CIVIL ENGINEERING FORMULAS

SOIL AND EARTHWORK FORMULAS 193

(8.30)

where quultimate bearing capacity of soil, lb/ft^2 (kg / m^2 )
ccohesion, lb/ft^2 (kg / m^2 )
angle of internal friction, degree
dryunit weight of dry soil, lb/ft^3 (kg / m^3 )
bwidth of footing, ft (m)
ddepth of footing below surface, ft (m)
Kpcoefficient of passive pressure



e2.718...

For footings below the surface, the ultimate bearingcapacity of the soil may
be modified by the factor 1Cd/b. The coefficient Cis about 2 for cohesion-
less soils and about 0.3 for cohesive soils. The increase in bearing capacity with
depth for cohesive soils is often neglected.

SETTLEMENT UNDER FOUNDATIONS

The approximate relationship between loads on foundations and settlement is

(8.31)

where qload intensity, lb/ft^2 (kg/m^2 )
Psettlement, in (mm)
ddepth of foundation below ground surface, ft (m)
bwidth of foundation, ft (m)
C 1 coefficient dependent on internal friction
C 2 coefficient dependent on cohesion

The coefficients C 1 andC 2 are usually determined by bearing-plate loading tests.

SOIL COMPACTION TESTS

Thesand-cone methodis used to determine in the field the density of com-
pacted soils in earth embankments, road fill, and structure backfill, as well as
the density of natural soildeposits, aggregates, soil mixtures, or other similar
materials.It is not suitable, however, for soils that are saturated, soft, or friable
(crumble easily).

q

P

C (^1)  1 
2 d
b



C 2

b

tan^45 



2 

2

qu

c

tan



1

2

dryb 2 Kp (Kpe^ tan 1)