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.

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.

To accelerate the dissipation of excess pore water pressure, enhance the bearing capacity of piles, and mitigate long-term settlement in soft ground, a novel green and lowcarbon pile foundation technology, termed the precast drainage pile (PDP) technology, is proposed. This innovative approach integrated precast pipe piles with prefabricated vertical drains (PVDs) attached to their sides. The piles were installed using static pile pressing and were subsequently subjected to vacuum-induced negative pressure to facilitate soil consolidation, which enhances the resource utilization rate of pile foundations and promotes the sustainable utilization of soft soil foundations. To investigate the bearing characteristics of the PDP, this study combined the shear displacement method for piles with the consolidation theory of soft soil foundations. A calculation model for the load-settlement behavior of precast piles, accounting for the influence of vacuum-induced soil consolidation, was derived, establishing a method for analyzing the load transfer mechanism of PDPs. The reliability of the theoretical model was validated through comparisons with engineering test results. Building on this foundation, the influence of factors such as consolidation period and pile length on the bearing characteristics of PDPs was analyzed. The results demonstrated that, compared to a 10 m precast pile without drainage, the ultimate bearing capacity of single piles with drainage durations of 3, 7, 14, and 28 days increased by 7.3%, 12.7%, 20.3%, and 29.6%, respectively. Furthermore, under a 7-day drainage condition, the bearing capacity of piles with lengths of 10 m, 20 m, and 30 m increased by 12.7%, 12.8%, and 13.1%, respectively. Overall, the findings of this study provide a theoretical basis for the research, development, and design calculations of this new sustainable pile technology.

This paper puts forward a vibrable prefabricated vertical drain (V-PVD) that combines vibrators on PVD to alleviate the clogging on PVD and enhances the reinforcement effect of vacuum preloading method. To validate the reinforcement effect of V-PVD, a full-scale on-site test was conducted including four zones with different V-PVD installations. The ground surface settlement and pore water pressure in each zone were monitored. In addition, a comparative analysis was conducted on vane shear strength and water content before and after soil reinforcement. The test results indicates that the vibrable prefabricated vertical drain in vacuum preloading method can effectively improve the soil reinforcement effect. The ground surface settlement increased by 20.9% to 43.8% compared to conventional vacuum preloading method, and the dissipation value of pore water pressure increased by 17.1% to 58.6%, and vane shear strength increases by 5.9% to 24.5%. The activation of the vibrator helps to remove clogging around PVD, and the more vibrators installed on PVD surface, the better the soil reinforcement effect is achieved. However more vibrators installed on PVD, the drainage area on the PVD surface was influenced and drainage efficiency reduced initially, which implies that a reasonable installation of vibrator should be considered in practice.

Soft clays are prevalent in coastal areas of Australia, exhibiting low bearing capacity and considerable settlement upon loading, and must be improved as subgrades to meet the increasing demand for railway transportation soft soils beneath railway embankments are often subjected to train-induced cyclic loads generating higher excess pore water pressure (EPWP), reduced bearing capacity, and deformations under poor drainage conditions. These often lead to reduced efficiency in transportation and maintenance costs. Thus, it is important to investigate the behaviour of soft soils subjected to heavy cyclic loading and preventative actions. This paper provides a comprehensive review of the role of Prefabricated Vertical Drains (PVDs) in mitigating failures associated with railway subgrades under cyclic loading.

This paper offers valuable insights for advancing the consolidation of dredged slurry, alleviating blockage, and the application of vacuum preloading-airbag pressurization (VP-AP) technology in engineering practice. This study conducted laboratory model tests on the consolidation of sludge using prefabricated vertical drains-vacuum preloading, prefabricated horizontal drains-vacuum preloading, and VP-AP methods to further investigate the effectiveness of the VP-AP technique in strengthening the consolidation of dredged slurry. Comparative analysis was conducted on the macroscopic and microscopic differences in soil drainage characteristics, settlement, water content, shear strength, and soil particle morphology under the three treatment methods. The results show that the VP-AP method surpasses traditional vacuum preloading techniques in soil consolidation, effectively guaranteeing the consolidation of deep soil layers and enhancing the uniformity and stability of foundation strength. In addition, the microstructural analysis reveals that the VP-AP method can effectively mitigate the decrease in drainage efficiency caused by the clogging of the PVD and improve the structure of the soils, allowing a significant increase in the mechanical properties of the soils. In conclusion, the VP-AP technology demonstrates significant advantages in drainage efficiency, consolidation effectiveness, thus it has a widespread application potential in engineering practices for treating soft ground and deserves further in-depth study.

Nowadays, the utilization of prefabricated vertical drains (PVDs) or prefabricated horizontal drains (PHDs) in combination with vacuum preloading (VP) has emerged as a prevalent and effective strategy for treating dredged slurry. Nevertheless, both of these methods possess certain inherent limitations. In this study, three groups of parallel model experiments are conducted to compare the effectiveness of PVDs, PHDs and PHDs-PVDs under step VP in treating dredged slurry. Firstly, the water discharge, settlement and pore water pressure are monitored during the experiments. Then, the shear strength and water content of the soil at various locations after experiments are measured and the soil profiles at different cross sections are gauged. Additionally, soil excavation is conducted to evaluate the deformation characteristics of PHDs and PVDs. Finally, a scanning electron microscopy analysis is to assess the clogging of filter membranes. The results indicate that the proposed method can combine the advantages of both PHDs and PVDs, effectively enhancing the treatment effectiveness of the slurry. These findings elucidate the dewatering and reinforcement mechanism of PHDs-PVDs-VP and provide valuable insights for its practical engineering application.

Previous studies have demonstrated that saturated normally consolidated and lightly over-consolidated clays undergo contraction when heated due to a reduction in preconsolidation pressure. A linear constitutive model is proposed to describe the thermal contraction, with this model, governing equations are developed for the coupled thermo-hydro-mechanical (THM) consolidation induced by a prefabricated vertical thermo-drain (PVTD). Corresponding semi-analytical solutions are derived employing the Laplace transform and validated via comparison with experimental results, existing numerical model, and custom finite element method (FEM) model. Subsequently, comprehensive parametric analyses are carried out to investigate the THM coupling consolidation behaviors of the clays. Outcomes show that aside from surcharge load, generation of excess pore water pressure in soils can also be induced by thermal contraction, difference in thermal expansibility between pore water and soil grains, and thermo-osmosis, where the influence of thermal contraction on the excess pore water pressure is the most prominent among the three factors.

Vertical drain assisted by vacuum and/or surcharge preloading is an effective method for improvement of soft ground with high water content. A large settlement will occur, and the water flow may deviate from the Darcy's law. The creep is also non-negligible in estimating the long-term settlement of such soft ground. To accurately predict the consolidation process, this study develops an axisymmetric finite strain consolidation model based on Barron's free-strain theory incorporating the creep, radial and vertical flows, non-Darcian flow law, and void ratio-dependent hydraulic conductivity during the consolidation process. First, to mathematically validate the model and highlight the new model's features, the existing model not considering the creep and the non-Darcy flow is also adopted as a reference for comparison based on a benchmark simulation. Then, Rowe cell tests involving non-Darcian flow are simulated by the new model to experimentally validate the predictive performance. Furthermore, the model is applied to simulate the consolidation process of a long-term monitoring embankment to examine the applicability of the model for engineering practice. All results demonstrate that the model is capable of accurately describing the consolidation of soft soils with vertical drains under combined loading with features of creep and non-Darcy flow.

A system of vacuum preloading combined with partially penetrating prefabricated vertical drains (PP-PVDs) is an effective solution for promoting the consolidation of the dredged marine clay. However, a significant and traditionally challenging-to-predict amount of deformation or settlement occurs. Therefore, it is necessary to introduce a three-dimensional large-strain consolidation model to consider the length of the vertical drain to determine the consolidation time and degree of consolidation (DoC), and associated settlement. The predictions using the proposed analytical model provide fair agreements with the field data and those in the literature. Parametric studies reveal that to achieve a 90% DoC within 100 days in soft soil, the optimal penetration depth for PP-PVDs would be 0.7 times the depth of the soil layer. With the increase of DoC, the ratio of excess pore water pressure to applied vacuum pressure (u/P) in the whole soil layer moves toward 1.0. With the increase of PVD penetration ratio (H1/H), more DoC is required to dissipate the excess pore water pressure in the top improved soil layer.