1.3. Structure

The shearing strength is affected by: – soil composition: mineralogy, grain size and grain size distribution, shape of particles, pore fluid type and content, ions on grain and in pore fluid. – Initial state: State can be described by terms such as: loose, dense, overconsolidated, normally consolidated, stiff, soft, etc. – Structure: Refers to the arrangement of particles within the soil mass; the manner in which the particles are packed or distributed. Features such as layers, voids, pockets, cementation, etc, are part of the structure.

Shear strength in soil is influenced by various factors. The first factor is soil composition, which includes the types of minerals in the soil, the size and distribution of soil grains, the shape of these particles, and the characteristics of pore fluids. Next, the initial state of the soil, described by terms like loose, dense, or soft, impacts how the soil will behave under stress. Lastly, the structure of the soil, which involves how particles are organized, including aspects like layers or voids, is critical in determining its strength.

Think of soil as a jigsaw puzzle. Each piece represents a different factor: the material (composition) of each piece shapes how well they fit together. If the pieces are loose (like a poorly assembled puzzle), the whole structure can collapse under pressure. On the other hand, if they are tightly fit and well arranged (like a completed puzzle), the assembly is sturdy and able to withstand stress.

This theory states that a material fails because of a critical combination of normal stress and shear stress, and not from their either maximum normal or shear stress alone.

The Mohr-Coulomb Failure Criteria helps us understand how and when materials like soil fail. According to this theory, it's not just about having too much normal stress (the weight of the soil above) or shear stress (the sideways force) that causes failure. Instead, it’s the specific combination of these stresses that leads to failure. This is important when predicting how soils will behave under various loads.

Imagine trying to push a heavy box across a floor. If you push too hard without enough grip (normal stress), it may slide easily and fall. Conversely, if the box is too light and you try to push it sideways without enough push behind (shear stress), it might tip over. Just like this, Mohr-Coulomb explains that both types of stress must be considered together to understand when the 'box' (or soil) will fail.

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