A stratum of sand and a stratum of clay have the same thickness of 3 m. The coefficient of compressibility of sand is 1/5th of coefficient of compressibility of clay and the permeability of sand is 1 0,000 times that of the clay. As suming the same void ratio, the ratio of the consolidation time for the clay to that of the sand is
coefficient of consolidation
using 1 for sand and 2 forclay
As the thickness of both layer is same, so for same degree of consolidation:
If the time required for 50% consolidation of a remoulded sample of clay with single drainage is t, then the time required to consolidate the same sample of clay with same degree of consolidation but with double drainage is
For single drainage,
For double drainage,
⇒ or, T2 = t1/4
Match List- I and List - II on the basis of Terzaghi's one dimensional consolidation theory and select the
correct answer using the codes given below the lists (Notations have their usual meaning):
The unit of the coefficient of consolidation is
Tv is constant and unit less d is drainage path, unit is centimeter (cm) t is time of consolidation , unit is sec.
∴ unit of Cv = cm2/ sec
When the primary consolidation process in a soil is complete, then
Only excess pore pressure completely dissipates and effective stresses increase
The ultimate consolidation settlement of a structure resting on a soil
ultimate consolidation settlement is given by,
so as initial void ration e0 , increase ultimate settlement decrease.
A normally consolidated clay layer settles by 25 mm when the effective stress is increased from 15 kPa to 30 kPa. If the effective stress is later increased further from 30 kPa to 60 kPa, then the additional settlement would be
These are two equations for calculating the total settlement. The coefficient of volume compressibility (mv) depends up on the stress range and therefore not a constant. However compression index (Cc) is constant for a normally consolidated clay.
= ΔH2 = ΔH1 = 25 mm
Two specimens of clay A and B are tested in a consolidation apparatus.
If (mv)A = 3.6 x 10-4 m2/ kN and
(mv)B = 1.8 x 10-4 m2/kN,
(Cv)A = 3.8 x 10-4 cm2/s,
(Cv)B = 1.9 x 10-4 cm2/s,
then the ratio kA/kB is equal to
In consolidation testing, curve fitting method is used to determine
Curve fitting methods like (1) square-root of time method and (2) logarithm of time method are used to determine coefficient of consolidation. The curve between dial gauge reading and time t obtained in the laboratory by testing the soil sample is similar in shape to the theoretical curve between U and Tv obtained from the consolidation theory. This similarity between the laboratory curve and the theoretical curve is used for the determination of the coefficient of consolidation (Cv) of the soil.
When the degree of consolidation is 50% , the time factor is about