Question

Three tube wells of 20cm diameter each forming an equilateral triangle at distance 100m on side. The coefficient of permeability is 4.15 * 10^-4 m/s, drawdown is 4m and aquifer is 30m thick. If radius of influence is 245m, what is the discharge in each well?

(a) 0.033 m^3/s

(b) 0.040 m^3/s

(c) 0.036 m^3/s

(d) 0.042 m^3/s

This question was posed to me during an interview.

The origin of the question is Well Hydraulics in chapter Well Hydraulics of Geotechnical Engineering I

Answer 1

Correct answer is (c) 0.036 m^3/s

Easiest explanation: Given,

Interface among three wells,

B=100m

Radius of tube well=10cm=0.1m

coefficient of permeability is 4.15 * 10^-4 m/s

drawdown (H-h)=4m

aquifer=30m

radius of influence=245m

the discharge is given by,

\(q_1=q_2=q_3= \frac{2πkb(H-h)}{log_e \frac{R^3}{rB^2}} \)

\(q_1=q_2=q_3= \frac{2π*4.15 * 10^{-4}*30*4}{log_e  \frac{245^3}{0.1*100^2}} \)

∴ q1=q2=q3=0.033 m^3/s.