Most Problems Aren’t Surprises
They’re assumptions that didn’t hold once construction starts
Most problems on a construction project aren’t actually surprises. They just look that way once work begins. In reality, a lot of the risk is already there—buried in assumptions about soil conditions, groundwater, and how recommendations will actually perform in the field. Those assumptions often make sense on paper, but the issue is when they’re treated as guaranteed conditions.
Where assumptions come from
Geotechnical reports are built on limited data. Borings are spaced across a site, and conditions between those points are interpreted rather than directly observed. Groundwater is recorded at a specific time under specific conditions, and recommendations are developed from that snapshot. None of this is inherently wrong—it’s how geotechnical engineering works. But it does mean that assumptions are unavoidable. It’s often assumed that conditions are relatively consistent across the site, that moisture and groundwater won’t vary significantly, and that materials encountered during construction will behave as expected. Sometimes those assumptions hold. Often, they don’t.
What happens when they don’t
Once construction begins, conditions are no longer theoretical. Excavation exposes variability, weather changes moisture conditions, and loads are applied to soils that may not behave exactly as anticipated. When assumptions don’t match reality, the response is usually immediate. Undercut limits expand, stabilization becomes necessary, foundation recommendations are revisited, schedules shift, and costs increase. At that point, the issue is often described as a “surprise,” but in most cases the possibility already existed—it just wasn’t fully accounted for.
Why it happens so often
The problem isn’t that assumptions exist; it’s how they’re used. Issues tend to arise when assumptions are treated as fixed conditions, when variability isn’t considered during planning, and when recommendations are applied without context. It’s often easier to move forward with a simplified interpretation of a report than to account for uncertainty. That approach works on paper, but it rarely holds up once construction starts and real conditions are exposed.
What actually helps
The goal isn’t to eliminate assumptions—that’s not realistic. The goal is to recognize where they exist and account for them early in the process. This typically involves reviewing geotechnical reports with a focus on variability rather than just conclusions, identifying where recommendations depend on conditions that may change, and understanding how those assumptions impact construction methods and sequencing. Evaluating these factors before construction begins allows for better planning and reduces the likelihood of costly adjustments later.
Final thought
Most problems aren’t surprises. They’re assumptions that didn’t hold once construction started. Recognizing that early is what separates projects that adapt from those that are forced to react.
About the Author
Nathan McNallie is a geotechnical consultant focused on report review, construction advisory, and identifying project risk before it becomes a field issue.
