A novel crossing power governance approach was proposed to mitigate the effects of crossing power in the traction power supply system while taking regenerative braking energy utilization into account. First, the power flow under different operating conditions was derived based on the structure of the continuous power supply system, and the method for detecting crossing power was analyzed. Second, a power transfer and energy storage unit was set using the single-phase combined co-phase traction substation, and the working mechanism of the improved system was analyzed. Then, a cooperative control strategy of crossing power governance was proposed by combining the upper control strategy of power distribution and negative sequence satisfactory compensation with the lower control strategy of converter control. Finally, the amount of crossing power was calculated using the experimental data of a railway line, and the cost-effectiveness of the governance measure was evaluated. In addition, the accuracy and efficacy of the proposed scheme were verified by simulation. The research results show that the proposed system and its control strategy can effectively mitigate the crossing power and regenerative braking energy, with the utilization rate of the crossing power of the power transfer and energy storage unit exceeding 70% in the case of traction substation and traction network loss. The system is highly economical and feasible.

With the rapid development of suburban railways and oil and gas pipelines, parallel laying or cross-laying is inevitable for suburban railways and buried pipelines. In order to assess the impact of the traction power supply system of suburban railways on the safe operation of oil and gas pipelines, firstly, the mathematical model of the alternating current (AC) traction power supply system of the suburban railways and the adjacent buried pipelines was established, and the simulation based on CDEGS software was conducted. Next, the two cases of the oblique approach and parallel approach were unified by the equivalent distance method. The influence mechanism of the traction power supply system of the suburban railways on the adjacent buried pipeline was investigated, and the influence of factors including soil resistivity, distance between the conductor and the buried pipeline, locomotive load current, parallel length of railway and buried pipeline, pipeline coating resistivity, and number of current harmonics of electric multiple units on the inductive coupling voltage distribution along the pipeline was investigated. Finally, combined with the setting of a through ground line, four schemes to suppress the inductive coupling voltage were put forward for comparative analysis. The results show that the error of the equivalent distance method is within 5% when the ratio of the maximum distance to the minimum distance between the traction power supply system of the suburban railway and the buried pipeline is less than 4.5. The maximum value of the inductive coupling voltage of the pipeline increases with increasing soil resistivity. The decrease in the inductive coupling voltage is 50.6% when the distance between the suburban railway and the buried pipeline varies from 50 m to 250 m. The increase in the inductive coupling voltage rises significantly when the locomotive load current varies from 200 A to 1 000 A. The inductive coupling voltage increases from 22.6 V to 170.7 V when the parallel length varies from 2 km to 10 km. The harmonic content and the number of harmonics have a significant influence on the inductive coupling voltage. The best inductive coupling voltage suppression effect is achieved by adding a return line on the basis of the through ground line.

In order to improve the energy utilization of photovoltaic (PV) power generation under partial shading conditions (PSCs), an improved and fast global maximum power point tracking (GMPPT) algorithm was proposed. Firstly, the output characteristics of PV array under PSCs were researched, and the output curve of PV array was divided into constant current region (CCR) and constant voltage region (CVR) according to the relationship between knee point and open circuit voltage. Then, the operation principles of the traditional maximum power trapezium (MPT) algorithm and the improved and fast GMPPT algorithm were analyzed. The improved and fast GMPPT algorithm is based on the MPT algorithm, where the search interval is limited by dynamic upper and lower limits of voltage, and CCR with a long adjustment time was skipped to further improve the tracking speed. Finally, the effectiveness of the proposed algorithm was verified by simulation and experiment. The experimental results reveal that the minimum tracking time of the improved and fast GMPPT algorithm is 4.0 s, and the scanning voltage and the energy loss of the proposed algorithm are 17.34 V and 98.19 J, respectively. Compared with the traditional global scanning algorithm and the MPT algorithm, the proposed algorithm decreases tracking time by 68.25% and 68.00%, lowers scanning voltage by 74.86% and 75.63%, and reduces energy loss by 58.19% and 62.31%, respectively.

In order to determine the thermal aging characteristics of the vehicle-mounted cable terminal stress control tube and its influence on the insulation performance of cable terminal under thermal aging conditions, firstly, the macro-dielectric characteristics and micro-aging law of vehicle-mounted cable terminal stress control tube were determined through experimental research. Secondly, based on the analysis of the electrical conductivity, polarization, and loss characteristics of the stress tube material under thermal aging, the dielectric characteristic curves under different aging periods were obtained. Finally, a finite element model of the electric field of the vehicle-mounted cable terminal was established by considering the aging characteristics of the stress control tube, and the electric field distribution of the cable terminal of the stress control tube was calculated based on the dielectric parameters under thermal aging. The results show that the electrical conductivity increases most significantly at 140 ℃ and reaches the maximum value of 1.1 × 10⁻¹⁰ S/m at a field intensity of 50 kV/m. The relative dielectric constant reaches the minimum value of 14.00 at high temperature (140 ℃) for 20 days. In addition, trap hindrances such as folding and breaking of polymer long chain are enhanced during pyrolysis reaction, and the dielectric loss increases. In terms of functional group characteristics and microstructure of the stress control tube, thermal aging results in pyrolytic polymerization of olefin polymers in stress control tube materials, forming chemical stereoscopic defects. In addition, the cracking of polymer spherulites and the formation of inorganic oxidation products on the surface of the stress control tube sample are intensified, and the physical and chemical properties of the sample surface are changed. Simulation results show that under thermal aging conditions, the electric field distortion area inside the cable terminal presents a trend of expanding, creeps along the stress control tube towards the terminal high voltage, and finally stabilizes at the junction of the main insulation layer of ethylene propylene rubber (EPR) and stress control tube.

Converting alternating current (AC) cables into direct current (DC) operation is of great significance to achieve new energy generation connected to the grid and increase power supply capacity. A 35 kV AC cross-linked polyethylene (XLPE) cable was taken as the research object, and temperature field simulation of the three-core AC cable was carried out through the finite element method under three kinds of DC topologies: three-wire bipole, monopole, and bipole. At the same time, common influencing factors in the distribution network were considered, such as distance from hot water pipes, cable cluster laying, and current imbalance, so as to explore the influence of these factors on the ampacity of the cable when the AC cable was changed to the DC operation. The results show that under the same operating temperature, the 35 kV AC XLPE cable has the smallest ampacity when operating under the monopolar DC topology and the largest ampacity under the three-wire bipolar DC topology. When the horizontal distance between AC cable and urban water supply pipes is 2.0 m, and the vertical distance is 0.5 m, the ampacity of cables operating under the above kinds of DC topologies is reduced by about 3.0%. The maximum ampacity can be increased by 90 A as the asynchronous peak value is loaded when the cable cluster is laid. The cable ampacity increases first and then decreases with increasing current imbalance, and it reaches the maximum value when the current imbalance is 0. The research results can provide some reference for converting 35 kV AC XLPE cables into DC operation.

In infrared low-light scenes, railway object intrusion detection faces low detection accuracy, and it is difficult to achieve lightweight real-time detection. Therefore, a lightweight detection method of railway object intrusion based on convolutional block attention module (CBAM) enhancement was proposed. Firstly, the Darknet53 feature extraction network was improved by deep separable convolution to achieve lightweight extraction of railway object intrusion characteristics in infrared low-light scenes. Secondly, semantic-guided infrared spectral pooling was used for feature enhancement to improve the feature quality of infrared image downsampling. Then, a shuffled-CBAM was proposed to achieve feature extraction and fusion of key infrared targets and improve the accuracy of infrared target detection. Finally, the lightweight anchor-free network was used to predict the output result of railway object intrusion, overcoming the deficiency of poor real-time performance due to non-maximum value suppression operation with anchor frame detection, and it reduced calculation load and speeded up the detection efficiency. The experimental results show that the lightweight model has higher detection accuracy, and the size of the model is reduced by 179.01 MB after the improvement. The detection rate is increased to 39 frames/s, which is 3.9 times that of the YOLOv4 method. Compared with other detection methods, the proposed method can detect infrared railway object intrusion quickly and accurately.

In order to study the influence of surface ultrasonic rolling processing (SURP) on the fatigue properties of EA4T axle steel, the EA4T axle steel specimens were firstly treated by SURP technology, and the surface properties of the treated specimens were analyzed. The 3D surface morphologies, roughness, hardness, residual stress, full width at half maximum (FWHM), and crystal size were investigated. Then, the fatigue tests were carried out on the EA4T axle steel specimens using a rotary bending fatigue testing machine. The stress–fatigue life (S-N) curves and crack propagation behaviors were obtained, and the effect of SURP on fatigue properties and crack propagation behaviors of EA4T axle steels was analyzed. Finally, a back propagation (BP) neural network was used to establish the fatigue life prediction model of SURP EA4T axle steel, which took load stress amplitude, surface roughness, surface FWHM, surface hardness, hardened layer depth, surface residual stress, and depth of residual stress layer as input. In addition, the life of SURP EA4T axle steel specimens was predicted. The results show that SURP can reduce the surface roughness of the specimens to 0.17 μm and remove the groove morphology. Meanwhile, the surface hardness of the specimens is improved to 420 HV, and a surface residual stress of about −500 MPa and a residual stress layer with a depth of about 550 μm are introduced. There are conventional fatigue limits for grinding specimens, grinding with polishing specimens, as well as SURP specimens. The fatigue properties of grinding specimens and grinding with polishing specimens are basically the same, with a fatigue limit of 355 MPa. The fatigue property of SURP specimens is improved significantly, with a fatigue limit of 455 MPa, an increase of 28% compared with the grinding specimens. Fatigue fracture observations show that the fatigue cracks of all specimens initiate from the surface, and SURP cannot change the fatigue damage mechanism of the specimen. SURP can increase the threshold value of crack propagation of the specimen from 6.29 MPa·m^1/2 to 11.21 MPa·m^1/2, and it can slow down the crack initiation and propagation of short cracks, thus significantly improving the fatigue property of EA4T axle steel. The fatigue life prediction model of SURP EA4T axle steel has a prediction accuracy of 88.5%.

In the linear displacement measurement, the printed circuit board (PCB)-based new inductive displacement sensors is easy to lead to short-period errors in manufacturing, assembly, and other process links because of its large pitch. Among the types of short-period errors caused, the first-order and fourth-order errors are the most common short-period errors in PCB-based inductive linear displacement sensors. Therefore, in order to reduce the first-order and fourth-order errors, the generation mechanism of these two kinds of errors was first studied from the output signals, and then an error self-correction method that did not depend on external reference was proposed. Firstly, the sources of short-period first-order and fourth-order errors and the functions of the two errors with the original sine (SIN) and cosine (COS) signals of the sensor were analyzed theoretically. Then, a short-period error function model based on the characteristics of the original SIN and COS signals of the sensor was established, and the corresponding parameters of the first-order and fourth-order errors in the error function model were calculated based on the measured data of the sensor prototype. Finally, the first-order and fourth-order error models were used for the error compensation of the sensor prototype. The results of prototype experiments show that the peak-to-peak value of the error after compensation is reduced from 51.6 μm to 36.2 μm. The short-period first-order error is reduced by about 64.5%, and the short-period fourth-order error is reduced by about 83.0%.

The development of urban rail transit plays an important role in alleviating urban traffic congestion, and its regenerative braking energy utilization technology has attracted much attention. At present, the inverter regenerative braking energy utilization technology includes the topology structure of the feedback circuit, vehicle-network voltage relationship, and feedback device optimization. Other regenerative braking energy utilization technologies include various energy storage types such as supercapacitor energy storage, flywheel energy storage, and battery energy storage. On this basis, the regenerative braking energy utilization technology in urban rail transit based on inverter feedback and energy storage feedback was systematically and comprehensively reviewed, and the characteristics, trends, and key research issues in the development process of the technology were pointed out in terms of improving energy storage density, system stability, and device life, so as to provide guidance for further exploration and commercial development in this field. In addition, the research trends of regenerative braking energy utilization technology in urban rail transit were analyzed, and future research can focus on system topology optimization, energy storage capacity, system stability, service life, and technical and economic analysis.

The characteristic value of train wheelsets is closely related to the speed, and the quantitative analysis of wheelset faults requires signals with a certain length collected at a certain speed. However, such a signal is difficult to be obtained by the system working in the variable speed condition. Therefore, a signal reconstruction method that did not require any velocimeters was proposed to realize the above quantitative analysis. This method used short signal segments to splice the constant speed signals under the acceleration and deceleration conditions. Firstly, a short-time Fourier transform (STFT) peak search method was adopted to obtain the speed curve and extract multiple signal segments passing through a specified speed. Secondly, the signal segments were converted into an angular domain signal, and the phase difference between signals was determined by cross-power spectra density (CPSD). Then, according to the phase difference and the length of the front signal, the splicing position of signals was obtained, and interpolation and fusion techniques were used to ensure the continuity of spliced signals. Finally, the spliced angular domain signal was resampled into the time domain signal. A rotor test bench with a similar wheelset structure has verified that during acceleration and deceleration of a cracked shaft, the frequency spectrums of the spliced signals of each speed obtained by this method are highly close to the frequency spectrums of the constant speed signals obtained by the experiment. The relative errors of the 1x and 3x values between the spliced signal of 15.0 Hz and the constant speed signal are only 0.9% and 1.0%, respectively. After adding noise to the signals to be spliced and shortening them to 1.5 cycles, the splicing phase error does not exceed 10°.

Wheel polygonal wear will deteriorate the vibration environment of rail vehicles, lead to resonance fatigue failure of structural components, and seriously threaten driving safety. To study the formation mechanism of wheel polygonal wear of metro vehicles, the dynamic line tracking test was carried out, and the vertical coupling finite element model and dynamics model of the track were established. In addition, the iterative simulation analysis of long-term wheel-track wear was carried out. The results show that the wheel polygonal wear of 7–9th order occurs in the measured vehicle, which leads to the forced vibration of 50–70 Hz, and the frequency is close to that of the P₂ force during the coupling vibration of the wheel-track system. Through the iterative simulation analysis of wheel wear, it is determined that P₂ force resonance of the wheel-rail system caused by periodic irregular rail joint weld is the root cause of the 7th–9th order wheel polygonal wear. Under the long-term action of P₂ force, the floating slab track bed and the ladder sleeper track bed of steel spring will cause 8th and 15th order wheel polygonal wear, respectively.

The departure tracking interval is one of the main bottlenecks that limit the 3-minute tracking operation of trains, and compressing the departure tracking interval can effectively improve line capacity. The departure tracking process of high-speed trains was first analyzed, and a pre-departure annunciator was set at a certain distance inside the outbound annunciator, making the train have a certain initial speed and shortening the remaining outbound distance when the outbound annunciator was open. At the same time, the principle of “failure-oriented safety” for the pre-departure process was put forward to ensure that the train did not cross the outbound annunciator. Then, based on the analysis of factors affecting the compression of departure tracking interval, the curves of train control mode under different pre-departure schemes were studied. Finally, the high-speed yard of Shanghai Hongqiao Station was studied, and the results show that the departure tracking interval can be compressed by the proposed method. The compression effect increases first and then decreases with the increase in the pre-departure distance, and the maximum compressible departure tracking interval can be more than 26 s if the pre-departure distance reaches 200 m of the effective lengths of the arrival-departure track.

The periodic change of intersection signals in urban road systems leads to the uncertain delay of vehicle travel. In order to reduce the delays of vehicles at signal-controlled intersections, an improved hyperpath searching algorithm was proposed with the minimization of travel time on the road segments and the expected delay at the intersections as the optimization goal. First, according to the probability distribution function of vehicles arriving at the intersection, the expected waiting time and the turning movement proportion were derived. Then, the high-performance hyperpath searching algorithm was developed with the introduction of the label setting algorithm. Finally, the improved hyperpath searching algorithm was applied to the road network at Xinjiekou area, Nanjing, and the optimal hyperpath set was used to evaluate the applicability of the algorithm. The results show that compared with the shortest path strategy, hyperpath searching algorithm reduces the intersection delay and the total travel time by 67.1% and 22.3%, respectively as drivers shift to a driving route in the optimal hyperpath set. Furthermore, the hyperpath-based strategy can optimize the trip distribution in the road network, alleviating traffic congestion and contributing to flow equilibrium.

In order to determine the influence range of non-point source traffic congestion and identify key road sections, the risk field strength theory and the regional growth method were introduced to improve the plume model. The maximum and core influence ranges were determined, and key road sections were identified. First, the “source-path-sink” of non-point source traffic congestion was defined, and the “source” risk field strength model of non-point source traffic congestion was constructed based on the traffic survey data and traffic status data in Guiyang in 2021. By considering the traffic influence of different land use properties and the adjustment coefficient of different road grades for calibration, the identification model of the maximum influence range was established based on different “source” risks, and the regional growth method was introduced to establish a model for determining the influence range of the core area of the road section. Finally, based on the traffic volume, length, and time of the road section, the damage evaluation index of the road section with traffic congestion was constructed, and quantitative research on the degree of traffic congestion was carried out. The original model, the improved model, and the actual situation were compared. The results show that different land use properties and different road grades have different influences on traffic congestion in road sections. The improved identification model of influence range based on different “source” risks is more effective, and the prediction accuracy is increased by 3.54%, which is closer to the actual situation. With the regional growth method, the accuracy of the influence range of the core area of the road section with traffic congestion is higher, which is 2.66% different from the actual situation. In summary, a new idea for the delineation of the cumulative risk range of urban non-point source traffic congestion and the determination of key risk paths is provided, also serving as a theoretical basis for further governance of different types of traffic congestion.

In order to study the energy distribution inside the high-speed solenoid valve and the coupling relationship between the energy parameters and the dynamic response, the performance of the high-speed solenoid valve was optimized. Firstly, the dynamic model of the high-speed solenoid valve was established based on the finite element method, and the accuracy of the model was validated through the experimental data. Secondly, based on the D-optimal design of experiments and the method of least squares, the response surface prediction model of the solenoid valve’s dynamic response characteristics was constructed, with the energy parameters as the factors. Finally, based on the meta-analysis method, the simulation analysis of the dynamic response of the high-speed solenoid valve with significant energy parameters and parameter interactions was carried out. The results show that the eddy energy E₁ is the relatively sensitive parameter affecting the response time of high-speed solenoid valve opening T_o among the single parameters, and T_o increases by about 25% with the increase in E₁. The interaction between E₁ and damping energy E₃ and between E₁ and Joule energy E₄ is the highly sensitive parameter affecting T_o, and the interaction between E₁ and E₄ is the highly sensitive parameter affecting the response time of closing T_c. The results also find that the factors that play a dominant role in the interaction parameters change with the range of values.

In order to solve the problem of ground screw connection under large load of transmission angle steel tower, an embedded twelve ground screw joint structure was proposed. Based on the plastic yield line theory of stiffness difference evolution, the influence of the position of ground screws and the stiffness difference between ground screws and tower foot plates was considered, and the theoretical formula of uneven internal force between embedded ground screws and external ground screws under uplift load was derived. Then, combined with 24 sets of refined numerical analysis, the influence of different ground screw diameters, ground screw spacings, and tower foot plate thicknesses on the differences in uplift forces of internal and external ground screws was studied, and the correction coefficient of stiffness difference was calibrated. Finally, the theoretical formula was verified by 72 sets of numerical experiments. The research results show that the embedded twelve ground screw structure can improve the uplift bearing capacity of the joint by 40%–50% compared with the traditional eight ground screw structure; when the internal ground screw is arranged on the orthogonal line of the external ground screw, the uneven distribution coefficient of internal force of the internal and external ground screws under the uplift load is about 1.1, and it does not change with the diameter of the ground screw and the thickness of the tower foot plate. When the internal screw is close to the external screw along the diagonal, the uneven distribution coefficient of the internal force of the internal screw will decrease, but when the thickness of the tower foot plate increases, the uneven distribution coefficient will increase. The calculation results based on the plastic yield line theory of stiffness difference evolution of the tower foot plate are compared with the numerical simulation results. The average value of the ratio of the theoretical uneven distribution coefficient to the numerical uneven distribution coefficient is 1.01, and the coefficient of variation is 0.03.

The increasing speed of high-speed trains makes the dynamic problem of sound barriers prominent. In this study, the dynamic amplification factor of vertical sound barriers caused by high-speed trains was taken as the research object to explore the vibration characteristics and influencing parameters of vertical sound barriers. Firstly, the finite element model of the vertical sound barrier on a high-speed railway bridge was established, and its basic dynamic characteristics were analyzed. Then, the vibration law of the sound barrier under the fluctuating wind load of 400 km/h train was studied, and the dynamic amplification factor of the sound barrier steel structure was calculated based on it. Finally, the vibration response and dynamic amplification factor of the sound barrier were analyzed with multiple parameters. The results show that the dynamic amplification factor of the sound barrier column with a height of 5.0 m is about 2.76 when the train’s speed is 400 km/h. The distance between the installed sound barrier and the center line of the track is increased from 3.8 m to 4.7 m, and the dynamic amplification factor of the bending moment response is reduced by 0.3. The dynamic magnification factors of the bending moment responses of sound barrier columns with a height of 2.3, 3.3, and 5.0 m are 1.64, 2.52, and 2.76, respectively. The transverse displacement of the top is increased from 0.45 mm to 3.80 mm, while the bending moment of the bottom is increased by 26.8% and 60.8%, respectively. Increasing the height of the sound barrier is not conducive to the vibration characteristics of the structure.

The curve of the transition section of the terrain model at bridge sites in complex mountainous areas directly affects the accuracy of the wind tunnel experiment or numerical simulation results. To study the ideal form of line shape used in the boundary transition section of the terrain model at the bridge site, the principle of constructing line shape of the transition section was put forward based on the two ideas of setting up the transition section. The numerical simulation method was used to compare the three types of typical line shapes of the transition section in terms of the flow separation characteristics, mean wind speed profiles, wind attack angle profiles, and distribution of turbulent kinetic energy along the route under the uniform flow. The influence law of the slope change of the transition section on the flow field was also explored. The results show that the sine-squared curve exhibits superior characteristics compared with other line shapes, with a maximum shear stress difference of 3.77 × 10⁻³ Pa at the same location in terms of flow separation characteristics, a maximum wind speed difference of 0.09 m/s in terms of transitional performance of wind, and a maximum turbulent kinetic energy difference of 1.46 × 10⁻³ J. These findings provide important insights for selecting the line shape of the transition section of the terrain model at bridge sites.

In order to reveal the influence of the bending space effect on natural vibration frequency weakening, the additional deflection caused by the shear lag effect was selected as the generalized displacement, and the warping additional deformation of box girder was incorporated into the total kinetic energy of the system. The bending variational solution of the natural vibration frequency of box girder considering the influence of shear deformation, shear lag, and their double effects was established by using the Hamilton principle. The difference ratio parameter of spatial effect on natural vibration frequency weakening was introduced, and the influence of the section size and the side-to-middle span on the difference ratio parameter was analyzed in detail. The example analysis shows that the analytical solution of the natural vibration frequency of the box girder considering shear derformation and double effects is in good agreement with the finite element numerical solution. A larger frequency order indicates a greater weakening degree of each effect to the natural vibration frequency. The double effect is the most significant, which reduces the natural vibration frequency of simply supported and continuous box girders by 4.72% and 4.80% respectively for the first-order frequency. The larger span width ratio, width-to-height ratio, and side-to-middle span ratio indicate a smaller difference ratio of natural vibration frequency. A larger plate width ratio is accompanied by a smaller difference ratio of natural vibration frequency considering shear lag and double effect and a larger difference ratio of natural vibration frequency considering shear derformation . At the same span width ratio, shear lag and shear derformation effects weaken the natural vibration frequency to the same extent. At the different width-to-height ratio ratios, the shear lag effect weakens the natural vibration frequency to almost the same extent, and the shear derformation effect has a more significant impact. Low-order natural vibration frequency can be calculated using a box girder without a cantilever plate.

To ensure the construction safety of the complex spatial grid structure, the optimization analysis and monitoring of the construction process were carried out. An open single-layer spherical reticulated shell structure with a large rise-to-span ratio was taken as an example, and the construction process of this complex special-shaped structure was simulated through finite element analysis (FEA). By changing the boundary conditions of the support, the shape of the rib axis, and the support mode of the temporary support jig frame, different FEA models were established. The stress variations of key members and the structural displacement were analyzed to optimize the construction process. On this basis, the arc rod model with a temporary support jig frame was used as the final calculation model for construction process simulation, and the calculation results before and after unloading were compared with the on-site monitoring data to verify the accuracy of the FEA model in simulating the construction process. The failure sensitivity of the temporary support jig frame was further studied to avoid structural safety problems. The results show that the FEA model is consistent with the actual structure. The stress of each measuring point before and after unloading changes slightly, and the maximum tensile and compressive stress changes are 10.61 MPa and −5.67 MPa, respectively. The special-shaped spherical reticulated shell with a large rise-to-span ratio is in a controllable state during construction. The failure of a certain temporary support jig frame would have a great influence on member stress and structural displacement in the adjacent area. The maximum change of the member stress is 28.00 MPa, and that of the vertical displacement is 13 mm. Therefore, the reliability of the support jig frame shall be ensured during the construction.

The dam foundation leakage problem has been a key factor affecting the overall safety of reservoir dams. To effectively and accurately detect dam foundation leakage, the magnetoelectric method based on M sequence correlation identification technology was applied to the dam leakage detection based on the pseudo-random identification principle. Firstly, the distribution of magnetic induction intensity, mean square error, and variation coefficient under various leakage depth conditions were characterized through the analysis of physical model experiments. Then, various leakage forms, high-resistance shielding layers, and leakage channel numbers were designed, so as to obtain the response characteristics of the detection results to the inclined channel, high-resistance shielding layer, and multiple leakage channels. Finally, the field test of Hongshiyan Dam in Yunnan Province was conducted to study the feasibility of this technology. The results show that under different burial depth conditions, the variation coefficients of maximum magnetic induction intensity vary within 2%. Along the inclined leakage channel, the magnetic induction intensity decreases slowly, and the ridge direction of the magnetic field contour map can be considered as the inclined leakage direction. The magnetic induction intensity is affected by the high-resistance shielding layer and has an error between 10% and 20%. The multiple leakage channels can be reflected by the concentrative distribution of abnormal zones in magnetic field contour maps. The leakage directions are observed in the field test, containing NW300°, SW265°, W215°, and NW305°, respectively.

New geological phenomena have been found in the structural geological mapping of Niba Mountain tunnel field of Ya’an to Xichang section of Beijing−Kunming Expressway. To demonstrate the nature of the Niba Mountain fault zone and new tectonic phenomena of regional geological tectonic significance, using quartz particle morphology scan, geological mechanics and rockmass mechanics theory and numerical simulation analysis method, first elaborated the area of Niba Mountain tunnel engineering geological environment and the new tectonic phenomena, and then discusses the Niba Mountain fault zone boundary faults and tectonic activity, Secondly, the regional geological tectonic significance of the neotectonic phenomenon is discussed. Finally, the existence of the neotectonic phenomenon and the rationality of the evidence of the regional tectonic new framework are demonstrated by numerical simulation analysis. The results show that: 1) the Niba Mountain fault zone has obvious neotectonic activity characteristics; 2) the Niba Mountain fault zone to which the new tectonic deformation phenomenon belongs has genetic homology with the Xianshuihe active fault zone in the “Y” shaped active tectonic zone in western Sichuan, which is the southeast extension of the Xianshuihe fault zone; 3) the Niba Mountain fault zone and its southeastern extension fault (Ebian−Mabian−Leibo segment) and the “Y” shaped active tectonic zone in western Sichuan constitute the original “X” type tectonic model, and have the conditions for the breeding of moderate and strong earthquake activities.

Grout penetration in the unsaturated formation is a complex multiphysics process. In order to analyze more accurately the penetration characteristics of grout in saturated and unsaturated formations and estimate the range of grout penetration and grout compaction area, a multiphysics coupling model for unsaturated porous media was developed based on mixture theory. A novel five-degree-of-freedom eight-node quadrilateral axisymmetric Serendipity element was constructed through the secondary development of ABAQUS, so as to realize the numerical solution of soil deformation, soil porosity, pore pressure, and grout concentration distribution during grouting. The state variables, such as soil saturation and permeability coefficient, were updated in real time. The effects of grout water-cement ratio, grouting pressure, initial dry density, and water content of soil on the grouting in silty sand were analyzed with a three-dimensional axisymmetric grouting example, and the fitting curves of horizontal and vertical diffusion distance of grout with the above factors were obtained. The results show that the range of grout penetration is most significantly influenced by the water-cement ratio, followed by the grouting pressure, and it is least influenced by the water content and dry density of soil; the range of grout penetration increases with the increase in the water-cement ratio, especially when the water-cement ratio is greater than 1.0; a compacted area will be formed around the grouting pipe, where the soil is simultaneously subject to the grouting pressure and pore pressure; with the increase in the distance from the grouting pipe, the porosity of the soil gradually decreases in the compacted area and gradually recovers outside the compacted area, while the compacted area increases with the increase in the grouting pressure. The research results can provide theoretical guidance for calculating the grouting reinforcement in the soil.

In order to investigate the influence of the drainage boundary, which can better reflect the actual permeability, on the land subsidence caused by over-exploitation of groundwater, firstly, a one-dimensional consolidation model of aquitard caused by the dropping of groundwater table in phreatic aquifer with continuous drainage boundary was established by introducing the continuous drainage boundary, where the pore pressure decayed exponentially with time. Secondly, the general analytical solutions of the model and the analytical solutions of two special dewatering models for the instantaneous dropping of the groundwater table and the single-stage and constant-rate dropping of the groundwater table were obtained by using the method of separate variables. Then, the correctness of the analytical theory in this paper was preliminarily verified by the degeneracy of the analytical solutions under certain conditions. Finally, the single-stage and constant-rate dropping of the groundwater table was taken as an example, and the consolidation curves of the aquitard under different interface parameters B were calculated based on the analytical solutions. In addition, the influence of interface parameter B on the consolidation behaviors was analyzed emphatically. The results show that the maximum error rate is 13% by comparing the theoretically calculated settlement curve with the experimental settlement curve, which further indicates that the continuous drainage boundary is closer to the actual permeable boundary. Furthermore, larger interface parameter B indicates (better water permeability of the drainage boundary) a faster pore pressure dissipation rate, faster consolidation rate, and shorter consolidation time, but the final consolidation state is not affected.

In order to explore the variation of settlement and stress of the karst cave backfill and natural accumulation layer at different depths, a giant karst cave backfill project in the Yujingshan tunnel of Chengdu—Guiyang railway was studied. A 1∶100 laboratory centrifugal model test was carried out to analyze the long-term deformation law of the inhomogeneous natural soft accumulation layer at the bottom of the karst cave, in which the river sand with a particle size of less than 2 mm was used to simulate the karst cave backfill, and the western Sichuan clay was used to simulate the soft soil layer at the bottom of the karst cave. The reliability of the laboratory test was verified by field monitoring results. The results show that the deformation of the karst cave backfill basically reaches a stable state within 1.5 years after the termination of construction, and the deformation is about 86.9% of the total settlement; the deformation of the soft soil layer is the main component of the soil deformation at the bottom of the tunnel, and its deformation accounts for about 87.5% of the total settlement. The settlement at the bottom of the tunnel is positively correlated with the thickness of the soft soil layer, and when the thickness of the soft soil layer is less than 12.5 cm, it has less influence on the settlement at the bottom of the tunnel. The difference in settlement deformation between the model test and the on-site monitoring is only 3.83%, indicating that the experiments conducted in this article can reflect the long-term deformation characteristics of the soil at the bottom of the tunnel.

To improve the economic benefits of engineered cementitious composite (ECC) and control the repair cycle, the polypropylene fiber-sulfoaluminate cement-based (PP-SACC) repair materials were designed with polypropylene fiber featuring low cost and sulfoaluminate cement featuring fast hardening and early strength employed as the key components. The influence of water-binder ratio, fiber content, and aggregate size on the bending properties of the repair materials was explored. In addition, the grey relation model was used to comprehensively evaluate PP-SACC under all working conditions. The results indicate that the fiber content is the most important factor that affects the strength, toughness, and crack characteristics. The influence factors of fiber content on initial crack strength, toughness index, and average crack width are −0.68, 0.79, and −0.98, respectively. The aggregate size can significantly affect the crack characteristics. The influence factor of quartz sand size on the average crack width is −0.86. The water-binder ratio also greatly affects the strength and toughness, and a reasonable water-binder ratio is beneficial to leverage the bridging effect of the fiber. The PP-SACC repair material has excellent toughness and flexural hardening properties.