Determination of co efficient of consolidation method

1. Determination of Co-efficient of Consolidation Method

2. 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.

3. Methods Generally used methods are: Square root of time fitting method Logarithm of time fitting method

4. 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.

5. Time Consolidation Curve

6. Co-efficient of Consolidation ( Cv ) From curve, c v ( cm 2 /sec) T 90 = time factor when U is 90% d = drainage path t 50 = time when U is 50% U = percent of primary consolidation

7. 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 .

8. Logarithm of time fitting method Construct a plot of dial reading vs. log of time To determine H o = Initial height of specimen R start = 0 (if you zeroed the dial at the beginning of the test) R 50 you determine from the plot

9. Coefficient of Consolidation ( c v ) Casagrande log time method: R 50 determine R o , when U = 0% this is NOT your first reading determine R 100 , when U = 100% then average to find R 50 , which then graphically corresponds to t 50

10. R100 Ro

11. Ro R100 R50 = (R100-Ro) / 2

12. Coefficient of Consolidation ( c v ) c v ( cm 2 /sec) T 50 = time factor at U = 50% d = drainage path t 50 = time at U = 50% U = percent of primary consolidation If U avg = 50%, T 50 = 0.197

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