CGSeso Engineering & Construction

We are currently involve in a soil investigation project for a Proposed Belfry Structure of the Sto Niño De Congreso Parish in Caloocan. Our drilling equipment was caught on camera this morning during the blessing of the project. The blessing was performed by the Bishop of Caloocan and the congressman of Caloocan was also present in the said ceremony.

📷 Sir Teng Gayya

WHEN THE PLATE LOAD TEST SAID IT WAS SAFE BUT THE SOIL SAID OTHERWISE!!

At the Transcona Grain Elevator, plate load tests indicated acceptable bearing behavior. Yet during the first filling, the structure tilted rapidly, not over decades, but almost immediately. Why? It is because of the real and physical limitations of the plate load test results.

A plate load test mobilizes stress only to a shallow depth (roughly 1–2 plate widths). That means:

❌ Deeper soft clay layers were never mobilized/ affected by the bearing stress

❌ Undrained shear deformation in those layers was missed

❌ The test captured near-surface stiffness, not the true foundation stress bulb

When the full foundation load was applied, stresses reached the deeper clay, triggering large undrained settlements and rotation even though bearing capacity was not exceeded.

The lesson

The plate load test answered:
✔ Is the upper soil stiff enough?

But failed to answer:
❌ What happens when stresses reach deeper, weaker layers?

This case strongly influenced Karl Terzaghi and the modern emphasis on subsurface profiling and settlement control, not just surface testing.

Practice reminder

If a plate load test is used to “prove” a shallow foundation is OK, especially where soft clays may exist at depth, think again.

👉 The critical layer is often below the test zone

👉 Failure can be rapid, not time-dependent
Foundations don’t only fail slowly.
Sometimes, they fail the moment the real load arrives.

Images :
1. Geostrata
2. Civil Web