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# Determination of co efficient of consolidation method

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### Determination of co efficient of consolidation method

1. 1. Determination of Co-efficient The similarity between the laboratory curve and theoretical curve is used for the determination of the co-efficient of consolidation (Cv) of soil.
2. 2. Methods Generally used methods are:  Square root of time fitting method  Logarithm of time fitting method
3. 3. Square root of time fitting method This 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.
4. 4. Time Consolidation Curve
5. 5. Co-efficient of Consolidation (Cv) From curve, cv (cm2/sec) T90 = time factor when U is 90% d = drainage path t50 = time when U is 50% U = percent of primary consolidation
6. 6. Logarithm of time fitting method This 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.
7. 7. Logarithm of time fitting method Construct a plot of dial reading vs. log of time To 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
8. 8. 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
9. 9. RoR100
10. 10. RoR50 = (R100-Ro) / 2R100
11. 11. Coefficient of Consolidation (cv)  cv (cm2/sec)  T50 = time factor at U = 50%  d = drainage path  t50 = time at U = 50%  U = percent of primary consolidation  If Uavg = 50%, T50 = 0.197