14.531 hydraulic conductivity - umass lowellfaculty.uml.edu/.../14.531hydraulicconductivity.pdfv =...
TRANSCRIPT
![Page 1: 14.531 Hydraulic Conductivity - UMass Lowellfaculty.uml.edu/.../14.531HydraulicConductivity.pdfv = Discharge Velocity (i.e. quantity of water in ... k = Hydraulic Conductivity (i.e](https://reader034.vdocument.in/reader034/viewer/2022042117/5e95b08b15b028107a02f7bf/html5/thumbnails/1.jpg)
14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
BERNOULLI’S EQUATION
Zg
vu hw
2
2
Where:
h = Total Headu = Pressurev = Velocityg = Acceleration due to Gravityw = Unit Weight of Water
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Zg
vu hw
2
2
Therefore:
Zu hw
v ≈ 0(i.e. velocity of water in soil is negligible).
v ≈ 0
BERNOULLI’S EQUATION IN SOIL
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Figure 5.1. Das FGE (2005).
CHANGE IN HEADFROM POINTS A
& B (H)BA h hh
B
w
BA
w
A ZuZu h
BA h hh
Lh i
BA h hh
h can be expressed in non-dimensional form
Where:i = Hydraulic GradientL = Length of Flow between
Points A & B
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Figure 5.2. Das FGE (2005).
VELOCITY (v) VS. HYDRAULIC GRADIENT (i)General relationship shown in Figure 5.2
Three Zones:1. Laminar Flow (I)2. Transition Flow (II)3. Turbulent Flow (III)
For most soils, flow is laminar. Therefore:
v i
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
DARCY’S LAW (1856)
Where:v = Discharge Velocity (i.e. quantity of water in
unit time through unit cross-sectional areaat right angles to the direction of flow)
k = Hydraulic Conductivity (i.e. coefficient ofpermeability)
i = Hydraulic Gradient* Based on observations of flow of water through clean sands
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Kk w
HYDRAULIC CONDUCTIVITY (k)
Where: = Viscosity of Water
K = AbsolutePermeability(units of L2)
Soil Typek
(cm/sec)k
(ft/min)Clean Gravel 100-1 200-2
Coarse Sand 1-0.01 2-0.02
Fine Sand 0.01-0.001 0.02-0.002
Silty Clay 0.001-0.00001
0.002-0.00002
Clay < 0.000001 <0.000002
Typical Values of k per Soil Type
after Table 5.1. Das FGE (2005)
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Figure 5.3. Das FGE (2005).
DISCHARGE AND SEEPAGE VELOCITIES
svvAvAq Where:
q = Flow Rate(quantity of water/unit time)
A = Total Cross-sectional AreaAv = Area of Voidsvs = Seepage Velocity
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
nv
eev
VV
VV
vV
VVvv
LAAAv
AAAvv
vAAAvq
s
v
s
v
v
svs
v
sv
v
svs
svsv
11
)(
)()()(
Figure 5.3. Das FGE (2005).
DISCHARGE AND SEEPAGE VELOCITIES
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
EXAMPLE PROBLEM: FIND i AND q
CL (Impervious Layer)
CL (Impervious Layer)
SM (k = 0.007 ft/min)
12 ft
175 ft
25 ft
15 ft
12°
GIVEN: REQUIRED:Find Hydraulic Gradient (i)and Flow Rate (q)
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
CL (Impervious Layer)
CL (Impervious Layer)
SM (k = 0.007 ft/min)
12 ft
175 ft
25 ft
15 ft
Hydraulic Gradient (i):
067.0
12cos17512
ftfti
Lhi
12°
ftftq
ftftftq
kiAq
min//109.6
)1)(12)(cos15)(067.0(min
007.0
33
Rate of Flow per Time (q):
GIVEN: SOLUTION:
EXAMPLE PROBLEM: FIND i AND q
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
HYDRAULIC CONDUCTIVITY: LABORATORY TESTINGConstant Head(ASTM D2434)
Falling Head(no ASTM)
Figure 5.4. Das FGE (2005). Figure 5.5. Das FGE (2005).
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Constant Head(ASTM D2434)
AhtQLk
tkiAAvtQ )(Where:
Q = Quantity of water collectedover time t
t = Duration of water collection
tLhkAQ
Figure 5.4. Das FGE (2005).
HYDRAULIC CONDUCTIVITY: LABORATORY TESTING
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Falling Head(No ASTM)
2
110303.2
hhLog
AtaLk
dtdhaA
Lhkq
hdh
AkaLdt
Where:A = Cross-sectional area of Soila = Cross-sectional area of Standpipe
Figure 5.5. Das FGE (2005). 2
1loghhe
AkaLt
Integrate from limits 0 to t
Integrate from limits h1 to h2
after rearranging above equation
after integration
or
HYDRAULIC CONDUCTIVITY: LABORATORY TESTING
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
210sec)/( cDcmk
Uniform Sands - Hazen Formula(Hazen, 1930):
Where:c = Constant between 1 to 1.5D10 = Effective Size (in mm)
eeCk
1
3
1
Sands – Kozeny-Carman(Loudon 1952 andPerloff and Baron 1976):
Where:C = Constant (to be determined)e = Void Ratio
85.024.1 kek
Sands – Casagrande(Unpublished):
Where:e = Void Ratiok0.85 = Hydraulic Conductivity @ e = 0.85
e
eCkn
12
Normally Consolidated Clays(Samarasinghe, Huang, and Drnevich, 1982):
Where:C2 = Constant to be determined experimentallyn = Constant to be determined experimentallye = Void Ratio
HYDRAULIC CONDUCTIVITY: EMPIRICAL RELATIONSHIPS
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Void Ratio (e)k
(cm/sec)1.2 0.6 x 10-71.52 1.52 x 10-7
k1k2
C2
e1n
1 e1
C2e2
n
1 e2
Example 5.6 Das PGE (2005).
GIVEN:Normally consolidated clay with e and k measurements from 1D Consolidation Test.
SOLUTION:Using (Samarasinghe, Huang, and Drnevich, 1982) Equation:
2.252.2
52.12.1
sec/52.1sec/6.0 n
cmcmSubstituting
knownquantities
REQUIRED:Find k for same clay with a void ratio of 1.4.
HYDRAULIC CONDUCTIVITY: EMPIRICAL RELATIONSHIPSEXAMPLE – NORMALLY CONSOLIDATED CLAYS
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
sec/101.14.11
4.1sec)/710581.0(
sec/10581.0
2.112.1sec/106.0
1
75.4
4.1
72
5.47
1
121
cmxcmxk
cmxC
cmx
eeCk
e
n
Example 5.6 Das PGE (2005).
5.42.252.2
52.12.1
sec/52.1sec/6.0
n
cmcm n
HYDRAULIC CONDUCTIVITY: EMPIRICAL RELATIONSHIPSEXAMPLE – NORMALLY CONSOLIDATED CLAYS
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
STRATIFIED SOILS: EQUIVALENT HYDRAULIC CONDUCTIVITYHORIZONTAL DIRECTION
Figure 5.7. Das FGE (2005).
Considering cross-section of Unit Length 1.
Total flow through cross-section can be written as:
nn HvHvHvqHvq
1...111
2211
Where:v = Average Discharge Velocityv1 = Discharge Velocity in Layer 1
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
nnnHH
eqeqH
ikvikvikv
ikv
;...;; 222111
)(
Figure 5.7. Das FGE (2005).
Substituting v=ki into q equation and using H to
denote Horizontal Direction
Noting that ieq=i1=i2=…=in
)...(12211)( nHnHHeqH HkHkHk
Hk
Where: kH(eq) = Equivalent Hydraulic Conductivityin Horizontal Direction
STRATIFIED SOILS: EQUIVALENT HYDRAULIC CONDUCTIVITYHORIZONTAL DIRECTION
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
n
n
hhhh
vvvv
...
...
21
21
nVnVeqV ikikHhk ...11)(
Figure 5.8. Das FGE (2005).
Total Head Loss = hh = Sum Head Loss in Each Layer
and
Using Darcy’s Law (v=ki) into vequation and using V to denote
Vertical Direction
Where: kV(eq) = Equivalent Hydraulic Conductivityin Vertical Direction
STRATIFIED SOILS: EQUIVALENT HYDRAULIC CONDUCTIVITYVERTICAL DIRECTION
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
rhdrdhkq 2
1
2
1
2
2 h
h
r
rhdh
qk
rdr
FIELD PERMEABILITY TESTING BY PUMPING WELLSUNCONFINED PERMEABLE LAYER UNDERLAIN BY IMPERMEABLE LAYER
Figure 5.9. Das FGE (2005).
)(
log303.2
22
21
2
110
hhrrq
k field
Field Measurements Taken:
q, r1, r2, h1, h2
q = Groundwater Flow into Wellq also is rate of discharge from
pumpingEquation:
can be re-written as
Solving Equation:
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
rHdrdhkq 2
1
2
1
2
2h
h
r
rdh
qkH
rdr
Figure 5.10. Das FGE (2005).
)(727.2
log
21
2
110
hhHrrq
k field
Field Measurements Taken:q, r1, r2, h1, h2
q = Groundwater Flow into Wellq also is rate of discharge from
pumpingEquation:
can be re-written as
Solving Equation:
FIELD PERMEABILITY TESTING BY PUMPING WELLSWELL PENETRATING CONFINED AQUIFER
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
after Casagrande and Fadum (1940) and Terzagi et al. (1996).
SOILPERMEABILITY
ANDDRAINAGE
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
From FHWA IF-02-034 Evaluation of Soil and Rock Properties.
Good drainage
10-8 10-910-710-610-510-410-310-210-11.0101102 10-8 10-910-710-610-510-410-310-210-11.0101102
Poor drainage Practically impervious
Clean gravel Clean sands, Clean sand and gravel mixtures
Impervious sections of earth dams and dikes
“Impervious” soils which are modif ied by the effect of vegetation and weathering; f issured, weathered clays; fractured OC clays
Pervious sections of dams and dikes
Very f ine sands, organic and inorganic silts, mixtures of sand, silt, and clay glacial till, stratif ied clay deposits, etc.
“Impervious” soils e.g., homogeneous clays below zone of weathering
Drainage property
Application in earth dams and dikes
Type of soil
Direct determination of coefficient of permeability
Indirect determination of coefficient of permeability
*Due to migration of f ines, channels, and air in voids.
Direct testing of soil in its original position (e.g., well points). If properly conducted, reliable; considerable experience required. (Note: Considerable experience
also required in this range.)
Constant Head Permeameter; little experience required.
Constant head test in triaxial cell; reliable w ith experience and no leaks.
Reliable;Little experiencerequired
Falling Head Permeameter;Range of unstable permeability;* much experience necessary to correct interpretation
Fairly reliable; considerable experience necessary (do in triaxial cell)
Computat ion:From the grain size distribution(e.g., Hazen’s formula). Only applicable to clean, cohesionless sands and gravels
Horizontal Capillarity Test:Very little experience necessary; especially useful for rapid testing of a large number of samples in the f ield w ithout laboratory facilities.
Computat ions:from consolidation tests; expensive laboratory equipment and considerable experience required.
10-8 10-910-710-610-510-410-310-210-11.0101102 10-8 10-910-710-610-510-410-310-210-11.0101102
COEFFICIENT OF PERMEABILITYCM/S (LOG SCALE)
SOIL PERMEABILITY AND DRAINAGE
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
LAPLACE'S EQUATION OF CONTINUITYSteady-State
Flow around an impervious
Sheet Pile Wall
Consider water flow at Point A:
vx = Discharge Velocity in x Direction
vz = Discharge Velocity in z Direction
Y Direction Out Of PlaneFigure 5.11. Das FGE (2005).
x
z
y
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
dxdydzzvv
dzdydxxv
v
zz
xx
Consider water flow at Point A(Soil Block at Pt A shown left)
Rate of water flow into soil block in x direction:
vxdzdyRate of water flow into soil block in z direction:
vzdxdy
Figure 5.11. Das FGE (2005).
Rate of water flow out of soil block in x,z directions:
LAPLACE'S EQUATION OF CONTINUITY
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
0
0
zv
xv
ordxdyvdzdyv
dxdydzzvvdzdydx
xv
v
zx
zx
zz
xx
Consider water flow at Point A(Soil Block at Pt A shown left)
Figure 5.11. Das FGE (2005).
Total Inflow = Total Outflow
LAPLACE'S EQUATION OF CONTINUITY
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
02
2
2
2
zhk
xhk
zhkikv
xhkikv
zx
zzzz
xxxx
Consider water flow at Point A(Soil Block at Pt A shown left)
Figure 5.11. Das FGE (2005).
Using Darcy’s Law (v=ki)
LAPLACE'S EQUATION OF CONTINUITY
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: DEFINITION OF TERMSFlow Net: Graphical Construction used to calculate groundwater flow through soil. Comprised of Flow Lines and Equipotential Lines.Flow Line: A line along which a water particle moves through a permeable soil medium.Flow Channel: Strip between any two adjacent Flow Lines.Equipotential Lines: A line along which the potential head at all points is equal.
NOTE: Flow Lines and Equipotential Lines must meet at right angles!
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Figure 5.12a. Das FGE (2005).
FLOW NETSFLOW AROUND
SHEET PILE WALL
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Figure 5.12b. Das FGE (2005).
FLOW NETSFLOW AROUND
SHEET PILE WALL
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
1.The upstream and downstream surfaces of the permeable layer (i.e. lines ab and de in Figure 12b Das FGE (2005)) are equipotential lines.
2.Because ab and de are equipotential lines, all the flow lines intersect them at right angles.
3.The boundary of the impervious layer (i.e. line fg in Figure 12b Das FGE (2005)) is a flow line, as is the surface of the impervious sheet pile (i.e. line acd in Figure 12b Das FGE (2005)).
4.The equipontential lines intersect acd and fg(Figure 12b Das FGE (2005)) at right angles.
FLOW NETS: BOUNDARY CONDITIONS
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Figure 5.13. Das FGE (2005).
FLOW NETSFLOW UNDER ANIMPERMEABLE
DAM
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
nqqqq ...321
Figure 5.14. Das FGE (2005).
q k h1 h2
l1
l1 k h2 h3
l2
l2 k h3 h4
l3
l3 ...
h1 h2 h2 h3 h3 h4 ... HNd
Rate of Seepage ThroughFlow Channel (per unit length):
Using Darcy’s Law (q=vA=kiA)
Potential DropWhere:
H = Head DifferenceNd = Number of Potential Drops
FLOW NETS: DEFINITION OF TERMS
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
Figure 5.12b. Das FGE (2005).
d
f
NHN
kq
If Number of Flow Channels = Nf, then the total flow for all channels per unit length is:
Therefore, flow through one channel is:
dNHkq
FLOW NETSFLOW AROUND SHEET PILE WALL EXAMPLE
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
GIVEN:
Flow Net in Figure 5.17.Nf = 3Nd = 6kx=kz=5x10-3 cm/sec
DETERMINE:
a. How high water will rise in piezometers at points a, b, c, and d.
b. Rate of seepage through flow channel II.
c. Total rate of seepage.
Figure 5.17. Das FGE (2005).
FLOW NETSFLOW AROUND SHEET PILE WALL EXAMPLE
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
mmm 56.06
)67.15(
SOLUTION:
Potential Drop = dN
H
At Pt a:Water in standpipe =(5m – 1x0.56m) = 4.44m
At Pt b:Water in standpipe =(5m – 2x0.56m) = 3.88m
At Pts c and d:Water in standpipe =(5m – 5x0.56m) = 2.20m
Figure 5.17. Das FGE (2005).
FLOW NETSFLOW AROUND SHEET PILE WALL EXAMPLE
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETSFLOW AROUND SHEET PILE WALL EXAMPLE
SOLUTION:
dNHkq
k = 5x10-3 cm/seck = 5x10-5 m/sec
q = (5x10-5 m/sec)(0.56m)q = 2.8x10-5 m3/sec/m
fd
f qNN
HNkq
q = (2.8x10-5 m3/sec/m) * 3q = 8.4x10-5 m3/sec/m
Figure 5.17. Das FGE (2005).
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: RULES FOR CREATINGFLOW NETS (FROM UTEXAS)
1. Head drops between adjacent equipotential lines must be constant (or, in those rare cases where this is not desirable, clearly stated, just as in topographic contour maps)!
2. Equipotential lines must match known boundary conditions.
3. Flow lines can never cross.
Flow Line
Equi.
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: STEPS FOR DRAWING(LADD, MIT)
1. Draw problem in ink.2. Draw in known equipotential and flow
boundary lines.3. Sketch 2 or 3 flow lines.4. Draw corresponding equipotential
lines (check for squares and ┴ intersections)
5. Keep adjusting (and adjusting, and adjusting…)
Flow Line
Equi.
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: RULES FOR CREATINGFLOW NETS (FROM UTEXAS)
4. Refraction of flow lines must account for differences in hydraulic conductivity.
5. For isotropic media.a) Flow lines must intersect equipotential
lines at right angles.b) The flow line-equipotential polygons
should approach curvilinear squares, as shown in the Figure to the right.
Flow Line
Equi.
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: RULES FOR CREATINGFLOW NETS (FROM UTEXAS)
6. The quantity of flow between any two adjacent flow lines must be equal.
7. The quantity of flow between any two stream lines is always constant.
Flow Line
Equi.
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: DRAWING PROCEDURE(AFTER HARR (1962, P. 23)
1. Draw the boundaries of the flow region to scale so that all equipotential lines and flow lines that are drawn can be terminated on these boundaries.
2. Sketch lightly three or four flow lines, keeping in mind that they are only a few of the infinite number of curves that must provide a smooth transition between the boundary flow lines. As an aid in spacing of these lines, it should be noted that the distance between adjacent flow lines increases in the direction of the larger radius of curvature.
3. Sketch the equipotential lines, bearing in mind that they must intersect all flow lines, including the boundary streamlines, at right angles and that the enclosed figures must be (curvilinear) squares.
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: DRAWING PROCEDURE(FROM HARR (1962, P. 23)
4. Adjust the locations of the flow lines and the equipotential lines to satisfy the requirements of step 3. This is a trail-and-error process with the amount of correction being dependent upon the position of the initial flow lines. The speed with which a successful flow net can be drawn is highly contingent on the experience and judgment of the individual. A beginner will find the suggestions in Casagrande (1940) to be of assistance.
5. As a final check on the accuracy of the flow net, draw the diagonals of the squares. These should also form smooth curves that intersect each other at right angles.
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: EXAMPLES
Unconfined groundwater flow nets on a slope
Wrong Wrong
Correct!
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: EXAMPLES
Cross-sectional flow net of a homogeneous and isotropic aquifer (Hubbert, 1940).
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: EXAMPLES
Contour map of the piezometric surface near Savannah, Georgia, 1957, showing closed contours resulting from heavy local groundwater pumping (from Bedient, after USGS Water-Supply Paper 1611).
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14.531 ADVANCED SOIL MECHANICSHydraulic Conductivity
FLOW NETS: DAM EXAMPLES