Efficient Torque-Installed Pile Use in Southern California-Paper

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Torque-installed piles are full-displacement screwed pipe piles with a closed-end conical tip. In Southern California, they are often used for small- to medium-capacity foundations in urban settings because installation is relatively fast, quiet, and low-vibration, with little or no spoil. They are particularly effective in loose to medium-dense, potentially liquefiable soils overlying a competent bearing layer, but are generally unsuitable where cobbles or boulders are present.<br /><br />Pile capacity depends strongly on installation quality. Piles should be advanced in one controlled, continuous motion, with torque and crowd adjusted to soil resistance. Excessive predrilling, withdrawing and readvancing piles, or prolonged spinning without penetration can disturb the soil or damage the tip, reducing capacity. Withdrawn piles may also suffer structural fatigue and should not be reused without integrity testing. Load tests are important because proprietary pile designs and installation methods make capacity estimates uncertain.<br /><br />Three Southern California case histories illustrate these issues. At LAX, piles installed with excessive predrilling and repeated readvancement failed load tests, while piles installed continuously with limited predrilling passed. A second LAX project showed that piles meeting torque-based refusal criteria could be shallower than permitted minimum depths; dynamic testing helped verify their capacity and highlighted the need to coordinate installation criteria with reviewing agencies. In the San Fernando Valley, a properly installed pile passed compression and tension tests, while a refurbished pile with a damaged, replaced tip failed, likely due to structural fatigue.<br /><br />Load tests on 12-inch-diameter piles indicated ultimate compression and tension capacities generally in the 400–500-kip range. Overall, torque-installed piles can be an effective deep-foundation option when subsurface conditions are appropriate, installation is performed by experienced contractors, and project-specific testing and acceptance criteria are established.

Keywords

torque-installed piles

full-displacement

screwed pipe piles

closed-end conical tip

southern california

load testing

liquefiable soils

installation quality

dynamic testing

deep foundations