Civil Engineering - Soil Mechanics and Foundation Engineering - Discussion

Critical Hydraulic Gradient:

The critical hydraulic gradient is the point at which the hydraulic force exerted by the water flow equals the resisting force of the soil particles. When this gradient is reached, soil particles begin to move, which can lead to soil erosion or piping. Essentially, it’s the threshold gradient that can cause instability in the soil structure.

Exit Gradient:
The exit gradient refers to the hydraulic gradient at the downstream end of a structure, such as a dam or a levee. It is the gradient at the point where water exits the soil. If the exit gradient exceeds the critical hydraulic gradient, it can lead to soil erosion and potential failure.

Exit gradient depends upon head loss and seepage length

The total head loss H between the last two equipotential lines is 0.62 m. The distance between the two equipotential lines on the downstream end in the X area is 3.3 m.

The exit gradient is then computed as 0.62 divided by 3.3 making the upward gradient 0.19.

The critical exit gradient differs from the critical hydraulic gradient.

Critical exit gradient is the ratio of seepage head loss to the length of seepage it means it not related to specific gravity or voids ratio.

It is directly proportional to head loss and inverse to the length of seepage.

Thanks.

@All.

You may plot the variation of the critical gradient by keeping G or e constant.

You will find a straight line in the graph paper. So we can say that the critical gradient is directly proportional to G or e. So, the Correct answer is c & d.

The critical hydraulic gradient is the hydraulic gradient at which particles start to flow out of a soil sample.

The exit gradient is the hydraulic gradient at the point where water leaves the soil and enters the free water downstream.

The critical exist gradient of seepage water in soils, is increased with increase in specific gravity.

The critical exist gradient of seepage water in soils, is increase with decrease void ratio.

The answer is directly proportional to the specific gravity because no matter of G-1. G is maximum as compared to 1. So directly proportional to the specific gravity.

Its has directly proportional to G and inversely proportional to E. So answer should be c and d. But there is no this type of answer so it will non of these.

Directly proportional to Specific gravity also. Actually,

i = (G-1)/(1+e) where i is critical gradient.

G is spec. gr.
e is void ratio.

Value of critical exit gradient is 1. So it doesn't depend on any factor. Hydraulic gradient depends on Specific gravity and void ratio.