SOIL

Soil may be defined as the accumulation of unconsolidated sediments and deposits of

solid particles as a result of the integration of rocks.
 On the other hand, rocks may be defined as natural aggregate of minerals connected
by the strong bonding of attractive forces classified as consolidated materials.
 Scientifically, most of the non-organic materials identified as soil has originated from
rocks as the parent material.
SOIL 
Soil may be defined as the accumulation of unconsolidated sediments and deposits of
solid particles as a result of the integration of rocks. On the other hand, rocks may be
defined as natural aggregate of minerals connected by the strong bonding of attractive
forces classified as consolidated materials. Scientifically, most of the non-organic
materials identified as soil has originated from rocks as the parent material.

SOIL AND ITS ORIGIN

 From the earliest civilization up to the present time, soil is the most important material
that influenced mankind in his struggle for survival. The material where man grows his
food, build his homes, roads, and ultimately his final destination.
 The soil referred to in this study, is the material used to build with, or on that acts in
combination with other forces of nature to make structures and land forms. The material
classified under the field of Geotechnics.

THREE MAJOR CLASSES OF ROCKS

 Igneous rock – is the result from the cooling and hardening of molten rock called
magma that has originated from deep within the earth. Sedimentary rock
 Sedimentary rock – are formed from accumulated deposit of soil particles or remains
of certain organisms that have harden by pressure or cemented by materials.
Metamorphic rock – are rocks resulted from metamorphism due to changes n
temperature, pressure and plastic flow, changing the original rock structure and mineral

composition of the rock..

CATEGORIES OF SOIL
 Residual Soil or Sedimentary Soil – is formed from the weathering of rocks or
accumulation of organic materials remained at the location of their origin.
 Transported Soil – are those materials transported from their place of origin.
• Transportation may result materials remained at the due to the effects of gravity,
wind, water, glaciers of human activity.

WEATHERING
Chemical & Solution Weathering
•Refers to decomposition of rock due to chemical reactions that occur as a result of
exposure to atmosphere, temperature changes, reaction with water or other materials.
•Climate, topography, drainage and vegetative cover have great influences on the
chemical or solution

Mechanical Weathering
•Refers to physical disintegration due to effects of wind, rain, running water or tectonic
forces.
TYPES OF SOIL
1. GRAVEL 2. SAND 3. SILT 4. CLAY
 Gravel and sand are universally known as coarse grain soil because of their individual
particles that are large enough to distinguish without magnification.
 Silt and clay are considered as fine grain soil because of their tiny particles.
o Particles larger than gravel are commonly referred to as cobbles or boulders
o Silt or clay is classified based on the plasticity or non plasticity of the materials.
 Over a varying range of moisture content, clay soil is plastic and sticky. When dried,
possesses strong resistance to crushing. Silt soil has little or no plasticity and when dried
has very little or no strength at all.

CHARACTERISTICS OF SOIL
 It is very common to encounter five to ten or more distinct types of soil along a
kilometer of road. Change of soil types at frequent intervals has become a rule rather
than exemption.
Behavior of soil mass could be determined based on the characteristics of individual soil
particles such as:
1. Grain size
2. Grain shape
3. Surface texture and electrical surface charges, resulted from chemical composition
and molecular structures.

 Regardless of the differences in grain sizes as classified, the common objective is to

establish a basis for relating the particle size to soil behavior.

CHARACTERISTICS OF SOIL
 General Characteristic and Classification of soil particles are enumerated as follows:
a) Gravel consist of rock fragments more or less rounded by water action or abrasion.
b) Fine sand has particles that are more angular than the coarse sand.
c) Coarse sand is usually rounded like gravel with which it is found and generally
contains the same materials.
d) Silt sand is similar to fine sand wit the same mineral composition. They are found as
rock flour in glacial moraines.
e) Clay is plate like, scale like, or rod like in shape as a result of chemical weathering.
Because of their smaller sizes, its performance is influenced by moisture and surface
chemistry.
f) Colloidal clay is a finer clay particle that remains suspended in water and does not
settle under the force of gravity.

CHARACTERISTICS OF SOIL
 For most purposes, coarse grain materials are considered satisfactory construction
material. On the other hand, silts soil will create problems in areas where the ground has
moisture movement due to capillary action.
 Soil that contains clay would be troublesome, making the design and construction
more difficult. As a rule of thumb, soil with clay should not be used to the roadway
surfaces.

CLASSIFICATION FOR SOILS

I. The texture classification of soil depending on the grain size

distribution classified namely:

II. The Unified Soil Classification System, was introduced by the U.S Army
Corps and the Bureau of Reclamations. Letters were used instead of
numbers to designated the different groups. The mechanical analysis and the
liquid and plastic limit tests are the primary classification tools.
This system classifies soils into two broad categories:
1. Coarse-grained soils that are gravelly and sandy in nature with less than 50%
passing through the No. 200 sieve. The group symbols start with prefix of G or S. G
stands for gravel or gravelly soil, and S for sand or sandy soil.
2. Fine-grained soils are 50% or more passing through the No. 200 sieve. The group
symbols start with prefixes of M, which stands for inorganic silt, C for inorganic clay,
or O for organic silts and clays. The symbol Pt is used for peat, muck, and other highly
organic soils.
 Other symbols used for the classification are:
 W-well graded
 P-poorly graded
 L-low plasticity (liquid limit less than 50)
 H-high plasticity (liquid limit more than 50)
 III. American Association of State Highway and Transportation Officials
Classification System
 The AASHTO System of soil classification was developed in 1929 as the Public Road
Administration classification system. It has undergone several revisions, with the present
version proposed by the Committee on Classification of Materials for Subgrades and
Granular Type Roads of the Highway Research Board in 1945 (ASTM designation D-3282;

AASHTO method M145).

COMPOSITION OF SOIL
 Soil deposit consists of solid particles and void spaces between particles, either
partially or completely filled with water. Void spaces not completely filled with water, are
either filled with air or other gases. Therefore, soil deposits are composed of solid, liquid,
and gas.
 Engineers are interested to know the properties of soil deposit, especially, the strength
and compressibility because they are necessary in determining the bearing capacity and
stability of the foundation.

Strength and compressibility of the soil is directly related to:

1. Soil density weight per unit volume
2. Water content of the soil
3. Void ratio
4. Degree of saturation

SOIL REACTION TO DENSITY

 Density of soil is its mass per unit volume. It is sometimes expressed as “Wet Weight”
or the total weight including water. The air volume in the soil substantially decreases as
soil particles become dense when compacted. The most important consideration in
pavement work, is to decrease the moisture content of the coarse grain soil.
 To decrease the moisture content, is to increase the density to improve the physical
properties of the soil. High compaction of the sub-grade and base of the coarse grain
materials is an accepted practice. On the other hand, over compaction of clay with high
affinity of water, may result to big trouble unless confined by superimposed load like the
weight of an over laying fill. This type of materials when compacted will mix on water
and expand resulting to road surface failure.
IN-PLACE DENSITY AND UNIT WEIGHT
 In-place density, refers to the volumetric weight expressed in pound per cubic foot, or
kilo Newton per cubic meter, or mega grams per cubic meter of soil in the undisturbed
condition or compacted fill.
 For coarse grain soil, the higher the density or unit weight, the stronger the shear
strength, and the lesser the tendency to settlement by compression.
 Determination of In Place Density or Unit weight is made on borrow pit soils to
determine the shrinkage volume or swell result as the soil is transported and compacted
at the fill location. The standard practice is to test the in-place density of the soil after
dumping on site, to determine whether, compaction is necessary.
RELATIVE DENSITY
 For granular soil, the shear strength and resistance to compression are related to the
density of the soil. Higher strength and resistance to compression are developed by the
soil when it is dense, or compact condition, than when it is in a loose condition. In a
dense condition, the soil void ratio is low and high on loose condition.