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.

The Freshwater-Saltwater Interface

07/24/26

“What makes the interface between saltwater and freshwater so unique?”

Freshwater and saltwater have substantially different properties. When they meet in coastal aquifers, they form a Freshwater-Saltwater Interface. The freshwater-saltwater interface is a transition zone where freshwater “floats” as a layer above the zone of transition (which in turn “floats” above more pure saltwater) because of saltwater’s greater density. The further down you go in a coastal aquifer, the saltier the groundwater becomes. Coastal aquifer infrastructure operators must be careful with the freshwater-saltwater interface, because overpumping can lead to upconing of saltwater and result in saltwater intrusion.  

Force Main Discharge Elevation

07/21/26

“How can we quantify the height a force main must pump to?”

Force mains pump wastewater to overcome elevational or frictional differences. The height they must pump to is called the Force Main Discharge Elevation. Wastewater does not need pumping to move once it reaches the force main discharge elevation since it will go downhill with gravity. The force main discharge elevation does not need to be above the pump inlet since the pump might be present to work against frictional losses only.