Which one of the following is an assumption made by Coulomb in the development of his earth pressure theory for sand and for active state?

Explanation:

Coulomb developed his earth pressure theory in 1776, which is one of the earliest theories to analyze lateral earth pressures. Several assumptions were made by Coulomb in the development of his earth pressure theory for sand and for active state conditions. Of the options provided:

The rupture surface is a non-uniform surface: This is incorrect. Coulomb assumed that the failure surface is planar or straight in nature, rather than a non-uniform surface.

There is a wall friction on the pressure surface: This is correct. A unique part of Coulomb's earth pressure theory is the acknowledgement of wall-soil friction. Coulomb considered the frictional interaction between the retaining wall and the soil which can reduce the lateral earth pressure on a retaining structure.

Failure is three-dimensional: This is incorrect. Coulomb's earth pressure analysis is primarily based on a two-dimensional failure mechanism, not three-dimensional.

The soil is cohesive: This is incorrect. Coulomb's earth pressure theory is often applied to cohesionless soils like sand, not cohesive soils. The parameters used in analysis, such as the angle of internal friction, are relevant for cohesionless soils.