u/constrobot

Why can a vertical excavation in clay sometimes remain standing while a similar excavation in sand collapses?

This article examines the concept of critical unsupported height, including:

The role of cohesion in soil strength

Rankine active earth pressure theory

Tension crack formation

The physical origin of the factor 4 in the equation:

Hc = 4c / (γ√Ka)

It also discusses why geotechnical engineers are often cautious about relying on cohesion for permanent designs, despite the surprisingly large unsupported heights predicted by theory.

A useful read for civil engineers, geotechnical engineers, engineering students, and anyone interested in slope stability and excavation behavior.

https://constructmagazine.com/critical-unsupported-height-in-clays/

Lateral Force Resisting Systems (LFRS) are fundamental to building performance under wind and earthquake loading.

Common systems include:

• Shear walls
• Braced frames
• Moment-resisting frames
• Dual systems
• Core and outrigger systems

Each offers different advantages in terms of stiffness, ductility, architectural flexibility, and cost.

For engineers and designers here: which LFRS do you use most often, and what factors typically drive your selection?

Why can adding stairs to a structural model suddenly create soft-story or torsional irregularity warnings?

We recently explored an interesting issue reported by users of a structural analysis software: a building model behaves normally until reinforced concrete stairs are added, after which soft-story or torsional irregularity warnings appear.

The article discusses both possibilities:

The stairs may genuinely affect structural behavior by adding stiffness and changing load paths.

The software may struggle with story-based code checks, center-of-rigidity calculations, diaphragm assumptions, or post-processing routines when inclined stair elements connect multiple stories.

It also examines potential software improvements and practical ways engineers can investigate whether the warning is physical or numerical.

https://constructmagazine.com/stairs-affecting-building-stiffness-in-structural-analysis/

Have you encountered similar behavior in structural software?

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When engineers encounter expansive soils near water, deep piles are often viewed as the default solution. But are they always necessary?

The answer depends on what is actually controlling the site's performance.

Expansive clays are known for shrink-swell behavior, but shoreline environments can introduce a completely different set of challenges. If soils remain close to saturation, the governing concerns may instead be:

low undrained shear strength,

consolidation settlement,

bearing capacity failure,

lateral spreading,

scour and erosion,

internal erosion mechanisms.

This distinction is important because the foundation solution should address the most likely failure mechanism rather than the soil classification alone.

Deep piles offer several advantages. They bypass problematic upper soils, transfer loads to stronger layers at depth, and can provide excellent settlement control. However, temporary works often involve practical constraints that significantly influence foundation selection.

In confined shoreline areas, pile installation may require large equipment, stable working platforms, crane access, and significant mobilization costs. In some projects, these constructability issues can become just as important as the geotechnical design itself.

For this reason, many temporary heavy-load platforms are successfully built using ground improvement techniques such as geogrid-reinforced platforms, crushed stone working mats, stone columns, geocells, and load transfer platforms.

Temporary structures also operate under different design assumptions than permanent facilities. In some cases, larger settlements may be acceptable if they remain predictable and manageable throughout the temporary service period. Monitoring systems such as settlement plates, inclinometers, and piezometers can also provide valuable performance data and increase confidence in ground improvement solutions.

In practice, the debate is rarely "piles versus shallow foundations." Many successful projects use hybrid solutions that combine both approaches.

The most effective design is often not the most conservative one, but the one that safely achieves the required performance while remaining practical, economical, and constructible.

What has been your experience on temporary shoreline projects? Do you generally favor piling, ground improvement, or hybrid solutions?

Full article: https://constructmagazine.com/piles-or-ground-improvement-for-onshore-temp-works/

​Just wanted to share a quick appreciation post for these blooms. Every year I forget how stunning the yellow and red variety is until they actually pop up. They literally look like little brushstrokes of fire. Nature really knows what it’s doing with color theory.