# How do you calculate undrained shear strength?

## How do you calculate undrained shear strength?

The principal stress difference (deviator stress) (P1 – P3) is computed as the axial piston load divided by the corrected area of the sample and plotted as a function of the axial strain. The undrained shear strength (su) is defined as one-half of the peak value of (P1 – P3).

Table of Contents

**What is undrained shear strength ratio?**

Undrained Shear Strength Ratio Ladd and Foott (1974) and Mesri (1975) show that the undrained shear strength can be normalized with respect to the effective overburden stress. The resulting ratio, Su /v0, where v0 is the effective overburden stress, is termed the undrained shear strength ratio.

**What is undrained shear strength of soil?**

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. Undrained Shear Strength is not a fundamental soil parameter as compare to drained strength. Undrained shear strength is more easier and cheaper. 0.

### Is undrained shear strength same as bearing capacity?

Bearing capacity can be estimated as multiples of the undrained shear strength. For drained analysis, you need an estimate of the effective friction angle phi’ which is mobilised when you load the soil with the footing until it fails.

**Why is undrained shear strength important?**

The undrained cyclic shear strength has to be evaluated to calculate the capacity under cyclic loads. The undrained cyclic shear strength should be obtained for various stress paths. The remolded shear strength is an important parameter because it is used to calculate the penetration resistance of the skirt walls.

**What is CU value of soil?**

The uniformity coefficient (Cu) is defined as the ratio of D60 to D10. A value of Cu greater than 4 to 6 classifies the soil as well graded. When Cu is less than 4, it is classified as poorly graded or uniformly graded soil. Uniformly graded soil has identical particles with Cu value approximately equal to 1.

#### What is Cu in clay soil?

The undrained shear strength (cu) is considered one of the most basic para- meter characterizing soils in engineering practice. The particular importance of cu is in the case of clayey soil. This parameter also is the basis for the classification of soil according to the ISO standard.

**What affects undrained shear strength?**

The increase in undrained shear strength with axial strain rate can be attributed to a reduction in the magnitude of excess pore water pressure, with similar reductions in magnitude for all the degrees of saturation considered.

**What is the difference between cohesion and undrained shear strength?**

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.

## Why does undrained shear strength increase with depth?

Undrained shear strength is not a fundamental soil parameter. It generally varies over depth as a function of insitu confining stress at a given depth. Note that larger confining stress reduces void ratio over the historical time. By the decrease of void ratio, undrained shear strength increases.

**What is CU and CC in soil?**

Uniformity Coefficient(Cu) and Coefficient of Curvature(Cc) of Soil. The uniformity coefficient (Cu), curvature coefficient (Cc) and the effective size (D10) are the grading characteristics of the soil. These are the geometric properties of a grading curve that describe a particular type of soil.

**How is Cu value calculated?**

Thus, Cu = D60/D10

- D60 = Size of the particle corresponding to 60% finer and,
- D10 = Size of the particle corresponding to 10% finer.

### What is the undrained shear strength of stiff clay?

75 ~ 150 kPa

Typical values of shear strength

Undrained shear strength | su (kPa) |
---|---|

Stiff soil | su = 75 ~ 150 kPa |

Firm soil | su = 40 ~ 75 kPa |

Soft soil | su = 20 ~ 40kPa |

Very soft soil | su < 20 kPa |

**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”.

**Why does undrained strength increase with depth?**

#### Does undrained shear strength vary with depth?

Undrained shear strength is not a fundamental soil parameter. It generally varies over depth as a function of insitu confining stress at a given depth.

**How do you calculate CC and CU?**

Cu = D60/D10. Cc – Coefficient of curvature. Cc = (D30)^2 /(D60)(D10).

**What does D10 D50 and D90 mean?**

D10: The portion of particles with diameters smaller than this value is 10% D50: The portions of particles with diameters smaller and larger than this value are 50%. Also known as the median diameter. D90: The portion of particles with diameters below this value is 90%.