. Tables T5, T6, and T7 and Figures F3, F4, and F5 give XRD results of the three random powder samples. Note that the intensity is plotted on a log scale.
The experiments performed on each section are listed in Table T2. All of the variables are defined in Table T3. Included in this report are the data collected from the experiment program. For interpretation of these results, refer to Tan (2004).
Atterberg limits were performed on eight undisturbed samples and one oven-dried sample (Table T2). The results of the tests can be found in Table T4. Interestingly, performing Atterberg limits on an oven-dried sample significantly decreases the liquid limit.
Figure 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). From this chart, a cohesive soil has high plasticity if it has a liquid limit >50% and low plasticity if the liquid limit is <50%. Furthermore, a soil is predominantly clay if it plots above the A-line and mostly silt if it plots below the A-line. Based on this chart, the Hydrate Ridge soil classifies as a high-plasticity silt (MH) or high-plasticity organic soil (OH). In addition, analysis reveals that the soil classifies as MH and not OH because the ratio of the oven-dried liquid limit to the undisturbed liquid limit is >75%. In general, however, there is little variation in the Atterberg limits, suggesting the soil consists of the same basic material.
Loss on ignition was performed on eight samples (Table T2). Table T4 gives the results and shows that loss on ignition is constant with depth and relatively large.
Particle size distribution was performed on a sample from Section 204-1244C-13H-3 (Table T2). Figure F2 gives the particle size distribution curve. The distribution curve shows that the soil contains 50% clay-size particles. Together with the plasticity index, the resulting activity is close to 1. This result is typical of the clay mineral illite.
The specimens prepared using random powder preparation are shown in Table T2. The X-ray diffractometer was rotated between 6° and 56° 2. Tables T5, T6, and T7 and Figures F3, F4, and F5 give XRD results of the three random powder samples. Note that the intensity is plotted on a log scale.
Table T2 gives a list of the specimens used in calcite-treated random powder preparation. Table T4 gives the calcium carbonate content of the soil. Tables T8, T9, T10, T11, T12, and T13 and Figures F6, F7, and F8 show the results of calcite-treated random powder testing. The results of the two random powder samples show a significant amount of nonclay particles.
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. Table T2 shows the samples that were tested using this preparation. Tables T14, T15, and T16 and Figures F9, F10, and F11 show XRD results on the clay-size fraction of random powder samples.
Table T17 gives a summary of the details and conditions of each CRSC test. The first section of the table gives the water content (wc), plastic limit (wp), and liquid limit (wl) for each tube, as discussed in "Index Tests." The water content is taken from the soil trimmings. Also indicated is the number of observations (#obs) and standard deviation (SD) for each water content measurement. The Atterberg limits are discussed in "Index Tests," and are an average for each tube.
The next section of the table gives the specimen data such as the natural water content (wn), plasticity index (Ip), total density (
t), initial void ratio (ei), initial saturation (Si), and specific gravity (Gs). The natural water content and specific gravity were taken from Tréhu, Bohrmann, Rack, Torres, et al. (2003). 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 third section of the table gives the test conditions such as the backpressure (ub) and the strain rate (
/t). The backpressure gives the pressure at which the specimen is saturated.
The last section of the table gives consolidation properties such as the compression index, recompression index, and in situ hydraulic conductivity. The compression index refers to the slope of the normally consolidated portion of the compression curve while in e-log (
´v) space. The compression index (Cc) ranges from 0.340 to 0.704 (average = 0.568). Cc is fairly constant to a depth of 79 mbsf, after which Cc decreases downhole. The recompression index refers to the slope of the unload–reload portion of the curve while in e-log (´v) space. The recompression index (Cr) ranges from 0.035 to 0.064 (average = 0.052). Cr is constant throughout the depth. It must be noted that the recompression index varies with the amount of unloading that occurs. As such, the quoted recompression indexes are for unloading to an OCR of 10. The in situ hydraulic conductivity is obtained by extrapolating the hydraulic conductivity to the in situ void ratio. The in situ hydraulic conductivity varies between 1.5 x 10–7 and 3 x 10–8 cm/s with no trend with depth.
Figures F12, F13, F14, F15, F16, F17, F18, F19, F20, F21, F22, F23, F24, F25, F26, F27, F28, and F29 show the consolidation curves in both e-log (´v) and -log (´v), normalized excess pore pressure, coefficient of consolidation (cv), strain energy, and hydraulic conductivity (k) for each CRSC test. The CRSC data can be found in tabular form in Tables T18, T19, T20, T21, T22, T23, T24, T25, T26, T27, T28, T29, T30, T31, T32, T33, T34, and T35. The first column of the table gives the time each measurement was made. The second column gives the strain () in percent. The third, fourth, and fifth columns give the vertical stress ( v), pore pressure (u), and cell pressure ( cell), respectively. The sixth column gives the effective stress (´v), which is defined as
´v = v – 2/3(u – cell). (1)
The seventh column gives the void ratio (e). The eighth column gives the excess pore pressure, which is defined as
cell. (2)
The ninth and tenth columns give the hydraulic conductivity (k) and coefficient of consolidation (cv), respectively. The following are the equations used to define these parameters:
x H2 x 
)/(2 x 
ub), and (3)
ub) ( v/t). (4)
The eleventh and twelfth columns give the normalized excess pore pressure (U/ v) and the work, which is used for the strain energy calculations. The following equation is used to measure the work:
i + i – 1)/2] x ln[(1 – i – 1)/(1 – i)]. (5)
It must be noted that all stresses are measured in ksc (kgf/cm2). The conversion of ksc to SI units is 1 kPa = 98.07 kPa.
Table T36 gives the details and conditions of each CKoU triaxial for the consolidation stage of the test. The first and second sections refer to the same parameters in the CRSC results. The third section gives the initial effective stress (i) and backpressure (ub). In this section, a refers to the axial strain at the end of saturation. vol is the water inflow necessary to saturate the soil and system. Included in this section is the B-value, which is used to test the degree of saturation of the sample. A sample with a B-value of 100 ± 2 means that it has been fully saturated after the backpressure saturation stage. The fourth section of this table gives the general consolidation results. This section gives the preconsolidation pressure (´p) using the strain energy method, the strain rate (/t), and the compression index (Cc). The fifth section gives the consolidation properties at the maximum stress condition. a and vol give the axial and volumetric strain at this condition, whereas ´vm gives the maximum vertical effective stress. ts gives the length of time the stress was held constant, and Kc gives the maximum lateral stress ratio (´h/´v). The sixth section gives the consolidation properties at the preshear condition. For normally consolidated specimens, the maximum stress condition is the preshear condition; hence, these consolidation properties are the same. For overconsolidated specimens, the vertical effective stress is reduced, causing the maximum stress condition to differ from the preshear condition; hence, certain consolidation properties will be different. a and vol give the axial and volumetric strain at the end of unloading, whereas ´vc gives the consolidation vertical effective stress. ts gives the length of time the stress was held constant, and Kc gives the lateral stress ratio (´h/´v) after unloading. OCR indicates the overconsolidation ratio at the end of unloading.
Table T37 gives the details, test conditions, and strength properties for the undrained shearing stage of each test. The strength properties are given for both the case when maximum shear occurs and when either maximum obliquity or the end of shearing is reached. Obliquity refers to the ratio of the normalized shear stress to the normalized mean effective stress (q/p´). The normalized undrained strength ranges from 0.29 to 0.35, whereas the friction angle ranges from 27 to 37 at peak strength.
Incidentally, maximum obliquity also occurs when the friction angle is the greatest. It must be noted that shearing in extension was performed after shearing in compression for tests on Samples 204-1244B-1H-4, 138–148 cm, 4H-6, 125–135 cm, 204-1244C-9H-5, 115–125 cm, and the resedimented sample (TX 644).
Figures F30, F31, F32, F33, F34, F35, F36, F37, F38, F39, F40, F41, F42, F43, F44, F45, F46, F47, F48, and F49 show the consolidation and undrained shearing results for each triaxial test. The odd-numbered figures show the consolidation results including the consolidation curve in e-log (´v) and -log (´v) space, lateral stress ratio, strain energy, and stress path for each test. The even-numbered figures show the undrained shearing results including the normalized shear stress vs. strain, normalized excess pore pressure and shear-induced pore pressure, normalized secant modulus, friction angle, and normalized stress path for each test. The results of the consolidation and undrained shearing portions of the triaxial tests can be found in Tables T38, T39, T40, T41, T42, T43, T44, T45, T46, T47, T48, T49, T50, T51, T52, T53, T54, T55, T56, and T57. The first column of the table gives the time each measurement was made. The second, seventh, and eighth columns give the axial strain (a), volumetric strain (vol), and void ratio (e), respectively. The third and fourth columns give the vertical effective stress (´v) and the horizontal effective stress (´h), respectively. The fifth and sixth columns give the mean effective stress (p´) and shear stress (q), respectively. The following equations are used to define the mean effective stress and shear stress:
´v + ´h)/2, and (6)
v – h)/2. (7)
The ninth column gives the lateral stress ratio, which is defined as
´h/´v . (8)
The tenth column gives the work, which is used for the strain energy method of calculating the preconsolidation pressure. Equation 5 gives the equation used to calculate work. The eleventh column gives the area of the specimen at midheight. The twelfth column gives the applied backpressure (ub). The thirteenth, fourteenth, and fifteenth columns give the axial membrane correction, radial membrane correction, and axial drainage correction, respectively. Similar to the CRSC tests, all stresses are measured in ksc (kgf/cm2). The conversion of ksc to SI units is 1 kPa = 98.07 kPa.
