A new design approach for direct embedment foundations (for power line supports)

An improved model has been developed for the analysis and design of directly embedded, single-pole transmission structures subject to high overturning moments. The model uses a multispring, nonlinear subgrade modulus approach to predict the load deflection response and ultimate capacity of direct embedment foundations placed in a multilayered soil subsurface profile, and with uniform or multilayered annulus backfill. To verify the predictive capabilities of the model, ten full-scale lateral load tests were conducted on directly embedded transmission poles. The model is described, and a comparison is made between the results of full-scale load tests and model predictions of the ultimate overturning moment capacity and load deflection behavior. The semiempirical model has been implemented in the computer program MFAD (Moment Foundation Analysis and Design) contained in EPRIs TLWorkstation. The results of 10 full-scale load tests demonstrate that the model, on the average, conservatively underpredicts ultimate moment capacity by approximately 20% and has a coefficient of variation of 12%. The model is also a good predictor of moment-deflection and moment-rotation response for well-compacted backfill materials, conservatively overpredicting deflection by approximately 16% and rotation by approximately 8%.<>