Faulty or inadequate soil investigation is a leading cause of helical pier failure because it results in inaccurate geotechnical data, which is fundamental to deep foundation performance.
According to the provided content, faulty investigation leads to failure through the following mechanisms:
- Inaccurate Bearing Capacity: Underestimating the soil’s bearing capacity leads engineers to select helical plates that are too small for the actual site conditions. This causes the piers to displace weak soil rather than supporting the load, resulting in damaging differential settlement.
- Incorrect Embedment Depth: Inadequate subsurface exploration often leads to piers being installed at depths that are too shallow. If the piers do not bypass weak strata or active settlement zones, they fail to reach a stable load-bearing stratum.
- Negative Skin Friction: A lack of proper data regarding groundwater levels and soil consolidation can lead to unforeseen negative skin friction. This occurs when settling soil grips the pier shaft and exerts a downward "dragload" that can exceed the original design capacity of the pile.
Common investigation mistakes include the use of outdated borehole logs, ignoring groundwater conditions, and failing to perform site-specific tests like Cone Penetration Tests (CPTs). These errors create uncertainty in the soil modulus values needed to specify the correct pier configuration.
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