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<br /> <br /> <br /> <br />23 <br /> <br />Figure 11: Variation of the cone factor (𝑵𝒌∗) with plasticity index <br />for clays <br />Drained shear strength parameters (c’, φ’) for clays <br />vary depending on consolidation of the clay. As shown <br />previously in Figure 8, the Mohr-Coulomb strength <br />envelope for normally consolidated clays goes through <br />the origin of stress and the effective stress cohesion <br />(c’) is equal to zero. Typical values of peak effective <br />stress friction angle (φ’) for normally consolidated clays <br />are provided in Table 3. For overconsolidated clays, the <br />Mohr-Coulomb strength envelope is generally curved <br />in the low stress range and approximated as linear <br />over the normal stress range of interest for the <br />analysis, which may result in an “apparent” effective <br />stress cohesion (c’). Typical peak values of φ’ and c’ for <br />compacted clays corresponding to a relative <br />compaction of 100 percent of the Standard Proctor <br />maximum dry density are given in Table 4. <br /> <br /> <br /> <br />Table 3: Typical Values of Peak Friction Angle (φ’) for Normally <br />Consolidated Claysa <br /> <br /> <br />Table 4: Typical Peak Drained Strengths for Compacted Cohesive <br />Soils <br /> <br /> <br />Silts <br />Silts have an interesting soil particle composition, as <br />they can behave similarly to either fine sands or clays. <br />When the term fine-grained is used, it almost always <br />includes silts in this category. But silts themselves can <br />be divided into two general categories, non-plastic and <br />plastic. Non-plastic silts behave more like fine sands, <br />while plastic silts behave more like clays. Evaluating <br />whether a unit of silt is non-plastic or plastic can be <br />achieved using the Atterberg Limit laboratory test <br />(refer to “Soil Characterization (Part 1) – Here’s the <br />Dirt”). <br />Since silts can have a wide range of permeabilities, it <br />can be difficult to predict if these soils will behave as <br />drained or undrained under various loading conditions. <br />Reference: Duncan, Wright, and Brandon (2014) <br />Reference: Duncan, Wright, and Brandon (2014) <br />Reference: Duncan, Wright, and Brandon (2014)