EFFECT OF INTERMEDIATE DRAINS AND LEAKAGE THROUGH SHEETPILE LINES ON THE ' UPLIFT PRESSURES

Abstract

The stability of a hydraulic structure. founded on p, meable soil haste be ensured against uplift pressures and piping. The problem of seepage under such structures belongs to a general class of confined flow problems . for which the method . of solution by conformal mapping was indicated by Pavlovsky (17) and Khosla (12) . These solutions are based on the assumption that the cutoffs are absolutely impervious and flow takes place around them. In practice, however, it has been found impossible to provide a leakage free cutoff pile below the foundation, unless ,it is made of concrete and constructed monolithically with the apron. In steel sh iles leakage may be due to improper Interlocking or corrosion of sheetpile. In case of cast nsitu diaphragms the leakage may take place through faulty joints..Imperfections may also occur in case of grout curtains constructed using lines of grout holes. Brahma (3) studied the effect of , single apening in a fully penetrating single cutoff resting an permeable soil of finite depth. Dachler (8) and Anbraseys (1) determined the effect of leakage through a fully penetrating cutoff with several equally spaced openings. Intermediate filters or drains can be provided below hydraulic structures founded on permeable soil to reduce uplift pressures resulting in appreciable savings. Melenshchenko (14) and Numerov(16) determined the effect of drainage hole below an impervious floor. Zamerin (21) obtained the effect of plane drainage on the flow below a flat floor or a single overfall founded on infinite depth of permeable soil.