This study conducted load-bearing capacity tests to quantitatively analyze the impact of permafrost degradation on the vertical load-bearing capacity of railway bridge pile foundations. Meanwhile, a prediction model vertical load-bearing capacity for pile foundations considering permafrost degradation was developed and validated through these tests. The findings indicate that the permafrost degradation significantly influences both the failure patterns of the pile foundation and the surrounding soil. With the aggravation of permafrost degradation, damage to the pile foundation and the surrounding soil becomes more pronounced. Furthermore, permafrost degradation aggravates, both the vertical ultimate bearing capacity and maximum side friction resistance of pile foundations exhibit a significant downward trend. Under unfrozen soil conditions, the vertical ultimate bearing capacity of pile foundations is reduced to 20.1 % compared to when the permafrost thickness 160 cm, while the maximum side friction resistance drops to 13.2 %. However, permafrost degradation has minimal impact on the maximum end bearing capacity of pile foundations. Nevertheless, as permafrost degradation aggravates, the proportion of the maximum end bearing capacity attributed to pile foundations increases. Moreover, the rebound rate of pile foundations decreases with decreasing permafrost thickness. Finally, the results confirm that the proposed prediction model can demonstrates a satisfactory level of accuracy in forecasting the impact of permafrost degradation on the vertical load-bearing capacity of pile foundations.

A series of finite element analyses, conducted on the basis of modified triaxial tests incorporating radial drainage, were carried out to investigate the lateral deformation and stress state characteristics of prefabricated vertical drain (PVD) unit cells under vacuum preloading. The analyses revealed that the inward horizontal strain of the unit cell increases approximately linearly with the vacuum pressure (Pv) but decreases non-linearly with an increase in the initial vertical effective stress (sigma ' v0). The variations in the effective stress ratio, corresponding to the median excess pore water pressure during vacuum preloading of the PVD unit cell, were elucidated in relation to the Pv and sigma ' v0 using the simulation data. Relationships were established between the normalized horizontal strain and normalized effective stress ratio, as well as between the normalized stress ratio and a composite index parameter that quantitatively captures the effects of vacuum pressure, initial effective stress, and subsoil consolidation characteristics. These relationships facilitate the prediction of lateral deformation in PVD-improved grounds subjected to vacuum preloading, utilizing fundamental preloading conditions and soil properties. Finally, the proposed methodology was applied to analyze two field case histories, and its validity was confirmed by the close correspondence between the predicted and measured lateral deformation.

Seismic activity often triggers liquefaction in sandy soils, which coupled with initial vertical tensile loads, poses a significant threat to the stability of suction bucket foundations for floating wind turbines. However, there remains a notable dearth of studies on the dynamic response of these foundations under combined seismic and vertical tensile loads. Therefore, this study developed a numerical method for analyzing the dynamic response of suction bucket foundations in sandy soils under such combined loading conditions. Through numerical simulations across various scenarios, this research investigates the influence of key factors such as seismic intensity, spectral characteristics, as well as the magnitude and direction of tensile loads on the seismic response of suction buckets. The results revealed that the strong earthquake may cause the suction bucket foundation of floating wind turbines to fail due to excessive vertical upward displacement. This can be attributed to that the accumulation of excess pore water pressure reduces the normal effective stress on the outer wall of bucket, and consequently decreases the frictional resistance of bucket-soil interface. Additionally, the above factors significantly influence both the vertical displacement of the suction bucket and the development of pore pressure in the surrounding soil. The findings can provide valuable insights for the seismic safety assessment of suction bucket foundations used in tension-leg floating wind turbines.

It is crucial to ensure the safety and stability of pipelines buried in slopes during installation and operation. In this paper, the interaction between a pipe and soil was investigated via laboratory model tests. The effects of the slope angle and pipe position on the slope horizontal deformation and pipe mechanical properties were investigated. Furthermore, the restraint effect of tire strip reinforcement (TSR) on slope deformation and its impact on pipe stress and strain were analyzed. The results revealed that the potential sliding surface is located at the middle of the slope. The pipe location has a significant effect on the horizontal surface deformation of the slope, whereas the slope angle has a small effect on the stress and strain of the pipe. In addition, the use of the TSR not only reduces the horizontal surface deformation of the slope but also partially alleviates the vertical stress on the crown of the pipe. As the pipe moves away from the loading plate, the circumferential stress distribution changes from a symmetric state to an asymmetric state, with the most critical location moving from the spring line to the top. The test results provide reliable experimental data to support the design of pipes buried within a slope.

Despite the complexity of real earthquake motions, the incident wavefield excitation for soil-structure interaction (SSI) analysis is conventionally derived from one-dimensional site response analysis (1D SRA), resulting in idealized, decoupled vertically incident shear and compressional waves for the horizontal and vertical components of the wavefield, respectively. Recent studies have revealed potentially significant deviation of the 1D free-field predictions from the actual three-dimensional (3D) site response and obtained physical insights into the mechanistic deficiencies of this simplified approach. Particularly, when applied to vertical motion estimation, 1D SRA can lead to consistent overprediction due to the refraction of inclined S waves in the actual wavefield that is not correctly accounted for in the idealized vertical P wave propagation model. However, in addition to the free-field site response, seismic demands on structures and non-structural components are also influenced by the dynamic characteristics of the structure and SSI effects. The extent to which the utilization of vertically propagating waves influences the structural system response is currently not well understood. With the recent realization of high-performance broadband physics-based 3D ground motion simulations, this study evaluates the impact of incident wavefield modeling on SSI analysis of representative building structures based on two essential ingredients: (1) realistic spatially dense simulated ground motions in shallow sedimentary basins as the reference incident motions for the local SSI model and (2) high-fidelity direct modeling of the soil-structure system that fully honors the complexity of the incident seismic waves. Numerical models for a suite of archetypal two-dimensional (2D) multi-story building frames were developed to study their seismic response under the following incident wavefield modeling conditions: (1) SSI models with reference incident waves from the 3D earthquake simulation, (2) SSI models with idealized vertically incident waves based on 1D SRA, and (3) conventional fixed-base models with base translational motions from 1D SRA. The impact of these modeling choices on various structural and non-structural demands is investigated and contrasted. The results show that, for the horizontal direction, the free-field linear and nonlinear site amplification and subsequent dynamic filtering of the base motions within the structure can be reasonably captured by the assumed vertically propagating shear waves. This leads to generally fair agreements for structural demands controlled by horizontal motions, including peak inter-story drifts and yielding of structural components. In contrast, vertical seismic demands on structures are overpredicted in most cases when using the 1D wavefields and can result in exacerbated structural damage. Special attention should be given to the potentially severe vertical floor accelerations predicted by the 1D approach due to the combined effects of fictitious free-field site amplification and significant vertical dynamic amplification along the building height. This can pose unrealistic challenges to seismic certification of acceleration-sensitive secondary equipment necessary for structural and operational functionality and containment barrier design of critical infrastructures. It is also demonstrated that vertical SSI effects can be more significant than those in the horizontal direction due to the large vertical structural stiffness and should be considered in vertical floor acceleration assessments, especially for massive high-rise buildings.

In this study, a flexible vertical graphene (VG) strain sensor was developed for monitoring geogrids deformation. The VG material was fabricated using radio frequency plasma-enhanced chemical vapor deposition, followed by spin-coating a polydimethylsiloxane (PDMS) solution for film curing, resulting in a flexible sensor within a PDMS substrate. The VG sensor was integrated with a wireless Bluetooth data acquisition system for automated and remote strain measurement. The stability performance of VG sensors was examined and effectively improved through cyclic loading tests in the laboratory. The drift ratio of electrical resistance before cyclic loading tests is 37.01%, which is reduced to only 0.5% after cyclic loading tests. Calibration tests show that the maximum measurement resolution and maximum measurement range of VG sensors is 0.7 micro-strain and 40000 micro-strain, respectively, indicating that VG sensors are highly effective for both high-strain resolution identification and large-strain measurement. Pullout tests demonstrate an average error of 5.67% between VG sensors and fiber Bragg grating sensors, suggesting that VG sensors are a promising alternative for large strain, wireless, and long-term geogrid monitoring.

In view of the challenges posed by construction on deep soft coastal ground, this study introduces the precast drainage pile (PDP) technology. This innovative approach combines precast pipe piles with prefabricated vertical drains, installed through static pile pressing and subsequently subjected to vacuum negative pressure for the consolidation of surrounding soil. To evaluate the efficacy of PDP technology, a comparative analysis was conducted between precast pile and PDP, incorporating field testing and numerical simulation. The investigation focused on the evolution of excess pore water pressure, deformation, and pile bearing capacity. Results indicated that vacuum negative pressure drainage could induce rapid initial dissipation of pore water pressure, followed by a slower rate. Excess pore pressure decreased more rapidly and significantly closer to the drained pile, aligning with drainage consolidation theory. After 5 days of consolidation, the PDP exhibited a 16% increase in ultimate bearing capacity compared with the undrained pile. Numerical simulation outcomes closely matched field measurements. The enhancement in pile bearing capacity was found to correlate hyperbolically with drainage time, culminating in a 26.5% ultimate increase. The research achievements facilitate the development of new pile technologies in coastal soft soil areas.

During pile installation, construction disturbances alter soil mechanical properties near the pile, significantly affecting the dynamic response of the pile. This paper develops a three-dimensional (3D) analytical model to investigate the vertical dynamic response (VDR) of a pile in radially inhomogeneous saturated soil. Firstly, by employing the separation variable method and incorporating the continuity and boundary conditions of the soilpile system, the exact solution of the whole system in the frequency domain was derived. Subsequently, the timedomain velocity response under semi-sinusoidal vertical excitation is obtained using Fourier inverse transform and the convolution theorem. The accuracy and superiority of the proposed solution were validated through comparison with previous analytical solutions. Finally, the developed solution is then used to examine the impact of parameters of saturated soil and pile on the VDR of a pile. The results demonstrate that the proposed saturated model better captures the VDR of a pile in radially inhomogeneous saturated soil compared to the single-phase model. The VDR of a pile is significantly influenced by the pore water, porosity, disturbed degree and range of the saturated soil, as well as the elastic modulus of the pile.

The rail network invariably encounters soft subgrades consisting of shallow estuarine clayey deposits. Cyclic loading generated by the passage of trains causes deformation and corresponding development of excess pore water pressure (EPWP), which dissipates during the rest periods between two consecutive trains. This paper presents an experimental study describing the effect of yield stress and EPWP responses upon intermittent cyclic loading (i.e. with rest periods), and the associated consolidation with the combination of vertical and radial drainage by way of a prefabricated vertical drain (PVD). Based on the laboratory data, the normalised yield stress for cyclic loading (NYCL) is introduced as an insightful parameter to define a novel empirical relationship between the yield stress, cyclic stress amplitude and the initial effective stress. The experimental results indicate that, as the NYCL increases, the peak EPWP decreases and, during the rest periods, the EPWP reaches a stable equilibrium faster without causing further settlement. Furthermore, this study demonstrates that the accumulated EPWP caused by cyclic loading can be further reduced when using a larger width of PVD for a given unit cell radius. An analytical model inspired by empirical parameters for predicting EPWP is proposed, capturing the effects of NYCL and the PVD characteristics.

The dynamic response of piles is a fundamental issue that significantly affects the performance of pile foundations under vertical cyclic loading, yet it has been insufficiently explored due to the limitations of experimental methods. To address this gap, a hydraulic loading device was developed for centrifuge tests, capable of applying loads up to 2.5 kN and 360 Hz. This device could simulate the primary loading conditions encountered in engineering applications, such as those in transportation and power machinery, even after the amplification of the dynamic frequency for centrifuge tests. Furthermore, a design approach for model piles that considers stress wave propagation in pile body and pile-soil dynamic interaction was proposed. Based on the device and approach, centrifuge comparison tests were conducted at 20 g and 30 g, which correspond to the same prototype. The preliminary results confirmed static similarity with only a 1.25% deviation in ultimate bearing capacities at the prototype scale. Cyclic loading tests, conducted under various loading conditions that were identical at the prototype scale, indicated that dynamic displacement, cumulative settlement, and axial forces at different burial depths adhered the dynamic similarity of centrifuge tests. These visible phenomena effectively indicate the rationality of centrifuge tests in studying pile-soil interaction and provide a benchmark for using centrifuge tests to investigate soil-structure dynamic interactions.