1999-05-03_GENERAL DOCUMENTS - M1974052

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- r 120 GROUNDWATER AND SEEPAGE (Sec.55-5 Sec.5-51 CONFINED FLOW 121 1.5 position of the piling on the discharge for various combinations of depth 14 of embedment and size of structure. It is apparent from Fig. 5-18 that although the discharge is a maximum when the sheetpile is at the center �I I.3 ' of the structure, the variation with position is small (Fig. 5-19). Hence .2 - 0.8 _ -Position A 1.1 :.:,. j --- Position B or B' 1 . 7 1.07 0.9144 /D D 07 J4 •'s 0.2 ><��R7.nSt"/imor/.11tam.ACFI.S 06 0.5 050 0.,5 0 0.4 r 00 0 0.2 0.4 0.6 0.8 0.3 r.25 r/T FIG.6-19 0.2 /50 for design purposes the magnitude of the discharge for any position of , o t the piling may be taken as that with the piling set at the center (Fig. 3 5-17). 0 Figure 5-17 demonstrates that the quantity of seepage decreases as 0 0.1 0.2 0.3 0.4 6.5 0.6 0.7 0.8 0.9 1.0 SIT either the depth of the sheetpile or the width of the weir increases; however the benefit to be gained by increasing the depth of sheetpile Fla. 5-17. (Ayer Polabarinoua-Kochina [1161.) embedment is seen to decrease sharply as the ratio of the width of the weir to the thickness of the permeable layer increases. Indeed, for half- widths larger than the thickness, the quantity of seepage is seen to be /r=V4 °/r=t/° almost independent of the depth of embedment unless the sheetpile r---26 0.6 /r=1/J °/r=1/IF extends close to the base of the permeable layer. Thus little or no t D material advantage is to be gained by increasing the piling depth for ratios of b/T z 1 unless the piling can be driven into the impervious E 0.3 ,/T=114 b/r=vz base. This is particularly noteworthy, as with increasing depths of +� /r driving the risk of faulty connections between the individual piling sec- T. d�= o RD '.' �;�� r boas is also likely to increase. 0.4Finally, to obtain the discharge for other than flabbottom structures, we note that in Sec. 5-2 any streamline can be taken as an impervious boundary. Hence, recalling that q - o+y, by defining +(, = 0 along the 'F 0.3 base of the structure, one may obtain a good approximation to the dis- SI x; :i 0 charge quantity by assigning 1L = -q to any streamline in the vicinity of ' r/6 -' the impervious boundary. The rather insensitive nature of K'/K FIG. 5-18 obviates the need for greater refinement.