AbstracVIn this investigation fabric-property relationships were studied in a silty fine sand sized crushed basalt-an artificial 'soil' that has previously been used to simulate lunar soil. The fabric was characterized by measuring preferred orientations of grains, and pore size distribution was determined by mercury intrusion porosimetry. When deposited by pouring, the grains acquired strong preferred orientations in the horizontal direction and formed pores between 1 and 30 #m dia. Densification by static or dynamic compaction resulted in near random grain arrangement and pore sizes between 0.1 and 10 ~m dia.Strength in direct shear and one-dimensional compressibility with the associated lateral stresses were measured. The strength was up to 30 per cent higher when the sample was sheared normal to the preferred orientation of grains than when the shearing was parallel to the orientation direction. This is to be expected, as shearing across the preferentially oriented grains should involve breakage or reorientation of many grains. At a given initial void ratio the compressibility of statically compacted specimens was larger (up to 30 per cent higher axial strain) than that of dynamically compacted specimens at very low stresses. At higher stresses both samples exhibited equal compressibility, suggesting that the grains become more randomly arranged at low void ratios (comparing samples of equal initial void ratios).
Effects of methods of specimen preparation on fabric and compressibility were investigated in a medium grain-sized sand. The effect of vibratory compaction was compared with the effect of pluviation by characterizing the particle arrangements and measuring compressibility in a specially fabricated oedometer. The lateral stresses during compression were also measured.
Specimens densified by vibration in layers had random grain orientation up to 100 percent relative density. When vibration was continued beyond the time interval needed for achieving 100 percent relative density, the grains acquired a preferred orientation. Pluviated specimens had randomly oriented grains at both low and high densities.
The loose, pluviated specimens were much more compressible than the dense specimens prepared by the same procedure. The dense specimens when prepared by vibration were less compressible than the pluviated specimens. The lateral stresses were higher in the loose pluviated specimens than in the dense pluviated specimens during loading. On unloading, the same trend was present initially but reversed at lower axial loads. This trend was also measured in the specimens prepared by vibration.
The use of marine high-resolution geophysical profiling data, seafloor soil samples, and accepted land-based methods of analysis have provided a means of assessing the regional geotechnical conditions and relative slope stability of the portion of the Gulf of Alaska Continental Margin known as the Kodiak Shelf. Eight distinct types of soils were recognized in the study; the seafloor distribution of these indicates a complex geotechnical setting. Each soil unit was interpreted as having a distinct suite of geotechnical properties and potential foundation engineering problems. Seven categories of relative slope stability were defined and mapped. These categories range from "highest stability" to "lowest stability," and are based on the degree of slope of the seafloor, type of soil underlying the slope, and evidence of mass movement. The results of the analysis indicate that the highest potential for soil failure exists on (1) the slopes forming boundaries between the submarine banks and the broad sea valleys, and (2) the upper portion of the continental slope, where evidence of past slope failure is common. Also of concern are gently sloping areas near the edges of submarine banks where evidence of possible tension cracks and slow downhill creep was found.
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