Determination of co efficient of consolidation methodPresentation Transcript
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.
Methods Generally used methods are: Square root of time fitting method Logarithm of time fitting method
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.
Time Consolidation Curve
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
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.
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
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
RoR50 = (R100-Ro) / 2R100
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