Soil Structure - Soil Physics - Lecture Slides, Slides of Soil Physics

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Outline

• Announcements
• Where were we?
• Soil Structure (particles)

Where were we?

Soil strength

Soil structure

Specifically, most soil structure exists because of cohesiondocsity.com

Classification of structure:

Platy Blocky Crumb Granular Columnar Prismatic Angular Subangular …

Granular

Classification of structure: Blocky

Classification of structure: Prismatic

Classification of structure: Columnar

Figure & Ground

Why soil structure (particles)?

Particles & Pores

Figure and Ground

Dual networks Triangular & honeycomb

Dual networks Voronoi & Delaunay

Structure implies not random

This might be a preferential arrangement

Based on chance, you shouldn’t find lots of this: Clay should hang out with the other particles, too.

Why do clay quasicrystals

(and other non-random structures)

form?

Drivers of structure (particles)

Gravity: if it can’t stand, it will fall Stability: if it’s not stable, it will soon change

Climate, life, parent material

Water, heat, roots: different ways energy disturbs the soil, shaking it into a more stable configuration

Fragmentation systems

When an aggregate is dropped, there is usually a power-law distribution of pieces:

d f

N r r

−

This is characteristic of fragmentation systems. It implies that larger pieces are easier to break than smaller pieces.

r

N

( r

log ( r )

log

[ N

( r

)]

slope = – df

Causes / consequences of hierarchical structure

• Small structures tend to be denser than large structures
• Small structures are more stable than large structures
• Bonds within and between small structures are stronger than bonds within and between large structures
• Spaces (pores) between large structures are bigger than those between small structures

In soil, these structures are called aggregates

Aggregate properties

• Size, shape, distribution
• Strength versus physical forces
• Strength versus chemical forces

Fragmentation Dry sieving Rupture

Wet sieving

Granular structure

Eventually, physicists try to treat everything as spheres…