Search

A reclamation project was undertaken in Zhuhai, China, covering an area of 11.35 km2 with a clay-slurry thickness of 30 m. It is interesting to find a good reinforcement method, which is more suitable for strengthening such a large-scale dredged clay-slurry ground. Evidence from engineering practice shows that vacuum preloading or vacuum preloading combined with surcharge preloading method technology has certain advantages. However, further data is required to verify their performance in the field. This paper presents a case study using the conventional vacuum preloading and vacuum preloading combined with surcharge preloading method (vacuum pressure of 90 kPa, surcharge height of 3 m) to improve the thick clay-slurry ground for a subgrade engineering project in Zhuhai, China. A series of field monitoring, in-situ tests, and laboratory tests were performed to evaluate their treatment effect by analysis of vacuum degree, ground surface settlement, layered settlement, consolidation degree, lateral displacement, excess pore water pressure dissipation, and vane shear strength. The results showed that the ground treated via vacuum preloading combined with surcharge preloading method was more effective than conventional vacuum preloading. The vacuum degree of vacuum preloading combined with surcharge preloading method was slightly lower than that of conventional vacuum preloading, decreasing with depth. The settlement is increased by 55.56%, average consolidation degree is enlarged by 40.9%, lateral displacement can be augmented by 2.4 times, pore water pressure coefficient is less than 0.6, and undrained shear strength is amplified by 22.2%. These findings can be used to guide the design of the combined preloading method of the subgrade engineering project along the east coast of China. [ABSTRACT FROM AUTHOR]

AbstractThis 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. [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]

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]