Consolidation Settlement Examples 1_Solutions(2)-2

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Consolidation Settlement – Examples 1

1. A horizontal layer of clay of saturated unit weight 22kN/m3 is 8.0m thick and is

overlain y a !.0m thick granular layer "unit weight 1#.$kN/m3%. &round'water level

occurs at a de(th of 2.0m elow the surface of the granular material.

A consolidation test carried out an a sam(le of the clay gave the following results)

*ressure

kN/m2

+am(le thickness

mm

0 1#.8,

2$ 1#.$0

$0 1#.30

100 1#.02

200 18.-$

!00 18.$,

0 1#.30

After the swelling stage the moisture content of the sam(le was determined as 2-.2.

f the (article s(ecific gravity is 2.,8 otain the void ratio / effective stress (lot for

the sam(le. A foundation is to e constructed on the surface of the sand and it ise(ected that this will suect the centre of the clay layer to a vertical stress increase

of -$kN/m2. etermine the consolidation settlement of the clay.

2. 4he readings elow were otained from an oedometer test on a s(ecimen of saturated

clay. 4he load was held constant for 2! hours efore the addition of the net

increment. At the end of the last load increment the load was removed and the

sam(le allowed to swell for 2!'hours at the end of which time its thickness was

determined as 1-.#2mm and its moisture content found to e 31.8. 4he s(ecific

gravity of the soil was 2.,,.

"a% *lot the e/( curve for this s(ecimen.

"% etermine the coefficient of volume com(ressiility for a stress range of 220'

3,0kN/m2.

"c% 5se these data to otain the ultimate consolidation settlement of a !.0m thick

layer of this material when suected to an average effective stress 220 to

3,0kN/m2

.

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*ressure

kN/m2

+am(le thickness

mm

0 1#.,0

2$ 1#.2$

$0 18.#8

100 18.,1

200 18.1!

!00 1-.,8

800 1-.2!

3. A fleile raft foundation 10m 6 20m is to e constructed at a de(th of 2.0m in a

granular material of thickness 10.0m and eerts a gross contact (ressure of

2$0kN/m2

. A clay layer of thickness 2.0m is located at a de(th '10.00m elow ground

level "0.00m% and rockhead is located at '12.00m. &round water level occurs at

'2.00m7 the saturated unit weights of the granular soil and the clay are res(ectively

1#kN/m3 and 22kN/m

3 the granular soil can e assumed to e fully saturated aove

(ermanent water tale.

"i% calculate the elastic settlement of the clay layer elow the (lan centre of the

foundation given that u 9 12:N/m2.

"ii% y considering the stress increase at the centre of the clay layer calculate the

ultimate consolidation settlement of the clay layer elow the (lan centre given

that the moisture content of the clay is 3$ and the s(ecific gravity of the clay

(articles is 2.,$. ;c for the clay is 0.!0.

Note) elastic settlement of a clay layer resting on a rigid ase isu

2

8

0%1"


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4he granular material aove water tale can e regarded as saturated. ?ou estimate

that the foundation eerts a "gross% contact (ressure of 230kN/m2. e(resentative

sam(les from the clay layer were tested in an oedometer and gave the following

results shown elow.

t is e(ected that (um(ing o(erations will lower ground water level from its eisting

level "'1.-$m% to '-.00m. Assuming 1' consolidation conditions (revail determine

the consolidation setttlement that will occur at the centre of the uilding if the water

tale remains at its new level.

*ressure kN/m2

Boid atio

$0 0.-3

100 0.,8200 0.,2

300 0.$8

!00 0.$!

+tate any assum(tions or a((roimations in you solution.

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Consolidation Settlement Examples 1_Solutions(2)-2