Question

An embankment will be filled at a site. Before filling the embankment, a soil specimen with a height of 20mm is sampled from the middle of a normally consolidated clay which has a thickness of 4 m. A consolidation test reveals that the soil has a pre-consolidation pressure of 120 kPa, compression index C_c = 0.16, initial void ratio of 0.85. (1) If the settlement of the clay layer is 38.6 mm due to the extra loading from the embankment, the total stress P at the middle of the clay layer will be _________ (kPa). (2) For the soil specimen, the change of its thickness is 0.34 mm when the consolidation test is finished while the change of its thickness is 0.17 at time t. If the clay layer is singly drained, how long it takes the clay layer to reach a consolidation degree of 50%? __________(answer as a function of t)

Group of answer choices

a. 200.5 kPa, 20000 t

b. 233.9 kPa, 20000 t

c. 181.0 kPa, 160000 t

d. 155.2 kPa, 160000 t

Answer 1

(1)The eq. of consolidation settlement is,

Given datas,

Sc =38.6 mm

H=4000 mm

Here, We consider for middle layer of clay = 2000mm

C_c =0.16

e0 =0.85

p0= 120 kpa

(2)degree of consolidation occured in time t =

Time factor for U= 99.995%

For single drainage condition h= 20mm

Coefficient of consolidation, Cv = Tv*h²/t =78.57/t

For 50% consolidation time factor

Time taken for reach 50% consolidation =Tv*h²/Cv =0.251*t= 0251*60*60*24*t =21686.4t

a. 200.5 kPa, 20000 t