Accurate foundation monitoring and analysis require a reliable, stable reference point. Traditional methodologies often rely on internal reference points located within a home, but these points are inherently unstable. Internal reference points rest on the home’s foundation slab, which is subject to movement caused by drainage issues, plumbing leaks, or settlement. This instability makes it impossible to accurately diagnose foundation movement over time.

In contrast, an external reference point, such as a deep-driven helical pier, provides a far superior benchmark for measuring foundation stability. These external points are unaffected by the same environmental factors that influence a foundation slab and offer a virtually immovable standard for consistent and accurate measurements.

Instability of Internal Reference Points

Internal reference points are often placed on or within the foundation slab itself, which is typically 4 to 24 inches thick. However, the slab is not a static structure—it is part of the foundation system and thus susceptible to various forces that can cause movement, including:

1. Shallow Foundation Depth: The slab’s depth is within the soil zone most affected by changes in moisture content. Seasonal soil expansion and contraction, caused by variations in precipitation, drainage issues, or landscaping, can cause the slab to shift.

2. Drainage and Plumbing Issues: Water infiltration from poor drainage or plumbing leaks can alter the soil’s moisture content beneath the slab, resulting in heaving of the foundation. This movement directly impacts the position of the reference point.

3. Settlement Over Large Spans: Foundation movement typically occurs over large spans, causing uneven shifts in the slab. The internal reference point may rise, sink, or tilt in unpredictable ways, making it impossible to extrapolate accurate data from it.

4. Lack of Isolation: Since the internal reference point is part of the slab, any movement in the foundation can translates to a shift in the reference point, rendering it unreliable for long-term monitoring.

Stability of External Reference Points

External reference points, such as deep-driven helical piers, provide a solution to the instability of internal reference points. These piers are designed to penetrate deep into stable soil strata, well below the zone influenced by moisture fluctuations. Their installation and characteristics make them ideal for use as static benchmarks in foundation monitoring.

Key Advantages of External Helical Piers as a Benchmark

1. Depth Beyond Moisture Influence: Helical piers can reach depths of 20 feet or more, well past the active zone of soil where moisture changes occur. This ensures that the pier

remains unaffected by seasonal or environmental soil fluctuations.

2. Exceptional Load Capacity: Helical piers have a capacity to support 20,000 pounds or more. When used as reference points, they carry no structural load, making it virtually impossible for them to settle or fail under normal conditions.

3. Isolation from Foundation Movement: Since the pier is installed outside the foundation’s influence zone, it is unaffected by issues such as plumbing leaks, drainage problems, or the foundation’s settlement. This isolation ensures that the pier remains stable regardless of what happens to the foundation.

4. Verification Through Redundancy: In cases where absolute certainty is required, a second external helical pier can be installed as a “benchmark to the benchmark.” By regularly comparing measurements between the two piers, it can be verified that both remain static, providing additional confidence in the accuracy of the reference point.

Statistical Improbability of Movement

The likelihood of movement in a properly installed helical pier is extraordinarily low. Because the pier does not support any weight and is anchored into stable soil layers, it is not subject to the forces that commonly cause foundation movement. This makes the external reference point statistically improbable to move, ensuring long-term reliability for foundation monitoring.

Conclusion

Internal reference points are inherently unstable due to their location within the foundation slab, which is subject to movement caused by soil expansion, drainage issues, plumbing leaks, and settlement. These factors render internal points unreliable for accurate long-term foundation monitoring.

External static reference points, such as deep-driven helical piers, provide a stable and reliable alternative. Their depth, isolation from the foundation, and immense load capacity ensure that they remain unaffected by environmental or structural changes. In cases requiring absolute certainty, redundant external piers can be used for verification. By adopting external reference points, engineers and inspectors can ensure accurate and consistent measurements, leading to better foundation diagnostics and more effective solutions.

Tony Cooper

President

All-Pro Foundation Repair