2. Basic Characteristics of Soil
Soils consist of grains (mineral grains, rock,
etc.) with water and air in the voids between
grains. The water and air contents are
readily changed by changes in conditions
and location: soils can be perfectly dry
(have no water content) or be fully saturated
(have no air content) or be partly saturated
(with both air and water present). Although
the size and shape of the solid (granular)
content rarely changes at a given point, they
can vary considerably from point to point.
3. Basic Characteristics of Soil
Soil as an engineering material
The term "soil" means different things to different people: To a geologist it
represents the products of past surface processes. To a pedologist it
represents currently occurring physical and chemical processes. To an
engineer it is a material that can be:
built on: foundations to buildings, bridges.
built in: tunnels, culverts, basements.
built with: roads, runways, embankments, dams.
supported: retaining walls, quays.
Soils may be described in different ways by different people for their different
purposes. Engineers' descriptions give engineering terms that will convey some
sense of a soil's current state and probable susceptibility to future changes (e.g. in
loading, drainage, structure, surface level).
5. The three Phases of Soil
Solids, Liquids, and Gaseous Phases
The soil as a porous medium consists of three phases that are
dynamic and interrelated in composition. A mineral soil can consist of
the following composition:
a) Solid phase constitutes the soil matrix (clay
minerals, organic matter)
50%
b) Liquid phase, consists of soil water and
dissolved substances (soil solution) 25%
c) Gaseous phase is the soil atmosphere 25%
11. Basic Relationships for calculating Phase
diagram components
Weight --Wt = Ww + Ws
Volume --Vt = Vv + Vs = Va + Vw + Vs
Unit Weight (Density)
This is also known as (same thing by different names)
- Bulk Density
- Soil Density
- Unit Weight
- Wet Density
12. Definitions
Water content (w) is a measure of the
water present in the soil.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
S
W
M
M
w
Expressed as percentage.
Range = 0 – 100+%.
X 100%
13. Definitions
Void ratio (e) is a measure of the void volume.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
S
V
V
V
e
14. Definitions
Porosity (n) is also a measure of the void
volume, expressed as a percentage.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
T
V
V
V
n X 100%
Theoretical range: 0 – 100%
15. Definitions
Degree of saturation (S) is the percentage of
the void volume filled by water.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
V
W
V
V
S
Range: 0 – 100%
X 100%
Dry
Saturated
16. Definitions
Bulk density (m) is the density of the soil in the
current state.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
T
T
b
V
M
Units: t/m3, g/ml, kg/m3
17. Definitions
Saturated density is the density of the soil when the
voids are filled with water.
Submerged density is the effective density of the
soil when it is submerged.
w
sat
sub
18. Definitions
Dry density is the density of the soil in dry state.
soil
air
water
Vs
Va Ma=0
Ms
Mw
Mt
Vw
Vv
Vt
T
S
d
V
M
Units: t/m3, g/ml, kg/m3
28. Soil Structure granular
prismatic
Refers to the way soil particles cling
together to form soil units or
aggregates, while leaving pore space
to….
– Store air.
– Store water.
– Store nutrients.
– Allow root
penetration.
29. Types of Soil Structure
There are five types of soil structures.
They are:
– Single grain
– Granular
– Platy
– Blocky
– Prismatic
31. Soil Structure - Granular
Is the best for most
plants.
Particles cling together to
form rounded
aggregates.
It is commonly found in
A horizons.
Peds are small usually
between 1 to 10
millimeters.
32. Soil Structure - Platy
Usually found in E
horizons.
Large, thin peds.
Plate-like &
arranged in
overlapping
horizontal layers.
33. Soil Structure - Blocky
Particles cling
together in angular
aggregates.
Typical of soils with
high clay content.
Typical of B
horizons.
Peds are large
about 5 to 50
millimeters.
34. Soil Structure - Massive
Soil has no visible
structure.
Hard to break apart
& appears in very
large clods.
36. Soil Structure
More important to
producers who grow
plants in natural
soils because….
– Producers of
container grown
plants add
ingredients to make
growing media
desirable.
37. Factors that affect Soil Structure
Kind of clay
Amount of organic matter
Freezing and thawing
Wetting and drying
Action of burrowing organisms
Growth of root systems of plants
38. Soil composition
About 50% of the soil
should be solid
particles.
– 45% - Minerals
– 5% - Organic Matter
About 50% of soil
should be pore space.
– 25% - Air/Pore Space
– 25% - Water
39. Soil pH
pH has the most impact on the availability of
nutrients in the soil/media.
pH Scale
– Ranges from 0 to 15.
– Indicates the level of acidity or alkalinity.
– 7 is considered neutral.
– Everything greater than 7 is considered alkaline
(basic).
– Everything less than 7 is considered acidic.
41. Ideal pH
The ideal pH of most ornamental plants
& lawn/turfgrasses is 5.5 to 7.0.
42. Particle Density
The weight of a soil with no pore space
The weight of a solid block of quartz
2.65 grams per c.c (166 pounds per
cubic foot)
43. Organic soil
Db 0.8 Mg/m3
Bulk Density
The mass of a volume of undisturbed
soil
Bulk densities range from 1.0 grams per
c.c. to 1.8 grams per c.c
BD= weight dry soil = g
Volume dry soil cm3
44. Effects of Bulk Density
Engineering properties
Water movement
Rooting depth of plants
45. Soil Porosity
Total pore space is a measurement of
the soil volume that holds air and water
Porosity = wet weight – dry weight(g) x
100 divided by the soil volume (cm3)
Example 900-650 x 100 divided by
500=50%
46. Soil Porosity
Can also be determined by
Porosity= 100%-(BDX100)
Porosity=100%-(1.3 x 100)=50%
2.65
47. Soil Porosity
sand loam clay
Volume of large pores
Volume of small pores
Large
amount
Amount
of
pore
space
