Soil Cohesion

08/14/26

“How do soil particles bind together?”

Soil is quite fascinating. An untold number of discrete solid particles clump together to make the surface of our planet. And these soil particles are attracted to each other through Cohesion. Cohesion is strongest in clay sands and is the non-frictional component of soil shear strength.

Soil Slope Failure

08/13/26

“What causes soil to slide down a slope?”

Soil may rest on an inclined slope. This soil is balanced when the forces pushing the soil down (such as its weight) are counterbalanced by resistive forces (such as the soil shear strength). When the forces pulling down overpower the resistive forces, the soil will slide down in what’s called a Soil Slope Failure. Many factors can cause a soil slope failure, from rainwater weakening the effective stress of a soil to earthquakes to excessive weight over the soil to vegetation root loss. Landslides are an example of soil slope failure. People can prevent soil slope failure by implementing protective measures such as installing retaining walls, planting rooted vegetation, and covering soil during rainstorms. Soil slope failure is an important factor to look out for in development projects.

Detention Tank Overflow Pipes

08/12/26

“Why do detention tanks have overflow pipes?”

Detention tanks are used to control water overflow all over the world. However, if a large flooding event happens and there’s a massive amount of runoff, it can overwhelm and even destroy the system. People can install Detention Tank Overflow Pipes above the orifices to ensure excess water can flow out before infrastructure damage occurs.

Image credit: https://www.reddit.com/

Liquid Limit

08/11/26

“When does playdough-like become liquid-like when you add enough water?”

Soils are very sensitive to environmental changes. When playdough-like fine-grained soils past the plastic limit are inundated with enough water, they become liquid-like, and their internal shear strength collapses. This can lead to infrastructure failures when the ground can no longer provide support. The point when the liquid-like behavior takes over is called the Liquid Limit.

Plastic Limit

08/06/26

“How do rigid fine-grained soils become playdough-like when you add enough water?”

Dry fine-grained soils are rigid. But when you add enough water, they become moldable and playdough-like. The transition point in moisture content is called the Plastic Limit.

Atterberg Limits 

08/05/26

“How can we describe how fine-grained soil properties change with water content?”

Fine-grained soils are found throughout this planet. However, they may or may not always be dry. If you progressively add water to fine-grained soils, the specimen will progress from hard solids to moldable, putty-like material and even to complete liquid-like behavior. The Atterberg Limits describe the water content boundaries for these property boundaries.

Gap-Graded Soil

08/04/26

“How do we classify soil that’s missing intermediate particle sizes?”

Soil can contain a range of particle sizes. However, some samples are missing one or more intermediate particle ranges. These Gap-Graded Soils typically have strange drainage properties because of the uneven gaps. Gap-graded soil is typically classified as a poorly-graded soil because it lacks a continuous particle size distribution.

Poorly-Graded Soil

08/03/26

“How do we classify soil that’s almost exclusively composed of one particle size?”

Soil comes in all sorts of shapes and sizes. Soil samples that are only composed of a small number of grain sizes close together are labelled Poorly-Graded Soil. Poorly graded soil often drains well because of the uniformly-sized gaps, but also weakens it for structural support because of the extra voids. Engineers must measure the soil distribution before construction begins.