Episode 8 – Mechanically Stabilized Earth Walls: Cutting into Rock for Reinforcement

One of the situations that often raises eyebrows on site is when we cut into rock behind the wall facing to place reinforcements. To many non-geotechnical professionals, it looks counterintuitive. Why weaken solid rock?

The reality is that an MSE wall does not rely only on the facing or the backfill. It works as a complete system where reinforcement length is key for internal, external, and global stability. Without sufficient embedment length, the wall simply cannot function as designed.

 FHWA guidelines actually recognize this situation. They allow what is known as benching in rock—where reinforcement lengths are staggered because of rock cut geometry. But this comes with strict conditions. The foundation must be competent, such as sound rock or soils with SPT N60 above 50. And the design must check both external stability and overall slope stability, including wedge and circular failures.

 Some simplified rules are often applied:

• Represent the stepped wall as an equivalent rectangular block for external stability checks

• Maintain a minimum base length of 0.4H or 2.5 m (whichever is greater)

• Keep reinforcement length differences between zones less than 0.15H

 To conclude, when we see rock on site, we cannot ignore reinforcement embedment. The wall only performs as a system when every element is doing its job.