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.

Internal Friction Angle of Soil

07/28/26

“How can we quantify how well soil particles resist shear failure?”

Soil particle bodies will collapse and fail when there’s a large enough shear stress applied to them. But how can we quantify this? Well, what if we were to take the soil body, place it on a theoretical inclined plane, and tilt the platform until the soil body collapses? The angle at which the body collapses is known as the Internal Friction Angle of Soil, and is the most widely used way to measure how well soil particles resist shear failure. The internal friction angle of soil is governed by the equation internal friction angle of soil = tan((shear stress due to friction)/(normal stress acting on soil))^-1. The higher the normal stress on the soil, the more it can resist shear stresses.

Why Flat Roofs Are Not Actually Flat

07/27/26

“Why are flat roofs not actually flat?”

Building descriptions should be accurate to their name. But flat roofs completely buck this trend. Flat roofs typically have a small degree of slope (typically ten degrees of less) to allow water to runoff the roof to avoid pooling. This is Why Flat Roofs Are Not Actually Flat.