A laboratory investigation has been made of formation factor‐porosity relationships (formation factor being the ratio of the resistivity of a porous medium to the resistivity of the pore‐fluid), using natural and artificial sand samples whose grains varied widely in both size and shape. All samples obeyed Archie’s law, [Formula: see text] (where FF is the formation factor and n is the porosity) including mixtures of two differently shaped particle types. The exponent m was dependent on the shape of the particles, increasing as they became less spherical, while variations in size and spread of sizes appeared to have little effect. The results have been combined to produce an FF/n relationship, with an error “envelope”, which may be applicable to marine sediments in general, being in agreement with published data for marine clays. It is also suggested that the exponent m may be a better measure of the “tortuosity” of porous media than the formulas quoted in the literature.

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& DENZIL TAYLOR SMITH IntroductionVARIOUS THEORIES have been advanced to relate the attenuation coefficient and the velocity of propagation of compressional waves through a two phase medium, such as a :marine sediment, to the elastic moduli, densities and relative concentration of the two Constituents. The main difficulty in a natural sediment is the mathematical formulation .of the complicated interaction between the particles. In general, the usefulness of most of the developed equations has been restricted by the simplifying assumptions that were used to formulate this interaction.The relationship between the acoustic and geotechnical properties of a marine sediment is essentially a multivariate problem. In this case, where the understanding of the underlying control of the various geotechnicaI parameters on the acoustic parameters is in-Complete, a large quantity of data must be analysed. Large quantities of apparently unrelated data, or data related in some obscure manner, can often be analysed numeri-Cally and in this respect multiple regression analysis is a very powerful method. By this means an effective prediction equation can be developed for the dependent variable in terms of several independent variables. Some of the variables considered may be redundant and, as such, may be eliminated to concentrate the final computation on the variables ranking highest in their control of the dependent variables. As a result of finding the most :significant variables, some idea may be then obtained of the physical relationships between the dependent and independent variables. With this knowledge of the main control parameters, the fundamental relationships between the acoustic and geotechnical properties can be examined much more effectively in conjunction with existing theoretical studies. Sediment structureAn unconsolidated deep-sea sediment in its natural environment can be regarded as a :mixture of sand and silt in a clay matrix, the whole being saturated with saline water. The proportions of each of the constituents present in the sediment, as well as the type of mineral and the salinity of the sea water, control the basic structure of the sediment Q.From an examination of the total correlation coefficients the best prediction equations are seen to be: and and V = 1"336+0"092tzs+ 0"101 7 V = 1"616 +0-090 t, s+0"002 n V = 1"416-0.007 M,~+O.091 7-280 at University of Otago on October 2, 2015 http://qjegh.lyellcollection.org/ Downloaded from

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HAMDI, FALAH A.I. and TAYLOR SMITH, D. 1981, Soil Consolidation Behavior Assessed by Seismic Velocity Measurements, Geophysical Prospecting 29, 7 15-729.Large gravity platforms are often used as alternatives to the more conventional pilesupported structures in hydrocarbon exploitation. A gravity structure, as opposed to the piled structure, is sitting on the sea floor by virtue of its weight and base width; as such it poses considerable problems for the site investigation engineer. One such problem is the calculation of the settlement of the structure and its time history; these depend upon the permeability and compressibility of the soil and its drainage conditions. The required data are usually obtained by sampling for subsequent laboratory testing. The collection of an undisturbed sample is beset by problems so that the consolidation behavior of the foundation material can only be inadequately assessed by laboratory testing. However, a series of laboratory consolidation experiments during which seismic velocities have been measured on the sample as consolidation proceeds shows that it is possible to reconstruct the stress-strain and time-dependent curves from the seismic data, once the initial void ratio and permeability of the soil are known. This leads the way to an in situ technique for predicting settlement using a combination of geophysical techniques (electrical resistivity and seismic velocities) to obtain the required engineering properties.