Effect of Elastic Non-Linearity of Soil and Pile on Uplift Capacity of Transmission Tower Foundation-Paper

Paper

Pdf Summary

The study investigates the uplift capacity of transmission-tower foundations supported by bored, cast-in-place piles in silty sand. A 1.3 m-high model tower was tested with piles of 50 mm diameter and length-to-diameter ratios (L/d) of 4, 6, and 8. Tower loading produced simultaneous tension in some piles and compression in others. Researchers measured uplift, settlement, and horizontal displacement until failure.<br /><br />Measured ultimate loads increased with pile embedment: 810 N for L/d = 4, 950 N for L/d = 6, and 1,150 N for L/d = 8. Uplift capacity was largely mobilized at approximately 5 mm displacement—10% of the pile diameter. Settlements in compression piles remained below the specified limiting value, indicating that failure occurred first in the uplift-loaded piles.<br /><br />Three theoretical methods—Meyerhof, Awad and Ayoub, and a standard cylindrical failure model—underestimated measured capacities. Meyerhof’s estimates were generally closest to the test results. The calculated contribution of shaft friction to total uplift capacity rose with pile slenderness, from 26% at L/d = 4 to 40.66% at L/d = 6 and 47.9% at L/d = 8.<br /><br />The findings highlight the importance of pile embedment and skin friction in resisting tower uplift loads, and show that tension piles can govern foundation failure even when compression piles have not reached their settlement limit. The study is based on field tests of a small-scale model in one soil type, so its results may not directly represent full-scale foundations or other ground conditions.

Keywords

uplift capacity

transmission tower foundations

bored piles

cast-in-place piles

silty sand

pile embedment

shaft friction

tension piles

compression piles

model tower test