Consolidation Theory Examples

Example 1 The Following results were obtained from an oedometer test on a specimen of saturated clay. A layer of this clay 8m thick lies below a 4m depth of sand, the water table being at the surface. For both soils, the saturated unit wt=21kN/m3 A 4m depth of fill of unit weight 21kN/m3 is placed on the sand over an extensive area. 429 214 107 54 27 Pressure(kN/m2) 0.994 1.068 1.144 1.217 1.243 Void ratio

Determine the final settlement due to consolidation of the clay. Continued… Example1 Determine the final settlement due to consolidation of the clay. Solution: The settlement of the clay layer

Appropriate values of e are obtained from the following figure: Continued… Example1 Appropriate values of e are obtained from the following figure: The clay layer will be divided into four sub-layer, hence H = 2000mm

Continued… Example1 To get the settlement:

Example 2 A soil profile is shown in the Fig. If a uniformly distributed load is applied at the ground surface, what is the settlement of the clay layer caused by primary consolidation if: A) The clay is normally consolidated B) The preconsolidation pressure=190kN/m2 C) The preconsolidation pressure=170kN/m2 Cs=1/6 Cc

Continued… Example 2

A) The average effective stress at the middle of the clay layer is Continued… Example 2 A) The average effective stress at the middle of the clay layer is

B) The average effective stress at the middle of the clay layer is Continued… Example 2 B) The average effective stress at the middle of the clay layer is

C) The average effective stress at the middle of the clay layer is Continued… Example 2 C) The average effective stress at the middle of the clay layer is

Example 3 In an oedometer test, a specimen of saturated clay 19mm thick reaches 50% consolidation in 20 min. How long would it take a layer of this clay 5m thick to reach the same degree of consolidation under the same stress and drainage conditions? How long would it take the layer to reach 30% consolidation?

Continued… Example 3

Continued… Example 3

Example 4 The time rate settlement data shown below is for the increment from 20 to 40 kPa from the test. The initial sample height is 2.54cm, and there are porous stones on the top and at the bottom of the sample. Determine Cv by the log time- fitting procedure.

Continued… Example 4 Dial reading (mm) Elapsed time (min) 4.041 3.927 0.1 3.879 0.25 3.830 0.5 3.757 1 3.650 2 3.495 4 3.282 8 3.035 15 2.766 30 2.55 60 2.423 120 2.276 240 2.184 505 2.040 1485

Continued… Example 4

Continued… Example 4