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SECTION . • Double Wall Tanks ♦ 4' through 10' diameter tanks require: Pad Dimension ♦ 4' through 10' diameter tanks require: ♦ Paving at grade must extend at least 12" beyond tank ❑ Minimum of 18" (24" preferred) between adjacent perimeter in all directions (see figure 7). tanks. FIGURE 7 ❑ Minimum of 18"(24"preferred)between tank sides/ ends and the walls of the excavation. r—A -� A-12 -A- Minimum ♦ 12' diameter tanks require: n ' Ll 24" between adjacent tanks. ; z'Ma m mu U 24" between tanks sides/ends, and the walls of the excavation (see figure 5). UNSTABLE EXCAVATIONS (FIGURE s) A 18•Minimum 24•Preferred -112A-, -A- -112-- Maximum Burial Depth Tank Tank ' ♦ Diia. UL requirements specify that the depth of cover must a. D 2a•Reqaired not exceed 7' (see figure 7). on 12'Tank ❑ For all size tanks. 1;2 Tank Dia, 1/2 Tank Dia. 112 Tank Dia. ❑ For both traffic and no traffic conditions. s =` — ♦ For deeper burial depths, contact Tank Technical ♦ Muck, bog, peat, swamp or landfill type areas where Support. the soil is soft or in areas with expansive clay soils. or have less than 750 lbs./sq. ft. cohesion per ASTM Minimum Burial Depth NoTraffic Load and No Mechani- D2166 (Test Methods for Unconfined Compressive cal Anchoring (4'-10'diameter tanks) Strength of Cohesive Soil), or have ultimate bearing capacity less than 3500 lbs./ NOTE: When mechanical anchoring is required,refer sq. ft. to chart (section A7)for minimum burial depths (see ♦ In unstable excavation, tanks require: figure 8). ❑ Minimum 18" (24" preferred) between adjacent FIGURE 8 tanks. (24" required for 12' diameter tanks). ❑ Minimum of 1/2 the tank diameter from ends and sides of tanks to excavation walls (see fig- LA 12"Backfill a .ure 6). a"Reinfor Concrete♦ May require a reinforced concrete pad under tank. ♦ Contact soils consultant for recommendations. ♦ Filter fabric hole liner is recommended for soils (see 12"Beddin "Filter Fabric"section for list and further requirements): ❑ With less than 250 lbs./sq.ft.cohesion or, ♦ Tanks need a minimum cover of 24" backfill OR 12" of ❑ With ultimate bearing capacity of less than 500 lbs./ backfill plus 4" reinforced concrete (see figure 8). ♦ Local codes may require deeper minimum burial depth. AS. B RIAL DEPTH AND COVER (12' diameter tanks) Excavation Depth ♦ Tanks need a minimum cover of 42" backfill OR 38" ♦ All tank holes must be deep enough to: backfill plus 4" reinforced concrete. ❑ Allow a minimum of 12" and a maximum of 24" Minimum Burial Depth H-20 Traffic Loads and No Me- required backfill bed over the hole bottom or con- chanical Anchoring crete pad. (4' - 10' diameter tanks) Traffic Pad Reinforcement NOTE: When mechanical anchoring is required,refer ♦ The reinforcements in the concrete traffic slab must be to chart(section A7)for minimum burial depths. properly sized for job conditions and traffic loads to as- sure concrete surface pad integrity. 8