Rip rap fails when the hydrodynamic forces acting on individual stones exceed their resistance to movement. Stone resistance is primarily a function of mass — heavier stones require more force to dislodge. The design of a rip rap layer involves calculating the median stone size required to remain stable under the design flow condition, typically expressed as D50. Our two grades — 8-18" and 18"+ — bracket the most common size requirements in civil drainage, stormwater, and channel engineering applications. For projects with specific hydraulic design requirements, we can confirm which grade aligns with your D50 specification and provide gradation information to support the submission.

D50 gradation aligned / 8 to 18" standard range / 18"+ armourstone range / Hydraulic design support

Angular stone performs significantly better than rounded stone in rip rap applications because it interlocks when placed. Interlocking stones act collectively — when flow attempts to dislodge one stone, the adjacent stones resist the movement through mechanical contact. Rounded stone does not interlock; individual stones are only held by their own mass, and progressive failure can occur as individual stones roll and create voids that destabilise the layer. Our rip rap is sourced from quarried rock crushed to angular form, providing the interlock geometry that engineered rip rap layers depend on for sustained performance under flow loading.

Angular — collective interlock / Resists progressive failure / Adjacent stone support / Sustained hydraulic performance

Installing the entrance pad over a geotextile fabric layer separates the stone from the native subgrade, preventing fines migration upward into the pad that would progressively fill voids and reduce effectiveness. It also keeps the stone recoverable at the end of the project — the pad can be stripped and the stone screened and reused on the same or a subsequent project rather than being mixed with soil and disposed of. For project managers managing material costs across multiple active sites, the ability to reuse entrance rock is a practical efficiency. We can supply in bulk for single-site use or in quantities suited to a stock-and-rotate programme across multiple projects.

Geotextile separation recommended / Stone recoverable and reusable / Fines migration prevented / Multi-site rotation possible