The uplift pressure on a dam can be controlled by i) constructing cutoff under upstream face ii) constructing drainage channels bet-ween the dam and its foundation iii) by pressure grouting in foundation The corret answer is A. only (i) B. both (i) and (ii) C. both (i) and (iii) D. (i), (ii) and (iii)

The correct answer is D. (i), (ii) and (iii).

Uplift pressure is the pressure exerted by water on the underside of a dam. It is caused by the weight of the water above the dam. Uplift pressure can cause a dam to fail if it is not properly controlled.

There are a number of ways to control uplift pressure. One way is to construct a cutoff under the upstream face of the dam. A cutoff is a barrier that prevents water from flowing under the dam. It can be made of concrete, steel, or other materials.

Another way to control uplift pressure is to construct drainage channels between the dam and its foundation. Drainage channels allow water to flow away from the dam, reducing the uplift pressure.

Pressure grouting is a technique that can be used to fill voids in the foundation of a dam. This helps to prevent water from entering the foundation and causing uplift pressure.

All of these methods can be used to control uplift pressure and prevent dam failure.