Shallow cut-and-cover underground structures, such as subway stations, are traditionally designed as rigid boxes (moment-resisting connections between the main structural members), seeking internal hyperstaticity and high lateral (transverse) stiffness to achieve important seismic capacity. However, since seismic ground motions impose racking drifts, this proved rather prejudicial, with great structural damage and little resilience. Therefore, two previous papers proposed an opposite strategy seeking low lateral (transverse) stiffness by connecting the structural elements flexibly (hinging and sliding). Under severe seismic inputs, these structures would accommodate racking without significant damage; this behaviour is highly resilient. The seismic resilience of this solution was numerically demonstrated in the well-known Daikai station (Kobe, Japan) and a station located in Chengdu (China). This paper is a continuation of these studies; it aims to extend, deepen, and ground this conclusion by performing a numerical parametric study on these two stations in a wide and representative set of situations characterised by the soil type, overburden depth, engineering bedrock position, and high- and lowlateral-stiffness of the stations. The performance indices are the racking displacement and the structural damage (quantified through concrete damage variables). The findings of this study validate the previous remarks and provide new insights.

The ability to predict the soil mechanical parameters swiftly is critical for off-road vehicle mobility. This paper introduces a novel interpretation methodology for determining critical soil mechanical parameters by impact penetration tests, enabling rapid and remote assessment of terramechanics properties. Initially, the method employs the Mohr-Coulomb constitutive model and the Coupled Eulerian-Lagrangian (CEL) finite element method to generate a dataset of soil impact penetration resistance and acceleration responses. Subsequently, a Radial Basis Function (RBF) neural network is employed as a surrogate model and integrated with the Nondominated Sorting Genetic Algorithm II (NSGA-II) to accurately interpret parameters such as density, cohesion, internal friction angle, elastic modulus, and Poisson's ratio. Experimental validation using sand and silty clay from Yangbaijing, Tibet, confirmed the accuracy and robustness of the method. The results indicate that the mean absolute percentage error for interpreted values was below 25%, with relative errors for some key parameters even below 10%. Furthermore, each single-condition calculation was completed on a standard computer in less than one minute. Comparative analyses with other algorithms, including MIGA and POS, demonstrated the superior performance of NSGA-II in avoiding local optima. The proposed interpretation framework offers a rapid, reliable, and remote solution for identifying the soil mechanical properties. Its potential applications range from disaster mitigation and emergency response operations to extraterrestrial soil exploration and other scenarios where in-situ investigations are challenging.

Seismic fragility denotes the probabilities of a system exceeding some prescribed damage levels under a range of seismic intensities. Classical seismic fragility studies in slope engineering usually construct fragility functions by making some assumptions for fragility curve shape, and always neglect spatial variability of soil materials. In this study, an assumption-free method on the basis of probability density evolution theory (PDET) is proposed for seismic fragility assessment of slopes. The random input earthquakes and spatially-variable soil parameters in slope are simultaneously quantified. By the proposed method, assumption-free fragility curves of a slope are established without limiting the fragility curve shape. The obtained fragility results are also compared with those from two classic parametric fragility methods (linear regression and maximum likelihood estimation) and Monte Carlo simulation. The results demonstrate that the proposed assumption-free method has potential to gives more rigorous and accurate fragility results than classical parametric fragility analysis methods. With the proposed method, more reliable fragility results can be obtained for slope seismic risk assessment.

To study the degree of strength parameter deterioration (DSPD) of Lushi swelling rock in the high slope area under wetting-drying cycles, 114 samples are remodeled. Wetting-drying cycle and triaxial tests are conducted to comprehensively analyze the influence of dry density, wetting-drying cycle path, and number of wetting-drying cycles on the strength deterioration characteristics of Lushi swelling rock. Using the fitting analysis and function superposition methods, the DSPD model of Lushi swelling rock under wetting-drying cycles is established, which considers the previous four influencing factors. The influence of the DSPD of Lushi swelling rock on the stability of high slopes under rainfall seepage and circulation conditions is studied. Lushi swelling rock exhibits significant strength deterioration characteristics under wetting-drying cycles. The overall DSPD for cohesion is higher than that of the internal friction angle. Under rainstorm conditions, strength deterioration leads to a shallower depth of the critical slip surface of the slope and a smaller safety factor. After eight rounds of rainfall seepage and circulation, the safety factor gradually decreases by approximately 14%-28%. This study provides and verifies the DSPD model of Lushi swelling rock under wetting-drying cycles, and the results could provide a basis for disaster prediction and the optimization design of swelling rock slopes.

The horizontal displacement of monopile under cyclic loading is subject to uncertainty due to variations in metocean conditions and soil parameters at offshore wind farms. However, the current design for cyclically loaded monopiles relies on the p-y method recommended by API and DNV, which does not accurately capture the horizontal displacement of the monopiles. In this study, finite element simulations are performed using ABAQUS, where the soil is modeled with the Einav-Randolph model to account for soil softening effects. The impact of parameter uncertainties, such as soil stiffness, undrained shear strength, and the pile-soil friction coefficient, on the reliability index of the monopile's horizontal displacement for different length diameter (L/D) ratios is investigated. A case study is provided to assess the horizontal displacement reliability of a monopile under cyclic loading. The results show that the horizontal displacement reliability index decreases as the coefficient of variation (COV) of the random variables, the correlation coefficient, and the monopile's L/D ratio increase. Conversely, the reliability index increases with an increase in the allowable horizontal displacement. The horizontal displacement reliability index is most sensitive to soil stiffness, followed by undrained shear strength and pile-soil friction coefficient. The findings of this study offer valuable insights into how parameter uncertainties influence the horizontal displacement of monopiles under cyclic loading.

Landslides, which are a type of process-based geological hazard, exhibit stagewise characteristics that serve as important guidance for the prevention and mitigation of slope engineering disasters. The cross-correlation and randomness of soil parameters can influence the evolution of landslide characteristics. This paper, based on the spatial variability of slope soil parameters, combines copula theory and the material point method (MPM) to establish a Monte Carlo-random material point method considering the cross-correlation of soil parameters. This resulting method is called copula-RMPM. It investigates the probability distributions of slope instability and landslide large deformation characteristics, such as sliding distance, landslide thickness, collapse range, and volume of sliding mass. The results indicated that in the study of soil parameter characteristics, failure probability increases with increased correlation coefficient. Also, failure probability showed a positive correlation with the variability coefficient of cohesion and internal friction angle, with failure probability being more sensitive to the variability coefficient of the internal friction angle. The landslide large deformation characteristics generally follow the normal distribution; they exhibit significant fluctuations in sliding distance and sliding mass area despite the relatively small variability coefficient. Compared with the results of random field simulation of soil parameters, the probability of landslide large deformation characteristics obtained by deterministic soil parameters is often lower. Therefore, the probability distribution of landslide large deformation characteristics obtained by the Monte Carlo-random material point method considering the cross-correlation of soil parameters is more meaningful for engineering guidance.

Silt is widely utilized as a filling material in transportation construction, However, it frequently suffers from problems, such as excess pore water pressure buildup, settlement, and mud pumping. Wicking geotextiles have emerged as a sustainable solution by improving both drainage and reinforcement capacities, yet their optimal design parameters remain unclear. To address this gap, a series of tests were performed to investigate the effects of compaction degree, reinforcement configuration (number, spacing, position), and specimen geometry on the mechanical and consolidation of silt reinforced with wicking geotextiles. The results reveal that the failure mechanism of reinforced silt progresses through four distinct stages, which the wicking geotextile improved interparticle contact, delays crack initiation, and improves post-peak stability. Wicking geotextiles significantly improve strength, particularly at lower compaction degrees, by restraining crack propagation and promoting uniform stress distribution. Optimal mechanical performance was achieved with three reinforcement layers and compaction degrees of 93-95 %. Mid-depth placement of a single layer or uniform spacing of multiple layers produced the best outcomes. Although non-uniform spacing provided advantages at early deformation stages, it ultimately induced premature failure, whereas uniform spacing (= 1.27 exhibited improved ductility, while larger specimens with multiple layers demonstrated improved post-peak stability. Wicking geotextiles accelerated drainage and void ratio reduction but concurrently decreased the compression modulus. These findings contribute to a more comprehensive understanding of the mechanical and hydraulic responses of wicking geotextile-reinforced silt and provide practical insights for the design and optimization of reinforced subgrades.

The mechanical behaviour of soil subject to shear loading or deformation is typically considered either completely drained or undrained. Under certain conditions, these drained and undrained scenarios can represent boundaries on the allowed volumetric strain. There is growing interest in exploring the response under intermediate conditions where partial drainage is allowed, particularly in the development of new approaches to mitigate the risk of liquefaction induced failure and the design of off-shore structures. This study uses the discrete element method (DEM) to investigate the effect of partial drainage conditions on the mechanical behaviour of spherical assemblies. Samples with different interparticle friction values are isotropically compressed and then subjected to undrained, drained, and partially drained triaxial shearing. The partially drained conditions are simulated in the DEM samples by applying a controlled volumetric strain that is a fraction of the drained volumetric strain. Results on loose samples indicate that allowing drainage enhances peak shear resistance and can also prevent liquefaction. Moreover, dense samples show a substantial increase in shear resistance when small changes in drainage and volumetric strain take place. The peak stress ratio and the stress ratio at the phase transformation point are insensitive to the drainage level. There is a linear correlation between the state parameter and the drainage level at the peak stress ratio and the phase transformation point. This observation could be used to trace partially drained stress-paths and could also aid the development of uncoupled constitutive models that account for drainage effects.

This study investigates the strain-rate-dependent mechanical properties of unsaturated red clay under varying temperatures and matric suction conditions through triaxial shear tests on red clay fill materials from the Sichuan-Tibet Railway region. The tests were conducted with multiple shear strain rates, complemented by advanced microstructural analysis techniques such as mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM), to examine the evolution of pore structure. The results indicate that high matric suction significantly reduces the rate-dependency of strength in red clay fill materials, whereas temperature has a relatively smaller effect. As matric suction increases, the strain-rate parameter decreases across different temperatures, with a diminishing rate effect observed at higher suction levels. Compared to temperature, strain rate has a more pronounced influence on failure time. An increase in strain rate leads to a significant reduction in failure time. At low strain rates, failure time exhibits substantial variability, while at high strain rates, the effects of temperature and matric suction on failure time become less significant. Under high-temperature conditions, the strength of red clay is enhanced, and failure time is delayed. These findings provide critical theoretical support for controlling settlement deformation and predicting failure times of subgrade fill materials under complex climatic conditions, offering valuable insights for engineering applications.

Ground vibrations from operating railway in tunnels is a significant obstacle to sustainable development of subway. The backfill grouting layer, formed during shield tunneling, serves as a critical medium in propagation of tunnel vibrations, highlighting its potential in vibration mitigation. A semi-analytical model for the tunnelgrouting layer-soil system is proposed in this study, in order to clarify the influence of backfill grouting layer on the dynamic responses in a half-space, subjected to tunnel vibrations. In establishment of the closed-form solution, the tunnel and grouting layer are considered as two nested hollow cylinders embedded in a halfspace, with applying the Fourier transform and wave transformation. As a validation, the numerical results from the proposed semi-analytical model are compared with those reported in literature. Parametric studies, with respect to the geometric configuration (i.e., the thickness) and material parameters (i.e., the Young's modulus, material damping, and density) of the backfill grouting layer in the mitigation of tunnel vibrations, are carried out. It is found that incorporation of the backfill grouting layer significantly changes the dynamic responses of the soil and, by appropriately designing its material parameters, especially the Young's modulus, effective mitigation of tunnel vibrations can be achieved.