Landslide Mechanics

 

Work in groups of two to complete these questions..  Each group should hand in their work by the end of the day.  There is no formal write up.

 

 

1.  Use the slide demo program to perform a sensitivity analysis of the infinite slope equation.  Do this by holding three parameters constant and varying the fourth parameter.  Note carefully what happens to ÒFÓ the factor of safety.  When it drops below 1, the slope will fail.

 

Set the following as default values:

 

density (rho) at 2000 kg/m2

h (slab thickness) at 1 m

alpha (failure plane) slopes at 15 degrees

g at 9.8 m s2

c=0  and hÕ=0 (dry granular material, no cohesion)

 

With ALL OTHER parameters at their default values, vary EACH of the parameters below over the following ranges.  SKETCH graphs of your results both for driving and resisting force for each sensitivity test.  Each test should include at least five values.

 

dry density 800 to 3000 kg/m2

h 0.2 to 20 m

alpha 0 to 90 degrees

 

 

You should finish this part of the exercise with three sets of graphs relating driving and resisting force to changing input parameters.  Below each graph summarize in one sentence how changing a particular parameter affects the driving and resisting forces.

 

What is the single most important parameter controlling slope stability? _______________

 

 

 

2.  Examine the resisting forces of Earth materials.  Do this by plotting the relationship of  shear strength versus normal force for the two sets of data given below.  Make sure that strength is plotted on the vertical axis and normal force on the horizontal axis.

 

 

                 A                                                                     B

normal force    strength                       normal force    strength           all data in pascals

                                                                                                                  kg/(m s2)

1209

897

1209

4684

2567

1910

2567

5796

6789

4567

6789

9152

10240

7415

10240

11070

14230

9891

14230

14161

 

Given a normal force of 4000 pascals what will be the shear strengths of the two materials?

 

A

 

B

 

 

 

Generalize the data above using a mathematical formulation. Hint...what do the data define?  What is the formula for this pattern?

 

 

FOR A

 

 

FOR B

 

How do you relate your formulation to the formulation in the handout I gave you?  What is the tangent, (tan) f, doing in the equation?

 

 

 

 

 

 

 

 

 

 

 

 

3.  Investigate the importance of groundwater on slope stability and the factor of safety.  Set the model to

 

dry density (rho) at 1800 kg/m2

wet density (rho) at 2000 kg/m2

h at 2 m

phi angle at 30

cohesion at 0

alpha at 20 degrees

g at 9.8 m s2

 

Make a graph of driving and resisting forces versus water table elevation (hÕ) above failure plane.  At what water table elevation above the failure plane will the slope fail?

 

 

 

TRY AGAIN WITH COHESION...

 

 

dry density (rho) at 1800 kg/m2

wet density (rho) at 2000 kg/m2

h at 2 m

phi angle at 30

cohesion at 10,000 pascals (weak sandy clay)

alpha at 20 degrees

g at 9.8 m s2

 

Make a sketch graph of driving and resisting forces versus water table elevation (hÕ) above failure plane.  At what water elevation above the failure plane will the slope fail?  Is this realistic?