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illMIIIII -IIIII-1 = IIIII-IIIII-11 11111-11111 Shadow of 45-degree angle =11111-11111 -11111-1 l� I :11111=11111=11 IIIII-11111 18" 18" 18" =11111-11111 —=11111 - III Hill — =1 I I I I I i i M IND— �IIIII I=I I 18" Stable Soil11111m 1093 11 M,M, - - = — FIGURE 5-4 5.3.3.UNSTABLE IN SITU SOIL CONDITIONS — _ _ CAUTION FIGURE 5-6 Xerxes recommends that the tank owner seek the advice of 5.4.1.1.Ensure that downward forces from loads carried by the a local foundation professional engineer if the in situ soil is foundations and supports of nearby structures(constructed extremely soft or inherently unstable(for example,peat, before or after tank installation)are not transmitted to the tanks. quicksand,muck,landfill,very soft or highly expansive clay,underground stream,etc.). 5.4.2.Typically,the way to check the placement of the tank in relationship to a nearby structure is to do the following: 5.3.3.1.If the soil has less than 750 lbs./sq.ft.cohesion as calculated from an unconfined compression test;or in soils 5.4.2.1.Determine the depth of burial needed for the tank. having an ultimate bearing capacity of less than 3,500 lbs./sq.ft.; 5.4.2.2.Locate the footing of the structure to be considered. or where soil will not maintain a vertical wall,the excavation must allow a minimum space equal to half the diameter of the tank 5.4.2.3.Determine the line that would fall into the ground from a between the excavation wall and both the side and the endcap of 45-degree angle drawn downward from the comer(s)of the the tank,to enhance lateral resistance.(See FIGURE 5-5.) footing of the foundation that is closest to the tank. 5.3.3.2.The spacing between adjacent tanks is to be at least 18 5.4.2.4.The tank must not fall within the"shadow"of the 45- inches.(See FIGURE 5-5.) degree-angle line drawn from the foundation's footing.(See vz FIGURE 5-6.) Tank Dia. 5.4.2.5.If the tank would fall within this"shadow,"do one of the 18"1 following to ensure that the tank does not fall within the I =I!I "shadow":a.)move the tank away from the existing building, b.)move the foundation of the building to be constructed away from the tank,or c.)deepen the footing of the planned building's = M foundation. 1/2 Tank Dia. 1/2 Tank Dia. 5.5.GEOTEXTILE pilloilligglill 11 Unstable Soil 5.5.1.The tank owner or the owner's technical representative is 111110111111 responsible for determining whether a geotextile or an alternate FIGURE 5-5 filtering technique is appropriate for a specific installation. Geotextile allows the passage of water,but prevents the 5.3.3.3.A reinforced concrete slab may be required under the tank migration and mixing of in situ soil and the select backfill as a foundation in the excavation where the bottom is unstable. material.Geotextile helps preserve the integrity of the select 5.4.TANK LOCATION—NEARBY STRUCTURES backfill envelope,which surrounds and supports the tank. CAUTION 5.5.2.Xerxes recommends that geotextile be used when the Xerxes recommends that the tank owner seek the advice of tank is installed in: a local foundation professional engineer to determine the areas with frequently changing groundwater conditions or proper placement of a tank excavation near any existing areas subject to tidal fluctuations, structure(s).Improper placement may result in tank and/or unstable soils such as cited in SECTION 5.3.3., other property damage. water conditions with silty in situ soil. 5.4.1.The location of a tank can be affected by the location of 5.5.3. For further information conceming geotextile specifica- nearby structures.When selecting a tank site,care must be taken tions and installation procedures,consult the geotextile to avoid undermining the foundations of existing structures or new supplier's installation guidelines or instructions. buildings to be constructed.(See FIGURE 5-6.) 12