Determinationof

Co-efficient of Consolidation Method

Determination of Co-efficientThe similarity between the laboratory curve and theoretical curve is used for the determination of the co-efficient of consolidation (Cv) of soil.

MethodsGenerally used methods are:

Square root of time fitting method

Logarithm of time fitting method

Square root of time fitting methodThis method, developed by Taylor, utilizes

theoretical relationship between U and √Tv.The relationship is linear up to value of u

equal to about 60%.It was observed that at U=90%, value of √Tv

is 1.15 times value obtained by extension of the initial straight line portion.

A curve is plotted from consolidation test results between dial gauge reading (R) as ordinate and √T.

Time Consolidation Curve

Co-efficient of Consolidation (Cv)From curve,

90

290

t

dTcv

cv (cm2/sec)T90 = time factor when U is 90%d = drainage patht50 = time when U is 50%U = percent of primary consolidation

Logarithm of time fitting methodThis method, developed by A.

Casagrande, determines 100% U on semi log plot of laboratory time consolidation curve by theoretical curve between U and log Tv.

Logarithm of time fitting methodConstruct a plot of dial reading vs. log of

timeTo determine

Ho = Initial height of specimen

Rstart = 0 (if you zeroed the dial at the beginning of the test)

R50 you determine from the plot

2

)( 5050

startodr

RRHH

Coefficient of Consolidation (cv)Casagrande log time method: R50

determine Ro, when U = 0%this is NOT your first reading

determine R100, when U = 100%then average to find R50, which then graphically corresponds to t50

0.065

0.070

0.075

0.080

0.085

0.090

0.095

0.100

0.105

0.110

0.115

0.1 1 10 100 1000 10000

Time (min)D

ial R

eadi

ngs

(in)

0.065

0.070

0.075

0.080

0.085

0.090

0.095

0.100

0.105

0.110

0.115

0.1 1 10 100 1000 10000

Time (min)D

ial R

eadi

ngs

(in)

R100

Ro

0.065

0.070

0.075

0.080

0.085

0.090

0.095

0.100

0.105

0.110

0.115

0.1 1 10 100 1000 10000

Time (min)D

ial R

eadi

ngs

(in)

Ro

R100

R50 = (R100-Ro) / 2

Coefficient of Consolidation (cv)cv (cm2/sec)T50 = time factor at U

= 50%d = drainage patht50 = time at U = 50%U = percent of

primary consolidationIf Uavg = 50%, T50 =

0.197

50

250

t

dTcv

Thank You