Dredged Material Research Articles

3D HYDRODYNAMIC MODELING TO CHARACTERISE THE BEHAVIOUR OF THE DISPOSAL OF DREDGED MATERIAL USING A VERTICAL TREMIE PIPE

Dredge plume modelling forms an integral part of the supporting studies for EIA applications for both capital and maintenance dredging projects. The behaviour of dredge plumes is function of many variables, many of which are unknown at the time of undertaking the studies. As such engineering judgment, previous project experience (including engaging dredging contractors) and available literature form part of the tools used to characterize the behaviour of dredge plumes. This paper summarises two case studies where underwater disposal (using a vertical tremie pipe) of dredge material from a cutter section (CSD) was simulated in order to meet the regulatory standard at the edge of mixing zone.

Gas production from dredged sediment

The anaerobic degradation of sediment organic matter leads to considerable gas production in constructions made from sediments and in landfills where contaminated sediments are disposed of, inducing problems with the mechanical stability of constructions or necessitating extraction and treatment of gas. However, little is known about the magnitude of gas generation from dredged sediment, hence validated input parameters for gas production modelling are missing. On the occasion of drillings performed for the installation of inclinometers on a mono-landfill for contaminated dredged sediment, eleven waste layers of known were sampled. Samples were analysed for gas generation in a long-term laboratory incubation experiment carried out for 757 days. It was found that the residual gas potential of the deposited dredged material ranged between 2 and 12 m3 MgDW−1, relating to 3–11% of the organic matter being degraded. Correlation analyses with material properties suggest a strong role of nitrogen, either directly or as indicative parameter, with the gas potential increasing with total nitrogen content and the share of degradable carbon decreasing with increasing TOC/TN ratio. The by far greatest share of organic matter was bound in the heavy density fraction >1.4 g cm−3, suggesting that the readily available light organic matter pool had already been depleted during pre-treatment of the dredged sediment in dewatering fields and the subsequent years of landfilling. Consequently, the correlation of the remaining gas potential with heavy fraction nitrogen was even stronger than for bulk nitrogen. The gas potential as revealed from the long-term test correlated well with short-term values, but outreached the commonly applied potential measured for 21 days by the factor of four. The data improve the state of knowledge on gas production from the large mineral waste stream of dredged material and serve to improve gas production modelling for these types of wastes. The strong correlation of gas potential to TN suggests that TN may serve as a proxy to estimate total gas potential.

Petroleum hydrocarbons - a necessity of monitoring in a dredged material in the Polish coastal zone

Petroleum hydrocarbons (PHCs) are toxic for the water organisms and in sediments they may last for a very long time. The Baltic Sea is an area exposed to the PHCs due to highly developed shipping. In Poland, there is a lack of legal standards specifying guidelines regarding handling dredged material containing PHCs, excavated in waterways, roadsteads, and in port basins, and there are no standards specifying their acceptable concentration in sediments. Therephore petroleum hydrocarbons in the excavated dredged material are rarely examined at the Polish coasts. In years 2009-2018 only 4% of sediments were examined in terms of their content. Indicated that only the sediments from the open sea did not contain PHCs, the other ones were very or moderately contaminated with PHCs. Collected results clearly indicate that sediment should be monitored in terms of the PHC content, in most cases should not be thrown back to the sea. In most cases they may be stored onshore, but only on wastelands, mainly industrial and transport areas. Some of them may also be used in the areas of cleaner lands, i.e. forests, wood- and bush-covered lands, recreation and leisure areas.

Beneficial Uses of Dredged Material in Green Infrastructure and Living Architecture to Improve Resilience of Lake Erie

To maintain the navigational depth, 1.15 million cubic meters (1.5 million cubic yards) of sediment is dredged out from the federal harbors every year from Lake Erie, Ohio Coast. Treating this huge amount of dredged material is a major challenge due to the mobilization of potential contaminants causing depreciation in water quality and depletion of valuable land. Rather than treating the dredged material as a waste, we suggest investigating alternative ways to recycle and reuse the material within Green Infrastructure (GI) and living architecture applications. This study identifies potential applications of the dredged material in bioretention and vegetative roof systems, and examines the role of dredged material in these edaphic conditions. The paper discusses the beneficial uses of dredged material in GI by investigating the quality of dredged material and performances of GI built using dredged material through laboratory and field-testing. Preliminary results of a growth media using dredged material for the vegetative roof have been developed in lab/field studies that possess the performance values comparable to the current commercial product. The growth media containing lightweight aggregate, made from the dredged material, is observed to have high water retention capacity and high unit weight in comparison to a commercial product. The growth media leachate water test demonstrated the water quality to be comparable to the drained water from the commercial product. The growth media overwintered and advanced a rare plant species, Viola pedatifida, which is similar to conventional media. The beneficial uses of dredged material in the GI will help maintain the economic viability of harbors and ports along the shoreline of Lake Erie in Ohio and GIs, which were built using dredged material that can help address storm water management issues in urban areas due to extensive impervious surfaces.

Suitability of Silt Deposits of Irrigation Tanks in Angunakolapelessa, Sri Lanka for Engineering Applications

Dry zone of Sri Lanka is the main contributor to the rice supply in the island nation. Since this zone is prone to long droughts, a large network of agricultural tanks had been built over 1500 years ago to overcome the adverse impacts of the droughts experienced in the zone. Due to poor maintenance and negligence, there is siltation in some of these tanks and as a result of this the water storage of the tanks is not at the optimum level . This study was focused mainly on ten such tanks situated in the Angunakolapelessa Divisional Secretariat Division in the Hambantota District . These tanks require dredging to be at their optimum capacities. It has therefore become necessary to investigate the possible uses of dredged material , i.e., for erosion mitigation, since ad-hoc dumping of erodible dredged materials would in turn adversely affect the capacities of the other tanks located downstream of the cascade. Thirty soil samples were collected from a depth of 300 mm and laboratory tests were conducted on them to study their soil properties. Particle size distribution and Atterberg Test results show that the samples contain mostly clay-silt sediments and according to USCS and USDA classifications, most of them can be classified as silty loam. Standard Proctor Compaction Tests conducted on the samples indicate that the soils have a low maximum dry density and a high optimum moisture content which indicate that the soils tested cannot be recommended for use in embankment/road construction. However, these soils could be reused in erosion barriers/berms erected in agricultural fields. Proper management of irrigation tanks avoiding siltation caused by erosion is recommended to ensure food security and sustainable water management.

Assessment of the potential for dredged material dispersal from dumping sites in the Gulf of Gdańsk

PurposeEnvironment-friendly management of sites used for disposal of locally generated sedimentary material involves designation of an optimal dumping site location which will render the dredged material re-usable for beneficial purposes. The objective of this research was to determine whether wind, waves, and currents can induce transport of sediment from offshore dumping sites located at intermediate depths in the southern Baltic.Materials and methodsThe problem was addressed by exploring potential sediment transport from two sites located in the Gulf of Gdańsk at depths of about 20 m. A total of 29 combinations of hydrodynamic variables, representing the most extreme possible situations in the area, including eight theoretical uniform wind fields over the entire Baltic Sea from the W, NW, N, NE, E, SE, S, and SW sectors, the wind speed of 30 m s−1, as well as 21 historical extreme storms, retrieved from the HIPOCAS project database, were used.Results and discussionThe bottom velocities resulting from waves and currents at the dumping sites considered were computed using wave models (WAM, SWAN) and the M3D hydrodynamic model (based on the POM model). To estimate the velocities critical for bedload transport, formulae developed by Soulsby (1997) and Sawamoto and Yamashita (Proc Coastal Sediments 87:415–423, 1987) were used. The volumetric bedload transport was computed based on Meyer-Peter and Müller (1948). The model simulations demonstrated that, for the storm conditions analyzed, the current velocity in the area of the two dumping sites would be so low that it would practically not affect the magnitude of the bottom sediment transport. Thus, the resultant volume of bedload transported would be equal to that generated by the wave action. For the heaviest historical storm, the maximum transport is about 3 × 10−5 m2 s−1.ConclusionsUnder conditions of theoretical storms, the bottom orbital velocities would be higher and the resultant sediment transport would reach almost 7 × 10−5 m2 s−1 for northerly winds. However, this value is still very low compared with the volume of sediment being dumped. The findings of this study may prove useful in designation of future dumping sites.

Stabilization of Silty Clayey Dredged Material

AbstractThis paper compares experimental results on the stabilization of clayey dredged material (DM) using quicklime (QL), hydrated lime (HL), portland cement (PC), and Class F fly ash (FA). The D...

Numerical simulation of dynamics of sediments disposed in the marine coastal zone of the south-eastern Baltic

Three dumping sites located at the south-eastern part of the Baltic Sea at shallow depths near the shore of the Sambian Peninsula are considered. The first and second ones are located south and north of the Vistula Lagoon inlet, and are used now for disposing dredged material extracted from the Kaliningrad Seaway Canal. The third dumping site is located near the northern shore of the Sambian Peninsula, east of Cape Gvardeyskiy and assigned for disposing the dredged material extracted from the fairway to the Pionerskiy Port located nearby. All three dumping sites are located either in front of or not far from the eroded segments of the shore. The question behind the study is: Is it possible that disposed material is naturally transported from the damping site to the shore and accumulates there to protect it from erosion? A numerical hydrodynamic transport 3D model (MIKE) was used to model sediment transport under different wind actions. The winds with the speed stronger than 15 m/s wash out disposed material completely from the dumping site and spread it over a wide area with a negligible layer thickness. Winds of about 7–10 m/s transport material along the shore at a distance of a few kilometres; that may be useful for shore protection. Winds with a speed of about 5 m/sec or less do not lead to resuspension of sediments. The first location of the dumping site looks very ineffective for potential protection of the shore nearby. On the other hand, the second and especially the third locations are favourable for the transport of disposed material to the shore; the most favourable conditions are at onshore or alongshore currents.

Consolidation Behavior of Fly Ash-Based Geopolymer-Stabilized Dredged Mud

AbstractPorts use soft dredged material for land reclamation to address land scarcity and environmental constraints. Land reclaimed with soft dredged material has the properties of high compressibi...

Dynamic analysis of an immersed tunnel in Izmir

The original design of the planned Izmir Bay Immersed Tube Tunnel, considered it to be a continuous subsea tunnel for the whole length of about 7.6 km. But this was later changed into having 2 shorter tubes of 2.7 km long each connected thru’ a 2.2 km long artificial island created in the middle of the bay from the excess dredged material, a concept which also reduces costs and increases efficiency. This island will serve as a venue for the 2025 Expo Exhibition, which Izmir city will apply to organize in the future. Reason for the research study was to provide a preliminary design, using a dynamic analysis, during the current pre-feasibility stage, of the immersed tunnel to show whether it can be built across the Izmir Bay. This paper takes into account the new alignment and presents the results of a 2-D dynamic analysis conducted of the prefabricated 100m long tunnel elements, sitting within a backfilled dredged ditch, dug after the recommended ground improvement was carried out. Analyses considered staged construction and the results showed that: Tunnel units and its surrounding soils inside the dredged ditch act together to provide a better earthquake response with a damping effect of the earthquake force; Tunnel units do not float to the sea surface, but continued to stay inside the dredged ditch and applied positive stresses to the foundations during the design earthquakes. As there was no floating, there was no need for anchoring the tunnel to ditch bottom; Tunnel units and immersion joints (made of specified strong elastomer material) continued to stay in compression longitudinally and provided a superb water-tightness level; There were no risky (un-tolerable) ground deformations during, after striking of the design earthquakes. Total vertical and differential displacements of the tunnel units and in the surrounding soils were all at acceptable levels; Concrete surface crack widths occurring in the tunnel units, during striking of the design earthquakes were also found to be allowable. Study results show that the tunnel elements can withstand Mw=7 short duration ( 10 sec) earthquakes without major damages to their structure

Enhanced dewatering optimizes compactibility of processed dredged material

Purpose The utilization of dredged material in dike construction as a substitute for traditionally used aged marsh sediment is considered an advisable option with respect to ecological as well as economic aspects. As a prerequisite to the application, the equivalency with respect to soil physical and mechanical properties of the materials has to be verified. Previous investigations on the compactibility of dredged materials used for dike construction had shown that the bulk densities of these materials were considerably lower than bulk densities of aged marsh sediments. The aim of the investigations presented in this paper was to analyze whether the compactibility of the processed dredged material could be improved by enhanced dewatering of the material prior to construction. It was hypothesized that a decreased water content of the material would allow higher bulk densities to be achieved during construction and hence the soil physical properties would become more comparable to those of the aged marsh sediments.

Effects of Sediment Application on Nyssa aquatica and Taxodium distichum Saplings

The decline of Taxodium distichum forests along the Gulf Coast of North America is partly due to elevation loss and subsequent flooding. In many coastal wetlands, a common approach for coastal restoration is to rebuild elevation through the application of dredge material, but this technique has not been used widely in coastal forests due to concerns of negatively impacting trees. This experiment explored growth responses of Nyssa aquatica and T. distichum saplings to applications of low salinity dredge material (0.08 ± 0.001 ppt) in a greenhouse setting. Compared to controls, saplings of T. distichum grown in 7 and 15 cm sediment depths had greater final height, and increased stem and total biomass. In contrast, N. aquatica did not respond to sediment application. The absence of a negative response to sediment application in these two species indicates that dredge material application has the potential to improve the ecosystem health of sinking swamp forests by raising their elevation. We recommend that field trials applying sediment additions in coastal forests include careful monitoring of ecosystem responses, including seed bank expression, seedling regeneration, and root and canopy production.

Model Test Study on Dredge Slurry Vacuum Preloading

Dredge materials with the water content more than 80% have been used for land reclamation in Tianjin, China. The dredge is transferred by pipeline to the reclamation place and then strengthened with the vacuum preloading technique. It has been found that with the thickness of the filled dredge layer becomes larger and larger, the quality of soil improvement is not as good as expected. Field investigation shows that after vacuum preloading the vane test strength can reach 50kPa at the ground surface, but decreases along with depth dramatically. The model test is carried out to detect the factors that may influence the efficiency of using vacuum preloading to improve dredge soil foundation. The water content, vacuum pressure and undrained strength are measured during the test. Test results indicate that the undrained strength decreases and the water content increases along with the depth below the ground surface and the distance away from the PVD even at the time when the consolidation degree should have reached 99% according to the conventional consolidation theories. The excavated soil profile shows that the PVDs undergo drastic distortion because of the large deformation of the dredge soil surcharged by vacuum pressure, which will decrease the drainage efficiency of the PVDs.

Enhanced mobility of non aqueous phase liquid (NAPL) during drying of wet sand

Enhanced upward mobility of a non aqueous phase liquid (NAPL) present in wet sand during natural drying, and in the absence of any external pressure gradients, is reported for the first time. This mobility was significantly higher than that expected from capillary rise. Experiments were performed in a glass column with a small layer of NAPL-saturated sand trapped between two layers of water-saturated sand. Drying of the wet sand was induced by flow of air across the top surface of the wet sand. The upward movement of the NAPL, in the direction of water transport, commenced when the drying effect reached the location of the NAPL and continued as long as there was significant water evaporation in the vicinity of NAPL, indicating a clear correlation between the NAPL rise and water evaporation. The magnitude and the rate of NAPL rise was measured at different water evaporation rates, different initial locations of the NAPL, different grain size of the sand and the type of NAPL (on the basis of different NAPL-glass contact angle, viscosity and density). A positive correlation was observed between average rate of NAPL rise and the water evaporation while a negative correlation was obtained between the average NAPL rise rate and the NAPL properties of contact angle, viscosity and density. There was no significant correlation of average NAPL rise rate with variation of sand grain size between 0.1 to 0.5mm. Based on these observations and on previous studies reported in the literature, two possible mechanisms are hypothesized –a) the effect of the spreading coefficient resulting in the wetting of NAPL on the water films created and b) a moving water film due to evaporation that “drags” the NAPL upwards. The NAPL rise reported in this paper has implications in fate and transport of chemicals in NAPL contaminated porous media such as soils and exposed dredged sediment material, which are subjected to varying water saturation levels due to drying and rewetting.

Consolidated Undrained Triaxial Compression Tests and Strength Criterion of Solidified Dredged Materials

Consolidated undrained triaxial compression tests were performed to investigate the shear strength behavior of the solidified dredged materials (SDM). The variation law of deviator stress and excess pore water pressure with the increase of the applied confining pressure was investigated. It is found that the shear strength envelope is consisted of two lines, and there exists a transitional stress on the intersection point. The undrained shear strength develops slightly with the increase of applied normal stress in the preyield state. However, the undrained shear strength increases significantly in the postyield state, and the strength envelope is nearly a straight line with the extension through the origin. Based on the triaxial test data and the binary medium model, a strength criterion considering strength evolution mechanism is proposed and the relevant parameters of the strength criterion were discussed. Comparisons of the predicted results and experimental data demonstrate that the proposed strength criterion can properly describe the strength evolution rules of the SDM.

New Experiences in Dike Construction with Soil-Ash Composites and Fine-Grained Dredged Materials

Abstract The supporting structure inside a coastal dike is often made of dredged non-uniform sand with good compaction properties. Due to the shortage of natural construction material for both coastal and river dikes and the surplus of different processed materials, new experiments were made with sand-ash mixtures and fine-grained dredged materials to replace both dike core and dike cover materials resulting in economical, environmentally friendly and sustainable dikes. Ash from EC Gdańsk and dredged sand from the Vistula river were mixed to form an engineering material used for dike construction. The optimum sand-ash composites were applied at a field test site to build a large-scale research dike. Fine-grained dredged materials from Germany were chosen to be applied in a second full-scale research dike in Rostock. All materials were investigated according to the standards for soil mechanical analysis. This includes basic soil properties, mechanical characteristics, such as grain-size distribution, compaction parameters, compressibility, shear strength, and water permeability. In the field, the infiltration of water into the dike body as well as the erosion resistance of the cover material against overflowing water was determined. Results of both laboratory and field testing are discussed in this paper. In conclusion, the mixing of bottom ash with mineral soil, such as relatively uniform dredged sand, fairly improves the geotechnical parameters of the composite, compared to the constituents. Depending on the composite, the materials may be suitable to build a dike core or an erosion-resistant dike cover.

Impact of disposal of dredged material on sediment quality in the Kaohsiung Ocean Dredged Material Disposal Site, Taiwan

Kaohsiung Ocean Dredged Material Disposal Site (KODMDS) that located in the southwest offshore of Taiwan, has been annually disposed about 500,000 ton dredged sediments of Kaohsiung Harbor from 2003 to 2012. Five sediment cores collected from KODMDS and three from nearby reference sites were analyzed to evaluate their sedimentation rates, vertical profiles of heavy metal, and heavy metal pollution indices to assess the impact of dumping harbor dredged sediments into the ocean on the sediment quality in KODMDS. The sedimentation rate of 0.24 cm/y was estimated by the 210Pb method, which means that the effected depth of the top layer of a core of D1 was affected in the period of dumping dredging sediments. The vertical distribution of heavy metals in the sediment cores from KODMDS showed the concentrations of most heavy metals were slightly elevated in the top layers of the sediment cores, which may be affected by the dumping of harbor dredged sediments. According to the analyzed results of the heavy metal pollution indices, the level of heavy metal pollution, the potential eco-toxicity and the potential ecological risk of the sediments in KODMDS exhibited only a slight increase, which indicated that the increase in concentration of heavy metals may potentially pose the insignificant impact on benthos inhabiting the disposal site.

Impact of seasonal vertical stratification on the dispersion patterns of dredging plumes off the south coast of Korea

Simultaneous satellite and ship-borne surveys have been conducted to investigate the dispersion patterns of dredging plumes off the south coast of Korea in two contrasting seasons (spring and autumn). The distribution of total suspended solid (TSS) derived from sequential satellite imagery showed that the dredging plumes in spring developed over longer distances along the surface current than those in autumn. In spring, the deep and strong stratified condition in the water column contributed to the increase in radius of plume dispersion along the water surface. In autumn, the shallow and vertically well-mixed (or un-stratified) condition in the water column enhanced sinking of suspended dredged materials. This difference is due to the Brunt-Väisälä frequency being higher in spring (0.0183s−1) than in autumn (0.0123s−1). Although the sediment-laden overflow significantly increased TSS near the surface during the dredging period, the TSS contribution to water column stratification was only 2.3−5.6% of the thermohaline contribution. Therefore, the seasonal variation of thermohaline density is the main factor determining the dispersion patterns of dredging plumes in the study area.

Anatomy of a decision II: Potential effects of changes to Tier I chemical approaches in Canadian Disposal at Sea program sediment assessment protocols.

The effects of possible changes to the Canadian 2-tiered assessment framework for dredged material based on outcomes of the 2006 Contaminated Dredged Material Management Decisions Workshop (CDMMD) are evaluated. Expanding on the "data mining" approach described in a previous paper, which focused solely on chemical lines of evidence, the efficacy of Tier 1 approaches (increases to the number of chemical analytes, use of mean hazard quotients, and the use of a screening bioassay) in predicting toxicity are evaluated. Results suggest value in additional work to evaluate the following areas: 1) further expanding minimum chemical requirements, 2) using more advanced approaches for chemical interpretation, and 3) using a screening-level bioassay (e.g., Canadian solid-phase photoluminescent bacteria test) to determine whether it would complement Tier 1 chemistry as well as or better than the solvent-based Microtox™ test method evaluated in the present study. Integr Environ Assess Manag 2017;13:1072-1085. © 2017 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Effects of Curing Time and Fly Ash Content on Properties of Stabilized Dredged Material

AbstractProperties of raw dredged material (RDM) stabilized with self-cementing Class C fly ash (FA) were evaluated for beneficial use in geotechnical construction applications. Emphasis was placed...