18.10 Taylor's Charts

Step-by-Step Tutorial: Understanding and Using Taylor's Charts for Slope Stability Analysis

1. Introduction to Taylor's Charts and Stability Number (n):

   • Taylor's charts are used in undrained analysis of slopes and were produced by a person named Taylor.
   • The stability number (n) is a dimensionless number defined as n = CM / (γ * H), where CM is the mobilized cohesion, γ is the unit weight of the soil in the slope, and H is the height of the slope.
   • Mobilized cohesion (CM) is calculated as the cohesion of the soil divided by the factor of safety.

2. Types of Taylor's Charts:

   • Taylor produced two charts for undrained analysis:
     • Chart 1: Used for general cases except when the angle of friction of the soil is 0 and when the slope angle is less than 53 degrees.
     • Chart 2: Specifically used when the angle of friction of the soil is 0 and the slope angle is less than 53 degrees.

3. Using Taylor's Chart 1:

   • On the horizontal axis, plot the slope angle, and on the vertical axis, plot the stability number.
   • To use the chart:
     • Determine the slope angle and project vertically upwards until you intersect with the angle of friction line on the chart.
     • Project horizontally across until you intersect with the stability number axis.
     • Use the known values of unit weight of the soil, height of the slope, cohesion, and factor of safety to calculate the mobilized cohesion and factor of safety.

4. Using Taylor's Chart 2:

   • On the horizontal axis, plot the depth factor D.
   • To use the chart:
     • Find the depth factor D and project upwards to the slope angle.
     • Project horizontally across to find the stability number.
     • Calculate the mobilized cohesion and factor of safety using the known values.

5. Case Study - Determining Factor of Safety:

   • For Case 1:

     • Given parameters: Unit weight of soil = 18.5 kN/m³, undrained cohesion = 30 kPa, undrained angle of friction = 0 degrees, and slope angle = 65 degrees.
     • Use Chart 1 as the slope angle is greater than 53 degrees.
     • Calculate mobilized cohesion, then factor of safety.

   • For Case 2:

     • Given parameters: Unit weight of soil = 19 kN/m³, undrained cohesion = kPa (value not provided), undrained angle of friction = 0 degrees, and slope angle = 30 degrees.
     • Use Chart 2 as the slope angle is less than 53 degrees.
     • Calculate mobilized cohesion, then factor of safety.

6. Conclusion:

   • Taylor's charts provide a useful tool for analyzing slope stability based on various parameters.
   • By following the steps outlined above and applying the calculations to the given parameters, you can determine the factor of safety for different slope conditions using Taylor's charts.

7. Thank you for watching and learning about Taylor's Charts for slope stability analysis!