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XERMES <br /> ���F�FATI�N <br /> Xerxes RST-II Septic Tank <br /> Buoyancy Calculations <br /> NTRODUCTION <br /> The following provides an approxirtt-Lte calculation for the net positive huoyaricy of <br /> the Xerxes RST-11 septic tank- The tank is cylindrical with hemispherical heads and a <br /> flange extending around the periphery at mid height The soil Surrounding the tank <br /> exerts a buoyant force as if it were a fluid. The buoyant force is resisted by the weight <br /> of the tank and an associated soil prism above the tank- The soil prism includes soil <br /> directly over the lank plus a wedge-shaped volume which also resists movement <br /> resulring from the huoyanL fol-CO. <br /> The following table provides terminology which is also illustrated in Figure 1, <br /> r tank radius (in) AV=, gross soil volume over head (1701 <br /> h soil cover (in) AV, gross soil volurne over shell (fr' <br /> LOA overall tank length (in) AVt tank volume above flange (f[3) <br /> f flange width (in) (« water specific weight (lb/1`0) <br /> Rr riser radius (in) YS wet soil specific weight (lb!ft') <br /> Ls shell length (in) 6t't tank weight (lb) <br /> Lr riser length (in) \V, weight of risers and lids (lb) <br /> \'t'st,it soil weight (lb) Fbt total tank buoyant force (ib) <br /> Fl, net negative buoyancy (lb) FS safety factor against flotation <br /> TA\K SUOYAN'IFORCE <br /> The tank buoyant force is the nominal tank capacity obtained frorn the design <br /> drawings times the density of water- In addition the tank riser (not shown in Figure <br /> 1) capacity found from drawing dimensions is also included. The total tank huovaTa <br /> force is The. sum of the buoyant forces of the rank body ttrld the risers: <br /> Fbt =Z"(,,(AV,> rr iZrzi r� <br /> SC)II_ PRISM -%VEIGHTS <br /> The soil WCight componerus are shown by the shaded sections in Figure 1- The >for s <br /> volume is formed by the Lrapezoidai areas OABC: The net soil volume is the gross <br /> valurne minus the VOILtrne occupied by the Lank itself <br /> CORPORATE OFFIOEr750+ XERXES AVSNUE SOUTH.MINNEAPOUS.M14NESn TA 5540•. <br /> PHONE(952'H2? 13SC r?Y.'9521 iya7-t.�T^ <br />