1 CE281-Geotechnical Engineering I
Permeabilit y Test
PERMEABILITY TEST
OBJECTIVE
To determine the coefficient of permeability (k for a gi!en soil sample "sing falling head method# INTRODUCTION
Permeability (or hydra"lic cond"cti!ity refers to the ease $ith $hich $ater can flo$ thro"gh a soil# This property is necessary necessar y for estimating the %"antity of "ndergro"nd seepage "nder !ario"s hydra hydra"l "lic ic cond condit itio ions ns&& for for in!e in!esti stiga gatin ting g prob proble lems ms in!o in!ol! l!in ing g the the p"mp p"mpin ing g of $ater $ater for for "ndergro"nd constr"ction& and for making stability analyses of earth dams and earth-retaining str"ct"res that are s"b'ect to seepage forces# ne of the ma'or physical parameters of a soil that controls the rate of seepage thro"gh it is hydra"lic cond"cti!ity& other$ise other$ise kno$n as the coefficient of permeability# There are t$o standard laboratory test methods to determine the hydra"lic cond"cti!ity of soil) 1# The The cons consta tant nt hea head d tes testt meth method od ) "sed "sed for for perm permea eabl blee soil soilss (k*1 (k*1++-, , cms cms 2# The The fal falli ling ng head head test test met metho hod d ) "se "sed d fo for les lesss per perm meabl eablee so soils ils (k.1 (k.1++-, , cm cms s THEORY
/alling head test method The falling head permeability test is a common laboratory testing method "sed to determine the permeability of permeability of fine grained soils $ith intermediate and lo$ permeability s"ch as silts and clays# This testing method can be applied to an "ndist"rbed sample# Principal of the falling head method is based on 0arcys la$ $hich $as proposed by enry 0arcy& a /rench scientist in 1834# It is a simple e%"ation for the discharge !elocity of $ater thro"gh sat"rated soils#
v = ki $here5 v 6 0ischarge !elocity& $hich is the %"antity of $ater flo$ing in "nit time thro"gh a "nit cross sectional area of soil at right angle to the direction of flo$& k 6 6 Coefficient of permeability i 6 ydra"lic gradient The rate of flo$ of the $ater thro"gh the specimen at any time t can be gi!en by& h dh q = k A =−a l dt $here5 q 6 flo$ rate a 6 cross-sectional area of the standpipe A 6 A 6 cross-sectional area of the soil specimen
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Permeabilit y Test
Figure 1: Diagram of the Falling-head Falling-head Method
The e%"ation "sed to calc"late the coefficient of permeability is) k =
( )
h0 al ln A ( t 1− t 0 ) h1
9hen the e%"ation is arranged in the form of y 6 m:& ln
( ) h0 h1
= kA ( t −t ) al
1
0
$here5 a 6 cross-sectional area of the standpipe A 6 cross-sectional area of the soil specimen l 6 length of the soil sample t 1 – t 0 6 the time inter!al h0 6 initial $ater le!el height from the bottom of the apparat"s to the ;ero mark le!el of the stand pipe h1 6 height height meas"red meas"red $ith time from the bottom bottom of the apparat"s apparat"s to the $ater le!el The coefficient of permeability (k can be determined "sing the gradient (m of the graph ln
( ) h0 h1
m=
against
( t −t ) # 1
0
kA al Therefore&
k =
mal A
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Permeabilit y Test
The coefficient of permeability is defined as the rate of flo$ of $ater "nder laminar flo$ conditions thro"gh a "nit cross-sectional area of a poro"s medi"m "nder a "nit hydra"lic gradient and standard temperat"re conditions# The "nit of k is ms#
MATERIALS AND APPARATUS APPARATUS
1# 2# # ,# 3# 4# ?#
/allin /alling g ead ead Permea Permeabil bility ity
eas >eas"r "rin ing g 'ar 'ar# >ete >eterr scal scale# e# Contai Container ner to collect collect e:cess e:cess $ater $ater
Figure 2: Permeameter
Figure 3: Falling 3: Falling ead Permea!ilit" A##aratu$
PROCEDURE
1# /irs /irst& t& it has has been been chec checke ked d $het $hethe herr the the !al! !al!ee is clos closed ed and and the the t"be t"be conn connec ecti ting ng the the permeameter and standpipe is tight& also a container has been place to collect the e:cess $ater falling from the !al!e# 2# 7e:t& $ater $ater has been been filled in from the the top of the the glass glass standpipe standpipe "p to the ;ero mark# mark# # =oil specimen specimen has has been kept to to get sat"rate sat"rate for some time time and $hen the the $ater le!el le!el dropped& dropped& again $ater has been filled "p to the $ater ;ero mark le!el# ,# Then& h+ has been meas"red from the bottom of the apparat"s to the ;ero mark le!el "sing the meas"ring tape# 3# The The !al! !al!ee has has been been opened opened and $ater $ater has has been been allo$e allo$ed d to discha discharg rgee thro thro"g "gh h it for fi!e fi!e min"tes time inter!al# 4#
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Permeabilit y Test
?# =imilar =imilarly ly record record the height height of $ater in the glass standpi standpipe pe in e!ery 3 min"tes min"tes time inter!a inter!all for abo"t 3+ min"tes# 8# @sing @sing the the recor recorded ded reading readingss the grap graph h
ln
( ) h0 h1
( t −t ) has been plotted#
against
1
0
A# The coefficien coefficientt of permeability permeability&& k has been been fo"nd by the gradient gradient of the graph# graph#
CALCULATIONS
=pecimen Calc"lation 1# The The cros cross-s s-sect ectio ional nal area area (a (a of the standpipe& A =
πd
2
4
0.02
(¿ ( ¿ ¿ 2 )
π
4
=¿
A
−4
A =3.143 x 10 m
2
2# The The cros cross-s s-sect ectio ional nal area area ( A A of the soil specimen& A =
πd
2
4
0.1
(¿ ( ¿ ¿ 2 )
π
4
A =¿ −3
2
A =7.857 x 10 m
# The The grad gradien ientt (m (m of the the gra graph ph m=
m
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ln
() h1
h2
against
( t −t ) 2
1
is&
m=
kA a
y 2− y 1 x 2− x 1
− = 0.888 0.121 ( 35−5 ) x 60
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5 CE281-Geotechnical Engineering I − 4 −1 m= 4.26 x 10 s
Permeabilit y Test
,# The coeffi coefficien cientt of permeabi permeability lity (k& (k& k =
mal A
( 4.26 x 10− ) (3.143 x 10− )( 127.3 x 10− ) 4
k =
4
3
−3
7.857 x 10
−6
−1
k =2.169 × 10 ms
RESULTS
t (min
h0 (cm
h1 (cm
h0 h1
ln
( ) h0 h1
+
1,+#2
1,+#2
1
+
3
1,+#2
12,#2
1#2A
+#121
1+
1,+#2
11+#2
1#2?2
+#2,1
13
1,+#2
A?#
1#,,1
+#43
2+
1,+#2
83#?
1#44
+#,A2
23
1,+#2
?3#
1#842
+#422
+
1,+#2
43#A
2#12?
+#?33
3
1,+#2
3?#?
2#,+
+#888
,+
1,+#2
3+#
2#?8?
1#+23
,3
1,+#2
,#A
#1A,
1#141
3+
1,+#2
-
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Permeabilit y Test −6
−1
The calc"lated coefficient of permeability& k =2.169 × 10 ms
DISCUSSION
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Permeabilit y Test
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Permeabilit y Test
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Permeabilit y Test
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Permeabilit y Test
CONCLUSION
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Permeabilit y Test
REFERENCES:
Bra'a ># 0as Dhaled =obhan (2+12 Prin%i#le$ (2+12 Prin%i#le$ of &eote%hni%al 'ngineering & 8th edition& @nited =tates# Permea!ilit" te$t( nlineF&
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