Wall-In-A-Box: Back-of-Wall Behavior in Coulomb Earth Pressure Theory
Discussed in this Video
Short on time? Here are this video’s key takeaways…
Coulomb Earth Pressure Theory assumptions don’t always apply to retaining walls, especially for cantilever or stepped-back walls.
The Wall-in-a-Box tool reveals real soil behavior, including multiple failure planes and soil wedges contributing to wall stability.
Engineers must adapt analysis methods based on wall geometry to ensure accurate, lasting designs.
This video introduces key concepts and example methods for calculating earth pressure across different retaining wall systems. While not an exhaustive guide, it’s designed to spark curiosity and encourage deeper exploration into the fascinating world of earth pressure theory.
n this follow-up to our deep dive on Coulomb Earth Pressure Theory, we look closer at a critical yet often overlooked component: the back of the wall. Jamie Johnson, PE, Director of Innovation at Redi-Rock, uses the Wall-in-a-Box demonstration tool to explore how different types of retaining walls challenge the assumptions of classic earth pressure calculations.
You’ll see side-by-side comparisons of how failure forms:
- A mass gravity retaining wall with a straight back, where Coulomb assumptions hold true.
- A cantilever retaining wall with a heel, where soil above the heel acts as part of the wall, revealing dual failure planes.
- A precast modular block (PMB) wall with varying unit widths, where small wedges form at step-backs, suggesting composite behavior.
With Wall-in-a-Box, we can illustrate that real-world wall behavior often deviates from textbook assumptions - and that accurate design requires thoughtful consideration of geometry, friction, and soil interaction. Every structure reacts uniquely to vertical stress and changing site conditions, especially on a natural slope.
Whether you’re designing simple gravity walls or complex modular systems, this video encourages engineers to look beyond standard theory and apply critical thinking backed by experience and visual insight.
Curious about how Redi-Rock’s integrated wall systems can support your next project? Download the Precast Modular Block Design Manual, Vol. 1 - co-authored by Jamie Johnson, PE - for expert guidance on retaining wall design and installation. It’s the industry’s go-to resource for engineers working with precast modular solutions.
Contributing Expert
Jamie Johnson, PE
Jamie possesses more than 30 years of design experience in civil engineering. He began as a consulting engineer working for a small civil engineering and surveying firm in northern Michigan. Jamie joined Redi-Rock International in 2006 where he held multiple roles including staff engineer, chief engineer, and director of operations. He is currently director of innovation for Redi-Rock’s parent company, Aster Brands. Jamie holds Bachelor and Master of Science Degrees in Civil Engineering from Virginia Tech University and is a registered professional engineer in the state of Michigan.
While experiencing his mid-life crisis a few years ago, Jamie purchased an E flat tuba. He has survived the crisis and has since added a B flat tuba and a Baritone to the collection that also includes his original tenor and alto trombones. It goes without saying that he likes to toot his own horn.
