Q1: Which one of the following statements is true for Mohr-Coulomb envelope ?

ANS:E - All the above.

1. Coulomb suggests that the relationship between shear strength and normal stress is adequately represented by the straight line: This statement reflects one of the key principles of Coulomb's theory of shear strength. Coulomb proposed that the relationship between shear strength and normal stress for soils can be represented by a straight line on a graph known as the Mohr-Coulomb envelope. The slope of this line represents the angle of internal friction, and the intercept on the shear stress axis represents cohesion.
2. The generalised Mohr theory suggests that, though the shear stress depends on the normal stress, the relation is not linear: The general Mohr theory, which is a fundamental concept in continuum mechanics, explains how stress and strain vary within a material body. While it does consider the relationship between shear stress and normal stress, it doesn't necessarily propose a linear relationship. The Mohr-Coulomb theory, which is based on Coulomb's principles, suggests a linear relationship for shear strength under certain conditions, but the general Mohr theory allows for more complex relationships between stress components.
3. Coulomb and Mohr suggest that a definite relationship exists among the principal stress and the angle of internal friction: Both Coulomb's theory of shear strength and the Mohr theory of stress relate to the concept of principal stresses and angles of internal friction. However, they don't directly suggest a definite relationship between principal stress and the angle of internal friction. The angle of internal friction is a material property that influences shear strength but may not have a direct relationship with principal stresses.
4. For an ideal pure friction material, the straight line passes through the origin: This statement refers to the behavior of materials with pure friction, where there is no cohesion present. In such idealized cases, the Mohr-Coulomb envelope, which represents the relationship between shear stress and normal stress, passes through the origin of the graph. This indicates that there is no shear stress when there is no normal stress, which is a characteristic of pure frictional behavior.