Coupling effect of cement-stabilization and biopolymer-modification on the mechanical behavior of dredged sediment

Nowadays,biopolymer stabilization as a promising eco-friendly approach in soft ground improvement has attracted wide attentions.However,the feasibility of using biopolymer as a green additive of cementstabilized dredged sediment(CDS)with high water content is still unknown.In this study,guar gum(GG)and xanthan gum(XG)were adopted as typical biopolymers,and a series of unconfined compressive strength(UCS),splitting tensile strength(STS)and scanning electron microscopy(SEM)tests were performed to evaluate the mechanical and microstructural properties of XG-and GG-modified CDSs considering several factors including biopolymer modification,binderesoil ratio and wateresolid ratio.Furthermore,the micro-mechanisms revealing the evolutions of mechanical properties of biopolymermodified CDS were analyzed.The results indicate that the addition of XG can effectively improve the strength of CDS,while the GG has a side effect.The XG content of 9%was recommended,which can improve the 7 d-and 28 d-UCSs by 196%and 51.8%,together with the 7 d-and 28 d-STSs by 118.3%and 42.2%,respectively.Increasing the binderesoil ratio or decreasing the wateresolid ratio significantly improved the strength gaining but aggravated the brittleness characteristics of CDS.Adding XG to CDS contributed to the formation of microstructure with more compactness and higher cementation degrees of ordinary Portland cement(OPC)-XG-stabilized DS(CXDS).The micro-mechanism models revealing the interactions of multiple media including OPC cementation,biopolymer film bonding and bridging effects inside CXDS were proposed.The key findings confirm the feasibility of XG modification as a green and high-efficiency mean for improving the mechanical properties of CDS.

Clean-up and disposal process of polluted sediments from urban rivers

In this paper, the discussion is concentrated on the properties of the polluted sediments and the combination of clean-up and disposal process for the upper layer heavily polluted sediments with good flowability. Based on the systematic analyses of various clean-up processes, a suitable engineering process has been evaluated and recommended. The process has been applied to the river reclamation in Yangpu District of Shanghai City, China. An improved centrifuge is used for dewatering the dredged sludge, which plays an important role in the combination of clean-up and disposal process. The assessment of the engineering process shows its environmental and technical economy feasibility, which is much better than that of traditional dredging-disposal processes.

Dredged marine soil stabilization using magnesia cement augmented with biochar/slag

Dredged marine soils(DMS)have poor engineering properties,which limit their usage in construction projects.This research examines the application of reactive magnesia(rMgO)containing supplementary cementitious materials(SCMs)to stabilize DMS under ambient and carbon dioxide(CO_(2))curing conditions.Several proprietary experimental tests were conducted to investigate the stabilized DMS.Furthermore,the carbonation-induced mineralogical,thermal,and microstructural properties change of the samples were explored.The findings show that the compressive strength of the stabilized DMS fulfilled the 7-d requirement(0.7-2.1 MPa)for pavement and building foundations.Replacing rMgO with SCMs such as biochar or ground granulated blast-furnace slag(GGBS)altered the engineering properties and particle packing of the stabilized soils,thus influencing their performances.Biochar increased the porosity of the samples,facilitating higher CO_(2) uptake and improved ductility,while GGBS decreased porosity and increased the dry density of the samples,resulting in higher strength.The addition of SCMs also enhanced the water retention capacity and modified the pH of the samples.Microstructural analysis revealed that the hydrated magnesium carbonates precipitated in the carbonated samples provided better cementation effects than brucite formed during rMgO hydration.Moreover,incorporating SCMs reduced the overall global warming potential and energy demand of the rMgO-based systems.The biochar mixes demonstrated lower toxicity and energy consumption.Ultimately,the rMgO and biochar blend can serve as an environmentally friendly additive for soft soil stabilization and permanent fixation of significant amounts of CO_(2) in soils through mineral carbonation,potentially reducing environmental pollution while meeting urbanization needs.

Efficient stabilization of dredged sludge with high water content using an improved bio-carbonation of reactive magnesia cement method

This study proposed an improved bio-carbonation of reactive magnesia cement(RMC)method for dredged sludge stabilization using the urea pre-hydrolysis strategy.Based on unconfined compression strength(UCS),pickling-drainage,and scanning electron microscopy(SEM)tests,the effects of prehydrolysis duration(T),urease activity(UA)and curing age(CA)on the mechanical properties and microstructural characteristics of bio-carbonized samples were systematically investigated and analyzed.The results demonstrated that the proposed method could significantly enhance urea hydrolysis and RMC bio-carbonation to achieve efficient stabilization of dredged sludge with 80%high water content.A significant strength increment of up to about 1063.36 kPa was obtained for the bio-carbonized samples after just 7 d of curing,which was 2.64 times higher than that of the 28-day cured ordinary Portland cement-reinforced samples.Both elevated T and UA could notably increase urea utilization ratio and carbonate ion yield,but the resulting surge in supersaturation also affected the precipitation patterns of hydrated magnesia carbonates(HMCs),which weakened the cementation effect of HMCs on soil particles and further inhibited strength enhancement of bio-carbonized samples.The optimum formula was determined to be the case of T?24 h and UA?10 U/mL for dredged sludge stabilization.A 7-day CA was enough for bio-carbonized samples to obtain stable strength,albeit slightly affected by UA.The benefits of high efficiency and water stability presented the potential of this method in achieving dredged sludge stabilization and resource utilization.This investigation provides informative ideas and valuable insights on implementing advanced bio-geotechnical techniques to achieve efficient stabilization of soft soil,such as dredged sludge.

Restoration or Rehabilitation of the Faleme River Affected by Mining Activities: What Methods?

The Faleme River, a West Africa long transboundary stream (625 km) and abundant flow (>1100 million m3) is affected by severe erosion because of mining activities that takes place throughout the riverbed. To preserve this important watercourse and ensure the sustainability of its services, selecting and implementing appropriates restorations techniques is vital. In this context, the purpose of this paper was to present an overview of the actions and techniques that can be implemented for the restoration/rehabilitation of the Faleme. The methodological approach includes field investigation, water sampling, literature review with cases studies and SWOT analysis of the four methods presented: river dredging, constructed wetlands, floating treatment wetlands and chemical precipitation (coagulation and flocculation). The study confirmed the pollution of the river by suspended solids (TSS > 1100 mg/L) and heavy metals such as iron, zinc, aluminium, and arsenic. For the restoration methods, it was illustrated through description of their mode of operation and through some case studies presented, that all the four methods have proven their effectiveness in treating rivers but have differences in their costs, their sustainability (detrimental to living organisms or causing a second pollution) and social acceptance. They also have weaknesses and issues that must be addressed to ensure success of rehabilitation. For the case of the Faleme river, after analysis, floating treatment wetlands are highly recommended for their low cost, good removal efficiency if the vulnerability of the raft and buoyancy to strong waves and flow is under control.

Numerical Modelling of Sediment Particle Transportation on a Navigation Inlet Using the Particle Tracking Model (PTM)

This paper investigates particle transportation using a numerical model application approach to understand the final fate of suspended sediment particle masses due to a dredging operation in a navigational harbor inlet using PTM (Particle Tracking Model). The investigation applied PTM and simulated particle transportation at a navigational harbor called St Jerome Creek Inlet in Chesapeake Bay in Maryland. The United States Army Corps of Engineers (USACE), Maryland District, designed jetties for the inlet, which, when constructed, would minimize dredging requirements from once in a two-year period to once in a ten-year period. In the meantime, due to the frequent dredging requirements of the inlet, there exists a need to understand the fate of the suspended sediments from the dredging operations to assess the environmental impact on the aquatic environment and the coastal community. This study used PTM to simulate the transportation of sediments in a 30-day period during a dredging operation. Ten sediment source locations were selected as possible sites from which dredged materials could be introduced into the flow system. The model output was analyzed to draw conclusions. Results showed that most suspended sediment particle masses moved from their initial site locations and settled along the shoreline, whilst the sediments that found their way out of the inlet system towards the ocean migrated southward and settled approximately 6 miles at the tip of the mainland. The objective of the study is to track sediment particles from a dredging operation. This would be significant in tracking possible contaminants in an aquatic environment for future environmental management decisions.

Tailings Dam Mining, Theoretical Considerations, and Circular Economy: A Review

Mining in tailings dams has emerged as a strategic alternative for mining companies for both economic and environmental reasons. Owing to technological limitations in recent decades, many of these dams have high metal contents, emphasizing the need to evaluate the quality of these residues, especially considering the technological advancements in current concentration plants. An economic viability analysis associated with reusing these materials is crucial. From an environmental point of view, improving mining techniques for dams by considering both safety and feasibility is an advantageous option in decommissioning processes and alignment in the circular economy. In this context, representing these tailings in terms of grade quality and granulometry, as well as the associated contaminants, is essential. Geostatistical estimation and simulation methods are valuable tools for modeling tailings bodies, but they require a reliable sampling campaign to ensure acceptably low errors. From an operational perspective, tailings recovery can be conducted via dry methods, such as mechanical excavation, or hydraulic methods, such as dredging or hydraulic blasting. Dredging is a commonly used method, and cutter suction dredgers, which require pumping to transport fragmented material, are the most commonly used tools. In this paper, some practical applications of geostatistical methods for resource quantification in tailings dams will be discussed. Additionally, the main mining methods for tailings recovery in dams will be presented. Emphasis will be given to the dredging method, along with the key analysis parameters for sizing dredgers, pumps, and pipelines.

An Overview of the Concept of Regional Sediment Management

In this article we described the concept of ＂regional sediment management＂ （RSM）, and identified opportunities for and impediments to implementing regional approaches to sediment management, and also summarized the background information and applications of RSM. Furthermore, we considered the needs of RSM studies and, suggested the framework for developing RSM strategies, and described the specific studies for the Xiamen region.

Experimental Research on the Dewatering of Dredged Sediment from Dianchi Lake

[Objective] The technological parameter suitable for the dewatering of dredged sediment from Dianchi Lake was studied.[Method] By means of the treatment method of sewage sludge in sewage treatment plant,flocculants including FeCl3,Al2(SO4)3 and PAM were taken as dewatering agents which were added in dredged sediment.[Result] The results showed that Al2(SO4)3 had better dewatering effect than FeCl3 and PAM,and the optimum dosing quantity of Al2(SO4)3 in dredged sediment was 170 mg/L,in addition,the water quality of supernatant met the first class B standard of GB18918-2002 and could be directly discharged to nature water without pollution.[Conclusion] The study could provide a simple and feasible way for the rapid dewatering of dredged sediment from Dianchi Lake,which would be convenient for the disposal and resource utilization of dredged sediment.

Significance of dredging on sediment denitrification in Meiliang Bay,China:A year long simulation study

An experiment for studying the effects of sediment dredging on denitrification in sediments was carried out through a one-year incubation of undredged （control） and dredged cores in laboratory. Dredging the upper 30 cm of sediment can significantly affect physico-chemical characteristics of sediments. Less degradation of organic matter in the dredged sediments was found during the experiment. Denitrification rates in the sediments were estimated by the acetylene blockage technique, and ranged from 21.6 to 102.7 nmol N2/（g dry weight （dw）-hr） for the undredged sediment and from 6.9 to 26.9 nmol N2/（g dw-hr） for dredged sediments. The denitrification rates in the undredged sediments were markedly higher （p 〈 0.05） than those in the dredged sediments throughout the incubation, with the exception of February 2006. The importance of various environmental factors on denitrification was assessed, which indicated that denitrification was regulated by temperature. Nitrate was probably the key factor limiting denitrification in both undredged and dredged sediments. Organic carbon played some role in determining the denitrification rates in the dredged sediments, but not in the undredged sediments. Sediment dredging influenced the mineralization of organic matter and denitrification in the sediment; and therefore changed the pattern of inherent cycling of nitrogen.

Influence of Sediment Dredging on Chemical Forms and Release of Phosphorus

A laboratory experiment was carried out through a six-month incubation of undredged （control） and dredged cores to study the effect of sediment dredging on phosphorus （P） release from the sediment in the Taihu Lake. During the experiment, dredging the upper 30 cm layer could efficiently reduce the interstitial PO4^3-P concentration and different P forms in the sediment. The P fluxes of the undredged and dredged cores ranged from -5.1 to 3047.6 and -60.7 to 14.4μg·m^-2·d^-1, respectively. The fluxes of the dredged cores were generally lower than those of the control. Differences in the fluxes between the dredged and undredged cores were statistically significant （P 〈 0.05） from March to June 2006. The sediment P in the dredged cores had a lower release potential than that in the control. Dredging can be considered as a useful measure for rehabilitating the aquatic ecosystem after the external P loading in the Talhu Lake catchment was efficiently reduced.

Municipal sludge as landfill barrier material

The aim of this research is to find substitute barrier materials for natural clay from two kinds of municipal sludge: waterworks sludge(S_w) and dredging sludge(S_d). Laboratory tests were performed firstly to determine their Atterberg limits and hydraulic conductivity. Based on the results, the use of waterworks sludge was recommended. Then, shear strength tests were performed and it was found the shear resistance property of waterworks sludge is strong enough to maintain slope stability. In order to evaluate the possibility of secondary pollution, the heavy metal contents of waterworks sludge was determined and the results indicated that secondary pollution is unlikely happened. Finally, economic analysis proves that reusing waterworks sludge as barrier will reduce the lost a great for both landfill and waterworks. Based on the results, waterworks sludge was proposed to use and a further long-term simulated landfill test was suggested.

Comparison of Remolded Shear Strength with Intrinsic Strength Line for Dredged Deposits

Chandler proposed the intrinsic strength line to correlate the undrained shear strength of samples one-dimensionally consolidated from slurry with the void index proposed by Burland. The undrained shear strength on the intrinsic strength line is different from the remolded undrained shear strength that is an important parameter for design and construction of land reclamation. The void index is used in this study for normalizing the remolded strength behavior of dredged deposits. A quantitative relationship between remolded undrained shear strength and void index is established based on extensive data of dredged deposits available from sources of literature. Furthermore, the normalized remolded undrained shear strength is compared with intrinsic strength line. The comparison result indicates that the ratio of undrained shear strength on the intrinsic strength line over remolded undrained shear strength increases with an increase in applied consolidated stress.

Influence of Reclamation Works on the Marine Environment in a Semi-Enclosed Bay

The flow and seawater exchange rates have been predicted using a two-dimensional numerical model and a Lagrangian method for a semi-enclosed shallow bay where reclaiming and dredging works are scheduled. The wind effect on the flow and material transport has been emphasized, and a thirty-year mean value of wind has been considered in the numerical simulation. As a whole, even after the reclaiming and dredging are conducted, the flow pattern looks similar to the original state. However, velocity variations up to 20% to 100% appear in the vicinity of the construction area. In the case of summcr wind forcing, the seawater exchange rate increases from 71.6% to 82.9% after the reclaiming and dredging, as indicated by a particle-tracking method. On the contrary, in the case of winter wind forcing, thc seawater cxchange rate appears to be 97.2% under natural conditions but decrcases slightly to 93.2% aftcr the rcclaiming and dredging. Thus, the wind forcing plays an important role in controlling the seawater exchangc rates. The seawater cxchange rate is further improved by 15% if the dredging is simultaneously carried out with the reclaiming. This suggests that the dredging can be an effective means to mitigate the variation of flow.

High-efficiency stabilization of dredged sediment using nano-modified and chemical-activated binary cement

High-efficiency disposal of dredged sediment(DS)has become an imperative geo-environmental engineering issue due to the limited landfilling space and severe environmental burdens.This study firstly developed a novel high-efficiency nano-modified and chemical-activated binary cement(NBC),which was composed of binary cement(BC)consisting ordinary Portland cement(OPC)and ground granulated blast-furnace slag(GGBS),chemical-activator and nano-modifier.The effects of chemical-activation and nano-modification on the strength development of BC-stabilized DS(BCDS),and the optimum mix of NBC were respectively achieved via a series of unconfined compressive strength and orthogonal tests.Then,the high-efficiency and economic applicability of NBC in DS stabilization were evaluated by comparing with OPC.Furthermore,the microstructure and mineral composition evolutions inside NBCstabilized DS(NDS)were explored by conducting X-ray diffraction(XRD)and scanning electron microscopy(SEM)tests.The results show that both chemical-activation and nano-modification could effectively improve the strength gain of BCDS,and compared with single chemical-activator and nanomodifier,the composite chemical-activators and nano-modifiers exhibited better performances.Based on BC with OPC/GGBS mass ratio of 1:1,both anhydrous sodium metasilicate/anhydrous sodium sulfate(SM/SS)and nano-SiO_(2)/nano-MgO(NS/NM)with mass ratio of 1:9 were respectively determined to be optimum chemical-activator and nano-modifier.The optimum mass ratio of BC,SM/SS and NS/NM was 20:2:1,i.e.the optimum mix of NBC.Compared with OPC,NBC exhibited higher stabilization efficiency and better economic applicability.The generation of calcium silicate hydrate(CSH),calcium aluminate hydrate(CAH)and ettringite contributed to the formation of dense cemented soil matrix inside NDS,and a conceptual micro-mechanism model characterizing the strength development under the coupling action of chemical-activation and nano-modification was proposed.

Experiment Study of the Evolution of Coral Sand Particle Clouds in Water

The motion of particle clouds(i.e.,sediment clouds)usually can be found in engineering applications such as wastewater discharge,land reclamation,and marine bed capping.In this paper,a series of laboratory tests are conducted on coral sand to investigate the shape feature of the single particle and the mixing processes of the coral sand particle clouds.The shape of coral sand particle is measured and quantified.The experimental results demonstrate that the shape of coral sand particles tends to be spherical as the particle size decreases,and empirical equations were established to explain the variation of D50 and fS,50 of coral sand.Compared with the silica sand,the evolution of the coral sand particle cloud still experiences three stages,but the threshold for the Reynolds number of particle clouds entering the next stage changes.Further,the normalized axial distance of the coral sand particle clouds is 58%smaller.The frontal velocity exhibits similar varying tendency for the coral sand particle cloud.Considering the difference in shape between coral sand particles and silica sand particles,a semi-empirical formula was proposed based on the original silica sand prediction formula by adding the shape factor and the experimental data of 122μm≤D_(50)≤842μm.It can predict the frontal velocity of the coral sand particle clouds.

MODEL STUDY OF DREDGED CHANNEL SILTATION IN OFFSHORE OPEN WATER

Based on the model study, the siltation of dredged channel under the condition of clear water and sediment-water mixture in Lianyun Harbor, Jiangsu Province and the experimental method under complex hydrodynamic elements such as tides, winds, waves and tidal currents are studied. The regularities of the variation of the velocity in the dredged channel in clear water are discussed as well. A group of curves such as water depth, velocity and angle has been plotted as a guide to the selection of a proper direction for a dredged channel. The intensity of siltation and the rate of deposition in the condition of sediment-water mixture, and the relationship between the dimensions of the dredged channel and the deposition amount can be estimated.

Modelling Impact of Dredging and Dumping in Ebb-Flood Channel Systems

For a channel-shoal system in a funnel-shaped basin the impact of dredging and dumping is investigated using a complex process-based model. First, the residual flow and sediment transport circulations are analysed for the channel-shoal pattern, which has emerged after a longterm model simulation. Results are compared to the Western Scheldt estuary, which forms the inspiration for this study. Subsequently, different dredge and dump scenarios are modelled, according to a conceptual model, in which ebb- and flood-channels and enclosed shoals form morphodynamic units (cells) with their own sediment circulation. Model results show that dumping sediment in a channel further reduces the channel depth and induces erosion in the opposite channel, which enhances tilting of the cross-section of the cell and eventually can lead to the degeneration of a multiple channel system into a single channel. The impact of different dredging and dumping cases agrees with results from a stability analysis. This means that this type of model applied to a realistic geometry can potentially be used for better prediction of the impact of human interventions.

Modification of nanoparticles for the strength enhancing of cementstabilized dredged sludge

This paper investigates the effectiveness of nano-modification on the strength enhancement of cementstabilized dredged sludge(CDS).Three types of nanoparticles including nano-SiO2(NS),nano-Al2O3(NA)and nano-MgO(NM)were used as cement admixtures for dredged sludge stabilization.Effects of single nanoparticle content,mass ratio of composite nanoparticles and curing time on the strength development of CDS were evaluated via a series of unconfined compressive strength(UCS)tests.The pH evolutions of CDS caused by nanoparticles were also examined by a range of pH tests.Furthermore,micromechanisms reflecting the strength evolutions were analyzed by performing scanning electron microscopy(SEM)and X-ray diffraction(XRD)tests.The results indicated that adding nanoparticles can significantly improve the UCS of CDS.For single nano-modification,the optimum contents of NS,NA and NM were 4%e6%,6%and 8%,which can increase the 7-and 28-d UCSs of CDS by 38%and 50%,17%and 35%,65%and 67%,respectively.Compared with single nano-modification,composite nano-modifications were more effective in improving the strength gain of CDS.The optimum mass ratios of composite nanoparticles,namely NS/NA,NS/NM and NA/NM,were 9/1,3/7 and 3/7,respectively.Based on the strength growth rate,the composite nanoparticles with NS/NM of 3/7 were highly recommended.The addition of nanoparticles obviously affected the pH evolution of CDS,which was mainly determined by the difference of OHproduction and consumption inside nano-modified CDS.The microstructural analysis revealed that C-S-H and C-A-H gels are the main cementitious products,and the addition of nanoparticles can obviously contribute to a denser and more homogenous microstructure of CDS.

STUDY ON PREDICTION FOR TRANSPORT AND DIFFUSION OF DREDGED MATTER IN JIAOZHOU BAY, CHINA

The finite element method was used to simulate the currents of Jiaozhou Bay and the nearcoast areas, and then established the model of the transport and diffusion of suspended particulate matter there. The transport and diffusion of dredged matter near the discharging field were estimated; and the results were used to analyze the effects of the suspended particulate matter on the marine environment.