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Air-booster vacuum preloading (AVP) without sand blanket and surcharge vacuum preloading (SVP) methods were used to treat two adjacent areas in a foundation reinforcement project on Donghai Island, Zhanjiang City, Guangdong Province, China. In this study, engineering characteristics of the AVP foundation were obtained through analyzing monitoring data. Results showed that the AVP method obtained superior foundation consolidation results compared to SVP method. This study proposed a new simplified mechanical model for AVP, with a single PVD (prefabricated vertical drain) centered and the air-booster pipes symmetrically distributed around the PVD, applied equivalent air-booster pressure to the drainage boundary. Furthermore, this study established a mathematical analytical model for predicting consolidation settlement based on the proposed simplified model. By comparing the theoretical settlement value with the measured value, this paper verifies the rationality of the analytical solution. Finally, this study analyzed the effects of well resistance, smearing effect, compression index, and permeability index ratio on consolidation characteristics. Land reclamation projects will generate a large amount of dredged ultrasoft soil foundation. The AVP method can achieve superior foundation treatment effects by injecting gas into soil mass through air-booster pipes. The results of this case study demonstrate that the AVP method has substantial advantages compared to the conventional vacuum preloading method. The AVP method can increase foundation settlement, shorten the time for foundation treatment construction, and improve the foundation reinforcement effect. In addition, the AVP method can alleviate PVD clogging and maintain soil permeability, while simultaneously avoiding the excessive use of dredging sand. Therefore, the AVP method can lead to potential economic benefits and protect the natural environment, and it is a method worth considering. Moreover, the mathematical model for predicting consolidation settlement of the AVP method was proposed based on new mechanical assumptions, which can be applied as a reference for settlement prediction in relevant engineering, and the rationality has been verified through comparison with measured settlement results. [ABSTRACT FROM AUTHOR]

Dredged fills have been widely used as a filling material to meet the demand for land resources during land reclamation in coastal areas. When the conventional vacuum preloading (CVP) method is used to reinforce dredged fill foundations, clogging and accumulation of a dense silt layer significantly reduce the lateral soil permeability of the soil surrounding prefabricated vertical drains (PVDs), leading to a poor reinforcement effect. To address these issues, this paper presents a laboratory model study to evaluate the reinforcement effect of a new method, the stepped-alternating vacuum preloading method (SAVP), in comparison to the CVP method. A series of laboratory model tests were conducted to compare the results of the new SAVP method and the CVP method. The model tests used water discharge, discharge rate, and surface settlement to compare both methods. Additionally, vane shear strength and moisture content were measured after reinforcement. This study evaluates the performance of the SAVP method and proposes an optimal preloading pattern that demonstrates best performance in delaying clogging formation and alleviating the accumulation of a dense silt layer on the surface of the PVDs. [ABSTRACT FROM AUTHOR]

The vacuum preloading method is widely applied in dredged sludge reinforcement, however, prefabricated vertical drain (PVD) clogging affects the effectiveness of ground reinforcement and leads to significant uneven settlement. To alleviate these deficiencies, this paper proposed an alternating prefabricated radiant drain vacuum preloading (APRD-VP) method considering the advantages of the alternating vacuum preloading (A-VP) method (delaying clogging) and prefabricated radiant drain vacuum preloading (PRD-VP) method (combining horizontal drainage and alleviating uneven settlement). The laboratory model experiments were conducted to explore the treatment effect of APRD-VP method, and the particle image velocimetry technology was employed to observe clogging range surrounding PVD. The experimental results demonstrate that APRD-VP method displayed a better reinforcement effect than the traditional method by analysis of water discharge, settlement, pore water pressure, water content, and vane shear strength. By investigating the clogging formation development for APRD-VP method, the maximum clogging range on both sides of the drainage board has been reduced by 3.15% and 14.02%. In addition, the empirical relationship between clogging range and settlement was established to can better judge and predict clogging range, which can lay the foundation for establishing the theory of computation of soft soil ground design suitable for APRD-VP method. • An alternating prefabricated radiant drain vacuum preloading method was proposed. • The effectiveness of the alternating prefabricated radiant drain vacuum preloading method was demonstrated. • The movement of soil particles around the drainage board was observed and the clogging range was determined. [ABSTRACT FROM AUTHOR]

The large amount of dredged soil produced annually by rivers, lakes, seas, and oceans affects the ecological environment. Dredged material such as soft clay, which has high fluidity and high water content, is often utilized for building ground in engineering practice. Conventional vacuum preloading can effectively treat such soil but has a deprived consolidation effect. To improve the treatment effect, in this study, prefabricated radiant drain (PRD) vacuum preloading technology is proposed innovatively by adding prefabricated horizontal drains (PHDs) based on a prefabricated vertical drain (PVD). And a four-way connector is designed to connect PVD and PHDs, PHDs are attached to PVD to transmit vacuum pressure. A series of laboratory tests are run to compare and analyze the differences between conventional PVD and PRD vacuum preloading. The water discharge, average surface settlement, water content, and undrained shear strength values are analyzed. Then the parametric analysis of PHD spacings and length-width ratios (characterizing PHD length) are investigated. Overall, with the new PRD method, the consolidation effect of soft clay ground with a water content of 80% is improved by approximately 15%. [ABSTRACT FROM AUTHOR]

The high-water-content sludge produced through dredging seriously restricts marine ecological environments. Vacuum preloading methods (involving prefabricated vertical drains (PVDs)) are widely used to dewater and consolidate sludge ground, but these methods require long treatment periods and have deprived reinforcement effects. To overcome the limitations of PVD vacuum preloading, a prefabricated radiant drain (PRD) vacuum preloading method is proposed is this study by adding a prefabricated horizontal drain (PHD) to the PVD framework. Physical model tests are conducted under PVD and PRD vacuum preloading conditions, and a large-strain three-dimensional finite element (FE) model is established and validated against the physical model test data. FE parametric analyses are also conducted to evaluate the key factors influencing the PRD, i.e., the PHD length and spacing. The results show that the reinforcement effect of PRD vacuum preloading is better than that of PVD vacuum preloading. The ground settlement effect increases as the PHD length increases and the PHD spacing decreases. The settlement and pore water pressure metrics show elliptical distributions with an increasing PHD length. Through this work, an applicable sludge ground treatment design procedure is suggested based on parametric analyses; these findings can provide a reference for designing sludge ground treatments in the future. [ABSTRACT FROM AUTHOR]

Newly dredged fills feature a high moisture content and a high floating mud content. Based on the conventional vacuum preloading (CVP) method, this article presents a new method of air-booster vacuum preloading (AVP) to reinforce newly dredged fills for different air-booster periods (45, 60 and 90 min). Compared with other methods, this new method features no sand cushion and adopts a self-developed air-booster pipe and a water–air separation device. A series of laboratory model tests were performed to explore the effect of the improved AVP method for the enhancement of newly dredged fills. A comparison of variables monitored during reinforcement (vacuum pressure, surface settlement, water discharge and pore-water pressure) and after reinforcement (water content, vane shear strength, SEM and MIP) indicates that the reinforcement effect of the AVP method is superior to that of the CVP method; the former can effectively alleviate the problem of prefabricated vertical drain (PVD) clogging, greatly reducing engineering costs and significantly shortening construction periods. [ABSTRACT FROM AUTHOR]

This paper describes a full-scale test on a very soft clay ground around 70,000 m2, which is conducted in Huizhou of Guangdong Province, China, to present a new method of vacuum preloading method. A novel moisture separator was developed, which can automatically regulate the vacuum pressure variation by changing the volume of the gas inside it. A large quantity of water drained by the proposed moisture separators can be directly used as a surcharge loading, which would shorten the ground improvement time and save costs as well. Three levels of silt-prevention prefabricated vertical drains were used in the treating process to accelerate the consolidation. In addition, the vacuum preloading method also included an effective radial drainage device which would strengthen the dredged soft clay fill in a deep layer. In the in situ test, tens of piezometers and settlement plates were installed to measure the variations of excess pore water pressures and settlement of two stages of observation points at different positions in the ground. The results show that the largest average consolidation settlement was 314.1 cm and made a saving of more than 66% in power consumption compared with traditional method. It demonstrates that this adopted method is an efficient, cost-effective, and environmentally friendly method for improving sites with low bearing capacity and high compressibility soils. [ABSTRACT FROM PUBLISHER]

Air booster vacuum preloading is a newly improved method applied in land reclamation projects. Highly pressurized air can provide an additional pressure difference between the prefabricated vertical drain (PVD) and injection point, thereby increasing the hydraulic gradient and generating small fractures that can improve the soil permeability and the transmission efficiency of the vacuum pressure. However, with a premature activation time, the pressurized air can create air channels connected to the PVD, which may drastically decrease the vacuum pressure. With a delayed activation time, the strength of the dredged clay may be too high to permit fractures, thus limiting the permeability improvement. In this study, soils with degrees of consolidation (DOCs) of 0%, 40%, 60%, and 80% were selected for testing the efficacy of initial booster activation times in four tests. The results show that the pressurizing groups were more effective in improving the consolidation of soils, and the best effect of the use of air booster is obtained when soil has been consolidated to a DOC of 60%. The lower soils of the pressurized groups showed greater increase rates than those demonstrated by conventional vacuum preloading. [ABSTRACT FROM AUTHOR]