Innovative Application of Geophysical Techniques for Design of Direct-Embedded Pole Structures

This paper reports a Southern Company-wide research effort to develop a geophysical method (Spectral Analysis of Surface Waves, SASW) for determining the stability design of directly embedded pole structures. For transmission lines, directly embeding of pole structures is a rapid construction process. The conventional design approach recommends a 10% of pole height plus two feet embedment depth, but does not differentiate between pole types, design loads, or inherent soil stiffness and strength. This paper describes the SASW soil analysis and an analytical method for determining the moment equilibrium of a directly embedded pole. The SASW method relies on the generation of small-strain stress wave propagation through soil media utilizing non-intrusive equipment. The tests have proven to be relatively easy to conduct, and inexpensive when compared to soil borings. Hence, it is an ideal technique for rapid site characterization. The analytical method determines pole stability and soil strain by limiting the ground line deflection. The results from five field studies with different site conditions prove that the method makes accurate predictions of pole capacities when compared with actual pull tests.