Hongtao Fu

Improved Vacuum Preloading Method for Consolidation of Dredged Clay-Slurry Fill

AbstractAn improved vacuum preloading method was developed to consolidate clay-slurry fill that is hydraulically placed in seawater for land reclamation. This method adopted both a vacuum and an air-pressurizing system. In the vacuum system, a new connector to connect each prefabricated vertical drain (PVD) directly to a horizontal vacuum pipe is used in lieu of a horizontal sand blanket. In the air-pressurizing system, compressed air is injected into the soil to accelerate consolidation. Field pilot tests using both the improved and the existing vacuum preloading systems were carried out at the same site. The testing data showed that better consolidation results were achieved using the improved vacuum preloading method.

Influence of Soluble Salt on Electro-Osmotic Consolidation of Soft Clay

A series of electro-osmotic consolidation laboratory tests was conducted to investigate the influence of soluble salt on the electro-osmotic consolidation of soft clay. Remolded soil samples with different salinities of KCl, NaCl, and CaCl2 were tested in the modified electro-osmosis oedometer experimental system. Final water content, vane shear strength, and pH value of test soil samples were analyzed by monitoring the changes in the electric current, volume of drainage, and vertical settlement during the tests. The results showed that addition of soluble salts can improve the electro-osmotic consolidation of soft clay. However, excessive salinity will reduce the efficiency of electro-osmotic consolidation. The optimal salinity of the soluble salt was determined for each type of salt. Moreover, an improved consolidation efficiency can be achieved by using CaCl2 rather than KCl or NaCl.

Experimental Comparison of Electro-Osmotic Consolidation of Wenzhou Dredged Clay Sediment Using Intermittent Current and Polarity Reversal

ABSTRACT The electroosmosis method is regarded especially suitable for the disposal of dredged clay sediment, but its excessive power consumption and electrode corrosion has limited its widespread application. Thus, intermittent current and polarity reversal are applied to offset its drawbacks. This study aims to examine the consolidation effect and internal relationship between the two approaches and optimize their time settings. Laboratory tests were performed with the same intermittent ratio and different reversal ratios. The test results demonstrated that intermittent current with comparatively greater intermittent times and a higher reversal ratio achieved a better drainage effect during the electroosmosis process and soil uniformity after test and the drainage in the reverse direction was lesser than that in the forward direction. The drainage effect during the power-off mode for 1 h was equivalent to that in the reverse electrifying mode for 0.2–0.25 h. Sharp increases in the current were induced by each intermittent current and polarity reversal. Although the polarity reversal approach improved the drainage effect, it partly increased the energy consumption. Compared with the intermittent current approach, reducing the reverse electrifying period to improve soil consolidation is feasible for application to engineering practice.

Undrained cyclic behavior of overconsolidated marine soft clay under a traffic-load-induced stress path

ABSTRACT To reduce the settlement induced by long-term traffic loads, the surcharge preloading method is widely used to improve the characteristics of marine soft clay subgrade. However, its effectiveness needs clarification. This paper presents the test results for the cyclic behavior of normal and overconsolidated marine soft clay under stress paths that simulate traffic loading through hollow cylinder apparatus. Test results show that the overconsolidation ratio significantly influences the axial strain, pore water pressure, stress–strain loops, and resilient modulus of soft clay specimens. Moreover, regression analysis on results under stress path with principal stress rotation predicts the permanent strain for overconsolidated marine soft clay.

Estimation of Influence Scope of Lateral Displacement of Soft Ground under Vacuum Pressure with PVD

The application of vacuum pressure to a treated area not only induces vertical settlement and inward lateral displacement but also causes the formation of tension cracks near the ground surface. In general, the strain method is applied to calculate the lateral displacement at the boundary of a treated area; however, the influence scope of lateral displacement has not yet been presented. Based on the in situ data of soft clayey soil foundation treated by vacuum consolidation, lateral displacement was estimated in the influence scope in this study. To calculate the influence scope of lateral displacement induced by vacuum pressure, the ratio of the lateral displacement within the influence scope to the ground surface settlement under the centre of the treated area is defined as the maximum value of the lateral displacement (ELD) within the influence scope. This paper proposes a direct relationship between ELD and the distance from the treated area boundary (Lx), considering the length of the prefabricated vertical drain. In addition, the FEA (finite-element analysis) is used to simulate the process of vacuum preloading to reinforce soft soil foundation. The influence scope simulated is almost close to the calculated value Lx. Accordingly, the safety distance between the boundary of the treated area and the surrounding building can be estimated when the soft soil foundation is consolidated by using a vacuum preloading method.