Types of soil, properties & uses in construction, here we described types of soil based on quality, size and moisture their properties and uses for construction and plantation.
What is Soil
Soil is a natural powder of rocks which may contain air, water, and any other substance laying there and which are used for construction and plantation purpose.
Types of Soil Based on Quality
There are six types of soil based on its quality.
- Clayey soil
- Sandy soil
- Silty soil
- Loamy soil
- Peaty soil
- Chalky soil
1. Clayey Soil
This type of soil gives the lumpy and sticky feel in wet condition.
In the dry condition, it converts into a hard rock soil.
The best soil for plantation because of its nutrients.
It is tough to drain clay particles from the soil.
2. Sandy Soil
This type of soil is easy to drain.
It get dry quickly because of its more air content.
Not good for plantation, lack of nutrients.
3. Silty Soil
This type of soil is easy to drain and smooth in touch.
It’s easy to cultivate than clayey soil.
Easy to drain.
Good for plantation but not like clayey soil.
4. Loamy Soil
This type of soil is easy to cultivate and full of nutrients.
It’s easy to drain and retains moisture.
5. Peaty Soil
This type of soil is good for plantation.
It contains a higher amount of organic matter but fewer nutrients.
6. Chalky Soil
This type of soil contains overlays chalk and limestone bedrock.
It’s easy to drain.
It’s not good for plantation.
Types of Soil (Classification of Soil)
Basically, the soil types or classification are done into the following two groups.
- General or engineering classification
- Geological classification
General or Engineering Types of Soil (based on Size)
The soil is classified in the following way from engineering points of view.
- Fine-grained soil
- Coarse-grained soil
- Organic soil
1. Fine-Grained Soil
It is soil-like silt or clay having the size of particle less than 0.075 mm. Some particle of these soil is not visible to the eye and the soil is impermeable it is also called as cohesive soil.
2. Coarse-Grained Soil
It is soil like sand or gravel having particle sizes between 0.075 mm to 4.75 mm. There is no cohesion between soil particle and the soil is permeable it is also called cohesionless soil granular soil.
3. Organic Soil
It is the soil containing organic materials such as decomposed remains of plants and animals the soil is consecrated in top 50 mm to 300 mm layer of the soil this soil is acidic spongy and undergo considerable change volume in the presence of water and pressure the soil is not suitable for civil engineering works.
Geological classification is based on the source of the material and the manner in which it was brought to its present position.
On a geological basis, the soil can be classified into two groups.
- Residual soils
- Transported soils
Soils that remain at the place of the disintegration of parent rock are called residual soil. Igneous rock such as granite or basalt and sedimentary rocks like sandstone, shale or limestone are the parent material for residual soil.
Soils which carried away from there place of disintegration to some other place by transporting agencies are called transported soil.
The different transporting agencies are water, wind, ice, and gravity.
The soil can be further sub-classified into different types.
Types of Soil (Based on Moisture)
On the basis of moisture content or water content available in the soil can be classified into the following three groups.
- Partially saturated soil
- Fully saturated soil
- Dry soil
1. Partially Saturated Soil
The soil in which voids are partly filled water and partly with air is called partially saturated soil. The soil contents all the three constituents of soil i.e. soil particles ( solid ), air and water in its natural form.
2. Fully Saturated Soil
The soil voids are completely filled with water is called fully saturated the soil. This soil contains only two constituents of soil namely particles ( solid ) and water.
3. Dry Soil
The soil in which voids are filled with air is called dry soil. This soil contains only two constituents of soil namely soil particles ( solid ) and air. The dry soil in its natural form and two phases diagram the dry soil.
The soil profile is the vertical section of a soil mass, showing the nature and sequence of the various layers as developed by deposition or weathering or both.
The soil profile is said to be simple or regular. If the boundaries between different layers of soil is more or less parallel. The soil profile is called erratic if the boundaries between soil layers are irregular.
The soil profile represents the alternates n the original deposit of soil materials that have been brought about by the weathering agencies. Therefore the soil profile is also termed as weathering profile.
A soil horizon is a name given to different layers of soil in a soil profile, depending on the properties and depth of the layers. The major classification of soil horizon is termed as A. B. C. D. the sub-classification of the major horizon is termed as A1, A2, A3…. B1, B2, B3, B4 etc.
1. A Horizon
The upper layer of the soil profile is called A horizon or topsoil or surface soil. It has the same color and texture throughout its depth. The thickness of a horizon is very between 50 mm to 600 mm. As this soil is of organic nature, it is not suitable for engineering purposes.
2. B Horizon
The subsoil immediately below a horizon is called B horizon or subsoil. It has a different color than a horizon. It has the same color and texture through its depth. The thickness of this layer is between 100 mm to 2400 mm. This horizon is important for the shallow foundations.
3. C Horizon
The un-weathered parent material lying below B horizon is called C horizon. It has the same color and texture through its depth. The thickness of this horizon varies from 50 mm to 300 mm. This horizon provides built material for the construction of soil structures such as dams.
4. D Horizon
The layer below C horizon is termed as D horizon. The horizon consists of solids rock gravel or clay. The depth of D horizon cannot be determined. This layer is in its original condition for formation.
Construction of Soil Profiles and its Uses
For the construction of the soil profile of an area boring are made on the area at known intervals and all the necessary boring data’s are collected. These boring are represented by vertical lines to scale and spacing of boring are also shown to scale.
Along each boring line the separate soil layer, it indicated clearly by points. The points of the same soil layer are different boring lines that are connected by a smooth curve to show the most likely stratification.
The arrangement of various layers between the boring may differ considerably if the soil conditions are erratic, irregular and disturbed, etc. The groundwater table WT and the foundation level of the proposed structure should also be indicated on the soil profile.
The soil profile becomes further helpful if the essential engineering data such as the unconfined compressive. Strength of penetration resistance, permeability, shear strength, etc. is indicated on the soil profile.
The soil profile is useful to engineering for the following purpose.
Soil profile gives
- subsoil data graphically.
- changes in properties of soil with reference to depth.
- useful data for the design foundation.
- the volume of materials of different properties which is available below ground level and which can be used for engineering.
Construction of Soil
The soil has three constituents namely soil particles solid, air and water. These three constituents are blended together to form a complex material. This complex material is called soil. The space occupied by air and water in a soil mass is termed as voids in the soil mass.
The diagram which represents the three constituents of soil, air, solid and water separately in a graphical form is called a phase diagram. Phase diagram calculation works simple and it can be classified as two phases and three-phase diagram.
Particles Size Distribution
Particle Size Classification
The process of classifying a given soil sample according to the particle size is termed as size classification.
Texture of Soil
It is defined as the percentage of three main fractions i.e. sand, silt and clay present in the soil.
Particle Size Analysis
The process of determining the texture component of the soil is called as particle size analysis or mechanical analysis. It is also defined as the process of finding the percentage of various sizes of particles in the soil.
There is two methods used to sieve analysis of soil.
a) Sieve analysis
b) Wet sieve analysis
The screening process of separating the coarser and finer fraction of soil is called sieve analysis.
The procedure of this test is given below –
- Take 300 to 400 grams of soil.
- IS sieve usually used are 40, 20, 10, 4.75, 2, 1 mm and 600, 300, 150, 75 microns.
- Arrange sieves in order of their mesh openings. Largest sieve should keep at the top and the smallest at the bottom. A cover is provided at the top and a receiver is kept at the bottom.
- Put the soil sample on the top sieve.
- Fit the whole assembly on the sieve shaking machine or do it manually.
- Shaken the assembly for 10 to 20 minutes.
- Find the weight of the portion of the soil retained in each sieve.
- percentage of portion retained on each sieve is given by P1 = W1 / W * 100, where W1 is weight retained on that sieve, W is the total weight of the sample.
- Percentage of soil sample passing through each sieve is given by PS1 = 100 – P1, PS2 = 100 – ( P1 + P2 ), PS3 = 100 – ( P1 + P3 ) etc.
- Represent the result as a graph between size and percentage passing on a semi-logarithmic graph paper.
Wet Sieve Analysis ( Sedimentation Analysis )
In wet sieve analysis procedure the soil sample finer than 75 microns is kept in water and the analysis is based on stoke law. Stoke law says that the velocity at which soil grains settle in a suspension depends on the sieve wet and size of the grain if all other factors are kept consent.
In the usual analysis, it is assumed that the soil particles are spherical and have the same specific gravity that is average specific gravity. Thus it is clear that the water that coarser particles of soil will settle more quickly than the finer ones.
The sedimentation analysis is done either with the help of a hydrometer or a pipette in both method equations based on stokes law or used to find the percentage of finer material in the sample.
Particle Size Distribution Curve
The result of particle size analysis or mechanical analysis is plotted on a logarithmic scale. A particle size distribution curve gives an idea about the type and gradation of the soil. A curve placed higher up on to the left represents a fine-grained soil while a curve placed to the right represents coarse-grained soil.
A soil is said to be well graded if it has a good representation of particles of all sizes. A soil is poorly graded or uniformly graded if it has an excess of certain particles and deficiency of others, or it as most of the particles of about the same size.
Size D 10 is called the effective size or effective diameter of soil. The detain represent the size in mm such that 10 % of the particles are final than that size.
The coefficient of uniformity or uniformity coefficient is a measure of particle size range is given by the ratio of D 60 and D 10 size.
IWCU = D 60 / D 10
Cu = coefficient of uniformity
D 60 = The size in mm such that 60 % of the particle are finer than the size.
D 10 = The size in mm such that 10 % of the particle
Coefficient of curvature represents the shape of the particle size curve is given by
Cc = (D30) / D10 * D60
D10, D30, D60 = same as above and
Cc = coefficient of curvature
Cu = one for uniformly graded soil
Cu > 4 for gravels
Cu < 6 for sands
Cc = 1 to 3 for well-graded soil
The property of the soil material which is inclined its resistance to flow is called consistency. This term is mostly used for fine-grained soils such as clay, silt etc.
States of Fine-Grained Soil
Fine-grained soils can exist it may one of the following states
- Liquid state
- Plastic state
- Semi-solid state
1. Liquid State
A fine-grained soil mixed with a large quantity of water is said to be a liquid state. In this state, the solid does not offer any resistance so deformation.
2. Plastic State
A fine-grained soil mixed with water to such an extent that the shape of the soil can be changed without producing surface cracks. Then the state of the soil is said to be in the plastic state. In this state, the soil offers resistance to deformation.
3. Semi-Solid State
When the moisture contained in a fine-grained soil is reduced to such an extent that cracks start forming on the surface of the soil. Then the soil is said to be in a semi-solid state. In this state, the soil loses plasticity.
4. Solid State
When the moisture contain is further reduced to such an extent that no further change in volume takes place in the clay soil mass that is no shrinkage takes place. The soil is said to be in solid-state. The color of the soil change in this state and the soil takes on a lighter shade.
Plasticity of Soil
It is the property of soil which enables the material to suffer deformation without cracks and noticeable elastic recovery.
Consistency Limit of Soil
The percentage of moisture contents at which the soil passes from one state to another are called the consistency limit. These limits are helpful in classifying the soil and to find its suitability for various civil engineering work.
The consistency limits are called as atterberg limits.
Atterberg limits are three and described below.
1. Liquid Limit
Liquid limit is the state between liquid and plastic state of soil and It’s also defined as the minimum moisture content at which the soil is still in liquid state but has a small shear strength or resistance against flowing. It is found by conducting liquid limit test.
It is the boundary ( state ) between the plastic and semi-solid state of the soil. The minimum moisture content at which the soil can be rolled into 3 mm thread without showing any sign of cracks is the plastic limit. It can be found by conducting plastic limit test.
3. Shrinkage Limit
It is the boundary between the semi-solid and solid-state of soil. It is also defined as the maximum moisture content at which a reduction in water content will not cause a decrease in the volume of the soil mass.
PI = LL – PL
plasticity index measures plasticity classifies the fine-grained soils according to their plastic behavior.
Bearing Capacity of Soil
For any structure, the best foundation bed available on earth is a hard rock bed because it can withstand very heavy loads safely.
However, the hard rock beds are not available everywhere and therefore many times the foundation of the structure has to placed soil beds. In such cases the stress and settlement of soil below foundation should be within safe limits to avoid foundation failures to achieve this knowledge of bearing capacity of the soil is very essential.
Some important terms used in foundation engineering are defined below.
Foundation is that part of a structure which in direct contact with the ground and which transmits the load from the structure to the ground.
A footing is a portion of the foundation of a structure that transmits loads directly to the soil.
It is the supporting foundation that carries the load from the foundation.
The property of soil or rock support load or them is called as bearing capacity. Different types of bearing capacities are defined below.
The maximum unit pressure that soil can stand without shear failure or without excessive settlement of the structure is called the ultimate bearing capacity of the soil. This is also called as ultimate bearing value or ultimate soil pressure.
When the term bearing capacity is used without any prefix. It can be understood to be the ultimate bearing capacity of the soil.
2. Safe Bearing Capacity
The maximum pressure which the soil can carry safely without any risk of shear failure is called as safe bearing capacity of the soil. It can be calculated by dividing the ultimate bearing capacity by a number called a factor of safety.
The value of factor of safety depends on the important and kind of structure to be constructed and it usually took between 2 to 5.
The design of foundations is carried out by using the values of the safe bearing capacity of the soil.
Surface Compaction Of Soil
1. Compaction of Soil
The process of increasing the dry density of soil by artificially rearranging packing the soil particles together into a closed state of the contract under dynamic loads is called compaction of soil is a rapid process and can be achieved by rolling, tamping or vibrations.
Compaction of soil is an important process as it helps to give certain desirable physical properties to the soil for proper behavior of soil under loads.
The compaction of soil is important for the following purpose:
a) To increase the density, bearing capacity and shear strength of the soil.
b) To reduce permeability and absorption of soil.
c) To decrease settlement and movement of soil under loads.
2. Consolidation of Soil
The process of gradual removal of water from pores of saturated soil by pressure which acts for a long period is called consolidation of soil.
Consolidation is a slower process of decreasing the volume of a soil mass, whereas compaction is a quicker process of reducing the volume of a soil mass by dynamic loading, when a load is applied or increased in a soil which is not fully saturated a comparatively sudden reduction in the volume of the soil occurs, which is mainly due to expulsion and compression of air in the voids.
The phenomenon is termed as initial consolidation. If the equilibrium is not attained after initial consolidation, further reduction in volume which is mainly due to squeezing out of water forms the voids.
The deduction of volume consolidation, thus for a partially saturated soil initial consolidation process primary consideration. Even after the reduction of all excess hydrostatic pressure to zero for after removal of all pore water.
3. Compressibility of Soil
The decrease in the volume of a soil mass under pressure is known as compression. The property of soil to decrease in volume under pressure is called compressibility and is indicated by the change in volume of a soil per unit increase of pressure.
4. Settlement of Soil
The downward displacement of soil due to a decrease in the volume of voids is called settlement. If the contact pressure at the base of the footing on the sol is uniform, the settlements may be uniform and tolerable provided the structure can withstand such settlements.
Non-uniform or differential settlement of a structure may be disastrous, leading to cracking, damaging rigidly and eventually the structure may collapse.
The term differential settlement is used when some parts of a structure settle more than others. Uniforms settlement is the settlement that is brought about when the entire structure under uniform pressure distribution in a uniform homogeneous soil structure settles every without causing additional stresses in the structure.
Some of the main factors causing settlement of soil are listed below:
a) Static loads on the soil.
b) Dynamic loads on soil such as vibrations etc.
c) Fluctuation in the elevation of the ground water table.
d) Settlement due to excavation.
e) Mining operations, tunnel construction, and underground erosion.
f) Freezing and thawing of the soil.
Important Points for Students
1. Soil Mechanics
The branch of physical science which deals with properties nature and performance of soil as construction and foundation material is called soil mechanics.
The purpose of soil mechanics is to replaced the empirical methods by scientific methods for design foundation and earthen structures. It also called as Geo technique.
2. Soil Engineering
Soil mechanics applied to engineer problems is called soil engineering.
3. Foundation Engineering
The branch of engineering which deals with study design construction and maintenance of foundations of buildings and engineering structure is called foundation engineering.
4. Importance of Soil Mechanics
The knowledge of soil mechanics is useful for following major purpose is in civil engineering.
Investigation design and construction of
- the foundation for different structures.
- highway and runway pavement.
- embankments and excavation.
- underground and earth retaining structures.