Computers in Geology    GEOL 372

Lesson 4 - Modeling with Excel

Goal Seek   Find a specific result for a cell containing a formula by adjusting the value of one of the cells referenced in that formula.

  1. On the Tools menu, click Goal Seek.
  2. In the Set cell box, enter the reference for the cell that contains the formula you want to resolve.
  3. In the To value box, type the result you want.
  4. In the By changing cell box, enter the reference for the cell that contains the value you want to adjust. This cell must be referenced by the formula in the cell you specified in the Set cell box.

 

Simplified Slope Stability Analysis   Calculate the factor of safety (Fs) for a slope using the following equation and values.

Fs = (S*L*T)/(W*sinq)

S = shear strength of material along slip plane = 9x104 N/m2 (clay)

L = length of slip plane = 50m

T = unit thickness = 1m

W = weight = AxUxT

A = area = 500m2

U = unit weight = 1.6x104N/m3

q = dip of slip plane

 

Set your worksheet up like the example below.

Experiment by changing various parameters and observing the effect on slope stability.  Use Conditional Formatting to make text appear red when Fs is greater than or equal to 1.25.

Use Goal Seek to determine conditions that produce Fs values greater than 1.25.