Lateral Pile Analysis: Episode 7 - Three Rock p–y Models

Both RSPile and LPile offer three p–y models for rock

On paper, they look tidy and straightforward. In practice, it is rarely that clean.

Before selecting a rock model in your lateral pile analysis, it helps to understand where these models came from and what they actually assume.

The three available models correspond roughly to:
• Strong or vuggy limestone
• Weak fractured rock behaving like dense granular soils
• Massive intact rock

Each one is built on full-scale test data, but the key point is that these models assume rock that behaves like a consistent and continuous material. That is not what we encounter on most real projects.

If the rock mass has:
• Soil filled joints
• Open fractures
• Shear zones
• Highly variable RQD
…then these models will mislead you.

In these cases, the right approach is site-specific testing or full-scale lateral load testing, not a generic p–y curve. 

This is where engineering judgement matters. Matching the model to the real behaviour of the ground is far more important than selecting a curve from a dropdown.

In the course, I go through each of the three-rock p–y models, when they make sense, and when they don’t.