Ronald C. Chaney

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.

Liquefaction in the coastal environment: An analysis of case histories

Abstract The stability of coastal and underwater slopes and seafloor sediments is of major importance for waives, breakwaters, pipelines, jacket platforms, and gravity platforms. A major source of instability in cohesionless sediments is the result of the liquefaction. This paper explores the various mechanisms causing liquefaction in the marine environment and then reviews a large number of case studies.

Earthquake Effects on Soil-Foundation Systems

The damage resulting from earthquakes may be influenced in a number of ways by the characteristics of the soils in the affected area. Where the damage is related to a gross instability of the soil, resulting in large permanent movements of the ground surface, association of the damage with the local soil conditions is readily apparent. Thus, for example, deposits of loose granular soils may be compacted by the ground vibrations induced by the earthquake, resulting in large settlements and differential settlements of the ground surface. Typical examples of damage due to this cause are shown in Figures Figure 16.1 and Figure 16.2 Figure Figure 16.1 shows an island near Valdivia, Chile, which was partially submerged as a result of the combined effects of tectonic land movements and ground settlement due to compaction in the Chilean earthquake of 1960. Figure Figure 16.2 shows differential settlement of the backfill of a bridge in the Niigata earthquake of 1964.

Methods of Predicting the Deformation of the Seabed due to Cyclic Loading

The stability of underwater slopes and seafloor sediments is of major importance for offshore structures such as pipelines, jacket platforms and gravity platforms. In this paper laboratory simulation studies of marine slopes under cyclic loading are analyzed. Results indicate that the development of slope movement is dependent on (1) soil strength, (2) bottom pressure, (3) depth of unstable zone and pore-water pressure generation. To predict slope performance requires (a) quantifying the soil response to cyclic and static loading (total or effective stress analysis), and (b) selection of the appropriate slope stability technique (limit equilibrium or finite element method). Tables are presented comparing total and effective stress analysis as well as the various methods of slope stability analysis. On the basis of this study it was concluded that the permanent deformation procedure utilizing the finite element method is the most general.

Suggested Test Method for Determination of Thermal Conductivity of Soil by Thermal-Needle Procedure

A method is proposed for determining the thermal conductivity k or thermal resistivity p of soils. The procedure is based on the use of a transient heat method in which a thermal needle is used to create a linear heat source, and a thermocouple is used to monitor temperature changes with time. This suggested method describes the basic procedure. Information is also presented on the construction and calibration of the thermal needle.

Triaxial Testing of Marine Sediments with High Gas Contents

Gas types, zonation present in marine sediments, the corresponding mechanism of bubble formation, and methods of performing triaxial tests on gassy sediments are discussed. Gases (methane and hydrogen sulfide; methane gaspredominates) may be found either in solution or in the bubble phase in the sediment. A method to estimate the amount of gas that theoretically comes out of solution is shown. The result of gas bubbles is a reduction in the bulk modulus of the pore fluid. The bulk modulus of a gas-water mixture decreases with increasing fluid pressure. Results of decreasing bulk modulus are shown to reduce the pore pressure increment per application of a load increment. Triaxial testing techniques are recommended when (1) gas is in solution, (2) gas is in the bubble phase, and (3) gas is still evolving.

Sampling and Preparation of Marine Sediments

The recent development in the exploitation of the resources of the ocean floors of the world for petroleum, natural gas, and other minerals, along with waste disposal has resulted in an increased interest in the application of geotechnical sciences to the marine environment (Anderson, 1981; Chaney, 1984; Chaney and Fang, 1985, 1986; Chaney et al., 1986; Fang and Chaney, 1985, 1986; Fang and Owen, 1977; Lee, 1985; Richards and Chaney, 1981, 1982; Winterkorn and Fang, 1971). The selection of an offshore site is essential for most seafloor engineering projects. It is a process strongly influenced by engineering judgment that is often constrained by economic, political, environmental, and societal considerations. Fletcher (1969) considers that the purpose of an offshore site investigation is to “secure such information by procedures appropriate to the project and to report the findings in sufficient technical detail to provide a basis for economic studies and design decisions.” The process of site evaluation from the recognition of a siting problem to the development of a problem solution involves a number of discrete steps as shown in Figure 2.1 (Chaney et al., 1985). These steps are: (1) determination of environmental loading, (2) site reconnaissance, (3) development of a stratigraphic model based on both a combination of sampling and in-situ testing, and (4) interpretation of data.

Measurement of Residual/Remolded Vane Shear Strength of Marine Sediments

The measurement of both residual and remolded shear strength using the vane shear apparatus is discussed. Residual shear strength is defined to be measured after 90 degrees of vane rotation. In contrast, remolded shear strength is dependent on whether it is measured by vane remolding or hand remolding. To accomplish vane remolding, a minimum of three vane revolutions are required. The relative strengths of the various remolding methods show that (1) field vane remolding gives highest strength, (2) followed by either laboratory vane remolding or hand remolding. Order of the last two appears to depend on soils plasticity. Vane remolding is shown to be influenced by a soils anisotropy while hand remolding is not. Case studies are presented for a DSDP site in the North Pacific and the Mississippi Fan in the Gulf of Mexico. Standardization and measurement procedures to obtain repeatable and comparable results are presented. (A) For the covering abstract see IRRD 863366.

Marine Slope Stability — A Geological Approach

On one hand, the literature of marine slope instability and marine slides is voluminous. Extensive bibliographies are given in the many papers comprising this volume. On the other hand, basic information available to geoscientists on how marine slides or slope instability can be investigated is widely scattered. This paper attempts to fill the gap by briefly discussing mthods for preliminary surveys, sampling, and analysis. Emphasis is placed on providing elementary information for geoscientists who might be starting geotechnical studies. More elegant or detailed treatments on this subject are available elsewhere in this volume and in the science and engineering literature.

Dynamic Properties of Some Eastern Mediterranean Marine Sediments

A series of resonant column tests on sediments from offshore Haifa, Israel are presented in this paper. Samples were obtained from both the Akhziv submarine canyon and the undisturbed slope located on the continental terrace of Northern Israel in the Eastern Mediterranean using a gravity corer in 59 to 699 m of water depth. The continental shelf of northern Sinai, Israel, and Lebanon is made of 1–2-km-thick Nile-derived sediments of the Pliocene–Quaternary age that were transported to the northeast by the counterclockwise contour current system of the Southeastern Mediterranean Sea, and accumulated along the continental margin. The sediments tested consist of dark grey silty clays (MH/CH). The sedimentological pattern over the continental shelf and the adjacent parts of the deep-sea Levant Platform essentially consists of continuous hemipelagic sedimentation of the Nile-derived sediments along the continental margin and frequent episodic earthquake triggered sediment slumping with redistribution down slope. The soft sediments described in this paper were trimmed for use in the resonant column apparatus using an osmotic knife in the shape of a split mold. The resonant column utilized in this study was a fixed free apparatus. The total unit weight of the specimens ranged from 14.31 to 17.98 kN/m3, whereas the water content varied from 40 % to 95 %. Maximum shear modulus varied with depth of water, location on the shelf and in the canyon. For the undisturbed slope, the maximum shear modulus is approximately 25 to 29 MPa. For the canyon flank, the modulus ranged from 4.2 to 17.2 MPa. This is in contrast to the canyon bed where shear modulus ranged from 220 to 334 MPa. The increase in shear modulus of the canyon bed sediments is believed a result of either or both internal structure or slight cementation in the Akhziv material based on a combination of previous triaxial testing and site geology. The corresponding damping ratio ranges from 0.5 % to 4 % as a function of shear strain and effective stress. Modulus and damping test results are compared with other marine sediments: offshore Eureka, CA; Navarin Basin, Bering Sea; Gulf of Mexico; and Casablanca and the Santa Barbara Channel California.