Factor of Safety for Submerged Embankment with Sudden Drawdown

[tzx9633]

Homework Statement

Determine the factor of safety (in regard to
cohesion only) for a submerged
embankment 30.5 m (100 ft) high whose
upstream face has an inclination of 30°. The
soil properties are gtotal=18.85 kN/m3 (120
pcf), c = 37.6 kN/m2 (700 psf), f=10°
b) What is the factor of safety if the
embankment experiences the effects of a
sudden drawdown?

Homework Equations

The Attempt at a Solution

Pls refer to the solution attached , I think it's wrong because when there's drawdown , there's no water . So , the ysub should be (18.85-9.81) , am i right ?

 

[jrmichler]

In a sudden drawdown, there is water. It's in the embankment, and it's trying to get out.

It's similar to the case of an Earth dam that is not wide enough for the total water height difference between upstream and downstream sides.

A local Earth dam developed a spring on the downstream face during spring runoff. It turned out that the downstream face should have had a slope of 3:1, but was only 2.6:1. Also, much of the soil in the dam was not properly compacted. That dam was removed last summer.