Random-Field Characterization of Fissuring in Clay

Secondary geologic features, such as fissures, greatly influence soil physical properties and mechanical behavior. Because laboratory element-scale experiments often fail to capture these features due to the small specimen size, in situ tests such as the cone penetration test (CPT) often are used to characterize potentially fissured soil under in situ conditions. However, current CPT-based soil characterization charts lack information on the secondary fabric of soil. To address this, this study applies the zero-mean weakly stationary random-field model to assess inherent soil variability with respect to CPT parameters, including corrected cone resistance (qt), sleeve friction (fs), and penetration-induced pore pressure (u2). Results show that intact clays exhibit a scale of fluctuation (δ) value (an indicator of the range of correlated domains) about three times larger than fissured clays for all three CPT parameters, with a value of 0.45 m separating the two categories. The study concludes that qt is the optimal parameter for evaluating fissures, and the procedures outlined can be used to differentiate fissured and intact clays at other sites.