Ch: 1 3. A construction site need s to be predrained in order to allow for the e

Question

Ch: 1 3. A construction site need s to be predrained in order to allow for the excavation shown in This will require dropping the groundwater observations of the drawdown from other the plan and cross-sectional drawings below. table 5 m below its current location. From wells in the area, the radius of influence, rO, is estimated to be 825 m. Compute the pumping rate required to lower the groundwater table using the well array shown. (25 points)1 ab r= 40 50m Well array , Excavation Plan view Well array 5 m 15 m- aquifer30m1 25 m. I k 3x 10-cm/s Aquiclude Elevation view

Explanation / Answer

The rectangular system of wells can be represented as an equivalent circular well of radius r = (ab/pi)0.5

So, r = (40 x 50 / pi)0.5 = 25.23 m

K = 0.3 cm/s = 0.003 m/s

Radius of influence (R) = 825 m

At distance R, steady-state head = 30 m

At distance r, steady-state head = 25 m

Pumping rate required, q = k x pi x (H2 - h2) / ln(R/r) = 0.003 x pi x (302 - 252) / ln(825/25.23) = 0.743 m3/s

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