According to the Mohr-Coulomb failure criterion in soils, which of the following statements are INCORRECT?

A: Shear strength is attributable to the interlocking of soil particles and cohesion.

B: Shear strength is only attributable to the internal friction between particles.

C: The Y-intercept represents friction of soils.

D: The Mohr-coulomb failure envelope is a straight line.

Mohr-Coulomb Failure Criterion in Soils:

The Mohr-Coulomb failure criterion is a mathematical model that describes the response of materials such as soils and rocks to shear stress as a function of normal stress. It is widely used in geotechnical engineering to predict the failure conditions of soil and rock masses.

Analysis of Statements:

• Statement A: "Shear strength is attributable to the interlocking of soil particles and cohesion."
  • This statement is correct. The shear strength of soil is generally considered to be due to two main components: the frictional resistance due to the interlocking of particles (internal friction) and the cohesive forces between soil particles (cohesion).
• Statement B: "Shear strength is only attributable to the internal friction between particles."
  • This statement is incorrect. Shear strength is not solely due to internal friction; cohesion also plays a significant role in the shear strength of soils.
• Statement C: "The Y-intercept represents friction of soils."
  • This statement is incorrect. In the Mohr-Coulomb failure criterion, the Y-intercept of the failure envelope represents the cohesion (c) of the soil, not the friction. The slope of the failure envelope represents the angle of internal friction (ϕ).
• Statement D: "The Mohr-coulomb failure envelope is a straight line."
  • This statement is correct. The Mohr-Coulomb failure envelope is represented by a straight line in the plot of shear stress versus normal stress.

Conclusion:

• The incorrect statements are B and C.