Vibration generated by train operations inevitably exerts negative impacts on the surrounding environment. As a commonly adopted vibration control measure along the transmission path, vibration isolation piles have been widely implemented. This study, based on traditional vibration isolation pile technology, proposes for the first time an improved structural design combining rubberized concrete and a top cap beam as a comprehensive solution aimed at enhancing vibration isolation performance. Furthermore, scientific modeling is conducted based on model tests, and the vibration isolation performance of various pile types in single-row and triple-row configurations is subsequently investigated. The results indicate the following: 1. Ground surface vibration behind the piles attenuates in a "wave-like" pattern with increasing distance. Installation of different types of single-row piles effectively reduces vibration levels behind the piles; however, a vibration amplification effect is observed in front of the piles. 2. Among triple-row configurations, the hexagonal arrangement demonstrates superior vibration isolation performance behind the piles compared to the square arrangement. 3. Compared to conventional concrete vibration isolation piles, the incorporation of rubber significantly enhances the vibration isolation effectiveness behind the piles for both single-row and hexagonal triple-row configurations. 4. Improved vibration isolation piles exhibit excellent performance in mitigating vibrations both in front of and behind the piles. Moreover, their vibration isolation capacity is positively correlated with the depth of the top cap beam, indicating promising potential for practical applications.

To investigate how aggregate geometry influences mortar damage initiation and connectivity, this study develops a morphology-based, three-dimensional mesoscale finite element model with conforming aggregate-mortar meshes and interfacial transition zone (ITZ) cohesive elements. Pair-level statistics over more than one thousand neighboring aggregate pairs are used to relate corridor mortar damage to the minimum surface-to-surface gap gmin, the pair-axis angle θz, and a geometric confinement index GCI=sin⁡θz/gmin. Finite element damage results are extracted at both aggregate-pair and mortar-element levels, and combined with gradient boosting regression, activation-order analysis, and connected-component analysis to quantify damage magnitude, damage sequence, path selection, and spatial connectivity. Results show that: (1) inter-aggregate spacing and its derived descriptors are the most influential predictors of mortar damage, collectively accounting for more than 52% of the total model importance; (2) High-GCI aggregate pairs are preferentially activated at damage onset, with 23 of the 50 highest-GCI pairs activated during the initial damage stage, compared with 6.14 expected under random selection; (3) damage connectivity evolves from isolated local activation to a global aggregate-spanning network, with the activated-pair ratio increasing from 12.2% to 74.1% as the activated-pair network expands to span all aggregates; (4) late-stage severe damage is systematically biased toward high-GCI aggregate pairs, whose mean GCI exceeds the global average by 30%.

To assess how staged vertical excavation of an overlying foundation pit affects invert-filling disengagement in a shield tunnel, a three-dimensional model was developed to explicitly incorporate the invert-filling, staggered-joint segmental lining, reinforcement cages, and bolts, with diaphragm walls and steel struts serving as temporary supports. A framework based on a coordinate-mesh index was established to locate and quantify interface disengagement. Nonlinear regression and k-means clustering were employed to derive deformation-control thresholds from disengagement indicators, enabling quantitative risk assessment and supporting early-warning decisions. The main findings are as follows: (1) As excavation deepens, the tunnel-invert-filling interface undergoes three progressive stages: edge-induced tension-shear degradation, waist-centered disengagement, and central detachment with residual compressive contact at both ends. (2) Vertical settlement rebound ratio (SRR) and lateral convergence rebound ratio (CRR) exhibit nonlinear correlations with disengagement volume. Disengagement remains Stable when SRR < 6.364 % and CRR < 8.403 %; Alert when SRR is between 6.364 % and 24.572 % or CRR between 8.403 % and 23.483 %; and Critical beyond these limits. (3) Volumes of 0.0014-0.0959 m(3) denote the Alert state, whereas volumes >0.0959 m(3) indicate severe disengagement. (4) CRR governs disengagement-volume prediction (>96 % importance), with a 95 % probability of reaching Critical state at threshold-exceeding the 91 % probability associated with SRR.

Real aggregate geometry contains hierarchical morphological information that can affect mesoscale stress transfer, ITZ degradation, and mortar plastic localization. However, mesoscale models usually introduce aggregate geometry as a whole, making it difficult to determine which geometric component controls each mechanical response. This study therefore builds a matched four-level RVE system from a structured-light scanned crushed-stone library, consisting of spherical, ellipsoidal, convex polyhedral, and computational aggregate models. A geometry retention index (GRI) based on Wadell sphericity was defined to decompose the geometry recovery path into three stages: morphological anisotropy, angularity, and surface roughness with curvature irregularity; their mechanical contributions were assessed under identical material parameters, volume fraction, and loading conditions. The results indicate that (1) aggregate geometry has limited influence on the elastic modulus and peak stress, whose ranges are only 2.2% and 4.5%, but strongly affects the post-peak response, with the residual load-bearing ratio rising from 0.407 to 0.489; (2) angularity is the dominant geometric stage for post-peak load transfer, contributing 53.7% of the residual-load-bearing-ratio increase and changing ITZ damage from smooth-interface spreading to localized degradation with extensive low-damage interfaces; and (3) surface roughness and curvature irregularity reduce the aggregate stress concentration factor (SCF) from 27.5 to 17.4 while raising the peak equivalent plastic strain (PEEQmax) from 0.074 to 0.098, showing the importance of computational aggregate geometry for surface-detail-sensitive local responses under the examined quasi-static compression condition.

To quantify the influence of real aggregate morphology on aggregate-mortar interfacial transition zone (ITZ) damage initiation and evolution in concrete, this study combines nonlinear threephase mesoscale finite element modeling with real-aggregate geometric descriptors and machine-learning-informed feature analysis. The model represents real-shaped aggregates, a mortar phase described by concrete damaged plasticity, and zero-thickness cohesive interfaces with nonlinear degradation. Directionality, normal-loading coupling, surface morphology, and curvature statistics describe aggregate geometry, while cohesive SDEG (Scalar Stiffness Degradation) defines aggregate-level mean and peak ITZ damage. Feature-group incremental gradient boosting regression (GBR) and rank-correlation analyses are used to identify damage-relevant geometry-damage associations. Results show that: (1) mean ITZ damage is mainly associated with aggregate-scale orientation and surface normal-loading coupling; coupling and directionality increase cross-validated R-2 by 0.188 and 0.162, and the surface-normal descriptor <(n(z)(2))over bar> gives the strongest partial correlation (rho(p) = 0.697). (2) Peak-damage evolution is more closely related to fine surface complexity during the pre-peak damage-growth stage; the curvature-roughness descriptor f(HC) and surface-angularity descriptor (beta) over bar show the most pronounced associations with peak-damage level and growth characteristics. (3) The two damage indicators provide complementary information on ITZ degradation. Mean SDEG reflects aggregate-scale interfacial degradation, whereas peak SDEG captures localized damage concentration. Reliable mesoscale modeling of ITZ damage requires preserving real aggregate geometry.

Invert-filling disengagement within shield tunnels is a common issue in urban rail transit. To better study the failure mode of invert-filling disengagement, splitting tensile tests were conducted on the interface specimens between the shield tunnel segments and the invert-filling. The bond-slip curves of the interface were systematically obtained. Based on the concepts of multivariate normal distribution and confidence statistics, the interface constitutive model was fitted using the Monte Carlo method, the least squares method, and the mini-batch gradient descent method. The research results indicate that: (1) The stress-strain curve of the shield tunnel segment-invert-filling interface is in the form of a multi-segment line, comprising three turning points, which are the low-stress stiffness turning point, the high-stress stiffness turning point, and the bond strength limit point. (2) During the elastic deformation period, the interface stiffness is not a constant value but varies in stages. The interface stiffness values for the three stages are 6.24 x 10"9N/m, 2.15 x 10"9N/m, and 8.29 x 10"9N/m, respectively. (3) The constitutive model indicates that the bond energy of the shield tunnel-invert-filling interface is 105.28 J/m"2, the elastic deformation energy is 100.02 J/m"2, and the dissipation energy is 5.26 J/m"2. The interface bond strength is 1.25 MPa.

Stray current can cause corrosion of underground structural rebar, adding rubber particles to the invert-filling concrete is an effective prevent method to reduce stray current corrosion. In our research, the corrosion calculation model of multi-ring shield tunnel containing rubber concrete invert-filling was established, the coupling analysis of electric field and chemical field in composite structures was realized through mesoscale simulations, and the accuracy of calculation model was verified by full-scale test. Through calculation, the corrosion characteristic of segment rebar and bolt of multi-ring shield tunnel were investigated under different rubber content. The result shows that adding rubber particles to the invert-filling can not only reduce the corrosion current density of segment rebar and tunnel bolt effectively, but also affect the distribution form of rebar corrosion current density in both circumferential and longitudinal directions. When the rubber content increases from 5% to 20%, the maximum corrosion density of segment rebar and tunnel bolt will decrease from 31% to 58% and 30% to 32%, respectively. Under different stray current leakage modes, when the rubber content and input voltage are the same, the segment and bolt corrosion current density under single rail-two points leakage mode is greater than that in the two rails-single point leakage mode.

This study proposes an electro-chemo-mechanical coupling 3D mesoscale model to simulate the corrosioninduced cracking behavior under direct stray current in steel fiber reinforced rubber concrete (SFRRC). The accuracy of the mesoscale calculation model is verified through model test. The effects of rubber content and steel fiber content on the potential distribution, corrosion rate, and corrosion-induced cracking behavior in SFRRC are investigated. The morphological differences of the cracks are analyzed by geometric fractal method. The results show that increasing the rubber content in SFRRC significantly reduces the voltage and corrosion rate of steel fibers, whereas increasing the steel fiber content produces the opposite effect. This is because steel fibers at higher volume fractions are more likely to come into mutual contact within the SFRRC matrix, thereby promoting the formation of a continuous conductive network. The circumferential distribution of steel fiber corrosion current density is non-uniform, primarily due to the surrounding rubber particles interfering with potential transfer in SFRRC, which in turn alters the spatial distribution pattern of the rust layer on the steel fibers. As rubber content increases, the fractal dimension of corrosion-induced cracks in SFRRC decreases nonlinearly. When rubber content rises from 6 % to 15 %, the fractal dimension decreases by 6-26 %. With rubber content held constant, a higher steel fiber content corresponds to a greater degree of corrosion-induced cracking. Specifically, when steel fiber content increases from 0.6 % to 1.5 %, the fractal dimension increases by 8-24 %.

Rubber mortar is increasingly utilized in transportation, construction, and repair projects, where compressive strength serves as a critical performance indicator. The size range and morphology of rubber granules significantly influence the compressive strength of rubber mortar. This paper employs a close-up photogrammetry technique to capture scanned images of waste rubber granules and to measure their size range and morphological indices. The generation and distribution of waste rubber granules are facilitated by Python programming, while the analysis is conducted through numerical simulation methods. The key findings are as follows: (1) the size range and morphology of rubber granules exert minimal influence on the elastic modulus of rubber mortar during the elastic phase; (2) for rubber granules of the same ellipticity, a shorter minor axis correlates with an increased load stress that rubber mortar can endure at the same strain level, and it supports a quicker attainment of peak stress, after which there is a rapid decline in stress; (3) for a consistent size range of rubber granules, those with smaller ellipticity facilitate greater load-bearing capacity in rubber mortar under identical deformation levels. This results in a higher peak stress during the continuous deformation of the specimen, thereby enhancing its compressive strength.

Installing steel plate inside subway shield tunnel is one of the main methods to improve structural bearing capacity, but stray current will corrode steel plate and lead to the structural stiffness degradation. In this paper, a refined 3D numerical calculation model of the shield tunnel containing multi-rings steel plate is established, which is coupled with electrochemical corrosion and mechanical analysis. The mechanical parameters of equal thickness steel plate under different corrosion proportions are obtained by corrosion and tensile test, and the concrete damage plasticity constitutive and trilinear cohesive zone constitutive are adopted in the calculation model to simulate segment damage and steel plate bonding failure. Furthermore, a full-scale test of three rings shield tunnel containing steel plate is carried out to verify accuracy of the numerical model for mechanical calculation. Finally, the corrosion range and proportion of steel plate under stray current are obtained by calculation, the tunnel deformation, damage and internal force variation under different corrosion conditions are all studied. The result shows: the corroded areas of steel plate are all concentrated at the joint position of shield tunnel at arch waist under stray current. Convergence deformation and joint opening of shield tunnel increase nonlinearly with local average corrosion proportion, when local average corrosion proportion reached to 14 %, the structure deformation will increase about 25-31 %. With the change of corrosion conditions, the internal force of shield tunnel will appear transfer and local amplification effects. Under the same corrosion conditions, the change in stray current leakage mode has little impact on damage range of shield tunnel.

Steel spring floating slab is a mass-spring vibration isolation system as a vibration reduction measure widely used in metro. Steel spring vibration isolator is a vibration isolation component with a certain stiffness, which relies on its own elasticity to absorb vibration energy. Stray current will accelerate the corrosion of steel spring vibration isolators and thus affect the overall vibration reduction effect of the steel spring floating slab. Adding an appropriate amount of rubber particles to concrete can improve its corrosion resistance. In this paper, a refined three-dimensional numerical model of floating slab for calculating steel springs corrosion is established, and its rationality is verified through a model test involving track structures and rubber concrete specimens. The results show that: (1) Only the steel spring near the current output end will have a linear change in potential, and local electrochemical corrosion will occur at its bottom. (2) Adding rubber can significantly reduce the potential and corrosion current density of the steel spring. When the rubber content increases from 2.5% to 20%, the potential and corrosion current density of the steel spring near the current output end are reduced by about 9-30 %. (3) The potential and corrosion current density of the steel spring near the current output end in the current "doublesided input and single-sided output" mode are higher than those in the current "single-sided input and singlesided output" mode, but the reduction rate of its potential and corrosion current density under various rubber contents is lower than the latter.

It was a challenge to monitor concrete structure crack under complex environmental action. To obtain conductive hydrogel material with higher stretchability, signal response sensitivity and stability to monitor concrete structure cracking, the conductive hydrogel reinforced by different content of cellulose nanocrystals, which is called polyacrylic acid-cellulose nanocrystals (PAA-CNC), were developed in this paper. The performance improvement of PAA-CNC was studied by scanning electron microscope, resistance, uniaxial tensile and cyclic tensile test. Finally, the concrete crack monitoring accuracy of PAA-CNC was verified by three-point bend loading test. The result showed that combining cellulose nanocrystals with hydroxyl in conductive hydrogels can form uniformly dispersed micelles and three-dimensional network structure, which can increase the ionic conductive path and connection strength between molecules. When cellulose nanocrystals content of hydrogel was 0.12%, the effective strain sensing range and sensitivity within the range reached the maximum. When the content of cellulose nanocrystals was 0.12, the effective strain sensing range and sensitivity of PAA-CNC will reach maximum value. Compared with other contents of cellulose nanocrystals, PAA-CNC0.12 can produce a stable signal response when tested and quickly recover to the initial resistance after cyclic stretching. The crack width obtained by PAA-CNC0.12 does not exceed 5% of that obtained by digital image correlation equipment.

Prefabricated construction technology has been widely used in the construction of subway stations due to the advantages of excellent material quality, short construction periods, and low environmental pollution, but the joint is the weakest area of prefabricated structures under environmental load. To further enhance the joint mechanical properties, a 3D finite element model of prefabricated subway stations containing prestressed steel strand joints is established; the cooling method and concrete plastic damage constitutive model are adopted to simulate the prestress effect and concrete cracking. Based on numerical simulation, the bending stiffness and shear stiffness of prestressed steel strand joints are compared to bolted joints, and the deformation and damage mechanics of prefabricated subway stations containing different types of joints under surface overloads are studied. The results show that replacing bolted joints with prestressed steel strand joints can significantly improve the joint bending stiffness and shear stiffness. When the prestress of steel strands increases to 120 kN, the maximum vertical displacement reduction rate of the joint will reach 52%. For the prefabricated subway station structures, replacing bolted joints with prestressed steel strand joints will not affect the joint deformation development trend but will change the distribution law of internal forces. When the prestress of steel strands is 80 kN, the maximum vertical and horizontal deformation reduction rates will reach 36% and 38%; the larger the surface overload, the more significant the decrease.

The reduction of the mechanical properties of rubberized concrete can be alleviated by surface treatment of rubber particles, which changes the interface between cement and rubber particles. The dynamic properties of the rubber-mortar interface under different bonding states were explored by performing four-point bending tests on the rubberized concrete beams. The free decay method was used to test the damping ratios of rubberized concrete beams with different interfaces and damage states. Isight was used to build an inversion analysis platform to determine the damping ratios of the rubber-mortar interfaces with different bonding states. The results show that: (1) Compared with the water treatment, the damping ratio of rubberized concrete modified by sodium hydroxide decreased by 3.01 %, while zinc stearate modification increased the damping ratio by 15.37 %; (2) The average increase in the damping ratio of zinc stearate rubberized concrete was 14.51 % for each damage level. Sodium hydroxide resulted in a 75.4 % decrease in the rubber-mortar interfacial damping ratio, while zinc stearate increased the interfacial damping ratio by 381.9 %; (3) The relationship among the normal bond strength, fracture energy and interface damping ratio was fitted by a planar relation formula.

In areas with large temperature differences, the uneven distribution of temperatures in the CRTSⅢ ballastless track slab due to daytime sunlight can cause warpage deformation, leading to periodic rail irregularities that increase the wheel-rail impact of high-speed vehicles and accelerate track structure damage. Therefore, it is necessary to study the dynamic contact relationship between the composite slab and the base plate during vehicle running. The results of the study show that: 1) Under the influence of temperature gradients, the composite slab tends to deform elliptically. With a positive temperature gradient, the middle part of the track slab bulges upward, causing the slab to be supported by its four corners. Conversely, with a negative temperature gradient, the four corners of the track slab bulge upward, resulting in the slab being supported by its center. 2) Temperature gradients can lead to separation between the composite slab and the base plate, reducing the contact area between layers. During vehicle running, the contact area between layers gradually increases, but the separation cannot be completely closed. 3) The temperature gradient significantly affects the vertical displacement of the track. The vertical displacement in the middle of the slab increases with a positive temperature gradient. In contrast, the vertical displacement at the ends of the slab increases with a negative temperature gradient. 4) The stress of self-compacting concrete at the side position significantly increases under a positive temperature gradient, with the vertical stress increasing by 2.7 times when the temperature gradient increases from 0 to 90℃·m−1.

Shield tunnels are constructed by assembling segment, and this construction method will produce a large number of joints. As the component with the largest contact area in the joints of the shield tunnel, the cork-rubber gasket has a significant effect on the transmission of train-induced vibration waves between the segments. In order to study the influence of cork-rubber gasket on the transmission of train-induced vibration waves in the circumferential direction, based on the hammering test of high-speed railway shield tunnel, a dynamic calculation model for high-speed railway shield tunnel was constructed, and the influence of elasticity modulus of cork-rubber gasket on the propagation of train-induced vibration waves was investigated. The results show that: (1) the longitudinal joints of high-speed railway shield tunnels can weaken high-frequency vibration waves more than low-frequency vibration waves; (2) the lower the modulus of elasticity of cork-rubber gasket is, the greater the attenuation of the peak of the temporal range of vibration acceleration of train-induced vibration waves after they pass through the longitudinal joints; (3) compared with the cork-rubber gasket of high elasticity, the cork-rubber gasket with low elasticity can improve the damping effect of the longitudinal joints on low-frequency bands (0-500 Hz) effectively. This research offers new methodologies for optimising vibration isolation in shield tunnels and contributes to the advancement of tunnel design for high-speed rail systems.

［Objective］During the operation of urban rail transit, the train operation induced vibration can damage buildings and precision instruments along the line, and even affect people's daily lives. Therefore, effective vibration reduction measures need to be studied. ［Method］The long-mileage open-cut section tunnel of Xiong'an Rail Transit R1 Line is taken as an example, which uses rubber soil instead of plain fill. With numerical simulation method, a corresponding tunnel-stratum finite element model is established in ABAQUS software to analyze the vibration isolation effect of different rubber soil damping ratios on open-cut tunnels. ［Result & Conclusion］Using rubber soil with a damping ratio of 0.04 for backfilling can reduce the ground vertical vibration acceleration by 6.2% and the vibration acceleration level by 1.1% at most; using rubber soil with a damping ratio of 0.06 for backfilling can reduce the ground vibration acceleration by 11.4% and the vibration acceleration level by 1.3% at most. The vib-ration isolation effect of rubber soil with the above two damping ratios on open-cut tunnels is quite obvious. At the same measuring point, the reduction amount of vibration acceleration and vibration acceleration level by rubber soil with a damping ratio of 0.06 is generally greater than that by rubber soil with a damping ratio of 0.04, with the maximum reduction rates reaching 5.2% and 0.667% respectively.

A novel numerical method that used a FEM coupled with a virtual element method was proposed to evaluate the drying shrinkage of concrete repair systems. The stress distribution, crack development of the concrete repair systems due to drying shrinkage were investigated using this method. (1) The mortar along the tangent direction of the aggregate boundary was subjected to the aggregate constraint, allowing shrinkage cracks to form easily. The overlay first developed a significant number of microcracks on surface, followed by debonding at both ends of the interface. (2) Owing to the confinement of the aggregate below the surface, the surface tensile stress of the overlay had a 'hump' distribution. After cracking, the surface was divided into several contraction zones, with tensile and compressive stresses applied to the boundary and interior of the contraction zone, respectively. (3) As the interface de-bonded, the tensile and shear stresses of the interface began to increase from both sides and moved inward. The rise in local compressive and shear stresses were induced by the constraint of the aggregate in the bonding interfacial region. (4) Tensile stress caused the first damage, and the shear stress caused interface debonding to evolve.