Kenneth R. Demars

Dredging, remediation, and containment of contaminated sediments

This conference was held June 23--24, 1994 in Montreal, Canada. One purpose of this conference was to provide a multidisciplinary forum for exchange of state-of-the-art information on identifying tests, methods, procedures, and materials, used in support of dredging, treatment, and containment of contaminated sediments that are in need of standardization. Another objective was to provide a forum for discussion of past dredging practices and future directions, including the effects of sediment properties and behavior, equipment requirements, and the impact of regulations. Individual papers have been processed separately for inclusion in the appropriate data bases.

Unique Engineering Properties and Compression Behavior of Deep-Sea Calcareous Sediments

This study examines the individual particles comprising a typical deep-sea calcareous clay as a means of explaining their unique engineering properties and compression behavior. The scanning electron microscope is used todetermine calcareous particle geometry, size, and packing, and the effect of one-dimensional compression on microstructure and particle fracture. The sediments examined in this study have carbonate contents of 40 to 90 percent, including 5 to 10 percent of sand-sized Foraminifera, the remainder being fine, silt-sized nannofossils. The Foraminifera and nannofossils are hollow and capable of storing large quantities of intraparticle water. When subjected to moderate compression stresses, the Foraminifera particles are susceptable to fracture and release intraparticle water, whereas the nannofossils exhibit minor fracturing or chipping at particle contact points. Carbonate contents should be routinely performed as an index property on deep-sea sediment specimens to determine the presence of hollow nannofossil and foram particles.

Erosion control using wood waste materials

The field experiments presented here investigated the required thickness of wood waste materials used as a mulch to protect a soil slope against erosion. Each of the materials was subjected to large-scale erosion control testing at a field site with a slope of 1 vertical to 2 horizontal. Fourteen test cells (5′ W × 30′ L each) were prepared with different wood waste treatments; nine contained erosion control mulch applications at thicknesses of 3/4 to 3 inch. Two cells were left untreated as reference cells and three other cells were untreated but contained erosion control structures including wood waste filter berm, geosynthetic silt fence and hay bale silt barrier. The erosion control performance of each cell treatment was evaluated for 11 storm events of varying rainfall magnitude and intensity. Calibrated tipper buckets were used to measure the runoff from each cell and collection buckets were used to sample runoff and determine the mass of sediment eroded from each cell. Total rainfall and intensity of each storm was measured with an electronic rain gauge. The results showed that 0.75 inches of wood waste material is sufficient to reduce the erosion to levels below commonly used treatments. Using thicker applications of wood waste did not reduce the erosion much below that obtained with 0.75 inches. This effect was demonstrated with three different wood waste materials. In addition, one of the wood wastes (paper mill wood waste) was used as a filter berm to control eroded soil particles. The behavior of this berm was compared to standard methods of controlling these particles such as hay bales and geosynthetic silt fence, and found superior. Laboratory tests are planned to quantify the properties of wood waste that produce good filtering action in berms.

Interaction of multiple helical earth anchors embedded in granular soil

This experimental program studies the behavior of groups of helical earth anchors embedded in granular soil. This was performed by the use of laboratory and field anchor‐pullout tests. A literature review of existing anchor‐capacity theories and related material is presented. Laboratory and field group‐anchor pullout tests were conducted to study the mutual interaction behavior of the individual anchors. Results indicate that the group pullout capacity is a function of the horizontal spacing between anchors and that the exterior anchors in a closely spaced group carry the greatest proportion of the load at impending failure. Empirical equations were developed to predict the pullout capacity of groups of anchors.

The Rapid Carbonate Analyzer

A gasometric method is proposed for measuring soil carbonate content. The device consists of an enclosed acrylic cylinder in which soil carbonate reacts with acid to produce carbon dioxide gas. For a constant volume reactor, the carbon dioxide gas pressure is directly related to the soil carbonate content at completion of the reaction. The effect of several variables, including particle size, acid concentration, and carbonate mineralogy, on the reaction time is considered. This method has the advantages of accuracy to within ±5%, high analytical speed, low cost, and minimal operator skill. It is well suited for both laboratory and field use.

Geotechnical Engineering Issues in Ocean Waste Disposal: A Review

Marine pollution has received considerable attention during the past few years as the news media has focused on such topics as contaminated seafoods, algae blooms, fish and mammal kills, and dirty beaches. The source of these pollution problems are many and include: sewage outfalls, industrial discharges, storm runoff from agricultural lands and metropolitan areas, waste sludges, dredge materials, and highly concentrated chemical and radioactive wastes. Although the United Nations has banned marine dumping, there is still the problem of legacy wastes and low level discharges into the coastal zone. Disposal of these wastes in the marine environment typically involves either: their placement directly on or within the seabed or dilution in the water column. If wastes are diluted in the water column, they have the potential to be adsorbed onto the surface of sediment particles which are settling to the seabed. As particles settle through the water column they are subjected to extensive dispersal and may eventually be injested by bottom-feeding organisms or bio-accumulation by plankton and, thus, enter the food chain. Geotechnical engineers working as members of multidisciplinary teams apply quantitative knowledge about the behavior and physical performance of earth materials toward designing systems for disposing of these wastes in the oceans and aid in monitoring waste disposal sites. In dredged material disposal geotechnical engineers assist in selecting disposal equipment, predict stable characteristics of dredged material mounds, design mound caps, and predict erodibility of the material. With sewage outfalls, geotechnical engineers design foundation and anchor elements, estimate scour potential around the outfalls, and determine the stability of deposits made up of discharged materials. Geotechnical engineers also consider the influence that pollutants have on the engineering behavior of marine sediment and the extent to which changes in behavior affect the performance of structures founded on the sediment. In each of these roles, careful application of geotechnical engineering principles can contribute toward more efficient and environmentally safe disposal operations.

Settlement analyses of shallow ocean‐dredged material mounds

Abstract Contaminated dredge materials are frequently excavated from harbors and estuaries in heavily populated coastal areas such as Connecticut. These materials are barged to a regulated shallow ocean disposal site and discharged to the seabed to form a mound. A cap layer of clean material is placed over the mound to isolate the contaminants from the water column. Consolidation settlement of the mound and seabed is initiated by mound construction. In this study, the settlement of three mounds was measured by successive precision bathymetric surveys for a period of several years. Laboratory consolidation tests were performed on core samples from the disposal site and mounds. These data are used to model the mound consolidation using Terzaghi and finite strain theories. Predicted mound settlements are compared with measured settlements. Compression properties of the mound and seabed are used to develop an equation for cap thickness.