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I TOP VIEW I ] 24 8' B 48" MY —R• II CUNDIi10Ns 36' - TRAFFIC I — NOTE:Numbers in brackets[J 'STABLE SOIL I rz"_ _ refer to 12'tanks. 4. 'I FIGURE 4-3 FIGURE 4-5 STABLE SOIL CONDITIONS Where shoring is not required to maintain a vertical wall from top Tanks not subjected to traffic loads must have a minimum cover to bottom of the excavation,and the soil is stable,the minimu q depth of 24 [48]inches of backfill,or 12[36]inches backfill plus spacing between the sidewall or endcap of the tank and side of 4 inches of reinforced concrete or 6 inches of asphalt. excavation must be 18 inches[24 inches for 12'tanks]. If more than one tank is to be installed in the same hole,there must be at least 18 inches between the tanks. ` I , �j TOPVIEW 112 rANK 0u. le- �,, - 113f' =1111 1 III 46" CON(! EONS No TRAFFIC _ I/2 TANK DIA. 112 TANK CIA. NOTE:Numbers in brackets[] ! – � � refer to 12'tanks. �I Iz•I ' —� _ ' UNSTABLE SOIL - . FIGURE 4-4 FIGURE 4-6 UNSTABLE SOIL CONDITIONS If the soil has less than 750 lbs./sq.ft.cohesion as calculated from I' Tanks in high water areas not subjected to traffic loads must have a an unconfined compression test;or in soils having an ultimate minimum of 36[481 inches of backfill covering. bearing capacity of less than 3500 lbs./sq.ft.;or where soil will not WARNING:In a non traffic installation,insure that the areas above maintain a vertical wall,the excavation must allow a minimum i the tanks will never be subject to traffic loads. space equal to 1/2 the diameter of the tank between the side and . NOTE:These depths of cover are MINIMUMS in all cases. endcap of the tank and the excavation wall.The spacing between s adjacent tanks, 18 inches remains the same. NOTE:Asphalt and concrete pads must extend a minimum of 12 inches beyond - tank in all directions. WARNING:If the soil is extremely soft or inherently unstable, NOTE:Maximum burial depth is 7 feet of cover overtop of tanks. e.g.peat,quicksand,very soft or expansive clay,etc.,Xerxes NOTE:Unattached manway riser(ifpresent)must not transmit load from the recommends that the tank owner seek the advice of a local concrete slab to the tank.There must be a minimum 6 inch space between the foundation professional engineer. bottom of the riser and the top of the tank. FILTER FABRIC TANK SPACING The tank owner or his technical representative is responsible for NOTE:These are minimum spacings and must be increased as needed to determining whether filter fabric or an alternate filtering technique accommodate deadmen or anchor slabs.Refer to Section 7 on tank anchoring. is appropriate for a specific installation. Filter fabric allows the j Always allow sufficient clearanceto allow the deaden en to be set outside of the tank shadow. passage of water but prevents the migration and mixing of native soil and backfill material. It preserves the integrity of the backfill envelope which supports the tank. Polyethylene film is not considered an effective material to prevent migration of pea gravel,crushed stone and native soil;it may tear or degrade while in service. Xerxes recommends that filter fabric be used when the tank may be installed in: •areas with frequently changing ground water conditions or areas subject to tidal fluctuations, •unstable soils such as bog,swamp,landfill or mud, •water conditions with silty soil.