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[Introduction] Pulse inductor is an important component of the oscillation discharge circuit in the quench protection system. In the oscillating discharge circuit, the pulse inductor and charging capacitor are used to oscillate and generate high pulse currents, causing the current flowing through the vacuum circuit breaker to reverse and create an artificial zero-crossing point, thus completing the switch breaking. However, under the condition of 120 kA current, due to the action of the electromagnetic force, the connecting bar below the pulse inductor will deform, causing equipment damage and greatly reducing the reliability of the auxiliary oscillation zero-crossing circuit. Therefore, it is necessary to conduct electromagnetic field analysis on the 120 kA pulse inductor and optimize the electromagnetic field distribution around it. [Method] Firstly, the commutation process of the auxiliary oscillation zero-crossing circuit was analyzed to establish a three-dimensional model of the pulse inductor, and the concept of magnetic field shielding percentage was introduced. Secondly, the influence of shielding plates with different materials and shapes on electromagnetic field distributions was calculated by using finite element simulation. Then the influence of different materials and shapes on shielding percentage was analyzed, and eddy current losses under different shapes were calculated. Finally, the deformation degree of the connecting bar under different shielding structures was calculated in the structural module. [Result] The results show that the use of different materials or structures in the shielding plates influences the magnetic induction intensity and electromagnetic force received by the connecting bar. [Conclusion] The circular aluminum shielding plate has a better optimization effect for the electromagnetic field distribution. This method also lays a foundation for the electromagnetic shield design of pulse inductors.

The grid-based multi-velocity field technique has become increasingly popular for simulating the Material Point Method (MPM) in contact problems. However, this traditional technique has some shortcomings, such as (1) early contact and contact penetration can occur when the contact conditions are unsuitable, and (2) the method is not available for contact problems involving rigid-nonrigid materials, which can cause numerical instability. This study presents a new hybrid contact approach for the MPM to address these limitations to simulate the soil and structure interactions. The approach combines the advantages of point-point and point-segment contacts to implement contact detection, satisfying the impenetrability condition and smoothing the corner contact problem. The proposed approach is first validated through a disk test on an inclined slope. Then, several typical cases, such as granular collapse, bearing capacity, and deformation of a flexible retaining wall, are simulated to demonstrate the robustness of the proposed approach compared with FEM or analytical solutions. Finally, the proposed method is used to simulate the impact of sand flow on a deformable structure. The results show that the proposed contact approach can well describe the phenomenon of soil-structure interaction problems.

Abstract The seismic deterioration effects of anchor cables and slope structural planes are often neglected in the dynamic stability analysis of anchored rocky slopes to the extent that the stability of slopes is overestimated. In this paper, a dynamic calculation method for anchored rocky slopes considering the seismic deterioration effect is established, and a stability evaluation method for anchored rocky slopes based on the Gaussian mixture model is proposed. The seismic deterioration effect on the stability of anchored rocky slopes is quantitatively analyzed with an engineering example, and the relationship between seismic intensity and the failure probability of slopes is clarified. The results show that compared with the calculation method without considering the seismic deterioration effect, the minimum safety factor and post-earthquake safety factor obtained by the proposed method in this paper are smaller. The number of seismic deteriorations of the slope is used as the number of components of the Gaussian mixture model to construct the failure probability model of the slope, which can accurately predict the failure probability of anchored rocky slopes. The research results significantly improve the accuracy of the stability calculation of anchored rocky slopes, which can be used to guide the seismic design and safety assessment of anchored rocky slopes.

To explore the evacuation situation of the underground space in the Starting Area of Guangzhou International Financial City under fire, personal evacuation was simulated with Pathfinder in three zones. Then, the visual animation and the human flow rate diagram were obtained and analyzed. A fire-risk assessment model based on a combined weighting and the technique for order of preference by similarity to ideal solution (TOPSIS) is proposed to assess the fire risk of three zones. First, six second-level indices were determined from three aspects: regional safety evacuation, regional fire prevention, and regional fire extinguishment. The value of regional safety evacuation was determined by the results of the evacuation simulation. Second, the subjective and objective weights of the second-level indices were determined based on the analytic hierarchy process and entropy weight method, respectively, and a combined weighting method was adopted to reflect the subjective and objective weights. Next, TOPSIS was used to calculate the relative closeness between each scheme and the ideal scheme. The relative closeness is an evaluation index used to determine the fire-risk level of three zones. It was found that the fire-risk level of Zone Ⅰ is high, requiring large-scale rectification. The fire-risk level of Zone Ⅱ is low, and the fire toughness is strong. The fire-risk level of Zone Ⅲ is medium and needs local rectification.

Due to the increasingly tight energy supply situation, thermal insulation mortar is more and more widely used in the exterior wall insulation layer of buildings in various countries. However, the existing academic papers have less research on the key properties of thermal insulation mortar such as fire resistance and economic feasibility. Based on the previous research results, this study selected silica fume as an admixture to improve the comprehensive performance of insulation mortar. The goal is to develop a high-performance fireproof insulation mortar. This paper focuses on the fire resistance of the improved insulation mortar. The results show that silica fume mixed into the mortar will play a fine particle filling and hydration gelation cooperation, and the amount of silica fume mixed from 0 to 10% can significantly improve the bond strength and compressive strength of the mortar. For the thermal conductivity and dry density of mortar, there is a certain increase in the range of silica fume dosing from 0 to 4%, while the range of silica fume dosing from 4% to 10% decreases again. Silica fume has a favorable effect on improving the fire resistance of insulating mortar, and the mortar with 10% admixture of silica fume has about 28.30% lower mass loss rate after high temperature and about 14.73% higher relative compressive strength after high temperature after 28 days of maintenance. The final selected optimum admixture of silica fume is 10%, and the best ratio of raw materials is cement: aggregate: water: dispersible emulsion powder: fly ash: diabase rock powder: AOS foaming agent: gelatin: silica fume = 1: 1.67: 2: 0.045: 0.15: 0.225: 0.035: 0.02: 0.138.

Locking-steel-pipe (LSP) piles connect with adjacent joints to form a pile row enclosure structure. Due to the advantages of quick construction, efficiency in installation, and recycle utilization, the connected LSP piles are frequently used as retaining structure in deep excavation. However, systematic studies of the deformation mechanism of the LSP pile retaining structure are rarely reported, and it still lack of experimental evidence to optimize the design. In this study, a braced supported excavation experimental model test in sand was designed and conducted to investigate the deformation characteristics of LSP pile retaining structure. Three dimensional (3D) printing technique was creatively applied to manufacture LSP model piles. The experimental results show that, a “S” shaped distribution of bending moments is observed along pile shaft when excavation is executed; the deflection of pile shaft develops deep-seated movements toward the excavation side as excavation went deeper, resulting in a “bowl” ground settlement. With the deflection of LSP piles, a rotating trend was occurred between pairs of locking joint, and the severe open deformation of locking joint arose on excavation side. There was a gradual reduction in earth pressure behind the LSP pile retaining wall with excavation depth. The earth pressure between two struts level had no obvious changing, owing to the supported effect of inner struts.

Crack detection plays a critical role in ensuring road safety and maintenance. Traditional, manual, and semi-automatic detection methods have proven inefficient. Nowadays, the emergence of deep learning techniques has opened up new possibilities for automatic crack detection. However, there are few methods with both localization and segmentation abilities, and most perform poorly. The consistent nature of pavement over a small mileage range gives us the opportunity to make improvements. A novel data-augmentation strategy called CrackMover, specifically tailored for crack detection methods, is proposed. Experiments demonstrate the effectiveness of CrackMover for various methods. Moreover, this paper presents a new instance segmentation method for crack detection. It adopts a redesigned backbone network and incorporates a cascade structure for the region-based convolutional network (R-CNN) part. The experimental evaluation showcases significant performance improvements achieved by these approaches in crack detection. The proposed method achieves an average precision of 33.3%, surpassing Mask R-CNN with a Residual Network 50 backbone by 8.6%, proving its effectiveness in detecting crack distress.

ObjectiveHuman working memory is impaired when individuals are exposed to high altitudes, however, whether the capacity of visual working memory is affected remains unclear. This study combined a lateralized change detection task and event-related potentials analysis to explore changes in visual working memory capacity among individuals who emigrated from a low-altitude environment to Tibet (a high-altitude environment).Materials and methodsThirty-five college students were recruited from Tibet University as the high-altitude (HA) group, and thirty-six low-altitude (LA) students were enrolled from South China Normal University (sea level) as the LA group. We measured participants' contralateral delay activity (CDA) under different memory loads.ResultsERP component analysis showed that both the HA and LA groups reached an asymptote at memory load four. However, the contralateral and ipsilateral activity of the HA and LA groups shows different patterns. The results showed a significantly larger contralateral activity for the LA group than for the HA group at memory load one (p = 0.04, Cohen's d = 0.52) and load three (p = 0.02, Cohen's d = 0.61). Additionally, we found marginally larger contralateral activity at memory load four for the LA group (p = 0.06, Cohen's d = 0.47), but not at memory load two (p = 0.10) or load five (p = 0.12). No significant differences were observed for ipsilateral activity. In addition, we observed that the HA group performed larger ipsilateral activity than contralateral activity under each memory load, compared with the LA group.ConclusionThese findings demonstrated that the attentional resource of long-term HA exposure is more captured by task-irrelevant information, potentially due to impaired inhibitory control, which makes it difficult for them to exclude the interference of task-irrelevant information.

The structural performance of shield tunnel structures is highly susceptible to degradation under complex environmental loads, with the most common manifestation being bolt preload loss. In this study, a shield tunnel numerical simulation model was established to analyze the seismic response of shield tunnels with varying degrees of bolt preload loss. Firstly, the deformation patterns of shield tunnel structures under seismic loads were analyzed. Subsequently, ellipticity and joint opening were selected as seismic resilience assessment indicators based on the mechanical response. A seismic resilience assessment model was then established, including three states: normal state, affected state, and recovered state. The results show a direct relationship between the recovery capacity of tunnel structures and the initial performance of the lining structure, as well as the magnitude of the load. The lower the degree of structure degradation, the greater the structural recovery capacity. Additionally, there is a positive correlation between residual deformation and the initial performance loss of shield tunnel structures, as well as the intensity of seismic loads. This study contributes to enriching the theoretical framework for the seismic resilience assessment of shield tunnels, which have significant implications and provide valuable references for engineering safety.

Shield tunnels can experience preload loss in their connecting bolts during the operational phase, leading to changes in tunnel structure stiffness, which, in turn, affect the seismic performance of shield tunnels. A refined three-dimensional model of shield tunnel was established using the finite element method to study the impact of preload loss in connecting bolts on the seismic dynamic response of shield tunnels. An artificial viscoelastic boundary was used to simulate the propagation of seismic waves from an infinitely distant field. This study investigated the effects of different levels of preload loss on the seismic response of shield tunnels. In addition, the Arias intensity, which can reflect the degree of seismic impact on structures, was used to analyse the extent of damage to the tunnel. The conclusions drawn from the study are as follows: As the level of preload loss increases, the tightness of the segments during the static phase gradually deteriorates, and the maximum joint opening during the seismic loading phase continues to increase. Post-earthquake non-recoverable ellipticity and radial deformation progressively increase with an increase to preload loss level. Overall tunnel damage becomes more significant with the degree of preload loss increases depending on the Arias intensity. Preload loss leads to a decrease in the overall structural stiffness and an increase in longitudinal relative displacement. In conclusion, preload loss also affects structural failure mode and seismic performance. These research findings are of reference value for enhancing the seismic performance of shield tunnel structures and ensuring engineering safety.

Various adjacent construction projects are inevitably encountered during the large-scale construction of urban underground transportation. The case of a twin shield tunnel excavated below an existing multi-arch culvert bridge in close vicinity has not yet been thoroughly studied. A case of a shield tunnel excavation below an existing multi-arch culvert bridge in Foshan is presented. First, a fully coupled three-dimensional model incorporating fluid and solid interactions was established to simulate the twin shield tunnel excavation below the existing multi-arch culvert bridge in close vicinity. Subsequently, the numerical model was validated using the modified Peck empirical formula. Finally, the influence of different foundation reinforcement deformation moduli, tunnel excavation face support pressures and grouting pressures on ground deformation was discussed. The results indicate that the area most significantly affected by the excavation of the tunnel passing underneath is not within the section of the multi-arch culvert bridge after applying the foundation reinforcement design. The area most significantly impacted is concentrated as the shield tunnel commences excavation and advances beneath the location corresponding to the 1-hole of the steel corrugated pipe. The range of influence of the ground disturbance extends approximately 7 m in front of the excavation face before the tunnel passed through. The range of ground disturbance decreases to 4–6 m in front of the excavation face after the tunnel passed through. The excavation face support pressure and grouting pressure have a minor impact on the settlement of the multi-arch culvert bridge under this reinforcement design. The results provide useful references for the reinforcement design for tunnel excavation adjacent to existing structures.

The critical problem restricting the development and application of phase change energy piles is that adding phase change materials to concrete generally reduces its thermal conductivity. Therefore, exploring a scheme to improve the heat transfer performance of phase change energy piles is necessary. In this study, steel fibers were added to energy piles to enhance the heat exchange capacity between the pile and the surrounding soil. The model tests were conducted on two types of energy piles: a fiber-reinforced pile and a fiber-reinforced phase change pile. Based on laboratory tests, a three-dimensional thermo–hydro–mechanical coupled finite-element model was established to characterize the phase transformation process of FRPC piles accurately. Then, the thermal parameters of the phase change concrete pile were optimized and analyzed to explore the feasibility of improving the application of the phase change pile. The results reveal that the cooling condition where the initial ground temperature was higher than the phase change temperature was more suitable for the FRPC pile. When the flow rate was increased by 50%, the peak heat power of the FRPC pile increased by 25.7%. There is an optimal economic flow rate to balance the system’s energy consumption and heat power in different conditions. Increasing thermal conductivity and specific heat capacity are effective solutions to improve the heat transfer capacity of concrete piles. The energy pile that was enhanced with the high-thermal-conductivity PCM is a good choice to improve long-term operation performance.

The complex distribution of synchronous grouting pressure results in excessive tunnel deformation and various structural diseases, especially for ultra-large-diameter shield tunnels. In this study, to reduce the risk of tunnel failure, a three-dimensional refined finite element model was established for the Wuhan Lianghu highway tunnel project, taking into account the non-uniform distribution of synchronous grouting pressure. This study focuses on investigating the development patterns of internal forces, deformations, and damages in segment structures under varying grouting pressure ratios. The results indicate that the primary failure mode of a segment is tensile failure occurring at the outer edge of the arch. Moreover, an increased ratio of grouting pressure between the arch bottom and top leads to a higher positive bending moment value and greater tensile damage at the arch waist. The tunnel ring gradually exhibits distinct “horizontal duck egg” shape deformation. When the grouting pressure ratio is 2.8, there is a risk of tensile cracking at the outer edge of the arch waist. At this time, the segment convergence deformation is 39.71 mm, and the overall floating amount reaches 43.12 mm. This research offers engineering reference for the prediction of internal forces and deformations in ultra-large-diameter shield tunnels during grouting construction, thereby facilitating their application in the development of resilient cities.

The introduction of fibres into soil can effectively improve its engineering properties. Systematically understanding the unsaturated mechanical properties of fibre-reinforced soil is highly significant. Moreover, there is currently no suitable model for describing the water-retention characteristics of unsaturated fibre-reinforced soil. The purpose of this study is to propose a model for the soil–water characteristic curve (SWCC) that can accurately describe unsaturated fibre-reinforced soil. The research focuses on unsaturated sand reinforced with PP fibres. A series of compression and direct shear tests were performed to investigate the mechanical behaviour. In addition, the SWCC was measured using the axis-translation technique. Based on the van Genuchten (VG) model, a modified model considering fibre reinforcement (VG-CFR) is developed for quantitatively analysing the influence of fibre content on the SWCC. The results showed that the established VG-CFR model can reflect the water-retention characteristics of fibre-reinforced sand.

The Shenzhen Ma Wan area has special geotechnical conditions, with more than 50% of the area being reclaimed rock formations. Riprap reclamation strata are particularly susceptible to significant deformation upon stress release. To comprehensively comprehend the reaction of existing pipelines to the excavation of an adjacent deep foundation pit within the riprap reclamation strata, an interaction of the soil–pipeline was conducted by encompassing both scaled model tests and numerical simulations based on a cross-sea channel project. Firstly, scaled model tests were performed on a soil–pipeline interaction caused by excavation. Subsequently, the numerical model was verified by comparing the numerical simulation results with the scaled model test results. Then, the internal force, strain of the pipeline, and soil surface deformation under the conditions of a soil layer with riprap were analyzed, and the results were compared with the case without riprap. Finally, the influence of the support structures was analyzed. The results indicated that the presence of the riprap in strata led to a 19% increase in vertical displacement of the ground surface and a 35% increase in the pipeline bending moment compared with the case without riprap in the same strata. The maximum internal force and strain occurred at an inclined angle of 45° in the pipeline section. Furthermore, it was found that the first lateral support after excavation played a pivotal role in controlling the overall deformation of the foundation pit. The changes in stiffness in the lateral support were more sensitive to the horizontal displacement than the vertical displacement of the pipeline. The results provide valuable insights for the design and safety evaluation of engineering projects in riprap reclamation strata.

Aiming at the problem of electromagnetic vibration of the water-filled submersible induction motor (WSIM), a method of opening auxiliary slots on the rotor side is proposed to weaken the air-gap field harmonics caused by the rotor slot permeance harmonics. By analyzing the research status of electromagnetic vibration of the WSIM and the composition of the air-gap magnetic field of the motor, the idea that the auxiliary slots mainly affect the air-gap field harmonics by changing the air-gap permeance of the motor is put forward. The mathematical model of air-gap permeance of WSIM is established to simulate the influence of auxiliary slots on the air-gap permeance. Through the parametric analysis of the mathematical model, the change of auxiliary slot size is simulated. The air-gap permeance waveform is decomposed by the two-dimensional Fourier transform, and then the variation of the air-gap permeance harmonics with the size of the auxiliary slot is analyzed. Finally, the finite element simulation model of the WSIM with the auxiliary slots is established, and the waveform of the air-gap flux density of the motor is analyzed to verify the effectiveness of the mathematical model. Meanwhile, the results show that after opening the auxiliary slot, the radial electromagnetic force of the motor was reduced by 28.4%.

The arrangement of multiple culverts has gradually increased in road engineering. However, the arrangement will face a series of risks in both the construction and operation stages. A numerical model was established to analyze the construction and operation safety of multiple steel corrugated pipe arch culverts by using a fully fluid–solid coupling two-dimensional (2D) model of a highway project. The sensitivity of factors affecting the settlement of the composite foundation such as modulus and depth of ground reinforcement was discussed. Based on the results of the 2D model, a fully fluid–solid coupling three-dimensional (3D) model was established to study the influence of dynamic cyclic vehicle load on the mechanical properties of multiple steel corrugated pipe arch culverts. The ground deformation, soil stress and pore pressure, structure stress, and deformation were analyzed. The results show that the maximum settlement of the soil in the arch culvert area is at the junction of the two different arch culverts after construction. The maximum vertical deformation of the structure appears at the vault, and the arch waist is prone to stress concentration. Under cyclic vehicle dynamic load, the ground deformation, structural stress, and arch culvert subgrade deformation showed a rapid growth stage, and then tended to be stable. The weak points in the structure during the construction and operation stages were revealed, which can provide a useful reference for the design and construction of multiple steel corrugated pipe arch culverts.

The underground space in the Starting Area in the Guangzhou International Financial City is being developed to save resources and improve land benefits. However, high-density development has increased the likelihood of fires. Therefore, PyroSim and Pathfinder were used in this study to investigate the fire smoke flow and personnel evacuation in the underground space in the Starting Area. Firstly, the 2D temperature cloud map and the temperature and visibility recorded by sensor A over time of Zone I in the Starting Area were analyzed. Then, the 3D smoke diffusion, the 3D temperature diffusion map, and the value of thermocouple and smoke obscuration recorded by sensors of Zone II were analyzed. Next, smoke flow of Zones III to V in the Starting Area under different fire source positions was simulated. Finally, the personnel evacuation model was established to simulate the personnel flow rate and density. The simulation results show that the available safe evacuation time for people is 530 s when all the firefighting facilities fail and fire breaks out in Zone I. For large public spaces, the overall spread speed of fire is fast, which requires the use of the fire control system in time to control the spread of fire. Fortunately, the space of evacuation time is relatively sufficient; it only takes 143 s to evacuate personnel safely in Zone II, which is sufficient compared to the time for the fire to completely spread. Suggestions were made for fire safety management, such as evacuating personnel to the safety exits of other adjacent areas during a fire and installing linkage fire alarm systems in large public space s.

Energy piles are a new type of heat exchange systems with buried pipes in a pile foundation, which optimize a ground source heat pump system for the utilization of shallow geothermal energy. In this study, based on the principle of similarity, the thermo-mechanical behavior of the model energy pile with a large cross-section in saturated sandy soil was experimentally evaluated. The pre-cast model concrete pile with a diameter of 0.2 m and length of 1.5 m was buried in saturated sand in a steel box with dimensions of 2.5 m × 2.5 m × 2.0 m (length × width × height). The pile was heated using water in the polyethylene (PE) pipe, which was connected to a water cycle temperature controller. At a constant inlet water temperature of 55 °C, three thermal cycles were carried out with the same heating and cooling periods and different water flow rates. The temperature distributions in the pile and soil, in addition to the pore pressure, soil pressure, and displacement of the pile, were monitored to clarify the thermo-mechanical behavior of the pile and soil. The heat transfer efficiency was analyzed based on the temperature difference and water flow rates. The measured strain at different locations in the pile under cyclic thermal loading revealed that the uneven strain that developed in a pile body should be considered for its long-term application. Furthermore, focus should be directed toward the long-term unrecoverable displacement of the energy pile due to the thermal plastic strain and thermal consolidation of the soil.

A new stiffened composite pipe pile was developed for improving the foundation of reclaimed ground in ocean engineering. To study the bearing capacity of the stiffened composite pipe pile group, a combination of field test and finite element method was used. Firstly, field tests were performed on the proposed single stiffened composite pipe pile. The single stiffened composite pipe pile model was verified by comparing the numerical simulation results with the field test results. The load transfer mechanism from the stiffened core to the cemented soil and the surrounding soil was clarified. Further, a 3D finite element model of the stiffened composite pipe pile group was established based on the single stiffened composite pipe pile model. Finally, the bearing capacity of the pile group and the stress distribution of each pile were analysed and the influence of the pile spacing on the pile bearing capacity was discussed. The results showed that the axial stress of both the side and corner piles decreased rapidly with an increase in the pile spacing, and the stress-bearing ratio decreased. The stress-bearing ratio of the central pile increases with an increase in pile spacing. The smaller the pile spacing, the larger the load proportion of the composite pile group and the larger the foundation settlement. The optimal design scheme was a composite pile with a 500 mm stiffened core diameter, 700 mm outer cemented soil diameter, and a spacing between piles of four times the cemented soil diameter (2.8 m) considering the group pile bearing capacity and the economic benefits of the project. These results provide a reference for the design and construction of stiffened composite piles for ground improvement projects.

The development and utilization of underground space is an effective way to make intensive use of resources, solve "big city disease" and achieve high-quality development. The expansion and renovation of underground space in a central urban area is likely to cause serious damage to surrounding structures. In this study, a deep foundation excavation for the reconstruction of an urban subway station in the Greater Bay Area was chosen for analysis using the finite element method. Different from common excavation engineering, the interaction between the three coupling factors of train dynamic load, foundation excavation, and viaduct pile foundation were analyzed. Six different cases were calculated considering different working conditions of excavation depth and train dynamic load. Soil was evaluated using modified Cam-Clay model. The physical parameters of the soil were determined through on-site and laboratory tests. The results were compared with monitoring data, and the accuracy of the finite element model was verified. The settlement and influence range of the soil, and displacement and internal forces of viaduct piles were analyzed. The maximum settlement of the soil occurred in the direction of the short side of the foundation pit. The maximum value was approximately 0.53 times the excavation depth. The settlement increased by approximately 49% when applying the train load. The dynamic load had an aggravating influence on the horizontal displacement of the top of the pile, with a maximum increase of 51%. Moreover, the dynamic load increased the negative bending moment of the viaduct piles. This study provides a reference for the design and construction of geotechnical engineering projects.

A proper treatment of granite residual soil (GRS) in geotechnical practices requires both macro and microscopic evaluations. In this study, uniaxial and oedometric compression tests were conducted to investigate the mechanical properties of the saturated untreated and cement-treated GRS. Meanwhile, XRD, SEM, and MIP tests were conducted to identify the presence and types of C–S–H and the changes in the pore structure after cement treatment. The effects of cement treatment on the uniaxial compressive strength, secant modulus, compressibility, and vertical yielding pressure were revealed and the mechanisms of the soil structure to be modified through cement treatment were clarified based on the test results. A threshold volumetric cement content of 2–3% was determined based on the mechanical properties and microstructural characteristics of the saturated cement-treated GRS. Cement contents below this threshold would produce inadequate cementation between the soil particles. In contrast, cement contents above this threshold are considered inefficient because the transformation of the soil structure from single-porosity to dual-porosity increases the total porosity and retards the strength and stiffness gains.

Voids, a common defect in tunnel construction, lead to the deterioration of the lining structure and reduce the safety of tunnels. In this study, ground-penetrating radar (GPR) was used in tunnel lining void detection. Based on the finite difference time domain (FDTD) method, a forward model was established to simulate the process of tunnel lining void detection. The area of the forward image and the actual void area was analyzed based on the binarization method. Both the plain concrete and reinforced concrete lining with various sizes of air-filled and water-filled voids were considered. The rationality of the model was verified by measured data. It was observed that the response mode of voids can be hyperbolic, bowl-shaped, and strip-shaped, and this depends on the void’s width. Compared with the air-filled voids, water filling increases the response range of the voids and produces a virtual image. Although the diffracted wave caused by a steel bar will bring about significant interference to the void response, the center position of the voids can be accurately located using 3D GPR.

To reduce or evaluate the damage of tunnels in seismically active areas when earthquakes happen, it is very important to quickly predict the tunnel damage. This study proposes an anti-entropy–fuzzy analytic hierarchy process (FAHP) combination weighting method for tunnel earthquake damage prediction. The tunnel cross section is a symmetrical structure. The method uses tunnel damage data from the tunnels in a region where earthquake disasters have occurred as sample data to calculate the standard earthquake damage index. The weights of evaluation factors are determined by combining the FAHP and anti-entropy weighting. The correction coefficient of each evaluation factor is obtained by considering the degree of each evaluation factor’s influence on the average damage index. Then, the earthquake damage and the corresponding damage degree of each tunnel are obtained by weighting calculation. In this study, 55 tunnels in the Wenchuan earthquake-affected area are taken as analysis cases. In these cases, 45 cases of damage tunnels are used as sample data, and 10 random tunnels are used as training cases. The calculated results are compared with the observed results. The proposed method is confirmed simple and easy to implement, which can greatly reduce the workload of field investigation, calculation and analysis. The results is of great significance to the rapid earthquake emergency assessment and post earthquake recovery of tunnels.

Piles, which are always exposed to dynamic loads, are widely used in offshore structures. The dynamic response of the pile-soil-superstructure system in liquefiable soils is complicated, and the interaction between the pile and soil and the pile volume effect are the key influencing factors. In this study, a water-soil fully coupled dynamic finite element-finite difference (FE-FD) method was used to numerically simulate the centrifuge shaking table (CST) test of a four-pile group in saturated sand soil. An interface contact model was proposed to simulate the pile-soil interaction, and a solid element was used to consider the volume effect of the pile. The acceleration responses of the soil and pile, settlement deformation, excess pore water pressure, and bending moment were examined. The results show that the bending moment response of the two piles parallel to the shaking direction show minor differences, while the two piles perpendicular to the shaking direction show almost the same distribution. The values of excess pore water pressure at the same depth but different azimuth angles around the pile are also different. The numerical simulation can accurately reproduce soil deformation and pile internal force during and after dynamic loading.

Pile–anchor structures are widely used in foundation excavation and slope reinforcement due to their safety and reliability. However, the pile–anchor structures have the common problem of the prestress loss of anchor cables, which may reduce the stability of the structures. To accurately predict the prestress loss of anchor cables, a new prestress loss calculation model was established, and the availability of the prestress loss calculation model was verified through engineering cases. Meanwhile, aiming at the long-term prestress loss of anchor cables, the coupled creep behavior of anchor cable–rock and soil was studied and an anchor cable–rock and soil coupled creep model suitable for pile–anchor structures is proposed. The model test confirms that the coupled creep model could accurately describe the coupled creep behavior of the anchor cable and the rock and soil mass. The models provide a theoretical basis for the study of the prestress of anchor cables in pile–anchor structures, and have a guiding significance for the design and construction in foundation excavation and slope engineering.

Phase change material (PCM) is a substance that can absorb or release sufficient latent heat at phase transition. By encapsulating phase change paraffin in hollow steel balls in the concrete, an energy pile with PCM was innovatively produced to improve energy efficiency for the ground heat pumping system. Laboratory tests were carried out on both PCM energy pile and traditional concrete pile to evaluate the thermo mechanical performance. Two piles were heated and cooled through inside tubes at a constant flow rate. The laboratory tests on the two piles were symmetrical for the two horizontal directions in geometry, and heat transfer process follows conservation laws of energy. The temperature response of the pile and soil, internal strain, pile displacement, pore pressure, and soil pressure under heating-cooling cycles were examined. Compared with the traditional concrete pile, the PCM energy pile can effectively reduce the surrounding soil temperature. The use of PCM in the pile can improve the capacity of heat storage and make the pile more effective in heat exchange. Non-uniform thermal strain and accumulations of heat and irrecoverable displacement were observed in the repeated heating-cooling process. The study can provide references for the practical implication of PCM energy piles.

To reduce the thermal response and improve the heat storage capacity of energy piles, a phase change (PC) energy pile was proposed. This innovative PC pile is made of concrete containing macro-encapsulated PCM hollow steel balls (HSB) as coarse aggregates. A numerical model was developed to simulate the thermo-mechanical behaviors of the PC pile under thermal cycles and sustained loading. The computational model is a three-dimensional model that is symmetrical for the two horizontal directions in geometry. Heat transfer process follows conservation laws of energy. The numerical model was validated by the experiments conducted on the PC pile and the results show that the model can reproduce the major thermo-mechanical effects. Then, the model was used to compare the performance between the ordinary concrete pile and the PC pile in saturated sand under the same experimental conditions, where the piles were considered to be thermo-elastic in nature and the sand was considered as a Mohr–Coulomb elastic-plastic material. The thermo-mechanical response of the PC pile under different thermal loads was analyzed. The results show that at the end of heating, the temperature, strain, and displacement of the PC pile were lower than those of the ordinary pile. As the thermal loading increased, the range of temperature change in the soil around the PC pile increased, as well as the strain and displacement of the pile. The residual strain and plastic displacement after the temperature cycles also increased with the increase of thermal loading. Therefore, when designing phase change energy piles, full consideration should be given to the matching of thermal loads and PC temperature, so as to balance the heat transfer rate of the pile and the thermal response.

The construction of metro tunnels in urban areas often encounters existing underground structures, such as the pile foundations of adjacent existing buildings. Under the mutual effects and impacts of pile foundation load and tunnel excavation, the soil around tunnel and pile foundations can experience stress redistribution or even yield prior to support installation, which could adversely affect and even damage the adjacent pile foundations. This paper proposes an effective prediction model consisted of axisymmetric tunnel and pile foundation to investigate the shape and range of potential plastic zones induced by tunnel excavation adjacent to pile foundations. Then the results obtained from the proposed method are compared with the existing approaches and numerical simulations, which shows that the shape of the potential plastic zone develops towards a butterfly shape in a gravity field, similar to those from numerical simulations. Finally, a parametric analysis is performed to investigate the influences of different parameters, such as soil parameters, axisymmetric boundary conditions, and pile parameters on the boundaries of the potential plastic zone. This proposed prediction model might provide a certain basis for making protective measures for existing pile foundations influenced by tunnel excavation, and provide a quick estimate of the boundaries of the potential plastic zone induced by tunnel excavation adjacent to pile foundations in a gravity field, thus resulting in time and cost savings.