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B . Bedding and Foundations : <br /> 1 . Class A (Concrete Cradle or Concrete Arch Bedding ) <br /> This class of bedding shall be used only where specifically shown in <br /> the Drawings or directed by the Engineer. If the use of a concrete <br /> cradle is required , the pipe shall be bedded in a monolithic concrete <br /> cradle with a minimum thickness equal to 1 /4 the outside pipe diameter <br /> or to a minimum of four inches under the barrel , whichever is greatest , <br /> ' and extending up the sides of the pipe to a height equal to 1 /2 of the <br /> outside pipe diameter. The cradle shall have an overall width equal to <br /> 1 - 1 /4 of the outside diameter of the pipe or a minimum width equal to <br /> ' the outside diameter of the pipe plus eight inches , whichever is greater. <br /> The concrete shall have a minimum 28 day compressive strength of <br /> 2 , 500 psi . <br /> 2 . Class B ( First-class Bedding ) <br /> a . Where Class B Bedding is required , the trench shall be excavated <br /> below the planned bottom of the pipe to a depth equal to 1 /4 the <br /> ' nominal diameter of the pipe , or 6 inches , whichever is greater. <br /> The over-excavated depth shall be backfilled using either Type 1 <br /> or Type 3 materials , carefully compacted and shaped to provide a <br /> uniform support for the lower portion of the pipe barrel . Shaping <br /> under the pipe bells shall be so that the bell does not support the <br /> pipe and joints can be made without bedding material interference . <br /> ' b . At the option of the CONTRACTOR , Class B Bedding may be <br /> used in place of Class C (Ordinary Bedding ) provided that the <br /> exercise of this option shall create no additional expense to the <br /> OWNER . <br /> c . If Type 1 material is used , construct a dam at minimum 200- foot <br /> intervals , across the full trench width for the height of the Type 1 <br /> material . The purpose for this dam is to prevent the Type 1 <br /> material from serving as a channel or conduit for the flow of <br /> groundwater along the outside of the pipe . <br /> 3 . Class C ( Ordinary Bedding ) <br /> a . For Class C Bedding the pipe shall be placed on undisturbed <br /> native soil and in such a manner that the lower portion of the pipe <br /> barrel is uniformly supported for the full length of the barrel . The <br /> trench bottom shall be hand shaped to provide a firm support for <br /> ' the pipe . Excavation under the bell shall be sufficient so that the <br /> bell does not support the pipe and the joint can be made without <br /> interference . <br /> b . Use Class C Bedding for all pipeline construction unless <br /> unsuitable bedding material is encountered , or unless shown <br /> otherwise on the Contract Drawings , or unless the CONTRACTOR <br /> Last revised 9/ 10/02 02220- 17 EAST GIFFORD <br /> RIPublic Works\Keithmstormeter Projects\Gifford East\Construction Contract\Technical Specifications\nnal Specifications\Division <br /> ' 2\02220 - Excavation and Back411 .doc <br />