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.

For many solids, irreversible deformation is often accompanied by changes in the internal structure, impacting the reversible responses, a phenomenon termed elasto-plastic coupling. This coupling has been observed experimentally in various geomaterials, including clayey and sandy soils, as well as hard and soft rocks. Fabric anisotropy, which characterizes the internal structure, is a distinct feature of soils and significantly influences both reversible and irreversible behaviors. In this study, we adopted a coupling formulation based on the framework of anisotropic critical state theory (ACST) to describe the anisotropic elasto-plastic coupling response of soils. The formulation incorporates a deviatoric fabric tensor F, which consistently quantifies the internal structure of soils in both reversible and irreversible range, into a hyperelastic formulation and a plastic model, respectively. A novel evolution rule of F, defined based on the current stress ratio and plastic strain, is proposed, where the direction gradually aligns with the loading direction and the norm achieves different asymptotic values depending on the applied loading paths. This allows for the representation of evolved anisotropy effects on elasticity, dilatancy and strength simultaneously, providing a natural description of elasto-plastic coupling. Within this coupling framework, any anisotropic model within ACST can serve as the plastic platform for developing the elasto-plastic coupling models with anisotropic hyperelasticity. Herein, a bounding surface plastic model is utilized for illustration. The proposed model's performance is demonstrated by especially comparing simulated results to test data on evolving elastic stiffness ratios and overall elastoplastic responses under varying monotonic and cyclic loading conditions.

As a relatively new method, vacuum preloading combined with prefabricated horizontal drains (PHDs) has increasingly been used for the improvement of dredged soil. However, the consolidation process of soil during vacuum preloading, in particular the deformation process of soil around PHDs, has not been fully understood. In this study, particle image velocimetry technology was used to capture the displacement field of dredged soil during vacuum preloading for the first time, to the best of our knowledge. Using the displacement data, strain paths in soil were established to enable a better understanding of the consolidation behavior of soil and the related pore water pressure changes. The effect of clogging on the deformation behavior and the growth of a clogging column around PHD were studied. Finite element analysis was also conducted to further evaluate the effects of the compression index (lambda) and permeability index (ck) on the soil deformation and clogging column. Empirical equations were proposed to characterize the clogging column and to estimate the consolidation time, serving as references for the analytical model that incorporates time-dependent variations in the clogging column for soil consolidation under vacuum preloading using PHDs.

The lateral cyclic bearing characteristics of pile foundations in coastal soft soil treated by vacuum preloading method (VPM) are not well understood. To investigate, static lateral cyclic loading tests were conducted to assess the impact of treatment durations and sealing conditions on pile performance. Results indicated that vacuum preloading significantly improved soil properties, with undrained shear strength (S-u) increasing by up to 36.5 times, especially in shallow layers. Longer treatment durations boosted the ultimate lateral bearing capacity by up to 125%, although the effect decreased with depth, suggesting an optimal duration. Sealing conditions had minimal impact on capacity but affected S-u distribution and pile behaviour. Analysis of p-y curves revealed that longer durations improved soil resistance in shallow layers, while shorter durations provided consistent resistance across depths. Sealed conditions enhanced displacement capacity. The API specification predicted soil resistance accurately for lateral displacements under 0.1D but showed errors for larger displacements. These findings emphasise the need for optimising VPM parameters to enhance pile-soil interaction and lateral cyclic performance. The study offers guidance for applying VPM in soft soil foundation engineering and balancing performance with cost efficiency.

A large-strain model was developed to study the consolidation behavior of soil deposits improved with prefabricated vertical drains and subjected to surcharge and vacuum preloading. The smear effect resulting from the installation of drains was incorporated in the model by taking the average values of permeability and compressibility in the smear zone. The dependence of permeability and compressibility on void ratio and the effects of non-Darcian flow at low hydraulic gradients were also incorporated in the model. The creep effect was also taken into account for secondary consolidation of soft soil deposits. The model was applied to two different embankments located at Suvarnabhumi International Airport, Thailand, and Leneghan, Australia. It was observed that the creep effect led to an additional settlement of 12%-17% after the primary consolidation phase. The study further demonstrated that creep settlements increased with the non-Darcian effect. The difference between surface settlement results with and without the creep effect increased from about 12% to 15% when the non-Darcian parameter (n) increased from 1 to 1.6. However, beyond a threshold value of n >= 1.6, the influence of non-Darcian flow on creep settlement diminished. The value of average and actual effective stresses increased by about 13% and 17%, respectively, when the value of n increased from 1 to 2. However, the impact of n on effective stresses became negligible for values of n >= 2.5. The rate of consolidation decreased approximately by about four times when the permeability ratio ((k) over tilde (u)/(k) over tilde (s)) increased from 1 to 5.

Addressing the current issues of poor resource utilization of waste fibers and ineffective vacuum preloading reinforcement for dredger fill, we developed a modified fiber plastic drainage plate based on the modification treatment of waste fibers. Using gradient ratio tests and indoor vacuum preloading model tests, we compared and analyzed the clogging characteristics of various modified fiber filter membranes, as well as the effects and patterns of vacuum preloading using different types of drainage plates on soft soils. The results show that the anti-clogging effect of the modified fiber filter membrane with a pore size of more than 119 mu m is better. The modified fiber drainage plate is superior to the ordinary split-type plastic drainage plate in terms of settlement, water output, vacuum degree, pore water pressure, soil moisture content, and vane shear strength. The drainage plate with a filter membrane pore size of 119 mu m exhibits the best reinforcement effect. Compared to the ordinary split-type plastic drainage plate, it has a lower cost, reduces moisture content by an average of 6.4%, and increases vane shear strength by an average of 7.8 kPa. This fully demonstrates that the modified fiber drainage plate not only provides excellent reinforcement in engineering applications but also reduces costs, aligning with the national goals for infrastructure construction and economic green sustainable development.

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.

Bottom vacuum preloading (BVP) is the method of applying vacuum pressure at the bottom zone of soils to generate pore-water pressure difference between the top and bottom boundaries, thereby achieving the consolidation drainage. This study conducted a large-size model test to explore the engineering feasibility of combining self-weight and BVP to treat construction waste slurry (CWS). Through the treatment of the measures of self-weight consolidation (0-26 d) and BVP with a water cover (26-78 d), the average water content of CWS declined from 255.6% to 115.9%, and the volume reduction ratio reached 0.476. However, since these two measures could properly treat only the bottom CWS, the measures of BVP with the mud cover (78-141 d) and the natural air-drying (141-434 d) were performed to further decrease the CWS water content near the upper zone. The latter two-stage measures reduced the average water content of CWS to 84.9% and increased the volume reduction ratio to 0.581. Moreover, the measurements suggested that the treated CWS largely exhibited a shear strength of 10 kPa or more. Overall, the proposed approach appeared some engineering feasibility to treat CWS, and the performed test study could act as a reference for the practical treatment of CWS.

The traditional vacuum preloading method of prefabricated vertical drain (PVDs) has been widely used in practical engineering. However, the serious clogging effect around PVDs in the process of vacuum-preloading reinforcement can easily lead to a series of problems such as uneven settlement and large lateral displacement of soil after reinforcement, which seriously affects the application of PVDs in marine clay foundation treatment. In this paper, the effect of combined treatment of marine clay by geotextiles and PVDs on reducing the clogging effect around PVDs was studied by laboratory model experiment. The effects of geotextiles with different diameters and spacings on the surface settlement, excess pore water pressure and lateral displacement of the reinforced soil were analysed. The experimental results show that this method has obvious help on alleviating the above problems, thus providing a reference for the application of geotextile combined with vacuum preloading method to treat marine clay foundation in engineering practice.

This case study proposed a novel electro-osmosis PRD vacuum preloading method to solve dredging sludge treatment issues: difficulty in draining from soil showing large volume, non-uniform settlement, and low strength. To verify the effectiveness of the new method, four kinds of physical model tests integrating particle image velocimetry (PIV) technique of traditional vacuum preloading (VP), prefabricated radiant drain vacuum preloading (PRD-VP), electro-osmotic vacuum preloading (EO-VP), and EO-PRD-VP methods are conducted. The water discharge, average surface settlement, pore water pressure, water content, and undrained shear strength after treatment, clogging range, relationship between clogging range and water discharge rate, and relationship between clogging range and average surface settlement are investigated. For those model tests, it is demonstrated that EO-PRD-VP method has the best advantage in volume reduction, uniform settlement, and strength improvement. Water discharge is enlarged by 13-33%. The differential settlement can reach 2.3 cm, decreased by 28-56%. The undrained shear strength can reach 12 kPa, increased by 1-2 times. In addition, the clogging range development is described, for the given water discharge rate and average surface settlement, clogging range of EO-PRD-VP method is the minimum. The empirical equations between clogging range and water discharge rate, clogging range, and average surface settlement are established to predict the clogging range, which can lay the foundation for developing the consolidation theory of EO-PRD-VP method.