Gravity Dam Uplift Pressure Distribution

Indian standard recommendation provides guidelines for the calculation of uplift pressure in a gravity dam. The uplift pressure is the hydrostatic pressure acting in the upward direction at the base of the dam. It is necessary to consider uplift pressure as it can cause the dam to lift off its foundation.

Uplift Pressure Distribution Assumption

The Indian standard recommendation assumes that the uplift pressure in a gravity dam acts over a certain area. The area over which the uplift pressure acts depends on the location of the point under consideration. The options provided in the question are:

(a) 100% of the area
(b) 75% of the area
(c) At toe plus 1/3rd the difference of hydrostatic pressure at heel and toe
(d) At heel plus 1/3rd the difference of hydrostatic pressure at heel and toe

Explanation of Uplift Pressure Distribution

The correct option is (c) At toe plus 1/3rd the difference of hydrostatic pressure at heel and toe. This means that the uplift pressure at any point in the dam is assumed to act over an area that starts at the toe and extends a certain distance towards the heel. The distance is determined by adding 1/3rd of the difference between the hydrostatic pressure at the heel and the toe to the toe distance.

This assumption is based on the fact that the uplift pressure is maximum at the toe of the dam and decreases towards the heel. The uplift pressure distribution is also affected by the seepage conditions in the foundation. In general, the uplift pressure is assumed to act over a smaller area in case of high seepage conditions.

Conclusion

In conclusion, the uplift pressure in a gravity dam is assumed to act over a certain area according to Indian standard recommendation. The correct option for the uplift pressure distribution assumption is (c) At toe plus 1/3rd the difference of hydrostatic pressure at heel and toe. It is important to consider the uplift pressure while designing a gravity dam to ensure its stability.