What is the undrained shear strength of clay?
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What is the undrained shear strength of clay?
The undrained shear strength (su) is defined as one-half of the peak value of (P1 – P3). For CU tests, the slower strain rates of Raymond should be retained to more closely approximate field rates of loading. The UU test provides a measure of Su at the in situ water content of the sample.
Where does undrained shear strength come from?
Compared to drained strength ( c ′ , ϕ ′ c’, \phi’ c′,ϕ′), undrained shear strength is often much easier and cheaper to measure. It can be derived from an unconfined compression test (UU triaxial), vane shear test or simply using a pocket penetrometer.
How does pore water pressure affect soil strength?
The strength of a soil comes from friction between the soil particles. As we learned in Soil Mechanics I, when pore water is present in the pores (or voids) of a soil, the pore water pressure u pushes the soil particles apart and reduces the stress between the particles (Figure 1).
Is undrained shear strength the same as undrained cohesion?
Based on analysis that undrained shear strength coincides with 50 percentile of distribution data meanwhile undrained compressive strength is around twice of cohesion for testing using unconfined pressure. This relationship is the most familiar equation.
What is the difference between drained and undrained shear strength?
Drained Shear Strength: The soil is free to dilate or contract during shear if the soil sample is totally drained. Undrained Shear Strength: Whenever water is not allowed to flow in or flow out of the soil then the stress path is called as undrained stress path.
What is drained and undrained shear strength?
What is the undrained shear strength of sand?
Typical values of shear strength
| Undrained shear strength | su (kPa) | |
|---|---|---|
| Compact sands | 0 | 35° – 45° |
| Loose sands | 0 | 30° – 35° |
| Unweathered overconsolidated clay | ||
| critical state | 0 | 18° ~ 25° |
What is seepage pressure?
What is Seepage Pressure? When water flows through soil pores a viscous friction is exerted on it which causes transfer of energy between soil and water. This water pressure applied on soil which tends it to percolate is called as seepage pressure.
What causes pore water pressure?
Pressure develops due to: Water elevation difference: water flowing from higher elevation to lower elevation and causing a velocity head, or with water flow, as exemplified in Bernoulli’s energy equations. Hydrostatic water pressure: resulting from the weight of material above the point measured.
Is clay drained or undrained?
Clay behavior depends on the rate of loading (or unloading). When “fast” stress changes take place then clay behavior is typically modeled as “Undrained” while slow stress changes or long term conditions are typically modeled as “Drained”. In the software, the default behavior of a clay type soil is set as “Undrained”.