MOHR’S COULOMB THEORY By Geotechnaical eng

Mohr Coulomb

1. MOHR’S COULOMB THEORY Presented by :- Viraj Gurav :-2102051 ISE -2 Geotechnical Engineering

2. INTRODUCTION The shear strength of soil is the resistance to deformation by continuous shear displacement of soil particles upon the action of a shear stress. Shear strength is the principal engineering property which controls the stability of a soil mass under loads. It governs the bearing capacity of soils. The stability of slopes, the earth pressure against retaining wall, etc

3. TYPES OF STRESS At any point in a strained material, there exist three mutually perpendicular planes on which only direct stresses are acting , i.e. no shearing stresses acting. These are known as principal planes. The largest of these is called the major principle stress (σ1), the smallest, the minor principal stress (σ3), and the third one is called the intermediate principal stress (σ2).

4. DEFINATION Cohesion (c) :- The attraction between the molecules of the same material is called cohesion. The cohesion of soil depends upon, 1.Fineness of clay particles. 2.Types of clay mineral. 3.Amount of clay 4. Water content of soil Internal friction:- The friction resistance between the individual soil particles at their contact points is known as internal friction. Angle of internal friction(Ф):- It represents the frictional resistance between soil particles, which is directly proportional to the normal stress.

5. MOHR’S COULOMB THEORY Coulomb, in his investigations observed that one component of the shearing strength, called the intrinsic cohesion is constant for a given soil and is independent of the applied stress. • The shear strength of a soil at a point on a particular plane was expressed by coulomb as a linear function of the normal stress on that plane, as S or ﺡ = C + σ tanφ Where, S = shear strength of the soil C = apparent cohesion σ = normal stress on the failure plane φ = angle of internal friction

6. TYPES OF SOIL Types of soils based on total strength: 1. Cohesionless soil (φ – soil ) : These are the soil which do not have cohesion . So, C = 0. These soil derive the shear strength from the intergranular friction. These soils are also called frictional soils . Equation for shear strength is, S or ﺡ = σ tanφ Examples : sands and gravels

7. 2 . Purely cohesive soil (C - soil) :- These are the soils which exhibit cohesion but, the angle of shearing resistance, φ = These soil are called C – soils. Equation for shear strength is S or ﺡ = C Example : saturated clays

8. 3 . Cohesive frictional soils (C – φ soil ):- These are composite soil having C and φ both. These are also called C – φ soils. The equation for shear strength is , S or ﺡ = C + σ tanφ Examples : clayey sand, silty sand, sandy clay.

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