The in situ hydraulic conductivity is obtained by extrapolating the hydraulic conductivity to the in situ void ratio. As such, the quoted recompression indexes are for unloading to an OCR of 10. It must be noted that the recompression index varies with the amount of unloading that occurs. The recompression index ( C r) ranges from 0.035 to 0.064 (average = 0.052). The recompression index refers to the slope of the unload–reload portion of the curve while in e-log ( ´v) space. C c is fairly constant to a depth of 79 mbsf, after which C c decreases downhole. The compression index ( C c) ranges from 0.340 to 0.704 (average = 0.568). The compression index refers to the slope of the normally consolidated portion of the compression curve while in e-log ( ´v) space. The last section of the table gives consolidation properties such as the compression index, recompression index, and in situ hydraulic conductivity. The backpressure gives the pressure at which the specimen is saturated. The third section of the table gives the test conditions such as the backpressure ( u b) and the strain rate ( / t). The plasticity index describes the range over which the soil behaves plastically and is defined as the difference between the liquid and plastic limit. The natural water content and specific gravity were taken from Tréhu, Bohrmann, Rack, Torres, et al. The next section of the table gives the specimen data such as the natural water content ( w n), plasticity index ( I p), total density ( t), initial void ratio ( e i), initial saturation ( S i), and specific gravity ( G s). The Atterberg limits are discussed in "Index Tests," and are an average for each tube. Also indicated is the number of observations (#obs) and standard deviation (SD) for each water content measurement. The first section of the table gives the water content ( w c), plastic limit ( w p), and liquid limit ( w l) for each tube, as discussed in "Index Tests." The water content is taken from the soil trimmings. Table T17 gives a summary of the details and conditions of each CRSC test. Tables T14, T15, and T16 and Figures F9, F10, and F11 show XRD results on the clay-size fraction of random powder samples. Table T2 shows the samples that were tested using this preparation. In order to accurately identify the clay-size particles, XRD was performed on random powder samples containing only the clay-size fraction of the soil. The results of the two random powder samples show a significant amount of nonclay particles. Tables T8, T9, T10, T11, T12, and T13 and Figures F6, F7, and F8 show the results of calcite-treated random powder testing. Table T4 gives the calcium carbonate content of the soil. Table T2 gives a list of the specimens used in calcite-treated random powder preparation. Note that the intensity is plotted on a log scale. Tables T5, T6, and T7 and Figures F3, F4, and F5 give XRD results of the three random powder samples. The X-ray diffractometer was rotated between 6° and 56° 2. The specimens prepared using random powder preparation are shown in Table T2. This result is typical of the clay mineral illite. Together with the plasticity index, the resulting activity is close to 1. The distribution curve shows that the soil contains 50% clay-size particles. Figure F2 gives the particle size distribution curve. Particle size distribution was performed on a sample from Section 204-1244C-13H-3 (Table T2). Table T4 gives the results and shows that loss on ignition is constant with depth and relatively large. Loss on ignition was performed on eight samples (Table T2). In general, however, there is little variation in the Atterberg limits, suggesting the soil consists of the same basic material. From this chart, a cohesive soil has high plasticity if it has a liquid limit >50% and low plasticity if the liquid limit is 75%. Interestingly, performing Atterberg limits on an oven-dried sample significantly decreases the liquid limit.įigure F1 shows the results of the Atterberg limits tests plotted on a plasticity chart in order to determine the soil classification based on the Unified Soil Classification System ASTM D2487 (ASTM International, 2004a). The results of the tests can be found in Table T4. Atterberg limits were performed on eight undisturbed samples and one oven-dried sample (Table T2).
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