Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 3 FUNDAMENTAL PRINCIPLES
3 FUNDAMENTAL PRINCIPLES
3.1 BASIC WEIGHT-VOLUME RELATIONSHIPS
Soil mass is generally idealized as a three phase system consisting of solid particles, water and air
as illustrated in diagram in Figure 3.1. Owing to the three different components of soils, complex
states of stresses and strains may exist in a soil mass. The various volume changes phenomena
encountered in geotechnical engineering, such as deformation, consolidation, collapse, compaction,
expansion, shrinkage etc. can be described in term of the various volumes of these components in
the soil mass. Thus, knowledge of the relative proportion of each component and their various
inter-relationships can give an important insight into engineering behavior of a particular soil.
The weight-volume relationships of the soil mass are readily available in most soil mechanics
textbooks. Most of these relationships are as summarized in Table 3.1 and Table 3.2.
Soil particles
Volume
V a
Air
Weight
W a ≈0
Voids (filled with
water and air)
V
V v
V w
V s
Water
Solid
W w
W s
W
1 unit
Figure 3.1 Unit Soil Mass and Phase Diagram
Table 3.1 Definition and Typical Values of Common Soil Weight-Volume Parameters
Typical Range
Parameter Symbol Definition English SI
W
Unit weight
90 – 130 lb/ft 3 14 – 20 kN/m 3
V
W
Dry unit weight
s
d
60 – 125 lb/ft 3 9 – 19 kN/m 3
V
W
Unit weight of water
w
w
62.4 lb/ft 3 9.8 kN/m 3
V
Buoyant unit weight b sat - w 28 – 68 lb/ft 3 4 – 10 kN/m 3
Degree of saturation
Moisture content
Void ratio
Porosity
Specific gravity of solids
(Source: Donald P. Coduto, [6])
S
w
e
n
G s
V w
V v
x 100% 2 – 100% 2 – 100%
W w
x 100%
W s
3 – 70% 3 – 70%
V v
V s
0.1 – 1.5 0.1 – 1.5
V v
V x 100% 9 – 60% 9 – 60%
W s
V s w
2.6 – 2.8 2.6 – 2.8
March 2009 3-1