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EXCAVATION &TANK CLEARANCE <br /> 6. EXCAVATION&TANK CLEARANCE 6.2.1.2. Soil less than 750 IbsJsq.ft.cohesion per <br /> ASTM D2166(Test Method for Unconfined <br /> ! Compressive Strength of Cohesive Soil),or <br /> have an ultimate bearing capacity less <br /> Do not enter the tank excavation unless in compliance than 3,500 1 bsJsq.ft. <br /> with OSHA regulations. Follow OSHA guidelines for <br /> tank excavation.Collapsing excavation walls can cause <br /> injury or death. <br /> If the soil is unstable,the tank owner should consult a <br /> 6.1. Stable Excavations professional engineer to ensure a proper installation <br /> 6.1.1. For different diameter tanks that are adjacent and avoid the potential for tank or property damage. <br /> to each other,refer to Supplemental <br /> Documents(Section 21). 6.2.2. A soils consultant can provide additional <br /> 6.1.2. When your excavation is in stable,undisturbed recommendations,including when a <br /> soil;use the minimum spacings(per Figure 6-1 reinforced pad is needed under the tank. <br /> and Table 6-1). 6.2.3. When a bottom pad is used,it should extend <br /> Figure 6-1 to the excavation walls. <br /> 6.2.4. Unstable excavations may also require <br /> B A A geotextile fabric(see Section 7). <br /> 6.2.5. When the soil is unstable,with or without <br /> shoring, use the minimum spacings <br /> (per Figure 6-2 and Table 6-2). <br /> Figure 6-2 <br /> / B A A <br /> / B B <br /> Stable Soil \\ \ \\ \ \ <br /> Table 6-1 <br /> 8'DiameterTanks B B <br /> Minimum w/12"x12"CSIDeadmen <br /> A 18"(457mm) 24"(61omm) Unstable Soil <br /> B 18"(457mm) 24"(610mm) Table 6-2 <br /> 4;6;10'DiameterTanks 8'DiameterTanks <br /> Minimum w/18"x8"CSI Deadmen Minimum w/12"x12"CSI Deadmen <br /> A 18"(457mm) 36"(914mm) A 18"(457mm) 24"(610mm) <br /> B 24"(61omm) 24"(61omm) B 1/2 Tank Dia. 'h Tank Dia. <br /> 12'DiameterTanks 4;6,10'DiameterTanks <br /> Minimum w/18"x8"CSI Deadmen Minimum w/18"x8"CSIDeadmen <br /> A 24"(61omm) 36"(914mm) A 18"(457mm) 36"(914mm) <br /> B 24"(61omm) 24"(610.m) B '/2 Tank Dia. '/2 Tank Dia. <br /> Spacing between tanks placed end to end will follow the"B"spacing 12'DiameterTanks <br /> minimum value. <br /> Minimum w/18"x8"CSI Deadmen <br /> 6.2. Unstable Excavations A 24"(610mm) 36"(914mm) <br /> 6.2.1. An unstable excavation is any of the following: B 1/2 Tank Dia. 1/2 Tank Dia. <br /> 6.2.1.1. Muck,bog,peat,swamp,quicksand, Spacing between tanks placed end to end will follow the"B"spacing <br /> flowing water,landfill type areas or minimum value. <br /> any other situations where the soil is <br /> inherently unstable. <br /> 12 <br />