Research purposes: At present, there are few research results on ultra deep circular diaphragm walls, and the understanding on its deformation characteristics lags behind engineering practice. This paper takes the south anchor ingot ultra-deep circular foundation pit of Qipanzhou Yangtze River Highway Bridge as the research object, and deduces the horizontal displacement formula by establishing the plane polar coordinate equation. FLAC^3D is used to establish a three-dimensional model with uneven geological conditions, and the overall mechanical characteristics and deformation rules of the circular diaphragm wall are compared and analyzed.
Research conclusions: (1)The calculated, monitored and simulated values of deep horizontal displacement vary little at the same depth, the bedrock has a significant anchoring effect on the diaphragm wall.(2)The variation law of circumferential stress is similar to the variation of deep horizontal displacement; the position of the maximum circumferential stress is close to the point of the maximum deep horizontal displacement.The transverse distribution of circumferential stress is relatively uniform and the transverse variation law of the maximum point of circumferential stress is similar to a cosine function.(3)The conclusion can provide reference for practical engineering applications and for the analysis of the mechanical properties and deformation law of super deep circular diaphragm walls.

Research purposes: With the continuous accumulation of service time, the subgrade of high-speed railways will inevitably undergo aging, resulting in an increasingly aggravating trend of mud pumping disease. Research on the migration characteristics of fine particles under the dynamic loads of high-speed trains is of great significance for analyzing the evolution mechanism of subgrade diseases such as railway mud pumping. In this paper, experiments on the migration of fine particles in saturated silty sand subgrade under the dynamic loads of high-speed trains are carried out, and the effects of different fine particle contents (silt content), dynamic load amplitudes, etc. on the excess pore water pressure, axial strain and fine particle migration characteristics of soil samples are analyzed.
Research conclusions: (1) In the experiment, the intrinsic mechanism of fine particle migration was explored by controlling the fine particle content in subgrade soil samples, and it was concluded that an increase in fine particle content would enhance the peak value of excess pore water pressure in silty sand-filled subgrade soil samples. (2) Increasing both the amplitude and frequency of dynamic loads would augment the peak excess pore water pressure, with the increase in frequency being unfavorable to the dissipation of excess pore water pressure within the subgrade soil; as the excess pore water pressure gradient increases, the average migration height of fine particles in the soil samples also rises. (3) The results of this experimental study are of great significance for understanding the disaster-causing mechanism of mud pumping in high-speed railway subgrades.

Research purposes: The traditional slope anchorage reaction structure has the problems of a single internal structure, insufficient bearing capacity, and low construction efficiency. In this paper, a new type of precast slope anchorage reaction structure with built-in composite steel is proposed. By designing six kinds of joint specimens with different skeletons and steel ratios, the local pressure test of these joints is carried out indoor. The failure mode, crack development law, bearing capacity, and deformation characteristics of each specimen are compared and analyzed to explore the mechanical properties of the structure.
Research conclusions: (1) The failure mode of the specimens is characterized by local pressure splitting along the diagonal of the local pressure area from the top through the side to the bottom.(2)The crack range and the maximum crack width of the embedded composite steel specimen are significantly smaller than those of the pure steel specimen. And the crack propagation before the failure of specimens with embedded composite steel lasts longer, which indicates that the structure has good plastic deformation capacity. (3) The square steel tube of the joint has strong constraint capacity, which enhances the joint compressive capacity of the new reaction structure. The ultimate load of the pure steel specimen and the steel and steel bar composite specimen increase by 13% and 17% respectively compared to the pure steel bar specimen. (4) The deformation coordination capacity is better than that of the pure steel bar specimen with spiral reinforcement, and the transverse strain development of steel tube confined concrete is more gentle. (5) The results can provide new approaches for the design of counter-force structures and the study of bearing capacity of slope anchorage engineering.

Research purposes: During the service life of concrete structures, there will be a certain degree of stiffness degradation. To investigate the impact of concrete structure stiffness degradation on the vibration of existing rail-box girder systems, this study is conducted against the backdrop of high-speed trains traveling at 400 km/h. A coupled rail-box girder system model incorporating stiffness degradation is established, and the correlations between high-speed railway service life, stiffness degradation, and system vibration response is analyzed in order to elucidate the trend of stiffness degradation and evolution of vibration in high-speed railways after speed-up operation.
Research conclusions: (1) With the continuous increase of service time of the rail-box girder system and the action of long-term train moving loads, the stiffness of the rail-box girder system will continue to degrade. The rate of stiffness degradation decreased sharply in the early period of system service, stabilized in the middle period, and continued to increase after more than 53 years of system service. After 60 years of service, the system stiffness will degrade to less than 88.7% of the initial stiffness. (2) With the continuous stiffness degradation, the vibration response of the rail-box girder system will continue to increase. In the 60th year of service, the vibration displacement of the track plate and box girder roof will increase by 22.15% and 11.58% respectively. (3) The stiffness degradation reduces the natural vibration frequency of the track-box girder system, in which the first-order natural vibration frequency decreases from 5.69 Hz to 5.47 Hz. (4) The research results can provide a theoretical basis for the speed increase of the existing track-box girder system to 400 km/h and its safe operation management.

Research purposes: In order to quickly and effectively identify wheel-rail corrugation on the metro line, a corrugation characterization research is conducted with measured axle box vertical vibration acceleration data. First, the basic conditions of the actual line and the basic parameters of the measurement were described. Then, the acceleration data were subjected to a partitioned frequency domain transform and the corresponding eigenfrequencies and amplitudes were extracted, so as to determine the corrugation degree and the distribution interval. Finally, combined with field investigation, the validity of the interval analysis method was verified.
Research conclusions: (1) Axle box vertical vibration acceleration amplitudes can be used to identify the damage degree of rail corrugation and wheel polygon, and to determine the interval location of damage occurrence. (2) Axle box vertical vibration acceleration eigenfrequencies can be used to identify rail corrugation and wheel polygon damages, and are able to determine the occurrence intervals of both damages. (3) The measurements of operating vehicle wheels and specific track intervals validate the feasibility of the corrugation interval analysis method, and the method can provide references for metro maintenance and repair operations due to its ability to quickly identify wheel-rail corrugation.

Research purposes: The construction of railway bridges continues to extend into high-intensity seismic areas such as southeast Tibet, west Sichuan, and northwest Yunnan, where the combined seismic isolation system of "seismic isolation bearing + metal damper" is widely used. To find out the influence of earthquake characteristics and structural characteristics on the seismic performance of the combined isolation system, this paper takes railway prototype bridges and prototype piers as the engineering background,it establishes 22 bridge models with different pier heights and pier height differences, and explores the changes in pier stiffness and stiffness ratio of adjacent piers. The influence mechanism of site type change, and long-period and near-fault characteristics on structural seismic response is presented, and the applicable conditions and scope of the railway bridge combined seismic isolation system are proposed.
Research conclusions: (1) With the increase of pier height, the bending moment of pier bottom gradually increases, and the deformation of bearings gradually decreases; With the increase of height difference between adjacent piers, the bending moment of high pier increases gradually, and the deformation of low pier bearings increases gradually. Long-period, near-field earthquakes and weak fields will limit the adaptability of the combined isolation system. (2) For Class I to II sites, the combined seismic isolation system is applicable when the longitudinal stiffness of piers is not less than 396 kN/cm; For Class III and Class IV sites, the longitudinal stiffness of piers should respectively be greater than 634 kN/cm and 1 056 kN/cm. (3)In Class I and II sites, the combined seismic isolation system is applicable when the longitudinal stiffness ratio of adjacent piers is not less than 0.3; In Class III and Class IV sites, the longitudinal stiffness ratio of adjacent piers should be greater than 0.39 and 0.55, respectively. (4) For Class II sites, under the long-period and near-field earthquakes, the combined seismic reduction and isolation system is suitable for bridge structures with longitudinal stiffness of piers greater than 1 207 kN/cm. (5) The research ideas and conclusions of this paper have guiding significance for standardizing the seismic isolation design of railway bridges and for determining reasonable design parameters, and can provide support for the formulation of relevant technical standards.

Research purposes: In order to investigate the functional damage of high-speed railroad extradosed cable-stayed bridges, combined with engineering practice, this paper establishes a fragility research framework, takes uncertainty into consideration, adopts incremental dynamic analysis method(IDA), carries out functional fragility analysis, generates component and system functional fragility curves, and deeply investigates the difference and connection between functional and bearing damage.
Research conclusions: (1) At the component level, in high-speed railroad extradosed cable-stayed bridges the highest damage exceedance probability is caused by changes in girder end angle, and it is necessary to strengthen the control of functional damage of bridges in earthquakes.(2) Under the low-intensity earthquakes, the probability of exceeding the bearing damage is greater than that of the functional damage for the slight and moderate damage, and the probability of exceeding the functional damage is gradually increased along with the increase of the intensity of the ground shaking until the serious damage state, and the bridge is most fragile to the functional damage.(3) In terms of systematic damage, the structure is most prone to functional damage for moderate and serious damage. The functional damage of HSR is different from the traditional bearing susceptibility, and the difference is large.(4) This study provides reference for the bridge seismic functional damage on the post-earthquake bridge operation safety assessment and seismic design, which is of theoretical and practical significance.

Research purposes: The steel box composite beam with corrugated steel webs is a new type of steel-concrete structure, and the study of its mechanical properties helps optimize the design of this type of structure. This paper introduces the influence of the self-equilibrium condition on shear warping stress, and the elastic control differential equations of the composite box girders are established using the energy variational method. Furthermore, based on theoretical exploration, finite element simulation and experimental research, a refined analysis of the mechanical properties of this new composite box girder is achieved.
Research conclusions: (1) The stronger the boundary constraint conditions of steel box composite beams with corrugated steel webs, the more significant the influence of self-equilibrium conditions on their mechanical properties. The influence rate of the self-equilibrium condition is between 3.5% and -3.5% for the simply supported box girder. However, the influence of the self-equilibrium condition increases dramatically in the continuous composite box girder, and its influence rate reaches -23.6% at the intersection of the steel base slab and the webs under concentrated load, compared to 13.1% under the uniform load. (2) The self-equilibrium condition has a significant impact on the shear lag effect of these new continuous composite box girders. Compared with the traditional shear lag theory, the self-equilibrium condition under uniform load enhances the shear lag effect of the composite box girder. At the intersection of the steel base slab and webs, the traditional theoretical shear lag coefficient is 1.25, while the theoretical value in this paper is 1.42. However, the concentrated load is the opposite. At the intersection of the steel base slab and webs of the composite box girder, the traditional theory and the theoretical shear lag coefficients in this paper are 1.64 and 1.28, respectively. (3) The calculation accuracy by this method has been significantly improved, and the normal stress value of its steel base slab is about 20 times that of the RC top slab.(4)Therefore, this paper accurately analyzes the mechanical properties of the composite box girder with corrugated steel webs and steel base slab, clarifies the influence law of the self-equilibrium condition on mechanical properties, which will promote the improvement of the design theory of such structures.

Research purposes: In response to a series of problems such as severe cracking, excessive deflection, and intensified vibration of existing railway short-span bridges under large axle load transportation conditions, taking the replacement construction of more than 30×12.0 m-span slab beams on a heavy-haul railway as the background, static load tests, numerical simulations and practical engineering applications were used to conduct static adaptability tests and ultimate bearing capacity research on a new type of short-span integral prestressed slab beam under large axle load transportation conditions, and to explore the rapid replacement technology of short-span beams on busy trunk lines.
Research conclusions: (1) Under the 1.2 times design static live load, the load strain/displacement curves at key positions of the short-span integral prestressed slab beam show linear changes, and the measured strain and displacement of each control section are smaller than the theoretical calculation values. During the experiment, the plate beam did not crack and remained in the elastic working stage. (2) The results show that the mid-span moment of the integral plate girder is 1.67×10⁴ kN·m when the damage occurs, and the damage is characterized by the collapse of the concrete at the top. (3) By adopting the overall frame replacement technology of "crane+trolley", it is possible to replace the entire hole plate beam within four hours of skylight time. (4) The research results of this paper can provide a reference for the strengthening and renovation of heavy-haul railway bridges.

Research purposes: Because of the prominent temperature effect of the Corrugated Steel Web (CSW) composite box girder, as well as the problems of inconvenient calculation and difficulty in application and promotion, this paper establishes a new beam element: the CSW beam element. The displacement shape function of the CSW beam element is derived based on the polynomial displacement distribution mode, and the stiffness matrix of the CSW beam element is derived according to the principle of virtual work. Based on the principle of minimum total potential energy, the temperature force array under the temperature load effect of the top slab and steel web is derived. Finally, the temperature effect is integrated into the calculation of the CSW beam element, laying a theoretical foundation for the integration of the CSW beam element into the widely used rod-system structure finite element system.
Research conclusions: (1) A comparison of the calculation results of three models shows that the overall variation trend of vertical displacement of the three models is consistent, and their peak values are relatively close, with the maximum relative error not exceeding 5%, which proves that the calculation results derived from the theory in this paper under static loads and temperature loads are consistent. (2)A calculation program for CSW beam bridges is compiled using MATLAB. By comparing its calculation results with those of the ANSYS model and test results, the correctness of the derived formulas and the calculation program is verified. (3) The method can effectively consider the influence of temperature fields on the mechanical properties of structures and provide technical support for the analysis of CSW beam bridges in complex environments.

Research purposes: With the increasing development of tunnel engineering toward greater burial depths and longer distances, the Tunnel Boring Machine (TBM) has been widely adopted due to its advantages of high automation, minimal environmental disturbance, and high construction efficiency.However, in hard rock strata, TBM performance struggles to align with the encountered geological conditions. Adjustments to key boring parameters are predominantly dependent on operator’s experience, and there is a lack of effective rock fragmentation optimization strategies. This frequently leads to impeded advance rates, overloading of cutting tools, and significant project delays. Therefore, based on CSM model a Simplified CSM Model (SCSM) is proposed to express the relationship between tunneling parameters and geological environment. According to the limit performance constraints of equipment thrust, torque and slag discharge, the feasible region of tunneling parameter optimization problem is partitioned, and the optimal control parameters are solved by multi-mode.
Research conclusions: (1) Based on field tunneling data from the ​Yinsong Project, a critical thrust empirical formula is derived via linear fitting. Based on the Hanjiang-to-Weihe River Project, a rock-breaking mode zoning model is established by incorporating critical thrust and the FPI (Field Penetration Index). Within the partitioned feasible domain, ultra-hard rock is defined according to TBM performance limits, and optimization strategies,including a ​rock abrasion mode for ultra-hard rock and tailored approaches for schist and mixed modes are proposed. (2)Applied to the section K29+169.2~K33+613.1of the Hanjiang-to-Weihe River Project-Lingnan Section, the proposed strategies reduce tunneling energy consumption by 5.5% and significantly improve progress. (3) Results demonstrate that the multi-modal parameter optimization strategy fully exploits TBM performance in medium-to-low strength rocks, while enabling multi-objective optimization balancing schedule and energy efficiency in ultra-hard rock conditions.

Research purposes: To investigate the damage characteristics of the large-diameter shield tunnel under high water pressure, a prototype loading failure test was conducted on a staggered-joint segment structure using the “Shield Tunnel Structural Loading Device”, based on the Sutong GIL comprehensive gallery project shield tunnel. The failure process of the segment structure was analyzed, and the failure mechanism and bearing performance of the segment structure were explored, to provide a reference for the design of high water pressure large-diameter shield tunnels.
Research conclusions: (1) The deformation of the segment structure shows a "horizontal duck egg" shape, with a maximum diameter change rate of 9.52‰, and a maximum longitudinal seam opening of 12.87 mm. (2) The inner curved surfaces of the arch top and the arch bottom are subjected to tensile cracking and failure, with a maximum crack width of 4.5 mm and 11.5 mm, respectively. The total length of the cracks is 54.80 m, with a total of 235 cracks, mainly longitudinal cracks. The outer curved surface of the left arch foot and the right arch shoulder are subjected to tensile cracking and failure. The total length of the cracks is 64.70 m, with a total of 65 cracks and a maximum width of 0.1 mm. (3) The failure of the segment goes through three stages: elasticity, elastic-plastic deformation, and failure. The cracking has little effect on the overall stiffness reduction of the structure. The mechanism of the segment failure is that as the depth of the crack increases, the steel bars enter a yielding state. The central axis of the segment continuously moves upward, reducing the effective bearing area of the core concrete, resulting in a gradual decrease in the stiffness of the segment structure until a geometrically variable mechanism is formed. The decrease in bending moment and eccentricity, the increase in displacement, and the decrease in structural bearing capacity lead to local instability and failure of the segment structure. The ultimate bearing load of the segment is 2 827.2 kN, and the safety factor of the ultimate bearing capacity is 1.632. (4) The research results can provide a reference for the design of high-pressure, large-diameter shield tunnels.

Research purposes: Aiming at the difficulty of dynamic early warning during the construction of tunnels with different levels of large deformation in extreme high ground stress environments, this paper, taking an extremely high ground stress soft rock tunnel in Sichuan as the engineering background, carries out quantitative research on ground stress inversion and the laws of large deformation of surrounding rock. A ground stress inversion program based on a genetic algorithm is developed to provide reliable ground stress boundary conditions for numerical simulation. Synergistic evolution curves of surrounding rock and support structures under different levels of large deformation are constructed, and through coupling analysis of the curves, dynamic early warning thresholds for surrounding rock stability are determined. The weight of displacement contribution rate is introduced to realize dynamic quantification of deformation contribution values of each step in different construction stages.
Research conclusions: (1) The intelligent inversion model of ground stress based on genetic algorithms integrates the geological tectonic field and monitoring data to achieve accurate reconstruction of the extremely high ground stress field with a 95% confidence level. (2) A surrounding rock-support co-evolution curve is constructed, the critical correlation between the cross-evolution node of the characteristic curve and surrounding rock instability is revealed, and the stability discrimination and early warning index is proposed. (3) A dual-control dynamic early warning system of "large deformation grade-construction stage" is proposed, forming a full-cycle decision chain of "monitoring-diagnosis-regulation", which provides a basis for ensuring the safety of tunnel construction and formulating practical early warning strategies. (4) The research results provide technical support for graded early warning and precise prevention and control of large deformation disasters during the construction of tunnels with extremely high ground stress, and offer valuable references for similar tunnel projects under complex geological conditions.

Research purposes: The sharp increase in data volume at the railway power supply cluster monitoring data center can easily cause delays in the monitoring system, posing a huge threat to the safety of railway power supply. For the massive power data processing problems, the industry generally uses database technology to cache hot data, the existing cache replacement strategy hit rate is not high, it is difficult to effectively respond to the complex and variable data access load patterns and other issues. Based on the existing cache replacement strategies, this paper designs a new VCRS cache replacement strategy. By comparing it with traditional cache algorithms, the efficiency of this method is verified.
Research conclusions: (1) The proposed VCRS cache replacement strategy is improved on the basis of the LRU algorithm, which uses "time" as the elimination index, and the LFU algorithm, which uses "frequency" as the elimination index, and it can make full use of cache resources to improve the access performance of the whole system. (2) VCRS cache replacement method can obtain higher cache hit rates than LRU and LFU under different data access scenarios, and the time consumption is comparable to that of the existing method. (3) The results of this research can be applied in the field of railway power supply cluster monitoring, which provide a new way of thinking to improve the fast response of the monitoring system.

Research purposes: To explore the regularity of surface settlement caused by the construction of super-large section double-line tunnel, this paper relies on the 8714 project of the Stockholm Metro Blue Line extension in Sweden, adopts numerical simulation to analyze the deformation characteristics and surface settlement laws of super-large section tunnel under different excavation methods and double-line construction spacings, and aims to obtain an appropriate excavation method and double-line construction spacing, thereby providing a reference for similar engineering constructions.
Research conclusions: (1) The arch deformation and surface settlement during the tunnel excavation process prove that the double-sidewall heading excavation method is the most suitable, and the damage to the surrounding rock stability is the smallest. (2) After the double-line tunnel excavation, the surface horizontal settlement curve presents the ‘V’ shape. Due to the stacking effect of double-line tunnel successive construction, the maximum settlement position is biased to the tunnel of the later construction. (3) The larger the interval between the excavation surface of the double-line tunnel, the less disturbed the tunnel surrounding rock and the smaller the ground surface settlement value after construction, so it is recommended to take the method of excavating the left line first and then the right line in actual construction. (4) The research results provide a reference for the design and construction of similar super-large section double-line tunnels.

Research purposes: The geometric shape of rail transit U-shaped beams is unique, and there is a lack of research on their temperature field. It is urgent to obtain the distribution law of solar radiation temperature field on U-shaped beams, to provide a basis for the accurate calculation of temperature effects. This paper studies the temperature field of a rail transit U-shaped beam in Qingdao using on-site testing and numerical simulation methods. Based on measured solar radiation intensity data, the relevant parameters of the clear sky theory model are adjusted, a three-dimensional transient finite element analysis model of the U-shaped beam temperature field is established, and its boundary conditions and initial conditions are determined. The numerical calculation of the temperature field is compared with the on-site measured results for verification, and further comparisons are made between the solar radiation temperature gradients of U-shaped beams and box beams.
Research conclusions: (1) At noon in July, the maximum temperature difference in the cross-section reaches 17°C, with the upper surface of the top and bottom plates having the highest temperatures. The vertical downward temperature along the height direction of the top and bottom plates shows a nonlinear decreasing trend. (2) The shading effect of the U-shaped beam web results in the temperature in the shadow area of the bottom plate being lower than that in the illuminated area, creating a significant horizontal temperature difference. (3) Except near the beam ends, the temperature distribution of the U-shaped beam changes only slightly along the vertical direction. Due to the bidirectional heat convection at the edges of the outer surface of the U-shaped beam, the temperature is closer to the ambient temperature, forming a banded temperature distribution around it. (4) Compared with box beams, U-shaped beams do not have the shading effect of the top plate, resulting in significant differences in solar radiation temperature gradients between the two. It is necessary to further study the normative mode and magnitude of U-shaped beam temperature gradients. (5) This study provides references for the design, operation and maintenance of U-shaped beams.

Research purposes: High-speed rail (HSR) plays a crucial role in fostering China’s new development paradigm and promoting high-quality growth. To address the dual challenges of expanding debt and stagnant operational efficiency of China’s HSR, this study constructs a “cost reduction-revenue expansion-sustainability” analytical framework. It employs the activity-based costing method to meticulously analyze the cost constitution, utilizes break-even and sensitivity analysis approach to identify key profitability drivers, and quantitatively evaluates HSR’s comprehensive advantages based on the “Energy-Economy-Environment” (3E) theory.
Research conclusions: (1) The average operational cost of China’s HSR is 0.372 yuan/ (passenger -kilometer), with capital cost (46.15%) as the dominant component, followed by transportation cost (36.16%). (2) The daily train densities required to achieve cash-flow balance and full cost break-even are 25 and 84 respectively. (3) Sensitivity analysis reveals that increasing the occupancy rate is the most effective factor in lowering the break-even point, followed by reducing construction costs. (4) Key pathways for enhancing operational efficiency include: implementing refined life-cycle cost management, diversifying revenue streams, and leveraging the comparative green advantages of HSR. (5) The study findings provide valuable references for HSR investment and operational management, thereby contributing to the sustainable development of the HSR in China.

Research purposes: At present, research on the whole-process cost control system based on cost information and data is relatively rare, and the research on the nonlinear prediction and control of the engineering investment target needs to be further deepened.In view of the unavoidable investment overrun problem of large-scale construction enterprises' construction projects, this paper takes a large-scale construction enterprise's housing construction project as an example, and comprehensively integrates cosine similarity algorithm, BP neural network, saliency theory, earned value method and PDCA cycle,to achieve the effective control of investment in construction projects for large construction enterprises.
Research conclusions: (1) From the perspective of the engineering construction enterprise, making full use of the advantages of large construction enterprises,including rich construction experience and sufficient historical cases, this study establishes a database of completed projects of large construction enterprises, providing a basis for subsequent research. (2) By adopting the cosine similarity algorithm, BP neural network and saliency theory, this study constructs a three-level prediction model for construction project investment targets from three perspectives: total investment target, sub-item project and measure project investment target and labor cost, material cost and construction equipment use cost investment target , improving the accuracy of investment target forecasting.(3) Using earned value method and PDCA cycle management concept, dynamic analysis and optimization of significant sub-item project investment targets is achieved, and the establishment of a graded early warning system for investment deviations enables effective construction project investment control.(4) This study can provide reference for large construction enterprises' construction project investment control.