Profile of a weir on permeable foundation is shown in figure I and an elementary profile of upstream pile only case' according to Khosla's theory is shown in figure II. The uplift pressure heads at key points Q, R and S are 3.14 m, 2.75 m and 0 m, respectively (refer figure II).

What is the uplift pressure head at point P downstream of the weir (junction of floor and pile as shown in the figure I)?

This question was previously asked in

GATE CE 2016 Official Paper: Shift 2

Option 2 : 1.25 m

CT 1: Ratio and Proportion

2536

10 Questions
16 Marks
30 Mins

__Concept:__

**The percentage of uplift pressure of the weir is given by,**

\(\phi = \frac{h}{H} \times 100\)

Where,

h = uplift pressure heads

H = operating head of weir

**Calculation:**

h_{Q} = uplift pressure head at point Q = 3.14 m

hR = uplift pressure head at point R = 2.75 m

hS = uplift pressure head at point S = 0 m

we know that

\(\phi = \frac{h}{H} \times 100\)

\(\begin{array}{l} {\phi _R} = \frac{{2.75}}{4} \times 100 = 68.75\% \\ {\phi _P} = 100 - {\phi _R} = 31.25\% \\{\phi _P} = \frac{{Pressure\;head\;at\;point\;P}}{{Total\;head}} \times 100\\ 31.25 = \frac{h}{4} \times 100 \end{array}\)

h = 1.25 m

∴ Uplift Pressure head at point P = 1.25 m