Abstract:The original backbone of the SSD network was replaced with a lightweight MobileNetV2 network. At the same time, the channel attention mechanism SENet structure was introduced to apply different weights to different channels of the feature map, making it more conducive to detection. Using the crack data in three different environments to fuse, a new data set was built so that the network can better learn crack objects in different environments, further improving the network′s recognition ability and speeding up the network′s reasoning speed. The anchor in the original SSD network were set according to the general data set, and the data type concerned in the detection of structural surface cracks was relatively single. The K-means algorithm was used to cluster the anchor suitable for the crack data set, which speeded up the convergence of the model and was more efficient than the original one. The model had higher accuracy. Finally, the accuracy of the improved algorithm is 3.6% higher than that of the previous one, and the detection speed is as much as 2 times that of the previous one, which is enough to meet real -time detection, the algorithm can provide a faster and more accurate detection method for the detection of structural apparent cracks in practical engineering.

Abstract:In response to the problems that the sandy soil in the water-rich sand layer is prone to collapse, resulting in the weakening of bentonite slurry friction reduction effect and the increasing jacking force caused by construction halt during the restart, a series of pipe-jacking model tests are conducted to investigate the influence of different mud sand content and different resting time on the effect of mud drag reduction and the changing characteristics of pipe jacking force. The results show that as the sand content of the mud increases, the friction between the pipe jacking and the mud interface increases exponentially. The pure slurry can reduce the friction force by 90%. When the sand content of the slurry is less than 20%, the sand content has little effect on the friction reduction effect, and the friction reduction effect is only reduced by 5%. With the increase of sand content in slurry, the effect of resting time on friction force between jacking pipe and slurry interface increases. When the sand content of the slurry is less than 60%, the residual jacking force of the pipe-soil interface is not relevant to the resting time. When sand content reaches 80%, the residual friction strength increases about 6% to 8% after 24 h resting.

Abstract:In order to investigate the effects of new twin tunneling on the longitudinal displacement of existing shield tunnel, Pasternak double parameters of the elastic foundation and Euler -Bernoulli beam model is employed to consider the new tunnel, existing tunnel skew angle and the tunnel excavation causing factors such as ground loss. The new double line tunnel excavation caused by free field vertical displacement of surrounding soils is determined by Loganathan-Poulos solution and superposition principle, and null space method is used to calculate the settlement deformation of the existing tunnel. Taking Shenzhen Metro Line 9 passing under Metro Line 4 as an example, the predicted results by the null space method is compared with the field-measured data. The effect of horizontal distance, ground loss, skew angle and depth of the new tunnel on existing tunnel settlement is further analyzed. The results show that the distance between the two lines of the new tunnel significantly affects the settlement of the existing tunnel in a range of 7 times its outer diameter. The settlement decreases with the increase of the distance, the settlement domain increases as the distance increases. The settlement pattern changes from "V" to "W". When the distance is larger than 7 times the outer diameter of the new tunnel, the settlement and pattern tend to be stable. In addition, ground loss, skew angle and the depth of the new tunnel significantly influences the settlement. It increases with the increase of ground loss, and decreases with the skew angle and the depth of the new tunnel.

Abstract:Based on the Box-Behnken response surface method, a three-factor, three-level test was designed using Design-Expert 8.0.6 software with 5%~15% ceramic powder, 10%~20% ordinary silicate cement and 5%- 15% quicklime as the factors considered to investigate the effects of each factor on the compressive strength and softening of gypsum-based composite cementitious materials at 7 d and 28 d ages coefficients at 7 d and 28 d. The effect of each factor on compressive strength and softening coefficient was analyzed by quadratic regression fitted model ANOVA to determine the magnitude of the influence of each factor on admixture and the optimal mix ratio. The results showed that the effects of ceramic powder and cement admixture on 7 d and 28 d compressive strength were highly significant, followed by quicklime; the admixture of ceramic powder on softening coefficient was significant, followed by quicklime, and cement was the most inferior. The optimal ratio is 10.88% of ceramic powder, 15.51% of cement and 10.65% of quicklime, with a prediction error of no more than 10% verified by the test. The research results provide a test basis for further optimization of the constructability, selfwarming and durability of gypsum-based composite cementitious materials.

Abstract:In this paper, the effects of cement content, water glass content and curing age on the impermeability performance of silty clay were discussed by indoor penetration test, scanning electron microscopy（SEM） and Xray diffraction（XRD） test on the typical silty clay in Nanchang. The results showed that the permeability coefficient of improved silty clay decreased at a rate of 3 orders of magnitude higher than that of 14~28 d at a curing age of 7~14 d. With the continuous increase of cement content, the permeability coefficient of improved silty clay decreased and the decline rate gradually decreased. The increase of water glass content can significantly reduce the permeability coefficient of improved silty clay. Cement-water glass can synergistically improve the impermeability of silty clay, and the optimal ratio of 24% cement + 6% water glass has an optimal dosage. Compared with the improved silty clay with single cement, the incorporation of water glass does not change the main phase composition of the hydration product, but promotes the hydration reaction, and increases the yield of hydration products such as C-S-H gel and C-A-S-H calcium vanadite, and greatly reduced the number of pores and fractures between soil particles.

Abstract:To study the stress characteristics of deep water foundation steel cofferdams during construction, taking the 6# pier deep water foundation of Dingjiazhou Bridge as an example, finite element method ABAQUS software was used to establish a calculation model for single and double wall built-up structure steel cofferdams and traditional double wall steel cofferdams. The stress and deformation of different structural steel cofferdams were calculated, and the mechanical behavior changes of steel cofferdams were analyzed. The research results indicate that the stress situation of single and double wall built-up structure steel cofferdams is more reasonable compared to traditional double wall steel cofferdams. The weakest position of the entire structure occurs between two horizontal ring plates on the bulkhead concrete, and stress concentration is prone to occur at the position where the outer wall plate contacts the horizontal truss. However, the maximum deformation and stress values of the outer wall plate are 9.69 mm and 122 MPa, respectively, which meet the requirements of the specifications. In addition, by comparing the numerical simulation results with the on-site monitoring results, it can be seen that the numerical simulation results of each measurement point are basically consistent with the on-site monitoring results, with an error rate of less than 15%. The actual structure is more inclined towards safety, indicating that numerical simulation can accurately evaluate the mechanical behavior of single and double wall built-up structure steel cofferdams in actual engineering.

Abstract:The subway station in a coastal city is located in soft soil, the diaphragm wall is used as the enclosure structure. The trench wall is unstable in the construction process. In this paper, the causes of trench wall instability are analyzed and a series of measures are taken. The results show that the ratio of wall protective mud and the time of trench formation are the main factors affecting the stability； the extra-deep diaphragm wall, needs to comprehensive analysis from the slotting time, the weight of the steel cage and other aspects to decide the framing design； for L -shape and Z -shape and other special amplitude diaphragm wall, the use of the three -axis mixing pile to reinforcement the trench wall, can greatly improve the stability of trench wall and ensure the safety of engineering construction.

Abstract:With the background of the Fujiang Bridge project, which is a prestressed concrete continuous rigidframe bridge, a construction method for one-time pouring of edge span linear section and closure section using a hanging basket is proposed for edge span linear section construction under complex terrain. The feasibility of the hanging basket method is analyzed using structural mechanics theory and MIDAS CIVIL finite element software, focusing on the main beam deflection, hanging basket structural safety, and internal forces of girder. The study shows that the one-time pouring of edge span linear section and closure section using a hanging basket has minor inpact on the mid-span side box girder internal forces and deflection after bridge completion, but has a certain influence on the vertical deformation of the edge span girder. Therefore, the pre-camber values of the box girder need to be adjusted timely during construction. Compared with traditional construction scheme, the maximum increase in the compressive stress on the worst section of the main beam after completion is 15%, which is within reasonable and controllable range. Considering the safety of the hanging basket, it can meet the safety requirements during construction by using optimization methods such as adding front and rear suspension rods. The results show that the one-time pouring of edge span linear section and closure section using a hanging basket is feasible, and this new construction method has been successfully applied in the construction of the Fujiang Bridge.

Abstract:With the deployment of China′s transportation power strategy, the high-speed railway network is continuing to expand. The demand for railway passenger travel is steadily increasing. Facing the huge high-speed railway passenger transport market, how to use intelligent and efficient deep learning technology to build a combined prediction model is a challenge. This paper integrates a variety of factors affecting ticket purchases and is committed to explore the changes in passenger ticket purchase demand on each day of the pre-sale period in real time. This shows that it′s becoming an urgent problem to provide an efficient and reliable prediction model for passenger ticket pre-sale period for the railway department. This paper takes the historical ticket purchase data of high-speed railway passengers between OD（origin-destination） on the Shanghai-Kunming high-speed railway line as an example. The combined prediction model considers the number of tickets purchased on each day of the pre-sale period of the historical continuous departure date, the date of the departure date, statutory holiday, and seasonal characteristics. The research shows that the combined prediction model based on deep learning CNN-LSTM has better predictive power than the parameter model and machine learning model, which provides a theoretical reference for the dynamic adjustment of fares in the railway passenger transport market.

Abstract:In order to accurately detect the looseness position and degree of railway fasteners during service, a looseness detection algorithm of railway fasteners based on wavelet packet energy spectrum and improved BP neural network is proposed. First of all, referring to the current specifications, seven different loosening conditions of railway fasteners are designed on the spot, and the corresponding vertical vibration acceleration signals of rail under each condition are collected in turn; Then, the collected vertical vibration acceleration signal of the rail is decomposed by 7 layers of dB40 wavelet packet to obtain the corresponding wavelet packet node energy ratio data information under each working condition. On this basis, a vector dissimilarity coefficient index (VDC) is designed from the perspective of distance and dimension to realize the positioning of loose fasteners; In addition, according to the characteristics of the data, the particle swarm optimization algorithm is used to improve the BP neural network, build the PSO-BP railway fastener looseness detection model, and conduct parameter sensitivity analysis. The research results show that the minimum value of VDC of railway fastenings in healthy state is 0.17, and the maximum value is 0.41, which is significantly less than the VDC value of railway fastenings in each loose state. Based on this, accurate positioning of single and multiple loose fastenings can be achieved; The constructed PSO-BP railway fastener looseness detection model can achieve accurate detection of fastener looseness. When the number of neurons in the hidden layer is set to 20, the model detection effect is the best, and the corresponding recognition accuracy is 98.66%.

Abstract:SiC particle reinforced aluminum matrix composites have broad application prospects in the field of rail transit. However, this material is prone to brittle phases that affect the quality of joints during the melting welding process, which restricts the development of SiC particle reinforced aluminum matrix composites. Ti and Si element compensation is applied to suppress the brittle phase of Al₄C₃ and laser powder welding of SiCp/ 2009Al composite materials. Ti and Si element compensation is used to suppress the brittle phase of Al₄C₃, and laser powder welding is conducted on SiCp/2009Al composite materials. SEM and XRD are used to analyze the microstructure of the welded joint. The hardness and tensile properties of the joint are tested using a vickers hardness tester and a universal testing machine, respectively, in order to analyze the influence of Ti₅Si₃ content on the microstructure and mechanical properties of the joint. The results indicate that the addition of Ti₅Si₃ has a significant effect on inhibiting the decomposition of SiC particles and the formation of Al₄C₃ brittle phase through their reaction with Al, but the Al₄C₃ brittle phase is not found in the weld seam; with the increase of Ti₅Si₃ content, the distribution density and size of Al₃Ti in the weld microstructure first decrease and then increase, the morphological integrity of the fusion zone first increases and then decreases, and the width of the heat-affected zone first decreases and then increases; with the increase of Ti₅Si₃ content, and the tensile strength of the joint shows a trend of first increasing and then decreasing, the tensile strength of the welded joint with 20% Ti₅Si₃ powder added is 2.8 times that of the welded joint with 50% Ti₅Si₃ powder added.

Abstract:Vehicle suspension is one of the important components of the vehicle driving system, mainly for bearing the weight of the body and reducing the excitation from the road surface, whose performance directly affects the safety and handling stability of the vehicle. It also has a great impact on the riding comfort of the occupants. The traditional passive suspension structure parameters are fixed, the vibration damping effect is limited, and the semi-active suspension can change the damping and stiffness of the suspension through the control algorithm, which can achieve the same control effect as the active suspension, and the structure is simpler and lower in cost than the active suspension. Air springs and magnetorheological dampers can change the stiffness and damping of semi-active suspension, respectively, and are important for semi-active suspension damping. On the basis of introducing the working principle and single control strategy of magnetorheological semi-active air suspension, this paper focuses on the composite control strategy of magnetorheological semi -active air suspension, and finally discusses the development trend and problems of magnetorheological semi-active air suspension, so as to provide further reference for the technical development of magnetorheological semi-active air suspension.

Abstract:Aiming at the battery pack of chassis power exchange for electric vehicles, a locking device for rapid power change is designed to realize the rapid locking and unlocking of the battery. In order to verify the structural safety of the device, the static and modal characteristics of the device under two typical limit conditions were analyzed by finite element ANSYS software. The results show that the maximum stress of the device under the two working conditions is located at the lock body, and its maximum stress values are 207.63 MPa and 264.18 MPa, respectively, which meet the strength design requirements of the selected materials, and the natural frequencies of the first six modes of the device are greater than the excitation frequencies of the electric vehicle, so the car will not resonate with the device during driving.

Abstract:In view of the in creasingly serious environmental vibration problem of urban rail transit, this paper takes the rubber floating slab, a commonly used vibration isolation measure in urban rail transit, as the research object, and studies and improves its low -frequency control performance from the perspective of elastic waves. The periodic boundary conditions of the rails are modelled using plane wave series, and the energy generalisation of full-paved, strip-paved, and point-paved rubber floating plate track structures is calculated using the energy method，the band gap characteristics of the rubber floating plate are finally obtained by scanning the wave number variations. The periodic boundary conditions and positive symmetrical boundary form constraint matrices, and the linear expression method is adopted to process the boundary conditions to obtain the unknown coefficients that can be varied. By scanning the variation, the bandgap characteristics of the rubber floating slab are obtained. The accuracy of the proposed method is verified using the finite element method. The results show that the cut-off frequency of the first order band gap of the full-paved type is the largest, and the strip-paved type and the dot-paved type have lower cut-off frequency and wider passband bandwidth. The cut-off frequency of the first order band gap increases with the increase of the stiffness of the rubber pad. The dynamic vibration absorber for floating slab accurately controls the elastic wave, providing new ideas and methods for the application of low-frequency vibration control of rubber floating slab tracks.

Abstract:A new numerical algorithm is presented to solve steady-state nonlinear heat conduction problems by combining the scaled boundary finite element method and the Kirchhoff transformation. In order to eliminate the nonlinearity related to the temperature dependence of the thermal conductivity, the Kirchhoff transformation is utilized to convert the nonlinear partial differential governing equation into the Laplace equation, and therefore iterative computation can be avoided. As a semi-analytical numerical method that combines the advantages of finite element method and boundary element method, the scaled boundary finite element method only requires the boundary without fundamental solution to be discretized. After the numerical solutions with high precision in the transformation space are calculated by the scaled boundary finite element method, the inverse transformation is required to derive the temperature field. Several numerical examples are presented to verify that the proposed method is effective for steady-state nonlinear heat conduction problem.

Abstract:A graph whose graphic metric space is isomorphic to some subspace of an l₁-space is called l₁-embeddable. A mono -4 -gons cyclohexane molecular graph refers to a 2 -connected planar graph embedded in a plane with exactly one quadrilateral face, the rest are hexagonal faces, and the inner vertices degree are 3 and the boundary vertices degree are 2 or 3. It is proved that when there are only two adjacent 3-degree vertices on the quadrilateral, the mono-4-gons cyclohexane graph is l₁-embeddable, and the others are not.