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.

Coastal Freshwater Reservoirs

08/02/26

“How can we create freshwater reservoirs over ocean water?”

Freshwater reservoirs are some of the most critical pieces of infrastructure for people. However, they can take up large areas of land. But what if we were to construct it on ocean water? Well, we can use physical barriers to create a boundary around the mouth of a river and allow freshwater to pour to make a Coastal Freshwater Reservoir. When there is a heavy rainstorm or too much water from the river, the flood gates open to let water out into the ocean. Coastal freshwater reservoirs can free up land space that otherwise would have been used by a land-based system. Examples of coastal freshwater reservoirs include Marina Barrage in Singapore (pictured) and Plover Cove in Hong Kong.

Soil Failure 

08/01/26

“At what point does soil fail?”

Soil is the base support for all types of physical structures and loads. When more shear stress is applied than the soil’s shear strength, the soil will undergo Soil Failure and slide. Soil failure can lead to structural collapse, such as in the floodwall sliding during Hurricane Katrina.

Soil Shear Strength

07/31/26

“How can we measure soil’s resistance to sliding from an applied force?”

Soil is literally the foundation of human civilization. From nurturing the plants we grow to supporting the buildings we live in, soil is a critical factor. One of the most important aspects of soil is its ability to resist sliding from an applied force, also called the Soil Shear Strength. Soil shear strength comes from the friction of its interlocking cohesive particles and its internal weight. Soils need to have a strong enough shear strength to support heavy structures.

Soil Permeability

07/30/26

“How can we quantify how easily water can pass through soil?”

Water can pass through soil through its pores and voids. Soil Permeability, or the ease with which water can move through soil, depends on the soil’s particle size, void ratio, soil structure, and more. Soil permeability is represented by the constant k and is in units of distance per time unit.

Benefits and Drawbacks of Flat Roofs

07/29/26

“What are the benefits and drawbacks of flat roofs?”

Flat roofs sit on top of buildings around the world. They offer simple, affordable construction and can serve as a space for people to gather. Flat roofs also make it easier to grow vegetation and install solar panels. However, their (nearly) flat design make it easy for water to pool and snow to pile on, resulting in structural damage. Because of the Benefits and Drawbacks of Flat Roofs, flat roofs are better suited for warm, dry climates like Egypt or inland California.