Rectification of Tilted Transmission Tower Using Micropile Underpinning Method

Abstract

The purpose of this paper was to report a rectification method that was used for plumbing a tilted transmission tower supported by a shallow foundation over a soft clay layer. The restoration method involves the installation of the grouted micropiles at the perimeter of the foundation. Hydraulic jacks resting on the top of micropiles and steel brackets attached to the existing foundation were used to lift the tilted transmission tower. The micropile construction processes, as well as the rectification data, are reported and analyzed in this study. The outcomes of the rectification case history highlight the effectiveness of the postgrouting technique for the micropile, because it was able to increase the axial compressive bearing capacity of the micropile almost 2.5 times compared with the nongrouted steel-pipe micropile, based on the pilot pile load test results. The increase in compressive bearing capacity of the micropile was crucial to guarantee the safety and serviceability requirements of the rectified transmission tower.