Modified Iowa formula for vertical deflection of buried flexible pipe

In this paper, the classical work of Spangler is revisited to derive a modi fied Iowa formula for estimating vertical deflection of flexible pipe. Duri ng the derivation process, the approach suggested by Spangler is faithfully followed. No new assumptions or empirical elements are introduced beyond t hose originated by Spangler. Once the vertical deflection formula is establ ished, its reliability is verified against field deflection measurement dat a supplied by Spangler. Then, a few parametric studies are conducted using the horizontal and vertical deflection modified Iowa formulas to gain furth er insights into the pipe-soil interaction problem as revealed by the work of Spangler. Finally, the paper concludes by offering a summary and then po inting out a few key issues that need to be remembered when applying the cl assical approach pioneered by Spangler.