Module 2 - Soil Formation, Structure, and Classification in Soil Mechanics

Weathering Process

The process of breaking down rocks into smaller pieces.

Mechanical Weathering and Chemical Weathering

Two main types of weathering.

Quartz

Which mineral is more resistant to weathering?

Clay minerals such as illite, kaolinite, and montmorillonite.

Secondary products of weathering that can form from stable minerals.

Soil Formation

The process whereby water-soluble parts in the soil are dissolved and washed out by rainfall or percolating subsurface water.

Soil Profile

A natural succession of zones or strata below the ground surface, altered by weathering processes.

Transported Soil

Soils that are moved by physical processes to other locations.

Lacustrine soils, Alluvial or fluvial soils, Glacial soils, Aeolian soils, Marine soils.

Types of Transported Soil

Residual Soil

Soils that remain where they were formed and cover the rock surface from which they derive.

Organic Soil

Soils formed from decomposed aquatic plants in coastal areas and glaciated regions.

Classification of coarse-grained soils based on grain size.

Soils with an average grain size greater than 0.075 mm, such as gravels and sands.

Classification of fine-grained soils based on grain size.

Soils with an average grain size less than 0.075 mm, such as silts and clays.

Cohesion, which is bonding caused by intermolecular attraction.

What property do fine-grained soils exhibit that coarse-grained soils do not?

Bentonite

A soil designation for decomposed volcanic ash containing a high percentage of montmorillonite, known for high shrinkage and swelling.

Black Cotton Soil

A black soil with a high percentage of montmorillonite and colloidal material, also known for high shrinkage and swelling.

Boulder Clay

Glacial clay containing all sizes of rock fragments, also referred to as 'Glacial till'.

Caliche

A soil conglomerate of gravel, sand, and clay cemented by calcium carbonate.

Hard pan

Densely cemented soil that remains hard when wet, often found in boulder clays or glacial tills.

Laterite

A deep brown soil with a cellular structure that hardens on exposure to air due to hydrated iron oxides.

Loam

A mixture of sand, silt, and clay particles in approximately equal proportions, sometimes containing organic matter.

Loess

Uniform wind-blown yellowish-brown silt or silty clay that exhibits cohesion when dry but loses it when wet.

Marl

A mixture of calcareous sands or clays with clay content not more than 75% and lime content not less than 15%.

Moorum

A mixture of gravel and red clay.

top-soil

The surface material that supports plant life.

varved clay

Clay and silt of glacial origin, characterized by alternating layers of thicker silt varves from summer and thinner clay varves from winter.

Soil Structure

The arrangement and state of aggregation of soil grains.

Single-grained structure, Honey-comb structure, Flocculent structure.

Three common types of soil structure.

Single-grained structure

It is typical of coarse-grained soils with a particle size greater than 0.02 mm, where gravitational forces predominate.

Honey-comb structure

A structure that occurs in fine-grained soils, especially in silt and rock flour, where inter-particle surface forces play a significant role.

Flocculent structure

A structure characteristic of fine-grained soils such as clays, formed by inter-particle forces leading to flocculation.

Soil texture

The appearance of the surface of a soil material, largely reflected by particle size, shape, and gradation.