Colloid effect on clogging mechanism of hydraulic reclamation mud improved by vacuum preloading

Abstract

Many cases of artificial soft clay foundation constructed by hydraulic filling and improved by the vacuum preloading show the clogging phenomenon in the surrounding soil, which compromises the improvement quality. To clarify the clogging mechanism and the formation of soil columns, the vacuum process was tracked from macro to micro by laboratory model tests. Results show that the soil column with higher strength (density) and lower water content was formed surrounding the prefabricated vertical drainage (PVD). Mercury intrusion porosimetry (MIP) tests revealed that the pore-entrance diameter of the soil column after 50 and 43 days of vacuum application ranged from 100 to 600 nm, and that at peak it is 300 nm. However, the mean diameter of the colloidal particles in tail water decreases from 1000 to 100 nm with continuous vacuum application, and then becomes stable at about 100 nm after 43 days. After re-visiting the vacuum process of the hydraulic reclamation mud, the pore-size distribution of surrounding soils and particle-size distribution of the tail water, the clogging was explained by the filling of the pores of the soil column by the colloidal particles in pore water. This mechanism differentiates the artificial foundation improved by vacuum preloading from the natural foundation for the presence of rich colloidal particles in pore water.

Consolidation Considering Clogging Effect under Uneven Strain Assumption

“…As found by Hong et al (2010) and Cao et al (2014), compressibility and permeability of dredged fills are related to the void ratio, which can be expressed as (14) where e and e0 are the void ratios of the soil at any time and at the initial time respectively, eL is the void ratio of soil at the liquid limit, ′ is the effective stress, , is the remolded yield stress, / * is the inherent compression parameter, and $22 *…”

“…is the void ratio of remolded soil at an effective stress of 100 kPa, which can be expressed as ultrasoft, with a water content over the liquid limit and with essentially no shear strength (Wang et al, 2018), the effective stress could be considered as 0 initially, which could also be obtained by substituting e0 into Eq. (14). Because the final reduction of the pore water pressure was measured to be 38 kPa at the boundary of the effective zone, the compressibility curve of this sample could be drawn according to Eq.…”

“…However, the slurry has some properties that are extremely unfavorable for further construction, including high water content, low bearing capacity, and high compressibility (Zeng et al, 2016;Deng et al, 2019, Fang et al, 2019, all of which need to be improved.…”

Experimental Study on the Influencing Factors of Treatment of Landfill Sludge Using Vacuum Preloading with the Fenton Reagent

“…Table 5 shows the shear strength of case 3 after vacuum preloading was still rather low, and the shear strength of case 1 and case 2 had increased to different degrees, but the strength distribution was inhomogeneous; case 2 had the highest shear strength, with a maximum value of 5.8 kPa, followed by case 3 with a maximum value of 3.4 kPa and case 3 with a minimum value of 1.1 kPa; the shear strengths of case 1 and case 2 at a distance of 3 cm from the PVD were 3.4 times and 4.1 times those at 13 cm, respectively, indicating that dense "soil piles" with poor permeability were formed near the PVD [29,36,37]. The soil piles were formed by the movement and aggregation of fine particles towards the PVD under the action of permeability.…”

Studying the soil column formation in soft soil improved by vacuum preloading via coupled scale‐up CFD‐DEM simulations

“…To solve the land resource shortage, some large-scale land reclamation projects are being conducted in some coastal regions and countries, such as the Oufei project in Zhejiang province of eastern China and the Pulau Tekong island reclamation project on the northeastern coast of Singapore. As the hydraulic soil dredged from the sea to construct land has an extremely high initial water F I G U R E 1 Schematic of the laboratory model tests conducted by Deng et al 6 of hydraulic slurry improved by vacuum preloading. In that experiment, the newly dredged slurry with the initial water content of 67.2% was stored in a test barrel with a diameter of 28 cm.…”