Urban water supply systems (UWSSs) are highly vulnerable to earthquakes because of damage to both water distribution networks (WDNs) and freshwater treatment plants (WTPs) that produce potable water. Existing studies often neglect how damage to WTP facilities, such as pumps and chlorination rooms, cascades to affect the seismic serviceability of UWSSs. This study presents a framework to evaluate seismic serviceability of UWSSs by considering damage to WTP facilities and WDN pipelines. The framework combines the state-tree model to analyze the effects of facility damage on WTP performance, the hydraulic model to reveal the serviceability reduction induced by performance degradation of WTP and WDN, and the Quasi Monte Carlo simulation depicting probabilistic damage scenarios. Furthermore, to reduce the computational burden of the coupled models, a Dual-layer Graph Neural Network based on the Principal Neighborhood Aggregation (DGNN-PNA) operator is established to evaluate UWSS serviceability. Validation on three real WTPs and three benchmark WDNs shows that internal WTP damage and system configuration strongly influence UWSS seismic serviceability. DGNN-PNA delivers the best overall predictive performance, accelerates 5000-scenario evaluation by 222–2,369 times, and demonstrates cross-UWSS transferability, with transfer NMAE as low as 4.12% and R2 as high as 0.958.

Severe earthquake event significantly disrupts urban infrastructure systems, inducing complex recovery challenges due to numerous damages of system components and limited recovery resources. Existing recovery models assume that repair crews can access all damage locations without limitations, overlooking the fact that each crew is usually assigned to a specific working zone. This study proposes a recovery optimization model for urban infrastructure systems that incorporates spatial zone constraints of repair crews. In the model, the repair actions for each damaged component are taken as decision variables, with the objective of maximizing the system resilience index (RI) and a constraint requires each crew to complete tasks within its designated zone before supporting other zones. The model is reformulated as a decentralized partially observable Markov decision process (POMDP) and solved using a multi-agent deep reinforcement learning algorithm, namely QMIX. The proposed model is applied to three water distribution systems with different operational characteristics. Results show that the partitions of repair crews’ working zones reduce movement distances of crew by 48.24%–58.45%. Additionally, the QMIX algorithm outperforms the genetic algorithm with RI improvements of 0.17%–3.02% and the greedy algorithm with improvements of 0.85%–8.55%.

With the increasing application of prefabricated structures in underground utility tunnels, developing reliable and construction-friendly connections has become critical for seismic safety. This study investigates the out-of-plane seismic performance of precast composite sidewalls with spiral stirrup sleeve grouted lap-splice connections at the bottom joint. Full-scale cyclic tests were conducted on three precast composite sidewalls with axial compression ratios of 0.05, 0.10, and 0.15, and the results were compared with those of a monolithic cast-in-place sidewall. It was found that the failure modes of the precast composite sidewall and the cast-in-place sidewall were different. The precast and cast-in-place sidewalls exhibited different damage patterns because the horizontal joint altered the stress transfer and damage development in the connection region. Nevertheless, under the same axial compression ratio, the precast composite sidewall exhibited seismic performance comparable to that of the cast-in-place specimen in terms of load-carrying capacity, ductility, stiffness, and energy dissipation. Increasing the axial compression ratio reduced concrete spalling and horizontal joint opening while significantly enhancing the load-carrying capacity. Compared with the specimen with an axial compression ratio of 0.05, the peak loads of the specimens with axial compression ratios of 0.10 and 0.15 increased by 18.42% and 29.60%, and the cumulative energy dissipation increased by 3.14% and 10.55%, respectively, whereas the ductility factors decreased by 0.37% and 15.02%. This indicates that increasing axial compression enhances strength by improving the resistance of the compression zone but reduces deformation capacity at higher compression levels. A tri-linear restoring-force model was further established based on the characteristic response points, and the predicted backbone and hysteresis curves agreed well with the experimental results. The proposed connection and restoring-force model provide experimental evidence and a simplified analytical approach for the seismic design and nonlinear analysis of precast composite sidewalls in underground utility tunnels.

This study proposes an M-y simplified analysis model to evaluate the lateral response of large-diameter monopile foundations in sand. The model establishes a nonlinear relationship between sectional bending moment and lateral displacement using a hyperbolic tangent function, and considers the pile-soil relative stiffness effect as well as the contribution of base-constrained moment, thereby more accurately reflecting the mechanical characteristics of rigid and semi-rigid monopiles. To validate the applicability of the proposed model, a large-scale physical model test was conducted on the dynamic response of an offshore wind turbine monopile foundation under combined wind and wave loading. Comparative results show that the proposed M-y model can well reproduce the initial stiffness and ultimate bearing capacity of rigid monopile foundations. Compared with the traditional API-recommended p-y curve method, the proposed approach demonstrates significant advantages in predicting lateral load-deformation response while maintaining analytical simplicity.

The pipe-soil interaction (PSI) plays a critical role in the assessment of the serviceability and structural safety of buried water pipelines under external loads, including seismic activity, ground displacement, and fault rupture. Historical earthquake damage investigations have consistently demonstrated that pipeline joints constitute a critical weak link in water supply networks, exhibiting significant vulnerability during seismic events. However, limited existing studies addressed the effects of enlarged outer diameter of push-on joints on axial PSI behavior, resulting in potentially an underestimation of joint response to external loadings. This study investigates the nonlinear PSI behavior through a series of axial loading tests conducted at prescribed loading rates in a customdesigned sand box. The effects of joint type, burial depth, and loading rate on the ultimate bearing capacity and failure modes were investigated in this experimental study. The experimental results indicate that the axial PSI behavior of the buried straight pipe specimen exhibits pronounced rate dependence, with axial resistance forces increasing substantially with loading rate. The enlarged outer diameter of push-on joints induces soil disturbance, leading to distinct surface heaving and tensile cracks in the surrounding soil. This effect gradually increases with increasing pipe specimen burial depth. Notably, the peak axial PSI force of the push-on jointed pipe specimen increased by about 50.6% compared to a straight pipe specimen at a burial depth of 0.8 m. Besides, a modified axial frictional resistance model was developed by incorporating the bulge effect at the bell end of the push-on joint with explicit consideration of the joint orientation. Validation against experimental results confirms the proposed model demonstrates superior predictive accuracy compared to conventional approaches.

Abstract Large-diameter monopiles are extensively used to support onshore bridges, port terminals, and offshore wind farms due to their high load-bearing capacity, low settlement and excellent seismic performance. Meanwhile, the conventional p–y curves that are primarily derived from tests on small-diameter flexible piles, cannot capture the mechanical behavior of large-diameter rigid monopiles under complex dynamic loads. This study employs validated numerical simulations using OpenSees, calibrated against shaking table test results, to systematically investigate the lateral bearing characteristics of large diameter monopiles in sandy soils. The analysis highlights significant discrepancies in the initial stiffness, ultimate resistance, and displacement prediction when using conventional p–y curves. To address these limitations, a modified p–y curve formulation is proposed by introducing correction factors for initial stiffness ( $$\:\alpha\:$$ ), ultimate resistance ( $$\:\beta\:$$ ), and characteristic displacement ( $$\:\gamma\:$$ ), thereby refining the key parameters of the conventional p–y curve. The proposed model is validated through comparing its predictions with both physical and numerical experiments. The comparison demonstrated its accuracy in representing the pile-soil interaction behavior of large-diameter monopiles embedded in sandy sites.

In this paper, a three-dimensional (3D) finite element model (FEM) was established to investigate the seismic failure mechanisms of the bridge system in liquefiable site. Meanwhile, two reinforcement strategies were proposed and their effectiveness was evaluated. The results show that the soil liquefaction causes symmetrical lateral spreading on both sides of the valley. The deformation of the piers and piles far exceeds their yield level. The deck occurs differential vertical deformation. The ductility demands of structures are significantly reduced by increasing the number of abutment piles. This study provides a theoretical foundation for seismic design and reinforcement of bridges in complex liquefiable river valleys.

This study develops a three-dimensional fluid-particle coupling numerical model based on the discrete element method (DEM), incorporating point cloud volume sampling technology to achieve high-precision dynamic calculation of particle porosity. The model comprehensively considers the coupling effects of pore structure evolution on pore water pressure fields, establishing governing equations that couple porosity-change-induced (PI) and diffusion-induced (DI) pressurization/depressurization mechanisms. The accuracy of the proposed method is validated through three classical benchmark problems: Terzaghi’s one-dimensional consolidation, undrained triaxial tests, and the Mandel-Cryer effect. Using this approach, the complete process from liquefaction instability to reconsolidation densification in saturated loose sand is successfully simulated, accurately reproducing key liquefaction phenomena including excess pore water pressure accumulation and dissipation as well as microscopic pore structure reorganization. The study achieves quantitative separation of the relative contributions of PI and DI mechanisms during liquefaction, revealing that they synergistically constitute the fundamental control system of the entire process: the liquefaction triggering stage is primarily dominated by the PI mechanism, the development stage shows gradually increasing influence of the DI mechanism, and the reconsolidation stage is entirely controlled by the DI mechanism. This numerical framework provides a powerful tool for in-depth understanding of the fundamental physical mechanisms of soil liquefaction, offering significant theoretical and practical value for prediction and risk assessment of seismic liquefaction hazards.

Inconsistent deformations of layers' interfaces in inclined locally liquefied sites may influence the seismic response of extended infrastructure during earthquake. A series of large-scale shaking table tests were conducted using a three-directional laminated shear box to investigate the influence of non-liquefied zone on inclined locally liquefied site. To monitor the site dynamic response during shaking, accelerometers and pore pressure transducers were distributed along the soil profile, and laser displacement sensors were installed at the ground surface. It was observed that when the site experienced local liquefaction, it developed continuous transverse cracks at the interfaces between liquefied and non-liquefied zones. This created drainage pathways and resulted in more significant macro-phenomena such as surface cracks and sand boiling. The locally liquefied site exhibits discontinuous slip bands due to mechanical discontinuities at the sand-clay interface, which effectively restrict lateral deformation. In contrast, the fully liquefied site undergoes rigid-body sliding with continuous slip bands, resulting in more significant lateral spreading. Furthermore, locally liquefied site exhibited opposite acceleration amplification effects within the liquefied and non-liquefied zones under higher excitation intensity; compared with fully liquefied site, it had a higher acceleration amplification because of the non-liquefied zone. It was also observed that the locally liquefied site exhibited relatively lower liquefaction severity and a smaller liquefaction extent compared to the fully liquefied site, due to the influence of the interface. Finally, locally liquefied site developed bell-shaped shear strain distribution due to the combined effects of the interface and site inclination, with the mid-zone strain exceeding twice that at the sides. However, the fully liquefied site shows high strain in both the middle and right zones.

The internal aggregate skeleton governs the mechanical behavior of asphalt mixtures, yet accurate 3D quantitative analysis of this structure remains challenging due to the limitations in high-fidelity model generation. This study establishes a digital framework integrating spherical harmonics and an impulse-based physics engine to generate 3D skeletons with controllable aggregate morphology. Three asphalt mixtures were virtually compacted with varying aggregate roughness (spherical harmonics degrees 0-15). Quantitative indices-particle inclination angle, contact number, and contact area-were introduced to evaluate spatial orientation and inter-particle interactions. Results reveal that increased surface roughness inhibits particle rotation, effectively increasing inclination angles in all mixtures. However, contact characteristics exhibit divergent trends: roughness reduces contact density in gap-graded and dense-graded mixtures due to friction-inhibited packing, whereas open-graded mixtures benefit from enhanced morphological interlocking, resulting in increased effective contact area. Furthermore, larger aggregates consistently achieve stable horizontal alignment and higher contact connectivity. This framework provides a robust digital tool for virtual mixture design, enabling the pre-fabrication optimization of skeletal structures by explicitly linking aggregate morphology to mesoscopic contact mechanisms.

Urban power-water systems (PWSs) exhibit complex dependence that exacerbates the degradation of their infrastructure service capacity under earthquake hazards. Existing earthquake risk analysis frameworks for PWSs usually characterize the system dependencies as binary states through joint failure probabilities, which fail to capture the dynamics of cascading failure among dependent PWSs. From the perspective of energy transfer among the dependent infrastructure systems, this study proposes a novel seismic performance analysis framework for urban PWS to reveal the energy transfer amid the power system (PS), water distribution system (WDS), and terminal users, which integrates power flow and water hydraulic models. A dual-network model is first constructed to characterize PWS with directional dependency between power substations and water treatment plants. Seismic damage samples of PWS are then generated by seismic fragility models of components and quasi-Monte Carlo simulations. Finally, two real-world PWS cases are employed to validate the effectiveness of this framework. Results show that the proposed framework is capable of depicting the WDS performance that lies between the fully and non-power supply, which is usually higher than the estimations by the previous binary-dependent failure model of the PWS, providing a new perspective for disaster risk reduction of PWS.

This study proposes an efficient three-dimensional (3D) coupled finite element (FE) modelling method to reveal the seismic response of bridge systems under complex site conditions. This method is based on a multi-software cooperative framework, incorporating variable permeability coefficient models, Mohr-Coulomb (point-surface) non-linear contact elements, and 3D free-field reaction boundary conditions, and it employs parallel solution methods to enhance computational efficiency. The accuracy of the method is verified through the cyclic torsional shear test on saturated sand and a shaking table test on a liquefiable site-pile-superstructure system. On this basis, nonlinear response analyses of typical bridges under different site conditions are conducted. The results show that liquefaction of saturated sand induces significant lateral spreading of the site and differential settlement of bridge decks, whereas non-liquefiable sites are dominated by overall settlement. The slope effect further amplifies site and structural deformation under liquefiable conditions. The proposed modelling method accurately reproduces the seismic response of bridge systems in liquefiable river valleys.

Offshore wind turbine (OWT) structures are subjected to wind and wave loads throughout their service period. These loads typically exhibit random characteristics, different directions, and asymmetry. In the present research, the dynamic response of OWT has been simplified by representing wind and wave loads as a unidirectional horizontal force. However, the changing direction of wind and waves is demonstrated through extensive ocean field measurements. When only the co-directional action of wind and wave loads is considered, the resulting dynamic response is not representative of actual conditions. To address this issue, a self-developed loading simulation system designed for complex marine environmental conditions is employed. Under physical model test conditions at a scale of 1:100, experimental studies are conducted on the dynamic response of OWT under asymmetric wind-wave loads. Based on measured data from the eastern sea area, typical wind-wave misalignment angles are selected. And the dynamic response is analyzed at different misalignment angles and wind speeds. The significant impact of asymmetric wind-wave loads on the dynamic response of OWT has been demonstrated by the results of the study. By comparing the maximum bending moment at mud surface under different conditions, the condition with the wind speed of 1.8 m/s and the 22.5 degrees wind-wave misalignment angle is identified as potentially the most unfavorable. The design, operation, and maintenance of OWT structures in eastern sea areas have gained significant research significance and engineering value through this study.

Offshore wind turbine system (OWT) is usually subjected to complex dynamic loads during the service period. Besides, different dynamic response of OWT will be presented under different operating conditions. In the analysis on the dynamic response of OWT under small-scale indoor testing conditions, components such as the tower, hub, and blades are mostly simplified as mass blocks. Meanwhile, the dynamic response of tower is primarily analyzed in the existing research. However, the effects of the dynamic response of seabed and pile-soil interaction on the deformation of the superstructure are neglected. To address the above problem, an integrated loading system was designed in this paper. The real-time wind, wave and current loads can be simulated. The objective of this paper is to investigate the dynamic response characteristics of OWT structure and seabed under different operating condition. The results show that the maximum force and deformation of OWT structure are reached under rated wind speed condition. The effect of blade aerodynamic load plays a dominant role in the deformation of OWT structure when the external environment exceeds the rated wind speed. The understanding of the dynamic response characteristics of OWT can be enhanced through the regularities and conclusions derived from this research.

The Stress Partition constitutive Framework (SPF) for methane hydrate-bearing sediment (MHBS) assumes that the soil matrix and hydrate share effective stress and experience the same strain, enabling accurate representation of stress transfer between the two components during loading and hydrate phase change. This framework facilitates separate constitutive models for the soil matrix and hydrate based on their individual mechanical properties. Under the SPF-MHBS framework, a constitutive model is proposed to describe the mechanical behavior of MHBS with and without hydrate dissociation. The soil matrix component adopts the Clay and Sand Unified Hardening (CSUH) model, incorporating the equivalent void ratio to account for hydrate effects on the soil matrix. An isotropic elastic damage model is adopted for the hydrate, considering the influence of hydrate content, temperature, and pressure on its mechanical properties. The constitutive model is first used to simulate discrete element method (DEM) numerical tests on hydrate-bearing sediment, allowing for direct validation of the stress partition concept via DEM measurement of the stress borne by the matrix and hydrate under various conditions. The performance of the proposed model for real hydrate-bearing Toyoura sand is then evaluated by simulating a comprehensive set of 23 tests using a single parameter set. Results show that it accurately describes isotropic compression and triaxial shear behaviors of MHBS under varying void ratios, hydrate contents, confining pressures, temperatures, and pore pressures, and more importantly, reflect the stress and strain during hydrate dissociation induced by heating and depressurization.

While various methods exist for assessing urban rainwater and flood resources, there is a lack of targeted evaluation for the rainwater harvesting potential of areas equipped with sponge city facilities. This study employs the Yield Before Spillage (YBS) principle to design rainwater collection tanks for sponge facilities under different design return periods, conducting a specialized assessment of the rainwater resource potential in built-up sponge facility areas within the "Dongsheng-Kangbashi-Ejin Horo Banner" urban cluster. The results indicate that the collection potential follows the patterns of "wet year > normal year > dry year" and "Ejin Horo Banner > Kangbashi District > Dongsheng District." A rainwater collection tank designed for a 5-year return period (p = 5a) is more applicable to the study area. The sponge facilities in the study area achieve an annual runoff volume control rate exceeding 85%, effectively alleviating drainage pressure. The conclusions demonstrate that the YBS method can effectively assess the rainwater and flood resources of sponge facilities in arid regions. Tanks designed for the three different return periods all meet the rainwater retention requirements of sponge cities across various hydrological years. In arid areas, tanks designed for lower return periods are sufficient for harnessing rainwater collection potential, offering lower costs.

In-depth research on the influence of soil-structure interaction on the failure modes and seismic performance of prefabricated assembled monolithic (PAM) underground frame structures is of great significance for improving their seismic design. This study investigates the effects of soil-structure interaction on the seismic performance of PAM underground frame structures based on a proposed spring-structure system testing method. Taking a two-storey, three span PAM subway station as an example, two cases of 1:10 scaled model tests were conducted. The test results indicated that: The presence of soil delays the initial cracking IDR of the PAM underground frame structure and enhances its resistance to lateral collapse. However, it reduces the horizontal deformation capacity of the structure, leading to stricter IDR limits under different performance states. Soil-structure interaction affects the damage mechanisms and deformation patterns of multi-storey PAM underground frame structures, improve the energy dissipation efficiency of PAM underground frame structures, but accelerate the rate of stiffness degradation and strength degradation of PAM underground frame structures. Additionally, numerical simulation analysis of the test conditions was conducted based on the ABAQUS software. The hysteresis curves and failure modes obtained were in good agreement with the test results. Both the test and numerical analysis results provide a foundation for the application of PAM structures in underground engineering.

The macroscopic performance of particulate-reinforced composites (PRCs) depends fundamentally on their internal mesostructural properties. We propose a novel, high-fidelity computational framework to digitally reconstruct and evaluate these complex mesostructures. The method integrates Spherical Harmonics (SH) for multi-scale morphological reconstruction, impulse-based physics-engine compaction to explicitly capture geometric friction, and a novel Position-Based Dynamics (PBD) bubble inflation algorithm for realistic, interconnected void topologies. Furthermore, an automated mesh-level contact detection strategy preserves interparticle force chains. Micromechanical simulations using this framework reveal a critical stress transmission trade-off: particle surface roughness enhances geometric friction but simultaneously induces contact patch division. This geometric discretization disrupts uniform force chains, resulting in highly localized load-transfer pathways. Crucially, this contact patch division dominates the macroscopic dynamic viscoelastic response under small-strain conditions. Ultimately, this framework establishes a rigorous digital pathway for elucidating cross-scale structure-property relationships in heterogeneous PRCs.

The Urban Water Supply System (UWSS) relies on the interdependent operation of Water Treatment Plants (WTPs), Water Distribution Networks (WDNs), and storage tanks to ensure reliable water delivery. Earthquake events frequently cause structural damage and functional disruptions to both WTPs and WDNs. However, existing studies on the seismic serviceability and resilience evaluation of UWSS primarily focus on service interruptions resulting from pipeline damage within the WDN, while the cascading effects of WTP failures on water supply services remain insufficiently addressed. To bridge this gap, this study proposes a coupled method for seismic serviceability analysis and resilience assessment of UWSS, incorporating seismic damages to both WTPs and WDNs and accounting for WTP supply degradation and pipeline-induced water losses. In the hydraulic model of UWSS, the WTP is represented by a reservoir and a pump, and the pump curve is adjusted to simulate varying water supply capacities. Finally, the proposed method is applied to benchmark cases to validate its effectiveness in reflecting the degradation of WTP capacity. Results indicate that neglecting WTP capacity degradation substantially overestimates the UWSS and nodal serviceability by 70 % and 80 %, respectively, which greatly impacts the damage recovery sequence of WDN.