Question

1. For a clean sand, if the relative density of the sand is increased, the friction angle, φ, will

a. decrease b. increase c. stay the same

2. In general, a well graded gravel will have a friction angle, φ, that is __________ the friction angle of a poorly graded gravel of the same relative density

a. less than b. greater than c.equal to

3. Loose sands sometime liquefy during earthquakes, but dense sands never do. Why?

Answer 1

1. For clean sand, if the relative density of the sand is increased, the friction angle, , will also Increase.

We get the directly proportional relationship between the two from various empirical and experimental works. Two of them are:

• Meyerhoff's Empirical Relation:

Friction Angle	Relative Density (DR) (%)	Description
25-30	0-15	Very Loose
27-32	15-35	Loose
30-35	35-65	Medium
35-40	65-85	Dense
>40	85-100	Very Dense

• Experimental Work Done By HERLE (1997) on Hochstetten Gravel

Peak Friction Angle ()	Relative Density (DR)(%)
43	60
45	70
50	80
60	90

Hence, the answer of the Question 1 is option(b) i.e. increase.