Classification Of Soil (autosaved).docx

CLASSIFICATION OF SOIL ACCORDING TO MODE OF FORMATION Purpose of Soil Classification; Soil classification systems are established to help people predict soil behaviour and to provide a common language for soil scientists. The National Cooperative Soil Survey and the USDA developed the Soil Taxonomy classification system, which is used worldwide.

Here is the classification of soil SOIL

Residual soil

Organic soil

Marine soil

Glacial soil

Pyroclastic soil

1. Residual soil Definition The soil that is remaining after the soluble elements have been dissolved and the part of the earth's surface consisting of humus and disintegrated rock. Properties and characteristics; Residual soils are products of chemical weathering and thus their characteristics are dependent upon environmental factors of climate, parent material, topography and drainage, and age. These conditions are optimized in the tropics where well‐drained regions produce reddish lateritic soils rich in iron and aluminum sesquioxides and kaolinitic clays. Conversely, poorly drained areas tend towards montmorillonitic expansive black clays. Andosols develop over volcanic ash and rock regions and are rich in allophane (amorphous silica) and metastable halloysite. The geological origins greatly affect the resulting engineering characteristics. Both lateritic soils and andosols are susceptible to property

changes upon drying, and exhibit compaction and strength properties not indicative of their classification limits. The degree of weathering of the residual soils from the Bukit Timah granitic formation appeared to be reasonably uniform, decreasing only gradually with increasing depth. The degree of weathering of the residual soils from the sedimentary Jurong formation was variable, normally dependent on the parent rock types such as mudstone, siltstone and limestone. The results of the analysis of index properties, engineering properties, SEM and porosimetry tests indicated that the variation in the properties of the residual soils at different depths was largely influenced by the pore-size distributions that vary in accordance with the degree of weathering. A higher degree of weathering would result in a higher pore volume and a larger range of pore-size distribution. It is therefore possible to use the variation in the pore volume and the pore-size distribution through a weathered profile as an indication of the variation in the degree of weathering with depth.

The Jurong formation covers the south, southwest and west of Singapore, with a variety of sharply folded sedimentary rocks, including conglomerate, sandstone, shale, mudstone, limestone and dolomite. It was deposited during late Triassic to early or mid-Jurassic. The formation has been severely folded and faulted in the past as a result of tectonic movement.

The geology of Singapore consists of four main formations: (a) igneous rocks consisting of the Bukit Timah granite and the Gombak norite, occupying the north and central-north region; (b) sedimentary rocks of the Jurong formation, occupying the west and southwest region; (c) Quarternary deposit of the Old Alluvium in the eastern region; and (d) recent alluvial deposits of the Kallang formation, distributed throughout the island

Table of Loss on ignition (LOI) results of residual soils from Singapore Depth (m)

Degree of weathering

Soil type

Loss on ignitiona

Bukit Timah granitic formation 4–5

Grade VI

Sandy silt

4.8%

8.5–9.5

Grade VI

Sandy silt

5.1%

14–15

Grade V

Silty sand

2.0%

Jurong sedimentary formation 2–3

Grade IV

Silty sand

0.5%

7.5–8.5

Grade IV

Silty sand

1.1%

14–15

Grade IV

Silty sand

0.9%

25.5–26.2

Grade III

Silty sand

0.8%

Effect of weathering on index propertie; Index property test results indicated that as weathering extends to greater depths, appreciable variations in particle size distribution, specific gravity, natural water content, total density, liquid and plastic limits are observed. Total density and void ratio; Weathering leads to a porous structure due to the considerable leaching of minerals from the soil. Water and air replace the soluble minerals resulting in a porous structure. In the upper layers of residual soils, porosity and void ratio are higher, therefore the water and air phases

occupy more space compared to the lower layers. As a result, total density is lower near the surface. At greater depths porosity decreases, resulting in an increase in total density. Therefore, the variation in total density as well as the variation in dry density reflects the variation in the degree of weathering. The total density of the residual soils from the Bukit Timah granitic formation ranged from 1.6 to 2.0 Mg/m3 with increasing depth.

Effect of weathering on pore-size distribution; The effect of weathering on micropore size was assessed using mercury intrusion porosimetry tests. The relationship between cumulative pore volume and mean micropore diameter for residual soils from different depth in the Bukit Timah granitic and Jurong sedimentary formations is shown in fig given below;

2. Organic soil Organic Soil and Amendments. Organic soilscontain organic matter that is rich in many nutrients and minerals. The scientific definition of organic soilis "Of, relating to, or derived from living matter."Organic soil consists of decaying plant material, microorganisms, worms, and many other things.

One way that may be easier to think about it is to substitute the word “organic” for the word “living.” Organic soil is a soil that is created by the decomposition of plant and animal materials to create a nutrient and mineral rich mini-ecosystem with microorganisms that feed and breathe life back into the soil. Or, to put it another way, organic soil is how soil exists in nature. Before chemicals were added. Before synthetic and modified ingredients depleted the soil of its natural power, this is how soil existed. Think of the forest floor. Leaves and trees fall, fruits and vegetables grow and are eaten, animals feed and leave waste. All of this activity directly impacts the soil and creates a power-packed foundation for future growth. It creates a soil that is “living.”

Benefits; There are quite a lot actually. The most obvious one is the environmentally friendly aspect of it. Using organic soil is using a soil that is made up of all natural ingredients. Simply put, it is putting soil made from the environment, back into the environment. That creates soil sustainability that over time continues to further enrich your soil. More lush, healthier plants, fruits and vegetables that are safe for you and your family and safe for the environment. Because organic soil is composed of nutrient and mineral rich elements, your plants will grow stronger cell wells, giving them added layers of protection from pests and disease. This eliminates the need to buy chemical heavy pesticides that introduce synthetic elements to your plants. The nutrients in organic soils also provide a natural protection making plants more resistant to diseases. All of this adds up to stronger pest and diseases resistant plants that save

you from having to spend more to keep them healthy. Adding organic material to native soil helps contribute to the balance of drainage and retention of water. In most cases organic material helps keep water in the soil longer than synthetic soils. This means that what you are growing will have better access to the water it needs and that translates to less frequent watering. Organic fertilizer; As nutrient packed as organic soils are, plants still need fertilizer. Nitrogen deficiency is one of the major causes for plants to shrivel up and turn yellow. This can easily be solved by introducing a fertilizer regimen. When growing fruits and vegetables, which are notorious for being heavy feeders, make sure you add an organic fertilizer to your soil at the time of planting to ensure success. Physical properties of organic soils; Soil and peats are greatly dependent to a large degree on porosity and pore-size distribution. These in turn are related to particle-size distribution. Naturally, peat has very high natural water content due to its natural water-holding capacity. These soils include organic matters as shown;

Organic soils occupy less than 1% of the world’s land area. Generally, in these soils, organic

.matter content is more than 20%. In fact, Organic soils may hold 200 – 400% of its own dry weight in water. On the basis of stage of breakdown of original plant materials, organic soils have been classified into following two groups: 1. Peat soil: Organic soils, which have slightly decayed or non-decayed plant materials are called peat soils. In peat soils, original plant deposits can be identified, especially in the upper horizons. Peat soils are coarse textured or fine- textured depending on the nature of deposited plant residues. 2. Muck soil: Organic soils having markedly decomposed original materials are termed as muck soil. Muck soils are usually fine- textured because of well decomposition of original plant deposits. In the comprehensive Soil Taxonomy classification system, organic soils are identified as the order Histosols. Characteristics of Organic (Peat and Muck) Soils: (A) Physical Characteristics: (i) Colour: The colour of cultivated organic soils is dark brown to deep black. (ii) Bulk density: The bulk density of organic soils is quite low in comparison to mineral soils. Bulk density of well composed organic soil is only 0.20-0.30 compared to 1.3-1.5 for mineral soils. Thus, organic soils are light weight when dry. (iii) Soil structure: The surface layer of organic soils are granular or crumby. Its cohesion and plasticity are low compared to mineral soils. Organic soils are therefore, porous, open and easy to cultivate. (iv) Water-holding capacity: Compared to mineral soils, organic soils having high water-holding capacity. Therefore, a given layer of organic soil at optimum moisture will supply only slightly more water to plants than a comparable mineral soil.

B) Chemical Characteristics: (i) Cation exchange capacity: Cation exchange capacity of organic colloids are higher than those for the inorganic colloids (Table 11.1).

(ii) Soil pH: pH of an organic soil at a given percentage base saturation is generally lower than that of a representative mineral soil. Organic soils are highly acidic with a pH value less than 5.5. (iii) Buffering capacity: Histosols have a higher buffering capacity than mineral soils. (iv) Carbon-Nitrogen ratio: The representative organic soil possesses a high carbon-nitrogen ratio (20:1) compared to 12:1 for a representative mineral soil. Even so organic soils show vigorous nitrification (nitrate release) in spite of their high C/N ratio. Apparently some of the carbon in peats is very resistant to microbial attack and is not readily usable by general purpose decay organisms. Consequently, these organisms are not excessively encouraged, and they do not tie up the nitrates. (v) Availability of nutrients in organic soils. Nitrogen. Nitrogen content in organic soils are high in comparison with a mineral soil.

Characteristics of organic soil; Parent Material: Organic soils are formed by the accumulation of partially decomposed organic matter. Physical Traits: These soils are dark in colour, lightweight, and high weight.

3. Marine soil; Marine deposits are sediments that accumulate in a marine (ocean or sea) environment. These sediments are later exposed and subjected to soil development because either the ocean floor was uplifted or the water receded. Marine deposits are predominantly of clay size (occasionally may contain some shells), very well sorted, devoid of coarse particles, and usually unstratified (show no layers). In addition, some species also colonize the rhizosphere of plant roots and even plant tissues. They have evolved complex morphological and physiological responses enabling them to adapt to large changes in their environments, for example adjusting to climatic variation or competition from other organisms inhabiting the same niche. In a similar manner to a filamentous fungus, they colonize the particulate environment of the soil by growing branching multigenomic hyphae that form a ramifying network in order to exploit a localized nutrient source. As saprophytes, they are responsible for the breakdown of complex biological polymers and, consequently, for carbon and nitrogen turnover. The spores can then be dispersed by physical agents or the activities of motile animals inhabiting the same niche. The streptomycetes produce an unparalleled diversity of bioactive secondary metabolites that have been exploited in medicine and agriculture as antibiotics, anti-cancer agents, immunosuppressants and pesticides.

System Technology and Science The seismic refraction methods have been used for many years as an exploration reconnaissance tool and for civil engineering applications on land. In recent years, the technique has been applied with great success to shallow marine soil investigations. A seismic source at the seabed is used to induce an acoustic pressure wave into the soil. Typically, in shallow water, an air gun is used but for deepwater operation, a mechanical percussion device provides a better option. As the pressure wave passes through the soil layers, some of its energy is refracted along sedimentary boundaries before returning to the soil surface where it is picked up by a hydrophone streamer. The length of the streamer and the number of hydrophones determines the depth of recorded penetration and the resolution of the information – the longer the streamer the greater the depth of penetration recorded but the lower is the resolution. For detailed imaging of the topmost 3–5 m, a typical streamer is 24–30 m in length containing some 48 hydrophones. Marine biome; The soil in the ocean has some of the richest soil for plants to grow. There are Sand, kelp, mud, small pieces of coral in the soil. The kelp and Phytoplankton make about 50% of our oxygen. Marine clay; It is a type of clay found in coastal regions around the world. In the northern, deglaciated regions, it can sometimes be quick clay, which is notorious for being involved in landslides. Marine clay is a particle of soil that is dedicated to a particle size class, this is usually associated with USDA’s classification with sand at 0.05mm, silt at 0.05-.002mm and clay being less than 0.002 mm in diameter. Paired with the fact this size of particle was deposited within a marine system involving the erosion and transportation of the clay into the ocean. Soil particles become suspended when in a solution with water, with sand being affected by the force of gravity first with suspended silt and clay still floating in solution. This is also known as turbidity, in which floating soil particles create a murky brown color to a water solution. These clay particles are then transferred to the abyssal plain in which they are deposited in high percentages of clay. A soil is only considered a clay if it has above 55% total clay content. This is due to the way in which the clay reacts to things like water, heat and other chemicals. Once the clay is deposited on the ocean floor it can change its structure through a process

known as flocculation, process by which fine particulates are caused to clump together or floc. These can be either edge to edge flocculation or edge to face flocculation. Relating to individual clay particles interacting with each other. Clays can also be aggregated or shifted in their structure besides being flocculated.

Characteristics of marine soil; A comprehensive study on the geotechnical characteristics of marine soils deposited across the world has been done. One of the distinguishing features of this study is that all the soil samples used in this study were recovered by using a single type of sampling technique (by following the Japanese standard sampling method), and all the samples were transported to and tested in a single laboratory under the guidance and supervision of the author. Thus, it is considered that all data obtained in this study are free from differences in sample quality as well as testing method and subjectivity of interpretation. Many established empirical relations, especially relations to the plasticity index ( Ip), were carefully examined using the soil data obtained in this study.

4. Glacial soil; Soil composed of boulder clays, moraines, etc., which were formed by the action of ice during the Pleistocene age. Early stages of soil formation; Strip-mining and the construction of spoil banks composed of unweathered, clay loam textured, moderately calcareous glacial till has provided a model system for studying soil formation in the semi-arid grasslands of southern Saskatchewan. Revegetation of fresh spoils probably occurred within a year or two and includes many native and introduced grasses and herbs. On spoil banks 28–40 years old soluble salts, particularly sodium salts, had leached to considerable depth. Greater soluble cation contents in the surface horizons, as compared to 2.5–5 or 5–10-cm layers, indicated a cycling of these nutrients by vegetation. Nitrogen has accumulated at a rate of 2.43 ± 0.12g/m2/yr, organic carbon at a rate of 28.2 ± 4g/m2/yr, suggesting that organic-matter levels characteristic of regional soils could be accumulated in 250–350 years. Cation-exchange capacities increased with the accumulation of organic matter. The fractional composition and spectral properties of humic acids indicated that the humus of soils 28 years old was similar to that of the normal, regional soils. Carbonate weathering appears to be quite slow in grassland environments.

Characteristics of glacial soil; A large volume of geological literature exists on glacial soils, which are common throughout the world's temperate zone. In the UK they account for some 60% of all soils and globally 10%. There is little published information on geotechnical characteristics despite the number of ground investigations. Glacial soils can vary from deformed basal layers that retain many of the original features of those layers to unsorted mixtures of gravel, sands, silts and clays to

laminated clays. They can be deposited through a process of pressure and shear beneath a glacier as it advances, or be deposited when the ice melts. This creates a spatially variable soil which contains features that impact on the mass behaviour and lead to wide variation in results from a single source of glacial soil, making the selection of design parameters difficult. Routine sampling may not pick up these features. Tills are deposited in such a way that their characteristics do not necessarily conform to soil mechanics theory and empirical relationships created from studies of gravitationally compacted soils. Hence developing the ground model depends on knowledge of the genetic classification, creating a regional database to enhance data from new investigations, tests on reconstituted tills and a consistent framework to evaluate the mechanical characteristics.

Glacial till; Till or glacial till is unsorted glacial sediment. Till is derived from the erosion and entrainment of material by the moving ice of a glacier. It is deposited some distance down-ice to form terminal, lateral, medial and ground moraines.

PROPERTIES AND CHARACTERISTICS OF GLACIAL TILL The following are the general properties of glacial till: 

They are dense and stiff, and this density and stiffness is a function of the mode of transportation rather than the process of consolidation.

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Ablation deposits within lodgment/deformation till contain less dense and softer material. The degree of consolidation depends on drainage profile and stiffness of underlying soils.

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They behave as a 'drained' material because of the stiffness even though they have low permeability. Glaciers are extremely effective at eroding and transporting these materials and everything from clay- to boulder-sized particles are moved as one large mass. As a result, ground-up bedrock, plant fragments, and even animal remains can be found in glacial till. Over time, with the process of erosion and weathering, the components break down to form soil that is very rich in minerals, which can be turned into a high-grade farmland.

Lateral Moraines- These consist of rock debris and sediments that have been loosened from the walls beside a valley glacier and have been built up in ridges along the sides of it. Medial Moraines- These are long ridges of till that result when lateral moraines come together as two tributary glaciers and merge to form a single glacier. As more tributary glaciers join the main body of ice, a series of roughly parallel medial moraines develop on the surface of main glacier. End Moraines- This is a large, crescent-shaped pile of till that builds up at the end of a glacier. This is further divided into: Terminal Moraine: It is the ridge of till that marks the farthest advance of the glacier before it starts to recede. Recessional Moraine: It develops at the front of the receding glacier, and a series of such moraines mark the path of a retreating glacier.

Ground Moraines- This is the thin, widespread layer of till that is deposited across the surface as an ice sheet melts. Varve It consists of one light‐colored bed and one dark‐colored bed that represent a single year's deposition. The light‐colored layer is mainly silt that was deposited rapidly during summer, and the dark layer consists of clay and organic material that was formed during the winter. The age of a glacial lake can be determined from the number of varves that have formed at the bottom of the lake.

Eskers These are the long, winding ridges of outwash that are deposited in streams flowing through ice caves and tunnels at the base of the glacier. They are generally well sorted and cross‐ bedded, and as such, esker sands and gravels eventually choke off the waterway. Kettle and Kettle Lakes Sometimes, the rapid buildup of sediments can bury isolated blocks of ice. When this ice melts, the resulting depression is called a kettle. Kettle lakes are bodies of water that occupy such kettles.

5. Transported soil; Transported soils form from weathered material deposits, which are transported by natural forces to a new site, away from the site of origin. The type of transport soil is determined by the agent, such as wind, water, ice or snow, that assists in its transportation.

Properties of transported soil; 

Water-transported Soil. Swift-running water is capable of moving a considerable volume of soil.

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Glacial Deposits. Compaction and re-crystallization of snow lead to the formation of glaciers.

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Wind-transported Soils. ...

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Gravity Deposits.

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Swamp and Marsh Deposits. Characteristics of transported soil; Transported soils form from weathered material deposits, which are transported by natural forces to a new site, away from the site of origin. The type of transport soil is determined by the agent, such as wind, water, ice or snow, that assists in its transportation. Several types of transported soils exists, including colluvial, alluvial, glacial and aeolian. Colluvial soil is transported by gravity. Alluvial soil is moved by running water. Glacial soil is formed from the interaction of ice and snow. Heavy ice masses push glacial soils from one place to another. Aeolian soil is moved by wind. This soil can be classified into dunes or loess. Transported soils form from weathered material deposits, which are transported by natural forces to a new site, away from the site of origin. The type of transport soil is determined by

the agent, such as wind, water, ice or snow, that assists in its transportation. 2. Aeolian soil; Eolian (or aeolian) sediments are wind deposited materials that consist primarily of sand or silt-sized particles. Eolian (or aeolian) sediments are wind deposited materials that consist primarily of sand or silt-sized particles. These materials tend to be extremely well sorted and free of coarse fragments. Some rounding and frosting of mineral grains is detectable. Aeolian environment The term loess (meaning “crumbly” in German) is used to describe silt textured eolian material. Loess can be interpreted as an accumulation of wind-blown dust, usually of glacial origin. Typically it has no horizontal stratification, but occurs in a single massive layer. A large proportion of the material may consist of fresh, sharp-cornered particles of silicate minerals such as feldspars, quartz, and mica that make it light brown or yellow in color. Loess has a small amount of clay, so it is not sticky but rather slippery sediment. A very high angle of repose of this sediment allows it to erode into very steep slopes or cliffs. The central and northwestern areas of the United States, Ukraine, eastern China, and eastern and central Europe all have significant deposits of loess. Agriculture has thrived in these areas since prehistoric humans took advantage of the rich soil to grow crops. The central and northwestern areas of the United States, Ukraine, eastern China, and eastern and central Europe all have significant deposits of loess. Agriculture has thrived in these areas since prehistoric humans took advantage of the rich soil to grow crops.

DIFFERENCE BETWEEN RESIDUAL SOIL AND TRANSPORTED SOIL; Transported soil is blown or washed away from its parent rock.Soil that remains at the place of formation is called residual soil. It is usually formed from chemical or physical weathering and eventually covers the parent rock. the characteristics of residual soil depends on the that of the parent rock.