Geotechnical Engineering

DHARM

SHALLOW FOUNDATIONS 615

2.

Firm clay or silty clay

extending to great depth

Df > frost depth and zone of

swelling and shrinkage

Spread footings most appro-

priate for conventional

needs. Piles may be used

only if unusual forces such

as uplift are expected.

3.

Soft clay extending to great

depth

Df > frost depth and zone of

swelling and shrinkage

Spread footing appropriate

for low or medium loading,

if not too close to soft clay.

Deep foundations may be

required for heavy loading.

4.

Loose sand extending to

great depth

Df > frost depth and depth of

erosion

Spread footings may settle

excessively. Raft founda-

tion may be appropriate.

Spread footings may be

used if the sand is com-

pacted by vibrofloatation.

Driven piles or augered

cast-in-place piles may also

be used.

5.

or

Soft clay but firmness in-

creasing with depth extend-

ing to great depth

Friction piles or piers would

be satisfactory if some set-

tlement could be tolerated.

Long piles would reduce

settlement. Raft foundation

or floating foundation may

also be considered.

6. Deep foundation-piles,
   piers, caissons—bearing di-
   rectly on/in the rock.

××

7.

Hard clay extending to

great depth

Spread footings in upper

sand layer would probably

experience large settlement

because of underlying soft

clay layer. Drilled piers

with a bell formed in the

hard clay layer, or other pile

foundation may be consid-

ered.

(Contd.)...

3 m Firm clay

Df

or

7.5m (Soft)

7.5 m (Medium)

(firmer)

20 m Soft clay

Rock

2.5 m Compact sand

3.5 m Medium clay

Df

Df