Page 260 - Civil Engineering Formulas

194 CHAPTER EIGHT

Characteristics of the soil are computed from
3
3
Volume of soil, ft (m )
weight of sand filling hole, lb (kg)
(8.32)
3
3
density of sand, lb/ft (kg/m )
100(weight of moist soil weight of dry soil)
% Moisture (8.33)
weight of dry soil
weight of soil, lb (kg)
3
3
Field density, lb/ft (kg/m ) (8.34)
3
3
volume of soil, ft (m )
field density
Dry density (8.35)
1 % moisture/100
100(dry density)
% Compaction (8.36)
max dry density
Maximum density is found by plotting a density–moisture curve.
Load-Bearing Test
One of the earliest methods for evaluating the in situ deformability of
coarse-grained soils is the small-scale load-bearing test. Data developed
from these tests have been used to provide a scaling factor to express the set-
2
2
tlement of a full-size footing from the settlement of a 1-ft (0.0929-m )
1
plate. This factor / is given as a function of the width B of the full-size
1
bearing plate as
1 2B 2 (8.37)
1 B
From an elastic half-space solution, E can be expressed from results of a plate
s
load test in terms of the ratio of bearing pressure to plate settlement k as
v
2
k v (1 )
/4
E s (8.38)
4B/(1 B) 2
where represents Poisson’s ratio, usually considered to range between
0.30 and 0.40. The E equation assumes that is derived from a rigid, 1-ft
1
s
(0.3048-m)-diameter circular plate and that B is the equivalent diameter of
the bearing area of a full-scale footing. Empirical formulations, such as the
/ equation, may be significantly in error because of the limited footing-
1
size range used and the large scatter of the database. Furthermore, considera-
tion is not given to variations in the characteristics and stress history of the
bearing soils.