Introduction

Soil is SOLIDS, WATER, AND AIR. When water is poured on the floor it will get spread over the area. It has some resistance between its layers, this property is called viscosity. Oil has been more viscous than water.

Angle of Repose

In case of soil, which is a mixture of solids, water and air, it wont spread like water. It has some shear strength. It will form a cone like structure. And the angle of this cone is called angle of internal friction or angle of repose. It is freely standing. Viscosity and shear strength are somewhat same.

Cohesion

Some soils has cohesion due to water contained in it, which is an attractive force, for example clay.  A vertical cut may stand in some soil, example: laterite soil.

Failure Plane

Failure may have wedge shape but actually it is curvy. Do you notice when a compound wall is built and one side is filled with red earth, due to weight of soil we think the wall will lean towards the fill, but it wont, it will lean on the other side, which is due to the passive earth pressure.

Shear Strength

An equation for shear strength of soil an equation of a straight line, can be obtained from its properties cohesion angle of repose and the applied vertical stress.

Consolidation

Soil is being compressed by its own weight or with weight of structure on it. Soil is considered as semi infinite. Another formula can be formed using vertical and horizontal stress on it which is called K0 condition.

Water Table

Height of water table is another interest of study. The soil will be acted on by buoyant force, that is its buoyant unit weight is studied to predict the behavior.

Settlement or Compaction

A structure may be collapsed due to the movement of foundation soil, or shear failure. Upheaval of soil is also another cause. Water table will reduce the strength of soil. When a load is applied water squeezed out of the soil from its voids, that is its compacted, or we can say settlement of soil is occurred. Water content is a factor for compaction. There is an optimum moisture content for maximum compact