Well Hydraulics Civil Engineering (CE) Notes | EduRev

Civil Engineering SSC JE (Technical)

Civil Engineering (CE) : Well Hydraulics Civil Engineering (CE) Notes | EduRev

The document Well Hydraulics Civil Engineering (CE) Notes | EduRev is a part of the Civil Engineering (CE) Course Civil Engineering SSC JE (Technical).
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Chapter 4:
Well Hydraulics

SPECIFIC YIELD (Sy:
The specific yield of an unconfined aquifer is the ratio of volume of water which will flow under saturated condition due to gravity effects to the total volume of aquifer (V).Well Hydraulics Civil Engineering (CE) Notes | EduRev
where, VWY = Volume of water yielded under gravity effect and V = Total volume of water.

SPECIFIC RETENTION:
The specific retention of an unconfined aquifer is the ration of volume of water retained against gravity effect to the total volume of aquifer (V)

Well Hydraulics Civil Engineering (CE) Notes | EduRev
where Vwr =  Volume of water retained under gravity effect

Remember:- 
S+SR=n where, n = porostiy

COEFFICIENT OF TRANSMISSIBILITY:
T=kH
where,
H = Thickness
K = Coefficient of permeability

UNCONFINED AQUIFER:

 Well Hydraulics Civil Engineering (CE) Notes | EduRev

(a) Theims Theory

 Well Hydraulics Civil Engineering (CE) Notes | EduRev

Where,
q = Rate of flow in m3/s
h1 = Height of water table of 1st observation well
h2 = Height of water table of 2nd observation well
s1 = Drawdown of 1st test well
s2 = Drawdown of 2nd test well.
h1 + s1 = h+ s2
S1 = Drawdown of 1st test well
S2 = Drawdown of 2nd test well
r1 and r2 are radius of 1st and 2nd observation wells respectively.

(b) Dupits Theory:
Well Hydraulics Civil Engineering (CE) Notes | EduRev
Well Hydraulics Civil Engineering (CE) Notes | EduRev
where, S = Drawdown in the well
K = Permeability coefficient in m/s.
R = Radius of influence in ‘m’
150m ≤ R ≤ 300m
r = Radius of test well in ‘m’.
Results of dupits theory are not accurate because ‘R’ is based on empirical relation.

CONFINED AQUIFER:

Well Hydraulics Civil Engineering (CE) Notes | EduRev 

(i) Theims theory:
Well Hydraulics Civil Engineering (CE) Notes | EduRev
(ii) Dupits theory
Well Hydraulics Civil Engineering (CE) Notes | EduRev

SPHERICAL FLOW THROUGH WELL
qs=k2πrs, R = Radius of well
S = Drawdown
qs = Rate of flow through spherical well in m3/s
 Well Hydraulics Civil Engineering (CE) Notes | EduRev
Well Hydraulics Civil Engineering (CE) Notes | EduRev

PUMPING-IN-TEST
(a) Open end test
 Well Hydraulics Civil Engineering (CE) Notes | EduRev
where, r = radius of pipe, h = head of water above the base of pipe, it may include gravity head and pressure head.

(b) Tacker test
Well Hydraulics Civil Engineering (CE) Notes | EduRev
where, L = Length of perforated section of pipe

Well Hydraulics Civil Engineering (CE) Notes | EduRev
r = Radius of pipe
h = head of which water is added

 OPEN WELL (RCUPERATION TEST):
 Well Hydraulics Civil Engineering (CE) Notes | EduRev
where,
 Well Hydraulics Civil Engineering (CE) Notes | EduRev
Volume = A. H
A = Area of well
C/A = specific yield or specific Capacity of an open well.
T = Time in ‘sec’
h1 = Position of water table of t = 0
h2 = position of water table of t = T
Well Hydraulics Civil Engineering (CE) Notes | EduRev


VALUES OF PERMEABILITY:

 SOILK (cm/sec)Degree of
 permeability
1. Coarse Gravel>1High
2. Fine gravel-Fine sand1 to 10-2medium
 
3. Silt-Sand admixtures,loose silts, rock flour and loess10- 2 to 10-4Low
4. Dense slit, clay silt
admixutures,non-homogenous clays
10-4 to 10-6Very low
5. Homogenous clays< 10-6Impervious
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