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.

A series of geopolymers were synthesized by employing phosphoric acid (PA) as activator to activate low-calcium fly ash (FA) and metakaolin(MK), and geopolymer mortar was prepared using PA-activated FA-MK geopolymer and dredged soil. The PA-activated low-calcium FA geopolymer typically exhibited low compressive strength. Incorporating MK introduced reactive aluminum, which enhanced the compressive strength of the geopolymer. This strength improvement was further amplified as the M:F ratio (MK:FA ratio) increased. Under a certain M:F ratio, there existed an optimum H3PO4/Al2O3 molar ratio that maximized the compressive strength of geopolymer. A positive correlation was observed between the M:F ratio and the optimum H3PO4/Al2O3 molar ratio, with the latter exhibiting a gradual increase from 0.56 (M:F ratio = 0:1) to 0.64 (M:F ratio = 0.4:0.6) and ultimately 0.86 (M:F ratio= 1:0). The compressive and flexural strengths of the geopolymer mortar were significantly affected by the geopolymer/soil ratio and the PA concentration. When the actual PA concentration in geopolymer mortar approached the optimum PA concentration for the geopolymer paste, the mortar achieved its best mechanical properties. The stabilization of dredged soil using PA-activated geopolymer demonstrates significant sustainability benefits, while their cost-effectiveness and mechanical performance require further optimization. This research provides new approaches and data support for the reuse of low-calcium FA and dredged soil.

This study aimed to address the challenges of solid waste utilization, cost reduction, and carbon reduction in the treatment of deep-dredged soil at Xuwei Port in Lianyungang city of China. Past research in this area was limited. Therefore, a curing agent made from powdered shells was used to solidify the dredged soil in situ. We employed laboratory orthogonal tests to investigate the physical and mechanical properties of the powdered shell-based curing agent. Data was collected by conducting experiments to assess the role of powdered shells in the curing process and to determine the optimal ratios of powdered shells to solidified soil for different purposes. The development of strength in solidified soil was studied in both seawater and pure water conditions. The study revealed that the strength of the solidified soil was influenced by the substitution rate of powdered shells and their interaction with cement. Higher cement content had a positive effect on strength. For high-strength solidified soil, the recommended ratio of wet soil: cement: lime: powdered shells were 100:16:4:4, while for low-strength solidified soil, the recommended ratio was 100:5.4:2.4:0.6. Seawater, under appropriate conditions, improved short-term strength by promoting the formation of expansive ettringite minerals that contributed to cementation and precipitation. These findings suggest that the combination of cement and powdered shells is synergistic, positively affecting the strength of solidified soil. The recommended ratios provide practical guidance for achieving desired strength levels while considering factors such as cost and carbon emissions. The role of seawater in enhancing short-term strength through crystal formation is noteworthy and can be advantageous for certain applications. In conclusion, this research demonstrates the potential of using a powdered shell-based curing agent for solidifying dredged soil in an environmentally friendly and cost-effective manner. The recommended ratios for different strength requirements offer valuable insights for practical applications in the field of soil treatment, contributing to sustainable and efficient solutions for soil management.

Dredged soil has the disadvantages of high moisture content and low strength, making it unsuitable for practical engineering application. However, a gelling agent system composed of ground granulated blast-furnace slag (GGBS) and carbide slag (CS) can enhance the strength of dredged soil. Additionally, phosphogypsum (PG) can react with the products of this system (calcium silicate hydrate) to form ettringite and improve strength. In this study, CS, GGBS, and PG were selected to solidify dredged soil with high moisture content. The flowability test, unconfined compression test, and direct shear test were employed to evaluate the engineering properties of the dredged soil, while the scanning electron microscope test (SEM), X-ray diffraction test (XRD), nuclear magnetic resonance test (NMR), and toxicity characteristic leaching procedure test (TCLP) to investigate the microstructure evolution of the cured dredged soil. The results indicated that the decreased flowability of cured dredged soil showed a decreasing trend with increased curing agent content. The strength of cured dredged soil increased first and then decreased, and increased finally with the increase of PG content. The optimum PG content was identified as 10 % when the GGBS content was set as 15 %. The internal friction angle of cured dredged soil increased with increased PG content. The change of pore structure and hydration reaction were identified as the main root cause for the change of sample strength. The new cementing material composed of CS, GGBS and PG can effectively resolve the insufficient strength and high water content problems of dredged soil, while having negligible impact on the environment. Moreover, since it is made up of industrial by-products, it has a lower carbon footprint than the traditional cementing materials of lime or cement.

The weak mechanical properties of dredged soil can be improved by using cementing agents. Comprehensive investigation of the efficacy of stabilizing methods, including Portland cement (PC) and alkali-activated ground granulated blast-furnace slag (CaO-GGBS), cementing agent content from 12% to 16%, and curing methods in different initial moisture content of soils, organic matter content, and soil types was carried out. Experimental results showed that dredged soils have stronger properties using CaO-GGBS than PC. Maximum strength was found by using the highest CaO-GGBS content of 16%. The increase of organic matter content can weaken the enhanced properties of dredged soils stabilized by CaO-GGBS. The highest shear strength of specimens stabilized by CaO-GGBS occurred in dredged soils with 20% sand while the greatest yield strength in e-log p ' space was found in dredged soils with 30% sand. A modified constitutive model based on the framework for cemented geomaterials proposed by Gens and Nova has been developed. The ability of the model to reproduce the mechanical behavior capturing strength development with curing period was explored.

Bayer Red mud (BRM) and phosphogypsum (PG) are known as two main industrial wastes around the world. Previous studies have demonstrated the contribution of BRM and PG in cement -based hydration reactions, but their collaborative role is still pending in cement -stabilized dredged soil. In this study, the collaborative role of BRM and PG was examined by comparing micro -macro properties of stabilized clay with different initial water contents, cement contents and BRM/PG proportions. The chemical and microscopic results are found highly complementary, indicating existence of alkali -activation effects, pore -filling effects and cementation damage effects in stabilized clay. The pH of 8% cement -stabilized clay increases by about 0.5 after addition of 10% alkaline BRM, which activates clay mineral in dredged soils and results in more sufficient pozzolanic reactions. In addition, the pore -filling effect of ettringite is much more contributory in soils with a higher water content of 140%. Such positive effects significantly weaken as the water content decreases to 80%, the cementation damage effects come into picture instead. The unconfined compressive strength (UCS) after 7 days curing nearly triples with an optimal proportion of BRM and PG, demonstrating effectiveness of the proposed approach. As the water and cement contents increase, the optimal proportion of BRM and PG evolves from R7.5P2.5 into R5P5.