and then increases, reaching the lowest value at about 45°; Under the action of high confining pressure, the difference of the overall movement and rotation of the block is more significant, and the block orientation angle of the block has a greater influence on the strength of the sample.【Conclusion】Regardless of the nature of the soil matrix in the soil-rock mixture, confining pressure, stone content and stone inclination angle have significant effects on the mechanical properties of the soil-rock mixture. Therefore, the construction of the fault fracture zone should be combined with the above factors for comprehensive analysis, and a reasonable advance support scheme should be summarized.

Abstract:【Objective】In order to provide a little basis for improving the settlement maintenance standard of double block ballastless track, the uneven settlement damage problem of double block ballastless track subgrade is studied.【Method】A three-dimensional finite element model of double-block ballastless track with uneven settlement of roadbed is established, it aims to analyse the spatial stress and the deformation law of each component of the track structure under the action of roadbed settlement. On this basis, a static damage classification and evaluation method for differential settlement of double block ballastless track subgrade is proposed.【Result】The results show that when the settlement wavelength is 20 m, the amplitude has a great influence on the stress-deformation and inter-layer seam of the track structure. The settlement amplitude is 10, 15, 20 mm and above, and the damage rating is Ⅱ, Ⅲ and Ⅳ respectively. When the settlement amplitude is 10 mm, the smaller the wavelength is, the easier the void phenomenon is to occur among the layers of the track structure. The settlement wavelengths of 12~16 m have a great influence on the damage of track structure, and the maximum longitudinal tensile stresses of track slab exceed the limit value 3.50 MPa. So, it is recommended that the settlement damage rating of wave band below 20 m is the grade Ⅲ, and that of wave band above 20 m is grade Ⅱ.【Conclusion】In order to facilitate the“scientific repair and accurate repair”of high-speed rail intelligent operation and maintenance, it is suggested that the settlement damage level should be associated with the static geometric allowable deviation management value of the line track, the maintenance level should be consistent with the damage level, and the comprehensive maintenance of settlement should be controlled within 15 mm.

Abstract:【Objective】To carry out research on damage identification and state assessment of bridge structures, this paper makes a comparative study on two analytical methods for dynamic characteristics of cracked simply supported beams. [Method] Based on the basic ideas of transfer matrix method and segmented mode function method, a massless torsion spring was used to simulate the local flexibility caused by cracks. Two solving methods for the dynamic characteristics of simply supported beams with arbitrary numbers of cracks were derived using recursive method and Heaviside function, and compared and analyzed with the finite element results of ANSYS.【Result】For single-crack, double-crack, and triple-crack beams, both methods yielded results that are well matched with the finite element results, demonstrating high computational accuracy. Compared to the transfer matrix method, the segmented mode shape function method exhibits higher computational efficiency in calculating the natural frequencies of beams with multiple cracks, especially for higher-order frequencies. The maximum difference in computation time under triple cracking is 16.51 seconds. As the number of cracks increaseds, the computation time for natural frequencies using the transfer matrix method increases to 2.85 times and 13.30 times, while for the segmented mode shape function method is increasing to 1.10 times and 5.43 times. The computation time using the transfer matrix method significantly increases and shows an exponential growth trend. The variation in crack depth has a minor impact on computational efficiency.【Conclusion】Exploring the impact of crack depth and quantity on the computational efficiency of two methods has significant practical significance for improving the efficiency and accuracy of bridge structural damage identification.

Abstract:【Objective】To investigate the impact of surface surcharge on the settlement of adjacent tunnels,the longitudinal deformation of the tunnel is calculated and analyzed.【Method】A two-stage analysis method was adopted. In the first stage, the Boussinesq solution was used to calculate the vertical additional force exerted on nearby subway tunnels due to surface surcharge. In the second stage, the subway tunnel was modeled as an Euler beam supported by the Pasternak foundation, simplifying the structural representation. By utilizing the RayleighRitz method, functional expressions for each system component were formulated, leading to the establishment of the total energy equation. The control equation was subsequently solved through the application of the variational principle. The obtained results were compared to measured data to validate the effectiveness of the proposed method. Finally, the research explored the impact of offset distance d, tunnel burial depth z, surcharge p, and surcharge range B and L on settlement.【Result】The research findings indicate a significant impact on settlement within the range of (0.5~1)L directly below and on both sides of the surcharge. As d increases, the maximum settlement of the tunnel gradually decreases. There is a linear relationship between p and w_max and the larger the pile surcharge, the greater the maximum settlement is. Increasing L and B initially leads to gradual settlement increase, followed by stabilization. L exerts a greater influence on w_max compared to B.【Conclusion】The method can effectively calculate the longitudinal deformation of the tunnel caused by ground loading, and it is in good agreement with the measured data, which can determine the safety of the tunnel lining under ground loading.

Abstract:【Objective】In order to improve the effect of periodic maintenance for ballasted high-speed railway, and standardize the construction process for bed cleaning of ballasted high-speed railway.【Method】Time-domain curves of Track Quality Index (TQI) and scatter plots of TQI were drawn Based on the dynamic monitoring data from January 2019 to May 2023 for Shanghai—Chengdu line Hefei—Nanjing section.【Result】The shortest time from the last cycle of maintenance when the track enters the“wear and tear period”was 12 months, when the TQI change rate is greater than 2%, the correspording TQI value was TQI≥4.0 mm. Based on the TQI data measured before and after each process during cleaning construction in Shanghai—Chengdu line Hefei-Nanjing section from October to November 2022, the average decrease of TQI by each process was calculated. Grading evaluation of track quality for ballasted high-speed railway was proposed, combining the acceptance requirements or construction and TQI value of track before bed cleaning. TQI time-frequency curve exhibits a“bathtub curve”characteristic. Maintenance of the bed should be carried out before the“aging phase”. The TQI criterion for the periodic maintenance of ballasted high-speed railway was proposed: TQI≥4.0 mm, and periodic maintenance for ballasted high-speed railway track was recommended to be a 12 months cycle. A grading and control evaluation for ballasted high-speed railway bed cleaning operations was proposed, and the static track quality should meet the following criteria after construction: TQI≤5.0 mm after cleaning and three times tamping and two times stabilizing(3D2W), TQI≤4.5 mm after 5D3W, TQI≤4.0 mm after 7D4W, TQI≤3.0 mm after precise tamping 1, and TQI≤2.5 mm after precise tamping 2.【Conclusion】A reference is provided for the management and construction of ballasted high-speed railway bed cleaning.

Abstract:【Objective】In order to deeply explore the reasonable construction scheme of railway trough beam bridges under complex construction conditions, this paper conducted a systematic study on reconstruction and expansion scheme for such bridges.【Method】Taking the reconstruction and expansion project of a railway trough beam bridge overpassing an expressway as the research object, and facing the complicated construction conditions such as the overlap of the main beam spatial position before and after the reconstruction and the need to maintain traffic, this study conducted a detailed comparative analysis of the structural load-bearing capacity, construction techniques, and traffic diversion for the high-level cast-in-place followed by beam lowering method and the off-site precast incremental launching method.【Result】The research results indicate that the safety factors and stress calculation indicators for the trough beams are all within the acceptable thresholds, meeting the standards. Particularly, the off-site precast incremental launching scheme exhibits higher stress reserves. The high-level cast-in-place followed by beam lowering scheme has a greater beam lowering height and stricter construction requirements, while the off-site precast incremental launching method has lower risks during construction and less impact on the traffic under the bridge. The segmented incremental launching method can effectively solve the problem of jacking difficulty for variable height girders. During the incremental launching process, the side walls of existing frames can be utilized as temporary piers, maximizing the use of existing structures. Both schemes require the implementation of traffic diversion measures during the construction process, but theoretically, there is no need to interrupt the traffic under the bridge.【Conclusion】Both schemes can meet the requirements for maintaining traffic, and the off-site precast incremental launching method demonstrates significant advantages over the high-level cast-in-place followed by beam lowering method in terms of stress reserves, safety factors, and construction risks.

Abstract:【Objective】In order to explore the degree of synergy between the level of high-quality development of cities in the Yangtze River Economic Belt and the level of high-speed rail networks.【Method】In this paper, the entropy power method was used to measure the level of high-quality economic development of 106 cities in the Yangtze River Economic Belt from 2008 to 2020, and the level of high-speed rail network was comprehensively measured by combining the social network analysis method. Subsequently, the coupling coordination model was applied to analyse the degree of coupling coordination between the two systems. And on this basis, the spatial effect of the degree of coupled coordination was investigated by using the Moran index.【Result】The results show that both the level of high-speed railway network and the high-quality development of urban economy in the Yangtze River Economic Belt as a whole have been improving year by year, and the degree of coupling and coordination between the two shows a positive correlation spatially, but there is a phenomenon of unbalanced development. Among them, the degree of coupling and coordination between the two systems in the lower reaches of the Yangtze River and Class A cities has improved relatively fast and is significantly higher than that in other regions. It is worth noting that some cities have significant control and influence in the HSR network of the Yangtze River Economic Belt, while others are almost marginalised.【Conclusion】The synergistic development of the urban economy and high-speed rail network in the Yangtze River Economic Belt has been steadily improving, and in the subsequent policy formulation, we will try to ensure that the high-speed rail will be able to serve all important nodes, and better promote the economic interconnection between cities.

Abstract:【Purpose】In order to solve the problems of target smoke misdetection and low detection accuracy in complex scenes.【Method】Improve and optimize the YOLOv7 algorithm which was on the current best performing object detector, replaces the PAFPN structure in the Neck part of the original model with the asymptotic feature pyramid structure AFPN and uses ECIoU as the objective regression loss function, and verifies it on the selfconstructed dataset SM-datase and Pycharm platform.【Result】Experimental results show that the accuracy of the improved algorithm was increased by 1.3% to 68.6% compared with the original YOLOv7 model, the average accuracy mAP is increased by 1.8% to 64.6% compared with the original YOLOv7 model, and the computational complexity of the improved algorithm is only 82.5 GFLOPs, which was 27.4% lower than that of the original YOLOv7 model.【Conclusion】Based on the improved YOLOv7 algorithm, the algorithm proposed in this paper can not only reduce the computational complexity of the network but also improve the detection accuracy in complex scenes, which provides a new idea for the follow-up research of smoke detection in complex scenes.

Abstract:【Objective】In order to ensure the timely arrival of goods and enhance the reliability of cold chain road-rail intermodal transport, this paper addresses path optimization under conditions of varying demand. 【Method】The concept of path time reliability was introduced under uncertain time conditions, with the reliability of a route scheme defined as the minimum time reliability of all paths. A multi-objective optimization model was constructed with the goals of minimizing total transportation cost, minimizing carbon emissions, and maximizing reliability. The model was solved using the NSGA-Ⅱ combined with an elite strategy to compute examples, analyzing the effects of different reliability strategies and uncertain timing on route optimization.【Result】The optimized model focused on reliability achieves an average reliability close to 0.9, with a broader distribution of Pareto solutions. The impact of uncertain road transportation time on reliability is more significant compared to uncertain waiting transfer times.【Conclusion】The optimization model proposed in this paper effectively provides high-reliability paths to meet the needs of different carriers.

Abstract:【Objective】Aiming at the problem that the general target detector is not directly applied to remote sensing image detection, a remote sensing image target detection algorithm based on improved RetinaNet is proposed. [Method] The algorithm combines the advantages of dynamic selection of down-sampling blocks and convolution kernels. Firstly, the improved downsampling module (IDM) on the base feature extraction network ResNet50 was introduced, which performed multiple down-sampling processing on features. Then the spatial receptive field was dynamically selected by using the convolution kernel selection mechanism to model the multiscale semantic information of the scene. Finally, the classification and regression results of the target object were obtained.【Result】Experimental results show that the proposed method improves mAP by 3.2 percentage points on the large-scale remote sensing image object detection dataset DOTA compared to the orignal RetinaNet network.【Conclusion】The mechanism of introducing a downsampling module and dynamically selecting the size of the convolution kernel has improved the recognition ability of multi-scale remote sensing targets to a certain extent.

Abstract:【Objective】In order to study the joint optimization problem of metro passenger-freight cotransportation and timetable under the train-dedicated mode, the relationships between trains, demands and potential spacetime trajectories are reconstructed and an integer linear programming model is formulated instead of the traditional nonlinear programming model.【Method】The objective function of this model includes the number of freight trains in use, the waiting time of passenger demand as well as the detention time of freight demand. The restriction conditions to be met mainly include the flow balance constraints of passenger and freight demands, the capacity constraints of passenger and freight trains, the longest waiting time constraint of passenger demand and the longest detention time constraint of freight demand. By relaxing the integer-type variables of passenger and freight flows, the primal model could be equitably transformed into a mixed integer programming model, which can improve the solving efficiency of the model. Taking the original Batong Line of Beijing Metro as the background information, a series of numerical examples were designed and then solved by commercial solver Gurobi.【Result】The experimental results show that Gurobi can solve the relaxation model faster than the primal model; and compared with the original timetable, the optimized timetable can reduce the generalized cost.【Conclusion】The proposed method can not only meet the needs of subway passenger and freight cotransportation in the split mode, but also effectively control the influence of metro freight on passenger demand under this mode.

Abstract:【Objective】To address the lack of a comprehensive evaluation system for the optimization of equivalent conicity schemes for high-speed train wheel-rail interaction, a method based on an improved fuzzy analytic hierarchy process is proposed.【Method】Fourteen evaluation indicators were selected based on key dynamic factors influencing equivalent conicity and used to construct an indicator decomposition model. The improved three-scale fuzzy analytic hierarchy process was applied to determine the indicator weights. Three equivalent conicity models were established in the dynamic simulation software Simpack, with baseline indicator values computed and dimensionless normalization performed. A fuzzy evaluation membership matrix was constructed to develop a fuzzy theoretical evaluation system, and the comprehensive scores of the three schemes were obtained.【Result】The scores for the three equivalent conicity schemes are as follows: Scheme M1 scored 26.2%, outperforming Scheme M2 (17.9% ) and Scheme M3 (16.2% ), making M1 the optimal choice. Dynamic simulation comparisons between two significantly different schemes further validate the consistency of the evaluation system's conclusions with the simulation results, confirming the reliability of the proposed method.【Conclusion】 The proposed method effectively evaluates equivalent conicity schemes for high-speed trains and provides a scientific basis for optimizing scheme selection.

Abstract:【Objective】The purpose of this study is to develop high-performance copper matrix composites to meet the requirements of the braking system of high-speed trains after the operating speed is increased.【Method】The orthogonal experimental method was used to study the copper matrix composites with Cu-Ni-Si-Cr alloys as the matrix systematically, and to investigate the effects of the alloying element ratios of Ni, Cr and Si in the alloys on the mechanical properties and tribological properties of the copper matrix composites.【Result】The hardness and strength of the copper matrix composites with Cu-7Ni-1.75Si-0.75Cr as the matrix were the highest, 49.90 HBW and 171.98 MPa respectively. The results of the orthogonal experiments on the friction factor and the amount of wear were analyzed, and the comprehensive performance of the copper matrix composites with Cu-7Ni-1.75Si-0.75Cr as the matrix was the best. Its friction coefficient increases and then decreases with the increase of temperature under the condition of 25~650 ℃, and the amount of wear increases, and the highest friction coefficient of copper matrix composites is found at 450 ℃. The wear mechanism changes from abrasive wear to oxidative wear and abrasive wear.【Conclusion】The alloying of copper matrix by orthogonal experimental method is of great significance to effectively improve the friction factor and wear resistance of copper matrix composites for brake pads at high temperatures.

Abstract:【Objective】Aiming at evaluating whether the structural performance of a passenger-vehicle front suspension lower control arm could meet the design requirements.【Method】Firstly, the lower control arm grid model was established based on finite element technique, the modal analysis results showed that its first three modal formations were obtained. Secondly, the force and moment of the lower control arm were extracted based on front suspension dynamic model, the lower control arm was strength analyzed by adopting inertia release method, its stress were obtained. Lastly, the thickness of lower control arm was parameters optimized, so the optimal structural parameters were obtained.【Result】Its first three modal formations were outside the external excitation frequency range, so it could meet vibration characteristics requirements. Its stress were lower than the material yield value, so it could meet the strength performance requirements. The structural performance of lower control arm could meet the design standards after optimization, its weight had been reduced by 12.5%.【Conclusion】The analysis method could provide effective reference and reference for the design and optimization of the similar product, it had very important practical engineering significance.

Abstract:【Objective】To address the severe performance loss after model pruning,a compression algorithm based on filter attenuation and self-knowledge distillation is proposed. [Method] This method utilized a filter attenuation mechanism to preserve the information of redundant filters, thereby minimizing the model difference before and after pruning, and reducing the performance loss caused by pruning. Meanwhile, an annealing attenuation function was introduced during the pruning process to dynamically change the attenuation of filters, enabling a fast and efficient search for the optimal substructure of the model and improving the convergence speed of the model. Additionally, self-knowledge distillation was employed for knowledge transfer between the pre-trained model and the compressed model. [Result] The results show that this compression algorithm improves the model accuracy by 0.12 percentage points while reducing the FLOPs of the VGG-16 model by 37.3% . [Conclusion] This method provides a more stable and efficient model compression approach for convolutional neural networks.