The present paper describes the development of an instrumented impact cone penetrometer for a direct measurement of in situ strength properties of a soil target. The developed penetrometer, in addition to providing acceleration signatures (as obtained by previous investigators), is capable of recording cone thrust and local side friction simultaneously and continuously. The procedures have been outlined for estimating in situ strength properties and soil type of the target materials throughout the penetrated depth from the output records of these sensors. Typical test results generated from an on-going experimental program aimed at providing the data for (1) understanding the penetration mechanism, (2) development of penetration theory, and (3) designing the penetrometer for field tests, i.e. in situ testing of ocean floor soils, are also presented.
The penetration rate effect on the strength of clay and sand was studied by constant velocity penetration tests performed with various velocities up to 2.662 f.p.s. (81.14 cm/s). The clay and sand targets were of various strengths and moisture contents. The construction of the penetrometer is similar to that used in static tests, and in each test the cone resistance, sleeve friction, and penetration velocity were recorded.Experimental results indicated that for granular soils the effects of penetration velocity on cone and sleeve friction resistances are insignificant, whereas, for cohesive soils, the increase in penetration velocity causes an increase in the cone and friction resistances. It is found that for the cohesive soils the ratio of dynamic to static strength is directly proportional to the logarithm of the penetration velocity ratio. The proportionality constant of this relationship defined as soil viscosity coefficient depends on the physical properties of the soil and the soil strength and its value increases as the strength of the soil decreases. For the tested soils various values of the soil viscosity coefficient are proposed for different strength ranges. The validity of the analytical relationship is established for penetration velocities ranging from 0.0044 f.p.s. (0.13 cm/s) to 18 f.p.s. (550 cm/s).
Abstract. The redevelopment of disused docks around Liverpool into areas suitable for shops, offices, housing and recreational watersports has necessitated the maintenance of good water quality in these areas. The main source of water to the docks is the River Mersey, which contains high concentrations of nutrients, encouraging algal blooms ‐ including potentially nuisance species ‐ in the enclosed dock basins. Since 1988 an extensive monitoring programme has been run sampling the hydrography, plankton and benthos of the docks. During this period there has been an improvement in water quality, including a reduction in summer phytoplankton biomass and anoxic bottom water. There are strong indications that phytoplankton biomass has been severely reduced by the filter feeding of Mytifus edulis. Changes in the composition of the benthic community since 1988 suggest that the large population of M. edulis is now suffering from limited recruitment. The long‐term development and stability of the system is discussed with reference to community succession and its link to ecosystem functioning.
The Irish Sea is showing early signs of eutrophication extending offshore, beyond localized inshore effects, according to an unusually long time series of measurements taken in the central Irish Sea. Background levels of dissolved inorganic forms of nitrogen and phosphorus have risen substantially over the last 30 to 40 years. This rise has coincided with a significant rise in phytoplankton biomass, measured as chlorophyll a, during the late spring bloom. Contrary to trends in other coastal seas, the increase in N and P was not accompanied by a decline in silicate; in fact, a small but significant increase in Si was noted in autumn and winter. This may be related to the well‐mixed conditions over much of the Irish Sea. However, the common assumption that there are no anthropogenic sources of dissolved Si may not be valid in this area and requires further consideration.
1. The main impacts on marine ecosystems are summarised and the potential for their restoration is discussed in relation to their key features. Rocky shores, seagrass beds and disused docks are focused on. 2. The term restoration is used to describe intervention in the recovery process of a marine ecosystem, with a view to enhancing the process, but not necessarily forcing the system to recover to its original condition. 3. Rocky shore systems are subject to shellfish and seaweed exploitation, point source pollution, diffuse impacts such as tributyl tin and acute impacts such as oil spills. The consideration of whether to employ restoration or allow natural recovery is discussed in relation to these systems. 4. Seagrass systems have suffered serious declines in many parts of the world due to the direct and indirect effects of human impacts. In the North Atlantic a wasting disease first noted in the 1930s caused a serious decline in the subtidal seagrass Zostera marina. The link between this disease and the marine slime mould Labrynthula zosterae is now well established. Human impacts on seagrass systems allow the disease to gain a foothold. Attempts at restoring seagrass beds have met with some success, but it is suggested that the action of conservation of remaining beds and better management of human activities may be the best approach. 5. Disused docks occur in many parts of Britain and Europe. Active management of the physical environment by mixing and biomanipulation by filter feeding organisms have led to improvements in water quality and ecosystem function. Thus healthy marine ecosystems have been restored to inner city areas, although these artificial marine lakes have few natural equivalents and are different from the original ecosystem at the site. 6. When compared to freshwater ecosystems, the scope for coastal and marine restoration is limited although the capacity for recovery is greater. Copyright © 1999 John Wiley & Sons, Ltd.
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